101 Virginis (also designated CY Boötis) is a red giant variable star located in the constellation Boötes. It was originally catalogued as 101 Virginis by John Flamsteed due to an error in the recorded position. When it was later confirmed as a variable star, it was found to lie within the borders of the constellation Boötes rather than Virgo, and was subsequently given the variable star designation CY Boötis.
Characteristics
101 Virginis is a red giant star of spectral type M3IIIa, currently on the asymptotic giant branch (AGB) of its evolutionary track. Its apparent visual magnitude ranges from approximately 5.74 to 5.90, making it faintly visible to the naked eye under good observing conditions. It is classified as a semi-regular variable star of type SRb. The variability is not strongly defined, but a primary period of about 23 days and a secondary period of about 340 days have been reported.
Distance and Physical Properties
Based on parallax measurements from the Hipparcos and Gaia missions, the star is located at a distance of approximately 970 light-years (about 300 parsecs) from the Sun. It has a radius of roughly 38 to 77 times that of the Sun (estimates vary across sources) and a luminosity approximately 1,080 times that of the Sun. Its effective temperature is around 3,700 K. The star is moving closer to the Sun with a heliocentric radial velocity of approximately −11 km/s.
Binary Status
CY Boötis is listed in the Hipparcos catalogue as a "problem binary" — a star that was suspected of being a multiple system but for which the Hipparcos observations did not yield a satisfactory solution. Subsequent observations have consistently shown it to be a single star.
Designations
In addition to 101 Virginis and CY Boötis, the star is catalogued under numerous other identifiers, including HD 125180, HR 5352, HIP 69829, SAO 100956, BD+15 2690, IRAS 14150+1529, and 2MASS J14172843+1515478, among others.
