Massive Stellar Content of the Galactic Supershell GSH 305+01-24
  The distribution of OB stars along with that of H$\alpha$, $^{12}$CO, dust
infrared emission, and neutral hydrogen is carried out in order to provide a
more complete picture of interactions of the young massive stars and the
observed supershell GSH 305+01-24. The studied field is located between
$299^\circ \le l \le 311^\circ$ and $-5^\circ \le b \le 7^\circ$. The
investigation is based on nearly 700 O-B9 stars with $uvby\beta$ photometry
currently available. The derived stellar physical parameters were used to
establish a homogeneous scale for the distances and extinction of light for
major apparent groups and layers of foreground and background stars in
Centaurus and study the interaction with the surrounding interstellar medium.
The distance to the entire Centaurus star-forming complex is revised and a
maximum of the OB-star distance distribution is found at 1.8$\pm$0.4 (r.m.s)
kpc. The massive star component of GSH 305+01-24 is identified at about 85-90 %
completeness up to 11.5-12 mag. The projected coincidence of the OB stars with
the shell and the similarities between the shell's morphology and the OB-star
distribution indicate a strong interaction of the stellar winds with the
superbubble material. We demonstrate that these stars contribute a sufficient
wind injection energy in order to explain the observed size and expansion
velocity of the supershell. The derived stellar ages suggest an age gradient
over the Coalsack Loop. A continuous star-formation might be taking place
within the shell with the youngest stars located at its periphery and the open
cluster NGC 4755 being the oldest. A layer of very young stars at 1 kpc is
detected and its connection to both GSH 305+01-24 and the foreground GSH
304-00-12 H I shells is investigated.
