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1. Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members: III. Constraints from a subgiant

   https://doi.org/10.1051/0004-6361/202140911  

   Brogaard, K. ; Grundahl, F. ; Sandquist, E. L. ; Slumstrup, D. ; Jensen, M. L. ; Thomsen, J. B. ; Jørgensen, J. H. ; Larsen, J. R. ; Bjørn, S. T. ; Sørensen, C. T. ; et al ( May 2021 , Astronomy & Astrophysics)

   Context. Models of stellar structure and evolution can be constrained using accurate measurements of the parameters of eclipsing binary members of open clusters. Multiple binary stars provide the means to tighten the constraints and, in turn, to improve the precision and accuracy of the age estimate of the host cluster. In the previous two papers of this series, we have demonstrated the use of measurements of multiple eclipsing binaries in the old open cluster NGC 6791 to set tighter constraints on the properties of stellar models than was previously possible, thereby improving both the accuracy and precision of the cluster age. Aims. We identify and measure the properties of a non-eclipsing cluster member, V56, in NGC 6791 and demonstrate how this provides additional model constraints that support and strengthen our previous findings. Methods. We analyse multi-epoch spectra of V56 from FLAMES in conjunction with the existing photometry and measurements of eclipsing binaries in NGC6971. Results. The parameters of the V56 components are found to be M p  = 1.103 ± 0.008  M ⊙ and M s  = 0.974 ± 0.007  M ⊙ , R p  = 1.764 ± 0.099  R ⊙ and R s  = 1.045 ± 0.057  R ⊙ , T eff,p  = 5447 ± 125 K and T eff,s  = 5552 ± 125 K, and surfacemore »[Fe/H] = +0.29 ± 0.06 assuming that they have the same abundance. Conclusions. The derived properties strengthen our previous best estimate of the cluster age of 8.3 ± 0.3 Gyr and the mass of stars on the lower red giant branch (RGB), which is M RGB  = 1.15 ± 0.02  M ⊙ for NGC 6791. These numbers therefore continue to serve as verification points for other methods of age and mass measures, such as asteroseismology.« less
2. Extremely precise age and metallicity of the open cluster NGC 2506 using detached eclipsing binaries

   https://doi.org/10.1093/mnras/staa2855  

   Knudstrup, E ; Grundahl, F ; Brogaard, K ; Slumstrup, D ; Orosz, J A ; Sandquist, E L ; Jessen-Hansen, J ; Lund, M N ; Arentoft, T ; Tronsgaard, R ; et al ( October 2020 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Accurate stellar parameters of stars in open clusters can help constrain models of stellar structure and evolution. Here, we wish to determine the age and metallicity content of the open cluster NGC 2506. To this end, we investigated three detached eclipsing binaries (DEBs; V2032, V4, and V5) for which we determined their masses and radii, as well as four red giant branch stars for which we determined their effective temperatures, surface gravities, and metallicities. Three of the stars in the DEBs have masses close to the cluster turn-off mass, allowing for extremely precise age determination. Comparing the values for the masses and radii of the binaries to BaSTI (a Bag of Stellar Tracks and Isochrones) isochrones, we estimated a cluster age of 2.01 ± 0.10 Gyr. This does depend on the models used in the comparison, where we have found that the inclusion of convective core-overshooting is necessary to properly model the cluster. From red giant branch stars, we determined values for the effective temperatures, the surface gravities, and the metallicities. From these we find a cluster metallicity of −0.36 ± 0.10 dex. Using this value and the values for the effective temperatures, we determine the reddening to be E(b − y) = 0.057 ± 0.004 mag. Furthermore, we derivedmore »the distance to the cluster from Gaia parallaxes and found 3.101 ± 0.017 kpc, and we have performed a radial velocity membership determination for stars in the field of the cluster. Finally, we report on the detection of oscillation signals in γ Dor and δ Scuti members in data from the Transiting Exoplanet Survey Satellite (TESS) mission, including the possible detection of solar-like oscillations in two of the red giants.« less
3. Double degenerate candidates in the open cluster NGC 6633

   https://doi.org/10.1017/S1743921320001040  

   Barnett, Joseph W. ; Williams, Kurtis A. ( October 2019 , Proceedings of the International Astronomical Union)

   Abstract The study of white dwarfs, the end stage of stellar evolution for more than 95% of stars, is critical to bettering our understanding of the late stages of the lives of low mass stars. In particular, the post main sequence evolution of binary star systems is complex, and the identification and analysis of double degenerate systems is a crucial step in constraining models of binary star systems. Binary white dwarfs in open star clusters are particularly useful because cluster parameters such as distance, metal content, and total system age are more tightly constrained than for field double degenerates. Here we use the precision astrometry from the Gaia Data Release 2 catalog to study two other white dwarfs which were identified as candidate double degenerates in the field of the open star cluster NGC 6633. One of the two objects, LAWDS 4, is found to have astrometric properties fully consistent with that of the cluster. In such a case, the object is significantly overluminous for a single white dwarf, strongly indicating binarity. The second candidate binary, LAWDS 7, appears to be inconsistent with cluster membership, though a more thorough analysis is necessary to properly quantify the probability. At present wemore »are proceeding to model the photometric and spectroscopic data for both objects as if they were cluster member double degenerates. Results of this latter analysis are forthcoming. Our results will add crucial data to the study of binary star evolution in open star clusters.« less
4. Evolved Eclipsing Binaries and the Age of the Open Cluster NGC 752*

   https://doi.org/10.3847/1538-3881/ac9c59  

   Sandquist, Eric L. ; Buckner, Andrew J. ; Shetrone, Matthew D. ; Barden, Samuel C. ; Pilachowski, Catherine A. ; Deliyannis, Constantine P. ; Harmer, Dianne ; Mathieu, Robert ; Meibom, Søren ; Frandsen, Søren ; et al ( December 2022 , The Astronomical Journal)

   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 ± 0.010 M ⊙ , R 1 = 2.185 ± 0.004 ± 0.008 R ⊙ , M 2 = 1.184 ± 0.001 ± 0.003 M ⊙ , and R 2 = 1.200 ± 0.003 ± 0.005 R ⊙ . 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:more »M 1 = 1.717 ± 0.011 M ⊙ and M 2 = 1.175 ± 0.005 M ⊙ . The radius of the main-sequence primary star near 2.9 R ⊙ 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.« less
5. Dynamical fates of S-type planetary systems in embedded cluster environments

   https://doi.org/10.1093/mnras/stac1973  

   Ellithorpe, Elizabeth A. ; Kaib, Nathan A. ( July 2022 , Monthly Notices of the Royal Astronomical Society)

   The majority of binary star systems that host exoplanets will spend the first portion of their lives within a star-forming cluster that may drive dynamical evolution of the binary-planet system. We perform numerical simulations of S-type planets, with masses and orbital architecture analogous to the Solar system’s four gas giants, orbiting within the influence of a $0.5\, \mathrm{M}_{\odot }$ binary companion. The binary-planet system is integrated simultaneously with an embedded stellar cluster environment. ∼10 per cent of our planetary systems are destabilized when perturbations from our cluster environment drive the binary periastron towards the planets. This destabilization occurs despite all of our systems being initialized with binary orbits that would allow stable planets in the absence of the cluster. The planet–planet scattering triggered in our systems typically results in the loss of lower mass planets and the excitement of the eccentricities of surviving higher mass planets. Many of our planetary systems that go unstable also lose their binary companions prior to cluster dispersal and can therefore masquerade as hosts of eccentric exoplanets that have spent their entire histories as isolated stars. The cluster-driven binary orbital evolution in our simulations can also generate planetary systems with misaligned spin–orbit angles. This is typicallymore »done as the planetary system precesses as a rigid disc under the influence of an inclined binary, and those systems with the highest spin–orbit angles should often retain their binary companion and possess multiple surviving planets.

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