The Evolution of Helium White Dwarfs: Applications to Millisecond Pulsars
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We present a grid of evolutionary tracks for low-mass white dwarfs with helium cores in the mass range from 0.179 to 0.414 M_sun. The lower mass limit is well suited for comparison with white dwarf companions of millisecond pulsars (MSP). The derived cooling ages are of the order of 10^9 yrs due to residual nuclear burning. The cooling ages are consistent with age estimations of MSP systems based on the pulsars' spin-down. For example, for the system PSR 1012+5307 we derived a white dwarf cooling age of 6 +/-1 Gyr in good agreement with the spin-down age of 7 Gyr. For the companion mass we found M=0.19 +/- 0.02 M_sun. We studied other MSP systems as well selecting only systems with well given ages and/or masses, and determined the effective temperatures and surface gravities of the companion white dwarfs with the present evolutionary models.
2 pages, 1 figure, also available from http://www.mpifr-bonn.mpg.de/div/speckle/publications.html, to appear in: Pulsar Astronomy - 2000 and Beyond, IAU Coll. 177, M. Kramer, N. Wex, R. Wielebinski (eds.), ASP Conf. Series
2 pages, 1 figure, also available from http://www.mpifr-bonn.mpg.de/div/speckle/publications.html, to appear in: Pulsar Astronomy - 2000 and Beyond, IAU Coll. 177, M. Kramer, N. Wex, R. Wielebinski (eds.), ASP Conf. Series