Tycho-B: an unlikely companion for SN 1572

TL;DR

This study investigates whether Tycho-B is a surviving companion of SN 1572 by analyzing its UV spectrum and distance, finding no evidence of Fe absorption and suggesting it is likely a foreground star.

Contribution

The paper provides the first UV spectral analysis of Tycho-B to test its association with SN 1572, offering insights into the nature of potential supernova companions.

Findings

No Fe II absorption detected in Tycho-B's spectrum.

Tycho-B's luminosity distance indicates it is likely a foreground star.

Fe in Tycho's SNR may be more highly ionized than expected.

Abstract

If some or all Type Ia SNe arise from accretion onto a massive WD from a companion, then the companion will remain in some form after the SN explosion. Tycho-B is an unusual, relatively hot star along the line of sight to Tycho's SNR -- conclusively shown to be a Type Ia -- and has been suggested as such a companion. If the interior of Tycho's SNR contains unshocked Fe, and if Tycho-B is either within the SNR shell or in the background, then one might hope to see evidence of this in the UV spectrum. Such is the case for SN\,1006, where spectra of the background Schweizer-Middleditch star, as well as two AGNs, show broad absorption lines of Fe II. To test this idea, we have used STIS on HST to obtain a UV spectrum of Tycho-B. The observed spectrum, however, shows no evidence of Fe II absorption. Furthermore, a luminosity distance estimate using UV and optical spectra of Tycho-B suggests that the star is consistent with a foreground interloper. We conclude either that Tycho B is nearer than Tycho's SNR, or that all of the Fe in the interior of Tycho's SNR is more highly ionized.