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thespacedoctor / marshall_webapp_wiki

An object management and communication webapp for astronomical transient surveys
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Add the delta-mag #136

Open smarttgit opened 6 years ago

smarttgit commented 6 years ago

Add ATLAS delta mag for nuclear transients. For all nuclear transients, use the Wpflx values to give us a mag with which we can compare the transient flux.

John Tonry says we should be able to use the Wpflx simply with the MAGZPT from the ddc header, since the Wpflx has already ben scaled appropriately. This makes it pretty simple to give a dm for the ATLAS detected objects anyway.

For Gaia - surely there is already a delta-mag defined, since it is not a difference imaging survey and therefore by definition it triggers on a delta mag

Add the delta-mag to the ticket for all nuclear transients (only NTs needed)

From John Tonry Well...

It's complicated, but perhaps better than you think.

When hotpants runs it computes a flux ratio between the image and the wallpaper. This flux ratio is saved as KSUMMED. (Actually there are 64 different versions for each hotpants chunk, KSUMMED is the median of all of them, assuming that we can do photometry better than hotpants on a little chunk.)

This implies that the zeropoint of the wallpaper, as warped onto the particular image, is MAGZPT +/- 2.5*log(KSUMMED). (Never quite sure of the sign, sorry.)

But wait, you can't do forced photometry without an correction, so that has to be added into the zeropoint used to convert forced photometry fluxes to real fluxes. Therefore imdiff_det.sh figures out for the warped wallpaper, given its PSF.

Finally, at last, imdiff_det.sh creates the wpflux values by multiplying the tphot values by a correction for the KSUMMED and the

, with the intent that the zeropoint of the Wpflx values *is* the MAGZPT of the image itself. Therefore you should take that comment at face value: MAGZPT means the same MAGZPT as appears in the diff image header, the ddc header, and the ATLAS observation database. - John P.S. Incidentally the wallpaper zeropoint is uniformly something (25.0 as I recall) but it's also complicated because the wallpaper does *not* have a uniform plate scale.
thespacedoctor commented 6 years ago

Wpflx is calculated for each non-forced photometry detection NOT for forced photometry measurements. As the next best effort I've associated out a Wpflx measurement from the location of one of the source's non-forced detections with its forced photometry detections in the marshall database. Hopefully this will be good enough.