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Dr. Sarah Martell (ARI/ZAH) wins one of this year's Ernst Patzer Prizes for the best refereed publication by a Heidelberg junior scientist

About 50% of field stars in the halo of the Milky Way initially formed within globular clusters. This exciting result was recently published in an outstanding paper by Dr. Sarah Martell (ARI/ZAH) entitled “Light Element Abundance Variations in the Galactic Halo”. Her paper was selected to receive one of this year's Ernst Patzer Prizes for the best refereed publication by a young Heidelberg astronomer at MPIA or ZAH.

Dr. Sarah Martell, working at the Astronomisches Rechen-Institut (ARI) at ZAH in the research group of Prof. Dr. Eva Grebel, is an expert on light element abundance variations in globular clusters. While the origin of these abundance variations is not fully understood, they are found among stars in all Galactic globular clusters. Present-day globular clusters are generally believed to be the survivors of a once much more numerous globular cluster population that has decayed with time. However, it is unclear what role globular clusters have played in the assembly of the Galactic halo field population. Earlier spectroscopic analyses of small samples of field stars have not found the light element abundance variation patterns typical of globular clusters in the halo population, a finding that has been used to argue against a prominent contribution of globular clusters to the field. The current picture of halo formation relies mainly on accretion of stars from dwarf galaxies that are captured by the Milky Way.

In her paper on “Light Element Abundance Variations in the Galactic Halo”, which was published recently in Astronomy & Astrophysics (Martell & Grebel, 2010, A&A, 519, A14), Dr. Martell scrutinized the connection between globular clusters and field stars. She revisited this intriguing question quantitatively by exploiting the vast stellar spectroscopic database of the Sloan Digital Sky Survey (SDSS). Using SDSS-II/SEGUE spectra of over 1900 G- and K-type halo giants, she identified for the first time a subset of halo field stars with globular-cluster-like abundance patterns. This subset of halo giants is likely the result of globular cluster dissolution into the Galactic halo, suggesting that the fraction of halo field stars which initially formed within globular clusters may be as large as 50%. Dr. Martell's study is the first quantitative observational constraint on the contribution of globular clusters to the halo field star population.

The Ernst Patzer Prize consists of a certificate and a 2000 Euro award. The Patzer Prize Colloquium will take place on Friday, December 3, 2010 at 3:15 p.m. in the lecture hall of MPIA.