Unique White Dwarfs Accompanying Recycled Pulsars

Abstract

I introduce the two classes of pulsar, white-dwarfbinaries, and describe for each what we have learned from a specificsystem, PSR J1012+5307 and PSR B0655+64, respectively, summarisingwhat has been done, presenting new results, and discussing what thefuture may hold. Briefly, for the companion of PSR J1012+5307 wefind a DA spectrum, and infer a mass of about 0.16Msun, the lowestamong all spectroscopically identified white dwarfs. Combined with aradial-velocity orbit, a neutron-star mass between 1.5 and 3.2Msun (95%conf.) is derived. The companion of PSR B0655+64 shows strong Swan C2bands, i.e., it is a DQ star. Unlike anything reported for other DQs,however, it shows variations in strength of the bands by a factor two.Most likely, the variations are periodic, with a period of about9.7h. This is substantially shorter than the 1-day orbital period,which can likely be understood in terms of its past evolution.