2009/07/24 - Michael Wood-Vasey

Here's a summary of my looking over the past couple of weeks at the PS1 MD fields from the July data release of June (and some previous) images. I've been looking from the perspective of detecting transient and variable objects.

Overall notes:

• The subtractions are only fair and need to be better. The most common issue is an effective PSF/astrometric mismatch leading to dipoles.

• The Transient Classification Server is going to need more information about candidates than currently available.

• The stacks appear over-smoothed. This leads to positive and negative excursions covering many pixels that masquerade as PSFs.

• Sky subtraction oversubtracts near large extended galaxies such as NGC 4258 (MD06 skycell.073).

• Masking of center of galaxies seems excessive. Galaxies that should not be near the saturation limit still have their cores masked. Need to collect more specific examples for analysis.

TCS More Information Requests

• Aperture and PSF flux at locations of diff.cmf objects in template and input images.
• Aperture mag curve of growth for candidates. This should help with dipoles (which roughly conserve flux).
• Addition of calibration zeropoints to CMF files: populate CAL_PSF_MAG and store overall corresponding zeropoint in header. (Is zeropoint for given PSF or "infinite" aperture 1 count/sec?).