Photo: ESO Online Digitized Sky Survey
Chemically most unusual star: GY Andromedae
On this blue star Promethium can be found, a very rare and radioactive chemical element. This is known from no other star. This is astonishing, because even the most stable Promethium isotope has a half-life of only 17.7 years.
Therefore the Promethium must be continuously created anew by the star. How it does this is not known.
From its state of development GY Andromedae reminds of Alpha-2 Canum Venaticorum. The star is orbited by an invisible companion every 273 days.
Constellation: Andromeda
Distance: 455 light-years
Spectral class: B9pe
Visual magnitude: 6.27 - 6.41
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