Volume 422, Number 3, August II 2004
|Page(s)||1045 - 1052|
|Section||Stellar structure and evolution|
|Published online||16 July 2004|
First detection of a lithium rich carbon star in the Draco dwarf galaxy: Evidence for a young stellar population
Dpto. Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain e-mail: firstname.lastname@example.org
2 INAF-Osservatorio Astronomico di Collurania, 64100 Teramo, Italy
3 Main Astronomical Observatory, National Academy of Sciences, Zabolotnoho 27, Kiev-127 03680, Ukranie
Accepted: 29 April 2004
We present a spectroscopic study of D461, a giant star belonging to Draco dwarf spheroidal galaxy. From spectral synthesis in LTE we derive a lithium abundance of ϵ(Li) = and a C/O ratio between 3 and 5. This is the first detection of a lithium rich C-star in a dwarf spheroidal galaxy. Basing on stellar models of appropriate chemical composition, we show that a similar C enrichment is compatible with that expected for a low mass low metallicity thermally pulsing AGB star, undergoing few third dredge up episodes. The position in the – diagram of D461 is also compatible with this theoretical scenario. In particular, the low effective temperature, lower than that expected for a low metallicity giant star, is a consequence of the huge increase of the envelope opacity occurring after the carbon dredge up. The Li enrichment may be explained if a deep circulation would take place during the interpulse period, the so called cool bottom process. In spite of the low resolution of our spectra, we derive a lower limit for the carbon isotopic ratio, namely 12C/, and a constraint for the Ba abundance, namely . The proposed scenario also fits these further constraints. Then, we estimate that the mass of D461 ranges between 1.2 and 2 , which corresponds to an age ranging between 1 and 3 Gyr. We conclude that this star is more massive and younger than the typical stellar population of Draco.
Key words: stars: carbon / stars: abundances / stars: evolution / stars: AGB and post-AGB / galaxies: local group
© ESO, 2004
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.