Omega2 Aquarii

For other stars with this Bayer designation, see ω Aquarii.

Omega² Aquarii is a star^[12] system in the equatorial constellation of Aquarius. Its name is a Bayer designation that is Latinised from ω² Aquarii, and abbreviated Omega² Aqr or ω² Aqr. The system can be seen with the naked eye as a faint point of light, having an apparent visual magnitude of 4.49.^[3] The approximate distance to this star, 149 light-years (46 parsecs), is known from parallax measurements.^[2]

Omega² Aquarii

Location of ω2 Aquarii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius[1]
Right ascension	23h 42m 43.345s[2]
Declination	−14° 32′ 41.66″[2]
Apparent magnitude (V)	4.49[3]
Characteristics
Spectral type	B9 V[4] + A5V[5]
U−B color index	−0.12[3]
B−V color index	−0.04[3]
Astrometry
Radial velocity (Rv)	+3.2±2.3[6] km/s
Proper motion (μ)	RA: +98.578 mas/yr[2] Dec.: −66.231 mas/yr[2]
Parallax (π)	20.8948±0.1589 mas[2]
Distance	156 ± 1 ly (47.9 ± 0.4 pc)
Absolute magnitude (MV)	+1.20[1]
Details
A
Mass	2.6+0.15 −0.14[7] M☉
Radius	1.94±0.06[8] R☉
Luminosity	37[1] L☉
Surface gravity (log g)	4.22±0.03[8] cgs
Temperature	10,504±91[8] K
Rotation	10.6546 h[9]
Rotational velocity (v sin i)	148[10] km/s
Age	109+90 −70[7] Myr
Other designations
ω2 Aqr, 105 Aquarii, BD−15 6476, FK5 894, GC 32931, GJ 9836, HD 222661, HIP 116971, HR 8988, SAO 165842, PPM 242001, WDS J23427-1433A[11]
Database references
SIMBAD	data

This is a B-type main-sequence star with a stellar classification of B9 V.^[4] In 1953, astronomers H. L. Johnson and W. W. Morgan selected it as the MK standard for stars of class B9.5V.^[13] It has an estimated age of 109^[7] million years and is spinning rapidly with a projected rotational velocity of 148 km/s,^[10] giving it a rotation period of 10.6546 h.^[9] The star has 2.6^[7] times the Sun's mass and nearly double the radius of the Sun.^[8] It is radiating 37^[1] times the luminosity of the Sun from its photosphere at an effective temperature of 10,504 K,^[8] giving it the blue-white hue of a B-type star.^[14]

In 1983, this was catalogued as a spectroscopic binary star system with components classed B9V and B9.5V.^[5] However, a 2012 survey by R. Chini et al found the star to have a constant radial velocity.^[12] There is a companion star at an angular separation of 5.7 arcseconds that shares a common proper motion with the primary. It is an A-type main-sequence star with a visual magnitude of 9.5.^[5] This system is among the 100 strongest stellar X-ray sources within 163 light-years (50 parsecs) of the Sun. It is emitting an X-ray luminosity of 1.2×10³⁰ erg·s⁻¹. The source for this X-ray emission is unknown.^[15]