AstroNote 2025-263

Photometric observations obtained with the 1.82-m Plaskett telescope are differential (SDSS gr filters) and measured from stars in either the Sloan Digital Sky Survey (Skyserver) or the Pan-STARRS release 1 (PS1) Survey - DR1.

The transient host galaxy light in our photometric measurement is minimized via one of two methods: Reference images are downloaded from the PanSTARRS image access (Flewelling, H. A., et al.) and are convolved, using the nightly PSF to match our images. The reference is then subtracted from our co-added images. A secondary photometric standard is defined and retained on the subtracted image using a pixel mask. 

A second method involves creating a model galaxy, using the IRAF artdata packages, scaling it to the images and subtracting the host galaxy. The differential photometry  was then performed using Image Reduction and Analysis Facility (IRAF) (Tody, D. 1986, "The IRAF Data Reduction and Analysis System").

Several different secondary standards were used from SDSS DR16 (Ahumada+, 2020) and PS1 Survey DR1 (Chambers+, 2016) to perform differential photometry using Image Reduction and Analysis Facility. 

*z values are photoZ (KD-tree method) and spectrscopic z from Sloan Digtial Sky Survey (SDSS) Sky Server. * host_g magnitudes are also derived from Sloan Digtial Sky Survey (SDSS) Sky Server.