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A post-asymptotic giant branch (post-AGB) star known as HD 179821 turns out to be significantly less massive than previously thought, according to a new study. Using new data from ESA's Gaia satellite, astronomers found that HD 179821 is not a supergiant, which was suggested by previous observations, but is rather a solar-mass star. The finding is presented in a paper published January 28 on arXiv.org.
Discovered about a century ago, HD 179821 (also designated IRAS 19114+0002) is a star in the constellation of Aquila, surrounded by a detached dust shell. The star is currently classified as a post-AGB supergiant of spectral type G5 Ia.
Observations - HD - Distance - Star - Subject
However, although several spectroscopic observations of HD 179821 have been conducted, the exact distance to this star remains a subject of debate. Some studies suggest that it is located about 19,500 light years from the Earth, while others cite a much closer distance of some 12,700 light years. Discrepancy in the distance estimates leaves uncertainties regarding the star's mass and evolutionary status.
Gaia's second data release, known as Data Release 2 (DR2), has the potential to resolve such uncertainties as it offers high-precision positions, parallaxes and proper motions for more than 1.3 billion sources in the sky. A team of astronomers led by Mudumba Parthasarathy of the Indian Institute of Astrophysics in Bangalore used DR2 data to obtain the parallax of HD 179821, which allowed them to make new distance calculations.
Parallax - HD - Mas - Inference - Procedure
The parallax of HD 179821 was found to be approximately 0.31 mas. Employing an inference procedure developed by other researchers in 2018, Parthasarathy's team calculated...
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