The low wind expansion velocity of metal-poor carbon stars in the Halo and the Sagittarius stream

Abstract

We report the detection, from observations using the James Clerk Maxwell Telescope, of CO J $=$ 3$\to$ 2 transition lines in six carbon stars, selected as members of the Galactic Halo and having similar infrared colors. Just one Halo star had been detected in CO before this work. Infrared observations show that these stars are red (J-K $>$3), due to the presence of large dusty circumstellar envelopes. Radiative transfer models indicates that these stars are losing mass with rather large dust mass-loss rates in the range 1--3.3 $\times$$10^{-8}$M${}_{\odot }$yr${}^{-1}$, similar to what can be observed in the Galactic disc. We show that two of these stars are effectively in the Halo, one is likely linked to the stream of the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph), and the other three stars certainly belong to the thick disc. The wind expansion velocities of the observed stars are low compared to carbon stars in the thin disc and are lower for the stars in the Halo and the Sgr dSph stream than in the thick disc. We discuss the possibility that the low expansion velocities result from the low metallicity of the Halo carbon stars. This implies that metal-poor carbon stars lose mass at a rate similar to metal-rich carbon stars, but with lower expansion velocities, as predicted by recent theoretical models. This result implies that the current estimates of mass-loss rates from carbon stars in Local Group galaxies will have to be reconsidered.

10 pages, 7 figures, accepted for publication in MNRAS

References in corpus (12)

• Near-Infrared Photometry of Carbon Stars
• A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud
• The Magellanic zoo: Mid-infrared Spitzer spectroscopy of evolved stars and circumstellar dust in the Magellanic Clouds
• Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud
• Dust-driven Winds and Mass Loss of C-rich AGB Stars with subsolar Metallicities
• A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud
• Effects of Metallicity on the Chemical Composition of Carbon Stars
• The trigger of the AGB superwind: the importance of carbon
• Carbon-Rich Mira Variables: Kinematics and Absolute Magnitudes
• Dust mass-loss rates from AGB stars in the Fornax and Sagittarius dwarf Spheroidal galaxies
• Metal-rich carbon stars in the Sagittarius Dwarf Spheroidal galaxy
• Cool carbon stars in the halo: new very red or distant objects

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• The mass-loss rates of red supergiants at low metallicity: Detection of rotational CO emission from two red supergiants in the Large Magellanic Cloud
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• Planetary Nebula Populations and Kinematics