Philip E. Hodge

Point-spread function modeling for the James Webb Space Telescope

We describe software which models the Point Spread Function of the James Webb Space Telescope. The software is designed to be expandable to incorporate optical and instrument data as they become available. An initial model of the detector used in the Near Infra-red Camera has been used to generate realistic stellar images.

First year of STIS on-orbit calibration and science observing

This paper provides a high level summary of STIS, the space telescope imaging spectrograph, and describes the principle hurdles overcome during the servicing mission orbital verification in order to bring STIS to operational status as HSTs optical and UV spectrograph. Also described are the approach taken to develop STIS for effective GO use and the approach taken to the on-orbit calibration of this complex and capable instrument. Lastly, we provide a description of the current operational and calibration status of STIS, including many recent results. STIS is performing extremely well as a science instrument. Monitoring projections suggest it should continue to operate effectively throughout its projected 13 year mission, barring unforeseen effects or complications.

In-flight performance of the faint object camera of the Hubble Space Telescope

An overview of the Faint Object Camera and its performance to date is presented. In particular, the detectors efficiency, the spatial uniformity of response, distortion characteristics, detector and sky background, detector linearity, spectrography, and operation are discussed. The effect of the severe spherical aberration of the telescopes primary mirror on the cameras point spread function is reviewed, as well as the impact it has on the cameras general performance. The scientific implications of the performance and the spherical aberration are outlined, with emphasis on possible remedies for spherical aberration, hardware remedies, and stellar population studies.

The COS FUV channel: on-orbit performance trends and early characterization of a new detector lifetime position

The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope in May 2009, and has been collecting ultraviolet spectra since then. The Far Ultraviolet channel of COS uses an efficient optical design and a two-segment, large-format Cross Delay Line microchannel plate detector to obtain spectra at medium and low resolution in the far ultraviolet. While the overall instrument performance has been excellent, several long-term trends in performance have been noted and are being addressed. These include a slow decrease in overall sensitivity, which is independent of the illumination and may be due to a degradation of the photocathode with time. In addition, the detector microchannel plates are showing severe gain sag in the regions where the most photons have fallen. As a result, we are in the process of moving the spectra to a new, nearly pristine, location on the detector. This will be the first of several additional lifetime positions which will allow us to collect high-quality spectra for many years to come. We will discuss the factors that led to our decision on where to move next and our progress in moving there, including details of the enabling and calibration activities which are being performed at the new location, and the anticipated performance. We will also address strategies that will be implemented in order to prolong the life at this and subsequent positions.

Characterization, modeling, and management of the COS FUV detector lifetime

The Far Ultraviolet (FUV) detector of the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) uses a large-format, two-segment microchannel plate detector with a Cross Delay-Line anode. Since the installation of COS into HST in 2009, the detector’s properties have continually evolved, and changes to both sensitivity and microchannel plate gain have been observed. In order to maximize the lifetime of the detector, we have been monitoring its local properties as a function of time, cumulative exposure, and other factors, and we have constructed models to predict its future evolution. These models will allow us to actively manage the microchannel plate high voltage levels and the location of the spectra on the detector in order to extend its life without limiting its scientific use. We are also tracking the global sensitivity of the detector, which has been decreasing since installation; the rate of degradation has been found to vary with time, and appears to be correlated with solar activity.

The COS calibration pipeline and verification process

The Cosmic Origins Spectrograph,1 COS, will be installed in the Hubble Space Telescope (HST) during the next servicing mission. This will be the most sensitive ultraviolet spectrograph ever flown aboard the HST. The calibration pipeline (CALCOS), written in Python, has been developed by the Space Telescope Science Institute (STScI) to support the calibration of HST/COS data. As with other HST pipelines, CALCOS uses an association table to specify the data files to be included, and employs header keywords to specify the calibration steps to be performed and the reference files to be used. CALCOS is designed with a common underlying structure for processing far ultraviolet (FUV) and near ultraviolet (NUV) channels which, respectively, use a cross delay line and a Multi Anode Microchannel Array (MAMA) detector. The pipeline basics and channel dependent specifics are presented. The generation and application of the current reference files, derived from ground-based calibration data, is described, along with the pipeline verification process and results. The CALCOS calibration includes pulse-height filtering and geometric correction for the FUV channel; flat-field, deadtime, and Doppler correction for both channels. Methods for obtaining an accurate wavelength calibra-tion using the on-board spectral line lamp are described. The instrument sensitivity is applied to the background corrected spectrum to produce the final flux calibrated spectrum.

In-flight performance of the Faint Object Camera of the Hubble Space Telescope: III

This paper gives an update on the performance of the faint object camera following the highly successful installation of the corrective optics in COSTAR during the servicing mission. We review the effect that COSTAR has had on the point spread function and detector quantum efficiency, and discuss the improvements in our knowledge of sensitivity, PSF variations, camera distortion, and nonlinearity. The status of the f/48 relay, which has been successfully turned on a number of times, is reviewed.