Create code that plots star positions on fov maps/ Polaris Investigation

[STSpencer]

At the minute the positions of bright stars are only plotted in the camera images. Write code to put them in the sky fov maps.

• Run low mag limit polaris field with reduced fov, but same healpix density as a check, both with and without the bright stars library correction applied.

• Write simple star location code that takes the fits file and a WCS entry and plots positions of stars in the fov map.

[STSpencer]

I've done a run on Polaris with min gaia magnitude turned down to 8 from 15, but with healpix level still set to 11. This saves a bit more compute time than I thought (~-1.5 hours) but causes some weird effects in the fov maps that I'm not entirely sure of the origin of:

The highlighted star positions are still a bit off, but there's clearly a very bright source very near the centre of the images so Polaris is definitely being taken into account, so that's good:

and that star is definitely polaris (1Alp UMi ) according to astropy:

I'd been assuming the UTC timezone correction needed to be applied to the final star tracking part of the code (in fromfits.py), but now I'm not so sure (I think it might need to be taken into account in the obsalt and obsaz variables passed to NSB during the fits file generation). I'm going to give that a try now.

[STSpencer]

Alright, this is what you get applying UTC time corrections to the obsalt and obsaz nsb input parameters:

It seems to be a bit closer to reality, there's one really bright source close to the centre of the field (which I'm sure is Polaris). So my questions now are:

Is this close enough to reality for us to tolerate for practical purposes? Albeit other sources like issues #13 and #14 might rotate in the field more.

If not, does anyone have any ideas for what other parameters to change (the set of parameters at the top of savefield.py , fromfits.py and in mypycat.txt on this repo are the versions used for this run)? The only one I can think of is perhaps the various epochs in the ICRS transformations, but that should be a really small (<arcsec)effect.

I'm also advocating that we keep to mag 15 as the lower gaia limit from now on. It's worth spending an extra hour every run if it avoids weird smearing out of the bright stars on healpix maps that we see with the mag 8 variants (I think this is a bug in nsb).