The Optical Gravitational Lensing Experiment. UBVI Photometry of Stars in Baade's Window

• Autorzy: Paczyński B. , Udalski A. , Szymański M. , Kubiak M. , Pietrzyński G. , Soszyński I. , Woźniak P. , Żebruń K.
• Języki publikacji: EN

Abstrakty

EN

We present UBVI photometry for 8530 stars in Baade's Window obtained during the OGLE-II microlensing survey. Among these are over one thousand red clump giants. 1391 of them have photometry with errors smaller 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. The corrected colors of the red clump giants: (U-B)₀, (B-V)₀, and (V-I)₀ are very well correlated, indicating that a single parameter determines the observed spread of their values, reaching almost 2 mag in the (U-B)₀. It seems most likely that heavy element content is the dominant parameter, but it is possible that another parameter: the age (or mass) of a star moves it along the same trajectory in the color-color diagram as the metallicity. The current ambiguity can be resolved with spectral analysis, and our catalog may be useful as a finding list of red clump giants. We point out that these K giants are more suitable for a fair determination of the distribution of metallicity than brighter M giants. We also present a compilation of UBVI data for 308 red clump giants near the Sun, for which Hipparcos parallaxes are more accurate than 10%. Spectral analysis of their metallicity may provide information about the local metallicity distribution as well as the extent to which mass (age) of these stars affects their colors. It is remarkable that in spite of a number of problems, stellar models agree with observations at the 0.1-0.2 mag level, making red clump giants not only the best calibrated but also the best understood standard candle.

Słowa kluczowe

EN

galaxy: center; Hertzsprung-Russel (HR) diagram; stars: abundances; stars: fundamental parameters

• Wydawca: Copernicus Foundation for Polish Astronomy
• Czasopismo: Acta Astronomica
• Rocznik: 1999
• Tom: Vol. 49, No. 3
• Strony: 319--339
• Opis fizyczny: Bibliogr. 33 poz., rys., tab., wykr.

Twórcy

autor

Paczyński B.

• Princeton University Observatory, Princeton, NJ 08544-1001, USA

autor

Udalski A.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

autor

Szymański M.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

autor

Kubiak M.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

autor

Pietrzyński G.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

autor

Soszyński I.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

autor

Woźniak P.

• Princeton University Observatory, Princeton, NJ 08544-1001, USA

autor

Żebruń K.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

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