AA Tauri
Star in the constellation Taurus
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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.[3] The star is located approximately 439 light-years (135 parsecs) away from the Sun based on parallax, and is drifting further away with a radial velocity of +17 km/s.[5]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Taurus |
| Right ascension | 04h 34m 55.42019s[2] |
| Declination | +24° 28′ 53.0336″[2] |
| Apparent magnitude (V) | 12.2 to 16.1[3] |
| Characteristics | |
| Spectral type | K7Ve[4] |
| Variable type | T Tauri-type?[4] |
| Astrometry | |
| Radial velocity (Rv) | 16.98±0.04[5] km/s |
| Proper motion (μ) | RA: +5.323 mas/yr[2] Dec.: −20.680 mas/yr[2] |
| Parallax (π) | 7.4255±0.0868 mas[2] |
| Distance | 439 ± 5 ly (135 ± 2 pc) |
| Details | |
| Mass | 0.76[6] M☉ |
| Radius | 1.81[6] R☉ |
| Luminosity | 0.8[6] L☉ |
| Temperature | 4,060[6] K |
| Rotational velocity (v sin i) | 12.8±1.1[5] km/s |
| Age | 2.4[6] Myr |
| Other designations | |
| AA Tau, GCRV 55202, GSC 01833-00851, IRAS F04318+2422, 2MASS J04345542+2428531, XEST 25-026, AN 196.1930, CSI+24-04319, MHA 259-17, 2E 0431.8+2422, UBV 4396, 2E 1098, XEST 25-OM-003[7] | |
| Database references | |
| SIMBAD | data |
The stellar classification for this object is K7Ve,[4] matching a K-type main-sequence star that displays emission features. It is an eruptive variable of the T Tauri type[3] 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,[6] and is spinning with a projected rotational velocity of 13 km/s.[5] AA Tauri is radiating 80% of the luminosity of the Sun at an effective temperature of 4,060 K.[6]
Variability
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".[9] The periodic variations are ascribed to eclipses of the star by a warped dust disk around it.[10]
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.[8]
Search for companions
In their 2003 paper, Bouvier et al. invoked the possible presence of a substellar object to explain peculiar and periodic eclipses occurring to the young star every 8.3 days, though they considered it unlikely that such a companion could be responsible for said variability.[9] They inferred a mass of 20 times that of Jupiter for the perturbing object and an orbital separation of 0.08 Astronomical Units. Later studies found no evidence for a planet, instead finding multiple rings with accretion streams between them.[10]
Gaia astrometry shows evidence of a proper motion anomaly, suggesting the presence of a stellar companion.[1]