FUSE Archival Instrument Handbook

Figure 2‑2: Exploded view of the FUSE instrument structure. This figure illustrates the relationship between the photograph of the assembled, flight-ready, FUSE instrument in the previous figure and the schematic of the optical layout of the telescope and spectrograph

Figure 2‑3: Schematic of the LiF1 and SiC1 FPAs shown relative to the instrument optical design and beam size (top), with a detail of the FPAs and their relationship to the Rowland Circle and the IPCS coordinate system (bottom). In the LiF channel, light from the star field in the vicinity of the target is reflected into an FES camera

Figure 2‑4: The locations of the FUSE apertures projected on the sky for a slit position angle of 0° with North in the -Y direction. Positive aperture position angles correspond to a counter-clockwise rotation of the apertures on the sky. In the FPA coordinate system the LWRS, HIRS, and MDRS apertures are centered at Y= -118.07”, -10.27”, and +90.18”, respectively. This diagram represents only a portion of the FPA; the full active area is ~19arcmin Î 19 arcmin

Figure 2‑5: Photograph of the FUVS in a clean room at University of Colorado Boulder just prior to shipment to Johns Hopkins University, with the major optical components identified

Figure 2‑6: Wavelength coverage, dispersion directions, and image locations for the FUSE detectors. In this figure, the coordinate system as used for the detectors is shown, where X is the dispersion direction

Figure 2‑7:The astigmatic height of the FUSE spectra are shown in these figures. The units of both axes for both the top and bottom figures are detector elements, or pixels

Figure 2‑8: Molecular hydrogen emission spectrum recorded by detector 1B. This figure shows the full extent of the segment in the Y direction (1024 pixels) but only a very small extent in X (1000 pixels or about 6 Å). This image was constructed by adding together 6 different images, each made with the lamp source illuminating an individual aperture. From the top to the bottom of the image, the spectra are LiF (MDRS aperture), LIF (HIRS aperture), LiF (LWRS aperture), SiC (MDRS aperture), SiC (HIRS aperture), and SiC (LWRS aperture). The pinholes were not illuminated. The LiF spectra are centered at ~1160 Å while the SiC spectra are centered at ~930 Å

Figure 2‑9: Drawing showing the light path inside the FES

Figure 2‑10: Diagram of an FES-A image with its different coordinate frames. The raw FES CCD coordinates are (X_FES, Y_FES) with its origin at the lower left corner of the image. The FES IPCS coordinates as projected onto the sky are (X_IPCS, Y_IPCS) with its origin located below the HIRS aperture. The exact location and size of the three apertures are not on scale

Figure 3‑1: ACS coordinate frames. Red: original, Green: revised for magnetic control system

Figure 4‑1: The log of the count rate, normalized to unity, is shown plotted as a function of the X-position of a point-source image relative to the center of the HIRS aperture in each channel. This is equivalent to the convolution of the telescope PSF with the HIRS aperture.

Figure 4‑2: Same as Figure 4 1 above, but for the MDRS aperture

Figure 4‑3: Same as Figure 4 1 above, but for the LWRS aperture

Figure 4‑4: Peakup scans over 5 successive orbits for observation P203:04:01. The count rates as a function of scan step are shown in different colors; the first scan of the observation is plotted in black and shows the largest channel alignment errors. FPA adjustments required in subsequent orbits were much smaller

Figure 4‑5: Spectral resolution measured from ISM absorption lines along the line of sight to K1-16.

Figure 4‑6:Spectral resolution measured from ISM absorption lines along the line of sight to RX J2117+3412.

Figure 4‑7: The in-flight derived effective area as a function of wavelength for each detector segment. Each curve for a given detector segment represents a snapshot of the effective area as a function of time and wavelength. The family of curves for each segment represents the degradation of the effective area over the eight year on-orbit lifetime of the mission

Figure 4‑8: Spectral images of a stellar spectrum obtained in the LiF1 channel for each aperture are plotted for detector segment 1A. The grey scale is inverted, so that regions of high count rate appear dark. The narrow vertical lines are absorption features arising from interstellar gas, primarily H2. The broad horizontal stripes are shadows cast by the detector QE grid wires, aka the "worms".

Figure 4‑9: As in Figure 4-8 above, but for LiF1B. Note the strong worm feature in the LWRS spectral image.

Figure 4‑10: As in Figure 4-8 above, but for LiF2A. In addition to the worm features present in each spectral image, faint single-pixel-wide horizontal moire patterns are evident, which are an artifact of the distortion corrections.

Figure 4‑11: As in Figure 4-8 above, but for LiF2B.

Figure 4‑12: As in Figure 4-8 above, but for SiC1A.

Figure 4‑13: As in Figure 4-8 above, but for SiC1B.

Figure 4‑14: As in Figure 4-8 above, but for SiC2A.

Figure 4‑15: As in Figure 4-8 above, but for SiC2B. Worms are weak or not present. The very thin white jagged line running across the MDRS spectral image is an artifact from the distortion correction; some residual vertical distortion is present in the HIRS and MDRS spectral images beyond pixel 12000.

Figure 4‑16: For a single observation (S505702) the position of the LiF1A Lyman-β airglow line on the detector is shown as a function of time. Each point represents the average position on the detector of ~500 consecutive airglow photons.

Figure 4‑17: The same data as in Figure 4‑16 is shown both before (top panel) and after (bottom panel) the CalFUSE grating motion correction is applied

Figure 4‑18: A binned portion of detector segment 1B illuminated in flight by the stim lamp, using just photons with pulse heights of (a) 2, (b) 4, (c) 8, and (d) 16. The x range covers 1200 pixels, while y includes the full height of the detector. The shadows of the two sets of grid wires are clearly seen in the vertical direction, but because of the binning in y, the horizontal wires are difficult to see. It is obvious from comparing these figures that there is an apparent shift in the position of the grid wires as a function of pulse height. The dark horizontal bands show regions where a large amount of exposure has caused gain variations.

Figure 4‑19: A small portion of a LiF spectrum on segment 1A, showing the same data both with and without the CalFUSE walk correction applied; the two spectra are offset in the y axis by an arbitrary amount so that the differences can be seen more easily. The walk-corrected spectrum has a different wavelength scale and shows higher resolving power

Figure 4‑20: Gain sag on detector segment 1A. The mean pulse height is shown as a function of X pixel at two Y locations on the detector: at the LiF LWRS spectrum location (solid line) and in a background region (dotted line) in September 2000 (exposure M9980101001 - red) and in September 2007 (M9986701001 - green). The gain of the background region increased substantially during the mission due to the increases in high voltage, and remained fairly flat as a function of x pixel. The LiF1 LWRS region, however, shows a significant gain variation as a function of x. The gain sag at Lyman-β (x ≈ 7000) is especially obvious

Figure 4‑21: An example of the count rate as a function of time during an event burst showing a high-frequency component is 10 seconds. The size, spatial distribution, and temporal profile of the bursts varied significantly during the mission

Figure 4‑22: A portion of one detector showing an example of a scalloped burst

Figure 4‑23: An example of a very large checkerboard burst on Segment 1A, shown in FARF coordinates. Note that the checkerboard pattern is distorted, while the spectrum remains undistorted

Figure 4‑24: Segment 2A with a high detector background

Figure 4‑25: Segment 2B with a high detector background

Figure 4‑26: Temperatures measured by two of the detector thermistors during a two day period beginning on 29 August 2002 (MJD 52515), along with the high voltage on detector segment 1A at the same time. These data are taken from the engineering snapshots, and therefore are only collected during science exposures. The orbital variation of the ~1º C of the temperatures is seen, superimposed on longer-term variations, such as that due to the high voltage dropping to zero at ~1.2 days

Figure 4‑27: The X shift (shift of the mean position of the two stims) and stretch (change in separation between the two stim pulses) on segment 1A, measured from the stim pulses for the same time period shown in Figure 4‑13. Large changes in both shift and stretch are seen when the high voltage shuts down

Figure 4‑28: A small section of a flat field taken before launch. This region covers 950 x 150 pixels of a single segment. The hexagonal multifiber bundles are visible, as are some brush marks and dead spots on the left side of the image. This image contains ~100 counts per pixel

Figure 4‑29: This small section of a segment 2B ground flat shows the most prominent Moiré pattern, visible as the nearly vertical ripples running across the image. The ripples have a peak-to-peak amplitude of +/-15% and a period of ~9 pixels in X (~54 microns or ~1.5 resolution elements)

Figure 4‑30: An isolated Type I dead zone on segment 1A is shown. This dead spot is not completely black at the center, but the sensitivity is down by a factor of ~4 from the surrounding region

Figure 4‑31: An isolated Type II dead zone on segment 1A is shown. Note the bright outer rim. The spot is located at (X, Y) = (10515, 530), and it has a diameter of 40 pixels in X and 25 in Y (~250 microns). The Y1=Y2 feature is also prominent

Figure 4‑32: Y projection of the normalized counts in a segment 2B stim lamp image for pulse heights 24 to 31. At a pulse height of 24 or below, all Y pixels in the active region have counts. For pulse heights above 24, however, counts are discarded symmetrically about pixel 512. Note that the shape of each projection is determined by the gain of the segment as a function of position

Figure 4‑33: Raw data from the far right edge of segment 1A in a stim lamp exposure. Counts that should have been lost beyond the active area to the right are instead folded back into the active region

Figure 4‑34: FES-A 1 × 1 image (A1080201001fesafraw.fit) of the field of view in the direction of the globular cluster NGC 6723

Figure 4‑35: FES intensities (top) and positional errors (bottom) compared with HST GSC values

Figure 4‑36: A raw image from FES-A with a high level of scattered light is shown. The dark border seen on all sides is the aperture mask. The spectrograph apertures are visible: MDRS, HIRS, and LWRS in order from left to right. Light scattered by the edges of the HIRS aperture cause it to appear bright in this image. The dimpled region surrounding the apertures is an artifact of the manufacture of the FPA mirrors. The feature centered at X=97, Y=344, that appears somewhat oblong is a glint caused by a defect in the FPA surface. It extends roughly +/-5 pixels along either axis, and may move +/-5 pixels in the vertical direction, depending on the FPA position. There are a few other defects on the LiF1 FPA, but they are small and are rarely seen.

Figure 4‑37: A raw FES-B image with a high level of scattered light is shown. The dark border seen on three sides is the aperture mask. The spectrograph apertures are visible: LWRS, HIRS,MDRS in order from left to right. Light scattered by edges of HIRS make it appear bright in this image. The dimpled region surrounding the apertures is an artifact of the manufacture of the FPA mirrors. A long scratch in the FPA is visible on the left side of the image.

Figure 6‑1 Left: FUSE mirror resting face-up on flexures prior to integration into the mirror assembly. Right: Backside of the FUSE primary mirror illustrating the aggressive lightweighting of the Zerodur mirror substrate

Figure 6‑2: Face-on view of mirror actuator assembly showing the three actuators and composite structure

Figure 6‑3: Left: Dummy aluminum mirror with actuator assembly (ref Ohl). Right: Full flight mirror assembly, including pie-pan thermal enclosure and aperture stop. 98

Figure 6‑4: The actuator locations relative to the mirrors and the IPCS coordinate frame

Figure 6‑5: Expanded view of the detector stack mounting in the FUSE detector. The QE grid is held by the frame at the top, and the curved MCPs are mounted to a cylindrical surface to match the Rowland circle

Figure 6‑6: A FUSE detector Vacuum Assembly mounted to the detector mounting bracket in the spectrograph cavity. The door assembly is at the top, with the light baffle protruding. Two ion pumps are visible at the front right, and the high voltage filter module, charge amplifiers, and timing amplifiers are visible behind them. The ladder-like structures at the top on either side of the detector are spectrograph baffles.

Figure 6‑7: Electronics Assembly and Stim Lamp Assembly of the spare detector

Figure 6‑8: Block diagram of the encoding electronics for the FUSE detectors

Figure 6‑9: Functional Block Diagram of the Detector Electronics Assembly (hardware and software)

Figure 6‑10: Detector X shift, as measured by the change in position of the stim pulses, for all four segments during the mission. Long term trends appear to dominate short term temperature effects, particularly on segments 1B and 2B

Figure 6‑11: Positions of SEUs during the mission. The dashed line shows the SAA region used by Mission Planning after 17 September 2003. No events occur below -25º due to the orbit of the satellite

Figure 6‑12: HVIA, HVIB, and AUXI during a crackle

Figure 6‑13: Number of crackles and mini-crackles vs. time

Figure 6‑14: Orbital Dependency of Image Motion for Selected Targets

Figure 6‑15: xy alignment scans as depicted using the Alignment Tool Graphical Analysis. These data are discussed in Section 6.7.4

Figure 6‑16: Example of Channel Alignment Tool (ChAT) Results

Figure 6‑17: (Revised) One Wheel Mode Alignment Scan Pattern

Figure 6‑18: One Wheel Mode Alignment Scan Pattern Results

Figure 6‑19: Additional ChAT Sample Results

Figure 6‑20: Time series of individual mirror motions executed to maintain co-alignment of the LiF channels

Figure 6‑21: Time series of individual mirror motions executed to maintain co-alignment of the SiC channels

Figure 6‑22: The range of motion for each of the Lif1 (top) and LiF2 (bottom) mirrors illustrating that although to co-alignment position for each actuator exhibits a secular drift with time, this change is small and well within the range of travel for each of the actuators

Figure 6‑23: The range of motion for each of the SiC1 and SiC2 mirror actuators

Figure 6‑24: LiF2B data over an orbital period illustrating that the spectral motion observed with the GMA shroud at 19 C (top) is shifted/offset by ~5-6 pixels from the data acquired with the GMA shroud at the nominal 23 C (bottom)

Figure 6‑25: Optical element layout for LiF1, SiC1 channels

Figure 6‑26: Optical element layout for LiF2, SiC2 channels

Figure 6‑27: Optical element layout, top view

Figure 6‑28: Line drawing of an FPA mechanism, showing the two-axis stage and aperture plate

Figure 6‑29: Details of optics layout at detector surfaces

Figure 6‑30: Positions of optical elements

Figure 6‑31: Side views of instrument, showing the structure, optics, baffles, electronics, and radiators. Left: Y-Z view, Right: X-Z view

Figure 6‑32: Section views of a primary mirror. Top: "pie-pan" enclosure, intermediate plate and bench are shown, with positions of the actuators. Bottom: mirror dimensions and vertex position are shown

Figure 6‑33: Close-up view of light paths at the FPA-FES interface

Figure 6‑34: A section view of a grating mount assembly and grating are shown

Figure 6‑35: Functional block diagram showing the flow of events through the detector electronics (1 of 2). Counts incident on the detector can be lost (1) at the digitizer; (2) due to counts falling outside the Active Image Mask; and (3) in the Round Robin, which combines the data from two segments on one detector. 169

Figure 6‑36: Functional block diagram showing the flow of events through the detector electronics (2 of 2). Counts can be lost (4) in the IDS if the count rate is above 32,000 cps (HIST only); (5) due to screening by the SIA table (HIST only); (6) in the IDS if the count rate is above 8,000 cps (TTAG); (7) if the FIFO fills (TTAG); or between the spacecraft and the ground system

Figure 6‑37: Apparent count rate as a function of time for exposure Q11401001, which was obtained in TTAG mode, despite having a count rate of more than 100,000 counts per second. For the first ~520 seconds the count rates on all four segments were constant, with their sum limited to the 8,000 cps TTAG data bus limit. For the remainder of the exposure, regular data dropouts appeared as the FIFO filled

Figure 6‑38: Detector dead time performance

Figure 6‑39: Updated live-time calibration curves.

Figure 8‑1: This typical FUSE guide star plot shows the usable guide stars and aperture positions. The pixel coordinate scale is for FES-A. The orientation of North and East is shown in the lower left corner

Table of Tables

Table 2.2‑1: FUSE Instrument Specifications; Channel 1

Table 2.2‑2: FUSE Instrument Specifications – Channel 2

Table 2.4‑1: Apertures

Table 2.4‑2 FPA locations and pointing offsets for a typical FP-split pattern

Table 2.5‑1: Spectrograph and Grating Properties

Table 2.5‑2: Wavelength Ranges for Detector Segments

Table 2.6‑1: Detector Specifications

Table 2.7‑1: FES Camera Characteristics

Table 2.7‑2: FES CCD Characteristics

Table 2.7‑3: Center Positions of the Three Apertures and the Reference Point in FES-A and FES-B 1 × 1-binned Images

Table 4.3‑1: Spectral resolving power of the FUSE instrument with the low resolution, LWRS, aperture. These initial numbers were based on the channel with the best resolution performance at the specified wavelength. At the shortest wavelengths SiC2 has higher resolution than SiC1, and at the longest wavelengths the LiF1 spectral resolution is superior to LiF2

Table 4.3‑2: Summary of worms identified in the FUSE data

Table 4.4‑1: Default high voltage values used during the mission

Table 4.4‑2: ASC thresholds used during normal operations

Table 6.1‑1: FUSE Mirror Properties

Table 6.2‑1: History of FPA Z-axis motions. The first three columns give the observation ID, date, and start time for the observation immediately following a change in FPA Z position

Table 6.3‑1: Detector Specifications

Table 6.3‑2: Detector 1 Thermistors

Table 6.3‑3: Summary of detector mask changes during the mission

Table 6.3‑4: Detector masks and counters

Table 6.3‑5: Selected DPU Diagnostic Codes

Table 6.3‑6: DPU code versions used during normal operations. Different values were used during stim lamp exposures

Table 6.3‑7: SiC HIRS SIA Tables used during the mission

Table 6.3‑8: SiC MDRS SIA Tables used during the mission

Table 6.3‑9: SiC LWRS SIA Tables used during the mission

Table 6.3‑10: LiF HIRS SIA Tables used during the mission

Table 6.3‑11: LiF MDRS SIA Tables used during the mission

Table 6.3‑12: LiF LWRS SIA Tables used during the mission

Table 6.3‑13: SEUs by detector and memory core

Table 6.3‑14: Number of mini-crackles and crackles during the mission. The values in parentheses are the diagnostic value (in hex) issued by the detector

Table 6.6‑1: Initial in-flight telescope focus adjustments made November 23, 1999. Adjustments in the focus (Z) direction are limited to 10 micron increments of the FPAs. Small residual errors account for the slight departures from integral 10 micron changes in the adjustment values above. The true uncertainty in the magnitude of the computed focus adjustment was at least 30 microns

Table 6.6‑2: Spectrograph focus adjustments executed on December 12^th, 1999 as a result of the I817 post-launch programs

Table 6.6‑3: Spectrograph focus adjustments executed as a result of the I817 and I819 post-launch programs. The spectrograph focus adjustments implemented March 16^th, 2000, were used for nominal operations for the remainder of the FUSE mission

Table 7.2‑1: IRU (gyro) Chronology of Events

Table 7.3‑1: FUSE Reaction Wheel events

Table 8.2‑1: Optical distortion coefficients for FES-A

Table 8.2‑2: Optical distortion coefficients for FES-B

Table 8.2‑3: Reference Point positions in corrected pixel coordinates

Table 9.2‑1: Airglow emission lines seen during orbital day when looking up

Table 9.2‑2: Strongest airglow emission lines seen looking down during orbital day. 189

Table 10.1‑1: FUSE development and operations personnel