U Orionis

Variable star in the constellation Orion
U Orionis
Location of U Orionis (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Orion
Right ascension 05h 55m 49.17076s[1]
Declination +20° 10′ 30.6779″[1]
Apparent magnitude (V) 4.8 - 13.0[2]
Characteristics
Spectral type M6e-M9.5e[2]
B−V color index +2.07[3]
Variable type Mira[2]
Astrometry
Parallax (π)3.4924 ± 0.1820 mas[1]
Distance930 ± 50 ly
(290 ± 10 pc)
Details
Mass0.88[4] M☉
Radius370±96[5] R☉
Luminosity7,000[6] L☉
Surface gravity (log g)−0.44[4] cgs
Temperature2,641[4] K
Metallicity [Fe/H]0.54[4] dex
Other designations
U Ori, BD+20°1171a, HD 39816, HIP 28041, HR 2063, SAO 77730[7]
Database references
SIMBADdata

U Orionis (abbreviated U Ori) is a Mira-type variable star in the constellation Orion. It is a classical long period variable star that has been well observed for over 120 years.

Discovery

U Orionis in the center of the image at approx visual mag. 12 on February 5th 2017

It was discovered on 1885 December 13 by J.E. Gore and initially it was thought to be a nova in the early stages of decline (Gore's Nova and NOVA Ori 1885 as still listed in SIMBAD), but a spectrum taken at Harvard showed features similar to that of Mira. Thus U Orionis became the first long period variable to be identified by a photograph of its spectrum.[8]

Location

U Orionis lies less than half a degree east of the small-amplitude variable star χ1 Orionis and less than an arc-minute from the much fainter eclipsing variable UW Orionis. χ1 Orionis is slightly brighter than U Orionis at its brightest maximum, while UW Orionis is more than a thousand times fainter, similar to U Orionis at minimum.

Stellar parameters

The visual band light curve of U Orionis, from AAVSO data[9]

The star has a low effective temperature (variable with the pulsations, but roughly 2,700 K), a large and bloated radius of 370 R☉,[5] and a high luminosity, 7,000 times higher than the Sun.[6] If the Sun were replaced with U Orionis, its radius would extend beyond Mars's orbital zone (about 1.7 astronomical units).

Possible planetary system

According to Rudnitskij,[10] a 12- to 15-year "super-periodicity" has been observed. The author infers such periodicity could coincide with the revolution period of an invisible companion, probably planetary. So far no clear hint of planetary objects has been detected.

References

  1. ^ a b c 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. ^ a b c Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. ^ Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  4. ^ a b c d Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevic, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; de Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (1 August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. ISSN 0004-6361. S2CID 131780028.
  5. ^ a b Van Belle; et al. (1996). "Angular Size Measurements of 18 Mira Variable Stars at 2.2 microns". Astronomical Journal. 112: 2147. Bibcode:1996AJ....112.2147V. doi:10.1086/118170.
  6. ^ a b Mondal & Chandrasekhar (2004). "Evidence of asymmetry in Mira variable U Ori". Monthly Notices of the Royal Astronomical Society. 348 (4): 1332–1336. Bibcode:2004MNRAS.348.1332M. doi:10.1111/j.1365-2966.2004.07454.x.
  7. ^ "V* U Ori". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 25 January 2018.
  8. ^ Monck (1887). "Mr Gore's Nova Orionis". The Observatory. 10: 69–71. Bibcode:1887Obs....10...69M.
  9. ^ "Download Data". aavso.org. AAVSO. Retrieved 1 October 2021.
  10. ^ Rudnitskij (2002). "Molecular Masers in Variable Stars". Publications of the Astronomical Society of Australia. 19 (4): 499–504. Bibcode:2002PASA...19..499R. doi:10.1071/AS02018.
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