The Multiband Imaging Photometer for the Space Infrared Telescope Facility

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The Multiband Imaging Photometer for the Space
Infrared Telescope Facility

• William B. Latter
• (SSC/MIPS Instrument Scientist)
• George H. Rieke
• (MIPS Principal Investigator)
• and
• The MIPS Instrument Team

The Solar System and Circumstellar Dust Disks
Prospects for SIRTF 18 - 20 August 1999 Dana
Point, CA
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Outline

• Introduction to the MIPS
• Origin of the MIPS
• Instrument capabilities
• The MIPS Instrument
• Basic Layout
• The MIPS Detectors
• Some MIPS Science
• MIPS Detector Behavior
• Calibration Plans

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What/Who is the MIPS?

• The Multiband Imaging Photometer for SIRTF (MIPS)
  is the long wavelength instrument on SIRTF (? 20
  to 180 mm)
• Some of the Team
• George H. Rieke (U. Arizona), Principal
  Investigator
• Erick Young (U. Arizona), Deputy PI, Detector
  Lead
• Chad Engelbracht, Arizona MIPS Scientist
• William B. Latter, SSC/MIPS Scientist
• Jocelyn Keene, JPL MIPS Scientist
• Douglas Kelly, MIPS Test Scientist
• Ball Aerospace building the instrument
• University of Arizona GeGa focal plane arrays
• See http//sirtf.caltech.edu/Observing/Tools/html
  /mips.html
• and http//mips.as.arizona.edu

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Origin of the MIPS

• MIPS is an instrument that is based on simple
  principles.
• Imaging at 24, 70, and 160 mm.
• 70 ?m is longest wavelength without a strong
  confusion limit.
• 24 mm at geometric mean between 8 mm (IRAC long
  band) and 70 mm.
• 160 mm at geometric mean between 70 mm and 350 mm
  (accessible from ground).
• Super resolution is an important science goal.
• Requires pixels lt l/2.5D.
• At 70 mm, such small pixels would be limited in
  sensitivity by cosmic ray hits.
• Scale change at 70 mm needed to provide both
  super resolution and sensitivity.
• Science requires ability to measure SEDs at more
  than 3 wavelengths.
• A scan mirror was required to modulate signals to
  overcome detector 1/f noise.
• Creative use of the scan mirror provides the
  above capabilities, plus efficient operating
  modes.

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Multiband Imaging Photometer for SIRTF Basic
Capabilities
Array Format
Field of View (')
Pixel Size (")
F/
l/Dl
l (mm)
Band
Mode
24mm
4
20.5 26.5
7.4
5.1x5.1
2.4
128x128
70mm
5.1x5.1
60 80
3.5
Survey
32x32
9.4
18.7
Super Resolution
3.5
70mm
2.6x2.6
60 80
32x32
4.9
37.4
70mm
14 24
4.0x0.3
52 99
32x24
9.4
18.7
S.E.D.
5.1x0.5 (effective)
160mm
4
2x20
15
140 180
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Point Extended Source Saturation Limits
(in one sample) 24 mm
8 Jy (1 Jy/Pixel) 70 mm
8 Jy (1.4 Jy/Pixel) 160 mm 8 Jy (1
Jy/Pixel)
Sensitivity (mJy) (5 s in 500 s) 24 mm
370 70 mm 1400 160 mm 22.5 mJy (160
mm is model dependent confusion limited)
See http//sirtf.caltech.edu/Observing/Tools/html
/mips.html and http//mips.as.arizona.edu
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The MIPS MechanicalDesign and Layout
Imaging Mirrors

• Aluminum Baseplate
• 21 Reflective Optic Elements
• Mirror Support Brackets
• 3 Focal Plane Assemblies
• 8 Filters
• CSMM
• Masks, Baffles, Paint
• Cover (not shown)
• Cables (not shown)
• Electrical Thermal Feed Throughs

70 mm FPA
160 mm FPA
Pick-off Mirrors
24 mm FPA
CSMM
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Where the Light Goes
70mm Pupil Imaging Mirror
160 mm Fold Mirror
160 mm Pupil Mirror
Slit Mirror
160 mm FPA
24mm Pupil Imaging Mirror
70mm FPA
Flat Field Relay Mirror 2
24mm Camera Mirror 1
160mm Camera Mirror
Narrow Field Fold Mirror
24mm Camera Mirror 2
Periscope Mirror 1 (above) Periscope Mirror 2
(below)
24mm FPA
Flat Field Relay Mirror 1
Grating
24mm Fold/Pupil Mirror
24mm Band Scan Mirror
70mm Band Scan Mirror
Narrow Field Camera Mirror
24mm Pick-off Mirror
70mm Pick-off Mirror
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The MIPS is Real!
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And very black inside, too.
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MIPS Focal Plane Arrays

• 24 mm Band
• 128 x 128 pixel SiAs BIB detector array
• Developed by Boeing-North American
• IRS Team has lead development responsibility

• 70 mm Band
• 32 x 32 pixel GeGa photoconductor array
• Developed and constructed at the Steward
  Observatory
• Detector material from Lawrence Berkeley
  Laboratory
• Custom cryogenic readouts ( CRC-696 )

• 160 mm Band
• 2 x 20 pixel stressed GeGa photoconductor array
• Developed and constructed at the Steward
  Observatory
• Detector material from Lawrence Berkeley
  Laboratory
• Custom cryogenic readouts ( CRC-696 )

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70 mm Qualification Array with Filter Holder
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2 x 20 GeGa Stressed Array
MIPS 160 micron band
Stressed array footprint
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The MIPS Flight CryogenicScan Mirror Mechanism
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MIPS in the SIRTF Focal Plane
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MIPS ScienceThe Potential
The MIPS 70 micron sky These are
logarithmically scaled versions of comparison
images generated for MIPS, SOFIA, ISO, and IRAS.
A test field was "observed" with with each
instrument for 24 hours, taking into account
sensitivity, image scale, and field of view. The
IRAS image has very large pixels and is really
only capable of detecting the infrared cirrus in
this field. The ISO image has better spatial
resolution but is limited by the small
field-of-view and low sensitivity of the arrays.
SOFIA has excellent spatial resolution but a
correspondingly small field-of-view and is
limited in sensitivity because it uses warm
optics. Courtesy of Chad Engelbracht
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Simulated 24 and 70 micron Observations of
Circumstellar Disks
Below are simulated 70 mm observations convolved
with a model of the SIRTF Point Spread Function.
Left to Right Vega, 1/10 as much dust as Vega, a
point source. All are on a logarithmic brightness
scale.
Left are simulated 24 mm observations convolved
with a model of the SIRTF PSF on a logarithmic
brightness scale. The left image is Vega. On the
right is the difference of a Vega-like star with
1/100 times less dust and a point source of the
same total flux.
Simulations by Ned Wright (UCLA)
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MIPS ScienceThe Possibilities

• MIPS provides the last opportunity in the
  foreseeable future to observe at far infrared
  wavelengths from space. Even with a 5 year
  mission, MIPS time will likely be in strong
  demand. Examples of potential science programs
  include
• Extragalactic
• Detailed IR maps of galaxies such as M33
  structure, star formation, cirrus.
• Cosmology and the early universe with large area
  mapping.
• Far-IR properties of quasars and ultraluminous
  galaxies.
• Galactic
• Survey star formation sites, and examine the
  earliest stages of stellar birth.
• Examine the temperature, structure, and dust
  composition of the ISM surrounding sites of
  massive star formation.
• Structure and frequency of proto-planetary debris
  disks.
• Solar System
• Cometary debris, structure, and composition.
• Counts and colors of Kuiper Belt objects.
• Detailed studies of the Zodiacal dust.
• You make up you own!

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The MIPS AstronomicalObserving Templates

• MIPS Photometry Super Resolution Imaging
• Imaging photometry and high resolution imaging at
  24, 70, and 160 ?m.

• MIPS Freeze-frame Scan-mapping
• Telescope scanning at 24, 70, and 160 ?m for
  large field maps

• MIPS Spectro-Photometry or Spectral Energy
  Distribution (SED)
• ?/?? 14 - 25 covering 52 - 99 ?m.

• MIPS Total Power Measurement
• Zero level reference observations for absolute
  brightness of very extended sources.

• Because of the expected science demands and
  pointing limitations for SED, the
  Photometry/Super Resolution and Scan AOTs have
  been selected to be available for Cycle 1
  observing. The other two AOTs will be available
  for Cycle 2.
• Important Operational Features
• Array operation is identical for all modes, as
  is data grouping.
• Commanding, stimulator, and scan mirror
  operation is very similar for all modes.
• Solar System tracking is currently supported for
  all MIPS AOTs.

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How the GeGa Detector Arrays Behave

• Bulk photoconductors have multiple time constant
  response.
• Infrared-active and high impedance regions are
  identical.
• Changes in illumination result in changes in
  space charge that occur
• at roughly the RC time constant of this high
  impedance region.
• At the same time, simple generation-recombination
  of charge carriers
• occurs quickly.
• Consequently
• Initial background plays a key role in behavior,
  since it sets initial R in RC.
• Transient for light on is slower than for
  light off.
• Space charge adjustments near contacts can
  overshoot, resulting in hook.
• In addition, CR hits compensate the material,
  changing the detector
• response characteristics (and eventually
  increasing noise).
• The MIPS implementation is robust
• MIPS uses a DC-stable readout process that gives
  good recovery from transients.
• Neither detectors nor readouts are subject to
  damage at SIRTF CR dose levels.

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Mitigation for Photoconductor Misbehavior

• Stimulator flashes included in normal
  data-taking at 1/( 2 min).
• Will allow calibration to be tracked and fitted.
• Extensive modeling of basic physics is underway
  to understand the details
• For example, the effects of a stimulator flash
  on the calibration it is measuring.
• Extensive ground testing of fight detectors
  under typical observing conditions.
• Scan mirror allows rapid modulation of signals
  so all measurements rely
• as much as possible on the fast response.
• Pure fast response has excellent photometric
  characteristics.
• Strategies included to anneal detectors to
  remove CR effects periodically all
• work by flooding detector with charge carriers to
  restore equilibrium.
• Thermal anneal raises detector temperature
  briefly.
• Bias boost causes the detector to break down
  electrically.
• Photon flood illuminates it with a bright
  source.
• Raw data frames sent to ground to permit further
  optimization of reduction.
• Coadds of adjacent frames can be used to reduce
  data rate.

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Calibration ofMIPS Data

• Requirement MIPS shall be able to repeat
  photometric measurements of bright sources to
  better than 4, with 5 absolute flux
  calibration.
• The instrument allows measurement of dark
  current, flat field, responsivity, etc.
• Scan mirror can be used to put arrays in the dark
  as well as select flat field projector for
  spectral energy distribution mode.
• Scan mirror moves sources around on array.
• Improves sampling
• Robust behavior in the presence of bad pixels
• Keeps detectors in fast response regime
• The scan mirror and stimulator operation are
  closely synchronized with the observing modes.
• Track responsivity changes
• Measure flat field
• Maintain flux calibration
• The definition of a few standard observing modes
  aids in calibration repeatability.

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Summary

• MIPS is a powerful, versatile, and operationally
  simple instrument.
• The four MIPS AOTs provide accurate photometric
  and super resolution observations of compact
  objects, sensitive and efficient large area
  mapping, low resolution spectroscopy, and the
  ability to make absolute flux measurements of
  very diffuse material.
• Photometry/Super Resolution and Scan AOTs
  available at launch. The remaining two will be
  available for Cycle 2.
• Instrument operation and carefully planned
  observing and calibration strategies are designed
  to mitigate difficulties inherent to germanium
  detectors.