New BRITE-Constellation observations of the roAp star α Cir^⋆

¹ University of Vienna, Institute for Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: werner.weiss@univie.ac.at
² Kleine Strasse 9, 14482 Potsdam, Germany
³ Graz University of Technology, Institute of Commun. Networks and Satellite Commun., Infeldgasse 12, 8010 Graz, Austria
⁴ Silesian University of Technology, Department of Electronics, Electrical Engineering and Microelectronics, Poland
⁵ ESO, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
⁶ Florida Gulf Coast University, Department of Chemistry and Physics, 10501 FGCU Blvd S, Fort Myers, FL 33965, USA
⁷ Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
⁸ Uppsala University, Department of Physics and Astronomy, Box 516, 75120 Uppsala, Sweden
⁹ Université de Montréal, Dept. de physique, CP 6128 Succ. C-V, Montréal, QC H3C 3J7, Canada
¹⁰ American Association of Variable Star Observers, 49 Bay State Rd., Cambridge, MA 02138, USA
¹¹ Royal Military College, Dept. of Physics and Space Science, PO Box 17000 Station Forces, Kingston, ON K7K 0C6, Canada
¹² University of Innsbruck, Institute for Astro- and Particle Physics, Technikerstrasse 25, 6020 Innsbruck, Austria

Received: 4 May 2020
Accepted: 28 July 2020

Abstract

Context. Chemically peculiar (CP) stars with a measurable magnetic field comprise the group of mCP stars. The pulsating members define the subgroup of rapidly oscillating Ap (roAp) stars, of which α Cir is the brightest member. Hence, α Cir allows the application of challenging techniques, such as interferometry, very high temporal and spectral resolution photometry, and spectroscopy in a wide wavelength range, that have the potential to provide unique information about the structure and evolution of a star.

Aims. Based on new photometry from BRITE-Constellation, obtained with blue and red filters, and on photometry from WIRE, SMEI, and TESS we attempt to determine the surface spot structure of α Cir and investigate pulsation frequencies.

Methods. We used photometric surface imaging and frequency analyses and Bayesian techniques in order to quantitatively compare the probability of different models.

Results. BRITE-Constellation photometry obtained from 2014 to 2016 is put in the context of space photometry obtained by WIRE, SMEI, and TESS. This provides improvements in the determination of the rotation period and surface features (three spots detected and a fourth one indicated). The main pulsation frequencies indicate two consecutive radial modes and one intermediate dipolar mode. Advantages and problems of the applied Bayesian technique are discussed.