No surviving companion in Kepler's supernova

TL;DR

A detailed survey of Kepler's supernova remnant found no evidence of a surviving companion star, supporting scenarios where the explosion originated from double-degenerate or core-degenerate systems rather than a single companion.

Contribution

This study provides the deepest search to date for a companion star in Kepler's supernova remnant, constraining the progenitor models through high-resolution spectroscopy and proper motion analysis.

Findings

No fast rotating companion stars detected

Stellar velocities consistent with Galactic models

Luminosity limits favor double-degenerate or core-degenerate scenarios

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 solar luminosities in the 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 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 vrot sin i are very well determined. There are no fast rotating stars as vrot sin i < 20 km/s. The radial velocities from the spectra and the proper motions determined from HST images are compatible with those expected from the Besan\c{c}on 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.