Pi Aquarii

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π Aquarii
Aquarius constellation map.svg
Red circle.svg
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]
Distance 780 ± 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
Mass 10.7±0.7 [8]   M
Radius 6.2 [9]   R
Luminosity 7,302 [10]   L
Temperature 27,094 [9]   K
Metallicity [Fe/H]−0.02 [6]   dex
Rotational velocity (v sin i)215 [11]  km/s
Age 10.0±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
SIMBAD data

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]

Contents

A white-light light curve for Pi Aquarii, adapted from Naze et al. (2020) PiAqrLightCurve.png
A white-light light curve for Pi Aquarii, adapted from Nazé et al. (2020)

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]

In culture

Pi Aquarii was called Seat /ˈsæt/ by Grotius in the 17th century, but the name has rarely been used since. [14]

In Chinese, 墳墓 (Fén Mù), meaning Tomb , refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii. [18] Consequently, the Chinese name for π Aquarii itself is 墳墓四 (Fén Mù sì, English: the Fourth Star of Tomb.) [19]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Wasat al Achbiya (وسط الأخبية - wasath al ahbiyah), which was translated into Latin as Media Tabernaculorum, meaning the middle of luck of the homes (tents). [20] This star, along with γ Aqr (Sadachbia), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent. [21] [22] [23]

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  23. γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), π Aqr as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and ζ Aqr as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). η Aqr should be designated as al Achbiya consistently, but it was not designated as the Arabic name except the name Hydria (Greek) or Deli (Hebrew)