Pi Aquarii

π Aquarii
Location of π Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 22h 25m 16.62285s[1]
Declination +01° 22′ 38.6346″[1]
Apparent magnitude (V) 4.42 - 4.87[2]
Characteristics
Spectral type B1III-IVe[3]
U−B color index −0.98[4]
B−V color index −0.03[4]
Variable type γ Cas[2]
Astrometry
Radial velocity (Rv)+4.0[5] km/s
Proper motion (μ) RA: +17.83[1] mas/yr
Dec.: +2.41[1] mas/yr
Parallax (π)4.17 ± 0.28 mas[1]
Distance780 ± 50 ly
(240 ± 20 pc)
Absolute magnitude (MV)−2.09[6]
Orbit[7]
Period (P)84.07±0.02 d
Semi-major axis (a)≥ 0.96 AU
Eccentricity (e)0.0 (fixed)
Periastron epoch (T)2,450,318.5±13.2 JD
Argument of periastron (ω)
(secondary)		0.0 (fixed)°
Semi-amplitude (K1)
(primary)		16.7±0.2 km/s
Semi-amplitude (K2)
(secondary)		101.4±0.2 km/s
Details
A
Mass10.7±0.7[8] M☉
Radius6.2[9] R☉
Luminosity7,302[10] L☉
Temperature27,094[9] K
Metallicity [Fe/H]−0.02[6] dex
Rotational velocity (v sin i)215[11] km/s
Age10.0±5.0[8] Myr
Other designations
π Aqr, 52 Aquarii, BD+00 4872, FK5 1585, HD 212571, HIP 110672, HR 8539, SAO 127520[12]
Database references
SIMBADdata

Pi Aquarii, Latinized from π Aquarii, is the Bayer designation for a binary star in the equatorial constellation of Aquarius. This system has an apparent visual magnitude of a mean apparent magnitude of +4.57.[4] Based upon parallax measurements, it is located at a distance of roughly 780 light-years (240 parsecs) from Earth.[1] It is drifting further away with a radial velocity of +4 km/s.[5]

A white-light light curve for Pi Aquarii, adapted from Nazé et al. (2020)[13]

This is a binary star system with an orbital period of 84.1 days.[14][15] The primary component is a B1 giant or subgiant star.[3] This is a large star with nearly eleven[8] times the mass and over six times the radius of the Sun.[9] Pi Aquarii shines about 7,300[10] times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of 27,094 K,[9] giving it the blue-hued glow of a B-type star.[16] It is spinning rapidly with a projected rotational velocity of 215 km/s.[11] The nature of the secondary is unknown; some analyses have suggested it is an A- or F-type main-sequence star,[7] but the possibility of a white dwarf has not been ruled out.[17]

Pi Aquarii is notable for having undergone a transition from a Be star (showing hydrogen emission lines) into an ordinary B-type star.[15] It is classified as a Gamma Cassiopeiae type[2] variable star and its brightness varies from magnitude +4.45 to +4.71; a range of 0.28. The dominant variability period, 83.8±0.8 days, is nearly the same as the orbital period.[15] Pi Aquarii has a reasonable chance of becoming a supernova some day.[14]

  1. ^ a b c d e f Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b c Cite error: The named reference GCVS was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference slettebak was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference aass34_1 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference scfs was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Bjorkman_et_al_2002 was invoked but never defined (see the help page).
  8. ^ a b c Cite error: The named reference mnras410_1_190 was invoked but never defined (see the help page).
  9. ^ a b c d Cite error: The named reference mnras189_601 was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference an331_4_349 was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference apj573_1_359 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Naze was invoked but never defined (see the help page).
  14. ^ a b Cite error: The named reference Kaler was invoked but never defined (see the help page).
  15. ^ a b c Cite error: The named reference ibvs6023_1 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference csiro was invoked but never defined (see the help page).
  17. ^ Tsujimoto, Masahiro; Hayashi, Takayuki; Morihana, Kumiko; Moritani, Yuki (2023). "X-ray and optical spectroscopic study of a γ Cassiopeiae analog source π Aquarii". Publications of the Astronomical Society of Japan. 75 (1): 177–186. arXiv:2211.10803. Bibcode:2023PASJ...75..177T. doi:10.1093/pasj/psac099.