7 Arietis

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.

7 Arietis
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 01h 55m 51.03925s[1]
Declination +23° 34′ 38.3465″[1]
Apparent magnitude (V) 5.76[2]
Characteristics
Spectral type K1 III[3]
U−B color index +1.04[4]
B−V color index +1.185[4]
Astrometry
Radial velocity (Rv)+15.95[5] km/s
Proper motion (μ) RA: +11.44[1] mas/yr
Dec.: -10.05[1] mas/yr
Parallax (π)5.85 ± 0.46[1] mas
Distance560 ± 40 ly
(170 ± 10 pc)
Details
Radius21[6] R☉
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
SIMBADdata

This is listed as 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]

The eclipsing binary nature of this star has been disputed by Italian astronomer Ennio Poretti.[9] Observations made as part of the British Astronomical Association eclipsing binaries program by Tristram Brelstaff were also unable to confirm eclipses.[10]

References
  1. van Leeuwen, F. (November 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. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
  3. 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.
  4. "7 Ari". SIMBAD. 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:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272, S2CID 17804304.
  6. 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:
  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, arXiv:1312.3474, 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.
  9. Poretti, Ennio (1984). "RR Ari: Not a variable star". Astrophysics and Space Science. 106: 201–203. Bibcode:1984Ap&SS.106..201P. doi:10.1007/BF00653927. S2CID 120037068.
  10. Isles, J. E. (1985). "Eclipsing Binaries, Andromeda To Camelopardalis, in 1972-1983". Journal of the British Astronomical Association. 96: 27–32. Bibcode:1985JBAA...96...27I.
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