21 Arietis

21 Arietis
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 02h 15m 42.77662s[1]
Declination +25° 02′ 34.9627″[1]
Apparent magnitude (V) 5.57[2] (6.40/6.48)[3]
Characteristics
Spectral type F6 V[4]
U−B color index +0.00[5]
B−V color index +0.50[5]
Astrometry
Radial velocity (Rv)−44.3 km/s
Proper motion (μ) RA: −89.72[1] mas/yr
Dec.: −86.42[1] mas/yr
Parallax (π)19.58 ± 0.61 mas[1]
Distance167 ± 5 ly
(51 ± 2 pc)
Absolute magnitude (MV)2.03[2]
Orbit[6]
Period (P)23.70 ± 0.12 yr
Semi-major axis (a)0.2353 ± 0.0011″
Eccentricity (e)0.6816 ± 0.0037
Inclination (i)104.52 ± 0.16°
Longitude of the node (Ω)236.44 ± 0.22°
Periastron epoch (T)1986.192 ± 0.012
Argument of periastron (ω)
(secondary)		84.16 ± 0.16°
Details
21 Ari A
Mass1.338 ± 0.032[7] M☉
Surface gravity (log g)4.12[8] cgs
Temperature6,299[8] K
Metallicity [Fe/H]+0.02[8] dex
Rotational velocity (v sin i)12.6[9] km/s
Age2.2[2] Gyr
21 Ari B
Mass1.374 ± 0.027[7] M☉
Other designations
BD+24 329, FK5 1059, HD 13872, HIP 10535, HR 657, SAO 75238, WDS J02157+2503.[5]
Database references
SIMBADdata

21 Arietis (abbreviated 21 Ari) is a binary star[3] system in the northern constellation of Aries. 21 Arietis is the Flamsteed designation. It has a combined apparent visual magnitude is 5.57;[2] the brighter member is magnitude 6.40 while the fainter star is magnitude 6.48.[3] The distance to this star system, based upon an annual parallax shift of 19.58 mas,[1] is 167 light-years (51 parsecs). The pair orbit each other with a period of 23.70 years and an eccentricity of 0.68.[3]

The system was initially thought to be a triple system in 1981, since the orbit of the system predicted a mass greater than would be expected from its F6V spectral type.[10] This was later rejected because the distance to the system was overestimated. However, while observing the spectrum of the system, it was found that a giant planet may be causing radial velocity variations. The purported planet would have a mass of 1.40 ± 0.36 MJ, an orbital period of 925 days and orbit the primary star.[7]

  1. ^ a b c d e f Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference cgssn09 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference mnras389_2_869 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference aj1_74_916 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference aj111_370 was invoked but never defined (see the help page).
  7. ^ a b c Muterspaugh, Matthew W.; Lane, Benjamin F.; Kulkarni, S. R.; Konacki, Maciej; Burke, Bernard F.; Colavita, M. M.; Shao, M.; Hartkopf, William I.; Boss, Alan P.; Williamson, M. (2010). "The Phases Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems". The Astronomical Journal. 140 (6): 1657. arXiv:1010.4048. Bibcode:2010AJ....140.1657M. doi:10.1088/0004-6256/140/6/1657. S2CID 59585356.
  8. ^ a b c Cite error: The named reference apj1_354_310 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference aaa493_3_1099 was invoked but never defined (see the help page).
  10. ^ Couteau, P.; Morel, P. J. (1982). "Is 21 Ari = Cou 79 a multiple system?". Astronomy and Astrophysics. 105: 323. Bibcode:1982A&A...105..323C.