Milky Way astrometry in DP0

Hello, I was wondering about investigating what kind of astrometric accuracy will be realistically achievable with LSST.

For some background, I’m in the SMWLV collaboration, and what astrometric accuracy we can expect from LSST is a recurring question. Personally, I’m an observer focusing on Milky Way star clusters, and I also have a Python package originally made to work with Gaia data that I’d like to update to work with LSST+other survey data too.

I think that DP0 would be a really good opportunity for us to work out what kind of astrometric accuracy and characteristics we could expect after some years of LSST data gathering, helping us to plan for different science cases this would enable and at what points they would be possible, as well as giving us some test data to test software on.

I looked into DP0 the best that I could, and what I found is that it does contain stars - but I am not sure what (if any) astrometry has also been simulated for them. The best I could find is that DC2 did contain astrometry (section 5.3), although I don’t think it simulated gathering astrometry using the LSST science pipeline (last paragraph of section 4.2).

So my questions are:

  • Does DP0 contain astrometry for stars?
  • If yes: how realistic is it, and how was it generated?
  • If no: would it be possible to have full astrometric fitting be simulated at some point in the future?

Thank you for your help!


Hi Emily-

Unfortunately, the DP0/DC2 simulations did not include proper motions (I think the simulations actually did have proper motions, but since the pipelines weren’t equipped to handle them at the time of the simulations, they were omitted from the catalogs – see the last sentence of Sec. 4.2, right before Sec. 4.2.1 in the DC2 paper). I also don’t believe there are plans for any additional simulations (though folks more involved in DESC might know better than I do), and there are definitely no plans from the Rubin Project to serve additional data releases that are based on simulated datasets.

While the Rubin Science Pipelines now use a version of the gbdes astrometry tools (originally developed for DES), there likely will not be publicly available datasets containing proper motions (or parallaxes) measured by the Pipelines until at least Data Release 1. One could (re-)process existing datasets with the pipelines to get a feel for the tools, but I’m guessing that’s not really what you’re looking for.

One other option would be to inject artificial sources into DP0 data, then re-run the processing to test the astrometric quality. The tools exist to do that, but it may take some effort. Happy to talk more about it if you’re interested.

Hope this is helpful!

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Thanks for raising this topic, and for the reply. Good to know those details.

Is there a dedicated astrometry working group in the LSST project? If not, are people interested in creating one?

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I think SMWLV would be very interested to pursuing this topic, given the science interests. I’m happy to do my part to facilitate discussion!

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Thank you for your reply and for clarifying lots of details about DP0/DC2!

I think that we would be interested in trying to play around with astrometric data early, either in DP0 or maybe in the fall if there’s any commissioning data that hits well characterised stars/star clusters. Given that quite a few people are interested in astrometry, maybe we can try and get a working group together within the SMWLV collaboration and go from there.

So we’ll potentially get back to you on the idea of inserting sources into DP0 - if it isn’t too difficult, then I think it would be good to do. Thanks again!

I think there are a lot of different groups interested in this, which is awesome!

So on the LSSTC slack I just set up #smwlv-astrometry, which anyone interested is welcome to join. There may be relevance for people in other science collaborations too (e.g. I think I heard about uses of astrometry for AGN and quasars at some point.)

There, we can chat about next steps - we can think about if we want to commit to something like a data challenge using DP0, which I hope will be a good starting point to work out what science possibilities we can expect from LSST over the next few years.


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