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30.3 FOS Paper Products

The FOS paper products are a package of summary text and diagnostic graphics that can be generated for any set of FOS observations. The FOS products were redesigned in 1996 to enhance their clarity and usefulness. Paper products can be generated for any FOS data by using pp_dads which is in the STSDAS hst_calib.paper_prod package. In order to generate a full set of FOS paper products you will need the following six types of files: .d0h/.d0d, .c0h/.c0d, .c1h/.c1d, .shh/.shd, .jih/.jit, and .pdq (the first four sets are required to obtain a minimal set of products). Please refer to the task help file for information on how to run this package.

The FOS paper products produce title pages for an observation series and several pages of summary and diagnostics for each rootname in the series. At the exposure level three generic types of output are produced:

30.3.1 Title Pages

The first (cover) page produced by pp_dads lists the proposal number and the name of the Principal Investigator. A closing page is produced that is virtually identical to the cover page.

Following the first page is a list of targets for the observations and a list of the individual exposures (see Figure 30.1). On this listing each exposure has a data quality flag that will be set if any .pdq file comment of sufficient severity exists. These comments are printed on the HST Performance Summary section of the Observation Summary paper product page for the relevant exposure. Many .pdq file comments are benign, so a raised data quality flag should simply serve as an indication that you need to check further. The presence of a telemetry gap in the data is not sufficient to cause the data quality flag to be set, but all telemetry gap messages from the .pdq file will also be printed on the HST Performance Summary section of the Observation Summary paper product page.

30.3.2 Observation Summary Page

This one-page summary sheet (see Figure 30.8) is divided into sections that describe basic exposure characteristics, telescope performance characteristics (OMS summary), calibration pipeline performance, and OPUS data quality evaluation comments.

Exposure Summary

The right-hand section of the page presents information from keywords that characterize the exposure, including target name, proposal-specified coordinates (not actual telescope pointing), disperser, aperture, observing mode, total exposure time, observation date, aperture position angle on sky, substepping and overscanning values, mean total dark per pixel for the exposure, mean scattered light correction per pixel (if applicable), and average readout time (for RAPID mode only).

OMS Summary

The OMS (Observatory Monitoring System) Summary presents, if the jitter file information is available, the jitter plot (jitter ball) which shows samplings made every six seconds of the spacecraft motion about nominal pointing in the (V2,V3) plane. The plot is always scaled based upon the extrema of the data being plotted. Also included is a summary of the rms jitter in V2 and V3 in units of milliarcseconds, as well as the number of recenterings and losses-of-lock during the exposure. More information about OMS engineering data is available in Appendix C.


Any comments found in the .pdq file are printed following the OMS statistics in the HST Telescope Performance Summary section. These comments include those made by OPUS personnel in their routine post-observation review of the observational data quality and automatic comments included by OPUS observation-evaluation software. Although such comments are often benign, the presence of most is sufficient to cause the Observation List observational quality flag to be set to "not OK."

Pipeline Performance

A listing of pipeline calibration anomalies, if any, is presented in the lower-left corner of the page.

30.3.3 Exposure Diagnostic Plots

For the purpose of data quality assessment, this is the most important section of the FOS paper products. Depending upon the observing mode, 0-3 pages of diagnostic plots and diagrams are produced for each individual exposure. Table 30.7 lists the types of plots that are generated for each observing mode. Following is a description of each type of plot:

Flux vs. Wavelength

Two plots are provided (see Figure 30.5). The upper plot is a standard calibrated flux (.c1 file) vs. wavelength (.c0 file) with the display auto-scaled to the data extrema. The lower plot presents log(flux) vs. wavelength. Points with zero or negative values prior to the log operation are not plotted. This plot is made only for ACCUM and RAPID mode. For ACCUM mode, the last data group is plotted; for RAPID the first group is plotted.

Corrected Counts vs. Wavelength

Corrected counts are the count-rates in each pixel of the .c5 file (raw observational data that have been corrected for all instrumental effects except the instrumental sensitivity correction to calibrated fluxes) multiplied by the effective exposure of each pixel. In this manner we plot a quantity that is easily manipulated (take the square root) to give a good approximation of the formal statistical S/N as a function of wavelength (see Figure 30.6).

The wavelength scale (from the .c0 file) is magnified by plotting the first half of the observed wavelength range in the upper half of the diagram and the balance of the spectrum in the lower half of the display.

This plot is made only for ACCUM, RAPID, and dispersed-light IMAGE mode. For ACCUM mode, the last data group is plotted and for RAPID the first group is plotted. For IMAGE mode all y-steps are plotted vs pixel number as IMAGE mode spectra are not wavelength calibrated.

Group Counts

Again the ordinate is "corrected counts." Here we plot the sum of the corrected counts over all pixels for each readout of the diode array vs. readout (group) number for all readouts in the exposure (see Figure 30.7). Note that the left-hand vertical axis is labeled in counts, but the right-hand vertical axis is labeled in percent of the maximum ordinate value. This provides an easy way of assessing the consistency of the counts between groups.

This plot provides a light curve of the target during the observations. This is an interesting display for variable objects, and it is also an easy way to assess the photometric repeatability of the measures and the stability of the telescope and the instrument during an entire observation.

We strongly recommend that the group counts plot be inspected for every ACCUM and RAPID mode observation in your data since it is a quick way to identify many of the more common problems that can affect FOS data.

This plot is made only for ACCUM and RAPID modes. For ACCUM mode, the individual groups are decomposed to produce the counts actually accumulated during each readout.

ACQ/BINARY Deflection Diagram

There are several portions of this diagram (see Figure 30.3). Up to a maximum of eleven individual accumulated counts vs. pixel number (detector x-axis) plots are given. The first three correspond to mappings of the middle, lower, and upper thirds of the 4.3 aperture respectively. The remainder are for each of the magnetic deflections used to place the target on a y-edge of the diode array (and thereby produce a signal roughly half of the maximum detected in the first three images). The group number and Y-base for the deflection is printed on each plot.

To the left of these count-level plots is a diagram showing the relative y-position of diode center (in Y-base units) of each individual step in the binary search sequence. The final derived target Y-base position is also marked. Recall that one diode height is 256 Y-base units.

The calculated (x,y) and equivalent (V2,V3) offsets are given in arcseconds. The x-offset is also given in pixels and the y-offset in Y-bases.

A compass rose showing the orientation of the detector +x and +y axes with respect to north and east on the sky is also given. The sense of the x-axis in the count-level plots and the y-direction in the deflection graphic are identical to the sense of the same directions illustrated in the compass rose.

ACQ/PEAK Scan Diagram

This diagram shows the relative position of each dwell point in an ACQ/PEAK scan pattern plotted in the FOS detector (x,y) plane (see Figure 30.4). Note that x and y are displayed as if we are viewing the sky by looking through the detector from its back side. A compass rose shows the correct orientation of north and east on the sky. Ordinal numbers are printed next to each scan position as are the total counts detected during each dwell.

ACQ/PEAK is a "return-to-brightest" (for peakup) algorithm. No attempt to centroid the contours or interpolate a position intermediate between dwell points is made. The dwell point with the highest number of counts is marked as the location to which the telescope moved after the peakup sequence. Check the OMS jitter ball, if available, to insure that no significant positioning errors occurred in the slew to the brightest location.

The calculated (x,y) and equivalent (V2,V3) offsets are given in arcseconds. The x- and y-step sizes for the scan pattern are also given.

The distribution of counts in each ACQ/PEAK pattern can be used to estimate the degree of centering error after movement to the brightest dwell point.

Grayscale Image

A grayscale plot is made of the two-dimensional image in the FOS instrument coordinate (x,y) plane (see Figure 30.2). The units on both axes are FOS pixels. For a standard post-COSTAR ACQ image 1 pixel corresponds to approximately 0.075". A rule depicting the scale of 1" is also given.

A grayscale vs. counts key is provided. The orientation of the detector coordinates relative to north and east is provided via a compass rose.

This plot is provided only for IMAGE mode observations that use the MIRROR and for standard ACQ images.

30.3.4 Calibration Summary Page

This page (see Figure 30.9) presents in successive columns all calfos switch settings for each step in the calibration process, their status, the reference file or table used, the pedigree (if available) of the reference file, and a description of the action of each calibration switch or step. The shaded banner again gives logsheet line number, observation rootname, and proposal ID.

Figure 30.1: Visit Summary Listing

Figure 30.2: ACQ Image Plot

Figure 30.3: ACQ/BINARY Plot

Figure 30.4: ACQ/PEAK Plot

Figure 30.5: F vs and log F vs Plot

Figure 30.6: Corrected Counts vs Plot

Figure 30.7: Group Count Plot

Figure 30.8: Observation Summary Page with Jitter Ball

Figure 30.9: Calibration Summary Page

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Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved. Last updated: 01/14/98 14:29:35