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מאמרים קשורים
Cross-correlation of the 2XMMi catalogue with Data Release 7 of the Sloan Digital Sky Survey
The Survey Science Centre of the XMM-Newton satellite released the firstincremental version of the 2XMM catalogue in August 2008. Containingmore than 220 000 X-ray sources, the 2XMMi was at that time the largestcatalogue of X-ray sources ever published and thus constitutes anunprecedented resource for studying the high-energy properties ofvarious classes of X-ray emitters such as AGN and stars. Thanks to thehigh throughput of the EPIC cameras on board XMM-Newton accuratepositions, fluxes, and hardness ratios are available for a substantialfraction of the X-ray detections. The advent of the 7th release of theSloan Digital Sky Survey offers the opportunity to cross-match two majorsurveys and extend the spectral energy distribution of many 2XMMisources towards the optical bands. This implies building extensivehomogeneous samples with a statistically controlled rate of spuriousmatches and completeness. We here present a cross-matching algorithmbased on the classical likelihood ratio estimator. The method developedhas the advantage of providing true probabilities of identificationswithout resorting to heavy Monte-Carlo simulations. Over 30,000 2XMMisources have SDSS counterparts with individual probabilities ofidentification higher than 90%. At this threshold, the sample has only2% spurious matches and contains 77% of all expected SDSSidentifications. Using spectroscopic identifications from the SDSS DR7catalogue supplemented by extraction from other catalogues, we build anidentified sample from which the way the various classes of X-rayemitters gather in the multi dimensional parameter space can be analysedand later used to design a source classification scheme. We illustratethe interest of this clean source sample by investigating two scientificuse cases. In the first example we show how these multi-wavelength datacan be used to search for new QSO2s. Although no specific range ofobserved properties allows us to efficiently identify Compton ThickQSO2s, we show that the prospects are much better for Compton Thin AGN2and discuss several possible multi-parameter selection strategies. In asecond example, we confirm the hardening of the mean X-ray spectrum withincreasing X-ray luminosity on a sample of over 500 X-ray active starsand reveal that on average X-ray active M stars display bluer g - rcolour indexes than less active ones. Although this catalogue of2XMM-SDSS sources cannot be used directly for statistical studies, itnevertheless represents an excellent starting point to select welldefined samples of X-ray-emitting objects.The corresponding fits file can be downloaded from the XCat-DB home page(http://xcatdb.u-strasbg.fr/).The file also contains line information for all SDSS spectroscopicentries matching a 2XMM source. Results from the cross-correlation withthe 2XMM DR3 are also available at the same location. The 2XMMi/SDSS DR7cross-correlation data file is also available at the CDS via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/527/A126
| 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.
| 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.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| Dwarf K and M stars of high proper motion found in a hemispheric survey
A recently completed visual/red spectral region objective-prism surveyof more than half the sky found some 2200 dwarf K and M stars ofnegligible proper motion (Stephenson, 1986). The present paper adds the1800-odd spectroscopically identified dwarfs that did prove to havesignificant proper motions. About half of these had previous spectralclassifications of some sort, especially by Vyssotsky (1952, 1956). Forthe great majority, the present coordinates are more accurate thanprevious data. The paper includes about 50 stars with unpublishedparallaxes, likely to have parallaxes of 0.05 arcsec or more. Combiningthe present data with the first paper suggests that the number oflow-proper-motion stars in that paper was not unreasonable.
| New subdwarfs. IV - UBV photometry of 1690 high-proper-motion stars
A photometric list of 1690 stars of known high proper motion is used tosearch for potential high-velocity stars of various metallicity valuesin order to find candidates for trigonometric programs on subdwarfs andto enlarge the sample with which to study the relation between stellarkinematics and metal abundance. A list of 113 stars with tangentialspace velocities of 300 km/s or greater is obtained, the highesttangential velocity relative to the sun being 630 km/s. By using thevariation of the tangential velocity with longitude and adopting thegalactic rotation at the solar circle to be 220 km/s, the rotation ofthe subdwarf system is estimated at 0 + or - 50 km/s from the transversevelocity alone, in agreement with determinations based on other methods.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Intermediate-band photometry of late-type stars. VIII - Nonvariable stars in the halo population near the sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979ApJ...229..158E&db_key=AST
| Intermediate band photometry of late-type stars. II - Some stellar groups
Observations on the (R, I) system and a modified Stromgren system ofmembers of six stellar groups are used to demonstrate the chemicalhomogeneity of some 70% or 80% of the members assigned to the groups onthe basis of kinematics. The groups discussed are the Hyades, Wolf 630,Arcturus, Groombridge 1830, and Kapteyn's Star Groups as well as ananonymous group of a half dozen subdwarfs with (U, V) near (-150, -320)km/s. Standards for a previously described photometric system areextended, and additional F- and G-type standards for the (R, I) systemare presented. A simple relation is derived for computing the Fe/Habundance ratio for most stars in the corrected (R-I) interval from +0.2to +0.45 magnitude.
| Lowell proper motions III : proper motion survey of the Northern Hemisphere with the 13-inch photographic telescope of the Lowell Observatory
Not Available
| Lowell proper motions II : proper motion survey of the Northern Hemisphere with the 13-inch photographic telescope of the Lowell Observatory
Not Available
| New proper motion stars and errata
Not Available
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | בתולה |
| התרוממות ימנית: | 13h02m51.36s |
| סירוב: | -02°40'26.3" |
| גודל גלוי: | 11.373 |
| מרחק: | 44.823 פארסק |
| תנועה נכונה: | -313.9 |
| תנועה נכונה: | 40.6 |
| B-T magnitude: | 14.566 |
| V-T magnitude: | 11.637 |
קטלוגים וכינוים:
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INHABITED SKY
