Teegarden's Star, also known as SO025300.5+165258, is a star in the constellation Aries which was found in 2003 to have a very large proper motion (5.06±0.03 arcsec/year). Only seven stars with such large proper motions are currently known.
It appears to be a red dwarf, a class of low temperature and low luminosity stars. This would explain why it was not discovered earlier, since it has an apparent magnitude of only 15.4 (and an absolute magnitude of 17.47).
The parallax was initially measured as 0.43±0.13 arcsec. This would have placed its distance at only 7.50 light years, making Teegarden's Star only the third star in order of distance from the Sun, ranking between Barnard's Star and Wolf 359. However, even at that time the anomalously low luminosity (the absolute magnitude would have been 18.5) and high uncertainty in the parallax suggested that it was in fact somewhat farther away, still one of the Sun's nearest neighbors but not nearly as high in the ranking in order of distance. More recent distance measurements of 12.5–12.6 light years appear to have confirmed this.
Teegarden's Star was discovered on images taken by the NEAT program operated by NASA. Its name comes from its principal discoverer, Dr. Bonnard Teegarden , an astrophysicist at NASA's Goddard Space Flight Center.
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