A Grid of FASTWIND NLTE Model Atmospheres of Massive Stars (original) (raw)
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Astronomy & Astrophysics, 2020
Aims. We present a database of 43 340 atmospheric models (∼80 000 models at the conclusion of the project) for stars with stellar masses between 9 and 120 M⊙, covering the region of the OB main-sequence and Wolf-Rayet stars in the Hertzsprung-Russell diagram. Methods. The models were calculated using the ABACUS I supercomputer and the stellar atmosphere code CMFGEN. Results. The parameter space has six dimensions: the effective temperature Teff, the luminosity L, the metallicity Z, and three stellar wind parameters: the exponent β, the terminal velocity V∞, and the volume filling factor Fcl. For each model, we also calculate synthetic spectra in the UV (900−2000 Å), optical (3500−7000 Å), and near-IR (10 000−40 000 Å) regions. To facilitate comparison with observations, the synthetic spectra can be rotationally broadened using ROTIN3, by covering v sin i velocities between 10 and 350 km s−1 with steps of 10 km s−1. Conclusions. We also present the results of the reanalysis of ϵ Ori ...
Communications in Computer and Information Science
We present a database of 45,000 atmospheric models (which will become 80,000 models by the end of the project) with stellar masses between 9 and 120 M ⊙ , covering the region of the OB main sequence and W-R stars in the H-R diagram. The models were calculated using the ABACUS I supercomputer and the stellar atmosphere code CMFGEN. The parameter space has 6 dimensions: the effective temperature T eff , the luminosity L, the metallicity Z, and three stellar wind parameters, namely the exponent β , the terminal velocity V ∞ , and the volume filling factor F cl. For each model, we also calculate synthetic spectra in the UV (900-2000Å), optical (3500-7000Å), and near IR (10000-30000Å) regions. To facilitate comparison with observations, the synthetic spectra were rotationally broaden using ROTIN3, by covering v sin i velocities between 10 and 350 km/s with steps of 10 km/s, resulting in a library of 1 575 000 synthetic spectra. In order to demonstrate the benefits of employing the databases of pre-calculated models, we also present the results of the re-analysis of ε Ori by using our grid.
A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
2008
S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700 ≤ T eff (K) ≤ 4000, 0.50 ≤ C/O ≤ 0.99, 0 ≤ log g ≤ 5, [Fe/H] = 0., −0.5 dex, and [s/Fe] = 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980, MNRAS, 190, 441) that ZrO bands in warm S stars (T eff > 3200 K) are not caused by the C/O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V − K and J − K photometric indices, are used to select T eff , C/O, [Fe/H] and [s/Fe]. The Geneva U − B 1 and B 2 − V 1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at T eff = 3200 K, a change of C/O from 0.5 to 0.99 has a strong impact on V − K (2 mag). Conversely, a range of 2 mag in V − K corresponds to a 200 K shift along the (T eff , V − K) relationship (for a fixed C/O value). Hence, the use of a (T eff , V − K) calibration established for M stars will yield large errors for S stars, so that a specific calibration must be used, as provided in the present paper. Using the atmospheric parameters derived by our method for the sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy among S stars reveals itself very clearly as a bimodal distribution in the effective temperatures. Moreover, the increase of s-process element abundances with increasing C/O ratios and decreasing temperatures is apparent among intrinsic stars, confirming theoretical expectations.
A grid of S stars MARCS model atmospheres
Journal of Physics: Conference Series, 2011
S-type stars are late-type giants whose atmosphere is enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. A large grid of S-star model atmospheres has been computed covering the range 2700 ≤ T eff (K) ≤ 4000 with 0.5 ≤ C/O ≤ 0.99. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle T eff , C/O and [s/Fe]. A "best-model finding tool" was developed using a set of well-chosen indices and checked against photometry as well as low-and high-resolution spectroscopy. It is found that applying M-star model atmospheres (i.e., with a solar C/O ratio) to S stars can lead to errors on T eff up to 400 K. We constrain the parameter space occupied by S stars of the vast sample of Henize stars in terms of T eff , [C/O] and [s/Fe].
Coudé-feed stellar spectral library – atmospheric parameters
Astronomy & Astrophysics, 2010
Context. Empirical libraries of stellar spectra play an important role in different fields. For example, they are used as reference for the automatic determination of atmospheric parameters, or for building synthetic stellar populations to study galaxies. The CFLIB (Coudé-feed library, Indo-US) database is at present one of the most complete libraries, in terms of its coverage of the atmospheric parameters space (T eff , log g and [Fe/H]) and wavelength coverage 3460-9464 Å at a resolution of ∼1 Å FWHM. Although the atmospheric parameters of most of the stars were determined from detailed analyses of high-resolution spectra, for nearly 300 of the 1273 stars of the library at least one of the three parameters is missing. For the others, the measurements, compiled from the literature, are inhomogeneous. Aims. In this paper, we re-determine the atmospheric parameters, directly using the CFLIB spectra, and compare them to the previous studies. Methods. We use the ULySS program to derive the atmospheric parameters, using the ELODIE library as a reference. Results. Based on comparisons with several previous studies we conclude that our determinations are unbiased. For the 958 F, G, and K type stars the precision on T eff , log g, and [Fe/H] is respectively 43 K, 0.13 dex and 0.05 dex. For the 53 M stars they are 82 K, 0.22 dex and 0.28 dex. And for the 260 OBA type stars the relative precision on T eff is 5.1%, and on log g, and [Fe/H] the precision is respectively 0.19 dex and 0.16 dex. These parameters will be used to re-calibrate the CFLIB fluxes and to produce synthetic spectra of stellar populations.
Commission 36: Theory of Stellar Atmospheres
Proceedings of the International Astronomical Union, 2010
Pulsating stars and asteroseismology Classically variable stars, and 'ordinary' solar-type ones. Inverting observed pressure-mode frequencies into atmospheric structure. Mass-loss mechanisms in pulsating stars. Effects of rapid rotation on pulsation.
Astronomy and Astrophysics, 2022
Aims. We performed a spectral fitting for a set of O-type stars based on self-consistent wind solutions, which provide mass-loss rate and velocity profiles directly derived from the initial stellar parameters. The great advantage of this self-consistent spectral fitting is therefore the reduction of the number of free parameters to be tuned. Methods. Self-consistent values for the line-force parameters (k, α, δ) sc and subsequently for the mass-loss rate,Ṁ sc , and terminal velocity, ∞,sc , are provided by the m-CAK prescription introduced in Paper I, which is updated in this work with improvements such as a temperature structure T (r) for the wind that are self-consistently evaluated from the line-acceleration. Synthetic spectra were calculated using the radiative transfer code FASTWIND, replacing the classical β-law for our new calculated velocity profiles (r) and therefore making clumping the only free parameter for the stellar wind. Results. We found that self-consistent m-CAK solutions provide values for theoretical mass-loss rates of the order of the most recent predictions of other studies. From here, we generate synthetic spectra with self-consistent hydrodynamics to fit and obtain a new set of stellar and wind parameters for our sample of O-type stars (HD 192639, 9 Sge, HD 57682, HD 218915, HD 195592, and HD 210809), whose spectra were taken with the high-resolution echelle spectrograph HERMES (R = 85 000). We find a satisfactory global fit for our observations, with a good accuracy for photospheric He I and He II lines and a quite acceptable fit for H lines. Although this self-consistent spectral analysis is currently constrained in the optical wavelength range alone, this is an important step towards the determination of stellar and wind parameters without using a β-law. Based on the variance of the line-force parameters, we establish that our method is valid for O-type stars with T eff ≥ 30 kK and log g ≥ 3.2. Given these results, we expect that the values introduced here are helpful for future studies of the stars constituting this sample, together with the prospect that the m-CAK self-consistent prescription may be extended to numerous studies of massive stars in the future.
Comparison between model atmospheres and spectra from early-type stars
Symposium - International Astronomical Union, 1965
To assist in the interpretation of ultraviolet continuum observations, we present observational features of a grid of non-grey model atmosphères in strict radiative equilibrium which have effective temperatures in the range 10000 °K to 20000 °K and surface gravities 103 and 104. For three models, we add the blended wings of the higher Balmer and Lyman hydrogen lines and include in an approximate way further effects of line blanketing in the ultraviolet. Finally, we present a preliminary calculation of the effect of departures from L. T. E. on the continuous flux.To examine the validity of the models, we compare the predicted continuous flux and predicted line profiles with the corresponding observed quantities for Vega and Sirius.We consider the question of discrepancies between theory and observations in the ultraviolet from the viewpoint of these new calculations, and find generally good agreement with recent observations made by T. Stecher.
Study of Stellar atmosphere models
, Roll Number 419PH2151 hereby declare that this thesis entitled Study of Stellar atmosphere models presents my original work carried out as a postgraduate student of NIT Rourkela and, to the best of my knowledge, contains no material previously published or written by another person, nor any material presented by me for the award of any degree or diploma of NIT Rourkela or any other institution. Any contribution made to this research by others, with whom I have worked at NIT Rourkela or elsewhere, is explicitly acknowledged in the dissertation. Works of other authors cited in this dissertation have been duly acknowledged under the sections "Reference" or "Bibliography". I have also submitted my original research records to the scrutiny committee for evaluation of my dissertation. I am fully aware that in case of any non-compliance detected in future, the Senate of NIT Rourkela may withdraw the degree awarded to me on the basis of the present dissertation.
A grid of MARCS model atmospheres for late-type stars
Astronomy & Astrophysics, 2008
Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 10 4 model atmospheres for stars with 2500 K ≤ T eff ≤ 8000 K, −1 ≤ log g = log (GM/R 2) ≤ 5 (cgs) with various masses and radii, −5 ≤ [Me/H] ≤ +1, with [α/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This includes "CN-cycled" models with C/N = 4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 ≤ ξ t ≤ 5 km s −1. We also list thermodynamic quantities (T , P g , P e , ρ, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.