Site
ALMA is constructed on the Chajnantor plateau, at 5000 m altitude, near San Pedro de Atacama, in northern Chile. The Array Operations Site (AOS) is the location of the ALMA array and of the correlator building on the Plateau. All operations control and antenna maintenance is performed from the Operations Support Facility (OSF), at ~2800 m altitude. The antennas are currently being assembled at the OSF, in the contractors' areas. The antennas will be transported by Otto and Lotte, at the OSF (integration, tests, maintenance), between the OSF and the AOS (30 km road), and at the AOS (change of configuration).

Webcam at the OSF: camera1, camera2.


Array
  • 50 12-m antennas; 2  types of antennas (delivered by the US/Vertex and EU/Alcatel);
  • 4 12-m antennas (JP/MELCO) equipped for single-dish measurements (wobbling secondary), to measure the zero-spacings;
  • 12 7-m antennas (JP/MELCO), to measure the short-spacings, or make additional (calibration) measurements; they form the ALMA Compact Array (ACA);
  • Continuous reconfiguration of the array, from a compact configuration (max. baseline ~ 200 m) to the most extended Y+ configuration (14 km); the full cycle can be 12 to 18 months;

Receivers
All ALMA and ACA antennas will be equipped 6 receiver bands. At a later stage of the ALMA developments, up to 10 bands may be installed in the cryostats.
Band
 Frequency
range (GHz)
Bandwidth
 Trec
 Produced by
1
 31-45

not built
2
 67-90

not built
3
 84-116
 2x4 GHz (2SB)
 37
 HIA
4
 125-163
 2x4 GHz (2SB)
 51
 NAOJ
5
 163-211
 2x4 GHz (2SB)
 65
 OSO
6
 211-275
 2x4 GHz (2SB)
 83
 NRAO
7
 275-373
 2x4 GHz (2SB)
 147
 IRAM
8
 385-500
 2x4 GHz (2SB)
 196
 NAOJ
9
 602-720
 8 GHz (DSB)
 175
 SRON
10
 787-950
 8 GHz (DSB)
 230
 NAOJ

Band 3, 4, 6, 7, 8, 9 are in the baseline project. Development of band 5 (for 6 antennas only) and band 10 are also taking place. Bands 1 and 2 are not being built. The receiver temperatures are the specs (max. Trec over 80% of the RF band); see the ESO front-end pages for more details.

The table below gives the correspondance between the Plateau de Bure and the ALMA bands, in the atmospheric windows that can be observed with the PdBI.

Atmospheric window
 PdBI
 ALMA
3 mm
 Band 1
 Band 3
2 mm
 Band 2
 Band 4
1.3 mm
 Band 3
 Band 6
0.8 mm
 Band 4
 Band 7

The exact frequency coverage may be slightly different at the edges of the bands. Note that, PdBI band 4 (to be installed in winter 2008/09) are copies of the ALMA band 7 mixers.

Correlator

The ALMA correlator is installed in a building at the high-altitude site (AOS). It is composed of four quadrants, each of which can process data coming from 16 different antennas (the complete correlator can thus process 64 antennas). The ACA array has its own correlator.

The ALMA memo 556 gives more detailed information on the (many) correlator modes available. Only a subset of these modes are planned to be available during the Early Science.


Sensitivity
The ESO web site provides an on-line ALMA sensitivity estimator.
Caution: point-source sensitivity only depends on the collecting area. Brightness sensitivity - which is the number to check for extended sources - depends on the angular resolution. Doubling the angular resolution (e.g. from 0.5 to 0.25 arcsec) implies a brightness sensitivity reduced by a factor four (e.g. from 0.1 to 0.4 K rms).  This is because the angular resolution is improved while the collecting area remains the same. Please consider this effect when planning observations: the brightness sensitivity depends on the angular resolution.


ALMA data reduction
The ALMA data reduction package will be CASA, developed by NRAO. The beta version has been released in October 2007, a patch 1 is available since April 2008.

The native data format for ALMA will be the ALMA Science Data Model (ASDM). The current version is 5.0.
Observing time on ALMA

There is no guaranteed time on ALMA. For the time being, there are no plans to have specific large or key programs. There should be one Time Allocation Committee (TAC) per partner, i.e. one for the European community. ESO has ~35% of the ALMA observing time (~35% for the North American partners, ~20% for the Eastern-Asia partners, and 10% for Chile).