SED-Mode Slit Profile

Principal: psmith
Deputy: jstansberry, dfrayer, nanyoa
Data Monkey(s):
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 24 hours
Last Updated:

Objective

To determine in detail the position and throughput profile of the SED slit.

Description

A bright source, preferably of 70µm flux standard, is placed in the SED slit. The CSMM is used to move the source 1.5 pixels away, and then the object is stepped across the slit in steps of 0.25 pixels, taking 12 steps. Each of the 12 DCEs is followed by a CSMM chop to a sky position 2 arcminutes away. The result is a 12 position scan across the SED slit with 12 accompanying DCEs at the sky positions. Repeat the process for 6 positions along the slit to get detailed information about slit orientation and throughput along the slit. The steps along the slit should be approximately +96, +64, +32, 0, -32, -64, and -96 arcsec from the midpoint of the slit. The bright target should be a photometric calibrator. The recommended photometric standard is HD163588 (RA=17h53m31.73s, DEC=+56d52m21.5s).

Data Collected

For each position along the slit, The CSMM will be stepped by 0.25 pixel and a DCE will be obtained for each CSMM and for its corresponding sky position ~2' away. This process will be repeated for several positions along the slit. A specialized IER will be used to perform this IOC task.

Data Reformatting Requirements

Array Data Desired:

70 µm

Data Reformatting Option:

Special Instructions:

Task Dependencies

Calibration Dependencies

Output and Deliverable Products

The location of the center of the SED slit, its orientation relative to the dispersion axis, and the width of the SED slit will be determined to verify the results of MIPS-138. The location of spectra on the 70 µm array as a function of slit position will be mapped to verify or correct the SED-mode distortion model. If a photometric calibration star is observed, these observations will yield an initial spectrophotometric calibration for the MIPS SED observing mode.

Data Analysis

For each position along the slit:
  1. Data will be run through mips_sloper using the default settings.
  2. Subtract sky DCEs from corresponding target DCEs.
  3. Sum 32-pixel rows in the dispersion direction (IDL script).
  4. Determine total flux in spectrum after subtracting a fit to the residual background (IDL script).
  5. Plot flux as a function of CSMM position and determine slit center and width (half-power points; IDL script).
  6. Reformat data so that IRAF tasks can be used (NaN conversion).
  7. Sum all DCEs for each position along the slit (IDL script or IRAF task "imsum").
  8. Use IRAF "noao.twodspec" tasks to measure pixel position of the spectrum along the dispersion direction. Results will determine how well aligned the array is to the dispersion axis. Differences seen between slit positions will be the result of optical distortions.
The data analysis IDL scripts for this task have been developed by M. Blaylock (lead), P. Smith, and J. Stansberry and can be found here (documentation on how to use the IDL scripts can be found here). After obtaining the results for all slit positions, the center positions will be plotted as a function of distance along the slit which will give the tilt of the slit with respect to the CSMM axis of motion. The results also yield the position along the slit as a function of spacecraft position.

If a flux calibration star is used as the target object:

  1. A one-dimensional spectrum will be extracted from the average or median of the CSMM positions that gave the brightest spectra for each target position along the slit using the IRAF "noao.twodspec.apextract" tasks.
  2. Sensitivity functions will be constructed for each slit position using the IRAF "noao.onedspec.senfunc" (and "standard") tasks.
  3. If there are no significant differences in the derived sensitivity functions for the various slit positions, an average sensitivity function will be formed. If significant variations in the sensitivity the function are discovered as a function of slit position, the data analysis will have be re-examined (esp. sky subtraction, slit width, telescope pointing, etc.) to verify that this dependence in real. If verified, the instrumental sensitivity will be supplied over various ranges of slit positions.

Software Requirements

Actions Following Analysis

Appropriate coefficients for the distortion corrections for SED mode in the spatial direction will be given to MIPS_enhancer. Data for the slit location and orientation will be supplied as verification that the telescope pointing is good enough to place point sources within 1-2 arcsecs of the middle of the slit.

Failure Modes and Responses

If success is achieved for only 3 or more of the slit positions sampled, the task may not have to be repeated.

Additional Notes

Target chosen should be a bright 70 µm flux standard star. The recommended flux standard given a launch date of August 23, 2003 is HD163588 (RA=17h53m31.73s, DEC=+56d52m21.5s).