A Survey for TNOs Using the APS POSS I Database
by Edward Rhoads
Under the supervision of Professor Roberta Humphreys and Professor Chick Woodward
The digitized first epoch Palomar Observatory Sky Survey (POSS I) is an ideal and unused archive for the purpose of data mining Trans-Neptunian Objects (TNOs). The POSS I survey has positions accurate to 0.3'', and covers over three quarters of the sky within 15 degrees of the ecliptic. Overall, there are 232 plates within 15 degrees of the ecliptic which have been scanned by the Automated Plate Scanner (APS) project (Pennington et al 1993) from which we can potentially discover TNOs with diameters of 500 km or larger. Out of the 232 plates within 15 degrees of the ecliptic, 165 plates were analyzed. 148 of these plates were found to be useful for a reliable TNO search. Each plate covers 38.4 square degrees of sky, and the raw sky coverage on the 165 plates was 6343 square degrees. When accounting for overlap in TNO phase space and the area of the plates covered by stars and galaxies, the effective sky coverage area for this search was 4931 square degrees for Plutinos, and 4992 square degrees for classical TNOs; making this survey one of the most extensive to date. To refine the search we first determined the expected TNO parameters on these plates such as motion between the red and blue plates, the O-E color, and ellipticity using known TNOs. During the time between exposures on the POSS I O and E elds (30-40 minutes), the motion in Right Ascension (RA) for a TNO or Centaur is expected to be between 1'' to 5''. Also, the direction of movement, within the errors, was expected to be within 20 degrees of parallel to the ecliptic. Using Varuna, Quaoar, and Pluto the expected O-E color is between 1.0 (0.2 magnitudes bluer than the color of Pluto) and 4.0 (a very red limit). The ellipticity on the O plate and the E plate are found to lie within 0.2 of each other. Finally, real objects are expected to have diameters consistent with the seeing of the plate, and solar system objects are expected to have diameters consistent with their movement during the plate exposure. Using these constraints, computer codes were used to separate TNO candidates from the millions of objects on each plate, and lists of possible TNO, Centaur, and asteroid candidates were created. Every candidate that remains after the various criteria had been applied were visually inspected in order to determine if it was a potential solar system object. The results of this massive survey yielded 17 reliable TNOs and TNO candidates, including Pluto, Quaoar, and Varuna. In addition to the TNOs, 28 Centaur and 31 Asteroid candidates were found. Also, Quaoar was pre-covered, and the Main Belt Asteroid (395) Delia was also recovered.