Using original data and incorporating similar data from previous studies we investigated the effect of extra line-broadening in the atmosphere of Galactic O-stars. Our results suggest that if not taken into account, the extra broadening can lead to significant overestimation of the measured v sin i. The effect is not large (less than 30 kms), and

The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due

The MAGIC experiment was upgraded to a two-telescope system in 2009. Unlike other Imaging Air Cherenkov Telescope arrays, MAGIC has operated for five years exclusively in monoscopic mode, and the single telescope analysis was optimized throughout this time. To improve the analysis, we used techniques like the random forest event classification

Multi-epoch HST images have been obtained for the pre planetary nebulae CRL618, CRL2688, and Hen3-1475. Each object shows clear and idiosyncratic expansion patterns. CRL618 consists of several well defined fingers with sharp tips. The lengths of the tips have increased by identical factors, ˜7%, over the course of seven years, suggesting a common

The Tremaine-Weinberg method is a well-known model-independent technique for measuring density wave pattern speeds in spiral galaxies. Here we show how it can be applied to the data cubes (maps of surface brightness and velocity) obtained in Halpha emission using a Fabry-Perot spectrometer. One of the main difficulties, the discontinuity of the

The optical spectra of objects classified as QSOs in the SDSS DR6 are analyzed with the aim of determining the value of the fine structure constant in the past and then check for possible changes in the constant over cosmological timescales. The analysis is done by measuring the position of the fine structure lines of the [OIII] doublet (λλ4959 and