White Dwarf Donors in Ultracompact Binaries: The Stellar Structure of Finite-Entropy Objects

By C. Deloye, L. Bildsten. 2003

139 citations recorded by the source corpus.

We discuss the mass-radius (M-R) relations for low-mass (M < 0.1 M☉) white dwarfs (WDs) of arbitrary degeneracy and evolved (He, C, O) composition. We do so with both a simple analytical model and models calculated by integration of hydrostatic balance using a modern equation of state valid for fully ionized plasmas. The M-R plane is divided into three regions where either Coulomb physics, degenerate electrons, or a classical gas dominates the WD structure. For a given M and central temperature Tc, the M-R relation has two branches differentiated by the model's entropy content. We present the M-R relations for a sequence of constant-entropy WDs of arbitrary degeneracy parameterized by M and Tc for pure He, C, and O. We discuss the applications of these models to the recently discovered accreting millisecond pulsars. We show the relationship between the orbital inclination for these binaries and the donor's composition and Tc. In particular, we find from orbital inclination constraints that the probability XTE J1807-294 can accommodate a He donor is approximately 15%, while for XTE J0929-304 it is approximately 35%. We argue that if the donors in ultracompact systems evolve adiabatically, there should be 60-160 more systems at orbital periods of 40 minutes than at orbital periods of 10 minutes, depending on the donor's composition. Tracks of our mass-radius relations for He, C, and O objects are available in the electronic version of this paper.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/47c69b344f6b191e2e373aa548fdfefe900696e5

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Citations in the corpus

• Detecting gravitational wave emission from the known accreting neutron stars (2008, methodology): “For ultracompact systems with Porb <∼ 80 minutes, the companion must be a white dwarf, a helium star, or a highly evolved helium-rich secondary (Rappaport & Joss 1984; Deloye & Bildsten 2003; Nelemans, Jonker & Steeghs 2006).”
• Formation and evolution of compact binaries in globular clusters – II. Binaries with neutron stars (2007, background): “According to the theory of irradiated disks (Dubus et al. 1999) and the evolution of UCXBs (Deloye & Bildsten 2003),1036 ergs/s is roughly the criticalLX for maintaining persistent accretion. in’t Zand et al. (2007) present a table of 40 persistent X-ray bursters, which shows a striking lowLX pileup”
• Formation of millisecond pulsars with CO white dwarf companions – II. Accretion, spin-up, true ages and comparison to MSPs with He white dwarf companions (2012, background): “…has evolved into a semidegenerate substellar remnant (< 0.08M⊙) – possibly aided by evaporation caused by the illumination from the pulsar following an ultra-compact LMXB phase (Podsiadlowski 1991; Deloye & Bildsten 2003; van der Sluys et al. 2005; Bailes et al. 2011; van Haaften et al. 2012).”
• Six new candidate ultracompact X-ray binaries (2007, background): “…and 2) the donor’s low-mass (i.e., a few hundredths of a solar mass) inner core is stripped from its outer layers yielding an unimpeded view of the ashes of the stellar nuclear burning which can be studied when dumped on a companion neutron star or black hole (e.g., Deloye & Bildsten 2003).”
• Mass transfer between double white dwarfs (2003, methodology): “While on this issue, it is worth emphasizing that we use a zero-temperature mass-radius relation for both white dwarfs, whereas we can expect larger radii for a given mass from finite entropy effects, depending upon the time taken to reach contact (Deloye & Bildsten 2003).”