[X] My Assistant

[Mongo]

A November 22 image of ISON by schmidtcamera2500:

Hello

Under bright sky i observed Ison on Nov. 22 from Austria.

Image with Apo 80/400 and CCD KAI 110002

RGB 60sec L-9x60sec

Regards
MJ

[scalbers]

Greetings,

Nice view above. Overall this past week ISON has been about a magnitude brighter than my earlier light curve. So I've bumped it up by this amount going into the future. This puts it just within naked eye visibility (on average - neglecting temporary surges) during the post-perihelion period in December. This is about the visibility of PANSTAARS in March. These comparisons are valid for 40N latitude.

Assuming the power law stays at about n=3 I get a peak perihelion magnitude of about -7. So close to the sun it may be invisible, except from areas with low amounts of aerosols (e.g. in mountains).

http://laps.noaa.gov/albers/ast/eph/ISON.2012S1.co.html

http://laps.noaa.gov/albers/ast/eph/ISON_h....2012S1.co.html

I made a visual sighting back on Nov 17th with 10x50 binoculars.

Steve

[Mongo]

Some more images of pre-perihelion ISON.

Taken by Bob Lukasik on November 20

Details:

A good three degrees of tail are visible. The image is a composite from a stack of six second images with the foreground layered back in. Canon XTi - 6 sec - Nikon 50mm lens - ISO 800 - BYEOS

Taken by Kouji Ohnishi on November 22

Details:

Approach of the comet and Mercury in Twilight (22 Nov 2013) 22 Nov 2013 AM5h10m (JST) at KIRIGAMINE, Nagano, Japan.

COMET ISON (C/2012 S1) Tail to rise above the clouds.

Details:135mm(Carl Zeiss Apo-Sonnar T* 2/135), F=4.5, Canon EOS5DMkIII, ISO1600, 10sec exposure.

[Mongo]

ISON photo by Peter Lawrence on November 22:

Details:

Comet ISON from the morning of November 22nd taken from outside the Isaac Newton Telescope at the Roques de los Muchachos Observatory on the island of La Palma.

[Mongo]

ISON almost lost in the morning twilight, photo taken by Juan Carlos Casado on November 24.

Details:

This picture of Comet ISON obtained today Sunday 24th November at 6: 25 UT, from Teide Observatory (IAC).

The image is a combination of 4 photos (to increase S / N ratio) taken with a telephoto lens of 300 mm f/2.8, 4 s exposure at ISO 3200.

The comet was over the distant island of Gran Canaria (above a sea of clouds), 1 hour before sunrise and only 16 ° elongation.

The exceptional atmospheric conditions of Teide Observatory have allowed to capture this image of comet almost on the horizon near to the Sun.

[Mongo]

New STEREO video of comets ISON and Encke is now up here.

[Mongo]

Oh-oh, comet ISON might have disintegrated

There is a possibility that ISON has fallen apart in the past few days. Its gas production rate has apparently fallen off a cliff while its dust production rate is through the roof, which is consistent with disruption/disintegration of the nucleus, while it has failed to brighten in the past couple of days as would have been expected if it were still intact. Or this could possibly be a minor splitting event which happens to coincide with a temporary switching off of the major jets.

The next few days should tell us one way or the other what is going on with ISON.

Discussion on conets-ml:

post by Michal Drahus at 6:42 this morning:

Dramatic fading of ISON's molecular emission lines

Hi All,

Comet ISON has been closely monitored at the IRAM millimeter telescope in Spain by Israel Hermelo (IRAM Granada) and myself (Caltech/NRAO) for the last 6 days. We observe consistent, rapid fading of the molecular emission lines between Nov. 21 and Nov. 25 by at least a factor of 20 (likely more). This may indicate that the nucleus is now at best marginally active or that... it no longer exists.

Regards,
Michal

post by skyweek at 7:03 this morning:

Re: Dramatic fading of ISON's molecular emission lines

But on the STEREO HI1-A beacon image http://stereo.gsfc.nasa.gov/browse/2013/11...11801_s7h1A.jpg from one hour ago the comet looks like it always did in recent days: how does that 'compute' ...?

Daniel

post by kaos at 7:26 this morning

Re: Dramatic fading of ISON's molecular emission lines

Hi Michal,

This is in agreement with yesterday observation of Terry Lovejoy. He measured the magnitude 4 so comet has little faded then instead expected brightening to near 3 mag in case of health state. Afrho measure few days ago indicate huge increase of dust production. Total disintegration make sense.

Regards,
Jakub

post by kaos at 7:28 this morning

Re: Dramatic fading of ISON's molecular emission lines

Hi Dan,

That is the problem. Comet looks the same instead of healthy brightening.
Jakub

post by biver_nicolas at 7:49 this morning

Re: Dramatic fading of ISON's molecular emission lines

Michal,

Did you check for ephemeris offsets, too?

The comet has been constantly peaking tailward (or as if it was a bit late on its orbit) compared to the predicted position. the JPL#48 orbit solution compensated part of the offset we saw with JPL#44 mid-november, but there was still some residual and astrometry on the 22 still indicated about 5" offset. - this can also be the not so good sign that comet is loosing integrity and a large part is trailing behind the predicted position due to outgassing reaction.

Otherwise little brightening over last days may indeed indicate decrease in activity... I failed to see it Nov. 24.27 (m1>3 at least, but I saw stars to magnitude 5.7 3deg. above the comet), in strong twilight but with good sky transparency.

Nicolas

post by ejehin at 8:04 this morning

Re: Dramatic fading of ISON's molecular emission lines

Hello ,

From the last images we got Saturday morning (Nov 23) with TRAPPIST and comet at 6 deg above horizon, the production rates droped by a factor 3 which was quite a big drop indeed in 24 hours, but it could still be the "expected" decrease after Nov. 19 outburst (as we are still not below the level of activity before the outburst). The inner coma was still looking ok as the previous days.

Of course if it dropped now by 20 in the last 48hrs this is really bad news...

About AfRho, it went down too , not up. The huge values I have seen on Nov 21-22 might be due to background contamination and gas contamination in the R filter. The TRAPPIST AfRho from dust continuum windows went down not up after Nov. 21.

Cheers,
Emmanuel

post by P. Clay Sherrod at 8:10 this morning

Re: Dramatic fading of ISON's molecular emission lines

I tend to agree with/follow the STEREO images and the physical nature of the comet as ascertained there.

In the very bright twilight and the low altitude conditions of ISON at this time, I do not believe that spectral analysis of molecular emission lines can be relied upon for determination of the physical state of this comet.

The strong physical appearance of the nucleus and/or condensation from both the STEREO as well as a handful of excellent images from yesterday morning show that the comet structurally has not changed appreciably.

Clay

post by Jakub Černý at 8:30 this morning

Re: Dramatic fading of ISON's molecular emission lines

Hi Clay,

IRAM observing comet on millimeter radio waves, which allows it to observe it even on daylight.

STEREO and SOHO has very poor resolution, for example they failed to catch disintegration of comet Lovejoy 1.6 day after perihelion. Their only contribution is following brightening trend of comet, which should brightening now from like 3 mag to -2 / -8 magnitude in perihelion.

Best regards,
Jakub

posted by Michal Drahus at 9:46 this morning

Re: Dramatic fading of ISON's molecular emission lines

Hi All,

Daniel: What we're observing are the HCN molecules emitted within about 1 hr of the moment of observation. (This is approximately the lifetime of HCN at the current heliocentric distance before the molecules are destroyed by the solar UV, and this is also approximately the escape time of the molecules form the sensitive region of the telescope's beam, equal to 9" in FWHM.) In other words, our data show what's going on with the comet essentially "now" and not few hours or days ago. Instead, optical images are dominated by "slow" dust and the STEREO data also suffer from the poor resolution, so this type of data would react to nucleus disappearance with a considerable delay, as pointed out by Jakub.

Nicolas: All good points. We examined the offsets as carefully as we could. The todays's upper limit of Ta* = 20 mK in HCN(3-2) was obtained using JPL#51 dated Nov. 22. Our Nov. 21 measurement at about 400 mK was obtained using the earlier solution, which gives about 7" offset for that date compared to JPL#51. The Nov. 21 measurement can be therefore somewhat underestimated (perhaps by about a factor of 2), hence we realistically consider the factor-of-twenty fading as the minimum drop -- it was likely larger. We also took a spectral map of 0'.5x0'.5, which confirmed the offset, so we feel that we have this issue under control.

Clay: As explained by Jakub, the millimeter and sub-millimeter telescopes are insensitive to the daylight background. The software-enforced Sun-avoidance radius of IRAM is... 1 deg.

Regards,
Michal

Twitter @SungrazerComets:

@NickAstronomer 1h
Our team/CARA filed our AFRHO data for #ISON, the dust production rate is staggering

@SungrazerComets 1h
Right -- again that's evidence for a nucleus that fell apart... But also perhaps not!

[MahFL]

If ISON breaks up will there still be something to see come 4 Dec ?

[djellison]

If it breaks up, you'll find out if a broken up ISON is visible on Dec 4th......on Dec 4th.

Facetious - but accurate. We don't know. Comets are not that predictable. There are far far too many variables.. "If it breaks up" you say. When. How. How slowly. How quickly. What solar wind might come into play.

It will do what it will do, and there's really not much point in second guessing it.

[Mongo]

ISON from Mercury (click on thumbnail for larger image):

Date acquired: 01:54:30 UTC on November 20, 2013
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)

Of Interest: MESSENGER image of comet C/2012 S1 (ISON) during its closest approach to Mercury. At that time, ISON was approximately 22.5 million miles (36.2 million kilometers) from MESSENGER and 42.1 million miles (67.8 million kilometers) from the Sun. The image is 7° by 4.7° in size and has been slightly magnified and smoothed to enhance the faint tail of the comet. The tail was oriented at an angle to MESSENGER at the time and is foreshortened in this image; however, some faint structure can still be seen.

[MahFL]

I was just looking at the SolarSystemScope model and I did not realise ISON effectively goes around half the Sun in one day that being the 28th of course.

[Mongo]

A follow-on post to the "Has ISON disintegrated?" thread on comerts-ml, with a reply:

posted by Jean-Baptiste at 14:38 this afterneen:

Re: Dramatic fading of ISON's molecular emission lines

Hi Michal,

I'd like to offer an alternative point of view. As of now, we do not know the orientation of ISON's spins axis, and the distribution of active areas. The monitoring of activity has not shown significant jets, apart from the coma wings, which suggests homogeneous distribution of volatiles on the surface. However nobody knows how long such homogeneous surface can remain intact.

You might remember that for comet Holmes we saw a huge increase of activity, compatible with the whole surface being active, but then later this activity faded and the comet displayed some jets, indicating that only part of the surface was still releasing material.

It could be that we have reached this stage now with ISON, and part of the surface is significantly less active than before, due to either the loss of volatiles, or a change of spin axis orientation/illumination conditions on the surface.

In that case I expect to see many jets when we start resuming the optical monitoring in a couple of weeks.

cheers,
Jean-Baptiste

reply to post, by ejehin at 16:00 this afternoon:

Re: Dramatic fading of ISON's molecular emission lines

Dear Jean-Baptiste,

With TRAPPIST we are observing two bright jets in gaseous species since Nov 4 when the comet woke up, and we might have a periodic signal from those jets from day to days, then after the first strong outburst on Nov 13, the two jets got brighter and we could observe also dust in the same position (thanks to our dust continuum filters).

What you call the wings are I think extension of those jets, with the dust pushed away more and more from solar radiation (the wings were narrower the last nights we observed the comet).

So I rather beleive the activity was strongly linked to those regions, that were turning on and off in quite strong way during those outbursts. So I do not think they were indicating the disruption of the nucleus.

Maybe, after the last outburst the regions are now exhausted.

But if the nucleus is still in one piece, activation of other regions or of the whole nucleus might indeed still be possible.

This is also an optimistic scenario,

Cheers,
Emmanuel

and another post by Matthew Knight at 18:38 this evening:

Re: Dramatic fading of ISON's molecular emission lines

I concur with Emmanuel. We have narrowband R and CN images from the 0.8-m robotic telescope at Lowell Observatory from November 1-12. Enhancements such as removal of an azimuthal median profile showed two features in the CN images at PAs near 0 and 200 deg, with the PA changing nightly by maybe +/-20 deg. The morphology looked very similar to the wings reported by Boehnhardt et al., and especially the azimuthal median filtered images by Ye et al. (http://groups.yahoo.com/neo/groups/comets-ml/conversations/messages/22355).

Matthew

[Mongo]

Maybe ISON is increasing in brightness after all. Post by filipfratev at 15:36 this afternoon:

Re: Dramatic fading of ISON's molecular emission lines

Hi all,

What I tried to measure from STEREO fits is this ( I don't know how informative can be that):

21/11 09h m1=2.49m ref1 1.63 ref2 4.42 ref3 -0.65
22/11 09h m1=2.45m ref1 1.61 ref2 4.39 ref3 -0.65 delta = -0.04m
23/11 09h m1=1.82m ref1 1.62 ref2 4.39 ref3 -0.65 delta = -0.63m
24/11 00h m1=2.07m ref1 1.67 ref2 4.46 ref3 -0.64 delta = +0.25m corrected = + 0.2m

Indeed m1 is not real and I consider only the differences in magnitude (delta). From the above log the magnitude increased by about 0.6m from 22 to 23 (9h UT's), which agrees somehow with the last visual observations. Also we can see a drop for 24/11/2013 that was also indicated by visual observers. However today the comet looks brighter that yesterday significantly, but I don't have access to 24-25/11 fits.

In other words according to STEREO images I don't think that the comet died. At 2h UT today we should have access to the SOHO images.

Regards,
Filip

It has always been possible that the observed decline in brightness would be only temporary, due to a "pause" in jet activity, but that ISON would resume brightening as it approaches the Sun. The most recent STEREO images look likely to support this, once today's calibrated FITS files are released.

[Explorer1]

Here's the perspective from Mercury:
http://messenger.jhuapl.edu/gallery/scienc...p?image_id=1304
Press release here: http://messenger.jhuapl.edu/news_room/details.php?id=246

[Mongo]

post by Alan Watson at 18:05 this evening:

Re: Dramatic fading of ISON's molecular emission lines

Gidday all

Current publicly available stereo fits images across 20131120-23 show many of the ground observed features. Jets are seen rotating, material is released at regular cycle from the top, north up, suggesting to me that only a portion of the nucleus is active. At a particular orientation material is swept away. The nucleus looks correctly elongated, due to motion, in log scaled images.

Please try to include the dynamic stereo info in your discussions , says an enthusiastic amateur.

Seeking knowledge, kind regards Alan