Young stellar objects often show photometric variability, which is well examined at optical wavelengths, but more and more infrared data are also available. The wavelength dependence of the variability carries information on the physical cause of the changing brightness. Here, we examine seven T Tauri-type stars known for their large amplitude variability selected from the Campaign 13 field of the Kepler K2 mission. We complemented the K2 light curves by multifilter optical monitoring observations made with the 90 cm Schmidt telescope of Konkoly Observatory, and by 3.6 and 4.5 μm infrared photometry with a 20 hours cadence using the Spitzer Space Telescope. We found that the wavelength dependence of the observed variability is not consistent with changing interstellar extinction. We suggest that the brightness changes are due to variable accretion, causing a variable illumination of the inner disk.

The UBVRI photometric follow-up of SN 2011fu has been initiated a few days after the explosion, shows a rise followed by steep decay in all bands and shares properties very similar to that seen in case of SN 1993J, with a possible detection of the adiabatic cooling phase at very early epochs. The spectral modeling performed with SYNOW suggests that the early-phase line velocities for H and Fe ii features were ~ 16000 km s−1 and ~ 14000 km s−1, respectively. Studies of rare class of type IIb SNe are important to understand the evolution of the possible progenitors of core-collapse SNe in more details.

We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 µJ are focused to intensities ranging between 1013 and 1017 W/cm2. We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV and optical spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and atomic and ionic line emission. Our experimental results are in good agreement with simulations.

We present the results of space-based photometric and ground-based spectroscopic observing campaigns on the γ-ray binary LS 5039. The new orbital and physical parameters of the system are similar to former results, except we found a lower eccentricity. Our MOST-data show that any broad-band optical photometric variability at the orbital period is below the 2 mmag level. Light curve simulations support the lower value of eccentricity and imply that the mass of the compact object is higher than 1.8 M⊙.

We present medium resolution spectroscopy (λ/Δλ ≈ 7,000) covering 6500-6750 Å of three emission stars in the highly reddened young open cluster NGC7128. Two of them were previously unknown. The known Be star (V1814 Cyg) is an irregular variable; one of the newly discovered stars is an eclipsing binary (V1481 Cyg) (Jerzykiewicz et al., 1996.). Physical parameters of the cluster have been determined from new UBV and uvbyHβ photometric measurements.

A preliminary orbit has been derived for the high luminosity, 27-d classical Cepheid T Mon. Velocities for the hot companion have been measured from an HST GHRS spectrum and 3 IUE spectra. The companion velocities are inconsistent with binary orbital motion and it is likely that the companion is itself a short period binary. The HST spectrum also shows that the companion is a chemically peculiar star, probably magnetic.

We present the results of follow-up ground-based photometric and spectroscopic observations of a sample of variable stars discovered by the Hipparcos satellite.

Gamma-velocities of bright contact binary stars (VW Cep, SW Lac, AB And, OO Aql) have been computed using cross-correlation. The template spectra were synthesized with a newly developed computer code WGMODEL.

We study the velocities of specific stellar absorption lines of Cepheid-type variable stars determining line bisector velocities from newly obtained high-resolution echelle spectra. We compare these velocities with recent CORAVEL measurements of Cepheids to reveal systematic differences of 2 – 3 kms−1.

New physical parameters of selected Cepheid variables classified as CW or CEP (Type II) in GCVS are presented. The analysis is based on published light and radial velocity curves. Two of the stars turned out to be classical Cepheids.

AU Peg, a short period BL Her-type variable, is unique among short period Cepheids. It is a member of a close binary system with an unseen companion. In t his paper the pulsational period variation is presented. It is shown that the period variation is very rapid and highly non-linear. It seems that there is no simple explanation of this phenomena by standard evolution or tidal interaction.

AW Per is a well-known binary Cepheid. Recently Welch & Evans (1989) determined a spectroscopic orbit. Evans (1989) pointed out that the spectral type of the companion is incompatible with the mass function of the system. We re-determined the orbit of AW Per using both photometric and spectroscopic data. The result of the simultanuous least-squares fit can be seen on Fig.l. The orbital elements are very close to the results of Welch & Evans. After correcting for the companion, the Cepheid's light and velocity curves were analyzed with the surface-brightness method. The details of the analysis will be published in MNRAS (Vinko, 1992). The mass of AW Per was found to be 6 solar masses, which confirms the mass-problem of the secondary. Observations are planned to continue at Konkoly Observatory.