We report on the RXTE follow up observations of the black hole candidate IGR J17091-3624 (ATEL #3144, #3159, #3167, #3203) after the report of mHz quasi-periodic oscillations (QPO -- ATEL #3225) and 'heartbeat' oscillations similar to those of GRS 1915+105 (ATEL #3230). The 'heartbeat' oscillations first seen on March 19th (ATEL #3230) at ~25 mHz

We have used images from the Advanced Camera for Surveys on the Hubble Space Telescope in Hα, and in the neighboring continuum, to produce flux-calibrated images of the large spiral galaxy M51 and the dwarf irregular NGC 4449. From these images, we have derived the absolute luminosities in Hα, the areas, and the positions with respect to the

The theory of radiative transfer for polarized radiation, developed from Quantum Electrodynamics for the interpretation of solar observations, predicts the existence of a variety of physical phenomena that, in many cases, would deserve being directly tested through laboratory experiments, also in view of possible practical applications. In this

A brief description of the new 1.5-meter solar telescope GREGOR located at the Observatorio del Teide in Tenerife will be given. GREGOR will provide a spatial resolution of about 75 km on the Sun, and with its light collecting capability we will be able to study the development of small magnetic features with high cadence. From the beginning, it

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Obtaining the magnetic properties of non-resolved structures in the solar photosphere is always challenging and problems arise because the inversion is carried out through the numerical minimization of a merit function that depends on the proposed model. We investigate the reliability of inversions in which the stray-light contamination is obtained