Teegarden's Star

Teegarden's Star /ˈtiːɡɑːrdənz/ (SO J025300.5+165258, 2MASS J02530084+1652532, LSPM J0253+1652) is an M-type red dwarf[3] in the constellation Aries, about 12 light-years from the Solar System. Although it is near Earth it is a dim magnitude 15 and can only be seen through large telescopes. This star was found to have a very large proper motion of about 5 arcseconds per year. Only seven stars with such large proper motions are currently known.[1]

Teegarden's Star
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension  02h 53m 00.85s[1]
Declination +16° 52′ 53.3″[1]
Apparent magnitude (V) 15.13[2]
Characteristics
Spectral type M7.0 V[3]
Apparent magnitude (B) ~17.21[1]
Apparent magnitude (V) ~15.40[1]
Apparent magnitude (R) ~14.1[4]
Apparent magnitude (I) ~10.4[4]
Apparent magnitude (J) 8.394 ± 0.027[5]
Apparent magnitude (H) 7.883 ± 0.040[5]
Apparent magnitude (K) 7.585 ± 0.046[5]
Astrometry
Radial velocity (Rv)68.3[6] km/s
Proper motion (μ) RA: +3,386[7] mas/yr
Dec.: –3,747[7] mas/yr
Parallax (π)259.25 ± 0.94[8] mas
Distance12.58 ± 0.05 ly
(3.86 ± 0.01 pc)
Absolute magnitude (MV)17.22[9]
Details
Mass0.08[3] M☉
Radius0.127±0.004[10] R☉
Luminosity0.00073[10] L☉
Temperature2,637[11] K
Metallicity [Fe/H]−0.55[11] dex
Rotational velocity (v sin i)10±4[6] km/s
Age>8[12] Gyr
Other designations
Teegarden's Star, 2MASS J02530084+1652532, APM EO0425-0315372, FBS L 14-17, FBS 0250+167, GAT 1370, LSPM J0253+1652, SO J025300.5+165258, USNO-A2.0 1050-00774305, USNO-B1.0 1068-00028941.[1]
Database references
SIMBADdata
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)
Teegarden's Star (top, center) is the 24th-nearest known star (system) to the Solar System.

Discovery

Teegarden's Star was discovered in 2003 using asteroid-tracking data that had been collected years earlier. This data set is a digital archive created from optical images taken over a five-year period by the Near-Earth Asteroid Tracking (NEAT) program using two 1 m telescopes on Maui, Hawaii. The star is named after the discovery team leader, Bonnard J. Teegarden, an astrophysicist at NASA's Goddard Space Flight Center.[13]

Teegarden's star showing proper motion at two year intervals.

Astronomers have long thought it was quite likely that many undiscovered dwarf stars exist within 20 light-years of Earth, because stellar-population surveys show the count of known nearby dwarf stars to be lower than otherwise expected and these stars are dim and easily overlooked. Teegarden's team thought that these dim stars might be found by data mining some of the huge optical sky survey data sets taken by various programs for other purposes in previous years. So they reexamined the NEAT asteroid tracking data set and found this star. The star was then located on photographic plates from the Palomar Sky Survey taken in 1951. This discovery is significant as the team did not have direct access to any telescopes and did not include professional astronomers at the time of the discovery.[13]

Properties

Teegarden's Star is classified as a red dwarf as its approximate calculated mass of 0.08 times that of the Sun is narrowly above the limit of brown dwarfs.[14] The inherent low temperatures of such objects explain why it was not discovered earlier,[15] since it has an apparent magnitude of only 15.1[2] (and an absolute magnitude of 17.22[9]). Like most red and brown dwarfs it emits most of its energy in the infrared spectrum.[16]

The parallax was initially measured as 0.43 ± 0.13 arcseconds. This would have placed its distance at only 7.50 light-years, making Teegarden's Star only the third star system in order of distance from the Sun, ranking between Barnard's Star and Wolf 359.[13] 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. A more accurate parallax measurement of 0.2593 arcseconds was made by George Gatewood in 2009, yielding the now accepted distance of 12.578 light-years.[8]

Planetary system

Observations by the ROPS survey in 2010, published in 2012, showed variation in Teegarden's star's radial velocity, though there was insufficient data to make claims of planet detection at that time.[17]

In June 2019, scientists conducting the CARMENES survey at the Calar Alto Observatory announced evidence of two Earth-mass exoplanets orbiting the star within its habitable zone;[12][18] Teegarden's Star b orbits inside the optimistic habitable zone, the equivalent in the solar system would be in-between Earth and Venus, whereas Teegarden's Star c orbits on the outer edge of the conservative habitable zone, similar to Mars.[12]

According to one group of researchers, who were specifically studying this star, both planets could have maintained a dense atmosphere and so therefore there would be a high likelihood that at least one may harbour liquid water.[19] However, another group of scientists, looking at Earth-sized planets in general in the habitable zones of stars, give Teegarden's b a 3% chance, and Teegarden's c only a 2% chance, of having even retained an atmosphere.[20]

The Teegarden's Star planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥1.05+0.13
−0.12 M⊕		 0.0252+0.0008
−0.0009		 4.91±0.0014 0+0.16
−0		 — —
c ≥1.11+0.16
−0.15 M⊕		 0.0443+0.0014
−0.0015		 11.409±0.009 0+0.16
−0		 — —
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See also

References
  1. "2MASS J02530084+1652532 -- Brown Dwarf (M<0.08solMass)". SIMBAD – Centre de Données astronomiques de Strasbourg. Retrieved 2012-01-01.
  2. Lépine, Sébastien; Hilton, Eric J.; Mann, Andrew W.; Wilde, Matthew; Rojas-Ayala, Bárbara; Cruz, Kelle L.; Gaidos, Eric (2013). "A Spectroscopic Catalog of the Brightest (J < 9) M Dwarfs in the Northern Sky". The Astronomical Journal. 145 (4): 102. arXiv:1206.5991. Bibcode:2013AJ....145..102L. doi:10.1088/0004-6256/145/4/102.
  3. Davison, Cassy L.; White, R. J.; Henry, T. J.; Riedel, A. R.; Jao, W.-C.; Bailey, J. I.; Quinn, S. N.; Cantrell, J. R.; Subasavage, J. P.; Winters, J. G. (2015). "A 3D Search for Companions to 12 Nearby M Dwarfs". The Astronomical Journal. 149 (3): 106. arXiv:1501.05012. Bibcode:2015AJ....149..106D. doi:10.1088/0004-6256/149/3/106.
  4. Monet, David G.; et al. (February 2003), "The USNO-B Catalog", The Astronomical Journal, 125 (2): 984–993, arXiv:astro-ph/0210694, Bibcode:2003AJ....125..984M, doi:10.1086/345888
  5. Cutri, R. M.; et al. (June 2003), "2MASS All Sky Catalog of point sources", The IRSA 2MASS All-Sky Point Source Catalog, NASA/IPAC, Bibcode:2003tmc..book.....C
  6. Tanner, Angelle; et al. (November 2012), "Keck NIRSPEC Radial Velocity Observations of Late-M Dwarfs", The Astrophysical Journal Supplement, 203 (1): 7, arXiv:1209.1772, Bibcode:2012ApJS..203...10T, doi:10.1088/0067-0049/203/1/10.
  7. Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854
  8. George Gatewood; et al. (January 2009). "Allegheny Observatory Parallaxes for Late M Dwarfs and White Dwarfs". The Astronomical Journal. 137 (1): 402–405. Bibcode:2009AJ....137..402G. doi:10.1088/0004-6256/137/1/402.
  9. Henry, Todd J.; et al. (December 2006), "The Solar Neighborhood. XVII. Parallax Results from the CTIOPI 0.9 m Program: 20 New Members of the RECONS 10 Parsec Sample", The Astronomical Journal, 132 (6): 2360–2371, arXiv:astro-ph/0608230, Bibcode:2006AJ....132.2360H, doi:10.1086/508233.
  10. Dieterich, Sergio B.; Henry, Todd J.; Jao, Wei-Chun; Winters, Jennifer G.; Hosey, Altonio D.; Riedel, Adric R.; Subasavage, John P. (May 2014), "The Solar Neighborhood. XXXII. The Hydrogen Burning Limit", The Astronomical Journal, 147 (5): 25, arXiv:1312.1736, Bibcode:2014AJ....147...94D, doi:10.1088/0004-6256/147/5/94.
  11. Rojas-Ayala, Bárbara; et al. (April 2012), "Metallicity and Temperature Indicators in M Dwarf K-band Spectra: Testing New and Updated Calibrations with Observations of 133 Solar Neighborhood M Dwarfs" (PDF), The Astrophysical Journal, 748 (2): 93, arXiv:1112.4567, Bibcode:2012ApJ...748...93R, doi:10.1088/0004-637X/748/2/93
  12. Caballero, J. A.; Reiners, A.; Ribas, I.; Dreizler, S.; Zechmeister, M.; et al. (12 June 2019). "The CARMENES search for exoplanets around M dwarfs. Two temperate Earth-mass planet candidates around Teegarden's Star" (PDF). Astronomy & Astrophysics. Bibcode:2019arXiv190607196Z. doi:10.1051/0004-6361/201935460. ISSN 0004-6361.
  13. Teegarden, B. J.; et al. (May 20, 2003). "Discovery of a New Nearby Star" (PDF). The Astrophysical Journal Letters. 589 (1): L51–L53. arXiv:astro-ph/0302206. Bibcode:2003ApJ...589L..51T. doi:10.1086/375803.
  14. Kaltenegger, Lisa; Traub, Wesley A. (June 2009). "Transits of Earth-like Planets". The Astrophysical Journal. 698 (1): 519–527. arXiv:0903.3371. Bibcode:2009ApJ...698..519K. doi:10.1088/0004-637X/698/1/519.
  15. Reid, Neill I.; Hawley, Suzanne L. (2013), New Light on Dark Stars: Red Dwarfs, Low-Mass Stars, Brown Dwarfs, Springer Praxis Books, p. 342, ISBN 978-1-4471-3663-7.
  16. Kaler, James B. (2011), Stars and Their Spectra: An Introduction to the Spectral Sequence, Cambridge University Press, pp. 126, 132, ISBN 978-0-521-89954-3.
  17. Barnes J.R.; et al. (July 2012). "ROPS: A New Search for Habitable Earths in the Southern Sky". Monthly Notices of the Royal Astronomical Society. 424 (1): 591–604. arXiv:1204.6283. Bibcode:2012MNRAS.424..591B. doi:10.1111/j.1365-2966.2012.21236.x.
  18. University of Göttingen (18 June 2019). "View of the Earth in front of the Sun – International research team discovers two new Earth-like planets near Teegarden's star". EurekAlert!. Retrieved 18 June 2019.
  19. Wandel, Amri; Tal-Or, Lev (2019). "On the Habitability of Teegarden's Star Planets". The Astrophysical Journal. 880 (2): L21. arXiv:1906.07704. Bibcode:2019ApJ...880L..21W. doi:10.3847/2041-8213/ab2df7. ISSN 2041-8213.
  20. Rodriguez-Mozos, J. M.; Moya, A. (October 2019). "Erosion of an exoplanetary atmosphere caused by stellar winds". Astronomy & Astrophysics. 630. Table A.4. arXiv:1908.06695. Bibcode:2019A&A...630A..52R. doi:10.1051/0004-6361/201935543.
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