HD 93795: a late-B supergiant star with a square circumstellar nebula

TL;DR

This paper reports the discovery of a square-shaped circumstellar nebula around the late-B supergiant star HD 93795, analyzes its properties, and discusses its possible binary merger origin and association with Car OB1.

Contribution

It presents the first identification of a square nebula around HD 93795 and proposes a binary merger scenario for its formation, combining infrared imaging and spectral analysis.

Findings

HD 93795 is a B9 Ia star that recently left the main sequence.

The nebula around HD 93795 is square and axisymmetric, observed at 24 microns.

HD 93795 may be associated with the Car OB1 star cluster.

Abstract

We report the discovery of a square axisymmetric circumstellar nebula around the emission-line star HD 93795 in archival Spitzer Space Telescope 24 micron data. We classify HD 93795 as an B9 Ia star using optical spectra obtained with the Southern African Large Telescope (SALT). A spectral analysis carried out with the stellar atmosphere code FASTWIND indicates that HD 93795 only recently left the main sequence and is evolving redward for the first time. We discuss possible scenarios for the origin of the nebula and suggest that HD 93795 was originally a binary system and that the nebula was formed because of merger of the binary components. We also discuss a discrepancy between distance estimates for HD 93795 based on the Gaia data and the possible membership of this star of the Car OB1 association, and conclude that HD 93795 could be at the same distance as Car OB1.