Searching Heavily Obscured Post-AGB Stars and Planetary Nebulae I. IRAS
  Candidates with 2MASS PSC Counterparts
  The transition from the Asymptotic Giant Branch (AGB) to the planetary nebula
(PN) phase is critical in the shaping of PNe. It is suggested that the most
asymmetric PNe are the descendant of massive AGB stars. Since these AGB stars
are believed to evolve into heavily obscured post-AGB stars and PNe, the
compilation of a sample of bona fide obscured post-AGB stars and PNe is
important to help understand the formation of asymmetric PNe. We have used
2MASS, Spitzer GLIMPSE, MSX, and IRAS data in search of the near-IR
counterparts of a sample of 165 presumably obscured IRAS post-AGB and PN
candidates, and DSS red images to identify the optical counterparts among the
objects detected in the near-IR. The IR spectral energy distributions (SEDs) in
the wavelength range from 1 to 100 microns of the sources with unambiguous
near-IR counterparts have been analyzed using appropriate colour-colour
diagrams. We have identified the near-IR counterparts of 119 sources out of the
165 IRAS post-AGB and PN candidates in our sample. The improved astrometric
coordinates of these sources have allowed us to find optical counterparts for
59 of them, yielding a reduced sample of 60 optically obscured post-AGB star
and PN candidates. Among the 119 sources with near-IR counterparts, only 80
have unambiguous identifications in the 2MASS Point Source Catalogue.
