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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.
| A spectroscopic survey of the youngest field stars in the solar neighbourhood. I. The optically bright sample
Aims: We present the first results of an ambitious ground-basedobservation programme conducted on 1-4 m class telescopes. Our sampleconsists of 1097 active and presumably young stars, all of them beingoptical (Tycho Catalogue) counterparts of ROSAT All-Sky Survey X-raysources in the northern hemisphere. In this paper, we concentrate on theoptically brightest (V_T?slant 9.5 m) candidates (704 objects). Weacquired high-resolution optical spectroscopy in the H? and/orlithium spectral regions for 426 of such stars without relevant data inthe literature. We describe the star sample and the observations and westart to discuss the physical properties of the investigated stars. Methods: We used a cross-correlation technique and other toolsdeveloped by us to derive accurate radial and rotational velocities andto perform an automatic spectral classification for both single starsand double-lined systems. The spectral subtraction technique was used toderive chromospheric activity levels and lithium abundances. Weestimated the fraction of young single stars and multiple systems instellar soft X-ray surveys and the contamination by more evolvedsystems, like RS CVn binaries. We classified stars on the basis of theirlithium abundance and give a glimpse of their sky distribution. Results: The sample appears to be a mixture of quite youngPleiades-like and Hyades-like stars plus an older lithium-poorpopulation probably born within the last 1-2 Gyr. Seven stars with alithium abundance compatible with the age of IC 2602 (about 30 Myr) oreven younger were detected as well, although two appear to belithium-rich giants.The discovery of a large number of highly ormoderately lithium-rich giants is another outcome of the present survey. Conclusions: The contamination of soft X-ray surveys by oldsystems in which the activity level is enhanced by tidal synchronisationis not negligible, especially for K-type stars. Five stars with lithiumcontent close to the primordial abundance are probably associated withalready known moving groups in the solar neighbourhood. Some of them aregood post-T Tauri candidates according to their positions in the HRdiagram.Based on observations collected at the Observatoire de Haute Provence(France) and the Catania Astrophysical Observatory (Italy). Data for the426 stars is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/504/829
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| The general catalogue of trigonometric [stellar] paralaxes
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Osservazione e dati astrometrici
| Costellazione: | Giraffa |
| Ascensione retta: | 06h36m02.88s |
| Declinazione: | +74°17'34.7" |
| Magnitudine apparente: | 8.881 |
| Distanza: | 50.226 parsec |
| Moto proprio RA: | -49.8 |
| Moto proprio Dec: | -160.9 |
| B-T magnitude: | 9.752 |
| V-T magnitude: | 8.953 |
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