On the Period Doubling Behaviour of Three W Vir Stars
Emese Plachy1, G´abor B. Kov´acs1·2and Emese Forg´acs-Dajka2
1. Konkoly Observatory, MTA CSFK, Budapest, Hungary
2. E¨otv¨os Lor´and University, Department of Astronomy, Budapest, Hungary
We examined archive data of W Vir type stars to search and study period doubling behaviour. We discovered that W Vir, the eponym of the group, and SZ Mon both show interchanging events in the order of the deep and shallow minima during the past decades. We also demonstrate that ST Pup, known for its strong period change, also exhibited a period doubling episode.
1 Introduction
The alternation of the low- and high-amplitude cycles in the light curve of classi- cal pulsating stars, called period doubling (PD), is the manifestation of nonlinear interaction between near-resonant radial modes. It is a characteristic of RV Tau stars, but recently it was discovered in RR Lyrae, BL Her, and W Vir type stars (for details we refer to Plachy et al. (2017) and the references in there) and in a classical Cepheids as well (Moln´ar et al., 2017). The temporal variation of period doubling has not been studied in detail yet, however, interchanges in the order of low- and high-amplitude cycles were examined in RR Lyrae and RV Tau stars (Plachy et al., 2014). Theoretical calculations predict possible period ranges where PD can be ex- pected in BL Her and W Vir type stars (Smolec, 2016), but only a few observational examples have been reported so far. We present here some results of our systematic search for PD in archive data of W Vir type stars.
2 Results
We used the ASAS (Pojmanski, 1997) and the Harvard DASCH photometry (Grind- lay et al., 2009), the latter is available only for W Vir. The alternation of cycles can be visualized in phased light curves folded by twice the pulsation period. In Fig. 1 we plotted phased light curves for different time epochs to demonstrate the interchange in PD for the stars W Vir and SZ Mon. We also show that ST Pup displayed PD right before its period increased from 18.69 days to 19.13 days.
Acknowledgements. This project has been supported by the Lend¨ulet LP2014-17 Program of the HAS, and by the NKFIH K-113117, K-115709 and PD-121203 grants of the Hungarian National Research, Development and Innovation Office. EP was supported by the J´anos Bolyai Research Scholarship of the HAS. The DASCH project at Harvard is grateful for partial support from NSF grants AST-0407380, AST-0909073, and AST-1313370.
310?PTA Proceedings?June, 2018?vol. 6 pta.edu.pl/proc/v6p310
On the Period Doubling Behaviour of Three W Vir Stars
9 9.5 10 10.5 11 11.5 12 12.5
W Vir
(DASCH) HJD 2410000-2415000 (DASCH) HJD 2415000-2418000 (DASCH) HJD 2418000-2422000
9 9.5 10 10.5 11 11.5 12 12.5
W Vir
(DASCH) HJD 2422000-2435000 (DASCH) HJD 2445000-2448000 9
9.5 10 10.5 11 (ASAS-3) HJD 2445000-2455200
9 9.5 10 10.5 11
SZ Mon
(ASAS-3) HJD 2452000-2453500 (ASAS-3) HJD 2453500-2454150
0 0.2 0.4 0.6 0.8 1
(ASAS-3) HJD 2454150-2455200
9 9.5 10 10.5 11
0 0.2 0.4 0.6 0.8 1
ST Pup
Phase (ASAS-3) HJD 2451500-2452400
0 0.2 0.4 0.6 0.8 1
Phase (ASAS-3) HJD 2452400-2453600
W Vir: P=17.270773 d SZ Mon: P=16.337069 d ST Pup: P=18.693706 d
Fig. 1: Folded light curves of W Vir, SZ Mon and ST Pup in different epochs (V mag). Note that the different passbands of DASCH and ASAS-3 photometry were not transformed. The variation of the minima is clearly visible.
References
Grindlay, J., et al., in W. Osborn, L. Robbins (eds.) Preserving Astronomy’s Photographic Legacy: Current State and the Future of North American Astronomical Plates, Astro- nomical Society of the Pacific Conference Series, volume 410, 101 (2009)
Moln´ar, L., et al.,MNRAS 466, 4009 (2017),arXiv: 1612.06722
Plachy, E., et al., in J. A. Guzik, W. J. Chaplin, G. Handler, A. Pigulski (eds.) Precision Asteroseismology,IAU Symposium, volume 301, 473–474 (2014),arXiv: 1401.1429 Plachy, E., et al.,MNRAS 465, 173 (2017),arXiv: 1610.05488
Pojmanski, G.,Acta Astron.47, 467 (1997),arXiv: astro-ph/9712146 Smolec, R.,MNRAS 456, 3475 (2016),arXiv: 1512.01550
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