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Variable B-type star in the constellation Aquarius From Wikipedia, the free encyclopedia
Omicron Aquarii, Latinized from ο Aquarii, is the Bayer designation for a variable star in the equatorial constellation of Aquarius. Visible to the naked eye, it has an apparent visual magnitude of +4.71.[2] Parallax measurements put it at a distance of roughly 440 light-years (130 parsecs) from Earth.[1] It is drifting further away with a radial velocity of +11 km/s.[5] The star is a candidate member of the Pisces-Eridanus stellar stream.[12]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Aquarius |
Right ascension | 22h 03m 18.84403s[1] |
Declination | –02° 09′ 19.3067″[1] |
Apparent magnitude (V) | +4.71[2] |
Characteristics | |
Spectral type | B7 IVe[3] |
U−B color index | –0.39[2] |
B−V color index | –0.11[2] |
Variable type | γ Cas[4] |
Astrometry | |
Radial velocity (Rv) | +11.0[5] km/s |
Proper motion (μ) | RA: +24.66[1] mas/yr Dec.: –11.16[1] mas/yr |
Parallax (π) | 7.49 ± 0.23 mas[1] |
Distance | 440 ± 10 ly (134 ± 4 pc) |
Absolute magnitude (MV) | −0.89[6] |
Details | |
Mass | 4.2[7] M☉ |
Radius | 4.0±0.3[7] R☉ |
Luminosity | 340[6] L☉ |
Surface gravity (log g) | 3.13[8] cgs |
Temperature | 13,464±164[9] K |
Metallicity [Fe/H] | −0.16[6] dex |
Rotational velocity (v sin i) | 282±20[10] km/s |
Other designations | |
Database references | |
SIMBAD | data |
It has the traditional star name Kae Uh, from the Chinese 蓋屋 (Mandarin pronunciation Gài Wū).[13] In Chinese astronomy, 蓋屋 is the rooftop, an asterism consisting of ο Aquarii and 32 Aquarii.[14] Consequently, the Chinese name for ο Aquarii itself is 蓋屋一 (Gài Wū yī, English: the First Star of Roofing.)[15]
The spectrum of Omicron Aquarii fits a stellar classification of B7 IVe;[3] the luminosity class of IV suggests that this is a subgiant star that is exhausting the supply of hydrogen at its core and is in the process of evolving into a giant star. The 'e' suffix on the class indicates that the spectrum shows emission lines of hydrogen, thus categorizing this as a Be star. It is rotating rapidly with an equatorial rotational velocity of 368 km/s, which is ~96% of the star's critical rotation velocity of 391 km/s.[7] The emission lines are being generated by a decreted circumstellar disk of hot hydrogen gas.[10] This disk has been globally stable for at least twenty years, as of 2020.[7] It is likely a single star, with no stellar companions.[17]
Omicron Aquarii has 4.2 times the mass of the Sun, four[7] times the Sun's radius, and is radiating 340[6] times the luminosity of the Sun from its photosphere at an effective temperature of 13,464 K.[9] It is classified as a Gamma Cassiopeiae type[4] variable star and its brightness varies from magnitude +4.68 down to +4.89.[18]
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