Individual stars spotted in Andromeda's bulge
OBSERVATOIRE DE PARIS NEWS RELEASE
Posted: January 17, 2001
An individual team, including an astronomer of Observatoire de Paris, has recently observed for the first time individual stars in a very dense -- but very interesting -- zone of an external galaxy, enabling for the first time an eagerly awaited comparison with the corresponding zone (bulge) of our Galaxy (Milky Way).
A team of astronomers (including Pascale Jablonka, from Paris-Meudon Observatory and UMR 8631 of CNRS) took this opportunity to study with the Hubble Space Telescope at visible (WFPC2) and infrared (NICMOS) wavelengths, metal-rich stellar populations in globular clusters and field stars close to or in the bulge of M31. They obtained images of the central part (bulge) of M 31 in two colors, and have analyzed these images, which include two globular clusters. These analyses pioneered the field of studies in extremely crowded environments, a difficult observation. They give the first precise picture of a galaxy bulge besides the one of our own Galaxy. With these images, they are able to:
Several conclusions could be made, in particular that the globular clusters seen from the ground in projection on M31 bulge are genuine bulge clusters which formed from the same gaseous material as the bulge field stars. No intermediate age population has been detected. The clusters' very high chemical enrichment and old age indicate that they were formed, as was the bulge, in the very early stages of the galaxy history. The bulge field stellar population presents a large dispersion in abundances and an apparent sharp cut at low metallicity, very similar to what is seen in the bulge of our own Galaxy.