The adopted nuclear magnitudes  A catalog of observed  Plots of V(1,0,0) vs r

Defining our ``best estimates'' for the nuclear magnitudes

Several criteria have been taken into account when assigning H_N values to the JF comets. Furthermore, we have classified the adopted nuclear magnitudes into four quality classes. We now present some general considerations that were used for H_N assignment and quality classification.

• We require consistency of several observations taken at somewhat different heliocentric distances.
• In many cases, different observers give discordant magnitudes. Typically, a set of corrected nuclear magnitudes by Scotti is fainter than another set of data. The weight given to the Scotti data then depends on the number of his observations, their spacing in r, and their internal consistency. A single observation is usually discarded, a couple of closely spaced observations is given low weight, while if there are three or more data points well spaced in r and in good mutual agreement we give to their mean a strong weight in the derived magnitude.
• We take special care of comets that show a strong trend for the nuclear magnitudes to get fainter with increasing r. If there is not a clear indication of a leveling off and if the observations do not approach the aphelion distance, the quality class assigned is usually the worst. The adopted magnitude is a mean of the faintest, more distant observations, and this should be taken as an upper limit to the true magnitude of the comet nucleus.
• Total magnitudes at r > 3 AU are included for purposes of comparison with nuclear magnitudes measured at similar distances. If the total magnitudes are much brighter than the nuclear ones, this is an indication that the comet keeps active all along the orbit. On the other hand, if the total magnitudes are similar to the nuclear ones, the comet may have little or no activity.
• In line with our choice of not placing much weight on single observations or close pairs, whether discordant or consistent, even if these data are of the CCD kind, we have discarded almost all comets where the only data were such. The only comet included in this category was 97P/Metcalf-Brewington, where the observations were taken at far heliocentric distances and the comet was inactive (Licandro et al. [1999a]).

Our definition of the quality classes (QC) is as follows:

QC 1: These are our best nuclear magnitudes for which we have many observations spread along a wide range of heliocentric distances and from more than one observer. The uncertainty in the adopted nuclear magnitude is less than or about +/- 0.3 mag.

QC 2: These are fairly good estimates based on several observations spread throughout a wide range of r, or few observations but made at very large r. The uncertainty is estimated to be between +/- 0.3 and +/- 0.6 mag.

QC 3: These are estimates made at different r with a somewhat larger scatter than for the previous class. The uncertainty should be between +/- 0.6 and +/- 1 mag.

QC 4: These are poor estimates, either because they rely upon old data, or upon very few observations, or because the observations show a large scatter. Some of them can only be considered as a lower limit to the nuclear magnitude (i.e., the true magnitude of the comet nucleus is fainter than the quoted value). The uncertainty is generally well above +/- 1 mag.

2000-03-07