Technical handbook alma

However, Band 5 is actually more sensitive in this region and the Observing Tool will force the selection of this band. Bandwidth Per Polarization: 7. For spectral line observations, the width of the resolution element in which the user is interested should be entered.

Water Vapour Column Density: The "Automatic Choice" option will select an appropriate value according to the input frequency.

Alternatively, the user may override this with their own choice. Note though that the OT will always use the automatically-chosen option when calculating a project's estimate time. See the Weather page for further information on weather statistics and atmospheric transmission. ALMA is an interferometer, consisting of a large array of m antennas the "m array" , with baselines up to 16 km, and an additional compact array of 7-m and m antennas to greatly enhance ALMA's ability to image extended targets, located on the Chajnantor plateau at m altitude.

The antennas can be placed on pads in different locations on the plateau in order to form arrays with different distributions of baseline lengths. More extended arrays will give higher spatial resolution, more compact arrays give better sensitivity for extended sources. This array will mostly stay in a fixed configuration and is used to image large scale structures that are not well sampled by the ALMA m array. An interferometer is an instrument that samples the visibility function, which is the Fourier transform of the sky brightness distribution.

This visibility function V u,v is measured as a function of position in the u-v plane. The coordinates u and v simply describe the vectorial separation between each pair of interferometer elements measured in wavelengths, as seen from the source. In order to obtain images, the raw visibility data need to be Fourier transformed. Fully calibrated data cubes are delivered to the user. However, the imaging and subsequent deconvolution is a non-unique procedure, so users may want to redo these steps to optimize the data products for their scientific objectives.

The frequency range available to ALMA is divided into different receiver bands. Data can only be taken in one band at a time. For comparison, a frequency of GHz translates to a wavelength of approximately 1mm. Band 1 around 40 GHz is under construction, and band 2 around 80 GHz might be added in the future.

The m Array will not be sensitive to emission larger than the MRS: it will spatially filter out that emission, leaving holes sometimes called bowls on scales larger than the MRS. This is true even if you make a mosaic that covers a larger target size than the MRS. Depending on the range of angular scales important for your science, you may need the complete ACA, or just the 7-m Array.

However, the sensitivity and quality of your images will be negatively affected. Since interferometric observations must be Fourier transformed before an image can be made, it is sometime not intuitive to visualize what your images will look like. Figure 7. The bandwidth for continuum observations is 7. Spectral lines can be observed with resolutions ranging from 0. Spectral lines and their frequencies can be researched using the spectral line database Splatalogue , which is also available from within the OT.

An overview of Splatalogue is available here. Check out this link to learn more about the wealth of molecular lines that have been observed to date. The angular resolution and LAS needed to observe your target will determine the antenna configuration or configurations and consequently the period of the year when your target will be observed.

If you are planning a high frequency observation check carefully that the period needed for its observation does not coincide with the Altiplanic winter due to the requested angular resolution or daytime due to the requested angular resolution and the target visibility at the ALMA site. Table A1 shows the mapping of antenna configurations to angular resolution and LAS for several representative frequencies.

The registration tab can be found at the top banner of this page. Proposal preparation involves development of the Scientific Justification, optimizing the observational parameters in the OT, and providing a Technical Justification within the OT. Proposals are subject to peer review for scientific value, and to expert assessment for technical feasibility. The Scientific Justification is a free format document which is uploaded as a pdf into the OT.

It is recommended you use the provided Proposal Template to ensure you include all required aspects of your proposal. The guidelines for writing your Scientific Justification are given in Section 5. Each Science Goal requires an accompanying Technical Justification.

This allows to confirm the technical feasibility of your experiment, i. The Technical Justification is a form within the OT where you must justify the observational setup sensitivity, imaging and correlator configuration , as well as non-standard requests. Any item that requires written justification will be highlighted for you when you 'validate' the proposal in the OT. The Science Goal contains the complete observational setups: spatial coordinates and imaging characteristics, frequency band, spectral windows and spectral resolutions, sensitivity requirements and integration time for one or more science targets.

ALMA will use the Science Goals to build one or more Scheduling Blocks SBs , which provide the controlling inputs for the telescope control, which is the reason the Science Goals must have strict limitations. Three doppler corrections types can be selected, depending on the source velocity. Two approximations to the true relativistic velocity are generally used: radio velocities for Galactic targets and optical velocities for extragalactic observations.

The Observation mode for each science goal depends on the expected structure and distribution of your targets. ALMA operations will automatically select the array configurations that will deliver a resolution within your required range of resolutions - thus you will not choose the configuration s ; instead you specify the range of angular resolutions that make your science feasible, and the Largest Angular Structure LAS expected for your targets.

The OT can set up standard baseband and spectral window spw frequencies for continuum observations, avoiding parts of the spectrum with high atmospheric opacity. Spectral lines and their frequencies can be selected from Splatalogue , which is available standalone, and also from within the OT, for plotting on your graphical spectral setup display.