Iota Apodis

Iota Apodis is a binary star^[3] system in the southern circumpolar constellation of Apus. Its identifier is a Bayer designation that is Latinized from ι Apodis, and abbreviated Iot Aps or ι Aps, respectively. This system is a faint target at an apparent visual magnitude of 5.41,^[2] but still visible to the naked eye from suitably dark skies. The distance to this star can be gauged from parallax measurements, yielding an estimate of 1,020 light-years (310 parsecs) with a 6% margin of error.^[1] The system is drifting closer with a heliocentric radial velocity of −4.3 km/s.^[4]

ι Apodis

Location of ι Apodis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Apus
Right ascension	17h 22m 05.876s[1]
Declination	−70° 07′ 23.54″[1]
Apparent magnitude (V)	5.41[2] (5.90/6.46)[3]
Characteristics
Spectral type	B9 V + B9.5 V[3]
U−B color index	−0.23[2]
B−V color index	−0.04[2]
Astrometry
Radial velocity (Rv)	−4.3[4] km/s
Proper motion (μ)	RA: −1.881 mas/yr[1] Dec.: −11.363 mas/yr[1]
Parallax (π)	3.1948±0.1853 mas[1]
Distance	1,020 ± 60 ly (310 ± 20 pc)
Orbit[5]
Period (P)	59.32±3.0 yr
Semi-major axis (a)	0.115±0.005″
Eccentricity (e)	0.172±0.050
Inclination (i)	69.4±3.0°
Longitude of the node (Ω)	119.6±4.0°
Argument of periastron (ω) (secondary)	270.5±7.0°
Details
ι Aps A
Mass	3.89±1.02[5] M☉
ι Aps B
Mass	3.45±0.90[5] M☉
Other designations
ι Apodis, Iot Aps, ι Aps, CPD−69 2719, FK5 642, HD 156190, HIP 84979, HR 6411, SAO 257491, WDS J17221−7007[6]
Database references
SIMBAD	data

The dual nature of this system was announced by W. S. Finsen in 1960, who reported an angular separation of 0.104 arcseconds.^[7] Their orbit has an angular separation of 0.091 arcseconds^[3] with an estimated orbital period of 59.32 years and an eccentricity (ovalness) of 0.17.^[5] Both stars are B-type main sequence stars, which indicates they shine with a blue-white hue.^[8] The brighter component has a stellar classification of B9 V and an apparent magnitude 5.90, while the second member is a B9.5 V star with a magnitude of 6.46. They are about 3.89 and 3.45 times as massive as the Sun, respectively.^[5]

Naming

In Chinese caused by adaptation of the European southern hemisphere constellations into the Chinese system, 異雀 (Yì Què), meaning Exotic Bird, refers to an asterism consisting of ι Apodis, ζ Apodis, β Apodis, γ Apodis, δ Octantis, δ¹ Apodis, η Apodis, α Apodis and ε Apodis. Consequently, ι Apodis itself is known as 異雀二 (Yì Què èr, English: the Second Star of Exotic Bird.)^[9]