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Pulkovo NEO Page

Central Astronomical Observatory at Pulkovo Official Site

Central Astronomical Observatory at Pulkovo
of Russian Academy of Sciences, St.-Petersburg, Russia


General InformationGeneral Information


Occultations of Stars by AsteroidsOccultations of Stars by Asteroids

Ephemeris SupportEphemeris Support

Apparent close Approaches to the StarsApparent close Approaches to the Stars

Estimation of Accuracy of the ObservationsEstimation of Accuracy of the Observations




CCD observations are processed with the help of the APEX software package created at Pulkovo Observatory. This Windows application serves for determination of spherical coordinates and magnitudes of the objects. It has some useful qualities such as the possibility to take account of the chromatic refraction, the use of additional frame formats and various models of approximation and reduction.

The following methods may be used for determination of a center of object’s image:

- a center of gravity,

- a circularly symmetric Gaussian with 5 parameters,

- an ellipsoidal Gaussian with 6 parameters.

The result of measurements is the list of objects’ coordinates in an instrumental rectangular coordinate system. Then these data are to be transferred to the spherical coordinates using the methods of 6 or 8 plate constants.

The objects’ coordinates are referred to the system of chosen star catalog. Now APEX can use the HIPPARCOS, TYCHO-2, UCAC2 and USNO (A2.0, SA2.0, B1.0) star catalogs.

Besides coordinates the photometric data can be obtained. The semiautomatic and automatic modes serve for estimation of total brightness of an object taking into account the background level.

The measurement process includes the following steps:

1. identification of stars with the catalog browser that shows the appropriate star field,

2. choice of reference stars with mouse,

3. measurement of rectangular frame coordinates of objects and reference stars taking account of predefined background parameters,

4. calculation of the spherical coordinates of objects.

As a result one gets a list of objects with measurements and their errors. If the measurement errors for some reference star are too large this star can be excluded as reference one and treated as an additional object. But the list of reference stars is to be refreshed before the new cycle of measurements.


1. A.V.Devyatkin, A.N.Gritsuk, D.L.Gorshanov, E.V.Kornilov. APEX - the software package for processing astronomical CCD observations. Izvestia GAO, 2000, 214, pp.455-468 (in Russian).