AstroNote 2024-156

We present differential (Gaia G) magnitudes of selected transients using comparison stars from the Gaia DR3 catalogue for observations obtained using the 0.76-m Baker-Nunn Schmidt telescope + 4K CCD (FLI Microline with 16803 chip) at the Rothney Astrophysical Observatory (University of Calgary, Canada). The observations are un-filtered, however, the CCD response curve is similar to the Gaia G filter; thus we define the filter designation is G'.  

Photometric observations obtained with the 1.82-m Plaskett telescope are differential (SDSS gri 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").

This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.