- ID:
- ivo://CDS.VizieR/J/A+A/386/1001
- Title:
- Thermal emission from low-field neutron stars
- Short Name:
- J/A+A/386/1001
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new grid of LTE model atmospheres for weakly magnetic (B<~10^10^G) neutron stars, using X opacity and equation of state data from the OPAL project and employing a fully frequency- and angle-dependent radiation transfer. Model spectra for low-field neutron stars with three different photospheric compositions are presented: (1) pure hydrogen atmospheres, (2) atmospheres with solar abundances, and (3) pure iron atmospheres. Each grid covers 29 effective temperatures log(Teff[K])=5.10-6.50 in steps of 0.05. The model spectra are tabulated as angle-averaged unredshifted (surface) Eddington fluxes. All spectra have been calculated for a canonical neutron star configuration, M_ns_=1.4M_{sun}_, R_ns_=10km, corresponding to a surface gravitational acceleration of log(g)=14.386. The same model grids are also available as XSPEC tables at http://legacy.gsfc.nasa.gov/docs/xanadu/xspec/models/gbr.html
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- ID:
- ivo://CDS.VizieR/J/A+A/457/265
- Title:
- The VLT-FLAMES Survey of Massive Stars
- Short Name:
- J/A+A/457/265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An analysis is presented of VLT-FLAMES spectroscopy for three Galactic clusters, NGC 3293, NGC 4755 and NGC 6611. Non-LTE model atmosphere calculations have been used to estimate effective temperatures (from either the helium spectrum or the silicon ionization equilibrium) and gravities (from the hydrogen spectrum). Projected rotational velocities have been deduced from the helium spectrum (for fast and moderate rotators) or the metal line spectrum (for slow rotators). The origin of the low gravity estimates for apparently near main sequence objects is discussed and is related to the stellar rotational velocity. The atmospheric parameters have been used to estimate cluster distances (which are generally in good agreement with previous determinations) and these have been used to estimate stellar luminosities and evolutionary masses. The observed Hertzsprung-Russell diagrams are compared with theoretical predictions and some discrepancies including differences in the main sequence luminosities are discussed. Cluster ages have been deduced and evidence for non-coeval star formation is found for all three of the clusters. Projected rotational velocities for targets in the older clusters, NGC 3293 and NGC 4755, have been found to be systematically larger than those for the field, confirming recent results in other similar age clusters. The distribution of projected rotational velocities are consistent with a Gaussian distribution of intrinsic rotational velocities. For the relatively unevolved targets in the older clusters, NGC 3293 and NGC 4755, the peak of the velocity distribution would be 250km/s with a full-width-half-maximum of approximately 180km/s. For NGC 6611, the sample size is relatively small but implies a lower mean rotational velocity. This may be evidence for the spin-down effect due to angular momentum loss through stellar winds, although our results are consistent with those found for very young high mass stars. For all three clusters we deduce present day mass functions with Gamma-values in the range of -1.5 to -1.8, which are similar to other young stellar clusters in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/156
- Title:
- Ti and Fe lines in red supergiants
- Short Name:
- J/ApJ/751/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed non-LTE (NLTE) calculations for red supergiant (RSG) stars are presented to investigate the influence of NLTE on the formation of atomic iron and titanium lines in the J band. With their enormous brightness at J band RSG stars are ideal probes of cosmic abundances. Recent LTE studies have found that metallicities accurate to 0.15 dex can be determined from medium-resolution spectroscopy of individual RSGs in galaxies as distant as 10 Mpc. The NLTE results obtained in this investigation support these findings. NLTE abundance corrections for iron are smaller than 0.05 dex for effective temperatures between 3400 K and 4200 K and 0.1 dex at 4400 K. For titanium the NLTE abundance corrections vary smoothly between -0.4 dex and +0.2 dex as a function of effective temperature. For both elements, the corrections also depend on stellar gravity and metallicity. The physical reasons behind the NLTE corrections and the consequences for extragalactic J-band abundance studies are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/457/637
- Title:
- UBVJHK synthetic photometry of Galactic O stars
- Short Name:
- J/A+A/457/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The development of powerful infrared observational techniques enables the study of very extincted objects and young embedded star-forming regions. This is especially interesting in the context of massive stars that form and spend a non negligible fraction of their life still enshrouded in their parental molecular cloud. Spectrophotometric calibrations are thus necessary to constrain the physical properties of heavily extincted objects.
- ID:
- ivo://CDS.VizieR/J/A+A/472/241
- Title:
- UV Flux distributions of gamma Dor stars
- Short Name:
- J/A+A/472/241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It seems that the recently identified class of pulsating stars, the gamma Dor type-variables, includes objects with different metal abundances and a large percentage of binaries. We looked for indicators of metal abundance peculiarities and stellar binarity in a sample of 40 confirmed gamma Dor stars. Absolute magnitudes from Hipparcos parallaxes and UV magnitudes, from the S2/S68 experiment on board the TD1 satellite, are retrieved from databases and compared with predicted values. A set of non variable normal stars is used to check the consistency of this analysis and also serve as reference stars. Twenty-nine stars of the gamma Dor star sample, which is 73% of it, are discovered having abnormal UV fluxes constantly showing UV flux excesses compared to those computed with the atmospheric parameters (Teff, logg, and metallicity) determined from calibration of the uvbyBeta indices. The reason for this UV excess of flux at 196.5nm and at 236.5nm, which was previously known only for HD 209295, cannot be ascribed to binarity alone. An extra source of UV flux or less UV absorption - yet unknown - must be present.
- ID:
- ivo://CDS.VizieR/J/A+A/523/A64
- Title:
- UV properties of starbursts
- Short Name:
- J/A+A/523/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have computed evolutionary synthesis models covering metallicities from PopIII to solar, a wide range of IMFs, and two star-formation histories (bursts and constant star-formation). The detailed predictions these models, including their time dependence, are given here. The predicted quantities include ionising fluxes, UV continuum properties, recombination line strengths (for Ly{alpha}, HeII and other lines), as well as several other quantities of interest. The models provided here cover a wider range of parameter space than our earlier calculations (Schaerer, 2003A&A...397..527S, Cat. VI/109).
- ID:
- ivo://CDS.VizieR/J/ApJ/855/134
- Title:
- UV spectrum of molecular hydrogen in the Sun
- Short Name:
- J/ApJ/855/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ultraviolet (UV) lines of molecular hydrogen have been observed in solar spectra for almost four decades, but the behavior of the molecular spectrum and its implications for solar atmospheric structure are not fully understood. Data from the High-Resolution Telescope Spectrometer (HRTS) instrument revealed that H2 emission forms in particular regions, selectively excited by a bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models, sampling a broad range of temperature stratifications and radiation conditions. Stratification plays the dominant role in determining the population densities of H2, which forms in greatest abundance near the continuum photosphere. However, opacity due to the photoionization of Si and other neutrals determines the depth to which UV radiation can penetrate to excite the H2. Thus the majority of H2 emission forms in a narrow region, at about 650km in standard one-dimensional (1D) models of the quiet Sun, near the {tau}=1 opacity surface for the exciting UV radiation, generally coming from above. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can be satisfactorily reproduced in 1D stratified atmospheres, without including three-dimensional or time-dependent thermal structures. A detailed comparison to observations from 1205 to 1550{AA} is presented, and the success of this 1D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels in HRTS spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A89
- Title:
- Very metal poor stars in MW halo
- Short Name:
- J/A+A/608/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, -4<=[Fe/H]<~-2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in Paper I. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [alpha/Fe]=0.3 for each of the alpha-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in alpha/Fe with increasing metallicity in the Bootes I ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is better correlated with Mg than Fe and that its origin is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs, that is Bootes I, UMa II, and Leo IV, are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg]=-1.3 and [Ba/Mg]=-1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H]<-2, is the strongest.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A124
- Title:
- Visibilities of stellar oscillation modes
- Short Name:
- J/A+A/531/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kepler produces a large amount of data used for asteroseismological analyses, particularly of solar-like stars and red giants. The mode amplitudes observed in the Kepler spectral band have to be converted into bolometric amplitudes to be compared to models. We give a simple bolometric correction for the amplitudes of radial modes observed with Kepler, as well as the relative visibilities of non-radial modes. We numerically compute the bolometric correction c_K-bol_ and mode visibilities, for different effective temperatures Teff within the range 4000-7500K, using a similar approach to a recent one from the literature. We derive a law for the correction to bolometric values: c_K-bol_=1+a_1_(Teff-To)+a_2_(Teff-To)^2^, with To=5934K, a_1_=1.349e-4K^-1^, and a_2_=-3.120e-9K^-2^ or, alternatively, as the power law c_K-bol_=(Teff/To)^alpha^ with alpha=0.80. We give tabulated values for the mode visibilities based on limb-darkening, computed from ATLAS9 model atmospheres for Teff in [4000,7500]K, logg in [2.5,4.5], and [M/H] in [-1.0,+1.0]. We show that using LD profiles already integrated over the spectral band provides quick and good approximations for visibilities. We point out the limits of these classical visibility estimations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/2428
- Title:
- WASP-31b:HST/Spitzer transmission spectral survey
- Short Name:
- J/MNRAS/446/2428
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Hubble Space Telescope optical and near-IR transmission spectra of the transiting hot-Jupiter WASP-31b. The spectrum covers 0.3-1.7 {mu}m at a resolution R~70, which we combine with Spitzer photometry to cover the full-optical to IR. The spectrum is dominated by a cloud deck with a flat transmission spectrum which is apparent at wavelengths >0.52{mu}m. The cloud deck is present at high altitudes and low pressures, as it covers the majority of the expected optical Na line and near-IR H_2_O features. While Na I absorption is not clearly identified, the resulting spectrum does show a very strong potassium feature detected at the 4.2{sigma} confidence level. Broadened alkali wings are not detected, indicating pressures below ~10 mbar. The lack of Na and strong K is the first indication of a sub-solar Na/K abundance ratio in a planetary atmosphere (ln[Na/K]=-3.3+/-2.8), which could potentially be explained by Na condensation on the planet's night side, or primordial abundance variations. A strong Rayleigh scattering signature is detected at short wavelengths, with a 4{sigma} significant slope. Two distinct aerosol size populations can explain the spectra, with a smaller sub-micron size grain population reaching high altitudes producing a blue Rayleigh scattering signature on top of a larger, lower lying population responsible for the flat cloud deck at longer wavelengths. We estimate that the atmospheric circulation is sufficiently strong to mix micron size particles upwards to the required 1-10 mbar pressures, necessary to explain the cloud deck. These results further confirm the importance of clouds in hot Jupiters, which can potentially dominate the overall spectra and may alter the abundances of key gaseous species.
