Iota Arae
Star in the constellation Ara
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Iota Arae is a binary star system in the southern constellation of Ara. Its name is a Bayer designation that is Latinized from ι Arae, and abbreviated Iota Ara or ι Ara. The system has a combined apparent visual magnitude of 5.2. Based upon the Bortle Dark-Sky Scale, this means it is visible to the naked eye from suburban skies. Parallax measurements yield a distance estimate of 920 light-years (281 parsecs), give or take a 20 light-year margin of error. It is drifting closer to the Sun with a radial velocity of around −19 km/s.[6]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ara[1] |
| Right ascension | 17h 23m 16.07624s[2] |
| Declination | −47° 28′ 05.5057″[2] |
| Apparent magnitude (V) | 5.18–5.26[3] |
| Characteristics | |
| Spectral type | B2 IVe + sdO[4] |
| U−B color index | −0.82[5] |
| B−V color index | −0.11[5] |
| R−I color index | −0.08 |
| Variable type | BE[3] |
| Astrometry | |
| Radial velocity (Rv) | −19.0±7.4[6] km/s |
| Proper motion (μ) | RA: −6.209 mas/yr[2] Dec.: −17.699 mas/yr[2] |
| Parallax (π) | 3.5613±0.0904 mas[2] |
| Distance | 920 ± 20 ly (281 ± 7 pc) |
| Absolute magnitude (MV) | −2.06[1] |
| Orbit[4] | |
| Period (P) | 176.17±0.04 |
| Inclination (i) | 46±6° |
| Periastron epoch (T) | 2458654.2±0.5 HJD |
| Semi-amplitude (K1) (primary) | 5.80±0.06 km/s |
| Semi-amplitude (K2) (secondary) | 57.6±0.6 km/s |
| Details | |
| ι Ara A | |
| Mass | 8.3±0.4[7] M☉ |
| Radius | 6.3[2] R☉ |
| Luminosity | 10,864[8] L☉ |
| Surface gravity (log g) | 4.18[8] cgs |
| Temperature | 20,172[2] K |
| Rotational velocity (v sin i) | 340[8] km/s |
| Age | 30.0±7.4[7] Myr |
| ι Ara B | |
| Mass | 1.06±0.29[4] M☉ |
| Radius | 0.61±0.09[9] R☉ |
| Luminosity | 437[9] L☉ |
| Temperature | 33,800[9] K |
| Other designations | |
| ι Ara, NSV 8566, CD−47°11484, FK5 3379, GC 23470, HD 157042, HIP 85079, HR 6451, SAO 227886, PPM 322888[10] | |
| Database references | |
| SIMBAD | data |
The primary component is an evolved subgiant star with a stellar classification of B2 IVe.[4] The 'e' notation indicates the spectrum displays emission lines, which means this is a Be star that is surrounded by hot, circumstellar gas. It is spinning rapidly with a projected rotational velocity of 340 km/s.[8] The Doppler effect from this rotation is causing the absorption lines to widen and become nebulous.
Iota Arae has around 8.3[7] times the mass of the Sun and is shining brightly with 10,864 times the Sun's luminosity.[8] This energy is being radiated into space from the outer atmosphere at an effective temperature of 20,172 K,[2] giving it the characteristic blue-white hue of a B-type star.[12] The General Catalog of Variable Stars classifies it as a BE variable star, ranging from visual magnitude 5.18 to 5.26 with a period of 13.36 hours.[3] In a study of the Hipparcos data, it was found to vary in brightness by 0.054 in magnitude with no clear period.[13]
This is a spectroscopic binary system with an orbital period of 176 days. The companion is a subdwarf O star with a mass similar to the Sun but only 61% of the Sun's radius.[4]