Parameters
Select which parameters you want to examine:
'astrom' Table Parameters
The 'astrom' database table stores information describing the astrometric fit to each POSS I field in
the MAPS Catalog. The following astrometric fit parameters are stored for each field in the MAPS Catalog:
Field Name 
Definition 
possfield 
MAPS POSS I Field Name 
possnumber 
MAPS POSS I Field Number 
catalog 
Astrometric catalog used for the data reduction. Either 'lick' for the Lick Northern Proper Motion Catalog or 'acrs' for the Astrographic Catalog of Reference Stars (ACRS). 
epoch 
Epoch used for astrometric fit. Always '1950'. 
x_zpc, y_zpc 
The horizontal and vertical zero point corrections applied to data before astrometric reduction (in microns). 
init_rot 
Initial rotation of astrometric fit (in degrees). 
num_cal_stars 
The number of calibration stars used in astrometric calibration. 
x_ctr, y_ctr 
The center of the plate (in ERE). 
ra_ctr, decl_ctr 
The center of the plate in equatorial B1950.0 coordinates on the FK4 system used for the astrometric fit. 
raJ_ctr, declJ_ctr 
The center of the plate in ecliptic J2000.0 coordinates on the FK5 system (precessed from ra_ctr, decl_ctr). 
l_ctr, b_ctr 
The center of the plate in Galactic coordinates on the l^{II} system (precessed from ra_ctr, decl_ctr). 
rarms, declrms 
The RMS of the Right Ascension and Declination fit (in arcseconds). 
dx, x_x, x_y, x_xr2, dy, y_x, y_y, y_yr2 
These are the coefficients of the plate solution used (corresponding to
dX, Xx, Xy, Xxr, dY, Yx, Yy, Yyr2 in the equations below).
The plate model that maps these modified coordinates, (x,y) to standard
coordinates on the celestial sphere (i.e. the focallengthnormalized
gnomic projection, (X,Y), of RA and Dec) is given by:
X = dX + (Xx)*x + (Xy)*y + (Xxr2)*(r^2) where r^2 = x^2 + y^2
Y = dY + (Yx)*x + (Yy)*y + (Yyr2)*(r^2)
dX and dY are given in microns, and represent the difference between the
true and nominal plate centers. The remaining terms are dimensionless
derivatives. Note that one cannot apply the plate solution coefficients
directly to the plate positions in the MAPS catalog because the steps of
correcting for distortion, recentering, rotating, flipping, and
normalization by focal length are all performed internally in the data reduction before this
astrometric fit is applied.
