The five hypervelocity stars are larger and brighter than typical white dwarfs but smaller and dimmer than main-sequence stars
of the same temperature.
* Yellow dwarfs are main-sequence stars
of comparable mass to the Sun, with a surface temperature between 5,300 and 6,000 K.
are all powered by hydrogen fusion in their cores; they're fusing four hydrogen atoms to produce a single atom of helium, and releasing a huge amount of energy in the process.
The third type of potential donor in an AM CVn system is the evolved main-sequence star
. In this case, the secondary star does not cause a common envelope, but fills its Roche lobe near the end of the main sequence (terminal-age main sequence or TAMS).
Either the star is so young that it hasn't finished contracting or so old--about 500 million years--that it has had time to expand its girth after becoming a main-sequence star
. Both explanations could account for the star's low surface gravity.
For nearly a decade, Beta Pictoris has reigned as the only mature, main-sequence star
with an encircling disk of dust - perhaps much like the disk from which our solar system evolved 4.6 billion years ago - that astronomers have clearly imaged.
The white star is an A2 dwarf--a main-sequence star
that's still burning hydrogen in its core.
The secondary is usually a late-type main-sequence star
. In the absence of a significant white dwarf magnetic field, material from the secondary passes through an accretion disc before settling on the surface of the white dwarf.
As many S&cT readers know by now, this otherwise nondescript main-sequence star
in Cygnus displayed a series of unpredictable and unexplained dimmings of its starshine in the four years the Kepler spacecraft observed it (S&T: Feb.
Kappa is itself a close (27") pair of orange giants, which contrast nicely with 8 Herculis, a white 4-class main-sequence star
On April 11th, he found WD 1145 undergoing dimmings that looked similar to cases where a transiting planet sheds material if it orbits too close to a normal, much larger main-sequence star
. Saul Rappaport (MIT) had been the first to report on those finds.
Composed of a white dwarf and a main-sequence star
, the system boasts a massive planet closely orbiting the star.