GW Orionis

GW Orionis in the constellation Orion (yellow circle)
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 29m 08.3929s[1]
Declination +11° 52′ 12.666″[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: −2.351±0.061[1] mas/yr
Dec.: −0.396±0.043[1] mas/yr
Parallax (π)2.4510 ± 0.0623 mas[1]
Distance1,330 ± 30 ly
(410 ± 10 pc)
Orbit[5]
PrimaryGW Orionis A
CompanionGW 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)151+1
−2[5]°
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]
PrimaryGW Orionis AB
CompanionGW Orionis C
Period (P)4246±66 d
Semi-major axis (a)9.19±0.32 AU
Eccentricity (e)0.13±0.07
Inclination (i)130+28
−27[5]°
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
Mass2.74+0.15
−0.52[5][6] M☉
Temperature5780±100[4] K
Rotational velocity (v sin i)43[4] km/s
Age0.3–1.3[5] Myr
GW Orionis B
Mass1.65+0.10
−0.31[5][6] M☉
Temperature5250±100[4] K
Rotational velocity (v sin i)50[4] km/s
Age0.3–1.3[5] Myr
GW Orionis C
Mass0.88+0.85
−0.19[5][6] M☉
Age0.3–1.3[5] Myr
Other designations
MHA 265-2, HD 244138, HIP 25689, TYC 708-1901-1, 2MASS J05290838+1152126[7]
Database references
SIMBADdata

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.

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, published in 1991. 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 detected directly in 2011 using the IOTA interferometer located on Mount Hopkins in Arizona.[10]

Variability

Visual band light curves for several eclipse minima of GW Orionis, adapted from Czekala et al. (2017)[5]

GW Orionis is a variable star with quasi-periodic brightness changes. The apparent magnitude varies between 9.7 and 10.4 with dimming events of between 0.1 and 0.7 magnitudes roughly every 30 days, as well as more sinusoidal variations with an amplitude of 0.2 magnitudes over 11.6 years.

An initial interpretation of the variability was that a disk of material around component B was eclipsing component A and causing the dimming events, but it is now thought that the eclipses are caused by partial obscuration of both stars by a much larger ring which precesses around the pair.[5]

Protoplanetary disk

The inner ring of GW Orionis: model and SPHERE observations

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] Observations of the disk made with the Atacama Large Millimeter Array identified three separate dust rings located at ~46, 188, and 338 astronomical units from the center of the system. The three rings have estimated dust masses 74, 168, and 245 times that of the Earth. According to Jiaqing Bi and coauthors, the outermost ring is the largest protoplanetary dust ring they are aware of. The dust rings are misaligned and the innermost dust ring is eccentric, probably due to ongoing dynamical interactions between the triple stars and the circumtriple disk.[6]

Schematic diagram showing a proposed geometry of the GW Orionis system
Schematic diagram showing a proposed geometry of the GW Orionis system.[6]
ALMA self-calibrated dust continuum map of the GW Orionis system
ALMA self-calibrated dust continuum map of the GW Orionis system.[6]

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]

References

  1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  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. S2CID 119210837.
  4. ^ a b c d e f 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. S2CID 119238386.
  5. ^ a b c d e f g h i j k l m n o p 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. S2CID 73629935. When we combined the RV constraints with the disk-based constraint on Mtot, we found stellar masses of MA = 2.7 M⊙, MB = 1.7 M⊙, and MC = 0.9 M⊙, to a precision of ± 0.3 M⊙
  6. ^ a b c d e f Bi, Jiaqing; et al. (2020). "GW Ori: Interactions between a Triple-star System and Its Circumtriple Disk in Action". The Astrophysical Journal. 895 (1). L18. arXiv:2004.03135. Bibcode:2020ApJ...895L..18B. doi:10.3847/2041-8213/ab8eb4. The stellar masses have been constrained to be ~2.7, 1.7, and 0.9 M⊙, respectively (Czekala et al. 2017)
  7. ^ "GW Ori". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-21.
  8. ^ a b 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. S2CID 14305837.
  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. S2CID 119328687.
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