Harvard Plate Collection Metcalf Telescope

Digital Access to a Sky Century @ Harvard
A New Look at the Temporal Universe

DASCH Data Release 2 (DR2)

October 7, 2013

The Digital Access to a Sky Century @ Harvard (DASCH) project is pleased to release its second production data release (DR2), covering Galactic latitude b = +75 to +60deg, joining results from DR1 and the 5 Development Fields from which the hardware and software pipelines for DASCH were developed. These represent ~6% of the Harvard plate data (1885 - 1992; full-sky). A brief overview of DASCH is given in Grindlay et al (2012) Opening the 100-Year Window for Time Domain Astronomy in arXiv:1211.1051 or IAU Symposium Vol. 285 p 29-34 . Additional project papers are listed in the DASCH publications web page. Digitized images (11 micron pixels) of ~33,600 plates and their fully reduced WCS solutions and SExtractor-based photometry of every resolved object are available from this Data Release from the ~90Tb of data on disk now available. Light curves (LCs) typically include ~1000 points for an object with magnitude B ~12-13. LCs may be retrieved from input coordinates or SIMBAD object names for up to 10 at a time, and LC plots, data and images for each then downloaded individually.

We plan to release, 3 additional 15deg increments in galactic latitude (b = 60 to 15deg) as DR3 - DR5, followed by DR6 - DR10 for the southern galactic cap (b = -90 to -15deg) and then DR11 - DR12 (b = -15 to +15) for the Galactic Plane, all by 2017. The maps at the left illustrate this release strategy in galactic and equatorial coordinates: red indicates released areas and green indicates areas currently being scanned.

Release Fields
Region Galactic Longitude (l) degrees Galactic Latitude (b) degrees RA hoursRA degrees Dec degreesRadius degreesSquare degreesPlates
DR1 0 to 360 75.00 to 90.00 12h51m 192.86 27.13 15 702 10001
DR2 0 to 360 60.00 to 75.00 1984 17192

The Development Fields are listed in the Table below and are centered on the coordinates given. Since adjacent fields have not yet been scanned, they are increasingly incomplete with increasing radius. Most of the 3C273 field has been integrated into the DR2 release. Additional fields will be integrated into the Production scanning as they are covered in the data release plan described above. The counts of plates do not add up to the total plates in the release because many plates cover portions of multiple release regions.

Development Fields
Region Galactic Longitude (l) degrees Galactic Latitude (b) degrees RA hoursRA degrees Dec degreesRadius degreesSquare degreesPlates
M44 205.91 32.48 8h40m 130.09 19.67 5 78.5 2820
3C273 289.96 64.36 12h29m 187.27 2.05 5 78.5 2214
Baade's Window 1.03 -3.91 18h03m 270.88 -30.02 5 78.5 2480
Kepler Field 76.34 13.45 19h22m 290.73 44.50 8 201.1 3938
LMC 280.47 -32.89 5h23m 80.89 -69.76 5 78.5 6444

Release Fields Coverage Plots vs. Limiting Magnitude

All limiting magnitude coverage plots below have a resolution of one degree. The red angular borders around the coverage area are artifacts of the plot shading algorithm. The plots below show that the GSC2.3.2 calibration catalog has the largest range of magnitude coverage (7-18) while the APASS DR6 calibration catalog and the Kepler Input Catalogs have ranges of approximately 9 to 17. The APASS DR6 catalog provides the most accurate photometry calibration, but is not yet complete in all regions of the sky. The wide field patrol plates which make up most of the collection have a limiting magnitude of approximately 12 before circa 1935 and 14 after that date. For each field, the GSC2.3.2 calibration catalog results appear on top, and the APASS DR6 catalog results appear on bottom. From left to right, the limiting magnitudes of the plots are 10, 12, 14, and 16.

DR1: b = 75deg to 90deg

This field is centered on the North Galactic Pole and has a radius of 15 degrees. The APASS DR6 calibration catalog is not complete in this region.

DR2: b = 60deg to 75deg

This field is centered on the North Galactic Pole and extends from galactic latitude +60 to +75.

M44 Cluster Field

This field is the first scanned because of the availability of accurate photometric catalogs.

3C273 Quasar Field

This field is the second scanned to investigate the usefulness of DASCH photometry for the study of quasars. Except for 44 plates, this field is now part of DR2.

Baade's Window Field

This field is the third scanned to study algorithms for nova searches and to test DASCH astrometry and photometry in crowded fields. The APASS DR6 catalog is not complete in this region.

Kepler Field

This field is the fourth scanned to take advantage of the superior accuracy of the Kepler Input Catalog over the GSC2.3.2 catalog for the calibration of DASCH plates. Kepler Input Catalog calibrations are available for this field only and are shown in the middle set of graphs.

Large Magellanic Cloud Field

Because of the historic discoveries made by Henrietta Leavitt, the LMC field provides the deepest magnitude coverage and highest plate density for the Harvard plates scanned to date. Improved photometry (for crowded fields) will be done for both the LMC and Baade's Window when these fields are re-processed for Production scanning.


The DASCH project at Harvard is grateful for partial support from NSF grants AST-0407380, AST-0909073, and AST-1313370; which should be acknowledged in all papers making use of DASCH data.

We acknowledge the one-time gift of the Cornel and Cynthia K. Sarosdy Fund for DASCH, and thank Grzegorz Pojmanski of the ASAS project for providing some of the source code on which the DASCH web-interface is based.

The ongoing AAVSO Photometric All-Sky Survey (APASS) has improved DASCH photometric calibration and is funded by the Robert Martin Ayers Sciences Fund.