2002/08/07 by Lars Bildsten · 2 citations
Earth and Planetary Sciences · Physics and Astronomy · #Adiabatic process #Angular momentum #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Classical mechanics #High-pressure geophysics and materials #Instability #Low Mass #Mechanics #Millisecond #Millisecond pulsar #Orbital period #Physics #Pulsar #Pulsars and Gravitational Waves Research #RADIUS #Roche lobe #Stars #Thermodynamics #White dwarf #astro-ph
paper · pdf · doi:10.1086/344085
published as Astrophys.J. 577 (2002) L27-L30 · to appear in Astrophysical Journal Letters
arxiv created 2002/08/07 · openalex publication_date 2002/09/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
The discovery of two accreting millisecond X-ray pulsars in binaries with ≈43 minute orbital periods allows for a new probe of the donor's structure. For XTE J1751-305, only a hot white dwarf (WD) can fill the Roche lobe. A cold He WD is a possible solution for XTE J0929-314, although I will show that evolutionary arguments make a hot WD more likely. In addition to being larger than the T = 0 models, these finite entropy, low-mass ( M c < 0.03 M ☉ ) WDs have a minimum mass for a fixed core temperature. If they remain hot as they lose mass and expand, they can "evaporate" to leave an isolated millisecond radio pulsar. They also adiabatically expand upon mass loss at a rate faster than the growth of the Roche radius if the angular momentum deposited in the disk is not returned to the donor. If the timescale of the resulting runaway mass transfer is shorter than the viscous timescale in the outer disk, then the mass transfer instability of Ruderman & Shaham for He WDs would be realized. However, my estimates of these timescales still make the instability unlikely for adiabatic responses. I close by noting the possible impact of finite temperature WDs on our understanding of AM CVn binaries.