Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| 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.
| X-ray-selected M dwarfs and the diffuse X-ray background
A systematic optical identification program was carried out forserendipitous X-ray sources discovered by the Einstein Observatory. Atotal of 104 were detected above the threshold flux of 3 x 10 to the-13th ergs/sq cm per sec in the 114 sq deg survey region; 11 of these104 sources are dM stars. Including X-ray-selected M dwarfs from the LMCsurvey, the Medium Sensitivity Survey, and the Einstein Deep Survey, adwarf M star composite X-ray spectrum was constructed; the best-fitthermal model yields kT = 1.3 + or - 0.3 keV, consistent with typicalactive star spectra. An M dwarf X-ray luminosity function was alsoconstructed and it is concluded that the integrated contribution to thediffuse soft (0.28-1.0 keV) X-ray background from such stars is lessthan 10 percent, a factor of more than about 2 lower than previousestimates. This result is consistent with a limit on the dwarf M starcontribution derived from a spectral decomposition of the observed X-raybackground spectrum.
| A catalogue of four-color photometry of late F-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..705P&db_key=AST
| Etude pour chaque champ de l'absorption et de la repartition des vitesses radiales EN fonction de la distance.
Not Available
| La mesure des vitesses radiales auprisme objectif. VI. -Liste des vitesses radiales déterminées au prisme objectif à vision directe
Not Available
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Cassiopeia |
| Ascensió Recta: | 00h00m41.64s |
| Declinació: | +62°10'33.2" |
| Magnitud Aparent: | 7.053 |
| Distancia: | 38.373 parsecs |
| Moviment propi RA: | -46.9 |
| Moviment propi Dec: | -43.3 |
| B-T magnitude: | 7.657 |
| V-T magnitude: | 7.103 |
Catàlegs i designacions:
|
