Evolved Eclipsing Binaries and the Age of the Open Cluster NGC 752* * Based on observations made with with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Eric L. Sandquist, Andrew J. Buckner, Matthew D. Shetrone, Samuel C. Barden, Catherine A. Pilachowski, Constantine P. Deliyannis, Dianne Harmer, Robert Mathieu, Søren Meibom, Søren Frandsen, Jerome A. Orosz

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Abstract

We present analyses of improved photometric and spectroscopic observations for two detached eclipsing binaries at the turnoff of the open cluster NGC 752: the 1.01 days binary DS And and the 15.53 days BD +37 410. For DS And, we find M 1 = 1.692 ± 0.004 ± 0.010M , R 1 = 2.185 ± 0.004 ± 0.008R , M 2 = 1.184 ± 0.001 ± 0.003M , and R 2 = 1.200 ± 0.003 ± 0.005R . We either confirm or newly identify unusual characteristics of both stars in the binary: the primary star is found to be slightly hotter than the main-sequence turnoff and there is a more substantial discrepancy in its luminosity compared to models (model luminosities are too large by about 40%), while the secondary star is oversized and cooler compared to other main-sequence stars in the same cluster. The evidence points to nonstandard evolution for both stars, but most plausible paths cannot explain the low luminosity of the primary star. BD +37 410 only has one eclipse per cycle, but extensive spectroscopic observations and the Transiting Exoplanet Survey Satellite light curve constrain the stellar masses well: M 1 = 1.717 ± 0.011M and M 2 = 1.175 ± 0.005M . The radius of the main-sequence primary star near 2.9R definitively requires large convective core overshooting (>0.2 pressure scale heights) in models for its mass, and multiple lines of evidence point toward an age of 1.61 ± 0.03 ± 0.05 Gyr (statistical and systematic uncertainties). Because NGC 752 is currently undergoing the transition from nondegenerate to degenerate He ignition of its red clump stars, BD +37 410 A directly constrains the star mass where this transition occurs.

OriginalsprogEngelsk
Artikelnummer6
TidsskriftAstronomical Journal
Vol/bind165
Nummer1
Antal sider32
ISSN0004-6256
DOI
StatusUdgivet - jan. 2023

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