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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 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.
| High-Resolution Spectroscopic Follow-up of OGLE Planetary Transit Candidates in the Galactic Bulge: Two Possible Jupiter-Mass Planets and Two Blends
We report the results of our campaign to follow up spectroscopicallyseveral candidate extrasolar transiting planets from the OGLE-III surveyin the direction of the Galactic center, announced in 2001. All of theseobjects present shallow and periodic dips in brightness that may be dueto planetary companions. Our Keck I/High Resolution Echelle Spectrometer(HIRES) observations have revealed two interesting cases (OGLE-TR-10with a period of 3.1 days and OGLE-TR-58 with a period of 4.3 days) thatshow no radial velocity variations at the level of 100-200 ms-1. If orbited by companions, their masses would be similarto Jupiter. With the information in hand (including the light curves) weare not able to rule out that these candidates are instead the result ofcontamination from an eclipsing binary in the same line of sight (a``blend''). We also discuss the case of OGLE-TR-56, which was recentlyreported by Konacki et al. to have a Jupiter-size companion, on thebasis of an earlier analysis of our data and we present supportinginformation. Two other candidates, OGLE-TR-3 and OGLE-TR-33, show clearevidence that they are blends. We describe tests carried out tocharacterize the stability of the HIRES spectrograph and its impact onthe determination of precise velocities for faint stars (V>=15 mag)using exposures of a thorium-argon lamp as the wavelength reference.Systematic effects are at the level of 100 m s-1 or smallerand tend to dominate the total error budget. We also evaluate theprecision attainable using the iodine gas absorption cell as analternative fiducial, and we propose a simplified version of thestandard procedure employed for high-precision Doppler planet searchesthat is very promising. Results from both this method and the classicalThAr technique show the feasibility of spectroscopic follow-up for fainttargets in the range V=14-17. We point out also that the high incidenceof contamination from blends and other false positives in the OGLE-IIIsurvey already mentioned by Konacki et al. is potentially a seriousconcern not only for other similar surveys of relatively faint stars butalso for future space missions to search for transits due to extrasolarplanets as small as the Earth.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
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Datos observacionales y astrométricos
| Constelación: | Andrómeda |
| Ascensión Recta: | 23h45m24.65s |
| Declinación: | +39°07'24.2" |
| Magnitud Aparente: | 10.264 |
| Distancia: | 49.801 parsecs |
| Movimiento Propio en Ascensión Recta: | 267.4 |
| Movimiento Propio en Declinación: | -94.6 |
| B-T magnitude: | 11.401 |
| V-T magnitude: | 10.358 |
Catálogos y designaciones:
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