Comet Elenin - The recovery

[NickH]

Thought I would share the latest on what we've been working on

after seeing the post from NASA saying to basically forget Comet Elenin...today 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!

COMET C/2010 X1 (ELENIN)

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 http://bit.ly/q5QCM7 and

http://bit.ly/pXxtpY (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

http://bit.ly/qOx8oF. Sostero, Guido, and Howes then subtracted the field

stars to obtain the images posted at URL http://tinyurl.com/64fbkcb. 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.

[NickH]

And the images -

Remanzacco Observatory - Comets & Neo: "Debris cloud" of comet C/2010 X1 (Elenin)