Contents
Images
Upload your image
DSS Images Other Images
Related articles
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
| New X-Ray Clusters in the Einstein Extended Medium-Sensitivity Survey. I. Modifications to the X-Ray Luminosity Function
The complete ensemble of Einstein Imaging Proportional Counter (IPC)X-ray images has been reprocessed and reanalyzed using a multiaperturesource detection algorithm. A catalog of 772 new source candidatesdetected within the 38' diameter central regions of the 1435 IPC fieldscomprising the Extended Medium-Sensitivity Survey (EMSS) has beencompiled. By comparison, 478 EMSS sources fall within the same area ofsky. A randomly selected subsample of 133 fields was examined; 73sources were detected and compared with 49 original EMSS sources in thesame region of sky. We expect, on the basis of confusion statistics,that most of these sources either are the summation of two or more lowercount-rate point sources that fall within the larger detection aperturesor are single point sources. An optical imaging study discovered onepossible cluster of galaxies among 43 identified sources, suggestingthat <=2.3% of the full catalog of sources are extrapolated to beactual distant (z>=0.14) clusters whose extended X-ray structure keptthem from being detected in the EMSS despite having sufficient totalflux. We have constructed other subsamples specifically selected tocontain those X-ray sources most likely to be clusters based uponadditional X-ray and optical criteria. Both a database search and anoptical imaging study of these subsamples have found several new distantclusters, setting a firm lower limit on the number of new clusters inthe entire catalog. Given both the numbers of new EMSS clusters andtheir spectroscopic or photometric redshifts, we estimate that theoriginal EMSS cluster sample is 72%-83% complete. We update the Henry etal. EMSS distant (z>=0.14) cluster sample with more recentinformation and use the redshifts and X-ray luminosities for these newEMSS clusters to compute revised X-ray luminosity functions (XLFs) inthe three redshift shells defined by Henry et al. The addition of thesenew high-z, high-LX clusters to the EMSS is sufficient toremove the requirement for ``negative'' evolution at high LXout to z~0.5. Although the best estimate of the EMSS XLF at z=0.3-0.6and logLX=44.9-45.2 ergs s-1 falls 1σ belowthe low-z (<0.3) XLF, the optical identification of the full 772source catalog remains incomplete. We conclude that the EMSS hassystematically missed clusters of low surface brightness. Since allX-ray cluster surveys are less sensitive to low surface brightnessemission, they may also be affected.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Meridian observations made in Brorfelde (Copenhagen University Observatory) 1975-76.
This catalogue presents positions for selected faint stars mainly fromAGK3 observed with the 7" transit circle at Brorfelde. The stars aredistributed in 43 selected areas around radio sources and are suitableas reference stars for measuring the optical counterparts to the radiosources. The obscr 'itioi cre carried out from 1975.16 to 1976.04, andevery star was observed at least two times giving a m.s.e. of "13 forthe catalogue positions given in the FK4 system. These positions usedtogether with AGK3 proper motions will in the period 1975 to 1980 have am.s.e. at the epoch ranging from `:13 to `:15, which is less than halfof what is expected when using AGK3 positions. Key words: transit circle- catalogue of positions
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Παρθένος |
| Right ascension: | 12h54m53.29s |
| Declination: | +11°28'52.1" |
| Apparent magnitude: | 9.118 |
| Proper motion RA: | -43.1 |
| Proper motion Dec: | 8.5 |
| B-T magnitude: | 9.628 |
| V-T magnitude: | 9.161 |
Catalogs and designations:
|
