daschlab.exposures Module

Tables of information about exposures on photographic plates.

The main class provided by this module is Exposures, instances of which can be obtained with the daschlab.Session.exposures() method.

Every photographic plate worth scanning was exposed at least once, but some were exposed multiple times. This means that on a given plate image, the same pixel may correspond to multiple different RA/Dec values, and a single RA/Dec may occur at several different pixel locations, if the multiple exposures overlapped each other.

For each plate that was successfully scanned, there is at least one “mosaic”, which is the DASCH terminology for a single large FITS image made from a plate scan. There can in principle be multiple mosaics per plate. Each mosaic is analyzed to search for as many WCS solutions as can be found.

Ideally, each WCS solution corresponds to an exposure of the plate. However, we also have external information about what plates have exposures, based on historical observing logbooks. WCS solutions may or may not be identifiable with known exposures. Sometimes there are fewer WCS solutions than logged exposures; sometimes there are more. Furthermore, the logbooks may provide information about exposures on plates that haven’t been scanned at all.

An exposure associated with a WCS solution to a mosaic is said to “have imaging” data available. This module deals with both exposures that have imaging, and those that do not. Some exposures lack imaging because the associated plate was not scanned at all; some lack imaging because it was not possible to associate that exposure with a WCS solution.

Classes

Exposures([data, masked, names, dtype, ...])	A table of DASCH exposure information.
ExposureRow(table, index)	A single row from an Exposures table.
ExposureSelector(exposures, apply)	A helper object that supports Exposures filtering functionality.