Table of contents

We present the first pilot study of jets from young stars conducted with X-shooter, on the ESO/Very Large Telescope. As it offers simultaneous, high-quality spectra in the range 300–2500 nm, X-shooter is uniquely important for spectral diagnostics in jet studies. We chose to probe the accretion/ejection mechanisms at low stellar masses examining two targets with well-resolved continuous jets lying on the plane of the sky: ESO-HA 574 in Chameleon I and Par-Lup3-4 in Lupus III. The mass of the latter is close to the sub-stellar boundary (M_⋆ = 0.13 M_☉). A large number of emission lines probing regions of different excitation are identified, position–velocity diagrams are presented, and mass outflow/accretion rates are estimated. Comparison between the two objects is striking. ESO-HA 574 is a weakly accreting star for which we estimate a mass accretion rate of $\log (\dot{M}_{{\rm acc}}) = -10.8 \pm 0.5$ (in M_☉ yr⁻¹), yet it drives a powerful jet with $\dot{M}_{{\rm out}}$ ∼ 1.5–2.7 × 10⁻⁹ M_☉ yr⁻¹. These values can be reconciled with a magneto-centrifugal jet acceleration mechanism assuming that the presence of the edge-on disk severely depresses the luminosity of the accretion tracers. In comparison, Par-Lup3-4, with stronger mass accretion ($\log (\dot{M}_{{\rm acc}}) = -9.1 \pm 0.4$ M_☉ yr⁻¹), drives a low-excitation jet with about $\dot{M}_{{\rm out}}$ ∼ 3.2 × 10⁻¹⁰ M_☉ yr⁻¹ in both lobes. Despite the low stellar mass, $\dot{M}_{{\rm out}}$/$\dot{M}_{{\rm acc}}$ for Par-Lup3-4 is at the upper limit of the range usually measured for young objects, but still compatible with a steady magneto-centrifugal wind scenario if all uncertainties are considered.

Pulsating extreme horizontal branch (EHB) stars offer the unique opportunity to use asteroseismology to probe their fundamental parameters and thus constrain one of the more poorly understood phases of stellar evolution. However, they have been observed only among the field population, which necessarily prevents asteroseismological tools from being applied to globular cluster EHB stars. We launched a search for rapid EHB pulsators in ω Cen on the basis of fast time-series photometry obtained with EFOSC2 at the New Technology Telescope. Fourier analysis uncovered four multi-mode oscillators with rather similar periods between 84 and 124 s and amplitudes up to 2.7% of the mean stellar brightness. Initially, it was assumed that these stars constitute the globular cluster counterparts to the EC 14026 stars, rapid subdwarf B pulsators with T_eff  ∼  31,000 K that have been extensively studied among the field population, yet a subsequent atmospheric analysis of FORS MXU spectra reveals effective temperatures closely clustered around 50,000 K, implying that the four ω Cen variables are in fact helium-poor subdwarf O (sdO) stars rather than EC 14026 pulsators. It remains to be seen whether they are related to the one significantly hotter sdO oscillator known among the field star population, or belong to a hitherto unknown class of stellar pulsator that can now be subjected to asteroseismological scrutiny.

We discuss the observable effects of enhanced black hole mass loss in a black hole–neutron star (BH–NS) binary, due to the presence of a warped extra spatial dimension of curvature radius L in the braneworld scenario. For some masses and orbital parameters in the expected ranges the binary components would outspiral—the opposite of the behavior due to energy loss from gravitational radiation alone. If the NS is a pulsar, observations of the rate of change of the orbital period with a precision obtained for the binary pulsar B1913+16 could easily detect the effect of mass loss. For M_BH = 7 M_☉, M_NS = 1.4 M_☉, eccentricity e = 0.1, and L = 10 μm, the critical orbital period dividing systems that inspiral from systems that outspiral is P ≈ 6.5 hr, which is within the range of expected orbital periods; this value drops to P ≈ 4.2 hr for M_BH = 5 M_☉. Observations of a BH–pulsar system could set considerably better limits on L in these braneworld models than could be determined by torsion-balance gravity experiments in the foreseeable future.

The existence of a significant flux of antiprotons confined to Earth's magnetosphere has been considered in several theoretical works. These antiparticles are produced in nuclear interactions of energetic cosmic rays with the terrestrial atmosphere and accumulate in the geomagnetic field at altitudes of several hundred kilometers. A contribution from the decay of albedo antineutrons has been hypothesized in analogy to proton production by neutron decay, which constitutes the main source of trapped protons at energies above some tens of MeV. This Letter reports the discovery of an antiproton radiation belt around the Earth. The trapped antiproton energy spectrum in the South Atlantic Anomaly (SAA) region has been measured by the PAMELA experiment for the kinetic energy range 60–750 MeV. A measurement of the atmospheric sub-cutoff antiproton spectrum outside the radiation belts is also reported. PAMELA data show that the magnetospheric antiproton flux in the SAA exceeds the cosmic-ray antiproton flux by three orders of magnitude at the present solar minimum, and exceeds the sub-cutoff antiproton flux outside radiation belts by four orders of magnitude, constituting the most abundant source of antiprotons near the Earth.

We present 10 new Spitzer detections of fullerenes in Magellanic Cloud Planetary Nebulae, including the first extragalactic detections of the C₇₀ molecule. These new fullerene detections together with the most recent laboratory data permit us to report an accurate determination of the C₆₀ and C₇₀ abundances in space. Also, we report evidence for the possible detection of planar C₂₄ in some of our fullerene sources, as indicated by the detection of very unusual emission features coincident with the strongest transitions of this molecule at ∼6.6, 9.8, and 20 μm. The infrared spectra display a complex mix of aliphatic and aromatic species such as hydrogenated amorphous carbon grains (HACs), polycyclic aromatic hydrocarbon clusters, fullerenes, and small dehydrogenated carbon clusters (possible planar C₂₄). The coexistence of such a variety of molecular species supports the idea that fullerenes are formed from the decomposition of HACs. We propose that fullerenes are formed from the destruction of HACs, possibly as a consequence of shocks driven by the fast stellar winds, which can sometimes be very strong in transition sources and young planetary nebulae (PNe). This is supported by the fact that many of our fullerene-detected PNe show altered [Ne iii]/[Ne ii] ratios suggestive of shocks as well as P-Cygni profiles in their UV lines indicative of recently enhanced mass loss.

We present a study of the evolution of the galaxy velocity dispersion function (VDF) from z = 0 to z = 1.5 using photometric data from the Ultra-Deep and the NEWFIRM Medium-Band Survey in the COSMOS field. The VDF has been measured locally using direct kinematic measurements from the Sloan Digital Sky Survey (SDSS), but direct studies of the VDF at high redshift are difficult as they require velocity dispersion measurements of many thousands of galaxies. Taylor et al. demonstrated that dynamical and stellar masses are linearly related when the structure of the galaxy is accounted for. We show that the stellar mass, size, and Sérsic index can reliably predict the velocity dispersions of SDSS galaxies. We apply this relation to galaxies at high redshift and determine the evolution of the inferred VDF. We find that the VDF at z ∼ 0.5 is very similar to the VDF at z = 0. At higher redshifts, we find that the number density of galaxies with dispersions ≲ 200 km s⁻¹ is lower, but the number of high-dispersion galaxies is constant or even higher. At fixed cumulative number density, the velocity dispersions of galaxies with log  N[Mpc⁻³] < −3.5 increase with time by a factor of ∼1.4 from z ∼ 1.5–0, whereas the dispersions of galaxies with lower number density are approximately constant or decrease with time. The VDF appears to show less evolution than the stellar mass function, particularly at the lowest number densities. We note that these results are still somewhat uncertain and we suggest several avenues for further calibrating the inferred velocity dispersions.

Results of a detailed abundance analysis of the solar twins 16 Cyg A and 16 Cyg B based on high-resolution, high signal-to-noise ratio echelle spectroscopy are presented. 16 Cyg B is known to host a giant planet while no planets have yet been detected around 16 Cyg A. Stellar parameters are derived directly from our high-quality spectra, and the stars are found to be physically similar, with ΔT_eff = +43 K, Δlog g = −0.02 dex, and Δξ = +0.10 km s⁻¹ (in the sense of A − B), consistent with previous findings. Abundances of 15 elements are derived and are found to be indistinguishable between the two stars. The abundances of each element differ by ⩽0.026 dex, and the mean difference is +0.003 ± 0.015 (σ) dex. Aside from Li, which has been previously shown to be depleted by a factor of at least 4.5 in 16 Cyg B relative to 16 Cyg A, the two stars appear to be chemically identical. The abundances of each star demonstrate a positive correlation with the condensation temperature of the elements (T_c); the slopes of the trends are also indistinguishable. In accordance with recent suggestions, the positive slopes of the [m/H]–T_c relations may imply that terrestrial planets have not formed around either 16 Cyg A or 16 Cyg B. The physical characteristics of the 16 Cyg system are discussed in terms of planet formation models, and plausible mechanisms that can account for the lack of detected planets around 16 Cyg A, the disparate Li abundances of 16 Cyg A and B, and the eccentricity of the planet 16 Cyg B b are suggested.

We report the discovery of a threshold in the H i column density of Galactic gas clouds below which the formation of the cold phase of H i is inhibited. This threshold is at N_H i = 2 × 10²⁰ cm⁻²; sight lines with lower H i column densities have high spin temperatures (median T_s ∼ 1800 K), indicating low fractions of the cold neutral medium (CNM), while sight lines with N_H i ⩾ 2 × 10²⁰ cm⁻² have low spin temperatures (median T_s ∼ 240 K), implying high CNM fractions. The threshold for CNM formation is likely to arise due to inefficient self-shielding against ultraviolet photons at lower H i column densities. The threshold is similar to the defining column density of a damped Lyα absorber; this indicates a physical difference between damped and sub-damped Lyα systems, with the latter class of absorbers containing predominantly warm gas.

Many hydrogen-deficient stars are characterized by surface abundance patterns that are hard to reconcile with conventional stellar evolution. Instead, it has been suggested that they may represent the result of a merger episode between a helium and a carbon–oxygen white dwarf. In this Letter, we present a nucleosynthesis study of the merger of a 0.4 M_☉ helium white dwarf with a 0.8 M_☉ carbon–oxygen white dwarf, by coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a post-processing code. The resulting chemical abundance pattern, particularly for oxygen and fluorine, is in qualitative agreement with the observed abundances in R Coronae Borealis stars.

Using 3 s plasma and magnetic field data from the Wind spacecraft located in the solar wind well upstream from Earth, we report observations of isolated, pulse-like Alfvénic disturbances in the solar wind. These isolated events are characterized by roughly plane-polarized rotations in the solar wind magnetic field and velocity vectors away from the directions of the underlying field and velocity and then back again. They pass over Wind on timescales ranging from seconds to several minutes. These isolated, pulsed Alfvén waves are pervasive; we have identified 175 such events over the full range of solar wind speeds (320–550 km s⁻¹) observed in a randomly chosen 10 day interval. The large majority of these events are propagating away from the Sun in the solar wind rest frame. Maximum field rotations in the interval studied ranged from 6° to 109°. Similar to most Alfvénic fluctuations in the solar wind at 1 AU, the observed changes in velocity are typically less than that predicted for pure Alfvén waves (Alfvénicity ranged from 0.28 to 0.93). Most of the events are associated with small enhancements or depressions in magnetic field strength and small changes in proton number density and/or temperature. The pulse-like and roughly symmetric nature of the magnetic field and velocity rotations in these events suggests that these Alfvénic disturbances are not evolving when observed. They thus appear to be, and probably are, solitary waves. It is presently uncertain how these waves originate, although they may evolve out of Alfvénic turbulence.

We fitted the optical to mid-infrared (MIR) spectral energy distributions of ∼15,000 type-I, 0.75 < z < 2, active galactic nuclei (AGNs) in an attempt to constrain the properties of the physical component responsible for the rest-frame near-infrared (NIR) emission. We combine optical spectra from the Sloan Digital Sky Survey and MIR photometry from the preliminary data release of the Wide-field Infrared Survey Explorer. The sample spans a large range of AGN properties: luminosity, black hole mass, and accretion rate. Our model has two components: a UV-optical continuum source and very hot, pure-graphite dust clouds. We present the luminosity of the hot-dust component and its covering factor, for all sources, and compare it with the intrinsic AGN properties. We find that the hot-dust component is essential to explain the (rest) NIR emission in almost all AGNs in our sample, and that it is consistent with clouds containing pure-graphite grains and located between the dust-free broad-line region and the "standard" torus. The covering factor of this component has a relatively narrow distribution around a peak value of ∼0.13, and it correlates with the AGN bolometric luminosity. We suggest that there is no significant correlation with either black hole mass or normalized accretion rate. The fraction of hot-dust-poor AGNs in our sample is ∼15%–20%, consistent with previous studies. We do not find a dependence of this fraction on redshift or source luminosity.

We investigate the column density distribution function of neutral hydrogen at redshift z = 3 using a cosmological simulation of galaxy formation from the OverWhelmingly Large Simulations project. The base simulation includes gravity, hydrodynamics, star formation, supernovae feedback, stellar winds, chemodynamics, and element-by-element cooling in the presence of a uniform UV background. Self-shielding and formation of molecular hydrogen are treated in post-processing, without introducing any free parameters, using an accurate reverse ray-tracing algorithm and an empirical relation between gas pressure and molecular mass fraction. The simulation reproduces the observed z = 3 abundance of Lyα forest, Lyman limit, and damped Lyα H i absorption systems probed by quasar sight lines over 10 orders of magnitude in column density. Self-shielding flattens the column density distribution for N_H i > 10¹⁸ cm⁻², while the transition to fully neutral gas and conversion of H i to H₂ steepen it around column densities of N_H i = 10^20.3 cm⁻² and N_H i = 10^21.5 cm⁻², respectively.

We have employed emission-line diagnostics derived from DEIMOS and NIRSPEC spectroscopy to determine the origin of the [O ii] emission line observed in six active galactic nucleus (AGN) hosts at z ∼ 0.9. These galaxies are a subsample of AGN hosts detected in the Cl1604 supercluster that exhibit strong Balmer absorption lines in their spectra and appear to be in a post-starburst or post-quenched phase, if not for their [O ii] emission. Examining the flux ratio of the [N ii] to Hα lines, we find that in five of the six hosts the dominant source of ionizing flux is AGN continuum emission. Furthermore, we find that four of the six galaxies have over twice the [O ii] line luminosity that could be generated by star formation alone given their Hα line luminosities. This strongly suggests that AGN-excited narrow-line emission is contaminating the [O ii] line flux. A comparison of star formation rates calculated from extinction-corrected [O ii] and Hα line luminosities indicates that the former yields a five-fold overestimate of the current activity in these galaxies. Our findings reveal the [O ii] line to be a poor indicator of star formation activity in a majority of these moderate-luminosity Seyferts. This result bolsters our previous findings that an increased fraction of AGN at high redshifts is hosted by galaxies in a post-starburst phase. The relatively high fraction of AGN hosts in the Cl1604 supercluster that show signs of recently truncated star formation activity may suggest that AGN feedback plays an increasingly important role in suppressing ongoing activity in large-scale structures at high redshift.

Asteroid (596) Scheila was reported to exhibit a cometary appearance and an increase in brightness on UT 2010 December 10.4. We used the IRCS spectrograph on the 8 m Subaru telescope to obtain medium-resolution spectra of Scheila in the HK band (1.4–2.5 μm) and low-resolution spectra in the KL band (2.0–4.0 μm) on UT 2010 December 13 and 14. In addition, we obtained low-resolution spectroscopy using the SpeX spectrograph on the 3 m NASA Infrared Telescope Facility on UT 2011 January 4 and 5. The spectrum of Scheila shows a consistent red slope from 0.8 to 4.0 μm with no apparent absorption features, resembling spectra of D-type asteroids. An intimate mixing model suggests that the amount of water ice that might be present on the surface of Scheila is no more than a few percent. The spectrum of the Tagish Lake chondrite matches the asteroid's spectrum at shorter wavelengths (λ < 2.5 μm), but no hydration features are observed at longer wavelengths on Scheila. Our analysis corroborates other studies suggesting that the comet-like activity of Scheila is likely not caused by the sublimation of water ice. The dust coma and tail may be results of a recent impact event.

The recent discovery of day-long gamma-ray flares in the Crab Nebula, presumed to be synchrotron emission by PeV (10¹⁵ eV) electrons in milligauss magnetic fields, presents a strong challenge to particle acceleration models. The observed photon energies exceed the upper limit (∼100 MeV) obtained by balancing the acceleration rate and synchrotron radiation losses under standard conditions where the electric field is smaller than the magnetic field. We argue that a linear electric accelerator, operating at magnetic reconnection sites, is able to circumvent this difficulty. Sufficiently energetic electrons have gyroradii so large that their motion is insensitive to small-scale turbulent structures in the reconnection layer and is controlled only by large-scale fields. We show that such particles are guided into the reconnection layer by the reversing magnetic field as they are accelerated by the reconnection electric field. As these electrons become confined within the current sheet, they experience a decreasing perpendicular magnetic field that may drop below the accelerating electric field. This enables them to reach higher energies before suffering radiation losses and hence to emit synchrotron radiation in excess of the 100 MeV limit, providing a natural resolution to the Crab gamma-ray flare paradox.

We present the first survey of electric field data using the ARTEMIS spacecraft in the solar wind to study inertial range turbulence. It was found that the average perpendicular spectral index of the electric field depends on the frame of measurement. In the spacecraft frame it is −5/3, which matches the magnetic field due to the large solar wind speed in Lorentz transformation. In the mean solar wind frame, the electric field is primarily due to the perpendicular velocity fluctuations and has a spectral index slightly shallower than −3/2, which is close to the scaling of the velocity. These results are an independent confirmation of the difference in scaling between the velocity and magnetic field, which is not currently well understood. The spectral index of the compressive fluctuations was also measured and found to be close to −5/3, suggesting that they are not only passive to the velocity but may also interact nonlinearly with the magnetic field.

Characterization of migration in gravitationally unstable disks is necessary to understand the fate of protoplanets formed by disk instability. As part of a larger study, we are using a three-dimensional radiative hydrodynamics code to investigate how an embedded gas giant planet interacts with a gas disk that undergoes gravitational instabilities (GIs). This Letter presents results from simulations with a Jupiter-mass planet placed in orbit at 25 AU within a 0.14 M_☉ disk. The disk spans 5–40 AU around a 1 M_☉ star and is initially marginally unstable. In one simulation, the planet is inserted prior to the eruption of GIs; in another, it is inserted only after the disk has settled into a quasi-steady GI-active state, where heating by GIs roughly balances radiative cooling. When the planet is present from the beginning, its own wake stimulates growth of a particular global mode with which it strongly interacts, and the planet plunges inward 6 AU in about 10³ years. In both cases with embedded planets, there are times when the planet's radial motion is slow and varies in direction. At other times, when the planet appears to be interacting with strong spiral modes, migration both inward and outward can be relatively rapid, covering several AUs over hundreds of years. Migration in both cases appears to stall near the inner Lindblad resonance of a dominant low-order mode. Planet orbit eccentricities fluctuate rapidly between about 0.02 and 0.1 throughout the GI-active phases of the simulations.

We focused on "sit-and-stare" observations of an outflow region at the edge of active region NOAA 10942 on 2007 February 20 obtained by the Extreme ultraviolet Imaging Spectrometer on board Hinode. We analyzed the data above the base of the outflow and found both continuous outflows and waves, which propagate from the base of the outflow. The spectra at the base of the outflow and at higher locations show different properties. The line profiles show blue-side asymmetry at the base of the outflow where nonthermal broadening becomes large because of fast upflows generated by heating events. On the other hand, at higher locations line profiles are symmetric and the intensity disturbances vary in phase with the velocity disturbances. The correlations between the intensity and velocity disturbances become noticeable at higher locations, so this indicates evidence of (at least locally) upward propagating slow-mode waves along the outflow. We also found a transient oscillation of different period in the wavelet spectrum. This indicates that a different wave is additionally observed during a limited period. High cadence spectroscopic observations revealed intermittent signatures of nonthermal velocities. Each of them seems to correspond to the base of the propagating disturbances. Furthermore, a jet was captured by the sit-and-stare observations across the slit. The similarity of line profiles of the outflow and the jet may indicate that the flows and waves originate in unresolved explosive events in the lower atmosphere of the corona.

We outline a model for the heating of hydrogenated amorphous carbon (HAC) dust via the release of stored chemical energy and show that this energy (∼12 kJ mole⁻¹) is sufficient to heat dust grains of classical size (50–1000 Å) to temperatures at which they can emit at 3.3 μm and other "UIR" wavelengths. Using laboratory data, we show that this heating process is consistent with a concentration of a few percent of dangling bonds in HAC and may be initiated by the recombination of trapped H atoms. We suggest that the release of chemical energy from dust represents an additional source of excitation for the UIR bands relaxing the previous requirement that only stochastically heated molecules having fewer than ∼50 atoms can produce emission at 3.3 μm.

We study the scaling between bulge magnitude and central black hole (BH) mass in galaxies with virial BH masses ≲ 10⁶ M_☉. Based on careful image decomposition of a snapshot Hubble Space TelescopeI-band survey, we found that these BHs are found predominantly in galaxies with pseudobulges. Here we show that the M_BH–L_bulge relation for the pseudobulges at low mass is significantly different from classical bulges with BH masses ⩾10⁷ M_☉. Specifically, bulges span a much wider range of bulge luminosity, and on average the luminosity is larger, at fixed M_BH. The trend holds both for the active galaxies from Bentz et al. and the inactive sample of Gültekin et al. and cannot be explained by differences in stellar populations, as it persists when we use dynamical bulge masses. Put another way, the ratio between bulge and BH mass is much larger than ∼1000 for our sample. This is consistent with recent suggestions that M_BH does not scale with the pseudobulge luminosity. The low-mass scaling relations appear to flatten, consistent with predictions from Volonteri & Natarajan for massive seed BHs.