Lalande 21185

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Lalande 21185
Observational Data
Designation Lalande 21185
NSV 18593
HD 95735
Right ascension 11h 03m 20.194s[1]
Declination +35° 58' 11.5682"[1]
Constellation Ursa Major
Type of object Star
Magnitude Apparent Mag: 7.47[2]
Absolute Mag: 10.44[3]
Astrometry
Distance from Earth 8.32 ly
Radial velocity -85.0±0.9 km/s[4]
Proper motion RA: -580.46 ±0.95 mas/yr[1]
Dec.: -4769.95 ±0.53 mas/yr[1]
Parallax 392.52±0.91 mas[1]

Lalande 21185 is the closest system to Sol after Proxima Centauri, Alpha Centauri, Barnard's Star, and Wolf 359. Located in the constellation of Ursa Major, it is only 8.3 light years away, although due to its low apparent magnitude of 7.5, it's invisible to the unaided eye.[5]

The star is a red dwarf with a spectral luminously M2.1 Vne and only contains about 40% of the mass of our own star. Lalande 21195 is also 46% of our Sun's diameter and is only six-tenths of a percent as bright.[6] The star's metallicity is only 63% of that of our Sun, based on the amount of iron present.[7]

Lalande 21185 is actually moving perpendicular to the galactic plane at a relative velocity of 47 km/s. Based on this observation, the star likely is one of the "thick disk" stars of our galaxy, belong to the Milky Way's thick disk, which has an average thickness of 3,500 light years. Most stars that belong to this group are metal-poor stars that move in an eccentric orbit relative to the galactic plane.

The star was first recorded by Joseph-Jérôme Lefrançais de Lalande in 1801 when he produced his catalog of some 47,390 stars in his Histoire Céleste Française, the largest star catalog of its day.

Planets

In 1996 an astronomical team reported detecting two possible planets orbiting Lalande 21185.[8] The closer of the two is estimated to exist some 2.2 AUs from its parent star and is 90% of Jupiter's mass. The further possible planet may exist at the distance of 11 AUs and may be 1.6 times Jupiter's mass. At this time neither world has been independently confirmed.[9]

For an earth like world to have liquid water, such a world would have to be only some 0.22 AUs away, half the distance of Mercury and would complete its orbit in 56 days. Most likely such a world would be tidally locked to the star, meaning one side would have perpetual day while the other side would be shrouded in perpetual night.

References

  1. 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (2007). Validation of the new Hipparcos reduction. Astronomy & Astrophysics, 474(2), pp.653-664. arXiv:0708.1752
  2. T., O. (1985). Photoelectric photometry of stars near the North Galactic Pole. II. Astronomy and Astrophysics Supplement Series, 61, pp.331-339. Astrophysics Data System
  3. From definition of absolute magnitude, using apparent magnitude (+7.47) and distance (8.32 ly) given here.
  4. Nidever, D., Marcy, G., Butler, R., Fischer, D. and Vogt, S. (2002). Radial Velocities for 889 Late‐Type Stars. The Astrophysical Journal Supplement Series, 141(2), pp.503-522. arXiv:astro-ph/0112477
  5. Lalande 21185 from solstation.com
  6. http://joy.chara.gsu.edu/RECONS/TOP100.posted.htm
  7. Cayrel de Strobel, G., Hauck, B., François, P., Thévenin, F., Friel, E., Mermilliod, M. and Borde, S. (1992). A catalogue of [Fe/H] determinations: 1991 edition. Astronomy and Astrophysics Supplement Series, 95, pp.273-336. Astrophysics Data System
  8. Astrophysics Data System
  9. Henry, G., Baliunas, S., Donahue, R., Fekel, F. and Soon, W. (2000). Photometric and CaiiH and K Spectroscopic Variations in Nearby Sun‐like Stars with Planets. III. The Astrophysical Journal, 531(1), pp.415-437. Astrophysics Data System