Astron. Astrophys. 349, 649-659 (1999)

2. Observations and reduction

CCD imaging of comets in the range 3 AU R_h 6 AU was carried out between 24th & 31st August 1995 using the 1-m Jacobus Kapteyn Telescope on the Island of La Palma. Only the first 4 nights were photometric. Table 1 lists the observational circumstances for each comet observed. A TEK pixel CCD was used at the f/15 cassegrain focus resulting in an image scale of 0.33 arcsec per pixel. A log of all cometary observations is listed in Table 2. All images were taken through one of the RGO Harris R & V filters and the KPNO B filter. All cometary images were obtained with the telescope tracking at the sidereal rate with the exception of 86P/Wild 3 and 120P/Mueller 1 which were differentially tracked at their respective apparent motions. A number of observations of the standard field SA92 (Landolt 1992) in all 3 filters were taken throughout the 4 nights along with bias and twilight flat field exposures for the calibration of the images. Counts from the standard stars were measured through apertures of 6.6 arcsec radii in order to conform with apertures used by Landolt (1992) and converted to instrumental magnitudes. Atmospheric extinction coefficients for the B, V, and R filters were then calculated for each of the 4 photometric nights. For comets with only R band imaging, we found that the uncertainty introduced when assuming a comet colour in the conversion of instrumental to apparent magnitudes was negligible. Object detection was achieved by their known motion relative to the background stars. Detection was immediate in some cases but for others such as 43P/Wolf-Harrington several images were shifted and then coadded to give a larger signal to noise ratio. Image processing and photometry was performed with the IRAF/CCDRED (Massey 1997), IRAF/APPHOT (Davis 1989) & IRAF/DAOPHOT (Davis 1994) packages on the Northern Ireland STARLINK node.

Table 1. Observational geometry for all comets. R_h and are the heliocentric and geocentric distances respectively. is the phase angle.

Table 2. B, V, & R filter observations for all comets. All images were obtained with the telescope tracking at the sidereal rate unless otherwise stated.

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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