Title: Observing with the Multiband Imaging Photometer for the Space Infrared Telescope Facility
1Observing with the Multiband Imaging Photometer
for the Space Infrared Telescope Facility
- William B. Latter
- SSC/MIPS Instrument Scientist
- SIRTF Science Center
- and
- George H. Rieke
- MIPS Principal Investigator
The Solar System and Circumstellar Dust Disks
Prospects for SIRTF 18 - 20 August 1999 Dana
Point, CA
2Outline
- Current MIPS Sensitivity Estimates
- How to Observe with the MIPS
- The AOTs and the AOT inputs
- The MIPS observing strategies
- Cosmic Rays and the MIPS
- Calibration Strategy
- The MIPS Data Products
3MIPS Sensitivity
See Observing with SIRTF -- MIPS at the SSC Web
Site for additional information and
Photometry/Super Resolution Charts
24 mm ? ISO ? 100 70 mm ? ISO ? 20 160 mm ? ISO ?
6 (incl. confusion) MIPS includes 2-D arrays at
24 and 70 microns for improved mapping and
imaging compared to ISO.
4MIPS Photometry andSuper Resolution AOT
- Use Accurate photometric measurements at 24, 70,
and 160 microns using sequences of fixed
pointings. - Options
- One, two, or all three bands.
- Single frame exposure 3, 10, or 30 seconds (24
?m) and 3 or 10 seconds (70 and 160 ?m). - Super resolution or survey pixel scale at 70 ?m.
(Pixel sampling at 24 and 160 ?m is adequate for
super-resolution processing.) - An option will allow positioning a source off the
arrays (for background measurement) with objects
lt 4 arcminutes in extent. - Number of cycles to repeat the sequence.
5The Photometry/SuperResolution AOT Form
6Sub-pixel Samplingwith MIPS
7160 micron Observing Strategy
At 160 Microns, the MIPS array consists of two
20-pixel rows separated by a dead row.
Scan mirror motions allow efficient dithering and
completion of fully sampled field
8MIPS Scan Map AOT
- Use Simultaneous mapping in the 24, 70, and 160
micron bands using combined cryogenic scan mirror
and telescope motions to freeze the image on the
arrays. - Scan strips are made with minimum overhead,
making this mode very efficient when compared to
other point and shoot modes. - Options
- Size of the region to be mapped in scan lengths,
offset steps, and number of scan legs. - Scan rates (approximate)
- 3 arcseconds/second (results in 100 seconds
integration per point) - 7.5 arcseconds/second (results in 40 seconds
integration per point) - 20 arcseconds/second (results in 15 seconds
integration per point) - Number of map repeats.
- The orientation of the scan direction on the sky
cannot be specified without scheduling
limitations.
9MIPS Scan Mirror and Spacecraft Motions
10MIPS Scan Map FOV (24 µm and 70 µm)
Each source appears in 10 consecutive frames
Each source appears in 5 consecutive frames
FOV change equal to four 160 µm pixels (63.6) in
/- Y direction
Alternate between
FOV change equal to three 160 µm pixels (47.7)
in /- Y direction
and
FOV change equal to one 160 µm pixel (15.9) in
/- Y direction
One frame FOV (5.1 x 5.1)
Slow/Medium (Normal) Scan
Fast Scan
11MIPS Scan Map FOV (24 µm and 70 µm)
Cross-scan frame offset is highly exaggerated
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Scan Depth in Frame Overlap
10
Frame Depth
One frame FOV (5.1 x 5.1)
Scan Track
5.1?
12MIPS Scan Map FOV (160 µm)
Fast Scan
Slow/Medium (Normal) Scan
Each source appears in one frame
FOV change equal to four 160 µm pixels (63.6) in
/- Y direction
Alternate between
FOV change equal to three 160 µm pixels (47.7)
in /- Y direction
and
FOV change equal to one 160 µm pixel (15.9) in
/- Y direction
One frame FOV (0.8 x 5.1) 2 columns separated
by 1 dead column
13MIPS Spectral EnergyDistribution AOT
- Use Long wavelength (52 - 99 ?m) low resolution
(R 20) spectral measurements by using a
sequence of inertially pointed or tracked
positions. - Uses the MIPS spectrometer with a FOV of 18.8 x
4' and the 32x32 GeGa detectors. - Options
- Single frame exposure time 3, 10, or 30 seconds.
- Offset (chop) distance.
- Number of cycles to repeat the sequence.
- Direction of offset (chop) - a scheduling
restriction.
14MIPS Total Power Mode AOT
- Use To establish the true zero level for
measurements of very extended sources. - The instrument uses the scan mirror first to
expose the arrays to the sky, and then place the
arrays in the dark and expose again. - Standard mode The cycle is executed five times
using an exposure time of 10 seconds per
position. Raw data mode is used for the 24 micron
array -- sending all samples to the ground. - Optional
- Single frame exposure time 3, 10, or 30 seconds.
- Number of exposure cycles.
- Number of times to repeat the sequence.
15Cosmic Rays
- Highly redundant sky coverage in scan mode or
multiple dithers mitigate cosmic-ray effects on
the data
- These images were taken from a MIPS sky
simulation that includes the effects of cirrus
and background galaxies in a realistic way. We
can combine a series of such images into a
simulated scan map of a whole field.
16Calibration Strategy
- From the Observers viewpoint, absolute flux
calibration will be tied to the frequent
stimulator flashes and to periodic observations
of well-calibrated celestial standards. - The general strategy as it is currently planned
includes - The fundamental MIPS flux calibration will be
against normal stars. - Atmospheric models will be used to extrapolate
the well determined calibration at 10 ?m into the
far infrared. - MIPS calibrator stars will be observed at the
start and end of instrument campaigns. - The stimulators will be used as relative
calibrators, to allow the instrument response to
be referred to the signals from the celestial
standards without actually observing them. For
the GeGa arrays the stimulators will be flashed
approximately every 2 minutes. The Si array will
need infrequent stimulator calibrations. - Flat fielding
- The stimulator and internal flat field projector
illumination patterns to be calibrated by uniform
sky. - Annealing the arrays
- Ionization damage will need to be removed from
the MIPS germanium focal planes roughly every
three hours. Three methods are available
thermal anneal, bias boost, and photon flood. The
SiAs focal plane will be annealed about once per
week.
17MIPS Data Products
- Raw Data products
- Unprocessed FITS format image files (24, 70, and
160 mm arrays acquire data in all observing
modes, not all is useful science data). - Basic Calibrated Data (BCD) products
- Highest quality final calibrated data that can be
obtained from an automated pipeline system. The
SSC is required to ensure that absolute
calibration of all 3 instruments is consistent to
within 10. Processing will include, as a
minimum - linearization
- flat-fielding
- flux calibration
- CR removal
- Correction for optical distortions
- Dispersion correction (SED)
- FITS format image files (or 2-D SED frames) are
not assembled into maps, scans, or shift and
added dither patterns. - Browse Quality Data (BQD) products
- Maps and dithers shift and added using available
pointing knowledge only. - Extracted SED into 1-D spectrum.
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