Pi Aquilae

Pi Aquilae is a binary star^[3] system in the equatorial constellation of Aquila, about 3° to the north of the bright star Altair.^[4] Its name is a Bayer designation that is Latinised from π Aquilae, and abbreviated Pi Aql or π Aql. The apparent visual magnitude of the system is 5.85,^[3] making it faintly visible to the naked eye from dark suburban skies. Based upon an annual parallax shift of 6.39 mas, the distance to this system is approximately 511 light-years (157 parsecs).^[2]

Pi Aquilae

Location of π Aquilae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquila[1]
Right ascension	19h 48m 42.059s[2]
Declination	+11° 48′ 57.22″[2]
Apparent magnitude (V)	5.85 (6.47 + 6.75)[3]
Characteristics
Spectral type	G8 III: + A1 V[3][4]
Astrometry
π Aql A
Radial velocity (Rv)	+12.6[4] km/s
Proper motion (μ)	RA: +17.838 mas/yr[2] Dec.: −9.891 mas/yr[2]
Parallax (π)	6.3883±0.0342 mas[2]
Distance	511 ± 3 ly (156.5 ± 0.8 pc)
Absolute magnitude (MV)	−0.22[1]
Details
π Aql A
Luminosity	108[1] L☉
Temperature	5,937+1,255 −569[5] K
π Aql B
Radius	10.9+0.5 −0.9[6] R☉
Luminosity	74.3±0.9[6] L☉
Surface gravity (log g)	4.5[6] cgs
Temperature	5,128+226 −105[6] K
Other designations
π Aql, 52 Aquilae, BD+11 3994, HIP 97473, HR 7544, SAO 105282, WDS J19487+1149A[7]
A: HD 187259
B: HD 187260
Database references
SIMBAD	data
	A
	B

The binary nature of this system was first discovered by William Herschel in 1785.^[4] The primary component is a magnitude 6.47^[3] giant star with a stellar classification of G8 III:.^[3] A companion star at an angular separation of 1.437 arcseconds is an A-type main-sequence star with a classification of A1 V.^[3] It is slightly fainter, with an apparent magnitude of 6.75.^[3]