DASCH Data Release 7 (DR7) is the legacy of DASCH, the multi-decade effort to digitize Harvard College Observatory’s Astronomical Photographic Glass Plate Collection for scientific applications. The primary DASCH DR7 data product is a catalog of astrophysical lightcurves referenced to APASS DR8, containing 23,574,404,199 measurements of 252,458,490 sources covering the entire sky across the years ~1880–1990.
DASCH DR7 also includes an additional lightcurve database referenced to ATLAS-refcat2 (which must be used carefully); high-precision scans of 429,274 glass photographic plates at 11 μm spatial resolution; astrometric calibrations of about 97% of those scans; photometric calibrations of about 89% of them; around 800,000 photographs of the plates and their paper jackets; around 166,000 photographs of the observing logbooks documenting the plates and selected historical astronomer notebooks discussing them; databases of information regarding the Harvard Plate Stacks holdings; raw data and calibrations from the DASCH scanner; the source code to the entire DASCH software stack; logs related to the DR7 data processing; all available supporting materials; and an exhaustive inventory of the DASCH data archive, which holds 33,791,530 files totaling 745,627,062,858,355 bytes (around 678 TiB) of data.
Getting Started: About DASCH DR7
The Introduction to DASCH slide deck presents an overview of DASCH from an astronomer’s perspective.
We recommend that astronomers retrieve and analyze DASCH data using Jupyter notebooks and the daschlab Python package. The Introduction to daschlab video gives an overview of what this is like.
The DR7 Data Products document lists the specific data products provided in DR7.
Users of DASCH data are encouraged to subscribe to the DASCH Astrophysics email list for discussion and announcements.
Accessing and Using DASCH DR7
Launch a cloud-based quicklook notebook to investigate a source. (Assumes familiarity with DASCH and daschlab.)
The Python package daschlab is the recommended toolkit for retrieving and analyzing DASCH data.
Starglass is a portal for exploring the HCO plate collection, aimed at non-scientists as well as scientists.
See the Data Access page for further information, including links to the old “Cannon” data access portal.
For bulk data access, reach out to the email list. See the Data Products page for information about what is available.
Tutorials
If you’re not sure where to start, try a tutorial.
- RY Cnc
- This tutorial slide deck shows you how to recreate the daschlab analysis shown in the introductory video using a cloud-based notebook. If you’re running the software locally, you can download the notebook to your computer (right-click and “Save Link As” since GitHub just shows you the JSON).
- HD 5501 - Handling Source Splitting
- This tutorial notebook shows how to use daschlab to address the “source splitting” Known Issue. The link at left will launch a cloud-based version of the notebook, which might be slow. If you’re running the software locally, you can download the notebook to your computer (right-click and “Save Link As” since GitHub just shows you the JSON).
How-to Guides
- Install daschlab
- For substantial DR7 data analysis, you will probably want to install daschlab in your own computing environment. This guide explains how to do that.
- Reduce Lightcurves
- Recommended procedures for reducing DASCH lightcurve data.
- Cite & Acknowledge DASCH
- If you are writing a scholarly manuscript based on DASCH data, you should mention DASCH in the acknowledgments section and cite the relevant DASCH papers and software.
- Starglass API Guide
- Documentation of the Starglass API, which can be used for automated retrieval of non-scientific data relating to the DASCH plates.
Explainers
These documents provide additional information about the DASCH DR7 data.
- Known Issues
- As with any survey, the DASCH data display various known issues. This page summarizes them and provides links to more in-depth discussions.
- DASCH Data Access
- A summary of different methods for accessing the DASCH data.
- Legacy Data Guide
- The Legacy Data Guide is an older document that is, frankly, quite confusing, but it contains details that have not yet been documented anywhere else. It may be helpful in deciphering obscure aspects of the DASCH data.
- Pipeline Overview
- Another old document giving an overview of DASCH data processing. Several aspects are out-of-date.
Reference Information
- Lightcurve Columns
- Definitions of columns in DASCH lightcurve tables, anchored to the naming conventions used by daschlab.
- Exposure List Columns
- Definitions of columns in DASCH exposure lists, anchored to the naming conventions used by daschlab.
- Catalog Columns
- Definitions of columns in DASCH source catalogs, anchored to the naming conventions used by daschlab.
- Value-Added Mosaic FITS File Contents
- Definitions of the contents of the “value-added” mosaic files created by daschlab. These are whole-plate images stored in the FITS format.
- Photometric Calibration ASDF File Contents
- Definitions of the contents of DASCH photometric calibration metadata files. These are stored in the Advanced Scientific Data Format.
- daschlab API Docs
- API reference documentation for the daschlab Python package.
- Colorterms
- Reference material regarding DASCH “colorterms,” which diagnose the kind of emulsion used on each plate.
- Web API Docs
- Reference documentation for web APIs that support low-level DASCH data access. Most users should just use daschlab.
About Data Release 7
DASCH DR7 was prepared by Peter K. G. Williams and released on December 29, 2024.
Previous data releases were not archived as distinct entities and are no longer available, but they are entirely superseded by DR7. Information about DR6 has been preserved for reference.
Acknowledgments
See the DASCH acknowledgments page for information about the funders that made DASCH possible.
PKGW would like to thank Daina Bouquin for securing the funding that made Data Release 7 possible, as well as the entire staff of the Wolbach Library for their role in ensuring the project’s successful completion.
See also the DASCH Team page and Citing & Acknowledging DASCH.
Other Resources
- Direct download the template “Quicklook” notebook (right-click and “Save Link As”)
- DASCH Announcements email list
- DASCH Publications
- Starglass
- About the DASCH Project
- About the DASCH Scanner
- About the DASCH Team