Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: clusters individual: NGC 419

Sortuj według:

Ogranicz wyniki do:

The Optical Gravitational Lensing Experiment. Population Effects on the Mean Brightness of the Red Clump Stars

Udalski A.

Acta Astronomica

1998

Vol. 48, No. 3

383--404

We present an empirical test indicating that the mean I-band magnitude of the red clump stars, used as the standard candle in the recent distance determinations to the Magellanic Clouds and other objects, is age independent for intermediate age (2-10 Gyr) stars. Fifteen star clusters of age ≈1.5-12 Gyr from the LMC and SMC (ESO121SC03, SL663, NGC 2155, NGC 2121, SL388, SL862, NGC 121, L1, KRON3, NGC 416, L113, NGC 339, L11, NGC 419, NGC 411) were observed and their color-magnitude diagrams are presented. The mean I-band brightness of the red clump in these clusters is constant and its mean extinction-free magnitude is: I0=17.88±0.05 mag and I0=18.31±0.07 mag at the mean metallicity of -0.8 dex and -1.2 dex for the LMC and SMC clusters, respectively. For older objects (>10 Gyr) the brightness of the red clump, which converts into the red part of the horizontal branch, fades by about 0.3-0.4 mag, setting an important limitation on the red clump stars method of distance determination. The red clump distance moduli to the Magellanic Clouds from the new independent data set are: m-M=18.18±0.06 mag and m-M=18.65±0.08 mag for the LMC and SMC, respectively, in very good agreement with previous determinations. Weak dependence of the mean I-band brightness of the red clump on metallicity and its independence of age for intermediate age population (2-10 Gyr) of stars as well as the most precise calibration as compared to other standard candle candidates makes the red clump stars method one of the most accurate steps in the distance scale ladder. Key words: Magellanic Clouds - Galaxies: distances and redshifts - distance scale - clusters individual: ESO121SC03, SL663, NGC 2155, NGC 2121, SL388, SL862, NGC 121, L1,