What is MillimetreWave Astronomy and why is it different

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What is Millimetre-Wave Astronomyand why is it
different?

• Michael Burton
• University of New South Wales

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Some Millimetre Basics

• MM 112mm, Sub-MM 0.31mm
• CMBR (T 2.7K ??? 1mm)
• Molecular rotational lines
• Polar molecules (have dipole moment)
• eg CO (E1 5K), HCN, CS, HCO
• Cold thermal continuum (dust)
• Thermal processes F B?? 2kT?2/c2 . ?x
• Problem Atmosphere (O2, H2O)

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The Millimetre Advantage

• Thermal Processes ??B? ?0.5-2 ?2
• Decay Rates (linear molecules) ?3
• Doppler Widths ?0.5 ?
• Level Population (TgtgtTJ gJ?J) ?
• Number of Photons ?-1
• Energy ?
• Spatial Resolution ?-1

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Transparancies

• Electromagnetic Spectrum
• MM transmission for 4mm H2O
• MM transmission for 11mm H2O
• Some bright MM-lines

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Brightness Temperature
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Atmospheric Transmission
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The 3mm Millimetre Spectrum
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Physical Parameters you can derive!

• Temperature Tex, TBrightness
• Density nH2 (ncrit ? range of densities
  present!)
• Column Density N (when optically thin)
• Optical Depth (use isotope ratios)
• Mass (with scale length)
• Abundances different species
• Velocities line widths, centres, shapes
• Infall, outflow, mass transfer rates
• ? Constrain the properties of your source!!

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16272-4837SEST molecular line survey

• Gradient Trot 27 4 K
• Intercept N(H2) 1 x 1024 cm-2
• (? comes in as well)
• Size Column n(H2) 6 x 105 cm-3
• With Volume Mass 6 x 103 M?

Garay et al, 2002
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16272-4837 SEST kinematical studies
Optically Thick

• Evidence for infall
• (profile of optically thick lines)
• Modelling Vinfall 0.5 km s-1
• - Speed Density Size
• dMinfall/dt 10-2 M? yr-1
• Evidence for outflow from wings
• - Extent Voutflow 15 km s-1

Optically Thin
Wide Wings
Brooks et al, 2002
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Mopra Current Capabilities

• 22-m Telescope for ? gt 3mm
• 85115 GHz SIS receiver (2.6 3.5 mm)
• 35 beam _at_ 100 GHz
• Tsys 150K(_at_85GHz) 300K (_at_115GHz)
• Beam Efficiency
• ?mb (86 GHz) 0.49, ?mb (115 GHz) 0.42
• ?xb (86 GHz) 0.65, ?xb (115 GHz) 0.55
• Bandwidth 64, 128 or 256 MHz (200 - 800 km/s)
• 1024 Channels (0.2 - 0.8 km/s per channel)
• 2 Polarizations
• 1 frequency or 1 polarization SiO 86 GHz
• Must Nod No chopping
• OTF Mapping

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Methanol Maser-selected Hot Molecular Core Survey
CH3CN CH3OH HCO H13CO N2H HCN
HNC 7 lines 86 Sources
Purcell
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On the Fly Mapping with MopraThe Horsehead
Nebula
Optical
12CO
13CO
6 arcmin
Tony Wong
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Tony Wong
0.17 km/s channel spacing
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OTF Mapping Specifications

• For a 300 x 300 map
• 1400 spectra (31 x 46)
• 35 resolution
• 0.17 km/s resolution
• 120 km/s bandwidth
• Dual polarization
• ? 0.3K per channel, per beam
• 70 minutes / grid
• Upto 7 grids / transit
• Processed with LIVEDATA GRIDZILLA packages

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The DQS in 13CO Mopra OTF Mapping
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Tsou
How many photons have we lost (or gained)?
Trec
Tatm
Signal on-source
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Sky (Reference, Off)
Difference
Source (On)
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Some Radiative Transfer

• Radiative Transfer dI?/ds -?? I? ??
• Kirchoff (LTE) ?? / ?? B?(T)
• ? Radiative Transfer dI?/d? I? B?(T)
• Solution I?(s) I?(0)e- ? ?(s) B?(T)(1 - e- ?
  ?(s))
• Source Atmosphere

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Obtaining DataSignal from Source and Reference

• TSig CTRTA(1-e-?0secz)TS e-?0secz
• TRef CTRTA(1-e-?0secz)
• TSig-TRef/TRef TS e-?0secz /
  TRTA(1-e-?0secz)
• Show Plots of Opacity Brightness Temperature
• TBB CTRTA
• TSig-TRef/TBB - TRef TS/TA

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Calibrating DataGated Total Power

• GTPRef C TRef
• GTPPaddle CTA TR
• GTPPaddle - GTPRef / GTPRef
• TAe- ?0secz / TRTA(1-e-?0secz)
• GTPHot - GTPCold CTHot - TCold
• Atmosphere Liquid Nitrogen

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Calibrating Data

• TSig-TRef/TRef / GTPPaddle - GTPRef /
  GTPRef
• TSource / TAtmosphere
• Actually TSource TSource / Efficiency
• Usually written as TMB TA / ?
• (note the different notation)

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Mopra Upgrades

• 8 GHz Digital Filter Bank
• Zoom modes
• 4(?) lines simultaneously
• MMIC receiver
• Easier tuning
• Higher Tsys
• May loose 115 GHz end?
• 7 mm receiver
• New ATNF project?
• Focal Plane Array???
• Ultra-wide band correlator???
• Needs source of funds

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Australias MMWave Radio Telescopes
3 mm
12 mm
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Australia Telescope Compact Array

• National Facility
• Built for 110 GHz operation
• MM-upgrades
• 3 mm (85-105 (115) GHz)
• 5 x 22m antennas
• EW-array NS-spur
• Currently 84.9-87.388.5-91.3 GHz
• 12 mm (22-25 GHz)
• 6 x 22m antennas
• 2 GHz bandwidth upgrade
• 7 mm (45 GHz) upgrade planned
• 6 antennas
• FPAs???
• With ultra-wide-band correlators??

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Water Vapour and Phase Fluctuations
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MillimetreInterferometry
H2O Turbulence ? Seeing
Brightness Temperature
R Sault

• Poses special challenges
• Significant atmospheric opacity, mostly due to
  H2O
• Fluctuations in H2O produce phase shifts
• These increase with both baseline and frequency
• Instrumental requirements (e.g. surface,
  pointing, baseline accuracy) are more severe
• Need more bandwidth to cover same velocity range
  (1 MHz ? ? (mm) km/s)

Desai 1998
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ALMAAtacama Large Millimetre Array
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Antarctica??