4.1. WFPC2 observations and astrometry
The WFPC2 observations used to study 53W002 at the highest possible
resolution were the same as those discussed in
Section 2.1.1, except that 53W002
itself was put inside the PC.
The PC noise is largely limited by read-noise and dark-current, and
large-scale gradients in the flat-fielded images are
3% of sky (cf.
W94a,
Windhorst et al. 1998;
W98).
For the interpretation below, one needs to know the exact location in
the PC-images
of 53W002's highest-resolution VLA source, which has
0".15 FWHM
(W91).
W98 show
that, after correcting the WFPC2 positions for a small systematic
VLAFK5-HSTGSSS
offset, the high resolution VLA 8.44 GHz
(W91) and 15 GHz
(S97;
S97) images coincide
with 53W002's optical center - and likely its AGN
(Section 4.2.1) - to within
3 PC pixels.