The star T Tauri with NGC 1555 cloud nearby.
Epoch J2000 Equinox J2000
|Right ascension||04h 21m 59.43445s|
|Declination||+19° 32′ 06.4182″|
|Apparent magnitude (V)||10.27|
|U−B color index||+0.80|
|B−V color index||+1.22|
|Variable type||T Tauri|
|Radial velocity (Rv)||+24.6 km/s|
|Proper motion (μ)|| RA: +15.51 mas/yr |
Dec.: -13.67 mas/yr
|Parallax (π)||6.9290 ± 0.0583 mas|
|Distance||471 ± 4 ly |
(144 ± 1 pc)
|Primary||T Tau N|
|Companion||T Tau S|
|Semi-major axis (a)||2.9+5.4|
|Longitude of the node (Ω)||156 ± 11°|
|Periastron epoch (T)||B 1967+25|
|Argument of periastron (ω)|
|Primary||T Tau Sa|
|Companion||T Tau Sb|
|Period (P)||27 ± 2 yr|
|Semi-major axis (a)||85+4|
|Longitude of the node (Ω)||92+26|
|Periastron epoch (T)||JD 2450131+208|
(1996 Feb 17)
|Argument of periastron (ω)|
|T Tau Sa|
|Mass||2.12 ± 0.10 M☉|
|T Tau Sb|
|Mass||0.53 ± 0.06 M☉|
T Tauri is a variable star in the constellation Taurus, the prototype of the T Tauri stars. It was discovered in October 1852 by John Russell Hind. T Tauri appears from Earth amongst the Hyades cluster, not far from ε Tauri, but it is actually 420 light-years behind it and was not formed with the rest of them. The cloud to the west of the system is NGC 1555, known more commonly as Hind's Variable Nebula.
Although this system is considered to be the prototype of T Tauri stars, a later phase in a protostar's formation, it is a very atypical T Tauri star.
The system has three stars: T Tauri North (T Tau N), T Tauri South A (T Tau Sa), and T Tauri South B (T Tau Sb). T Tau N is estimated to be approximately 300 AU away from the southern binary, with the separation of the binary believed to be approximately 7 AU with an orbital period of 27.2±0.7 years. The orbit of T Tau N about the southern binary is poorly constrained, with the period ranging from 400 years to 14,000 years as of 2020. T Tau N has a mass of ~2.1 M☉, T Tau Sa is estimated to be 2.0–2.3 M☉, and T Tau Sb is estimated to be approximately 0.4–0.5 M☉.
The southern binary is visible mainly in infrared, which is likely due to a circumbinary ring that is blocking the optical light (if there is any optical light leaking through, it must be at a magnitude of less than 19.6), while the accretion disk of T Tau N is believed to be nearly perpendicular to our line of sight, thus allowing us to see T Tau N in the optical. The southern binary's brightness varies dramatically over seemingly short timescales in the infrared. It is believed this variability is due to both the matter in the circumbinary ring not being uniform, thus varying the light let through as it orbits the binary, and due to the individual components of the binary flaring up as they accrete matter. It is unknown which mechanism contributes the most to the variability.
As of 2020, T Tau Sb is passing through the plane of the T Tau S circumbinary ring, and is currently dimming as the ring blocks its light.
All three stars are believed to be in the T Tauri phase. During this phase, a star does not undergo nuclear fusion within its core; it shines due to the residual heat given off by its collapse. This causes a T Tauri star to vary in brightness over the course of weeks or months as they accrete matter. An important mechanic in star formation are the jets that are formed by the accretion, which function similarly to the jets of a quasar or an active galactic nucleus (AGN). These jets form due to the magnetic fields formed in the accretion disk, and as a side effect, they carry away excess angular momentum from the star. Without this mechanism, a star would not be able to accrete to more than 0.05 M☉.
The T Tauri system has been of particular interest to astronomers because it is by no means a typical T Tauri star. The complex outflow system created by the jets is poorly understood, particularly in how it evolves over time. It is believed there are four jets, with two coming from T Tau N, and two coming from T Tau S (the jets of Sa and Sb appear to either combine, or Sb does not produce significant jets).
Surrounding the system are three distinct Herbig-Haro Objects. These are patches of nebulosity caused by the jets interacting with the interstellar medium. They can be thought of as shock fronts for the jets as the fast moving material slams into the cold gas and dust surrounding the system.
HH155 is the NGC 1555 cloud, otherwise known as Hind's Variable Nebula, and HH255 is nebulosity much closer to the star system itself, otherwise known as Burnham's Nebula. HH355 is even closer to the stars, likely caused by interactions of the jets.
As typical for the young stars, all three stars of T Tauri system are surrounded by a compact disks trimmed by star-star interaction. The disk around T Tauri N has a gap around 12 AU radius, indicating a presence of orbiting Saturn-mass planet within a gap.
(in order from star)
|T Tauri N protoplanetary disk||24±4 AU||25.2±1.1°||—|
|T Tauri Sa protoplanetary disk||3.9±0.1 AU||52.8±0.6°||—|
|T Tauri Sb protoplanetary disk||3.2±0.3 AU||63.2±0.9°||—|
The nebula NGC 1554 is believed to be associated with T Tauri. In the 1860s, Hind's nebula had faded from view for nearly all astronomers on Earth, including Hind himself, but Otto Wilhelm von Struve, having the third most powerful telescope in the world at the time, could still see it. In 1868, Struve reported a patch of nebulosity that he believed to be distinct from Hind's Nebula, and this was confirmed by a contemporary, Heinrich Louis d'Arrest. Over the course of the next 10-20 years, the nebula faded from view and Hind's Nebula came back into view of most astronomers at the same time. It is likely Struve truly did observe something, especially considering d'Arrest confirmed it, but as of 2021 there is no agreed upon explanation for what caused this phenomena.
The exact dynamics of the outflow system of T Tauri, particularly its evolution, is poorly understood. It is possible some sort of interaction between the jets in the past may have caused the phenomena that Struve observed, but more data on at least the orbital constraints of T Tau N and how the jets interact currently will be needed before any concrete theory can be reached.
In the 2014 video game Elite: Dangerous, the star system and surrounding nebula are featured as a location that players can visit. It is slightly further from Earth in the game than real life, and incorrectly simulates the star system itself, with T Tau N being represented by a main-sequence G-type star, and T Tau S being represented by a similar main-sequence G-type star (instead of a binary with two T Tauri stars). Notably, there is a small starport in the system called Hind's Mine that is in the ring system of a fictional gas giant in orbit of T Tau N, notable for its large distance from most other settled systems.