Alcor B is a red dwarf orbiting Alcor, a small cool star found only recently because the glare of its bright white companion had hidden it.
At a glance
| type | red dwarf (class M) |
|---|---|
| distance from the Sun | 84.7 light-years (26 pc) |
| its light left it | 84.7 years ago |
| luminosity | 0.03 × the Sun |
| radius | 0.3 × the Sun |
| surface temperature | 3,200 K |
Read off the piece’s own catalogue, the same values it draws with.
About Alcor B
Alcor B is a red dwarf, a star much smaller, cooler and dimmer than the Sun. It orbits Alcor closely enough on the sky that it was lost in the white star’s glare until adaptive optics, which correct the blurring of the atmosphere, picked it out. Two separate teams reported it independently.
Its discovery mattered for the Mizar–Alcor question: the companion shares Alcor’s motion, and the system as a whole strengthens the case that Alcor travels with Mizar, making the group a family of six stars.
Red dwarfs are the most common stars in the Galaxy, yet almost none can be seen with the naked eye; Alcor B is no exception.
What you see in the piece
Fly to Alcor and B appears as a dim red point near the white star; its colour is its cool surface, and from Earth it is far below what the eye can see.
Questions
Does Alcor have a companion?
Yes. Alcor B is a red dwarf close to Alcor, found with adaptive optics after the bright star’s glare had hidden it.
How hot is Alcor B?
Its surface is about 3,200 K, which is why it is red, and it shines only 0.03 × the Sun.