Atacama Large Millimeter/submillimeter Array (ALMA) ######################## 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#2011.0.00015.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." ################################################################################### This Readme file contains a description of HL Tau Band 4 Science Verification data, scripts and data products. There are four ALMA execution blocks (ASDMs) observed in low spectral resolution mode (TDM). Angular resolutions achieved for the continuum data are 49 x 41 mas. The Calibrated Data and Reference Images provided here were produced using CASA version 4.7.2. ######################## COMMENTS: This is ALMA Science Verification data of the protostellar disk source HL TAU taken at Band 4 in pure TDM (continuum only) mode. There are 4 individual datasets that make up the final combined dataset. These each have staggered observation times to cover slightly different u,v space and to achieve a well distributed coverage in the u,v plane. Only one of the four datasets has a grid quasar targeted as a flux calibrator (EB - X7b8) however, all four dataset have common bandpass, phase calibrator, and check sources. Given the strong nature of the bandpass and also considering tests undertaken using the other sources, the bandpass is used to bootstrap the correct flux scaling to the datasets without a specific flux calibrator. The flux scale files of each respective dataset indicate the consistency between the fluxes of the phase calibrator and the check source in all datasets. The spectral index of the check source is also consistent between data sets and also the phase calibrator considering its lower signal-to-noise. Note that the phase calibrator is a radio galaxy, and is a double source. It has a secondary weak component 0.2" to the north-west at the ~8% level of the main central peak. Extensive checks were made to ensure there were no issues with tranferred phases. These involved using the check source as a stand-in calibrator for HLTau to ensure the same structure is replicated, and also by calibrating the check source using the phase calibrator to ensure a point source is recovered. There are no issues using the original phase calibrator as the primary gain calibrator. The datasets were concatenated and slightly spectrally averaged prior to imaging, to improve imaging speed. Imaging was then conducted using TCLEAN. The resulting beam sizes for these Band 4 observations range from 42 x 33 mas before selfcalibration, to 49 x 41 mas after final phase and amplitude selfcalibration. NOTE the slightly reduced resolution is due to flagging of solutions during selfcalibration as the source has low signal-to-noise on the longest baselines. Self-calibration was performed as an iterative process, starting by solving long term phase offsets (related to any long term remaining atmopsheric fluctuations and also any residual antenna position uncertainties) and progressing to shorter times to solve for shorter term atmospheric residuals. At each stage of self calibration solutions are applied to the visibilities and then a new image is produced. This means that a new model with higher signal-to-noise is produced in each iteration. Self calibration was continued down to the 'inf' timescale (~60 seconds), at which stage flagging of solutions and a degraded image resolution was minor. Self-calibration on shorter timescale is not possible if the longer baseline data is to be kept as the signal-to-noise is too low (<3) and these data are significantly flagged. The final image (HLTau_B4_continuum_pcal3_apcal.image.pbcor.fits) has: Beam Size = 49 x 41 mas Peak Flux = 4.18 mJy/bm Noise Level = 0.0126 mJy/bm Signal to Noise (Dynamic range) = 332 For comparison the pre-self-calibration image (HLTau_B4_continuum.image.pbcor.fits) has: Beam Size = 42 x 33 mas Peak Flux = 2.63 mJy/bm Noise Level = 0.0129 mJy/bm Dyn. range = 204 ######################## HLTau_Band4_Scripts.tgz contains the calibration and imaging scripts: * uid___A002_Xacdf75_X1389.ms.scriptForCalibration_noplots.py * uid___A002_Xacdf75_X15e2.ms.scriptForCalibration_noplots.py * uid___A002_Xace764_X7b8.ms.scriptForCalibration_noplots.py * uid___A002_Xace764_Xa09.ms.scriptForCalibration_noplots.py * HLTau_Band4_scriptForImaging.py HLTau_Band4_UncalibratedData.tgz contains the raw data: Four ASDM datasets: * uid___A002_Xacdf75_X1389 * uid___A002_Xacdf75_X15e2 * uid___A002_Xace764_X7b8 * uid___A002_Xace764_Xa09 HLTau_Band4_CalibratedData.tgz contains the calibrated uv-data: * uid___A002_Xacdf75_X1389.ms.split.cal * uid___A002_Xacdf75_X15e2.ms.split.cal * uid___A002_Xace764_X7b8.ms.split.cal * uid___A002_Xace764_Xa09.ms.split.cal To re-create these calibrated datasets you would need to execute the calibration scripts (e.g uid___A002_Xacdf75_X1389.ms.scriptForCalibration_noplots.py) provided in HLTau_Band4_Scripts.tgz HLTau_Band4_ReferenceImages.tgz contains the continuum image products: * HLTau_B4_continuum.image.pbcor.fits (without self-calibration) * HLTau_B4_continuum_pcal1.image.pbcor.fits * HLTau_B4_continuum_pcal2.image.pbcor.fits * HLTau_B4_continuum_pcal3.image.pbcor.fits * HLTau_B4_continuum_pcal3_apcal.image.pbcor.fits (final image with self-calibration) The reference images can be re-created by executing the imaging script (HLTau_Band4_scriptForImaging.py). ################################################################################### HOW TO EXECUTE THE CALIBRATION SCRIPTS (1) Put an ALMA ASDM and the corresponding calibration script in the same directory (2) In CASA 4.7.2 e.g. execfile('uid___A002_Xacdf75_X1389.ms.scriptForCalibration.py') HOW TO EXECUTE THE IMAGING SCRIPT (1) Put the four *.ms.split.cal and the imaging script in the same directory (2) In CASA 4.7.2 execfile('HLTau_Band4_scriptForImaging.py')