CCD PHOTOMETRY OF ASTEROID 487 VENETIA

A. William Neely NF/ Observatory Rt. 15 Box 760 San Lorenzo, NM 88041 EMAIL NFO@micro.wnmu.edu CCD observations in V of the asteroid 487 Venetia were made at the NF/ Observatory during the 1992 apparition. The synodic rotational period was 12.73 .12 hours. The lightcurve amplitude was m=.20 .02. There are no previously published results. Introduction Asteroid 487 Venetia is listed as a type S asteroid (Tholen, 1989). It has a diameter of 64.2km 3.1km and albedo of .22 with an absolute magnitude of 8.21V.(Tedesco, 1989). During February and March of 1992 the asteroid was in a favorable position and phase. The asteroid was listed as a "Photoelectric Photometer Opportunity" in the Minor Planet Bulletin(Harris, 1992). The photometric studies were conducted by A. William Neely. Observations The CCD exposures were made through a Johnson V filter on a CRAF- Cassini 1024x1024 CCD with opposite quadrants silvered allowing frame transfer of a 512x512 pixel image. The pixel size is 1.2 arc seconds. The chip and amplifier noise is 25 electrons. Full well is 100,000 electrons. The telescope is a .45m newtonian. Control of the observatory was by digital radio link, and has been described elsewhere (Neely, 1989). The images were stored on tape and analyzed with PCVISTA (written by Michael Richmond at Berkeley). The comparison and check stars were within the frame of the CCD image. This reduced the differential atmospheric extinction to negligible levels and allowed data collection on nights with marginal seeing. The comparison star was calibrated with a Landolt field, cluster PG0918(Landolt, 1983), for the February 29, 1992 UD data only. 200 second integrations were obtained for all data points. Dark fields were taken before each exposure. Approximately 60 exposures were taken per night. The dark and bias fields were subtracted at the time of readout and the frame was flatfielded before being stored on tape for later analysis. All the flatfields were "twilight flats". Results CCD observations of the asteroid were made on 1992 UD's: February 29, March 14, March 17, March 20, March 21, and March 22. Observational circumstances for 487 Venetia are shown in Table 1. The synodic rotational period was calculated using a minimum phase error method similar to Stellingwerf(1978). This method determined a period of 12.73 .12 hours with two unequal minima per rotation. The phase corrected data is shown in Figure 1. Acknowledgements This work was supported by a grant from NASA administered by American Astronomical Society and a grant from the Theodore Dunham Jr. Fund for Astronomical Research. Additional thanks to Larry Miller for his improvements on PCVISTA and to Fred Treasure who kept the radio link up through a very difficult lightning season. References Harris, A. W. (1992),"Photoelectric Photometer Opportunities". The Minor Planet Bulletin. 19, 1, 5-6. Landholt, A. U. (1983),"UBVRI Stars Around the Celestial Equator". Astronomy J. 88, 439-460. Neely, A. W. (1989),"The Automatic Radio Linked Telescope (ARLT) at the NF/ Observatory". In Remote Access Automatic Telescopes(Hayes, D. and Genet R. M., Ed.), pp. 141-150. Fairborn Press, Tucson. Stellingwerf, R. F. (1978),"Period Determination using Phase Dispersion Minimization". Ap. J. 224, 953. Tedesco, E. P. (1989),"Asteroid Magnitudes, UBV Colors, and IRAS Albedos and Diameters". In Asteroids II (R. Binzel, T. Gehrels and M. Shapley Matthews, Ed.), pp. 1090-1138. University of Arizona Press, Tucson. Tholen, D. J. (1989). "Asteroid Taxonomic Classifications". In Asteroids II (R. Binzel, T. Gehrels and M. Shapley Matthews, Ed.), pp. 1139-1150. University of Arizona Press, Tucson. Table I. Observational circumstances for 487 Venetia Date Long RA(2000) Dec AU to Earth VMag* 2/29/92 152 27 10 17.2 21 1 1.7881 5.1 12.2 3/14/92 155 22 10 6.3 22 17 1.86 10.2 12.3 3/17/92 156 0 10 4.4 22 28 1.881 11.1 12.4 3/20/92 156 37 10 2.7 22 38 1.905 12.3 12.5 3/21/92 156 50 10 2.2 22 41 1.913 12.6 12.5 3/22/92 157 3 10 1.6 22 41 1.923 12.9 12.5 *magnitudes are estimated except for 2/29/92 which was calibrated to PG0918 .06.