Science Highlight




Release of Science Verification data from the ALMA Long Baseline Campaign

A new installment of Science Verification data is available. This release contains several new datasets corresponding to four targets observed as part of the 2014 ALMA Long Baseline Campaign in order to demonstrate the long baseline (~10 km), high angular resolution, capability of ALMA. Maximum baselines used ranged from 12.2 to 14.9 km. Details of the campaign and targets are listed on the Science Verification web page.

The targets are:
• Juno: observations of continuum in Band 6 (233 GHz). It also demonstrates the ephemeris capability. The angular resolution achieved ranges from 32 x 24 milli-arcseconds (mas) to 42 x 36 mas.
• Mira: observations of several SiO transitions (isotopologues and vibrational states) and continuum in Bands 3 and 6. In Band 6, spectral windows also covered an H2O line. Angular resolutions achieved for the continuum data are 70 x 60 mas and 34 x 24 mas in Bands 3 (94 GHz) and 6 (231 GHz), respectively.
• HL Tau: observations of continuum and spectral line in Band 3, and continuum only in Bands 6 & 7. In Band 3, the following lines were covered by two spectral line tunings: 12CO J=1-0 & CN N=1-0 (~115/113 GHz), HCN & HCO+, J=1-0 (~89 GHz). Angular resolutions achieved for the continuum data are 85 x 61 mas, 35 x 22 mas, and 30 x 19 mas in Bands 3 (102 GHz), 6 (233 GHz) and 7 (344 GHz), respectively. It was necessary to uv-taper the spectral line data so the resulting angular resolution is coarser (up to 1 arcsec).
• SDP.81: observations of continuum and spectral lines in Bands 4, 6 & 7. Spectral windows covered the redshifted CO J=5-4 line in Band 4, the CO J=8-7 line and H2O, 2(0,2)-1(1,1) line in Band 6, and the CO J=10-9 line in Band 7. Angular resolutions achieved for the continuum data are 60 x 54 mas, 39 x 30 mas and 31 x 23 mas in Bands 4 (151 GHz), 6 (236 GHz), and 7 (290 GHz), respectively. It was necessary to uv-taper the spectral line data so the resulting angular resolution is coarser (up to 169 mas).

The Science Verification data sets are available through the ALMA Science Portal. The following data products are available:
• Raw, uncalibrated data to allow users to try their hands at a complete data reduction process. 
• Calibrated uv-data, allowing users to perform data analysis and post-processing. In some cases, particularly where spectral line datasets are very large, a smaller continuum-only calibrated dataset is also provided. The calibrated data product does not include self-calibration, where relevant.
• Calibration tables are provided in the case that self-calibration was performed. This will allow users to self-calibrate the provided calibrated uv-data if desired. Alternatively, users can perform self-calibration by executing the provided imaging scripts.
• Reference images generated from the full reduction of the above data sets. 
• Calibration and Imaging Data Reduction scripts are provided as suggestions for data reduction. These scripts can be executed to produce the calibrated data and/or reference images provided. A user may wish to perform a complete reduction starting from the raw data, for example to try their hands at a complete data reduction process. Or, a user may, for example, wish to execute only the imaging script to try different clean parameters. The imaging scripts will be provided on a CASA guide page.
• README file containing a summary of the data and data products, plus any other important information.

We hope that you will find that the quality of these datasets is impressive, but please remember that ALMA Science Verification data is taken as part of Extension and Optimization of Capabilities (EOC), and we are continuously testing new observing modes. These observations are made using new equipment and software and thus may contain more idiosyncrasies than data released to PIs in Early Science.

A fifth Long Baseline target, 3C 138, which was observed in continuum in Bands 3 & 6 to demonstrate the polarization capability, will be released in a separate installment along with the previous polarization SV target 3C 286 (not observed at long baselines) and a CASA guide demonstrating the reduction of polarization data.

We thank the large number of staff at the JAO and the ARCs who have participated in the EOC and Science Verification activities, observations and data reduction that made this release possible.

Reminder: In order to reduce and/or analyze the ALMA data, users need to use the Common Astronomy Software Applications (CASA) package. The CASA package can be accessed through http://casa.nrao.edu. Feedback on the data and on the CASA software is always welcome!