Magnetic fields and star formation in low-mass Magellanic-typeand peculiar galaxies

Aims. We investigate how magnetic properties of Magellanic-type and perturbed objects are related to star-forming activity, galactic type, and mass. Methods. We present radio and magnetic properties of five Magellanic-type and two peculiar low-mass galaxies observed at 4.85 and/or 8.35 GHz with the Effelsberg 100 m telescope. The sample is extended to 17 objects by including five Magellanic-type galaxies and five dwarf ones. Results. The distribution of the observed radio emission of low-mass galaxies at 4.85/8.35 GHz is closely connected with the galactic optical discs, which are independent for unperturbed galaxies and those which show signs of tidal interactions. The strengths of total magnetic field are within 5−9 μG, while the ordered fields reach 1−2 μG, and both these values are larger than in typical dwarf galaxies and lower than in spirals. The magnetic field strengths in the extended sample of 17 low-mass galaxies are well correlated with the surface density of star formation rate (correlation coefficient of 0.87) and manifest a power-law relation with an exponent of 0.25 ± 0.02 extending a similar relation found for dwarf galaxies. We claim that the production of magnetic energy per supernova event is very similar for all the various galaxies. It constitutes about 3% (1049 erg) of the individual supernovae energy release. We show that the total magnetic field energy in galaxies is almost linearly related to the galactic gas mass, which indicates equipartition of the magnetic energy and the turbulent kinetic energy of the interstellar medium. The Magellanic-type galaxies fit very well with the radio-infrared relation constructed for surface brightness of galaxies of various types, including bright spirals and interacting objects (with a slope of 0.96 ± 0.03 and correlation coefficient of 0.95). We found that the typical far-infrared relation based on luminosity of galaxies is tighter and steeper but more likely to inherit a partial correlation from a tendency that larger objects are also more luminous. Conclusions. The estimated values of thermal fractions, radio spectral indices, and magnetic field strengths of the Magellanic-type galaxies are between the values determined for grand-design spirals and dwarf galaxies. The confirmed magnetic field-star formation and radio-infrared relations for low-mass galaxies point to similar physical processes that must be at work in all galaxies. More massive, larger galaxies have usually stronger magnetic fields and larger global star formation rates, but we show that their values of magnetic energy release per supernova explosion are still similar to those of dwarf galaxies

Period changes of the sample of eclipsing binaries with active chromospheres

In this work we present results derived from analysis of the O-C behaviour of ten eclipsing binary systems: AR Lac, CG Cyg, HP Aur, MM Her, RS CVn, RT And, SV Cam, V471 Tau, WW Dra and CF Tuc. It was proved on the basis of moments of minima compiled from the literature and new ones determined from recent observations, that these binaries show long term (19-91 years) modulations of their orbital periods, clearly visible in their O-C diagrams. Two possible explanations for this effect are considered: (1) the light-travel time effect due to the presence of a third body orbiting the eclipsing systems; (2) the Applegate mechanism predicting period modulation by changes in the distribution of angular momentum as a star goes through its activity cycles. It was found that in the case of four systems the existence of a third star, orbiting the binary, is a more plausible explanation of observations

Determination of physical parameters of the eclipsing binary V729 Cyg

We report new BVRI photometric observations of an eclipsing, massive binary V729 Cyg taken between 2008 and 2011. We performed light curve modeling of the new data and those available in the literature using the Wilson-Devinney code. The best fit was obtained for a contact configuration, similarly to results derived previously by other investigators. However, a huge temperature difference of about 10 000K - 12 000K was derived, inconsistent with theoretical calculations. Ruling out a possibility of V729 Cyg being a semi-detached system harbouring an accretion disk, we determined physical parameters of components

Optical monitoring of FRII-type radio quasars

We present preliminary results of optical monitoring of sample of FRII-type radio quasars. The optical observations were made with three telescopes, among them one robotic, spanning a time interval longer than two years. Variability in the range of a fraction of a magnitude was observed for all eight targets. We applied the structure function to analyse the brightness changes. The slope of the structure function is only consistent with the disk instability model for two sources; the other sources show values between of the disk instability and starburst models. Finally we argue that such monitoring would be most suitable as a long-term, complementary program for robotic telescopes

Analysis of the O-C changes in the sample of chromospherically active binaries

W pracy prezentuję wyniki analizy zmian O-C dziesięciu układów zmiennych zaćmieniowych: AR Lac, CG Cyg, HP Aur, MM Her, RS CVn, RT And, SV Cam, V471 Tau, WW Dra and CF Tuc. Na podstawie archiwalnych momentów minimów zebranych z literatury oraz wyznaczonych z nowych obserwacji okazało się, że układy te wykazują długookresową (19 do 91 lat) fluktuację w ich okresach orbitalnych. Do analizy tej zmienności posłużyły diagramy O-C.Efekt ten można wytłumaczyć na dwa sposoby: pierwszy z nich to obecność trzeciego ciała orbitującego wokół układu podwójnego. Druga możliwość to mechanizm Applegate, według którego modulacje okresu zmienności powodowane są zmianami w rozkładzie momentu pędu w gwieździe wraz z cyklem aktywności chromosferycznej.W sześciu przypadkach istnienie trzeciego ciała okrążającego układ podwójny, okazało się być lepszym wytłumaczeniem obserwacji.In the thesis I present results of analysis of the O-C behaviour of ten eclipsing binary systems: AR Lac, CG Cyg, HP Aur, MM Her, RS CVn, RT And, SV Cam, V471 Tau, WW Dra and CF Tuc. On the basis of times of minima compiled from the literature and newly determined from recent observations,it turned out that these binaries show a long term (19-91 years) modulation of their orbital periods, clearly visible in their O-C diagrams. This effect is explained in two ways: the first possibility is a light time travel effect caused by a presence of a third body orbiting the eclipsing system. The other possibility considered is the period change due to the Applegate machanism. Within this hypothesis, the period modulation isexplained by changes in distribution of angular momentum as a star goes throughits activity cycle.It was found that in case of six systems the existence of a third star, orbiting the binary, is the most plausible explanation of observations

Investigation of O-C changes in a sample of eclipsing binary systems

In this work we present results of analysis of the O-C behaviour for 79 eclipsing binary systems selected from the Kreiner's database. These systems show long time scale, possibly cyclic, modulations of their orbital periods on the timescale of a few years to several decades. We consider two possibilities to explain the observed O-C changes: (1) the Light Time Travel Effect due to the presence of a third body in the system, and (2) the Applegate effect, in which orbital period modulation is caused by cyclic changes of gravitational quadrupole momentum when a star goes through its magnetic activity cycles. Within the former explanation, the orbital parameters of a hypothetical third body are fitted using the Monte Carlo method and the lower mass limit for the third companion is calculated. As a result, we derived that in 21 cases the mass of the third body exceeds the Neutron Star mass limit

Observational verification of the limb-darkening law based on Kepler data

We present preliminary results obtained from modeling of light curves of a sample of contact binaries observed by the Kepler spacecraft. Our study was aimed at verifying which of the three most commonly used limb-darkening formulations fits the high quality Kepler data the best. We limited our work to twelve binary systems showing flat-bottomed minima, and we found that for ten of them the square root limbdarkening law led to the best fits

Massive companions of binary systems

AbstractWe examined the O-C diagrams of eclipsing binary systems and selected these exhibiting cyclic shape, either sinusoidal or quasi sinusoidal. Assuming these variations being due to the Light Time Travel effect (LTE), we estimated the parameters of companions with the Monte Carlo method. As a result, we identified nearly two dozen of eclipsing systems that might have companions with a minimum mass larger than that of a neutron star. Their masses fall into the range between 1.7 and 34 solar masses. This sample of triples with high mass companions can be confirmed with the help of observations gathered by Gaia: parallaxes and astrometric measurements.</jats:p