L and T dwarfs in the Hyades and Ursa Major moving groups

We have used the moving cluster method to identify three L dwarfs and one T dwarf in the Ursa Major/Sirius moving group (age 400 Myr). Five L dwarfs and two T dwarfs are found to belong to the Hyades moving group (age 625 Myr). These L and T dwarfs define 400- and 625-Myr empirical isochrones, assuming that they have the same age. Moving group membership does not guarantee coevality

The ages of L dwarfs ⋆

Low-mass stars and brown dwarfs undergo a significant change in luminosity over the first hundred million years (hereafter Myr) of their life (Baraffe et al. 1998; Burrows et al. 2001). As brown dwarfs fade inexorably with time, estimating their age is importan

Proper motions of field L and T dwarfs

The proper motion measurements for 143 previously known L and T dwarfs are presented. From this sample we identify and discuss 8 high velocity L dwarfs. We also find 4 new wide common proper motion binaries/multiple systems. Using the moving cluster methods we have also identified a number of L dwarfs that may be members of the Ursa Major (age ~400 Myr), the Hyades (age ~625 Myr) and the Pleiades (age ~125 Myr) moving groups

Narrow-band X-ray polarizing filters.

We review past and current attempts to measure X-ray polarization in celestial sources and describe research activity into a new family of materials which have been shown to exhibit linear dichroism at X-ray wavelengths. Such materials could add a polarimetry capability to the high energy resolution detectors proposed for future, high effective area, X-ray astrophysical observatories such as Constellation-X and XEUS. They have the potential to achieve useful minimum detectable polarization values for a number of sources in a sensible exposure time with XEUS

The early- and late-time spectral and temporal evolution of ORB 050716

We report on a comprehensive set of observations of gamma-ray burst 050716, detected by the Swift satellite and subsequently followed-up rapidly in X-ray, optical and near-infrared (NIR) wavebands. The prompt emission is typical of long-duration bursts, with two peaks in a time interval of T90= 68 s (15–350 keV). The prompt emission continues at lower flux levels in the X-ray band, where several smaller flares can be seen on the top of a decaying light curve that exhibits an apparent break around 220 s post-trigger. This temporal break is roughly coincident with a spectral break. The latter can be related to the extrapolated evolution of the break energy in the prompt γ-ray emission, and is possibly the manifestation of the peak flux break frequency of the internal shock passing through the observing band. A possible 3σ change in the X-ray absorption column is also seen during this time. The late-time afterglow behaviour is relatively standard, with an electron distribution power-law index of p= 2; there is no notable temporal break out to at least 10 d. The broad-band optical/NIR to X-ray spectrum indicates a redshift of z≳ 2 for this burst, with a host-galaxy extinction value of EB−V≈ 0.7 that prefers a small magellanic cloud (SMC)-like extinction curve

A Wide Field Auroral Imager (WFAI) for Low Earth Orbit Missions

A Wide Field Auroral Imager (WFAI) for Low Earth Orbit Mission

High resolution spectroscopy of G191-B2B in the extreme-Ultraviolet

We report a high-resolution (R = 3000-4000) spectroscopic observation of the DA white dwarf G191-B2B in the extreme-ultraviolet band 220-245 Å. A low-density, ionized He component is clearly present along the line of sight, which if completely interstellar implies a He ionization fraction considerably higher than is typical of the local interstellar medium. However, some of this material may be associated with circumstellar gas, which has been detected by analysis of the C IV absorption-line doublet in a Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum. A stellar atmosphere model assuming a uniform element distribution yields a best fit to the data that includes a significant abundance of photospheric He. The 99% confidence contour for the fit parameters excludes solutions in which photospheric He is absent, but this result needs to be tested using models allowing abundance gradients