AA Tauri


AA Tauri is a young variable star in the equatorial constellation of Taurus, located in the Taurus-Auriga star-forming region. It is too faint to view with the naked eye, having an apparent visual magnitude that varies from 12.2 down to 16.1.[2] The star is located approximately 447 light years away from the Sun based on parallax, and is drifting further away with a radial velocity of +17 km/s.[4]

AA Tauri
AA Tauri star and planet.png

Artist's impresion of AA Tauri and possible substellar companion
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension 04h 34m 55.42227s[1]
Declination +24° 28′ 53.0383″[1]
Apparent magnitude (V) 12.2 to 16.1[2]
Spectral type K7Ve[3]
Variable type T Tauri-type?[3]
Radial velocity (Rv)16.98±0.04[4] km/s
Proper motion (μ) RA: +3.483[1] mas/yr
Dec.: −20.987[1] mas/yr
Parallax (π)7.2888 ± 0.1295 mas[1]
Distance447 ± 8 ly
(137 ± 2 pc)
Mass0.76[5] M
Radius1.81[5] R
Luminosity0.8[5] L
Temperature4,060[5] K
Rotational velocity (v sin i)12.8±1.1[4] km/s
Age2.4[5] Myr
Other designations
AA Tau, GCRV 55202, XEST 25-026, AN 196.1930, GSC 01833-00851, 2MASS J04345542+2428531, CSI+24-04319, MHA 259-17, 2E 0431.8+2422, IRAS 04318+2422, UBV 4396, 2E 1098, IRAS F04318+2422, XEST 25-OM-003[6]
Database references

The stellar classification for this object is K7Ve,[3] matching a K-type main-sequence star that displays emission features. It is an eruptive variable of the T Tauri type[2] with an estimated age of 2.4 million years. The object has 76% of the mass of the Sun, 181% of the Sun's radius,[5] and is spinning with a projected rotational velocity of 13 km/s.[4] AA Tauri is radiating 80% of the luminosity of the Sun at an effective temperature of 4,060 K.[5]


A visual band light curve for AA Tauri, adapted from Bouvier et al. (2013).[7] The main plot shows the long term variation, and the inset plot shows the periodic variation after the dramatic dimming in 2011.

AA Tauri shows brightness variations of one to two magnitudes over an 8.2-day period. The brightness has been described as "roughly constant, interrupted by quasi-cyclic fading episodes".[8] The periodic variations are ascribed to eclipses of the star by a warped dust disk around it.[9]

In 2011, AA Tauri faded by about two magnitudes and has remained at the fainter level since then. The star also became significantly more reddened. The eight-day variations continue, with a maximum brightness now around magnitude 14 and magnitude 16.5 at its faintest. It is theorised that the root cause of this dimness is a warp in the accretion disk, located at a distance of 7.7 AU or more from the centre, that was brought into the line of sight by its elliptical motion around the central star.[7]

A possible planetary systemEdit

In their paper of 2003, Grinin et al. invoke the possible presence of a substellar object to explain peculiar and periodic eclipses occurring to the young star every 8.3 days.[8] They infer a mass of 20 times that of Jupiter for the perturbing object and an orbital separation of 0.08 Astronomical Units. Later studies find no evidence for a planet, instead finding multiple rings with accretion streams between them.[9]

The AA Tauri planetary system
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (unconfirmed) ≤20 MJ 0.08 8.5 0


  1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. ^ a b c Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. ^ a b c Herbig, G. H. (1977). "Radial velocities and spectral types of T Tauri stars". Astrophysical Journal. 214: 747–758. Bibcode:1977ApJ...214..747H. doi:10.1086/155304.
  4. ^ a b c d Nguyen, Duy Cuong; et al. (February 2012). "Close Companions to Young Stars. I. A Large Spectroscopic Survey in Chamaeleon I and Taurus-Auriga". The Astrophysical Journal. 745 (2): 25. arXiv:1112.0002. Bibcode:2012ApJ...745..119N. doi:10.1088/0004-637X/745/2/119. S2CID 119265730. 119.
  5. ^ a b c d e f g Güdel; et al. (2007). "The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST)". Astronomy and Astrophysics. 468 (2): 353–377. arXiv:astro-ph/0609160. Bibcode:2007A&A...468..353G. doi:10.1051/0004-6361:20065724. S2CID 8846597.
  6. ^ "AA Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-08-10.
  7. ^ a b Bouvier, J.; Grankin, K.; Ellerbroek, L. E.; Bouy, H.; Barrado, D. (2013). "AA Tauri's sudden and long-lasting deepening: Enhanced extinction by its circumstellar disk". Astronomy & Astrophysics. 557: A77. arXiv:1304.1487. Bibcode:2013A&A...557A..77B. doi:10.1051/0004-6361/201321389. S2CID 216079418.
  8. ^ a b Bouvier; et al. (2003). "Eclipses by circumstellar material in the T Tauri star AA Tau. II. Evidence for non-stationary magnetospheric accretion". Astronomy and Astrophysics. 409: 169–192. arXiv:astro-ph/0306551. Bibcode:2003A&A...409..169B. doi:10.1051/0004-6361:20030938. S2CID 15140780.
  9. ^ a b Loomis, Ryan A.; Öberg, Karin I.; Andrews, Sean M.; MacGregor, Meredith A. (2017). "A Multi-ringed, Modestly Inclined Protoplanetary Disk around AA Tau". The Astrophysical Journal. 840 (1): 23. arXiv:1704.02006. Bibcode:2017ApJ...840...23L. doi:10.3847/1538-4357/aa6c63. S2CID 119370612.