GG Tauri

GG Tauri, often abbreviated as GG Tau, is a quadruple or 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 two (possibly three) stars orbiting each other in a hierarchical triple system, and another binary star system more distant from the central system.[13]

GG Tauri

Artist's impression of the disk surrounding GG Tauri A and B
Credit: ESO/L. Calçada
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
GG Tauri A
Right ascension  04h 32m 30.31s[1]
Declination +17° 31′ 41.0″[1]
Apparent magnitude (V) 12.25 ± 0.03 / 14.70 ± 0.06[2]
GG Tauri Ba
Right ascension  04h 32m 30.25s[3]
Declination +17° 31′ 30.9″[3]
Apparent magnitude (V) 17.11 ± 0.07[2]
GG Tauri Bb
Right ascension  04h 32m 30.31s[4]
Declination +17° 31′ 29.9″[4]
Apparent magnitude (V) 19.94 ± 0.08[2]
Characteristics
Spectral type K7 / M0.5 / M5 / M7[5]
U−B color index +0.06[6]
B−V color index +1.38[6]
Variable type T Tauri
Astrometry
Radial velocity (Rv)12.0[7] km/s
Proper motion (μ) RA: 15.6[8] mas/yr
Dec.: -21.1[8] mas/yr
Distance450 ly
(140[9] pc)
Orbit[10]
PrimaryGG Tau Aa
CompanionGG Tau Ab
Period (P)403+67
−32 yr
Semi-major axis (a)429 mas
(60 AU)
Eccentricity (e)0.44+0.02
−0.03
Inclination (i)132.5°
Longitude of the node (Ω)131+3
−8°
Periastron epoch (T)2463400+1470
−5420
Argument of periastron (ω)
(secondary)		19+9
−10°
Details
GG Tau Aa
Mass0.78 ± 0.09[11] M☉
Luminosity0.84[5] L☉
Age1.5[5] Gyr
GG Tau Ab
Luminosity0.71[5] L☉
Age1.5[5] Gyr
GG Tau Ba
Mass0.12 ± 0.02[11] M☉
Luminosity0.096[5] L☉
Age1.5[5] Gyr
GG Tauri Bb
Mass0.04 ± 0.003[11] M☉
Luminosity0.015[5] L☉
Age1.5[5] Gyr
Other designations
GG Tau, WDS J04325+1732, TYC 1270-897-1[12]
Database references
SIMBADdata

The system is unusual because it contains two distinct circumstellar disks: one surrounding the entire system, and another surrounding the primary component of the system.[13]

Properties

GG Tauri consists of four (possibly five) stars, which are T Tauri stars – a class of variable stars that show irregular changes in brightness.[14] 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;[5] the age of the system is estimated to be 1.5 million years.[9]

A dynamical study of the system found the masses of the four stars to be: 0.78 M☉ for GG Tauri Aa, 0.68 M☉ for GG Tauri Ab, 0.12 M☉ for GG Tauri Ba, and 0.04 M☉ for GG Tauri Bb. At 0.04 M☉, GG Tauri has a substellar mass and is a brown dwarf.[11] 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 A has been calculated.[10]

Interferometric techniques have been used to observe GG Tauri Ab, the lower-mass component of the central system. GG Tauri Ab may actually be a double 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.[15]

Circumstellar disks

T Tauri stars are usually surrounded by circumstellar disks. These disks coalesce into protoplanets and then into planets.[14] The inner disk around GG Tauri has a mass of about 0.1 M☉, or about the mass of Jupiter,[16] at a temperature of about 20 to 30 K.[17] 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.[13]

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.[18] Observations taken in 2014 showed similar results.[13] 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.[19]

A "gap" in the larger circumstellar disk has been detected at the three-o'clock position, at a position angle of about 268°.[20] First seen in 2002,[2] it was confirmed to be the result of interstellar material shadowing part of the disk.[20]

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See also
  • HL Tauri, a T Tauri star with a protoplanetary disk
  • BD−22 5866, a quadruple star system with relatively low mass

References
  1. "** LEI 3Aa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 10 February 2017.
  2. Krist, John E.; Stapelfeldt, Karl R.; Watson, Alan M. (2002). "Hubble Space Telescope/WFPC2 Images of the GG Tauri Circumbinary Disk". The Astrophysical Journal. 570 (2): 785–792. arXiv:astro-ph/0201415. Bibcode:2002ApJ...570..785K. doi:10.1086/339777.
  3. "** LEI 3Ba". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 10 February 2017.
  4. "** LEI 3Bb". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 10 February 2017.
  5. White, Russel J.; Ghez, A. M.; Reid, I. Neill; Schultz, Greg (1999). "A Test of Pre-Main-Sequence Evolutionary Models across the Stellar/Substellar Boundary Based on Spectra of the Young Quadruple GG Tauri". The Astrophysical Journal. 520 (2): 811–821. arXiv:astro-ph/9902318. Bibcode:1999ApJ...520..811W. doi:10.1086/307494.
  6. Smak, J. (1964). "On the colors of T Tauri stars and related objects". Astrophysical Journal. 139: 1095. Bibcode:1964ApJ...139.1095S. doi:10.1086/147851.
  7. Joy, Alfred H. (1949). "Bright-Line Stars among the Taurus Dark Clouds". Astrophysical Journal. 110: 424. Bibcode:1949ApJ...110..424J. doi:10.1086/145217.Accessed using SIMBAD.
  8. Zacharias, N.; Urban, S. E.; Zacharias, M. I.; Wycoff, G. L.; Hall, D. M.; Germain, M. E.; Holdenried, E. R.; Winter, L. (2003). "VizieR Online Data Catalog: The Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2)". CDS/ADC Collection of Electronic Catalogues. Bibcode:2003yCat.1289....0Z.Accessed using SIMBAD.
  9. Piétu, V.; Gueth, F.; Hily-Blant, P.; Schuster, K.-F.; Pety, J. "High resolution imaging of the GG Tauri system at 267 GHz". Astronomy & Astrophysics. 582. arXiv:1102.4029. Bibcode:2011A&A...528A..81P. doi:10.1051/0004-6361/201015682.
  10. Köhler, R. (2011). "The orbit of GG Tauri A". Astronomy & Astrophysics. 530. arXiv:1104.2245. Bibcode:2011A&A...530A.126K. doi:10.1051/0004-6361/201016327. Note: "most plausible orbit" is given in the starbox above.
  11. Beust, H.; Dutrey, A. (2005). "Dynamics of the young multiple system GG Tauri. I. Orbital fits and inner edge of the circumbinary disk of GG Tau A". Astronomy and Astrophysics. 439 (2): 585–594. Bibcode:2005A&A...439..585B. doi:10.1051/0004-6361:20042441.
  12. "V* GG Tau". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 11 February 2017.
  13. "Astronomers Examine Ezekiel-like 'Wheel in a Wheel' in Binary System GG Tauri-A". Sci-News.com. 30 October 2014. Retrieved 10 February 2017.
  14. "T Tauri Stars | COSMOS". Retrieved 11 February 2017.
  15. Di Folco, E.; Dutrey, A.; Le Bouquin, J.-B.; Lacour, S.; Berger, J.-P.; Köhler, R.; Guilloteau, S.; Piétu, V.; Bary, J.; Beck, T.; Beust, H.; Pantin, E. (2014). "GG Tauri: the fifth element". Astronomy & Astrophysics. 565 (2). arXiv:1404.2205. Bibcode:2014A&A...565L...2D. doi:10.1051/0004-6361/201423675.
  16. Scaife, Anna M. M. (2013). "The long-wavelength view of GG Tau A: rocks in the ring world". Monthly Notices of the Royal Astronomical Society. 435 (2): 1139–1146. arXiv:1307.5146. Bibcode:2013MNRAS.435.1139S. doi:10.1093/mnras/stt1361.
  17. Andrews, Sean M.; et al. (2014). "Resolved Multifrequency Radio Observations of GG Tau". The Astrophysical Journal. 787 (2). arXiv:1404.5652. Bibcode:2014ApJ...787..148A. doi:10.1088/0004-637X/787/2/148.
  18. Beck, Tracy L.; Bary, Jeffrey S.; Dutrey, Anne; Piétu, Vincent; Guilloteau, Stéphane; Lubow, S. H.; Simon, M. (2012). "Circumbinary Gas Accretion onto a Central Binary: Infrared Molecular Hydrogen Emission from GG Tau A". The Astrophysical Journal. 754 (1). arXiv:1205.1526. Bibcode:2012ApJ...754...72B. doi:10.1088/0004-637X/754/1/72.
  19. Nelson, Andrew F.; Marzari, F. (2016). "Dynamics of Circumstellar Disks. III. The Case of GG Tau A". The Astrophysical Journal. 827 (2). arXiv:1605.02764. Bibcode:2016ApJ...827...93N. doi:10.3847/0004-637X/827/2/93.
  20. Krist, J. E.; K. R. Stapelfeldt; Golimowski, D. A.; Ardila, D. R.; Clampin, M.; Martel, A. R.; Ford, H. C.; Illingworth, G. D.; Hartig, G. F. "HST/ACS Images of the GG Tauri Circumbinary Disk". American Astronomical Society. 34: 1319. arXiv:astro-ph/0508222. Bibcode:2002AAS...20113601K. doi:10.1086/497069.
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