Removing the hydrogen-rich layers from a main sequence star exposes the helium-rich core. Such stripped helium stars are known at high and low masses, but not at intermediate masses, despite theoretical predictions that they should be common. In a new study, astronomers from the University of Toronto and elsewhere used ultraviolet photometry to identify candidate stripped helium stars in two nearby dwarf galaxies — the Large and Small Magellanic Clouds — and then observed 25 such candidate stars with optical spectroscopy. Most of these systems were shown to be binary systems, in which the companion stars probably stripped the outer hydrogen-rich layers off the helium stars.
The hydrogen-rich outer layers of massive stars can be removed by interactions with a binary companion.
Theoretical models predict that this stripping produces a population of hot helium stars of 2 to 8 solar masses, however, only one such system has been identified until now.
“This was such a big, glaring hole. If it turned out that these stars are rare, then our whole theoretical framework for all these different phenomena is wrong, with implications for supernovae, gravitational waves, and the light from distant galaxies,” said Dr. Maria Drout, an astronomer at the University of Toronto.
“This finding shows these stars really do exist.”
“Going forward, we are going to be able to do much more detailed physics with these stars.”
“For example, predictions for how many neutron star mergers we should see are dependent on the properties of these stars, such as how much material comes off of them in stellar winds.”
“Now, for the first time, we’ll be able to measure that, whereas people have been extrapolating it before.”
Dr. Drout and her colleagues designed a new survey to look in the ultraviolet part of the spectrum where extremely hot stars emit most of their light.
Using data from the Swift Ultra-Violet/Optical Telescope, the astronomers collected brightnesses…
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