Browsing by Subject "low-mass white dwarf"
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Item Constraining Low-Mass White Dwarf Binaries from Ellipsoidal Variations(2018-07) Bell, K.J.; Hermes, J. J.; Kuszlewicz, J.S.; Castanheira, B.; Vanderbosch, Z.; Montgomery, M.Stars are stretched by tidal interactions in tight binaries, and changes to their projected areas introduce photometric variations twice per orbit. Hermes et al. (2014) utilized measurements of these ellipsoidal variations to constrain the radii of lowmass white dwarfs in eight single-lined spectroscopic binaries. We refine this method here, using Monte Carlo simulations to improve constraints on many orbital and stellar properties of binary systems that exhibit ellipsoidal variations. We analyze the recently discovered tidally distorted white dwarf binary system SDSS J1054-2121 in detail, and also revisit the Hermes et al. (2014) sample. Disagreements in some cases between the observations, ellipsoidal variation model, and Gaia radius constraints suggest that extrinsic errors are present, likely in the surface gravities determined through model atmosphere fits to stellar spectra.Item Evolution and Asteroseismology of Pulsating Low-Mass White Dwarfs(2018-07) Calcaferro, L.M.; Corsico, A.H.; Althaus, L.G.; Romero, A.D.; Kepler, S.O.; Castanheira, B.; Vanderbosch, Z.; Montgomery, M.Many low-mass white dwarfs are being discovered in the field of our galaxy and some of them exhibit g-mode pulsations, comprising the extremely low-mass variable (ELMV) stars class. Although it is generally believed that these stars are characterized by thick H envelopes, the existence of low-mass WDs with thin H envelopes is also possible from stellar evolution considerations. We have performed detailed asteroseismological fits to all the known ELMVs to search for a representative model by employing a set of fully evolutionary models that are representative of low-mass He-core white dwarf stars with a range of stellar masses [0.1554-0.4352]M , effective temperatures [6000 - 10000] K, and also with a range of H envelope thicknesses -5:8 ~< log(MH/M*) ~< -1.7, hence expanding the space of parameters. We found that some of the stars under analysis are characterized by thick H envelopes, but others are better represented by models with a thin H envelope.