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On the Photometric Variability of Red Clump Giants
Hipparcos photometry of the 308 red clump giants identified by Paczynskiet al. (1999) is investigated. These stars are found to be quite stableduring the three years of observation, but questions remain about longerterm stability.
| The Optical Gravitational Lensing Experiment. UBVI Photometry of Stars in Baade's Window
We present UBVI photometry for 8530 stars in Baade's Window obtainedduring the OGLE-II microlensing survey. Among these are over onethousand red clump giants. 1391 of them have photometry with errorssmaller than 0.04, 0.06, 0.12, and 0.20 mag in the I, V, B, and U-band,respectively. We constructed a map of interstellar reddening. Thecorrected colors of the red clump giants: (U-B)_0, (B-V)_0, and (V-I)_0are very well correlated, indicating that a single parameter determinesthe observed spread of their values, reaching almost 2 mag in the(U-B)_0. It seems most likely that heavy element content is the dominantparameter, but it is possible that another parameter: the age (or mass)of a star moves it along the same trajectory in the color-color diagramas the metallicity. The current ambiguity can be resolved with spectralanalysis, and our catalog may be useful as a finding list of red clumpgiants. We point out that these K giants are more suitable for a fairdetermination of the distribution of metallicity than brighter M giants.We also present a compilation of UBVI data for 308 red clump giants nearthe Sun, for which Hipparcos parallaxes are more accurate than 10%.Spectral analysis of their metallicity may provide information about thelocal metallicity distribution as well as the extent to which mass (age)of these stars affects their colors. It is remarkable that in spite of anumber of problems, stellar models agree with observations at the0.1-0.2 mag level, making red clump giants not only the best calibratedbut also the best understood standard candle.
| UBVRI photometry of FKSZ stars. II
The results of UBVRI photometry for 169 stars of the Faint FundamentalStars Catalog (Zverev, 1957) in the declination zone lambda of between-30 and -60 deg are presented. Observations were obtained between May1984 and February 1987 using the 50-cm ESO telescope at La Silla.Tabular data presented include the number of the star in the E-regions,the V magnitude, the (B-V), (U-B), (V-R), and (R-I) colors, and thespectral types.
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