Stellar content of the young supershell GSH 305+01-24
  We combine several surveys at different wavelengths with intermediate-band $
uvby\beta$ photometry to examine the correlation between the location of the
OB-stars in the Centaurus star-forming field and the neutral and ionized
material in GSH 305+01$-$24 supershell seen in the same direction. Based on
homogeneous distances of nearly 700 early-type stars, we are able to select
spatially coherent stellar groupings and to revise the classical concept of the
Cen OB1 association. We argue that this star-forming field is closer to the Sun
than estimated before, at a distance of $1.8\pm0.4$ kpc, instead of the
classical 2.5 kpc. The region shows striking similarities between the stellar
distribution and H$\alpha$ and H I emission morphologies, suggesting that the
observed shell passes a stage through which the number of ionizing photons
emerging from the central association is not sufficient to ionize the entire
shell. Stellar masses and ages, calculated via the latest evolutionary models
are used to evaluate whether these stars can be the energy source for the
supershell.
