Towards a consistent model of the hot quadruple system HD 93206 = QZ Carinæ

I. Observations and their initial analyses^⋆,⋆⋆

¹ Astronomical Institute of Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
e-mail: Petr.Harmanec@mff.cuni.cz
² Department of Physics, High Point University, One University Way, High Point, NC 27268, USA
³ Dr. Karl Remeis-Observatory & ECAP, Astronomical Institute, Friedrich-Alexander-University Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
⁴ Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, Germany
⁵ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile
⁶ Instytut Astronomiczny, Uniwersytet Wrocławski, Kopernika 11, 51-622 Wrocław, Poland
⁷ Instituto de Astronomia, Geofísica e Ciencias Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP, Brazil
⁸ Auckland Observatory, PO Box 24180 Royal Oak, Auckland, New Zealand
⁹ Variable Stars South, PO Box 173 Awanui 0451, New Zealand
¹⁰ Variable Stars South, Congarinni Observatory, Congarinni, NSW 2447, Australia
¹¹ Variable Stars South, and Astronomical Society of Southern Africa, Henley Observatory, Henley on Klip, Gautenburg, South Africa
¹² AAVSO, 106 Hawking Pond Road, Center Harbor, NH 03226, USA
¹³ Mirranook Observatory, Boorolong Rd Armidale, NSW 2350, Australia
¹⁴ Hvar Observatory, Faculty of Geodesy, Zagreb University, Kačićeva 26, 10000 Zagreb, Croatia
¹⁵ Eukaryotic Pathogens Innovation Center, Clemson University, Clemson, SC 29634, USA

Received: 30 August 2021
Accepted: 8 April 2022

Abstract

The hot nine-component system HD 93206, which contains a gravitationally bounded eclipsing Ac1+Ac2 binary (P = 5.9987 d) and a spectroscopic Aa1+Aa2 (P = 20.734 d) binary can provide important insights into the origin and evolution of massive stars. Using archival and new spectra, and a rich collection of ground-based and space photometric observations, we carried out a detailed study of this object. We provide a much improved description of both short orbits and a good estimate of the mutual period of both binaries of about 14 500 d (i.e. 40 years). For the first time, we detected weak lines of the fainter component of the 6.0 d eclipsing binary in the optical region of the spectrum, measured their radial velocities, and derived a mass ratio of M_Ac2/M_Ac1 = 1.29, which is the opposite of what was estimated from the International Ultraviolet explorer (IUE) spectra. We confirm that the eclipsing subsystem Ac is semi-detached and is therefore in a phase of large-scale mass transfer between its components. The Roche-lobe filling and spectroscopically brighter component Ac1 is the less massive of the two and is eclipsed in the secondary minimum. We show that the bulk of the Hα emission, so far believed to be associated with the eclipsing system, moves with the primary O9.7 I component Aa1 of the 20.73 d spectroscopic binary. However, the weak emission in the higher Balmer lines seems to be associated with the accretion disc around component Ac2. We demonstrate that accurate masses and other basic physical properties including the distance of this unique system can be obtained but require a more sophisticated modelling. A first step in this direction is presented in the accompanying Paper II (Brož et al.).