Fossil groups (FGs) are galaxy systems with masses and X-ray haloes comparable to to those of groups and clusters of galaxies, but whose optical light is dominated by a single, large elliptical galaxy surrounded by much fainter companions. Their early assembly leaves enough time for L* galaxies to merge and makes FGs the oldest and most relaxed

The planetary nebulae (PNe) of M 31 are receiving considerable attention as probes of its structure and chemical evolution in a galactic environment that is putatively similar to the Milky Way. We have obtained deep spectra for about 30 luminous PNe in M 31's inner disk and beyond (R gal < 105 kpc). The entire ensemble of PNe exhibit O/H ~ 2/3

We present BVR photometric observations of PKS 0736+017. Variations with different timescales and amplitudes were observed. Throughout our observations, an unusual tendency to redden with increased brightness was detected.

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments for ESA's far infrared and submillimetre observatory, Herschel. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 x 25 pixels, each, and two filled Si bolometer arrays with 16 x 32 and 32 x 64 pixels, respectively, to perform

We present a summary of current research on planetary nebulae and their central stars, and related subjects such as atomic processes in ionized nebulae, AGB and post-AGB evolution. Future advances are discussed that will be essential to substantial improvements in our knowledge in the field.

The primordial abundance of 4He, YP, is one of the hottest themes in present-day astronomy, mostly due to its cosmological relevance. The disagreement between different determinations has been currently reduced to the 1-2% level, but these differences are still large enough to have deep implications for Big-Bang nucleosynthesis. It is therefore