April 12th by Gregg Hallinan:
As you are aware, the VLASS is a concept for a next generation VLA sky survey with the expanded VLA, similar in scope to the the NVSS and FIRST sky surveys conducted with the old VLA. The NRAO has engaged the community to develop the science case and scope for such a survey, which would likely involve <10,000 hours over a 5-year period, if approved. At some point, the resulting science case and survey definition will undergo peer review to establish whether the survey would justify the ~20% loss in observing time for the community.
To date, there have been 3 separate groups discussing how a VLASS might deliver Extragalactic, Galactic and Transient science. The definitions from each group have been quite disparate covering a wide range in depth and frequency. In order to progress a convergence towards a final VLASS definition, a telecon was held yesterday involving the transient, extragalactic and galactic working group co-chairs to establish a single survey definition to bring back to our respective groups to discuss. We agreed that the following would be a good starting point, given the feedback from the wider groups thus far...
The VLASS would be an S-band survey with complete sky coverage between -10 < dec < +75. It would extend below declinations of -10 to encompass all of the Galactic Plane and Bulge that reaches above an elevation of 20 degrees from the VLA site. Thus, the survey would include:
~21,000 sq. deg extragalactic to 50 uJy between -10 < dec < +75, using B-config [6350 hours including 25% overhead]
~2800 sq. deg of the Galactic Plane (~ +/- 5 deg) and Bulge (~ +/- 10 deg) to 30 uJy using A-config [2350 hours including 25% overhead]
Total time request for the VLASS would be ~8,700 hours, i.e., 20% VLA usage over 5 years.
The extragalactic fields may involve as many as 16 epochs. Assuming that the VLASS observing would be grouped in semesters, this would yield a typical cadence of ~ 1 month, but epochs could be spaced within a semester to probe timescales of weeks - years.
The galactic plane fields may involve as many as 40 epochs. Assuming that the VLASS observing would be grouped in semesters, this would yield a typical cadence of ~ 1 week, but epochs could be spaced within a semester to probe timescales of minutes - years.
The final cadence will be subject to consideration and approval by the technical and programmatic working groups.
Please send any comments or feedback on this current definition.
What science does this enable?
What science is excluded by this definition?
How can it be tweaked to improve your science?
Is this definition way off the mark for transient science?
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