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arXiv · 1209.2563

Carbon enrichment of the evolved stars in the Sagittarius dwarf spheroidal

Iain McDonald·Jennifer R. White·Albert A. Zijlstra·Lizette Guzman Ramirez·Cezary Szyszka·Jacobus Th. van Loon·Eric Lagadec·Olivia C. Jones
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Abstract

We present spectra of 1142 colour-selected stars in the direction of the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy, of which 1058 were taken with VLT/FLAMES multi-object spectrograph and 84 were taken with the SAAO Radcliffe 1.9-m telescope grating spectrograph. Spectroscopic membership is confirmed (at >99% confidence) for 592 stars on the basis of their radial velocity, and spectral types are given. Very slow rotation is marginally detected around the galaxy's major axis. We identify five S stars and 23 carbon stars, of which all but four carbon stars are newly-determined and all but one (PQ Sgr) are likely Sgr dSph members. We examine the onset of carbon-richness in this metal-poor galaxy in the context of stellar models. We compare the stellar death rate (one star per 1000-1700 years) to known planetary nebula dynamical ages and find that the bulk population produce the observed (carbon-rich) planetary nebulae. We compute average lifetimes of S and carbon stars as 60-250 and 130-500 kyr, compared to a total thermal-pulsing asymptotic giant branch lifetime of 530-1330 kyr. We conclude by discussing the return of carbon-rich material to the ISM.

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Iain McDonald, Jennifer R. White, Albert A. Zijlstra, Lizette Guzman Ramirez, Cezary Szyszka, Jacobus Th. van Loon, Eric Lagadec, Olivia C. Jones. 2012-09-12. Carbon enrichment of the evolved stars in the Sagittarius dwarf spheroidal. https://doi.org/10.1111/j.1365-2966.2012.22109.x

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