Data Release 4
The APPLAUSE Data Release 4 (DR4) is the fourth release of archives of digitized photographic plates, along with metadata about the plates (gathered by transcription of available material), digitized observation logbooks, and table data extracted from the images.
APPLAUSE DR4 contains:
- images and metadata from 27 plate archives/collections from Hamburg, Bamberg, Potsdam, Tautenburg, Tartu and Vatican Observatory;
- 125473 scans of 97703 photographic plates;
- metadata for 94090 plates with a total of 139539 exposures;
- 113960 images of logbook pages and plate covers;
- 219 logbooks;
- astrometric solutions for 68399 plates;
- photometric calibration for 66328 plates;
- 4.486 billion extracted sources (individual detections), of which 2.132 billion with matched Gaia EDR3 designations, 1.256 billion unique matches.
The majority of extracted sources have their positions (right ascension and declination) calibrated with the help of the Gaia EDR3 catalogue. A classification - based on machine learning - of all sources provides a likelihood for distinguishing between objects and artifacts.
Extracted sources have their magnitudes calibrated, using the Gaia EDR3 photometry as reference. The calibrated magnitudes together with observation times form light curves that can be extracted from the database.
The following sky coverage plots show the distribution of extracted sources in the sky. It can be seen that with the addition of the Northern Sky catalog from Bamberg, the whole sky is covered more evenly (compared to APPLAUSE DR3), there are now even more observations from the Northern sky.
Time coverage is illustrated in the following figure. The oldest scanned plate in DR4 is from 1893, belonging to the Potsdam Carte du Ciel archive. The youngest plate is from 1998, obtained with the ESO 1-metre Schmidt telescope at La Silla, Chile.
Mollweide field-of-view plots of plates in the APPLAUSE DR4 archives are found here: Archives of APPLAUSE
Please be aware that we have reassigned a number of plates to different archives, because a closer study of the metadata suggested this. The most obvious reassignment is the DR2 archive 201 (Bamberg Southern Sky Patrol), which was split into three archives in DR3 to clarify that the observations took place in different locations. Plates with archive_id 203 were observed in South Africa, those with archive_id 204 are from New Zealand, and finally those with archive_id 205 were observed in Argentina.
The archives are build on extended metadata, especially we wanted to easily distinguish between location and telescopes and instruments, the latter two sometimes completely taken to other locations.
Plate scans and metadata were processed with PyPlate version 4.0 (subversions 4.0.10 through 4.0.12).