Thursday, 27 October 2011

Never give up !!!

So, after seeing the post from NASA saying to basically forget Comet we get this.. read it all...the second section (Starting Z Sekanina) is critical!! (Cropped version of the full CBET)

To say we're thrilled would be an understatement!

Giovanni Sostero, Ernesto Guido, and Nick Howes report on their attempts
to image comet C/2010 X1 (cf. IAUC 9226) after its solar conjunction, using
several robotic scopes that were operating under excellent sky conditions in
New Mexico and at Mauna Kea on Oct. 9.5 and 10.6 UT, yielding no sign of the
comet at low altitude. Several stacked exposures taken on Oct. 10.6 with the
2.0-m f/10 Ritchey-Chretien "Faulkes Telescope North" show no trace of the
comet within the 10' x 10' field-of-view centered on the comet's ephemeris
(limiting magnitude around 20.5). But after stacking unfiltered CCD images
taken in moonlight by Guido, Sostero, and Howes on Oct. 21.38 and 21.48 UT
remotely using the GRAS 0.1-m f/5 APO refractor at the Mayhill station in New
Mexico (field-of-view 3.9 deg x 2.6 deg; scale 3".5 pixels), they found
something moving on the sky background via blinking the two sets that were
separated by about 2 hours: an extremely faint and diffuse blob of tentative
size 14' x 8' (elongated toward p.a. 300 deg) with no obvious condensation
that is close to the ephemeris position (roughly 3'.5 east-southeast of the
prediction), moving apparently with the comet's motion.

Guido, Sostero, and Howes confirmed their detection of the comet's
"cloud" in observations obtained on Oct. 23.4 with the same refractor, the
cloud being roughly 40' long with a 6' extension near the expected position
of the comet. Images are posted at website URLs and (with an "X" marking the the ephemeris position in
the second image); an animation showing the motion with respect to the
X-marked movement of the expected comet's position is shown at website URL Sostero, Guido, and Howes then subtracted the field
stars to obtain the images posted at URL They
note that the sunward part of the "cometary cloud" appears much sharper
compared to the anti-solar direction; the diffuse shape of the comet appears
to be somehow "conical", about 1.5 deg long overall, with a maximum
thickness of about 10' on the side toward the solar direction, and the oval
shape of the "cometary cloud" then thins significantly tailward (p.a. about
300 deg). The "brightest" part of this extremely faint blob of light is
located about 4'.3 in p.a. 77 deg (east-northeast) when compared to the
nominal position of the MPC ephemeris.

Z. Sekanina, Jet Propulsion Laboratory, writes that the deep CCD images
of the disintegrated comet taken in the past few days, especially the high-
quality processed image from Oct. 23.37 UT by E. Guido et al., show enough
detail to allow simple modeling and a preliminary interpretation of the
surviving tail. The sharp cigar-shaped trail near the southern end of this
dust-ejecta cloud points at position angle 290 +/- 1 deg, which, interpreted
as a synchrone, implies a fairly brief dust-emission event centered on Aug. 16
+/- 4 days, in fair agreement with a rather sharply peaked light curve on
Aug. 13-14 and with Mattiazzi's report of the comet's notable fading from Aug.
17 on (CBET 2801). Despite the near-zero inclination of the comet's orbital
plane to the ecliptic, the geometry from the earth has been relatively
favorable. Because of the small geocentric distance, the earth was on the
Aug. 23 almost 7 deg below the orbit plane, when this picture was taken, and
since the sheet of dust in the plane was spreading toward the earth, it
projected essentially to the north of the trail in an approximately 160-deg-
wide fan. The prolonged radius vector was directed at p.a. 277 deg and thus
made an angle of 13 deg with the sharp trail.
Because of their fan-like distribution in the orbit plane, the image
shows not only the ejecta from the first half of August, but from the comet's
entire active period, starting far from the sun on the way to perihelion.
(Comets arriving from the Oort cloud are generally known to be considerably
active at large heliocentric distances on their way in; C/2010 X1 is one such
example.) Because the bright tip of the cigar-shaped trail lies on the line-
of-variation, it apparently represents the location of the most sizable debris
ejected during the mid-August dust-emission event; relative to the ephemeris
position, the perihelion time was late by some 0.06 day (Sept. 10.79 instead
of 10.73 TT), and this deceleration is equivalent to a sudden change in the
orbital velocity of more than 50 m/s, primarily in the direction away from
the sun. Whereas the comet's orbital motion may have non-gravitationally
decelerated even before the mid-August event (though not enough to detect
computationally), the bulk of the effect should be due to the evolution in
the past 10 weeks or so. Since this velocity change is too high for fragments
several meters across or larger, they must have been short-lived (like in the
case of C/1999 S4; e.g., Weaver et al. 2001, Science 292, 1329) and soon must
have given birth to ever smaller fragments in a cascading fashion. The
largest debris surviving to date is perhaps in the centimeter range.

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