We present the results of a program to derive the complete star-formation history of the Local Group dwarf irregular galaxy Leo A (DDO 69). Leo A is a low-luminosity (Mv = -11.7), very gas-rich (M(HI)/LB = 1.6) galaxy. Our analysis is based on color-magnitude diagrams derived from deep HST/ACS imaging; the CMDs reach well below the oldest main

The peculiar variable star V838 Mon underwent an extremely unusual outburst in early 2002. Unlike a classical nova, V838 Mon has remained very cool throughout its outburst. It is illuminating the most spectacular light echo in astronomical history, which is being imaged regularly with the Hubble Space Telescope (HST) as well as from the ground. In

We investigate the orientation of the axes and angular momentum of dark matter halos with respect to their neighboring voids using high-resolution N-body cosmological simulations. We find that the minor axis of a halo tends to be aligned along the line joining the halo with the center of the void and that the major axis tends to lie in the plane

A large set of high-precision, full-Stokes spectro-polarimetric observations of prominences in He I D3, Hα, and Hβ lines has been recorded with the ZIMPOL polarimeter at the Gregory-Coudé Telescope in Locarno. The observational technique allows us to obtain measurements free from seeing-induced spurious effects. The instrumental polarization is

Recordings of the full Stokes vector of filaments in the Hα and He I D3 lines were obtained at the Gregory-Coudé telescope in Locarno with the polarimeter ZIMPOL. The aim was to perform preliminary studies to explore the presence of forward scattering polarization. The observations show linear polarization signatures, whose interpretation is still

We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å, that were candidates to be used in the Helioseismic and Magnetic Imager (HMI) for observing Doppler velocity and the vector magnetic field. The line profiles were studied using the Mt. Wilson Observatory, the Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope