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Knowledgebase: ALMA Observing Tool (OT)
How can I request Atacama Compact Array (ACA) observation time?
Posted by Sarah Wood, Last modified by Sarah Wood on 02 April 2019 01:24 PM

The Atacama Compact Array (ACA) will be automatically selected by the Observing Tool (OT) when needed (see the section "Imaging Considerations - Arrays and Configurations" in the ALMA OT User Manual). The OT will decide whether the ACA is needed, based on the PI-requested "largest angular scale" (LAS). This value is compared to the "Maximum Recoverable Scale" (MRS) of the 12-m Array (as listed in Table A-1 of the  ALMA Proposer's Guide). If LAS>MRS, then the ACA will be used. This selection cannot be overridden by the user.

There is also the possibility to request ACA stand-alone observations using the appropriate button. TP stand-alone observations are not permitted.

Note that Total Power (TP) observations are only allowed for spectral line observations in Band 3-8. For Band 9 and Band 10 observations or continuum observations in any band, the TP array is not allowed and such projects requesting the ACA must additionally have a PI-requested LAS that is less than the Maximum Recoverable Scale for the ACA 7-m Array (as listed in Table A-2 of the ALMA Proposer's Guide). 

For more details, see the relevant section in the ALMA Technical Handbook. For a video explanation on the definition of Largest Angular Scale, please follow: Largest Angular Scale Video

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