Table of contents

We have obtained a smooth time series for the electric vector position angle (EVPA) of the blazar OJ 287 at centimeter wavelengths, by making ±nπ adjustments to archival values from 1974 to 2016. The data display rotation reversals in which the EVPA rotates counterclockwise for ∼180° and then rotates clockwise by a similar amount. The timescale of the rotations is a few weeks to a year, and the scale for a double rotation, including the reversal, is 1–3 yr. We have seen four of these events in 40 yr. A model consisting of two successive outbursts in polarized flux density, with EVPAs counterrotating, superposed on a steady polarized jet, can explain many of the details of the observations. Polarization images support this interpretation. The model can also help to explain similar events seen at optical wavelengths. The outbursts needed for the model can be generated by the supermagnetosonic jet model of Nakamura et al. and Nakamura & Meier, which requires a strong helical magnetic field. This model produces forward and reverse pairs of fast and slow MHD waves, and the plasma inside the two fast/slow pairs rotates around the jet axis, but in opposite directions.

Detailed modeling of the recent star formation histories (SFHs) of post-starburst (or "E+A") galaxies is impeded by the degeneracy between the time elapsed since the starburst ended (post-burst age), the fraction of stellar mass produced in the burst (burst strength), and the burst duration. To resolve this issue, we combine GALEX ultraviolet photometry, SDSS photometry and spectra, and new stellar population synthesis models to fit the SFHs of 532 post-starburst galaxies. In addition to an old stellar population and a recent starburst, 48% of the galaxies are best fit with a second recent burst. Lower stellar mass galaxies (log M_⋆/M_☉ < 10.5) are more likely to experience two recent bursts, and the fraction of their young stellar mass is more strongly anticorrelated with their total stellar mass. Applying our methodology to other, younger post-starburst samples, we identify likely progenitors to our sample and examine the evolutionary trends of molecular gas and dust content with post-burst age. We discover a significant (4σ) decline, with a 117–230 Myr characteristic depletion time, in the molecular gas to stellar mass fraction with the post-burst age. The implied rapid gas depletion rate of 2–150 M_☉ yr⁻¹ cannot be due to current star formation, given the upper limits on the current star formation rates in these post-starbursts. Nor are stellar winds or supernova feedback likely to explain this decline. Instead, the decline points to the expulsion or destruction of molecular gas in outflows, a possible smoking gun for active galactic nucleus feedback.

We summarize and reanalyze observations bearing on missing galactic baryons, where we propose a consistent picture for halo gas in L ≳ L* galaxies. The hot X-ray-emitting halos are detected to 50–70 kpc, where typically M_hot(<50 kpc) ∼ 5 × 10⁹M_⊙, and with density n ∝ r^−3/2. When extrapolated to R₂₀₀, the gas mass is comparable to the stellar mass, but about half of the baryons are still missing from the hot phase. If extrapolated to 1.7R₂₀₀–3R₂₀₀, the ratio of baryon to dark matter approaches the cosmic value. Significantly flatter density profiles are unlikely for R < 50 kpc, and they are disfavored but not ruled out for R > 50 kpc. For the Milky Way, the hot halo metallicity lies in the range 0.3–1 solar for R < 50 kpc. Planck measurements of the thermal Sunyaev–Zel'dovich (SZ) effect toward stacked luminous galaxies (primarily early type) indicate that most of their baryons are hot, are near the virial temperature, and extend beyond R₂₀₀. This stacked SZ signal is nearly an order of magnitude larger than that inferred from the X-ray observations of individual (mostly spiral) galaxies with M_* > 10^11.3M_⊙. This difference suggests that the hot halo properties are distinct for early- and late-type galaxies, possibly due to different evolutionary histories. For the cooler gas detected in UV absorption line studies, we argue that there are two absorption populations: extended halos, and disks extending to ∼50 kpc, containing most of this gas, and with masses a few times lower than the stellar masses. Such extended disks are also seen in 21 cm H i observations and in simulations.

In this second paper in a series studying galaxy–galaxy lensing signals using Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we present our measurement and modeling of the lensing signals around groups of galaxies. We divide the groups into four halo mass bins and measure the signals around four different halo-center tracers: brightest central galaxies (BCGs), luminosity-weighted centers, number-weighted centers, and X-ray peak positions. For groups cross-identified in both X-ray and SDSS DR7, we further split the groups into low and high X-ray emission subsamples, both of which are assigned to two halo-center tracers, BCGs and X-ray peak positions. The galaxy–galaxy lensing signals show that BCGs, among the four candidates, are the best halo-center tracers. We model the lensing signals using a combination of four contributions: the off-center NFW host halo profile, subhalo contribution, stellar contribution, and projected two-halo term. We sample the posterior of five parameters, i.e., the halo mass, concentration, off-centering distance, subhalo mass, and fraction of subhalos, via a Monte Carlo Markov Chain (MCMC) package using the galaxy–galaxy lensing signals. After taking into account the sampling effects (e.g., Eddington bias), we found that the best-fit halo masses obtained from lensing signals are quite consistent with those obtained in the group catalog based on an abundance matching method, except in the lowest mass bin.

The Earth–Moon system is suggested to have formed through a single giant collision, in which the Moon accreted from the impact-generated debris disk. However, such giant impacts are rare, and during its evolution, the Earth experienced many more smaller impacts, producing smaller satellites that potentially coevolved. In the multiple-impact hypothesis of lunar formation, the current Moon was produced from the mergers of several smaller satellites (moonlets), each formed from debris disks produced by successive large impacts. In the Myr between impacts, a pre-existing moonlet tidally evolves outward until a subsequent impact forms a new moonlet, at which point both moonlets will tidally evolve until a merger or system disruption. In this work, we examine the likelihood that pre-existing moonlets survive subsequent impact events, and explore the dynamics of Earth–moonlet systems that contain two moonlets generated Myr apart. We demonstrate that pre-existing moonlets can tidally migrate outward, remain stable during subsequent impacts, and later merge with newly created moonlets (or re-collide with the Earth). Formation of the Moon from the mergers of several moonlets could therefore be a natural byproduct of the Earth's growth through multiple impacts. More generally, we examine the likelihood and consequences of Earth having prior moons, and find that the stability of moonlets against disruption by subsequent impacts implies that several large impacts could post-date Moon formation.

The solar corona is a hot, dynamic, and highly magnetized plasma environment whose source of energy is not yet well understood. One leading contender for that energy source is the dissipation of magnetohydrodynamic (MHD) waves or turbulent fluctuations. Many wave-heating models for the corona and the solar wind presume that these fluctuations originate at or below the Sun's photosphere. However, this paper investigates the idea that magnetic reconnection may generate an additional source of MHD waves over a gradual range of heights in the low corona. A time-dependent Monte Carlo simulation of the mixed-polarity magnetic field is used to predict the properties of reconnection-driven coronal MHD waves. The total power in these waves is typically small in comparison to that of photosphere-driven waves, but their frequencies are much lower. Reconnection-driven waves begin to dominate the total power spectrum at periods longer than about 30 minutes. Thus, they may need to be taken into account in order to understand the low-frequency power-law spectra observed by both coronal spectropolarimetry and in situ particle/field instruments. These low-frequency Alfvén waves should carry more magnetic energy than kinetic energy, and thus they may produce less nonthermal Doppler broadening (in comparison to photosphere-driven high-frequency waves) in emission lines observed above the solar limb.

We investigate a mechanism to produce a seed population enriched in heavy ions, such as those observed in ³He-rich solar energetic particle events. It is shown that if an initial particle population following a power law in energy nucleon⁻¹ passes through a small amount of material, at energies below the dE/dx Bragg peak, the greater affinity of heavier ions for electron pick-up results in their penetrating the material more easily. This results in an enhancement of heavy ions in the particle population that just barely penetrates the material. The bulk of the seed particles fall in the energy range of 10 s of keV nucleon⁻¹. It is supposed that some further process then energizes this seed population to produce the particles observed in interplanetary space. We find a broad range of parameters that produces enhancements comparable to Fe/O ∼ 8 commonly observed.

We report ALMA Cycle 3 observations in CO isotopes toward a dense core, MC27/L1521F in Taurus, which is considered to be at an early stage of multiple star formation in a turbulent environment. Although most of the high-density parts of this core are considered to be as cold as ∼10 K, high-angular resolution (∼20 au) observations in ¹²CO (J = 3–2) revealed complex warm (>15–60 K) filamentary/clumpy structures with the sizes from a few tens of astronomical units to ∼1000 au. The interferometric observations of ¹³CO and C¹⁸O show that the densest part with arc-like morphologies associated with the previously identified protostar and condensations are slightly redshifted from the systemic velocity of the core. We suggest that the warm CO clouds may be consequences of shock heating induced by interactions among the different density/velocity components that originated from the turbulent motions in the core. However, such a small-scale and fast turbulent motion does not correspond to a simple extension of the line–width–size relation (i.e., Larson's law), and thus the actual origin remains to be studied. The high-angular resolution CO observations are expected to be essential in detecting small-scale turbulent motions in dense cores and to investigate protostar formation therein.

We present the asteroseismic study of the early red-giant star KIC 4448777, complementing and integrating a previous work, aimed at characterizing the dynamics of its interior by analyzing the overall set of data collected by the Kepler satellite during the four years of its first nominal mission. We adopted the Bayesian inference code diamonds for the peak bagging analysis and asteroseismic splitting inversion methods to derive the internal rotational profile of the star. The detection of new splittings of mixed modes, which are more concentrated in the very inner part of the helium core, allowed us to reconstruct the angular velocity profile deeper into the interior of the star and to disentangle the details better than in Paper I: the helium core rotates almost rigidly about 6 times faster than the convective envelope, while part of the hydrogen shell seems to rotate at a constant velocity about 1.15 times lower than the He core. In particular, we studied the internal shear layer between the fast-rotating radiative interior and the slow convective zone and we found that it lies partially inside the hydrogen shell above r ≃ 0.05R and extends across the core–envelope boundary. Finally, we theoretically explored the possibility for the future capabilty to sound the convective envelope in the red-giant stars and we concluded that the inversion of a set of splittings with only low-harmonic degree l ≤ 3, even supposing a very large number of modes, will not allow us to resolve the rotational profile of this region in detail.

Large infrared and millimeter wavelength surveys of the Galactic plane have unveiled more than 600 new bubble H ii regions and more than 3000 candidate star clusters. We present a study of the candidate clusters MCM2005b72, DBS2003−157, DBS2003−172, and MCM2005b77 based on near-infrared spectroscopy taken with SofI on the NTT and infrared photometry from the 2MASS, VVV, and GLIMPSE surveys. We find that (1) MCM2005b72 and DBS2003−157 are subregions of the same star-forming region, H ii GRS G331.34−00.36 (bubble S62). MCM2005b72 coincides with the central part of this H ii region, while DBS2003−157 is a bright mid-infrared knot of the S62 shell. We detected two O-type stars at extinction ${A}_{{K}_{{\rm{s}}}}$ = 1.0–1.3 mag. Their spectrophotometric properties are consistent with the near-kinematic distance to GRS G331.34−00.36 of 3.9 ± 0.3 kpc. (2) DBS2003−172 coincides with a bright mid-infrared knot in the S36 shell (GRS G337.92−00.48), where we detected a pair of candidate He i stars embedded in a small cometary nebula. (3) The stellar cluster MCM2005b77 is rich in B-type stars, has an average ${A}_{{K}_{{\rm{s}}}}$ of 0.91 mag, and is adjacent to the H ii region IRAS 16137−5025. The average spectrophotometric distance of ∼5.0 kpc matches the near-kinematic distance to IRAS 16137−5025 of 5.2 ± 0.1 kpc.

Observations from the Ion and Neutral Camera (INCA) on the Cassini mission of energetic neutral atoms (ENAs) at ∼10 keV and ∼45 keV showed significant correlated time variations over relatively fast 2–3 yr timescales. These observed ENA variations have been interpreted as indicating limited scale lengths of ∼80–120 au along the line of sight for the size of the heliosphere. We show here, however, that rather than a heliosphere with a quasi-spherical shape, the INCA line-of-sight observations vary in response to episodic cooling and heating of the inner heliosheath plasma during periods of large-scale expansion and compression.

We publish a photometric redshift catalog based on imaging data of the South Galactic Cap u-band Sky Survey, Sloan Digital Sky Survey (SDSS), and Wide-field Infrared Survey Explorer. A total of seven photometric bands are used, ranging from near-ultraviolet to near-infrared. A local linear regression method is adopted to estimate the photometric redshift with a dedicated spectroscopic training set. The photometric redshift catalog contains about 23.1 million galaxies classified by SDSS. Using the training set with redshift up to 0.8 and r-band magnitude down to 22 mag, we achieve an average bias of $\overline{{\rm{\Delta }}{z}_{\mathrm{norm}}}=2.28\times {10}^{-4}$, a standard deviation of σ(Δz_norm) = 0.019, and a 3σ outlier rate of about 4.2%. The bias is less than 0.01 at z < 0.6 and goes up to about 0.05 at z ∼ 0.8. Compared with SDSS photometric redshifts, our redshift estimations are more accurate and have less bias.

The Carnegie-Irvine Galaxy Survey provides high-quality broadband optical images of a large sample of nearby galaxies for detailed study of their structure. To probe the physical nature and possible cosmological evolution of spiral arms, a common feature of many disk galaxies, it is important to quantify their main characteristics. We describe robust methods to measure the number of arms and their mean strength, length, and pitch angle. The arm strength depends only weakly on the adopted radii over which it is measured, and it is stronger in bluer bands than redder bands. The vast majority of clearly two-armed ("grand-design") spiral galaxies have a systematically higher relative amplitude of the m = 2 Fourier mode in the main spiral region. We use both one-dimensional and two-dimensional Fourier decomposition to measure the pitch angle, finding reasonable agreement between these two techniques with a scatter of ∼2°. To understand the applicability and limitations of our methodology to imaging surveys of local and distant galaxies, we create mock images with properties resembling observations of local (z ≲ 0.1) galaxies by the Sloan Digital Sky Survey and distant galaxies (0.1 ≲ z ≲ 1.1) observed with the Hubble Space Telescope. These simulations lay the foundation for forthcoming quantitative statistical studies of spiral structure to understand its formation mechanism, dependence on galaxy properties, and cosmological evolution.

The streaming instability (SI) is a mechanism to concentrate solids in protoplanetary disks. Nonlinear particle clumping from the SI can trigger gravitational collapse into planetesimals. To better understand the numerical robustness of the SI, we perform a suite of vertically stratified 3D simulations with fixed physical parameters known to produce strong clumping. We vary the numerical implementation, namely, the computational domain size and the vertical boundary conditions (vBCs), comparing newly implemented outflow vBCs to the previously used periodic and reflecting vBCs. We find strong particle clumping by the SI is mostly independent of the vBCs. However, peak particle densities are higher in larger simulation domains due to a larger particle mass reservoir. We report SI-triggered zonal flows, i.e., azimuthally banded radial variations of gas pressure. These structures have low amplitudes, insufficient to halt particle radial drift, confirming that particle trapping in gas pressure maxima is not the mechanism of the SI. We find that outflow vBCs produce artificially large gas outflow rates at vertical boundaries. However, the outflow vBCs reduce artificial reflections at vertical boundaries, allowing more particle sedimentation, and showing less temporal variation and better convergence with box size. The radial spacing of dense particle filaments is ∼0.15 gas scale heights (H) for all vBCs, which sets the feeding zone for planetesimal growth in self-gravitating simulations. Our results validate the use of the outflow vBCs in SI simulations, even with vertical boundaries close (≤0.4H) to the disk midplane. Overall, our study demonstrates the numerical robustness of nonlinear particle clumping by the SI.

The study of historical great geomagnetic storms is crucial for assessing the possible risks to the technological infrastructure of a modern society, caused by extreme space–weather events. The normal benchmark has been the great geomagnetic storm of 1859 September, the so-called "Carrington Event." However, there are numerous records of another great geomagnetic storm in 1872 February. This storm, which occurred about 12 years after the Carrington Event, resulted in comparable magnetic disturbances and auroral displays over large areas of the Earth. We have revisited this great geomagnetic storm in terms of the auroral and sunspot records in historical documents from East Asia. In particular, we have surveyed the auroral records from East Asia and estimated the equatorward boundary of the auroral oval to be near 242 invariant latitude, on the basis that the aurora was seen near the zenith at Shanghai (20° magnetic latitude, MLAT). These results confirm that this geomagnetic storm of 1872 February was as extreme as the Carrington Event, at least in terms of the equatorward motion of the auroral oval. Indeed, our results support the interpretation of the simultaneous auroral observations made at Bombay (10° MLAT). The East Asian auroral records have indicated extreme brightness, suggesting unusual precipitation of high-intensity, low-energy electrons during this geomagnetic storm. We have compared the duration of the East Asian auroral displays with magnetic observations in Bombay and found that the auroral displays occurred in the initial phase, main phase, and early recovery phase of the magnetic storm.

We present the results of an ultradeep, comprehensive radio continuum survey for the accretion signatures of intermediate-mass black holes (IMBHs) in globular clusters (GCs). The sample, imaged with the Karl G. Jansky Very Large Array and the Australia Telescope Compact Array, comprises 50 Galactic GCs. No compelling evidence for an IMBH is found in any cluster in our sample. In order to achieve the highest sensitivity to low-level emission, we also present the results of an overall stack of our sample as well as various subsamples, also finding nondetections. These results strengthen the idea that IMBHs with masses ≳1000M_⊙ are rare or absent in GCs.

Infrared interferometry of Seyfert galaxies has revealed that their warm (300–400 K) dust emission originates primarily from polar regions instead of from an equatorial dust torus as predicted by the classic AGN unification scheme. We present new data for the type 1.2 object ESO 323-G77 obtained with the MID-infrared interferometric Instrument and a new detailed morphological study of its warm dust. The partially resolved emission on scales between 5 and 50 mas (1.6–16 pc) is decomposed into a resolved and an unresolved source. Approximately 65% of the correlated flux between 8 and 13 μm is unresolved at all available baseline lengths. The remaining 35% is partially resolved and shows angular structure. From geometric modeling, we find that the emission is elongated along a position angle of 155° ± 14° with an axis ratio (major/minor) of 2.9 ± 0.3. Because the system axis is oriented in the position angle 174° ± 2°, we conclude that the dust emission of this object is also polar extended. A CAT3D-WIND radiative transfer model of a dusty disk and a dusty wind with a half opening angle of 30° can reproduce both the interferometric data and the SED, while a classical torus model is unable to fit the interferometric data. We interpret this as further evidence that a polar dust component is required even for low-inclination type 1 sources.

We report on the observation of fine-scale structure in the outer corona at solar maximum, using deep-exposure campaign data from the Solar Terrestrial Relations Observatory-A (STEREO-A)/COR2 coronagraph coupled with postprocessing to further reduce noise and thereby improve effective spatial resolution. The processed images reveal radial structure with high density contrast at all observable scales down to the optical limit of the instrument, giving the corona a "woodgrain" appearance. Inferred density varies by an order of magnitude on spatial scales of 50 Mm and follows an f⁻¹ spatial spectrum. The variations belie the notion of a smooth outer corona. They are inconsistent with a well-defined "Alfvén surface," indicating instead a more nuanced "Alfvén zone"—a broad trans-Alfvénic region rather than a simple boundary. Intermittent compact structures are also present at all observable scales, forming a size spectrum with the familiar "Sheeley blobs" at the large-scale end. We use these structures to track overall flow and acceleration, finding that it is highly inhomogeneous and accelerates gradually out to the limit of the COR2 field of view. Lagged autocorrelation of the corona has an enigmatic dip around 10 R_⊙, perhaps pointing to new phenomena near this altitude. These results point toward a highly complex outer corona with far more structure and local dynamics than has been apparent. We discuss the impact of these results on solar and solar-wind physics and what future studies and measurements are necessary to build upon them.

The magnetization of solar and extrasolar gas giants is critically dependent on the electronic and mass transport coefficients of their convective fluid interiors. We analyze recent laboratory experimental results on metallic hydrogen to derive a new conductivity profile for the Jovian-like planets. We combine this revised conductivity with a polytropic-based thermodynamic equation of state to study the dynamo action in 100 extrasolar giant planets varying from synchronous hot Jupiters to fast rotators, with masses ranging from 0.3 M_J to 15 M_J. We find dynamo cores larger than previous estimates, but consistent with the results from Juno, suggesting that the field generation in the more massive planets might be shallow-seated. Our results reveal that most extrasolar giants are expected to possess dipole surface magnetic fields in the range of 0.1–10 Gauss. Assuming radio emission processes similar to our solar giants, the stronger emitters are expected to have maximal cyclotron frequencies between 20 and 40 MHz and for those within few 10 pc, few have flux densities greater than 1 mJy. Our work places new bounds on the observational detectability of extrasolar magnetic fields.

We discuss the nature of a discrete, compact radio source (NGC 4725 B) located ≈1.9 kpc from the nucleus in the nearby star-forming galaxy NGC 4725, which we believe to be a new detection of extragalactic anomalous microwave emission (AME). Based on detections at 3, 15, 22, 33, and 44 GHz, NGC 4725 B is a microjansky radio source peaking at ≈33 GHz. While the source is not identified in optical (BVRI) photometry, we detect counterparts in the midinfrared Spitzer/IRAC bands (3.6, 4.5, 5.8, 8.0 μm) that appear to be associated with dust emission in the central region of NGC 4725. Consequently, we conclude that NGC 4725 B is a new detection of AME and is very similar to a recent detection of AME in an outer-disk star-forming region in NGC 6946. We find that models of electric dipole emission from rapidly rotating ultra-small grains are able to reproduce the radio spectrum for reasonable interstellar medium conditions. Given the lack of an optical counterpart and the shape of the radio spectrum, NGC 4725 B appears consistent with a nascent star-forming region in which young (≲3 Myr) massive stars are still highly enshrouded by their natal cocoons of gas and dust with insufficient supernovae occurring to produce a measurable amount of synchrotron emission.

A star enshrouded in a Dyson sphere with a high covering fraction may manifest itself as an optically subluminous object with a spectrophotometric distance estimate significantly in excess of its parallax distance. Using this criterion, the Gaia mission will in coming years allow for Dyson sphere searches that are complementary to searches based on waste-heat signatures at infrared wavelengths. A limited search of this type is also possible at the current time, by combining Gaia parallax distances with spectrophotometric distances from ground-based surveys. Here, we discuss the merits and shortcomings of this technique and carry out a limited search for Dyson sphere candidates in the sample of stars common to Gaia Data Release 1 and Radial Velocity Experiment (RAVE) Data Release 5. We find that a small fraction of stars indeed display distance discrepancies of the type expected for nearly complete Dyson spheres. To shed light on the properties of objects in this outlier population, we present follow-up high-resolution spectroscopy for one of these stars, the late F-type dwarf TYC 6111-1162-1. The spectrophotometric distance of this object is about twice that derived from its Gaia parallax, and there is no detectable infrared excess. While our analysis largely confirms the stellar parameters and the spectrophotometric distance inferred by RAVE, a plausible explanation for the discrepant distance estimates of this object is that the astrometric solution has been compromised by an unseen binary companion, possibly a rather massive white dwarf (≈1 M_⊙). This scenario can be further tested through upcoming Gaia data releases.

We isolate a set of quasars that exhibit emergent C iv broad absorption lines (BALs) in their spectra by comparing spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 and the SDSS/BOSS Data Releases 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. We find an emergence rate consistent with the previously reported disappearance rate of BAL quasars given the relative numbers of non-BAL and BAL quasars in the SDSS. We find that candidate newly emerged BALs are preferentially drawn from among BALs with smaller balnicity indices, shallower depths, larger velocities, and smaller widths. Within two rest-frame years (average) after a BAL has emerged, we find it equally likely to continue increasing in equivalent width in an observation 6 months later (average) as it is to start decreasing. From the time separations between our observations, we conclude that the coherence timescale of BALs is less than 100 rest-frame days. We observe coordinated variability among pairs of troughs in the same quasar, likely due to clouds at different velocities responding to the same changes in ionizing flux, and the coordination is stronger if the velocity separation between the two troughs is smaller. We speculate that the latter effect may be due to clouds having on average lower densities at higher velocities owing to mass conservation in an accelerating flow, causing the absorbing gas in those clouds to respond on different timescales to the same ionizing flux variations.

The high ionization state ions trace the hot gases in the universe, of which gaseous halos around galaxies are a major contributor. Following Qu & Bregman, we calculate the gaseous halo contribution to the observed column density distributions for these ions by convolving the gaseous halo model with the observed stellar mass function. The predicted column density distribution reproduces the general shape of the observed column density distribution—a broken power law with the break point at $\mathrm{log}\,N=14.0$ for O vi. Our modeling suggests that the high column density systems originate from galaxies for which the virial temperature matches the temperature of the ionization fraction peak. Specifically, this mass range is $\mathrm{log}\,{M}_{\star }=8.5\mbox{--}10$ for O vi, $\mathrm{log}\,{M}_{\star }=9.5\mbox{--}10.5$ for Ne viii, and higher for higher ionization state ions (assuming ${T}_{\max }=2{T}_{\mathrm{vir}}$). A comparison with the observed O vi column density distribution prefers a large radius model, where the maximum radius is twice the virial radius. This model may be in conflict with the more poorly defined Ne viii column density distribution, suggesting that further observations are warranted. The redshift evolution of the high column density systems is dominated by the change of the cosmic star formation rate, which decreases from z = 1.0 to the local universe. Some differences at lower column densities between our models and observations indicate that absorption by the intragroup (cluster) medium and intergalactic medium is also a contributor to the total column density distributions.

We report the discovery and spectroscopic confirmation of a very large star-forming galaxy, G6025, at ${z}_{\mathrm{spec}}\,=3.721\pm 0.003$. In the rest frame ≈2100 Å, G6025 subtends ≈24 kpc in physical extent when measured from the 1.5σ isophote, in agreement with the parametric size measurements that yield a half-light radius of 4.9 ± 0.5 kpc and a semimajor axis of 12.5 ± 0.1 kpc. It is also very UV-luminous ($\approx 5{L}_{\mathrm{UV},z\sim 4}^{* }$) and young (≈140 ± 60 Myr). Despite its unusual size and luminosity, the stellar population parameters and dust reddening (${M}_{\mathrm{star}}\sim {M}_{z\sim 4}^{* }$ and E(B − V) ∼ 0.18 ± 0.05) estimated from the integrated light are similar to those of smaller galaxies at comparable redshifts. The ground-based morphology and spectroscopy show two dominant components, both located off-center, embedded in more diffuse emission. We speculate that G6025 may be a scaled-up version of chain galaxies seen in deep HST imaging or, alternatively, a nearly equal-mass merger involving two super-L* galaxies in its early stage. It lies close to but not within a known massive protocluster at z = 3.78. We find four companions within 6 Mpc from G6025, two of which lie within 1.6 Mpc. While the limited sensitivity of the existing spectroscopy does not allow us to robustly characterize the local environment of G6025, it likely resides in a locally overdense environment. The luminosity, size, and youth of G6025 make it uniquely suited to study the early formation of massive galaxies in the universe.

We compare vertical profiles of the extraplanar Hα emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the "diffuse" extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar Hα emission. A strong correlation between the scale heights of the extraplanar Hα and UV emissions is also found; the scale height at Hα is found to be ∼0.74 of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in the galactic halos. The existence of eDust in galaxies where the extraplanar Hα emission is detected suggests that a larger portion of the extraplanar Hα emission than that predicted in previous studies may be caused by Hα photons that originate from H ii regions in the galactic plane and are subsequently scattered by the eDust. This possibility raise an advantage in studying the extraplanar diffuse ionized gas. We also find that the scale heights of the extraplanar emissions normalized to the galaxy size correlate well with the star formation rate surface density of the galaxies. The properties of eDust in our galaxies is on a continuation line of that found through previous observations of the extraplanar polycyclic aromatic hydrocarbons emission in more active galaxies known to have galactic winds.

As the earliest dated solids, calcium–aluminum-rich inclusions (CAIs) provide a unique window into the early solar system. However, for many elements, CAIs have been shown to exhibit a very different nucleosynthetic isotope signature from that of later-formed bulk meteorites. To explore this critical difference between solar system materials, we investigate a broad set of CAI samples for both mass-dependent and non-mass-dependent (nucleosynthetic) isotope variations in the siderophile element nickel (Ni). We find that fine-grained CAIs show little if any mass-dependent Ni isotopic fractionation, whereas coarse-grained inclusions exhibit a broad range of isotopically heavy signatures. Because mass-dependent variations appear to be coupled with nucleosynthetic anomalies in CAIs, a part of this Ni isotope variability could be due to thermal processing that acted on these samples. Nucleosynthetic Ni isotopic signatures show that CAIs share a genetic heritage with carbonaceous meteorites and provide a clear distinction from the isotopic reservoirs occupied by terrestrial Ni and non-carbonaceous meteorites. However, whereas nucleosynthetic Ni isotope heterogeneity in previously investigated bulk meteorites was ascribed to variation in the neutron-poor isotope ⁵⁸Ni, we here find that CAI signatures require variability in other, more neutron-rich Ni isotopes. Taken in aggregate with previous work, this highlights a change in the nucleosynthetic character from CAIs to later-formed solids that cannot be explained by variable admixture of a single presolar phase or material from a specific supernova shell. Instead, these data reveal the complex evolution of the solar system, including blending and reprocessing of matter from several generations and types of stars.

The feasibility of the double detonation mechanism—surface helium detonation followed by complete carbon detonation of the core—in a rotating white dwarf with mass ≃1 M_⊙ is studied using three-dimensional hydrodynamic simulations. A rapid rigid rotation of the white dwarf was assumed, so that its initial spherical geometry is considerably distorted. Unlike spherically symmetric models, we found that when helium ignition is located far from the spinning axis, the detonation fronts converge asynchronically at the antipodes of the ignition point. Nevertheless, the detonation of the carbon core still remains as the most probable outcome. The detonation of the core gives rise to a strong explosion, matching many of the basic observational constraints of Type Ia supernovae (SNe Ia). We conclude that the double detonation mechanism also works when the white dwarf is rapidly rotating. These results provide further evidence for the viability of sub-Chandrasekhar-mass models as well as some double degenerate models (those having some helium fuel at the merging moment), making them appealing channels for the production of SN Ia events.

We present 15 high-mass X-ray binary (HMXB) candidates in the disk of M31 for which we are able to infer compact object type, spectral type of the donor star, and age using multiwavelength observations from NuSTAR, Chandra, and the Hubble Space Telescope. The hard X-ray colors and luminosities from NuSTAR permit the tentative classification of accreting X-ray binary systems by compact object type, distinguishing black hole from neutron star systems. We find hard-state black holes, pulsars, and non-magnetized neutron stars associated with optical point-source counterparts with similar frequency. We also find nine non-magnetized neutron stars coincident with globular clusters and an equal number of pulsars with and without point-source optical counterparts. We perform spectral energy distribution (SED) fitting for the most likely optical counterparts to the HMXB candidates, finding seven likely high-mass stars and one possible red helium-burning star. The remaining seven HMXB optical counterparts have poor SED fits, so their companion stars remain unclassified. Using published star formation histories, we find that the majority of HMXB candidates—X-ray sources with UV-bright point-source optical counterpart candidates—are found in regions with star formation bursts less than 50 Myr ago, and three are associated with young stellar ages (<10 Myr). This is consistent with similar studies of HMXB populations in the Magellanic Clouds, M33, NGC 300, and NGC 2403.

Kiloparsec-scale dual active galactic nuclei (AGNs) are active supermassive black hole pairs co-rotating in galaxies with separations of less than a few kpc. Expected to be a generic outcome of hierarchical galaxy formation, their frequency and demographics remain uncertain. We have carried out an imaging survey with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) of AGNs with double-peaked narrow [O iii] emission lines. HST/WFC3 offers high image quality in the near-infrared (NIR) to resolve the two stellar nuclei, and in the optical to resolve [O iii] from ionized gas in the narrow-line regions. This combination has proven to be key in sorting out alternative scenarios. With HST/WFC3 we are able to explore a new population of close dual AGNs at more advanced merger stages than can be probed from the ground. Here we show that the AGN Sloan Digital Sky Survey (SDSS) J0924+0510, which had previously shown two stellar bulges, contains two spatially distinct [O iii] regions consistent with a dual AGN. While we cannot completely exclude cross-ionization from a single central engine, the nearly equal ratios of [O iii] strongly suggest a dual AGN with a projected angular separation of 04, corresponding to a projected physical separation of r_p = 1 kpc at redshift z = 0.1495. This serves as a proof of principle for combining high-resolution NIR and optical imaging to identify close dual AGNs. Our result suggests that studies based on low-resolution and/or low-sensitivity observations may miss close dual AGNs and thereby may underestimate their occurrence rate on ≲kpc scales.

Some authors have proposed that electron energy distributions in H ii regions and planetary nebulae may be significantly nonthermal, and κ-distributions have been suggested as being appropriate. Here it is demonstrated that the electron energy distribution function is extremely close to a Maxwellian up to electron kinetic energies of $\sim 13\,\mathrm{eV}$ in H ii regions, and up to $\sim 16\,\mathrm{eV}$ in planetary nebulae: κ-distributions are inappropriate. The small departures from a Maxwellian have negligible effects on line ratios. When observed line ratios in H ii regions deviate from models with a single electron temperature, it must arise from spatial variations in electron temperature, rather than local deviations from a Maxwellian.

Motivated by the work of Cooper & Showman, we revisit the chemical relaxation method, which seeks to enhance the computational efficiency of chemical kinetics calculations by replacing the chemical network with a handful of independent source/sink terms. Chemical relaxation solves the evolution of the system and can treat disequilibrium chemistry, as the source/sink terms are driven toward chemical equilibrium on a prescribed chemical timescale, but it has surprisingly never been validated. First, we generalize the treatment by forgoing the use of a single chemical timescale, instead developing a pathway analysis tool that allows us to identify the rate-limiting reaction as a function of temperature and pressure. For the interconversion between methane and carbon monoxide, and between ammonia and molecular nitrogen, we identify the key rate-limiting reactions for conditions relevant to currently characterizable exo-atmospheres (500–3000 K, 0.1 mbar to 1 kbar). Second, we extend chemical relaxation to include carbon dioxide and water. Third, we examine the role of metallicity and the carbon-to-oxygen ratio in chemical relaxation. Fourth, we apply our pathway analysis tool to diagnose the differences between our chemical network and that of Moses and Venot. Finally, we validate the chemical relaxation method against full chemical kinetics calculations in one dimension. For WASP-18b-, HD 189733b-, and GJ 1214-b-like atmospheres, we show that chemical relaxation is mostly accurate to within an order of magnitude, a factor of 2, and ∼10%, respectively. The level of accuracy attained allows for the chemical relaxation method to be included in three-dimensional general circulation models.

Analysis of high-resolution Magnetospheric Multiscale Mission plasma and magnetic field data directly reveals the exchanges of energy between electromagnetic and flow energy and between microscopic flows and random kinetic energy in the inhomogeneous turbulent magnetosheath. The computed rates of exchange are based on exact results from the collisionless Vlasov model of plasma dynamics, without appeal to viscous or other closures. The description includes analyses of several structures observed in intervals of burst mode data in the magnetosheath, revealing pathways of energy exchange at sub-ion scales. Time-series of the work done by the electromagnetic field, and the pressure–stress interaction, enable description of the pathways to dissipation in this low-collisionality plasma. This method does not require any specific mechanism for its application, such as reconnection or a selected mode, although with increased experience it will be useful for distinguishing between proposed possibilities.

The nearby open cluster NGC 752 presents a rare opportunity to study stellar properties at ages >1 Gyr. However, constructing a membership catalog for it is challenging; most surveys have been limited to identifying its giants and dwarf members earlier than mid-K. We supplement past membership catalogs with candidates selected with updated photometric and proper-motion criteria, generating a list of 258 members, a >50% increase over previous catalogs. Using a Bayesian framework to fit MESA Isochrones & Stellar Tracks evolutionary models to literature photometry and the Tycho-Gaia Astrometric Solution data available for 59 cluster members, we infer the age of and distance to NGC 752: 1.34 ± 0.06 Gyr and ${438}_{-6}^{+8}$ pc. We also report the results of our optical monitoring of the cluster using the Palomar Transient Factory. We obtain rotation periods for 12 K and M cluster members, the first periods measured for such low-mass stars with a well-constrained age >1 Gyr. We compare these new periods to data from the younger clusters Praesepe and NGC 6811, and to a theoretical model for angular momentum loss, to examine stellar spin-down for low-mass stars over their first 1.3 Gyr. While on average NGC 752 stars are rotating more slowly than their younger counterparts, the difference is not significant. Finally, we use our spectroscopic observations to measure Hα for cluster stars, finding that members earlier than ≈M2 are magnetically inactive, as expected at this age. Forthcoming Gaia data should solidify and extend the membership of NGC 752 to lower masses, thereby increasing its importance for studies of low-mass stars.

The formation mechanism of the hot gaseous halo associated with the Milky Way is still under debate. We report new observational constraints on the gaseous halo using 107 lines of sight of the Suzaku X-ray observations at 75° < l < 285° and $| b| \gt 15^\circ$ with a total exposure of 6.4 Ms. The gaseous halo spectra are represented by a single-temperature plasma model in collisional ionization equilibrium. The median temperature of the observed fields is 0.26 keV (3.0 × 10⁶ K) with a typical fluctuation of ∼30%. The emission measure varies by an order of magnitude and marginally correlates with the Galactic latitude. Despite the large scatter of the data, the emission measure distribution is roughly reproduced by a disk-like density distribution with a scale length of ∼7 kpc, a scale height of ∼2 kpc, and a total mass of ∼5 × 10⁷M_☉. In addition, we found that a spherical hot gas with the β-model profile hardly contributes to the observed X-rays but that its total mass might reach ≳10⁹M_☉. Combined with indirect evidence of an extended gaseous halo from other observations, the hot gaseous halo likely consists of a dense disk-like component and a rarefied spherical component; the X-ray emissions primarily come from the former, but the mass is dominated by the latter. The disk-like component likely originates from stellar feedback in the Galactic disk due to the low scale height and the large scatter of the emission measures. The median [O/Fe] of ∼0.25 shows the contribution of the core-collapse supernovae and supports the stellar feedback origin.

The solar mean magnetic field (SMMF) is referred to as the disk-averaged line-of-sight (LOS) magnetic field that also reflects the polarity imbalance of the magnetic field on the Sun. The origin of the SMMF has been debated over the past few decades, with one school of thought suggesting that the contribution to the SMMF is mostly due to the large-scale magnetic field structure, also called the background magnetic field, whereas other and more recent studies have indicated that active regions have a major contribution to the observed SMMF. In this paper, we re-investigate the issue of the origin of the SMMF by decomposing the solar disk into plages, networks, sunspots, and background regions, thereby calculating the variation in the observed SMMF due to each of these features. We have used full-disk images from Solar Dynamics Observatory (SDO)/AIA recorded at 1600 Å for earmarking plages, networks, and background regions and 4500 Å images for separating the sunspots. The LOS fields corresponding to each of these regions are estimated from the co-temporal SDO/Helioseismic and Magnetic Imager full-disk magnetograms. The temporal variation of the SMMF shows a near one-to-one correspondence with that of the background field regions, suggesting that they constitute the major component of the observed SMMF. A linear regression analysis based on the coefficient of determination shows that the background field dominates and accounts for 89% of the variation in the SMMF, whereas the magnetic field from the other features accounts for the rest 11%.

This paper continues the systematic investigation of diffusive shear instabilities initiated in Part I of this series. In this work, we primarily focus on quantifying the impact of nonlocal mixing, which is not taken into account in Zahn's mixing model. We present the results of direct numerical simulations in a new model setup designed to contain coexisting laminar and turbulent shear layers. As in Part I, we use the low Péclet number approximation of Lignières to model the evolution of the perturbations. Our main findings are twofold. First, turbulence is not necessarily generated whenever Zahn's nonlinear criterion JPr < (JPr)_c is satisfied, where J = N²/S² is the local gradient Richardson number, Pr = ν/κ_T is the Prandtl number, and (JPr)_c ≃ 0.007. We have demonstrated that the presence or absence of turbulent mixing in this limit hysteretically depends on the history of the shear layer. Second, Zahn's nonlinear instability criterion only approximately locates the edge of the turbulent layer, and mixing beyond the region where JPr < (JPr)_c can also take place in a manner analogous to convective overshoot. We found that the turbulent kinetic energy decays roughly exponentially beyond the edge of the shear-unstable region, on a lengthscale δ that is directly proportional to the scale of the turbulent eddies, which are themselves of the order of the Zahn scale (see Part I). Our results suggest that mixing by diffusive shear instabilities should be modeled with more care than is currently standard in stellar evolution codes.

We explore the influence of hot background temperatures in stellar clusters on the formation and evolution of photoevaporating disks. The disk forms from the gravitational collapse of a pre-stellar core. For a core with a relatively high temperature (>40 K), the angular momentum of the core is expected to be low. In the core-collapse stage, most of core mass directly falls onto the central star or the disk near the star. External photoevaporation is ineffective in this environment. The viscosity in the disk dominates its evolution, which leads to a high efficiency of the mass and angular momentum transports. The disk properties are determined by the core properties. In the vicinity of massive stars with strong external FUV fields, the disk can still survive when the background temperature is high (∼100 K). We suggest that the diversity of the molecular cloud core properties may lead to the diverse properties of the disk photoevaporation in clusters. We also consistently interpret the findings in NGC 1333 that low-mass disks (0.002–0.004 M_☉) can exist in such young clusters (1–2 × 10⁶ yr) with mild external photoevaporation.

The presence of SiS in space seems to be restricted to a few selected types of astronomical environments. It is long known to be present in circumstellar envelopes around evolved stars and it has also been detected in a handful of star-forming regions with evidence of outflows, like Sgr B2, Orion KL, and more recently, L1157-B1. The kinetics of reactions involving SiS is very poorly known and here we revisit the chemistry of SiS in space by studying some potentially important reactions of the formation and destruction of this molecule. We calculated ab initio potential energy surfaces of the SiOS system and computed rate coefficients in the temperature range of 50–2500 K for the reaction of the destruction of SiS in collisions with atomic O, and of its formation, through the reaction between Si and SO. We find that both of the reactions are rapid, with rate coefficients of a few times 10⁻¹⁰ cm³ s⁻¹, almost independent of temperature. In the reaction between Si and SO, SiO production is 5–7 times more efficient than SiS formation. The reaction of SiS with O atoms can play an important role in destroying SiS in envelopes around evolved stars. We built a simple chemical model of a postshock gas to study the chemistry of SiS in protostellar outflows and we found that SiS forms with a lower abundance and later than SiO, that SiS is efficiently destroyed through reaction with O, and that the main SiS-forming reactions are Si + SO and Si + SO₂.

We present atmospheric gas entropy profiles for 40 early-type galaxies and 110 clusters spanning several decades of halo mass, atmospheric gas mass, radio jet power, and galaxy type. We show that within ∼0.1R₂₅₀₀ the entropy profiles of low-mass systems, including ellipticals, brightest cluster galaxies, and spiral galaxies, scale approximately as K ∝ R^2/3. Beyond ∼0.1R₂₅₀₀ entropy profiles are slightly shallower than the K ∝ R^1.1 profile expected from gravitational collapse alone, indicating that heating by active galactic nuclei (AGN) feedback extends well beyond the central galaxy. We show that the K ∝ R^2/3 entropy profile shape indicates that thermally unstable cooling is balanced by heating where the inner cooling and free-fall timescales approach a constant ratio. Hot atmospheres of elliptical galaxies have a higher rate of heating per gas particle compared to those of central cluster galaxies. This excess heating may explain why some central cluster galaxies are forming stars while most early-type galaxies have experienced no significant star formation for billions of years. We show that the entropy profiles of six lenticular and spiral galaxies follow the R^2/3 form. The continuity between central galaxies in clusters, giant ellipticals, and spirals suggests perhaps that processes heating the atmospheres of elliptical and brightest cluster galaxies are also active in spiral galaxies.

We present a new cosmological probe for galaxy clusters, the halo sparsity. This characterizes halos in terms of the ratio of halo masses measured at two different radii and carries cosmological information encoded in the halo mass profile. Building on the work of Balmes et al., we test the properties of the sparsity using halo catalogs from a numerical N-body simulation of (2.6 Gpc h⁻¹)³ volume with 4096³ particles. We show that at a given redshift the average sparsity can be predicted from prior knowledge of the halo mass function. This provides a quantitative framework to infer cosmological parameter constraints using measurements of the sparsity of galaxy clusters. We show this point by performing a likelihood analysis of synthetic data sets with no systematics, from which we recover the input fiducial cosmology. We also perform a preliminary analysis of potential systematic errors and provide an estimate of the impact of baryonic effects on sparsity measurements. We evaluate the sparsity for a sample of 104 clusters with hydrostatic masses from X-ray observations and derive constraints on the cosmic matter density Ω_m and the normalization amplitude of density fluctuations at the 8 Mpc h⁻¹ scale, σ₈. Assuming no systematics, we find Ω_m = 0.42 ± 0.17 and σ₈ = 0.80 ± 0.31 at 1σ, corresponding to ${S}_{8}\equiv {\sigma }_{8}\sqrt{{{\rm{\Omega }}}_{m}}=0.48\pm 0.11$. Future cluster surveys may provide opportunities for precise measurements of the sparsity. A sample of a few hundred clusters with mass estimate errors at the few percent level can provide competitive cosmological parameter constraints complementary to those inferred from other cosmic probes.

HESS J1943+213 is a very high energy (VHE; >100 GeV) γ-ray source in the direction of the Galactic plane. Studies exploring the classification of the source are converging toward its identification as an extreme synchrotron BL Lac object. Here we present 38 hr of VERITAS observations of HESS J1943+213 taken over 2 yr. The source is detected with a significance of ∼20 standard deviations, showing a remarkably stable flux and spectrum in VHE γ-rays. Multifrequency Very Long Baseline Array (VLBA) observations of the source confirm the extended, jet-like structure previously found in the 1.6 GHz band with the European VLBI Network and detect this component in the 4.6 and 7.3 GHz bands. The radio spectral indices of the core and the jet and the level of polarization derived from the VLBA observations are in a range typical for blazars. Data from VERITAS, Fermi-LAT, Swift-XRT, the FLWO 48'' telescope, and archival infrared and hard X-ray observations are used to construct and model the spectral energy distribution (SED) of the source with a synchrotron self-Compton model. The well-measured γ-ray peak of the SED with VERITAS and Fermi-LAT provides constraining upper limits on the source redshift. Possible contribution of secondary γ-rays from ultra-high-energy cosmic-ray-initiated electromagnetic cascades to the γ-ray emission is explored, finding that only a segment of the VHE spectrum can be accommodated with this process. A variability search is performed across X-ray and γ-ray bands. No statistically significant flux or spectral variability is detected.

The line width of ions has been observed to be systematically narrower than that of the coexisting neutrals in molecular clouds and been interpreted as the signature of the decoupling of the neutral turbulence from magnetic fields in partially ionized medium. As a sequel of Li & Houde, here we present further observational evidence that supports these earlier proposals with the velocity coordinate spectrum analysis. We recover the turbulent energy spectra of HCN and HCO⁺ (4 − 3) in a starless molecular cloud in NGC 6334 where magnetic fields play a dynamically important role. Our analysis showed that the neutral spectrum is consistent with Kolmogorov type (${k}^{-5/3}$, where k is the wavenumber), while that of the ions is the same on the large scale, but steeper (∼k⁻²), for scales smaller than 0.404 pc. We carefully ruled out the possibilities that the spectrum difference can stem from the differences of ion and neutral optical depth and hyperfine structure.

Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow period–radius relations in the literature. Our very accurate physical parameter measurements allow us to calculate a purely empirical, tight period-mass–radius relation that agrees well with theoretical relations derived from non-canonical models. This empirical relation is a powerful tool to calculate accurate masses for single Cepheids for which precise radii can be obtained from Baade–Wesselink-type analyses. The mass of the type-II Cepheid κ Pav, 0.56 ± 0.08 M_⊙, determined using this relation is in a very good agreement with theoretical predictions. We find large differences between the p-factor values derived for the Cepheids in our sample. Evidence is presented that a simple period–p-factor relation shows an intrinsic dispersion, hinting at the relevance of other parameters, such as the masses, radii, and radial velocity variation amplitudes. We also find evidence that the systematic blueshift exhibited by Cepheids is primarily correlated with their gravity. The companion star of the Cepheid in the OGLE LMC-CEP-4506 system has a very similar temperature and luminosity, and is clearly located inside the Cepheid instability strip, yet it is not pulsating.

DQ Tau is a young low-mass spectroscopic binary, consisting of two almost equal-mass stars on a 15.8 day period surrounded by a circumbinary disk. Here, we analyze DQ Tau's light curves obtained by Kepler K2, the SpitzerSpace Telescope, and ground-based facilities. We observed variability phenomena, including rotational modulation by stellar spots, brief brightening events due to stellar flares, long brightening events around periastron due to increased accretion, and short dips due to brief circumstellar obscuration. The rotational modulation appears as a sinusoidal variation with a period of 3.017 days. In our model, this is caused by extended stellar spots 400 K colder than the stellar effective temperature. During our 80 day long monitoring, we detected 40 stellar flares with energies up to 1.2 × 10³⁵ erg and duration of a few hours. The flare profiles closely resemble those in older late-type stars, and their occurrence does not correlate with either the rotational or the orbital period. We observe elevated accretion rates of up to 5 × 10⁻⁸M_⊙ yr⁻¹ around each periastron. Our Spitzer data suggest that the increased accretion luminosity temporarily heats up the inner part of the circumbinary disk by about 100 K. We found an inner disk radius of 0.13 au, significantly smaller than expected from dynamical modeling of circumbinary disks. Interestingly, the inner edge of the disk corotates with the binary's orbit. DQ Tau also shows short dips of <0.1 mag in its light curve, reminiscent of the well-known "dipper phenomenon" observed in many low-mass young stars.

We use planetary nebulae (PNe) as probes to determine the Galactic radial oxygen gradients and other abundance patterns. We select data homogeneously from recent data sets, including PNe at large Galactocentric distances. The radial oxygen gradient calculated for the general PN population, which probes the region from the Galactic center out to ∼28 kpc, is shallow, with slope ∼−0.02 dex kpc⁻¹, in agreement with previous findings. We looked for time evolution of the metallicity gradient using PNe with different age progenitors as metallicity probes. We identify PNe whose progenitor stars are younger than 1 Gyr (YPPNe) and those whose progenitor stars are older than 7.5 Gyr (OPPNe) based on the comparison between evolutionary yields and elemental abundances of the PNe. By studying OPPNe and YPPNe separately, we found that (i) the OPPNe oxygen gradient is shallower (∼−0.015 dex kpc⁻¹) than that derived from YPPNe (∼−0.027 dex kpc⁻¹); (ii) the OPPNe inner radial distribution of oxygen is compatible with no gradient to the radial extent of the thick disk population (∼10 kpc), similarly to what has been observed in thick disk stars; and (iii) PNe (especially OPPNe) indicate that significant gradient slope is limited to Galactocentric distances between ∼10 and ∼13.5 kpc, as observed for open clusters and field stars. Outside this range, the distribution is almost flat. We found that the radial oxygen gradient is steeper for a PN population closer to the Galactic disk, similar to what is observed in the general stellar population by the SEGUE survey. We use our novel population dating to compare our results with current chemical evolutionary models and gradients from other Galactic populations for insight on galaxy chemical evolution.

We study the saturation effect on broad absorption line (BAL) variability through a variation phenomenon, which shows significant variation in Si iv BAL but no, or only small, change in C iv BAL (hereafter Phenomenon I). First, we explore a typical case showing Phenomenon I, quasar SDSS J153715.74+582933.9 (hereafter J1537+5829). We identify four narrow absorption line (NAL) systems within its Si iv BAL and two additional NAL systems within its C iv BAL, and confirm their coordinated weakening. Combining with the obvious strengthening of the ionizing continuum, we attribute the BAL variability in J1537+5829 to the ionization changes caused by the continuum variations. Second, a statistical study based on multiobserved quasars from SDSS-I/II/III are presented. We confirm that (1) the moderate anticorrelation between the fractional variations of Si iv BALs and the continuum in 74 quasars show Phenomenon I and (2) the sample showing BAL variations tends to have larger ionizing continuum variations. These results reveal the ubiquitous effect of the continuum variability on Phenomenon I and BAL variation. We attribute the relative lack of variation of C iv BALs in Phenomenon I to the saturation effects. Nonetheless, these absorbers are not very optically thick in Si iv and the ionization changes in response to continuum variations could be the main driver of their variations. Finally, we find that the saturation effect on BAL variability can explain many phenomena of BAL variations that have been reported before.

We present the polarization pulse profiles for 28 pulsars observed with the Arecibo Observatory by the North American Nanohertz Observatory for Gravitational Waves timing project at 2.1 GHz, 1.4 GHz, and 430 MHz. These profiles represent some of the most sensitive polarimetric millisecond pulsar profiles to date, revealing the existence of microcomponents (that is, pulse components with peak intensities much lower than the total pulse peak intensity). Although microcomponents have been detected in some pulsars previously, we present microcomponents for PSR B1937+21, PSR J1713+0747, and PSR J2234+0944 for the first time. These microcomponents can have an impact on pulsar timing, geometry, and flux density determination. We present rotation measures for all 28 pulsars, determined independently at different observation frequencies and epochs, and find the Galactic magnetic fields derived from these rotation measures to be consistent with current models. These polarization profiles were made using measurement equation template matching, which allows us to generate the polarimetric response of the Arecibo Observatory on an epoch-by-epoch basis. We use this method to describe its time variability and find that the polarimetric responses of the Arecibo Observatory's 1.4 and 2.1 GHz receivers vary significantly with time.

Using the group crossing time t_c as an age indicator for galaxy groups, we have investigated the correlation between t_c and the group spiral fraction, as well as between t_c and the neutral hydrogen gas fraction of galaxy groups. Our galaxy group sample is selected from the SDSS DR7 catalog, and the group spiral fraction is derived from the Galaxy Zoo morphological data set. We found that the group spiral galaxy fraction is correlated with the group crossing time. We further cross-matched the latest released ALFALFA 70% H i source catalog with the SDSS group catalog and have identified 172 groups from the SDSS survey whose total H i mass can be derived by summing up the H i mass of all the H i sources within the group radius. For the galaxies not detected in ALFALFA, we estimate their H i masses based on the galaxies' optical colors and magnitudes. Our sample groups contain more than eight member galaxies, they cover a wide range of halo masses and are distributed in different cosmic environments. We derived the group H i mass fraction, which is the ratio of group H i mass to the group virial mass. We found a correlation between the H i mass fraction and the group crossing time. Our results suggest that long timescale mechanisms such as starvation seem to play a more important role than short timescale processes like stripping in depleting H i gas in the SDSS galaxy groups.

Observations of interstellar dust are often used as a proxy for total gas column density N_H. By comparing Planck thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS, with accurate (opacity-corrected) H i column densities and newly published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth τ₃₅₃, reddening E(B − V), and the total proton column density N_H in the range (1–30) × 10²⁰ cm⁻², along sightlines with no molecular gas detections in emission. We derive an N_H/E(B − V) ratio of (9.4 ± 1.6) × 10²¹ cm⁻² mag⁻¹ for purely atomic sightlines at $| b| \gt 5^\circ$, which is 60% higher than the canonical value of Bohlin et al. We report a ∼40% increase in opacity σ₃₅₃ = τ₃₅₃/N_H, when moving from the low column density (N_H < 5 × 10²⁰ cm⁻²) to the moderate column density (N_H > 5 × 10²⁰ cm⁻²) regime, and suggest that this rise is due to the evolution of dust grains in the atomic interstellar medium. Failure to account for H i opacity can cause an additional apparent rise in σ₃₅₃ of the order of a further ∼20%. We estimate molecular hydrogen column densities ${N}_{{{\rm{H}}}_{2}}$ from our derived linear relations, and hence derive the OH/H₂ abundance ratio of X_OH ∼ 1 × 10⁻⁷ for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with ${N}_{{{\rm{H}}}_{2}}$ in the range ${N}_{{{\rm{H}}}_{2}}$ ∼ (0.1−10) × 10²¹ cm⁻². This suggests that OH may be used as a reliable proxy for H₂ in this range, which includes sightlines with both CO-dark and CO-bright gas.

We present the first paper of the series Origin of Metals around Galaxies, which aims to explore the origin of the metals observed in the circumgalactic and intergalactic media. In this work we extract and build catalogs of metal absorbers that will be used in future analyses, and make our results publicly available to the community. We design a fully automatic algorithm to search for absorption metal-line doublets of the species C iv, N v, Si iv, and Mg ii in high-resolution (R ≳ 30,000) quasar spectra without human intervention, and apply it to the high-resolution and signal-to-noise ratio spectra of 690 quasars, observed with the UVES and HIRES instruments. We obtain 5656 C iv doublets, 7919 doublets of Mg ii, 2258 of Si iv, and 239 of N v, constituting the largest high-resolution metal-doublet samples to date, and estimate the dependence of their completeness and purity on various doublet parameters such as equivalent width and redshift, using real and artificial quasar spectra. The catalogs include doublets with rest-frame line-equivalent widths down to a few mÅ, all detected at a significance above 3σ, and covering the redshifts between 1 < z ≲ 5, properties that make them useful for a wide range of chemical evolution studies.

We report the experimental observation of photon-bunching noise through shot noise measurements made on a pseudo-thermal state of light using balanced detection. A full theory describing the measurement is developed, and, in agreement with the theory, it is found that the shot noise variance in the balanced signal reproduces the time series of the flux of the primary incoherent beam. Moreover, when the average power of the pseudo-thermal light is varied, the balanced detection is seen to track this change. A comparison of direct detection and balanced detection of the thermal field shows that the balanced detection performs at least as well as the direct detection and under some conditions appears to outperform the direct detection. There is not necessarily a contradiction with quantum field theory, which predicts that at best the performance of the balanced detection should be equal to the direct detection because the direct detection process is subject to nonlinearity that has not been excluded by measurements (even though any tests we performed suggest that such effects are small). This is the first time that the bunching noise effect of high occupation number chaotic light via the shot noise of the field has successfully been measured, to the point of using it to infer the flux of the field. The findings may be relevant to radio receiver design, specifically from the viewpoint of sensitivity improvement.

We present Hubble Space Telescope (HST) absolute proper motion (PM) measurements for 20 globular clusters (GCs) in the Milky Way (MW) halo at Galactocentric distances ${R}_{\mathrm{GC}}\approx 10\mbox{--}100$ kpc, with a median per-coordinate PM uncertainty of 0.06 $\mathrm{mas}\,{\mathrm{yr}}^{-1}$. Young and old halo GCs do not show systematic differences in their 3D Galactocentric velocities, derived from combining existing line-of-sight velocities. We confirm the association of Arp 2, Pal 12, Terzan 7, and Terzan 8 with Sgr. These clusters and NGC 6101 have tangential velocity ${v}_{\tan }\,\gt 290$ km s⁻¹, whereas all other clusters have ${v}_{\tan }$ < 200 km s⁻¹. NGC 2419, the most distant GC in our sample, is also likely associated with the Sgr stream, whereas NGC 4147, NGC 5024, and NGC 5053 definitely are not. We use the distribution of orbital parameters derived using the 3D velocities to separate halo GCs that either formed within the MW or were accreted. We also assess the specific formation history of, e.g., Pyxis and Terzan 8. We constrain the MW mass via an estimator that considers the full 6D phase-space information for 16 of the GCs from ${R}_{\mathrm{GC}}=10$ to 40 kpc. The velocity dispersion anisotropy parameter $\beta ={0.609}_{-0.229}^{+0.130}$. The enclosed mass $M(\lt 39.5\,\mathrm{kpc})={0.61}_{-0.12}^{+0.18}\times {10}^{12}\,{M}_{\odot }$, and the virial mass ${M}_{\mathrm{vir}}={2.05}_{-0.79}^{+0.97}\times {10}^{12}\,{M}_{\odot }$. These are consistent with, but on the high side among, recent mass estimates in the literature.

We derive analytic estimates for the ability with which one can obtain precise, empirical stellar masses and radii via single-lined eclipsing binaries (EBs) in the era of Gaia and TESS. Including stars that host transiting substellar companions, such single-lined EBs already number in the hundreds from ground-based transit surveys and will comprise a major component of the science yield from the upcoming TESS mission. We explore the requirements for obtaining a given fractional precision on the masses and radii of single-lined EBs using primarily empirical means: radial velocity and eclipse measurements along with estimates of the primary's (1) surface gravity from high-resolution spectroscopy; (2) radius inferred from parallax, effective temperature, and bolometric flux; or (3) surface gravity and density from asteroseismology. We then compare these requirements to the precision obtained from invoking stellar models or empirical relations. We show that, for a fiducial transiting hot Jupiter system, precise, accurate, and essentially model-independent mass and radius measurements for such single-lined EBs will be possible in the era of Gaia. These will be comparable in precision to those obtained with double-lined EBs. Moreover, the systems for which these methods can be applied will vastly outnumber double-lined EBs, thereby possessing the potential to sample a more complete range of stellar types (such as M dwarfs); these systems will also, in many cases, be more amenable to precision metallicity and abundance determinations than are double-lined EBs.

We carry out magnetohydrodynamic (MHD) simulations of the quasi-static evolution and eruption of a twisted coronal flux rope under a coronal streamer built up by an imposed flux emergence at the lower boundary. The MHD model incorporates simple empirical coronal heating, optically thin radiative cooling, and field-aligned thermal conduction, and thus allows the formation of prominence condensations. We find that during the quasi-static evolution, prominence/filament condensations of an elongated, sigmoid morphology form in the dips of the significantly twisted field lines of the emerged flux rope due to runaway radiative cooling. A prominence cavity also forms around the prominence, which is best observed above the limb with the line of sight nearly along the length of the flux rope, as shown by synthetic SDO/AIA EUV images. The magnetic field supporting the prominence is significantly non-force-free despite the low plasma β. By comparing with a simulation that suppresses prominence formation, we find that the weight of the prominence is dynamically important and can suppress the onset of the kink instability and hold the flux rope in equilibrium for a significantly long time, until draining of the prominence plasma develops and reduces the weight of the prominence. The flux rope eventually develops the kink instability and erupts, producing a prominence eruption. The synthetic AIA 304 Å images show that the prominence is lifted up into an erupting loop, exhibiting helical features along the loop and substantial draining along the loop legs, as is often seen in observations.

We investigate the impact of the far-UV (FUV) heating rate on the stability of the three-phase interstellar medium using three-dimensional simulations of a $1\,{\mathrm{kpc}}^{2}$, vertically extended domain. The FUV heating rate sets the range of thermal pressures across which the cold ($\sim {10}^{2}\,{\rm{K}}$) and warm ($\sim {10}^{4}\,{\rm{K}}$) neutral media (CNM and WNM) can coexist in equilibrium. Even absent a variable star formation rate regulating the FUV heating rate, the gas physics keeps the pressure in the two-phase regime: because radiative heating and cooling processes happen on shorter timescales than sound wave propagation, turbulent compressions tend to keep the interstellar medium within the CNM–WNM pressure regime over a wide range of heating rates. The thermal pressure is set primarily by the heating rate with little influence from the hydrostatics. The vertical velocity dispersion adjusts as needed to provide hydrostatic support given the thermal pressure: when the turbulent pressure $\langle \rho \rangle {\sigma }_{z}^{2}$ is calculated over scales $\gtrsim 500\,\mathrm{pc}$, the thermal plus turbulent pressure approximately equals the weight of the gas. The warm gas volume filling fraction is $0.2\lt {f}_{w}\lt 0.8$ over a factor of less than three in heating rate, with f_w near unity at higher heating rates and near zero at lower heating rates. We suggest that cosmological simulations that do not resolve the CNM should maintain an interstellar thermal pressure within the two-phase regime.

Galactic outflows commonly contain multiphase gas, and its physical origin requires explanation. Using the Cholla Galactic OutfLow Simulations suite of high-resolution isolated galaxy models, we demonstrate the viability of rapid radiative cooling as a source of fast-moving (v ∼ 1000 km s⁻¹), cool (10⁴ K) gas observed in absorption-line studies of outflows around some star-forming galaxies. By varying the mass loading and geometry of the simulated winds, we identify a region of parameter space that leads to cool gas in outflows. In particular, when using an analytically motivated central feedback model, we find that cooling flows can be produced with reasonable mass-loading rates (${\dot{M}}_{\mathrm{wind}}/{\dot{M}}_{\mathrm{SFR}}\sim 0.5$), provided that the star formation rate surface density is high. When a more realistic clustered feedback model is applied, destruction of high-density clouds near the disk and interactions between different outflow regions indicate that lower mass-loading rates of the hot gas within the feedback region may still produce multiphase outflows. These results suggest an origin for fast-moving cool gas in outflows that does not rely on directly accelerating cool gas from the interstellar medium. These cooling flows may additionally provide an explanation for the multiphase gas ubiquitously observed in the halos of star-forming galaxies at low redshift.

Capella is a spectroscopic binary consisting of two G-type giants, where the primary (G8 iii) is a normal red clump giant while the secondary (G0 iii) is a chromospherically active fast rotator showing considerable overabundance of Li as Li-enhanced giants. Recently, Takeda & Tajitsu reported that abundance ratios of specific light elements (e.g., [C/Fe] or [O/Fe]) in Li-rich giants of high activity tend to be anomalously high, which they suspected to be nothing but superficial caused by unusual atmospheric structure due to high activity. Toward verifying this hypothesis, we determined the elemental abundances of the primary and the secondary of Capella based on the disentangled spectrum of each component, in order to see whether any apparent disagreement exists between the two, which should have been formed with the same chemical composition. We found that the primary is slightly supersolar (by ∼+0.1 dex), while the secondary is subsolar (by several tenths of dex) for heavier elements such as Fe, resulting in a marked discrepancy between the primary and secondary, though such a trend is not seen for light elements (e.g., C or O). These observational facts suggest that anomalously large [X/Fe] ratios found in Li-rich giants were mainly due to an apparent decrease of Fe abundance, which we speculate is caused by the overionization effect due to chromospheric UV radiation. We thus conclude that conventional model-atmosphere analysis would fail to correctly determine the abundances of fast-rotating giants of high activity, for which proper treatment of the chromospheric effect is required for deriving true photospheric abundances.

Low (≲1%) levels of circular polarization (CP) detected at radio frequencies in the relativistic jets of some blazars can provide insight into the underlying nature of the jet plasma. CP can be produced through linear birefringence, in which initially linearly polarized emission produced in one region of the jet is altered by Faraday rotation as it propagates through other regions of the jet with varying magnetic field orientation. Marscher has begun a study of jets with such magnetic geometries using the turbulent extreme multi-zone (TEMZ) model, in which turbulent plasma crossing a standing shock in the jet is represented by a collection of thousands of individual plasma cells, each with distinct magnetic field orientations. Here we develop a radiative transfer scheme that allows the numerical TEMZ code to produce simulated images of the time-dependent linearly and circularly polarized intensity at different radio frequencies. In this initial study, we produce synthetic polarized emission maps that highlight the linear and circular polarization expected within the model.

The hydrogen Lyman lines (91.2 nm < λ < 121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and they are enhanced during flares. We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s⁻¹. However, contrary to expectations, both redshifts and blueshifts were present and no dominant flow direction was observed. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, along with the radiative transfer code, RH, to simulate the evolution of the flaring chromosphere and the response of the Lyman lines during solar flares. We find that upflows in the simulated atmospheres lead to blueshifts in the line cores, which exhibit central reversals. We then model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instrument's properties. What may be interpreted as downflows (redshifted emission) in the lines, after they have been convolved with the instrumental line profile, may not necessarily correspond to actual downflows. Dynamic features in the atmosphere can introduce complex features in the line profiles that will not be detected by instruments with the spectral resolution of EVE, but which leave more of a signature at the resolution of the Spectral Investigation of the Coronal Environment instrument onboard the Solar Orbiter.

Using a cosmological N-body simulation that coevolves cold dark matter (CDM) and neutrino particles, we discover the local effects of massive neutrinos on the spatial distribution of CDM halos, reflected on the properties of Delaunay Triangulation (DT) voids. Smaller voids are generally in regions with higher neutrino abundance, so their surrounding halos are impacted by a stronger neutrino-free streaming. This makes the voids larger (surrounding halos are washed outward from the void center). On the contrary, larger voids are generally in regions with lower neutrino abundance, so their surrounding halos are less impacted by neutrino-free streaming, making the voids smaller (surrounding halos are squeezed toward the void center). This characteristic change of the spatial distribution of the halos suppresses the 2-point correlation function of halos on scales of ∼1 Mpc/h and significantly skews the number function of the DT voids, which can potentially serve as measurable neutrino effects in current or future galaxy surveys.

We reprise the analysis of Stassun & Torres, comparing the parallaxes of the eclipsing binaries reported in that paper to the parallaxes newly reported in the Gaia second data release (DR2). We find evidence for a systematic offset of −82 ± 33 μas, in the sense of the Gaia parallaxes being too small, for brightnesses (G ≲ 12) and for distances (0.03–3 kpc) in the ranges spanned by the eclipsing binary sample. The offset does not appear to depend strongly on distance within this range, though there is marginal evidence that the offset increases (becomes slightly more negative) for distances ≳1 kpc, up to the 3 kpc distances probed by the test sample. The offset reported here is consistent with the expectation that global systematics in the Gaia DR2 parallaxes are below 100 μas.

We calculate the radiative capture cross section for ⁷Be(α, γ)¹¹C and its reaction rate of relevance for the Big Bang nucleosynthesis (BBN). The impact of this reaction on the primordial ⁷Li abundance is revised including narrow and broad resonances in the pertinent energy region. Our calculations show that it is unlikely that very low energy resonances in ¹¹C of relevance for the BBN would emerge within a two-body potential model. Based on our results and a comparison with previous theoretical and experimental analyses, we conclude that the impact of this reaction on the so-called "cosmological lithium puzzle" is completely irrelevant.

Recent Galactic plane surveys of dust continuum emission at long wavelengths have identified a population of dense, massive clumps with no evidence for ongoing star formation. These massive starless clump candidates are excellent sites to search for the initial phases of massive star formation before the feedback from massive star formation affects the clump. In this study, we search for the spectroscopic signature of inflowing gas toward starless clumps, some of which are massive enough to form a massive star. We observed 101 starless clump candidates identified in the Bolocam Galactic Plane Survey (BGPS) in ${\mathrm{HCO}}^{+}$J = 1−0 using the 12 m Arizona Radio Observatory telescope. We find a small blue excess of $E=({N}_{\mathrm{blue}}-{N}_{\mathrm{red}})/{N}_{\mathrm{total}}=0.03$ for the complete survey. We identified six clumps that are good candidates for inflow motion and used a radiative transfer model to calculate mass inflow rates that range from 500 to 2000 ${M}_{\odot }$ Myr⁻¹. If the observed line profiles are indeed due to large-scale inflow motions, then these clumps will typically double their mass on a freefall time. Our survey finds that massive BGPS starless clump candidates with inflow signatures in ${\mathrm{HCO}}^{+}$J = 1−0 are rare throughout our Galaxy.

We present Atacama Large Millimeter/submillimeter Array observations of the 870 μm continuum and CO(4–3) line emission in the core of the galaxy cluster Cl J1449+0856 at z = 2, a near-IR-selected, X-ray-detected system in the mass range of typical progenitors of today's massive clusters. The 870 μm map reveals six F_870μm > 0.5 mJy sources spread over an area of 0.07 arcmin², giving an overdensity of a factor of ∼10 (6) with respect to blank-field counts down to F_870μm > 1 mJy (>0.5 mJy). On the other hand, deep CO(4–3) follow-up confirms membership of three of these sources but suggests that the remaining three, including the brightest 870 μm sources in the field (F_870μm ≳ 2 mJy), are likely interlopers. The measurement of 870 μm continuum and CO(4–3) line fluxes at the positions of previously known cluster members provides a deep probe of dusty star formation occurring in the core of this high-redshift structure, adding up to a total star formation rate of ∼700 ± 100 M_⊙ yr⁻¹ and yielding an integrated star formation rate density of ∼10⁴M_⊙ yr⁻¹ Mpc⁻³, five orders of magnitude larger than in the field at the same epoch, due to the concentration of star-forming galaxies in the small volume of the dense cluster core. The combination of these observations with previously available Hubble Space Telescope imaging highlights the presence in this same volume of a population of galaxies with already suppressed star formation. This diverse composition of galaxy populations in Cl J1449+0856 is especially highlighted at the very cluster center, where a complex assembly of quiescent and star-forming sources is likely forming the future brightest cluster galaxy.

We present a study of decimetric radio activity using the first high time cadence (0.5 s) images from the Giant Meterwave Radio Telescope (GMRT) at 610 MHz associated with GOES C1.4- and M1.0-class solar flares and a coronal mass ejection (CME) onset that occurred on 2015 June 20. The high spatial resolution images from GMRT show a strong radio source during the C1.4 flare located ∼500'' away from the flaring site with no corresponding bright footpoints or coronal features nearby. In contrast, however, strong radio sources are found near the flaring site during the M1.0 flare and around the CME onset time. Weak radio sources located near the flaring site are also found during the maximum of the C1.4 flare activity that show a temporal association with metric Type III bursts identified by the Solar Broadband Radio Spectrometer at Yunnan Astronomical Observatory. Based on a multiwavelength analysis and magnetic potential field source surface extrapolations, we suggest that the source electrons of GMRT radio sources and metric Type III bursts originated from a common electron acceleration site. We also show that the strong GMRT radio source is generated by a coherent emission process, and its apparent location far from the flaring site is possibly due to the wave-ducting effect.

We analyze the X-ray spectra of 19 main-sequence stars observed by Chandra using its LETGS configuration. Emission measure (EM) distributions are computed based on emission line measurements, an analysis that also yields evaluations of coronal abundances. The use of newer atomic physics data results in significant changes compared to past published analyses. The stellar EM distributions correlate with surface X-ray flux (F_X) in a predictable way, regardless of spectral type. Thus, we provide EM distributions as a function of F_X, which can be used to estimate the EM distribution of any main-sequence star with a measured broadband X-ray luminosity. Comparisons are made with solar EM distributions, both full-disk distributions and spatially resolved ones from active regions (ARs), flares, and the quiet Sun. For moderately active stars, the slopes and magnitudes of the EM distributions are in excellent agreement with those of solar ARs for $\mathrm{log}T\lt 6.6$, suggesting that such stars have surfaces completely filled with solar-like ARs. A stellar surface covered with solar X-class flares yields a reasonable approximation for the EM distributions of the most active stars. Unlike the EM distributions, coronal abundances are strongly dependent on spectral type, and we provide relations with surface temperature for both relative and absolute abundances. Finally, the coronal abundances of the exoplanet host star τ Boo A (F7 V) are anomalous, and we propose that this is due to the presence of the exoplanet.

The observations combined with theory of neutron star (NS) cooling play a crucial role in achieving the intriguing information of the stellar interior, such as the equation of state, composition, and superfluidity of dense matter. The traditional NS cooling theory is based on the assumption that the stellar structure does not change with time. The validity of such a static description has not yet been confirmed. We generalize the theory to a dynamic treatment; that is, continuous change of the NS structure (rearrangement of the stellar density distribution with the total baryon number fixed) as the decrease of temperature during the thermal evolution, is taken into account. It is found that the practical thermal energy used for the cooling is slightly lower than that estimated in a static situation, and hence the cooling of NSs is accelerated correspondingly but the effect is rather weak. Therefore, the static treatment is a good approximation in the calculations of NS cooling.

The hard X-ray emission in a solar flare is typically characterized by a number of discrete sources, each with its own spectral, temporal, and spatial variability. Establishing the relationship among these sources is critical to determining the role of each in the energy release and transport processes that occur within the flare. In this paper we present a novel method to identify and characterize each source of hard X-ray emission. The method permits a quantitative determination of the most likely number of subsources present, and of the relative probabilities that the hard X-ray emission in a given subregion of the flare is represented by a complicated multiple source structure or by a simpler single source. We apply the method to a well-studied flare on 2002 February 20 in order to assess competing claims as to the number of chromospheric footpoint sources present, and hence to the complexity of the underlying magnetic geometry/topology. Contrary to previous claims of the need for multiple sources to account for the chromospheric hard X-ray emission at different locations and times, we find that a simple two-footpoint-plus-coronal-source model is the most probable explanation for the data. We also find that one of the footpoint sources moves quite rapidly throughout the event, a factor that presumably complicated previous analyses. The inferred velocity of the footpoint corresponds to a very high induced electric field, compatible with the fields in thin reconnecting current sheets.

An Earth-like exoplanet orbiting a white dwarf (WD) would be exposed to different UV environments than Earth, influencing both its atmospheric photochemistry and UV surface environment. Through the use of a coupled 1D climate-photochemistry code, we model atmospheres of Earth-like planets in the habitable zone (HZ) of WDs for surface temperatures between 6000 and 4000 K, corresponding to about 7 billion years of WD evolution, and discuss the evolution of planetary models in the HZ during that evolution.

We implement a new semi-analytical approach to investigate radially self-similar solutions for the steady-state advection-dominated accretion flows (ADAFs). We employ the usual α-prescription for the viscosity, and all components of the energy–momentum tensor are considered. In this case, in the spherical coordinate, the problem reduces to a set of eighth-order, nonlinear differential equations with respect to the latitudinal angle θ. Using the Fourier expansions for all the flow quantities, we convert the governing differential equations to a large set of nonlinear algebraic equations for the Fourier coefficients. We solve the algebraic equations via the Newton–Raphson method, and investigate the ADAF properties over a wide range of model parameters. We also show that the implemented series are truly convergent. The main advantage of our numerical method is that it does not suffer from the usual technical restrictions that may arise for solving ADAF differential equations near the polar axis. In order to check the reliability of our approach, we recover some widely studied solutions. Further, we introduce a new varying α viscosity model. New outflow and inflow solutions for ADAFs are also presented, using Fourier expansion series.

The copper abundances of 29 metal-poor stars are determined based on the high-resolution, high-signal-to-noise ratio spectra from the UVES spectrograph at the ESO VLT telescope. Our sample consists of the stars of the Galactic halo, thick- and thin-disk, with [Fe/H] ranging from ∼−3.2 to ∼0.0 dex. The non-local thermodynamic equilibrium (NLTE) effects of Cu i lines are investigated, and line formation calculations are presented for an atomic model of copper including 97 terms and 1089 line transitions. We adopted the recently calculated photoionization cross sections of Cu i, and investigated the hydrogen collision by comparing the theoretical and observed line profiles of our sample stars. The copper abundances are derived for both local thermodynamic equilibrium (LTE) and NLTE based on the spectrum synthesis methods. Our results show that the NLTE effects for Cu i lines are important for metal-poor stars, in particular for very metal-poor stars, and these effects depend on the metallicity. For very metal-poor stars, the NLTE abundance correction reaches as large as ∼+0.5 dex compared to standard LTE calculations. Our results indicate that [Cu/Fe] is under-abundant for metal-poor stars (∼−0.5 dex) when the NLTE effects are included.

M55 (NGC 6809) and NGC 6362 are among the few globular clusters for which masses and radii have been derived to high precision for member binary stars. They also contain RR Lyrae variables, which, together with their non-variable horizontal-branch (HB) populations, provide tight constraints on the cluster reddenings and distance moduli through fits of stellar models to their pulsational and evolutionary properties. Reliable (m − M)_V estimates yield M_V and M_bol values of comparable accuracy for binary stars, because the V-band bolometric corrections applicable to them have no more than a weak dependence on effective temperature (${T}_{\mathrm{eff}}$) and [Fe/H]. Chemical abundances derived from the binary mass–M_V relations are independent of determinations based on their spectra. The temperatures of the binaries, which are calculated directly from their luminosities and the measured radii, completely rule out the low ${T}_{\mathrm{eff}}$ scale that has been determined for metal-deficient stars in some recent spectroscopic and interferometric studies. If [α/Fe] = 0.4 and [O/Fe] = 0.5 ± 0.1, we find that M55 has ${(m-M)}_{V}=13.95\pm 0.05$, [Fe/H] = −1.85 ± 0.1, and an age of 12.9 ± 0.8 Gyr, whereas NGC 6362 has ${(m-M)}_{V}=14.56\pm 0.05$, [Fe/H] = −0.90 ± 0.1, and an age of 12.4 ± 0.8 Gyr. The HB of NGC 6362 shows clear evidence for multiple stellar populations. Constraints from the RR Lyrae standard candle and from local subdwarfs (with Gaia DR2 parallaxes) are briefly discussed.

We present a study of X-ray source populations in M87, the cD galaxy of the Virgo cluster, using 12 archival Chandra observations with a total exposure of ∼680 ks spanning about a decade. A total of 346 point-like sources are detected down to a limiting 0.5–8 keV luminosity of 4 × 10³⁷ erg s⁻¹ and out to a galactocentric radius of ∼40 kpc. We cross-correlate the X-ray sources with published catalogs of globular clusters (GCs), derived from the ACS Virgo Cluster Survey and the Next Generation Virgo Cluster Survey. This results in 122 matches, making it one of the largest samples of GC-hosting X-ray sources in an external galaxy. These sources, most likely low-mass X-ray binaries (LMXBs), correspond to ∼5% of all known GCs within the Chandra field-of-view. Conversely, ∼50% of the detected X-ray sources are found in a GC. Moreover, red (metal-rich) GCs are ∼2.2 times more likely to host an X-ray source than blue (metal-poor) GCs. We also examine 76 currently known ultra-compact dwarf galaxies around M87 but find no significant X-ray counterparts. After statistically accounting for the cosmic X-ray background, we identify ∼110 field-LMXBs. The GC-LMXBs and field-LMXBs differ in their luminosity function and radial distribution, which indicates that the latter cannot be primarily originated from GCs. Using another set of deep Chandra observations toward ∼100 kpc northwest of the M87 center, we statistically constrain the abundance of field-LMXBs in the stellar halo, which is consistent with that found in the central region. We also identify 40 variable X-ray sources, among which one source is likely a black hole binary residing in a GC.

We present the results of an investigation of the dredge-up and mixing during the merger of two white dwarfs (WDs) with different chemical compositions by conducting hydrodynamic simulations of binary mergers for three representative mass ratios. In all the simulations, the total mass of the two WDs is ≲1.0 M_⊙. Mergers involving a CO and a He WD have been suggested as a possible formation channel for R Coronae Borealis (RCB)–type stars, and we are interested in testing if such mergers lead to conditions and outcomes in agreement with observations. Even if the conditions during the merger and subsequent nucleosynthesis favor the production of ¹⁸O, the merger must avoid dredging up large amounts of ¹⁶O, or else it will be difficult to produce sufficient ¹⁸O to explain the oxygen ratio observed to be of order unity. We performed a total of nine simulations using two different grid-based hydrodynamics codes using fixed and adaptive meshes and one smooth particle hydrodynamics (SPH) code. We find that in most of the simulations, >10⁻²M_⊙ of ¹⁶O is indeed dredged up during the merger. However, in SPH simulations where the accretor is a hybrid He/CO WD with a ∼0.1 M_⊙ layer of helium on top, we find that no ¹⁶O is being dredged up, while in the q = 0.8 simulation <10⁻⁴M_⊙ of ¹⁶O has been brought up, making a WD binary consisting of a hybrid CO/He WD and a companion He WD an excellent candidate for the progenitor of RCB stars.

High-time-resolution in situ wave observations show that Langmuir waves associated with solar type III radio bursts often occur as coherent localized one-dimensional magnetic-field-aligned wave packets with short durations of a few milliseconds and peak intensities well above the strong turbulence thresholds. In this paper, we report observations of a wave packet obtained by the time domain sampler of the STEREO WAVES experiment, which is unique in the sense that it is the most intense wave packet ever detected in association with a solar type III radio burst, with a peak intensity E_t ∼ 107 mVm⁻¹. We show that this wave packet provides evidence for (1) oscillating two-stream instability (OTSI), (2) a collapsing soliton formed as a result of OTSI, (3) the formation of a soliton–caviton pair, and (4) excitation of second and third harmonic electromagnetic waves. We also show that the peak intensity and spatial width satisfy the threshold condition for this wave packet to be the collapsing Langmuir wave packet formed as a result of nucleation processes even when δn_b > δn_p, where δn_b and δn_p are the levels of background and ponderomotive-force-induced density fluctuations, respectively. Thus, these observations provide unambiguous evidence for the spatial collapse of Langmuir waves in the source region of a type III radio burst, and the observed spectral evidence for OTSI and the ponderomotive-force-induced density cavity strongly suggest that OTSI is mostly likely responsible for the collapse of the observed wave packet.

We investigate the cause of the suppressed Balmer series and the origin of the white-light continuum emission in the X1.0 class solar flare on 2014 June 11. We use radiative hydrodynamic simulations to model the response of the flaring atmosphere to both electron and proton beams, which are energetically constrained using Ramaty High Energy Solar Spectroscopic Imager and Fermi observations. A comparison of synthetic spectra with the observations allows us to narrow the range of beam fluxes and low energy cutoff that may be applicable to this event. We conclude that the electron and proton beams that can reproduce the observed spectral features are those that have relatively low fluxes and high values for the low energy cutoff. While electron beams shift the upper chromosphere and transition region to greater geometrical heights, proton beams with a similar flux leave these areas of the atmosphere relatively undisturbed. It is easier for proton beams to penetrate to the deeper layers and not deposit their energy in the upper chromosphere where the Balmer lines are formed. The relatively weak particle beams that are applicable to this flare do not cause a significant shift of the τ = 1 surface and the observed excess WL emission is optically thin.

Though half of cosmic starlight is absorbed by dust and reradiated at long wavelengths (3 μm–3 mm), constraints on the infrared through the millimeter galaxy luminosity function (or the "IRLF") are poor in comparison to the rest-frame ultraviolet and optical galaxy luminosity functions, particularly at z ≳ 2.5. Here, we present a backward evolution model for interpreting number counts, redshift distributions, and cross-band flux density correlations in the infrared and submillimeter sky, from 70 μm–2 mm, using a model for the IRLF out to the epoch of reionization. Mock submillimeter maps are generated by injecting sources according to the prescribed IRLF and flux densities drawn from model spectral energy distributions that mirror the distribution of SEDs observed in 0 < z < 5 dusty star-forming galaxies (DSFGs). We explore two extreme hypothetical case studies: a dust-poor early universe model, where DSFGs contribute negligibly (<10%) to the integrated star formation rate density at z > 4; and an alternate dust-rich early universe model, where DSFGs dominate ∼90% of z > 4 star formation. We find that current submm/mm data sets do not clearly rule out either of these extreme models. We suggest that future surveys at 2 mm will be crucial to measuring the IRLF beyond z ∼ 4. The model framework developed in this paper serves as a unique tool for the interpretation of multiwavelength IR/submm extragalactic data sets, and will enable more refined constraints on the IRLF than can be made from direct measurements of individual galaxies' integrated dust emission.

Deep, pencil-beam surveys from ALMA at 1.1–1.3 mm have uncovered an apparent absence of high-redshift dusty galaxies, with existing redshift distributions peaking around z ∼ 1.5–2.5. This has led to a perceived dearth of dusty systems at z ≳ 4 and the conclusion, according to some models, that the early universe was relatively dust-poor. In this paper, we extend the backward-evolution galaxy model described by Casey et al. to the ALMA regime (in depth and area) and determine that the measured number counts and redshift distributions from ALMA deep field surveys are fully consistent with constraints of the infrared luminosity function (IRLF) at z < 2.5 determined by single-dish submillimeter and millimeter surveys conducted on much larger angular scales (∼1–10 deg²). We find that measured 1.1–1.3 mm number counts are most constraining for the measurement of the faint-end slope of the IRLF at z ≲ 2.5 instead of the prevalence of dusty galaxies at z ≳ 4. Recent studies have suggested that UV-selected galaxies at z > 4 may be particularly dust-poor, but we find that their millimeter-wave emission cannot rule out consistency with the Calzetti dust attenuation law, even by assuming relatively typical, cold-dust (T_dust ≈ 30 K) spectral energy distributions. Our models suggest that the design of ALMA deep fields requires substantial revision to constrain the prevalence of z > 4 early universe obscured starbursts. The most promising avenue for detection and characterization of such early dusty galaxies will come from future ALMA 2 mm blank-field surveys covering a few hundred arcmin² and the combination of existing and future dual-purpose 3 mm data sets.

A new measurement of a spatially extended gamma-ray signal from the center of the Andromeda galaxy (M31) has recently been published by the Fermi-LAT collaboration, reporting that the emission broadly resembles the so-called Galactic center excess (GCE) of the Milky Way (MW). The weight of the evidence is steadily accumulating on a millisecond pulsar (MSPs) origin for the GCE. These elements prompt us to compare these observations with what is, perhaps, the simplest model for an MSP population, which is solely obtained by rescaling of the MSP luminosity function that is determined in the local MW disk via the respective stellar mass of the systems. Remarkably, we find that without free fitting parameters, this model can account for both the energetics and the morphology of the GCE within uncertainties. For M31, the estimated luminosity due to primordial MSPs is expected to only contribute about a quarter of the detected emission, although a stronger contribution cannot be excluded given the large uncertainties. If correct, the model predicts that the M31 disk emission due to MSPs is not far below the present upper bound. We also discuss additional refinements of this simple model. Using the correlation between globular cluster gamma-ray luminosity and stellar encounter rate, we gauge the dynamical MSP formation in the bulge. This component is expected to contribute to the GCE only at a level of ≲5%, it could affect the signal's morphology. We also comment on the limitations of our model and on future perspectives for improved diagnostics.

Nonthermal electron acceleration via magnetic reconnection is thought to play an important role in powering the variable X-ray emission from radiatively inefficient accretion flows around black holes. The trans-relativistic regime of magnetic reconnection—where the magnetization σ, defined as the ratio of magnetic energy density to enthalpy density, is ∼1—is frequently encountered in such flows. By means of a large suite of two-dimensional particle-in-cell simulations, we investigate electron and proton acceleration in the trans-relativistic regime. We focus on the dependence of the electron energy spectrum on σ and the proton β (the ratio of proton thermal pressure to magnetic pressure). We find that the electron spectrum in the reconnection region is nonthermal and can be modeled as a power law. At low β, the slope, p, is independent of β and hardens with increasing σ as $p\simeq 1.8+0.7/\sqrt{\sigma }$. Electrons are primarily accelerated by the nonideal electric field at X-points, either in the initial current layer or in current sheets generated between merging magnetic islands. At higher values of β, the electron power law steepens, and the electron spectrum eventually approaches a Maxwellian distribution for all values of σ. At values of β near β_max ≈ 1/4σ, when both electrons and protons are relativistically hot prior to reconnection, the spectra of both species display an additional component at high energies, containing a few percent of particles. These particles are accelerated via a Fermi-like process by bouncing between the reconnection outflow and a stationary magnetic island

We present a new measurement of structure growth at z ≃ 0.08 obtained by correlating the cosmic microwave background (CMB) lensing potential map from the Planck satellite with the angular distribution of the 2MASS Photometric Redshift galaxies. After testing for, and finding no evidence for systematic effects, we calculate the angular auto- and cross-power spectra. We combine these spectra to estimate the amplitude of structure growth using the bias-independent D_G estimator introduced by Giannantonio et al. We find that the relative amplitude of D_G with respect to the predictions based on Planck cosmology is ${A}_{D}(z=0.08)=1.00\pm 0.21$, fully consistent with the expectations for the standard cosmological model. Considering statistical errors only, we forecast that a joint analysis between an LSST-like photometric galaxy sample and lensing maps from upcoming ground-based CMB surveys like the Simons Observatory and CMB-S4 can yield sub-percent constraints on the growth history and differentiate between different models of cosmic acceleration.

Ultra-diffuse galaxies (UDGs) are unusual galaxies with low luminosities, similar to classical dwarf galaxies, but with sizes up to ∼5 larger than expected for their mass. Some UDGs have large populations of globular clusters (GCs), something unexpected in galaxies with such low stellar density and mass. We have carried out a comprehensive study of GCs in both UDGs and classical dwarf galaxies at comparable stellar masses using Hubble Space Telescope (HST) observations of the Coma cluster. We present new imaging for 33 Dragonfly UDGs with the largest effective radii (>2 kpc), and additionally include 15 UDGs and 54 classical dwarf galaxies from the HST/ACS Coma Treasury Survey and the literature. Out of a total of 48 UDGs, 27 have statistically significant GC systems, and 11 have candidate nuclear star clusters. The GC specific frequency (S_N) varies dramatically, with the mean S_N being higher for UDGs than for classical dwarfs. At constant stellar mass, galaxies with larger sizes (or lower surface brightnesses) have higher S_N, with the trend being stronger at higher stellar mass. At lower stellar masses, UDGs tend to have higher S_N when closer to the center of the cluster, i.e., in denser environments. The fraction of UDGs with a nuclear star cluster also depends on environment, varying from ∼40% in the cluster core, where it is slightly lower than the nucleation fraction of classical dwarfs, to ≲20% in the outskirts. Collectively, we observe an unmistakable diversity in the abundance of GCs, and this may point to multiple formation routes.

We investigate the gamma-ray and X-ray emission from the transient gamma-ray source Fermi J0035+6131, which was discovered with the Fermi Large Area Telescope (LAT) near the Galactic plane at b = 13, and we discuss potential multi-wavelength counterparts of the gamma-ray source. Our analysis of over 9 years of Fermi LAT data revealed two flaring events lasting 10–30 hr during which the gamma-ray flux increased by a factor of >300 compared to the long-term average. We also analyzed X-ray data obtained with XMM-Newton and Swift and identified several sources with a hard X-ray spectrum inside the Fermi LAT confidence region. The two brightest X-ray sources have known counterparts at other wavelengths and are associated with the compact radio source VCS4 J0035+6130 and the B1 IV:nn star HD 3191, respectively. VCS4 J0035+6130, which is also detected in the near infrared, is likely an active galaxy serendipitously located behind the Galactic disk and is the most compelling candidate for the counterpart of the gamma-ray source. HD 3191 appears to be part of an X-ray binary with a compact companion and is unlikely to be associated with Fermi J0035+6131.

As one of the simplest molecules containing a peptide bond, N-methyl formamide (HCONHCH₃) represents a potential key molecule involved in the peptide bond polymerization in extraterrestrial ices. Detected tentatively toward the star-forming region Sgr B2(N2), the synthetic pathways have previously been elusive. By exploiting isomer-selective detection of the reaction products via photoionization, coupled with reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), we present compelling evidence for the formation of N-methyl formamide (HCONHCH₃) in astrochemically relevant ice mixtures of methylamine (CH₃NH₂) and carbon monoxide (CO), upon irradiation with energetic electrons as generated in the track of galactic cosmic ray particles (GCRs) penetrating interstellar ices. As one of the simplest molecules containing a peptide bond (–CO–NH–), N-methyl formamide could represent a benchmark involved in radiation-induced peptide bond polymerization in extraterrestrial ices, and thus bring us closer to revealing where in the Universe the molecular precursors linked to the origins of life might have been synthesized.

We present a near-infrared K-band R ≃ 1500 Keck spectrum of S68N, a Class 0 protostar in the Serpens molecular cloud. The spectrum shows a very red continuum, CO absorption bands, weak or nonexistent atomic metal absorptions, and H₂ emission lines. The near-IR H₂ emission is consistent with excitation in shocks or by X-rays but not by UV radiation. We model the absorption component as a stellar photosphere plus circumstellar continuum emission with wavelength-dependent extinction. A Markov Chain Monte Carlo analysis shows that the most likely model parameters are consistent with a low-temperature, low-gravity photosphere with significant extinction and no more than modest continuum veiling. Its T_eff ≃ 3260 K effective temperature is similar to that of older, more evolved pre-main-sequence stars, but its surface gravity log g ≃ 2.4 cm s⁻² is approximately 1 dex lower. This implies that the radius of this protostar is a factor of ∼3 larger than that of 10⁶ year old T Tauri stars. Its low veiling is consistent with a circumstellar disk having intrinsic near-IR emission that is less than or equal to that of more evolved Class I protostars. Along with the high extinction, this suggests that most of the circumstellar material is in a cold envelope, as expected for a Class 0 protostar. This is the first known detection and analysis of a Class 0 protostar absorption spectrum.

Using the data from the Solar Dynamics Observatory, the Ahead of Solar Terrestrial Relations Observatory, the Global Oscillation Network Group (GONG), and the Large Angle and Spectrometric Coronagraphs, the nearly 90° deflected eruption of a filament and the following coronal mass ejection (CME) occurring on the northern edge of AR 11123 on 2010 November 15 were presented in this paper. The filament was very small with the projected length of about 2.6 × 10⁴ km and centered at about ${\rm{S}}23^\circ$ W $38^\circ$. The potential-field source-surface model identified that the filament was located near the northern flank of a helmet streamer. The filament initially erupted northward to the nearby open fields with speeds from 151 to 336 km s⁻¹, resulting in a B7.6 subflare and some signatures of interchange reconnection. This suggested that the erupting filament interacted with the open fields at first. Then, guided by the highly-inclined open fields, it deflected about 90° southward on the plane of the sky to the magnetic minimum in the streamer configuration. In addition, the CME with the width of 64° and the central position angle of 221° was also deflected obviously in the inner corona to attain its final direction. Because the eruption failed to penetrate the open fields, these results corroborate the idea that open magnetic flux can act as a magnetic wall while a streamer belt can act as a potential well for coronal eruptions in the Sun.

Radiative transfer models were developed to understand the optical polarizations in edge-on galaxies, which are observed to occur even outside the geometrically thin dust disk, with a scale height of ≈0.2 kpc. In order to reproduce the vertically extended polarization structure, we find that it is essential to include a geometrically thick dust layer in the radiative transfer model, in addition to the commonly known thin dust layer. The models include polarizations due to both dust scattering and dichroic extinction, which are responsible for the observed interstellar polarization in the Milky Way. We also find that the polarization level is enhanced if the clumpiness of the interstellar medium, and the dichroic extinction by vertical magnetic fields in the outer regions of the dust lane are included in the radiative transfer model. The predicted degree of polarization outside the dust lane was found to be consistent with that (ranging from 1% to 4%) observed in NGC 891.

After discovery of the Fermi bubbles, giant structures observed from radio to X-ray monitoring have been widely discussed as possible evidence of past activities in the Galactic center (GC). We report here on the analysis of all the Suzaku archival data pointing around the giant-scale Loop I arc. The diffuse X-ray emission from the northern Loop I arc was well represented by the three-component model: (1) an unabsorbed thermal plasma with kT ≃ 0.1 keV either from the local hot bubble (LHB) and/or solar wind charge exchange (SWCX), (2) an absorbed thermal plasma regarded as a contribution from the Loop I and the Galactic halo (GH), and (3) an absorbed power-law component representing the cosmic X-ray background (CXB). The temperature of the absorbed thermal plasma was narrowly clustered in a range of 0.30 ± 0.02 keV along Loop I ("ON" regions), whereas the temperature was a little lower in the cavity adjacent to the bubbles and Loop I ("OFF" regions) with 0.24 ± 0.03 keV. The emission measure (EM) largely varied along the Galactic latitude b, and was well correlated with the count rate variation as measured with the ROSAT all-sky map in 0.75 keV. Although the amount of neutral gas does not provide any useful constraints on the distance to Loop I, the observed EM values clearly reject a hypothesis that the structure is close to the Sun; we argue that Loop I is a distant, kiloparsec structure in the GH. We discuss the origin of apparent mismatch in the morphologies of the Fermi bubbles and the Loop I arc, suggesting a two-step explosion process in the GC.

We present Hubble Space Telescope ultraviolet spectroscopy of the recurrent nova T Pyxidis obtained more than five years after its 2011 outburst, indicating that the system might not have yet reached its deep quiescent state. The ultraviolet data exhibit a 20% decline in the continuum flux from the pre-outburst deep quiescence state to the post-outburst near quiescent state. We suggest that a decline across each recurring nova eruption might help explain the proposed 2 mag steady decline of the system since 1866. Using an improved version of our accretion disk model as well as International Ultraviolet Explorer ultraviolet and optical data, and the 4.8 kpc distance derived by Sokoloski et al. (and confirmed by De Gennaro Aquino et al.), we corroborate our previous findings that the quiescent mass accretion rate in T Pyx is of the order of 10⁻⁶M_⊙ yr⁻¹. Such a large mass accretion rate would imply that the mass of the white dwarf is increasing with time. However, with the just-released Gaia DR 2 distance of ∼3.3 kpc (after submission of the first version of this manuscript), we find a mass accretion rate more in line with the estimate of Patterson et al., of the order of 10⁻⁷M_⊙ yr⁻¹. Our results predict powerful soft X-ray or extreme ultraviolet emission from the hot inner region of the high accretion rate disk. Using constraining X-ray observations and assuming that the accretion disk does not depart too much from the standard model, we are left with two possible scenarios. The disk either emits mainly extreme ultraviolet radiation, which, at a distance of 4.8 kpc, is completely absorbed by the interstellar medium, or the hot inner disk, emitting soft X-rays, is masked by the bulging disk seen at a higher inclination.

Observations of young open clusters (OCs) show a bimodal distribution of rotation periods that has been difficult to explain with existing stellar spin-down models. Detailed magnetohydrodynamic (MHD) stellar wind simulations have demonstrated that surface magnetic field morphology has a strong influence on wind-driven angular momentum loss. Observations suggest that faster rotating stars store a larger fraction of their magnetic flux in higher-order multipolar components of the magnetic field. In this work, we present an entirely predictive new model for stellar spin-down that accounts for the stellar surface magnetic field configuration. We show how a magnetic complexity that evolves from complex toward simple configurations as a star spins down can explain the salient features of stellar rotation evolution, including the bimodal distribution of both slow and fast rotators seen in young OCs.