Wednesday, August 31, 2011
Comet Elenin in STEREO H1B (August 25 and 26)
Once again, as with the previous posts I've zoomed and cropped these images of Comet Elenin from the STEREO H1B imager. There are asteroids on the 25 and 26th (although only one is obvious on the 26th). Here's the AVI animation of the August 25 images (1 Mb) and the AVI animation of the August 26 images (1 Mb).
I've plotted the intensity of comet Elenin images relative to a reference star (indicated on the image from the 26th) from the 18th to the 26th. I have the data from the 27th, but the comet passes over a bright star and I can't separate out the brightness of the comet from the star.
There is some dropped points on the 23rd when the imaging arefact of Mercury passed over the comet and reference star images. Again, click to embiggen.
As I've stated before, on calibrated images the comet has faded over 80% since the 19th, however, using this method of normalising (compared to how I did it on the calibrated images earlier) the drop is more like 70%.
Again, we have to factor in that it is further away from the H1B camera despite being closer to the Sun. I have not explicitly tried to calculate magnitudes, especially since Elenin is an extended source.
Anyway, important things to notice: The Coronal Mass Ejection that did all the fancy tail twirling hit between two flare-ups of the comet. The second peak (coming after the arrow showing where the peak CME hit, comes after the CME has washed over it (ie the big peak is not an artefact of the CME brightness adding to the comet, it genuinely gets brighter). The next peak is an aretfact form the comet crossing in from of a star, but the peak after that, although it crosses a star early, is probably also a flare.
After this, the intensity of the comet drops quite a bit; this corresponds to Michael Mattiazzo's August 22 UT image showing a big drop in intensity and Rob Kauffmans images showing the same drop on August 23 UT. After the 23rd there is another big drop that recovers slightly by the 26th.
Images from STEREO on the 27th (image right) don't show the same nucleus elongation that you see in Michaels images on the 27th, but with the STEREO images it's like looking through a pair of 7x30 binoculars compared to the telescopic images. I don't expect to see much until later images.