Theta Chamaeleontis

Theta Chamaeleontis, Latinized from θ Cha, is a single,^[7] orange-hued star located in the southern constellation of Chamaeleon. It is a dim star but visible to the naked eye with an apparent magnitude of 4.34.^[2] Parallax measurements by the Hipparcos spacecraft put the system at 155 light-years, or 47.6 parsecs away.^[1] It is moving away from the Sun with a radial velocity of +22 km/s.^[5]

θ Chamaeleontis

Observation data Epoch J2000      Equinox J2000
Constellation	Chamaeleon
Right ascension	08h 20m 38.54055s[1]
Declination	−77° 29′ 04.1173″[1]
Apparent magnitude (V)	4.34[2]
Characteristics
Spectral type	K2 IIIb CN0.5[3]
U−B color index	+1.19[4]
B−V color index	+1.16[4]
Astrometry
Radial velocity (Rv)	+21.70±0.7[5] km/s
Proper motion (μ)	RA: −129.05[1] mas/yr Dec.: +40.89[1] mas/yr
Parallax (π)	21.00 ± 0.14 mas[1]
Distance	155 ± 1 ly (47.6 ± 0.3 pc)
Absolute magnitude (MV)	+0.97±0.10[2]
Details[2]
Mass	0.94±0.27 M☉
Radius	11.5 R☉
Luminosity	60[6] L☉
Surface gravity (log g)	2.29±0.29 cgs
Temperature	4,570 K
Other designations
θ Cha, CPD−77° 383, FK5 318, HD 71701, HIP 40888, HR 3340, SAO 256503
Database references
SIMBAD	data

Theta Chamaeleontis is an evolved K-type giant star with a stellar classification of K2 IIIb CN0.5,^[3] where the suffix notation indicates the outer atmosphere has a mild overabundance of cyanogen. It has 0.94 times the mass of the Sun, and has expanded to 11.5 times as wide.^[2] The star is radiating 60^[6] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,570 K.^[2]

It has a visual companion, Theta Chamaeleontis B. This is a magnitude 12.44 star at an angular separation of 21.1 arcseconds from component A along a position angle of 237°, as of 2000.^[8]

References

1. van Leeuwen, F. (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. S2CID 18759600.
2. Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A.
3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
4. Johnson, H. L. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory. 4: 99. Bibcode:1966CoLPL...4...99J.
5. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
6. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
7. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
8. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.