Pearce's Star (AO Cassiopeiae) -- Binary Star in Cassiopeia
A Very Luminous Binary Star
AO Cassopeiae (Pearce’s Star) is one of the most massive double-stars known.
Both stars are type O blue-giants. It is still uncertain how massive they are. The
primary-star’s mass is estimated to be between 20.30 and 57.75 times that of our
sun while the secondary-star is estimated to be between 14.8 and 31.73 times that
of our sun. These two massive stars are orbiting each other every 3.52 days. They
are so close that, at least the primary star, is tear-shaped and very possibly sending
material into the secondary star; thus, becoming what is known as a Contact Binary
Star. The two stars eclipse each other as seen from Earth and therefore the
magnitude changes from 6.07 to 6.24 every couple of days. Stars this massive and this
close to each other are doomed for a violent end to their short lives.
I first read about this impressive binary star system while looking through Kanipe
& Webb’s “Annals of the Deep Sky, Volume 4” a few months ago. When I read about
this impressive binary system, I knew I had to see it for myself (even if it would only
appear as a single star in any telescope). With a bright-gibbous moon in the sky, it was
a perfect night to hunt for Pearce’s Star and get a drawing. Note that some star charts
label the star as “AO” while others do not label it at all, so check a couple of sources to
pin down its exact location before to take a look at it for yourself.