Theta Centauri

Theta Centauri

Location of θ Centauri (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Centaurus
Right ascension	14^h 06^m 40.94752^s[1]
Declination	–36° 22′ 11.8371″[1]
Apparent magnitude (V)	+2.06[2]
Characteristics
Spectral type	K0 III[3]
U−B color index	+0.90[2]
B−V color index	+0.99[2]
Astrometry
Radial velocity (Rv)	+1.3[4] km/s
Proper motion (μ)	RA: –520.53[1] mas/yr Dec.: –518.06[1] mas/yr
Parallax (π)	55.45 ± 0.20[1] mas
Distance	58.8 ± 0.2 ly (18.03 ± 0.07 pc)
Absolute magnitude (MV)	0.87[5]
Details
Radius	10.6[6] R☉
Luminosity	60[7] L☉
Surface gravity (log g)	2.75[8] cgs
Temperature	4,980[8] K
Metallicity [Fe/H]	0.03[8] dex
Other designations
Menkent, Haratan, 5 Centauri, CD−35 9260, FK5 520, Gl 539, HD 123139, HIP 68933, HR 5288, LHS 2858, SAO 205188.[9]

Theta Centauri (θ Cen, θ Centauri) is a star in the southern constellation of Centaurus, the centaur. It has the traditional Arabic name Menkent (possibly abbreviation of ألمنكب ألقنتوس - al mankib al-qanturis, meaning "shoulder of the Centaur"). This star has an apparent visual magnitude of +2.06,^[2] making it the fourth brightest member of the constellation. This star is close enough to the Earth that its distance can be measured using the parallax technique, yielding a value of 58.8 light-years (18.0 parsecs).^[1]

In Chinese, 庫樓 (Kù Lóu), meaning Arsenal, refers to an asterism consisting of θ Centauri, ζ Centauri, η Centauri, 2 Centauri, HD 117440, ξ¹ Centauri, γ Centauri, τ Centauri, D Centauri and σ Centauri.^[10] Consequently, θ Centauri itself is known as 庫樓三 (Kù Lóu sān, English: the Third Star of Arsenal.)^[11]

This is an evolved giant star with a stellar classification of K0 III.^[3] The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 5.46 ± 0.06 mas,^[12] which, at its estimated distance, equates to a physical radius of about 10.6 times the radius of the Sun.^[6] The outer envelope has an effective temperature of 4,980 K,^[8] giving it the orange-hued glow of a cool, K-type star.^[13] Soft X-ray emission has been detected from this star, which has an estimated X-ray luminosity of 1.4 × 10²⁷ erg s⁻¹.^[14]

References

1. van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
2. Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory 4 (99): 99. Bibcode:1966CoLPL...4...99J.
3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I", The Astronomical Journal 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637
4. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb (Astronomisches Rechen-Institut Heidelberg) 35 (35), Bibcode:1999VeARI..35....1W
5. Elgarøy, Øystein; Engvold, Oddbjørn; Lund, Niels (March 1999), "The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity", Astronomy and Astrophysics 343: 222–228, Bibcode:1999A&A...343..222E
6. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

   $\begin{align} 2\cdot R_* & = \frac{(18.03\cdot 5.46\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 21.2\cdot R_{\bigodot} \end{align}$

7. Kaler, James B., "MENKENT (Theta Centauri)", Stars (University of Illinois), retrieved 2012-03-01
8. Jones, K. L.; et al. (June 1992), "Spectroscopic investigation of cool giants and the authenticity of their reported microwave emission", Monthly Notices of the Royal Astronomical Society 256 (3): 535–544, Bibcode:1992MNRAS.256..535J, doi:10.1093/mnras/256.3.535
9. "LHS 2858 -- High proper-motion Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-03-01
10. (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
11. (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
12. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
13. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
14. Schroeder, K.-P.; Huensch, M.; Schmitt, J. H. M. M. (July 1998), "X-ray activity and evolutionary status of late-type giants", Astronomy and Astrophysics 335: 591–595, Bibcode:1998A&A...335..591S