skip to main content

Search for: All records

Creators/Authors contains: "Bauer, Evan B."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract Binary systems of a hot subdwarf B (sdB) star + a white dwarf (WD) with orbital periods less than 2–3 hr can come into contact due to gravitational waves and transfer mass from the sdB star to the WD before the sdB star ceases nuclear burning and contracts to become a WD. Motivated by the growing class of observed systems in this category, we study the phases of mass transfer in these systems. We find that because the residual outer hydrogen envelope accounts for a large fraction of an sdB star’s radius, sdB stars can spend a significant amount of time (∼tens of megayears) transferring this small amount of material at low rates (∼10 −10 –10 −9 M ⊙ yr −1 ) before transitioning to a phase where the bulk of their He transfers at much faster rates ( ≳10 −8 M ⊙ yr −1 ). These systems therefore spend a surprising amount of time with Roche-filling sdB donors at orbital periods longer than the range associated with He star models without an envelope. We predict that the envelope transfer phase should be detectable by searching for ellipsoidal modulation of Roche-filling objects with P orb = 30–100 minutes andmore »T eff = 20,000–30,000 K, and that many (≥10) such systems may be found in the Galactic plane after accounting for reddening. We also argue that many of these systems may go through a phase of He transfer that matches the signatures of AM CVn systems, and that some AM CVn systems associated with young stellar populations likely descend from this channel.« less
  2. Abstract

    We present the discovery of a new double-detonation progenitor system consisting of a hot subdwarf B (sdB) binary with a white dwarf companion with aPorb= 76.34179(2) minutes orbital period. Spectroscopic observations are consistent with an sdB star during helium core burning residing on the extreme horizontal branch. Chimera light curves are dominated by ellipsoidal deformation of the sdB star and a weak eclipse of the companion white dwarf. Combining spectroscopic and light curve fits, we find a low-mass sdB star,MsdB= 0.383 ± 0.028Mwith a massive white dwarf companion,MWD= 0.725 ± 0.026M. From the eclipses we find a blackbody temperature for the white dwarf of 26,800 K resulting in a cooling age of ≈25 Myr whereas ourMESAmodel predicts an sdB age of ≈170 Myr. We conclude that the sdB formed first through stable mass transfer followed by a common envelope which led to the formation of the white dwarf companion ≈25 Myr ago. Using theMESAstellar evolutionary code we find that the sdB star will start mass transfer in ≈6 Myr and in ≈60 Myr the white dwarf will reach a total mass of 0.92Mwith a thick helium layer of 0.17M. This will lead to a detonation that will likely destroymore »the white dwarf in a peculiar thermonuclear supernova. PTF1 J2238+7430 is only the second confirmed candidate for a double-detonation thermonuclear supernova. Using both systems we estimate that at least ≈1% of white dwarf thermonuclear supernovae originate from sdB+WD binaries with thick helium layers, consistent with the small number of observed peculiar thermonuclear explosions.

    « less
  3. Abstract

    We explore changes in the adiabatic low-order g-mode pulsation periods of 0.526, 0.560, and 0.729Mcarbon–oxygen white dwarf models with helium-dominated envelopes due to the presence, absence, and enhancement of22Ne in the interior. The observed g-mode pulsation periods of such white dwarfs are typically given to 6−7 significant figures of precision. Usually white dwarf models without22Ne are fit to the observed periods and other properties. The rms residuals to the ≃150−400 s low-order g-mode periods are typically in the range ofσrms≲ 0.3 s, for a fit precision ofσrms/P≲ 0.3%. We find average relative period shifts of ΔP/P≃ ±0.5% for the low-order dipole and quadrupole g-mode pulsations within the observed effective temperature window, with the range of ΔP/Pdepending on the specific g-mode, abundance of22Ne, effective temperature, and the mass of the white dwarf model. This finding suggests a systematic offset may be present in the fitting process of specific white dwarfs when22Ne is absent. As part of the fitting processes involves adjusting the composition profiles of a white dwarf model, our study on the impact of22Ne can provide new inferences on the derived interior mass fraction profiles. We encourage routinely including22Ne mass fraction profiles, informed by stellar evolution models, to futuremore »generations of white dwarf model-fitting processes.

    « less