Why is the VLT very efficient?

1. Why is the VLT very efficient? Fernando Comerón On behalf of Francesca Primas and Martino Romaniello

2. A great science machine in full production • Individual operation of 4 VLT Unit Telescopes (8.2m) and VLTI facility • 13 science instruments, including 2 VLTI instruments (more to come) • Support provided by a staff of over 80 people directly related to science operations (Europe and Chile), plus software developers • Over 2,500 hours of science observations performed each semester • Technical downtime below 3% • Weather downtime below 7%

3. A great science machine in full production • 702 VLT/VLTI runs approved in the current semester • 507 individual PIs in the current semester (169 of them new) • Nearly two refereed science papers using VLT data every day. • Thanks to excellent facilities and instrumentation, highly competent staff, and an advanced end-to-end operations model running over 60% in Service Mode.

4. Service Mode essentials • In Service Mode, time is allocated to programmes to be executed, not in time slots assigned long in advance, but spread over the observing semester as the conditions are optimal for each programme. • The VLT operations model was designed from the beginning to include a large fraction (at least 50%) of Service Mode observing: recognized as a key element to its scientific productivity and efficiency • Flexible scheduling adapts to the external conditions • Best observing conditions go to projects that really need them • Top rated projects get the highest execution priority • Some science cases require execution under a sustained period of stable excellent conditions. • Long monitoring series (months, years) easily manageable • Target of Opportunity observations less disruptive

5. Service Mode essentials • And other byproducts: • Time available to projects that can make use of worse-than-average conditions • Continue science with another instrument in case of instrument malfunction • Optimize calibrations by sharing them among several programs • Population of the archive with data obtained under well defined procedures The community has increasingly accepted and liked it!

6. End-to-end Service Mode in a nutshell • Sophisiticated long-term scheduling taking into account programme needs, statistical expectation on the conditions to be encountered, and many other factors. • Collection, optimization, and validation of fully pre-defined observations • Science operations policies that enhance the overall efficiency of the observatory, even if they may occasionally impact specific programmes. • Many heterogeneous factors taken into account in the short-term schedule. • Standard calibration plan. • Archival of all science, calibration, and environmental data

7. Dealing with a changing atmosphere in VLT Service Mode • Not one single set of constraints: • Most instruments operate with natural seeing, but some (NACO, SINFONI, CRIRES, VLTI…) use Adaptive Optics • Laser Guide Star performance especially sensitive to transparency • Wavelength range covered from 0.3 to 20 microns: relevant constraints are different

8. The promise of MCAO • Multi-Conjugate Adaptive Optics successfully demonstrated last year at the VLT. • Not regularly offered, but impressive results have triggered interest (and demand!) by the community • Illustrates new constraints on operations scheduling

9. Dealing with a changing atmosphere in VLT Service Mode • The current shortcomings • No prediction of the evolution of the conditions is systematically factored in the short term scheduling decisions • Short-term scheduling mainly based on current conditions and some guesswork based on historical knowledge • Limiting the length of individual observations to allow flexibility to changing conditions (increasing overheads) • Improved forecasting by better understanding relation between focal-plane image quality and DIMM measurements

10. Dealing with a changing atmosphere in VLT Service Mode • The uncertainty in the short-term evolution of the atmosphere leads to two short-term scheduling strategies: • “Risky”: starting the execution of observations with constraints very close to the current conditions • Pros: makes use of the best possible conditions and gives chance to the most demanding programmes • Cons: decreases efficiency by requiring frequent repetition of observations • “Conservative”: starting the execution of observations that allow for substantial deterioration of conditions • Pros: greater likelihood that the observation is completed within constraints • Cons: most demanding programmes left with little chances of execution, results below the best that the telescope can give • A sizeable fraction of observations (~20%) need to be repeated because conditions went outside constraints during the execution: an important, hidden source of inefficiency!

11. Can atmosphere prediction tools further help VLT operations? • In classical mode, weather prediction tools are a nice-to-have. In Service Mode, they are a boost of the efficiency • More robust short-term scheduling, better fulfillment of the goals of Service Mode • Demands to increase as new instrumentation comes on line (SPHERE…) • Probably the next major step in increasing the eficiency of the VLT Yes, absolutely!