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X Ophiuchi

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Not to be confused with χ (Chi) Ophiuchi.
X Ophiuchi
Location of X Ophiuchi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ophiuchus
Right ascension 18h 38m 21.132s[1]
Declination +08° 50′ 02.81″[1]
Apparent magnitude (V) 6.40[2] (5.9 to 9.2[3])
Characteristics
Spectral type M0-8e + K2:III[4]
M5e–M9e[3]
U−B color index 0.89[2]
B−V color index 1.32[2]
Variable type Mira[3]
Astrometry
Radial velocity (Rv)−71.46±0.27[5] km/s
Proper motion (μ) RA: 4.481 mas/yr[1]
Dec.: 14.781 mas/yr[1]
Parallax (π)5.1425 ± 0.3495 mas[1]
Distance630 ± 40 ly
(190 ± 10 pc)
Orbit[6]
Period (P)877.14±24.53 yr
Semi-major axis (a)0.822±0.090″
Eccentricity (e)0.446±0.026
Inclination (i)103.7±1.2°
Longitude of the node (Ω)130.1±0.3°
Periastron epoch (T)2,020.98±23.27
Argument of periastron (ω)
(secondary)		14.1±2.6°
Details
Mira variable
Radius349[7] R☉
Luminosity7,420[7] L☉
Temperature2,900[7] K
Other designations
X Oph, BD+08° 3780, GC 25485, HD 172171, HIP 91389, HR 7002, SAO 123744, PPM 166252, WDS J18384+0850AB[8]
Database references
SIMBADdata

X Ophiuchi is a binary star system in the equatorial constellation of Ophiuchus, abbreviated X Oph. It is a Mira variable that ranges in brightness from an apparent visual magnitude of 5.9 down to 9.2 with a period of 328.85 days.[3] The system is located at a distance of approximately 630 light years from the Sun based on parallax measurements,[1] but is drifting closer with a radial velocity of −71 km/s.[5]

This star was found to be variable by T. H. E. C. Espin in 1886.[9] The binary nature of this system was reported by W. J. Hussey in 1900, listing an angular separation of 0.22″ along a position angle of 195.2°.[10] L. Campbell used light curves of the star from 1904 to 1921 to find a variability period of 337 days. In 1922, G. Van Biesbroeck showed that only the northward member of the pair is variable.[9] P. W. Merrill in 1923 found a stellar classification of M6e for the variable component at maximum, while the secondary is K0. At minimum, the primary becomes fainter than the secondary.[11]

By 1959, the orbital arc of the pair had spanned an angle of 50°, providing an estimated orbital period of at least 500 years and a separation of 64 AU. Preliminary orbital models suggested a mass of 0.8 M☉ for the variable component and 1.2 M☉ for the K-type giant. The latter star showed an age of around five billion years. At that mass, the variable component must have undergone significant mass loss in order to have already evolved away from the main sequence. The K-type component may have received up to 0.1 M☉ from the donor star.[12]

A visual band light curve for X Ophiuchi, plotted from AAVSO data[13]

A 2007 model gives an orbital period of about 877 years with an eccentricity (ovalness) of 0.45.[6] The variable component is an oxygen-rich M-type Mira variable.[14] The duration, amplitude, and shape of the light curve is found to vary slightly from cycle to cycle. Some show a hump during the ascending curve.[15] Its estimated mass loss rate is 2.95×10−9 M☉·yr−1.[7] In 1992, a strong radio flare event was observed from this system at a frequency of 1,667 MHz.[16][14] This outburst came from an OH maser in the inner part of a shell surrounding the variable. Water in the shell is being photodissociated to create OH molecules.[17]

References

[edit]
  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. ^ a b c Ducati, J. R. (2002), "Catalogue of Stellar Photometry in Johnson's 11-color system.", VizieR Online Data Catalog, CDS/ADC Collection of Electronic Catalogues, 2237, Bibcode:2002yCat.2237....0D.
  3. ^ a b c d Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  4. ^ Keenan, Philip C.; et al. (1974), "Revised Catalog of Spectra of Mira Variables of Types ME and Se", The Astrophysical Journal Supplement Series, 28: 271, Bibcode:1974ApJS...28..271K, doi:10.1086/190318.
  5. ^ a b Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430: 165, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272, S2CID 17804304.
  6. ^ a b Novakovic, B. (June 2007), "Orbits of Ten Visual Binary Stars", Chinese Journal of Astronomy and Astrophysics, 7 (3): 415–420, Bibcode:2007ChJAA...7..415N, doi:10.1088/1009-9271/7/3/11.
  7. ^ a b c d Liu, Jiaming; Jiang, B. W.; Li, Aigen; Gao, Jian (April 2017), "On the silicate crystallinities of oxygen-rich evolved stars and their mass-loss rates", Monthly Notices of the Royal Astronomical Society, 466 (2): 1963–1986, arXiv:1612.02115, Bibcode:2017MNRAS.466.1963L, doi:10.1093/mnras/stw3165.
  8. ^ "X Oph", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2024-10-05.
  9. ^ a b Gingrich, C. H. (September 1922), "The variable star X Ophuichi", Astrophysical Journal, 56: 132–138, Bibcode:1922ApJ....56..132G, doi:10.1086/142694.
  10. ^ Hussey, William J. (November 1900), "Observations of one hundred new double stars", Astronomical Journal, 21 (485): 35–39, Bibcode:1900AJ.....21...35H, doi:10.1086/103240.
    Data for: 198. DM. +8°3780.
  11. ^ Merrill, P. W. (May 1923), "Spectroscopic observations of both components of the variable double star X Ophiuchi", Astrophysical Journal, 57: 251–256, Bibcode:1923ApJ....57..251M, doi:10.1086/142753.
  12. ^ Fernie, J. D. (September 1959), "The binary system X Ophiuchi", Astrophysical Journal, 130: 611, Bibcode:1959ApJ...130..611F, doi:10.1086/146750.
  13. ^ "Download Data". aavso.org. AAVSO. Retrieved 5 October 2024.
  14. ^ a b Etoka, S.; Le Squeren, A. M. (February 1995), "A Flare in the Mira X Oph", Astrophysics and Space Science, 224 (1): 455–456, Bibcode:1995Ap&SS.224..455E, doi:10.1007/BF00667902.
  15. ^ Marsakova, V. I.; Andronov, I. L. (1998), Dusek, J. (ed.), "Cycle-to-Cycle Changes of Mira-type Variable X Oph", Proceedings of the 20th Stellar Conference of the Czech and Slovak Astronomical Institutes. 5th - 7th November 1997. Brno, Czech Republic, Brno, p. 130, Bibcode:1998vsr..conf..130M, ISBN 80-85882-08-6.
  16. ^ Le Squeren, A. M.; Etoka, S. (March 1993), Marsden, B. G. (ed.), "X Ophiuchi", IAU Circular, 5724: 1, Bibcode:1993IAUC.5724....1L.
  17. ^ Etoka, S.; Le Squeren, A. M. (November 1996), "An OH maser flare in the Mira X Ophiuchi", Astronomy and Astrophysics, 315: 134–140, Bibcode:1996A&A...315..134E.
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