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Asteroseismology of old open clusters with Kepler: direct estimate of the integrated RGB mass loss in NGC6791 and NGC6819 | | A. Miglio
; K. Brogaard
; D. Stello
; W. J. Chaplin
; F. D'Antona
; J. Montalban
; S. Basu
; A. Bressan
; F. Grundahl
; M. Pinsonneault
; A. M. Serenelli
; Y. Elsworth
; S. Hekker
; T. Kallinger
; B. Mosser
; P. Ventura
; A. Bonanno
; A. Noels
; V. Silva-Aguirre
; R. Szabo
; J. Li
; S. McCauliff
; C. K. Middour
; H. Kjeldsen
; | | Date: |
20 Sep 2011 | | Abstract: | Mass loss of red giant branch (RGB) stars is still poorly determined, despite
its crucial role in the chemical enrichment of galaxies. Thanks to the recent
detection of solar-like oscillations in G-K giants in open clusters with
Kepler, we can now directly determine stellar masses for a statistically
significant sample of stars in the old open clusters NGC6791 and NGC6819. The
aim of this work is to constrain the integrated RGB mass loss by comparing the
average mass of stars in the red clump (RC) with that of stars in the
low-luminosity portion of the RGB (i.e. stars with L <~ L(RC)). Stellar masses
were determined by combining the available seismic parameters numax and Dnu
with additional photometric constraints and with independent distance
estimates. We measured the masses of 40 stars on the RGB and 19 in the RC of
the old metal-rich cluster NGC6791. We find that the difference between the
average mass of RGB and RC stars is small, but significant (Delta M=0.09 +-
0.03 (random) +- 0.04 (systematic) Msun). Interestingly, such a small DeltaM
does not support scenarios of an extreme mass loss for this metal-rich cluster.
If we describe the mass-loss rate with Reimers’ prescription, a first
comparison with isochrones suggests that the observed DeltaM is compatible with
a mass-loss efficiency parameter in the range 0.1 <~ eta <~ 0.3. Less stringent
constraints on the RGB mass-loss rate are set by the analysis of the ~ 2
Gyr-old NGC6819, largely due to the lower mass loss expected for this cluster,
and to the lack of an independent and accurate distance determination. In the
near future, additional constraints from frequencies of individual pulsation
modes and spectroscopic effective temperatures, will allow further stringent
tests of the Dnu and numax scaling relations, which provide a novel, and
potentially very accurate, means of determining stellar radii and masses. | | Source: | arXiv, 1109.4376 | | Services: | Forum | Review | PDF | Favorites | |
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