Impact of WSU on Spectral Index Determination and Calibration Methods

Impact of WSU on Spectral Index Determination and Calibration Methods Poster abstract: The Wideband Sensitivity Upgrade (WSU) promises to revolutionise ALMA's performance, particularly enhancing spectral index (alpha) determination and expanding calibration strategies. This poster highlights the significant advancements introduced by the WSU, focusing on its impact on the precision of alpha measurements and the calibration methods. The expanded frequency range and the wider bandwidth provided by the WSU will be instrumental in reducing the uncertainty of alpha measurements, which introduces a new realm of flux calibration possibilities. Also, the larger continuum bandwidth in ALMA observations raises the SNR of calibrator gain solutions, enabling the use of fainter, closer quasars as phase calibrators. This is especially beneficial in high-frequency (HF) bands, where accuracy in phase transfer is critical due to larger relative antenna position errors. Moreover, the increased SNR allows for more precise calibration of narrow spectral windows, providing greater resilience against instrumental drifts. It also opens up the potential for shorter calibration cycles, reducing residual phase errors, particularly important for long baseline and HF observations. Lastly, the WSU's broader bandwidth makes continuum self-calibration feasible for a larger number of science targets, significantly mitigating residual antenna position errors even when the SNR is low. This represents a major step forward in achieving higher accuracy and efficiency in astronomical research.