Acrux (Alpha Crucis)
A moderate telescope shows two similar B stars separated by 4 arc-seconds. Alpha1 is a B subgiant (visual magnitude 1.4, luminosity 25,000 Lsun, surface temperature 28,000 K). Alpha2, a B dwarf (visual magnitude 2.09, luminosity 16,000 Lsun, temperature 26,000 K).
Alpha2 is a 13-Msun single star but Alpha1 is a spectroscopic binary whose 14- and 10-Msun components are separated by about one AU and complete an orbit every 76 days. Alpha1 and Alpha2, with a minimum separation of 430 AU, take at least 1,500 years to circle around each other. Another B subgiant lies 90" away from the triplet but, despite its similar velocity through space, is probably a more distant star that happens to lie along the same line of sight.
Related entry• brightest stars
Related category• NOTABLE STARS
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