Digital Access to a Sky Century at Harvard. II: Initial Photometry and Astrometry

TL;DR

The DASCH project digitizes Harvard's extensive photographic plate collection, enabling century-long sky observations with accurate photometry and astrometry, demonstrated through initial results on plates of the Praeseppe cluster.

Contribution

This paper presents the development and initial results of a data-reduction pipeline for digitizing and analyzing Harvard's photographic plates from 1880 to 1985.

Findings

Achieved 0.1 mag photometry accuracy on most plates

Demonstrated century-long light curves of variable stars

Validated the pipeline with plates of Praeseppe (M44)

Abstract

Digital Access to a Sky Century @ Harvard (DASCH) is a project to digitize the collection of ~500,000 glass photographic plates held at Harvard College Observatory. The collection spans the time period from 1880 to 1985, during which time every point on the sky has been observed approximately 500 to 1000 times. In this paper we describe the results of the DASCH commissioning run, during which we developed the data-reduction pipeline and fine-tuned the digitzer's performance and operation. This initial run consisted of 500 plates taken from a variety of different plate-series, all containing the open cluster Praeseppe (M44). We report that accurate photometry at the 0.1mag level is possible on the majority of plates, and demonstrate century-long light-curves of various types of variable stars in and around M44.