56 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
NagymennyisĂ©gű változĂłcsillagászati Ă©szlelĂ©sek feldolgozása Ă©s analĂzise = Reduction and analysis of large-scale variable star data sets
A következĹ‘ három fĹ‘ tĂ©makört vizsgáltuk: (a) periodikus tranzit detektálás Ă©s extraszolaris bolygĂłk vizsgálata a HATNet es a WHAT automata távcsövek Ă©szlelĂ©sei alapján; (b) a MACHO adatbázis RR Lyrae csillagainak periĂłdus analĂzise; (c) pulzálĂł változĂłcsillagok elmĂ©leti Ă©s empirikus vizsgálata. A következĹ‘ eredmĂ©nyeket kaptuk. TĂ©ma (a): kis apertĂşrájĂş, teljesen automatizált távcsövek alkalmasak nĂ©hány millimagnitĂşdĂł pontosságĂş Ă©szlelĂ©sekre Ă©s forrĂł Jupiterek (HJ-k) detektálására; a BLS algoritmusunk hatásos eszköz periodikus tranzitok keresĂ©sĂ©ben; az adatfeldolgozás miatt fellĂ©pĹ‘ szisztematikák kiszűrĂ©sĂ©nek hatĂ©kony eszköze a TFA algoritmusunk; a HD 189733 HJ rendszer valĂłjában egy hármas rendszer, K fĹ‘- es M másod-komponensekkel, valamint a fĹ‘komponens körĂĽl keringĹ‘ bolygĂłval. TĂ©ma (b): az LMC-ben találhatĂł alapmĂłdusĂş RR Lyrae csillagok 12%-a mutat Blashko jelensĂ©get. Ez az Ă©rtĂ©k szignifikánsan magasabb, mint az Ăşjabb analizisĂĽnk alapján az elsĹ‘ felhangĂş csillagokra kapott gyakoriság, amely a rendelkezĂ©sre állĂł adatok felhasználásával 7.5%-nak adĂłdott. TĂ©ma (c): nincs ellentmondás az RR Lyrae Ă©s a Cepheida változĂłk alapján a Baade-Wesselink mĂłdszer segĂtsĂ©gĂ©vel számĂtott távolságok között. Az LMC távolságára konzisztens Ă©rtĂ©keket kaptunk; több irreguláris változĂł fĂ©nygörbĂ©jĂ©nek analizálása alapján további megerĹ‘sĂtĂ©st kaptunk ezen csillagok kaotikus pulzáciĂłjára. | 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
Night sky quality monitoring in existing and planned dark sky parks by digital cameras
A crucial part of the qualification of international dark sky places (IDSPs)
is the objective measurement of night time sky luminance or radiance. Modern
digital cameras provide an alternative way to perform all sky imaging either by
a fisheye lens or by a mosaic image taken by a wide angle lens. Here we present
a method for processing raw camera images to obtain calibrated measurements of
sky quality. The comparison of the night sky quality of different European
locations is also presented to demonstrate the use of our technique.Comment: in press: International Journal of Sustainable Lightin
On the feasibility of inversion methods based on models of urban sky glow
Multi-wavelength imaging luminance photometry of sky glow provides a huge amount of information on light pollution. However, the understanding of the measured data involves the combination of different processes and data of radiation transfer, atmospheric physics and atmospheric constitution. State-of-the-art numerical radiation transfer models provide the possibility to define an inverse problem to obtain information on the emission intensity distribution of a city and perhaps the physical properties of the atmosphere. We provide numerical tests on the solvability and feasibility of such procedures
Idő-frekvencia és nemlineáris rekonstrukciós módszerek alkalmazása = Application of time-frequency and nonlinear reconstruction methods
Olyan adatfeldolgozĂł mĂłdszereket dolgoztunk ki melyekkel a szabálytalan fĂ©nygörbĂ©k elemezhetĹ‘k. FĂ©lszabályos, RV Tauri Ă©s Mira csillagok fĂ©nyggörbĂ©it elemeztĂĽk. Az idĹ‘-frekvencia analĂzis segitsĂ©gĂ©vel kimutattuk, hogy a legtöbb esetben a domináns pillanatnyi frekvenciák nem stabilak, Ă©s a harmonikus csĂşcsok nem a domináns frekvenciával szinkronban változnak. Minez arra a következtetĂ©sre vezet, hogy ezek a csillagok a klasszikus Ă©rtelemben nem multiperiodikusak. HosszĂş fotoelektromos adatsor lĂ©tezik 5 csillagra. A fázistĂ©r globális rekonstrukciĂłja megerĹ‘sĂtette, hogy ezen csillagok fĂ©nygörbĂ©je jellegzetessĂ©gei alacsony dimenziĂłjĂş, kaotikus dinamika eredmĂ©nyekĂ©nt jöttek lĂ©tre. Ez a viselkedĂ©s kĂ©t rezonáns mĂłdus nemlineáris kölcsönhatásábĂłl Ă©s a pulzáciĂł erĹ‘s nemadiabatikusságábĂłl származik. BevezettĂĽnk egy hatásos mĂłdszert a csillagmodellezĂ©shez szĂĽksĂ©ges hidrokĂłdok fejlesztĂ©sĂ©re. A numerikus modellezĂ©s, az analitikus jelre Ă©pĂĽlĹ‘ idĹ‘-frekvencia analĂzis Ă©s az amplitĂşdĂł egyenletek mĂłdszereit kombinálva kidolgoztunk egy hatĂ©kony eljárást, amivel vizsgálhatĂł a modell csillagpulzáciĂł változása az instabilitási sávot átszelĹ‘ fejlĹ‘dĂ©si utak mentĂ©n. Ennek a rendszernek az elsĹ‘ alkalmazásakĂ©nt, rĂ©szleteiben elemeztĂĽk az RR Lyrae instabilitási sáv topolĂłgiáját Ă©s a mĂłdusszelekciĂł mechanizmusát. Eljárásunk lehetĹ‘sĂ©get ad arra, hogy a nagyon keskeny kĂ©tmĂłdusĂş tartományokat egyszerűen megtaláljuk Ă©s behatároljuk. | We developed and combined data processing tools to investigate irregular light variations. We analyzed the observed light-curves of semiregular, RV Tauri and Mira stars. With time-frequency analysis we demonstrated that in most cases the dominant instantaneous frequencies are not steady, and that the 'harmonic peak' does not vary synchronously with the dominant one. This has led to the conclusion that these stars are not multi-periodic in the usual sense of the word. Long term photoelectic data exist for 5 stars. The results of a global flow reconstruction technique give strong evidence that the light-curves of these stars are generated by a low dimensional chaotic pulsation dynamics. This behaviour arises from the nonlinear interaction of two resonant modes, and the high nonadiabaticity of the pulsations. We developed an efficient way for building hydrocodes for stellar modelling. Based on a mixture of numerical modeling, analytical signal time-series analysis, and amplitude equations, we intoduced a powerful methodology for studying the evolution of the pulsations of a given stellar model along its evolutionary track through the instability strip. As a first application of this system we analyzed in detail the modal topology and modal selection of the RR Lyr instability strip. Our methodology allows us to find and delineate the very narrow double mode regimes very effectively
On the Blazhko Effect in RR Lyrae Stars
The Blazhko effect is a long term, generally irregular modulation of the
light curves that occurs in a sizeable number of RR Lyrae stars. The physical
origin of the effect has been a puzzle ever since its discovery over a hundred
years ago. We build here upon the recent observational and theoretical work of
Szabo et al. on RRab stars who found with hydrodynamical simulations that the
fundamental pulsation mode can get destabilized by a 9:2 resonant interaction
with the 9th overtone. Alternating pulsation cycles arise, although these
remain periodic, i.e. not modulated as in the observations.
Here we use the amplitude equation formalism to study this nonlinear,
resonant interaction between the two modes. We show that not only does the
fundamental pulsation mode break up into a period two cycle through the
nonlinear, resonant interaction with the overtone, but that the amplitudes are
modulated, and that in a broad range of parameters the modulations are
irregular as in the observations. This irregular behavior is in fact chaotic
and arises from a strange attractor in the dynamics.Comment: 5 pages, 3 figure
Evaluating the summer night sky brightness at a research field site on Lake Stechlin in northeastern Germany
We report on luminance measurements of the summer night sky at a field site
on a freshwater lake in northeastern Germany (Lake Stechlin) to evaluate the
amount of artificial skyglow from nearby and distant towns in the context of a
planned study on light pollution. The site is located about 70 km north of
Berlin in a rural area possibly belonging to one of the darkest regions in
Germany. Continuous monitoring of the zenith sky luminance between June and
September 2015 was conducted utilizing a Sky Quality Meter. With this device,
typical values for clear nights in the range of 21.5-21.7
magarcsec were measured, which is on the order of the natural sky
brightness during starry nights. On overcast nights, values down to 22.84
magarcsec were obtained, which is about one third as bright as on
clear nights. The luminance measured on clear nights as well as the darkening
with the presence of clouds indicate that there is very little influence of
artificial skyglow on the zenith sky brightness at this location. Furthermore,
fish-eye lens sky imaging luminance photometry was performed with a digital
single-lens reflex camera on a clear night in the absence of moonlight. The
photographs unravel several distant towns as possible sources of light
pollution on the horizon. However, the low level of artificial skyglow makes
the field site at Lake Stechlin an excellent location to study the effects of
skyglow on a lake ecosystem in a controlled fashion.Comment: 20 pages, 8 figures, Journal of Quantitative Spectroscopy and
Radiative Transfer 201
Light Pollution Survey in Hungarian National Parks = Fényszennyezés felmérés a nemzeti parkokban
We have started a light pollution survey in the Hungarian national parks. We use a mobile laboratory consisting of digital cameras and robotic panorama heads to gather high-resolution panorama imaging radiometry. The same type of cameras with fish-eye lenses are used in fix monitoring stations. Parallel to the imaging radiometry, we measure the spectral distribution of the sky radiation. The spectroradiometry provides additional calibration check on the measurements and further information on the sources of light. The mobile laboratory provides an excellent spatial resolution at a given national park while the monitoring all-sky camera stations add the possibility to detect temporal changes in night sky quality. We developed new SI traceable metrics for the measurement of night sky quality. The RGB colour channels of the camera provide an optimal way to obtain multispectral radiance information. The selected metric is the band-averaged spectral radiance. Besides, we use a colour enhancement technique to find traces of different sources of night sky radiance. In the near future, we expect a large amount of high-quality data from the Hungarian national parks, which provide an outstanding possibility in light pollution related and atmospheric research. In the paper, we present the first results of the sky quality survey. ----- FÉNYSZENNYEZÉS FELMÉRÉS A NEMZETI PARKOKBAN FĂ©nyszennyezĂ©s-felmĂ©rĂ©st kezdtĂĽnk a magyarországi nemzeti parkokban. A vizsgálathoz digitális kamerákbĂłl Ă©s automata panorámafejekbĹ‘l állĂł hordozhatĂł laboratĂłriumot használunk, amellyel lehetĹ‘sĂ©g van a nagy felbontásĂş panorámalekĂ©pezĹ‘ radiometria vĂ©gzĂ©sĂ©re. Ugyanilyen tĂpusĂş kamerákat Ă©s halszemoptikákat állandĂł telepĂtĂ©sű mĂ©rőállomásokon is használunk. A lekĂ©pezĹ‘ radiometriával párhuzamosan az Ă©gbolt fĂ©nylĂ©sĂ©nek spektrális eloszlását is mĂ©rjĂĽk. A spektroradiometria járulĂ©kos kalibráciĂłs informáciĂłt szolgáltat a mĂ©rĂ©sekhez, ezen kĂvĂĽl segĂt a lehetsĂ©ges források megkĂĽlönböztetĂ©sĂ©ben is. A hordozhatĂł laboratĂłrium megfelelĹ‘ tĂ©rbeli felbontást szolgáltat a nemzeti parkokban, mĂg az állandĂł teljesĂ©gbolt-mĂ©rőállomások biztosĂtják azt az idĹ‘beli felbontást, amellyel az Ă©gboltminĹ‘sĂ©g változásait Ă©rzĂ©kelhetjĂĽk. Kidolgoztunk egy SI-egysĂ©gekre visszavezethetĹ‘ metrikát az Ă©gboltminĹ‘sĂ©g mĂ©rĂ©sĂ©hez, a kiválasztott metrika a sávátlagolt spektrális sugársűrűsĂ©g. Ezen kĂvĂĽl egy szĂnkiemelĂ©ses eljárást is alkalmazunk, amellyel az Ă©gbolt fĂ©nylĂ©sĂ©nek kĂĽlönbözĹ‘ forrásainak a jeleit detektálhatjuk. A közeljövĹ‘ben a magyarországi nemzeti parkokbĂłl nagy mennyisĂ©gű, jĂł minĹ‘sĂ©gű adatra számĂthatunk, ami kiválĂł lehetĹ‘sĂ©get ad a fĂ©nyszennyezĂ©ssel kapcsolatos Ă©s lĂ©gkörfizikai jellegű kutatá- sokhoz. A jelen cikkben bemutatjuk az Ă©gboltminĹ‘sĂ©g-felmĂ©rĂ©s elsĹ‘ eredmĂ©nyeit
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