Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse supernovae (SNe), which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB)
. In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of a massive white dwarf (WD) in a close binary. Here we investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequently be recycled to form MSPs and, if so, how they can observationally be distinguished from pulsars formed via the standard core-collapse SN channel in terms of their masses, spins, orbital periods and space velocities. Numerical calculations with a detailed stellar evolution code were used for the first time to study the combined pre- and post-AIC evolution of close binaries. We investigated the mass transfer onto a massive WD in 240 systems with three different types of non-degenerate donor stars: main-sequence stars, red giants, and helium stars. When the WD is able to accrete sufficient mass (depending on the mass-transfer rate and the duration of the accretion phase) we assumed it collapses to form a NS and we studied the dynamical effects of this implosion on the binary orbit. Subsequently, we followed the mass-transfer epoch which resumes once the donor star refills its Roche lobe and calculated the continued LMXB evolution until the end. We demonstrate that the final properties of these MSPs are, in general, remarkably similar to those of MSPs formed via the standard core-collapse SN channel. However, the resultant MSPs created via the AIC channel preferentially form in certain orbital period intervals. Finally, we discuss the link between AIC and young NSs in globular clusters. Our calculations are also applicable to progenitor binaries of SNe Ia under certain conditions. [Abridged]
Recent studies find that some early-type galaxies host Type II or Ibc supernovae (SNe II, Ibc). This may imply recent star-formation activities in these SNe host galaxies, but a massive star origin of the SNe Ib so far observed in early-type galaxies
has been questioned because of their intrinsic faintness and unusually strong Ca lines shown in the nebular phase. To address the issue, we investigate the properties of early-type SNe host galaxies using the data with Galaxy Evolution Explore(GALEX) ultraviolet photometry, and the Sloan Digital Sky Survey (SDSS) optical data. Our sample includes eight SNe II and one peculiar SN Ib (SN 2000ds) host galaxies as well as 32 SN Ia host galaxies. The host galaxy of SN 2005cz, another peculiar SN Ib, is also analysed using the GALEX data and the NASA/IPAC Extragalactic Database (NED) optical data. We find that the NUV-optical colors of SN II/Ib host galaxies are systematically bluer than those of SN Ia host galaxies, and some SN II/Ib host galaxies with NUV-r colors markedly bluer than the others exhibit strong radio emission. We perform a stellar population synthesis analysis and find a clear signature of recent star-formation activities in most of the SN II/Ib host galaxies. Our results generally support the association of the SNe II/Ib hosted in early-type galaxies with core-collapse of massive stars. We briefly discuss implications for the progenitors of the peculiar SNe Ib 2000ds and 2005cz.
