Image photometry. Intruder and variable detection

The program precisely measures the intensities of stars on the image and, by matching them with a catalog that holds reference magnitudes, photometrically calibrates the image. The magnitude of any object on the image can then be computed.

The user can select one comparison star, or several of them for ensemble photometry. Such comparison stars are saved into the database, ready to be reused on any subsequent image.
There are 2 methods for the photometry: the PSF photometry allows the quick analysis of an image. The aperture photometry is for very precise magnitude measurements. An aperture is made of an inner circle for the object to be measured and of an outer ring for the background; the apertures are also saved into the database, ready to be reused.
With an asteroid, the aperture may have orbital elements and then move with the object.

An image with apertures for the photometry.

A star on the image whose magnitude does not match the magnitude in a catalog is considered as a variable and is automatically outlined with a special symbol.

The objects on the image that are not in catalogs are considered as intruders and may be outlined with a special symbol. This feature may be especially useful with very large catalogs to detect asteroids, etc.

Detection of an outburst from TY PsA (Sep 17, 2004): the yellow square is for the comparison star, the blue ticks are for the control star, the white triangle was automatically by the program because TY PsA was measured as significantly brighter than in the GCVS catalog.

The variables and intruders can be robotically detected and saved to the database. The user may then select only the images that give alerts.
A selected object may be monitored and when its magnitude differs from the one previously recorded, the user is automatically alerted.
The algorithms are smart enough not to trigger phony alerts from obvious cosmics or hot pixels. The threshold for the variable detection may be parametrized, so as to be sensitive with precision photometric catalogs, and to be only coarse with other catalogs.

Images may be selected from the database by keywords and by coordinates. They may then be robotically analyzed to make bulk photometry.

Data from a selected astronomical object (magnitudes, heliocentric corrections, geocentric distances, statistical uncertainties, air mass, etc.) may be exported to third party programs (Microsoft Excel, MathCAD, ...) for further analysis (light curves, ...). They may also be exported for submission to organizations such as the MPC, the AAVSO, the CBA, VSNET. The ALCDEF format of the MPC is supported.

Digital Blink

The reference image is scanned and the celestial objects that are detected and measured are saved into an astronomical catalog. The new image is compared with the catalog and the differences (variable stars, intruders, etc) are outlined with symbols.

Blinking images

Two images of the same sky area can be overlapped and blinked. This is a classical way to detect supernova, asteroids and transient phenomena.

The intruders and variables detected on the images by matching them with catalogs can also be outlined with symbols on the blinked image.