288 research outputs found
Low-dimensional chaos in RR Lyrae models
The recent precise photometric observations and successes of the modelling
efforts transformed our picture of the pulsation of RR Lyrae stars. The
discovery of additional frequencies and the period doubling phenomenon revealed
that a significant interaction may occur between pulsational modes. The signs
of irregularities were detected both in observed light curves and hydrodynamic
calculations.
In this paper we present the analysis of four peculiar hydrodynamic model
solutions. All four solutions were found to be chaotic. The fractal (Lyapunov)
dimensions of their attractors were calculated to be ~2.2. We also investigated
possible resonances between the fundamental mode and the first overtone in the
dynamical neighbourhood of these models. The most important is the 6:8
resonance that was also detected in the Kepler observations of RR Lyrae itself.
These results reveal that the investigation of chaotic models is important in
discovering and understanding resonances in RR Lyrae stars.Comment: 7 pages, 8 figures, accepted for publication in MNRA
Constraining RRc candidates using SDSS colours
The light variations of first-overtone RR Lyrae stars and contact eclipsing
binaries can be difficult to distinguish. The Catalina Periodic Variable Star
catalog contains several misclassified objects, despite the classification
efforts by Drake et al. (2014). They used metallicity and surface gravity
derived from spectroscopic data (from the SDSS database) to rule out binaries.
Our aim is to further constrain the catalog using SDSS colours to estimate
physical parameters for stars that did not have spectroscopic data.Comment: 2 pages, 1 figure, proceedings of the RRL2015 - High-Precision
Studies of RR Lyrae Stars conference, to appear in the Communications from
the Konkoly Observator
A modulated RRd star observed by K2
We report the analysis of the double-mode RR Lyrae star EPIC 205209951, the
first modulated RRd star observed from space. The amplitude and phase
modulation are present in both modes.Comment: 2 pages, 3 figures, proceedings of the Joint
TASC2-KASC9-SPACEINN-HELAS8 Conference "Seismology of the Sun and the Distant
Stars 2016", to be published in EPJ Wo
Target selection of classical pulsating variables for space-based photometry
In a few years the Kepler and TESS missions will provide ultra-precise
photometry for thousands of RR Lyrae and hundreds of Cepheid stars. In the
extended Kepler mission all targets are proposed in the Guest Observer (GO)
Program, while the TESS space telescope will work with full frame images and a
~15-16th mag brightness limit with the possibility of short cadence
measurements for a limited number of pre-selected objects. This paper
highlights some details of the enormous and important work of the target
selection process made by the members of Working Group 7 (WG#7) of the Kepler
and TESS Asteroseismic Science Consortium.Comment: 4 pages, 1 figure, proceedings of the RRL2015 - High-Precision
Studies of RR Lyrae Stars conference, to appear in the Communications from
the Konkoly Observator
Metal-rich or misclassified? The case of four RR Lyrae stars
We analysed the light curve of four, apparently extremely metal-rich
fundamental-mode RR Lyrae stars. We identified two stars, MT Tel and ASAS
J091803-3022.6 as RRc (first-overtone) pulsators that were misclassified as
RRab ones in the ASAS survey. In the case of the other two stars, V397 Gem and
ASAS J075127-4136.3, we could not decide conclusively, as they are outliers in
the period-Fourier-coefficient space from the loci of both classes, but their
photometric metallicities also favour the RRc classification.Comment: 5 pages, 2 figures, published in IBVS:
http://ibvs.konkoly.hu/cgi-bin/IBVS?617
Amplitude Modulation in the ZZ Ceti Star GD 244
Previous studies of GD 244 revealed seven pulsation frequencies (two doublets
and three single periods) in the light variations of the star. The data
obtained at McDonald Observatory between 2003 and 2006, and our additional
measurements in 2006 and 2007 at Konkoly Observatory, allow the investigation
of the long-term pulsational behaviour of GD 244. We found that the 307.1 s
period component of one of the doublets show long-term, periodic amplitude
modulation with a time scale of ~740 days. Possible explanations are that
nonlinear resonant mode coupling is operating among the rotationally split
frequency components, or two modes, unresolved in the yearly data are excited
at ~307.1 s. This is the first time that such long-term periodic amplitude
modulation is published on a ZZ Ceti star.Comment: 4 pages, 2 figures, appeared in ASP Conference Series vol. 493, 2015
(eds.: P. Dufour, P. Bergeron, G. Fontaine, 19th European Workshop on White
Dwarfs, Montreal, Canada
- …