DOES THE OOSTERHOFF DICHOTOMY EXIST IN THE ANDROMEDA GALAXY? I. THE CASE OF G11
- INAF, Osservatorio Astronomico di Bologna, Bologna (Italy)
We present the first evidence that Oosterhoff type II globular clusters exist in the Andromeda galaxy (M31). On the basis of time-series photometry of the moderately metal-poor ([Fe/H] {approx}-1.6 dex) M31 globular cluster G11, obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope, we detected and derived periods for 14 RR Lyrae stars, of which five are found to lie inside the cluster tidal radius. They include three fundamental-mode (RRab) and two first-overtone (RRc) pulsators, with average periods (P{sub ab} ) = 0.70 days, and (P{sub c} ) = 0.40 days, respectively. These mean periods and the position of the cluster variable stars in the period-amplitude and period-metallicity diagrams all suggest that G11 is likely to be an Oosterhoff type II globular cluster. This appears to be in agreement with the general behavior of Milky Way globular clusters with similar metallicity and horizontal branch morphology.
- OSTI ID:
- 22167620
- Journal Information:
- Astrophysical Journal, Vol. 765, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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