Cycle 9
Observing Capabilities
Hiroshi Nagai, EA-ARC, ALMA Project, NAOJ

1. ALMA Basics

ALMA Arrays
12m array

ACA(7m array + TP array)Three Important Angular Scales
TW Hydra (Tsukagoshi+ 2019)

Largest angular size < MRS

FoVAR

Smoothly distributed emission overthe disk with some variation.

AngularResolution(AR)• Resolution element of image• Determined by the maximum
baseline length (λ/Dmax)

Maximum
Recoverable
Scale (MRS)• The largest structure that can beimaged without missing flux
• Determined by the minimum
baseline length (λ/Dmin)

Field of View(FoV)• FoV of a single telescope pointing• Equal to antenna beam sizeMosaicking / Multiple Pointing• Sources larger than single pointing FoV, or multiple sources spread over alarger area, must be mosaiced together using multiple pointings.
Single pointing

Mosaicking

Multiple pointingFrequency Bands• 10 receiver bands (Band 1&2 will be available future)• Multiple band data cannot betaken simultaneously.
• Atmospheric opacity and phasestability tends to be poor at
higher frequencies and at
frequencies near waterabsorption lines.
• Requires good weather
condition

Frequency vs. Weather

Instantaneous frequency coverage
Lower sideband

Upper sideband• ALMA receives signals in two sidebands (green-ish color).
• Up to four basebands can be placed either in a sideband or two sidebands. (not possible
to put 3 in one sideband and 1 in the other. )• Possible to place up to four spectral windows (spws) within each of these basebands(blue-ish bars) .
• Each spw forms a final contiguous spectrum (You will not receive data outside of spws)

Intermediate Frequency (IF) Range

4.5 GHz10 GHz4.5 GHz10 GHzFor the case of Band 6, IF range is from νLO1+/- 4.5 GHz to νLO1+/- 10 GHz, andtherefore the width of each sideband is 5.5 GHz.

Frequency Resolution

OT⇒

Polarization
Xpol, Ypol
Antenna m
Xpol, Ypol
Antenna n

ALMA correlator

𝑋𝑋𝑚𝑚 𝑋𝑋𝑛𝑛∗ = 𝐼𝐼 + 𝑄𝑄
𝑌𝑌𝑚𝑚 𝑌𝑌𝑛𝑛∗ = 𝐼𝐼 − 𝑄𝑄
𝑋𝑋𝑚𝑚 𝑌𝑌𝑛𝑛∗ = 𝑈𝑈 + 𝑖𝑖𝑖𝑖
𝑌𝑌𝑚𝑚 𝑋𝑋𝑛𝑛∗ = 𝑈𝑈 − 𝑖𝑖𝑖𝑖

XXDualFull• ALMA can provide full polarization products (XX, YY, XY, YX) so that one canproduce Stokes I, Q, U, and V images.
• At least ~3-hrs observation is required to calibrate instrumental polarization.

2. Cycle 9 Capabilities

New in Cycle 9• Fast regional mapping for solar total power observations• Spectral line VLBI in Band 3• Band 7 Continuum VLBI
• Band 8 up to C-10, Band 9 up to C-9, Band 8 up to C-8

Antennas, Receiver Bands• Number of antennas• ≧43 antennas in the 12-m Array.
• ≧10 7-m antennas (for short baselines) and 3 12-m antennas (for single dish) in theACA.
• Receiver bands• Bands 3, 4, 5, 6, 7, 8, 9, and 10.

Configuration

Config. Schedule

Time MultiplierBasic Observing Modes• Spectral line, continuum, mosaic observations• Spectral line and continuum observations with the 12-m Array and the 7-m Array inall bands• Single field interferometry (all bands) and mosaics (Bands 3 to 9) with the 12-m
Array and the 7-m Array• Single dish spectral line observations in Bands 3 to 8
• Spectral scan (useful for spectral survey and redshift search)• Up to 5 different tunings can be requested.
• Target of Opportunity• Large program• >50 hours for 12m array• >150 hours for 7m array

Polarization• 12m• Single pointing (within 1/3 of primary beam) of continuum and spectral line polarimetry are offeredin Bands 3-7 for linear polarization.
• Only continuum linear polarimetry for mosaicking with default continuum setup.
• Only single pointing within 1/10 of primary beam is offered in Bands 3-7 for circular polarization.
• Systematic error (minimum detectable degree of polarization)• Linear polarization: 0.1-0.2% of peak Stokes I flux and 1 degree in polarization position angle
within 1/3 of PB in both continuum and spectral line observations.
• Linear polarization mosaicking: Within the FWHM of a given pointing, the estimated upper
limits are 4 degrees in polarization position angle and 0.5% in polarization percentage.
• Circular polarization: 1.8% of peak Stokes I flux in both continuum and spectral resolution
observations.
• 7m• Only single pointing (<1/3 PB) or multiple pointings (each of pointing with 1<3 PB FoV), linear
polarization of continuum and spectral line is offered in Bands 3-7. No circular polarization, nomosaicking.
• The systematic error is the same as the 12m case.
• Data combination of 12m and 7m will not be supported.
• A maximum of 75 hrs will be offered.

Long Baseline at High Frequencies

TargetνHF

νLF• C-8/9/10 in Bands 7-10 may require Band-to-Band (B2B)
Phase calibrator
phase transfer calibration in order to find a nearby andsufficiently bright phase calibrator to ensure phasecalibration quality.
• The OT will automatically check the availability of suitable phase calibrators
during proposal validation and will automatically trigger the B2B mode
where required.
• The OT will emit an error if a source does not have a suitable calibrator evenwith B2B. PIs are advised to begin preparing their proposals early to ensurethat a suitable calibrator is available for their targets.
• A maximum of 45 hours observations will be available for the observations
requiring B2B calibrations.

VLBI• VLBI observations in Bands 3, 6 (both continuum and spectral line), & 7(only continuum in Band 7) will be conducted using a “campaign mode”(actual date will be set after the proposal review).
• VLBI observations will be permitted for science targets with correlated flux
densities < 0.5 Jy through use of a passive phasing mode. The user mustselect a bright (>0.5 Jy) phase calibrator (phasor), ideally within 6 or 3
degrees of the science target.
• The proposers are required to enter a VLBI total time requested.
• ALMA’s VLBI observing window in a given cycle will not exceed twoweeks, so if multi-epoch observations are requested, they must fit
within that time frame and the total time request must be theaggregate time of all observations.

Pulsar observations• Users can propose pulsar observations with the aid of phase-up mode thatworks as “a large single dish”.
• Only pulsar-science projects will be accepted for this mode.
• Both time domain data in PSRFITS format and standard interferometric data
will be provided.
• Time resolution of time domain data is an integer multiple of 8 μs.

Solar Observations• Proposals will be accepted for ALMA interferometric and Total Powerobservations.

• Will be conducted only during the periods when the 12-m Array is in one of theallowed configurations for the requested band, namely C-1 to C-4 for Band 3, C-1 toC-3 for Band 5, C-1 to C-3 for Band 6, and C-1 to C-2 for Band 7.
• The interferometric component of Solar observations will be conducted using a
special combined array comprising both 12-m and 7-m antennas (to ensure sufficient
short baselines).

• Observations may be performed using dual linear polarization (XX, YY) or
single polarization (XX) correlations; full polarization measurements are notcurrently offeredSolar Observations• The Total Power component of solar observations consists of fast-scanningmapping observations to recover the largest angular scales forinterferometric observations. Proposals requesting only Total Power singledish observations will not be accepted. The Total Power observations will betaken contemporaneously with the interferometric observation.
• Time cadence of full-sun images is about 10, 13, 15 and 25 minutes for Bands 3, 5, 6,and 7, respectively.
• Time cadence of fast regional mapping (small FoV around a region of interest)

Calibration Accuracies• Image dynamic range (Ipeak/rms)• ~100 for compact 12m arrays and ACA, ~50 for more extended than ~2km and at Bands 8,9, and 10 for
nominal phase calibration.
• Self-calibration will be required to achieve image DR of ~1000 or larger.

• Absolute flux accuracy• ~5% in Bands 3-5, ~10% in Bands 6-8, ~20% in Bands 9-10

• Spectral dynamic range (desired SNR per spectral resolution element)• Demonstrated ~1000 in Bands 3-6 (except for Ozone line at 183GHz in Band 5), ~400, 250, 170, and
150 in Bands 7, 8, 9, and 10, respectively, but spectral DR can depend on the brightness of bandpass
calibrator (see THB 10.4.6 for more details).

• Total power calibration accuracy• 5% in Bands 3-7, 15% in Band 8• Astrometric accuracy• At best ~5% of synthesized beam for angular resolution > 150 mas, ~10% of synthesized beam forhigher angular resolution.
• Choose “enhanced position accuracy” in the OT if you need astrometric accuracy better than thenominal one.