arXiv subjects

K. Smith

Publications and source records attributed to K. Smith.

96 records · Page 6Linked to original sources

arXiv2005

The Swift Ultra-Violet/Optical Telescope

The UV/Optical Telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (approximately 1 minute) UV and optical photons from the afterglow of gamma-ray bursts in the 170-600 nm band as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey-Chretien design with micro-channel plate intensified charged-coupled device detectors that record the arrival time of individual photons and provide sub-arcsecond positioning of sources. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.

astro-ph↗

arXiv2005

Spot the differences: The X-ray spectrum of SU Aur compared to TW Hya

We present high-resolution Chandra HETGS X-ray spectra of the classical T Tauri star SU Aur. The quiescent X-ray emission is dominated by a 20-40 MK plasma, which contrasts strongly with the cool 3 MK plasma dominating the X-ray emission of the CTTS TW Hya. A large flare occurred during the first half of our 100 ks observation, and we have modelled the emitting plasma both during this flare and during the apparently quiescent periods. During the flare, an extremely high temperature plasma component (at least 60 MK) accounts for the bulk of the emission. There is an indication of the presence of Fe XXVI emission at 1.78 Angstrom, which is maximally formed at 130 MK.

astro-ph↗

arXiv2004

New Perspectives on the X-ray Emission of HD 104237 and Other Nearby Herbig Ae/Be Stars from XMM-Newton and Chandra

We present new X-ray observations of the nearby Herbig Ae star HD 104237 (= DX Cha) with XMM-Newton, whose objective is to clarify the origin of the emission. Several X-ray emission lines are clearly visible in the CCD spectra, including the high-temperature Fe K-alpha complex. The emission can be accurately modeled as a multi-temperature thermal plasma with cool (kT < 1 keV) and hot (kT > 3 keV) components. The presence of a hot component is compelling evidence that the X-rays originate in magnetically confined plasma, either in the Herbig star itself or in the corona of an as yet unseen late-type companion. The X-ray temperatures and luminosity (log Lx = 30.5 ergs/s) are within the range expected for a T Tauri companion, but high resolution Chandra and HST images constrain the separation of a putative companion to less than 1 arcsec. We place these new results into broader context by comparing the X-ray and bolometric luminosities of a sample of nearby Herbig stars with those of T Tauri stars and classical main-sequence Be stars. We also test the predictions of a model that attributes the X-ray emission of Herbig stars to magnetic activity that is sustained by a shear-powered dynamo.

astro-ph↗

arXiv2003

Speckle interferometry of the HAeBe star V376 Cas

We report H- and K'-band speckle interferometric observations of the HAeBe star V376 Cas. Our observations show that the object is partially resolved. The visibility curves suggest three separate components: a large scattering envelope visible only in the H band, a component approximately 100 mas in radius, and a component with a Gaussian HWHM of approximately 8+/-3 mas, corresponding to approximately 5 AU at 600 pc distance, which contributes most of the flux. We compare the smallest structure to the radius of dust sublimation in the radiation field of the star and find that the radius is approximately six times larger than that expected. This may indicate that the inner regions of the system are in fact obscured by a flaring circumstellar disk or torus seen close to edge-on.

astro-ph↗

arXiv2003

Moving black holes via singularity excision

We present a singularity excision algorithm appropriate for numerical simulations of black holes moving throughout the computational domain. The method is an extension of the excision procedure previously used to obtain stable simulations of single, non-moving black holes. The excision procedure also shares elements used in recent work to study the dynamics of a scalarfield in the background of a single, boosted black hole. The robustness of our excision method is tested with single black-hole evolutions using a coordinate system in which the coordinate location of the black hole, and thus the excision boundary, moves throughout the computational domain.

gr-qc↗

arXiv1997

Preliminary Results for LP VPE X-Ray Detectors

Thick epitaxial layers have been grown using Low Pressure Vapour Phase Epitaxy techniques with low free carrier concentrations . This type of material is attractive as a medium for X-ray detection, because of its high conversion efficiency for X-rays in the medically interesting energy range.

physics.ins-det↗