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26.11.2009 19:52

The telescope is a 30 cm F2.9 "home made" and the detector is a modified webcam (Philips TouCam 740K SC)

The mount is manufactured with aluminium. It's a equatorial mount with two steppers motors of 200 steps (DEC) and 400 steps (AR). Both motors are controlled by computer with Mel Bartels software.

The optical system is compose of one parabolic mirror polished by my friend and amateur astronomer Walter Fontana. This mirror has 29 cm (11.4 inch) of diameter and 87.5 cm (34.5 inch) of focal length (F2.9).

The images are captured with a Philips Toucam 740K SC. The modified include: long time exposure and amplifier off. Addition the firmware went modified for captured in RAW format.

The video AVI is captured with K3CCD Tools software, modified with AVIRAW software, exported to BMP format with K3CCD and the processing with Maxim DL.

Alberto Ceretta

26.11.2009 19:52

One auxiliary refractor telescope (4cm F1.2) allows a wide field of view, for easy sky recognition. The camera is a Toucam 740K modified.

The field of view with this telescope is 4º X 3º and limit magnitude is a 11 in the city.

Alberto Ceretta

26.11.2009 19:52

Some of you already know: we moved at Friday to Aigua with Santiago Rolan. We wanted to try to the observation of the occultation by Varuna of the star UCAC2 40846256. As Santiago told me about his plans, I said this would be crazy, because the star would be 7 deg above the horizon at NNE. I was sure that an observation of a star with R 14.5 mag would not be possible. Anyway we drove to Aigua at the border of the zone Lavalleja - Maldonado at Friday afternoon.

Our site fort he observation was the house of fanmiliy García Gaudino, where we were awaited by Bernardo Pombo, teacher and astronomy fan. He wanted to help us with the observation. An observation would have not be possible without him and his family.
We set up the station (30 cm) and made a rehearsal in the first night and kept the station nearly completed for the night of Saturday/Sunday.

With an exposure of 5 sec. we could record stars as faint as 13 to 14 mag on this country side. Our goal was to measure the duration of the occultation (40 sec), so we wanted to avoid exposure times of more than 5 sec to improve the time resolution of the measurement. So we tried it with 5 sec.

I was surprised about the limiting magnitude we could get on this altitude but we could not detect the target star. Sometimes we could see the star, that was more I had expected before.
To summarize: We could not record the occultation. We learned a lot and we were very close to our goal.

Santiago is processing the images at the moment and we will be informed very soon about his results. I send you some images of the area of the observing site and an image of 4 frames at 5 sec added. You will get an impression what we achieved with 30 cm at a dark sky area (with moon) at a star altitude of 7 deg only.

26.11.2009 19:51

Report by Dr. Gonzalo Tancredi

I have done a more detail reduction of the set of images taken by Alberto Ceretta and Santiago Roland in Aigua.

The telescope was a 30cm home made and the detector was a modified webcam Philips TouCam 740K). More technical details about the equipment can be found in Alberto's webpage:

The observations were done from the roof of the house of the family
García-Gaudino and Bernardo Pombo, in a farm close to Aigua (Maldonado, Uruguay).
Lon = -54 48 03
Lat = -34 12 04

The sequence of images were recorded in a AVI file, and I have done the
following reduction:
* Split the AVI in separate BMP files. Each image has a typical expsoure time
of 5.4sec (it was the minimum exp. time for which the occulted star was barely
* Split the 3 colors (RGB) in 3 different files
* Add the 3 color images in a single Monochrome file giving a weight of 1 to
each color
* Substract a Master Dark (created in a similar way and after mean combining them)
* Compute a synthetic flat with median combination of 100 files
* Flat correction
* Align the images
* Add images in sequence of 5, we have done a running mean, i.e. we add images
1+2+3+4+5, then 2+3+4+5+6, 3+4+5+6+7, ...
Eveery combined images has a total exposure of ~ 27 sec.
* We have done Differential phootometry. We select a relative bright and
stable star as reference (the bright star at the ~ same dec as the occulted
star and to the left in Bruno's latest chart), and 3 check stars: the 14.0
star close to the occulted star, the 11.4 star in the chart, and a star up and
right from the 10.7 star.

The reduction was done with Maxim Dl Pro 5.02 and several scripts in Javascript.

I am attaching a Excel file with the results.
There are three sheets: one with the data, and two with the Plots, one for a long time interval and the other for a short one.

Each point corresponds to the photometry of the combination of 5 images of 5.4
sec each, with a total exposure of 27 sec. The Time axis corresponds to the mid time of the total exposure.

The symbols correspond to:
* violet diamond - the occulted star
* red square - reference star
* red triangle - check star 1
* blue square - check star 2
* brown circle - check star 3

We plot for a few points the +- errors, calculated with the following eqs.:
dM+ = -2.5 * log (1 + 1/SNR)
dM- = -2.5 * log (1 - 1/SNR)

There is a deep peak at 2:15:20 UT for the occulted star; where its magnitude
has a clear decrease and the SNR becomes very small (~1).
This is very close to the expected time for the occultation !!

I am tempted to conclude that the occultation was detected, but they might be
some critics to this conclusion:
* There are some other minor peaks of the same star, specially a few minutes
* The check star 1 (of similar brightness) present a noticeable peak a few
seconds after the big peak.

Nevertheless, the other peaks are less deep than the supposed occultation peak.

I have done some simulations in order to estimate the duration of the occultation.
I create some synthetic occultation lightcurves and I overplot the magnitudes
of the star.
>From a qualitative comparison of the curves, the duration of the occultation
could be estimated in the range 20-30sec.
I am attaching a plot with this comparison.

It is a pity that this is the only data that we can obtain for this occultation.
But, in view of the difficult circunstances of the occultation, we have done
the best that we can.

I am doubtful that we can use this data for scientific purposes, but it would
be a nice anecdote that the first occultation of a TNO was detected with a
homemade 30cm telescope, with a 100 dollars webcam, from a roof of farm and at
a height of 8deg !!
(Have a look to Alberto's webpage for some nice photos of the campaign)


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Astronomía desde el patio de casa. Bautizado como Astroblog por el amigo pparker. Mi blog se alimenta de tus comentarios. Alberto Ceretta Visitas desde 13/11/09:


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