The Red-giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities

The Red-giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities

The red-giant branch bump provides valuable information for the investigation of the internal structure of low-mass stars. Because current models are unable to accurately predict the occurrence and efficiency of mixing processes beyond convective boundaries, one can use the luminosity of the bump-a...

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Bibliographic Details
Published in:The Astrophysical journal 2018-06, Vol.859 (2), p.156
Main Authors: Khan, Saniya, Hall, Oliver J., Miglio, Andrea, Davies, Guy R., Mosser, Benoît, Girardi, Léo, Montalbán, Josefina
Format: Article
Language:eng
Subjects:
Astronomical models
Astrophysics
Diagnostic systems
Giant stars
Globular clusters
Low mass stars
Luminosity
Metallicity
Mixing processes
Physics
Probabilistic models
Red giant stars
Seismic properties
stars: evolution
stars: interiors
stars: low-mass
stars: luminosity function, mass function
Stellar models
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Summary:The red-giant branch bump provides valuable information for the investigation of the internal structure of low-mass stars. Because current models are unable to accurately predict the occurrence and efficiency of mixing processes beyond convective boundaries, one can use the luminosity of the bump-a diagnostic of the maximum extension of the convective envelope during the first-dredge up-as a calibrator for such processes. By combining asteroseismic and spectroscopic constraints, we expand the analysis of the bump to masses and metallicities beyond those previously accessible using globular clusters. Our data set comprises nearly 3000 red-giant stars observed by Kepler and with APOGEE spectra. Using statistical mixture models, we are able to detect the bump in the average seismic parameters max and , and show that its observed position reveals general trends with mass and metallicity in line with expectations from models. Moreover, our analysis indicates that standard stellar models underestimate the depth of efficiently mixed envelopes. The inclusion of significant overshooting from the base of the convective envelope, with an efficiency that increases with decreasing metallicity, allows us to reproduce the observed location of the bump. Interestingly, this trend was also reported in previous studies of globular clusters.
ISSN:0004-637X
1538-4357