Regulus 4?

Alpha Leonis A

Regulus is a blue-white main sequence star of spectral and luminosity type B7-8 Va,ne (NASA Stars and Exoplanet Database; Gray et al, 2003; and Mahipal Singh, 1982). The star may have a mass 3.4 times greater than Sol's, 3.14 times its diameter between the poles and 4.16 at the equator (Kenneth Croswell, 2005; McAlister et al, 2005); Henson, et al, 1989; and angular diameter in two colors from a Lunar occultation from Richard R. Radick, 1982), and 140 times its visual luminosity (240 times with ultraviolet). Originally thought to be around 300 million years old, the age of all three stars has recently been revised to around 50 million years old (Kenneth Croswell, 2005; McAlister et al, 2005; and Gerbaldi et al, 2001).

NASA Observatorium


Regulus A is hotter,
brighter, and bluer
than Vega or Sirius A,
but is cooler, dimmer,
and smaller than Spica.


See a discussion of
the "main sequence"
as part of stellar
evolution and death.

As a very young star, Regulus A appears to be a fast rotator with a rotational period of 15.9 hours and a substantial magnetic field around one kG (Kenneth Croswell, 2005; McAlister et al, 2005; Henson, et al, 1989; and Wolstencroft et al, 1981). Due to its fast rotation, the star is somewhat "pumpkin-shaped" (Kenneth Croswell, 2005), as interferometric observations and spectroscopic data suggest that indicate Star A's diameter is about 32 percent greater at the equator than between its poles (McAlister et al, 2005). According to the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 3982, excess infrared emission indicative of dust has been detected. Regulus A is a variable star designated CSV 101099 and NSV 4750. Useful catalogue numbers and designations for the star include: Alp or Alf Leo A, 32 Leo A, HR 3982, GJ 9316 A, Hip 49669, HD 87901, BD+12 2149, SAO 98967, FK5 380, Wo 9316 A, LTT 12716, and ADS 7654 A.

According to Robert Burnham, Jr. (1931-93), Regulus A has relatively distant, orange-red and red dwarf binary companions BC that were last observed to be separated by around 4,200 AUs. Their wide separation implies an orbital period of at least 130,000 years, according to Professor Jim Kaler's Stars page on Regulus. The Astronomiches Rechen-Institut at Heidelberg's ARICNS entry for Star B notes that the observed separation between Star A and its binary companions has been 177" at 307° from 1836 to 1960. (A review of young B-type stars with wide binaries is available from: Robert E. Murphy, 1969, pp. 1086-1087).

The distance from Regulus A where an Earth-type planet would be "comfortable" with liquid water is between 11.9 and 15.5 AUs -- between the orbits of Saturn and Uranus in the Solar System. At such distances from the star, such a planet would have an orbital period between 22 and 33 Earth years. If there is life on any Earth-type planet that has had time to cool to hold water orbiting very youthful Regulus A, it is likely to be primitive single-cell, anaerobic (non-oxygen producing) bacteria under constant bombardment by meteorites and comets as Earth was for the first billion years. Since there is unlikely to be free oxygen in the atmosphere of such a planet, it probably would not have an ozone layer (O₃) although Regulus A puts out a lot more hard radiation (especially ultraviolet) than Sol. Astronomers would find it very difficult to detect an Earth-sized planet around this star using present methods.

Alpha Leonis Ab?

H. Bond (STSci), R. Ciardullo (PSU), WFPC2, HST, NASA
(Regulus may have a close white dwarf companion -- like NGC 2440, above -- which
may have contributed mass that also increased the spin of Star A)

Alpha Leonis B

Star "B" is a orange-red main sequence dwarf star of spectral and luminosity type K1-2 V (McAlister et al, 2005; and Gies et al, 2008). It may have around 80 percent of Sol's mass, somewhat less than its diameter, and 31 percent of its luminosity.

© Torben Krogh & Mogens Winther,



(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)



Regulus B is an orange-red dwarf
star, like Epsilon Eridani at left
center of the meteor.

According to Robert Burnham, Jr. (1931-93), stars B and C have a combined visual luminosity of around 31 percent of Sol's. The most recently observation reported implied a separation around 98.9 AUs (4.163" at 77.5 ly) with a period around 2,000 years, based on the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 3982*. According to the Astronomiches Rechen-Institut at Heidelberg's ARICNS entry on Star C, the separation of stars B and C has varied between 3.9" at 93° in 1867 to 2.5" at 86° in 1943.

The orbit of an Earth-like planet (with liquid water) around Star B would be centered around 0.56 AU -- between the orbits of Mercury and Venus in the Solar System -- with an orbital period around 171 days. On a planet orbiting stars B or C, Regulus A would be so look like an extremely bright star that's six times as luminous as a Full Moon on Earth. Useful catalogue numbers and designations for the star include: Alp or Alf Leo B, 32 Leo B, GJ 9316 B, HD 87884, BD+12 2147, SAO 98966, Wo 9316 B, LTT 12714, and ADS 7654 B.

Alpha Leonis C

NASA -- larger image

Regulus C is a dim red dwarf star, like
Gliese 623 A (M2.5 V) and B (M5.8Ve) at lower right.