Journal
ASTROPHYSICAL JOURNAL
Volume 874, Issue 2, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/ab0c04
Keywords
open clusters and associations: general; open clusters and associations: individual (NGC 6791); stars: oscillations
Categories
Funding
- NSF [AST-1514676]
- NASA [NNX16AI09G]
- European Unions Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant [664931]
- NASA [NNX16AI09G, 903474] Funding Source: Federal RePORTER
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The helium abundance of stars is a strong driver of evolutionary timescales; however, it is difficult to measure in cool stars. We conduct an asteroseismic analysis of NGC 6791, an old, metal-rich open cluster that previous studies have indicated also has a high helium abundance. The cluster was observed by Kepler and has unprecedented light curves for many of the red giant branch stars in the cluster. Previous asteroseismic studies with Kepler data have constrained the age through grid-based modeling of the global asteroseismic parameters (Delta nu and nu(max)). However, with the precision of Kepler data, it is possible to do detailed asteroseismology of individual mode frequencies to better constrain the stellar parameters, something that has not been done for these cluster stars as yet. In this work, we use the observed mode frequencies in 27 hydrogen shell burning red giants to better constrain initial helium abundance (Y-0) and age of the cluster. The distributions of helium abundance and age for each individual red giant are combined to create a final probability distribution for age and helium abundance of the entire cluster. We find a helium abundance of Y-0 = 0.297 +/- 0.003 and a corresponding age of 8.2 +/- 0.3 Gyr.
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