Ylva Götberg’s second paper on the spectra of the stripped stars stripped is now accepted, featuring “obese subdwarfs”, “underweight Wolf-Rayet stars” and everything in between, including a demonstration of why astronomers are effectively colorblind, making these stars nearly invisible to us when they have a companion.
Y. Götberg, S. E. de Mink, J. H. Groh, T. Kupfer, P. A. Crowther, E. Zapartas, M. Renzo (2018) “Spectral models for binary products: Unifying Subdwarfs and Wolf-Rayet stars as a sequence of stripped-envelope stars”, accepted for publication in Astronomy and Astrophysics, preprint available here https://arxiv.org/abs/1802.03018.
Abel investigated the binary system ϕ Persei, using new data by Douglas Gies and collaborators. The system contains one star, a subdwarf, with about the same mass as the Sun, but it is 10 times hotter and nearly 10,000 times brighter. It contains a second star, a Be star, that is nearly 10 times as massive as the Sun, which is spinning very rapidly. It is thought that the hot star is the remaining core of a star that has lost its envelope, transferring part of it to the companion which is now spinning very fast.
A. Schootemeijer, Y. Gotberg, S. E. de Mink, D. R. Gies, E. Zapartas, Clues about the scarcity of stripped-envelope stars from the evolutionary state of the sdO+Be binary system phi Persei, accepted for publication in A&A, 2018 https://arxiv.org/abs/1803.02379 Continue reading
Published in Science 05 Jan 2018, “The number of stars that form at each mass is known as the initial mass function (IMF). For most masses, the IMF follows a power-law distribution, first determined by Edwin Salpeter in 1955. Fabian Schneider et al. used observations of the nearby star-forming region 30 Doradus (also known as the Tarantula Nebula) and combined these with stellar modeling to determine its IMF. They found more stars above 30 solar masses than predicted by the Salpeter distribution. Because the most massive stars also have the biggest influence on their surroundings—for instance, through ultraviolet radiation, stellar winds, supernova explosions, and production of heavy elements—this excess will have wide-ranging implications. ” Editor summary in journal science.
Guinness World Records 2017 book included massive overcontact binary VFTS 352 that was found in Tarantula Survey. (Quotation is not correct, but still cool this reached popular press so well. Clearly thanks to Luis Calçadaincredible artist impression.) `
Ylva’ Götberg’s paper has been accepted for publication in the journal Astronomy and Astrophysics. Find a link to the forthcoming paper here. She computed the first tailor made models for the structure, evolution and atmospheres of the very hot stars that can from in binary systems when a star loses its envelope by interaction with a companion. She shows that these stars emit most of their light as ionizing photons, at wavelengths so short that none of the currently existing astronomical facilities can actually detect them. This first paper explores how metallicity affects these stars, i.e. are stripped stars in our own galaxy different from stripped stars that formed in the early days of the universe when there were less metals available? Stay tuned for more. Further papers to come out soon.
All stars lose mass, in part in the form of a stellar wind. (Even our sun does so, which most known for the beautiful aurora that can be seen) How strong these winds are is not known very well. Measurements are affected by uncertainties such as how smooth or how clumped such winds are. Mathieu Renzo undertook a very careful study to investigate how the various prescriptions for stellar winds and their uncertainties affect the final mass and structure of stars. His paper is accepted for publication and can be obtained here.