Long-term, orbital, and rapid variations of the Be star V923 Aql = HD 183656^⋆,⋆⋆

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
e-mail: wolf@cesnet.cz, hec@sirrah.troja.mff.cuni.cz
² Hvar Observatory, Faculty of Geodesy, Zagreb University, Kačićeva 26, 10000 Zagreb, Croatia
³ Astronomical Institute, Czech Academy of Sciences, Fričova 298, 251 65 Ondřejov, Czech Republic
⁴ Physics & Astronomy Department, University of Victoria, PO Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
⁵ Erciyes University, Science Faculty, Astronomy and Space Sci. Dept., 38039 Kayseri, Turkey
⁶ Department of Space Sciences and Technologies, Akdeniz University, Faculty of Science, Antalya, Turkey

Received: 22 October 2020
Accepted: 12 January 2021

Abstract

We present the latest results of a long-term observational project aimed at observing, collecting from the literature, and homogenising the light, colour, and spectral variations of the well-known emission-line Be star V923 Aql. Our analysis of these parameters confirms that all of the observables exhibit cyclic changes with variable cycle length between about 1800 and 3000 days, so far documented for seven consecutive cycles. We show that these variations can be qualitatively understood within the framework of the model of one-armed oscillation of the circumstellar disk, with a wave of increased density and prograde revolution in space. We confirm the binary nature of the object with a 214.716 day period and estimate the probable system properties. We also confirm the presence of rapid light, and likely also spectral changes. However, we cannot provide any firm conclusions regarding their nature. A quantitative modelling study of long-term changes is planned as a follow-up to this work.