Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-precision astrometry on the VLT/FORS1 at time scales of few days   We investigate the accuracy of astrometric measurements with the VLT/FORS1
camera and consider potential applications. The study is based on two-epoch
(2000 and 2002/2003) frame series of observations of a selected Galactic Bulge
sky region that were obtained with FORS1 during four consecutive nights each.
Reductions were carried out with a novel technique that eliminates atmospheric
image motion and does not require a distinction between targets and reference
objects. The positional astrometric precision was found to be limited only by
the accuracy of the determination of the star photocentre, which is typically
200-300 microarcsec per single measurement for bright unsaturated stars
B=18-19. Several statistical tests have shown that at time-scales of 1-4 nights
the residual noise in measured positions is essentially a white noise with no
systematic instrumental signature and no significant deviation from a Gaussian
distribution. Some evidence of a good astrometric quality of the VLT for frames
separated by two years has also been found. Our data show that the VLT with
FORS1/2 cameras can be effectively used for astrometric observations of
planetary microlensing events and other applications where a high accuracy is
required, that is expected to reach 30-40 microarcsec for a series of 50 frames
(one hours with R filter).

24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int