Pixel Scaling for ACS and WFC3 cameras

[walyssonBarbosa]

Find out what the pixel scaling values for ACS (HRC, SBC, WFC) and WFC3 (UVIS, IR) cameras are.

[walyssonBarbosa]

I took a look at the handbooks and these are the values I found:

• ACS:
  • WFC: 0,049 arcsec/pixel
  • HRC: 0,027 arcsec/pixel
  • SBC: 0,032 arcsec/pixel
• WFC3:
  • UVIS: 0,04 arcsec/pixel
  • IR: 0,13 arcsec/pixel

These are the values for WFPC2 (I think we are not using the wide field chips):

• WF[2,3,4]: 0,1 arcsec/pixel
• PC1: 0,046 arcsec/pixel

[acviana]

Great. Once the we get your work merging jpl2db.py into build_master_finders_table.py merged back into master we can start working on incorporate this into the pipeline. This will allow us to run the new build_master_finders_table.py over all the cameras.

[walyssonBarbosa]

The pixel scaling value is used in build_master_finders_table.py. These are the lines using them:

delta_x = -1 * (record['jpl_ra'] - crval1) * (3600. / 0.05)
delta_y = (record['jpl_dec'] - crval2) * (3600. / 0.05)

So the pixel scaling value here is 0.05 and this is only for wfpc2 images.

[ktfhale]

We need to get calc_delta to know about the different instruments, so it can decide what pixel scaling to use. Fortunately, it looks like it's already being passed the hdulist, so we can just grab the header keyword inside of it.

Incidentally, it looks hdulist is being passed around a lot to places where all that's actually needed are a few keywords from its header. This isn't very memory-efficient. We should get the information we need from the FITS file, and close it as soon as possible.

[ktfhale]

Also, are we sure we're not using the WFPC2 wide-field chips? I mean, they are in the stitched-up AstroDrizzle images, from which we generate our pngs.

[ktfhale]

I've added the other pixel scales to calc_delta(), and replaced passing hdulist to insert_record() and update_record() with passing the header, as all those functions needed it for was a few keywords to be used in calc_delta() and calc_pixel_position() (at least to my knowledge).

But I am a bit concerned about only using the WFPC2 PC scale.

EDIT: So there's a setting in the AstroDrizzle cfg files called driz_sep_scale`, in units of arcsec/pixel. In the different cfg files, it's set to:

SBC and WFC: 0.05
HRC: 0.025
IR: 0.13
UVIS: 0.04
WFPC2: 0.05

These don't quite match the values above, but they're what we're using in AstroDrizzle. So I guess this supports using a value of 0.05 for WFPC2 in calc_delta()? I'm still uncertain about this, however.