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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
| Rapidly oscillating M giant stars?
The Hipparcos mission discovered a few dozen M giant stars with periodsP shorter than 10d. Similar stars may be found in other large data basesof new variables (e.g., OGLE). The three possible sources of themagnitude variations - pulsation, starspots and ellipsoidal deformation- are discussed in general terms. The parallaxes and V-I colour indicesare used to calculate radii and temperatures for all M giant variableswith P<100d. Masses are estimated from the positions of the stars ina Hertzsprung-Russell (HR) diagram, using evolutionary tracks. Usingthese data, it is shown that starspots can be ruled out as a variabilitymechanism in almost all cases, and ellipsoidal variations in about halfof the stars. Pulsation in very high-overtone modes appears to be theonly viable explanation for the stars with P<10d. Many of the starsmay be multiperiodic. IRAS data are used to deduce information aboutreddening and circumstellar dust. The apparently low level of mass-loss,as well as the kinematics and the spatial distribution of the stars,indicates that they are from a relatively young (i.e., thin disc) giantstar population.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Stellar H2O masers
Preliminary results of an observational program to determine theincidence of H2O maser emission among cool stars are discussed. To date,17 new H2O masers have been found which are associated with stars in theTwo-Micron Sky Survey or General Catalog of Variable Stars. An updatedcatalog of all known H2O/IR stars, including the most accurate availablepositions, is presented, and an analysis is given of the 0.9-20-micronphotometry of these sources from the Two-Micron Sky Survey and the AFGLInfrared Sky Survey. These photometric data suggest that there is astrong dependence of the detectability of H2O maser emission on2.2-micron brightness and that pumping by radiation near 2 microns isunlikely for some stars, but the flux near the 6.3-micron vibrationaltransition may be sufficient for all of them.
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