Sigma Aquarii

Sigma Aquarii, Latinized from σ Aquarii, is a double star in the equatorial constellation of Aquarius, positioned about 1.3° to the south of the ecliptic.^[10] Due to its proximity to the ecliptic, this star is subject to occultation by the Moon.^[11] It has a white hue and is visible to the naked eye with an apparent visual magnitude of 4.81.^[2] Based upon parallax measurements, the distance to this star is approximately 175 light-years (54 parsecs).^[1] It is drifting further away with a radial velocity of +11 km/s.^[12]

Sigma Aquarii

Location of σ Aquarii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius
Right ascension	22h 30m 38.82286s[1]
Declination	−10° 40′ 40.7031″[1]
Apparent magnitude (V)	4.81[2]
Characteristics
Spectral type	A0 IVs[3]
U−B color index	−0.14[2]
B−V color index	−0.08[2]
Astrometry
Radial velocity (Rv)	+11.7±0.6[4] km/s
Proper motion (μ)	RA: −5.708[1] mas/yr Dec.: −25.626[1] mas/yr
Parallax (π)	18.6424 ± 0.6871 mas[1]
Distance	175 ± 6 ly (54 ± 2 pc)
Absolute magnitude (MV)	0.29±0.23[5]
Details
Mass	2.87[6] M☉
Radius	2.87[5] R☉
Luminosity	105[6] L☉
Surface gravity (log g)	4.07[7] cgs
Temperature	10,115[6] K
Metallicity [Fe/H]	+0.44[7] dex
Rotational velocity (v sin i)	21[8] km/s
Age	30[5] Myr
Other designations
σ Aqr, 57 Aquarii, BD–11°5850, FK5 1591, HD 213320, HIP 111123, HR 8573, SAO 165134[9]
Database references
SIMBAD	data

The stellar classification of Sigma Aquarii is A0 IVs,^[3] indicating that it is a subgiant star. The s qualifier means that its absorption lines are sharp (narrow) in comparison with standard stars, caused by a relatively slow rotation. It has been categorized as a hot Am star,^[13] meaning that it is a chemically peculiar, although this is now considered doubtful.^[14] The spectrum displays at least double the normal abundances of elements like magnesium, aluminum and silicon, while helium and scandium are under-abundant. Calcium, normally deficient in Am stars, has near-normal abundance.^[13]

The Hipparcos catalogue identified Sigma Aquarii as a possible astrometric binary with an orbital period of 654 days.^[15]

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. Gaia DR2 record for this source at VizieR.
2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
3. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
4. Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169
5. Gerbaldi, M.; et al. (June 1999), "Search for reference A0 dwarf stars: Masses and luminosities revisited with HIPPARCOS parallaxes", Astronomy and Astrophysics Supplement, 137 (2): 273–292, Bibcode:1999A&AS..137..273G, doi:10.1051/aas:1999248.
6. Zorec, J; Royer, F (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy & Astrophysics. 537: A120. arXiv:1201.2052. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691. S2CID 55586789.
7. Gebran, M; Farah, W; Paletou, F; Monier, R; Watson, V (2016). "A new method for the inversion of atmospheric parameters of A/Am stars". Astronomy & Astrophysics. 589: A83. arXiv:1603.01146. Bibcode:2016A&A...589A..83G. doi:10.1051/0004-6361/201528052. S2CID 118549566.
8. Royer, F; Zorec, J; Gómez, A. E (2007). "Rotational velocities of A-type stars. III. Velocity distributions". Astronomy and Astrophysics. 463 (2): 671. arXiv:astro-ph/0610785. Bibcode:2007A&A...463..671R. doi:10.1051/0004-6361:20065224. S2CID 18475298.
9. "* sig Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-04.
10. Sinnott, Roger W.; Perryman, Michael A. C. (1997), Millennium Star Atlas, vol. 3, Sky Publishing Corporation and the European Space Agency, p. 1331, ISBN 0-933346-84-0
11. Trunkovsky, E. M. (February 2010), Rivinius, Th.; Curé, M. (eds.), "On Determination of Angular Sizes of Some Relatively Hot Stars by Lunar Occultation Observations and on Suggested Interferometric Investigation of these Stars", The Interferometric View on Hot Stars, Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias, vol. 38, pp. 127–132, Bibcode:2010RMxAC..38..127T
12. Wilson, R. E. (1953), "General Catalogue of Stellar Radial Velocities", Washington, Carnegie Institute of Washington D.C., Bibcode:1953GCRV..C......0W.
13. Adelman, S. J.; Young, J. M.; Baldwin, H. E. (February 1984), "Optical region elemental abundance analyses of B and A stars. II - The hot AM stars Omicron Pegasi and Sigma Aquarii and the marginal peculiar A star Nu CANCRI", Monthly Notices of the Royal Astronomical Society, 206 (3): 649–660, Bibcode:1984MNRAS.206..649A, doi:10.1093/mnras/206.3.649.
14. Renson, P; Manfroid, J (2009). "Catalogue of Ap, Hg Mn and Am stars". Astronomy and Astrophysics. 498 (3): 961. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788.
15. Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; et al. (July 1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P. Note about binarity

External links

• Image Sigma Aquarii