Theta1 Orionis A

θ1 Orionis A

Trapezium stars
Observation data
Epoch J2000      Equinox ICRS
Constellation Orion
Right ascension 05h 35m 15.84743s[1]
Declination −05° 23′ 14.3441″[1]
Apparent magnitude (V) 6.72 - 7.65[2]
Characteristics
Spectral type B0.5V[3] + G[4] + F PMS[5]
Variable type Algol[2]
Astrometry
Radial velocity (Rv)32.354±0.062[4] km/s
Proper motion (μ) RA: 4.81±0.10[6] mas/yr
Dec.: −2.53±0.12[6] mas/yr
Parallax (π)2.626±0.100 mas[6]
Distance1,272.0 ± 6.5 ly
(390±2 pc)[4]
Absolute magnitude (MV)−2.80[3]
Orbit[4]
PrimaryA1
NameA3
Period (P)65.433300±0.000019 days
Semi-major axis (a)178.56 ± 0.45 R☉ (0.8304 ± 0.0021 au)
Eccentricity (e)0.64383±0.00029
Inclination (i)87.090±0.014°
Periastron epoch (T)2,459,441.257±0.016 HJD
Argument of periastron (ω)
(secondary)		177.88±0.06°
Semi-amplitude (K1)
(primary)		28.499±0.082 km/s
Semi-amplitude (K2)
(secondary)		151.43±0.76 km/s
Details[4]
A1
Mass15.01±0.32 M☉
Radius4.20±0.05 R☉
Luminosity15,800+3,200
−2,700 L☉
Surface gravity (log g)4.37±0.01 cgs
Temperature30,500±800 K
Age0.7 Myr
A3
Mass2.825±0.145 M☉
Radius6.415±0.055 R☉
Luminosity54+11
−9 L☉
Surface gravity (log g)3.28±0.04 cgs
Temperature5,550±500 K
Age0.7 Myr
A2
Mass4[7][5] M☉
Other designations
41 Ori A, V1016 Ori, BD−05 1315A, HD 37020, HIP 26220, HR 1893
Database references
SIMBADdata

Theta1 Orionis A (θ1 Ori A) is a trinary star in the constellation Orion. The system consists of an close pair of eclipsing stars orbited by a visual companion farther away. Its apparent magnitude range is 6.72 to 7.65 with a period of 65.432 days. It is one of the main stars in The Trapezium in Orion, along with B, C, and D, as well as the fainter E.

Variability

A visual band light curve for V1016 Orionis, plotted from AAVSO data.[8] The inset plot, adapted from Lloyd and Stickland (1999),[9] shows the time around the eclipse minimum with an expanded scale.

θ1 Orionis A varies in brightness, showing dips from magnitude 6.72 to 7.65 every 65.432 days. These are caused by eclipses of the central pair. θ1 Orionis A has been assigned the variable star designation V1016 Orionis.[2]

System

θ1 Orionis A1 and θ1 Orionis A3 form an eclipsing binary system, where only the primary is detected in the spectrum.[10][11] The components orbit around each other with an orbital period of roughly 65.4 days, following a highly-eccentric path with a semi-major axis of 0.8304 ± 0.0021 au and an eccentricity of 0.644. The primary is an B0.5V star with a temperature of 30,500 K, 15 times the mass of the Sun, 4.2 times the Sun's radius, and a luminosity 16,000 times solar.[4] The secondary has been proposed to be a T Tauri star, possibly of spectral class A,[12][11] but later confirmed to be of spectral class G with a temperature of 5,600±500 K. It has a mass 2.8 times solar and an inflated radius of 6.4 times that of the Sun, radiating a luminosity 54 times brighter than the Sun's.[4]

θ1 Orionis A2 is an F-type pre-main-sequence star, 1.63 fainter than the inner pair in the K band and with an estimated mass of 4 solar masses. It was proven to be gravitationally bound to the system in 2018 using long-term astrometric measurements. Its separation from the inner pair has changed from 0.227" in 1995 to 0.193" in late 2011. At the system's distance, the angular separations correspond to a projected separation of 90–100 AU. Its orbital period has been determined at 214 years.[5]

References

  1. 1 2 Kounkel, Marina; Hartmann, Lee; Loinard, Laurent; Mioduszewski, Amy J.; Dzib, Sergio A.; Ortiz-León, Gisela N.; Rodríguez, Luis F.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Evans, Neal J.; Briceño, Cesar; Tobin, John (2014). "The Gould's Belt Very Large Array Survey. III. The Orion Region". The Astrophysical Journal. 790 (1): 49. arXiv:1406.1809. Bibcode:2014ApJ...790...49K. doi:10.1088/0004-637X/790/1/49. S2CID 119231061.
  2. 1 2 3 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  3. 1 2 Nieva, María-Fernanda; Przybilla, Norbert (2014). "Fundamental properties of nearby single early B-type stars". Astronomy & Astrophysics. 566: A7. arXiv:1412.1418. Bibcode:2014A&A...566A...7N. doi:10.1051/0004-6361/201423373. S2CID 119227033.
  4. 1 2 3 4 5 6 7 Sowell, James R.; Fekel, Francis C.; Henry, Gregory W.; Williamson, Michael H.; Armstrong, James D.; Aipa, Ryan; Stino, Martino (2026-07-13). "The Properties of V1016 Orionis, the Eclipsing Binary in the Trapezium System θ1 Orionis A". The Astronomical Journal. 172 (2): 78. doi:10.3847/1538-3881/ae7c7b. ISSN 0004-6256.
  5. 1 2 3 GRAVITY Collaboration; Karl, Martina; Pfuhl, Oliver; Eisenhauer, Frank; Genzel, Reinhard; Grellmann, Rebekka; Habibi, Maryam; Abuter, Roberto; Accardo, Matteo; Amorim, António; Anugu, Narsireddy; Ávila, Gerardo; Benisty, Myriam; Berger, Jean-Philippe; Blind, Nicolas (2018-12-01). "Multiple star systems in the Orion nebula". Astronomy and Astrophysics. 620: A116. arXiv:1809.10376. Bibcode:2018A&A...620A.116G. doi:10.1051/0004-6361/201833575. ISSN 0004-6361.
  6. 1 2 3 Kounkel, Marina; et al. (2017). "The Gould's Belt Distances Survey (GOBELINS) II. Distances and Structure toward the Orion Molecular Clouds". The Astrophysical Journal. 834 (2). 142. arXiv:1609.04041. Bibcode:2017ApJ...834..142K. doi:10.3847/1538-4357/834/2/142. S2CID 26439367.
  7. ↑ Grellmann, R.; Preibisch, T.; Ratzka, T.; Kraus, S.; Helminiak, K. G.; Zinnecker, H. (2013). "The multiplicity of massive stars in the Orion Nebula Cluster as seen with long-baseline interferometry". Astronomy & Astrophysics. 550: A82. arXiv:1301.3045. Bibcode:2013A&A...550A..82G. doi:10.1051/0004-6361/201220192. S2CID 6554786.
  8. ↑ "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  9. ↑ Lloyd, C.; Stickland, D. J. (November 1999). "The Nature of the Bright Early-Type Eclipsing Binary Theta 1 Ori A = V1016 Orionis". Information Bulletin on Variable Stars. 4809: 1. Bibcode:1999IBVS.4809....1L. Retrieved 8 February 2022.
  10. ↑ Bossi, M.; Gaspani, A.; Scardia, M.; Tadini, M. (1989). "Orionis A - A pre-main sequence low Q binary system?". Astronomy and Astrophysics. 222: 117. Bibcode:1989A&A...222..117B.
  11. 1 2 Vitrichenko, E. A.; Klochkova, V. G. (2000). "A Spectroscopic Study of V1016 Ori". Astronomy Letters. 26 (2): 104. Bibcode:2000AstL...26..104V. doi:10.1134/1.20373. S2CID 119402387.
  12. ↑ Petr, Monika G.; Coudé Du Foresto, Vincent; Beckwith, Steven V. W.; Richichi, Andrea; McCaughrean, Mark J. (1998). "Binary Stars in the Orion Trapezium Cluster Core". The Astrophysical Journal. 500 (2): 825. Bibcode:1998ApJ...500..825P. doi:10.1086/305751.
  13. Close, L. M.; Puglisi, A.; Males, J. R.; Arcidiacono, C.; Skemer, A.; Guerra, J. C.; Busoni, L.; Brusa, G.; Pinna, E.; Miller, D. L.; Riccardi, A.; McCarthy, D. W.; Xompero, M.; Kulesa, C.; Quiros-Pacheco, F.; Argomedo, J.; Brynnel, J.; Esposito, S.; Mannucci, F.; Boutsia, K.; Fini, L.; Thompson, D. J.; Hill, J. M.; Woodward, C. E.; Briguglio, R.; Rodigas, T. J.; Briguglio, R.; Stefanini, P.; Agapito, G.; et al. (2012). "High-resolution Images of Orbital Motion in the Orion Trapezium Cluster with the LBT AO System". The Astrophysical Journal. 749 (2): 180. arXiv:1203.2638. Bibcode:2012ApJ...749..180C. doi:10.1088/0004-637X/749/2/180. S2CID 119298839.
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