HD 77191
HD 77191 is a spectroscopic binary composed of a Sun-like variable star and a probable red dwarf, located in the zodiac constellation of Cancer. It has the variable-star designation HL Cancri. With an apparent magnitude of 8.88, it is too faint to be seen by the naked eye but observable using binoculars as a yellow-hued dot of light. It is located at a distance of according to Gaia EDR3 parallax measurements, and is receding from the Sun at a heliocentric radial velocity of 7.10 km/s.
The star is part of the Castor stream, a moving group of young stars that includes some of the brightest stars in the night sky, such as Castor, Fomalhaut, and Vega.
Stellar properties
The primary star is a G-type main-sequence star with the spectral type G0V, almost identical to the Sun in mass, effective temperature, and metallicity, but approximately 7% smaller in radius. Its spectrum shows clear signs of high stellar activity and a strong lithium doublet spectral line at wavelength 6707.8 Å, indicative of its youth, with an estimated age of. Accordingly, the star displays large starspots, which are responsible for slight variations in its brightness, first discovered in 2000 with a mean amplitude of about 0.025 mag and a period of . Hence, the star is classified as a BY Draconis variable.Data collected by Hipparcos suggested that the star was single, but radial velocity observations via the Coravel spectrograph at the University of Cambridge yielded a 44-day period orbit for a binary companion. By matching the primary's rotational velocities measured through Doppler broadening and its photometric period, the mass of the unseen secondary star is placed at roughly 0.38, making it likely a red dwarf.