Archive for the ‘Varuna 2008’ Category

Sonntag, Dezember 7th, 2008

First Reports from European Observers – “Clouded out”

 

Reports of observations in Europe were reported at “Occult Watcher” and Planoccult:

 

Gerhard Dangl (Austria), Jan Manek (Czech Republic), Wolfgang Rothe (Germany), Jean Lecacheux at Meudon Observatory (France) and Carles Schnabel (Spain) reporting “clouded out” for the event.

 

Waiting for more reports…

 

Oliver

Sonntag, Dezember 7th, 2008

Waiting for Observation Reports, 2008 Dec 07, 09:55 UT

 

(20000) Varuna has now passed the target star and we are awaiting the observation reports.

 

These images by EUMETSAT show the cloud cover at 00:00 UT and 03:00 UT respectively at the most promising observing places.

 

Southern Africa:

 

 EUMETSAT, Southern Africa, 2008 Dec 07, 00:00 UT

 

 EUMETSAT, Southern Africa, 2008 Dec 07, 03:00 UT

 

Brazil:

 

EUMETSAT, Northern Brazil, 2008 Dec 07, 00:00 UT

 

 EUMETSAT, Northern Brazil, 2008 Dec 07, 03:00 UT

 

Andrew Elliot from U.K. has sent a report to Planoccult. He tried the observation:

 

“Tonight I attempted the (20000) Varuna occultation ‚just in case…‘, and because the sky was totally clear.

The target star (Mr 14.2) was easily visible using a Watec 120N with 16-frame integrations (0.64 sec/frame), + 406mm S-C at f/10.  Unfortunately, the recording had to be abandoned around the time of the expected occultation due to ice forming on *both* sides of the Schmidt corrector plate (despite a dew zapper)!  At least this was ‚proof of concept‘ for future faint star occultations.”

 

Stay tuned…

 

Oliver

Freitag, Dezember 5th, 2008

A Finder Chart with “Red Photographic Magnitudes”

 

Bruno Sicardy has set another finder chart at his web page The possible Varuna stellar occultation of 6/7 December 2008  .

This map is the same as in message “Maps of Potential Observing Stations and Finder Charts “ (Dec 02 at the blog), but with „Red photographic magnitudes” added for several stars.

 

Oliver

 

Finder Chart with “Red Photographic Magnitudes” (13.05′ x 12.35′)

Dienstag, Dezember 2nd, 2008

Independed Prediction from MIT

 

The MIT (Massachusetts Institute of Technology) has published an independed prediction for the Varuna occultation:

 

Check the link for details.

 

Varuna.20081207 Occultation Dec 07, 2008

 

 

The prediction (2008 Nov 26) following the results taken from the analysis of 101 frames obtained at the Lowell 42-inch Telescope, du Pont Telescope, SMARTS 0.9m Telescope, and Swope Telescope.

 

There is no major path shift compared to the predictions by the Rio Group or Raoul Behrend.

 

Oliver

Dienstag, Dezember 2nd, 2008

Maps of Potential Observing Stations and Finder Charts

 

Bruno Sicardy has updated his web page The possible Varuna stellar occultation of 6/7 December 2008  with a map of potential observing sites near and inside the predicted path (path update Nov 29, Rio Group):

 

Potential Observing Sites

 

and according to the update by Raoul Brehrend (Nov 27):

 

Potential Observing Sites (Update R. Behrend, Nov 27)

 

 

 

A finder chart of the target star from Bruno’s webpage (DSS2.365 at 645nm, 13.05′ x 12.35′):

 

Finder Chart (13.05′ x 12.35′)

 

Additional to these maps you can find more finder charts for this occultation with different fields of view on the same web page:

 

20 deg

 

5 deg

 

1.5 deg

 

30 min

 

10 min

 

 

Less than 5 days to go…

 

Oliver

Montag, Dezember 1st, 2008

New Update by Steve Preston, Based on Astrometry from the Rio Group

 

Steve Preston has posted a new update for the Varuna event at:

 

http://asteroidoccultation.com/2008_12/1207_20000_20018.htm

 

This update uses most recent astrometry from Marcelo Assafin (Rio Group).

 

 Map of Prediction by Steve Preston, 2008 Nov 30, 23:46 UT

 

Steve has set the uncertainty larger than the formal uncertainty.

With the relatively small number of observations and the strong weighting for this recent astrometry he was reluctant to trust the formal uncertainties of the orbit fit.

 

Oliver

Sonntag, November 30th, 2008

The Probabilities of Positive Detection of Occultation for Stations at the Southern Hemisphere Based on Latest Predictions

 

Jean Lecacheux (IMCCE, France) wrote:

 

“The updated nominal path is shifted by 0″.2 or 6000 km south -unfortunately for all the European observers-, and now is predicted from the south tip of South-Africa (near 02:10 UT in early dawn) to south Brazil (near 02:15 UT at low elevation).

In the same time the „one sigma“ uncertainty was lowered to 0.12 Re (i.e. ten times better than before the new astrometry), whilst in consequence the probability of positive detection was boosted greatly.

Now it could reach up to 44 % from Porto Alegre (south Brazil), 40 % from Sao Paulo (Brazil), 37 %  from Cape Town (South-Africa), 14 % from Windhoek (Namibia), 8 % from  Recife (nordeste, Brazil), 1.5 % from Belem (Brazil) at the Amazon mouth…, and will be fully negligible from any place in the northern hemisphere.

Never any occultation by a Kuiper body, Pluto excepted, reached a likehood level so high.”

Sonntag, November 30th, 2008

New Prediction by the Rio Group (2008 Nov 29)

 

Another update calculated by Marcelo Assafin et al.at the web page The possible Varuna stellar occultation of 6/7 December 2008 (Bruno Sicardy)

 

Update as of 29 November 2008, using a recent star position derived from 62 observations of the star at Pic du Midi (T1M François Colas, T60 Bernard Trégon), St Sulpice (T60, Bernard Christophe) and Sozzago (T40, Frederico Manzini) reduced by Marcelo Assafin et al. (Rio group):

 

 Prediction by Rio Group, 2008 Nov 29

RA= 07h 29mn 48. 1725sec        DE= +25d 40′ 07.740″       (J2000/UCAC2)


and the following offset for Varuna (from 32 images taken at Pic du Midi T1M):


off_RA = +42mas    off_DE = -194mas.


Formal errors on this prediction, taken from rms and number of observations, are about 25 mas, or +/- 800 km, as shown by the dotted lines.

 

 

Details about this prediction:

 

 

On Sat, 29 Nov 2008, Marcelo Assafin wrote:

 

  In the following, I give updated astrometric results for Varuna and the star, from reductions using the PRAIA package. The observational sources are (many thanks to these heroes):

 

 – François Colas, Pic-du-Midi, France (T1M), run from 20 to 28 November 2008

 – Bernard Trégon at Pic-du-Midi, France (T60), run 21 November 2008

 – Federico Manzini at Sozzago, Italy (A12), run 25 November 2008

 – Bernard Christophe at St-Sulpice, France (947), run 25 November 2008

 

 

   Note that all the observations from our earlier report were re-reduced, so that the results reported here include all the observations made so far in the recent effort to derive offsets for Varuna and for the star. Unfortunately I have not yet been able to access the 36cm-telescope images from Jose Luis. Therefore these images are not yet included in our analysis.

 

   Below we give the details of the astrometric reductions and results for the star and for Varuna.

 

 

   Star position

 

   As before, I take as reference the star position which has been used in the first plots of the occultation by Dave Herald:

 

 

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

 

 

   Individual CCD frame solutions were obtained using the UCAC2 catalog and a 3rd degree  polynom for the reductions of the large field CCDs. Typically more than 200 stars were used per field. Mean errors  in (RA,Dec) were about 50mas.

 

  Taking the individual solutions from the (T60), (A12) and (947) sets, the offset in the star positions wrt the reference position above was:

 

 

T60:

  off_ra = +15mas (16mas)  (n=10)

  off_de = +27mas (14mas)  (n=10)

 

 

A12:

  off_ra = +20mas (22mas)  (n=15)

  off_de = +24mas (22mas)  (n=15)

 

 

947:

  off_ra = +20mas (15mas)  (n=37)

  off_de = +34mas (17mas)  (n=37)

 

 all telescopes together

  off_ra = +20mas (17mas)  (n=62)

  off_de = +30mas (18mas)  (n=62)

 

 

 

    In the global solution all large CCD frames were mixed and a 3rd degree polynom is used to place positions into the UCAC2 frame in the tangent plane. The star position from the global solution gives:

 

 

global:

  off_ra = +19mas (17mas)  (n=62)

  off_de = +30mas (18mas)  (n=62)

 

 

 

       Varuna offsets

 

   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.

 

Considering these individual solutions, the offsets wrt the JPL ephemeris were:

 

T1M: (20-21 November)

  off_ra = +077mas (093mas)  (n=18)

  off_de = -170mas (103mas)  (n=18)

 

 

T1M: (26-27 November)

  off_ra = +052mas (169mas)  (n=08)

  off_de = -156mas (112mas)  (n=08)

 

 

T1M: (27-28 November)

  off_ra = +089mas (91mas)  (n=06)

  off_de = -191mas (44mas)  (n=06)

 

 

T1M: all nights together

  off_ra = +073mas (113mas)  (n=32)

  off_de = -170mas (096mas)  (n=32)

 

 

Note that the use of the improved 2MASS and the 3rd degree polynom here is an improvement over the former solutions with 1rst degree polynom and about 5 UCAC2 stars, in the individual solutions.

 

 

   In the global solution for Varuna, all the large CCD frames (referred to the UCAC2) were mixed with the T1M individual frames (referred to the improved 2MASS as described above), using a 3rd degree polynom to place the positions into the UCAC2 frame in the tangent plane. The offsets wrt the JPL ephemeris from the global solution gives:

 

 

global:

  off_ra = +42mas (82mas)  (n=32)

  off_de = -194mas (69mas) (n=32)

Samstag, November 29th, 2008

Preparations for the „eventual“ event in Brazil


Marcelo Assafin (Rio Group) wrote:

 

  Felipe B. Ribas is starting to contact some stations in Brazil from amateurs which could try to observe the possible event (Sao Paulo, Brasilia city regions).

 

  The event is too low for the LNA observatory at Itajuba (IAU 874), with h=19 degrees, but we are in touch with the technical personnel to see if, and how, we can manage to observe the event with their 60cm automated telescope.

Freitag, November 28th, 2008

Comparing the Reductions

 

Bruno Sicardy presents three maps of different prediction calculations on his webpage The possible Varuna stellar occultation of 6/7 December 2008 .

 


1.

Prediction using the UCAC2 star position and NO offset on Varuna ephemeris

UCAC2 star position and NO offset

 

The following two predictions using the same data obtained from observations made at Pic du Midi:

2.

Update as of 25 November 2008, using a recent star position derived from observations made at Pic du Midi, reduced by Marcelo Assafin et al. (Rio group) and an offset for Varuna (18 positions from the Pic du Midi observations):

 Prediction Marcelo Assafin  et al. (Rio group)

Star position:  RA= 07h 29mn 48.1720sec   DE= +25d 40' 07.741"   (J2000/UCAC2)

Varuna offset: off_RA = +94mas ,  off_DE = -279mas

 

The dotted lines are typical errors on path, roughly +/-2000 km, or about +/-65 mas.

 

3.

Update 27 November 2008, using a recent star position and an Varuna offset derived from the same observations, but reduced by Raoul Behrend (Geneva):

Prediction Raoul Behrend (Geneva)

Star position:   RA= 07h 29mn 48.1720sec   DE= +25d 40' 07.748" (J2000/UCAC2)

Varuna offset: off_RA = +23mas,  off_DE = -185mas

 


How to read the maps:

 

Black lines: Varuna shadow, dotted lines: typical uncertainty band. The dots on the centre line are plotted every min, shadows move from right to left. The larger dot is geocentric closest approach, occurring at the UT time indicated at the bottom of the figure.

 

Comparing the second and the third maps with the first, the typical errors on the path are much smaller now.

 

Oliver