LSST Filters versus SDSS

Support Data Products
#1

I read somewhere that the LSST has six filters. Presumably these are u, g, r, i, z and Y.

Do these bands exactly match the SDSS bands in terms of central wavelength and bandwidth?

Regards: Paul

Interpreting Color-Color Diagrams for Presumed Variable Stars
#2

Does https://github.com/lsst/throughputs help? (I believe the technically correct answer is “they do not exactly match”.)

#3

Not even close. The LSST chips aren’t as hot in the blue (where we used special NR coating in the u band, both on the chips and the dewar window). In the red, SDSS z was cut off by the Si absorption of a thin CCD, so the LSST z is much bluer, narrower, and more sensitive. Then LSST puts a y band to the blue of z.

Look at the filter curves

#5

For a detailed quantitative comparison, and code and data to overplot
different versions of filter sets on top of each other, please see
http://speclite.readthedocs.io/en/latest/filters.html

#6

Hi @yorkpf, thank you for your question.

You are correct that the LSST has six filters, ugrizy. These bands do not exactly match the SDSS bands. For a quick comparison, see the relevant plots below, which are from http://speclite.readthedocs.io/en/latest/filters.html.

sdss2010
lsst2016

If you’re looking for more information or would like access to the transmission curves themselves, the best place to start is the left-hand menu bar of the “for scientists” page at https://www.lsst.org/scientists. There you will find a link to Filter Throughputs which takes you to a GitHub repository of filter transmission curves (https://github.com/lsst/throughputs). As the readme file describes, the LSST throughput curves are in the “baseline” directory, and those are the ones you should use to, e.g., calculate expected magnitudes. For a more detailed comparison of various filter systems with the LSST filters, and/or code to use to make plots like the ones shown above, visit http://speclite.readthedocs.io/en/latest/filters.html.

Thanks again for posting your question, and if you have any further questions on this topic please don’t hesitate to reply to this thread.

#7

Thanks Melissa - that was most helpful. I can take it from here.
Paul