The discovery of supersoft X-ray sources, described as massive white dwarfs burning accreted matter from their (more massive) companions, opens a new channel to type Ia supernovae (SNe Ia). According to conventional binary evolutionary theory, if the mass ratio of the donor to the white dwarf exceeds a critical value, the mass transfer becomes unstable, and a common envelope will be formed. However, recent calculations by Hachisu, Kato & Nomoto (1996) suggest a strongwind to stabilize the mass transfer when the mass transfer rate is higher than a certain value. Adopting the strong wind assumption, we have performed evolutionary calculations of white dwarf binaries, in which mass transfer occurs through Rochelobe overflow, to search for the progenitors of SNe Ia. We ndthat there are two types of systems that can produce SNe Ia. One is close binaries with ～2 to ～3.5 main-sequence or subgiant companions, and the initial orbital period of several tenth of a day to several days. The other is wide binaries with low-mass (～1M) red giant companions and long initial orbital period (tens to hundreds of days). The derived birth rate of SNe Ia in the Galaxy is roughly consistent with the observed one.

We investigate the spin evolution of the binary X-ray pulsar 2S 0114+650, which possesses the slowest known spin period of ～2.7 hours. We argue that, to interpret such long spin period, the magnetic field strength of this pulsar must be initially >～10 14 G, that is, it was born as a magnetar. Since the pulsar currently has a normal magnetic field ～1012 G, our results present support for magnetic field decay predicted by the magnetar model.

One of the most important questions in the study of compact objects is the nature of pulsars, including whether they are composed of β-stable nuclear matter or strange quark matter. Obser-vations of the newly discovered millisecond X-ray pulsar SAX J1808.4-3658 with the Rossi X-Ray Timing Explorer place firm constraint on the radius of the compact star. Comparing the mass-radius relation of SAX J1808.4-3658 with the theoretical mass-radius relation for neutron stars and for strange stars, we find that a strange star model is more consistent with SAX J1808.4-3658, and suggest that it is a likely strange star candidate.