We present calibration of the mean I-band brightness of red clump stars on metallic-ity. Red clump stars were proposed to be a very attractive standard candle for distance determination. The calibration is based on 218 nearby red giant stars whose high quality spectra allowed to determine accurate individual metal abundances. High quality par-allaxes (σπ/π < 10%) and photometry of these very br...

Gravitational microlensing provides a new technique for studying the surfaces of distant stars. Microlensing events are detected in real time and can be followed up with precision photometry and spectroscopy. This method is particularly adequate for studying red giants in the Galactic Bulge. We show that different properties of the stellar surface can be recovered from timedependent photometry ...

Context. The CoRoT mission has provided thousands of red-giant light curves. The analysis of their solar-like oscillations allows us to characterize their stellar properties. Aims. Up to now, the global seismic parameters of the pressure modes have been unable to distinguish red-clump giants from members of the red-giant branch. As recently done with Kepler red giants, we intend to analyze and ...

We report the first extensive study of stellar Rb abundances. High-resolution spectra have been used to determine, or set upper limits on, the abundances of this heavy element and the associated elements Y, Zr, and Ba in 44 dwarfs and giants with metallicities spanning the range −2.0 < [Fe/H] < 0.0. In metal-deficient stars Rb is systematically overabundant relative to Fe; we find an average [R...

Context. Observations and analysis of solar-type oscillations in red giant stars is an infant field of asteroseismic research with a number of open questions. Although stochastic oscillations have been firmly detected in red giants, both in radial velocity and photometric time series, the mostly too short or incomplete data sets complicate a detailed analysis. The french-led satellite CoRoT ind...

We present proper motion (μ) catalog of 5,078,188 stars in 49 Optical Gravitational Lensing Experiment II (OGLE-II) Galactic bulge fields, with the total area close to 11 square degrees. The proper motion measurements are based on 138 − 555 I-band images taken during four observing seasons: 1997-2000. The catalogue stars are in the magnitude range 11 < I < 18 mag. In particular, the catalogue i...

It has been known for a long time that low mass red giants (i.e., with initial mass lower than ∼ 2 M⊙) present chemical anomalies which are not predicted by the standard evolution theory. In particular, the models which neglect the transport of chemicals in the stellar radiative regions can not explain the observed behavior of the carbon isotopic ratio both in Pop I and II stars on the red gian...

We revisit the problem of why stars become red giants. We modify the physics of a standard stellar evolution code in order to determine what does and what does not contribute to a star becoming a red giant. In particular, we have run tests to try to separate the effects of changes in the mean molecular weight and in the energy generation. The implications for why stars become red giants are dis...

We revisit the problem of why stars become red giants. We modify the physics of a standard stellar evolution code in order to determine what does and what does not contribute to a star becoming a red giant. In particular, we have run tests to try to separate the effects of changes in the mean molecular weight and in the energy generation. The implications for why stars become red giants are dis...

Although globular cluster horizontal-branch (HB) morphology is determined primarily by the cluster metallicity, observations have shown that clusters with similar metallicities sometimes have very different HB's, indicating the existence of a second parameter. Sweigart (1997, 1999) suggested that deep mixing on the red giant branch (RGB) may be a second parameter if He is mixed into the stellar...