Marc D. Rafal

Long wavelength scattered light halos in ACS CCDs

During the ground calibration of the Space Telescope Imaging Spectrograph (STIS) large scattered light haloes were identified in images of point sources and long slit spectral images at long wavelengths (greater than 750 nm). The long wavelength scattering was traced to the SITe 1024 X 1024 CCD and its header package, raising concerns for the performance of the Advanced Camera for Surveys (ACS) CCD detectors. ACS is a third generation axial instrument for the Hubble Space Telescope (HST) and will be installed during the 1999 Servicing Mission. Two of the ACS imaging channels employ SITe CCDs, so the ACS team have conducted a study of the long- wavelength scattering, in collaboration with SITe, to assess the impact to the ACS science program and develop a solution. In this paper we discuss our solution, its implementation on ACS CCDs, and describe the results of initial tests.

Optical Ranicon detectors for photon counting imaging. I

We discuss the design and development of Ranicon detectors for optical photon counting imaging on ground‐based telescopes. The significant factors which determine the performance of these detectors are found to be the proximity focusing stage, the microchannel‐plate stack (MCP), and the signal processing electronics. For applications in optical astronomy, the low photon counting efficiency typically found with optical MCP‐based detectors, due to ion barrier films, presents an additional consideration. We review the performance of each stage of the Ranicon detector and the techniques for achieving optimal performance. A new approach to the signal processing electronics reduces nonlinearity, while achieving increased processing speeds and a position error corresponding to <21 μm FWHM. A significant improvement in detector performance is achieved with an advanced Ranicon incorporating a reduced proximity focusing gap and an unfilmed input plate in the MCP stack. The theoretical spatial resolution of both sta...

Advanced camera for surveys

The Advanced Camera for Surveys (ACS) is a third generation instrument for the Hubble Space Telescope (HST). It is currently planned for installation in HST during the fourth servicing mission in Summer 2001. The ACS will have three cameras.

Thermal design for the Advanced Camera for Surveys

The advanced camera for surveys (ACS) is a third generation science instrument scheduled for installation into the Hubble Space Telescope (HST) during the third servicing mission scheduled for 1999. ACS, along with the previously installed space telescope imaging spectrograph and near IR camera/multi-object spectrograph, consume significantly more power than the first generation of instruments. Additionally, the larger apertures of these instruments make parallel operations scientifically exciting. These parallel operations demand that all of the instruments operate in their highest power states simultaneously for extended periods of time. These and other factors have resulted in much higher temperatures inside the aft shroud where the ACS will be installed. As a result, new approaches are required to transfer heat inside the instrument and reject it away from the telescope. This paper describes the unique thermal systems required by the ACS. These include capillary pump loops and flexible and rigid heat pipes.

Hybrid analog/digital, large format, photon counting detectors for astronomy

The development of a new microchannel plate, photon counting detector with an analogue readout method based on a resistive anode is reported. This detector exhibits extremely high, stable electron gains of 108. At this gain, the spatial resolution is no longer primarily limited by the noise of the resistive anode so that digital methods of readout, such as discrete conductors, lose their advantage. These detectors can be readily scaled to 40mm and 70mm formats to match plate scales of 2 meter and larger telescopes. New, high speed digital electronics are described which replace older analogue methods and which fully exploit the high spatial and time resolution made possible by gains of this level. Analysis of the theoretical performance of this detector is performed and shows that the major limitation to the spatial resolution is the proximity focus of the photocathode and the first microchannel plate. The detector has been mated to an echelle spectrograph developed at the University of Michigan for installation on the new 2.4m facility at McGraw-Hill.

High-temporal-resolution imaging and spectroscopy with Ranicon detectors

A data-collection system for use in astronomical observations with the resistive-anode detectors (Ranicons) described by Paresce et al. (1979 and 1988) is briefly characterized. Analog signals from the Ranicon pass through 12-bit A/D converters and (along with time information from a digital clock) into a 64-bit FIFO buffer, and the photon positions are calculated by a high-speed arithmetic-logic system capable of an event rate of 30 kHz (so that, by Poisson statistics, only about 21 percent of events will be missed). Results from successful timing tests of the system on the 2.2-m telescope at ESO are presented graphically.