54 Leonis
Binary of two rapidly rotating A-type stars 321 light years away.
54 Leonis is a binary star system in the constellation Leo, roughly 321 light-years from the Sun. With a combined apparent magnitude of 4.30, it appears as a faint white star to the naked eye. The two stars are separated on the sky by 6.60 arcseconds at a position angle of 113°, as measured in 2017, which corresponds to a physical distance of about 533 AU (79,700 Gm).
The primary star, component A, has a magnitude of 4.477 and is classified as an A0 V main-sequence star, meaning it fuses hydrogen in its core. It spins rapidly, with a projected rotational velocity of 185 km/s, causing an oblate shape where the equatorial radius is about 8% larger than the polar radius. This star is roughly 411 million years old, with 2.4 times the Sun's mass and 4.9 times its radius.
The secondary, component B, is fainter at magnitude 6.29 and is also an A-type main-sequence star, class A2 Vn. The "n" suffix indicates broad, nebulous spectral lines due to its even faster rotation—a projected rotational velocity of 250 km/s. Its radius is about twice that of the Sun.
On March 3, 2013, at 01:48, the asteroid 729 Watsonia occulted the star HIP 53417.
- Distance
- 321 light years
- Combined apparent visual magnitude
- 4.30
- Angular separation (as of 2017)
- 6.60″
- Position angle (as of 2017)
- 113°
- Physical separation
- 533 AU (79,700 Gm)
- Primary (component a) magnitude
- 4.477
- Primary spectral type
- A0 V
- Primary mass
- 2.4 solar masses
- Primary radius
- 4.9 solar radii
- Primary projected rotational velocity
- 185 km/s
Lore & Background
The primary, component A, is an A-type main-sequence star with a stellar classification of A0 V, indicating it generates energy through hydrogen fusion at its core. It has a high rate of spin, with a projected rotational velocity of 185 km/s, giving it an oblate shape with an equatorial bulge estimated to be 8% larger than the polar radius. The star is roughly 411 million years old, with 2.4 times the mass of the Sun and about 4.9 times the Sun's radius.
The fainter secondary, component B, is a smaller A-type main-sequence star with a class of A2 Vn. The 'n' suffix indicates wide 'nebulous' lines due to rapid rotation. It spins with an even higher projected rotational velocity of 250 km/s and has about twice the Sun's radius. As of 2017, the pair had an angular separation of 6.60″ along a position angle of 113°, with a physical separation of around 533 AU (79,700 Gm).
Reader's Guide
The system 54 Leonis is notable as a binary composed of two A-type main-sequence stars, both exhibiting rapid rotation that distorts their shapes. The primary's oblate shape, with an equatorial bulge 8% larger than its polar radius, is a direct consequence of its high spin. The secondary's even faster rotation (250 km/s) and its 'A2 Vn' classification highlight the prevalence of rapid rotation among such stars. The physical separation of about 533 AU indicates a wide binary, where the components are far enough apart to have evolved independently. The system's combined magnitude of 4.30 makes it a faint naked-eye target in Leo. An occultation event involving asteroid 729 Watsonia and the star HIP 53417 occurred on March 3, 2013, providing a rare observational opportunity. The system serves as an example of how rotation affects stellar structure and classification in binary systems.
Did You Know?
- The primary star has an equatorial bulge 8% larger than its polar radius due to rapid rotation.
- The secondary star spins at a projected rotational velocity of 250 km/s, faster than the primary's 185 km/s.
- Asteroid 729 Watsonia occulted HIP 53417 on March 3, 2013 at 01:48.
- The pair's physical separation is about 533 AU, or 79,700 Gm.
More in Binary and Multiple Stars, Part 2 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced