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Motivated by the irregular and little-understood morphologies of z ~ 2-3 galaxies, we use nonparametric coefficients to quantify the morphologies of 216 galaxies that have been spectroscopically confirmed to lie at redshifts z = 1.8-3.4 in the GOODS-N field. Using measurements of UV and optical spectral lines, multiband photometric data, and stellar population models, we statistically assess possible correlations between galaxy morphology and physical observables such as stellar mass, star formation rate, and the strength of galaxy-scale outflows. We find evidence that dustier galaxies have more nebulous UV morphologies and that larger, more luminous galaxies may drive stronger outflows, but we otherwise conclude that UV morphology is either statistically decoupled from the majority of physical observables or determined by too complex a combination of physical processes to provide characterizations with predictive power. Given the absence of strong correlations between UV morphology and physical parameters such as star formation rates, we are therefore unable to support the hypothesis that morphologically irregular galaxies predominantly represent major galaxy mergers. Comparing galaxy samples, we find that IR-selected BzK galaxies and radio-selected submillimeter galaxies have UV morphologies similar to the optically selected sample, while distant red galaxies are more nebulous.

We present a new nonparametric method for determining mean 3D density and mass profiles from weak-lensing measurements around stacked samples of galaxies or clusters, that is, from measurement of the galaxy-shear or cluster-shear correlation functions. Since the correlation function is statistically isotropic, this method evades problems, such as projection of large-scale structure along the line of sight or halo asphericity, that complicate attempts to infer masses from weak-lensing measurements of individual objects. We demonstrate the utility of this method in measuring halo profiles, galaxy-mass and cluster-mass cross-correlation functions, and cluster virial masses. We test this method on an N-body simulation and show that it correctly and accurately recovers the 3D density and mass profiles of halos. We find no evidence of problems due to a mass sheet degeneracy in the simulation. Cross-correlation lensing provides a powerful method for calibrating the mass-observable relation for use in measurement of the cluster mass function in large surveys. It can also be used on large scales to measure and remove the halo bias and thereby provide a direct measurement of Ω_mσ₈.

We present the rest-frame optical (B, V, and R band) luminosity functions (LFs) of galaxies at 2 ≤ z ≤ 3.5, measured from a K-selected sample constructed from the deep NIR MUSYC, the ultradeep FIRES, and the GOODS-CDFS. This sample is unique for its combination of area and range of luminosities. The faint-end slopes of the LFs at z > 2 are consistent with those at z ~ 0. The characteristic magnitudes are significantly brighter than the local values (e.g., ~1.2 mag in the R band), while the measured values for Φ^⋆ are typically ~5 times smaller. The B-band luminosity density at z ~ 2.3 is similar to the local value, and in the R band it is ~2 times smaller than the local value. We present the LF of distant red galaxies (DRGs), which we compare to that of non-DRGs. While DRGs and non-DRGs are characterized by similar LFs at the bright end, the faint-end slope of the non-DRG LF is much steeper than that of DRGs. The contribution of DRGs to the global densities down to the faintest probed luminosities is 14%-25% in number and 22%-33% in luminosity. From the derived rest-frame U - V colors and stellar population synthesis models, we estimate the mass-to-light ratios (M/L) of the different subsamples. The M/L ratios of DRGs are ~5 times higher (in the R and V bands) than those of non-DRGs. The global stellar mass density at 2 ≤ z ≤ 3.5 appears to be dominated by DRGs, whose contribution is of order ~60%-80% of the global value. Qualitatively similar results are obtained when the population is split by rest-frame U - V color instead of observed J - K color.

We present deep, high angular-resolution HST NICMOS imaging in the Hubble Deep Field South (HDF-S), focusing on a subset of 14 distant red galaxies (DRGs) at z ~ 2.5 that have been preselected to have J - K > 2.3. We find a clear trend between the rest-frame optical sizes of these sources and their luminosity-weighted stellar ages as inferred from their broadband spectral energy distributions (SEDs). Galaxies whose SEDs are consistent with being dusty and actively star-forming generally show extended morphologies in the NICMOS images (r_e ≳ 2 kpc), while the five sources that are not vigorously forming stars are extremely compact (r_e ≲ 1 kpc). This trend suggests a direct link between the mean ages of the stars and the size and density of the galaxies and supports the conjecture that early events quench star formation and leave compact remnants. Furthermore, the compact galaxies have stellar surface mass densities that exceed those of local galaxies by more than an order of magnitude. The existence of such massive dense galaxies presents a problem for models of early-type galaxy formation and evolution. Larger samples of DRGs and higher spatial resolution imaging will allow us to determine the universality of the results presented here for a small sample.

We present a time-variability analysis of 29 broad absorption line quasars (BALQSOs) observed in two epochs by the Sloan Digital Sky Survey. These spectra are selected from a larger sample of BALQSOs with multiple observations by virtue of exhibiting a broad C IV λ1549 absorption trough separated from the rest frame of the associated emission peak by more than 3600 km s^-1. Detached troughs facilitate higher precision variability measurements, since the measurement of the absorption in these objects is not complicated by variation in the emission-line flux. We have undertaken a statistical analysis of these detached-trough BALQSO spectra to explore the relationships between BAL features that are seen to vary and the dynamics of emission from the quasar central engine. We have measured variability within our sample, which includes three strongly variable BALs. We have also verified that the statistical behavior of the overall sample agrees with current model predictions and previous studies of BAL variability. Specifically, we observe that the strongest BAL variability occurs among the smallest equivalent width features and at velocities exceeding 12,000 km s^-1, as predicted by recent disk-wind modeling.

We present a pilot study of the X-ray properties of intermediate-mass (~10⁵-10⁶M_☉) black holes in active galaxies using the Chandra X-ray telescope. Eight of the 10 active galaxies are detected with a significance of at least 3 σ, with X-ray luminosities in the range L_{0.5-2 keV} ≈ 10⁴¹-10⁴³ ergs s^-1. The optical to X-ray flux ratios are consistent with expectations, given the known correlations between α_ox and ultraviolet luminosity, while a couple of objects appear to be anomalously X-ray weak. The range of 0.5 to 2 keV photon indices we measure, 1 < Γ_s < 2.7, is entirely consistent with values found in samples of more luminous sources with more massive black holes. Black hole mass is evidently not a primary driver of soft X-ray spectral index. On the other hand, we do find evidence for a correlation between the X-ray power-law slope and both X-ray luminosity and Eddington ratio, which may suggest that X-ray emission mechanisms weaken at high Eddington ratios. Such a weakening may explain the anomalous X-ray weakness of one of our most optically luminous objects.

We build and test Parker wind models to apply to observations of large-scale (~100 pc) outflows from AGNs. These models include detailed photoionization simulations, the observed radially varying mass profile, adiabatic cooling, and approximations for clouds dragged along in the wind and the interaction of the wind with the circumnuclear ISM of the galaxy. We test this model against recent HST STIS observations of [O III] emission-line kinematics (in particular, we test against those observed in NGC 4151, but approximately the same kinematics is observed in NGC 1068 and Mrk 3) to constrain the viability of large-scale thermal winds in AGNs. We find that adiabatic cooling dominates in these outflows, decelerating Parker winds on large scales, making them highly unlikely as explanations of the observed kinematics.

The unification model for AGNs posits that Seyfert 2 galaxies are intrinsically like Seyfert 1 galaxies, but that their broad-line regions (BLRs) are hidden from our view. A Seyfert 2 nucleus that truly lacked a BLR, instead of simply having it hidden, would be a so-called true Seyfert 2. No object has as yet been conclusively proven to be one. We present a detailed analysis of four of the best true Seyfert 2 candidates discovered to date: IC 3639, NGC 3982, NGC 5283, and NGC 5427. None of the four have a broad Hα emission line, in either direct or polarized light. All four have rich, high-excitation spectra, blue continua, and HST images showing them to be unresolved sources with no host-galaxy obscuration. To check for possible obscuration on scales smaller than that resolvable by HST, we obtained X-ray observations using Chandra. All four objects show evidence of obscuration and therefore could have hidden BLRs. The picture that emerges is of moderate to high, but not necessarily Compton-thick, obscuration of the nucleus, with extranuclear soft emission extended on the hundreds of parsec scale that may originate in the narrow-line region. Since the extended soft emission compensates, in part, for the nuclear soft emission lost to absorption, both absorption and luminosity are likely to be severely underestimated unless the X-ray spectrum is of sufficient quality to distinguish the two components. This is of special concern where the source is too faint to produce a large number of counts, or where the source is too far away to resolve the extended soft X-ray-emitting region.

We present the energy-dependent power spectral density (PSD) and cross spectral properties of Mrk 766, obtained from combining data obtained during an XMM-Newton observation spanning six revolutions in 2005 with data obtained from an XMM-Newton long look in 2001. The PSD shapes and rms-flux relations are found to be consistent between the 2001 and 2005 observations, suggesting that the 2005 observation is simply a low-flux extension of the 2001 observation and permitting us to combine the two data sets. The resulting PSD has the highest temporal frequency resolution for any AGN PSD measured to date. Applying a broken power-law model yields break frequencies that increase in temporal frequency with photon energy. Obtaining a good fit when assuming energy-independent break frequencies requires the presence of a Lorentzian at (4.6 ± 0.4) × 10^-4 Hz whose strength increases with photon energy, a behavior seen in black hole X-ray binaries. The cross spectral properties are measured; temporal frequency-dependent soft-to-hard time lags are detected in this object for the first time. Cross spectral results are consistent with those for other accreting black hole systems. The results are discussed in the context of several variability models, including those based on inwardly propagating viscosity variations in the accretion disk.

In a series of papers, Nicastro et al. have reported the detection of z > 0 O VII absorption features in the spectrum of Mrk 421 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We evaluate this result in the context of a high-quality spectrum of the same source obtained with the Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over 955 ks of usable exposure time and more than 2.6 × 10⁴ counts per 50 mÅ at 21.6 Å. We concentrate on the spectrally clean region (21.3 < λ < 22.5 ), where sharp features due to the astrophysically abundant O VII may reveal an intervening, warm-hot intergalactic medium (WHIM). We do not confirm detection of any of the intervening systems claimed to date. Rather, we detect only three unsurprising, astrophysically expected features down to the log(N_i) ~ 14.6 (3 σ) sensitivity level. Each of the two purported WHIM features is rejected with a statistical confidence that exceeds that reported for its initial detection. While we cannot rule out the existence of fainter, WHIM related features in these spectra, we suggest that previous discovery claims were premature. A more recent paper by Williams et al. claims to have demonstrated that the RGS data we analyze here do not have the resolution or statistical quality required to confirm or deny the LETGS detections. We show that our analysis resolves the issues encountered by Williams et al. and recovers the full resolution and statistical quality of the RGS data. We highlight the differences between our analysis and those published by Williams et al. as this may explain our disparate conclusions.

The clustering properties of dark matter halos are a firm prediction of modern theories of structure formation. We use two large-volume, high-resolution N-body simulations to study how the correlation function of massive dark matter halos depends on their mass, assembly history, and recent merger activity. We find that halos with the lowest concentrations are currently more clustered than those of higher concentration, the size of the effect increasing with halo mass; this agrees with trends found in studies of lower mass halos. The clustering dependence on other characterizations of the full mass accretion history appears weaker than the effect with concentration. Using the integrated correlation function, marked correlation functions, and a power-law fit to the correlation function, we find evidence that halos that have recently undergone a major merger or a large mass gain have slightly enhanced clustering relative to a randomly chosen population with the same mass distribution.

We present spectra taken with the Infrared Spectrograph on Spitzer covering the 5-38 μm region of the 10 ultraluminous infrared galaxies (ULIRGs) found in the IRAS Bright Galaxy Sample (BGS). There is a factor of 50 spread in the rest-frame 5.5-60 μm spectral slopes, and the 9.7 μm silicate optical depths range from at least τ_9.7 ≤ 0.4 (A_V ~ 8) to τ_9.7 ≥ 4.2 (A_V ≥ 78). There is evidence for water ice and hydrocarbon absorption and C₂H₂ and HCN absorption features in 4 and possibly 6 of the 10 BGS ULIRGs, indicating shielded molecular clouds and a warm, dense ISM. We have detected [Ne V] emission in 3 of the 10 BGS ULIRGs, at flux levels of 5-18 × 10^-14 ergs cm^-2 s^-1 and [Ne V] 14.3/[Ne II] 12.8 line flux ratios of 0.12-0.85. The remaining BGS ULIRGs have limits on their [Ne V]/[Ne II]line flux ratios, which range from ≤0.15 to ≤0.01. Among the BGS ULIRGs, the AGN fractions implied by either the [Ne V]/[Ne II] or [O IV]/[Ne II] line flux ratios (or their upper limits) are significantly lower than implied by the MIR slope or strength of the 6.2 μm PAH EQW feature. There is evidence for hot (T > 300 K) dust in five of the BGS ULIRGs, with the fraction of hot dust to total dust luminosity ranging from ~1% to 23%, before correcting for extinction. When integrated over the IRAC-8, IRS blue peak-up, and MIPS-24 filter bandpasses, the IRS spectra imply very blue colors for some ULIRGs at z ~ 1.3. The large range in diagnostic parameters among the nearest ULIRGs suggests that matching survey results to a small number of templates may lead to biased results about the fraction of luminous dusty starbursts and AGNs at high z.

We present echelle spectrophotometry of the blue compact dwarf galaxy NGC 5253 obtained with the VLT UVES. We have measured the intensities of a large number of permitted and forbidden emission lines in four zones of the central part of the galaxy. We detect faint C II and O II recombination lines, the first time that these are unambiguously detected in a dwarf starburst galaxy. The physical conditions of the ionized gas have been derived using a large number of different line intensity ratios. Chemical abundances of He, N, O, Ne, S, Cl, Ar, and Fe have been determined following standard methods. C⁺⁺ and O⁺⁺ abundances have been derived from pure recombination lines and are larger than those obtained from collisionally excited lines (from 0.30 to 0.40 dex for C⁺⁺ and from 0.19 to 0.28 dex for O⁺⁺). This result is consistent with a temperature fluctuation parameter (t²) between 0.050 and 0.072. We confirm previous results that indicate the presence of a localized N enrichment in certain zones of NGC 5253 and detect a possible slight He overabundance in the same zones. The enrichment pattern agrees with that expected for the pollution by the ejecta of Wolf-Rayet (W-R) stars. The amount of enriched material needed to produce the observed overabundance is consistent with the mass lost by the number of W-R stars estimated in the starbursts. We discuss the possible origin of the difference between abundances derived from recombination and collisionally excited lines (the so-called abundance discrepancy problem) in H II regions, finding that a recent hypothesis based on the delayed enrichment by SN ejecta inclusions seems not to explain the observed features.

I present deep spectroscopy of four H II regions in the inner, metal-rich zone of the spiral galaxy M101 obtained with the LRIS spectrograph at the Keck telescope. From the analysis of the collisionally excited lines in two of the target H II regions, H1013 and H493, I have obtained oxygen abundances 12 + log(O/H) = 8.52 and 12 + log(O/H) = 8.74, respectively. These measurements extend the determination of the oxygen abundance gradient of M101 via the direct method to only 3 kpc from the center. The intensity of the C II λ4267 line in H1013 leads to a carbon abundance 12 + log(C/H) = 8.66, corresponding to nearly twice the solar value. From a comparison of the continuum temperature derived from the Balmer discontinuity, T(Bac) = 5000 K, and the line temperature derived from [O III] λ4363/λ5007, T[O III] = 7700 K, an average temperature T₀ = 5500 K and a mean square temperature fluctuation t² = 0.06 have been derived. Accounting for the spatial inhomogeneity in temperature raises the oxygen abundance obtained from the oxygen auroral lines to 12 + log(O/H) = 8.93. These findings are discussed in the context of the calibration of strong-line metallicity indicators, in particular of the upper branch of R₂₃. There is no evidence for the strong abundance biases arising from temperature gradients predicted theoretically for metal-rich H II regions.

We present observations of the 22 GHz H₂O megamasers in the circumnuclear disk of NGC 3079 obtained with the Green Bank Telescope. The data are analyzed for circular polarization due to the Zeeman-induced splitting of the H₂O maser lines. No circular polarization is detected, and we derive a 1 σ upper limit of 11 mG for the toroidal magnetic field at ~0.64 pc from the central black hole. This is the tightest upper limit for the magnetic field around a black hole to date. We use the magnetic field limit to derive an estimate of the mass accretion onto the central black hole. In addition to the polarimetric results, we present an observation of rapid variability in the maser lines, which we explain as weak interstellar scintillation. From the scintillation parameters, we estimate an intrinsic size of the mostly saturated maser features of ~12 μas. This is consistent with models assuming a thick, clumpy accretion disk.

We present a population synthesis study of NGC 4435, an early-type Virgo galaxy interacting with NGC 4438. We combine new spectroscopic observations obtained with the Spitzer Space Telescope IRS instrument with IRAC archival data and broadband data from the literature. The IRS spectrum shows prominent polycyclic aromatic hydrocarbon (PAH) features, low-ionization emission lines, and H₂ rotational lines arising from the dusty circumnuclear disk characterizing this galaxy. The central spectral energy distribution (SED), from X-ray to radio, is well fitted by a model of an exponential burst superimposed on an old simple stellar population. From the lack of high-excitation nebular lines, the [Ne III] λ15.5/[Ne II] λ12.8 ratio, the temperature of molecular hydrogen, and the fit to the full X-ray-to-radio SED we argue that the present activity of the galaxy is driven by star formation alone. The active galactic nucleus contribution to the ionizing flux is constrained to be less than 2%. The age of the burst is found to be around 190 Myr, and this is fully consistent with the notion that the star formation process was triggered by the interaction with NGC 4438. The mass involved in the rejuvenation episode turns out to be less than 1.5% of the stellar galaxy mass sampled in a 5'' central aperture. This is enough to render NGC 4435 closely similar to a typical interacting early-type galaxy with inverted Ca II [H+K] lines that will later turn into a typical cluster E+A galaxy and reinforces the notion that these objects are the result of a recent rejuvenation episode rather than a genuine delayed formation.

A nonlinear theory of the parallel diffusion of charged particles with perpendicular scattering and dynamical turbulence is obtained. The combination of the new parallel diffusion theory and the nonlinear guiding center theory shows good agreement with numerical simulations using typical parameters for a solar wind. Furthermore, the combination of the theories has a simpler mathematical form and is more computationally tractable than the weakly nonlinear theory.

There exists observational evidence that the interstellar medium has a fractal structure in a wide range of spatial scales. The measurement of the fractal dimension (D_f) of interstellar clouds is a simple way to characterize this fractal structure, but several factors, both intrinsic to the clouds and to the observations, may contribute to affect the values obtained. In this work, we study the effects that opacity and noise have on the determination of D_f. We focus on two different fractal dimension estimators, namely, the perimeter-area-based dimension (D_per) and the mass-size dimension (D_m). We first use simulated fractal clouds to show that opacity does not affect the estimation of D_per. However, D_m tends to increase as opacity increases, and this estimator fails when applied to optically thick regions. In addition, very noisy maps can seriously affect the estimation of both D_per and D_m, decreasing the final estimation of D_f. We apply these methods to emission maps of the Ophiuchus, Perseus, and Orion molecular clouds in different molecular lines, and we obtain that the fractal dimension is always in the range 2.6 ≲ D_f ≲ 2.8 for these regions. These results support the idea of a relatively high (>2.3) average fractal dimension for the interstellar medium, as traced by different chemical species.

Diffuse emission in the mid-infrared shows a wealth of structure, which lends itself to high-resolution structure analysis of the interstellar gas. A large part of the emission comes from polycyclic aromatic hydrocarbons (PAHs), excited by nearby ultraviolet sources. Can the observed diffuse emission structure be interpreted as column density structure? We discuss this question with the help of a set of model molecular clouds bathed in the radiation field of a nearby O star. The correlation strength between column density and "observed" flux density strongly depends on the absolute volume density range in the region. Shadowing and irradiation effects may completely alter the appearance of an object. Irradiation introduces additional small-scale structure, and it can generate structures resembling shells around H II regions in objects that do not possess any shell-like structures whatsoever. Nevertheless, with some effort, structural information about the underlying interstellar medium can be retrieved. In the more diffuse regime [n(H I) ≲ 100 cm^-3], flux density maps may be used to trace the 3D density structure of the cloud via density gradients. Thus, while caution definitely is in order, mid-infrared surveys such as GLIMPSE will provide quantitative insight into the turbulent structure of the interstellar medium.

In Spitzer/IRAC images obtained under the GLIMPSE Legacy Survey, we have identified a unique and provocative nebular object we call the "Southern Jellyfish Nebula." The Southern Jellyfish Nebula is characterized by a fan of narrow tendrils with extreme length-to-width ratios that emanate from the vicinity of a bright infrared point source embedded in a smaller resolved nebula. From CO observations of the Nebula's morphologically associated molecular cloud, we have derived a kinematic distance of 5.7 ± 0.8 kpc and a cloud mass of 3.2 ± 0.9 × 10³M_☉. The tendril-like ropes of the Nebula have widths of ~0.1 pc and lengths of up to ~2 pc. We have integrated the infrared spectral energy distribution (SED) of the point source to establish it as a massive young stellar object (MYSO), most likely forming alone, but possibly masking fainter cluster members. The shape of the SED is consistent with the shape of a late Class 0 SED model. Based on its far-IR luminosity of 3.3 ± 0.9 × 10⁴L_☉, the Southern Jellyfish's MYSO has a zero-age main sequence (ZAMS) spectral type of B0. Given the curious nature of this nebula, we suspect its peculiar IR-bright structure is directly related to its current state of star formation.

The continuum radiation of the Galactic region located at l = 85°, b = -0.5° is well defined by its 11 cm emission. The region, extended 3° in diameter, is cataloged as W80, and its optical images show the North America and Pelican Nebulae complexes. In this paper we present new distance measurements and physical parameters obtained from radio recombination line observations at a frequency near 1.4 GHz. Four structures are identified in the region under study: a near structure is located at a distance of about 0.7 kpc, another structure lies on the east side of W80 at a distance of 1.7 kpc, there is a concentration of ionized gas on the west side at a distance of 2.7 kpc, and a fourth structure is found further away at 3.3 kpc, which does not seem to belong to the W80 complex. The results are presented using the (X, Y, Z)-coordinates of the Galactic plane. The model used assumes a constant electron temperature T_e = 6800 K and also assumes homogeneity. Our results seem to indicate that the ionized hydrogen of W80 spreads along the line of sight instead of clumping at one distance. We obtain values of the electron density and the ionization parameter between n_e = 5 and 16 cm^-3 and U = 51 and 110 cm^-2 pc, respectively.

We present the results of an unbiased survey for 6.7 GHz methanol masers in the Galactic plane carried out using the 305 m Arecibo radio telescope. A total of 18.2 deg² was surveyed with uniform sampling at 35.2° ≤ l ≤ 53.7°, |b| ≤ 0.41°. The large collecting area of Arecibo and the sensitive C-Band High receiver allowed the survey to be complete at the level of 0.27 Jy, making this the most sensitive blind survey carried out to date. We detected a total of 86 sources, 48 of which are new detections. Most of the new detections have a peak flux density below 2 Jy. Many methanol masers are clustered, reflecting the formation of massive stars in clusters.

Most massive stars are found in the center of dense clusters and have a companion fraction much higher than their lower mass siblings; the massive stars of the Trapezium core in Orion have ~1.5 companions each. This high multiplicity could be a consequence of formation via a capture scenario, or it could be due to fragmentation of the cores that form the massive stars. During stellar formation circumstellar disks appear to be nearly ubiquitous. Their large radii compared to stellar sizes increase the interaction radius significantly, suggesting that disk interactions with neighboring stars could assist in capturing binary companions. This mechanism has been studied for stars of approximately solar mass and found to be inefficient. In this paper we present simulations of interactions between a 22 M_☉ star-disk system and less massive impactors in order to study the disk-assisted capture formation of binaries in a regime suited to massive stars. The formation of binaries by capture is found to be much more efficient for massive capturers. We discuss the effects of a mass-dependent velocity dispersion and mass segregation on the capture rates and consider the long-term survival of the resulting binaries in a dense cluster.

We characterize the small- and large-scale environment of the young star V1331 Cygni with high-resolution HST WFPC2 and Digitized Sky Survey images. In addition to a previously known outer dust ring (≈30'' in diameter), the WFPC2 scattered light image reveals an inner dust ring for the first time. This ring has a maximum radius of ≈6.5'' and is possibly related to a molecular envelope. Large-scale optical images show that V1331 Cyg is located at the tip of a long dust filament linking it to the dark cloud LDN 981. We discuss the origin of the observed dust morphology and analyze the object's relation to its parent dark cloud LDN 981. Finally, based on recent results from the literature, we investigate the properties of V1331 Cyg and conclude that in its current state the object does not show sufficient evidence to be characterized as an FU Ori object.

We present a census of the population of deeply embedded young stellar objects (YSOs) in the Perseus molecular cloud complex based on a combination of Spitzer Space Telescope mid-infrared data from the Cores to Disks (c2d) legacy team and JCMT SCUBA submillimeter maps from the COMPLETE team. The mid-infrared sources detected at 24 μm and having [3.6] - [4.5] > 1 are located close to the center of the SCUBA cores, typically within 15'' of their peaks. The narrowness of the spatial distribution of mid-infrared sources around the peaks of the SCUBA cores suggests that no significant dispersal of the newly formed YSOs has occurred. This argues against the suggestion that motions of protostars regulate the timescales over which significant (Bondi-Hoyle) accretion can occur. The YSOs are found to have red [3.6] - [4.5] and [8.0] - [24] colors, but not comparable red [5.8] - [8.0] colors. The most deeply embedded YSOs are found in regions with high extinction, A_V ≥ 5, similar to the extinction threshold observed for the SCUBA cores. All the SCUBA cores with high concentrations have embedded YSOs, but not all cores with low concentrations are starless. From the above considerations, a relatively unbiased sample of 49 deeply embedded YSOs is constructed. Embedded YSOs are found in 40 of the 72 SCUBA cores, with only three cores harboring multiple embedded YSOs within 15''. The equal number of SCUBA cores with and without embedded YSOs suggests that the timescale for the evolution through the dense prestellar stages, where the cores are recognized in the submillimeter maps and have central densities of 5 × 10⁴-1 × 10⁵ cm^-3, is similar to the timescale for the embedded protostellar stages. The current star formation efficiency of cores is estimated to be approximately 10%-15%. In contrast, the star formation efficiency averaged over the cloud lifetime and compared to the total cloud mass is only a few percent, reflecting also the efficiency in assembling cloud material into the dense cores actually forming stars.

TeV gamma rays emitted by gamma-ray bursts (GRBs) are converted into electron-positron pairs via interactions with the extragalactic infrared radiation fields. In turn, the pairs produced, whose trajectories are randomized by magnetic fields, will inverse Compton scatter off the cosmic microwave background photons. The beamed TeV gamma-ray flux from GRBs is thus transformed into a GeV isotropic gamma-ray flux, which contributes to the total extragalactic gamma-ray background emission. Assuming a model for the extragalactic radiation fields, the GRB redshift distribution, and the GRB luminosity function, we evaluate the contribution of the GRB prompt and scattered emissions to the measured extragalactic gamma-ray flux. To estimate this contribution we optimistically require that the energy flux at TeV energies is about 10 times stronger than the energy flux at MeV energies. The resulting gamma-ray diffuse background is only a small fraction of what is observed, allowing blazars and other sources to give the dominant contribution.

We develop and calibrate a realistic model flame for hydrodynamic simulations of deflagrations in white dwarf (Type Ia) supernovae. Our flame model builds on the advection-diffusion-reaction model of Khokhlov and includes electron screening and Coulomb corrections to the equation of state in a self-consistent way. We calibrate this model flame—its energetics and timescales for energy release and neutronization—with self-heating reaction network calculations that include both these Coulomb effects and up-to-date weak interactions. The burned material evolves postflame due to both weak interactions and hydrodynamic changes in density and temperature. We develop a scheme to follow the evolution, including neutronization, of the NSE state subsequent to the passage of the flame front. As a result, our model flame is suitable for deflagration simulations over a wide range of initial central densities and can track the temperature and electron fraction of the burned material through the explosion and into the expansion of the ejecta.

We consider the competition of the different physical processes that can affect the evolution of a flame bubble in a Type Ia supernovae: burning, turbulence and buoyancy. Even in the vigorously turbulent conditions of a convecting white dwarf, thermonuclear burning that begins at a point near the center (within 100 km) of the star is dominated by the spherical laminar expansion of the flame until the burning region reaches kilometers in size. Consequently, flames that ignite in the inner ≈20 km promptly burn through the center, and flame bubbles anywhere must grow quite large (indeed, resolvable by large-scale simulations of the global system) for significant motion or deformation occur. As a result, any hot spot that successfully ignites into a flame can burn a significant amount of white dwarf material. This potentially increases the stochastic nature of the explosion compared to a scenario in which a simmering progenitor can have small early hot spots float harmlessly away. Furthermore, the size at which the laminar flame speed dominates other relevant velocities sets a characteristic scale for fragmentation of larger flame structures, as nothing, by definition, can easily break the burning region into smaller volumes. This enables the development of semianalytic descriptions of the earliest phase of the propagation of burning in a Type Ia supernovae, which we present here. Our analysis is supported by fully resolved numerical simulations of flame bubbles.

The thermonuclear explosion of a massive white dwarf in a Type Ia supernova explosion is characterized by vastly disparate spatial and temporal scales. The extreme dynamic range inherent to the problem prevents the use of direct numerical simulation and forces modelers to resort to subgrid models to describe physical processes taking place on unresolved scales. We consider the evolution of a model thermonuclear flame in a constant gravitational field on a periodic domain. The gravitational acceleration is aligned with the overall direction of the flame propagation, making the flame surface subject to the Rayleigh-Taylor instability. The flame evolution is followed through an extended initial transient phase well into the steady state regime. The properties of the evolution of flame surface are examined. We confirm the form of the governing equation of the evolution suggested by Khokhlov in 1995. The mechanism of vorticity production and the interaction between vortices and the flame surface are discussed. Previously observed periodic behavior of the flame evolution is reproduced and is found to be caused by the turnover of the largest eddies. The characteristic timescales are found to be similar to the turnover time of these eddies. Relations between flame surface creation and destruction processes and basic characteristics of the flow are discussed. We find that the flame surface creation strength is associated with the Rayleigh-Taylor timescale. Also, in fully developed turbulence, the flame surface destruction strength scales as 1/L³, where L is the turbulent driving scale. The results of our investigation provide support for Khokhlov's self-regulating model of turbulent thermonuclear flames. Based on these results, one can revise and extend the original model. The revision uses a local description of the flame surface enhancement and the evolution of the flame surface since the onset of turbulence, rendering it free from the assumption of an instantaneous steady state of turbulence. This new model can be applied to the initial transient phase of the flame evolution, where the self-regulation mechanism yet to be fully established. Details of this new model will be presented in a forthcoming paper.

Two-dimensional axisymmetric simulations have shown that the postbounce accretion shock in core-collapse supernovae is subject to the spherical accretion shock instability, or SASI. Recent three-dimensional simulations have revealed the existence of a nonaxisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the postbounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady state model we are able to excite both one-, two-, and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.

We present a study of the Type IIn supernova (SN) 2005gl, in the relatively nearby (d ≈ 66 Mpc) galaxy NGC 266. Photometry and spectroscopy of the SN indicate that it is a typical member of its class. Pre-explosion Hubble Space Telescope (HST) imaging of the location of the SN, along with a precise localization of this event using the laser guide star assisted adaptive optics (LGS-AO) system at Keck Observatory, are combined to identify a luminous (M_V = -10.3 mag) point source as the possible progenitor of SN 2005gl. If the source is indeed a single star, it was likely a member of the class of luminous blue variable stars (LBVs). This finding leads us to consider the possible general association of SNe IIn with LBV progenitors; it is indeed supported by observations of other SNe, and the known properties of LBV stars. For example, we argue that should the prototypical Galactic LBV η Carina explode in a phase similar to its current state, it will likely produce a SN IIn. We discuss our findings in the context of current ideas about the evolution of massive stars and review the census of SNe with identified progenitors. The concept of the progenitor-SN map is introduced as a convenient means to discuss the present status and future prospects of direct searches for SN progenitors. We conclude that this field has matured considerably in recent years, and the transition from anecdotal information about rare single events to robust associations of progenitor classes with specific SN types has already begun.

We have made detailed calculations of the composition of magnetically driven jets ejected from a collapsar, based on long-term, magnetohydrodynamic simulations of a rapidly rotating, massive (40 M_☉) star during core collapse. We follow the evolution of the abundances of about 4000 nuclides from the collapse phase to the ejection phase and through the jet generation phase using two large nuclear reaction networks. We find that the r-process successfully operates in the jets, so that U and Th are synthesized abundantly when the progenitor has a large magnetic field (10¹² G) and a rapidly rotating core. The abundance pattern inside the jets is similar to that of the r-elements in the solar system. About 0.01 M_☉ of heavy, neutron-rich nuclei can be ejected from the collapsar. The detailed abundances depend on the nuclear properties of the mass model, β-decay rate, and fission, for nuclei near the neutron drip line. Furthermore, we find that p-nuclei are produced without seeds: not only can light p-nuclei, such as ⁷⁴Se, ⁷⁸Kr, ⁸⁴Sr, and ⁹²Mo, be abundantly synthesized in the jets, but also heavy p-nuclei, ¹¹³In, ¹¹⁵Sn, and ¹³⁸La. The amounts of p-nuclei in the ejecta are much greater than those in core-collapse supernovae. In particular, ⁹²Mo, ¹¹³In, ¹¹⁵Sn, and ¹³⁸La, which are deficient in these supernovae, are produced significantly in the collapsar ejecta.

Thermonuclear burning on the surface of a neutron star causes the expansion of a thin outer layer of the star, ΔR(t). The layer rotates slower than the star due to angular momentum conservation. The shear between the star and the layer acts to twist the star's dipole magnetic field, giving at first a trailing spiral field. The twist of the field acts in turn to "torque up" the layer, increasing its specific angular momentum. As the layer cools and contracts, its excess specific angular momentum causes it to rotate faster than the star, which gives a leading spiral magnetic field. The process repeats, giving rise to torsional oscillations. We derive equations for the angular velocity and magnetic field of the layer, taking into account the diffusivity and viscosity that are probably due to turbulence. The magnetic field causes a nonuniformity of the star's photosphere (at the top of the heated layer), and this gives rise to the observed X-ray oscillations. The fact that the layer periodically rotates faster than the star means that the X-ray oscillation frequency may "overshoot" the star's rotation frequency. Comparison of the theory is made with observations of Chakrabarty et al. of an X-ray burst of SAX J1808.4-3658.

Recent observations of pulsar wind nebulae and radio polarization profiles revealed a tendency for alignment between the spin and velocity directions in neutron stars. We study the condition for spin-kick alignment using a toy model, in which the kick consists of many off-centered, randomly oriented thrusts. Both analytical considerations and numerical simulations indicate that spin-kick alignment cannot be easily achieved if the proto-neutron star does not possess some initial angular momentum, contrary to some previous claims. To obtain the observed spin-kick misalignment angle distribution, the initial spin period of the neutron star must be smaller than the kick timescale. Typically, an initial period of 100 ms or less is required.

We present five recycled pulsars discovered during a 21 cm survey of approximately 4150 deg² between 15° and 30° from the Galactic plane using the Parkes radio telescope. One new pulsar, PSR J1528-3146, has a 61 ms spin period and a massive white dwarf companion. Like many recycled pulsars with heavy companions, the orbital eccentricity is relatively high (~0.0002), consistent with evolutionary models that predict less time for circularization. The four remaining pulsars have short spin periods (3 ms < P < 6 ms); three of these have probable white dwarf binary companions and one (PSR J2010-1323) is isolated. PSR J1600-3053 is relatively bright for its dispersion measure of 52.3 pc cm^-3 and promises good timing precision thanks to an intrinsically narrow feature in its pulse profile, resolvable through coherent dedispersion. In this survey, the recycled pulsar discovery rate was 1 per 4 days of telescope time or 1 per 600 deg² of sky. The variability of these sources implies that there are more millisecond pulsars that might be found by repeating this survey.

We report the finding of an unusual, weak precursor to a thermonuclear X-ray burst from the accreting millisecond pulsar SAX J1808.4-3658. The burst in question was observed on 2002 October 19 with the Rossi X-Ray Timing Explorer Proportional Counter Array (RXTE PCA). The precursor began ≈1 s prior to the onset of a strong radius expansion burst, lasted for about 0.4 s, and exhibited strong oscillations at the 401 Hz spin frequency. Oscillations are not detected in the ≈0.5 s interval between the precursor and the main burst. The estimated peak photon flux and energy fluence of the precursor are about 1/25 and 1/500 that of the main burst, respectively. From joint spectral and temporal modeling, we find that an expanding burning region with a relatively low temperature on the spinning neutron star surface can explain the oscillations, as well as the faintness of the precursor with respect to the main part of the burst. We discuss some of the implications of our findings for the ignition and spreading of thermonuclear flames on neutron stars.

We report on the first 10 weeks of RXTE observations of the X-ray transient XTE J1701-462 and conclude that it had all the characteristics of the neutron star Z sources, i.e., the brightest persistent neutron star low-mass X-ray binaries. These include the typical Z-shaped tracks traced out in X-ray color diagrams and the variability components detected in the power spectra, such as kHz QPOs and normal and horizontal branch oscillations. XTE J1701-462 is the first transient Z source and provides unique insights into mass accretion rate () and luminosity dependencies in neutron star X-ray binaries. As its overall luminosity decreased, we observed a switch between two types of Z source behavior, with the branches of the Z track changing their shape and/or orientation. We interpret this as an extreme case of the more moderate long-term changes seen in the persistent Z sources and suggest that they result from changes in . We also suggest that the Cyg-like Z sources (Cyg X-2, GX 5-1, and GX 340+0) are substantially more luminous (>50%) than the Sco-like Z sources (Sco X-1, GX 17+2, and GX 349+2). Adopting a possible explanation for the behavior of kHz QPOs, which involves a prompt as well as a filtered response to changes in , we further propose that changes in can explain both movement along the Z track and changes in the shape of the Z track. We discuss some consequences of this and consider the possibility that the branches of the Z will smoothly evolve into the branches observed in X-ray color diagrams of the less luminous atoll sources, although not in a way that was previously suggested.

We report on a 3 yr spectroscopic monitoring program of the Hα emission in the massive X-ray binary LS I +65 010 = 2S 0114+650, which consists of a B supergiant and a slowly rotating X-ray pulsar. We present revised orbital elements that yield a period of P = 11.5983 ± 0.0006 days and confirm that the orbit has a nonzero eccentricity e = 0.18 ± 0.05. The Hα emission profile is formed in the base of the wind of the B supergiant primary, and we show how this spectral feature varies on timescales that are probably related to the rotational period of the B supergiant. We also examine the X-ray fluxes from the Rossi X-ray Timing Explorer All-Sky Monitor instrument, and we show that the X-ray orbital light curve has a maximum at periastron and a minimum at the inferior conjunction of the B supergiant. We also show that the wind emission strength and the high-energy X-ray flux appear to vary in tandem on timescales of approximately 1 yr.

We present the results of an Hα monitoring campaign on the BeXRB and microquasar system LS I +61 303. We use radial velocity measurements of He I lines in our spectra to reevaluate the orbital elements and to better establish the time of periastron. We list equivalent widths and other parameters for the Hα emission line and discuss the orbital phase related variations observed. We call attention to a dramatic episode of emission weakening that occurred in less than 1 day that probably resulted from exposure to a transient source of ionizing radiation. We argue that the increase in Hα and X-ray emission following periastron probably results from the creation of an extended density wave in the disk created by tidal forces. We also discuss estimates of the size of the disk from the Hα equivalent width measurements, and we suggest that the disk radius from the average equivalent width corresponds to a resonant truncation radius of the disk while the maximum equivalent width corresponds to a radius limited by the separation of the stars at periastron. We note that a nearby faint companion is probably an unrelated foreground object.

We present Spitzer IRS observations of 11 intermediate polars (IPs). Spectra covering the wavelength range from 5.2 to 14 μm are presented for all 11 objects, and longer wavelength spectra are presented for three objects (AE Aqr, EX Hya, and V1223 Sgr). We also present new, moderate-resolution (R ~ 2000) near-infrared spectra for five of the program objects. We find that, in general, the mid-infrared spectra are consistent with simple power laws that extend from the optical into the mid-infrared. There is no evidence for discrete cyclotron emission features in the near- or mid-infrared spectra for any of the IPs investigated, nor for infrared excesses at λ ≤ 12 μm. However, AE Aqr, and possibly EX Hya and V1223 Sgr, do show longer wavelength excesses. We have used a cyclotron modeling code to put limits on the amount of such emission for magnetic field strengths of 1 ≤ B ≤ 7 MG. If cyclotron emission is occurring in the 5.2-14.0 μm bandpass, it constitutes less than 1% of the bolometric luminosity of any of the IPs. We were able to model the long-wavelength excess of V1223 Sgr and EX Hya with cyclotron emission from a 1 MG field, but the S/N of those data is very poor, and the reality of those excesses is not established. We attempted to model the long-wavelength excess of AE Aqr with cyclotron emission, but none of our models fit nearly as well as a simple, cool (T_BB = 140 K) blackbody. Given the apparent variability of this excess, however, synchrotron radiation remains a better explanation. We discuss our results in the context of the standard model for IPs.

We explore the potential usefulness of future gravitational microlensing surveys in studying binary properties such as the binary fraction and the distributions of binary separation and mass ratio by using the binary sample detectable through a channel of repeating events. For this, we estimate the rate of repeating microlensing events toward the Galactic bulge field based on standard models of dynamical and physical distributions of Galactic matter combined with models of binary separation and mass function. We find that the total number of repeating events expected to be detected from ~4 yr space-based surveys will be ~200-400, which is ~40-50 times higher than the rate of current surveys. We find that the high detection rate is due to the greatly improved sensitivity to events associated with faint source stars and low-magnification events. We find that the separation range of the binaries to be covered by the repeating events will extend up to 100 AU. Therefore, future lensing surveys should provide a homogeneous sample that will allow investigations of the statistical properties of Galactic binaries unbiased by brightness of the binary components.

We present a multiwavelength study of the central region of the Carina Nebula, including Trumpler 16 and part of Trumpler 14. Our analysis of the Chandra X-Ray Observatory archival data led to the identification of 454 X-ray sources. These sources were then cross-identified with optical photometric and spectroscopic information available from the literature and with newly obtained near-infrared (JHK_s) imaging observations. A total of 38 known OB stars are found to be X-ray emitters. All the O stars and early-B stars follow the nominal relation between the X-ray and bolometric luminosities, L_X ~ 10^-7L_bol. A few mid- to late-B stars are found to be associated with X-ray emission, likely attributable to T Tauri companions. We discovered 16 OB star candidates that suffer a large extinction in the optical wave bands. Some 300 sources have the X-ray and infrared characteristics of late-type pre-main-sequence stars. Our sample represents the most comprehensive census of the young stellar population in the Carina Nebula so far and should be useful for the study of the star formation history of this massive starburst region. We also report the finding of a compact (2' × 4') group of 10 relatively bright X-ray sources, all of which are detected in the near-infrared wavelengths and are highly reddened. The group is spatially coincident with the dark V-shaped dust lane bisecting the Carina Nebula and may be part of an embedded association. The distribution of the young stellar groups surrounding the H II region associated with Trumpler 16 is consistent with the collect-and-collapse scenario of triggered star formation.

We present a photometric and spectroscopic study of four G-K dwarfs, namely HD 166, Eri, χ¹ Ori, and κ¹ Cet. In three cases, we find a clear spatial association between photospheric and chromospheric active regions. For χ¹ Ori we do not find appreciable variations of photospheric temperature or chromospheric Hα emission. We applied a spot/plage model to the observed rotational modulation of temperature and flux to derive spot/plage parameters and to reconstruct a rough "three-dimensional" map of the outer atmosphere of κ¹ Cet, HD 166, and Eri.

We explore the sensitivity of limb-darkening coefficients computed from stellar atmosphere models to different least-squares fitting methods. We demonstrate that conventional methods are strongly biased to fitting the stellar limb. Our suggested method of fitting by minimizing the radially integrated squared residual yields improved fits with better flux conservation. The differences of the obtained coefficients from commonly used values are observationally significant. We show that the new values are in better agreement with solar limb-darkening measurements, as well as with coefficients reported from analyses of eclipsing binary light curves.

We present IRAC (3.6, 4.5, 5.8, and 8.0 μm) observations of the Chamaeleon II molecular cloud. The observed area covers about 1 deg² defined by A_V > 2. Analysis of the data in the 2005 c2d catalogs reveals a small number of sources (40) with properties similar to those of young stellar or substellar objects (YSOs). The surface density of these YSO candidates is low, and contamination by background galaxies appears to be substantial, especially for sources classified as Class I or flat spectral energy distribution (SED). We discuss this problem in some detail and conclude that very few of the candidate YSOs in early evolutionary stages are actually in the Cha II cloud. Using a refined set of criteria, we define a smaller, but more reliable, set of 24 YSO candidates.

We present commissioning data from the OSIRIS integral field spectrograph (IFS) on the Keck II 10 m telescope that demonstrate the utility of adaptive optics IFS spectroscopy in studying faint close-in substellar companions in the halos of bright stars. Our R ≈ 2000 J- and H-band spectra of the substellar companion to the 1-10 Myr old GQ Lup complement existing K-band spectra and photometry and improve on the original estimate of its spectral type. We find that GQ Lup B is somewhat hotter (M6-L0) than reported in the discovery paper by Neuhäuser and collaborators (M9-L4), mainly due to the surface gravity sensitivity of the K-band spectral classification indices used by the discoverers. Spectroscopic features characteristic of low surface gravity objects, such as lack of alkali absorption and a triangular H-band continuum, are indeed prominent in our spectrum of GQ Lup B. The peculiar shape of the H-band continuum and the difference between the two spectral type estimates is well explained in the context of the diminishing strength of H₂ collision-induced absorption with decreasing surface gravity, as recently proposed for young ultracool dwarfs by Kirkpatrick and collaborators. Using our updated spectroscopic classification of GQ Lup B and a reevaluation of the age and heliocentric distance of the primary, we perform a comparative analysis of the available substellar evolutionary models to estimate the mass of the companion. We find that the mass of GQ Lup B is 0.010-0.040 M_☉. Hence, it is unlikely to be a wide-orbit counterpart to the known radial velocity extrasolar planets, whose masses are ≲0.015 M_☉. Instead, GQ Lup A/B is probably a member of a growing family of very low mass ratio widely separated binaries discovered through high-contrast imaging.

Using a thermal-chemical model for the generic T Tauri disk of D'Alessio and colleagues, we estimate the strength of the fine-structure emission lines of Ne II and Ne III at 12.81 and 15.55 μm that arise from the warm atmosphere of the disk exposed to hard stellar X-rays. The Ne ions are produced by the absorption of keV X-rays from the K shell of neutral Ne, followed by the Auger ejection of several additional electrons. The recombination of the Ne ions is slow because of weak charge transfer with atomic hydrogen in the case of Ne⁺² and by essentially no charge transfer for Ne⁺. For a distance of 140 pc, the 12.81 μm line of Ne II has a flux ~10^-14 ergs cm^-2 s^-1, which should be observable with the Spitzer Infrared Spectrometer and suitable ground-based instrumentation. The detection of these fine-structure lines would clearly demonstrate the effects of X-rays on the physical and chemical properties of the disks of young stellar objects and provide a diagnostic of the warm gas in protoplanetary disk atmospheres. They would complement the observed H₂ and CO emission by probing vertical heights above the molecular transition layer and larger radial distances that include the location of terrestrial and giant planets.

We present a new, simple, fast algorithm to numerically evolve disks of inelastically colliding particles surrounding a central star. Our algorithm adds negligible computational cost to the fastest existing collisionless N-body codes and can be used to simulate, for the first time, the interaction of planets with disks over many viscous times. Although the algorithm is implemented in two dimensions—i.e., the motions of bodies need only be tracked in a plane—it captures the behavior of fully three-dimensional disks in which collisions maintain inclinations that are comparable to random eccentricities. The method simulates vertically optically thin disks of identical collisional, massless, inelastic, indestructible test particles. We subject the algorithm to a battery of tests for the case of an isolated narrow circular ring. Numerical simulations agree with analytic theory with regard to how particles' random velocities equilibrate, how the ring viscously spreads, and how energy dissipation, angular momentum transport, and material transport are connected. We derive and measure the critical value of the coefficient of restitution, above which viscous stirring dominates inelastic damping and the particles' velocity dispersion runs away.

We study the migration and resonant capture of planetesimals in a planetary system consisting of a gaseous disk analogous to the primordial solar nebula and a Neptune-like planet. Using a simple treatment of the drag force, we find that planetesimals are mainly trapped in the 3 : 2 and 2 : 1 resonances and that the resonant populations are correlated with the gaseous drag strength in a sense that the 3 : 2 resonant population increases with the stronger gaseous drag, but the 2 : 1 resonant population does not. Since planetesimals can lead to the formation of larger bodies similar to asteroids and Kuiper Belt objects, the gaseous drag can play an important role in the configuration of a planetary system.

With improving methods and surveys, the young field of extrasolar planet studies has recently expanded into a qualitatively new domain—terrestrial (mostly rocky) planets. The first such planets were discovered during the past year and a half, judging by their measured masses of less than 10 M_⊕ ("super-Earths"). They are introducing a novel physical regime that has not been explored before, as such planets do not exist in our solar system. Their compositions can be completely terrestrial, or they may harbor an extensive ocean (water and ices) above a rocky core. We model the structure and properties of the first super-Earth (mass ~7.5 M_⊕), discovered in 2005, illustrating the possible compositions and providing radius evaluations in view of future detection of similar planets by transits. We find that there exists a threshold in radius above which a super-Earth most certainly has an extensive water content. In the case of GJ 876d, this threshold is at about 12,000 km. Our results show that unique characterization of the bulk composition of super-Earths will be possible with future transit studies.

Using small automated telescopes in Arizona and Hawaii, the HATNet project has detected an object transiting one member of the double star system ADS 16402. This system is a pair of G0 main-sequence stars with age about 3 Gyr at a distance of ~139 pc and projected separation of ~1550 AU. The transit signal has a period of 4.46529 days and depth of 0.015 mag. From follow-up photometry and spectroscopy, we find that the object is a "hot Jupiter" planet with mass about 0.53M_J and radius ~1.36R_J traveling in an orbit with semimajor axis 0.055 AU and inclination about 85.9°, thus transiting the star at impact parameter 0.74 of the stellar radius. Based on a data set spanning 3 yr, ephemerides for the transit center are T_C = 2453984.397 + N_tr × 4.46529. The planet, designated HAT-P-1b, appears to be at least as large in radius, and smaller in mean density, than any previously known planet.

The spectra of solar wind magnetic fluctuations exhibit a significant power-law steepening at frequencies f > 1 Hz. The origin of this multiple scaling is investigated through dispersive Hall magnetohydrodynamics. We perform three-dimensional numerical simulations in the framework of a highly turbulent shell model and show that the large-scale magnetic fluctuations are characterized by a k^-5/3-type spectrum that steepens at scales smaller than the ion inertial length d_i, to k^-7/3 if the magnetic energy overtakes the kinetic energy, or to k^-11/3 in the opposite case. These results are in agreement both with a heuristic description à la Kolmogorov and with the range of power-law indices found in the solar wind.

The solar injections of near-relativistic (NR) electron events observed at 1 AU appear to be systematically delayed by ~10 minutes from the associated flare impulsive phases. We compare inferred injection times of 80 electron events observed by the 3DP electron detector on the Wind spacecraft with 40-800 MHz solar observations by the AIP radio telescope in Potsdam-Tremsdorf, Germany. Other than preceding type III bursts, we find no single radio signature characteristic of the inferred electron injection times. The injection delays from the preceding type III bursts do not correlate with the 1 AU solar wind β_p or B, but do correlate with densities n_e and inversely with speeds V_SW, consistent with propagation effects. About half of the events are associated with metric or decametric-hectometric (dh) type II bursts, but most injections occur before or after those bursts. Electron events with long (≥2 hr) beaming times at 1 AU are preferentially associated with type II bursts, which supports the possibility of a class of shock-accelerated NR electron events.

Here we present the first quantitative model of the inhomogeneous solar corona, which we call the composite and elementary loops in a thermally inhomogeneous corona (CELTIC) model. We develop a self-consistent statistical model that quantifies the distributions of physical parameters, i.e., the distributions of loop widths, N(w,T_e), electron densities, N(n_e,T_e), electron temperatures, N(T_e), and statistical correlations between them. The parameterized distributions are constrained by the observed triple-filter fluxes of the EUV corona measured at some 18,000 loop positions with TRACE in the temperature range of T_e ≈ 0.7-2.7 MK, as well as by the individual loop parameters (w,n_e,T_e) measured at these positions in ≈240 detected loops, mostly sampled in active regions. The CELTIC model is inverted from the TRACE data and reproduces both the fluxes of the composite (active region and quiet Sun) background corona and the distributions of loop parameters in a self-consistent way. The best-fit values constrain a statistical correlation between the density and temperature, i.e., ⟨n_e⟩ ∝ ⟨T_e⟩^α, with α = 0.9 ± 0.6, and between the loop width and temperature, i.e., ⟨w⟩ ∝ ⟨T_e⟩^β, with β = 1.3 ± 0.7, which can be related to the thermal pressure in a regime with a high plasma-β parameter. A possible explanation is a heating process located in the lower transition region or the upper chromosphere (e.g., as reproduced in the recent MHD simulations of Gudiksen and Nordlund), which produces sufficiently high electron densities, high plasma-β parameters, and thermally homogeneous loop cross sections as observed in elementary loop strands.

We apply a new method to determine the magnetic field in coronal loops, using observations of coronal loop oscillations. We analyze seven Doppler-shift oscillation events detected by SUMER in the hot flare line Fe XIX to obtain the oscillation periods of these events. The geometry, temperature, and electron density of the oscillating loops are measured from coordinated multichannel soft X-ray imaging observations from SXT. All the oscillations are consistent with standing slow waves in their fundamental mode. These parameters are used to calculate the magnetic field of coronal loops based on MHD wave theory. For the seven events, the plasma β is in the range 0.15-0.91 with a mean of 0.33 ± 0.26, and the estimated magnetic field varies between 21 and 61 G with a mean of 34 ± 14 G. With background emission subtracted, the estimated magnetic field is reduced by 9%-35%. The maximum background subtraction gives a mean of 22 ± 13 G in the range 12-51 G. We discuss measurement uncertainties and the prospect of determining coronal loop magnetic fields from future observations of coronal loops and Doppler-shift oscillations.

Local helioseismology techniques seek to probe the subsurface magnetic fields and flows by observing waves that emerge at the solar surface after passing through these inhomogeneities. Active regions on the surface of the Sun are distinguished by their strong magnetic fields, and techniques such as time-distance helioseismology can provide a useful diagnostic for probing these structures. Above the active regions, the fields fan out to create a horizontal magnetic canopy. We investigate the effect of a uniform horizontal magnetic field on the travel time of acoustic waves by considering vertical velocity in a simple plane-parallel adiabatically stratified polytrope. It is shown that such fields can lower the upper turning point of p-modes and hence influence their travel time. It is found that acoustic waves reflected from magnetically active regions have travel times up to a minute less than for waves similarly reflected in quiet regions. It is also found that sound speeds are increased below the active regions. These findings are consistent with time-distance measurements.

We have performed infrared spectroscopy of meteoritic calcium-aluminum-rich inclusions (CAIs) from the CV chondrites Leoville and Allende. While some previous studies have focused on the wavelength range λ < 25 μm, we aimed at a detection and identification of CAI bands at wavelengths from 6 to 75 μm. The resulting spectra have been compared with laboratory mineral spectra of typical CAI constituents such as melilite (a solid solution of gehlenite [Ca₂Al₂SiO₇] and åkermanite [Ca₂MgSi₂O₇]), spinel (MgAl₂O₄), diopside (CaMgSi₂O₆), and its Al- and Ti-rich variety fassaite. Sixteen bands in a type-B1 Leoville CAI transmittance spectrum could be assigned to melilite and spinel, 13 bands in the spectrum of a B3 Allende CAI were assigned to Al-Ti-diopside (fassaite), spinel, and nepheline; both cases were in accordance with the sample's respective mineralogical and chemical composition. CaO (lime) is not detected spectroscopically in the CAI spectra, as it is (contrary to previous notions) not even a trace component in CAIs, at least in their present (partially reprocessed) state. The astrophysical relevance of our study lies in the fact that the main CAI minerals such as melilite, Al-Ti-diopside (fassaite), spinel, and anorthite are expected to be present in protoplanetary disks. Hence, the detection of Ca,Al-minerals in protoplanetary disks should only be a matter of increased instrumental sensitivity, or spatial and spectral resolution, and quality (e.g., wavelength coverage) of comparative laboratory spectra.

Unidentified features in interstellar spectra (U lines) have persisted almost from the beginning of the field. In recent years, the number of such lines has rapidly increased in parallel with the sensitivity and frequency range of new observational facilities. Initially, the U lines often were from species considered exotic at the time, such as HCO⁺, but now the origins of these unidentified "weeds" are overwhelmingly from previously observed large molecules with dense spectra. The origin of the weeds problem lies in the nature of the spectroscopic approach that has typically been used in the millimeter and submillimeter spectral region: the bootstrap narrowband-observation, assignment, and theoretical prediction cycle. Unfortunately, the weeds arise from complex spectra involving many low-lying and often interacting vibrational states that are not typically part of the bootstrap process. This paper describes a purely experimental approach to this problem that does not require spectra assignment, but rather relies on the observation of complete spectra over a range of temperatures. It also discusses the potential for the use of these complete spectra in conjunction with the multiplex capabilities of modern radio telescopes for the detection of large species whose spectra consist of many relatively weak and ordinarily unobservable lines. This latter application will be made particularly challenging by the inhomogeneities and nonequilibrium characteristics of the interstellar medium. This approach is enabled by the FASSST (fast scan submillimeter spectroscopy technique) spectroscopic system and the use of collisional cooling cells to provide reference spectra at low temperature. Experimental and theoretical results are presented.

We have selected 14 J-dropout Lyman break galaxy (LBG) candidates with J₁₁₀ - H₁₆₀ ≥ 2.5 from the NICMOS Parallel Imaging Survey. This survey consists of 135 arcmin² of imaging in 228 independent sight lines, reaching average 5 σ sensitivities of J₁₁₀ = 25.8 and H₁₆₀ = 25.6 (AB). Distinguishing these candidates from dust-reddened star-forming galaxies at z ~ 2-3 is difficult and will require longer wavelength observations. We consider the likelihood that any J-dropout LBGs exist in this survey and find that if L is significantly brighter than L (a factor of 4), then a few J-dropout LBGs are likely. A similar increase in luminosity has been suggested by Eyles et al. and Yan et al., but the magnitude of this increase is uncertain.

We conduct two-dimensional (2D) hydrodynamical simulations of jets expanding in the intracluster medium (ICM). We find that for a fat, i.e., more or less spherical, bubble attached to the center to be formed, the jet should have high momentum flux and a large opening angle. Typically, the half-opening angle should be α ≳ 50^°, and the large momentum flux requires a jet speed of v_j ~ 10⁴ km s^-1. The inflation process involves vortices and local instabilities, which mix some ICM with the hot bubble. These results predict that most of the gas inside the bubble has a temperature of 3 × 10⁸ K ≲ T_b ≲ 3 × 10⁹ K, and that large quantities of the cooling gas in cooling flow clusters are expelled back to the intracluster medium, and heated up. The magnetic fields and relativistic electrons that produce the synchrotron radio emission might be formed in the shock wave of the jet.

The formation and growth of supermassive black holes is a key issue to unveil the secrets of galaxy formation. In particular, the gravitational recoil produced in the merger of unequal mass black hole binaries could have a number of astrophysical implications, such as the ejection of black holes from the host galaxy or globular cluster. We present estimates of the recoil velocity that include the effect of small eccentricities. The approach is especially suited for the last stage of the merger, where most of the emission of linear momentum in gravitational waves takes place. Supplementing our estimates with post-Newtonian approximations, we obtain lower and upper bounds that constrain previous recoil velocities estimates, as well as a best estimate that agrees with numerical simulations in the quasi-circular case. For eccentricities e ≤ 0.1, the maximum recoil is found for a mass ratio of M₁/M₂ ~ 0.38 with velocities in the range 79-216 km s^-1 (1 + e) and a best estimate of 167 km s^-1 (1 + e).

We announce the discovery of a new dwarf galaxy, Leo T, in the Local Group. It was found as a stellar overdensity in the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude diagram of Leo T shows two well-defined features, which we interpret as a red giant branch and a sequence of young, massive stars. As judged from fits to the color-magnitude diagram, it lies at a distance of ~420 kpc and has an intermediate-age stellar population with a metallicity of [Fe/H] = -1.6, together with a young population of blue stars of age ~200 Myr. There is a compact cloud of neutral hydrogen with mass ~10⁵M_☉ and radial velocity +35 km s^-1 coincident with the object visible in the HIPASS channel maps. Leo T is the smallest, lowest luminosity galaxy found to date with recent star formation. It appears to be a transition object similar to, but much lower luminosity than, the Phoenix dwarf.

Anisotropic turbulent cascades in the solar wind and interstellar medium (ISM) are investigated using three-dimensional incompressible magnetohydrodynamic (MHD) simulations with a numerical resolution of 256³. In the absence of an external magnetic field (B₀ = 0), the anisotropy in the MHD turbulent fluctuations is mediated primarily by the local magnetic field. The latter leads to a disparity in the spectral transfer of energy along and across the local mean magnetic field. While the anisotropic cascades give rise to the relationship _∥ ∝ between the parallel (_∥ ~ 1/k_∥) and perpendicular (_⊥ ~ 1/k_⊥) length scales of the eddies relative to the local magnetic field, the global energy is found to obey a Kolmogorov-like k^-5/3 anisotropic spectrum in our simulations where turbulence is predominantly subcritical. In the latter, the turbulent cascades are dominated by the nonlinear eddy turnover timescales compared to the linear Alfvén wave periods. The critical-balance criterion is therefore not necessarily satisfied in fully developed, strong, anisotropic, high plasma-β magnetofluid ISM turbulence.

The first results from a near-contemporaneous optical and infrared spectroscopic observing program designed to probe the detailed density structure of classical Be circumstellar disks are presented. We report the discovery of asymmetrical infrared emission lines of He I, O I, Fe II, and the Brackett, Paschen, and Pfund series lines of H I that exhibit an opposite V/R orientation (V > R) to that observed for the optical Balmer Hα line (V < R) in the classical Be star ζ Tau. We interpret these data as evidence that the density wave that characterizes ζ Tau's disk has a significantly different average azimuthal morphology in the inner disk region as compared to the outer disk region. A follow-up multiwavelength observational campaign to trace the temporal evolution of these line profile morphologies, along with detailed theoretical modeling, is suggested to test this hypothesis.

In the core accretion model, gas giant formation is a race between growth and migration; for a core to become a Jovian planet, it must accrete its envelope before it spirals into the host star. We use a multizone numerical model to extend our previous investigation of the "window of opportunity" for gas giant formation within a disk. When the collision cross section enhancement due to core atmospheres is taken into account, we find that a broad range of protoplanetary disks possess such a window.

Chondrules are high-temperature components of meteorites and are formed during flash heating episodes in the early solar system. From the presence of compound chondrules, which consist of an early formed unit enclosed within a later phase, it has been concluded that the chondrule formation event is repeatable. We report on the chronology of one Al-rich compound chondrule from the Allende meteorite, together with its mineralogy, petrography, and oxygen isotope composition. The earlier formed primary chondrule is rich in ²⁶Al with an initial ²⁶Al/²⁷Al ratio of (2.7 ± 1.0) × 10^-5, whereas the later formed secondary chondrule is depleted in ²⁶Al with an initial ²⁶Al/²⁷Al ratio of (9.9 ± 2.0) × 10^-6. The difference between the primary and secondary initial ratios corresponds to 1 Myr. We conclude that the primary unit formed during an earlier melting episode and went into a secondary melt that formed 1 Myr later during a later melting episode. The oxygen isotope composition of silicates in the primary and secondary phases shows varying degrees of ¹⁶O-depression but is similar to that of single chondrules from Allende meteorite specimens. Therefore, this primary chondrule in Allende stayed in the same dust reservoir for over 1 Myr and experienced multiple heating events, during which secondary and single chondrules were also produced.

We report high-precision measurements of nitrogen and carbon isotopic compositions of a carbon-bearing titanium-nitride (osbornite) in a calcium-aluminum-rich inclusion (CAI) from the CH/CB-like carbonaceous chondrite Isheyevo. The mineralogy and petrography of the CAI and thermodynamic calculations indicate that the osbornite formed by gas-solid condensation in a high-temperature (~2000 K) region of the solar nebula. Because isotopic fractionation at high temperature is small, the measured nitrogen [¹⁵N/¹⁴N = (2.356 ± 0.018) × 10 ^-3] and carbon [¹³C/¹²C = 0.01125 ± 0.00008; 1 σ] isotopic compositions of the Isheyevo osbornite are representative of the solar nebula and, hence, of the Sun. This conclusion is supported by the observations that (1) the measured ¹³C/ ¹²C ratio is indistinguishable from the spectroscopic determination of the ¹³C/¹²C ratio of the solar photosphere and (2) the measured ¹⁵N/¹⁴N ratio of osbornite is in excellent agreement with the Galileo spacecraft measurement of the nitrogen isotopic composition of the Jovian atmosphere, the second largest reservoir of nitrogen in the solar system. The inferred ¹⁵N/ ¹⁴N ratio of the solar nebula is also similar to the nitrogen isotopic composition of the vast majority of chondritic nanodiamonds, suggesting their solar nebula origin.

We carried out a statistical study of solar radio noise storms whose onset was in the aftermath of coronal mass ejections (CMEs) that occurred during 1997-2004, the first half of present solar cycle 23. The work is an attempt to understand the post-CME corona through observations of noise storms since the latter are considered to be closely related to structural changes there. The radio events were taken as the starting point for our study, and details about start time and location were available for 340 of them. We imposed the following conditions to verify the association between the above two phenomena: (1) the noise storm must have occurred ≤24 hr from the onset of a CME and (2) the central position angle of the CME must be located inside an angular span of ±45° with respect to the noise storm. We found that 196/340 noise storms were associated with CMEs. More interestingly, the time interval between CME liftoff and noise storm onset in all the above cases was ≤13 hr. We suggest that this represents the upper bound of the timescale over which coronal magnetic field reorganization had taken place in the aftermath of the aforementioned 196 noise storm associated CMEs. We also found that for a particular CME, the above temporal cutoff depends on its kinetic energy. Overall, it varies inversely with the logarithm of CME kinetic energy.

Spectroscopic measurements of a coronal bright point obtained with the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket instrument on 2006 April 12 show both upflows and downflows in all five of the best observed emission lines. Relative velocities on opposite sides of the feature were found to be ±15 km s^-1 in the line of He II 303.8 Å (formed at T ≈ 5 × 10⁴ K), ±14 km s^-1 in Mg IX 368.1 Å (T ≈ 9.5 × 10⁵ K), ±26 km s^-1 in Fe XIV 334.2 Å (T ≈ 2.0 × 10⁶ K), and ±35 km s^-1 in both Fe XVI 335.4 and 360.8 Å (T ≈ 2.5 × 10⁶ K). The latter are the hottest lines for which Doppler velocities have been reported in a bright point. Photospheric longitudinal magnetograms reveal that the photospheric magnetic fields underlying the bright point were canceling during the EUNIS observation. Based on existing bright point models, this suggests that the observed hot flows were associated with magnetic reconnection.

We study a possible connection of moving magnetic features (MMFs) and the overlying atmosphere using several sets of multiwavelength observations of sunspot areas from the photosphere to the corona. We find that as a collective phenomenon, very intense MMF formation anticorrelates with the presence of large-scale "stable" coronal loops: such loops are rooted at the side of sunspots with no or few MMFs rather than at the side of the penumbra/moat highly populated by MMFs. Conjectures to help understand the observed correlation between the preferable site of coronal loops and the deficiency of MMFs are discussed.