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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 findM1= 1.692 ± 0.004 ± 0.010M⊙,R1= 2.185 ± 0.004 ± 0.008R⊙,M2= 1.184 ± 0.001 ± 0.003M⊙, andR2= 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:M1= 1.717 ± 0.011M⊙andM2= 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.
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Mass Transfer as an Explanation for the Lifetime Travel Time Discrepancy in IT Librae
Abstract The eclipsing binary IT Librae is an unusual system of two B-type stars that is situated about 1 kpc above the Galactic plane. The binary was probably ejected from its birthplace in the disk, but the implied time of flight to its current location exceeds the evolutionary lifetime of the primary star. Here we present a study of new high-dispersion spectroscopy and an exquisite light curve from the Kepler K2 mission in order to determine the system properties and resolve the timescale discrepancy. We derive a revised spectroscopic orbit from radial-velocity measurements and determine the component effective temperatures through comparison of reconstructed and model spectra (T1= 23.8 ± 1.8 kK,T2= 13.7 ± 2.5 kK). We use the Eclipsing Light Curve code to model the K2 light curve, and from the inclination of the fit we derive the component masses (M1= 9.6 ± 0.6M⊙,M2= 4.2 ± 0.2M⊙) and mean radii (R1= 6.06 ± 0.16R⊙,R2= 5.38 ± 0.14R⊙). The secondary star is overluminous for its mass and appears to fill its Roche lobe. This indicates that IT Librae is a post-mass-transfer system in which the current secondary was the mass donor star. The current primary star was rejuvenated by mass accretion, and its evolutionary age corresponds to the time since the mass transfer stage. Consequently, the true age of the binary is larger than the ejection time of flight, thus resolving the timescale discrepancy.
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- Award ID(s):
- 1908026
- PAR ID:
- 10364009
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 163
- Issue:
- 4
- ISSN:
- 0004-6256
- Format(s):
- Medium: X Size: Article No. 177
- Size(s):
- Article No. 177
- Sponsoring Org:
- National Science Foundation
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