Astronomers believe the companion star took most of the hydrogen surrounding the exploding main star and continued to burn as a super-hot helium star
"Back in 2009, when we were just starting to understand this class, we predicted these supernovae were produced by a white dwarf and helium star
binary system," said team member Ryan Foley of the University of Illinois at Urbana-Champaign, who helped identify Type Iax supernovae as a new class.
He was also highly skeptical of one of the published conclusions: that the disrupted star was a rare helium star
Where the accretor is always a white dwarf, the donor star can be either a (helium or hybrid) white dwarf, a low-mass helium star or an evolved main-sequence star.
AM CVn stars with a helium-star donor are formed in a similar way, but in this case the giant that causes the common envelope is more massive and produces a helium star rather than a second white dwarf.
In that version, a neutron star slowly spirals in toward a massive helium star
, eventually colliding and producing a cataclysmic explosion of gamma rays.
Our biggest thrill came with discovery of the orbital period of the strange but wonderful helium star
AM Canum Venaticorum.
After its envelope has been dispersed, a high-mass binary consists of a compact helium star
and one that remains on the hydrogen-burning main sequence.
Some white dwarfs are classified as helium stars
as they have very strong helium lines and weak hydrogen lines .
The stellar classes discussed in detail at the conference include R Coronae Borealis stars, extreme helium stars
, Wolf-Rayet central stars of planetary nebulae, white dwarfs, and helium-rich subdwarf O and B stars.
It is thought that the progenitors are either massive helium stars
or a type of very large, very hot stars known as Wolf Rayet stars.
Since the 1940s astronomers have puzzled over the origin of helium stars
, giants much larger and hotter than the Sun but less massive.