Search Publications
In-Orbit Vignetting Calibrations of XMM-Newton Telescopes
Finoguenov, A.; Gondoin, P.; Aschenbach, B. +4 more
We describe measurements of the mirror vignetting in the XMM-Newton Observatory made in-orbit, using observations of SNR G21.5-09 and SNR 3C58 with the EPIC imaging cameras. The instrument features that complicate these measurements are briefly described. We show the spatial and energy dependences of measured vignetting, outlining assumptions made…
Anomalous Evolution of the Dwarf Galaxy HIPASS J1321-31
Knezek, Patricia M.; Saha, A.; Freeman, Kenneth C. +6 more
We present Hubble Space Telescope/WFPC2 observations of the dwarf galaxy HIPASS J1321-31. This unusual galaxy lies in the direction of the Centaurus A group of galaxies and has a color-magnitude diagram with a distinctive red plume of luminous stars. This feature could arise from (1) a red giant branch if the galaxy were much nearer than previousl…
Acoustic Wave Propagation in the Sun: Implications for Wave Field and Time-Distance Helioseismology
Thompson, M. J.; Rajaguru, S. P.; Tong, C. H. +2 more
We present results of the numerical simulation of acoustic wave propagation in the Sun's subphotospheric layers. A finite-difference code is used to calculate the pressure perturbation in the frequency domain. We show that the oscillatory seismic signals are closely associated with the solar density and sound speed structures. Owing to the acousti…
Search for a chromospheric resonator above sunspots
Kjeldseth-Moe, O.; Brekke, P.; Brynildsen, N. +2 more
We have recently observed thirteen sunspots, both with CDS on SOHO and TRACE. For each sunspot we investigate the oscillations in the chromosphere, transition region and corona. Above the umbra the power spectra show one dominant peak corresponding to a period of 3 minutes. The intensity oscillation amplitude increases with increasing temperature,…
Circumnuclear Structures in the Interacting Seyfert Galaxy NGC 1241: Kinematics and Optical/Infrared Morphology
Díaz, Rubén J.; Dottori, Horacio; Vera-Villamizar, Nelson +1 more
We studied the spiral pattern in the inner 6.5" (1''=257 pc) central regions of the interacting active nucleus galaxy NGC 1241 using Gemini North Telescope high-resolution Ks- and J-band images and Hubble Space Telescope (HST) Paα and H- and (V+R)-band images with high resolution in the range from ~0.1" to ~0.3" along with in…
Searching for Variable Stars in the Central Part of the Globular Cluster M22
Pietrukowicz, P.; Kaluzny, J.
Time-series data taken with the Hubble Space Telescope of three fields covering the central part of the globular cluster M22 have been analyzed in search of variable objects. We report identification of eleven periodic variables of which eight are new discoveries. The sample includes five certain contact binaries as well as one SX Phe star. Two ob…
Cosmic Gravitational Shear from the Hubble Space Telescope Medium Deep Survey
Casertano, Stefano; Griffiths, Richard E.; Ratnatunga, Kavan U.
We present a measurement of cosmic shear on scales ranging from 10" to 2' in 347 Wide Field Planetary Camera 2 (WFPC2) images of random fields. Our result is based on shapes measured via image fitting and on a simple statistical technique; careful calibration of each step allows us to quantify our systematic uncertainties and to measure the cosmic…
X-ray facility for the ground calibration of the X-ray monitor JEM-X on board INTEGRAL
Frontera, F.; Westergaard, N. J.; Lund, N. +12 more
We describe the X-ray facility developed for the calibration of the X-ray monitor JEM-X on board the INTEGRAL satellite. The apparatus allowed the scanning of the detector geometric area with a pencil beam of desired energy over the major part of the passband of the instrument. The monochromatic radiation is obtained with the use of a double cryst…
Free-Free Emission in the Far-Ultraviolet Spectral Range: A Resource for Diagnosing Solar and Stellar Flare Plasmas
Curdt, W.; Landi, E.; Doschek, G. A. +2 more
We report the detection of free-free (bremsstrahlung) emission near 1200 Å from a flare at the solar limb observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The observations consist of a time series of slit spectra at a fixed pointing that lasted a…
The sensitivity of the seismic solar model to Newton's constant
Silk, Joseph; Lopes, Ilídio P.
New experimental determinations of Newton's gravitational constant have been recently given. There are significant disagreements between these new measurements. We show that the high accuracy obtained with current standard solar models is such that the uncertainties in core temperature profiles arising from the uncertainties in G can be comparable…