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מאמרים קשורים
Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Precise radial velocities of giant stars. III. Spectroscopic stellar parameters
Context: A radial velocity survey of about 380 G and K giant stars isongoing at Lick observatory. For each star we have a high signal tonoise ratio template spectrum, which we use to determine spectroscopicstellar parameters. Aims: The aim of this paper is to presentspectroscopic stellar parameters, i.e. effective temperature, surfacegravity, metallicity and rotational velocity for our sample of G and Kgiant stars. Methods: Effective temperatures, surface gravities andmetallicities are determined from the equivalent width of iron lines, byimposing excitation and ionisation equilibrium through stellaratmosphere models. Rotational velocities are determined from the fullwidth at half maximum (FWHM) of moderate spectral lines. A calibrationbetween the FWHM and total broadening (rotational velocity and macroturbulence) is obtained from stars in common between our sample and thesample from Gray (1989, ApJ, 347, 1021). Macro turbulence is determinedfrom the macro turbulence vs. spectral type relations from Gray (2005,The Observation and Analysis of Stellar Photospheres). Results: Themetallicity we derive is essentially equal to the literature values,while the effective temperature and surface gravity are slightly higherby 56 K and 0.15 dex, respectively. A method comparison is performedwith 72 giants in common with Luck & Heiter (2007, AJ, 133, 2464),which shows that both methods give similar results. Our rotationalvelocities are comparable with those obtained by Gray (1989, ApJ, 347,1021), but somewhat higher than those of de Medeiros & Mayor (1999,A&AS, 139, 433), which is consistent with the different diagnosticsused to determine them. Conclusions: We are able to determinespectroscopic stellar parameters for about 380 G and K giant starsuniformly (112 stars are being analysed spectroscopically for the firsttime). For stars available in the literature, we find reasonableagreement between literature values and values determined in the presentwork. In addition, we show that the metallicity enhancement of companionhosting stars might also be valid for giant stars, with the planethosting giants being 0.13 ± 0.03 dex (i.e. 35 ± 10%) moremetal rich than our total sample of stars.Based on data obtained at UCO/Lick Observatory, USA. Table 4 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/1003
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דרקון |
| התרוממות ימנית: | 18h20m53.52s |
| סירוב: | +62°57'18.8" |
| גודל גלוי: | 8.891 |
| מרחק: | 262.467 פארסק |
| תנועה נכונה: | -3.3 |
| תנועה נכונה: | -7.7 |
| B-T magnitude: | 10.177 |
| V-T magnitude: | 8.998 |
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