294 research outputs found
The unique dynamical system underlying RR Lyrae pulsations
Hydrodynamic models of RR Lyrae pulsation display a very rich behaviour.
Contrary to earlier expectations, high order resonances play a crucial role in
the nonlinear dynamics representing the interacting modes. Chaotic attractors
can be found at different time scales: both in the pulsation itself and in the
amplitude equations shaping the possible modulation of the oscillations.
Although there is no one-to-one connection between the nonlinear features found
in the numerical models and the observed behaviour, the richness of the found
phenomena suggests that the interaction of modes should be taken seriously in
the study of the still unsolved puzzle of Blazhko effect. One of the main
lessons of this complex system is that we should rethink the simple
interpretation of the observed effect of resonances.Comment: 4 pages, 2 figures, RRL2015 - High-Precision Studies of RR Lyrae
Stars, Eds: Szabados, Szab\'o and Kinemuchi, in pres
Nonlinear Properties of the Semiregular Variable Stars
We demonstrate how, with a purely empirical analysis of the irregular
lightcurve data, one can extract a great deal of information about the stellar
pulsation mechanism. An application to R Sct thus shows that the irregular
lightcurve is the result of the nonlinear interaction of two highly
nonadiabatic pulsation modes, namely a linearly unstable, low frequency mode,
and the second mode that, although linearly stable, gets entrained through a
2:1 resonance. In the parlance of nonlinear dynamics the pulsation is the
result of a 4 dimensional chaotic dynamics.Comment: 8 pages to appear in "Mass-Losing Pulsating Stars and Their
Circumstellar Matter", Eds. Y. Nakada & M.Honma, ASSL Ser. (in press). a
version with better quality figures is available from
http://www.phys.ufl.edu/~buchler
The double-mode RR Lyrae variable BS Com
We present the frequency analysis of the multicolour time series photometry
of the field RRd variable BS Comae. The large number of data points in each of
the BV(RI)_c bands and the ~0.01 magnitude accuracy of the individual
measurements allow us a high precision analysis of the properties of the
combination frequencies due to nonlinear coupling. Through the combination of
the frequency spectra in different colors we show that except for the
components corresponding to the linear combinations of the two pulsation modes,
there are no other components present above the millimagnitude amplitude level.Comment: 4 pages, 7 figures, accepted for publication in A
Nagymennyiségű változócsillagászati észlelések feldolgozása és analízise = Reduction and analysis of large-scale variable star data sets
A következő három fő témakört vizsgáltuk: (a) periodikus tranzit detektálás és extraszolaris bolygók vizsgálata a HATNet es a WHAT automata távcsövek észlelései alapján; (b) a MACHO adatbázis RR Lyrae csillagainak periódus analízise; (c) pulzáló változócsillagok elméleti és empirikus vizsgálata. A következő eredményeket kaptuk. Téma (a): kis apertúrájú, teljesen automatizált távcsövek alkalmasak néhány millimagnitúdó pontosságú észlelésekre és forró Jupiterek (HJ-k) detektálására; a BLS algoritmusunk hatásos eszköz periodikus tranzitok keresésében; az adatfeldolgozás miatt fellépő szisztematikák kiszűrésének hatékony eszköze a TFA algoritmusunk; a HD 189733 HJ rendszer valójában egy hármas rendszer, K fő- es M másod-komponensekkel, valamint a főkomponens körül keringő bolygóval. Téma (b): az LMC-ben található alapmódusú RR Lyrae csillagok 12%-a mutat Blashko jelenséget. Ez az érték szignifikánsan magasabb, mint az újabb analizisünk alapján az első felhangú csillagokra kapott gyakoriság, amely a rendelkezésre álló adatok felhasználásával 7.5%-nak adódott. Téma (c): nincs ellentmondás az RR Lyrae és a Cepheida változók alapján a Baade-Wesselink módszer segítségével számított távolságok között. Az LMC távolságára konzisztens értékeket kaptunk; több irreguláris változó fénygörbéjének analizálása alapján további megerősítést kaptunk ezen csillagok kaotikus pulzációjára. | We have investigated the following three major topics: (a) periodic transit detection and extrasolar planetary studies based on large-scale photometric databases of the HATNet and WHAT automated telescopes; (b) frequency analysis of RR Lyrae stars in the MACHO database; (c) theoretical and empirical stellar pulsation studies. We obtained the following results. Topic (a): small aperture fully automated telescopes are able to gather few millimag precision photometric data and detect transits caused by hot Jupiters; our BLS algorithm is very efficient in searching for periodic transits; the effects of systematics due to errors in the data acquisition can be successfully filtered by our TFA algorithm; the hot Jupiter system HD 189733 is a triple system with a K primary and M secondary and the planet orbiting the primary. Topic (b): the incidence rate of the Blazhko stars pulsating in the fundamental mode is 12% in the LMC. This is significantly higher than that of the first overtone Blazhko stars (which is 7.5%, according to our new analysis of all available data. Topic (c): there is no contradiction between the distances derived by Baade-Wesselink analyses of RR Lyrae and Cepheid variables and they both yield consistent distances for the LMC; by analyzing the archival data of several irregular variables, we got further support for the presence of chaotic pulsations in these stars
Automated Nonlinear Stellar Pulsation Calculations: Applications to RR Lyrae stars. The Slope of the Fundamental Blue Edge and the First RRd Model Survey
We describe a methodology that allows us to follow the pulsational behavior
of an RR Lyrae model consistently and automatically along its evolutionary
track throughout the whole instability strip. It is based on the powerful
amplitude equation formalism, and resorts to a judicious combination of
numerical hydrodynamical simulations, the analytical signal time-series
analysis, and amplitude equations. A large-scale survey of the nonlinear
pulsations in RR Lyr instability strip is then presented, and the mode
selection mechanism is delineated throughout the relevant regions of parameter
space. We obtain and examine two regions with hysteresis, where the pulsational
state depends on the direction of the evolutionary tracks, namely a region with
either fundamental (RRab) or first overtone (RRc) pulsations and a region with
either fundamental (RRab) or double-mode (RRd) pulsations. The regions where
stable double-mode (DM, or RRd) pulsations occur are very narrow and hard to
find in astrophysical parameter (L, M, T_eff, X, Z) space with hydrodynamic
simulations, but our systematic and efficient methodology allows us to
investigate them with unprecedented detail. It is shown that by simultaneously
considering the effects of mode selection and of horizontal branch evolution we
can naturally solve one of the extant puzzles involving the topologies of the
theoretical and observed instability strips, namely the slope of the
fundamental blue edge. The importance of the interplay between mode selection
and stellar evolutionary effects is also demonstrated for the properties of
double-mode RR Lyr. Finally, the Petersen diagram of double-mode RR Lyr models
is discussed for the first time.Comment: 13 pages, 6 figures, accepted to be published in A&
Sixteenth century stove tiles from the main square of Pápa, Western Hungary
Stove tile fragments came to light during the excavations at the Main Square (Fő tér) in the town of Pápa (HU, Veszprém County) from a closed find assemblage dated to the 16th century. Their decoration could be identified as biblical and profane scenes. This article is aimed examining the origins and connections of these good quality pieces and their historical context at the beginning of the age of Reformation
Multiple and changing cycles of active stars I. Methods of analysis and application to the solar cycles
Long-term observational data have information on the magnetic cycles of
active stars and that of the Sun. The changes in the activity of our central
star have basic effects on Earth, like variations in the global climate.
Therefore understanding the nature of these variations is extremely important.
The observed variations related to magnetic activity cannot be treated as
stationary periodic variations, therefore methods like Fourier transform or
different versions of periodogramms give only partial information on the nature
of the light variability. We demonstrate that time-frequency distributions
provide useful tools for analyzing the observations of active stars. With test
data we demonstrate that the observational noise has practically no effect on
the determination in the the long-term changes of time-series observations of
active stars. The rotational signal may modify the determined cycles, therefore
it is advisable to remove it from the data. Wavelets are less powerful in
recovering complex long-term changes than other distributions which are
discussed. Applying our technique to the sunspot data we find a complicated,
multi-scale evolution in the solar activity.Comment: Accepted to Astronomy and Astrophysic
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