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Register a new userCreating and using large grids of pre-calculated model atmospheres for rapid analysis of stellar spectra
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Added by
Celia Rosa Fierro-Santill\\'an
Publication date
2021
fields
Physics
and research's language is
English
Authors
Janos Zsargo
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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$_{odot}$, 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 $T_{rm eff}$, the luminosity $L$, the metallicity $Z$, and three stellar wind parameters, namely the exponent $beta$, the terminal velocity $V_{infty}$, and the volume filling factor $F_{cl}$. For each model, we also calculate synthetic spectra in the UV (900-2000 Angstroms), optical (3500-7000 Angstroms), and near IR (10000-30000 Angstroms) 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 $epsilon$ Ori by using our grid.
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$Aims.$ We present a database of 43,340 atmospheric models ($sim$80,000 models at the conclusion of the project) for stars with stellar masses between 9 and 120 $M_{odot}$, covering the region of the OB main-sequence and Wolf-Rayet (W-R) stars in the Hertzsprung--Russell (H--R) 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 $T_{eff}$, the luminosity $L$, the metallicity $Z$, and three stellar wind parameters: the exponent $beta$, the terminal velocity $V_{infty}$, and the volume filling factor $F_{cl}$. For each model, we also calculate synthetic spectra in the UV (900-2000 A), optical (3500-7000 A), and near-IR (10000-40000 A) regions. To facilitate comparison with observations, the synthetic spectra can be rotationally broadened using ROTIN3, by covering vsin(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 $epsilon$ Ori using our grid to demonstrate the benefits of databases of precalculated models. Our analysis succeeded in reproducing the best-fit parameter ranges of the original study, although our results favor the higher end of the mass-loss range and a lower level of clumping. Our results indirectly suggest that the resonance lines in the UV range are strongly affected by the velocity-space porosity, as has been suggested by recent theoretical calculations and numerical simulations.
We present tests carried out on optical and infrared stellar spectra to evaluate the accuracy of different types of interpolation. Both model atmospheres and continuum normalized fluxes were interpolated. In the first case we used linear interpolation, and in the second linear, cubic spline, cubic-Bezier and quadratic-Bezier methods. We generated 400 ATLAS9 model atmospheres with random values of the atmospheric parameters for these tests, spanning between -2.5 and +0.5 in [Fe/H], from 4500 to 6250 K in effective temperature, and 1.5 to 4.5 dex in surface gravity. Synthesized spectra were created from these model atmospheres, and compared with spectra derived by interpolation. We found that the most accurate interpolation algorithm among those considered in flux space is cubic-Bezier, closely followed by quadratic-Bezier and cubic splines. Linear interpolation of model atmospheres results in errors about a factor of two larger than linear interpolation of fluxes, and about a factor of four larger than high order flux interpolations.
This paper describes the analysis of UVES and GIRAFFE spectra acquired by the Gaia-ESO Public Spectroscopic Survey in the fields of young clusters whose population includes pre-main sequence (PMS) stars. Both methods that have been extensively used in the past and new ones developed in the contest of the Gaia-ESO survey enterprise are available and used. The internal precision of these quantities is estimated by inter-comparing the results obtained by such different methods, while the accuracy is estimated by comparison with independent external data, like effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. Specific strategies are implemented to deal with fast rotation, accretion signatures, chromospheric activity, and veiling. The analysis carried out on spectra acquired in young clusters fields during the first 18 months of observations, up to June 2013, is presented in preparation of the first release of advanced data products. Stellar parameters obtained with the higher resolution and larger wavelength coverage from UVES are reproduced with comparable accuracy and precision using the smaller wavelength range and lower resolution of the GIRAFFE setup adopted for young stars, which allows us to provide with confidence stellar parameters for the much larger GIRAFFE sample. Precisions are estimated to be $approx$ 120 K r.m.s. in Teff, $approx$0.3 dex r.m.s. in logg, and $approx$0.15 dex r.m.s. in [Fe/H], for both the UVES and GIRAFFE setups.
The study of massive stars in different metallicity environments is a central topic of current stellar research. The spectral analysis of massive stars requires adequate model atmospheres. The computation of such models is difficult and time-consuming. Therefore, spectral analyses are greatly facilitated if they can refer to existing grids of models. Here we provide grids of model atmospheres for OB-type stars at metallicities corresponding to the Small and Large Magellanic Clouds, as well as to solar metallicity. In total, the grids comprise 785 individual models. The models were calculated using the state-of-the-art Potsdam Wolf-Rayet (PoWR) model atmosphere code. The parameter domain of the grids was set up using stellar evolution tracks. For all these models, we provide normalized and flux-calibrated spectra, spectral energy distributions, feedback parameters such as ionizing photons, Zanstra temperatures, and photometric magnitudes. The atmospheric structures (the density and temperature stratification) are available as well. All these data are publicly accessible through the PoWR website.
We present an outline of basic assumptions and governing structural equations describing atmospheres of substellar mass objects, in particular the extrasolar giant planets and brown dwarfs. Although most of the presentation of the physical and numerical background is generic, details of the implementation pertain mostly to the code CoolTlusty. We also present a review of numerical approaches and computer codes devised to solve the structural equations, and make a critical evaluation of their efficiency and accuracy.
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