Arc
Overview
This file describes the data model for the Arc image.
It is generally a simple combination of all input arc frames.
The image is written to disk as a multi-extension FITS file
prefixed by Arc in the Calibrations/ folder.
See Calibration Frame Naming for the naming convention.
Inspecting
The first extension is the combined image. You can view it with any standard image viewer, e.g.:
ginga Calibrations/Arc_A_1_01.fits
Most often you use only one arc frame and this appears very similar to the raw image. If you do stack several, the output could be quite different.
The image will also be a trimmed portion of the raw image and also re-oriented so that vertical is the spectral dimension with blue at the bottom, following the PypeIt Image Orientation.
Here is an screen shot of a ginga view
for an example from the shane_kast_red spectrograph.
Yup, an arc.
Trouble Shooting
If your image appears to be in err, here are the things to consider:
Is one or more of your input arc frames junk?
Is one or more of your input arc frames mis-labeled?
Current ArcImage Data Model
Internally, the image is held in
ArcImage,
which subclasses from PypeItImage and
DataContainer.
The datamodel written to disk is:
Version 1.3.0
HDU Name |
HDU Type |
Data Type |
Description |
|---|---|---|---|
|
… |
Empty data HDU. Contains basic header information. |
|
|
floating |
Primary image data |
|
|
Image mask |
||
|
The detector (see |
||
|
integer |
If a detector mosaic, this image provides the detector that contributed to each pixel. |