How do you design an automated astronomical survey that enables as much science as possible? For the past few years, the Rubin Observatory team has worked closely with the scientific community to focus on this question, and now Rubin Observatory is in the final stages of defining the initial survey strategy for the Legacy Survey of Space and Time (LSST).
During the 10-year LSST, Rubin Observatory will observe the Southern Hemisphere sky, collecting more than two million images with its 8.4-meter telescope and 3200 megapixel camera. In order to maximize the science that can be done with these observations, Rubin Observatory has engaged with the scientific community, over a period of years, to study how different observing strategies affect their science cases. Feedback from the scientific community, solicited at key intervals, has shaped the initial survey design and will continue to influence refinements and re-optimization of the survey up to and during operations.
Rubin data will enable science in many areas of astrophysics, and the cadence of the survey—when, where, how often, in what order, and with which filter images are taken—will have different impacts on different areas of study. Optimizing the survey strategy for one specific area of science usually involves a trade-off with another (e.g., observing more asteroids might mean observing fewer supernovae), and Rubin Observatory’s goal is to make the survey as broadly scientifically valuable as possible within and beyond four key science areas: probing the nature of dark matter and dark energy, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. To achieve that goal, the Rubin Project and the science community have coordinated closely to study and discuss different options.
During operations, the telescope will be controlled by an automated scheduler that uses artificial intelligence to make real-time decisions based on current conditions and observation history. The Rubin LSST Scheduler has now been used to run hundreds of simulations of different observing strategies (it only takes about six and a half hours for the Scheduler to simulate ten years of observations!) that scientists can study to determine how particular strategies impact their science cases. The Rubin Project has also developed open-access software tools to help scientists analyze the data from the simulations, so they can make science-driven recommendations.
Rubin Observatory formally sought input from the science community at three key points during the survey optimization process. In 2015, members of the Rubin science community produced the Community Observing Strategy Evaluation Paper (a document co-authored by over 100 scientists) which influenced the early phase of Rubin Observatory’s survey strategy optimization and the development of the Rubin Scheduler. In 2018, a call for Cadence White Papers expanded Rubin Observatory’s engagement with the science community and led to a new round of simulations provided by the Rubin survey strategy team.
In 2020, Rubin Observatory created the Survey Cadence Optimization Committee (SCOC), an advisory committee to the Rubin Operations Director charged with optimizing the survey cadence in the final phase of construction and throughout operations. The SCOC issued one more call for science community input (Cadence Notes), and then combined the results of analyses done by the Project and the science community to issue its Phase 1 recommendation in December 2021. Simulations of the SCOC’s recommended baseline strategy will be available soon, and the SCOC’s Phase 2 final recommendations are due at the end of 2022. The final baseline survey is planned to be implemented in the Rubin Scheduler in April 2023, but refinements and improvements will continue throughout the life of the ten-year LSST as the team continues to gather data and refine the model of what it means to maximize science.
More details about the Rubin LSST survey strategy optimization are available in this paper that opens an Astrophysical Journal Supplements (ApJS) Focus Issue dedicated to collecting scientific articles describing the community contributions to this process.
The latest cadence simulation announcement can be found on community.lsst.org
An informative presentation about the Rubin Scheduler, given by Rubin Staff Scientist Peter Yoachim, can be found on YouTube.