Stellar Mass Loss in Globular Clusters

Details Stellar Mass Loss in Globular Clusters Stellar Mass Loss in Globular Clusters

Oct 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt........10m&link_type=abstract

PhD Thesis, Keele University. 387 pages

Computer Science

3

Globular Clusters, Stars: Mass-Loss, Circumstellar Matter, Stars: Winds, Outflows, Infrared: Stars, Stars: Agb And Post-Agb

Scientific paper

This work investigates stellar mass loss in globular clusters. It comprises of optical and infra-red photometric imaging and spectroscopy, plus radio interferometry observations.
I present mid-infrared spectroscopic observations of stars in the globular clusters 47 Tucanae and ω Centauri, finding 47 Tuc V1 (and possibly V18) and ω Cen V6 surrounded by circumstellar silicate dust. ω Cen V42 may also be surrounded by carbon-rich dust.
Much of this work is devoted to finding the threshold for dust production and the mass-loss rates from cluster stars with both chromospherically- and dust- or pulsation-driven winds. Using very-high-resolution optical photometry, I have identified the transition between the two driving regimes as being at earlier spectral types than in solar-metallicity stars, suggesting that pulsation and continuum-driving become the dominant wind drivers at around K5-M3, or ~1500 Lsun.
In a similar vein, I have modelled spectral energy distributions of stars in ω Centauri using new photometry from the Spitzer Space Telescope and literature photometry. The total mass-loss rate for the cluster is & 1.2+/-0.6 x 10^-6 Msun yr-1, some 30% of which is from two stars - V6 and V42. This implies the cluster is being cleaned of gas and dust every ~10^5 years. Dust production appears to be efficient on both the red and asymptotic giant branches, even at the cluster's low metallicity ([Fe/H] = -1.62). I also derive a new distance to the cluster of 4850 ± 200 (statistical) ± 200 (systematic) pc with a reddening of E(B-V) = 0.08±0.02±0.02 mag and a differential reddening of delta[E(B-V)] < 0.02 mag.
Finally, I also present new observations of the high velocity hydrogen cloud in the vicinity of ω Centauri, finding that it is likely not associated with the cluster.

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