Lalande 21185

0.0025 L ☉

Lalande 21185 is a star of spectral type M2V. It is a red dwarf with weak luminosity of 1/ 40 of the sun, low mass of about 0.46 solar masses, and a relatively cool surface temperature of 3400 Kelvin. The apparent brightness in the V band is 7.5 mag and the absolute brightness like 10.5. The angular diameter was awarded the PTI ( Palomar Testbed Interferometer ) measured at 1.464 ± 0.03 milliarcseconds. This results in a diameter of 0.40 sun diameters or 555,000 km. The star is located in the constellation Ursa Major in 8.3 light years away. He is the sixth- closest known star to the Sun.

Its name comes from a compiled by Joseph Jerome Lefrancois Lalande de star catalog.

Search for planets around Lalande 21185

At the Sproul Observatory Peter van de Kamp certain since the 30s astrometric distances, proper motions and sought after dark companions of nearby stars. He discovered in 1941 ( after 1939 at Barnard's Star) is a disorder of the proper motion of Lalande 21185, was obtained from the suspects a companion with an orbital period of a little more than a year and a mass of about 0.06 solar masses. In 1951 the information changed for orbital period and the mass of 1.14 years, or about 0.03 solar masses. 1960 S. Lippincott was then at an orbital period of 8 years and a mass of about 0.01 solar masses. In 1971, there was only a sign of malfunction. In 1974 G. Gatewood found in the measurements at the Allegheny Observatory, dating back to 1930, no signs of a disturbance with a period of 8 years or less.

G. Gatewood measurements began in 1988 with the MAP ( Multichannel Astrometric Photometer ), which allowed a higher accuracy. In the same year the Lick Observatory began with its radial velocity measurements of Lalande 21185, which allowed a much higher accuracy than the astrometric measurements.

Shortly after the discovery of the first extrasolar planets by radial velocity measurement G. Gatewood was in 1996 due to its measurements at the Allegheny Observatory, and by means of the MSP, the discovery of two exoplanets around Lalande 21185 known: Lalande 21185b and 21185c Lalande.

Lalande 21185b will orbit the central star in about 2 AU distance and have a mass of 0.9 Jupiter masses. The orbital period of the exoplanet was indicated by measurements with MAP to about 5.8 years.

Due to an acceleration of the motion of Lalande 21185 according to the measurements of the Allegheny Observatory was closed on another planet Lalande 21185c. He was given as a mass of more than 1.5 Jupiter masses and will orbit the star in about 10 AU distance. It requires nearly 30 years to go around Lalande 21185 once. Since such a planet did not completely clarify the acceleration, also a third companion was suspected.

In 1998, Geoffrey Marcy and R. Paul Butler found no radial velocity variations in the over 10 years of measurements at the Lick. Thus, the inner planet is unlikely. Since then, it has become quiet around the " planet " to Lalande 21185.

External links and sources

  • Image
  • Http://www.solstation.com/stars/la21185.htm (in English)
  • Http://www.exoplaneten.de/lalande/
  • Individual star fifth size and darker
  • Big Dipper
Declination Color index Astrometry Light-year Intrinsic brightness Durchmusterung Smithsonian Astrophysical Observatory Star Catalog
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