| 1. |
- Piskunov, Nikolai, et al.
(författare)
-
Program Package for the Analysis of High Resolution High Signal-To-Noise Stellar Spectra
- 2017
-
Ingår i: Stars. - 9781583819043 ; , s. 509-513
-
Konferensbidrag (refereegranskat)abstract
- The program package SME (Spectroscopy Made Easy), designed to perform an analysis of stellar spectra using spectral fitting techniques, was updated due to adding new functions (isotopic and hyperfine splittins) in VALD and including grids of NLTE calculations for energy levels of few chemical elements. SME allows to derive automatically stellar atmospheric parameters: effective temperature, surface gravity, chemical abundances, radial and rotational velocities, turbulent velocities, taking into account all the effects defining spectral line formation. SME package uses the best grids of stellar atmospheres that allows us to perform spectral analysis with the similar accuracy in wide range of stellar parameters and metallicities from dwarfs to giants of BAFGK spectral classes.
|
|
| 2. |
- Ryabchikova, T., et al.
(författare)
-
Accuracy of atmospheric parameters of FGK dwarfs determined by spectrum fitting
- 2016
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:2, s. 1221-1234
-
Tidskriftsartikel (refereegranskat)abstract
- We performed extensive tests of the accuracy of atmospheric parameter determination for FGK stars based on the spectrum fitting procedure SpectroscopyMade Easy (SME). Our stellar sample consists of 13 objects, including the Sun, in the temperature range 5000-6600K and metallicity range -1.4-+0.4. The analysed stars have the advantage of having parameters derived by interferometry. For each star, we use spectra obtained with different spectrographs and different signal-to-noise ratios (S/N). For the fitting, we adopted three different sets of constraints and test how the derived parameters depend upon the spectral regions (masks) used in SME. We developed and implemented in SME a new method for estimating uncertainties in the resulting parameters based on fitting residuals, partial derivatives, and data uncertainties. For stars in the 5700-6600K range, the best agreement with the effective temperatures derived by interferometry is achieved when spectrum fitting includes the Ha and H beta lines, while for cooler stars the choice of the mask does not affect the results. The derived atmospheric parameters do not strongly depend on spectral resolution and S/N of the observations, while the uncertainties in temperature and surface gravity increase with increasing effective temperature, with minima at 50K in T-eff and 0.1 dex in log g, for spectra with S/N=150-200. A non-local thermodynamic equilibrium (NLTE) analysis of the Ti I/Ti II and Fe I/Fe II ionization equilibria and abundances determined from the atomic CI (NLTE) and molecular CH species supports the parameters we derived with SME by fitting the observed spectra including the hydrogen lines.
|
|
| 3. |
- Ryabchikova, T., et al.
(författare)
-
Evaluation of the Recent Atomic Data for Fe i Lines Based on Solar and Stellar Spectra
- 2019
-
Ingår i: Solar Physics. - : Springer Science and Business Media LLC. - 0038-0938 .- 1573-093X. ; 294:11
-
Tidskriftsartikel (refereegranskat)abstract
- We performed an extensive comparative analysis of the recent experimental data on Fe i transition probabilities (TP) based on the observed solar and stellar spectra. This work is part of the Vienna Atomic Line database (VALD) activities. Our motivation is to keep the VALD line list as complete as possible and provide VALD users with substantiated recommendations for the most accurate atomic data. For assessment of data quality we choose the "normal" (as opposed to peculiar and/or magnetic) Main Sequence sharp-line stars of different effective temperatures with accurately known atmospheric parameters: Sun, Procyon, HD 32115, and 21 Peg. Theoretical spectra of these stars were synthesized for 1D plane-parallel model atmospheres accounting for non-local thermodynamic equilibrium (NLTE) effects, and then they were compared with the observations. For all of the stars we derived atmospheric abundances based on the new and previous experimental TP. When using the new TPs the best agreement for iron is achieved with the TP of the Hannover group (Bard, Kock, and Kock, Astron. Astrophys.248, 315, 1991; Bard and Kock, Astron. Astrophys.282, 1014, 1994). The Hannover set is recommended as the primary source of transition probabilities in stellar abundance analysis. The new TP data significantly increase the number of spectral lines of Fe i in the optical and red spectral regions available for accurate abundance analysis of stars in a wide range of temperatures and metallicities. Comparison with the observed stellar spectra invalidates some new experimental data despite the small given uncertainty of the laboratory measurements. Finally, we note the importance of accurate line-broadening data.
|
|
| 4. |
- Yakunin, I., et al.
(författare)
-
The surface magnetic field and chemical abundance distributions of the B2V helium-strong star HD 184927
- 2015
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 447:2, s. 1418-1438
-
Tidskriftsartikel (refereegranskat)abstract
- A new time series of high-resolution Stokes I and V spectra of the magnetic B2V star HD 184927 has been obtained in the context of the Magnetism in Massive Stars Large Program with an Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and dimaPol liquid crystal spectropolarimeter at 1.8-m telescope of Dominion Astrophysical Observatory. We model the optical and UV spectrum obtained from the International Ultraviolet Explorer (IUE) archive to infer the stellar physical parameters. Using magnetic field measurements, we derive an improved rotational period of 9.531 02 +/- 0.0007 d. We infer the longitudinal magnetic field from lines of H, He, and various metals, revealing large differences between the apparent field strength variations determined from different elements. Magnetic Doppler Imaging using He and O lines yields strongly non-uniform surface distributions of these elements. We demonstrate that the diversity of longitudinal field variations can be understood as due to the combination of element-specific surface abundance distributions in combination with a surface magnetic field that is comprised of dipolar and quadrupolar components. We have reanalysed IUE high-resolution spectra, confirming strong modulation of wind-sensitive C IV and S IV resonance lines. However, we are unable to detect any modulation of the Ha profile attributable to a stellar magnetosphere. We conclude that HD 184927 hosts a centrifugal magnetosphere (eta(*) similar to 2.4(-1.1)(+22) x 10(4)), albeit one that is undetectable at optical wavelengths. The magnetic braking time-scale of HD 184927 is computed to be tau(J) = 0.96 or 5.8 Myr. These values are consistent with the slow rotation and estimated age of the star.
|
|
