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Calibrator Catalogue

A web-based user interface to the calibrator database is provided through the

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The ALMA Calibrator Source Catalogue is a database of astronomical measurements of calibrator sources, mostly bright quasars in the mm and sub-mm regime. It contains over 11000 ALMA measurements of over 1800 sources (1 July 2015). The most important properties are flux density with uncertainty at a given frequency and angular structure information or limits, and polarization measurements for some calibrators. External information had been provided via 'seed' catalogues, such as from VLA (Calibrator Manual), SMA1,  ATCA, CRATES, and coordinates from VLBI, and we acknowledge the institutions and individuals who contributed this effort. Note that the absolute flux density scale does not include the model uncertainty of the solar system object used as primary amplitude calibrator, and in some cases it can exceed the stated flux density error in the catalogue. Also, the observation and reduction procedures changed in mid-2012, so the measurements before this date may state flux density errors that underestimate the true uncertainty. 

A main use of the database is to allow the selection of bandpass and phase calibrators for science observations. It also contains a set of 30 quasars, grid sources evenly distributed over the sky, which are monitored regularly enough to provide amplitude calibration in addition to solar system objects. Calibrator sources are selected either manually during phase 2 preparation or by the astronomer on duty, or automatically via on-line queries during the execution of the observation. In each case suitable criteria regarding visibility, flux density and proximity to the science targets have to be specified. 

Calibrator observations, outside of science observations, are currently carried out in a special observing mode and have to be fully integrated into science operations. Equally, data reduction and database ingestion has to be automated via the ALMA Pipeline. Access for users is provided via a web-based user interface through the ALMA Regional Centers, and VO integration of special queries is planned for a future Cycle. The intention is to provide a more complex, public search tool for calibrator sources, which can also be accessed through the Observing Tool and included into the Scheduling Blocks.

The Query Form allows to specify various search criteria regarding position, frequency, flux density and time of the calibrator measurements. Equatorial coordinates in J2000 (ICRS) can be specified for the positional search. If no time constraint is given, the latest measurements per day, band and source will be returned. If a time constraint is given, all measurements will be shown with the results table sorted hierarchically by sources. Frequencies can be selected by ALMA band and/or with an additional frequency range. A given source name will first be resolved within the ALMA database, but if no match is found, the coordinates will be resolved via Sesame with a suggested search radius for a cross-check with the ALMA catalogue. The ALMA standard name is defined as the truncated 4-digit hexagesimal RA and DEC J2000 coordinates following the IAU standard. 

The Result Table can be formatted by adding or removing columns, and each column can be sorted. There is an option to download the result in a file (csv or json format). Structure information, expressed as the acceptable uv range, is available for sources where relevant for ranges of ALMA baseline. Uvmin and uvmax columns specify information about the structure of the source. Uvmin gives a detected extent of the source on baselines in klambda (or zero for a limit) and uvmax gives a detection of internal structure of the source resolved on baselines in klambda (or a limit). Coordinates in J2000 (ICRS) and coordinate errors are taken from the VLBI catalogues2. Flux density results are normally averaged over all spectral windows in a band, apart from band 3, where two results are given (for both sidebands, i.e. a lower and higher frequency separated by 12 GHz). Stated flux density uncertainties do not in all cases fully account for uncertainties in the planetary models used for the primary amplitude calibration.  

The Result Plot page displays a positional plot showing all sources as dots colored by bands, which can be specified, and their size representing the latest flux density. A flux density history plot opens when clicking on a source. Both plots can be zoomed, and further source and measurement information is provided in tooltips.

Questions and comments on the use of the interface and the calibrator catalogue are welcome via the ALMA help-desk. 

1 Updated 2016, Mark Gurwell, private communication

2 L. Petrov, C., Phillips, A. Bertarini, T. Murphy, E. M. Sadler, The LBA Calibrator Survey of southern compact extragalactic radio sources - LCS1, 2011, Mon. Not. Roy. Astron. Soc., 414(3), 2528–2539.