49 THE MINOR PLANET BULLETIN OF THE MINOR PLANETS SECTION OF THE BULLETIN ASSOCIATION OF LUNAR AND PLANETARY OBSERVERS VOLUME 31, NUMBER 3, A.D. 2004 JULY-SEPTEMBER 49. CCD PHOTOMETRY OF ASTEROIDS 970 PRIMULA AND ideal for individuals or universities with small research 1631 KOPFF USING A REMOTE COMMERCIAL departments. TELESCOPE The targets were selected from a list of asteroid photometry Pedro V. Sada opportunities published by Brian Warner on his Collaborative Eder D. Canizales Asteroid Lightcurve Link (CALL) website (Warner, 2003). Edgar M. Armada Selection criteria included: proximity of the two asteroids to each Departamento de Física y Matemáticas other and to a nearby suitable star calibration field to save on Universidad de Monterrey telescope slewing time, asteroid declination and closeness of Av. I. Morones Prieto 4500 Pte. opposition date to dates of observation for maximum nightly Garza García, N. L., 66238 coverage, appropriate asteroid magnitude to acquire enough MÉXICO counts for a S/N of at least 100 with 1-minute V-filtered [email protected] exposures, and a high reported asteroid absolute magnitude (H- value) to target the smallest asteroid size possible. (Received: 12 February) Usable data were collected on 2003 October 28-29 and November 04-05 for both asteroids. There was an additional night of data for CCD photometry of asteroids 970 Primula and 1631 1631 Kopff on November 15. All dates are UT. Two other nights Kopff obtained remotely at Tenagra Observatories of data were obtained but were not used because most of the during October and November 2003 is reported. A images showed evidence of clouds. In total, 117 images were synodic rotation period of 2.777 ± 0.001 hours is obtained and processed for 970 Primula, and 181 for 1631 Kopff, determined from four nights of observations for Primula. using a standard Johnson V photometric filter and 1-minute The resulting rotation period for Kopff is 6.683 ± 0.001 exposure times. Of these, 112 (95.7%) were used in the final hours from five nights of observations. Both observed analysis for 970 Primula and 170 (93.9%) for 1631 Kopff. The lightcurves were nearly symmetrical with amplitudes of rest were discarded because of asteroid proximity to stars. 0.18 ± 0.02 magnitudes for Primula and 0.41 ± 0.04 for Standard bias, dark current and flat field corrections were applied. Kopff. Five stars were used in each image as magnitude comparisons for the asteroid. A nearby star field, identified from the 'LONEOS Photometric Calibration Star List' (Skiff, 2003), was observed Observations each night for magnitude calibration. Stars with known magnitudes were used to determine the magnitudes of the asteroid The observations of 970 Primula and 1631 Kopff reported here comparison stars. were made with the Tenagra II telescope at Tenagra Observatories (MPC 926). The instruments used to gather the data were a Reduction and Results computerized 0.81m (32-inch) f/7 Ritchey-Chrétien telescope with a SITe-based 1024x1024x24 µm electronic imager yielding ~0.87 Times were corrected for light travel from the asteroid to the Earth arc-seconds per pixel for a field of view of ~15'x15' (Schwartz, and were taken to be at the mid-times of the image exposures. 2003). The chip temperature is set at –45° C and the images were Relative magnitudes from night to night were uncertain as 2x2 binned for file transfer economy since previous reports had different comparison star sets were used. This was dealt with by shown no apparent effect of binning on the photometry (Ditteon et using additive constants to bring all the data into the best al. 2003). Tenagra Observatories, directed by Michael Schwartz agreement possible. However, these arbitrary magnitude shifts and assisted by Paulo Holvorcem for minor planet and comet were small (≤0.04 magnitudes). Additional magnitude shifts were studies, offers commercial telescope time with two telescopes in also used to compensate for the intrinsic magnitude variation of southern Arizona. These are fully automated instruments. An the asteroids due to their change of distance with respect to the observer only needs to send instructions on which objects to Earth, and to phase angle variations (15.2°-11.1° for 970 Primula observe, and the imaging requests from several users are sorted and 14.2°-5.3° for 1631 Kopff). and executed throughout the night. The data are stored for immediate FTP retrieval, including calibration frames. This The best-fit rotational periods for the asteroids were obtained by convenient setup saves time, travel and lodging expenses and is computing the power spectrum of the time series of data (Scargle, Minor Planet Bulletin 31 (2004) 50 1982; Horne and Baliunas, 1986). The resulting synodic rotational period for 970 Primula from the data presented here is 2.777 ± 0.001 hours. The amplitude of the lightcurve is 0.18 ± 0.02 magnitudes (see Figure 1). For 1631 Kopff the resulting synodic rotational period was 6.683 ± 0.001 hours with an amplitude of 0.41 ± 0.04 magnitudes (see Figure 2). Both asteroids exhibited two similar maxima and minima per rotation. The time scale is given in rotational phase with the zero corresponding to 2003 November 04 at 12.0 hrs UTC (JD 2452948.0). The magnitude scale is also referenced to this epoch since it was the night that exhibited the best photometry. This is probably the first reported rotational period for these asteroids since they are not listed in A. Harris and B. Warner’s ‘Minor Planet Lightcurve Parameters’ list (Harris and Warner, 2003). Acknowledgments We would like to thank R. Hernández for contributing funds for these observations. Many thanks also for M. Schwartz and P. Holvorcem, from Tenagra Observatories, Ltd., for making remote observing possible, simple, and fun; and for providing Pro Bono time for this project, which was a real ‘hands-on’ learning Figure 1: Composite lightcurve of asteroid 970 Primula derived experience for students. from 112 observations and a 2.777-hour rotation period. References Ditteon, R., Tollefson, E., and Twarek, A. (2003). “Asteroid Photometry Using a Remote Commercial Telescope: Results for Asteroids 808, 1225, and 28753.” Minor Planet Bulletin 30, 76- 77. Harris, A. W. and Warner, B. D. (2003). “Minor Planet Lightcurve Parameters. ” Posted on the WWW: http://cfa- www.harvard.edu/iau/lists/LightcurveDat.html (2003 December 15 update). Horne, J. H. and Baliunas, S. L. (1986). “A Prescription for Period Analysis of Unevenly Sampled Times Series.” Astrophysical Journal 302, 757-763. Scargle, J. D. (1982). “Studies in Astronomical Time Series Analysis. II – Statistical Aspects of Spectral Analysis of Unevenly Spaced Data.” Astrophysical Journal 263, 835-853. Schwartz, M. (2003). “Tenagra Observatories, Ltd.” Posted on the WWW: http://www.tenagraobservatories.com/ Skiff, B. (2002). “LONEOS Photometric Calibration Star List.” Posted on the WWW: ftp://ftp.lowell.edu/pub/bas/starcats/ Figure 2: Composite lightcurve of asteroid 1631 Kopff derived loneos.phot (2003 July 15 update). from 170 observations and a 6.683-hour rotation period. Warner, B. D. (2003). “Potential Lightcurve Targets 2003 October – December. ” Posted on the WWW: http://www .minorplanetobserver.com/astlc/default.htm Minor Planet Bulletin 31 (2004) 51 172 BAUCIS — A SLOW ROTATOR lightcurve (particularly the minima) over the observing period of more than one month. A number of initial trials were done C.S. Bembrick between 1.5 and 2.25 days as Zeigler (1999) had listed a period of PO Box 1537, Bathurst, NSW 2795, Australia 51.25 hours. It rapidly became apparent that our data could not be [email protected] phased with that period. T. Richards A subset of the data was compiled using the six best nights and the 8 Diosma Rd, Eltham, Vic 3095, Australia “AVE” software (Barbera 2004) was used for a period search utilizing the Phase Dispersion Minimisation (PDM) method. G. Bolt Searching between 1.0 and 2.0 days yielded a distinct minimum in 295 Camberwarra Drive, Craigie, WA 6025, Australia the “periodogram” between 1.140 and 1.143 days – and also an alias at 1.7 days. Further refinement narrowed this to 1.142 days. B. Pereghy A number of trial phase plots, gradually folding in the additional 37 Hatfield St, Blakehurst, NSW 2221, Australia data, showed that 1.1424 days (27.417 hours) was the best fit to D. Higgins the data. 7 Mawalan St, Ngunnawal, ACT 2913, Australia The phase stacked composite lightcurve for the 2003 observations W. H. Allen is displayed in Figure 1 – with arbitrary zero phase (JD 83 Vintage Lane, RD 3 Blenheim, NZ 2452852.80) to best display the data on the phase plot. Magnitudes from individual nights were adjusted by an additive (Received: 14 March) constant to give a “best fit” to the phase stack. Note the varying depths of the minima which have changed over the observing period. The overall peak-to-peak variation between extrema was Lightcurve measurements of 172 Baucis in 1985 and 0.25 magnitudes in 2003. To a first approximation (using a tri- 1999 were inconclusive in determining the period of axial ellipsoid model), this implies a ratio a/b of 1.26, where a, b rotation. However in 2003 a combined effort by and c are the semi-axes of the ellipsoid and rotation is about the Southern Hemisphere observers derived a synodic shortest axis, c. rotation period of 27.417 ± 0.013 hours. The overall variation was 0.25 magnitudes in 2003, but appears to Data from other years were then individually folded at the derived have been 0.4 in 1999 and 0.35 in 1985. period. Zeigler’s 1985 data are compatible with this period although the lightcurve is fragmentary.