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file 1996-2000_S1-8_peng.readme.txt
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Contents:

199 frames of CCD images of the major satellites of Saturn (Mimas, Enceladus, 
Tethys, Dione, Rhea, Titan, Hyperion and Iapetus) are
obtained on 1-meter telescope at the Yunnan Observatory during the years of
1996-2000, are measured. These positions are compared to the ones computed with
the Vienne & Duriez ephemerides (TASS1.7). The calibrated parameters of the
CCD scale and orientation are determined by the comparison of their measurement
coordinates with computed positions of four bright satellites of Tethys, Dione,
Rhea and Titan.

A catalog 913 differential positions has been obtained. Analysis
of the data as inter-satellite positions shows that these observations of the
above mentioned four satellites have root-mean-square residuals of 0.04 arcsec
in the sense of (O-C)(Observed minus Computed). The positional measuring procedure
is proved to be good enough to obtain a small dispersion in the observations
for the major Saturnian satellites.

The format and the conventions of the present catalog are very near to the
one of (Strugnell & Taylor 1990). The coordinates are given apart
from a scale factor and from a rotation, but all astrometric corrections
are done. So, these positions are really astrometric ones in that
meaning that, no astrometric consideration is necessary to use them,
even if one wants to touch up the calibration. Nevertheless, the raw
pixels are also given in order to allow anyone to reduce again the
frames.

At the end of the catalog, there is  some lines which indicate how the 
reduction have been done and which corrections have been applied to get
 the coordinates. Specially, a column "catalog" indicates the source of 
the theoretical positions used to reduce the plates. 
Two other columns give the scale and the orientation of the frame. 
Note that the orientation refers to the true equator of the date. But 
it is possible to  touch up these parameters directly by comparing the 
"observed map" and the "computed map" (then given in the J2000 system, see 
Vienne, Thuillot & Arlot).

Reference of the catalog:

Peng Qingyu, Vienne A., Shen Kai Xian 2002, "Positional Measuring Procedure and 
CCD Observations for Saturnian Satellites" A&A 383, 296


Other references:

Vienne A., Thuillot W., Arlot J.E. 2001, Astrometric reduction of CCD
observations of planetary satellites without reference star, in Note
Sci. et Tech. de l'I.M.C.C.E., S077

Strugnell, P.R., Taylor, D.B. 1990, A&AS 83, 289


Format:

In a FORTRAN code, one line is read with the format:
(i3,i5,i3,f11.7,f7.3,2i4,i2,1x,a2,a1,i2,i1,
2(1x,f13.7),2i2,2(1x,f7.3),3i3,2f10.3)
The meanings of each parameter can be found in (Strugnell & Taylor
1990), but we recall them below with eventually, in parenthesis,
the differences with the original meaning:
* opp: opposition number, 1=1874 to 118=1995. 
* year,m,utc: year, month and utc date of the observation (one more
  digit for utc: f11.7) 
* tt-utc: TT-UTC in seconds (two more digits: f7.3) 
* obs: UAI observatory code from the Minor Planet Center, 
* ref: reference code of the catalog (we have chosen 301 for the present
  observations) 
* t.: observation type. 0=\alpha ,\delta  , 1=\Delta \alpha \cos \delta ,\Delta \delta  ,
  2=\Delta \alpha ,\Delta \delta  , 3=position angle, separation 
* obj.: subject satellite, reference satellite. 0 for Saturn, 1 to
  8 for S1 to S8 (* when there is no reference satellite that is for
  observation type 0 , C for the center of the plate which is not
  a physical object) 
* fl.: flags of presence of the first and second coordinates 
* obs1, obs2 : first and second coordinates (one more digit, it is
  0 when the coordinate is not present, see fl.) 
* s: reference system. 0=mean equator and equinox B1950, 1=true equator
  and equinox of date of observation, 2=mean equator and equinox of
  J2000 
* f: reference frame. 0=topocentric, 1=geocentric, 2=heliocentric 
* o-c1, o-c2: residuals of observations in arc-seconds (computed with
  TASS1.7 and with the format f7.3, it is 999.999 when the residuals
  are not computed and it is 888.888 when the residuals are greater
  than 100. in absolute value). 
* (r: the number of the satellite used as reference in the computation
  of o-c) 
* (-: no meaning in this series, index reserved) 
* (s: the number of the series, the scale and orientation are the same
  for all the observations of one series). 
* (xpix,ypix: original coordinates in pixels) 

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