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Post Info TOPIC: RR Lyrae
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Title: The soundtrack of RR Lyrae in Omega Cen at high-frequency
Authors: A. Calamida (STScI), S. K. Randall (ESO), M. Monelli (IAC), G. Bono, R. Buonanno, G. Strampelli (Univ. Tor Vergata), M. Catelan (PUC), V. Van Grootel (Univ. de Liege), M. L. Alonso (PUC), P. B. Stetson (NRC-HIA), R. F. Stellingwerf (Stellingwerf Consulting)

We present preliminary Sloan u',g'-band light curves for a sample of known RR Lyrae variables in the Galactic globular cluster Omega Cen. Results are based on the partial reduction of multi-band time series photometric data collected during six consecutive nights with the visitor instrument ULTRACAM mounted on the New Technology Telescope (La Silla, ESO). This facility allowed us to simultaneously observe in three different bands (Sloan u',g',r') a field of view of about 6x6 arcminutes. The telescope and the good seeing conditions allowed us to sample the light curves every 15 seconds. We ended up with a data set of about 6,000 images per night per filter, for a total of more than 200,000 images of the selected field. This data set allowed us to detect different kind of variables, such as RR-Lyraes, SX Phoenicis, eclipsing binaries, semi-regulars. More importantly, we were able for the first time to sample at high-frequency cluster RR Lyraes in the u',g'-band and to show in detail the pulsation phases across the dip located along the rising branch of RR-Lyraes.

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Blobrana


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Title: Nonlinear asteroseismology of RR Lyrae
Authors: L. Molnár, Z. Kolláth, R. Szabó, K. Kolenberg, S. Bryson, F. Mullally, S. E. Thompson

The observations of the Kepler space telescope revealed that fundamental-mode RR Lyrae stars may show various radial overtones. The presence of multiple radial modes may allow us to conduct nonlinear asteroseismology: comparison of mode amplitudes and frequency shifts between observations and models. Here we report the detection of three radial modes in the star RR Lyr, the eponym of the class, using the Kepler short cadence data: besides the fundamental mode, both the first and the ninth overtones can be derived from the data set. RR Lyrae shows period doubling, but switches occasionally to a state where a pattern of six pulsation cycles repeats instead of two. We found hydrodynamic models that show the same three modes and the period-six state, allowing for comparison with the observations.

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