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Antonio Cidadao (350mm LX200SCT : FLICM7 1E CCD camera)
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Here are some recent "strong"-methane and broadband near-infrared images.
Seeing continues to be rather unfavourable, amost not allowing to image the
SSTB WOS in broadband IR (some of them were not resolved). In winter, quite
a few fireplace chimneys immediately surround my roof-top site. Anyway, in
addition to the antecipated features, two NNTZ spots are seen in methane
the elongated area following BA is well demarcated by a dark rim (but not
methane bright in my oppinion), further processing the images reveal a
methane negative STB dark spot, but south of it is a SSTB oval that is
positive but not very marked in the visible. Jope that JPEG compression does
not spoil the existing detail. Also obtained more series of registered
methand-band filter pairs (889nm 5nm versus 18nm) to attempt image ratios.
Good observations.
Here is the methane data just sent, now as a short animation
Hi all
I'm attaching a preliminary image showing some results of performing
"image-ratios" between the two 889nm CW methane band filters I now use (info
previously shown). One of them has a FWHM of 5nm and the other 18nm. All the
analysis was made with bias-, dark- and flat-corrected raws, where data was
kept linear or subsequentially log transformed. No unsharps or other
processing was made. Original image sampling is shown, and the camera was
used at 2x2 binning mode (18x18um "super"pixels).
To perform image-ratios it is essential that images are registered and
planet rotation effect is not present, otherwhise small scale features like
ovals or NEBs projections can be poorly analysed (the belt-zone pattern may
be OK). However, even with the 14" telescope I feel the need to use at least
1min integration to get a proper S/N ratio. This is especially important for
the 5nm FWHM filter, where due to methane absorption the signal is very very
weak. One solution is produce planispheric projections from a long series of
images, which can be registered and averaged, only loosing info near the
limb due to planet rotation. Ratios are then made using two high S/N
registered planispheric projections, one from the 5nm filter and the other
from the 18nm one. However, limb data is important for methane-filtered
images, namely for the brightening at the poles and limb darkening
elsewhere. To solve these problems I preliminarily chose this approach:
With the camera set to obtain a series of images (specifically 5 images of
1min each to minimize planet rotation), and choosing a lag time of a couple
of secs between images (to allow the motorized filter wheel to change
filters), the following series of images was obtained:
18nm (FWHM filter) - 5nm - 5nm - 5nm - 18nm
I'm also considering this order, always obtaining a "symetric series" with
more images for the 5nm filter:
5nm -18nm - 5nm - 18nm - 5nm
Then, all images are registered with respect to the limb (the procedure is
confirmed blinking the images), and all obtained with a given filter are
averaged. Obviously, some blur will occur in 5min due to planet rotation
but it will be similarly distributed in the images obtained with different
filters. Therefore, the final image of the 5nm filter and for the 18nm
filter can be ascribed the same "time data", specifically the mid-exposure
of the middle image. I must refer that until now, with the 10" scope and the
5nm filter, I have mostly been using a single 5min integration.
Once images are obtained, image-ratios are strightforward. I just use one of
the images (e.g. the 18nm) as a plain "flat-field" image and ask the
software (I use AIP4WIN) to perform flat-field correction on the other image
(the 5nm image) or vice versa. This way there is no need to calculate those
boring "multiplicative coefficients"...
Please look at the data attached, specificaly limb darkening at the poles
and near the equator on the ratio images, also how the belts-zones appear on
these images (particularly the NTB at this moment), also the GRS and ovals
and NEBs projections.
It's interesting to see how the 5nm image "divided" by the 18nm image looks
like a normal methane image, with brighter polar hoods, EZ, GRS
anticyclonic ovals, also showing faint NEBs projections, but (only now?)
with a considerably darker NTB. Conversely, when it is the 18nm image that
is divided by the 5nm one, the resulting ratio-image resembles a far UV
image like those obtained by Cassini :-)
In short, this story that I find fascinating is just beginning, more images
were used but it needs to pass the proof of reproducibility and will benefit
from time-dependent Jovian atmospheric patterns to analyse. However I'm now
more and more convinced that although different results are obtained with
the different filters, both only probe the upper regions of the Jovian
atmosphere, and no significant "continuum-like" cloud patterns are seen. One
of the areas of Jupiter where to explore this issue is the SEB, comparing
broadnband IR data with carefully registered methane images. For instance
there are some results indicating that methane-bright rifts are dark in
continuum IR images, which is reasuring regarding significant
"continuum-leackage" even in this particular 18nm filter (well centered at
889nm). Returning to the methane filters, the 5nm filter would probe the
uppermost layers of the atmospheric hazes producing images with highly
contrasting polar hoods, EZ and GRS with respect to the remaining planet
areas. In turn, the 18nm filter produces a similar pattern on the images
lacking continuum-like information but also lacking the contrast inherent to
the 5nm filter. It would be highly exciting if this filter was truly also
probing lower altitude hazes without penetrating much deeper into the
atmosphere, since the way to address (and follow with time) this issue would
be by the image-ratio approach.
Please feel free to give me all your thoughts and advice, OK?
Best wishes
Antonio
p.s. I'm sending a "PNG" format image since it preserves much better than
"JPEG" the subtle brightness variations of methane images
≪アントニオ シダダオ ポルトガル≫
[Antonio Cidadao Oeiras - Portugal]
 ALPO-Japan Latest
Jupiter Section
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