1 Serpentis (1 Ser) is a
red giant in the
constellationVirgo 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 designationM 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]
^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.
^
abStephenson, C. B. (1960). "A study of visual binaries having primaries above the main sequence". The Astronomical Journal. 65: 60.
Bibcode:
1960AJ.....65...60S.
doi:
10.1086/108191.