- ID:
- ivo://CDS.VizieR/J/A+A/550/A103
- Title:
- Model 1D (LHD) and 3D (CO5BOLD) spectra
- Short Name:
- J/A+A/550/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To derive space velocities of stars along the line of sight from wavelength shifts in stellar spectra requires accounting for a number of second-order effects. For most stars, gravitational redshifts, convective blueshifts, and transverse stellar motion are the dominant contributors. We provide theoretical corrections for the net velocity shifts due to convection expected for the measurements from the Gaia Radial Velocity Spectrometer (RVS). We used a set of three-dimensional time-dependent simulations of stellar surface convection computed with CO5BOLD to calculate spectra of late-type stars in the Gaia RVS range and to infer the net velocity offset that convective motions will induce in radial velocities derived by cross-correlation. The net velocity shifts derived by cross-correlation depend both on the wavelength range and spectral resolution of the observations. Convective shifts for Gaia RVS observations are less than 0.1km/s for late-K-type stars, and they increase with stellar mass, reaching about 0.3km/s or more for early F-type dwarfs. This tendency is the result of an increase with effective temperature in both temperature and velocity fluctuations in the line-forming region. Our simulations also indicate that the net RVS convective shifts can be positive (i.e. redshifts) in some cases. Overall, the blueshifts weaken slightly with increasing surface gravity, and are enhanced at low metallicity. Gravitational redshifts amount up to 0.7km/s and dominate convective blueshifts for dwarfs, but become much weaker for giants.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/568/A7
- Title:
- Model SDSS colors for halo stars
- Short Name:
- J/A+A/568/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of tens of thousands of spectra of halo turnoff stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population "in situ" out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as flux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that best reproduces each observed spectrum. We use an optimization algorithm and evaluate model fluxes by means of interpolation in a pre-computed grid. In our analysis, we account for the spectrograph's varying resolution as a function of fiber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars at logg (cgs units) lower than 2.5. An analysis of stars in the globular cluster M13 reveals a dependence of the inferred metallicity on surface gravity for stars with logg<2.5, confirming the systematics identified in the comparison with the SSPP. We find that our metallicity estimates are significantly more precise than the SSPP results. We also find excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turnoff stars as flux calibrators efficiently excludes stars with high metallicities, but does not significantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with that expected from a dual halo system in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/439
- Title:
- Models of solar magnetic structures
- Short Name:
- J/ApJS/169/439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents semiempirical models of various solar magnetic structures, extending from the photosphere to the chromosphere. The models have been derived from non-LTE inversions of high-resolution spectropolarimetric observations of four CaII and FeI lines. The observed targets are dark and bright components of a sunspot umbra; dark and bright components of a sunspot penumbra; a canopy between two sunspots; a facula; and a network element. These models may be employed, e.g., to compute realistic synthetic Stokes spectra of photospheric and chromospheric lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/482
- Title:
- Models of the solar atmosphere. III.
- Short Name:
- J/ApJ/707/482
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Semiempirical atmospheric models of solar surface features as observed at moderate resolution are useful tools for understanding the observed solar spectral irradiance variations. Paper I described a set of models constructed to reproduce the observed radiance spectrum for solar surface features at ~2 arcsec resolution that constitute an average over small-scale features such as granulation. Paper II showed that a revision of previous models of low-chromospheric inter-network regions explains the observed infrared CO lines in addition to the UV and radio continuum from submillimeter to centimetric wavelengths. The present paper (1) shows that the CaII H and K line wing observations are also explained by the new quiet-Sun-composite model, (2) introduces new low-chromospheric models of magnetic features that follow the ideas in Paper II (Fontenla et al. 2007ApJ...667.1243F), (3) introduces new upper chromospheric structures for all quiet-Sun and active-region models, and (4) shows how the new set of models explains EUV/FUV observations of spectral radiance and irradiance. This paper also discusses the chromospheric radiative-loss estimates in each of the magnetic features. The new set of models provides a basis for the spectral irradiance synthesis at EUV/FUV wavelengths based on the features observed on the solar surface.
- ID:
- ivo://CDS.VizieR/J/A+A/558/A131
- Title:
- Model spectra of hot stars at the pre-SN stage
- Short Name:
- J/A+A/558/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the fundamental properties of core-collapse Supernova (SN) progenitors from single stars at solar metallicity. We combine Geneva stellar evolutionary models with initial masses of Mini=20-120M_{sun}_ with atmospheric/wind models using CMFGEN. We provide synthetic photometry and high-resolution spectra of hot stars at the pre-SN stage. For Mini=9-20M_{sun}_, we supplement our analysis using publicly available MARCS model atmospheres of RSGs. We employ observational criteria of spectroscopic classification and find that massive stars, depending on Mini and rotation, end their lives as red supergiants (RSG), yellow hypergiants (YHG), luminous blue variables (LBV), and Wolf-Rayet (WR) stars of the WN and WO spectral types. For rotating models, we obtain the following types of SN progenitors: WO1-3 (Mini<=32M_{sun}_), WN10-11 (25<Mini< 32M_{sun}_), LBV (20<=Mini<25M_{sun}_), G1 Ia+ (18<Mini<20M_{sun}_), and RSGs (9<=Mini<=18M_{sun}_). For non-rotating models, we find spectral types WO1-3 (Mini>40M_{sun}_), WN7-8 (25<Mini<=40M_{sun}_), WN11h/LBV (20<Mini<=25M_{sun}_), and RSGs (9<=Mini<=20M_{sun}_). Our rotating models indicate that SN IIP progenitors are all RSG, SN IIL/b progenitors are 56% LBVs and 44% YHGs, SN Ib progenitors are 96% WN10-11 and 4% WOs, and SN Ic progenitors are all WO stars. We find that not necessarily the most massive and luminous SN progenitors are the brighter ones in a given filter. We show that SN IIP progenitors (RSGs) are bright in the RIJHK_S filters and faint in the UB filters. SN IIL/b progenitors (LBVs and YHGs), and SN Ib progenitors (WNs) are relatively bright in optical/IR filters, while SN Ic progenitors (WOs) are faint in all optical filters. We argue that SN Ib and Ic progenitors from single stars should be undetectable in the available pre-explosion images with the current magnitude limits, in agreement with observational results.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A100
- Title:
- M-type AGB stars wind and dust models
- Short Name:
- J/A+A/626/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar winds of asymptotic giant branch (AGB) stars are commonly attributed to radiation pressure on dust grains, formed in the wake of shock waves that arise in the stellar atmospheres. The mass loss due to these outflows is substantial, and modelling the dynamical properties of the winds is essential both for studies of individual stars and for understanding the evolution of stellar populations with low to intermediate mass. The purpose of this work is to present an extensive grid of dynamical atmosphere and wind models for M-type AGB stars, covering a wide range of relevant stellar parameters. We used the DARWIN code, which includes frequency-dependent radiation-hydrodynamics and a time-dependent description of dust condensation and evaporation, to simulate the dynamical atmosphere. The wind-driving mechanism is photon scattering on submicron-sized Mg2SiO4 grains. The grid consists of ~4000 models, with luminosities from L*=890L_{sun}_ to L*=40000 L_{sun}_ and effective temperatures from 2200 to 3400K. For the first time different current stellar masses are explored with M-type DARWIN models, ranging from 0.75M_{sun}_ to 3 M_{sun}_. The modelling results are radial atmospheric structures, dynamical properties such as mass-loss rates and wind velocities, and dust properties (e.g. grain sizes, dust-to-gas ratios, and degree of condensed Si). We find that the mass-loss rates of the models correlate strongly with luminosity. They also correlate with the ratio L*/M*: increasing L*/M* by an order of magnitude increases the mass-loss rates by about three orders of magnitude, which may naturally create a superwind regime in evolution models. There is, however, no discernible trend of mass-loss rate with effective temperature, in contrast to what is found for C-type AGB stars. We also find that the mass-loss rates level off at luminosities higher than ~14000L_{sun}_, and consequently at pulsation periods longer than ~800 days. The final grain radii range from 0.25 to 0.6um. The amount of condensed Si is typically between 10 and 40%, with gas-to-dust mass ratios between 500 and 4000.
- ID:
- ivo://CDS.VizieR/J/ApJS/170/251
- Title:
- Multiplet table for neutral helium
- Short Name:
- J/ApJS/170/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper combines the precise determination of the energy levels of ^4^HeI from calculations and experiments with theoretical transition probabilities to present multiplet tables and finding lists for the fine structure of the helium atom. The tabulated transition rates and oscillator strengths include corrections for singlet-triplet mixing and spin-orbit coupling, but not the higher order relativistic terms nor the finite nuclear mass, although the latter are tabulated for future use. The results are consistent with laboratory lifetimes and oscillator strengths, but very few measurements are accurate enough to be stringent tests. An Appendix discusses the corrections for finite nuclear mass.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A64
- Title:
- New atmospheric parameters of MILES cool stars
- Short Name:
- J/A+A/585/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The full spectrum fitting of stellar spectra against a library of empirical spectra is a well-established approach to measure the atmospheric parameters of FGK stars with a high internal consistency. Extending it towards cooler stars still remains a challenge. We address this question by improving the MILES interpolator (Prugniel et al., 2011, Cat. J/A+A/531/A165; hereafter PVK) in the low effective temperature regime (Teff<4800K). We measure the biases of the determined parameters with respect to our updated compilation of parameters. After correcting some systematic effects, we compute a new interpolator that we finally use to redetermine the atmospheric parameters homogeneously and assess the biases. Based on an updated literature compilation, we determine Teff in a more accurate and unbiased manner compared to those determined with the original interpolator. The validity range is extended downwards to about Teff=2900K compared to 3500K previously. The measured parameters are restricted to the current sub sample of MILES, and we have shown that they are generally more reliable than those presented in PVK. But the small discontinuity between the PVK and new measurements is significant, in particular for Teff, and should be corrected if one needs to join the two series.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A57
- Title:
- New FeII energy levels from stellar spectra
- Short Name:
- J/A+A/520/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectra of B-type and early A-type stars show numerous unidentified lines in the whole optical range, especially in the 5100-5400{AA} interval. Because FeII transitions to high energy levels should be observed in this region, we used semiempirical predicted wavelengths and gf-values of FeII to identify unknown lines. Semiempirical line data for FeII computed by Kurucz are used to synthesize the spectrum of the slow-rotating, Fe - overabundant CP star HR6000.
- ID:
- ivo://CDS.VizieR/J/MNRAS/413/1515
- Title:
- New grids of Atlas9 models
- Short Name:
- J/MNRAS/413/1515
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New grids of Atlas9 models have been calculated using revised convection parameters and updated opacity-distribution functions, for chemical compositions intended to be representative of solar, [M/H]=+0.3,+0.5, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) abundances. The grids cover Teff=3.5-50kK, from logg=5.0 to the effective Eddington limit. Limb-darkening coefficients and synthetic photometry are presented in the UBVRIJHKLM, uvby, ugriz, WFCAM, Hipparcos/Tycho, and Kepler passbands for these models, and for Castelli's comparable 'new-ODF' grids. Flux distributions are given for the new models. The sensitivity of limb-darkening coefficients to the adopted physics is illustrated.
