1 / 31

What is Millimetre-Wave Astronomy and why is it different?

What is Millimetre-Wave Astronomy and why is it different?. Michael Burton University of New South Wales. Some Millimetre Basics. MM: 1–~12mm, Sub-MM: 0.3–1mm CMBR (T = 2.7K  = 1mm ) Molecular rotational lines Polar molecules (have dipole moment) eg CO (E 1 = 5K), HCN, CS, HCO +

dooley
Download Presentation

What is Millimetre-Wave Astronomy and why is it different?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What is Millimetre-Wave Astronomyand why is it different? Michael Burton University of New South Wales

  2. Some Millimetre Basics • MM: 1–~12mm, Sub-MM: 0.3–1mm • 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)……

  3. The Millimetre Advantage • Thermal Processes B 0.5-2 2 • Decay Rates (linear molecules) 3 • Doppler Widths 0.5 [?] • Level Population (T>>TJ; gJJ)  • Number of Photons -1 • Energy  • Spatial Resolution -1

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

  5. Brightness Temperature

  6. Atmospheric Transmission

  7. The 3mm Millimetre Spectrum

  8. 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!!

  9. 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

  10. 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

  11. Mopra: Current Capabilities • 22-m Telescope for  > ~3mm • 85–115 GHz SIS receiver (2.6 – 3.5 mm) • 35” beam @ 100 GHz • Tsys ~ 150K(@85GHz) – 300K (@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

  12. Methanol Maser-selected Hot Molecular Core Survey CH3CN CH3OH HCO+ H13CO+ N2H+ HCN HNC 7 lines; 86 Sources Purcell

  13. ‘On the Fly’ Mapping with Mopra:The Horsehead Nebula Optical 12CO 13CO 6 arcmin Tony Wong

  14. Tony Wong 0.17 km/s channel spacing

  15. 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

  16. The DQS in 13CO: Mopra OTF Mapping

  17. 0sec(z) 0 z Tsou How many photons have we lost (or gained)? Trec Tatm Signal on-source:

  18. Sky (Reference, Off) Difference Source (On)

  19. 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

  20. Obtaining Data:Signal from Source and Reference • TSig = C{TR+TA(1-e-0secz)+TS e-0secz} • TRef = C{TR+TA(1-e-0secz)} • [TSig-TRef]/[TRef] = TS e-0secz/ {TR+TA(1-e-0secz)} Show Plots of Opacity + Brightness Temperature • TBB = C{TR+TA} • [TSig-TRef]/[TBB - TRef] = TS/TA

  21. Calibrating Data:Gated Total Power • GTPRef = C’ TRef • GTPPaddle = C’{TA + TR} • [GTPPaddle - GTPRef] / GTPRef = TAe- 0secz / {TR+TA(1-e-0secz)} • GTPHot - GTPCold = C’{THot - TCold} Atmosphere Liquid Nitrogen

  22. Calibrating Data: • {[TSig-TRef]/[TRef]} / {[GTPPaddle - GTPRef] / GTPRef } = TSource / TAtmosphere • Actually TSource = T’Source / Efficiency • Usually written as TMB = TA* /  (note the different notation)

  23. 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……

  24. Australia’s MM–Wave Radio Telescopes 3 mm 12 mm

  25. Australia Telescope Compact Array • National Facility • Built for 1–10 GHz operation • MM-upgrades • 3 mm (85-~105 (115) GHz) • 5 x 22m antennas • EW-array + NS-spur • Currently 84.9-87.3+88.5-91.3 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??

  26. Water Vapour and Phase Fluctuations

  27. H2O Turbulence  Seeing Brightness Temperature MillimetreInterferometry 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

  28. ALMAAtacama Large Millimetre Array

  29. Antarctica??

More Related