LBV phenomenon and binarity: The environment of HR Car
  Luminous blue variable stars (LBVs) are of great interest in massive-star
evolution as they experience very high mass-loss episodes within short periods
of time. HR Car is a famous member of this class in the Galaxy. It has a large
circumstellar nebula and has also been confirmed as being in a binary system.
One means of gaining information about the evolutionary status and physical
nature of LBVs is studying their environments. We investigated the stellar
content within ~100 pc of HR Car and also its circumstellar nebula. Very Large
Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) observations of a
2'x2' region around the star highlight the incompleteness of stellar
classification for stars with magnitudes of V > 13 mag. Eight B0 to B9 stars
have been identified which may lie in close spatial vicinity to HR Car. For a
region with a radius of r =1.2 degree (~100 pc at a distance of 4.8 kpc) around
HR Car, existing catalogs list several late O-type and early B-type stars, but
only one early O-type star. Given the relatively low stellar and nebular masses
in the HR Car system, no early O-type stars and only a few late O-type stars
would be expected in association with HR Car. Instead, HR Car's location in a
point vector diagram suggests that HR Car is not isolated, but is part of a
moving group with a population of B-type stars in a spiral arm, and it has not
received a strong kick from a supernova explosion of a companion star or a
merger event. Potential binary evolution pathways for the HR Car system cannot
be fully explored because of the unknown nature of the companion star.
Furthermore, the MUSE observations reveal the presence of a fast outflow and
"bullets" that have been ejected at intervals of about 400 years. These
features may have been caused by recurrent mass transfer in the system.
