pi Aquarii

{{Starbox begin

| name = π Aquarii

}}

{{Starbox image

| image=

{{Location mark

|image=Aquarius constellation map.svg|alt=|float=center|width=280

|label=|position=right

|mark=Red circle.svg|mark_width=8|mark_link=π Aqr

|x=463|y=270

}}

|caption=Location of π Aquarii (circled)

}}

{{Starbox observe

| epoch = J2000

| ra = {{RA|22|25|16.623}}

| dec = {{DEC|+01|22|38.63}}

| appmag_v = 4.42 - 4.87

| constell = Aquarius

}}

{{Starbox character

| class = B1III-IVe

| b-v = −0.03

| u-b = −0.98

| variable = γ Cas

}}

{{Starbox astrometry

| radial_v = +4.0

| prop_mo_ra = +17.518

| prop_mo_dec = +2.563

| pm_footnote =

| parallax = 2.9761

| p_error = 0.1129

| parallax_footnote =

| absmag_v = −2.09

}}

{{Starbox orbit

| reference =

| period_unitless = {{val|84.07|0.02|u=days}}

| axis_unitless = {{val|0.96|ul=AU|p=≥ }}

| eccentricity = 0.0 (fixed)

| inclination =

| node =

| periastron = {{val|2450318.5|13.2|ul=JD|fmt=commas}}

| periarg = 0.0 (fixed)

| periarg_primary =

| k1 = {{val|16.7|0.2}}

| k2 = {{val|101.4|0.2}}

}}

{{Starbox detail

| component1 = A

| mass = {{val|10.7|0.7}}

| radius = 6.2

| luminosity = 7,302

| temperature = 27,094

| metal_fe = −0.02

| rotational_velocity = 215

| age_myr = {{val|10.0|5.0}}

| component2 = B

| mass2 = {{val|0.5|–|0.8}}

}}

{{Starbox catalog

| names = {{odlist | B=π Aqr | F=52 Aquarii | BD=+00 4872 | FK5=1585 | HD=212571 | HIP=110672 | HR=8539 | SAO=127520 }}

}}

{{starbox reference

| Simbad=*+pi+Aqr

}}

Pi Aquarii is a binary star system in the equatorial constellation of Aquarius. Its name is a Bayer designation that is Latinized from π Aquarii, and abbreviated Pi Aqr or π Aqr. This system has a combined apparent visual magnitude of +4.57, which is bright enough to be faintly visible to the naked eye. Based upon parallax measurements, it is located at a distance of approximately {{Convert|1100|ly|pc|abbr=off|lk=on}} from the Sun. It is drifting further away with a radial velocity of {{val|+4|u=km/s}}.

Properties

File:PiAqrLightCurve.png for Pi Aquarii, adapted from Nazé et al. (2020)]]

This is a binary star system with a period of 84.1 days in a circular orbit. The primary component is a B1 giant or subgiant star. This is a large star with nearly eleven times the mass and over six times the radius of the Sun. Pi Aquarii shines about 7,300 times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of {{val|27,094|ul=K|fmt=commas}}, giving it the blue-hued glow of a B-type star. It is spinning rapidly with a projected rotational velocity of {{val|215|u=km/s}}.

The secondary is likely a white dwarf star with a strong magnetic field and a mass of {{val|0.5|to|0.8|u=Solar mass}}. It is an X-ray source which is probably coming from accretion onto this object, making this an intermediate polar system. The accretion rate is {{val|4|–|7|e=−11|u=Solar mass}}·yr⁻¹.

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

In culture

Pi Aquarii was called Seat {{IPAc-en|'|s|iː|æ|t}} by Grotius in the 17th century, but the name has rarely been used since.

In Chinese, {{lang|zh|墳墓}} ({{lang|zh-Latn|Fén Mù}}), meaning Tomb, refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii. Consequently, the Chinese name for π Aquarii itself is {{lang|zh|墳墓四}} ({{lang|zh-Latn|Fén Mù sì}}, {{langx|en|the Fourth Star of Tomb}}.)

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). This star, along with γ Aqr (Sadachbia), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.

References

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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)