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Update Dec. 14th 2007:
Since this time last month (14 November) Holmes central coma has expanded from about 1/2 degree to 1 degree or so (70minutes as of the 14th Dec.). Assuming its integrated magnitude has not increased during this period (there is no evidence that it has), its angular size expansion alone has caused its surface brightness to decrease from a 4.4mag to a 5.5mag equivalent visual object (as a result of its contrast decreasing by about 60% and based on a calculated equivalency with background sky brightness).
So, in this time period Holmes has gone from easy naked eye visibility to invisibility under 5.5 NELM skies. Even if it's integrated magnitude holds steady at 2.5, it will disappear from dark skies (6.5 NELM) as well once it reaches a diameter of ~140 minutes, as at this point its surface brightness will be less than the background sky brightness.
Holmes progressive disappearance from increasingly darker skies over time is directly related to its continued expansion combined with an essentially static integrated magnitude. If its rate of increase and integrated mag hold, its effective disappearance from view will occur in about 2 more weeks for 6.0 NELM skies and about the end of January 2008 under 6.5 NELM dark skies.
(Above calculated using formulas published by R.N. Clark.)
(assumes growth of central coma at a rate of ~8 minutes arc per 6 days and a sustained integrated mag at ~2.5.)
Nov. 7th: new images for the 5th Nov and additional images for the 2nd.--see down page for earlier images & comment (Nov. 2, Oct 30) Be sure and check out the links at the bottom of this page for more interesting information about this fascinating comet.
NOTE on Processing: Initial processing was done in Meade Envisage (align and stack with dark subtraction) and final in IRIS. All post processing of the raw stacked and dark calibrated images out of Envisage was done by WAVELET ANALYSIS. Where i say "moderate wavelets" were used, this is primarily scale 3 used with some scale 4. Heavy is primarily scale 5 with some scale 4. Scale 1 was not used at all and scale 2 rarely and sparingly.
Wavelets are used here for multiresolution analysis of the comet's raw image. Wavelets (as i have used them here) are recognized as quite legitimate within astronomy--here is a technical paper detailing this technique and its applications on a professional level: Image processing and data analysis: The multiscale approach. They are also recognized as useful for the purposes i have put them to specifically upon cometary structures: Wavelet analysis.
Some wavelet/comet processing links:
Wavelet Analysis Reveals True Colors of Comet Use of wavelets for cometary detail: Shanghai Observatory Comet Hale-Bopp
Comet - Into the Nucleuscomet P/Swift-Tuttle, Calar Alto Observatory in Spain, jets with wavelet transform.
IAU Colloquium 168 Cometary Nuclei in Space and Time Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing
Observations of Comet 17P/Holmes From the Lunar & Planetary lab, University of Arizona, Carl Hergenrother. These images utilize rotational gradients upon nucleus features (jets)-- but show the same sort of structures seen in my images using simplier wavelet transforms. Very interesting!
November 5th, 2007
The comet has again expanded dramatically, from ~12.5' to ~16.7', primary coma measures. Under my urban skies I cannot detect the greenish ion/dust shell surrounding the bright coma nor the recently reported development of the blue ion tail. But there is plenty to see in the coma proper.....
The size evolution has been dramatic and relatively consistent in magnitude. The image above attempts to show both the size and the concurrent dimming that has been apparent visually to my eyes in this comet over the past week.
The above image is my "glamour shot" of the comet, probably the last one as cloudy weather has at last moved into my area. Regardless, the comet has grown to the point where it will soon (if not already (Nov 7th) be too large to fit even into the focally reduced image plane (f/8 to f/4.3) of my 6" refractor. This is the image the following two images are taken from.
This image shows the relative light intensity as a contour plot. In the center you can see the small pseudo-nucleus and then its primary jet and after that the confluence of the several secondary jets making a now brighter area than the pseudo-nucleus itself. This is a new development from the last date of observation, the 2nd Nov. Note as well that the forward "bow wave" noted in earlier images is no longer as prominent and defined nor broad either.
This is an interesting image, showing some detail of the primary jet as it leaves the pseudo-nucleus and is joined by secondary jets. Note the off-axis directionality of the primary jet...perhaps this could be evidence of the rotation of the nucleus proper and the presently venting major jet along with it?
The remaining images are taken from the above exposure stack. This image has its histogram optimized for broad contrast values (gaussian), differing from the previous image stack which has a log balanced histogram.
This is the false color version. All of the images i have published here are monochromatic *B&W), however the purpose of using false color is simply to enable a better visualization of differing intensities within the comet than is possible using grayscales alone, which in turn allows one to visually isolate certain structures, such as the pseudo-nucleus, jets, and inner and outer coma. The effect is pretty dramatic as well as illuminating. One could think of this as a "color-coded photon count" as that is exactly what it amounts to. For example the comet when viewed this way takes on a much more apparent "cometary" appearance than when viewed in grayscales alone. A certain amount of the outer coma, composed of ionized gases mixed with dust (the green surround seen in many dark sky images) now becomes visible.
Moderate wavelets applied to the histo-optimized raw image yields the above image. The application of wavelets in this manner serves to selectively emphasize a range of intensities within he image, in this case bringing out the fainter stars into more prominence as well as further contrasting the structures within the coma proper. Therefore we begin to see hints of the structure that the false color image, which did not have wavelets applied, is able to show so clearly.
Here the above image is presented in false-color. Comparing it to the previous false color image, we can see that the same structures are indicated but with wavelets applied they are demarcated more strongly. Note how the central jet is further defined,. Also of interest are the stars in the image. Note that the two brightest, bracketing the comet for and aft, have an intensity gradient (red central points) while the others do not. This is simply a reflection of the airy pattern of a stellar image which, when there are enough photons captured, is most intense in the center gradually falling off as distance from the peak intensity decreases.
Here is a 3D plot of the relative intensities in the original image without wavelets applied. The first thing that jumped out at me was the obvious decrease in the brightness of the pseudo-nucleus relative to the area where the jets conjoin. This could seem to indicate a decrease in the outgassing, mass shedding of the nucleus itself. IOW, the after effects of the event which caused this outburst are in definite decline.
Here is a closeup of the 3D plot of the central area of the comet from 30 Oct and 05 Nov. In the Oct30 plot the pseudo nucleus is obviously much more intense than the jet confluence area following it. By Nov 5th, the situation has reversed itself with the pseudo-nucleus definitely dimming in relation to the most intense area of it's cast-off material.
Here's an orientation chart to scale of where the comet was at the time it was observed. Unfortunately there was no bracketing stars with which to estimate the magnitude of the central areas of the comet--it was in a pretty desolate star field, devoid even of SAO catalog stars--which is why the Tycho catalog was resorted to.
November, 2, 2007
Here are two new additions to this image set, (posted Nov. 7th, 2007), showing the main and one secondary jet emanating from the pseudo-nucleus:
Nov 2nd observations Cont'd:
Comet Holmes has evolved dramatically in the last 72 hours. The after side of the coma is beginning to noticeably disintegrate /disperse and the central condensation as well as the pseudo-nucleus is also dimming considerably. As it has done since it's initial outburst, it is also gradually increasing in size:
Here are some raw images from the early morning of the 2nd Nov.:
This is the normal FOV of the camera at the native f/l of the 6" refractor, f/8. The pseudo nucleus is the dimmer of the two points within the central brighter part of the overall structure. The brightest one is a star, SAO 24187 at just over mag 7. Three days ago the whole comet fit--no longer... To get the entire structure into the FOV of the imager i had to resort to a focal reducer:
This increased the FOV by about 83%. The comet itself has enlarged about 45% from three days ago! I measure it now at about 12'30" in diameter.
It has also dimmed considerably. Based on the star within the Coma during this session's time period (it is SAO 24187 at 7.2 or 7.4 mag depending on which catalog you pick) the pseudo nucleus has dimmed by in excess of a full magnitude. This is quite noticeable visually as well. The image above is a crude intensity plot which shows this, but it was done with a V-filter so it should not be too far off reality.
There are still some evidence of jets visible coming off the pseudo nucleus. I caught two of them, others have caught three or more (usually when processed with a rotational filter algorithm).
Above is a negative view of the previous image which shows the jets a bit more clearly. Just in case you are wondering, they have been proven to be quite real by the pros and so are not just wishful artifacts of over enthusiastic processing after all! See this animation of the jets in action from the Pic Du Midi Observatory, University of Toulouse, France: Animation of jets in action There have been consistently three main jets over the past few days, the central one appearing to connect with the pseudo-nucleus, and two that fall a bit short of that point flanking the central jet on either side. I caught all three in one image taken on the 30th which you can see on the front page of this website--it is the last image on the right in that montage.
The comet is definitely beginning to loose it's integrity on the after edges as the image below alludes to rather strongly:
This image was made by applying very heavy and broad wavelets to a raw image. It shows gross patterns of disintegration of the after part of the coma, as well as the shock wave leading the comet.
Holmes is about 12.5 arcminutes in diameter at this time. This is a measurement of the bright portion as seen in these images, and does not include the ionized halo surrounding this are--that very dim but colorful (in images at least) halo is even larger with some reports having it at nearly the size of the fullmoon! (See the Comet Holmes page of the Calvin University Observatory for image sequences showing the differences between the dust cloud and the outer cyan-colored gas cloud.
space.com reported re; Comet Holmes a Oct. 26th 2007 that "...astronomers think they've found a hint of a tail. Don't expect to see it for yourself, however."
I think i got hold of that "tail" last night.
Compare the image below, from the University of Montreal's Mont Megantic Observatory:
...to this image I derived from the tenth image set i took on the 30th October below:
(published by Sky & Telescope Comet Holmes) There seems to be a inner envelope structure? The primary jet the Mont Megantic team sussed out is plain to see as well as a distinct & defined area of concentrated intensity behind it.
Here is a representative raw image from last night's session:
The bright field star to the left of the comet is SAO 24231 a 5.9th mag B8 spectral class star; it is al;so catalouged as Tycho 3338-1436 at 6.2mag.
(published by Sky & Telescope Comet Holmes)
and a negative version with some wavelets applied;
The features seem consistent. From this, the false color version i found colorful if not actually interesting:
The central condensation seems to have a tag along higher intensity zone..
Application of smaller wavelets yields this image:
Note that the central envelope structure is visible here and is identical in structure to that shown in the false color image I presented previously-- even though each image is from an entirely different set of images.
Some fun with the 3D intensity function:
This also indicates the concentration following the primary central condensation, the "star-like" bright center observers have all commented about. Its brightness at this point appears a bit less than the ~6th mag field star striking up boldly to the left of the image, but a bit more than the second highest spike, belonging to SAO 24241, listed at 7.1Mag. So, the central condensation would come in at about 6.5mag at the time this was taken, with the secondary, trailing condensation area contibuting at about magnitude 6.8 to the structure's overall brightness. Interestingly one can also see the small projection/spike through the Holmes envelope indicating one of the partially obscured field stars, catalouged as TYC 3338-357 at 8.9mag..
From another image set I applied the "Ramp" algorithm in IRIS and found evidence of a forward pressure wave perhaps? Notice the broad crescent forward and centered upon the central condensation:
(NOTE: See this similar contour image taken on 29 Oct. KANATA telescope Hiroshima University, Japan )
...and an application of larger wavelets to the original raw image shows some of the gross detail of the nebulous envelope and a whopper "bow wave":
I did ten sets (stacks) of images on the 30th October and the above are from three different sets, exposures etc as annotated per image. Raw images are fits stacks with darks applied and equalized in IRIS but no additional tinkering done. Image control software was Meade Envisage.
Comments & critique welcome.
Orientation chart for above images:
Reprocessed images to ascertain jet/streamer structure within coma and another image of the gross detail within the outer shell areas.
LINKS-- to similiar professional results, from the Higashi-Hiroshima Observatory (Hiroshima University, Japan) using their KANATA 1.5meter telescope: COMET 17P/HOLMES: images on 29 Oct.
Here is a contour image these folks derived:
COMET 17P/HOLMES: KANATA telescope contour image on 29 Oct.
Notice the dual areas of intensity are present here as well in the images above--and how there is also confirming evidence of the "shock wave" in front of the Comet...Note the similarity to the RAMP image above specifically.
Cloudbait Observatory's Comet Holmes Page Excellent page with more CCD image analysis of this comet. Don't miss it.
See also Christian Buil's page: Comet 17P/Holmes outburst with extensive spectroscopic as well as CCD image analysis.
Comet 17P/Holmes detailed finder chart courtesy of Astrosite GRONINGEN. best large scale chart i have run across. Along with HNSKY planetarium program (highly recommended), I used this to help identify the stars in the field of my Holmes images.
See the Comet Holmes page of the Calvin University Observatory for image sequences showing the differences between the dust cloud and the outer cyan-colored gas cloud.
Imaging Comet 17P/Holmes Richard Berry's analysis of Comet Holmes Nov. 4th with an excellent Larson-Sekanina rotational difference image.