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Phi Persei

The close double system one million years ago consisted of two stars with 6 times (star B) and 5 times (star A) the mass of the Sun. Then the bigger one started to expand and got swallowed up by its partner nearly completely. Left behind is the hot core of star B, in which still fusion processes take place. It is a visible progenitor star of a white dwarf. Normally this stadium is hidden underneath the surface of a red giant.
On the other hand star A, which without its partner would be nearing its end as well, received a huge amount of fresh hydrogen. Its rotational speed enormously was raised by that and the star got flattened. It is surrounded by a gas disk which is eight times wider than the star itself.

When finally in the far distant future star A will expand, then the tables will turn and star B will consume its hull.

Constellation: Perseus
Age: 10 million years
Distance: 720 light-years
Space between Phi Persei A and B: 1 AU
Orbit period of Phi Persei A and B: 127 days

Phi Persei A

Spectral class: B2Vpe
Visual magnitude: 4.09
Luminosity: 2000 * Sun
Mass: 9 * Sun

Phi Persei B

Visual magnitude: 6
Luminosity: 200 * Sun
Mass: 1 * Sun

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    Phi Persei
Graphic: Bill Pounds

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