GW Orionis

GW Orionis is a T Tauri type pre-main sequence hierarchical triple star system.[5][8] It is associated with the Lambda Orionis star-forming region and has an extended circumtrinary protoplanetary disk.

GW Orionis

Observation data Epoch J2000      Equinox J2000
Constellation	Orion
Right ascension	05^h 29^m 08.3905^s[1]
Declination	+11° 52′ 12.668″[1]
Apparent magnitude (V)	9.7–10.4[2]
Characteristics
Spectral type	G8V[3] or G3V[4]/K0V[4]
Astrometry
Radial velocity (Rv)	28.33±0.18[5] km/s
Proper motion (μ)	RA: −0.013±0.085[1] mas/yr Dec.: −0.497±0.052[1] mas/yr
Parallax (π)	2.4850 ± 0.0648[6] mas
Distance	1,310 ± 30 ly (400 ± 10 pc)
Orbit[5]
Primary	GW Orionis A
Companion	GW Orionis B
Period (P)	241.50±0.05 d
Semi-major axis (a)	1.25±0.05 AU
Eccentricity (e)	0.13±0.01
Inclination (i)	157±1°
Longitude of the node (Ω)	263±13°
Periastron epoch (T)	2456681±4 HJD
Argument of periastron (ω) (secondary)	197±7°
Semi-amplitude (K1) (primary)	8.34±0.15 km/s
Orbit[5]
Primary	GW Orionis AB
Companion	GW Orionis C
Period (P)	4246±66 d
Semi-major axis (a)	9.19±0.32 AU
Eccentricity (e)	0.13±0.07
Inclination (i)	150±7°
Longitude of the node (Ω)	282±9°
Periastron epoch (T)	2453911±260 HJD
Argument of periastron (ω) (secondary)	310±21°
Semi-amplitude (K1) (primary)	2.38±0.23 km/s
Details
GW Orionis A
Mass	2.80+0.36 −0.31[5] M☉
Temperature	5780±100[4] K
Rotational velocity (v sin i)	43[4] km/s
Age	0.3–1.3[5] Myr
GW Orionis B
Mass	1.68+0.21 −0.18[5] M☉
Temperature	5250±100[4] K
Rotational velocity (v sin i)	50[4] km/s
Age	0.3–1.3[5] Myr
GW Orionis C
Mass	1.15+0.40 −0.23[5] M☉
Age	0.3–1.3[5] Myr
Other designations
MHA 265-2, HD 244138, HIP 25689, TYC 708-1901-1, 2MASS J05290838+1152126[7]
Database references
SIMBAD	data

Observational history

GW Orionis first came to the attention of astronomers when it was published, as MHA 265-2, in a list of stars whose spectra have bright H and K lines of calcium.[9]

The multiple nature of GW Orionis was first discovered by Robert D. Mathieu, Fred Adams and David W. Latham during a radial velocity survey of late type H-alpha emission stars in the Lambda Orionis Association. Radial velocities of the primary star were measured from 45 high resolution spectra and were used to determine the orbital elements. A trend in the radial velocity residuals indicated either an additional stellar companion with an orbital period of years or a global asymmetric gravitational instability in a circumstellar disc.[8]

GW Orionis B and the third member of the system, GW Orionis C, were directly detected in 2011 using the IOTA interferometer located on Mount Hopkins in Arizona.[10]

Protoplanetary disk

GW Orionis has a large and massive protoplanetary disk surrounding it. The dust continuum emission suggests a disk radius of approximately 400 astronomical units.[11] The disk has an inclination of 137.6°.[5]

Orbital architecture

The A and B components of GW Orionis form a double-lined spectroscopic binary with a 241-day period while component C orbits the inner pair with an 11.5 year period. It is likely that at least one of the stellar orbital planes is misaligned with the plane of the protoplanetary disk by as much as 45°.[5]

Variability

A light curve covering 30 years revealed 30 day eclipse events varying in depth between 0.1 and 0.7 magnitudes as well as a 0.2 magnitude sinusoidal oscillation that is aligned with the AB–C orbital period. This suggests that the A–B pair may be partially obscured due to dust in the disk as the pair approaches apoastron in the hierarchical orbit.[5]

References

1. Brown, A. G. A.; et al. (2016). "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties". Astronomy and Astrophysics. 595. A2. arXiv:1609.04172. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512.Gaia Data Release 1 catalog entry
2. Shevchenko, V. S.; et al. (1998). "The quasi-Algol GW Ori: The nature of eclipses and estimation of the component masses". Astronomy Letters. 24 (4): 528–534. Bibcode:1998AstL...24..528S.
3. Fang, M.; et al. (2014). "GW Orionis: Inner disk readjustments in a triple system". Astronomy and Astrophysics. 570. A118. arXiv:1407.4959. Bibcode:2014A&A...570A.118F. doi:10.1051/0004-6361/201424146.
4. Prato, L.; et al. (2018). "Orbital Solution for the Spectroscopic Binary in the GW Ori Hierarchical Triple". The Astrophysical Journal. 852 (1). 38. arXiv:1711.09449. Bibcode:2018ApJ...852...38P. doi:10.3847/1538-4357/aa98df.
5. Czekala, Ian; et al. (2017). "The Architecture of the GW Ori Young Triple-star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses". The Astrophysical Journal. 851 (2). 132. arXiv:1710.03153. Bibcode:2017ApJ...851..132C. doi:10.3847/1538-4357/aa9be7.
6. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
7. "GW Ori". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-21.
8. Mathieu, Robert D.; et al. (1991). "The T Tauri spectroscopic binary GW Orionis". The Astronomical Journal. 101: 2184–2198. Bibcode:1991AJ....101.2184M. doi:10.1086/115841.
9. Joy, Alfred H.; Wilson, Ralph E. (1949). "Stars whose Spectra have Bright H and K Lines of Calcium". The Astrophysical Journal. 109: 231–243. Bibcode:1949ApJ...109..231J. doi:10.1086/145126.
10. Berger, J.-P.; et al. (2011). "First astronomical unit scale image of the GW Orionis triple system". Astronomy and Astrophysics Letters. 529. L1. arXiv:1103.3888. Bibcode:2011A&A...529L...1B. doi:10.1051/0004-6361/201016219.
11. Fang, M.; et al. (2017). "Millimeter observations of the disk around GW Orionis". Astronomy and Astrophysics. 603. A132. arXiv:1705.01917. Bibcode:2017A&A...603A.132F. doi:10.1051/0004-6361/201628792.