ALMA Observation overview

Kazuya Saigo (Chile Observatory, NAOJ)

ALMA (Atacama Large Millimeter/submillimeter Array)• Chajnantor plain of the Chilean Andes at an elevation of about 5000m• International collaboration project of EA, NA, EU + Chile• Observations are made based on the proposals from users(~1 year proposal cycle from 2011).

ALMA Regional Centers
NA ARCEU ARC- All researchers in the world have chances to get ALMA
observation time.
- ALMA observatory will carry out observations andEA ARC calibration/imaging for successful proposals.
- ALMA is a general purpose telescope. Users request
the desired observation by setting many parameters.
Here, I will explain some basic parameters.

Three important spatial scales I. Spatial Angular Resolution (AR)Spatial Angular Resolution is determined by antenna configuration and frequency.
* AR ~ λ /Lmax

where Lmax is the longest baseline lengthInterferometers can observe with extremely high spatial resolution.
Maximum angular resolution ~0.02arcsec[Lmax=16.2km, ν = 230GHZ (λ=1.3mm)]

Compact Antenna Configuration
VExtended Antenna Configuration

North poleVLmax

North poleLmaxUUExamples of ALMA High Spatial Resolution Observation
Protoplanetary DisksHL TauBand 4 (continuum)

AU scale hole in theTW Hydrae
Band 7 (continuum) Disk
Beam Size ~ 30 mas (1.6AU)
1 arcsec =140au
Beam ~30mas (4au)
ALMA Partnership et al., 2015, ApJ, 808, L3Andrews et al., 2016, ApJ, 820,L40

Three important spatial scales II. Maximum Recoverable Scale (MRS)
Maximum Recoverable Scale (MRS) and Largest Angular Scale (LAS)In principle, interferometer fail to sample information of the expanded structure.
MRS is the largest smooth angular structure that can be obtained in a given array
configuration (~ λ /Lmin Lmin is the shortest baseline length ).

30arcsec

User requests the largest spatial scale that you want to obtain (Largest Angular Scale =LAS )Note that it is not a target source size.
If it can not be obtained with a single array, ALMA observatory carry out multiple arrays observation.

Three important spatial scales III. Field of View (FoV)
Field of View (FoV)
In the interferometer observation, images can be obtained even with only single
pointing observation.
Sensitivity declines from the pointing center.
FoV is a region (size) with sensitivity having higher than
50% of that of the central position.

DantEx. FoV of 12m antenna at 230GHz is ~25arcsec* An image of a region larger than FoV can beobtained by Mosaic observation using multi pointing.

Key words for frequency setting• BandObservable range of each receiver
ALMA telescope covers with a range of 84GHz〜950GHz by 7
receivers (Band3 - band 10)• SPW (Spectral Window)
One frequency setting for observation (center frequency,frequency resolution). ALMA can observe multiple SPWs
simultaneously.

www.almaobservatory.org
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership among
Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by theEuropean Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S.
National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and theNational Science Council of Taiwan (NSC) and in Japan by the National Institutes of Natural Sciences (NINS) incooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe byESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated
Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint
ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning andoperation of ALMA.