The roAp star α Circinus as seen by BRITE-Constellation

Author(s): Werner Wolfgang Weiss, Hans-Erich Fröhlich, Andrzej Pigulski, A. Popowicz, Daniel Huber, Rainer Kuschnig, Theresa Rank-Lüftinger, Joao Alves, Manuel Güdel, Anthony F J Moffat, Jaymie M. Matthews, Hideyuki Saio, Alex Schwarzenberg-Czerny, C. Grant, O. F. Koudelka, Slavek M. Rucinski, Gregg A. Wade, Gerald Handler, Stefan Mochnacki, P. Orleanski, B. Pablo, Alexey Pamyatnykh, Tahina Ramiaramanantsoa, Jason F. Rowe, G. N. Whittaker, T. Zawistowski, E. Zoclonska, Konstanze Zwintz
Abstract: We report on an analysis of high-precision, multi-colour photometric observations of the rapidly-oscillating Ap (roAp) star α Cir. These observations were obtained with the BRITE-Constellation, which is a coordinated mission of five nanosatellites that collects continuous millimagnitude-precision photometry of dozens of bright stars for up to 180 days at a time in two colours (≈Johnson B and R). BRITE stands for BRight Target Explorer. The object α Cir is the brightest roAp star and an ideal target for such investigations, facilitating the determination of oscillation frequencies with high resolution. This star is bright enough for complementary interferometry and time-resolved spectroscopy. Four BRITE satellites observed α Cir for146 d or 33 rotational cycles. Phasing the photometry according to the 4.4790 d rotational period reveals qualitatively different light variations in the two photometric bands. The phased red-band photometry is in good agreement with previously-published WIRE data, showing a light curve symmetric about phase 0.5 with a strong contribution from the first harmonic. The phased blue-lband data, in contrast, show an essentially sinusoidal variation. We model both light curves with Bayesian Photometric Imaging, which suggests the presence of two large-scale, photometrically bright (relative to the surrounding photosphere) spots. We also examine the high-frequency pulsation spectrum as encoded in the BRITE photometry. Our analysis establishes the stability of the main pulsation frequency over the last ≈20 yr, confirms the presence of frequency f₇, which was not detected (or the mode not excited) prior to 2006, and excludes quadrupolar modes for the main pulsation frequency.
Based on data collected by the BRITE-Constellation satellite mission, built, launched and operated thanks to support from the Austrian Aeronautics and Space Agency, the University of Vienna, the Canadian Space Agency (CSA), the Foundation for Polish Science & Technology (FNiTP MNiSW), and National Centre for Science (NCN).The light curves and the reduced data for α Circinus are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via cdsarc.u-strasbg.fr/viz-bin/qcat Member of the BRITE Executive Science Team (BEST).Member of the Photometry Tiger Team (PHOTT).
Organisation(s): Department of Astrophysics
External organisation(s): University of Wrocław, Silesian University of Technology, The University of Sydney, Leibniz-Institut für Astrophysik Potsdam, SETI Institute, Aarhus University, Polish Academy of Sciences (PAS), Technische Universität Graz, University of Montreal, NASA Ames Research Center, Leopold-Franzens-Universität Innsbruck, University of British Columbia (UBC), Tohoku University, University of Toronto, Royal Military College of Canada
Journal: Astronomy & Astrophysics
Volume: 588
No. of pages: 10
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/201526997
Publication date: 04-2016
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/50e09b22-8e17-4ab6-b234-59856d4e8576