Phi Aquilae

Phi Aquilae, Latinized from φ Aquilae, is the Bayer designation of a binary star^[12] system in the equatorial constellation of Aquila. It has an apparent visual magnitude of +5.28^[2] and is visible to the naked eye. With an annual parallax shift of 14.198 mas,^[1] this star is located at a distance of approximately 230 light-years (71 parsecs) from Earth. It is drifting closer with a radial velocity of –27 km/s.^[4] Based on its motion through space, this system is considered a possible member of the nearby Argus association of co-moving stars, although it may be too old.^[13]

Phi Aquilae

Location of φ Aquilae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquila
Right ascension	19h 56m 14.25183s[1]
Declination	+11° 25′ 25.3931″[1]
Apparent magnitude (V)	+5.28[2]
Characteristics
Spectral type	A1 IV[3]
U−B color index	–0.02[2]
B−V color index	+0.00[2]
Astrometry
Radial velocity (Rv)	–27.2[4] km/s
Proper motion (μ)	RA: +32.826[1] mas/yr Dec.: +6.162[1] mas/yr
Parallax (π)	14.1980±0.1579 mas
Distance	230 ± 3 ly (70.4 ± 0.8 pc)
Absolute magnitude (MV)	+1.14[5]
Orbit[6]
Period (P)	3.32068 days
Eccentricity (e)	0.025
Periastron epoch (T)	JD 2423210.628
Argument of periastron (ω) (secondary)	43°
Semi-amplitude (K1) (primary)	37.2 km/s
Details
A
Mass	2.39[7] M☉
Radius	1.8–2.5[8] R☉
Luminosity	34[5] L☉
Surface gravity (log g)	4.30[9] cgs
Temperature	9,509[9] K
Metallicity [Fe/H]	+0.47[9] dex
Rotational velocity (v sin i)	27[10] km/s
Age	280[7] Myr
B
Mass	0.40[7] M☉
Other designations
φ Aql, 61 Aql, BD+11° 4055, FK5 3590, HD 188728, HIP 98103, HR 7610, SAO 105438[11]
Database references
SIMBAD	data

Phi Aquilae is a single-lined spectroscopic binary with an orbital period of 3.32068 days.^[6] The pair have a projected separation of 190.4 AU as of 2008.^[7] The primary component is a subgiant star with a stellar classification of A1 IV.^[3] The star is around 280^[7] million years old and is spinning with a projected rotational velocity of 27.^[10] It has 2.39^[7] times the mass of the Sun and somewhere in the range of 1.8–2.5^[8] times the Sun's radius. The outer atmosphere has an effective temperature of 9,509 K,^[9] giving it the white-hued appearance of an A-type star.^[14] It is radiating 34^[5] times the luminosity of the Sun.

The orbiting companion may be the source of the X-ray emission from this system, as stars similar to the primary component do not generally produce detectable levels of X-rays.^[15] It has 40% of the mass of the Sun.^[7]