Zeta Andromedae

Zeta Andromedae (Zeta And, ζ Andromedae, ζ And) is a star system in the constellation Andromeda. It is approximately 189 light years from Earth.

ζ Andromedae

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Andromeda
Right ascension	00^h 47^m 20.32547^s[1]
Declination	+24° 16′ 01.8408″[1]
Apparent magnitude (V)	3.92 to 4.14[2]
Characteristics
Spectral type	K1III + KV[3]
U−B color index	+0.90[4]
B−V color index	+1.12[4]
R−I color index	+0.59[4]
Variable type	ELL/RS[2]
Astrometry
Radial velocity (Rv)	−24.43 ± 0.1[5] km/s
Proper motion (μ)	RA: −101.17[1] mas/yr Dec.: −81.77[1] mas/yr
Parallax (π)	17.24 ± 0.26[1] mas
Distance	189 ± 3 ly (58.0 ± 0.9 pc)
Absolute magnitude (MV)	+0.14[3]
Orbit[3]
Period (P)	17.769426
Semi-major axis (a)	2.7 R*
Eccentricity (e)	0.0
Inclination (i)	65 ± 5°
Details
Aa
Mass	2.6 ± 0.4[3] M☉
Radius	15.9 ± 0.8[6] R☉
Luminosity	95.5[3] L☉
Surface gravity (log g)	2.8[3] cgs
Temperature	4,665 ± 140[6] K
Metallicity [Fe/H]	−0.30[3] dex
Rotation	17.77 days[7]
Rotational velocity (v sin i)	41.4 ± 0.2[3] km/s
Ab
Mass	0.75[3] M☉
Other designations
ζ And, Zeta Andromedae, Zeta And, 34 Andromedae, 34 And, BD+23 106, CCDM J00473+2416A, FK5 27, GC 940, HD 4502, HIP 3693, HR 215, IDS 00421+2344 A, PPM 90149, SAO 74267, WDS 00473+2416A.
Database references
SIMBAD	data

Zeta Andromedae is a spectroscopic binary whose primary is classified as an orange K-type giant with a mean apparent magnitude of +4.08. In addition to brightness variation due to the ellipsoidal shape of the giant primary star, the system is also an RS Canum Venaticorum type variable star. Its brightness varies from magnitude +3.92 to +4.14 with a period of 17.77 days, and its spectrum shows strong and variable Ca II H and K lines.[3] The orbital period of the binary is 17.77 days.

Location

This star's location in the constellation Andromeda can be seen in the following diagram:

Diagram of Andromeda constellation

Direct imaging

The primary component of this binary system, Zeta Andromedae Aa, is one of the few stars who has been imaged directly using Doppler imaging and long-baseline infrared interferometry. With direct imaging we can recover additional information about this star.

Additional star parameters[8]

Parameter	Value
Oblateness	1.060 ± 0.011
Polar radius	15.0 ± 0.8 R☉
Axis Inclination[lower-alpha 1]	70.0 ± 2.8 °
Pole angle[lower-alpha 2]	126 ± 1.9 °

Direct imaging also allowed observation of starspots, (the analogue to sunspots), on this star, and their asymmetric distribution showed that the magnetic field of the star is generated by a mechanism different from the solar dynamo.[8] A Sun-like differential rotation of the star was observed instead.[3]

Visual companions

The WDS lists more than one visual companion to the eclipsing binary.[4] B has common proper motion with A. C is probably only a line-of-sight companion that has no physical association. The parallax of the D component has been measured by Gaia and the distance of this star is much different.[9]

Multiple/double star designation: WDS 00473+2416[10] Component Primary Right ascension (α) Equinox J2000.0 Declination (δ) Equinox J2000.0 Epoch of observed separation Angular distance from primary Position angle (relative to primary) Apparent magnitude (V) Database reference B A 00^h 47^m 20.2^s +24° 16′ 33″ 1959 32.6″ 0° 15.3 C A 00^h 47^m 15.2^s +24° 15′ 03″ 1997 97.0″ 231° 13.6 D A 00^h 47^m 09.0^s +24° 15′ 33″ 2006 155.5″ 260° 10.80 SIMBAD

Naming

In Chinese, 奎宿 (Kuí Sù), meaning Legs (asterism), refers to an asterism consisting of ζ Andromedae, η Andromedae, 65 Piscium, ε Andromedae, δ Andromedae, π Andromedae, ν Andromedae, μ Andromedae, β Andromedae, σ Piscium, τ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ¹ Piscium. Consequently, the Chinese name for ζ Andromedae itself is 奎宿二 (Kuí Sù èr, English: the Second Star of Legs.)[11]

Notes

1. Azimuthal angle between the rotational axis and our line of sight
2. Longitudinal angle between the north pole and the East direction

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. zet And, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line August 29, 2008.
3. Kővári, Zs.; Bartus, J.; Strassmeier, K. G.; Oláh, K.; Weber, M.; Rice, J. B.; Washuettl, A. (2007). "Doppler imaging of stellar surface structure. XXIII. The ellipsoidal K giant binary ζ Andromedae". Astronomy and Astrophysics. 463 (3): 1071. arXiv:1301.0445. Bibcode:2007A&A...463.1071K. doi:10.1051/0004-6361:20065982.
4. HR 215, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line August 29, 2008.
5. Karataş, Y.; Bilir, S.; Eker, Z.; Demircan, O. (2004). "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution". Monthly Notices of the Royal Astronomical Society. 349 (3): 1069. arXiv:astro-ph/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. S2CID 15290475.
6. Korhonen, H.; Wittkowski, M.; Kovári, Zs.; Granzer, Th.; Hackman, T.; Strassmeier, K. G. (2010). "Ellipsoidal primary of the RS CVn binary ζ Andromedae . Investigation using high-resolution spectroscopy and optical interferometry". Astronomy and Astrophysics. 515: A14. arXiv:1002.4201. Bibcode:2010A&A...515A..14K. doi:10.1051/0004-6361/200913736. S2CID 118683792.
7. Strassmeier, Klaus G. (September 2009), "Starspots", The Astronomy and Astrophysics Review, 17 (3): 251–308, Bibcode:2009A&ARv..17..251S, doi:10.1007/s00159-009-0020-6
8. Roettenbacher, R.M.; Monnier, J.D.; Korhonen, H.; Aarnio, A.N.; Baron, F.; Che, X.; Harmon, R.O.; Kővári, Zs.; Kraus, S.; Schaefer, G.H.; Torres, G.; Zhao, M.; Ten Brummelaar, T.A.; Sturmann, J.; Sturmann, L. (2016). "No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry". Nature. 533 (7602): 217–220. arXiv:1709.10107. Bibcode:2016Natur.533..217R. doi:10.1038/nature17444. PMID 27144357. S2CID 4466687.
9. 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.
10. Entry 00473+2416, The Washington Double Star Catalog Archived April 12, 2008, at the Wayback Machine, United States Naval Observatory. Accessed on line August 29, 2008.
11. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日

External links

• Zeta Andromedae at Alcyone Software's Star Data Pages
• Image ζ Andromedae
• Rachael Roettenbacher, "How the face of a distant star reveals our place in the cosmos," Aeon Magazine [retrieved July 27, 2016]