DASCH for Days to Decades Time Domain Astronomy

Grindlay, Jonathan

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 1992. The data processing pipeline achieves ~0.1mag and ~0.5 3arcsec (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 on line 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.

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