A. Schwarzenberg-Czerny

The power density spectrum of NGC 5548 and the nature of its variability

ABSTRA C T We derive power density spectra in the optical and X-ray bands in the time-scale range from several yr down to ,1 d. We suggest that the optical power density spectrum consists of two separate components: long time-scale variations and short time-scale variations, with the dividing time-scale around 100 d. The shape of the short time-scale component is similar to the X-ray power density spectrum, which is consistent with the interpretation of short time-scale optical variations being caused by X-ray reprocessing. We show that the observed optical long time-scale variability is consistent with thermal pulsations of the accretion disc.

Asteroseismology of Hybrid Pulsators Made Possible: Simultaneous MOST Space Photometry and Ground-Based Spectroscopy of γ Peg

We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid β Cep/Slowly Pulsating B pulsator γ Peg. Frequency analyses reveal the presence of six gravity (g) modes of high radial order together with eight low-order β Cep oscillations in both data sets. Mode identification shows

Variability of accretion flow in the core of the Seyfert galaxy NGC 4151

This paper reports the analysis of variability data for the Seyfert 1 type active galaxy NGC 4151. It covers the optical flux history for the last 90 years and X-ray flux for last 27 years. It presents the power spectrum density and structure function, and, based on the features in these functions, discusses the properties of the accretion flow onto a supermassive black hole, presumably powering the active nucleus of the galaxy.

The Clusters AgeS Experiment (CASE): RR Lyrae variables in the globular cluster NGC 6362

ABSTRA C T We present V- and B-band charge-coupled device (CCD) photometry of 35 RR Lyr stars in the Southern hemisphere globular cluster NGC 6362. Fourier decomposition of the light curves was used to estimate the basic properties of these variables. From the analysis of the RRc stars we obtain a mean mass Ma 0:531 ^ 0:014 M(; luminosity log L=L(a 1:656 ^ 0:006; effective temperature T effa 7429 ^ 20 and helium abundance Ya 0:292 ^ 0:002: The mean values of the absolute magnitude, metallicity (on Jurcsik’s scale) and effective temperature for 14 RRab stars with ‘regular’ light curves are: MV a 0:86 ^ 0:01;âFe=Haa 20:93 ^ 0:04 and T effa 6555 ^ 25; respectively. From the B 2 V colours, periods and metallicities of the RRab stars we estimate the colour excess for NGC 6362 to be equal to EOB 2 VUa0:08 ^ 0:01: Using this value we derive the colours of the blue and red edges of the instability strip in NGC 6362 to beOB 2 VU BE a 0:17 andOB 2 VU RE a 0:43: From the relations between the Fourier coefficients of RRab and RRc stars and their absolute magnitudes we estimate the apparent distance modulus to NGC 6362 to be Om 2 MUV a 14:46 ^ 0:10: From the mean value of log L=L( of the RRc stars we obtain 14:59 ^ 0:03: The V-band light curves of three of the RRc stars exhibit changes in amplitude of over 0.1 mag on the time-scale of around one week. Near the radial first overtone frequency we find one or two peaks, which strongly suggests that these variables belong to the newly identified group of non-radial pulsating RR Lyr stars.

A complete census of variable stars in the upper half of the HR diagram in M 33

We have obtained 35 epochs of g′r′i′ data for the nearby galaxy M 33 over 500 days with the Canada‐France‐Hawaii Telescope. The one‐square degree camera MegaCam covers the whole galaxy. We describe here the goals of the survey, its implementation, the search for variable stars, a broad characterization of the categories of variable stars found, and some preliminary results.