Omega Piscium

Omega Piscium (Omega Psc, ω Piscium, ω Psc) is a star approximately 106 light years away from Earth, in the constellation Pisces. It has a spectral type of F4IV, meaning it is a subgiant/dwarf star, and it has a temperature of 6,600 kelvins. It may or may not be a close binary star system. Variations in its spectrum were once interpreted as giving it an orbital period of 2.16 days, but this claim was later debunked as false. It is 20 times brighter than the Sun and is 1.8 times greater in mass, if it is a single star.[11]

Omega Piscium
Location of ω Piscium (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Pisces
Right ascension  23h 59m 18.69064s[1]
Declination +06° 51′ 47.9562″[1]
Apparent magnitude (V) 4.01[2]
Characteristics
Spectral type F4 IV[3] or F4 V[4]
U−B color index +0.07[2]
B−V color index +0.42[2]
Astrometry
Radial velocity (Rv)+2.9±0.3[5] km/s
Proper motion (μ) RA: +150.35[1] mas/yr
Dec.: −112.12[1] mas/yr
Parallax (π)31.26 ± 0.15[1] mas
Distance104.3 ± 0.5 ly
(32.0 ± 0.2 pc)
Absolute magnitude (MV)+1.51[6]
Details
ω Psc A
Mass1.22[7] M☉
Luminosity21[6] L☉
Surface gravity (log g)3.74±0.14[7] cgs
Temperature6,641±226[7] K
Metallicity [Fe/H]−0.09[8] dex
Rotational velocity (v sin i)40.3[9] km/s
Age1.337[7] Gyr
Other designations
ω Psc, 28 Piscium, BD+06° 5227, FK5 902, HD 224617, HIP 118268, HR 9072, SAO 128513[10]
Database references
SIMBADdata

It is part of the drawn asterism in classic and modern renderings as the start of the tail, east of the Circlet of Pisces,[11] a near-circle which forms all but the tail (the head and body) of the western (fatter) "fish" in the constellation of two fishes.[12]

Right ascension

Considering stars with Flamsteed numbers, Greek letters, and proper names, Omega Piscium at J2000 is, namely in the year 2000 was, the named star with the highest right ascension (akin to terrestrial longitude). Due to the 26,000-year movement of the Earth's axis tracing an imperfect circle (axial precession), it has since increased to just beyond 0 hours, which it reached in J2013.

At the cusp of sunrise on the March Equinox in the present era the circlet appears just above the sunrise being the westernmost part of the asterism; the easternmost parts can be most easily seen after sunset, just above the sun on a maximal horizon, such as the sea. A month later the progress of the earth around the plane of the ecliptic (its orbit) by a mean 2 hours of Right Ascension (18° of orbit) means that the sun rises and sets in an outer part of Aries bordering Cetus.

Naming
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References
  1. van Leeuwen, F. (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.
  2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J.
  3. Griffin, R. F.; Redman, R. O. (1960), "Photoelectric measurements of the λ4200 A CN band and the G band in G8-K5 spectra", Monthly Notices of the Royal Astronomical Society, 120: 287, Bibcode:1960MNRAS.120..287G, doi:10.1093/mnras/120.4.287.
  4. Abt, Helmut A. (2009), "MK Classifications of Spectroscopic Binaries", The Astrophysical Journal Supplement, 180 (1): 117–18, Bibcode:2009ApJS..180..117A, doi:10.1088/0067-0049/180/1/117.
  5. 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.
  6. 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.
  7. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  8. Pace, G. (March 2013), "Chromospheric activity as age indicator. An L-shaped chromospheric-activity versus age diagram", Astronomy & Astrophysics, 551: 4, arXiv:1301.5651, Bibcode:2013A&A...551L...8P, doi:10.1051/0004-6361/201220364, L8.
  9. Schröder, C.; Reiners, A.; Schmitt, J. H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377.
  10. "ome Psc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-22.
  11. "Omega Psc". Archived from the original on April 30, 2007. Retrieved September 30, 2007.
  12. "Western Pisces". Archived from the original on June 15, 2007. Retrieved September 30, 2007.
  13. Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55: 430. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  14. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 8 日
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