35 Leonis

35 Leonis (HIP 53019, HD 89010) is a spectroscopic binary star system located in the constellation of Leo, next to the star Zeta Leonis. It is made up of a yellow subgiant star and a red dwarf star, which complete an orbit between each other every 537 days. With an apparent magnitude of 5.97, the system can be naked-eye visible only from dark skies. The distance to 35 Leonis, based from data from Gaia DR3, is 31.83 pc.

Properties
35 Leonis was discovered to be a binary system in 2024, after analysis from Daniel Echeverri et al. using vortex fiber nulling, which is a technique for detecting and characterizing faint stellar companions that are close to their parent star. The team derived a visual separation of 56.9 milliarcseconds between both components (35 Leonis A and B) using the CHARA array. Both stars are completing one orbit around each other every 537 day. The system classifies as a single-lined spectroscopic binary (SB1).

35 Leonis is located in the constellation of Leo, visually close to the star Zeta Leonis. The distance to the system is about 31.8 pc, as derived by Gaia DR3. With an apparent magnitude of 5.97, it is very faint and can be visible to the naked eye only in dark skies, not affected by light pollution. The absolute magnitude, i.e. the brightness of 35 Leonis if it was seen 10 pc away, is 3.56. The system is approaching Earth at a velocity of 33.8km/s. 35 Leonis the Flamsteed designation. Other designations for this system include HD 89010 from the Henry Draper Catalogue, HIP 53019 from the Hipparcos Catalogue and HR 4030 from the Bright Star Catalogue.

35 Leonis A
The main component, 35 Leonis A, is an evolved G-type main-sequence star that is evolving into a subgiant, based on its spectral class of G1.5V-IV. Gaia DR2 gives a radius of and a luminosity of, while Deka-Szymankiewicz et al. (2018) gives a luminosity of  and a radius of. The effective temperature of 35 Leonis A is $-200.342$ and its mass is. Other values for the temperature includes 5686 K from Deka-Szymankiewicz et al. and 5682.25 and 5705.7 K from Gaia DR2 and DR3 respectively. The age of the star is around 5.25 billion years, which is around 14% older than the Solar System.

35 Leonis B
The secondary component, 35 Leonis B, is a red dwarf star. It was detected in 2024 by Echeverri et al. The mass of 35 Leonis B is estimated at, based on a mass of for the primary component (35 Leonis A) and a mass ratio of 0.11. An effective temperature of $32.03$ and an upper limit in the rotational velocity of $2.12$ are derived from the vortex fiber nulling's parameters. Other characteristics, such as the radius and luminosity, are unknown.