Astrometric Reduction

Using the image processing tool, images in the FITS format can also be subject to astrometric processing by the PinPoint program (this software is not provided with C2A – see http://pinpoint.dc3.com/). You need to have this software installed on your computer to use the Astrometric Reduction function in C2A. If a FITS image is loaded, the Astrometry area becomes active. You then have to fill in the boxes that define the scale of the image and identify the centre of the image with approximate equatorial coordinates. You also have to choose a reference catalogue from the list of catalogues which is provided in the list box (and you must also have the original catalogues, which in several cases have different formats from those used by C2A). The astrometric reduction is then performed by clicking the left-most button in the Astrometry area just below the catalogue list. The Options button opens a window where you can define paths to the catalogues and the information to display on the image once astrometric reduction is complete.

Note that several colours are used to code stars resolved in the image:

• Yellow – a star which has been resolved and does not correspond to a reference star in the catalogue.
• Red – a star which has been resolved and does correspond to a reference star in the catalogue used.
• Blue – a star which has been resolved but is saturated and the astrometric information associated with it may be imprecise.

Once the astrometric analysis is done, you can copy into the clipboard information about the objects identified in the image. To do this, just right click on an object in a circle. The following contextual menu is then displayed:

You can copy into the clipboard:

• the position of the cursor in pixels
• the coordinates of the identified object
• the magnitude of the identified object
• the coordinates and the magnitude of the identified object

Once the astrometry resolution of an image is performed, C2A calculate the exact coordinates of the center of the image and report them into the RA and DE text areas (the background becomes yellow). The computed resolution of the image (in " per pixel) is also updated. Clicking the small telescope button in the Astrometry zone will then result into an automatic calibration of a telescope connected to your computer. This is the easiest way to calibrate accurately a telescope. Note that you can also center the current map on these coordinates by clicking the Center Map button .

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