We examine the star-forming history of the M31 disk during the past few hundred Myr. The luminosity functions (LFs) of main-sequence stars at distances R GC > 21 kpc (i.e., >4 disk scale lengths) are matched by models that assume a constant star formation rate (SFR). However, at smaller R GC the LFs suggest that during the past ~10 Myr the SFR was

HST images taken over a time span of 11 years show that the tips of its bright optical fingers have proper motions exceeding 1". At the presumed distance of 0.9 kpc, the proper motions are equivalent to projected speeds of over 400 km s^-1. However, optical STIS spectra (Riera et al 2011) and our narrow-band images from the tips of the fingers

Although the h and k lines of Mg II are expected to be of great interest for probing the upper solar chromosphere, relatively little is known about their polarization properties which encode the information on the magnetic field. Here we report the first results of an investigation whose main goal is to understand the physical mechanisms that

We identify an inner-belt, low-inclination origin for 1999JU3 through the Nu6 resonance. Within this region there are three possible sources, the Erigone and Polana families, and a background population of low-albedo and low-inclination asteroids.

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We report on UV and X-ray spectroscopy and broadband optical observations of the ultraluminous X-ray source in Holmberg II. Fitting various stellar spectral models to the combined, non-simultaneous data set, we find that normal metallicity stellar spectra are ruled out by the data, while low-metallicity, Z = 0.1 Z &sun;, late O-star spectra provide