V473 Lyr, a modulated, period-doubled Cepheid, and U TrA, a double-mode Cepheid, observed by MOST
- Author(s)
- L. Molnár, A. Derekas, R. Szabo, Rainer Kuschnig, Werner Wolfgang Weiss, Jaymie M. Matthews, C. Cameron, Anthony F J Moffat, Noel D. Richardson, B. Csák, A. Dózsa, P. Reed, L. Szabados, Bernard Heathcote, Terry Bohlsen, Paulo Cacella, Paul Luckas, Á. Sódor, M. Skarka, G. M. Szabo, E. Plachy, József Kovacs, N. R. Evans, Katrien Kolenberg, K. A. Collins, J. Pepper, Keivan G. Stassun, J. E. Rodriguez, R. J. Siverd, A. Henden, L. Mankiewicz, A. F. Zarnecki, A. Cwiek, M. Sokolowski, A. Pál, David B. Guenther, J. Rowe, Slavek M. Rucinski, Dimitar Sasselov
- Abstract
Space-based photometric measurements first revealed low-amplitude irregularities in the pulsations of Cepheid stars, but their origins and how commonly they occur remain uncertain. To investigate this phenomenon, we present MOST space telescope photometry of two Cepheids. V473 Lyrae is a second-overtone, strongly modulated Cepheid, while U Trianguli Australis is a Cepheid pulsating simultaneously in the fundamental mode and first overtone. The nearly continuous, high-precision photometry reveals alternations in the amplitudes of cycles in V473 Lyr, the first case of period doubling detected in a classical Cepheid. In U TrA, we tentatively identify one peak as the fX or 0.61-type mode often seen in conjunction with the first radial overtone in Cepheids, but given the short length of the data, we cannot rule out that it is a combination peak instead. Ground-based photometry and spectroscopy were obtained to follow two modulation cycles in V473 Lyr and to better specify its physical parameters. The simultaneous data yield the phase lag parameter (the phase difference between maxima in luminosity and radial velocity) of a second-overtone Cepheid for the first time. We find no evidence for a period change in U TrA or an energy exchange between the fundamental mode and the first overtone during the last 50 yr, contrary to earlier indications. Period doubling in V473 Lyr provides a strong argument that mode interactions do occur in some Cepheids and we may hypothesize that it could be behind the amplitude modulation, as recently proposed for Blazhko RR Lyrae stars.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- Kutztown University of Pennsylvania, University of Louisville, Vanderbilt University, Las Cumbres Observatory Global Telescope, American Association of Variable Star Observers (AAVSO), Polish Academy of Sciences (PAS), National Centre for Nuclear Research (NCBJ), Curtin University, Canadian Coast Guard College (CCGC), University of Toledo, Barfold Observatory, Southern Astro Spectroscopy Email Ring, University of Western Australia, University of Antwerp, Katholieke Universiteit Leuven, Lehigh University, University of Warsaw, Hungarian Academy of Sciences, Eötvös Loránd University Budapest, University of British Columbia (UBC), Cape Breton University, University of Montreal, Harvard-Smithsonian Center for Astrophysics, Fisk University, Saint Mary's University, University of Toronto
- Journal
- Monthly Notices of the Royal Astronomical Society
- Volume
- 466
- Pages
- 4009-4020
- No. of pages
- 12
- ISSN
- 0035-8711
- DOI
- https://doi.org/10.1093/mnras/stw3345
- Publication date
- 05-2017
- 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/3446b055-b033-4a33-9e3f-6e17a33602c8