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






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