############################################################################ This REAME file contains a description of the W51 ALMA Band 1 Science Verification data, calibration, scripts, and data products. The continuum, CS, SiO, CH3OH, and SO2 at 7 mm are observed. A few additional lines are detected. 20 antennas are used for the observations, and the baseline lengths range from 15 to 1080 m. The resolution achieved is ~1.8 x 1.2 arcseconds. The RMS achieved is ~0.8 mJy in the continuum image, and it is limited by the dynamical range. The maximum S/N is ~840. The RMS achieved in the line images range from 5 to 12 mJy per 0.4 km/s channel, depending on the line frequency and weighting parameter. Additional information can be found in the comments section included in this README. The Calibrated Data and Reference Images provided here were produced using CASA version 6.5.5. ############################################################################ W51_Band1_Scripts.tgz contains the calibration and imaging scripts: * uid___A002_X1048ed8_X4af7.ms.scriptForCalibration.py * uid___A002_X1050cd9_X8895.ms.scriptForCalibration.py * W51_Band1_SelfCalibration.py * W51_Band1_Imaging.py W51_Band1_UncalibratedData.tgz contains the raw data in tar packages: * uid___A002_X1048ed8_X4af7.tar * uid___A002_X1050cd9_X8895.tar W51_Band_Calibration.tgz contains the plots generated during the standard calibration of the data: * X4af7_plots * X8895_plots W51_Band1_SelfCalibration.tgz contains the self-calibration tables and plots of the gain solutions which are produced with the self-calibration script (W51_Band1_SelfCalibration.py) and are applied to the concatenated data after the standard calibration (uid___A002_X1048ed8_X4af7.ms.scriptForCalibration.py and uid___A002_X1050cd9_X8895.ms.scriptForCalibration.py). The self calibration is conducted with the continuum data, and the solutions are applied to both continuum and line data. W51_Band1_CalibratedData.tgz contains the self-calibrated uv data: * W51_Band1SV_apcal_CH3OH.ms * W51_Band1SV_apcal_CS.ms * W51_Band1SV_apcal_SiO.ms * W51_Band1SV_apcal_SO2.ms * W51_Band1SV_avgcont.apcal.ms * W51_Band1SV_noavg.apcal.ms W51_Band1SV_noavg.apcal.ms is the self-calibrated uv data containing all spectral windows without channel averaging. W51_Band1SV_avgcont.apcal.ms is the self-calibrated and channel-averaged continuum data. Others are the self-calibrated and continuum-subtracted line data. The self calibration is conducted with the continuum data, and the solutions are applied to both continuum and line data. To recreate these data, users can first execute the standard calibration scripts (uid___A002_X1048ed8_X4af7.ms.scriptForCalibration.py and uid___A002_X1050cd9_X8895.ms.scriptForCalibration.py), and then execute the self-calibration script (W51_Band1_SelfCalibration.py). W51_Band1_ReferenceImages.tgz contains the line and continuum image products: * W51_Band1SV_CH3OH_48372MHz.image.fits * W51_Band1SV_CH3OH_48372MHz.image.mom8.fits * W51_Band1SV_CH3OH_48372MHz.image.pbcor.fits * W51_Band1SV_CH3OH_48376MHz.image.fits * W51_Band1SV_CH3OH_48376MHz.image.mom8.fits * W51_Band1SV_CH3OH_48376MHz.image.pbcor.fits * W51_Band1SV_cont.image.tt0.fits * W51_Band1SV_cont.image.tt0.pbcor.fits * W51_Band1SV_CS.image.fits * W51_Band1SV_CS.image.mom8.fits * W51_Band1SV_CS.image.pbcor.fits * W51_Band1SV_SiO.image.fits * W51_Band1SV_SiO.image.mom8.fits * W51_Band1SV_SiO.image.pbcor.fits * W51_Band1SV_SO2.image.fits * W51_Band1SV_SO2.image.mom8.fits * W51_Band1SV_SO2.image.pbcor.fits These reference images can be recreated by executing the imaging script (W51_Band1_Imaging.py) with the calibrated uv data contained in W51_Band1_CalibratedData.tgz. ############################################################################ COMMENTS: +Observations Two executions (X4af7 and X8895) were carried out on Mar 25 and Apr 4, 2023 with total on-source time about 70 min. 18 antennas and 20 antennas participated to X4af7 and X8895, respectively. Typical PWV during observations was 2.6mm for X4a7f and 1.8mm for X8995. Maximum baseline length was about 1 km. The target source is W51, which is a well-known high-mass star forming region. In total 6 spectral windows (spw) are used to cover CH3OH, CS, SiO, and SO2 lines as well as the continuum emission. +Calibration Calibration was done using standard calibration script for QA2. Some additional flagging was added in the step=10 to flag out spurious-like features. J1924-2914 is used for bandpass calibration and flux scaling. The flux model for J1924-2914 was used from the measurement in Band 1 on Mar 30, 3023. In addition to Tsys and WVR correction, temporal gain time variation was calibrated using J1924+1540. +Self calibration The data after the standard calibration were concatenated, and lines were flagged to generate channel-averaged continuum data. The self calibration was conducted on the channel-averaged continuum data, and then the solutions were also applied to the concatenated data without channel averaging and line flagging. Five runs of phase-only calibration and one run of amplitude+phase calibration were done. During this process, the thresholds of tclean and solution intervals were gradually reduced in each run. The final amplitude+phase self calibration was done with a solution interval of one scan. After the self calibration, the RMS in the continuum image decreases by ~75%. +Maximum recoverable angular scale The 5th percentile of the baseline lengths is ~65 m, and the maximum recoverable angular scale is ~20”. Thus, due to the limited uv coverage and the complex structures in the target, the intensity distribution of the extended diffuse emission is more uncertain. +Continuum subtraction The continuum subtraction was conducted in individual narrow spectral windows for lines using uvcontsub. There are several bright continuum sources with different spectral profiles in the field, and uvcontsub was not able to properly subtract the continuum from the wide spectral windows of a ~2GHz bandwidth, so the data product does not include continuum-subtracted wide spectral windows. Users may select a part of the channels of the wide spectral window to do continuum subtraction or conduct continuum subtraction in the image domain. +Imaging All the reference images were generated using tclean with auto-masking. Robust parameters of Briggs weighting and parameters for auto-masking were adjusted to better present the structures of the emission. +Using the data for publication The following statement should be included in the acknowledgement of papers using the dataset listed above: "This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00021.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ." ############################################################################ HOW TO EXECUTE THE CALIBRATION SCRIPT: Note: AnalysisUtils are used for producing some plots. AnalysisUtils can be downloaded from https://casaguides.nrao.edu/index.php/Analysis_Utilities, and for the purpose of producing calibrated MSs, users can set applyonly = True when running the scripts. (1) Put the ALMA raw data and calibration scripts in the same directory (2) In CASA 6.5.5 > applyonly = True > execfile(‘uid___A002_X1050cd9_X8895.ms.scriptForCalibration.py’) > execfile(‘uid___A002_X1048ed8_X4af7.ms.scriptForCalibration.py’) HOW TO EXECUTE THE SELF-CALIBRATION SCRIPT: NOTE: mpicasa for parallel processing is used. (1) Put uid___A002_X1048ed8_X4af7.ms.split.cal, uid___A002_X1050cd9_X8895.ms.split.cal, and the self-calibration script in the same directory (2) In MPI CASA 6.5.5 > execfile(‘W51_Band1_SelfCalibration.py’) HOW TO EXECUTE THE IMAGING SCRIPT: NOTE: mpicasa for parallel processing is used. (1) Put W51_Band1SV_avgcont.apcal.ms, W51_Band1SV_apcal_CH3OH.ms, W51_Band1SV_apcal_CS.ms, W51_Band1SV_apcal_SiO.ms, W51_Band1SV_apcal_SO2.ms, and the imaging script in the same directory (2) In MPI CASA 6.55 > execfile(‘W51_Band1_Imaging.py’)