Context. We recently presented evidence that stable umbra-penumbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, Bstablever. In order to trigger the formation of a penumbra, large inclinations in the magnetic field are necessary. In sunspots, the penumbra develops and establishes by

We describe an experiment to measure calibration sources, the polarization of Cosmic Microwave Background Radiation (CMBR) and the polarization induced on the CMBR from S-Z effects, using a polarimeter, MITOPol, that will be employed at the MITO telescope. Two modulation methods are presented and compared: an amplitude modulation with a Fresnel

A new method of calculating microlensing magnification patterns is proposed that is based on the properties of the backward gravitational lens mapping of a lattice of polygonal cells defined at the image plane. To a first-order approximation, the local linearity of the transformation allows us to compute the contribution of each image-plane cell to

We investigate the feasibility of detecting quiescent black hole X-ray binaries using optical photometric techniques. To test this, we employ a combination of r-band and H α filters currently available at the Roque de los Muchachos Observatory. Photometric observations of four dynamical black holes (GRO J0422+320, A 0620-00, XTE J1118+480, and XTE

Context. The solar spectrum is a primary reference for the study of physical processes in stars and their variation during activity cycles. High resolution spectra of the Sun are easily obtained from spatially selected regions of the solar disk, while those taken over the integrated disk are more problematic. However, a proxy can be obtained by

Galactic black holes release an unknown fraction of their accreting matter and energy in the form of collimated outflows (or jets) that travel into the surrounding medium. Black Hole X-ray Binaries (BHXBs) are the essential laboratories for understanding the overall physics of the accretion process in these systems, and have provided us with a