TYCHO'S PEAK

by R. Lena, G. Di Iorio, A. Bares and C. Fattinnanzi

On 10 may 2003, at about 3:00 UT, R. Spellman reported a strange appearance near the Tycho's peak (private communication).
The image was taken with a supercircuits video camera and a TAL 100-RS refractor. The video and extracted images were processed.

Robert Spellman . Image of the stated "Tycho event" (north at the top and West IAU at the right) solar altitude 3.4° and colongitude 16.2°.

In our opinion a single observation/frame/image is "for definition" insufficient evidence to prove a real TLP. To show that the "streaks" are not due to change (for example artifacts) an independent and contemporaneous image by at least one other observer should have been
obtained. In this case also an "old visual observation" carried out during same times can give interesting informations . In our preceding papers (for example JALPO, 2002, 44, 4 pag 37-43) we showed that " imaging techniques are more susceptible to the recording artifacts than is visual observing".

By the other hand in High resolution images (LOrbiter and Clementine) we cannot see 2 distinct valleys compatible with the relative distance of two " streaks" near the peak. In Clementine imagery it is visible only 1 gap of the wall (east wall see below).

Clementine - Image of the East wall (to the top) and the cantral peak.

So, in our opinion, a topographical explanation is not possible for this event.
Furthermore also other streaks from nearby craters are visible. All the features have the same direction as visible in the processed frame below:

Tony Cook also suggested "a possible flare seeing effect" (private communication).

By the other hand Jeff Medekeff suggested "a form of video artifact that is introduced by the readout and amplification circuitry of the video camera" (Private Communication).

There are many sources of artifacts for a CCD cooled camera and for any fast-readout sensor such as video camera or webcams . Here the primary concerns are not just reflections or diffused light, but also spurious features (and fuzzy) due to acquisition of the images.
These kinds of artifacts , can also be introduced (at a minimum level for a CCD and at a maximum level for a videocamera) by a High intensity threshold, so that the brightest features in the dark area can appear "elongated" and fuzzy.

Results

In order to investigate this suggestion, we studied some our images of Tycho taken at the same
solar altitude (H=3.6°) but at sunset (colongitude 185,2°). The frames were taken with a classic cooled CCD HX 516 fitted to a Mewlon 250 mm F/12 under a variable seeing (III-II Antoniadi).
The sequences (below) were taken by Bares on 29 october 2002 (sunset H=3.6 col. = 185,2°) and the solar altitude over Tycho was the same of the Spellman's event .

The sequence shows a single frame for minute

2:00 UT

2:01 UT

2:02 UT

2:03 UT

3:33 UT- At this solar altitude the peak is not visible

The sequence shows fluctuations for many features so that these features (and the shape of Tycho's peak) must be considered spurious.
By the way this effect can be due to a diffusion light on the Chip.

Another artifact can be due to an overexposed frame. In this case ... the brightest features in the dark area appear very elongated.
The image taken on 2 april 2001 at 23:03 UT (with a Mewlon 250 F/12 + CCD HX 516, seeing
III Antoniadi) shows the effect due to an overexposed effect.

Clavius - overexposed frame by Bares.