ALMA B5 SCIENCE VERIFICATION ON VY CMa (Spectro-polarimetry observing mode) The observations were taken on 16 October 2016, from 05:45 to 12:09 UT, with a long gap at the middle of the observations (between 8:30 and 10:30 UT) due to the high elevation of the target. There was a total of 15 antennas participating in the observations. Two of these antennas (DV05 and DA58) were discarded, due to either too high system temperatures or bad-quality data. There are five spws in this dataset: two centered around 183.5 GHz (spws 0 and 1), and three at around 172 GHz (spws 2, 3, and 4). Spws 0, 3, and 4 have narrow channel widths (244 KHz), furthermore spw 1 is very close to the water atmospheric line. Spws 1 and 2 have channel widths of 1.95 MHz and so are about 8 times wider than spw 0. Hence, the most logical approach is to calibrate spw 0 by transferring the gain solutions from spw 1. This includes solving for phase (through an extra gain table) and amplitude (through non-normalised bandpass tables using provided bandpass calibrator fluxes) offsets between the spectral windows. Regarding spws 3 and 4, the signal from the calibrators is strong enough for a successful calibration without transferring phase solutions from spw 2. There were a total of three execution blocks. The observations to calibrate the bandpass are skipped in the second EB (observed as part of the polarisation session), whereas the bandpass calibrators on the first and last EBs are different, and the one in the first EB of poorer quality. Due to these limitations, we decided to perform the a priori calibration (i.e., WVR, Tsys, and antenna-positions) on each EB separately, but then concatenate the three EBs for the rest of the calibration, in order to optimize the calibration using the joint information from all three EBs. The polarization calibration close to the water line results in unrealistically high polarization-leakage terms, likely due to the (elevation-dependent) higher noise caused by the atmospheric absorption. Hence, the polarimetry on spws 0 and 1 should be taken with much care. In any case, the full-polarization images of the polarization calibrator are self-consistent among all the spws. Regarding spws 2 to 5, the polarization calibration is successful. No spectral features are seen, neither in the polarization calibrator data nor in the calibration tables, whereas clear spectral features (a systematic drift of the polarization angle accross the SiO line) are seen in the target. These signatures on the science target are thus deemed to be real. ################################## RE-GENERATING THE CALIBRATION: In order to re-generate the full calibration of these data, the user should: 1.- Perform the a-priori calibration on each Execution Block, by running all the steps in the following scripts: uid___A002_Xb978c3_X116b.ms.scriptForAPrioriCalibration_noplots.py uid___A002_Xb978c3_X1955.ms.scriptForAPrioriCalibration_noplots.py uid___A002_Xb978c3_X262a.ms.scriptForAPrioriCalibration_noplots.py The ASDM of each EB should be located in the current working directory when each of these scripts is being run. 2.- Concatenate the EBs and perform the ordinary calibration on the concatenated dataset. For this, you need to create a new directory and move the "*.split.cal" measurement sets (generated in the previous step) into that directory. Then, execute all the steps in the script: uid___A002_Xb978c3_concatenated.ms.split.scriptForCalibration_samedir_noplots.py 3.- Calibrate the full polarization: From the same directory where the previous step has been run, execute all the steps in: uid___A002_Xb978c3_concatenated.ms.split.cal.scriptForPolCalibration.py At this stage, the data is ready for imaging. ####################################### REGENERATING THE IMAGES: move the uid___A002_Xb978c3_concatenated.ms.split.cal.polcal calibrated file to an imaging directory. 4.- To generate diagnostic images of the calibrators, execute the steps in: VYCMa_scriptForImaging_Calibrators.py 5.- To image the science target, execute the steps in: VYCMa_scriptForImaging.py The imaging script includes a number of different steps. 0) First, mstransform is used to correct for velocity drift during the observations. This is done in order to be able to perform self-calibration on a single strong maser channel. 1) After this correction, the continuum is subtracted. 2,3) Several rounds of phase and amplitude self-calibration are performed on a strong isolated maser feature of SiO in spw3. These solutions are applied to all the data. 4) With the corrected data, a new continuum subtraction is performed. 5) The continuum is imaged in stokes I, using the channels away from the atmospheric water line. 6) Full polarisation images are created for the SiO maser in spw3. A dynamic range of >4000 is reached. 7,8) As the phase transfer between the SiO in spw3 and the H2O in spw0 is not optimal because of the atmospheric water line, a new phase and amplitude self-calibration is performed on the H2O maser. 9) The full H2O spw0 is imaged in Stokes I. In the strongest maser channels, a dynamic range of ~850 is reached. Note that because of the poor bandpass calibration in spw0, the flux scale of the H2O masers is likely fairly uncertain. I might be possible to further improve this by investigating the source continuum. ####################################### CONTENTS VYCMa_Band5_PolCalibrationInformation.pdf VYCMa_Band5_FullPol_UncalibratedData.tgz * uid___A002_Xb978c3_X116b * uid___A002_Xb978c3_X1955 * uid___A002_Xb978c3_X262a VYCMa_Band5_FullPol_CalibratedData.tgz * uid___A002_Xb978c3_concatenated.ms.split.cal.polcal VYCMa_Band5_FullPol_Scripts.tgz * uid___A002_Xb978c3_X116b.ms.scriptForAPrioriCalibration_noplots.py * uid___A002_Xb978c3_X1955.ms.scriptForAPrioriCalibration_noplots.py * uid___A002_Xb978c3_X262a.ms.scriptForAPrioriCalibration_noplots.py * uid___A002_Xb978c3_concatenated.ms.split.scriptForCalibration_samedir_noplots.py * uid___A002_Xb978c3_concatenated.ms.split.scriptForPolCalibration.py * VYCMa_scriptForImaging_Calibrators.py * VYCMa_scriptForImaging.py VYCMa_Band5_FullPol_ReferenceImages.tgz * VYCMa.spw0.pb.fits * VYCMa.spw0.pbcorr.fits * VYCMa.spw3.I.pb.fits * VYCMa.spw3.I.pbcorr.fits * VYCMa.spw3.Q.pb.fits * VYCMa.spw3.Q.pbcorr.fits * VYCMa.spw3.U.pb.fits * VYCMa.spw3.U.pbcorr.fits * VYCMa_B5.cont.pb.fits * VYCMa_B5.cont.pbcorr.fits --------------------------------------------------------------- Publications making use of these data must include the following statement in the acknowledgement: "This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00011.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC 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." In addition, publications from NA authors must include the standard NRAO acknowledgement: "The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."