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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.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| XID: Cross-Association of ROSAT/Bright Source Catalog X-Ray Sources with USNO A-2 Optical Point Sources
We quantitatively cross-associate the 18,811 ROSAT Bright Source Catalog(RASS/BSC) X-ray sources with optical sources in the USNO A-2 catalog,calculating the probability of unique association (Pid)between each candidate within 75" of the X-ray source position, on thebasis of optical magnitude and proximity. We present catalogs ofRASS/BSC sources for which Pid>98%, Pid>90%,and Pid>50%, which contain 2705, 5492, and 11,301 uniqueUSNO A-2 optical counterparts respectively down to the stated level ofsignificance. Together with identifications of objects not cataloged inUSNO A-2 due to their high surface brightness (M31, M32, ...) andoptical pairs, we produced a total of 11,803 associations to aprobability of Pid>50%. We include in this catalog a listof objects in the SIMBAD database within 10" of the USNO A-2 position,as an aid to identification and source classification. This is the firstRASS/BSC counterpart catalog which provides a probability of associationbetween each X-ray source and counterpart, quantifying the certainty ofeach individual association. The catalog is more useful than previouscatalogs which either rely on plausibility arguments for association ordo not aid in selecting a counterpart between multiple off-band sourcesin the field. Sources of high probability of association can beseparated out, to produce high-quality lists of classes (Seyfert 1/2s,QSOs, RS CVns) desired for targeted study, or for discovering newexamples of known classes (or new classes altogether) through thespectroscopic classification of securely identified but unclassifiedUSNO A-2 counterparts. Low Pid associations can be used forstatistical studies and follow-on investigation-for example, performingfollow-up spectroscopy of the many low-mass stars to search forsignatures of coronal emission, or to investigate the relationshipbetween X-ray emission and classes of sources not previouslywell-studied for their X-ray emissions (such as pulsating variablestars). We find that a fraction ~65.8% of RASS/BSC sources have anidentifiable optical counterpart, down to the magnitude limit of theUSNO A-2 catalog which could be identified by their spatial proximityand high optical brightness.
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Dades d'Observació i Astrometria
| Constel·lació: | Cepheus |
| Ascensió Recta: | 00h02m56.76s |
| Declinació: | +71°22'04.9" |
| Magnitud Aparent: | 9.13 |
| Moviment propi RA: | -1.9 |
| Moviment propi Dec: | -4.4 |
| B-T magnitude: | 10.75 |
| V-T magnitude: | 9.264 |
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