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Iota Arae

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ι Arae
Location of ι Arae (circled)
Observation data
Epoch J2000      Equinox J2000
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]
Distance920 ± 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
Mass8.3±0.4[7] M☉
Radius6.3[2] R☉
Luminosity10,864[8] L☉
Surface gravity (log g)4.18[8] cgs
Temperature20,172[2] K
Rotational velocity (v sin i)340[8] km/s
Age30.0±7.4[7] Myr
ι Ara B
Mass1.06±0.29[4] M☉
Radius0.61±0.09[9] R☉
Luminosity437[9] L☉
Temperature33,800[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
SIMBADdata

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]

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.

A light curve for Iota Arae, plotted from TESS data[11]

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]

References

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  1. ^ a b Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  2. ^ a b c d e f g Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. ^ a b c Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  4. ^ a b c d e Wang, Luqian; et al. (April 2023). "The Orbital and Physical Properties of Five Southern Be+sdO Binary Systems". The Astronomical Journal. 165 (5): 203. arXiv:2303.12616. Bibcode:2023AJ....165..203W. doi:10.3847/1538-3881/acc6ca. ISSN 1538-3881.
  5. ^ a b Kozok, J. R. (September 1985). "Photometric observations of emission B-stars in the southern Milky Way". Astronomy and Astrophysics Supplement Series. 61: 387–405. Bibcode:1985A&AS...61..387K.
  6. ^ a b Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ∼55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.
  7. ^ a b c Tetzlaff, N.; et al. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
  8. ^ a b c d e Zorec, J.; et al. (November 2016). "Critical study of the distribution of rotational velocities of Be stars. I. Deconvolution methods, effects due to gravity darkening, macroturbulence, and binarity". Astronomy & Astrophysics. 595: 26. Bibcode:2016A&A...595A.132Z. doi:10.1051/0004-6361/201628760. hdl:11336/37946.
  9. ^ a b c Wang, Luqian; et al. (2021). "The Detection and Characterization of Be+sdO Binaries from HST/STIS FUV Spectroscopy". The Astronomical Journal. 161 (5): 248. arXiv:2103.13642. Bibcode:2021AJ....161..248W. doi:10.3847/1538-3881/abf144.
  10. ^ "iot Ara". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-07-30.
  11. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  12. ^ "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived from the original on February 22, 2012. Retrieved 2012-01-16.
  13. ^ Lefèvre, L.; et al. (November 2009). "A systematic study of variability among OB-stars based on HIPPARCOS photometry". Astronomy and Astrophysics. 507 (2): 11411201. Bibcode:2009A&A...507.1141L. doi:10.1051/0004-6361/200912304.
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