Phi Aquilae

Phi Aquilae is a binary star^[13] system in the equatorial constellation of Aquila. Its name is a Bayer designation that is Latinized from φ Aquilae, and abbreviated Phi Aql or φ Aql. The system has an apparent visual magnitude of +5.28^[3] and is visible to the naked eye as a faint point of light. With an annual parallax shift of 14.7 mas,^[2] this star is located at a distance of approximately 221 light-years (68 parsecs) from Earth. It is drifting closer with a radial velocity of −27 km/s.^[6] Based on its motion through space, this system is a candidate member of the nearby Argus association of co-moving stars, although it may be too old.^[14]

Phi Aquilae

Location of φ Aquilae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquila[1]
Right ascension	19h 56m 14.252s[2]
Declination	+11° 25′ 25.40″[2]
Apparent magnitude (V)	+5.28[3]
Characteristics
Spectral type	A1 IV[4] + K1 V to M1 V[5]
U−B color index	−0.02[3]
B−V color index	+0.00[3]
Astrometry
Radial velocity (Rv)	−27.2±0.9[6] km/s
Proper motion (μ)	RA: +32.745 mas/yr[2] Dec.: +5.630 mas/yr[2]
Parallax (π)	14.7474±0.0869 mas
Distance	221 ± 1 ly (67.8 ± 0.4 pc)
Absolute magnitude (MV)	+1.14[1]
Orbit[5]
Period (P)	3.320669±0.000017 d
Eccentricity (e)	0
Periastron epoch (T)	2459445.0916±0.0011 JD
Argument of periastron (ω) (secondary)	43[7]°
Semi-amplitude (K1) (primary)	36.48±0.07 km/s
Details
A
Mass	2.39[8] M☉
Radius	1.8–2.5[9] R☉
Luminosity	28.2+0.6 −0.7[5] L☉
Surface gravity (log g)	4.30[10] cgs
Temperature	9,484±13[5] K
Metallicity [Fe/H]	+0.47[10] dex
Rotational velocity (v sin i)	27[11] km/s
Age	280[8] Myr
B
Mass	0.40[8] M☉
Other designations
φ Aquilae, φ Aql, 61 Aql, BD+11°4055, FK5 3590, GC 27604, HD 188728, HIP 98103, HR 7610, SAO 105438, PPM 137250, WDS J19562+1125AB[12]
Database references
SIMBAD	data

Phi Aquilae is a single-lined spectroscopic binary with an orbital period of 3.32067 days.^[5] The pair have a projected separation of 190.4 AU as of 2008.^[8] The primary component is a subgiant star with a stellar classification of A1 IV.^[4] The star is around 280^[8] million years old and is spinning with a projected rotational velocity of 27 km/s.^[11] It has 2.39^[8] times the mass of the Sun and somewhere in the range of 1.8–2.5^[9] times the Sun's radius. The outer atmosphere has an effective temperature of 9,509 K,^[10] giving it the white-hued appearance of an A-type star.^[15] It is radiating 34^[1] 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.^[16] It has 40% of the mass of the Sun.^[8] Based on photometric data from the TESS mission, the pair may undergo grazing eclipses. This implies an orbital inclination of at least 79°, and constrains the mass of the secondary to 0.5 M_☉.^[5]

A third component of this system was detected during the VAST survey. This faint component lies at an angular separation of 2.83 arcseconds, for a projected separation of 190 AU and an estimated orbital period of over 1,500 years.^[5]