Astronomy:Omicron Andromedae

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Short description: Variable star in the constellation of Andromeda
"1 Andromedae" and "1 And" redirect here. For the galaxy, see Andromeda I. For ι Andromedae, see Iota Andromedae. For other uses, see And 1.
Omicron Andromedae
Location of ο Andromedae (far right)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Andromeda
Right ascension  23h 01m 55.265s[1]
Declination +42° 19′ 33.66″[1]
Apparent magnitude (V) 3.62[2] (3.55 - 3.78[3])
Characteristics
Spectral type B6III[4] (B6IIIpe + A2p)[5]
U−B color index −0.53[2]
B−V color index −0.09[2]
Variable type γ Cas[6][3]
Astrometry
Radial velocity (Rv)−14.0[7] km/s
Proper motion (μ) RA: +22.99[8] mas/yr
Dec.: +0.88[8] mas/yr
Parallax (π)4.75 ± 0.53[8][9] mas
Distanceapprox. 690 ly
(approx. 210 pc)
Absolute magnitude (MV)−2.6[10]
Orbit[9]
PrimaryA
CompanionB
Period (P)118.0 yr
Semi-major axis (a)0.304″
Eccentricity (e)0.340
Inclination (i)107.4°
Orbit[11][12]
PrimaryAa
CompanionAb
Period (P)5.6 yr
Semi-major axis (a)0.061″
Eccentricity (e)0.22
Inclination (i)152.0°
Orbit[13][12]
PrimaryBa
CompanionBb
Period (P)33.01 days
Eccentricity (e)0.24
Semi-amplitude (K1)
(primary)		54.8±0.8 km/s
Semi-amplitude (K2)
(secondary)		71.6±0.8 km/s
Details
ο And Aa
Mass6.5±0.5[14] M☉
Radius11.5±1.3[14] R☉
Luminosity5,300±900[14] L☉
Temperature14,540±170[14] K
Rotational velocity (v sin i)240[15] km/s
Age52±9[14] Myr
ο And Ab
Mass4.51[12] M☉
ο And Ba
Mass3.74[12] M☉
ο And Bb
Mass2.86[12] M☉
Age50.1 ± 6.8[16] Myr
Other designations
Alfarasalkamil, 1 And, BD+41°4664, FK5 869, HIP 113726, HR 8762, SAO 52609, PPM 63726[17]
ο And A: HD 217675
ο And B: HD 217676
Database references
SIMBADdata

Omicron Andromedae, also named Alfarasalkamil,[18] is a star system in the northern constellation Andromeda. Its Bayer designation is Latinized from ο Andromedae, and is abbreviated Omi And or ο And, respectively. Based on parallax measurements, it is located at a distance of approximately 690 light years from Earth.[8] The system as a whole is classified as a blue-white B-type giant,[4] with a typical combined apparent magnitude of +3.62.[2] This is sufficiently bright that the star can be viewed with the naked eye on a dark night.

Nomenclature

This star was in the head of the traditional Arabic constellation Al Faras al Kamil, the Complete Horse, as opposed to Pegasus which is the front half of a horse.[19] The IAU Working Group on Star Names approved the name Alfarasalkamil for this star on 8 May 2025 and it is now so entered in the IAU Catalog of Star Names.[18]

It was also the brightest star of the obsolete constellation Honores Friderici.[20]

System

Omicron Andromedae is a multiple star containing at least three components. It may consist of two close pairs in a wider orbit, making a four-star system,[16] although the binarity of the primary star is in doubt.[12] This star system has a peculiar velocity of 34.5 ± 5.9 km/s, which qualifies it as a runaway star.[16]

The components A and B were first resolved in 1949, when they were reported to be separated by less than 0.1".[21] In 1975 they were separated by 0.375"[13] and by 2014 by only 0.21".[22] An orbit has been derived with a period of 118 years.[9] The companion is 2.3 magnitudes fainter than the primary star.[5]

In 1975, a companion was discovered by speckle interferometry only 0.05" from component A.[5] Components Aa and Ab orbit every 5.6 years,[11] although the existence of this companion is now doubted.[12]

A spectroscopic binary in the system was suspected and in 1988 it was confirmed. Although a clear 33.01 day period was seen, it was unclear which component was the pair seen in the spectrum.[13] Eventually, it was settled that component B was a close spectroscopic binary.[11]

Properties

A light curve for Omicron Andromedae, plotted from TESS data[23]

Omicron Andromedae is a Gamma Cassiopeiae type variable star and the system's brightness varies from magnitude +3.58 to +3.78. The variable component is the brightest and most massive star in the system, Aa.[3] Omicron Andromedae also shows variations with a period of about a day, similar to a β Lyrae-type eclipsing variable, but these are thought to be intrinsic to one of the components and not due to eclipses.[6]

The spectrum is predominantly that of a B6 giant star, from the brightest component in the system. It is a shell star and the spectrum contains emission lines with variable profiles.[5] Rapid variations in its spectrum have been reported.[24]

Spectral lines similar to an A2 star are also detectable in the spectrum and these are thought to originate in the B component.[5]

References

  1. ↑ 1.0 1.1 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Observatory. Bibcode: 1978ppch.book.....N. 
  3. ↑ 3.0 3.1 3.2 Samus, N. N. 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: B/GCVS. Bibcode: 2009yCat....102025S. 
  4. ↑ 4.0 4.1 Slettebak, A (1982). "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars". Astrophysical Journal Supplement Series 50: 55. doi:10.1086/190820. Bibcode: 1982ApJS...50...55S. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Olević, D.; Cvetković, Z. (2006). "Dynamical Masses of the Components in o Andromedae". The Astronomical Journal 131 (3): 1721. doi:10.1086/499539. Bibcode: 2006AJ....131.1721O. 
  6. ↑ 6.0 6.1 Zasche, P.; Wolf, M.; Hartkopf, W. I.; Svoboda, P.; Uhlař, R.; Liakos, A.; Gazeas, K. (2009). "A Catalog of Visual Double and Multiple Stars with Eclipsing Components". The Astronomical Journal 138 (2): 664–679. doi:10.1088/0004-6256/138/2/664. Bibcode: 2009AJ....138..664Z. 
  7. ↑ Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities". Washington: 0. Bibcode: 1953GCRV..C......0W. 
  8. ↑ 8.0 8.1 8.2 8.3 van Leeuwen, F. (1 November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. ISSN 0004-6361. Bibcode: 2007A&A...474..653V. 
  9. ↑ 9.0 9.1 9.2 Mitrofanova, A.; Dyachenko, V.; Beskakotov, A.; Balega, Yu.; Maksimov, A.; Rastegaev, D. (2021). "Speckle Interferometry of Nearby Multiple Stars. II. 2007-2020 Positional Measurements and Orbits of Sixteen Objects". The Astronomical Journal 162 (4): 156. doi:10.3847/1538-3881/ac1a78. Bibcode: 2021AJ....162..156M. "The mass sum calculated using the Hipparcos parallax is more plausible...". 
  10. ↑ Underhill, A. B. et al. (November 1979). "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars". Monthly Notices of the Royal Astronomical Society 189 (3): 601–605. doi:10.1093/mnras/189.3.601. Bibcode: 1979MNRAS.189..601U. 
  11. ↑ 11.0 11.1 11.2 Zhuchkov, R. Ya; Malogolovets, E. V.; Kiyaeva, O. V.; Orlov, V. V.; Bikmaev, I. F.; Balega, Yu.Yu; Safina, D. I. (2010). "Physical parameters and dynamical properties of the multiple star o and". Astronomy Reports 54 (12): 1134–1149. doi:10.1134/S1063772910120061. Bibcode: 2010ARep...54.1134Z. 
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 Tokovinin, Andrei (2018). "The Updated Multiple Star Catalog". The Astrophysical Journal Supplement Series 235 (1): 6. doi:10.3847/1538-4365/aaa1a5. Bibcode: 2018ApJS..235....6T. 
  13. ↑ 13.0 13.1 13.2 Hill, G. M.; Walker, G. A. H; Dinshaw, N; Yang, S; Harmance, P (1988). "Omicron Andromedae is quadruple". Publications of the Astronomical Society of the Pacific 100: 243. doi:10.1086/132161. Bibcode: 1988PASP..100..243H. 
  14. ↑ 14.0 14.1 14.2 14.3 14.4 Maestro, V.; Che, X.; Huber, D.; Ireland, M. J.; Monnier, J. D.; White, T. R.; Kok, Y.; Robertson, J. G. et al. (2013), "Optical interferometry of early-type stars with PAVO@CHARA - I. Fundamental stellar properties", Monthly Notices of the Royal Astronomical Society 434 (2): 1321, doi:10.1093/mnras/stt1092, Bibcode: 2013MNRAS.434.1321M 
  15. ↑ Balona, L. A.; Dziembowski, W. A. (October 1999). "Excitation and visibility of high-degree modes in stars". Monthly Notices of the Royal Astronomical Society 309 (1): 221–232. doi:10.1046/j.1365-8711.1999.02821.x. Bibcode: 1999MNRAS.309..221B. 
  16. ↑ 16.0 16.1 16.2 Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society 410 (1): 190–200. doi:10.1111/j.1365-2966.2010.17434.x. Bibcode: 2011MNRAS.410..190T. 
  17. ↑ "omi And". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=omi+And. 
  18. ↑ 18.0 18.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/. 
  19. ↑ "Al Faras ( الفرس )". IAU Working Group on Star Names. https://xing.fmi.uni-jena.de/mediawiki/index.php/Al_Faras. 
  20. ↑ "Honores Friderici". IAU Working Group on Star Names. https://xing.fmi.uni-jena.de/mediawiki/index.php/Honores_Friderici. 
  21. ↑ Wilson, R. H. (1950). "Observations of double stars". The Astronomical Journal 55: 153. doi:10.1086/106378. Bibcode: 1950AJ.....55..153W. https://zenodo.org/record/1855124. 
  22. ↑ Horch, Elliott P; Van Belle, Gerard T; Davidson, James W; Ciastko, Lindsay A; Everett, Mark E; Bjorkman, Karen S (2015). "Observations of Binary Stars with the Differential Speckle Survey Instrument. VI. Measures during 2014 at the Discovery Channel Telescope". The Astronomical Journal 150 (5): 151. doi:10.1088/0004-6256/150/5/151. Bibcode: 2015AJ....150..151H. 
  23. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  24. ↑ Diz, H. R. (December 2024). "Rapid Periodic Spectroscopic Variation of the H-alpha Line of the Be Shell Star omicron Andromedae". The Journal of the American Association of Variable Star Observers 52 (2): 202. Bibcode: 2024JAVSO..52..202D. 



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