Digitization of Astronomical Photographic Plate of China: Photometric Calibration of Single-exposure Plates and Release of Photometric Catalogs

TL;DR

This paper details the digitization and photometric calibration of 15,000 Chinese astronomical plates spanning a century, producing high-precision photometric catalogs for long-term astronomical studies.

Contribution

It introduces a novel calibration method for single-exposure plates, correcting systematic effects and achieving high photometric accuracy, and publicly releases the resulting catalogs.

Findings

Photometric precision typically around 0.15 mag across observatories.

Calibration method effectively corrects systematic effects.

Publicly available catalogs enable long-term astronomical research.

Abstract

The Chinese Plate-Digitizing Project has digitized a total number of about 30,000 astronomical plates from 11 telescopes of five observatories (SHAO, NAOC, PMO, YNAO, and QDO) in China, spanning nearly 100 years of observations. In this work, we present a photometric calibration method to calibrate about 15,000 single-exposure plates to the JKC photometric system. Using standard stars constructed from the BEST database, we have identified and corrected various systematic effects (including the magnitude term, color term, and flat-field term) to a high precision. The final photometric precision is typically 0.15, 0.23, 0.17, 0.11, 0.19 mag for plates collected in SHAO, NAOC, PMO, YNAO, and QDO, respectively, with best cases reaching 0.07, 0.08, 0.06, 0.05, and 0.11 mag, respectively. Candidates of variable sources are also identified. The catalogs are publicly available at the China National Astronomical Data Center. Such a dataset will provide a valuable resource for conducting long-term, temporal-scale astronomical research. Our calibration method can also be applied to other digitized astronomical plates in general.