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Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| An objective-prism survey for late M dwarf stars
An objective-prism survey in the red spectral region has been completedwhich covers approximately two percent of the sky at intermediate southgalactic latitudes. Catalogues of 142 stars classified as M2 and laterare presented which contain 73 dwarf stars, 41 giant stars, and 28 starsof uncertain luminosity class. Data obtained from photoelectric BVIphotometry and slit spectrograms are presented for several programstars. Surveys of this type are very effective in the detection ofmotion unbiased samples of late M dwarf stars. The value of such surveysin studies of the kinematic properties and space density of these starsis seriously jeopardized by systematic errors in the assignment ofspectral types for stars near the plate limit. This problem iscompounded by the rapid change of limiting magnitude with advancingspectral type.
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