18 Aquilae

18 Aquilae
Location of 18 Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 06m 58.60289s[1]
Declination +11° 04′ 16.4173″[1]
Apparent magnitude (V) 5.072
Characteristics
Spectral type B8 III[2]
U−B color index −0.44[3]
B−V color index −0.08[3]
Variable type Eclipsing[4]
Astrometry
Radial velocity (Rv)−18.6[5] km/s
Proper motion (μ) RA: −0.89[1] mas/yr
Dec.: −32.11[1] mas/yr
Parallax (π)6.43 ± 0.79 mas[1]
Distanceapprox. 510 ly
(approx. 160 pc)
Orbit[6]
PrimaryA
CompanionB
Period (P)205.16 yr
Semi-major axis (a)0.399″
Eccentricity (e)0.23
Inclination (i)134.3°
Orbit[6]
PrimaryAa
CompanionAb
Period (P)1.3023 d
Semi-amplitude (K1)
(primary)		27.6 km/s
Details
Aa
Mass5.6[6] M☉
Luminosity4,875[7] L☉
Rotational velocity (v sin i)50[2] km/s
Ab
Mass0.38[6] M☉
Luminosity12.7[7] L☉
B
Mass3.49[6] M☉
Other designations
Y Aquilae, 18 Aql, BD+10 3787, FK5 3525, HD 178125, HIP 93867, HR 7248, SAO 104488[8]
Database references
SIMBADdata

18 Aquilae (abbreviated 18 Aql) is a triple star[9] system in the constellation of Aquila. 18 Aquilae is the Flamsteed designation; it also bears the variable star designation Y Aquilae. It has an apparent visual magnitude of 5.07. The distance to this system can be estimated from the annual parallax shift of 6.43 mas, yielding a value of around 510 light-years (160 parsecs) away from Earth.

A light curve for Y Aquilae, plotted from TESS data[10]

The inner pair of stars in this system form a spectroscopic binary with a combined magnitude of 5.44 and an orbital period of 1.302 days. The primary component is a giant star with a stellar classification of B8 III.[2] Because the orbital plane is inclined near the line of sight, two form an eclipsing binary system. The eclipse of the primary component causes a 0.04 drop in magnitude, while the eclipse of the secondary results in a decrease of 0.03.[11] At an angular separation of 0.310 arcseconds is the magnitude 6.39 tertiary component.[9] This system has a high peculiar velocity of 29.7 ± 3.9 km/s relative to the neighboring stars.[12]

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