T Tauri with Hind's Variable Nebula to the right. Image credit: Two Micron All Sky Survey.
Location of T Tauri in the sky. Credit Jerry Lodriguss:
Like all members of its kind, T Tauri is an irregular variable. It has been known to shine as brightly as magnitude 9.3 and as dimly as magnitude 14, though for the past century or so it has tended toward the brighter end of this range. It can vary by a few tenths of a magnitude on nearly a daily basis without any discernible pattern.
Hind's Variable Nebula
Not far from T Tauri, Hind found a reflection nebula, now called Hind's Variable Nebula, which is illuminated at the whim of its unreliable neighbor. Hind's Variable Nebula is remarkable for its changes in brightness, which are due to wide variations in T Tauri itself. Discovered by Hind in 1852, it began to fade after 1861 and had disappeared from view to even the largest telescopes of the time by 1868. It was not seen again until 1890 when it was observed by Edward Barnard and Sherburne Burnham. Since the 1930s it has been gradually brightening but remains a challenge for the amateur observer.
In 1890, nearly 40 years after the discovery of T Tauri, Shelburn Burnham found that T Tauri is nestled within a much smaller nebula, now popularly known as Burnham's Nebula. When Burnham made his discovery, T Tauri was shining feebly at 14th magnitude – at the limit of most telescopes of the time. The condensed nebula appeared to be about arc-seconds in size in its longest dimension. T Tauri has been brighter than 10th magnitude since the early twentieth century making this feature very hard to detect. Burnham's Nebula can be discerned in an overexposed image of T Tauri as a bulge extending about 10 arc-seconds from the star. Unlike Hind's Variable Nebula, it is not believed to be a reflection nebula.
Other components of the T Tauri system
Much more recently, 30 arc-seconds west of the brightest point in Hind's nebula has been uncovered a Herbig-Haro object – a jet of the type commonly associated with young, mass-ejecting stars. As if all this were not enough, T Tauri turns out to have a binary companion, detected by its infrared glow, 0.5 arc-second to the south – hence known as T Tauri S, while T Tauri becomes T Tauri N – and there is even data to such that T Tauri is a triple-star system.