T. Ak

Solar-type cycles of the secondary stars in cataclysmic variables

We found cyclical variations in the quiescent magnitudes and outburst intervals of 21 dwarf novae, 1 nova and 1 nova-like star produced by the solar-type cycles of the late-type secondary components. More than 70% of individual systems in this work are rst studied by Fourier periodogram analysis. It seems that the mean cycle amplitudes of the quiescent magnitudes are considerably larger for SU UMa stars. Cyclical modulations of quiescent magnitudes found for the stars, which have orbital periods below the period gap, support the hypothesis that even almost fully convective secondaries may possess activity cycles. The estimated probability density functions show peaks at 9.7, 7.9 and 8.6 yrs for cataclysmic variables (CVs), single main-sequence stars (MS) and all stars (CVs+MS), respectively. Using a larger set of data, we conrm that there is no correlation of the cycle period with the rotational regime of the secondary star. It is also conrmed that cycle periods of CVs are in the range of those of single main-sequence stars. We note that the observational cycle parameters (i.e. cycle period, Pcyc, and cycle amplitude of quiescent magnitudes, m) do not seem in relation with any other parameter such as masses of primary and secondary stars, mean outburst interval, mean outburst duration, mean decline and rise rate of outbursts, absolute magnitudes in quiescent and outburst states etc.

A new absolute magnitude calibration with 2MASS for cataclysmic variables

Using reliable trigonometric measurements, we find that the absolute magnitude of cataclysmic variables depends on the orbital period and de-reddened (J −H)0 and (H −Ks)0 colours of 2MASS (Two Micron All Sky Survey) photometric system. The calibration equation covers the ranges 0.032 d < Porb ≤ 0.454 d , −0.08 < (J −H)0 ≤ 1.54, −0.03 < (H −Ks)0 ≤ 0.56 and 2.0 < MJ < 11.7; It is based on trigonometric parallaxes with relative errors of (��/�) ≤ 0.4. By using the period-luminositycolours (PLCs) relation, we estimated the distances of cataclysmic variables with orbital periods and 2MASS observations and compared them with distances found from other methods. We suggest that the PLCs relation can be a useful statistical tool to estimate the distances of cataclysmic variables.

Statistical analysis of the long-term visual light curve parameters of dwarf novae

The long-term visual light curve parameters of 36 dwarf novae are measured. The data is anayzed in search of likely relationships among the light curve parameters and system parameters. New relations of the orbital period with the mean light curve parameters are given. Our ndings for the correlation analysis of individual systems agree with some of the results in previous studies. Almost all of the systems in this study have a bimodal frequency distribution of the outburst duration. By comparing the observational correlations with their theoretical counterparts, we nd that the value of the viscosity parameter of the disk instability model is hot 0:2.

Transit timing analysis in the HAT-P-32 system

We present the results of 45 transit observations obtained for the transiting exoplanet HATP-32b. The transits have been observed using several telescopes mainly throughout the YETI (Young Exoplanet Transit Initiative) network. In 25 cases, complete transit light curves with a timing precision better than 1.4 min have been obtained. These light curves have been used to refine the system properties, namely inclination i, planet-to-star radius ratio R-p/R-s, and the ratio between the semimajor axis and the stellar radius a/R-s. First analyses by Hartman et al. suggests the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also the literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21 ms. Thus, we can exclude TTV amplitudes of more than similar to 1.5min.

SDSS J162520.29+120308.7 – a new SU Ursae Majoris star in the period gap

We report results of an extensive world-wide observing campaign devoted to the recently discovered dwarf nova SDSS J162520.29+120308.7 (SDSS J1625). The data were obtained during the July 2010 eruption of the star and in August and September 2010 when the object was in quiescence. During the July 2010 superoutburst SDSS J1625 clearly displayed superhumps with a mean period of

The Orbital Period of Nova V2540 Ophiuchi (2002)

P_{\rm sh}=0.095942(17)

A Photometric Study of the Newly Discovered Eclipsing Cataclysmic Variable SDSS J040714.78–064425.1

days (

The Distances of the Galactic Novae

138.16 \pm 0.02

On the Change of the Inner Boundary of an Optically Thick Accretion Disk around White Dwarfs Using the Dwarf Nova SS Cyg as an Example

min) and a maximum amplitude reaching almost 0.4 mag. The superhump period was not stable, decreasing very rapidly at a rate of

A comprehensive study of the open cluster NGC 6866

\dot P = -1.63(14)\cdot 10^{-3}