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Atacama Large Millimeter/ submillimeter Array - ALMA Charge 2 Al Wootten JAO Interim Project Scientist. Charge 2: Text.

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atacama large millimeter submillimeter array alma charge 2 al wootten jao interim project scientist
Atacama Large Millimeter/

submillimeter Array - ALMA

Charge 2

Al Wootten

JAO Interim Project Scientist

charge 2 text
Charge 2: Text
  • Revisit the question from April, 2007 of important correlator requirements for early science operations. In particular prioritizing the order of development of software modes. Compare broad early science requirements to correlator modes. Which modes enable the majority of the science? What other capabilities are important?
  • Note: I know of no early science requirements. I will show modes available and modes unavailable at Early Science.
early science proposed definition
Early Science – proposed definition
  • At least 16 antennas fully commissioned (more in process of integration)
  • Receiver bands 3, 4, 6, 7, 8, 9
  • Interferometry in single field or pointed mosaic mode
  • Significant (TBD) range of spectral modes, including TFB
  • Circular and linear polarization (not mosaic)
  • Single-dish mosaic (position and beam-switch) and OTF.
  • 2 frequency subarrays operational
    • Recall this is down from nominal four with rebaselining
correlator commissioning plan
Correlator Commissioning Plan

First commissioning and science verification begins at AOS end Q1 2009.

  • Numerous ALMA production components will at this point never have been commissioned: Correlators, Front Ends, Production antennas, Water Vapor Radiometers, …
  • Plan is to test procedures, inasmuch as possible, at ATF thru Q2 ‘08
    • Drawback: Not all production equipment, much is preproduction or prototype (antenna, receiver)
    • Correlator will now be 2-antenna copy of production correlator (change since Sept 2006)
  • Inasmuch as possible, continue this at OSF Q3-4 ‘08 (but AIV in charge)
    • All production equipment except correlator, which will be the 2-antenna correlator
    • Atmosphere not much different from VLA site, so some limitations on receiver band tests
    • One 35m baseline limits demonstration of phase correction
  • Finish this process, and begin commissioning as possible, at AOS before Early Science Decision Point in early 2010, when modes to be offered for Early Science will be frozen.
correlator commissioning
Correlator commissioning
  • Therefore modes planned now to be available for Early Science will be those which can be tested on the 2-antenna correlator at the ATF and perhaps at the OSF.
  • Or, a subset of those modes.
the alma correlators
The ALMA Correlators
  • NRAO Baseline Correlator (four quadrants for 64 antennas, BW: 8 GHz x 2; 2 bit sampling with limited 3 or 4 bit sampling)
    • First quadrant operating in NRAO NTC, to be retrofitted with Tunable Filter Bank enhancement (UBx)
    • Second quadrant being completed at NRAO NTC
    • First installation at AOS TB next year.
    • Detailed list of Observational Modes in ALMA Memo 556 (available at www.alma.nrao.edu)
  • ACA Correlator (NAOJ)
    • First installation at AOS TB next year.
baseline correlator overview
Baseline Correlator Overview
  • Observer may specify a set of disjoint or overlapping spectral regions, each characterized by
    • Bandwidth (31.25 MHz to 2 GHz)
      • Each 2 GHz baseband input (8 available) drives 32 tunable digital filters
    • Frequency (Central or starting)
    • Resolution (number of spectral points)
    • Number of polarization products: 1 (XX or YY), 2 (XX and YY) or 4 (XX, YY, XY, YX cross-polarization products)
    • Improved sensitivity options (4x4 bit correlation, or double Nyquist modes)
    • Temporal resolution depends upon mode (from 16 msec to 512 msec)
  • Simultaneous pseudo-continuum and spectral line operation
multiple spectral line windows
Multiple Spectral Line Windows
  • Multiple spectral windows
    • Within the 2 GHz IF bandwidth
    • For modes with total bandwidth 125 MHz to 1 GHz
    • Useful for high spectral resolution observations of e.g. several lines within IF bandwidth (examples to be shown)
  • Multi-resolution modes
    • Simultaneous high and low resolution
    • Line core and line wings simultaneously
      • Planetary Observations
      • Outflow/Core Observations
  • As an ALMA goal is ease of use, the Observing Tool will guide the observer through the maze of spectral line possibilities
2 antenna correlator
2-antenna Correlator
  • Of the modes of the bilateral correlator, the 2-antenna correlator supports modes 1-18 and mode 70 of the 70 modes listed in Memo 556.
    • Bandwidths of TFBs: 2 GHz, 1 GHz, 500 MHz, 250 MHz, 125 MHz, 62.5 MHz; 8192 channels (single polzn).
    • NO double Nyquist, 3 bit or 4 bit modes available.
  • Also: The bandwidth of the 2-antenna correlator is 4 GHz, not 8 GHz as with the bilateral correlator--two baseband pairs. The full bandwidth would be available for ES.
  • Single, dual, full polzn; 2bit only.
  • Question: Can the ASAC prioritize between modes 1-18, should it not be possible to commission all these modes for ES?
  • Let’s look at some examples.
water
Water
  • Star-forming Regions
    • Shocks, Warm chemically active regions
    • ALMA brings: High resolution, high brightness temperature sensitivity, spectral coverage & flexibility, polarization
  • Stars
    • Near-stellar environment, flow, B-fields
    • ALMA brings: High resolution, spectral coverage & flexibility, polarization
  • Galactic Nuclei
    • ALMA brings: High resolution, high sensitivity, spectral coverage, polarization
example multi transition setup
Example multi-transition setup
  • Goal: Measure water in five transitions simultaneously, some of which mase.
    • H2O J Ka,Kc 1029 936 321.23 GHz ~1800 K ortho
      • E.g. 3-4 Jy SMA; <1” => Tb >? K
    • H218O J Ka,Kc 515 422 322.97 GHz ~500 K para
    • H2O J Ka,Kc 515 422 325.15 GHz ~500 K para
    • H2O J Ka,Kc 523 616ν2 =1 336.23 GHz ~2939 K ortho
    • HDO 331-422 335.396
    • Also CH3OH, SO, SO2 lines
    • Use B7, LSB on maser lines, largest array
    • Dynamic Schedule picks superb weather
      • PWV=0.35mm
    • Beamsize = 0”.013; Tb rms~52K 8 hrs, DS~0.8mJy
    • 5s ints, data rate~30MB/s, dataset size ~860GB.
  • With 2-antenna correlator, one could do first two OR second two, or a mixture using only 2 baseband pairs.
an unfriendly but not obstinate atmosphere
An unfriendly but not obstinate atmosphere…

Chajnantor Atmosphere: 25%=> Tb rms~760K 8 hrs, S~12mJy

choose co isotopes science shepherd drsp sfi case
Choose CO Isotopes Science: Shepherd DRSP, SFI Case
  • Receiver Band: 6
  • Lines: CO(J=2-1), 13CO(J=2-1), C18O(J=2-1)
  • Frequencies (GHz): 230.538, 220.398, 219.560
  • Spectral Resolution (km/s): 0.3 km/s
  • Spectral Coverage (km/s): 150-200 km/s/line
  • Science goals: See DRSP
  • Continuum RMS: 0.03 mJy/beam
  • Line RMS per channel: 15 mJy/beam
  • 1. First LO setting: 225.5 GHz
  • 2. Second LO setting: 8.5 GHz
  • Our two extreme lines then end up at
    • 8.5-5.038=3.462 GHz and
    • 8.5-5.940=2.56 GHz.
alma b correlator setup tunable filter banks
ALMA-B correlator setup Tunable Filter Banks
  • Quadrant 1: CO(J=2-1) in the upper sideband.
  • Other outflow/core lines of interest
    • CO(2-1):
    • CH3OH 8(-1) - 7(0) E at 229.75876 GHz
      • (10 K in OMC1 vs 70 K for CO2-1)
    • SO2 11(5,7) - 12(4,8) at 229.34773 GHz
      • (1.9 K in OMC1)
  • CO: At 230 GHz, 125 MHz = 164 km/s bandwidth w/ 0.32 km/s resolution, ==> 512 channels/line
    • Mode 11, 2x2 bit correlation, 2 Polz, Nyquist
      • 125 MHz BW, 512 channels uses 1/8 of the correlator in 1 quadrant.
    • Mode 29, 2x2 bit corr, 2 Polz, 2*Nyquist
      • 125 MHz BW, 512 channels uses 1/4 of the correlator in 1 quadrant.
slide19
(cont)
  • CH3OH
    • Mode 12, 2x2 bit correlation, 2 Polz, Nyquist
    • 62.5 MH BW, 1024 channels (61 kHz) 0.08 km/s res @ 230 GHz.
    • Uses 1/4 of the correlator in the CO quadrant
    • Decimate the number of channels to decrease data rate:
      • /2 ==> 512 channels, 0.16 km/s resolution.
  • SO2
    • Mode 11 or 29, like CO, owing to expected linewidth
  • Quadrant 1: 3 lines, each with 512 channels using 3/4 of the correlator capacity
second quadrant
Second quadrant
  • 13CO & C18O (J=2-1) LSB
  • Other lines of interest within 2 GHz of these lines:
    • SO 6(5) - 5(4) @ 219.945391 GHz
      • (4.3 K in OMC1)
    • CH3OH 7(1) - 8(0) E @ 220.0786 GHz
      • (6.1 K in OMC1)
    • CH3CN 12(0,1,2,3,4) - 11(0,1,2,3,4)
      • lines centered on 220.730268 GHz
  • Use Mode 11 or 29 again
    • 3/4 of Q2 allocated
third and fourth quadrants
Third and Fourth Quadrants
  • Q3: Continuum USB
  • Q4: Continuum LSB
  • "Time Division Mode” 70
    • 2 GHz, 64 channels covering entire band.
      • Cut out channels with line contamination.
  • OR: 2GHz BW, more channels
      • Decimate according to data rate allowance
slide22
www.alma.info

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership among Europe, Japan and North America, in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere, in Japan by the National Institutes of Natural Sciences (NINS) in cooperation with the Academia Sinica in Taiwan and in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC). ALMA construction and operations are led on behalf of Europe by ESO, on behalf of Japan by the National Astronomical Observatory of Japan (NAOJ) and on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI).