Science IPT A. Wootten Lead NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Science IPTScience IPT

A. Wootten Lead

NRAO is a facility of the National Science Foundationoperated under cooperative agreement by Associated Universities, Inc.

Science IPT

ALMA Project

AMAC 24-25 March 2003

Science IPT Organization ChartSmallest IPT; ~5 members

Science IPT

ALMA Project

AMAC 24-25 March 2003

Science IPT Milestones

Science IPT

ALMA Project

AMAC 24-25 March 2003

Milestones

• 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

Configuration and Calibration formed focus for 2002-3

Science IPT

ALMA Project

AMAC 24-25 March 2003

Compact Array – Highest Brightness Sensitivity

All 64 antennas cluster withincircle of r~150m

Filling factor ofabout 50%

NS extension for high zenith angle objects.

All antennas accessible

Science IPT

ALMA Project

AMAC 24-25 March 2003

Compact Array Beam

Science IPT

ALMA Project

AMAC 24-25 March 2003

Holdaway Y+ Configuration (Early Version)

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

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

Science IPT

ALMA Project

AMAC 24-25 March 2003

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.

Science IPT

ALMA Project

AMAC 24-25 March 2003

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 < 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.

Science IPT

ALMA Project

AMAC 24-25 March 2003

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 polarizationsPosition 2 * 10-15 cm from the receiver * No polarizationGoal: Decision on whether to pursue this method following tests on IRAM 30m

Semi-Transparent Vane Device: 30m

1 2

Science IPT

ALMA Project

AMAC 24-25 March 2003

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.

Science IPT

ALMA Project

AMAC 24-25 March 2003

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 – 3.5 Supernovae – 3.6 Gamma ray bursts

• Theme 4: Solar system [Leader: Butler]– 4.1 Planetary atmospheres – 4.2 Asteroids and comets – 4.3 Extrasolar planets

Science IPT

ALMA Project

AMAC 24-25 March 2003

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/sensitivity.html

– Based on ALMA memo 393.

• Ninety ‘Proposals’ as of 2003-August-22

Science IPT

ALMA Project

AMAC 24-25 March 2003

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

Science IPT

ALMA Project

AMAC 24-25 March 2003

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 ΔG/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 ΔG/G ~ 10-3 in 1 sec—can 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.

Science IPT

ALMA Project

AMAC 24-25 March 2003

Holdaway’s 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.

Science IPT

ALMA Project

AMAC 24-25 March 2003

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.

Science IPT

ALMA Project

AMAC 24-25 March 2003

Compact Array – Highest Brightness Sensitivity