Precise Photometric Measurements from a 1903 Photographic Plate Using a Commercial Scanner

TL;DR

This study shows that commercial scanners can accurately measure stellar magnitudes from archival photographic plates, enabling cost-effective analysis of historical astronomical data with precision better than 0.10 mag.

Contribution

It introduces a practical photometric method using commercial scanners on archival plates, demonstrating its accuracy and potential for studying variable stars and transients.

Findings

Photometric precision better than 0.10 mag achieved

Scanner-based measurements dominated by plate noise

Potential discovery of a supernova candidate in NGC 7331

Abstract

We demonstrate the feasibility of determining magnitudes of stars on archival photographic plates using a commercially available scanner. We describe one photometric approach that could serve as a useful example for other studies. In particular, we measure and calibrate stellar magnitudes from a 1903 photographic plate from the Yerkes Observatory collection, and demonstrate that the overall precision from our methods is better than 0.10 mag. Notably, these measurements are dominated by intrinsic plate noise, rather than noise introduced through the scanning/digitization process. The low expense of this approach expands the scientific potential to study variable stars in the archives of observatory plate collections. We use the serendipitous discovery of a candidate transient at photographic magnitude $pg$ = 16.60 in the spiral galaxy NGC 7331 to illustrate our photometric methods. If this unknown source is a supernova, it would represent the fourth known supernova in NGC 7331.