We report on a multi-observatory campaign to examine asteroid 3200 Phaethon
during its December 2017 close approach to Earth, in order to improve our
measurements of its fundamental parameters, and to search for surface
variations, cometary activity and fragmentation. The mean colors of Phaethon
are B-V = 0.702 +/- 0.004, V-R = 0.309 +/- 0.003, R-I = 0.266 +/- 0.004,
neutral to slightly blue, consistent with previous classifications of Phaethon
as a F-type or B-type asteroid. Variations in Phaethon's B-V colors (but not
V-R or R-I) with observer sub-latitude are seen and may be associated with
craters observed by the Arecibo radar. High cadence photometry over phases from
20 to 100 degrees allows a fit to the values of the HG photometric parameters;
H = 14.57 +/- 0.02, 13.63 +/- 0.02, 13.28 +/- 0.02, 13.07 +/- 0.02; G = 0.00
+/- 0.01, -0.09 +/- 0.01, -0.10 +/- 0.01, -0.08 +/- 0.01 in the BVRI filters
respectively; the negative G values are consistent with other observations of F
type asteroids. Light curve variations were seen that are also consistent with
concavities reported by Arecibo, indicative of large craters on Phaethon's
surface whose ejecta may be the source of the Geminid meteoroid stream. A
search for gas/dust production set an upper limit of 0.06 +/- 0.02 kg/s when
Phaethon was 1.449 AU from the Sun, and 0.2 +/- 0.1 kg/s at 1.067 AU. A search
for meter-class fragments accompanying Phaethon did not find any whose on-sky
motion was not also consistent with background main belt asteroids.Comment: Accepted by the Astronomical Journal, 15 pages, 8 figures, 1 animated
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