Fig. 1
Grain B (marked with a ring) is moving against the stellar background (four stars marked with arrows). The images were taken 120 s apart, and these excerpts cover 1.9° × 2.1°. The images contain many fast grains that are smeared to tracks during the exposure (examples in the lower right panel). The images also contain numerous point sources that are not stars, and if they are real, they cannot easily be identified and tracked as individual moving grains in a sequence of images. Original images: WAC_2014-09-10T03.59.12.757Z_ID30_1397549800_F18.fts, WAC_2014-09-10T04.01.12.755Z_ID30_1397549200_F18.fts, WAC_ 2014-09-10T04.03.12.733Z_ID30_1397549400_F18.fts, WAC_2014-09-10T04.05.12.759Z_ID30_1397549800_F18.fts.
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