Dust, pulsation, chromospheres and their role in driving mass loss from red giants in Galactic globular clusters

Abstract

Context: Mass loss from red giants in old globular clusters affects the horizontal branch (HB) morphology and post-HB stellar evolution including the production of ultraviolet-bright stars, dredge up of nucleosynthesis products and replenishment of the intra-cluster medium. Studies of mass loss in globular clusters also allows one to investigate the metallicity dependence of the mass loss from cool, low-mass stars down to very low metallicities. Aims: We present an analysis of new VLT/UVES spectra of 47 red giants in the Galactic globular clusters 47 Tuc (NGC 104), NGC 362, omega Cen (NGC 5139), NGC 6388, M54 (NGC 6715) and M15 (NGC 7078). The spectra cover the wavelength region 6100-9900A at a resolving power of R = 110,000. Some of these stars are known to exhibit mid-infrared excess emission indicative of circumstellar dust. Our aim is to detect signatures of mass loss, identify the mechanism(s) responsible for such outflows, and measure the mass-loss rates. Methods: We determine for each star its effective temperature, luminosity, radius and escape velocity. We analyse the H-alpha and near-infrared calcium triplet lines for evidence of outflows, pulsation and chromospheric activity, and present a simple model for estimating mass-loss rates from the H-alpha line profile. We compare our results with a variety of other, independent methods. Results: We argue that a chromosphere persists in Galactic globular cluster giants and controls the mass-loss rate to late-K/early-M spectral types, where pulsation becomes strong enough to drive shock waves at luminosities above the RGB tip. This transition may be metallicity-dependent. We find mass-loss rates of ~10^-7 to 10^-5 solar masses per year, largely independent of metallicity.

23 pages, 17 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (8)

• The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity
• AGB stars in the Magellanic Clouds. II. The rate of star formation across the LMC
• Tracing the development of dust around evolved stars: The case of 47 Tuc
• Stellar Populations and Mass-Loss in M15: A Spitzer Detection of Dust in the Intra-Cluster Medium
• On the magnetic structure and wind parameter profiles of Alfven wave driven winds in late-type supergiant stars
• Observations of the Hot Horizontal-Branch Stars in the Metal-Rich Bulge Globular Cluster NGC 6388 - Indications of Helium Enrichment and a Lesson in Crowded Field Spectroscopy
• The period-luminosity relation of Mira variables in NGC 6388 and NGC 6441
• The impact of red giant mass loss on star cluster evolution

Cited by in corpus (20)

• Mass loss on the red giant branch: the value and metallicity dependence of Reimers' η in globular clusters
• Molecules and dust production in the Magellanic Clouds
• Giants in the globular cluster omega Centauri: dust production, mass loss and distance
• Evolution of Thermally Pulsing Asymptotic Giant Branch Stars IV. Constraining Mass-Loss & Lifetimes of Low Mass, Low Metallicity AGB Stars
• Spitzer Infrared Spectrographic point source classification in the Small Magellanic Cloud
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• A Spitzer Space Telescope Atlas of omega Centauri: The Stellar Population, Mass Loss, and the Intracluster Medium
• Ejection of globular cluster interstellar media through ionization by white dwarfs
• Spitzer Space Telescope evidence in NGC 6791: no super-mass-loss at super-solar metallicity to explain helium white dwarfs?
• An empirical mass-loss law for Population II giants from the Spitzer-IRAC survey of Galactic globular clusters
• Betelgeuse fainter in the sub-millimetre too: an analysis of JCMT and APEX monitoring during the recent optical minimum
• Mass Outflow and Chromospheric Activity of Red Giant Stars in Globular Clusters II. M13 and M92
• A Spitzer search for cold dust within globular clusters
• MCR-TRGB: A Multiwavelength-Covariant, Robust Tip of the Red Giant Branch Measurement Method
• A peculiar HI cloud near the distant globular cluster Pal 4
• Abundance analysis for long-period variables II. RGB and AGB stars in the globular cluster 47\,Tuc
• Red Supergiant Mass Loss and Mass-Loss Rates
• The loss of the intra-cluster medium in globular clusters
• Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae
• Theoretical investigation on the mass loss impact on asteroseismic grid-based estimates of mass, radius, and age for RGB stars