Mass Loss from Red Giant Branch (and AGB) Stars in Globular Clusters

Mass Loss from Red Giant Branch (and AGB) Stars in Globular Clusters Andrea Dupree Harvard-Smithsonian Center for Astrophysics AGB Workshop: 20 May 2010

Stellar Evolution • Outline is solid • Important aspects unresolved: mass loss, Second parameter…. • Globular clusters a classical testing ground to confront these issues

Problems remain • Mass loss necessary for evolution, but not detected directly • Mass lost not found in globular clusters • Metallicity [Fe/H] creates differences (‘first parameter’), • but…something else is at work…(‘second parameter’) Candidates for 2nd parameter: total cluster mass; age; environment; free-floating planets; primordial He abundance; post-mixing surface He abundance; CNO abundance; stellar rotation; mass loss; more than one… Here focus on mass loss from the cool stars …

How to detect mass loss • Cool stars with 2 relevant • attributes (based on the Sun, • mostly) • Chromosphere and coronas • T >Tphotosphere • 2. Dynamics controlled by • magnetic field configuration: • not spherically symmetric. • 3. Dust (historic mass loss) Yohkoh x-ray image of Sun Thus, need to choose diagnostics wisely, and expect variability Model of metal-poor giant

Hectochelle at MMT Fibre (240)-fed echelle (A. Szentgyorgyi & D. Fabricant) R~34,000; 1 degree FOV Outstanding for cluster studies Meszaros, S. et al. 2008, 2009, AJ

Dynamics from H-α Wing emission present in luminous stars Asymmetry varies But H-alpha core shift/asymmetry always indicates outflow (or static) Suggests pulsation in lower layers creates steady outflow at top of chromosphere Red giants in M92 Meszaros et al. 2009, AJ

Dynamics from H-α H-α core shift largest for luminous stars Velocities 0-~15 km s-1; variability in AGB stars Outflow speeds may distinguish AGB from RGB Meszaros et al. 2008 Meszaros et al. 2009 Flows are outflows; not escape speeds signaling a wind.

Higher up… Ca II K Ca K3 (●) indicates higher outflow velocity than H-α (×) K3 Magellan spectra of Omega Cen giants Meszaros et al. 2009, AJ

So, what about the mass loss rate? Only reliable way for M_dot from H-α uses non-LTE spherical models with mass flow Semi-empirical models of the atmospheres constructed for ~20 globular cluster red giants (M15, M92, M13) to match profiles Meszaros et al 2009

Current ‘laws’ overestimate mass loss “Reimer’s rate” ‘Dust’ rate (to be corrected; Boyer et al. 2010) Mass loss increases with L and with decreasing TEFF Suggestion of metallicity dependence Rates are ~order magnitude less than ‘Reimers’ and IR results Meszaros et al 2009

AGB Stars with ‘dust’ K479 K421 K479 Filled squares mark dusty AGB stars id’d by Spitzer (Boyer et al. 2006) K421 H-α mass loss rate similar to stars with no dust. H-α bisector velocity similar to stars with no dust.

K825 in M15 (RGB/AGB at tip)Direct evidence for pulsation Accelerating outflows ΔL [solar luminosities] ΔT [K] NO dust in K825: pulsations do not lead to dust production Pulsation period: ~350 days; LPV; [Fe/H]=-2.5 SED validates change in T and Luminosity McDonald, I. et al. 2010, MNRAS

Abundances returned to the ism… A lesson from the Sun… The helium abundance found in the solar wind varies depending on solar activity and wind speed…. (Kasper et al. 2007) HELIUM ABUNDANCE YEAR

Conclusions • Developing a consistent picture of mass loss in metal poor stars • H-alpha, Ca K give evidence for accelerating fast outflows from the majority of metal-poor field RGB and AGB stars • AGB objects show faster outflows and more variability than RGB stars • No difference in dynamics between ‘dusty’ stars and stars with no IR excess • Pulsation can drive outflow without dust • Inferred mass loss provides confirmation needed for stellar evolution calculations

Mass Loss from Red Giant Branch (and AGB) Stars in Globular Clusters