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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.
| K dwarfs and the chemical evolution of the solar cylinder
K dwarfs have lifetimes older than the present age of the Galactic disc,and are thus ideal stars for investigating the chemical evolution of thedisc. We have developed several photometric metallicity indicators for Kdwarfs, based on a sample of accurate spectroscopic metallicities for 34disc and halo G and K dwarfs. The photometric metallicities lead us todevelop a metallicity index for K dwarfs based only on their position inthe colour-absolute-magnitude diagram. Metallicities have beendetermined for 431 single K dwarfs drawn from the Hipparcos catalogue,selecting the stars by absolute magnitude and removing multiple systems.The sample is essentially a complete reckoning of the metal content innearby K dwarfs. We use stellar isochrones to mark the stars by mass,and select a subset of 220 of the stars, which is complete within anarrow mass interval. We fit the data with a model of the chemicalevolution of the solar cylinder. We find that only a modest cosmicscatter is required to fit our age-metallicity relation. The modelassumes two main infall episodes for the formation of the halo-thickdisc and thin disc, respectively. The new data confirm that the solarneighbourhood formed on a long time-scale of the order of 7 Gyr.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Photoelectric photometry of stars near the north Galactic pole. II
UBV photometric observations of about 700 stars near the north Galacticpole, obtained using single-channel photometers on the 40-cm and 60-cmCassegrain telescopes at Kvistaberg Observatory (during 1976-1983) andthe Spanish International Observatory (during 1984), respectively, aspart of a program including the stars to be observed by the Hipparcosspacecraft, are reported. The data are presented in a series of tablesand briefly characterized.
| Spectral classification of high-proper-motion stars
Spectral types have been found for about 900 stars of high proper motioncontained in the Lowell Observatory Northern Hemisphere proper-motionstar survey using all blue-region objective prism plates. The spectralclassification criteria are given. About eighty stars of largetangential velocity have been classified using slit spectrograms takenwith a 36-in. reflector. A new calibration of Luyten's absolutemagnitude vs reduced proper motion relation is made, and its dependenceon spectral type is investigated.
| Narrow-band photometry of G and K stars near the North Galactic Pole
Photoelectric narrow-band photometry obtained for 292 late-type starsbrighter than 10 m in the North Galactic Pole area is discussed. The g,n, k, m, f-system of Dickow et al. (1970) is used. The stars were chosenfrom two lists: (1) all stars of spectral type G5 or later in the HenryDraper Catalog (Cannon and Pickering, 1918-1924) within 15 deg of theNorth Galactic Pole, together with a few BD stars; and (2) all starsclassified as K or M giants and in Upgren's 25-31 deg zones (Upgren,1962). For most of the stars, estimates of the following quantities arederived: V-magnitude, R-I color, metal abundance, MV, and theduplicity parameter res(k).
| Trigonometric parallaxes of 50 stars.
Not Available
| Photovisual magnitudes of 418 dwarf M stars and 34 parallax stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956AJ.....61..219S&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Гончие Псы |
| Прямое восхождение: | 13h27m27.17s |
| Склонение: | +35°43'34.2" |
| Видимая звёздная величина: | 8.742 |
| Расстояние: | 27.571 парсек |
| Собственное движение RA: | -284 |
| Собственное движение Dec: | -324.9 |
| B-T magnitude: | 10.057 |
| V-T magnitude: | 8.851 |
Каталоги и обозначения:
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