Binary star system in the constellation Leo
 ;indicator name="01-sky-coordinates" ; ;templatestyles src="Template:Sky/styles.css" / ;Coordinates: &amp;de=&amp;zoom=&amp;show_grid=1&amp;show_constellation_lines=1&amp;show_constellation_boundaries=1&amp;show_const_names=1&amp;show_galaxies=1&amp;img_source=IMG_all 10h 07m 54s, +09° 59′ 51″ ;/indicator ;
! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000.0      Equinox J2000.0
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Spectral type
! style="text-align:left" | B−V 
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31 Leonis is a binary star system in the equatorial constellation of Leo. The system is visible to the naked eye in unresolved form, having a combined apparent visual magnitude of 4.39. An estimated distance of around 300 light years is obtained from the annual parallax shift of 11.02 mas as seen from Earth's orbit. At the current distance, interstellar extinction between Earth and 31 Leo diminished the apparent brightness by 0.12magnitudes. It is moving away from the Sun with a radial velocity of +39.8 km/s.
The primary member of 31 Leonis, component A, is an evolved K-type red giant with a stellar classification of K3.5 IIIb Fe-1:, where the suffix notation indicates an underabundance of iron in the spectrum. It has expanded to 34 times the Solar radius and is radiating around 283 times the Sun's luminosity from its photosphere at an effective temperature of 4,066 K. The magnitude 13.6 secondary, component B, lies at an angular separation of 7.9 arcseconds, as of 2008.
References.
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