The puzzling high velocity G5 supergiant star HD 179821 : new insight from Gaia DR2 data. (arXiv:1901.08995v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Parthasarathy_M/0/1/0/all/0/1">M. Parthasarathy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jasniewicz_G/0/1/0/all/0/1">G. Jasniewicz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thevenin_F/0/1/0/all/0/1">F. Th&#xe9;venin</a>

HD 179821 is classified as G5 Ia star. From the IRAS colors and spectral
energy distributions it was classified as a post-AGB star. But some studies
classify it as a massive (30 to 19 Msun ) post-red supergiant evolving to
become a Type II supernova. Its mass and evolutionary status remained a hotly
debated question even after several detailed spectroscopic studies as the
distance was not known. We use the parallax of HD 179821 from the second Gaia
data release, and deduce its distance 2959 +/- 409 pc and its absolute
magnitude MV = -5.7 +/- 0.3. Using the absolute magnitude determined in this
paper, we show that HD 179821 fits very well with post-AGB tracks in the H-R
diagram. Our results clearly confirm that HD 179821 is a post-AGB star of mass
in the range of 0.8 Msun. It is not a 30 Msun red supergiant. The progenitor
mass of this post-AGB star may be in the range of 4 Msun but may be a bit more.

HD 179821 is classified as G5 Ia star. From the IRAS colors and spectral
energy distributions it was classified as a post-AGB star. But some studies
classify it as a massive (30 to 19 Msun ) post-red supergiant evolving to
become a Type II supernova. Its mass and evolutionary status remained a hotly
debated question even after several detailed spectroscopic studies as the
distance was not known. We use the parallax of HD 179821 from the second Gaia
data release, and deduce its distance 2959 +/- 409 pc and its absolute
magnitude MV = -5.7 +/- 0.3. Using the absolute magnitude determined in this
paper, we show that HD 179821 fits very well with post-AGB tracks in the H-R
diagram. Our results clearly confirm that HD 179821 is a post-AGB star of mass
in the range of 0.8 Msun. It is not a 30 Msun red supergiant. The progenitor
mass of this post-AGB star may be in the range of 4 Msun but may be a bit more.

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