# 7 Arietis

7 Arietis
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 01h 55m 51.03925s[1]
Declination +23° 34′ 38.3465″[1]
5.76[2]
Characteristics
Spectral type K1 III[3]
U−B color index +1.04[4]
B−V color index +1.185[4]
Astrometry
Proper motion (μ) RA: +11.44[1] mas/yr
Dec.: -10.05[1] mas/yr
Parallax (π) 5.85 ± 0.46[1] mas
Distance 560 ± 40 ly
(170 ± 10 pc)
Details
Rotational velocity (v sin i) 1.8 ± 1.0[7] km/s
Other designations
RR Arietis, BD+22 284, FK5 2130, HD 11763, HIP 8993, HR 559, SAO 75030.[4]
Database references

7 Arietis (abbreviated 7 Ari) is a binary star[3] system in the northern constellation of Aries. 7 Arietis is the Flamsteed designation. The pair have a combined apparent visual magnitude of 5.76,[2] making it faintly visible to the naked eye from dark suburban skies. Based upon an annual parallax shift of 5.85 mas,[1] it is approximately 560 light-years (170 parsecs) distant from the Earth, give or take a 40 light-year margin of error.

This is an eclipsing binary system with a period of 47.9 days and has the variable star designation RR Arietis. During each eclipse of the primary star, the magnitude of the system decreases by 0.40. The eclipse of the secondary reduces the magnitude by 0.35.[8] The primary component of the system is an evolved giant star with a stellar classification of K1 III.[3] The measured angular diameter of this star is 1.14 ± 0.02 mas.[2] At the estimated distance of 7 Arietis,[1] this yields a physical size of about 21 times the radius of the Sun.[6]

## References

1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
2. ^ a b c Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
3. ^ a b c 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:, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
4. ^ a b c "RR Ari -- Variable Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-18.
5. ^ Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430 (1): 165–186, arXiv:, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272.
6. ^ a b 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:
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(170\cdot 1.14\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 42\cdot R_{\bigodot }\end{aligned}}}
7. ^ De Medeiros, J. R.; et al. (November 2002), "A catalog of rotational and radial velocities for evolved stars. II. Ib supergiant stars", Astronomy and Astrophysics, 395: 97–98, Bibcode:2002A&A...395...97D, doi:10.1051/0004-6361:20021214.
8. ^ Malkov, O. Yu.; et al. (February 2006), "A catalogue of eclipsing variables", Astronomy and Astrophysics, 446 (2): 785–789, Bibcode:2006A&A...446..785M, doi:10.1051/0004-6361:20053137.