Wyniki wyszukiwania - BazTech

Ograniczanie wyników

2 Acta Astronomica

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: Hertzsprung-Russel (HR) diagram

Sortuj według:

Ogranicz wyniki do:

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

Paczyński B., Udalski A., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Woźniak P., Żebruń K.

Acta Astronomica

1999

Vol. 49, No. 3

319--339

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.

Optical Gravitational Lensing Experiment. Distance to the Magellanic Clouds with the Red Clump Stars: Are the Magellanic Clouds 15% Closer than Generally Accepted?

Udalski A., Szymański M., Kubiak M., Pietrzyński G., Woźniak P., Żebruń K.

Acta Astronomica

1998

Vol. 48, No. 1

1--17

We present a new distance determination to the Large and Small Magellanic Clouds using the newly developed red clump stars method (Paczyński and Stanek 1998). This new, single-step, Hipparcos calibrated method seems to be one of the most precise techniques of distance determination with very small statistical error due to large number of red clump stars usually available. The distances were determined independently along four lines-of-sight located at opposite sides of each Magellanic Cloud. The results for each line-of-sight are very consistent. For the SMC we obtain the distance modulus: m-M=18.56±0.03±0.06 mag (statistical and systematic errors, respectively) and for the LMC: m-M=18.08±0.03±0.12 mag where systematic errors are mostly due to uncertainty in reddening estimates. Both distances will be refined and systematic errors reduced when accurate reddening maps for our fields are available. Distance moduli to both Magellanic Clouds are ≈0.4 mag smaller than generally accepted values. The modulus to the LMC is in good agreement with the recent determinations from RR Lyrae type stars and upper limit resulting from the SN1987A echo. We suspect that the distance to the LMC and SMC is shorter by about 15% than previously assumed: 42 kpc and 52 kpc, respectively. Calibrations of the period-luminosity relation for Cepheids which give overestimated distances to the LMC and SMC are probably incorrect and require urgent reanalysis. We also present our color-magnitude diagrams around the red clump for the LMC and SMC. We identify vertical red clump, first noted by Zaritsky and Lin (1997), in the color-magnitude diagram of both Magellanic Clouds and we interpret it as an evolutionary feature rather than unknown stellar population between the LMC and our Galaxy.