Archive for the ‘Uncategorized’ Category

Mittwoch, Januar 21st, 2009

We opened this website, because we have to go to the limits, to the limits of ourselves and to the limits of our planetary system. For the next years,the challenge of determing the structure of this dark world beyond Neptune is one of the big challange for all of us, for a worldwide community of amateurs and professionals, of small telescopes and of large institutions. Only if work together, we can solve the misteries of what is on the limits far out there..

Have a look at Varuna 2008, to see, how such collaboration can work!

Given on the 20th of January 2009

Wolfgang Beisker

International Occultation Timing Association / European Section

Research and Development

Dienstag, Dezember 23rd, 2008

Last Update on Varuna Astrometry from the Rio Group

 

Marcelo Assafin (Rio group) gives the last updated astrometric results for Varuna and its star, from a new global reduction solution which incorporated those last 30 images observed at the T1M at Pic du Midi in December 7 to 8, kindly provided by Francois Colas.

Reductions were made using the PRAIA package. The relevant output files from the PRAIA reductions are attached for study. The star and Varuna results are in separated files.

PRAIA output file format

 

Result – Star

 

Result – Varuna

 

In general, some T1M observations are centered in Varuna/star, others are shifted in a corner-in-center fashion to allow for a larger field coverage for the global solution. The large field-of-view images come from the T60 (pic du Midi) and 40cm (A12, Federico) observations. Note that both the star and Varuna appeared together in the same CCD frame for a few fields in the December 8 images. One can easily see which are these images by taking a look at the Julian Date.

The offsets in the first 2 columns of the output file are given wrt the respective reference positions. For Varuna, it is the JPL ephemeris (targets file) and for the star, it is the usual position below:

 

RA =  7h 29m 48.171s
DEC=  +25dg 40′ 7.71″

As usual, as a first step before the global solution, the Individual CCD frame reductions (from T1M observations only) were made using as reference frame the 2MASS catalog transformed into the UCAC2 frame by the tangent plane technique (with a 3rd degree polynom). Using this improved 2MASS, the small CCD fields from the T1M observations could be reduced with a 3rd degree polynom. Typically about 15 reference stars were present, which is not ideal for 3rd degree reductions (N=20 or higher), but is nevertheless acceptable. Mean errors in (RA,Dec) were about 70mas. The individual reductions for the large field images were made as before, using the UCAC2 stars and a 3rd degree polynom.

In the global solution, as usual, all the individual T1M and large field frames are mixed, again using a 3rd degree polynom to place the positions into the UCAC2 frame in the tangent plane.

From the global solution, the offsets wrt the reference positions in the sense „PRAIA – reference position“ were:

Star:

DacosD = +30mas  (36mas)
Dd         = +37mas (22mas)
N= 82 frames

Varuna:

DacosD = +48mas (79mas)
Dd         = -191mas (67mas)
N = 37 frames

Freitag, Dezember 19th, 2008

Varuna Occultation Observed After All? – Discussing the Data Recorded by the Aigua Team, Uruguay

 

From Uruguay:

Gonzalo Tancredi (Departamento de Astronomia, Instituto de Fisica, Facultad de Ciencias , Montevideo, Uruguay) has done a more detail reduction of the set of images taken by Alberto Ceretta and Santiago Roland in Aigua.

(See Blog: Report of the Observation Team at Aigua, Uruguay, Dec 13)

 

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:

http://blogs.montevideo.com.uy/aceretta

 

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

 

Gonzalo describes his data reduction:

 

“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 detectable).

* 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.

 Results of Reduction

 

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 later.

* 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.

 

 Simulation

 

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)”

 

From Switzerland:

Raoul Behrend (Geneva) will check the raw data for an independent reduction.

 

 From Australia:

Dave Herald (Canberra) has done already an interpretation of the data by the Aigua Team:

 

“I have to say that I am not _convinced_.

 

I have plotted directly the data columns Obj 1 [E], and Chk 1.

 

Plot by D. Herald

 

It is equivalent to Plot longt in the spreadsheet, limited to the purple and green points – and with the y-axis reversed. I have done this as it better shows the light curves. In my plot you can see that there are some similarities in the two light curves to the left of about 2:18:00 – with the blue curve being time-displaced compared to the red curve. Also of note is the increase in the peak noise levels from about the middle of the plot – suggesting that there was a change in atmospherics at around the time of the purported occultation.

 

Now let me analyse the detail of the light curve. First, let me assume that Varuna has no significant atmosphere. That is, the occultation should be relatively instantaneous, with a light drop to the magnitude of the star. The first test for the occultation is whether the light drop was sufficiently significant – with an expected drop of 5 mags. But the exposure was set at 5 secs because: „it was the minimum exp. time for which the occulted star was barely detectable“. If this is the case, excursions much beyond 1 magnitude would have been excursions into the background noise. In particular, I have trouble accepting that a 2-mag excursion in these conditions represents a real signal, rather than the effects of the background noise.

 

The second test is the nature of an occultation light curve in the absence of an atmosphere. In essence, there should be an abrupt drop, a flat bottom, and an abrupt rise.

The putative event could be consistent with such a light curve IF you postulate an occultation lasting about 12 secs centered a little after the mid-time of the maximum in the plot – such that the points on either side involve exposures where the occultation started/ended part-way through the exposure. But in the absence of other evidence, the light curve does not _demonstrate_ the existence of an occultation.

 

The alternative situation to consider is the possibility of Varuna having an atmosphere.

Assuming a duration of around 12 secs, the chord would have been very close to the edge of Varuna (on my calculation, about 98% out from the center of Varunna – assuming a spherical object). The problem then is that if there is sufficient atmosphere to have a significant effect on the occultation light curve, the effect will last for MUCH longer than the solid-body occultation. And the light curve is not consistent with this.

 

In conclusion:

– I cannot state with any definiteness that the light curve does NOT record an occultation

– there is nothing in the light curve that is particularly characteristic of an occultation light curve. The rational is temporal coincidence alone; and

– there are features in the light curve, and the observing conditions, which make noise a likely explanation.”

 

From France:

Bruno Sicardy (Paris) wrote:

 

Dear Gonzalo, Alberto,

 

 this is amazing! This could well be the first TNO occultation ever observed!!!

 

 The event is very close in time to the predictions. The Rio group predicted the center of event at Aigua around 02:14:55, Raoul Behrend

(Geneva) predicted an event centered around 02:14:30, and your event is at 02:15:20 or so…

 

 With your estimate of the event duration of 20-30 sec, and using a shadow speed of 20.8 km/sec, this would correspond to a chord of 420-620 km.

Spitzer data give a diameter of 500+/-100 km for Varuna (Stansberry et al, UoA Book 2008), while older IRAS data gave a diameter of ~1000 km (Lellouch 2002)

 

 Anyway, keeping the probably better 500 km diameter in mind, this would mean that the event was ~central at Aigua. In that case, the Rio prediction would the closest of the 3 we had at hand (Rio, Geneva, MIT), before the event, see my page:

 

http://calys.obspm.fr/~sicardy/07dec08_varuna/index.html

 

 This rises a very interesting issue, as the Pico do Dias light curve has apparently a high SNR and is negative (as was Belo Horizonte), which could be used to set firm upper limits on Varuna’s apparent size on that day (if elongated, the object may vary in apparent size).

 

 So, I do think that this detection, if confirmed, could be of high scientific interest, and should definitively be interpreted and published!

 

 It also shows that small instruments, used for both predictions and observations, are probably the best tools to detect TNO’s occultations.

 

 Cheers,

 

Bruno

 

 

The story about the occultation by Varuna is not over yet.

Stay runed at this blog…

 

Oliver

 

Montag, Dezember 15th, 2008

More Information by Alberto Ceretta (Observation Team Aigua, Uruguay)

 

Alberto has a blog where you can find more images of his expedition. (Reports are written in Spanish):

 

http://blogs.montevideo.com.uy/aceretta

 

Samstag, Dezember 13th, 2008

A Short Summary by Bruno Sicardy

 

 Bruno wrote at Dec 10:

 

– the Belo Horizonte data have been analyzed, and no event is reported between 02:11:06 UT and 02:28:56 UT

 

– Fortaleza: no observation due to problems with the telescope drive

 

– Brasilia: clouded out

 

– Asuncion, Paraguay: target to low above horizon for proper analysis

 

 So, there are only two actual observations, Pico do Dias and Belo Horizonte, and they are both negative

 

 Francois Colas took images at Pic du Midi the night after the event, with the target and Varuna at less than 1 arcn from each other. This should tell us where the shadow went…

 

Samstag, Dezember 13th, 2008

Updated Astrometic Results from the “Rio Group”

 

Marcelo Assafin (Rio group) wrote:

 

In the following, I give updated astrometric results for Varuna and the star, from 30 observations provided by Francois Colas at the T1M at Pic du Midi in December 7 to 8. Reductions were made using the PRAIA package. The relevant output files from the PRAIA reductions are attached for study.

Some of the observations are centered in Varuna/star, others are shifted in a corner-in-center fashion to allow for a larger field coverage for the global solution. Note that both the star and Varuna appeared together in the same CCD frame only for a few fields. The star and Varuna positions are given in the uotput file. One can easily see when they appeared together in the same CCD frame by looking at the Julian Date.

The offsets in the first 2 columns of the output file are given wrt the respective reference positions. For Varuna, it is the JPL ephemeris (targets file) and for the star, it is the usual position below:

 

RA =  7h 29m 48.171s
DEC=  +25dg 40′ 7.71″

Individual CCD frame solutions (from T1M observations only) were made using as reference frame the 2MASS catalog transformed into the UCAC2 frame by the tangent plane technique (with a 3rd degree polynom). Using this improved 2MASS, the small CCD fields from the T1M observations could be reduced with a 3rd degree polynom. Typically about 15 reference stars were present, which is not ideal for 3rd degree reductions (N=20 or higher), but is nevertheless acceptable. Mean errors in (RA,Dec) were about 70mas.

In the final, global solution, all the individual T1M frames were mixed, again using a 3rd degree polynom to place the positions into the UCAC2 frame in the tangent plane.

 

I leave to the readers the task of examining the star position and mostly, Varuna positions, so as to trace Varuna’s path in the sky wrt the star.

 

Best regards,

Marcelo Assafin (Rio group)

 

 PRAIA Output File Format

 

 targ_single_varuna_1

 

 targets

 

Samstag, Dezember 13th, 2008

Report of the Observation Team at Aigua, Uruguay

 

The team used a self-made telescope by Alberto Ceretta and a modified Philips comercial webcam.

 

This is the report by Alberto in Spanish. An English translation follows after his report. (Thanks to Diana Seiler, who made the translation for me.  Oliver)

 

Hola a todos.

 

Como algunos ya están enterados el Viernes fuimos con Santiago Roland rumbo a Aigua a intentar la observación del transito de Varuna por delante de la estrella UCAC2 40846256. Cuando Santiago me comento, le dije que estaba loco porque la ocultación se daría a unos 7 grados de altura en el horizonte NNE lo que para mi hacia imposible observar una estrella como esta de magnitud R 14.5. A pesar de que intente desalentarlo no pude y el Viernes a la tarde marchamos rumbo a la zona de Aigua en el limite departamental Lavalleja – Maldonado.

 

El lugar de destino para la observación fue la casa de la familia García-Gaudino donde Bernardo Pombo, docente de secundaria y aficionado a la astronomía, nos esperaba para colaborar con la observación. Hubiera sido imposible sin la ayuda de él y su familia.

 

Hicimos una primer noche de pruebas y puesta en estación del 30cm y dejamos todo medio pronto para la noche del Sábado al Domingo.

 

Las primeras pruebas mostraron que en el campo podíamos detectar estrellas de magnitud 13 y 14 con 5 segundos de exposición. Como el objetivo era medir la duración del transito (40seg), tiempos de exposición de mas de 5 segundos harían que la resolución en la medida fuera muy pobre, por lo que apostamos a tomar imágenes de 5 segundos.

 

Me quede sorprendido de la magnitud límite a la que llegamos en esa altura, si bien no detectábamos la estrella, por momentos parecía verse, cosa que para mi fue mucha mas de lo que esperaba.

 

Si bien el resultado en principio fue que no pudimos detectar la estrella a ocultar, el aprendizaje fue mucho y no estuvimos tan lejos de lograrlo.

 

Santiago esta procesando las imágenes de la ocultación y en breve tendremos algún informe. Les adelanto unas fotos de la zona y la suma de 4 cuadros de 5 segundos para que tengan una idea de lo que lográbamos con el 30 en un cielo oscuro (aunque con Luna) y  7 grados de altura.

 

Un saludo a todos, Alberto

 

(Translation English)

Hi all,

 

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.

 

Greetings to all,

 

Alberto

 

The self-made 30 cm telescope

 

The observing station with the 30 cm

 

4 frames of 5 sec exposure added

Samstag, Dezember 13th, 2008

Report from Freddy Doncel, Universidad Nacional de Asunción, Paraguay

 

It’s very sad, but we have not either been able to detect the occultation from the Observatory of the Universidad Nacional de Asunción, I made the reduction but we were not successful, by the low altitude of the object.

 

Greetings

 

Freddy

Montag, Dezember 8th, 2008

The Observation at Belo Horizonte, Brazil – Link to Data

 

Message from the observing team at Belo Horizonte, Brazil:

 

We have analized  the images taken from  02:11:06 UT until 02:28:56 UT and we can conclude that no event was detected. We will sooner work in a more detailed light curve. For those who are interested in our data, they are available at the following link:

 

http://ceamig-rea.net/occultations/081207_Varuna/Varuna_ocultation.rar

 

Cristovao

Eduardo

Breno

Centro de Estudos Astronomicos de Minas Gerais – CEAMIG

Montag, Dezember 8th, 2008

Reports from South America, Southern Africa and Europe

 

Bruno Sicardy has collected some observation reports from South America, Southern Africa and Europe and presents two solutions why the occultation was not detected:

 

Reports:

 

– Namibia:

* Marcus Hauser, HESS:

   clouded out

* Friedhelm Hund and Ansgar Gaedke, IAS/Hakos:

   clouded out

 

– Brazil:

* Marcelo Assafin and Felipe Braga Ribas, Pico dos Dias:

   clear weather, star acquired with **high SNR**, no event seen

* Cristovao Jacques, Eduardo Pimentel and Breno Loureiro, Belo   Horizonte:

   varying transparency due to clouds, a light curve is obtained, still   awaiting  processing

 

– Uruguay:

* Raul Salvo, Marcelo Traverso, Cristian Mateu, Andrea Sanchez and Gonzalo Tancredi, Los Molinos:

   very low SNR signal obtained, due to elevation of only ~10 deg

* Santiago Roland, Alberto Ceretta and Bernardo Pombo, Aigua:

   no observation possible due to very low elevation

* Eduardo Alvarez and Sebastian Bruzzone, Salto:

   no observation due to very low elevation

 

Other observations were attempted from locations well outside the predicted shadow path:

 

– UK:

* Andrew Elliott’s place.

   Star easily recorded, till ice prevented any observation

 

– Germany:

* Wolfgang Beisker, Munich:

    clouded out

 

– France:

* Bernard Christophe, St-Sulpice:

   star observed, no event detected

* Jean Lecacheux, Meudon:

   clouded out

* Francois Colas, Pic du Midi:

   clouded out

 

– Spain:

* Jose Luis Ortiz reports that no observations could be made from Calar Alto

 

 

Solutions:

 

 Since he event was not detected at Pico dos Dias, Brazil, in spite of high SNR we have two solutions:

 

(1) the shadow went south of Pico dos Dias, in which case the only stations that migth have observed an event would be the ones in Uruguay.

Now, only a very low SNR observation was made at Los Molinos. Still, is it possible to co-add several images to extract something from the Los Molinos experiment?

 

(2) the shadow went north of Pico dos Dias, as predicted, btw, by the MIT group:

http://occult.mit.edu/research/occultations/kbo/Varuna/Varuna.20081207/index.html

 

 In this case, the only stations where a positive event could have been seen are Belo Horizonte (where data **have** been acquired, but still require processing), Brasilia (any report?), Namibia (clouded out anyway), and Fortaleza (any report?). Any other stations in Brazil?

 

 Thanks a lot for the huge efforts put in this experiment, both for predictions and observations. Everything humanly possible was made to detect this event, that was probably the closest we went to detect for the 1st time a TNO occultation. It was also a good way to prove our capability to react before a event, and detect a faint star with modest instruments.

 

So, I hope that after this near miss, you are willing to pursue this kind of experiments to explore the solar system beyond Neptune…

 

Cheers,

 

Bruno