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