An atlas of omega Centauri at mid-infrared wavelengths

Details An atlas of omega Centauri at mid-infrared wavelengths An atlas of omega Centauri at mid-infrared wavelengths

Jun 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20648v&link_type=abstract

Spitzer Proposal ID #20648

Astronomy and Astrophysics

Astrophysics

Scientific paper

The most massive galactic globular cluster, Omega Centauri serves as a template for stellar and galactic astrophysics. The unusually large observed spread in metal abundance, from [Fe/H]=-2 to -0.5, still awaits a satisfactory explanation - proposed scenarios include self-enrichment, cluster mergers and the dissolution of a dwarf spheroidal galaxy. The population spread can also be used to our advantage to probe the evolution of low-mass stars across a range in metallicity that is not easily accessible elsewhere but which holds vital clues to our understanding of the early, metal-poor Universe. We propose to map the Omega Cen cluster with IRAC and MIPS to detect the stellar photospheres of all red giants as faint as ~100 Lsun. The resulting atlas and photometric catalogue will provide the by far deepest and least biased mid-IR inventory of the content of any large stellar system. In particular, it will result in a complete census of dust-producing red giants on the first ascent (RGB) and asymptotic (AGB) branches. This enables us to determine the rates and timescales for red giant mass loss and their dependence on metal abundance, elucidating the nature of the RGB mass loss and the second parameter that (besides metallicity) determines the Horizontal Branch morphology in intermediate-metallicity systems. It is essentially unknown how mass loss proceeds at low metallicities of [Fe/H]<-1, where dust condensation and coupling with the gas is expected to become extremely feeble. Yet dusty red giants are found in metal-poor globular clusters such as M15 at [Fe/H]=-2.2. Omega Cen offers us a rare opportunity to directly trace the evolution of mass loss across a crucial but largely uncharted regime in metallicity. Our proposed survey of Omega Cen with Spitzer does precisely that. Understanding the mass-loss mechanism in metal-poor stars may ultimately allow us to reliably reconstruct the initial phases of chemical enrichment in the high-redshift Universe.

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