Barnard's Star, by solstation.com at American Buddha Online Library

BARNARD'S STAR

by solstation.com

Barnard's Star, an old and very dim red dwarf, was once thought to have two Jupiter-class planets

System Summary

This dim star is the second closest to Sol after Alpha Centauri 3. It is located about 6.0 light-years away in the northernmost part (17:57:48.5+04:41:36.2, ICRS 2000.0) of Constellation Ophiuchus, the Serpent Holder -- west of Cebalrai or Kelb al Rai (Beta Ophiuchi). The star was named after its discoverer, noted astronomer Edward Emerson Barnard (1857-1923), who found in 1916 that the star has the largest known proper motion of all known stars (10.3 arcseconds per year). This high apparent speed is the result of its proximity to Sol as well as actual speed of travel through interstellar space. In fact, Barnard's Star is approaching Sol rapidly at 140 kilometers per second (87 miles/second) and will get as close as 3.8 light-years (ly) around 11,800 CE. Like other red dwarfs, however, it is not visible to the naked eye.

The Star

A very cool and dim, main sequence red dwarf (M3.8 Ve), Barnard's Star has less than 17 percent of Sol's mass (RECONS estimate), 15 to 20 percent of its diameter (Dawson and de Robertis, 2004; and Ochsenbein and Halbwachs, 1982, page 529), around 4/10,000th of its visual luminosity -- 0.00346 of its bolometric luminosity (Dawson and de Robertis, 2004), and between 10 and 32 percent of its abundance of elements heavier than hydrogen -- "metallicity" (John E. Gizis, 1997, page 820). According to calculations by Dr. Sten Odenwald, substituting Barnard's Star for Sol would give the Earth such a dim and very red Sun that it would only be 100 times brighter than the Full Moon, and so the planet would freeze solid at the surface.

Unlike Sol, Barnard's appears to be an old star that formed before the galaxy became much enriched with heavy elements (Monet et al, 1992, page 655). Its high space motion and sub-Solar metallicity suggests that the star is "intermediate Population II star," somewhere between a Halo and a disk star (Kürster et al, 2003; and John E. Gizis, 1997). Moreover, its low x-ray luminosity and presumed rotation period of 130.4 days also indicate that it is an old, inactive red dwarf. While the star may be as much as 10 or more billion years old, it may last another another 40 billion years or more before cooling into a black dwarf. A small star spot that was shrinking in size may have been observed on Barnard's recently with the Hubble Space Telescope (Benedict et al, 1998). Barnard's have been given the variable star designation V2500 Ophiuchus as well as the New Suspected Variable star designated NSV 9910. Some other useful star catalogue numbers include: V2500 Oph, Gl 699, Hip 87937, BD+04 3561a, LHS 57, LTT 15309, LFT 1385, G 140-24, Vys/McC 799, and Munich 15040.

Although Barnard's star may be around 10 billion years old, it is still burning core hydrogen as a small and cool member of the main sequence.

A Planetary System?

Astronomers have long sought to find perturbations ("wobbles") in this star's motion that could be due to planet-sized companions. During the late 1960s, Peter van de Kamp (1901-1995) announced the detection of possibly two coplanar and corevolving planets, whose estimated masses were fine-tuned in 1982 to be about 0.7 and 0.5 of Jupiter's mass with orbital periods of 12 and 20 years, respectively, in "approximately" circular orbits based on astrometric positions obtained from 1938 to 1981 (van de Kamp, 1982). Until his death in 1995, Van de Kamp devoted most of his life (at at Sproul Observatory at (Swarthmore College) to analyzing over 2,000 plates of Barnard's Star that he and his students had taken from 1938 through 1981.

Neither planet was ever verified, however, and more recent observations with the Hubble Space Telescope have failed to yield supporting evidence for a large Jupiter or brown dwarf sized object (Schroeder et al, 2000). Some astronomers suspected that van de Kamp's data were distorted by the cleaning and remounting of the telescope lens at Sproul, 25 years after he began his observations. In 1995, George G. Gatewood (director of the University of Pittsburgh's Allegheny Observatory) suggested that, while brown dwarfs exceeding Jupiter's mass by more than 10 times could not exist around Barnard's Star, planets having a mass smaller than Jupiter's may possibly be present. Subsequent astrometric measurements set even more stringent upper mass limits of 2.1 down to 0.37 Jupiter-masses for orbital periods of 50 up to 600 days (Benedict et al, 1999). (For more information about the search for planets around Barnard's through astrometric perturbation methods, go to George Bell's summary of Barnard's Star and van de Kamp's Planets.)

In 2003, a team of astronomers reported on two and a half years of high-precision radial velocity observations of Barnard's star that set even stricter limits on any large planets in circular orbits around this small star (Kürster et al, 2003). For the separation range of 0.017 to 0.98 AU, the team's data suggests the exclusion of any planet with msin(i) greater than 0.12 Jupiter-mass and mass greather than 0.86 percent of Jupiter's. Throughout the habitable zone around Barnard's star, that is 0.034 to 0.082 AU, the data appears to exclude planets with msin(i) greater than 7.5 Earth-masses and a mass greater than 3.1 times Neptune's.

In order to be warmed sufficiently have liquid water at the surface, an Earth-type rocky planet would have to be located very close to such a cool and dim red dwarf star like Barnard's, at around 0.034 to 0.082 AU, the Earth-Sun distance (Kürster et al, 2003). At such close distances, such a planet would probably be tidally locked -- with one side in perpetual day -- and race around the star in 5.75 to 21.5 (or three weeks). Some have suggested that any rocky planets that formed around Barnard's are likely to be sparse in the heavier elements of the atomic table, and that there may be a greater probability of gas giants made mostly of hydrogen and helium in cold, outer orbits.

Closest Neighbors

The following star systems are located within 10 ly of Barnard's Star.

Star System Spectra &
Luminosity Distance
(light-years)
Ross 154 M3.5 Ve 5.5
Sol G2 V 6.0
Alpha Centauri AB G2 V
K0 V 6.5
Proxima Centauri M5.5 Ve 6.6
BD-12 4523 AB M3 V
? 9.1
61 Cygni AB K3.5-5 Ve
K4.7-7 Ve 9.5
Struve 2398 AB M3 V
M3.5 V 9.5

Other Information

Up-to-date technical summaries on Barnard's Star can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS, NASA's 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.

One story is that the Ancient Greeks named this constellation after Aesculapius (the first doctor, a son of Apollo and Coronis, and grandfather of Hippocrates, the famous Greek physician). Aesculapius was killed by Zeus at the urging of Hades for threatening to make mankind immortal like the gods by bringing the dead back to life. In admiration of the doctor's skills, however, Zeus raised the doctor and the serpent from which he had first learned the medicinal usefulness of certain herbs into the heavens. Located along the equatorial region of the sky, Ophiuchus is one of the larger constellations. For more information and an illustration of the constellation, go to Christine Kronberg's Ophiuchus. For another illustration, see David Haworth's Ophiuchus.

Project Daedalus was developed by the British Interplanetary Society in the 1970s as a study proposal to send an unmanned, nuclear-powered spacecraft to Barnard's Star. Accelerating to one-tenth light speed using a deuterium/helium-3 nuclear fusion reaction to provide thrust, Daedalus was designed to put a sensor platform in orbit around Barnard's Star, enabling it to return data images just 56 years after its departure from Earth. For more information, go to Daedalus Origins or Adrian Mann's Starship Daedalus pages which include color illustrations of the proposed interstellar spacecraft -- see also Joe Bergeron's Daedalus Starship.

For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.

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