In PanSTARRS nomenclature, a detection is a source found in a single exposure or a stacked image. Each detection has associated quantities. Detections are combined into "objects" by spatial matching across different exposures and filters.
The starting point for the PS1 data archive is at the Pan-STARRS1 data archive home page.
Definition - what is a "detection"?
In PanSTARRS nomenclature, a detection is a source found in a single exposure or a stacked image. Detections are matched across exposures to define objects.
Detections are identified through a standard peak-finding algorithm. The image is convolved with an approximation of the PSF and then divided by a smoothed version of the variance image to define the significance image. Peaks are defined as locations where the significance image exceeds a target threshold, representing the square of the desired signal-to-noise ratio. Peaks are then ordered in decreasing significance, and peaks are retained only if a significant valley separates them from brighter nearby peaks.
The process of identifying detections is complex and involves multiple steps:
- Smooth the image with PSF (or a PSF estimate in the first pass)
- Smooth the variance with PSF**2
- To speed these up, a 1D Gaussian with FWHM matching the PSF is used.
- That is much faster and is only marginally different.
- If the difference matters, the image is of poor quality.
- Create a significance image by dividing image**2 / variance.
- Find all peaks above target S/N (squared).
- Perform a footprint analysis
- Generate isophotal footprint outlines (N sigma above sky).
- Assign peaks to their containing footprints.
- Cull insignificant peaks:
- Cull in descending order of brightness.
- A valid peak must be separated from a brighter peak by a significant valley.
- As a recent improvement: on the second pass, cull on the unsubtracted image