HB Narrowband Cometary Filters

Filter Calibration Updates

August 23, 2000
The paper The HB Narrowband Comet Filters: Standard Stars and Calibrations has now been published.

It can be found in: Icarus, vol. 147, pp 180-204, 2000

For information about reduction of data obtained with the HB filters, refer to this paper. Appendices A and D provide step-by-step instructions for reducing the data.

ASCII versions of the calibration coefficients and standard star magnitudes and positions are available below, so they don't need to be typed in. Also available are postscript versions of the figures that appear in the paper.

February 25, 2000
We have recently finished back-applying the new filter procedures to the old IHW filters. The calibrations for those filters will be added to this page in the near future.

During the IHW application, however, we found discrepancies in the results from the two sets. Specifically, these issues were related to changes in the band shape of C₂ and C₃ among different comets which were used for computing the gamma values, and to the ozone extinction (as a function of wavelength) used to compute the OH extinction coefficients.

In the former case, a more representative spectrum of C₂ and C₃ removed the discrepancy, resulting in changes to the associated gamma values. In the case of ozone extinction, an improved wavelength dependence has been adopted, which supersedes the function from Allen (1973). This resulted in a major correction to the IHW OH filter (due to the effects of a red-leak at 3600 angstroms), but only a small adjustment to the HB OH coefficients. In addition, the derived ozone thickness has now been compared with satellite measurements on a number of nights of observations, with excellent agreement.

Fortunately, the HB filters were fairly insensitive to the changes that were needed to bring the filters into agreement, which is why the problems were not discovered earlier. As it turns out, the reduction procedures that we describe in the paper were unaffected, and only one set of equations was altered (the ozone extinction, eq. 15-19, which is a polynomial fit and needed the constant term added back in). The primary manifestation of the changes occurred in the values of some of the coefficients listed in Tables 4-8. If you implemented the procedures for reducing the HB filter data using coefficients dated before 02/25/2000, you should correct the OH extinction equations and update the coefficients to the final values that are published in the paper.

Let me know if you have problems downloading or printing any of these files, and I can make arrangements to send them in some other manner (fax, mail, etc.)

ASCII files

A description of the files that can be obtained here

Standard star magnitudes (Includes the solar colors for the HB filters)

ASCII list of coefficients and constants

List of standard star positions

Postscript files

Filter Paper Pre-Preprint: Now that the paper has been published, copyright regulations require that we remove the preprint version from this site. See the above reference for the final version of the paper.

Figure 1. Filter transmission characteristics (106K)

Figure 2. Colors of the solar analogs (59K)

Figure 3. Distribution of standard stars (94K)

Figure 4. Colors of the flux standards (40K)

Postscript list of coefficients and constants (27K)

Flowchart 1 (239K) and Flowchart 2 (188K) show the logic used in the data reductions.