1 Serpentis (1 Ser) is ared giant in theconstellationVirgo with anapparent magnitude of 5.5. It is ared clump giant, a coolhorizontal branch star that is fusing helium in its core.[4] It has expanded to over 13 times the radius of theSun and although it is cooler at4,581 K it is 77 times more luminous. It is 322 light years away.
TheFlamsteed designation 1 Serpentis was given to the star when the constellationSerpens was combined with the constellationOphiuchus.[7] It was also given theBayer designationM Serpentis. When Ophiuchus and Serpens were separated into distinct constellations, 1 Serpentis was left over the border inLibra. Since then it has moved slightly and is now inVirgo.[8]
A 10th-magnitude companion star discovered byWilliam Herschel is86″ away.[9] It is at the same distance as 1 Ser and shares acommon proper motion,[10] It is considered likely to be a physical companion,[11] with the two stars separated by8,600 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]
^Houk, N.; Swift, C. (1999). "Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars, Vol. 5".Michigan Spectral Survey.5.Bibcode:1999MSS...C05....0H.
