We present high resolution images and high dispersion spectra of the planetary nebula IC 4593. Benefiting from superb seeing (0″.4), the narrowband images reveal the existence of a complex system of collimated knots in the inner 15″ of the nebula.The knots, which morphologically resemble outward facing bow-shocks, are located at different position

We present a critical analysis of linearization and preconditioning, the two most used approaches proposed for achieving the required linearity in the iterative solution of the multilevel transfer problem. By distinguishing from the outset between the response of the radiation field to the source function and opacity perturbations, we are able to

We report Keck high-resolution echelle spectroscopic observations of two very cool field dwarfs discovered by the near-IR photometric survey DENIS. DENIS-P J1228.2-1547 shows a conspicuous LiI resonance line that confirms it as an incontrovertible brown dwarf (BD). From the presence of Li, and its low surface temperature, we estimate from

In order to definitely prove the claim by Claeskens et al. (1996A&A...305L...9C) that J03.13 is a doubly imaged quasar, WFPC2 direct imaging and FOS spectroscopy of this compact system have been obtained with HST. These textbook case observations clearly show that J03.13 consists of two point-like images separated by 0.849"+/-0.001" with a

Fragment-fragment-$gamma$ triple coincident measurements of the $^{28}$Si + $^{28}$Si reaction at E$_{lab.}$ = 111.6 MeV carefully chosen to populate J = 38$^{+}$ resonance have been performed at the VIVITRON tandem facility by using Eurogam Phase II $gamma$-ray spectrometer. In the $^{28}$Si + $^{28}$Si exit-channel, the resonance behavior of the

In the previous papers of this series, we introduced the implicit integral method (IIM) to solve those radiative transfer (RT) problems in which the source function depends on an integral of the specific intensity of the radiation field over directions and frequencies. The IIM rests upon a forward-elimination, back-substitution scheme naturally