Theta Andromedae

Theta Andromedae is a binary star^[11] system in the northern constellation of Andromeda. Theta Andromedae, Latinized from θ Andromedae, is its Bayer designation. It is located at a distance of approximately 173 light-years (53 parsecs) from the Sun,^[1] and has an apparent visual magnitude of 4.6.^[2] On the Bortle Dark-Sky Scale, this makes it visible to the naked eye from outside urban regions. Based on its motion through space, this system appears to be a member of the Sirius supercluster.^[12]

Theta Andromedae

Location of θ Andromedae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda
Right ascension	00h 17m 05.50236s[1]
Declination	+38° 40′ 53.8886″[1]
Apparent magnitude (V)	4.61[2]
Characteristics
Evolutionary stage	main sequence[3]
Spectral type	A2 V[4]
U−B color index	+0.05[2]
B−V color index	+0.06[2]
Variable type	Constant[5]
Astrometry
Radial velocity (Rv)	0.9[6] km/s
Proper motion (μ)	RA: −57.551(307)[1] mas/yr Dec.: −14.795(155)[1] mas/yr
Parallax (π)	18.8747 ± 0.4251 mas[1]
Distance	173 ± 4 ly (53 ± 1 pc)
Absolute magnitude (MV)	−0.25[7]
Orbit[8]
Period (P)	1033+91 −77 days
Semi-major axis (a)	25+32 −13 mas
Eccentricity (e)	0.95+0.04 −0.40
Inclination (i)	69+8 −22°
Longitude of the node (Ω)	263+50 −156°
Periastron epoch (T)	238+343 −143
Argument of periastron (ω) (secondary)	89+175 −29°
Details
A
Mass	2.83±0.08[3] M☉
Luminosity	113[7] L☉
Surface gravity (log g)	3.95[9] cgs
Temperature	8,960[9] K
Metallicity [Fe/H]	+0.14[9] dex
Rotational velocity (v sin i)	102[3] km/s
Other designations
θ And, 24 Andromedae, BD+37°34, HD 1280, HIP 1366, HR 63, SAO 53777, PPM 65154[10]
Database references
SIMBAD	data

The brighter component is a white hued A-type main-sequence star with a stellar classification of A2 V.^[4] It is one of the least photometrically variable stars known.^[5] The star shows a high rate of rotation with a projected rotational velocity of 102 km/s.^[3] It has an estimated 2.8^[3] times the mass of the Sun and is radiating 113^[7] times the Sun's luminosity from its photosphere at an effective temperature of 8,960 K.^[9] The relatively high chemical abundances of iron and heavier elements suggests it may be a fast rotating Am star.^[5]

A stellar companion was detected in 1986 and reported in 1989.^[13] This fainter companion is separated from Theta Andromedae by 0.06 arcseconds.^[11] The secondary appears to be a massive, possibly A-type, star orbiting at a distance of around one astronomical unit with a period of 2.83 years and a large orbital eccentricity (ovalness) of 0.95.^[8]

Naming

In Chinese, 天廄 (Tiān Jiù), meaning Celestial Stable, refers to an asterism consisting of θ Andromedae, ρ Andromedae and σ Andromedae. Consequently, the Chinese name for θ Andromedae itself is known as 天廄一 (Tiān Jiù yī, English: the First Star of Celestial Stable.)^[14]

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
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. Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
4. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
5. Koçer, D.; et al. (2003), "Elemental abundance analyses with DAO spectrograms-XXVII. The superficially normal stars θ And (A2 IV), ϵ Del (B6 III), ϵ Aqr (A1. 5 V), and ι And (B9 V)", Astronomy & Astrophysics, 406 (3): 975–980, Bibcode:2003A&A...406..975K, doi:10.1051/0004-6361:20030620.
6. Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick (eds.), Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E.
7. 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.
8. Goldin, A.; Makarov, V. V. (September 2006), "Unconstrained Astrometric Orbits for Hipparcos Stars with Stochastic Solutions", The Astrophysical Journal Supplement Series, 166 (1): 341–350, arXiv:astro-ph/0606293, Bibcode:2006ApJS..166..341G, doi:10.1086/505939, S2CID 15673734.
9. Hill, G. M. (February 1995), "Compositional differences among the A-type stars. 2: Spectrum synthesis up to V sin i = 110 km/s", Astronomy and Astrophysics, 294 (2): 536–546, Bibcode:1995A&A...294..536H.
10. "tet And", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2021-05-31.
11. 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.
12. Palous, J.; Hauck, B. (July 1986), "The Sirius supercluster", Astronomy and Astrophysics, 162: 54–61, Bibcode:1986A&A...162...54P.
13. McAlister, Harold A.; et al. (February 1989), "ICCD Speckle Observations of Binary Stars. IV. Measurements During 1986-1988 from the Kitt Peak 4-m Telescope", Astronomical Journal, 97: 510, Bibcode:1989AJ.....97..510M, doi:10.1086/115001.
14. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 18 日 Archived 2011-05-21 at the Wayback Machine

External links

• Image Theta Andromedae