Chi Tauri

Chi Tauri (χ Tauri) is a star system in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 291 light years (89 parsecs) from Earth. The primary component has an apparent magnitude of about 5.4,[2] meaning it is visible with the naked eye.

This article is about the star system. For the Marvel Comics alien species, see Chitauri. For fraternities, see Chi Tau and Chi Tau (local).
Chi Tauri
Location of χ Tauri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
χ Tau A
Right ascension  04h 22m 34.944s[1]
Declination +25° 37′ 45.53″[1]
Apparent magnitude (V) 5.378[2]
χ Tau B
Right ascension  04h 22m 35.550s[3]
Declination +25° 38′ 03.22″[3]
Apparent magnitude (V) 8.423[4]
Characteristics
χ Tau A
Spectral type B9V[4]
U−B color index -0.12[5]
B−V color index -0.04[5]
χ Tau B
Spectral type F8 + G6 + K4 + K4[4]
U−B color index +0.10[5]
B−V color index +0.63[5]
Astrometry
χ Tau A
Radial velocity (Rv)+15.3 ± 3.4[4] km/s
Proper motion (μ) RA: 20.953[1] mas/yr
Dec.: -16.495[1] mas/yr
Parallax (π)11.0472 ± 0.1599[1] mas
Distance295 ± 4 ly
(91 ± 1 pc)
Absolute magnitude (MV)0.82 ± 0.18[4]
χ Tau B
Radial velocity (Rv)+14.694 ± 0.081[4] km/s
Proper motion (μ) RA: 15.766[3] mas/yr
Dec.: -20.396[3] mas/yr
Parallax (π)11.5348 ± 0.0857[3] mas
Distance283 ± 2 ly
(86.7 ± 0.6 pc)
Absolute magnitude (MV)3.85 ± 0.18 (total)
4.20 ± 0.18 (Ba)
5.27 ± 0.18 (Bb)
7.87 / 7.87 (Bc)[4]
Orbit[4]
Primaryχ Tau Ba
Companionχ Tau Bb
Period (P)17.602309 ± 0.000036 d
Eccentricity (e)0.2938 ± 0.0013
Inclination (i)53.3 ± 0.5°
Periastron epoch (T)2448891.649 ± 0.014
Argument of periastron (ω)
(secondary)		249.43 ± 0.33°
Semi-amplitude (K1)
(primary)		41.287 ± 0.080 km/s
Semi-amplitude (K2)
(secondary)		48.133 ± 0.080 km/s
Orbit[4]
Primaryχ Tau Bab
Companionχ Tau Bc
Period (P)3450.6 ± 6.1 d
Eccentricity (e)0.3560 ± 0.0068
Inclination (i)73 ± 6°
Periastron epoch (T)2447546.5 ± 9.7
Argument of periastron (ω)
(secondary)		250.3 ± 1.5°
Semi-amplitude (K1)
(primary)		8.625 ± 0.067 km/s
Details
Age200 ± 50[4] Myr
χ Tau A
Mass2.60 ± 0.05[4] M☉
Radius2.15[6] R☉
Surface gravity (log g)4.15 ± 0.14[7] cgs
Temperature10300 ± 300[4] K
Rotational velocity (v sin i)263[7] km/s
χ Tau Ba
Mass1.19[4] M☉
Surface gravity (log g)4.5[4] cgs
Temperature6180 ± 150[4] K
Rotational velocity (v sin i)1 ± 3[4] km/s
χ Tau Bb
Mass1.02[4] M☉
Surface gravity (log g)4.5[4] cgs
Temperature5620 ± 150[4] K
Rotational velocity (v sin i)1 ± 3[4] km/s
χ Tau Bc
Mass~0.70 / 0.70[4] M☉
Other designations
χ Tau, 59 Tau, BD+25° 707, HD 27638, HIP 20430, HR 1369, SAO 76573, ADS 3161 AB, CCDM J04226+2538AB
Database references
SIMBADχ Tau A
χ Tau B

The main component of the system is Chi Tauri A. It is a B-type main-sequence star. Its mass is 2.6 times that of the Sun and its surface glows with an effective temperature of 10,300 K. It may be a binary star itself, as suggested from astrometric data from Hipparcos, although no orbit could be derived.[4]

The secondary component of the system is Chi Tauri B, separated about 19″[4] from Chi Tauri A. It was thought to be a post-T Tauri star from its unusual spectrum,[8] but later studies ruled this out.[4] It is a double-lined spectroscopic binary—the two stars are not resolved but their spectra have periodic Doppler shifts indicating orbital motion. The two stars are an F-type star and a G-type star, respectively, and are designated Ba and Bb.[4]

The radial velocity of Chi Tauri B has a slow drift indicating the presence of another star in the system. Designated Chi Tauri Bc, this massive object is too dim to be detected, but it appears in Chi Tauri B's spectrum as an infrared excess. Because of this infrared excess, this unseen component is thought to be a pair of K-type main-sequence stars both with masses 70% of the Sun. The stars within the system appear to be dynamically interacting.[4]

Naming
  • With φ, κ1, κ2 and υ, it composed the Arabic were the Arabs' Al Kalbain, the Two Dogs.[9] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Kalbain were the title for five stars : φ as Alkalbain I, this star (χ) as Alkalbain II, κ1 as Alkalbain III, κ2 as Alkalbain IV and υ as Alkalbain V.[10]
  • In Chinese, 礪石 (Lì Dàn), meaning Whetstone, refers to an asterism consisting of χ Tauri, ψ Tauri, 44 Tauri and φ Tauri. Consequently, the Chinese name for χ Tauri itself is 礪石三 (Lì Dàn sān, English: the Third Star of Whetstone.).[11]
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References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  4. Torres, Guillermo (2006). "The Multiple System HD 27638". The Astronomical Journal. 131 (3): 1702. arXiv:astro-ph/0512254. Bibcode:2006AJ....131.1702T. doi:10.1086/500355.
  5. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. Pasinetti Fracassini, L. E.; et al. (2001). "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics". Astronomy & Astrophysics. 367 (2): 521–24. arXiv:astro-ph/0012289. Bibcode:2001A&A...367..521P. doi:10.1051/0004-6361:20000451.
  7. David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146.
  8. Lindroos, K. P. (1986). "A study of visual double stars with early-type primaries. V - Post-T Tauri secondaries". Astronomy and Astrophysics. 156 (1–2): 223–233. Bibcode:1986A&A...156..223L.
  9. Allen, Richard Hinckley (1899). Star-Names and Their Meanings. New York: G. E. Stechert. p. 413.
  10. Rhoads, Jack W. (November 15, 1971). "Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars" (PDF). Jet Propulsion Laboratory, California Institute of Technology. Cite journal requires |journal= (help)
  11. "天文教育資訊網" [AEEA (Activities of Exhibition and Education in Astronomy)] (in Chinese). 2006-05-22. Retrieved 2019-06-20.
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