Issue |
A&A
Volume 422, Number 3, August II 2004
|
|
---|---|---|
Page(s) | 1045 - 1052 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20040289 | |
Published online | 16 July 2004 |
First detection of a lithium rich carbon star in the Draco dwarf galaxy: Evidence for a young stellar population
1
Dpto. Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain e-mail: inma@ugr.es
2
INAF-Osservatorio Astronomico di Collurania, 64100 Teramo, Italy
3
Main Astronomical Observatory, National Academy of Sciences, Zabolotnoho 27, Kiev-127 03680, Ukranie
Received:
17
February
2004
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
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