This month’s gratuitous picture from the summit shows (at right) the M1M3 mass surrogate being washed. This took place on the maintenance level of the summit facility, and was a prelude to its receiving a full-surface coating, using the same procedure, under vacuum and in the mirror coating enclosure, that will be applied to the M1M3 mirror itself in due course.

LSST:UK has operated a Pool Travel Fund since the start of Phase A in 2015, enabling those without travel funding from LSST:UK Science Centre (LUSC) grants to apply for support to attend LSST-related scientific and technical meetings. These awards are made by the Executive Group, primarily on the basis of anticipated scientific return, and have proven to be an effective way to help UK researchers engage with the international Science Collaborations. The Exec has decided that this scheme should be broadened slightly, to allow a fraction (<25%) of the Pool Travel Fund to be used to help support LSST-related scientific and technical meetings held in the UK, where, for example, hosting a meeting here would be more beneficial scientifically, and better value-for-money, than sending multiple attendees to a meeting that would otherwise take place in the US. The page on the LSST:UK wiki providing information about the Pool Travel Fund has been updated to include this updated policy, plus links to new application forms to apply for travel and meeting support.

March sees the return of online events run by the Rubin Community Science Team for Data Preview 0 Delegates. A series of these Rubin Science Assemblies will run through to early May, while the annual Rubin Data Academy will take place on June 17, 18, 20 and 21.

Finally, we are delighted to announce that our very own Stephen Smartt (right), the LSST:UK Project Scientist, has been awarded a Royal Society Research Professorship. These are very prestigious awards - Stephen’s was one of only two awarded across the whole of science for 2024 - intended both to recognise past achievements and to support future successes. Analysis, and follow-up, of LSST transients is a major element of the research programme that Stephen intends to undertake with support from this award, and we look forward to hearing about the fruits of this success in the coming years.

MNRAS has recently published an article by Aaron Watkins and collaborators (including Sugata Kaviraj and Chris Collins) discussing the merits and pitfalls of different kinds of sky subtraction techniques.  The paper, Strategies for optimal sky subtraction in the low surface brightness regime, describes experiments using fully synthetic images to investigate three different techniques, two commonly used in low surface brightness surveys, another experimental.  

The study's results quantify the impact of undetected flux on sky models, which tends to bias estimated sky brightnesses high, risking over-subtraction of flux. If the sky is modelled with a complex function (for example, a high-order polynomial, or a spline interpolation), that over-subtraction can occur locally, leading to artificial divots surrounding extended objects like galaxies, or even objects which are simply located close together on the sky.  However, the results demonstrate that when a simple model is used, and when proper care is taken to mask detected astronomical objects to low surface brightness levels, this bias can be reduced to negligible amounts.  

Even for a survey as deep as LSST, any sky subtraction technique traditionally used in low surface brightness surveys can still be applied safely, so long as empirical corrections are made for scattered light and undetected faint sources.

The paper justifies the recommendations Watkins and collaborators have proposed to LSST's data management (DM) team regarding the survey's pipeline sky subtraction.  Working alongside DM, Watkins et al. found that the existing algorithm suffers from two problems: insufficient masking of low surface brightness flux, and too complex a sky model.  Following the paper's results, the team found that adjusting the algorithm to use a much simpler model, even without an improvement to the masking, proves very successful at minimizing the impact of the sky subtraction on the flux of extended or clustered objects.  In fact, a preliminary investigation suggests that the proposed revised algorithm might benefit more than just low surface brightness science: a number of DM's photometric quality metrics appear to improve slightly when the revised algorithm is used, compared to the default pipeline.  However, the full impact of the proposed change is still being investigated.

Examples of the synthetic images used to conduct the tests on sky subtraction routines, showcasing the kinds of model sources injected for four different experiment types.  

• The top-left panel shows a sparsely populated control field.  

• The top-right panel shows that same image, but convolved with an extended scattered light model derived from the Subaru Telescope's Hyper Suprime-Cam imager, to investigate the impact of that scattered light on sky models.

• The bottom-left panel shows an image simulating data processed through a typical low surface brightness--optimised data reduction routine, in which that scattered light is subtracted from the stars (but not the galaxies).

• Finally, the bottom-right panel shows an image which includes models of many faint, high-redshift sources drawn from the New Horizon simulation, to investigate the impact of undetected faint objects on sky models (also known as extragalactic background light).

Many of you are probably already talking to people outside the LSST:UK sphere about the exciting work you're doing on the project. We want to support everyone who wishes to do continue to do this, as well as those who wish to start, by ensuring they have the skills and information they need.

We're looking to develop science communication skills in team members to help us reach new audiences.

This is an opportunity for researchers to gain useful skills while highlighting the value of LSST:UK to others, especially non-specialist audiences. We're developing a network of researchers who have the confidence and know-how to communicate the complexity, aims and benefits of LSST:UK while igniting interest in science and research.

The Communications Officer, Eleanor O'Kane (email eokane@roe.ac.uk), will coordinate the training. We also have the considerable expertise of our Education and Public Engagement Officer Chris Lintottwithin the project. Skills will include working with the media, communicating complex messages and understanding how to connect with different audiences.  

The communications training schedule will be flexible and ongoing. The content will be flexible, and guided by the varying skills and interests in the team, from those with no experience to those who are already engaged in science communications.

Training may be online and where possible we will work with marketing and communication teams in Consortium institutions to deliver specialist skills.

The latest science release from Rubin outlines how a discovery could trigger a space mission to a fast moving target.

The first space mission to launch before a primary target has been identified is already in development: the ESA/JAXA Comet Interceptor mission is due to launch with the ESA ARIEL spacecraft in 2029. A Rubin discovery could see the multi-element spacecraft directed to a long-period solar system comet or interstellar object passing by the sun for the first time.

Rubin could also identify flyby opportunities for missions that are already in progress, including NASA’s Lucy, whose shape and orbit are represented in the image, left.

Colin Snodgrass, the Mission Deputy Principal Investigator for the ESA/JAXA Comet Interceptor, comments: “LSST is expected to discover vast numbers of Solar System objects, but what is really exciting for me is that we expect to discover new comets approaching the Sun for the first time at much larger distances than we currently do. This will help us answer questions about how cometary activity works far from the Sun, where it is too cold for water ice to sublimate, and also is a key enabling technology that allowed us to propose Comet Interceptor.

“We expect to have years to react to a discovery instead of months, and while this is still too short a time to plan and build a space mission from scratch, it is enough to get the spacecraft into the right place at the right time from a parking orbit in space. LSST:UK will make an important contribution to this through the Adler system that we are developing in Edinburgh and Belfast, that will (along with other goals) flag comets that could be potential mission targets amongst the LSST discoveries.”