The acoustic cutoff frequency (νac) is an important atmospheric parameter whose estimation has in the past been based on the study of power spectra that have yielded a wide range of values between 5300 and 5700 μHz. The discovery of a solar signal well beyond the acoustic cutoff frequency (pseudomodes) might lead one to think that the determination

We report on an observation performed with the Swift/XRT of the neutron-star X-ray transient Aql X-1 which was recently found to start a new outburst as inferred from an increase in source luminosity in the R and J band data (ATEL #869, #870). The Swift/XRT observation was performed between 31 July 2006 21:47 and 22:05 UT with a duration of 996

Aims.We searched for photometric variability in a sample of hot, hydrogen-deficient planetary nebula nuclei (PNNi) with "PG 1159" or "O VI" spectral type, most of them embedded in a bipolar or elliptical planetary nebula envelope (PNe). These characteristics may indicate the presence of a hidden close companion and an evolution affected by episodes

A consistent analysis, using non-LTE codes with sphericity and mass loss, of different ionization species in O star spectra observed from the far-UV to UV allowed us to constrain the long-time uncertain ionization equilibrium in the stellar winds, to quantify the role of soft X-rays from shocks and to reconcile otherwise discrepant UV line

Environmental differences in the stellar populations of early-type galaxies are explored using principal component analysis (PCA), focusing on differences between elliptical galaxies in Hickson Compact Groups (HCGs) and in the field. The method is model-independent and purely relies on variations between the observed spectra. The projections (PC1

The formation mechanism of brown dwarfs (BDs) and its relation to star and planet formation remains an open issue. A careful determination of the substellar mass function in open clusters at different ages and environments is one of the primary methods for addressing this. We have performed a deep, wide area, multiband photometric survey from which