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מאמרים קשורים
M dwarfs: effective temperatures, radii and metallicities
We empirically determine effective temperatures and bolometricluminosities for a large sample of nearby M dwarfs, for which highaccuracy optical and infrared photometry is available. We introduce anew technique which exploits the flux ratio in different bands as aproxy of both effective temperature and metallicity. Our temperaturescale for late-type dwarfs extends well below 3000K (almost to the browndwarf limit) and is supported by interferometric angular diametermeasurements above 3000K. Our metallicities are in excellent agreement(usually within 0.2dex) with recent determinations via independenttechniques. A subsample of cool M dwarfs with metallicity estimatesbased on hotter Hipparcos common proper motion companions indicates ourmetallicities are also reliable below 3000K, a temperature rangeunexplored until now. The high quality of our data allows us to identifya striking feature in the bolometric luminosity versus temperatureplane, around the transition from K to M dwarfs. We have compared oursample of stars with theoretical models and conclude that thistransition is due to an increase in the radii of the M dwarfs, a featurewhich is not reproduced by theoretical models.
| Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHKphotometry for over 100 M stars selected from an earlier paper on thebasis of apparent photometric constancy. L photometry has been obtainedfor stars brighter than about L = 6. Most of the stars have asubstantial number of UBV(RI)C observations and, it is hoped,will prove useful as red supplementary standards. Additionally, we listJHK photometry for nearly 300 Hipparcos red stars not selected asstandards, as well as L photometry for the brightest stars.
| New neighbours. V. 35 DENIS late-M dwarfs between 10 and 30 parsecs
This paper reports updated results on our systematic mining of the DENISdatabase for nearby very cool M-dwarfs (M 6V-M 8V, 2.0 <= I-J <=3.0, photometric distance within 30 pc), initiated by Phan-Bao et al.(\cite{phan-bao}, hereafter Paper I). We use M dwarfs with well measuredparallaxes (HIP, GCTP, ...) to calibrate the DENIS (MI, I-J)colour-luminosity relationship. The resulting distance error for singledwarfs is about 25%. Proper motions, as well as B and R magnitudes, weremeasured on archive Schmidt plates for those stars in the DENIS databasethat meet the photometric selection criteria. We then eliminate thegiants by a Reduced Proper Motion cutoff, which is significantly moreselective than a simple proper motion cutoff. It greatly reduces theselection bias against low tangential velocity stars, and results in anearly complete sample. Here we present new data for 62 red dwarfcandidates selected over 5700 square degrees in the DENIS database. 26of those originate in the 2100 square degrees analysed in Paper I, withimproved parameters here, and 36 were found in 3600 additional squaredegrees. 25 of those are new nearby dwarfs. We determine from thatsample of 62 stars a stellar density for 12.0 <= MI <=14.0 of /lineΦ{Icor}=(2.2 +/- 0.4)x 10-3 starspc-3 mag-1. This value is consistent withphotometric luminosity functions measured from deeper and smaller-fieldobservations, but not with the nearby star luminosity function. Inaddition we cross-identified the NLTT and DENIS catalogues to find 15similar stars, in parts of the sky not yet covered by thecolour-selected search. We present distance and luminosity estimates forthese 15 stars, 10 of which are newly recognized nearby dwarfs. Asimilar search in Paper I produced 4 red dwarf candidates, and we havethus up to now identified a total of 35 new nearby late-M dwarfs.
| 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.
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| 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.
| Erratum - Errors or Omissions in Star-Identifications in the General Catalogue of Trigonometric Stellar Parallaxes
Not Available
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | סרגל |
| התרוממות ימנית: | 15h49m38.36s |
| סירוב: | -47°36'34.2" |
| גודל גלוי: | 11.116 |
| מרחק: | 26.695 פארסק |
| תנועה נכונה: | 64.3 |
| תנועה נכונה: | -395.5 |
| B-T magnitude: | 13.301 |
| V-T magnitude: | 11.297 |
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