NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution

R. Handberg, K. Brogaard, A. Miglio, D. Bossini, Y. Elsworth, D. Slumstrup, Guy Davies, W.~J. Chaplin

Research output: Contribution to journalArticlepeer-review

47 Citations (Scopus)
140 Downloads (Pure)

Abstract

We present an extensive peakbagging effort on Kepler data of ∼50 red giant stars in the open star cluster NGC 6819. By employing sophisticated pre-processing of the time series and Markov Chain Monte Carlo techniques we extracted individual frequencies, heights and linewidths for hundreds of oscillation modes. We show that the ‘average’ asteroseismic parameter dν02, derived from these, can be used to distinguish the stellar evolutionary state between the red giant branch (RGB) stars and red clump (RC) stars. Masses and radii are estimated using asteroseismic scaling relations, both empirically corrected to obtain self-consistency as well as agreement with independent measures of distance, and using updated theoretical corrections. Remarkable agreement is found, allowing the evolutionary state of the giants to be determined exclusively from the empirical correction to the scaling relations. We find a mean mass of the RGB stars and RC stars in NGC 6819 to be 1.61 ± 0.02  and 1.64 ± 0.02 , respectively. The difference ΔM = −0.03 ± 0.01  is almost insensitive to systematics, suggesting very little RGB mass loss, if any. Stars that are outliers relative to the ensemble reveal overmassive members that likely evolved via mass-transfer in a blue straggler phase. We suggest that KIC 4937011, a low-mass Li-rich giant, is a cluster member in the RC phase that experienced very high mass-loss during its evolution. Such over- and undermassive stars need to be considered when studying field giants, since the true age of such stars cannot be known and there is currently no way to distinguish them from normal stars.
Original languageEnglish
JournalRoyal Astronomical Society. Monthly Notices
Early online date28 Jul 2017
DOIs
Publication statusE-pub ahead of print - 28 Jul 2017

Keywords

  • Astrophysics - Solar and Stellar Astrophysics
  • methods
  • data analysis
  • stars
  • oscillations

Fingerprint

Dive into the research topics of 'NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution'. Together they form a unique fingerprint.

Cite this