C/2001 A2 Linear Comet...
Comet C/2001 A2 linear observations from the Pic du Midi summit - Pyrénnés- France the 11th and 13rd of July 2001.

Comet C/2001 A2 Linear has been discovered the 3rd of January 2001 by LINEAR, (Lincoln Laboratory Near-Earth Asteroid Research project)

Orbital elements:

Epoch 2001 May 11.0 TT = JDT 2452040.5
T 2001 May 24.52062 TT Marsden
q 0.7790280 (2000.0) P Q
z +0.0008401 Peri. 295.32853 -0.47639168 +0.69524272
+/-0.0000017 Node 295.12564 -0.42477156 -0.71796661
e 0.9993455 Incl. 36.47538 -0.76981822 -0.03408083


The night of the 11th of July was very windy. One image over 5 was correct. All the exposures was of 30s. The 13rd of July night was more favorable as up to one image over 2 was useable.

All the image processings have been done with the free downloadable software by Christian Buil: Iris.

Comet overglow observed the 13rf of July

The comet showed an increased brightness of about one magnitude in the 13rd of July night. Despite the moon presence, the comet was visible with naked eyes. A noticeable extension of the coma is clearly visible, certainly due to a possible fragmentation of the comet.
In the same time, Christian Buil was recording comet spectra, with the prototype of what will the Spectr'Aude.

Instrumentation
ETX90 with camera Audine Kaf1600

The telescope is an ETX90 attached to a GP mount controlled by a sky sensor 2000.  The camera is an Audine with a KAF1600, with shutter.
All the exposures have been recorded in binning 2x2 mode. Star FWMH was about 1.8 pixels.

11th of  July 2001
The art of making flat-field...

It was not possible to make flat-fields at sunset by lack of time. During the night, two series of flat-field have been recorded. The first one on the clouds surrounding the moon, the second one on the white dome of the 1-meter telescope.

None of them was useable... Because dust visible on the comet images did not have the pattern than the ones on the flat-field images. It was necessary to use the comet images themselves by making a median composition then by aplying a gaussian filter to unflat the comet images. This does not give a perfect flat, specially around the comet itself because of the slow motion of the comet which cannot be eliminated by the median filter.

The root cause of this has been identified. Some light was penetrating through the eye-piece , and despite the flipping mirror, some light was illuminating from the side some dust creating a new pattern. Following nights, a cap was put instead of the eye-piece.
C/2001 A2 Linear

Médian of 19 images of 30 secondes, with selection of the best images over a serie of 87 images taken beetween 23:30 TU and 1:20 TU.
The registering of the 19 images has been done on the comet.

The flat-field used does not have a great quality as it was done using th cmet images themselves. An overbright area was created surrounding the comet center. See the flat-field section above.

Isophote Images
The shape apparently triangular surrounding the comet is certainly due to the local over compensation generated by the flat-field.

Comet motion

If the registration is done on a star instead of the comet center, the apparent motion of the comet can visualized.

To see the animation with 13 images (321Ko) - click here -

13rd of July 2001
Comet overglow

Surprise in the night of 12th-13th of July ! The comet is clearly visible without any telescope, despite the moon. The increased brightness was estimated to about one magnitude.

The shown image is the result of a composition of 27 exposures of 30s, selected from a serie of 57 images, taken beetween 1:20 TU and 2:30 TU

Seen with the 1-meter telescope of the Pic du Midi a tail of dust seems to extend in the opposite sun direction.

Isophotes Image
The image is comparable to the one of the 11th of July - no scale factor has been applied.

Rotational gradient processing
A rotational gradient , centered on the comet heart with an angle of 15 degres makes clearly visible two arcs and a long tail of dust in the opposite sun direction.

Unsharp mask filtering
An unsharp mask filtering "Unsharp 3 10 0" with Iris sofwtare makes appearing a short tail of dust...

Le 17 Juillet
Back to normal

The weathear did not allowed us to record more than 6 useable images.

Flat-field have been taken just after the images, and just before then rain...
by placing a white opaque paper at teh front of the telescope lighted with an electric lamp, and by paying attention to not saturate the image...

Isophotes Image
The image is comparable to the two above - no sclae factor has been applied.
The visible red dots are artefacts due to reamining stars which have not disappear after the median filtering due the low number of images used.

And since...
We have expected clear skies...