The system consists of two F-type stars more massive and hotter than the Sun. Both objects are larger than typical F-type main-sequence stars, which may be because they are evolving away from the main sequence. As such, they both received the luminosity class V-IV, with their spectra indicating an intermediate luminosity between main-sequence stars and subgiants.[4]
The two stars orbit each other every 1.094 days, separated by a mere 6.41 solar radii. As a result, both of them are gravitationally distorted and overfilling their Roche lobes, becoming a W Ursae Majoris variable (also known as a low mass contact binary).[4]
Observational history
YY CMi was first reported to be variable in August 1934 by Otto Morgenroth of the Sonneberg Observatory, who described it as an Algol variable with a magnitude range of 8.4 to 8.8.[9] The 1958 edition of the General Catalogue of Variable Stars listed it as a Beta Lyrae variable with a combined spectral type of F5. Krishna Damodar Abhyankar (1962) gave the spectral types F6III and A5V to the two components,[10] though this was noted to be incorrect in 1970 and, in 1981, the two were reclassified as evolved stars of roughly the types F6 and early G comprising a contact binary.[11] This evolved and contact nature of the system has been supported by subsequent studies,[12] but a re-examination of Abhyankar's light curves in 1999 yielded slightly earlier evolutionary stages and spectral types for the stars.[4]
^ abHøg, E.; et al. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars". Astronomy and Astrophysics. 355 (1): L27 –L30. Bibcode:2000A&A...355L..27H.
^ abCutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
