Volume 522, November 2010
|Number of page(s)||5|
|Section||Galactic structure, stellar clusters and populations|
|Published online||04 November 2010|
The connection between missing AGB stars and extended horizontal branches
INAF – Osservatorio Astronomico di Padova,
e-mail: firstname.lastname@example.org, email@example.com
2 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
3 Excellence Cluster Universe, Technische Universität München, Boltzmannstr. 2, 85748 Garching, Germany
Received: 16 July 2010
Accepted: 8 September 2010
Recent surveys confirm early results about a deficiency or even absence of CN-strong stars on the asymptotic giant branch (AGB) of globular clusters (GCs), although with quite large cluster-to-cluster variations. In general, this is at odds with the distribution of CN band strengths among first ascent red giant branch (RGB) stars. Norris et al. proposed that the lack of CN-strong stars in some clusters is a consequence of a smaller mass of these stars that cannot evolve through the full AGB phase. In this short paper we found that the relative frequency of AGB stars can change by a factor of two between different clusters. We also find a very good correlation between the minimum mass of stars along the horizontal branch (Gratton et al. 2010, A&A, 517, A81) and the relative frequency of AGB stars, with a further dependence on metallicity. We conclude that indeed the stars with the smallest mass on the HB cannot evolve through the full AGB phase, being AGB-manqué. These stars likely had large He and N content, and large O-depletion. We then argue that there should not be AGB stars with extreme O depletion, and few of them with a moderate one.
Key words: stars: abundances / stars: evolution / stars: Population II / globular clusters: general
© ESO, 2010
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.