Idő-frekvencia és nemlineáris rekonstrukciós módszerek alkalmazása = Application of time-frequency and nonlinear reconstruction methods

Olyan adatfeldolgozó módszereket dolgoztunk ki melyekkel a szabálytalan fénygörbék elemezhetők. Félszabályos, RV Tauri és Mira csillagok fényggörbéit elemeztük. Az idő-frekvencia analízis segitségével kimutattuk, hogy a legtöbb esetben a domináns pillanatnyi frekvenciák nem stabilak, és a harmonikus csúcsok nem a domináns frekvenciával szinkronban változnak. Minez arra a következtetésre vezet, hogy ezek a csillagok a klasszikus értelemben nem multiperiodikusak. Hosszú fotoelektromos adatsor létezik 5 csillagra. A fázistér globális rekonstrukciója megerősítette, hogy ezen csillagok fénygörbéje jellegzetességei alacsony dimenziójú, kaotikus dinamika eredményeként jöttek létre. Ez a viselkedés két rezonáns módus nemlineáris kölcsönhatásából és a pulzáció erős nemadiabatikusságából származik. Bevezettünk egy hatásos módszert a csillagmodellezéshez szükséges hidrokódok fejlesztésére. A numerikus modellezés, az analitikus jelre épülő idő-frekvencia analízis és az amplitúdó egyenletek módszereit kombinálva kidolgoztunk egy hatékony eljárást, amivel vizsgálható a modell csillagpulzáció változása az instabilitási sávot átszelő fejlődési utak mentén. Ennek a rendszernek az első alkalmazásaként, részleteiben elemeztük az RR Lyrae instabilitási sáv topológiáját és a módusszelekció mechanizmusát. Eljárásunk lehetőséget ad arra, hogy a nagyon keskeny kétmódusú tartományokat egyszerűen megtaláljuk és 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

Pulsating B-type stars in the young open cluster h Persei (NGC 869)

We announce the discovery of six Beta Cephei stars and many other variable stars in the young open cluster h Persei (NGC 869). The cluster seems to be very rich in variable B-type stars, similarly to its twin, Chi Persei (NGC 884).Comment: 5 pages, 5 figures, Proc. HELAS-II conference, Goettingen, 20-24 August 200

Stellar rotational periods in the planet hosting open cluster Praesepe

By using the dense coverage of the extrasolar planet survey project HATNet, we Fourier analyze 381 high-probability members of the nearby open cluster Praesepe (Beehive/M44/NGC 2632). In addition to the detection of 10 variables (of \delta Scuti and other types), we identify 180 rotational variables (including the two known planet hosts). This sample increases the number of known rotational variables in this cluster for spectral classes earlier than M by more than a factor of three. These stars closely follow a color/magnitude -- period relation from early F to late K stars. We approximate this relation by polynomials for an easier reference to the rotational characteristics in different colors. The total (peak-to-peak) amplitudes of the large majority (94%) of these variables span the range of 0.005 to 0.04 mag. The periods cover a range from 2.5 to 15 days. These data strongly confirm that Praesepe and the Hyades have the same gyrochronological ages. Regarding the two planet hosts, Pr0211 (the one with the shorter orbital period) has a rotational period that is ~2 days shorter than the one expected from the main rotational pattern in this cluster. This, together with other examples discussed in the paper, may hint that star-planet interaction via tidal dissipation can be significant in some cases in the rotational evolution of stars hosting Hot Jupiters.Comment: 17 pages, 13 figures, 5 tables; accepted for publication in MNRA

The Mass-Radius Relationship for Very Low Mass Stars: Four New Discoveries from the HATSouth Survey

We report the discovery of four transiting F-M binary systems with companions between 0.1-0.2 Msun in mass by the HATSouth survey. These systems have been characterised via a global analysis of the HATSouth discovery data, combined with high-resolution radial velocities and accurate transit photometry observations. We determined the masses and radii of the component stars using a combination of two methods: isochrone fitting of spectroscopic primary star parameters, and equating spectroscopic primary star rotation velocity with spin-orbit synchronisation. These new very low mass companions are HATS550-016B (0.110 -0.006/+0.005 Msun, 0.147 -0.004/+0.003 Rsun), HATS551-019B (0.17 -0.01/+0.01 Msun, 0.18 -0.01/+0.01 Rsun), HATS551-021B (0.132 -0.005/+0.014 Msun, 0.154 -0.008/+0.006 Rsun), HATS553-001B (0.20 -0.02/+0.01 Msun, 0.22 -0.01/+0.01 Rsun). We examine our sample in the context of the radius anomaly for fully-convective low mass stars. Combining our sample with the 13 other well-studied very low mass stars, we find a tentative 5% systematic deviation between the measured radii and theoretical isochrone models.Comment: 17 pages, 8 figures, accepted for publication in MNRA

HAT-P-55b: A Hot Jupiter Transiting a Sun-like Star

We report the discovery of a new transiting extrasolar planet, HAT-P-55b. The planet orbits a V = 13.207 +/- 0.039 sun-like star with a mass of 1.013 +/- 0.037 solar masses, a radius of 1.011 +/- 0.036 solar radii and a metallicity of -0.03 +/- 0.08. The planet itself is a typical hot Jupiter with a period of 3.5852467 +/- 0.0000064 days, a mass of 0.582 +/- 0.056 Jupiter masses and a radius of 1.182 +/- 0.055 Jupiter radii. This discovery adds to the increasing sample of transiting planets with measured bulk densities, which is needed to put constraints on models of planetary structure and formation theories.Comment: 7 pages, 4 figures, accepted for publication in PAS

HAT-P-56b: An inflated massive Hot Jupiter transiting a bright F star followed up with K2 Campaign 0 observations

We report the discovery of HAT-P-56b by the HATNet survey, an inflated hot Jupiter transiting a bright F type star in Field 0 of NASA's K2 mission. We combine ground-based discovery and follow-up light curves with high precision photometry from K2, as well as ground-based radial velocities from TRES on the FLWO 1.5m telescope to determine the physical properties of this system. HAT-P-56b has a mass of $2.18 M_J$, radius of $1.47 R_J$, and transits its host star on a near-grazing orbit with a period of 2.7908 d. The radius of HAT-P-56b is among the largest known for a planet with $M_p > 2 M_J$. The host star has a V-band magnitude of 10.9, mass of 1.30 $M_\odot$, and radius of 1.43 $R_\odot$. The periodogram of the K2 light curve suggests the star is a $\gamma$ Dor variable. HAT-P-56b is an example of a ground-based discovery of a transiting planet, where space-based observations greatly improve the confidence in the confirmation of its planetary nature, and also improve the accuracy of the planetary parameters.Comment: 13 pages, 11 figures, accepted by A

HATS-3b: An inflated hot Jupiter transiting an F-type star

We report the discovery by the HATSouth survey of HATS-3b, a transiting extrasolar planet orbiting a V=12.4 F-dwarf star. HATS-3b has a period of P = 3.5479d, mass of Mp = 1.07MJ, and radius of Rp = 1.38RJ. Given the radius of the planet, the brightness of the host star, and the stellar rotational velocity (vsini = 9.0km/s), this system will make an interesting target for future observations to measure the Rossiter-McLaughlin effect and determine its spin-orbit alignment. We detail the low/medium-resolution reconnaissance spectroscopy that we are now using to deal with large numbers of transiting planet candidates produced by the HATSouth survey. We show that this important step in discovering planets produces logg and Teff parameters at a precision suitable for efficient candidate vetting, as well as efficiently identifying stellar mass eclipsing binaries with radial velocity semi-amplitudes as low as 1 km/s.Comment: 11 pages, 10 figures, submitted to A