Pi Pegasi -- Optical Double Star in Pegasus
A Collection of Optical Double Stars
In binoculars, the twin bright yellow stars of Pi Pegasi (Pi-1 & Pi-2) standout as an attractive
double. Through the telescope a few dimmer stars lay near Pi-1, which seem to be
associated with it. None of these stars, based on modern measurements, are truly related
(gravitationally bound) to each other. Stars that appear to be doubles/multiples that are
really stars that are distant from each other but fall along the same line-of-sight as seen from
Earth are called Optical Double Stars.
It turns out that Pi-1 is a true binary star, but its companion is too close for amateur
telescopes to separate the pair. I have labeled those stars (B, C, D) that were once thought
to be associated with Pi-1 but are now thought not to be. There is also a star (DE) which is
included in older literature that was thought to also belong to Pi-1, but at magnitude 14.4, it
was too dim for me to see with the refractor from my suburban backyard.
Real or not, the apparent association of stars around, and including, Pi-1 and Pi-2 provide a
pleasing eyepiece view in both binoculars and telescopes.