Hipparcos red stars in the H_pV_T2 and VI_C systems

Abstract

For Hipparcos M, S, and C spectral type stars, we provide calibrated instantaneous (epoch) Cousins V - I color indices using newly derived H_pV_T2 photometry. Three new sets of ground-based Cousins VI data have been obtained for more than 170 carbon and red M giants. These datasets in combination with the published sources of V I photometry served to obtain the calibration curves linking Hipparcos/Tycho H_p-V_T2 with the Cousins V - I index. In total, 321 carbon stars and 4464 M- and S-type stars have new V - I indices. The standard error of the mean V - I is about 0.1 mag or better down to H_p~9 although it deteriorates rapidly at fainter magnitudes. These V - I indices can be used to verify the published Hipparcos V - I color indices. Thus, we have identified a handful of new cases where, instead of the real target, a random field star has been observed. A considerable fraction of the DMSA/C and DMSA/V solutions for red stars appear not to be warranted. Most likely such spurious solutions may originate from usage of a heavily biased color in the astrometric processing.

Based on observations from the Hipparcos astrometric satellite operated by the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997