Multi-Epoch BVRI Photometry for All Targets in M31 and M33 - Photometric Comparison and Check Stars

Comparison and Check Stars

The photometric solutions to the images in the Survey are computed using a list of comparison stars derived from the AAVSO Photometric All Sky Catalog (APASS). The list and how it is derived is described in a presentation to the 2020 Symposium on Telescope Science (see the publication page for the Survey. A list of stars used to check the photometry is presented in the same publication.

The IDs for the stars are automatically generated from the right ascension (RA) and V magnitude (V) of the star using the formula:

ID = INT((V-10)*10+0.5)+INT((RA-10)x100+0.5)/1000

These follow links are electronic copies of the lists provided in different formats.

The Lists

Plots

See the publication in the proceedings of the 2020 Society for Astronomical Sciences Symposium for details. These are color versions of the plots in the proceedings and the presentation.

Spatial distribution of comparison stars in M31

Spatial distribution of comparison stars in M31. The blue square is a 20x20 arcminutes, the approximate size of survey images.

Spatial distribution of comparison stars in M33

Spatial distribution of comparison stars in M33. The blue square is a 20x20 arcminutes, the approximate size of survey images.

Precision of phometric solultions by filter.

Histograms of the error in the photometric zero-point for each filter as computed from the standard deviation of the comparison stars in the ensemble photometric solution for each image. The same statistics for the old (2017) comparion stars are shown in gray.

Error in photometry as a function of brightness by filter.

A plot of the magnitudes and errors for more than 18,000 photometric measurements from Survey images.

Histograms of the deviation of check stars on images by filter.

Histograms of the difference between the check stars and their expected values for over >750 images in the Survey. The same statistics for photometry computed using the same checks and the old (2017) comparion stars are shown in gray.<

By John C. Martin, University of Illinois Springfield Henry R. Barber Research Observatory

Updated on 2020-05-21 UT-5