This page is intended to provide a starting point for those interested in getting involved in the Rubin LSST and LSST:UK. It assumes no prior knowledge of either, although most people reading it will know some of this material, so please use the table of contents below to skip to the bits that are new to you.
The Vera C. Rubin Observatory
The main component of the Vera C. Rubin Observatory is the Summit Facility currently under construction on Cerro Pachón in Chile. It comprises the 8.4-metre Simonyi Survey Telescope, on which will be mounted the 3.2-gigapixel LSST Camera, together with the Auxiliary Telescope (AuxTel, used for spectrophotometric calibration observations) and various ancillary services. The telescope has a novel, compact design, providing good image quality across a 3.5-degree field of view, plus the ability to move across the sky quickly and take relatively short (~30 second) exposures efficiently, with little time lost to prior stabilisation. Data from the camera will travel from Cerro Pachón to the Base Facility in Santiago, and then on to the US Data Facility (USDF) at SLAC. The Observatory has been designed as an end-to-end system, encompassing that journey from the summit all the way to the tools on the astronomer’s laptop with which they will analyse the final data products.
The Legacy Survey of Space and Time
For the first decade of its operational lifetime, the Rubin Observatory will conduct the Legacy Survey of Space and Time (LSST). The survey has four main science themes:
Probing data energy and dark matter
Taking an inventory of the solar system
Exploring the transient optical sky
Mapping the Milky Way
Those high-level goals drove the development of a design for the Observatory and the ten-year survey it will undertake, as described in the LSST overview paper by Ivezic et al (2008, arxiv:0805.2366). While some details of the survey specification remain to be optimised, its basic plan remains as outlined in that paper, notably:
~90% of the observing time will be devoted to the Wide-Fast-Deep (WFD) Survey, covering ~18,000 square degrees of the southern sky, with each field receiving ~800 visits (back-to-back pairs of 15 second exposures) distributed over the u, g, r, i, z and y bands. The predicted 5 sigma point source depths of the WFD data in each band is as follows:
single visit depth: u = 23.9, g = 25.0, r = 24.7, i = 24.0, z = 23.3 and y = 22.1
10-year stacked depth: u = 26.1, g = 27.4, r = 27.5, i = 26.8, z = 26.1 and y = 24.9
The remaining ~10% of the observing time will be divided amongst smaller programmes requiring different observing strategies, such as the Deep Drilling Field (DDF) programme, where selected fields will be observed much more frequently than in the WFD survey, to produce greater integrated depths and finer temporal sampling. The first four DDFs have already been selected, with more still to be agreed.
One aspect of the LSST design that is still being optimised is the observing strategy, which will determine how the ~800 visits in each field will be distributed across the ten years of the survey. Different temporal sampling distributions favour different science goals, so detailed analysis of a wide range of simulated survey strategies is being performed, to inform a decision as to how best to trade-off these conflicting preferences. This activity is being coordinated by the Survey Cadence Optimisation Committee, with input from Rubin Observatory staff and the scientific community.
LSST Data Products
There are three broad categories of LSST data product:
Prompt products. These are generated by a Difference Image Analysis pipeline that is run as soon as the images from each visit reaches the USDF. Each image is compared with a reference image of that field in the same band, and alerts are issued to record all celestial objects in that field that are significantly detected to have moved or changed brightness. Alerts will be issued from the USDF within a minute of the closing of the shutter in Chile at the end of the exposure from which they originate, allowing rapid follow-up observations of transient phenomena.
Data Release products. A range of static-sky data products - e.g. calibrated single visit and stacked images, together with object catalogues derived from them - will be released in a series of Data Releases. Two data releases are planned from the first year of survey operations, with annual releases thereafter. Each data release will reduce all extant data with the same set of software, so that each comprises a homogeneous dataset.
User-Generated products. The data release products will not be optimal for all possible science analyses, so the Observatory will accept, and publish alongside the data releases, some additional datasets generated by the community. These may include data from other instruments, as well as bespoke products generated by optimised re-reduction, or further analysis, of LSST data and intended for particular science analyses.
The Rubin LSST dataset will be huge: about 20 TB of image data will emerge from the camera every night, yielding several million alerts per night and a final data release catalogue database expected to exceed 15 PB in size, and containing information on ~20 billion galaxies, ~ 17 billion resolved stars and ~6 million solar system objects. Researchers will access this dataset through Data Access Centres (DACs) with the computational resources needed to support the storage and analysis of this vast volume of data. The alert stream will be world-public immediately, while each data release will become public after a proprietary period of two years, during which time it will only be accessible to data rights holders.
Rubin LSST Funding and Data Rights
The Rubin LSST is a billion-dollar project. Rubin construction is primarily being funded by the US, with the National Science Foundation (NSF) providing $437M for the construction of the telescope and site facilities, development of the data management system and of the Education and Public Outreach programme, while the Department of Energy (DOE) is funding the camera and associated systems to the tune of $168M. Additional contributions to camera construction have come from IN2P3, the French particle physics agency, while Brazil is providing the network from the summit to the USDF and, of course, Chile has provided the site.
In return for these contributions, all professional astronomers in the US and Chile will have data rights, while other international participants will earn rights to the proprietary data through contributions to Rubin LSST operations. Initially, this was expected to follow a subscription model - and, indeed, STFC had signed a Memorandum of Agreement (MoA) to secure data rights for a set of UK astronomers that way - but, more recently, the US funding agencies decided that these should be in-kind contributions, which can either help offset the $70M per year Rubin operating costs or add value to the US community’s exploitation of the Rubin LSST dataset through enhancing the range of user-generated products. Potential international participants submitted in-kind proposals in the autumn of 2020, and they are currently under review, with the expectation that data rights agreements will be signed by late summer 2021.
Rubin LSST Organisation
LSST Science Planning