First detection of a lithium rich carbon star in the Draco dwarf galaxy: evidence for a young stellar population

Abstract

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 log e(Li)=3.5+/-0.4 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 expectedfor a low mass low metallicity thermally pulsing AGB star, undergoing few third dredge up episodes. The position in the log g-log Teff 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/13C>40, and a constraint for the Ba abundance, namely 0.5<[Ba/Fe]< 2. The proposed scenario also fits these further constraints. Then, we estimate that the mass of D461 ranges between 1.2 and 2 $M_{\odot }$, 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.

10 pages, 5 figues. Accepted for publication in A&A

References in corpus (23)

• Dwarf Galaxies of the Local Group
• Abundance Patterns in the Draco, Sextans and Ursa Minor Dwarf Spheroidal Galaxies
• Cool bottom processes on the thermally-pulsing AGB and the isotopic composition of circumstellar dust grains
• The Star Formation History of the Local Group dwarf galaxy Leo I
• Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities
• s-Process Nucleosynthesis in Carbon Stars
• Nucleosynthesis of light elements inside thermally pulsing AGB stars I: the case of intermediate-mass stars
• The Draco and Ursa Minor dwarf spheroidals. A comparative study
• Intermediate mass stars: updated models
• The Star Formation History and the Morphological Evolution of the Draco Dwarf Spheroidal Galaxy
• The Chemical Composition of Carbon Stars II: The J-type stars
• Evolution and Nucleosynthesis of Zero Metal Intermediate Mass Stars
• Galactic chemical evolution of Lithium: interplay between stellar sources"
• The Mass-to-Light Ratios of the Draco and Ursa Minor Dwarf Spheroidal Galaxies. II. The Binary Population and Its Effect in the Measured Velocity Dispersions of Dwarf Spheroidal Galaxies
• MSX, 2MASS, and the LMC: A Combined Near and Mid Infrared View
• Hubble Space Telescope Observations of the Draco Dwarf Spheroidal
• Extended Star Formation in Dwarf Spheroidal Galaxies: the Cases of Draco, Sextans, and Ursa Minor
• Faint High Latitude Carbon Stars Discovered by the Sloan Digital Sky Survey: Methods and Initial Results
• Reprocessing the Hipparcos data for evolved giant stars II. Absolute magnitudes for the R-type carbon stars
• Cerium: the lithium substitute in post-AGB stars
• The identification of HCN and HNC in Carbon Stars: Model Atmospheres, Synthetic Spectra and Fits to Observations in the 2.7-4.0 micron Region
• The Nature of the Red Giant Branches in the Ursa Minor and Draco Dwarf Spheroidal Galaxies
• Lithium in LMC carbon stars

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• Deep Mixing in Evolved Stars: I. The Effect of Reaction Rate Revisions from C to Al
• s-Process in Low Metallicity Stars. III. Individual analysis of CEMP-s and CEMP-s/r with AGB models
• CS22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star
• Molecular opacities for low-mass metal-poor AGB stars undergoing the Third Dredge Up
• Metal-Poor Lithium-Rich Giants in the Radial Velocity Experiment Survey
• Lithium abundances in CEMP stars
• Lithium-Rich Giants in Globular Clusters
• Lithium-rich giants in the Galactic thick disk
• Deep Mixing in Evolved Stars. II. Interpreting Li Abundances in RGB and AGB Stars
• The Hobby-Eberly Telescope "Chemical Abundances of Stars in the Halo" (CASH) Project. I. The Lithium-, s-, and r-Enhanced Metal-Poor Giant HKII 17435-00532
• Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era
• Li-rich RGB stars in the Galactic Bulge
• The Gaia -ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc
• The puzzle of the CNO isotope ratios in AGB carbon stars
• The Draco dwarf galaxy in the near-infrared
• Carbon Stars in the Satellites and Halo of M31
• High resolution optical spectroscopy of IRAS 09425-6040 (=GLMP 260)
• The true nature of HE0057-5959, the most metal-poor Li-rich star
• Chemical analysis of carbon stars in the Local Group: I. The Small Magellanic Cloud and the Sagittarius dwarf spheroidal galaxy