The Progenitor of Supernova 2011dh Has Vanished

TL;DR

HST observations confirm the yellow supergiant was the progenitor of SN 2011dh, contradicting earlier models, and suggest a possible surviving companion star detectable in the future.

Contribution

This study provides direct evidence linking the yellow supergiant to SN 2011dh and challenges previous assumptions about the progenitor's nature.

Findings

The progenitor star has vanished after 641 days.

The yellow supergiant was almost certainly the supernova's progenitor.

A surviving companion star may be detectable in the future.

Abstract

We conducted Hubble Space Telescope (HST) Snapshot observations of the Type IIb Supernova (SN) 2011dh in M51 at an age of ~641 days with the Wide Field Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN HST images, has disappeared, implying that this star was almost certainly the progenitor of the SN. Interpretation of the early-time SN data which led to the inference of a compact nature for the progenitor, and to the expected survival of this yellow supergiant, is now clearly incorrect. We also present ground-based UBVRI light curves obtained with the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory up to SN age ~70 days. From the light-curve shape including the very late-time HST data, and from recent interacting binary models for SN 2011dh, we estimate that a putative surviving companion star to the now deceased yellow supergiant could be detectable by late 2013, especially in the ultraviolet. No obvious light echoes are detectable yet in the SN environment.