Lalande 21185

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Star
Lalande 21185
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Big Bear
Right ascension 11 h 03 m 20.2 s
declination + 35 ° 58 ′ 12 ″
Apparent brightness 7.49 likes
Typing
B − V color index +1.51 
U − B color index +1.13 
Spectral class M2 V
Variable star type BY 
Astrometry
Radial velocity (−85.8 ± 0.1) km / s
parallax (392.64 ± 0.67)  mas
distance (8.307 ± 0.014)  Lj
(2.547 ± 0.004)  pc  
Visual absolute brightness M vis +10.5 mag
Proper movement 
Rec. Share: (−580.27 ± 0.62)  mas / a
Dec. portion: (−4765.85 ± 0.64)  mas / a
Physical Properties
Dimensions approx. 0.46  M ☉
radius 0.40  R ☉
Luminosity

0.0025  L ☉

Effective temperature 3400  K
Metallicity [Fe / H] −0.20
(approx. 63% of the sun)
Other names
and catalog entries
Bonn survey BD + 36 ° 2147
Henry Draper Catalog HD 95735 [1]
Gliese catalog FY 411 [2]
Hipparcos catalog HIP 54035 [3]
SAO catalog SAO 62377 [4]
Tycho catalog TYC 2521-2279-1 [5]Template: Infobox star / maintenance / specification of the TYC catalog
2MASS catalog 2MASS J11032027 + 3558203 [6]
Other names Lalande 21185 • LHS 37

Lalande 21185 is a star of the spectral class M2V. It is a red dwarf with a weak luminosity of 1/40 of the Sun, low mass of approx. 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 is 10.5 mag. The angular diameter was measured with the PTI ( Palomar Testbed Interferometer ) to be 1.464 ± 0.03 milli-arcseconds. This results in a diameter of 0.40 solar diameters or 555,000 km. The star is located in the constellation Great Bear at a distance of 8.3 light years . This makes it the sixth closest known star to the sun .

Its name comes from a star catalog compiled by Joseph Jérôme Lefrançois de Lalande .

Search for planets around Lalande 21185

Lalande 21185 is one of the sun's closest neighbors.
Lalande 21185 is one of the sun's closest neighbors.

At the Sproul Observatory, Peter van de Kamp has been using astrometry to determine distances and proper movements since the 1930s and also looked for dark companions of nearby stars. In 1941 (after 1939 at Barnards Stern ) he discovered a disturbance in the proper motion of Lalande 21185, from which a companion with an orbital period of a little over a year and a mass of approx. 0.06 solar masses was assumed. In 1951 the information about the period of revolution and the mass changed to 1.14 years and approx. 0.03 solar masses. In 1960 S. Lippincott then gave an orbital period of 8 years and a mass of approx. 0.01 solar masses. In 1971 there were only signs of malfunction. In 1974 G. Gatewood found no evidence of a disturbance with a period of 8 years or less in measurements at the Allegheny Observatory dating back to 1930.

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

Shortly after the discovery of the first exoplanets by means of radial velocity measurement, G. Gatewood announced the discovery of two exoplanets around Lalande 21185 based on his measurements at the Allegheny Observatory and using the MAP : Lalande 21185b and Lalande 21185c.

Lalande 21185b is said to orbit the central star at a distance of approx. 2 AU and have a mass of 0.9 Jupiter's masses . The orbital period of the exoplanet was given as approx. 5.8 years according to measurements with MAP.

Due to an acceleration of the movement of Lalande 21185 according to the measurements of the Allegheny Observatory, another planet Lalande 21185c was concluded. It was given with a mass of more than 1.5 Jupiter and is said to orbit the star at a distance of about 10 AU. It takes him almost 30 years to circling Lalande 21185 once. Since such a planet did not seem to fully clarify the acceleration, a third companion was also suspected. In 1998, Geoffrey Marcy and R. Paul Butler found no radial velocity changes in the measurements at the lick, which took more than 10 years. This makes the inner planet improbable. Since then, until recently, the “planets” around Lalande 21185 have become quiet. In 2016, scientists announced the discovery of at least 100 new exoplanets. One of them around Lalande 21185. It orbits its star very closely and is therefore probably outside the habitable zone .

Web links

Individual evidence

  1. ↑ a b c Hipparcos catalog (ESA 1997)
  2. ↑ a b NSV 18593. In: VSX. AAVSO, accessed November 6, 2018 .
  3. ↑ Pulkovo radial velocities for 35493 HIP stars
  4. ↑ a b c Hipparcos, the New Reduction (van Leeuwen, 2007)
  5. ↑ calculated from apparent brightness and distance