Four luminous blue variables found to be much closer than previously assumed October 25, 2016 by Tomasz Nowakowski weblog Please Register or Log in to view the hidden image! AG Carinae (AG Car) - an example of a Luminous Blue Variable (LBV) star. Credit: Judy Schmidt/Hubble Space Telescope. (Phys.org)—A new study based on the first Gaia data release (DR1) reveals more accurate measurements of the distance of four canonical luminous blue variables (LBVs) in the Milky Way galaxy. According to a research paper published Oct. 20 on the arXiv server, they are much closer to Earth than previously thought. Published on Sept. 14, 2016, DR1 contains a catalog of over 1 billion stars with precise measurements of their brightness and positions in the sky. These data were obtained by ESA's Gaia satellite, which is completing the first-ever "galactic census"—the most detailed three-dimensional map of the Milky Way ever made. The release of DR1 offers the scientific community an excellent opportunity to improve knowledge of our stellar environment and to redefine some previous calculations. Read more at: http://phys.org/news/2016-10-luminous-blue-variables-closer-previously.html#jCp
https://arxiv.org/pdf/1610.06522v1.pdf The canonical Luminous Blue Variable AG Car and its neighbor Hen 3-519 are much closer than previously assumed ABSTRACT The strong mass loss of Luminous Blue Variables (LBVs) is thought to play a critical role in the evolution of massive stars, but the physics of their instability and their place in the evolutionary sequence remains uncertain and debated. A key to understanding their peculiar instability is their high observed luminosity, which for Galactic LBVs often depends on an uncertain distance estimate. Here we report direct distances and space motions of four canonical Milky Way LBVs— AG Car, HR Car, HD 168607, and (the LBV candidate) Hen 3-519—whose parallaxes and proper motions have been provided by the Gaia first data release. Whereas the distances of HR Car and HD 168607 are consistent with those previously adopted in the literature within the uncertainty, we find that the distances to Hen 3-519 and AG Car, both at ∼2 kpc, are much closer than the 6–8 kpc distances previously assumed. For Hen 3-519, this moves the star far from the locus of LBVs on the HR Diagram. AG Car has been considered a defining example of a classical LBV, but its lower luminosity also moves it off the S Dor instability strip. The lower luminosities allow AG Car and Hen 3-519 to have passed through a previous red supergiant phase, they lower the mass estimates for their shell nebulae, and imply that binary evolution is needed to account for their peculiar properties. These lower luminosities and initial masses for LBVs may also have important implications for understanding LBVs as potential supernova progenitors. Improved distances from next year’s Gaia data release, which will include additional LBVs, may alter our traditional view of LBVs. 1
