HARP ACSIS A BBand Survey Camera

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HARP / ACSIS A B-Band Survey Camera

• (Sub)Millimetre Observing TechniquesRussell O.
  Redman

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James Clerk Maxwell Telescope JCMT

• Mauna Kea, Hawaii
• High, dry site
• Above tropical inversion layer
• Good access to
• Communications
• Transportation
• Support facilities

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HARP / ACSISPartly Commissioned

• Spectral Imager
• Like visible-light IFU
• Datacubes instead of images

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Observing Bands Atmospheric Opacity
B
C
D
E

• Frequency Bands
• A RxA3 (211-279 GHz)
• B HARP-B (325-375 GHz)
• C N/A
• D RxW-D (620-710 GHz)
• E N/A
• Weather Bands
• 1 cso_tau 0.05
• 2 0.05 lt cso_tau 0.08
• 3 0.08 lt cso_tau 0.12
• 4 0.12 lt cso_tau 0.20
• 5 0.02 lt cso_tau
• B-Band
• Available 2/3 of the time
• Most productive band
• Equivalent to 850 ?m
• RxB3 needs replacement

A
Atmospheric transmission calculated (using the
IRAM ATM routine see text) as a function of
frequency in the submillimetre window for three
different water vapour pressures (1mm pwv is a
good' night, 0.5mm pwv exceptional', and 5mm
pwv is rather nasty'). Useful observations are
possible only in the 230 GHz region in the latter
case. http//docs.jach.hawaii.edu/JCMT/OVERVIEW/te
l_overview/
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How to build a better receiverDetectors better
or more?

• Power ?Temperature
• Historically, reduce TRX
• TRX (1-?) TAMB
• Close to photon-detecting
• Options
• Space-based telescopes
• More detectors
• Challenges
• Tight financial limitations
• Hard to make uniform sets of detectors
• HARP 4x4 array of detectors

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How to build a better receiverSingle or double
sideband?

• Signal (usually) in one sideband
• Signal and Image sidebands
• Noise from BOTH sidebands
• DSB sky adds ?TAMB in both SB
• SSB Direct image SB to TSSB
• (RxB3 could do both!)
• HARP SSB
• Use polarizing Mach-Zehnder interferometer as a
  SSB filter
• C2F is fixed, C2M moves (both curved!)
• Motion required for DSB too large
• TSSB 20 K
• ALWAYS check for strong lines in the image
  sideband!

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How to build a better receiverOptical design

• Curvature of projected FOV
• Unexpectedly bad for SCUBA
• 3-bolometer photometry
• Design goal for HARP
• Models show good performance
• Measured patterns in lab were poor for bottom row
• Alignment of the internal optics was far off
  center
• Fixed, but not re-measured
• Commissioning measurements are incomplete
• Stay tuned

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How to build a better receiverBeam size and
separation

• Diffraction-limited Optics
• Planck function _at_ 4 K
• Dewar is dark _at_ 10 ?m
• Dewar is bright _at_ 850 ?m!
• Detectors have horns to direct beams out aperture
• At design frequency
• CO (32) 345.7959899 GHz
• Separation 2 ? FWHM

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Beam Size and SeparationJiggle Maps

• Nyquist sampled image
• Every 1/2 BW
• 4?4 grid of samples
• (5?5 at 370 GHz)
• Switching
• Chop (with subreflector)
• Position (move telescope)
• Frequency (move LO)
• Under-Sampled Images
• 5-point
• 2 or 3-detector chopping
• 2x2 grid (FBW sampling)
• 1?1 grid (Stare mode)

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Beam Size and Separation Scan Maps

• Large-Area Mapping Mode
• Sweep telescope
• Sample regularly
• K-mirror rotates FOV to match grid axes (optional)

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How to build a better receiverRapid, Automated
Tuning

• Range 324-376 GHz
• Automated tuning
• Fast Program Changes
• Spectra Line Surveys
• Speed
• Goal 30 sec
• Actual lt 40 sec
• Similar specs to RxA3, RxB3
• (RxW gt 30 minutes!)
• Requires
• Reproducible tuning positions
• Versatile software

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AutoCorrelator Spectrometer and Imaging System

• Radio cameras have 2 parts
• Frontend HARP
• Backend ACSIS
• Built at DRAO
• etc

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First Light

• A very important moment for every
  instrument-building team
• Points to note
• Clean spectrum
• Sharp features
• Flat baseline
• Plausible calibration
• Caveats
• Not pointed
• Not focused
• Not central position of W75N
• No central detector

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REAL First Light

• New hardware/software
• HARP
• ACSIS
• K-Mirror
• IF-system
• OCS software
• Pointing
• Focus
• Observing modes
• Real-time display
• Data reduction software
• etc
• All had to work together for the first time
• Almost like re-commissioning the whole telescope

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Promise of things to come

• Orion
• CO (3-2)
• ? TA dv
• Orion
• Mean
• velocity

• Orion
• red and
• blue wings
• NGC1333
• CO (3-2)
• ? TA dv

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