7 Aquarii

7 Aquarii, abbreviated 7 Aqr, is a binary star[3] system in the zodiac constellation of Aquarius. 7 Aquarii is the Flamsteed designation. It is visible to the naked eye with an apparent visual magnitude of 5.5;[2] the brighter component is baseline magnitude 5.62 while the faint secondary is magnitude 11.4.[3] As of 2002, the pair had an angular separation of 2.10″ along a position angle of 165°.[10] The distance to this system, based upon an annual parallax shift of 4.9 mas,[1] is around 660 light years. It is moving closer to the Earth with a heliocentric radial velocity of −32 km/s.[7]

7 Aquarii
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension  20h 56m 54.02626s[1]
Declination −09° 41′ 51.1610″[1]
Apparent magnitude (V) 5.499[2] (5.62 + 11.4)[3]
Characteristics
Spectral type K4 III[4]
B−V color index +1.474±0.006[5]
Variable type Suspected[6]
Astrometry
Radial velocity (Rv)−32.4±1.6[7] km/s
Proper motion (μ) RA: −5.577[1] mas/yr
Dec.: −10.245[1] mas/yr
Parallax (π)4.9495 ± 0.1309[1] mas
Distance660 ± 20 ly
(202 ± 5 pc)
Absolute magnitude (MV)−0.61[5]
Details
Radius46[8] R☉
Luminosity403.66[5] L☉
Surface gravity (log g)1.650[2] cgs
Temperature3,990[2] K
Metallicity [Fe/H]−0.17[2] dex
Other designations
NSV 13419, BD−10° 5553, HD 199345, HIP 103401, HR 8015, SAO 144968, ADS 14449, WDS J20569-0942[9]
Database references
SIMBADdata

The primary component is an aging giant star with a stellar classification of K4 III.[4] It is a suspected variable star of unknown type with a maximum magnitude of 5.48.[6] The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 2.14±0.02 mas,[11] which, at its estimated distance, equates to a physical radius of about 46 times the radius of the Sun.[8] The star is radiating 404[5] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,990 K.[2]

References
  1. 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.
  2. McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I. Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
  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.
  4. Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
  5. 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.
  6. Samus, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S.
  7. Gontcharov, G. A. (2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  8. 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:
  9. "7 Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved October 22, 2018.
  10. Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  11. Richichi, A.; et al. (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.
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