No Surviving Companion in Kepler's Supernova

Abstract

We have surveyed Kepler¿s supernova remnant in search of the companion star of the explosion. We have gone as deep as 2.6 L ¿ in all stars within 20% of the radius of the remnant. We use FLAMES at the VLT-UT2 telescope to obtain high-resolution spectra of the stellar candidates selected from Hubble Space Telescope (HST) images. The resulting set of stellar parameters suggests that these stars come from a rather ordinary mixture of field stars (mostly giants). A few of the stars seem to have low [Fe/H] (<-1) and they are consistent with being metal-poor giants. The radial velocities and rotational velocities v rot sin i are very well determined. There are no fast rotating stars because v rot sin i < 20 km s-1 for all the candidates. The radial velocities from the spectra and the proper motions determined from HST images are compatible with those expected from the Besançon model of the Galaxy. The strong limits placed on luminosity suggest that this supernova could have arisen either from the core-degenerate scenario or from the double-degenerate scenario.