DASCH for Days to Decades Time Domain Astronomy

Abstract

The Digital Access to a Sky Century @ Harvard (DASCH) project has been underway for the past decade to digitize and fully reduce (photometry and astrometry) the ~450,000 glass plate images (not spectra) of the full sky taken by some ~30 Harvard telescopes from 1885 to 1992. The data processing pipeline achieves ~0.1 mag and ~0.5–3 arcsec (depending on plate series/scale) for all resolved stellar images (typically ~50,000) on each plate for the ~400 plates/day scanning and processing rate during full production. Nearly 1/3 of the plates are now online as of the 5th (of 12) data release, DR5. Unique time domain astronomy can be done for a vast range of objects; several examples will be shown. Of particular interest are rare extreme optical flares from accreting black holes, both stellar mass in black hole low-mass X-ray binaries (BH-LMXBs) and supermassive in active galactic nuclei (AGN). I will show examples of both. Just as full-production rate scanning/processing was to begin to finish by ~2018, a water main on Observatory Hill burst (on Jan 18, 2016) and flooded the DASCH lab, submerging some ~61,000 plates. These were quickly (within 2 days) removed to frozen storage (to prevent mold). Plate cleaning methods have now been developed (by the Harvard Weissman Preservation Center to fully restore them for scanning). Scanning is expected to resume in July 2016, with a new and faster scanner to enable the project to finish by late 2018.