| Description |
We discovered more than 400 compact shells in the MIPSGAL 24 microns survey of the Galactic plane. While only 10% of them are detected at shorter wavelengths, about a third are visible in the MIPSGAL 70 microns survey. About 15% of all the objects have been identified previously as planetary nebulae, supernova remnants, Wolf-Rayet stars, luminous blue variables. Spectroscopic follow-ups on a limited sample in the near-IR and mid-IR have revealed several dust-free planetary nebulae with very hot central white dwarf as well as a significant increase in the number of WR/LBV candidates. The remaining 350 or so unknown bubbles are also expected to be evolved stages of low- to high-mass stars that could account for the missing evolved stars in the Galaxy.
To determine the true nature of a significant fraction of the unidentified bubbles, we propose to observe 35 of the brightest objects in the MIPSGAL 70 microns images with PACS Range Spectroscopy. With these data we will constrain the origin of their far-IR emission. Comparing the proposed spectroscopic to those of known evolved stars from the MESS Guaranteed Time Key Program will allow us to unequivocally identify the MIPSGAL bubbles. The richness of the far-IR emission spectrum of these evolved stellar objects will also provide us with dust and gas (atomic and molecular) features, with which we will characterize in details the physical conditions within each bubble thanks to modeling of these features.
Unveiling hidden details of star and galaxy formation and evolution is the Herschel observatory.s statement, as the mission brochure.s cover shows. The observations that we propose here are in perfect resonance with that statement as we aim at lifting the veil on evolved stars hidden in the Galaxy. Furthermore, we propose observations that will build a synergy between two Key Programs (HiGAL and MESS). |
