IO Aquarii (also designated HD 196991, HIP 102041, IO Aqr) is a hierarchical triple star system in the constellation Aquarius.[3] The inner component is a detached double-lined eclipsing binary with a short orbital period, around which a low-mass, low-luminosity companion star moves on a wide, highly eccentric outer orbit.[3] Despite its relative brightness (apparent magnitude 8.8 except when in eclipse), the system's variability was not recognised until photometric observations by the Hipparcos satellite mission, after which the variable star designation IO Aqr was assigned by Kazarovets et al. (1999).[3]
The inner pair is a double-lined spectroscopic binary on a circular orbit with a period 2.368 days.[3] A third body orbits the inner binary on a much wider, highly eccentric orbit with a period estimated at ≳25,000 days (≳70 years).[3] The existence of the outer companion was established from two independent lines of evidence: periodic variations in eclipse timing (the light-travel time effect) and a faint additional peak in the broadening function of the spectra.[3]
References
- ↑ 1.0 1.1 1.2 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 2.0 2.1 Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports 61 (1): 80. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Graczyk, D.; Maxted, P. F. L.; Pietrzyński, G.; Pilecki, B.; Konorski, P.; Gieren, W.; Storm, J.; Gallenne, A. et al. (2015). "The Araucaria project. Precise physical parameters of the eclipsing binary IO Aquarii". Astronomy and Astrophysics 581: A106. doi:10.1051/0004-6361/201526211. Bibcode: 2015A&A...581A.106G.
- ↑ Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". Michigan Spectral Survey 5. Bibcode: 1999MSS...C05....0H.
- ↑ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759. doi:10.1134/S1063773706110065. Bibcode: 2006AstL...32..759G.
- ↑ "IO Aqr". Centre de Données astronomiques de Strasbourg. https://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+196991.
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