Figure 1 (click for rest of image,
48K): portion of data set showing higher albedo near focus
(invited speaker). Raw data.
I have recently embarked on an unfunded, longitudinal study of the albedo of the DPS(*). Because albedo is at least partially a function of spatial orientation, I decided to use a non-isotropic data set, maximizing the areas of highest variability. Later studies may involve more complete data.
The initial images were acquired on an observation run at the Bethesda, MD facility in November of 1994, using a Canon A-1 35-70 mm (equipment and observation techniques can be found in Roettger 1995 (in preparation)). The data are to be the first in a series to track the temporal evolution of DPS albedo. It is hoped that average albedo can be correlated with one or more parameters, such as age, sex, race, or hair color. The sample is distance-limited. Location and time were chosen to achieve as random a sample as possible, although systematics are expected. Overlapping images were acquired, and show a variation in the illumination, both ambient and instrumental. The data has not been corrected for illumination effects.
The initial data set, intended as a baseline measurement for the temporal study, turned up an unexpected (but unsurprising in retrospect) spatial variation. The albedo increases toward the focus (see Figure). Further study is needed to characterize the spatial variation quantitatively. There is some indication of an overall spectral variation (reddening), but this may be an artifact of the instrument and data reduction technique. An instrument for acquiring spectral information (under rather trying observing conditions) is being designed. Other improvements in the observing techniques are planned. Illumination irregularities are likely to be a significant variable, and will probably mask any (theoretically predicted) limb darkening effects. Image processing packages (IRAF and IDL-based) are being examined for legitimate methods to eliminate contamination from other objects, as the strong opposition effect from the chairbacks leaves a high uncertainty in the measured DPS albedo.
(*)American Astronomical Society, Division for Planetary Sciences (return to citation)
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Created 11 May 1995, last revised 15 June 1997
by Elizabeth E. Roettger, roettger@ix.netcom.com
URL: http://www.nthelp.com/eer/EERalbedo.html