Wind-accretion induced rapid rotation and a new class of active star

A physical model is presented to explain the occurrence of wide binary systems discovered at EUV wavelengths, such as 2RE J0044+093, which consist of a hot white dwarf and an ultra-rapidly rotating K-dwarf. It is difficult to explain the rapid rotation of the K-dwarf as a consequence of either youth or close binarity because of the length of the evolutionary and cooling time-scales for the white dwarf and the lack of any radial velocity variations. It is proposed that accretion of the slow, massive wind from the asymptotic giant branch (AGB) progenitor of the white dwarf, by the low-mass secondary in a detached configuration, can transfer sufficient angular momentum to produce these systems. For a range of AGB masses, and wind velocities of 10-20 km s(-1), it is found that secondary spin up to periods of less than 10 h can take place for final orbital separations of up to 100 au. If the secondaries are wind-accretion induced, rapidly rotating stars (or WIRRing stars), they could show signs of chemical enrichment in carbon and s-process elements, such as barium, that were present in the AGB wind. The detection of such overabundances would lend firm support for this hypothesis and provide an evolutionary link between WIRRing stars and Barium giants. It is also suggested that the rapidly rotating, late-type central stars of planetary nebulae, such as Abel 35, are the progenitors of WIRRing stars, seen shortly after the mass accretion phase.