AA Tau, a classical T Tauri star in the Taurus cloud, has been the subject of intensive photometric monitoring for more than two decades due to its quasi-cyclic variation in optical brightness. Beginning in 2011, AA Tau showed another peculiar variation—its median optical though near-IR flux dimmed significantly, a drop consistent with a 4-mag increase in visual extinction. It has stayed in the...

The evolution of high redshift galaxies in the two Hubble Deep Fields, HDF-N and HDF-S, is investigated using a cloning technique that replicates z ∼ 2 − 3 U dropouts to higher redshifts, allowing a comparison with the observed B and V dropouts at higher redshifts (z ∼ 4 − 5). We treat each galaxy selected for replication as a set of pixels that are k-corrected to higher redshift, accounting fo...

Even quiescent solar prominences may become active and sometimes erupt. These events are occasionally linked to coronal mass ejections. However we know very little about the plasma properties during the activation and eruption processes. We present new computations of the helium line profiles emitted by an eruptive prominence. The prominence is modelled as a plane-parallel slab standing vertica...

We present the discovery of an exceptional dimming event in a cool supergiant star Local Volume spiral M51. The star, dubbed M51-DS1, was found as part Hubble Space Telescope (HST) search for failed supernovae (SNe). supergiant, which is plausibly associated with very young ($\lesssim6$ Myr) stellar population, showed clear variability (amplitude $\Delta F814W\approx0.7$ mag) numerous HST image...

Geoengineering by stratospheric aerosol injection has been proposed as a policy response to warming from human emissions of greenhouse gases, but it may produce unequal regional impacts. We present a simple, intuitive risk-based framework for classifying these impacts according to whether geoengineering increases or decreases the risk of substantial climate change, with further classification b...

We examine the radius-luminosity (R-L) relation for blue galaxies in the Team Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan Digital Sky Survey sample and find that the R-L relation has evolved to lower surface brightness since z = 1. Based on the detection limits of GOODS this can not be explained by incompleteness in low surface-brightness galaxies. Number den...