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Chapter 5
Ancillary Files

This section describes additional data files available from the FUSE archive that can be used to support the analysis and understanding of FUSE data. Some of these data files were used by CalFUSE to produce the calibrated data products, and others contain information which can be used to verify the pointing, performance, or status of the satellite or instrument during data acquisition.

This chapter contains information potentially useful to the "Advanced" and "Intermediate" users. However its contents are not of immediate relevance to the "Casual" user. The file naming convention used throughout this chapter has been described in Section 4.1.2.

5.1 FES Image Files (*, *

Two nearly identical Fine Error Sensor (FES) cameras were available on FUSE. FES A was prime for most of the mission, and observed the LiF1A FPA. FES B became prime on 12 July 2005 and was used for the remainder of the mission. It observed the LiF2A FPA. Because the two cameras are on opposite sides of the instrument, the astronomical orientation in the images will appear flipped with respect to each other. Referring to the guide star plots for a given observation will provide confirmation of the expected astronomical orientation and star field expected for a given target (see Section 5.6 below).

An image from the active FES camera was routinely acquired at the end of an observation to allow verification of the pointing of the spacecraft. Depending on the phase 2 observing proposal instructions provided by the user, this FES image would be obtained either with the target in the observing aperture or at the reference point (55.18 " from the HIRS aperture, displaced towards the center of the FES field of view; see Fig. 2.2). By convention, this exposure always has exposure ID 701, which is used to distinguish this image from acquisition images.

Other FES images were obtained throughout each observation during the initial guide star acquisition and subsequent reacquisitions (usually after the target had been occulted). These images are also stored and are available to the observer, although the target may be offset or even absent in these images (e.g. if the target had drifted during occultation, etc.). These images have observation IDs and exposure IDs identical to the those used for the associated (usually directly following) FUV exposure. After the gyroless target acquisition software was loaded, it was routine to obtain multiple images during each acquisition, and also during reacquisitions resulting from loss of pointing stability. Each of the resulting images is stored in a separate extension in the FITS file. For most users, the final "end-of-observation" FES image (exposure 701) will be the only image of interest.

The active image area of the FES CCD images was 512 × 512 pixels, with pixel size of 2.55″. An unbinned image has 8 rows and 8 columns of overscan, resulting in a 520 × 520 raw image. These are the sizes for the FES images obtained at the end of each exposure. Binned images also have binned overscan, so a 2 × 2 binned image will have size 260 × 260 pixels. After the gyroless target acquisition software was loaded, 4 × 4 binned images were routinely obtained during acquisitions in addition to 2 × binned images, resulting in a size of 130 × 130 pixels.

The raw data (* files) are stored as unsigned integers in FITS extensions. The calibrated FES images (* images) are processed by stripping the overscan areas, and subtracting the bias level. Distortion maps of each FES camera were made and used onboard by the guidance system, but distortion corrections were not part of the calibration pipeline process, and so the calibrated images have not had this correction applied. Distortions are generally small, however. The calibrated data values are 4-byte floating-point numbers.

Figure 5.1 shows an example of a 512 × 512 FES A image. Note that the apertures are near the top of the image along the line defined by Y_FES = 399 (see Table 5.2. Once again, users will find the guide star plots (see Section 5.6) useful for verifying the astronomical orientation expected for a given observation.

The contents of an FES file are listed in Table 5.1 and the locations of the apertures in pixels coordinates are listed in Table 5.2 for both FES A and B at the nominal LiF FPA positions. Details of the distortion corrections and the conversion of FES pixel coordinates to sky coordinates are provided in Section 8 of the FUSE Instrument Handbook (2009).

Figure 5.1: A calibrated FES A image for exposure P1171901701. In this case, there is significant scattered light on the FPA, so that the apertures are visible (see Table 5.2), along with a few stars. (The distorted region around the apertures is an artifact of the manufacturing process.) Note that the colors are reversed in this image so that bright objects appear as black points.
\epsfig{figure=figs/FESA_reverse.eps, width=0.7\linewidth}

Table 5.1: Formats of Raw and Calibrated FES Image Filesa
FITS Extension Format Description
HDU 1: Empty (Header only)
HDU 2: FES Imagea
a Image size can be either 520 × 520, 260 × 260 or 130 × 130.

Table 5.2: Aperture Centers (1 × 1 binning)
MDRS 207 399 292 426
HIRS 247 399 252 425
LWRS 289 399 209 425

5.2 Time-Resolved Engineering Files (*,

Jitter Files (* At launch, the pointing stability of FUSE was approximately 0.3″ in the science X and Y axes. Since this is considerably smaller than the instrumental PSF, guiding performance was not an issue for observing. However, as the mission progressed, problems with the Attitude Control System (see Table 2.3) required magnetic torquer bars and magnetometers be used to help control the pointing. The ability of the torquer bars to stabilize the spacecraft depended on their orientation relative to the direction of the instantaneous Earth's magnetic field, which was a function of orbital position. As a result, large, rapid pointing deviations caused by temporary loss of pointing control could cause the target to move about in the aperture or leave it completely for part of an exposure. Figure 5.2 and 5.3 show examples of pointing performance and its effects on the FUSE count rates.

Figure 5.2: FUSE pointing in 1 second intervals for an exposure scheduled with stable pointing (left) and one with unstable pointing (right). For the former case, loops outside of the LWRS aperture occur while settling during the target acquisition. The target remains well-centered for the exposure. For the case with unstable pointing, excursions can take the target out of the aperture, but the target returns when pointing control is regained.

Figure 5.3: The time series of LiF2 count rates and pointing errors for the exposures shown in Fig. 5.2. For the one with stable pointing (left), the target remains well within the aperture and the count rate is constant during the exposure. For the other, when control becomes unstable, photons are lost when the target is out of the aperture (right).

The orientation of the telescope is described by a four-element quaternion. The spacecraft produced two sets of pointing estimates. The first was derived from the measured positions of two to six guide stars; these are referred to as the FPD (for Fine Pointing Data) quaternions. The second combines guide-star data with data from the gyroscopes and magnetometers. Since they are generated by the onboard ACS (Attitude Control System) computer, they are referred to as the ACS quaternions, although the former are not always available. The guide stars are generally more accurate than the gyroscopes and magnetometers, so the FPD quaternions are generally more accurate than the ACS estimates. The commanded quaternions for the target can be found from the telemetry stream or computed from the RA and DEC in the FITS file header (see the Instrument Handbook 2009, for more details).

The jitter data files contain time-resolved data of the spacecraft pointing relative to the commanded pointing and are used by CalFUSE to correct for these effects. These data are derived from the housekeeping files. This file is a binary table (see Table 5.3) with 1 s time resolution, and contains the following four variables:

is the time in seconds since the science exposure start time (DATEOBS and TIMEOBS keywords in the jitter header).

represent the difference in position between the telescope and the target in arcseconds along the science instrument X and Y axes.

is the tracking-quality flag. Its value ranges from 5 to -1, representing decreasing levels of fidelity for DX and DY: 5 means they were calculated from the FPD quaternions and the commanded quaternions extracted from the telemetry stream; 4 indicates they were calculated from the ACS quaternions and the commanded quaternions; 3 indicates they were calculated from a less-reliable state of the ACS and the commanded quaternions; 2 indicates they were calculated from the FPD quaternions and the target coordinates from the FITS header; 1 indicates they were calculated from the ACS quaternions and the target coordinates from the FITS header; 0 indicates that tracking information is unavailable; -1 indicates that the spacecraft never achieved known tracking, so the pointing is assumed to be bad.

Table 5.3: Format of Jitter Files a
FITS Extension Format Description
HDU 1:Empty (Header only)
HDU 2: Pointing Data (binary extension)
TIME FLOAT (seconds)
DX FLOAT Δ X position (arcsec)
DY FLOAT Δ Y position (arcsec)
a Sampled once per second, and dimension set length of the exposure.

Housekeeping Files (* In addition to providing inputs for the calculation of jitter parameters and the evaluation of pointing quality, the housekeeping files contain time-resolved engineering data used by CalFUSE to correct science data for instrument or pointing problems during exposures.

The housekeeping files are produced by the FUSE OPUS HSKP process from files of telemetry extracted from the FUSE telemetry database for each science exposure (TTAG or HIST). The time period included in the telemetry files begins 0.5-1.0 minutes before the science exposure and ends 1.0 minute after the science exposure ends, to ensure that all the necessary information is included.

A brief description of the contents of housekeeping file is given in Appendix D. The data are stored in a binary table. Array names are derived from the telemetry parameter in the engineering telemetry database. Telemetry values are placed in time bins according to the time at which the parameter is reported by the spacecraft (in units of MJD days). The update rates are given in Table 5.4. Due to lack of precision, the bins are not precisely integer seconds in length. Nominal update rates range from once per second to once every 16 s depending on the telemetry item, but different telemetry modes sometimes changed the rates. The time duration (in seconds) of the telemetry included in the file can be obtained from the value of NAXIS2 in the HDU2 header. Any parameter not reported in a given second is given the value of "−1" in the housekeeping file. Occasionally, parameters are reported twice in a second, in which case only the final value reported during that second is placed into the housekeeping file. Each type of parameter is checked for telemetry gaps based on its nominal update period. Gaps are reported in the trailer file for each exposure.

Table 5.4: Housekeeping Nominal Sample Periods
Parameter(s) Period (sec)
ATTQECI2BDY 2 (rarely, 0.2 s)
I_FPD 1a
any I_ not already covered 16
AQECI2BDYCMD 3 (rarely, 1 s)
a Only updated when using guide stars. The integration time for faint guide stars is 1.4 s.

5.3 Engineering Snapshot Files (*, *, *

The engineering snapshot data described in this section are somewhat of an anachronism, and are included primarily for completeness. The contents of all of these files are similar (see Appendix E), and provide a sampling of the satellite and detector telemetry at the time they were recorded.

Engineering telemetry and science data for FUSE were stored and downlinked in different data streams. Certain engineering parameters from the instrument, such as detector temperatures and voltages, were identified before launch as potentially being necessary for processing and calibrating the science data. To capture that information, engineering snapshots were taken at the beginning of an exposure and every 5 minutes thereafter, with a final one taken at the end. These data were transmitted in the science telemetry stream. The time of the first and last snapshot were used by OPUS to define the exposure start and stop time for the science data. Other snapshot data were used by OPUS to populate parameters in the FITS header for the exposure files. A subset of these data for the detector are available in the engineering snapshot files.

As the mission progressed, it was discovered that more engineering telemetry at higher sampling rates were needed for CalFUSE to properly process the science data. As a result, the housekeeping files, described in previous sections, were created from direct extractions from the engineering archive, and they were used to provide the necessary supplemental data.

Engineering snapshot data filenames have syntax as shown below, where *snapf* is used for standard engineering snapshot files, *snpaf* is used for engineering snapshots associated with FES A, and *snpbf* is used for engineering snapshots associated with FES B. Example file names are and

\{ pppp \} \{ tt \} \{ oo \} \{ eee \}
\left\{ \begin{arra...
...\ {\tt snpaf} \\ {\tt snpbf} \end{array} \right\}
{\tt .fit}

5.4 Association Tables (*

One Association Table is generated and used by OPUS (see Section 3.2) for each observation. The file is formed of two HDUs as shown in Table 5.5. HDU1 is a header containing basic information about the proposal, the observation and the target. HDU2 is a list of which files were associated with a given observation, their type and whether the files were found. An example is with a generic naming as follows.

\{ pppp \} \{ tt \} \{ oo \} {\}

Table 5.5:Format of the Association Table.
FITS Extension Format Description
HDU 1: Empty (Header only)
HDU 2: Exposure association information
MEMNAME STRING Exposure names

5.5 Mission Planning Schedule (MPS) Files (mps*.pdf)

This section describes the graphical timeline plots of the Mission Planning Schedules (MPS). These plots provide an overview of activities and orbital events throughout the mission and may be useful for placing observations and exposures into context. These plots indicate the PLANNED sequence of activities, and do not reflect any anomalies that might have occurred during actual execution of the observations. (For that see the daily count rate plots discussed in Section 5.7.) The MPS plots were generated for use by the Science Operations staff, and some of the items shown are specific to their needs. However, many of the parameters may be of interest to those who want to use the data as well. Hence, MPS plots have been added to the available FUSE products at MAST as part of the FUSE mission close-out activities.

The files are named according to the starting date of the MPS and FUSE orbit number (since launch). For instance: mps_2002_318_17869.001.pdf corresponds to an MPS which begins on year 2002, day 318 (e.g., November 14) and FUSE orbit number 17,869.

Figure 5.4 provides an example of a one day MPS timeline plot. The plots are PDF files, usually with a day per page, and Day/Universal Time as the abscissa. Each calendar day is broken into two panels, each covering 12 hours. During nominal operations, MPSs typically covered a one-week period, although actual times could be longer or shorter, depending on conditions at the time of planning. Later MPSs were usually multi-day schedules (up to 2 weeks in length) unless a re-delivery or re-plan had taken place.

MPS plots relevant to each observation can be accessed from the MAST preview pages. The link connects to the PDF file of the MPS containing the observation, but the user will need to page through the MPS file to find the specific observation of interest. Inspection of these plots allows the user to assess many aspects of the observation, including (for example) whether SAA passages impacted the scheduling, whether low or grazing earth limb angles may have caused unusual airglow in the observation, and which observations were scheduled before or after the observation of interest.

Figure 5.4: Example of an MPS timeline chart for a 24h period, demonstrating several of the features described in the text.
\epsfig{figure=figs/MPS-example-plot-1.eps, width=1.0\linewidth, angle=0}

A variety of parameters are shown in sub-panels along the ordinate of these plots. The parameters plotted on these plots changed during the course of the mission, reflecting changing operational constraints and the evolution of mission planning tools. The following is a complete list of all possible parameters (and explanations) that appear in various MPS timeline plots.

The instantaneous angle of the telescope boresight to the direction of spacecraft motion.
The angle of the boresight from the earth limb (lower dashed line indicates 10 degree limb angle; upper dashed line indicates 30 degree limb angle).
A bar showing the active observation, labeled with ProgramID:targetID:observationID, coordinates in degrees, target name, expected count rate and (late in the mission) the skew wheel bias. The bias values are:

Spacecraft slews, labeled with the beta angle (B), pole angle (P), roll offset (R), and hemisphere of the attitude at the end of the slew (+ or - roll offset angle: + north, - south), speed of the slew (LO or HI), and the delay in seconds (D) from the beginning of the observation to the start of the slew. A bar is shown for any commanded slew, with the first black section indicating the length of the slew start delay, the white section showing the slew duration, and the next black section indicating the slew settle time. The black bar between the short vertical lines indicates an acquisition or a small slew for, e.g. an offset acquisition.

Small slews and acquisitions. Acquisitions are labeled with the aperture (L - low, M - medium, H - high, R - reference point) and the acq_case. The acq_cases are:

- No Acq (acquisition) performed
- FUV (Far UltraViolet) Peak-up
- FES (Fine Error Sensor) Target Acq and FUV Peak-up
- FES Target Acq
- FES Guide Star Acq
- Unknown Star Acq
- GS (Guide Star) Re-Acq
- Offset Acq
- Offset Re-acq
- FES target correction only

Exposures, labeled with the exposure ID above the block and the exposure type below the block (T - Time Tag, H - Histogram, F - FES exposure, S - FPA adjustment for an FP-split, P - Peakup, A/C - Alignment scans, G - GNRA (Generic/Null Activity).

Bars on this line show the calculated periods where the spacecraft is passing through the SAA (South Atlantic Anomaly). FUV observations cease during these periods. An indicator of the SAA model in use is sometimes also shown.

Bars on this line indicate periods when the active target is occulted (behind the earth or below the earth limb threshold used for planning). If nothing is present on this line, the target was in the CVZ (Continuous Viewing Zone).

This stands for "Terminator Crossing". Bars effectively indicate when the target is being viewed during orbital night. Blank regions are orbital day.

Bars on this line indicate the positions of any ground station passes that were planned during the observation period. The passes are labeled with the ground station involved:
University of Puerto Rico at Mayaguez
Tracking and Data Relay Satellite System
A commercial station in Hawaii used early in the mission

Predicted positive torque authority (i.e. stable pointing) intervals. A solid black line indicates that the target should be in the slit (i.e., no or very few losses of torque authority). A yellow interval denotes expected pointing errors whose magnitude is up to 5 degrees. Larger errors correspond to red intervals (up to 10 degrees) and red crossed intervals, more than 10 degrees.

Bars on this line indicate periods when the detector high voltage is planned to be at full voltage (normal science data acquisition mode).

Data Volume stripchart, showing how much memory usage was expected on the science data recorders. The nominal limit of 100MB is indicated by the horizontal dashed line.

Predicted skew wheel momentum stripchart. The nominal operating range in effect for the particular MPS is shown by the dashed horizontal lines. Discrete numerical momentum values are plotted and referenced by the open circles on the stripchart line.

Also shown on some of the plots are colored regions, and vertical lines. These indicate:

Light Green:
Visibility intervals (unocculted, SAA free times) during which FUV exposures can occur.

Dark Green:
Acquisition intervals, indicates times when the acquisitions and re-acquisitions were allowed.

Periods when the "skew wheel axis to magnetic field" angle is suitable for skew wheel momentum unloading. A filled circle to the upper left of the pink region and an unfilled circle to the lower right of the pink region indicate times when the unloading is switched ON and OFF, respectively.

Red dashed line:
(Vertical). Indicates orbital noon.

Blue line:
(Vertical). Boundary between defined observations.

Table 5.6 lists the time ranges when different combinations of parameters were plotted on MPS plots.

Table 5.6: Dates for MPS Parameter Usage
Datesa MPS Nos. Parameters
1999-203 -- 2000-309 001-222 RAM, LIMB, OBS, SLEW, ACQ, EXP, SAA, OCC, TMX, GSP
2000-313 -- 2001-179 223-282 OBS, LIMB, SAA, OCC, NGT, SLW, ACQ, EXP, GSP, DV
2001-181 -- 2002-115 283-344 OBS, LIMB, SAA, OCC, NGT, S/A, HV, EXP, GSP, DV
2002-120 -- 2005-250 345-533 OBS, LIMB, SAA, OCC, NGT, TRQ, S/A, HV, EXP, GSP, DV
2005-264 -- 2007-262 534-633 OBS, MOM, SAA, OCC, NGT, TRQ, S/A, HV, EXP, GSP, DV
a The format is: YYYY-DDD -- YYYY:DDD

5.6 Mission Planning Guide Star Plots

Guide star plots (see Fig. 5.5) were used by the mission planners to identify potential field stars to use for tracking during each observation. Early in the mission, these manually selected stars were actually the ones passed to the ACS and used for tracking, but starting in 2005 the onboard software could find and use autonomously selected stars near each object. Hence, planners simply made a sanity check for available guide stars. The guide star plots show objects from the HST Guide Star Catalog superposed over the expected FES field of view, and show the positions of the apertures. These plots can be useful for interpreting FUSE pointings in crowded fields, especially when used in conjunction with the FES images (remembering that the target may be in the aperture, and thus not visible to the FES). The indicator of North and East on the guide star plots is also useful for interpreting the actual FES images obtained for an observation.

As with other FUSE products, guide star plots evolved in format over the mission, but most of the information given on the plots is straightforward to interpret. The location of the requested aperture is indicated as a box with cross-hairs, and the acq_case codes shown are the same ones used on the MPS plots (see section directly above). The FLDT numbers used to identify certain stars, and listed at the bottom of the plots, refer to an internal numbering system used by the mission planners. Guide star plots for each observation are accessible from the MAST preview pages.

Figure 5.5: Example of a mission planning guide star plot. The apertures are located at ~Y=400. The crosshairs show which aperture is being used, LWRS in this case.
Example of Mission Planning Guide Star Plot

5.7 Daily Count Rate Plots

These plots show the actual on-orbit sequence of FUSE activities, all orbital events, and any anomalies that occurred, with each plot covering a 24-hour period. To the "Intermediate" and "Advanced" user, these plots will be useful for placing observations into context since they provide a quick visual assessment of the actual execution of a given observation and indicate various times associated with each observation (i.e., high-voltage status, SAA passage, etc...) Figure 5.6 displays an example of such a plot. (For more details on the content of these plots and their generation, the user is referred to the Instrument Handbook (2009)). Each file contains 4 sets of plots with the count rates for SiC, LiF, FEC, and ACS counters. A brief description of the SiC plot is provided below. From top to bottom, one can read the following:

Figure 5.6: Example of a daily count rate plot. See text for details.
Sample daily count rate plot

Subplots 1-4 show for segments 1A, 1B, 2A, 2B the:
count rate (black); high voltage (red if nominal, blue if not); SAA times (blue horizontal shading); science data taken (green shading). The OBSID, target, TTAG/HIST flag, and aperture are also shown if the data are available; low limb angle times (orange shading); and low ram angle times (purple shading).

Subplot 5 shows the: Pole angle; Beta angle; Ram angle; Roll; RA; and OBSID (this will be marked at the time when the observation script began, which is normally well before the actual observation start time).

Subplot 6 shows the:
latitude; longitude; limb angle; Dec; and Day/Night Flag (shaded yellow if Day)

Subplot 7 shows the:
FPA positions; QMEAS flag (scaled); and AT_CMD_ATT flag (scaled).

Science Data Assessment Forms

Science data assessment forms, or SDAFs, were used internally by the operations team to provide a quick look assessment of science data quality for each observation. The assessment process was an important part of identifying problems, and if need be, placing revised observations back into the scheduling pool for timely re-execution. The SDAFs are available through the MAST Preview pages for each observation and provide some insight into how a given observation actually executed on-orbit in comparison to how it was planned.

Automated checking routines populated the majority of each SDAF. The software used information from the file headers, some of which was supplied by the user, and compared it to the actual data from each exposure to produce an overview of the success of the observation. This automated process was geared toward the typical FUSE target, which is to say, a moderately bright continuum source. The checks looked for the target in the expected aperture for all four channels and compared the exposure levels to provide an assessment of channel alignment. Hence, very faint sources and emission-line objects could look problematic to the automated process when in reality they might be just fine. Also, the software assumed that LiF1 was the guiding channel, and made comparisons of the other channels to LiF1. After July 12, 2005, when the guiding channel changed to LiF2 (i.e. to FES B), the software was not updated. Hence, some comparisons shown in the SDAF need to be taken in the context of the larger picture of FUSE operations. They are a useful, but imperfect, record of initial data quality assessment.

A brief description of each section of an SDAF is given below. An example SDAF is shown for reference in Fig. 5.7.

Figure 5.7: Example of a Science Data Assessment Form.
Sample SDAF

Summary Information: A table at the top of each SDAF provides summary information about the target and the observation, populated automatically from the file headers. Included are the actual achieved time for the observation as compared with the planned time in the timeline. If problems occurred, or if the processing deleted some data sections as bad, these numbers will be different.

Exposure checklist: This tabular section contains one line for each exposure in the observation. At left are the UT start time of each exposure and the integration achieved in that exposure (from the LiF1A segment). In the middle are the “Raw Data Check” blocks that use various symbols to indicate the presence (or absence) of data in the various channels and apertures. This raw data check scans all apertures for TTAG data or the primary aperture for HIST data. The key for this section includes:

An "X" indicates data is present at a level of at least twice the background level.
A "W" indicates data is present at 1.8-2.0 times the background level.
A "-" indicates data is not present.
A "D" indicates that the detector high voltage was off or significantly reduced, likely due to an anomaly.
Total exposure times are listed at the bottom of each raw data check for each channel. The full exposure time of each exposure is included in the total if the primary aperture is marked "X".

The example in Fig. 5.7 shows the source present in all exposures and in all LWRS (prime) apertures. Also, since the exposure times are the same for all four apertures, there was apparently no drifting of the target in and out of the various apertures. This is also confirmed by the Extracted Data Check blocks to the right, which show a consistent signal in LiF1 in all channels, and ratios near unity compared to the LiF1 for the other channels throughout the exposures. In crowded fields and for TTAG exposures, sources could sometimes be present in the non-prime apertures. If this was true, one would also see "X" or "W" in other apertures where flux was present. Finally, if telemetry indicated that the high voltage was down for a particular channel, the indicator would show "D" and no data would be present in that channel for that exposure.

Continuum Flux Check: Part of the exposure checklist also includes a check on the CalFUSE pipeline extracted output. This section of the SDAF provides a sanity check against expectations. For each FUSE target, the observer was asked to provide continuum fluxes at 950, 1050, and 1150 Å (if appropriate for their target type). The Continuum Flux Check box just makes a simple comparison of actuals against these expectations, and performs some comparisons between channels. The LiF1 fluxes are used as a benchmark. If the flux in another overlapping segment is significantly lower or higher, then a comment is added later in the form (see below). Also, if flux is detected in the extracted spectrum at a level greater than the LiF1 level and the raw data indicates that no data should be present, a warning is issued in the comments. In some cases, observers had only rough estimates of the expected fluxes, so it is not uncommon to see significant differences from unity. Also, lower values could indicate channel drifts are affecting the observation, especially for MDRS and HIRS observations. (Note again that data taken after 12 July 2005 did not use the LiF1 channel for guiding, but the SDAF software was never updated for this.)

Comments Section: This section contains a number of comments, exposure by exposure, generated by the CalFUSE processing sotfware as it processed the data. The example shows comments related to the presence of bursts and time removed because of them. Sometimes a general alert will be present in red, indicating a flux much lower than expected or similar criterion that can be measured automatically. Usually such problems would already be obvious from inspection of information at the top of the SDAF, but the red comment flags the probable causes of problems specifically. Warnings are more serious than alerts, and when initially issued, would prevent archiving of the data until an assessment was made by FUSE personnel. (Few if any warnings remain in the final SDAF forms generated in the reprocessing performed at the end of the mission, however.)

For observations made in the MDRS or HIRS apertures, the standard procedure involved performing a peak-up acquisition (sometimes multiple times per orbit) to align the channels at the beginning of the observation. When this is the case, one will find an ascii peak-up table appended to the end of the SDAF for that observation. This information is provided for completeness, but it is not expected that most users will need it for analyzing their data.

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