System Summary
This extremely faint star is the third closest to Sol after Alpha Centauri 3 and Barnard's Star. It is located only about 7.8 light-years away in the east central part (10:56:29+07:00.7, ICRS 2000.0) of Constellation Leo, the Lion -- south of Chertan or Coxa (Theta Leonis). However, the star is much too dim to be visible to the naked eye. It was discovered photographically by Max (Maximilian Franz Joseph Cornelius) Wolf (1863-1932), a pioneer of astrophotography who discovered hundreds of variable stars and asteroids, and about 5,000 nebulae by analyzing photographic plates and developing the "dry plate" in 1880 and the "blink comparator" in 1900 with the Carl Zeiss optics company in Jena, Germany.
Wolf 359 is a dim red dwarf star, as dim as Gliese
623 B (M5.8Ve) at lower right of Gl 623 A (M2.5V).
(See a Digitized Sky Survey field image around
Wolf 359 at the NStars Database.)
The Star
A very cool, main sequence red dwarf (M5.8Ve), Wolf 359 is our Sun's dimmest stellar neighbor within 10 ly, with less than 2/100,000th of Sol's luminosity. If our Sun, Sol, were replaced by Wolf 359, then an observer on Earth would need a telescope to see its round shape clearly, and daylight would be very dim with only ten times the brightness of full moonlight with Sol. On the other hand, Wolf 359 is a Flare Star (that has been designated with the variable star name CN Leonis) and so can brighten dramatically from time to time. Flares on Wolf 359, however, are rarer and not as violent as those observed on Proxima Centauri, Kruger 60 B, or UV Ceti.
Wolf 359 is a flare star, like UV Ceti (Luyten 726-8 B)
shown flaring at left. UV Ceti is an extreme example
of a flare star that can boost its brightness by five times
in less than a minute, then fall somewhat slower back
down to normal luminosity within two or three minutes
before flaring suddenly again after several hours.
The star has a mass around 9.2 to 13 percent of Sol's (RECONS estimate; and Caillault and Patterson, 1990, page 826), about 16 to 19 percent of Sol's diameter (Doyle and Butler, 1990, page 336; and Caillault and Patterson, 1990, page 826), and only around 2/100,000th of its luminosity. It may be less than 10 billion years old. The distance from the star where an Earth-type planet would be comfortable with liquid water is located around 0.005 AU, but at that distance, the rotation of the planet would be tidally locked with the star so that one side would have eternal daylight and the other would be in eternal darkness.
Some alternative names and useful star catalogue numbers are: CN Leonis, Gl 406, G 45-20, LFT 750, LTT 12923, and LHS 36.
Hunt for Substellar Companions
The Hubble Space Telescope was recently used to search for faint companions about Wolf 359. No large orbiting body (stellar or substellar, such as a brown dwarf) were found as close as the distance from the Earth to the Sun -- i.e., one AU -- from Wolf 359 (Schroeder et al, 2000). Previous searches using ground-based, photographic astrometry and infrared speckle methods had already failed to find a large orbiting body at greater distances from the star.
Life Around a Flare Star
Many dim, red (M) dwarf stars exhibit unusually violent flare activity for their size and brightness. These flare stars are actually common because red dwarfs make up more than half of all stars in our galaxy. Although flares do occur on our Sun every so often, the amount of energy released in a solar flare is small compared to the total amount of energy Sol produces. However, a flare the size of a solar flare occurring on a red dwarf star (such as Wolf 359) that is more than ten thousand times dimmer than our Sun would emit about as much or more light as the red dwarf itself, doubling its brightness or more.
Flare stars erupt sporadically, with successive flares spaced anywhere from an hour to a few days apart. A flare only takes a a few minutes to reach peak brightness, and more than one flare can occur at a time. Moreover, in addition to bursts of light and radio waves, flares on dim red dwarfs may emit up to 10,000 times as many X-rays as a comparably-sized solar flare on our own Sun, and so flares would be lethal to Earth-type life on planets near the flare star. Hence, Earth-type life around flare stars may be unlikely because their planets must be located very close to dim red dwarfs to be warmed sufficiently by star light to have liquid water (about 0.0042 AU for Wolf 359 with an orbital period of around 8 hours), which makes flares even more dangerous around such stars. In any case, the light emitted by red dwarfs may be too red in color for Earth-type plant life to perform photosynthesis efficiently.
Closest Neighbors
The following star systems are located within 10 ly of Wolf 359.
Star System Spectra &
Luminosity Distance
(light-years)
Ross 128 M4.1-5 Ve 3.8
Lalande 21185 M2.1 Ve 4.1
Wolf 424 AB M5.5 Ve
M5.5 Ve 7.3
DX Cancri M6.5Ve 7.7
LP 731-58 M6.5V 7.7
Sol G2 V 7.8
Proxima Centauri M5.5 Ve 8.2
Alpha Centauri AB G2 V
K0-1 V 8.3
Procyon 2 F5 V-IV
DA-F/VII 8.6
LTT 12352 M3.5 V 8.7
AD Leonis M3 Ve 8.8
Sirius AB A0-1 Vm
DA2-5/VII 9.0
Luyten's Star M3.5-5 V 9.8
DENIS 1048-39 M9 V? ~10
Other Information
Up-to-date technical summaries on this star can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS, the NStar Database, and the Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems. Additional information may be available at Roger Wilcox's Internet Stellar Database.
The Constellation Leo represents the Lion that Hercules (also a constellation) had to kill as one of his 12 tasks. For more information and an illustration of the constellation, go to Christine Kronberg's Leo. For another illustration, see David Haworth's Leo.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.