On the design of wide-field x-ray telescopes
X-ray telescopes having a relatively wide field-of-view and spatial resolution vs. polar off-axis angle curves much flatter than the parabolic dependence characteristic of Wolter I designs are of great interest for surveys of the X-ray sky and potentially for study of the Sun's X-ray emission. We discuss the various considerations affecting the design of such telescopes, including the possible use of polynomial mirror surface prescriptions, a method of optimizing the polynomial coefficients, scaling laws for mirror segment length vs. intersection radius, the loss of on-axis spatial resolution, and the positioning of focal plane detectors.
Wide-field x-ray imaging for future missions, including XEUS
It is well known that the Wolter I design for focusing X-ray telescopes provides perfect on-axis images, while, despite the absence of spherical aberration, the off-axis angular resolution rapidly degrades because of coma, field curvature and astigmatism. However, more general mirror designs than Wolter's exist in which primary and secondary mirror profiles can be described by polynomial equations. These power series solutions are particularly well indicated to be optimized, in order to achieve high imaging performances even at large off-axis incidence angles, despite a small degradation of the on-axis response. The concept, derived from the Ritchey-Chretien telescope widely used in optical astronomy, has already been experimentally proven for X-ray astronomical applications at the Brera Astronomical Observatory (Italy), in the context of the feasibility study of the Wide Field X-ray Telescope mission. Here we present a new design (including a model for slope errors and mechanical tolerances) for a X-ray telescope of medium-size class assuming monolithic mirror shells made of glass, optimized to have a Half Energy Width better than 5 arcsec over a 30 arcmin field of view (radius) and an effective area almost twice that one of Chandra. The use of polynomial mirrors seems extremely well suited also for the case of the XEUS optics. Indeed, the small aspect-ratio between the large focal length of the XEUS telescope (50 m) and the total mirror height (1 m) makes it very favorable to diminish the aberration effects due to the field curvature. With the assumption of mirror shells with polynomial profile it would be possible to achieve for XEUS an imaging response almost constant up to a field of view of 20 arcmin in radius.
Fragment Rotational State Distributions From The Dissociation Of NeIBr: Experimental And Theoretical Results
The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump–probe laser‐induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I–Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5±1.2 cm−1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8±1.2 cm−1. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck–Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calc...