Science IPT

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Science IPT

• A. Wootten
• Lead

NRAO is a facility of the National Science
Foundation operated under cooperative agreement
by Associated Universities, Inc.
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Science IPT Organization Chart
Smallest IPT 5 members
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Science IPT Milestones
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Milestones
Configuration and Calibration formed focus for
2002-3

• Configuration
• Level 2 Oct. 2002 J. Conway
• Plan for compact and intermediate configurations
  staked at Chajnantor
• Document approved construction planning under
  way.
• Level 2 June 2003 M. Holdaway
• Plan for Y configuration finalized, iteration
  with site engineers testing subsoil quality under
  way alternative locations proposed for possible
  problem sites.
• Level 2 June 2004 J. Conway
• Plan for Early Science configurations complete

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Compact Array Highest Brightness Sensitivity
All 64 antennas cluster within circle of
r150m Filling factor of about 50 NS extension
for high zenith angle objects. All antennas
accessible
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Compact Array Beam
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Holdaway Y Configuration (Early Version)

• Nearin sidelobe response optimized (6-7 goal)
• Uses older, less accurate but large coverage
  digital elevation maps, so 100m errors
• Positions staked out April 2003 plan submitted
  June 2003.

New Y configuration achieves better point
source discrimination performance than previous
or than ring designs.
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Milestones Calibration

• Level 2 February 2003 S. Guilloteau, Butler
  
• Review of calibration requirements with science
  examples complete.Includes - Phase - Amplitude
  - Bandpass - Baselines - Polarization -
  Illumination Offset Opacity - Decorrelation
  Correction - Pointing and Focus
• Level 2 April 2003 Hills, Richer
• Review of technical specifications for
  calibration items complete WVR, FTS,
  weather station
• Level 2 Q4 2003 B. Butler
• Calibration strategy finalized
• Level 2 September 2004
• Selection of WVR strategy
• Level 2 December 2004 Butler
• Review of tests of calibration strategies on
  prototype interferometer complete with evaluation
  receivers.

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Status of Calibration

• Draft plan available, discussed in Cal Group
  telecon
• Submitted to Project Q4 2003
• Some questions remain about amplitude calibration
• Semi-transparent vane tests suspended by FE Group
  at 30m
• No device appears capable of producing 1 goal
  errors
• Propose a specification of 3 accuracy lt 300
  GHz, 5 above
• Tests to begin at Berkeley of absolute
  calibration scheme as proposed by Welch,
  Guilloteau and Gibson.
• Implementation at ATF with evaluation front ends
  2004
• Status of WVR tests remains undecided.

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Semi-Transparent Vane Device 30m
Semi -Transparent Vane Device Purpose
provide accurate calibration, particularly for
nearly saturated detectors. Design Rotary
actuator (switch time 1 s) 90 and 230 GHz
observations Standard calibration
system Position 1 1.5 m from the receiver
Orthogonal linear polarizations Position 2
10-15 cm from the receiver No
polarization Goal Decision on whether to pursue
this method following tests on IRAM 30m
1 2
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Design Reference Science Plan

• Under construction, early compilation under way.
• Provides a quantitative reference for
• developing the science operations plan,
• for performing imaging simulations,
• for software design, and
• for other applications within the ALMA project.
  Specifically, it can be used to
• allow cross-checking of the ALMA
  specifications against "real" experiments
• allow a first look at the time distribution
  for
• configurations
• frequencies
• experimental difficulty (fraction of projects
  pushing ALMA specs)
• start developing observing strategies
• derive "use-cases" for the Computing IPT
• be ready in case some ALMA rescoping is
  required, or in case some ALMA specifications
  cannot be met.

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DRSP Themes

• Theme 1 Galaxies and Cosmology Leader
  Guilloteau
• 1.1 The high-redshift universe
• 1.2 Gravitational lenses
• 1.3 Quasar absorption lines
• 1.4 SZ with ALMA
• 1.5 Gas in galactic nuclei
• 1.6 The AGN engine
• 1.7 Galaxies in the local universe
• 1.8 ALMA and the Magellanic Clouds
  
• Theme 2 Star and planet formation Leader
  Wootten
• 2.1 Initial conditions of star formation
• 2.2 Young stellar objects
• 2.3 Chemistry of star-forming regions
• 2.4 Protoplanetary disks
• Theme 3 Stars and their evolution Leader
  Cox
• 3.1 The Sun
• 3.2 Mm continuum from stars
• 3.3 Circumstellar envelopes
• 3.4 Post-AGB sources

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Three Year Duration

• Theme 1 Galaxies and Cosmology 40 14.4
  months 10500 hr
• Theme 2 Star and Planet Formation 30 10.8
  months 7880 hr
• Theme 3 Stars and their evolution 20 7.2
  months 5250 hr
• Theme 4 Solar system 10 3.6
  months 2620 hr
• Employ sensitivities on the ESO ALMA Web at
• http//www.eso.org/projects/alma/science/bin/sensi
  tivity.html
• Based on ALMA memo 393.
• Ninety Proposals as of 2003-August-22

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Schedule

• Sep 1 First analysis by Project
  Scientists complete
• Sep 5-6 Presentation to ASAC
• Sep 22 Semi-final document sent to all
  contributors for review
• Oct. 1 Comments due
• Oct 15 Delivery of document to project

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Imaging Total Power Simulations

• A science requirement is to provide precise
  images at an angular resolution of 0.1. Here
  the term precise image means representing within
  the noise level the sky brightness of all points
  where the brightness is greater than 0.1 of the
  peak image brightness. This requirement applies
  to all sources visible to ALMA that transit at an
  elevation greater than 20 degrees. --Project
  Plan Chapter 2.
• Estimates suggest that the sky will permit this
  at Chajnantor, and the receiver complement will
  if the gain stability is ?G/G 10-4 in 1 sec
  (Wright Memo Welch Memo). This is a canonical
  value for cm receivers and has been obtained with
  mm receivers.
• However, the revolutionary ALMA receivers may not
  come within an order of magnitude of this
  stability. Preliminary Band 6 tests suggest ?G/G
  10-3 in 1 seccan ALMA meet the imaging goal
  above?
• Simulations of on the fly imaging under way show
  that the sky is not a limiting factor techniques
  of OTF may improve on this.

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Holdaways Simulation Suite

• AIPS implementation includes
• Latest atmospheric models (Pardo 2003)
• Site testing database (data 1996-2001 from site)
• ALMA array sensitivity from Draft Front End
  Specifications
• Antenna motion profiles from VERTEX documents 1
  msec grid
• Receiver gain stability
• Beam switching (nutator)
• Routine to produce statistics of site database
• Results include
• Optimal slew velocity, given particular weather
  conditions
• Very large parameter space, but one can select
  OTF parameters such that thermal noise rather
  than atmosperhic fluctuations dominate in all
  studied cases.
• Original surmise, that nutators are superfluous,
  is supported.
• Receiver stability is now the focus of the
  investigation.

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Dual Load Calibration System BIMA

• Purpose provide accurate calibration,
  particularly for nearly saturated detectors.
• Tests completed at BIMA writeup in progress.
  Tests concentrate on accurate and reproducible
  measurements of the coupling coefficient, on
  elimination of standing waves
• Standing waves
• Standing wave seen due to some mismatch in the
  coupling to the loads?
• Solution awaits measurement of the broadband
  coupling coefficient.
• Standing wave problem unsolved not understood.
• Test the scheme in interferometric mode,
  calibrate actual observations
• Replicate the system on a second antenna
• Outlook Probably not employed on ALMA but
  research continues through tests of alternative
  system during May for June decision.
• June 2003 Decision not to pursue this design.

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Compact Array Highest Brightness Sensitivity