Artist's impression of the disk surrounding GG Tauri A and B
Credit: ESO/L. Calçada
Epoch J2000 Equinox J2000
|GG Tauri A|
|Right ascension||04h 32m 30.31s|
|Declination||+17° 31′ 41.0″|
|Apparent magnitude (V)||12.25 ± 0.03 / 14.70 ± 0.06|
|GG Tauri Ba|
|Right ascension||04h 32m 30.25s|
|Declination||+17° 31′ 30.9″|
|Apparent magnitude (V)||17.11 ± 0.07|
|GG Tauri Bb|
|Right ascension||04h 32m 30.31s|
|Declination||+17° 31′ 29.9″|
|Apparent magnitude (V)||19.94 ± 0.08|
|Spectral type||K7 / M2 / M3 / M5 / M7|
|U−B color index||+0.06|
|B−V color index||+1.38|
|Variable type||T Tauri|
|Radial velocity (Rv)||12.0 km/s|
|Proper motion (μ)|| RA: 15.6 mas/yr |
Dec.: -21.1 mas/yr
|Distance||450 ly |
|Primary||GG Tau Aa|
|Companion||GG Tau Ab|
|Semi-major axis (a)||429 mas|
|Longitude of the node (Ω)||131+3|
|Periastron epoch (T)||2463400+1470|
|Argument of periastron (ω)|
|GG Tau Aa|
|Mass||0.78 ± 0.09 M☉|
|GG Tau Ab|
|GG Tau Ba|
|Mass||0.12 ± 0.02 M☉|
|GG Tauri Bb|
|Mass||0.04 ± 0.003 M☉|
GG Tauri, often abbreviated as GG Tau, is a quintuple star system in the constellation Taurus. At a distance of about 450 light years (140 parsecs) away, it is located within the Taurus-Auriga Star Forming Region. The system comprises three stars orbiting each other in a hierarchical triple system, and another binary star system more distant from the central system.
GG Tauri consists of five stars, which are T Tauri stars – a class of variable stars that show irregular changes in brightness. These stars are extremely young and more luminous than their main sequence counterparts, because they have not condensed into the normal size yet. The four components of GG Tauri stars are relatively cool K-type or M-type stars, with these spectral types: K7 for GG Tauri Aa, M0.5 for GG Tauri Ab, M5 for GG Tauri Ba, and M7 for GG Tauri Bb; the age of the system is estimated to be 1.5 million years.
A dynamical study of the system found the masses of the four components to be: 0.78 M☉ for GG Tauri Aa, 0.68 M☉ for GG Tauri Ab, 0.12 M☉ for GG Tauri Ba, and 0.12 M☉ for GG Tauri Bb. At 0.04 M☉, GG Tauri Bb has a substellar mass and is a brown dwarf. Orbital motion has been detected in the central system, but not in the outer pair (as its separation is too high). A preliminary orbit for GG Tauri Aa and Ab has been calculated. The orbit is moderately eccentric, and is probably not coplanar to the inner circumstellar disk, being misaligned by about 25 degrees.
Interferometric techniques have been used to observe GG Tauri Ab, the lower-mass component of the central system. GG Tauri Ab was found to be a binary star system comprising two red dwarfs (Ab1 = M2V, Ab2 = M3V), with a separation of about 4.5 AU. Its orbital period is currently estimated to be around 16 years. This would explain why the GG Tauri Ab's spectrum suggests an unusually low-mass star instead of the higher mass that was measured.
T Tauri stars are usually surrounded by circumstellar disks. These disks coalesce into protoplanets and then into planets. The inner disk around GG Tauri has a mass of about 0.1 M☉, or about the mass of Jupiter, at a temperature of about 20 to 30 K. However, because mass is currently accreting into the stars themselves, the inner disk must have been consumed, or another larger, circumstellar disk must have been supplying mass into the smaller disk.
A search for diatomic hydrogen gas near GG Tauri was conducted; H2 gas could be found up to 100 AU away from the center of the system, with significant emission also being detected 30 AU away. This emission was detected where a previous survey found gas streaming from the outer disk to the inner disk, so it was assumed that the emission resulted from mass falling from the inner disk to the outer disk. Observations taken in 2014 showed similar results. Indeed, observations of the circumstellar disk around GG Tauri found "sharply-defined features" around the disk: simulations of GG Tauri's disk indicate that these are likely due to the gravitational forces from the two stellar components.
A "gap" in the larger circumstellar disk has been detected at the three-o'clock position, at a position angle of about 268°. First seen in 2002, it was confirmed to be the result of interstellar material shadowing part of the disk.
The chemistry of circumstellar disks is important for understanding planetary formation. The inner disk, like other protoplanetary disks, is rich in simple molecules containing elements such as carbon and sulfur. In 2018, hydrogen sulfide (H
2S) was reported, and in 2021, thioxoethenylidene (CCS) was reported to exist within the disk. Both are the first instances of those species known in a protoplanetary disk. The chemical mechanisms related to their formation are not very well understood.