1_Serpentis
1 Serpentis
Red giant star in the constellation Virgo
1 Serpentis (1 Ser) is a red giant in the constellation Virgo with an apparent magnitude of 5.5. It is a red clump giant, a cool horizontal branch star that is fusing helium in its core.[3] It has expanded to over 13 times the radius of the Sun and although it is cooler at 4,581 K it is 77 times more luminous. It is 322 light years away.
The Flamsteed designation 1 Serpentis was given to the star when the constellation Serpens was combined with the constellation Ophiuchus.[7] It was also given the Bayer designation M Serpentis. When Ophiuchus and Serpens were separated into distinct constellations, 1 Serpentis was left over the border in Libra. Since then it has moved slightly and is now in Virgo.[8]
A 10th-magnitude companion star discovered by William Herschel is 86″ away.[9] It is at the same distance as 1 Ser and shares a common proper motion,[10] It is considered likely to be a physical companion,[11] with the two stars separated by 8,600 au.[12] It has a spectral type of G5 IV,[12] and it is slightly smaller and less luminous than the sun.[10]
A much more widely-separated 10th-magnitude star is also listed in multiple star catalogues,[9] but it is an unrelated background object.[13]