Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

SHELS: Testing Weak-Lensing Maps with Redshift Surveys

Abstract: Weak-lensing surveys are emerging as an important tool for the construction of "mass-selected" clusters of galaxies. We evaluate both the efficiency and completeness of a weak-lensing selection by combining a dense, complete redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), with a weak-lensing map from the Deep Lens Survey (DLS). SHELS includes 11,692 redshifts for galaxies with R ≤ 20.6 in the 4 deg2 DLS field; the survey is a solid basis for identifying massive clusters of galaxies with redshift z 0.55. The range of sensitivity of the redshift survey is similar to the range for the DLS convergence map. Only four of the 12 convergence peaks with signal to noise ≥3.5 correspond to clusters of galaxies with M 1.7 × 1014 M ☉. Four of the eight massive clusters in SHELS are detected in the weak-lensing map yielding a completeness of ~50%. We examine the seven known extended cluster X-ray sources in the DLS field: three can be detected in the weak-lensing map, three should not be detected without boosting from superposed large-scale structure, and one is mysteriously undetected even though its optical properties suggest that it should produce a detectable lensing signal. Taken together, these results underscore the need for more extensive comparisons among different methods of massive cluster identification.

SMART-X: Square Meter Arcsecond Resolution x-ray Telescope

Abstract: SMART-X is a mission concept for a 2.3 m 2 effective area, 0.5" angular resolution X-ray telescope, with 5' FOV, 1" pixel size microcalorimeter, 22' FOV imager, and high-throughput gratings.

Far-Ultraviolet Spectra of a Nonradiative Shock Wave in the Cygnus Loop*

Abstract: Spatial and spectral profiles of O VI emission behind a shock wave on the northern edge of the Cygnus Loop were obtained with the Far Ultraviolet Spectroscopic Explorer. The velocity width of the narrowest O VI profile places a tight constraint on the electron-ion and ion-ion thermal equilibration in this 350 km s-1 collisionless shock. Unlike faster shocks in SN 1006 and in the heliosphere, this shock brings oxygen ions and protons to within a factor of 2.5 of the same temperature. Comparison with other shocks suggests that shock speed, rather than Alfven Mach number, may control the degree of thermal equilibration. We combine the O VI observations with a low-resolution far-UV spectrum from the Hopkins Ultraviolet Telescope, an Hα image, and ROSAT PSPC X-ray data to constrain the preshock density and the structure along the line of sight. As part of this effort, we model the effects of resonance scattering of O VI photons within the shocked gas and compute time-dependent ionization models of the X-ray emissivity. Resonance scattering affects the O VI intensities at the factor of 2 level, and the soft spectrum of the X-ray rim can be mostly attributed to departures from ionization equilibrium. The preshock density is about twice the canonical value for the Cygnus Loop X-ray-emitting shocks.

Radio and EUV observations of a coronal hole

Abstract: We present observations of a coronal hole made with the EUV spectroheliometer of the Harvard College aboard Skylab and with ‘high resolution’ (2–4′) radio telescopes at Culgoora and Fleurs Australia and Bonn, West Germany. We attempt to derive the density and temperature distributions in the transition region and inner corona from the combined observations. No one ‘standard’ model can explain both sets of observations; characteristically, models based on EUV data yield higher radio brightnesses than are observed, while models based on radio data yield lower EUV line intensities than are observed. The discrepancy is essentially that the electron density inferred from the EUV data is about three times that inferred from the radio data.