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Observing with the Multiband Imaging Photometer for the Space Infrared Telescope Facility

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Annealing the arrays ... methods are available: thermal anneal, bias boost, and photon flood. The Si:As focal plane will be annealed about once per week. Dana ... – PowerPoint PPT presentation

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Title: Observing with the Multiband Imaging Photometer for the Space Infrared Telescope Facility


1
Observing 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
2
Outline
  • 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

3
MIPS 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.
4
MIPS 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.

5
The Photometry/SuperResolution AOT Form
6
Sub-pixel Samplingwith MIPS
7
160 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
8
MIPS 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.

9
MIPS Scan Mirror and Spacecraft Motions
10
MIPS 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
11
MIPS 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?
12
MIPS 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
13
MIPS 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.

14
MIPS 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.

15
Cosmic 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.

16
Calibration 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.

17
MIPS 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.

18
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