ALMA ACA Spectrometer

The ACA Spectrometer (ACASPEC) is a new spectrometer developed for science observations on the Total Power Array (TP Array) in the Atacama Compact Array (ACA). Led by KASI in collaboration with NAOJ, the ACASPEC replaces the functionality of the ACA Correlator (ACACORR) for the TP array. It utilizes general-purpose graphics processing units (GP-GPUs) to process signals in software. The ACASPEC enables independent operation of the TP Array, bringing improved observing efficiency, higher spectral dynamic range, and expandability for the upcoming Wideband Sensitivity Upgrade. Installed in February 2022 at ALMA Array Operations Site, ACASPEC achieved the first light, confirming that all the signal paths from the antennas to the archive were well-connected and processed. Following that, commissioning and science verification (CSV) activities were conducted. Consistency between the ACASPEC and the ACACORR was verified for various spectral setup parameters, the Jy/K conversion factor, and spectral shapes and intensity of emission lines. The spectral dynamic range better than 10000 has been confirmed using the CO line. In addition, the ACASPEC showed enough performance for calibration observations, such as pointing and focus using the cross-correlation products. Finally, end-to-end testing was conducted to verify all processes of TP observations, including connections with other ALMA subsystems. Data processing by the CASA Single-Dish pipeline worked properly for the ACASPEC data in standard On-the-fly mapping and TP spectral scan modes. Detailed comparisons for intensity using data cubes taken by the ACASPEC and the ACACORR also showed good agreement, with more than 85% of data points matching within 20% for both data sets. Following this success of the CSV testing, the ACASPEC will be offered to ALMA science operations in Cycle 10. In this poster, we will present the development of the ACASPEC system and the CSV results.