NU Orionis

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This article is about the designated variable star NU Orionis. It should not be confused with Nu Orionis, whose name is a Bayer designation.
NU Orionis

Image of Messier 43, with NU Orionis in the center
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 35m 31.3649s[1]
Declination −05° 16′ 02.582″[1]
Apparent magnitude (V) +6.80–6.93[2][3]
Characteristics
Spectral type B0.5V (Aa)[4] + A/B (B)[5] + B2V (C)[4]
Variable type INSA[2][3]
Astrometry
Radial velocity (Rv)67±1[6] km/s
Proper motion (μ) RA: +0.922 mas/yr[1]
Dec.: +1.718 mas/yr[1]
Parallax (π)2.4059±0.0585 mas[1]
Distance1,360 ± 30 ly
(420 ± 10 pc)
Orbit[4]
PrimaryAa
CompanionAb
Period (P)14.3027(7) days
Semi-major axis (a)0.36±0.01 au[5]
Eccentricity (e)<0.02
Inclination (i)70±4°
Periastron epoch (T)2,440,578.5(5) JD
Semi-amplitude (K1)
(primary)		50±8 km/s
Semi-amplitude (K2)
(secondary)		172±3 km/s
Orbit[4]
PrimaryA
CompanionC
Period (P)476±1 days
Semi-major axis (a)3.77±0.12 au[7]
Eccentricity (e)0.09±0.06
Inclination (i)70.1±0.9°
Periastron epoch (T)2,453,639(7) JD
Argument of periastron (ω)
(secondary)		100±5°
Semi-amplitude (K1)
(primary)		21±4 km/s
Semi-amplitude (K2)
(secondary)		47±6 km/s
Position (relative to AC)
ComponentB
Epoch of observation1999[8]
Angular distance470[8] mas
Projected separation195±4[5] AU
Details[7]
Aa
Mass16.4±0.4 M☉
Radius5.7±0.3 R☉
Luminosity26,900 L☉
Surface gravity (log g)4.15±0.05 cgs
Temperature31,100±500 K
Rotational velocity (v sin i)190±20 km/s
Age3+2
−1 Myr
Ab
Mass4.4±0.2 M☉
Radius2.5±0.3 R☉
Luminosity350 L☉
Surface gravity (log g)4.28±0.10 cgs
Temperature15,700±500 K
Rotational velocity (v sin i)8±3 km/s
Age3+2
−1 Myr
B
Mass3.8 M☉
Radius2.3 R☉
Luminosity190 L☉
Surface gravity (log g)4.28 cgs
Temperature14,000 K
Rotational velocity (v sin i)180 km/s
Age3+2
−1 Myr
C
Mass8.1±0.4 M☉
Radius3.6±0.4 R☉
Luminosity2,800 L☉
Surface gravity (log g)4.25±0.10 cgs
Temperature22,300±500 K
Rotation1.09468(7)[7] days
Rotational velocity (v sin i)104±10 km/s
Age3+2
−1 Myr
Other designations
BD−05°1325, HD 37061, HIP 26258, TYC 4774-906-1[9]
Database references
SIMBADdata

NU Orionis (HD 37061) is a quadruple star system in the Orion constellation. It is located in the emission nebula Messier 43 and is the main star ionizing it. The distance to the system is 1,360 light-years (420 parsecs), as determined by its stellar parallax.

Location

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NU Orionis is within Messier 43 (M43), an emission nebula and H II region[10] that is inside the Orion Nebula. It is the main star ionizing M43, with its radiation sculpting the nebula.[11]

Due to its faint apparent magnitude of 6.8,[12] NU Orionis cannot be seen with the unaided eye, requiring at least binoculars to be seen.[13] Messier 43 itself is magnitude 9, and can be seen with a small telescope. It culminates and is best seen in January.[11]

Image of NU Orionis (HD 37061 right side) and a proplyd (left side) from the James Webb Space Telescope.

NU Orionis was identified to be responsible for photoevaporation of several protoplanetary disks around stars in M43. These objects are also called proplyds. Two proplyds were discovered with the Hubble Space Telescope and later one additional proplyd was discovered with the James Webb Space Telescope.[14][15]

Variability

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NU Orionis light curve plotted from TESS data[16]

NU Orionis is classified as "INSA" in the General Catalogue of Variable Stars.[3] This acronym means that it is an Orion variable – a hot star with irregular variation – surrounded in nebulosity. The apparent magnitude varies from 6.80 to 6.93.[2] Such classification is typical of hot, very young stars in the early stages of evolution.[2] The estimated age of NU Ori is 3 million years.[7]

Star system

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NU Orionis was believed to be a single star until 1991, when spectroscopic observations revealed it to be a close binary[17] with an orbital period of about 19 days.[18] Subsequently, the distant companion HD 37061 B was discovered in 1999, at a distance of 470 milliarcseconds (mas).[8] In 2013, a candidate fourth member named HD 37061 C was announced, discovered using interferometry at a distance of 15 mas from the central pair.[19] It was confirmed in 2018.[5]

The primary component, NU Orionis Aa, is a B-type main-sequence star with 16.4 times the mass of the Sun and 5.7 times the radius of the Sun, radiating 27,000 times the solar luminosity. Its companion, NU Orionis Ab, orbits with a period of 14.3027 days[4] and is separated by 0.36 astronomical units;[5] the orbit is nearly circular.[4] The star has 4.4 times the mass and 2.5 times the radius of the Sun, radiating 350 times the radiation the Sun does.[7]

The tertiary NU Orionis C is a B-type main-sequence star[4] with 8.1 times the mass, 3.6 times the radius, and radiates 2,800 times the Sun's luminosity.[7] The star has a strong magnetic field. It orbits the Aa-Ab pair with an orbital period of 476 days (1.30 years)[4] and is separated by 3.77 au.[7]

The outer companion B is an A or B-main sequence star[5] with 3.8 times the mass, 2.3 times the radius and 190 times the Sun's luminosity.[7] It has a projected separation of 195 au to the inner triple, an orbit too large to currently have its elements measurable.[5]

The components Aa, B and C are rapid rotators, spinning with projected rotational velocities of 190, 180 and 104 km/s respectively. Component C's rotation period has been measured at around 1.09 days.[7]

See also

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References

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  1. ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b c d "VSX : Detail for NU Ori". vsx.aavso.org. Retrieved 2025-08-18.
  3. ^ a b c "NU Ori". General Catalogue of Variable Stars. Retrieved 2025-08-18.
  4. ^ a b c d e f g h Shultz, M.; Le Bouquin, J.-B.; Rivinius, Th; Wade, G. A.; Kochukhov, O.; Alecian, E.; Petit, V.; Pfuhl, O.; Karl, M.; Gao, F.; Grellmann, R.; Lin, C.-C.; Garcia, P.; Lacour, S.; Collaboration, MiMeS (January 2019). "NU Ori: a hierarchical triple system with a strongly magnetic B-type star". Monthly Notices of the Royal Astronomical Society. 482 (3): 3950–3965. arXiv:1810.13388. Bibcode:2019MNRAS.482.3950S. doi:10.1093/mnras/sty2985. ISSN 0035-8711.
  5. ^ a b c d e f g 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. ^ Abt, Helmut A. (January 1970). "Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory". The Astrophysical Journal Supplement Series. 19: 387. Bibcode:1970ApJS...19..387A. doi:10.1086/190215. ISSN 0067-0049.
  7. ^ a b c d e f g h i Aschenbrenner, P.; Przybilla, N. (2024-11-01). "Quantitative spectroscopy of multiple OB stars - I. The quadruple system HD 37061 at the centre of Messier 43". Astronomy & Astrophysics. 691: A361. arXiv:2410.23229. Bibcode:2024A&A...691A.361A. doi:10.1051/0004-6361/202451878. ISSN 0004-6361.
  8. ^ a b c Preibisch, Thomas; Balega, Yuri; Hofmann, Karl-Heinz; Weigelt, Gerd; Zinnecker, Hans (1999-12-01). "Multiplicity of the massive stars in the Orion Nebula cluster". New Astronomy. 4 (7): 531–542. Bibcode:1999NewA....4..531P. doi:10.1016/S1384-1076(99)00042-1. ISSN 1384-1076.
  9. ^ "HD 37061". SIMBAD. Centre de données astronomiques de Strasbourg.
  10. ^ Thum, C.; Lemke, D.; Fahrbach, U.; Frey, A. (1978-04-01). "M43 - an emission nebula in Orion". Astronomy and Astrophysics. 65: 207–213. Bibcode:1978A&A....65..207T. ISSN 0004-6361.
  11. ^ a b "Messier 43 - NASA Science". 2017-10-19. Retrieved 2025-03-09.
  12. ^ Ducati, J. R. (2002-01-01). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR Online Data Catalog. 2237. Bibcode:2002yCat.2237....0D.
  13. ^ Macrobert, Alan (28 July 2006). "Binoculars: Halfway to a Telescope". Sky & Telescope. American Astronomical Society. Retrieved 11 May 2024.
  14. ^ O'Dell, C. R. (2001-11-01). "New Proplyds, Outflows, Shocks, and a Reflection Nebula in M43 and the Outer Parts of the Orion Nebula". The Astronomical Journal. 122: 2662–2667. Bibcode:2001AJ....122.2662O. doi:10.1086/323720. ISSN 0004-6256.
  15. ^ Habart, Emilie; Peeters, Els; Berné, Olivier; Trahin, Boris; Canin, Amélie; Chown, Ryan; Sidhu, Ameek; Van De Putte, Dries; Alarcón, Felipe; Schroetter, Ilane; Dartois, Emmanuel; Vicente, Sílvia; Abergel, Alain; Bergin, Edwin A.; Bernard-Salas, Jeronimo (2024-05-01). "PDRs4All. II. JWST's NIR and MIR imaging view of the Orion Nebula". Astronomy and Astrophysics. 685: A73. arXiv:2308.16732. Bibcode:2024A&A...685A..73H. doi:10.1051/0004-6361/202346747. ISSN 0004-6361.
  16. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 18 August 2025.
  17. ^ Morrell, Nidia; Levato, Hugo (1991-04-01). "Spectroscopic Binaries in the Orion OB1 Association". The Astrophysical Journal Supplement Series. 75: 965. Bibcode:1991ApJS...75..965M. doi:10.1086/191556. ISSN 0067-0049.
  18. ^ Abt, Helmut A.; Wang, Ruyou; Cardona, Octavio (1991-01-01). "Spectroscopic Binaries in the Orion Nebula Cluster". The Astrophysical Journal. 367: 155. Bibcode:1991ApJ...367..155A. doi:10.1086/169611. ISSN 0004-637X.
  19. ^ Grellmann, R.; Preibisch, T.; Ratzka, T.; Kraus, S.; Helminiak, K. G.; Zinnecker, H. (2013-02-01). "The multiplicity of massive stars in the Orion Nebula Cluster as seen with long-baseline interferometry". Astronomy and Astrophysics. 550: A82. arXiv:1301.3045. Bibcode:2013A&A...550A..82G. doi:10.1051/0004-6361/201220192. ISSN 0004-6361.