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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
| The visually brightest early-type supergiants in the spiral galaxies NGC 2403, M81, and M101
Moderate-resolution spectroscopy of the candidate brightest blue starsin the nearby spirals NGC 2403, M81, and M101 reveals that many are notsingle stars, but compact H II regions, clusters, and multiple systems.This is an additional and serious limitation on their use as distanceindicators. The derivation of the luminosities of the confirmed singleblue supergiants is discussed, and, combining these results withprevious work on the brightest red supergiants, a brief discussion andcomparison of the evolution of their most massive stars are given. Theproperties of the brightest blue and red stars in NGC 2403 and M81 arebasically in agreement with the pattern of massive-star evolutionobserved in Local Group galaxies. The distance to M101 is stillcontroversial, but at the larger distance modulus, the luminosities ofits brightest early and late-type supergiants place them beyond theEddington limit for their initial mass and temperature.
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Osservazione e dati astrometrici
| Costellazione: | Pittore |
| Ascensione retta: | 05h34m42.58s |
| Declinazione: | -55°15'21.7" |
| Magnitudine apparente: | 8.668 |
| Distanza: | 414.938 parsec |
| Moto proprio RA: | 3 |
| Moto proprio Dec: | 7.2 |
| B-T magnitude: | 10.839 |
| V-T magnitude: | 8.848 |
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