EPOS Software Package 

V.N.L'vov, S.D.Tsekmeister
Central Astronomical Observatory of RAS at Pulkovo

EPOS (Ephemeris Program for Objects of the Solar system) is the Windows PC application for study and ephemeris support of observations of the Solar system objects. The orbital elements of asteroids and comets as well as the observatories' coordinates obtained via Internet are used by EPOS. It is also possible to use the data of modern numerical ephemerides (DE200/LE200, DE405/LE405, DE406/LE406) and star catalogs (Hipparcos, Tycho-2, UCAC2, USNO, etc.) that are distributed by the publishers on CDs, hard disks or via Internet. EPOS has bilingual (English and Russian) interface. EPOS (ver. 7.x) includes the following components:

- The main program. It controls the part of common data and transfers the control to one of the programs that solve the restricted set of tasks.

- "Catalogs of objects". This program stores in the internal database the orbital elements and other parameters of the minor bodies of the Solar system (now more than 500000 asteroids and nearly 3000 comets). This helps to browse, edit and export these data, to select the objects with respect to various conditions and to import the most recent data from the well known catalogs. One can get the histograms and distributions for various parameters. It is possible to work with numerous catalogs of objects (for example, NEAs, TNO, centaurs, Troyans, Hildas, etc.).

- "What to Observe". The program generates the list of objects observable at the specified place in the specified night. One can limit the values of visual magnitude, the object’s altitude and elongation from the Sun.

- "Ephemerides". This program calculates the ephemerides of various type and accuracy for the Solar system objects. The calculated values may be observable and geometric coordinates, and the osculating orbital elements. The observable are astrometric or apparent coordinates along with their first two derivatives or Pulkovo apparent motion parameters and a set of other values. The advantage of this program is the ability to create the list of necessary parameters located in the necessary order and properly formatted. The geometric are the rectangular and spherical coordinates of any object referred to the centers of the Sun, Moon or planets. The ephemerides may be calculated with various accuracy, from elliptic motion to high precision numerical integration of equations of motion taking into account the perturbations from all planets and some minor bodies. One can use the values of orbital elements or rectangular coordinates&velocities that are placed to the special input files with higher formal accuracy. Various combinations of elements and some group operations are possible in the ephemeris calculation.

- "O-C: Comparison of Observations with Calculations". This program compares observed coordinates and velocities with the calculated ones. This helps to evaluate the observational accuracy, to reveal the large errors, to identify the objects. Thus an observer can control the results of observations before sending them to Minor Planet Center.

- "Frame". The program visualizes the apparent motion of many objects against the star background. One can get the list of objects that are observable at the specified moment in the specified sky area. It is possible to obtain the histograms of distances, velocities and magnitudes for all objects in the specified space box. This helps in identification of objects and in the study of the structure of the Solar system.

- "Tracks". The program visualizes the path of apparent motion (the track) of any object (or many of them) against the star background. One can search for apparent approaches of the Solar system objects to the stars and find the "loops" where the direction of the object's apparent motion radically changes.

- "Orbits". This program visualizes the perturbed motion of many objects and groups of objects along their heliocentric orbits in space. It is possible to vary the observer’s position, the scale, the velocity and direction of motion, to switch on/off the numbers and names of the objects, their orbits, apsidal and nodal lines and the ecliptic plane. The picture may be saved in a BMP-file. The useful quality of the program is the opportunity to accumulate the images of the lines that helps to follow the orbital evolution in time.

- "Hazardous Objects". By this program one can get the current list of PHA – potentially hazardous objects for the Earth and other planets, and the list of close approaches of asteroids to the specified planet within the specified time span.

The EPOS data are used by some other programs, namely the programs for calculation of mutual phenomena (apparent close approaches and occultations), orbit improvement, planetary configurations, etc. By the special interface the APEX-II program uses the EPOS computational options.

So with the EPOS software package one can calculate the accurate ephemerides for many objects and get the quick illustration of their motion as well. This helps to support the existing observational programs, to develop the new ones and to put the ephemeris data at the disposal of the interested observers and publishers.

EPOS was used in research of the dynamical structures of the Solar system, in preparation and analysis of Pulkovo observations of asteroids and comets, 6-meter BTA observations of trans-Neptunian objects, in the near-Earth space control at FSU observatories, in the accuracy analysis of asteroidal observations of many world observatories and in other tasks.

The orbital elements of minor bodies may be downloaded here

The JPL DE405 numerical ephemeris binary data may be downloaded here

The Tycho star catalog binary data may be downloaded here