Astronomy:Chi Draconis

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Short description: Star in the constellation of Draco
χ Draconis
Location of χ Draconis (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Draco
Right ascension  18h 21m 03.38255s[1]
Declination +72° 43′ 58.2518″[1]
Apparent magnitude (V) 3.570 + 5.70[2]
Characteristics
Spectral type F7V + K1V[3]
U−B color index −0.06[4]
B−V color index +0.49[4]
Variable type Suspected[5]
Astrometry
Radial velocity (Rv)+32.4[6] km/s
Proper motion (μ) RA: +531.21[1] mas/yr
Dec.: −349.71[1] mas/yr
Parallax (π)121.80 ± 0.54[7] mas
Distance26.8 ± 0.1 ly
(8.21 ± 0.04 pc)
Absolute magnitude (MV)4.04[6]
Orbit[7]
Primaryχ Dra A
Companionχ Dra B
Period (P)280.551+0.005
−0.006 d
Semi-major axis (a)0.1234±0.0005″
Eccentricity (e)0.4244±0.0003
Inclination (i)73.65+0.25
−0.23°
Longitude of the node (Ω)230.4±0.3°
Periastron epoch (T)2,457,226.13±0.03
Argument of periastron (ω)
(secondary)		117.77±0.06°
Details
χ Dra A
Mass1.028±0.004[7] M☉
Radius1.159+0.029
−0.028[7] R☉
Luminosity1.88+0.14
−0.13[7] L☉
Temperature6,277±30[7] K
Metallicity [Fe/H]−0.51±0.03[7] dex
Rotation23.39±0.09 d[8]
Rotational velocity (v sin i)2.5[9] km/s
Age5.3[6] Gyr
χ Dra B
Mass0.735±0.003[7] M☉
Radius0.73±0.11[10] R☉
Luminosity0.29[10] L☉
Temperature4,940±200[10] K
Other designations
χ Dra, 44 Dra, NSV 10749, BD+72°839, FK5 695, GJ 713, HD 170153, HIP 89937, HR 6927, SAO 9087, LHS 3379, LTT 15438[11]
Database references
SIMBADdata

Chi Draconis is a binary star system in the northern constellation Draco, consisting of a pair of sun-like stars which complete an orbit around each other in 281 days. The two stars' visual apparent magnitudes are 3.6 and 5.7, making the system visible to naked eye.[2] Located at a distance of 26.78 light-years (8.210 parsecs) from the Sun, it is one of the 200 or so closest stars.[12]

Nomenclature

Chi Draconis (Latinized from χ Draconis, abbreviated χ Dra, Chi Dra) is the star system's Bayer designation. It also has the Flamsteed designation 44 Draconis. The two components are designated Aa and Ab in the Washington Double Star Catalog,[2] but are often referred to as Chi Draconis A and Chi Draconis B in research papers.[3][7]

In a 1971 NASA memorandum, this star system was listed with the name Alahakan.[13] According to R. H. Allen's Star Names, Al ʽAuhaḳān, meaning "the two black bulls, or ravens", was an Arabic name for χ and ψ Draconis, among other stars in Draco.[14]

In Chinese astronomy, this star is identified as Yùnǚsì (御女四), the fourth star of the asterism Yùnǚ (御女, Maids-in-waiting; also the name of 31 Leonis).[15] Alternatively, it may be Zhùshǐ (柱史, Official of Royal Archives),[16] usually identified as φ Draconis.[15] R. H. Allen (using a now outdated romanization of Chinese) said it was Kwei She.[14]

Properties

χ Draconis in optical light

χ Draconis is a double-lined spectroscopic binary system[17] whose components have been resolved using speckle interferometry.[4] Radial velocity and astrometric measurements reveal the two stars to complete an orbit in around 280 days, in a moderately eccentric orbit with semi-major axis of approximately 1 au. The distance between the two stars varies between about 0.58 au and 1.44 au along the orbit.[7]

Chi Draconis A

Chi Draconis A, the more massive of the two stars, is an F7 main sequence star. It has a mass fractionally higher than the Sun's,[7] and is slightly larger and hotter, resulting in it being 1.86 times as luminous as the Sun.[10] The star appears to be relatively metal-poor, with about 30% as much iron as the Sun's, and its age is estimated to be about five billion years.[6][7]

Chi Draconis A has a moderately low level of magnetic activity, with mean chromospheric activity S-index of around 0.177,[3] compared to the Sun's 0.1621±0.0008.[18] It appears to have a stable dipolar poloidal global magnetic field,[19][8] with no evidence of polarity reversals over the 5-year observational baseline, although significant changes to the field and magnetic cycling over longer timescales remains possible.[3] The modulation of this stable magnetic field enables the measurement of the star's rotation period. One work found the period to be 23.4 days,[8] although a subsequent work was unable to determine the period.[3] Additionally, it appears to rotate as a rigid body, with no evidence of differential rotation.[3]

Chi Draconis B

Chi Draconis B is a K1 main sequence star.[3] It has about three-quarters the mass of the Sun, and is both cooler and smaller. It is only about 0.29 times as luminous as the Sun.[10] It is calculated to be 2.13 magnitudes fainter than the primary, so it would be of sixth magnitude if visible alone.[20]

Circularly polarized light observations of the system failed to detect signatures of magnetic field for Chi Draconis B, indicating that its magnetic field at the time of observation is likely very weak or nonexistent.[3]

Visual companions

Multiple star catalogues list faint widely separated visible companion stars: a 12th-magnitude star and a 14th-magnitude star about 3′ (minutes) from χ Draconis, but only about 10″ (seconds) from each other.[2] Both have much smaller parallaxes than χ Draconis and are unrelated background objects.[21]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 2.2 2.3 Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (December 2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466–3471. doi:10.1086/323920. ISSN 0004-6256. Bibcode: 2001AJ....122.3466M. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Marsden, S C; Evensberget, D; Brown, E L et al. (2023-04-13). "The magnetic field and stellar wind of the mature late-F star χ Draconis A". Monthly Notices of the Royal Astronomical Society 522 (1): 792–810. doi:10.1093/mnras/stad925. ISSN 0035-8711. Bibcode: 2023MNRAS.522..792M. https://academic.oup.com/mnras/article/522/1/792/7093409. Retrieved 2026-09-23. 
  4. ↑ 4.0 4.1 4.2 Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven. Bibcode: 1991bsc..book.....H. 
  5. ↑ 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. 
  6. ↑ 6.0 6.1 6.2 6.3 Nordström, B. et al. (May 2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs". Astronomy and Astrophysics 418: 989–1019. doi:10.1051/0004-6361:20035959. Bibcode: 2004A&A...418..989N. 
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 Rudrasingam, Jonatan; Lund, Mikkel N.; Grundahl, Frank et al. (2026-09-21). "Asteroseismology and interferometry of the F7V spectroscopic binary $χ$ Draconis A in the TESS CVZ". Astronomy & Astrophysics. 
  8. ↑ 8.0 8.1 8.2 Lee, Byeong-Cheol; Gadelshin, D; Han, Inwoo et al. (2018-01-01). "Magnetic field and radial velocities of the star Chi Draconis A". Monthly Notices of the Royal Astronomical Society: Letters 473 (1): L41–L45. doi:10.1093/mnrasl/slx152. ISSN 1745-3925. Bibcode: 2018MNRAS.473L..41L. https://academic.oup.com/mnrasl/article/473/1/L41/4265269. Retrieved 2026-09-23. 
  9. ↑ Gray, D. F. (1984). "Measurements of rotation and turbulence in F, G, and K dwarfs". The Astrophysical Journal 281: 719. doi:10.1086/162149. ISSN 0004-637X. Bibcode: 1984ApJ...281..719G. http://adsabs.harvard.edu/doi/10.1086/162149. Retrieved 2026-09-23. 
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Torres, G.; Andersen, J.; Giménez, A. (2010). "Accurate masses and radii of normal stars: modern results and applications". The Astronomy and Astrophysics Review 18 (1–2): 67–126. doi:10.1007/s00159-009-0025-1. Bibcode: 2010A&ARv..18...67T.  See p. 56, entry #15.
  11. ↑ "chi Dra -- Star in double system". SIMBAD. Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=chi+Dra. Retrieved 2011-10-15. 
  12. ↑ Reylé, Céline; Jardine, Kevin; Fouqué, Pascal; Caballero, Jose A.; Smart, Richard L.; Sozzetti, Alessandro (30 April 2021). "The 10 parsec sample in the Gaia era". Astronomy & Astrophysics 650: A201. doi:10.1051/0004-6361/202140985. Bibcode: 2021A&A...650A.201R.  Data available at https://gruze.org/10pc/
  13. ↑ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology, https://ntrs.nasa.gov/api/citations/19720005197/downloads/19720005197.pdf. 
  14. ↑ 14.0 14.1 Allen, R. H. (1899), Star Names: Their Lore and Meaning, p. 210, https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Draco*.html 
  15. ↑ 15.0 15.1 "AEEA 天文教育資訊網" (in zh). http://aeea.nmns.edu.tw/2006/0606/ap060610.html. 
  16. ↑ Ridpath, Ian. "Star Tales – Draco". http://ianridpath.com/startales/draco.html. 
  17. ↑ Piccotti, Luca; Docobo, José Ángel; Carini, Roberta et al. (2020-02-21). "A study of the physical properties of SB2s with both the visual and spectroscopic orbits". Monthly Notices of the Royal Astronomical Society 492 (2): 2709–2721. doi:10.1093/mnras/stz3616. ISSN 0035-8711. Bibcode: 2020MNRAS.492.2709P. https://academic.oup.com/mnras/article/492/2/2709/5695748. Retrieved 2026-09-23. 
  18. ↑ Egeland, Ricky; Soon, Willie; Baliunas, Sallie et al. (2017-01-20). "The Mount Wilson Observatory S-Index of the Sun". The Astrophysical Journal 835 (1): 25. doi:10.3847/1538-4357/835/1/25. ISSN 0004-637X. Bibcode: 2017ApJ...835...25E. 
  19. ↑ Monin, D. N.; Fabrika, S. N.; Valyavin, G. G. (2002). "Magnetic survey of bright northern main sequence stars". Astronomy & Astrophysics 396 (1): 131–141. doi:10.1051/0004-6361:20021425. ISSN 0004-6361. Bibcode: 2002A&A...396..131M. 
  20. ↑ Hutter, D. J.; Zavala, R. T.; Tycner, C.; Benson, J. A.; Hummel, C. A.; Sanborn, J.; Franz, O. G.; Johnston, K. J. (9 November 2016). "Surveying the Bright Stars by Optical Interferometry. I. A Search for Multiplicity Among Stars of Spectral Types F-K". The Astrophysical Journal Supplement Series 227 (1): 4. doi:10.3847/0067-0049/227/1/4. Bibcode: 2016ApJS..227....4H. 
  21. ↑ Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 




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