We present high-quality (subarcsecond) optical narrowband CCD images of the planetary nebula NGC 6881, which reveal a highly collimated bipolar structure. A careful examination of the [N II] image and of the [N II]/[O III] and [N II]/Hα ratio images shows that NGC 6881 is a quadrupolar planetary nebula, that is, a twice bipolar planetary nebula

The primary science goal of the Kepler Mission is to provide a census of exoplanets in the solar neighborhood, including the identification and characterization of habitable Earth-like planets. The asteroseismic capabilities of the mission are being used to determine precise radii and ages for the target stars from their solar-like oscillations

We present new near-infrared (J and K) magnitudes for 114 RR Lyrae stars in the globular cluster ω Centauri (NGC 5139), which we combine with data from the literature to construct a sample of 180 RR Lyrae stars with J and K mean magnitudes on a common photometric system. This is currently the largest such sample in any stellar system. We also

We study the delay induced by gravitational light bending in the arrival times of signals emitted by an anisotropic source in rotation (pulsar). The shift of the direction of the allowed pulsar beam (a vector defined by the null geodesic connecting the pulsar to the observer) with orbital phase induces a delay arising from the movement of the

The first theoretical investigation of the formation of the linearly polarized solar line spectrum of a complex atom, neutral titanium, is presented. The process of formation of line polarization is modeled by simply considering a plane-parallel layer of Ti I atoms illuminated from below by the photospheric radiation field, and accounting for the

We make a quantitative comparison between spectral vs filter measurement and analysis techniques for extraction of solar vector magnetic fields from polarimetric data using as a basis the accurately calibrated, high angular resolution. Stokes profile data from the Advanced Stokes Polarimeter. It is shown that filter-based measurements deliver