Wolf 922

Wolf 922
Location of Wolf 922 (circled)
Observation data
Epoch J2000      Equinox ICRS
Constellation Capricornus
Right ascension 21h 31m 18.57s
Declination −09° 47′ 26.5″
Apparent magnitude (V) 11.96 – 11.99
A: 12.66
B: 14.76
Characteristics
Spectral type M4.0V + M
U−B color index 1.231
B−V color index 1.664
J−H color index 0.615
J−K color index 0.937
Variable type BY Draconis variable
Astrometry
Radial velocity (Rv)−56.3336±0.0188 km/s
Proper motion (μ) RA: 1246.510 mas/yr
Dec.: −61.066 mas/yr
Parallax (π)125.3±0.3 mas
Distance26.03 ± 0.06 ly
(7.98 ± 0.02 pc)
Absolute magnitude (MV)12.6
Orbit
PrimaryWolf 922 A
SecondaryWolf 922 B
Period (P)704.9±0.5 d
Semi-major axis (a)0.1448±0.0005″
Eccentricity (e)0.390±0.002
Inclination (i)49.8±0.4°
Longitude of the node (Ω)326.1±0.4°
Periastron epoch (T)51164.0±1.1
Argument of periastron (ω)
(secondary)		8.7±0.5°
Semi-amplitude (K1)
(primary)		5.21±0.02 km/s
Semi-amplitude (K2)
(secondary)		9.4±0.1 km/s
Details
Wolf 922 A
Mass0.270±0.004 M☉
Radius0.3 R☉
Metallicity [Fe/H]0.3 dex
Rotational velocity (v sin i)10 km/s
Wolf 922 B
Mass0.145±0.002 M☉
Other designations
BB Cap, NSV 13753, GJ 831, HIP 106255, CCDM J21313-0947AB, WDS J21313-0947AB, Ci 20 1288, G 26-7, LFT 1639, LHS 511, LPM 786, LTT 8556, NLTT 51428, PLX 5184, PM J21313-0947, PM 21286-1001, Wolf 922, TIC 71600113, TYC 5790-1233-1, GCRV 26194, GCRV 72228, GSC 05790-00182, 2MASS J21311859-0947263, WISEA J213119.47-094727.0, Gaia DR3 6894054664842632448
Database references
SIMBADdata

Wolf 922, also designated Gliese 831, is a nearby binary star composed of two low-mass red dwarfs in the zodiac constellation of Capricornus, close to the border with Aquarius. It has an apparent magnitude that varies between 11.96 and 11.99, far too faint to be seen by the naked eye from Earth but observable using a telescope with an aperture of 51 millimetres (2.0 in) or larger. It is located approximately 26 light-years (8.0 pc) distant based on parallax measurements, and approaching the Solar System at a heliocentric radial velocity of −56.33 km/s.

A visual band light curve for Wolf 922, adapted from Weis (1994)

In 1994, it was discovered to show long-term variations in brightness by Edward W. Weis at the Van Vleck Observatory. It was given the variable-star designation BB Capricorni and classified as a BY Draconis variable in 1997.

Observational history

As early as 1960, the star was suspected of experiencing perturbations and a period of about 1,500 days (4.1 years) was suggested. It was subsequently examined by Sarah Lee Lippincott, who, in 1979, determined that the perturbing companion star had a mass of between 0.13 and 0.20 M☉, and that it orbited the primary in a moderately eccentric (eccentricity 0.36) 1.93-year orbit. A 1987 paper proposed a circular (eccentricity 0.0) orbit with a period of 1.92 years, but a study in 2016 gives a 704.9-day (1.930-year) period and an eccentricity of 0.39, close to Lippincott's figures.

In 1997, the discovery of a third star was tentatively announced, which was described as a likely flare star with a very small mass (0.11 M☉) and luminosity, either located very close to A or B, or farther than about 0.5 arcseconds from the pair. The former possibility was ruled out by a follow-up study in 2000, which stated that if the object exists, it is likely bluer than the two red dwarfs, meaning it could be a white dwarf companion or an unrelated background object.

References

  1. 1 2 "Wolf 922". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 6 February 2025.
  2. 1 2 3 4 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.
  3. 1 2 3 Kazarovets, E. V.; Samus, N. N. (23 April 1997). "The 73rd Name-List of Variable Stars". Information Bulletin on Variable Stars. 4471: 1–45. Bibcode:1997IBVS.4471....1K.
  4. 1 2 3 4 5 6 7 Benedict, G. F.; Henry, T. J.; Franz, O. G.; et al. (1 November 2016). "The Solar Neighborhood. Xxxvii. The Mass–Luminosity Relation for Main-Sequence M Dwarfs". The Astronomical Journal. 152 (5): 141. arXiv:1608.04775. Bibcode:2016AJ....152..141B. doi:10.3847/0004-6256/152/5/141. ISSN 0004-6256.
  5. 1 2 Landolt, Arlo U. (1 May 2009). "UBVRI PHOTOMETRIC STANDARD STARS AROUND THE CELESTIAL EQUATOR: UPDATES AND ADDITIONS". The Astronomical Journal. 137 (5): 4186–4269. arXiv:0904.0638. Bibcode:2009AJ....137.4186L. doi:10.1088/0004-6256/137/5/4186. ISSN 0004-6256.
  6. 1 2 Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; et al. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
  7. ↑ Jönsson, Henrik; Holtzman, Jon A.; Prieto, Carlos Allende; et al. (1 September 2020). "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South". The Astronomical Journal. 160 (3): 120. arXiv:2007.05537. Bibcode:2020AJ....160..120J. doi:10.3847/1538-3881/aba592. ISSN 0004-6256.
  8. ↑ Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de la Vieuville, Geoffroy; Butler, C. J.; Paletou, F. (2019). "The Mass-Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs". The Astronomical Journal. 158 (2): 56. arXiv:1905.07921. Bibcode:2019AJ....158...56H. doi:10.3847/1538-3881/ab23fe.
  9. 1 2 3 4 Ségransan, D.; Delfosse, X.; Forveille, T.; et al. (December 2000). "Accurate masses of very low mass stars. III. 16 new or improved masses". Astronomy and Astrophysics. 364: 665. arXiv:astro-ph/0010585. Bibcode:2000A&A...364..665S.
  10. ↑ North, Gerald; James, Nick (2014). Observing Variable Stars, Novae and Supernovae. Cambridge University Press. p. 24. ISBN 978-1-107-63612-5.
  11. 1 2 Weis, Edward W. (1994). "Long term variability in dwarf M stars". The Astronomical Journal. 107: 1135. Bibcode:1994AJ....107.1135W. doi:10.1086/116925.
  12. 1 2 McNamara, Brian R.; Ianna, Philip A.; Fredrick, Laurence W. (1987). "The low-mass companion to Wolf 922". The Astronomical Journal. 93: 1245. Bibcode:1987AJ.....93.1245M. doi:10.1086/114405.
  13. ↑ Lippincott, S. L. (1979). "Low-mass unseen companions to two nearby red dwarfs, CC 1228 and Wolf 922". Publications of the Astronomical Society of the Pacific. 91: 784. Bibcode:1979PASP...91..784L. doi:10.1086/130588. ISSN 0004-6280.
  14. ↑ Franz, O. G.; Wasserman, L. H.; Henry, T. J.; et al. (December 1997). "HST Fine Guidance Sensor Discovery of a Third Component in the Low-Mass System Wolf 922 (Gliese 831)". Bulletin of the American Astronomical Society. 29: 1361. Bibcode:1997AAS...191.9302F.
  15. ↑ Henry, Todd J.; Franz, Otto G.; Wasserman, Lawrence H.; Benedict, G. Fritz; Shelus, Peter J.; Ianna, Philip A.; Kirkpatrick, J. Davy; McCarthy, Jr., Donald W. (20 February 1999). "The Optical Mass-Luminosity Relation at the End of the Main Sequence (0.08–0.20 M ⊙ )". The Astrophysical Journal. 512 (2): 864–873. doi:10.1086/306793. ISSN 0004-637X.