4 Comparison of the ALMA and Herschel - ESO

Figure 2: The numbered horizontal lines at the top show the coverage of ALMA receiver bands 3 to
10. Receiver bands 3, 6, 7 and 9 are in the North American-European bilateral plan. Receiver bands
4, 8 are to be contributed by Japan. There are plans for Japan to provide Band 10, dependent on R &
D work. Bands 1 and 2 are not yet planned. Six receivers for Band 5 will be provided by EC funding
in FP6. At any time, observations can be carried out with only one receiver band. The coloured curves
shows three atmospheric transmissions for total perceptible water vapour (pwv) amounts of 0.2, 0.5
and 1 mm for Mauna Kea (from http://www.submm.caltech.edu/cso/weather/atplot.shtml).
It is now certain that Japan will enter the ALMA project. Receiver Bands 4, 8 will also be
provided by Japan. There are plans for Japan to provide Band 10 eventually, after further
research and development. Japan will also provide the “ALMA Compact Array” (ACA)
that consists of twelve 7 m antennas to provide measurements of more extended structure
and four 12 m antennas, to be used in the single dish mode to measure the total flux density
of a source. The parameters of the ALMA project given in Table 1 reflect the result of a
rebaseline process for the bilateral array. At present 50 antennas are planned, with an increase
to 64 antennas if funding allows. An interactive sensitivity calculator for all ALMA Bands
except 1, 2 and 10 is at: http://www.eso.org/projects/alma/science/bin/sensitivity.html. This
calculator takes into account the effect of the Earth’s atmosphere.
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