Atmospheric parameters and element abundances (original) (raw)
Related papers
The Alpha Centauri binary system
Astronomy & Astrophysics, 2008
Context. The α Centauri binary system, owing to its duplicity, proximity and brightness, and its components' likeness to the Sun, is a fundamental calibrating object for the theory of stellar structure and evolution and the determination of stellar atmospheric parameters. This role, however, is hindered by a considerable disagreement in the published analyses of its atmospheric parameters and abundances. Aims. We report a new spectroscopic analysis of both components of the α Centauri system, compare published analyses of the system, and attempt to quantify the discrepancies still extant in the determinations of the atmospheric parameters and abundances of these stars. Methods. The analysis is differential with respect to the Sun, based on spectra with R = 35 000 and signal-to-noise ratio ≥1000, and employed spectroscopic and photometric methods to obtain as many independent T eff determinations as possible. We also check the atmospheric parameters for consistency against the results of the dynamical analysis and the positions of the components in a theoretical HR diagram. Results. The spectroscopic atmospheric parameters of the system are found to be T eff = (5847 ± 27) K, [Fe/H] = +0.24 ± 0.03, log g = 4.34 ± 0.12, and ξ t = 1.46 ± 0.03 km s −1 , for α Cen A, and T eff = (5316 ± 28) K, [Fe/H] = +0.25 ± 0.04, log g = 4.44 ± 0.15, and ξ t = 1.28 ± 0.15 km s −1 for α Cen B. The parameters were derived from the simultaneous excitation & ionization equilibria of Fe I and Fe II lines. T eff s were also obtained by fitting theoretical profiles to the Hα line and from photometric calibrations. Conclusions. We reached good agreement between the three criteria for α Cen A. For α Cen B the spectroscopic T eff is ∼140 K higher than the other two determinations. We discuss possible origins of this inconsistency, concluding that the presence of non-local thermodynamic equilibrium effects is a probable candidate, but we note that there is as yet no consensus on the existence and cause of an offset between the spectroscopic and photometric T eff scales of cool dwarfs. The spectroscopic surface gravities also agree with those derived from directly measured masses and radii. An average of three independent T eff criteria leads to T eff (A) = (5824 ± 26) K and T eff (B) = (5223 ± 62) K. The abundances of Na, Mg, Si, Mn, Co, and Ni and, possibly, Cu are significantly enriched in the system, which also seems to be deficient in Y and Ba. This abundance pattern can be deemed normal in the context of recent data on metal-rich stars. The position of α Cen A in an up-to-date theoretical evolutionary diagram yields a good match of the evolutionary mass and age (in the 4.5 to 5.3 Gyr range) with those from the dynamical solution and seismology, but only marginal agreement for α Cen B, taking into account its more uncertain T eff .
HST Be abundances in the Alpha Centauri system
Nuclear Physics A, 1997
High signal-to-noise (200 to 1) Hubble Space Telescope GHRS spectra of a Cen A (spectral type G2 V) and a Cen B (spectral type K1 V) in the Be II/~3130 region have been analyzed, for the purpose of making a precise determination of light element destruction in stars of approximately the same mass of the Sun's. Light element abundances in this stellar system can be used as a fundamental test of models of the outer structure of solar-type stars. Li, Be, and B are destroyed in progressively deeper layers in the outer regions of stars; thus their surface abundances are the observable consequences of internal processes. A detailed spectrum synthesis gives :Be/H] =-0.044-0.12 dex for a Cen A and-0.54+0.24 dex for a Cen B using a model atmosphere with :M/HI = +0.10 dex.
Chemical Abundances for 855 Giants in the Globular Cluster Omega Centauri (NGC 5139)
The Astrophysical Journal, 2010
We present elemental abundances for 855 red giant branch (RGB) stars in the globular cluster Omega Centauri (ω Cen) from spectra obtained with the Blanco 4m telescope and Hydra multifiber spectrograph. The sample includes nearly all RGB stars brighter than V=13.5, and span's ω Cen's full metallicity range. The heavy α elements (Si, Ca, and Ti) are generally enhanced by ∼+0.3 dex, and exhibit a metallicity dependent morphology that may be attributed to mass and metallicity dependent Type II supernova (SN) yields. The heavy α and Fe-peak abundances suggest minimal contributions from Type Ia SNe. The light elements (O, Na, and Al) exhibit >0.5 dex abundance dispersions at all metallicities, and a majority of stars with [Fe/H]>-1.6 have [O/Fe], [Na/Fe], and [Al/Fe] abundances similar to those in monometallic globular clusters, as well as O-Na, O-Al anticorrelations and the Na-Al correlation in all but the most metalrich stars. A combination of pollution from intermediate mass asymptotic giant branch (AGB) stars and in situ mixing may explain the light element abundance patterns. A large fraction (27%) of ω Cen stars are O-poor ([O/Fe]<0) and are preferentially located within 5-10 of the cluster center. The O-poor giants are spatially similar, located in the same metallicity range, and are present in nearly equal proportions to blue main sequence stars. This suggests the O-poor giants and blue main sequence stars may share a common origin. [La/Fe] increases sharply at [Fe/H] -1.6, and the [La/Eu] ratios indicate the increase is due to almost pure s-process production.
2014
The achievable level of precision on photospheric abundances of stars is a major limiting factor on investigations of exoplanet host star characteristics, the chemical histories of star clusters, and the evolution of the Milky Way and other galaxies. While model-induced errors can be minimized through the differential analysis of spectrally similar stars, the maximum achievable precision of this technique has been debated. As a test, we derive differential abundances of 19 elements from highquality asteroid-reflected solar spectra taken using a variety of instruments and conditions. We treat the solar spectra as being from unknown stars and use the resulting differential abundances, which are expected to be zero, as a diagnostic of the error in our measurements. Our results indicate that the relative resolution of the target and reference spectra is a major consideration, with use of different instruments to obtain the two spectra leading to errors up to 0.04 dex. Use of the same instrument at different epochs for the two spectra has a much smaller effect (∼0.007 dex). The asteroid used to obtain the solar standard also has a negligible effect (∼0.006 dex). Assuming that systematic errors from the stellar model atmospheres have been minimized, as in the case of solar twins, we confirm that differential chemical abundances can be obtained at sub-0.01 dex precision with due care in the observations, data reduction and abundance analysis.
Monthly Notices of The Royal Astronomical Society, 2007
We present a homogeneous set of stellar atmospheric parameters (T eff , log g, [Fe/H]) for MILES, a new spectral stellar library covering the range λλ3525 − 7500Å at 2.3Å (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous dataset of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.
Composition of Atmospheres of Normal and Peculiar stars
IARJSET, 2019
Context. The study of the chemical composition of stellar atmospheres is the main and most valuable source of information to determine the fundamental characteristics of stellar atmospheres, in one hand, and to studying the evolution of matter in the interior of stars, in the interstellar medium, and matter of the Galaxy, on the other hand. Aims. This study is to confirm that the effects of gravitational diffusion and light pressure begin to work, starting from specific degree of temperatures atmospheres of the main succession stars. Methods. Within the framework of this study, we processed Echelle spectra of the star "99Her" which have a spectral classes A-F, obtained with a 1.5-meter telescope PTT-150. In the investigation in question strengths of large numbers of absorption lines in stellar spectra were determined through photographic photometry of high resolution spectra, and the line strengths were than evaluated and converted into relative abundances on the basis of theoretical calculations of physical properties of model stellar atmospheres. Results. We determined the fundamental parameters of atmospheres:-the effective temperature, the acceleration of gravity, the micro-turbulent velocity. We also calculated the content of the chemical elements.
FASMA 2.0: A Python package for stellar parameters and chemical abundances
Journal of Open Source Software
Effective temperature (Teff), surface gravity (logg), and metallicity ([M/H]) are basic stellar atmospheric parameters necessary to characterize a star. Once these parameters are obtained, we can in turn, infer their chemical abundances of various elements and in conjunction with evolutionary models to estimate their evolution, i.e., mass and radius. In this work, we use spectroscopy as a powerful tool to extract this information from stellar atmospheres applied to stars with spectral type FGK both dwarfs and giants. The growing number of spectroscopic surveys dedicated to the study of the Galactic stellar populations has inflated the number of high quality spectra to several hundreds of thousands. This amount is expected to multiply with the forthcoming surveys, such as WEAVE (de Jong et al., 2019) and 4MOST (Dalton et al., 2014). The success of these surveys highly depends on the analysis tools to exploit sufficiently all spectral information. Moreover, it is a well-known axiom in exoplanetary studies that one can only determine the planetary properties once the ones of the host star are known. The planetary properties such as mass, radius, composition, are directly linked to their hosts and therefore, robust tools for the derivation of these parameters are necessary.
Astronomy & Astrophysics, 2005
Properties of stellar granulation are obtained by inverting spectra of the late-type stars α Centauri A and B. Our inversions are based on a multi-component model of the stellar photosphere and take into account the center-to-limb variation and rotational broadening. The different atmospheric components describe the areas harboring up-, down-and horizontal flows. The inversions are constrained by fitting not only the flux profiles, but also their line bisectors, and by using a simple mass conservation scheme. The inversions return the properties of convection at the stellar surface, including the stratification of the thermodynamic parameters, as well as fundamental parameters such as the gravitational acceleration, v sin i and the element abundances. For α Cen A (G2V) the derived stratifications of the temperature and convective velocity are very similar to the Sun, while for α Cen B (K1V) we find similar up-and downflow velocities, but lower horizontal speeds and a reduced overshoot. The latter is consistent with the smaller scale height of the atmosphere, while mass conservation arguments taken with the lower horizontal speed imply that the granules on α Cen B are smaller than on the Sun. Both these properties are in good agreement with the hydrodynamic simulation of Nordlund & Dravins (1990, A&A, 228, 155). The inversions also return the fundamental parameters (T eff , log g, abundances, v sin i, etc.) of the two stars. These values are on the whole in good agreement with literature values. Also, most of them do not strongly depend on the details of the inversion. However, importantly, the element abundances are 0.1 to 0.15 dex lower when a 2-or 3-component inversion is carried out than with a 1-component inversion.
Parent stars of extrasolar planets - VIII. Chemical abundances for 18 elements in 31 stars
Monthly Notices of the Royal Astronomical Society, 2007
We present the results of detailed spectroscopic abundance analyses for 18 elements in 31 nearby stars with planets. The resulting abundances are combined with other similar studies of nearby stars with planets and compared to a sample of nearby stars without detected planets. We find some evidence for abundance differences between these two samples for Al, Si and Ti. Some of our results are in conflict with a recent study of stars with planets in the SPOCS database. We encourage continued study of the abundance patterns of stars with planets to resolve these discrepancies.
Abundance analysis of a sample of evolved stars in the outskirts of Centauri
New Astronomy, 2010
The globular cluster ω Centauri (NGC 5139) is a puzzling stellar system harboring several distinct stellar populations whose origin still represents a unique astrophysical challenge. Current scenarios range from primordial chemical inhomogeneities in the mother cloud to merging of different sub-units and/or subsequent generations of enriched stars-with a variety of different pollution sources-within the same potential well. In this paper we study the chemical abundance pattern in the outskirts of ω Centauri, halfway to the tidal radius (covering the range of 20-30 arcmin from the cluster center), and compare it with chemical trends in the inner cluster regions, in an attempt to explore whether the same population mix and chemical compositions trends routinely found in the more central regions is also present in the cluster periphery. We extract abundances of many elements from FLAMES/UVES spectra of 48 RGB stars using the equivalent width method and then analyze the metallicity distribution function and abundance ratios of the observed stars. We find, within the uncertainties of small number statistics and slightly different evolutionary phases, that the population mix in the outer regions cannot be distinguished from the more central regions, although it is clear that more data are necessary to obtain a firmer description of the situation. From the abundance analysis, we did not find obvious radial gradients in any of the measured elements.