Field of View Star Counting

[STSpencer]

From Rich

As above but a bit more statistical, perhaps just querying gaia and making histograms. For example - if I tell you that we will have a slow signal chain that can detect all stars from mag 4 to mag 7, then how many on average per field of view will the camera detect? Can do this very roughly on the back of an envelope, but if there’s a more proper way then that would be very nice.

This should be do-able using the existing gaiacat txt catalog generated by nsb, then comparing whole sky coverage to field of view size, but will need new script to do it.

[STSpencer]

First crack at this using Hipparcos data using 10x10 degree bins:

It seems to me that the reason that the sky coverage is less than Rich's calculation in the mag4-7 band is that this takes into effect the higher stellar density in the galactic plane. That said, the sky coverage calculation is also probably a bit on the pessimistic side since in reality not all RA and DEC are visible from the southern site.

[RichardWhite109]

Very nice! I think that needing 30 stars per FoV is probably pessimistic, but I guess easy to check for 10 (and the correct answer is likely in between). 10 x 10 might be a bit optimistic... the total FoV is 8.8 deg, with a fully enclosed circle of ~7.8 deg diameter so that's ~2 times less area than 10x10. Suggest that 7x7 degree bins would be pretty close. All in all though, it looks like either mag 7 or 8 is probably the right answer.

[STSpencer]

7x7 degree bins:

[STSpencer]

Results updated with gaia data, they're slightly more optimistic but it doesn't make a huge change: Now onto seeing if I can figure out the visibility from Paranal.