Determination Of Atmospheric Parameters Research Articles

Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec

Context. An increasing number of high-resolution stellar spectra is available today thanks to many past and ongoing extensive spectroscopic surveys. Consequently, the scientific community needs automatic procedures to derive atmospheric parameters and individual element abundances. Aims. Based on the widely known SPECTRUM code by R. O. Gray, we developed an integrated spectroscopic software framework suitable for the determination of atmospheric parameters (i.e., effective temperature, surface gravity, metallicity) and individual chemical abundances. The code, named iSpec and freely distributed, is written mainly in Python and can be used on different platforms. Methods. iSpec can derive atmospheric parameters by using the synthetic spectral fitting technique and the equivalent width method. We validated the performance of both approaches by developing two different pipelines and analyzing the Gaia FGK benchmark stars spectral library. The analysis was complemented with several tests designed to assess other aspects, such as the interpolation of model atmospheres and the performance with lower quality spectra. Results. We provide a code ready to perform automatic stellar spectral analysis. We successfully assessed the results obtained for FGK stars with high-resolution and high signal-to-noise spectra.

Atmospheric parameters of 169 F-, G-, K- and M-type stars in the Kepler field★

The asteroseismic and planetary studies, like all research related to stars, need precise and accurate stellar atmospheric parameters as input. We aim at deriving the effective temperature (Teff), the surface gravity (log g), the metallicity ([Fe/H]), the projected rotational velocity (v sin i) and the MK type for 169 F, G, K, and M-type Kepler targets which were observed spectroscopically from the ground with five different instruments. We use two different spectroscopic methods to analyse 189 high-resolution, high-signal-to-noise spectra acquired for the 169 stars. For 67 stars, the spectroscopic atmospheric parameters are derived for the first time. KIC 9693187 and 11179629 are discovered to be double-lined spectroscopic binary systems. The results obtained for those stars for which independent determinations of the atmospheric parameters are available in the literature are used for a comparative analysis. As a result, we show that for solar-type stars the accuracy of present determinations of atmospheric parameters is +/- 150 K in Teff, +/- 0.15 dex in [Fe/H], and +/-? 0.3 dex in log g. Finally, we confirm that the curve-of-growth analysis and the method of spectral synthesis yield systematically different atmospheric parameters when they are applied to stars hotter than 6,000 K.

Coudé-feed stellar spectral library – atmospheric parameters

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 (Coude-feed library, Indo-US) database is at present one of the most complete libraries, in terms of its coverage of the atmospheric parameters space (Teff, log g and [Fe/H]) and wavelength coverage 3460 - 9464 A at a resolution of 1 A 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 Teff, 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 Teff 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.

BINARY CONTAMINATION IN THE SEGUE SAMPLE: EFFECTS ON SSPP DETERMINATIONS OF STELLAR ATMOSPHERIC PARAMETERS

Using numerical modeling and a grid of synthetic spectra, we examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for SEGUE targets measured using the SEGUE Stellar Parameter Pipeline (SSPP). To model undetected binaries that may be in the SEGUE sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G-K dwarf stars, as defined by SDSS color cuts, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, we synthesize a grid of model spectra from 3275 to 7850 K (~0.1 to 1.0 \msun) and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. We analyze both "infinite" signal-to-noise ratio (S/N) models and degraded versions, at median S/N of 50, 25 and 10. By running individual and combined spectra (representing the binaries) through the SSPP, we determine that ~10% of the blended G-K dwarf pairs with S/N>=25 will have their atmospheric parameter determinations, in particular temperature and metallicity, noticeably affected by the presence of an undetected secondary. To account for the additional uncertainty from binary contamination at a S/N~10, uncertainties of ~140 K and ~0.17 dex in [Fe/H] must be added in quadrature to the published uncertainties of the SSPP. (Abridged)

Lithium survey in evolved stars observed in the sacy project

AbstractThe primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.

FUSE observations of intermediate temperature DA: Atmospheric parameters and metal abundances

We present results from our analysis of a sample of DA white dwarfs having effective temperature below 25,000 K observed with the FUSE satellite with the goals of better understanding the origin of metals detected in the atmosphere of these stars. When possible, we combine the FUSE spectra with the IUE spectra and determine atmospheric parameters by fitting the Lyman line profiles. In general we find a good agreement with published values based on fits of the Balmer series. We observe that the continuum in the blue wing of the Lyman α line profile is generally lower in comparison with model spectra and that the discrepancy appears to become less important at higher effective temperature. The agreement between models and observations is excellent at wavelengths shorter than 1100 Å, which gives us confidence in the determination of atmospheric parameters. Finally, using adopted atmospheric parameters; we have performed a detailed analysis of the composition of these stars. In several instances, we have observed the presence of silicon and in one case that of carbon. For each star in the sample we have either measured or set an upper limit on the presence of key species such as CII, CIII, SiIII, and SiIV. We then compare the measured abundances with equilibrium abundance predicted by radiative levitation theory for each star. In this limited sample, we find that when detected, the abundance of silicon is in good agreement with theory. However there are several cases where the upper limits are smaller than the predictions and one case where it is considerably larger.

Nonadiabatic asteroseismology of GW vir stars

We present results from nonadiabatic stability calculation to determine the position of the GW Vir band in the log g -Teff diagram. With this method, we calculate the position of seven GW Vir stars. The results are consistent with and complementary to the spectroscopic determination of atmospheric parameters and the chemical compositions of these stars except for the newly discover GW Vir star VV 47. This discrepancy is discussed.

Nonadiabatic asteroseismology of GW Vir stars

We present and explore a new method involving a nonadiabatic stability calculation to determine the position of the GW Vir band in the log g — Teff diagram. With this method, we calculate the position of two GW Vir stars, PG 1159-035, log g = 6.80, Teff = 144, 500 K and PG 1707+427, log g = 7.38, Teff = 81, 500 K. The results are consistent with and complementary to the spectroscopic determination of atmospheric parameters and the chemical compositions of these stars.

Stars within 15 Parsecs: Abundances for a Northern Sample

We present an abundance analysis for stars within 15 pc of the Sun located north of -30° declination. We have limited our abundance sample to absolute magnitudes brighter than +7.5 and have eliminated several A stars in the local vicinity. Our final analysis list numbers 114 stars. Unlike Allende Prieto et al. in their consideration of a very similar sample, we have enforced strict spectroscopic criteria in the determination of atmospheric parameters. Nevertheless, our results are very similar to theirs. We determine the mean metallicity of the local region to be = -0.07 using all stars and -0.04 when interlopers from the thick disk are eliminated.

Spectroscopic Determination of Atmospheric Parameters of Solar-Type Stars: Description of the Method and Application to the Sun

A computer program has been developed for determining the fundamental model atmosphere parameters ($T_\mathrm{eff}$, $\log g$, $v_\mathrm{t}$, $[\mathrm{Fe/H}]$) of solar-type stars, which is based on the equivalent widths for a well-chosen set of Fe i and Fe ii lines. The basic principle of this method is to find the solution in the $(T_\mathrm{eff}$, $\log g$, $v_\mathrm{t})$ space, which minimizes the sum of the dispersion of the Fe i abundances and the square of the Fe i–Fe ii abundance difference. An application of this code to the observed solar equivalent widths turned out to yield satisfactory results, which are more or less consistent with the actual parameters of the Sun. The numerical performance of this approach as well as the errors involved in the resulting solutions are discussed.

Library of Medium‐Resolution Fiber Optic Echelle Spectra of F, G, K, and M Field Dwarfs to Giant Stars

We present a library of Penn State Fiber Optic Echelle (FOE) observations of a sample of field stars with spectral types F to M and luminosity classes V to I. The spectral coverage is from 3800 to 10000 Å with a nominal resolving power of 12,000. These spectra include many of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as the Balmer lines (Hα to H), Ca II H & K, the Mg I b triplet, Na I D1, D2, He I D3, and Ca II IRT lines. There are also a large number of photospheric lines, which can also be affected by chromospheric activity, and temperature-sensitive photospheric features such as TiO bands. The spectra have been compiled with the goal of providing a set of standards observed at medium resolution. We have extensively used such data for the study of active chromosphere stars by applying a spectral subtraction technique. However, the data set presented here can also be utilized in a wide variety of ways ranging from radial velocity templates to study of variable stars and stellar population synthesis. This library can also be used for spectral classification purposes and determination of atmospheric parameters (Teff, log g, [Fe/H]). A digital version of all the fully reduced spectra is available via ftp and the World Wide Web (WWW) in FITS format.

Differential Abundances of B-type Supergiants in M33

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.We compare our results with the abundances expected from studies of H II regions.

Stellar α Elements Abundance Gradient in M33

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the present study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. The determination of atmospheric parameters is based on analyses of silicon ionisation balance. Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy. We compare our results with the abundances expected from studies of HII regions.

The sphericity effects in model atmospheres of central stars of Planetary Nebulae

The model atmospheres of central stars of planetary nebulae are often calculated under the assumption of the plane-parallel geometry. This assumption seems to be reasonable for stars with relatively thin atmospheres like white dwarfs, where the thickness of the atmosphere is only few kilometers while the corresponding radius is about several thousands of kilometers. Nevertheless, calculations of a grid of pure hydrogen model atmospheres of hot white dwarfs demonstrated that this assumption may fail even for thin atmospheres (Kubát 1995). We found small differences between line profiles (about 1%) calculated under the assumption of plane-parallel and spherically symmetric atmospheres. Such differences are detectable by contemporary observational technique, and, consequently, may not be neglected. In addition, sphericity effects are important also in stars of other types (Kubát 1996). We decided to test the assumption of the plane parallel geometry also for sample model atmospheres of central stars of planetary nebulae. We assumed static atmospheres in radiative, hydrostatic, and statistical equilibrium (NLTE) consisting of hydrogen and helium. We calculated spherically symmetric and plane parallel model atmospheres of two central stars, namely LoTr4 and K1-27. Basic atmospheric parameters of these stars were adopted from Rauch et al. (1996, 1994), respectively. The atmospheric parameters for LoTr4(Teff = 120000K, log g = 5.5, M = 0.65M⊙, n(H)/n(He) = 0.5 yield a model with an extension (r(τR = 10–5)/r(τR = 2/3)) of 1.028. For K1-27, the atmospheric parameters (Teff = 100000K, log g = 6.5, M = 0.52M⊙, n(H)/n(He) = 0.2 produce only a small extension of 1.0035. The differences in temperature structure of our model atmospheres are more pronounced for a star with lower gravity and, consequently, larger extension. Continuum flux is lower for spherical atmospheres. This difference is larger for LoTr4, i.e. a star with more extended atmosphere, and almost negligible for K1-27. Paschen and Pickering He ii lines also show differences. These differences are quite large (several per cent) for α lines, and they decrease towards higher series members. Using plane-parallel model atmospheres instead of spherically symmetric ones introduces a systematic error into results. This error is present also in highly sophisticated NLTE line blanketed models. Due to the above mentioned differences one should avoid using lower series members (e.g. He ii 4686 å) for determination of atmospheric parameters (Teff, log g, abundances,…) from plane-parallel atmospheres. Details of our calculations will be presented in Astronomy and Astrophysics.

Higher Paschen lines in the spectra of early-type stars

We present observed and computed line profiles of Paschen lines in two nearly atmospheric absorption-free spectral regions: 8350 to 8790 A and around the P7 line. We show that the Edmonds, Schluter & Wells semi-empirical theory of line broadening is suitable for the computation of higher members of the Paschen series. We compare the variations of the equivalent widths of P7 and P14 with CCD observations of a sample of O9.5 to A0 stars. It is shown that such spectral characteristics are well suited to the determination of atmospheric parameters of stars.

On the influence of the convective efficiency on the determination of the atmospheric parameters of DA white dwarfs

view Abstract Citations (69) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Influence of the Convective Efficiency on the Determination of the Atmospheric Parameters of DA White Dwarfs Bergeron, P. ; Wesemael, F. ; Fontaine, G. Abstract A detailed calculation of model atmospheres for DA white dwarfs is presented where several versions of the mixing-length theory with different associated convective efficiencies are used. The predicted emergent fluxes, color indices, and equivalent widths are most sensitive to the assumed parameterization of the theory in the range T(eff) about 8000-15,000 K. This, is also the region where the Balmer jump is a most useful gravity discriminant. The implications of the calculations for previous determinations of atmospheric parameters of DA white dwarfs are discussed, and these results are shown to be much more model-dependent than previously believed. Publication: The Astrophysical Journal Pub Date: March 1992 DOI: 10.1086/171080 Bibcode: 1992ApJ...387..288B Keywords: Free Convection; Stellar Atmospheres; White Dwarf Stars; Computational Astrophysics; Spectral Line Width; Stellar Temperature; Astrophysics; CONVECTION; STARS: ATMOSPHERES; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (1)

How Precise are Spectroscopic Abundance Determinations Today?

It is shown that a great breakthrough has occurred in the accuracy of spectroscopic abundance analyses with the introduction of solid state light detectors, such as Reticons and CCDs. Because of uncontrolled systematic errors in photographic photometry, abundances derived from high dispersion photographic spectra can hardly be known with an accuracy better than 0.3 dex. This is well exemplified by the recent finding that the observational scatter is large even in the equivalent widths of the Utrecht Solar Atlas. A fortiori these uncertainties are present in the [Fe/H] stellar abundance Catalogue, chiefly based in its present form on photographic material. For the future the calibration of the [Fe/H] Catalogue with spectra taken with Reticon detectors is recommended. A signal/noise ratio of 300 to 500 is more important than an improvement in spectral resolution with a low signal/noise ratio. Then, the remaining uncertainties in the abundances will mostly reflect inaccuracies in atmospheric parameter determinations of the models and in the assumptions underlying model computations.

Atmospheric definition for Shuttle aerothermodynamic investigations

A procedure has been developed to estimate the freestream atmospheric properties along the Shuttle trajectory during atmospheric re-entry. The procedure utilizes measurement data obtained by NASA, NOAA, and the Air Force, and model data for regions where measured data are nonexistent. The results obtained are used to determine the best atmosphere-relative trajectory parameters during re-entry and to allow for an evaluation of the aerodynamic and aerothermodynamic characteristics of the Shuttle. A discussion of the method employed by the Langley Atmospheric Information Retrieval System, which is a computer code for the determination of atmospheric parameters, is presented. Results obtained from the first two Shuttle flights, STS-1 and STS-2, are also given with applications of these atmospheric parameters.

Some recent developments in acoustic remote sensing

New initiatives for real-time quantitative acoustic determinations of atmospheric parameters and structure are described. Included are methods for measurement of profiles of turbulence and temperature fluctuation strengths, inversion heights, the strength of capping inversions, and the characteristics of atmospheric gravity waves. The talk will briefly describe an echo interferometer using coherent detection of acoustic mean phase that may lead to a new method for remote sensing of mean temperature profiles. The talk will also include some preliminary experimental results.

18. Model Atmospheres for Hydrogen-Deficient White Dwarfs

The determination of atmospheric parameters for non-DA white dwarfs is investigated with the computed helium-rich model atmospheres by Bues (1970). Only poor predictions are possible from UBV colors alone for DB and DC stars. From uvby colors a determination of effective temperature is possible within 1000 K. Profiles of lines in different parts of the spectrum are necessary for better results.A deficiency of metal abundances for the cooler non-DA stars is obtained.