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

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