Abundances of Elements Lighter than Scandium in the Atmosphere of the Standard Giant Star α Sex (HD 87887, A0 III)

The abundances of elements lighter than scandium in the atmosphere of the A0 III giant, α Sex, are derived using archival ultraviolet and optical spectra. Most of the strongest lines present in the far-ultraviolet spectrum of α Sex can be attributed to chemical elements lighter than calcium. The synthesis of selected lines in the optical and ultraviolet yields new abundances, in particular for elements which have few lines in the optical range. Helium, oxygen, silicon and sulfur are found to have solar abundances, most other elements are underabundant. Aluminium may be marginally overabundant. The lines of chlorine are probably present in the FUV but they are too blended to derive the abundance of chlorine.

Observing and modelling the young solar analogue EK Draconis: starspot distribution, elemental abundances, and evolutionary status

ABSTRACT Observations and modelling of stars with near-solar masses in their early phases of evolution are critical for a better understanding of how dynamos of solar-type stars evolve. We examine the chemical composition and the spot distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma), we obtain the abundances of 23 elements with respect to the solar ones, which lead to a [Fe/H] = 0.03, with significant overabundance of Li and Ba. The s-process elements Sr, Y, and Ce are marginally overabundant, while Co, Ni, Cu, Zn are marginally deficient compared to solar abundances. The overabundance of Ba is most likely due to the assumption of depth-independent microturbulent velocity. Li abundance is consistent with the age and the other abundances may indicate distinct initial conditions of the pre-stellar nebula. We estimate a mass of 1.04 M⊙ and an age of $27^{+11}_{-8}$ Myr using various spectroscopic and photometric indicators. We study the surface distribution of dark spots, using 17 spectra collected during 15 nights using the CAFE Spectrograph (Calar Alto). We also conduct flux emergence and transport (FEAT) simulations for EK Dra’s parameters and produce 15-d-averaged synoptic maps of the likely starspot distributions. Using Doppler imaging, we reconstruct the surface brightness distributions for the observed spectra and FEAT simulations, which show overall agreement for polar and mid-latitude spots, while in the simulations there is a lack of low-latitude spots compared to the observed image. We find indications that cross-equatorial extensions of mid-latitude spots can be artefacts of the less visible southern-hemisphere activity.

The impact of asymmetric neutrino emissions on nucleosynthesis in core-collapse supernovae II – progenitor dependences

ABSTRACT We investigate the impact of asymmetric neutrino emissions on explosive nucleosynthesis in core-collapse supernovae (CCSNe) of progenitors with a mass range of 9.5–25 M⊙. We perform axisymmetric, hydrodynamic simulations of the CCSN explosion with a simplified neutrino transport, in which anticorrelated dipolar emissions of νe and ${\bar{\nu }}_{\rm e}$ are imposed. We then evaluate abundances and masses of the CCSN ejecta in a post-processing manner. We find that the asymmetric ν-emission leads to the abundant ejection of p- and n-rich matter in the high-νe and -${\bar{\nu }}_{\rm e}$ hemispheres, respectively. It substantially affects the abundances of the ejecta for elements heavier than Ni regardless of progenitors, although those elements lighter than Ca are less sensitive. Based on these results, we calculate the initial mass function-averaged abundances of the CCSN ejecta with taking into account the contribution from Type Ia SNe. For $m_{\rm asy} = 10/3{{\ \rm per\ cent}}$ and $10{{\ \rm per\ cent}}$, where masy denotes the asymmetric degree of the dipole components in the neutrino emissions, the averaged abundances for elements lighter than Y are comparable to those of the solar abundances, whereas those of elements heavier than Ge are overproduced in the case with $m_{\rm asy} \ge 30{{\ \rm per\ cent}}$. Our result also suggests that the effect of the asymmetric neutrino emissions is imprinted in the difference of abundance ratio of [Ni/Fe] and [Zn/Fe] between the high-νe and -${\bar{\nu }}_{\rm e}$ hemispheres, indicating that the future spectroscopic X-ray observations of a CCSN remnant will bring evidence of the asymmetric neutrino emissions if exist.

X-ray evolution of the nova V959 Mon suggests a delayed ejection and a non-radiative shock

ABSTRACT X-ray observations of shocked gas in novae can provide a useful probe of the dynamics of the ejecta. Here we report on X-ray observations of the nova V959 Mon, which was also detected in GeV gamma-rays with the Fermi satellite. We find that the X-ray spectra are consistent with a two-temperature plasma model with non-solar abundances. We interpret the X-rays as due to shock interaction between the slow equatorial torus and the fast polar outflow that were inferred from radio observations of V959 Mon. We further propose that the hotter component, responsible for most of the flux, is from the reverse shock driven into the fast outflow. We find a systematic drop in the column density of the absorber between days 60 and 140, consistent with the expectations for such a picture. We present intriguing evidence for a delay of around 40 d in the expulsion of the ejecta from the central binary. Moreover, we infer a relatively small (a few times 10−6 M⊙) ejecta mass ahead of the shock, considerably lower than the mass of 104 K gas inferred from radio observations. Finally, we infer that the dominant X-ray shock was likely not radiative at the time of our observations, and that the shock power was considerably higher than the observed X-ray luminosity. It is unclear why high X-ray luminosity, closer to the inferred shock power, is never seen in novae at early times, when the shock is expected to have high enough density to be radiative.

Chemical diversity among A–B stars with low rotational velocities: non-LTE abundance analysis

ABSTRACT We present accurate element abundance patterns based on the non-local thermodynamic equilibrium (non-LTE, NLTE) line formation for 14 chemical elements from He to Nd for a sample of nine A9 to B3-type stars with well-determined atmospheric parameters and low rotational velocities. We constructed new model atom of Zr ii–iii and updated model atoms for Sr ii and Ba ii by implementing the photoionization cross-sections from calculations with the Dirac B-spline R-matrix method. The NLTE abundances of He to Fe in the stars HD 17081, HD 32115, HD 160762, and HD 209459 are found to be consistent with the solar abundances, and HD 73666 being a Blue Straggler does not reveal deviations from chemical composition of the Praesepe cluster. Three of these stars with an effective temperature of lower than 10 500 K have supersolar abundances of Sr, Zr, Ba, and Nd, and our results suggest the presence of a positive correlation between stellar effective temperature and abundance. For each star, enhancement of Ba is higher than that for any other heavy element. We propose that the solar Ba abundance is not representative of the galactic Ba abundance at modern epoch. The status of HD 145788 was not clarified: This star has solar abundances of C to Si and enhancements of Sr to Ba similar to that for superficially normal stars of similar temperature, while Ca, Ti, and Fe are overabundant. The NLTE abundances of Vega support its status of a mild λ Bootis star.

Interstellar oxygen along the line of sight of Cygnus X-2

Interstellar dust permeates our Galaxy and plays an important role in many physical processes in the diffuse and dense regions of the interstellar medium (ISM). High-resolution X-ray spectroscopy, coupled with modelling based on laboratory dust measurements, provides a unique probe for investigating the interstellar dust properties along our line of sight towards Galactic X-ray sources. Here, we focus on the oxygen content of the ISM through its absorption features in the X-ray spectra. To model the dust features, we perform a laboratory experiment using the electron microscope facility located at the University of Cadiz in Spain, where we acquire new laboratory data in the oxygen K-edge. We study 18 dust samples of silicates and oxides with different chemical compositions. The laboratory measurements are adopted for our astronomical data analysis. We carry out a case study on the X-ray spectrum of the bright low-mass X-ray binary Cygnus X-2, observed by XMM−Newton. We determine different temperature phases of the ISM and parameterise oxygen in both gas (neutral and ionised) and dust form. We find Solar abundances of oxygen along the line of sight towards the source. Due to both the relatively low depletion of oxygen into dust form and the shape of the oxygen cross section profiles, it is challenging to determine the precise chemistry of interstellar dust. However, silicates provide an acceptable fit. Finally, we discuss the systematic discrepancies in the atomic (gaseous phase) data of the oxygen edge spectral region using different X-ray atomic databases as well as consider future prospects for studying the ISM with the Arcus concept mission.

NLTE modeling and spectroscopically derived abundances of lithium and beryllium for classical nova ejecta

Context. Extreme super-solar abundances of lithium and beryllium have been reported in recent years for classical novae based on absorption lines in ultraviolet and optical spectra during the optically thick stages, but these findings have not been compared with spectrum syntheses of the ejecta. Aims. We present a grid of nova ejecta models calculated with PHOENIX aimed at simulating the reported Li I and Be II features with super-solar abundances. Methods. We computed a sequence of models, finely exploring the parameter space of effective temperature, ejecta expansion velocity, and Li and Be overabundances. Results. Regardless of temperature and expansion velocity, the synthetic spectra for large Li and Be overabundances strongly disagree with those presented in recent literature. Assuming a wide range of Be overabundances (factors of 100 to 10 000 relative to solar), we predict a much stronger spectroscopic feature at Be II 3130 Å than those so far observed. A similar overabundance for Li would instead result in a barely observable change in the emitted flux at Li I 6709 Å. The observed extended absorption feature at 3131 Å reported in V838 Her and other novae appears even in zero-Be models with only solar abundances (which for novae are underestimates). Conclusions. The computed spectra do not support the lithium and beryllium abundances, and caution is warranted in the interpretation of the phenomenology.

Formation of aqua planets with water of nebular origin: effects of water enrichment on the structure and mass of captured atmospheres of terrestrial planets

ABSTRACT Recent detection of exoplanets with Earth-like insolation attracts growing interest in how common Earth-like aqua planets are beyond the Solar system. While terrestrial planets are often assumed to capture icy or water-rich planetesimals, a primordial atmosphere of nebular origin itself can produce water through oxidation of the atmospheric hydrogen with oxidizing minerals from incoming planetesimals or the magma ocean. Thermodynamically, normal oxygen buffers produce water comparable in mole number equal to or more than hydrogen. Thus, the primordial atmosphere would likely be highly enriched with water vapour; however, the primordial atmospheres have been always assumed to have the solar abundances. Here we integrate the 1D structure of such an enriched atmosphere of sub-Earths embedded in a protoplanetary disc around an M dwarf of 0.3$\, \mathrm{M}_\odot$ and investigate the effects of water enrichment on the atmospheric properties with focus on water amount. We find that the well-mixed highly enriched atmosphere is more massive by a few orders of magnitude than the solar-abundance atmosphere, and that even a Mars-mass planet can obtain water comparable to the present Earth’s oceans. Although close-in Mars-mass planets likely lose the captured water via disc dispersal and photoevaporation, these results suggest that there are more sub-Earths with Earth-like water contents than previously predicted. How much water terrestrial planets really obtain and retain against subsequent loss, however, depends on efficiencies of water production, mixing in the atmosphere and magma ocean, and photoevaporation, detailed investigation for which should be made in the future.

Searching for solar siblings in APOGEE and Gaia DR2 with N-body simulations

ABSTRACT We make use of APOGEE and $Gaia\,$ data to identify stars that are consistent with being born in the same association or star cluster as the Sun. We limit our analysis to stars that match solar abundances within their uncertainties, as they could have formed from the same giant molecular cloud (GMC) as the Sun. We constrain the range of orbital actions that solar siblings can have with a suite of simulations of solar birth clusters evolved in static and time-dependent tidal fields. The static components of each galaxy model are the bulge, disc, and halo, while the various time-dependent components include a bar, spiral arms, and GMCs. In galaxy models without GMCs, simulated solar siblings all have JR < 122 km $\rm s^{-1}$ kpc, 990 < Lz < 1986 km $\rm s^{-1}$ kpc, and 0.15 < Jz < 0.58 km $\rm s^{-1}$ kpc. Given the actions of stars in APOGEE and $Gaia\,$, we find 104 stars that fall within this range. One candidate in particular, Solar Sibling 1, has both chemistry and actions similar enough to the solar values that strong interactions with the bar or spiral arms are not required for it to be dynamically associated with the Sun. Adding GMCs to the potential can eject solar siblings out of the plane of the disc and increase their Jz, resulting in a final candidate list of 296 stars. The entire suite of simulations indicate that solar siblings should have JR < 122 km $\rm s^{-1}$ kpc, 353 < Lz < 2110 km $\rm s^{-1}$ kpc, and Jz < 0.8 km $\rm s^{-1}$ kpc. Given these criteria, it is most likely that the association or cluster that the Sun was born in has reached dissolution and is not the commonly cited open cluster M67.

3D Modeling of absorption by various species for hot jupiter HD209458b

ABSTRACT The absorption of stellar radiation observed at transits of HD209458b in resonant lines of OI and CII has not yet been satisfactorily modeled. In our previous 2D simulations we have shown that hydrogen-dominated upper atmosphere of HD209458b, heated by XUV radiation, expands supersonically beyond the Roche lobe and drags heavier species along with it. Assuming solar abundances, OI and CII particles accelerated by tidal forces to velocities up to 50 km/s should produce the absorption due to Doppler resonance at the level of 6–10 per cent, consistent with the observations. Since the 2D geometry does not take into account the Coriolis force in a planet reference frame, the question remained to which extent the spiraling of escaping planetary material and actually achieved velocity may influence the conclusions made on basis of 2D modeling. In the present paper we apply for the first time in studies of HD209458b a global 3D hydrodynamic multi-fluid model. The results confirm our previous findings that the velocity of the planetary flow is sufficiently high to match the widths of OI and CII resonant lines. To match absorption in those lines, including HI, with observations, the mass loss rate of HD209458b should be about 2.5·1011 g/s which is 3.5 times larger than that revealed by the 2D model. The other novel finding is that matching of the absorption measured in MgII and SiIII lines requires at least 10 times lower abundances of these elements than the Solar values.