L. A. M. Benner, M. C. Nolan, L. M. Carter, S. J. Ostro, J. D. Giorgini, C. Magri, and J. L. Margot
Abstract
Arecibo delay-Doppler (2380 MHz, 13 cm) radar images of Sigurd obtained during 2004 September 18-22 reveal an elongated, contact binary shape with a maximum visible range extent of at least 3.5 km. The lobes are generally rounded, have comparable dimensions, and are connected by a narrow neck. When oriented broadside on September 18, 20, and 21, a valley with a depth of ~400 m is visible between the lobes. Images obtained on September 20 and 21 also show a prominent facet that is at least 1 km long. Echo bandwidths vary by a factor of about 2.5 as the asteroid rotates and establish that Sigurd is among the most elongated NEAs imaged by radar. Among the handful of near-Earth asteroids imaged by radar that appear to have contact binary shapes, Sigurd is the largest. The images are consistent with the 8.5-h rotation period derived photometrically by Pravec et al. (1998, Icarus 136, 124-153) and Krugly et al. (2002, Icarus 158, 294-304). The images cover about three-fourths of a rotation, sufficient for least-squares estimation of Sigurd's three-dimensional shape.
MASTERLOG
<--- UTC --->
Samples/ rcsta rcend
Setup Code Band baud osod TXoff Runs HHMMSS-HHMMSS
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2004 September 18
CW no hop 5000 1 22 +200 4 171949-173625
4.0 us 8191 30.52 1 22 +2 1 174545-174800
0.2 us 65535 76.30 2 24 +2 13 175737-191348
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2004 September 19
0.5 us 16383 122.08 1 24 +2 14 182309-192937
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2004 September 20
CW no hop 5000 24 +200 1 170223-170448
0.5 us 16383 122.08 1 24 +2 3 171328-172605
2.0 us 4095 122.10 2 24 +2 2 172925-173656
0.5 us 16383 122.08 1 24 +2 3 173955-175232
2.0 us 4095 122.10 2 24 +2 2 175531-180302
0.5 us 16383 122.08 1 24 +2 3 180601-181838
2.0 us 4095 122.10 2 24 +2 2 182137-182908
0.5 us 16383 122.08 1 24 +2 3 183207-184444
2.0 us 4095 122.10 2 24 +2 2 184743-185514
0.5 us 16383 122.08 1 24 +2 3 185814-191051
2.0 us 4095 122.10 2 24 +2 2 191350-192121
0.5 us 16383 122.08 1 24 +2 3 192420-192420
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2004 September 21
CW no hop 5000 24 +200 3 170201-171214
0.5 us 16383 122.08 1 24 +2 3 171929-173754
2.0 us 4095 122.10 2 24 +2 2 173606-174355
0.5 us 16383 122.08 1 24 +2 3 174700-180007
2.0 us 4095 122.10 2 24 +2 2 180312-181101
0.5 us 16383 122.08 1 24 +2 3 181406-182713
1.0 us 8191 122.09 1 24 +2 2 183018-183807
0.5 us 16383 122.08 1 24 +2 3 184149-185456
1.0 us 8191 122.09 1 24 +2 2 185801-190550
0.5 us 16383 122.08 1 24 +2 3 191729-193041
1.0 us 8191 122.09 1 24 +2 1 193353-193625
0.5 us 16383 122.08 1 24 +2 1 193931-194203
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