Zdenek Mikulasek

Catalogue of variable stars in open cluster fields

Observatory and Planetarium of Johann Palisa, VSB – Technical University, Ostrava, Czech RepublicˇReceived 20 March, 2012; accepted 4 October 2012ABSTRACTContext.We present the first catalogue of known variable stars in open cluster regions and with up to two times the given clusterradius. This gives basic information about the distribution of variable stars in cluster fields for the complete sky.Aims.Knowledge of the variable star contents in open clusters is a significant advantage in their study. Analysing variabilit y of clustermembers and fields stars as well allows us to study the charact eristics of stars and clusters together. This catalogue of variable stars inopen cluster fields is the first step in supporting such studie s.Methods.We took all variable and suspected variable stars into account from the most complete collection, “The AAVSO VariableStar Index”, and did a cross-match of these stars with the most complete catalogue of galactic open clusters named DAML02.Results.Our on-line catalogue presently contains 18065 variable stars. We present the basic statistical distribution according to typesof variability.Key words. Open clusters and associations: general – Catalogues – Star s: variables: general – Proper motions

New analysis of the light time effect in TU Ursae Majoris

We investigate in detail the LiTE of the most probable binary candidate TU UMa. We used a new code applied on previously available and newly determined maxima timings to confirm binarity and refine parameters of the orbit of the RRab component in the binary system. The binary hypothesis is also tested using RV measurements. We used new approach to determine brightness maxima timings based on template fitting. This can also be used on sparse or scattered data. This approach was successfully applied on measurements from different sources. To determine the orbital parameters of the double star TU UMa, we developed a new code to analyse LiTE that also includes secular variation in the pulsation period. Its usability was successfully tested on CL Aur, an eclipsing binary with mass-transfer in a triple system that shows similar changes in the O-C diagram. Since orbital motion would cause systematic shifts in mean RVs (dominated by pulsations), we computed and compared our model with centre-of-mass velocities. They were determined using high-quality templates of RV curves of RRab stars. Maxima timings adopted from the GEOS database (168) together with those newly determined from sky surveys and new measurements (85) were used to construct an O-C diagram spanning almost five proposed orbital cycles. This data set is three times larger than data sets used by previous authors. Modelling of the O-C dependence resulted in 23.3-year orbital period, which translates into a minimum mass of the second component of about 0.33 M_s. Secular changes in the pulsation period of TU UMa over the whole O-C diagram were satisfactorily approximated by a parabolic trend with a rate of -2.2 ms/yr. To confirm binarity, we used RV measurements from nine independent sources. Although our results are convincing, additional long-term monitoring is necessary to unambiguously confirm the binarity of TU UMa.

Principal component analysis—an efficient tool for variable stars diagnostics

We present two diagnostic methods based on the ideas of principal component analysis and demonstrate their efficiency for sophisticated processing of multicolour photometric observations of variable objects.

The Kepler view of magnetic chemically peculiar stars

Magnetic chemically peculiar (mCP) stars exhibit complex atmospheres that allow the investigation of such diverse phenomena as atomic diffusion, magnetic fields, and stellar rotation. The advent of space-based photometry provides the opportunity for the first precise characterizations of the photometric variability properties of these stars. We carried out a search for new mCP stars in the Kepler field with the ultimate aim of investigating their photometric variability properties using Kepler data. As an aside, we describe criteria for selecting mCP star candidates based on light curve properties, and assess the accuracy of the spectral classifications provided by the MKCLASS code. As only very few known mCP stars are situated in the Kepler field, we had to depend largely on alternative (nonspectroscopic) means of identifying suitable candidates that rely mostly on light curve properties; in particular we relied on monoperiodic variability and light curve stability. Newly acquired and archival spectra were used to confirm most of our mCP star candidates. Linear ephemeris parameters and effective amplitudes were derived from detrended Kepler data. Our final sample consists of 41 spectroscopically confirmed mCP stars of which 39 are new discoveries, 5 candidate mCP stars, and 7 stars in which no chemical peculiarities could be established. Our targets populate the whole age range from zero-age main sequence to terminal-age main sequence and are distributed in the mass interval from 1.5 M_sun to 4 M_sun. About 25% of the mCP stars show a hitherto unobserved wealth of detail in their light curves indicative of complex surface structures. We identified light curve stability as a primary criterion for identifying mCP star candidates among early-type stars in large photometric surveys, and prove the reliability of the spectral classifications provided by the MKCLASS code.

Study of Eclipsing Binary and Multiple Systems in OB Associations. I. Orion OB1a- IM Monocerotis

All available photometric and spectroscopic observations were collected and used as the basis of a detailed analysis of the close binary IM Mon. The orbital period of the binary was refined to 1.19024249(0.00000014) days. The Roche equipotentials, fractional luminosities (in (B, V) and H_p bands) and fractional radii for the component stars in addition to mass ratio q, inclination i of the orbit and the effective temperature T_eff of the secondary cooler less massive component were obtained by the analysis of light curves. IM Mon is classified to be a detached binary system in contrast to the contact configuration estimations in the literature. The absolute parameters of IM Mon were derived by the simultaneous solutions of light and radial velocity curves. An evolutionary age of 11.5(1.5) Myr was obtained for IM Mon. Kinematical and dynamical analysis support the membership of the young thin-disk population system IM Mon to the Ori OB1a association dynamically. Finally, we derived the distance, age and metallicity information of Ori OB1a sub-group using the information of IM Mon parameters.

Revision of the photometric parameters of BS Cassiopeiae

Seven charge-coupled device (CCD) photometric times of light minimum of the overcontact binary BS Cas which were obtained from 2007 August to November and one CCD light curve in the R band which was observed on 2007 September 24 and October 15, are presented. It is found that the light curve of BS Cas has characteristics like a typical EW-type light variation. The light curve obtained by us is symmetric and shows total eclipses, which is very useful for determining photometric parameters with high precision. Photometric solutions were derived by using the 2003 version of the Wilson-Devinney code. It shows that BS Cas is a W-subtype overcontact binary (f = 27.5% +/- 0.4%) with a mass ratio of q = 2.7188 +/- 0.0040. The temperature difference between the two components is 190 K. Analysis of the O-C curve suggests that the period of AE Phe shows a long-term continuous decrease at a rate of dP/dt = -2.45 x 10(-7) d yr(-1). The long-time period decrease can be explained by mass transfer from the primary to the secondary.