1,026 research outputs found
Preliminary Analysis of SOHO/STEREO Observations of Sungrazing Comet ISON (C/2012 S1) Around Perihelion
We present photometric and morphological analysis of the behavior of
sungrazing comet C/2012 S1 ISON in SOHO and STEREO images around its perihelion
on 2013 November 28.779 UT. ISON brightened gradually November 20-26 with a
superimposed outburst on November 21.3-23.5. The slope of brightening changed
about November 26.7 and was significantly steeper in SOHO's orange and clear
filter images until November 27.9 when it began to flatten out, reaching a peak
about November 28.1 (), then fading before brightening
again from November 28.6 () until disappearing behind the
occulting disc. ISON brightened continuously as it approached perihelion while
visible in all other telescopes/filters. The central condensation disappeared
about November 28.5 and the leading edge became progressively more elongated
until perihelion. These photometric and morphological behaviors are reminiscent
of the tens of meter sized Kreutz comets regularly observed by SOHO and STEREO
and strongly suggest that the nucleus of ISON was destroyed prior to
perihelion. This is much too small to support published gas production rates
and implies significant mass loss and/or disruption in the days and weeks
leading up to perihelion. No central condensation was seen post-perihelion. The
post-perihelion lightcurve was nearly identical in all telescopes/filters and
fell slightly steeper than . This implies that the brightness was
dominated by reflected solar continuum off of remnant dust in the coma/tail and
that any remaining active nucleus was <10 m in radius.Comment: Accepted by ApJL; 11 pages of text (pre-print style), 3 figures, 1
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The Nucleus of Comet 10P/Tempel 2 in 2013 and Consequences Regarding Its Rotational State: Early Science from the Discovery Channel Telescope
We present new lightcurve measurements of Comet 10P/Tempel 2 carried out with
Lowell Observatory's Discovery Channel Telescope in early 2013 when the comet
was at aphelion. These data represent some of the first science obtained with
this new 4.3-m facility. With Tempel 2 having been observed to exhibit a small
but ongoing spin-down in its rotation period for over two decades, our primary
goals at this time were two-fold. First, to determine its current rotation
period and compare it to that measured shortly after its most recent perihelion
passage in 2010, and second, to disentangle the spin-down from synodic effects
due to the solar day and the Earth's orbital motion and to determine the sense
of rotation, i.e. prograde or retrograde. At our midpoint of 2013 Feb 24, the
observed synodic period is 8.948+/-0.001 hr, exactly matching the predicted
prograde rotation solution based on 2010 results, and yields a sidereal period
of the identical value due to the solar and Earth synodic components just
canceling out during the interval of the 2013 observations. The retrograde
solution is ruled out because the associated sidereal periods in 2010 and 2013
are quite different even though we know that extremely little outgassing,
needed to produce torques, occurred in this interval. With a definitive sense
of rotation, the specific amounts of spin-down to the sidereal period could be
assessed. The nominal values imply that the rate of spin-down has decreased
over time, consistent with the secular drop in water production since 1988. Our
data also exhibited an unexpectedly small lightcurve amplitude which appears to
be associated with viewing from a large, negative sub-Earth latitude, and a
lightcurve shape deviating from a simple sinusoid implying a highly irregularly
shaped nucleus.Comment: Accepted by AJ; 12 pages of text (pre-print style), 3 tables, 2
figure
CN Morphology Studies of Comet 103P/Hartley 2
We report on narrowband CN imaging of Comet 103P/Hartley 2 obtained at Lowell
Observatory on 39 nights from 2010 July until 2011 January. We observed two
features, one generally to the north and the other generally to the south. The
CN morphology varied during the apparition: no morphology was seen in July; in
August and September the northern feature dominated and appeared as a mostly
face-on spiral; in October, November, and December the northern and southern
features were roughly equal in brightness and looked like more side-on
corkscrews; in January the southern feature was dominant but the morphology was
indistinct due to very low signal. The morphology changed smoothly during each
night and similar morphology was seen from night to night. However, the
morphology did not exactly repeat each rotation cycle, suggesting that there is
a small non-principal axis rotation. Based on the repetition of the morphology,
we find evidence that the fundamental rotation period was increasing: 16.7 hr
from August 13-17, 17.2 hr from September 10-13, 18.2 hr from October 12-19,
and 18.7 hr from October 31-November 7. We conducted Monte Carlo jet modeling
to constrain the pole orientation and locations of the active regions based on
the observed morphology. Our preliminary, self-consistent pole solution has an
obliquity of 10 deg relative to the comet's orbital plane (i.e., it is centered
near RA = 257 deg and Dec=+67 deg with an uncertainty around this position of
about 15 deg) and has two mid-latitude sources, one in each hemisphere.Comment: Accepted by The Astronomical Journal; 23 pages of text, 2 tables, 8
figure
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