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.[ The star is located approximately away from the Sun based on stellar parallax, and is drifting further away with a radial velocity of +17 km/s.][
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The stellar classification for this object is K7Ve,[ matching a K-type main-sequence star that displays emission line features. It is an eruptive variable of the T Tauri type][ 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,][ AA Tauri is radiating 80% of the luminosity of the Sun at an effective temperature of 4,060 K.]
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".[ The periodic variations are ascribed to eclipses of the star by a warped dust disk around it.][
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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.[
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Search for planets
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.[ 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 find no evidence for a planet, instead finding multiple rings with accretion streams between them.][
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