I report the synodic period of asteroid (78) Diana
to be 7.313 +/- 0.027 hr with an amplitude of 0.258 +/- 0.008mag.

Fig.1 Differential photometry plot of MPL 78 Diana using AIP4Win ver. 2.1.10

Volunteer Observatory's 0.35m SCT operating at f/6.4  was used for observations of MPL 78 on 2007.01.03 UT. This instrument is described in detail here. 613  integrations spanning a time of 8.5 hrs were acquired using 30sec exposures with  an R band filter and an  SBIG ST10XME CCD, binned 2x2 operating at -30C. This asteroid was selected from the CALL website's "List of Potential Lightcurve Targets" ( B. Warner, Dr. Allan Harris,  2007). Chosen as a "Full Moon Project" this target was sufficiently bright to permit an excellent SNR to be achieved even with moonlight gradients in the image frames.Observations were started while the asteroid was < 30 degrees elevation. The R band filter limited the first order effects of atmospheric extinction and all observations were obtained within 0.01mag precision.

ACP ver 4.2 is used for observatory automation with Maxim DL 4.53 for CCD control and acquistion. The temperature tracking feature was also enabled in Maxim permitting temp compensation to be enabled for the Optec TCF-s focuser. CCD image calibration was performed utilizing master bias, darks and flat frames. Images were calibrated as well as plate solved immediately after acquisition using ACP /Maxim. AIP4Win version 2.1.10 was used to perform differential photometry of the calibrated data. The above Fig.1 plot was generated with MS Excel 2003. Lightcurve amplitude was determined to be 258 +/- 8 mmag using speadsheet analysis with error= SQRT ((error1)^2+(error2)^2). This should be regarded as a lower limit as it was computed from the sections of the lightcurve with complete coverage data of maxima and minima. It is likely that the maximum amplitude is a bit larger than the reported value. The spreadsheet also demonstrated the period to be ~7.3-7.4hrs.  MPO Canopus was utilized for differential photometry  to refine the period determination. The results of the analysis are graphically displayed in Fig. 2. A lapse of coverage for ~ 40 minutes occured during the run. This appears to be due to a spurious hardware error that occured shortly before the meridian flip. The problem corrected itself at the flip and successful image acquisition resumed.

Fig.2 ( Generated with MPO Canopus )

 

The period obtained agrees very closely with the value of  7.300 +/- 0.001 hrs. reported by Licchelli (2005) and is similar to the 7.225 hrs reported by Harris & Young, (1989). The amplitude is considerably different than the value of  0.150 mag cited by Licchelli (2005) .

Licchelli, D.   Minor Planet Bulletin Vol. 33, No. 1, p. 11 - 13 (2006)

Harris, A.W. and Young,  J.W. Icarus 81, 314-364 ( 1989 )
 
 
 

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