The Statistical Analyses of the White-Light Flares: Two Main Results About Flare Behaviours

We present two main results, based on the models and the statistical analyses of 1672 U-band flares. We also discuss the behaviours of the white-light flares. In addition, the parameters of the flares detected from two years of observations on CR Dra are presented. By comparing with the flare parameters obtained from other UV Ceti type stars, we examine the behaviour of optical flare processes along the spectral types. Moreover, we aimed, using large white-light flare data,to analyse the flare time-scales in respect to some results obtained from the X-ray observations. Using the SPSS V17.0 and the GraphPad Prism V5.02 software, the flares detected from CR Dra were modelled with the OPEA function and analysed with t-Test method to compare similar flare events in other stars. In addition, using some regression calculations in order to derive the best histograms, the time-scales of the white-light flares were analysed. Firstly, CR Dra flares have revealed that the white-light flares behave in a similar way as their counterparts observed in X-rays. As seen in X-ray observations, the electron density seems to be a dominant parameter in white-light flare process, too. Secondly, the distributions of the flare time-scales demonstrate that the number of observed flares gets a maximum value in some particular ratios, which are 0.5 or its multiples, and especially positive integers. The thermal processes might be dominant for these white-light flares, while non-thermal processes might be dominant in the others. To reach better results for the behaviour of the white-light flare process along the spectral types, much more stars in a wide spectral range, from the spectral type dK5e to dM6e, must be observed in the white-light flare patrols.Comment: 17 pages, 7 figures, 5 tabl

A Gamma Doradus Candidate In Eclipsing Binary BD And?

The BVR photometric light curves of the eclipsing binary BD And were obtained in 2008 and 2009. We estimated the mass ratio of the system as 0.97 and the photometric solutions were derived. The results show that BD And is a detached binary system, whose components have a little temperature difference of about 40 K. By analyzing photometric available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.011 days and a period of 9.6 years. The results indicate that the periodic oscillation could be caused by a third component physically attached to the eclipsing binary. After removing the light variations due to the eclipses and proximity effects, the light-curve distortions are further explained by the pulsation of the primary component with a dominant period of 1 day. In accordance with the position of the primary component on the Hertzsprung-Russell diagram and its pulsation period, the primary component of BD And could be an excellent gamma Doradus candidate. It is rarely phenomenon that a component of the eclipsing binary system is a gamma Doradus variable.Comment: 34 pages, 8 figures. arXiv admin note: text overlap with arXiv:1112.1916 by other authors without attributio

Rotation Modulations and Distributions of the Flare Occurrence Rates on the Surface of Five UV Ceti Type Stars

In this study, we considered stellar spots, stellar flares, and also the relation between these two magnetic proccesses that take place on UV Cet stars. In addition, the hypothesis about slow flares described by Gurzadyan (1986 Ap&SS, 125, 127) was investigated. All of these discussions were based on the results of three years of observations of UV Cet-type stars: AD Leo, EV Lac, V1005 Ori, EQ Peg, and V1054 Oph. First of all, the results show that stellar spot activity occurs on the stellar surface of EV Lac, V1005 Ori, and EQ Peg, while AD Leo does not show any short-term variability and V1054 Oph does not exhibit any variability. We report on new ephemerides for EV Lac, V1005 Ori, and EQ Peg, obtained from time-series analyses. The phases, computed at intervals of 0.10 phase length, where the mean flare occurence rates to obtain maximum amplitude; also, the phases of rotational modulation were compared in order to investigate whether there is any longitudinal relation between stellar flares and spots. Although the results show that flare events are related with spotted areas on stellar surfaces during some of the observing seasons, we did not find any clear correlation among them. Finally, it was tested whether slow flares are fast flares occurring on the opposite side of the stars according to the direction of the observers, as mentioned in a hypothesis developed by <A >Gurzadyan (1986). The flare occurence rates reveal that both slow and fast flares can occur in any rotational phases. The flare occurence rates of both fast and slow flares vary in the same way along the longitudes for all program stars. These results are not expected based on the case mentioned in the hypothesis.Comment: 24 pages, 15 figures, 6 tabels, 2011PASJ...63..427

Absolute Properties of An Overcontact Binary HH Boo

We obtained multi-colour light curves of HH Boo. We analysed the orbital period variation of the system. The analysis indicated that there is possible mass transfer from the second component to the primary or mass loss with -5.04x10-7 Msun per year. Re-analysing the available radial velocity curve, we analysed the light curves. The inclination (i) of the system was found to be 69.71(0.16) deg, while the semi-major axis (a) was computed as 2.246(0.064) Rsun. The mass of the primary component was found to be 0.92(0.08) Msun, while it was obtained as 0.58(0.06) Msun for the secondary component. The radius of the primary component was computed as 0.98(0.03) Rsun, while it was computed as 0.80(0.02) Rsun for the secondary component. We demonstrated that HH Boo should be a member of the A-type subclass of W UMa binaries.Comment: 20 pages, 5 figures, 4 table

V1135 Herculis: a double-lined eclipsing binary with an Anomalous Cepheid

BVR light curves and radial velocities for the double-lined eclipsing binary V1135\,Her were obtained. The brighter component of V1135\,Her is a Cepheid variable with a pulsation period of 4.22433$\pm$0.00026 days. The orbital period of the system is about 39.99782$\pm$0.00233 days, which is the shortest value among the known Type\,II Cepheid binaries. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained. Our analyses of the multi-colour light curves and radial velocities led to the determination of fundamental stellar properties of both components of the interesting system V1135\,Her. The system consists of two evolved stars, G1+K3 between giants and supergiants, with masses of M$_1$=1.461$\pm$0.054 \Msun ~and M$_2$=0.504$\pm$0.040 {\Msun} and radii of R$_1$=27.1$\pm$0.4 {\Rsun} and R$_2$=10.4$\pm$0.2 {\Rsun}. The pulsating star is almost filling its corresponding Roche lobe which indicates the possibility of mass loss or transfer having taken place. We find an average distance of d=7500$\pm$450 pc using the BVR magnitudes and also the V-band extinction. Location in the Galaxy and the distance to the galactic plane with an amount of 1300 pc indicate that it probably belongs to the thick-disk population. Most of the observed and calculated parameters of the V1135\,Her and its location on the color-magnitude and period-luminosity diagrams lead to a classification of an Anomalous Cepheid.Comment: 25 pages, 9 Tables, 9 Figures, Accepted Revista Mexicana de Astronom\'ia y Astrof\'isica. arXiv admin note: substantial text overlap with arXiv:1211.120

On the Influence of Magnetic Fields on the Structure of Protostellar Jets

We here present the first results of fully three-dimensional (3-D) MHD simulations of radiative cooling pulsed (time-variable) jets for a set of parameters which are suitable for protostellar outflows. Considering different initial magnetic field topologies in approximate $equipartition$ with the thermal gas, i.e., (i) a longitudinal, and (ii) a helical field, both of which permeating the jet and the ambient medium; and (iii) a purely toroidal field permeating only the jet, we find that the overall morphology of the pulsed jet is not very much affected by the presence of the different magnetic field geometries in comparison to a nonmagnetic calculation. Instead, the magnetic fields tend to affect essentially the detailed structure and emission properties behind the shocks at the head and at the pulse-induced internal knots, particularly for the helical and toroidal geometries. In these cases, we find, for example, that the $H_\alpha$ emissivity behind the internal knots can be about three to four times larger than that of the purely hydrodynamical jet. We also find that some features, like the nose cones that often develop at the jet head in 2-D calculations involving toroidal magnetic fields, are smoothed out or absent in the 3-D calculations.Comment: 13 pages, 3 figures, Accepted by ApJ Letters after minor corrections (for high resolution figures, see http://www.iagusp.usp.br/~adriano/h.tar

Detecting binary compact-object mergers with gravitational waves: Understanding and Improving the sensitivity of the PyCBC search

We present an improved search for binary compact-object mergers using a network of ground-based gravitational-wave detectors. We model a volumetric, isotropic source population and incorporate the resulting distribution over signal amplitude, time delay, and coalescence phase into the ranking of candidate events. We describe an improved modeling of the background distribution, and demonstrate incorporating a prior model of the binary mass distribution in the ranking of candidate events. We find a $\sim 10\%$ and $\sim 20\%$ increase in detection volume for simulated binary neutron star and neutron star--binary black hole systems, respectively, corresponding to a reduction of the false alarm rates assigned to signals by between one and two orders of magnitude.Comment: 7 pages, 3 figures, as accepted by Ap