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A prevailing open problem in planetary nebulae research, and photoionized gaseous nebulae research at large, is the systematic discrepancies in electron temperatures and ionic abundances as derived from recombination and collisionally…
Diagnostic diagrams of electron density - excitation for a sample of 613 planetary nebulae are presented. The present extensive sample allows the definition of new statistical limits for the distribution of planetary nebulae in the log…
One of the defining characteristics of a solar flare is the impulsive formation of very high temperature plasma. The properties of the thermal emission are not well understood, however, and the analysis of solar flare observations is often…
Gamma-ray emitting binaries (GREBs) are complex systems. Its study became in the last years a major endeavour for the high-energy astrophysics community, both from an observational and a theoretical perspective. Whereas the accumulation of…
The increasing sensitivity of instruments at X-ray and TeV energies have revealed a large number of nebulae associated with bright pulsars. Despite this large data set, the observed pulsar wind nebulae (PWNe) do not show a uniform behavior…
We report the results of infrared photometry on 39 extended red objects (EROs) in the Carina Nebula, observed with the Spitzer Space Telescope. Most EROs are identified by bright, extended 8.0 um emission, which ranges from 10'' to 40'' in…
The direct measurement of the extragalactic background light (EBL) is difficult at optical to infrared wavelengths because of the strong foreground radiation originating in the Solar System. Very high energy (VHE, E$>$100 GeV) gamma rays…
The study of the hard (E>10 keV) energy spectra of X-ray binary pulsars can give a wealth of information on the physical processes that occur close to the neutron star surface. Extreme matter regimes are probed, and precious information on…
The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes since the epoch of recombination. Direct measurements of the EBL in the near-IR to mid-IR waveband are extremely difficult due…
Planetary Nebulae (PNe) are very important kinematical tracers of the outer regions of early-type galaxies, where the integrated light techniques fail. Under ad hoc assumptions, they allow measurements of rotation velocity and velocity…
A recent progress in the study of $\gamma$-ray jets is reviewed, with a focus on some theoretical interpretations of the VHE emission from M87, and possibly other misaligned blazars; the connection betwe en the GeV breaks exhibited by…
The spectral energy distributions (SEDs) of dusty high-redshift galaxies are poorly sampled in frequency and spatially unresolved. Their form is crucially important for estimating the large luminosities of these galaxies accurately, for…
We have investigated the infrared properties of a sample of objects with IRAS colors typical of planetary nebulae. The selected objects have not yet evolved to the planetary nebula stage since they have no detectable radio continuum…
Non-Maxwellian $\kappa$ electron energy distributions (EEDs) have been proposed in recent years to resolve the so-called ``electron temperature and abundance discrepancy problem'' in the study of planetary nebulae (PNe). Thus the need to…
We present a homogeneous set of spectroscopic measurements secured with 4-meter class telescopes for a sample of 90 planetary nebulae (PNe) located in the direction of the Galactic bulge. We derive their plasma parameters and chemical…
We present a comprehensive study of the emission spectra from accreting sources. We use our new reflection code to compute the reflected spectra from an accretion disk illuminated by X-rays. This set of models covers different values of…
Line-formation calculations in the Rayleigh-Jeans tail of the spectral energy distribution are complicated by an amplification of non-LTE effects. For hot stars this can make quantitative modelling of spectral lines in the near-IR…
The nebula powered by the Vela pulsar is one of the best examples of an evolved pulsar wind nebula, allowing to access the particle injection history and the interaction with the supernova ejecta. We report on the INTEGRAL discovery of…
Since the last IAU symposium on planetary nebulae (PNe), several deep spectroscopic surveys of the relatively faint optical recombination lines (ORLs) emitted by heavy element ions in PNe and H II regions have been completed. New diagnostic…
To examine a recently proposed hypothesis that silicon nanoparticles are the source of extended red emission (ERE) in the interstellar medium, we performed a detailed modeling of the mean Galactic extinction in the presence of silicon…