Instrument Description
| A full description of the VISTA telescope and the instrument
is given in the
VISTA user manual and summarized on this page later.
We refer as well to the excellent WEB pages provided by the
VISTA consortium,
from where we have already extracted most of the content of the other VISTA
pages on the ESO domain.
|
|
Filters and Focal Field Geometry
The only moving part in the camera is the filter wheel. With the current complement of Z, Y, J, H, K
s and
NB1.18 filters there is one filter wheel position available to hold a further set of 16 filters (1 per detector).
The list of available filters is given in the following overview table:
| Filter |
Wavelength |
FHWM |
Comment |
| |
micron |
micron |
|
| Z |
0.88 |
0.12 |
in camera |
| Y |
1.02 |
0.10 |
in camera |
| J |
1.25 |
0.18 |
in camera |
| H |
1.65 |
0.30 |
in camera |
| Ks |
2.15 |
0.30 |
in camera |
| NB1.18 |
1.18 |
0.01 |
in camera |
The sixteen 2048x2048 pixel IR detectors (Raytheon VIRGO HgCdTe 0.84-2.5 micron) in the camera are not
buttable and are arranged as in the following figures which shows a diagram of the focal plane as would
be seen looking directly down the camera body (down the Z-axis which on the telescope points towards the
sky). On the sky (in the default instrument rotator position) +Y corresponds to N, and +X to West:
A single Integration of length DIT secs (or a co-added series of these known as an Exposure) produces a
sparsely sampled image of the sky known as a "Pawprint". The area of sky covered by the pixels of a "pawprint"
is 0.6 deg
2. Full almost uniform sky coverage of a "tile" of 1.501 deg
2 can
be achieved with six "pawprints", offset by ±47.5% in y at two respective x-positions offset by
95% of the detector size. Any sky position of a "tile" will fall at least on two of these six
pawprints.
Instrument Performance
The instrument is currently in its acceptance and verification phase.
The following preliminary summary of the instrument performance was sent to
the public survey and science verification PIs:
| pixel scale | 0.34 arcsecs/ pxl |
| best image quality achieved | 0.6 arcsecs including seeing, optics and sampling |
| estimated image quality | Paranal seeing convolved with the instrument PSF of 0.51 arcseconds |
| image distortion | <15% in the corners |
| photometric calibration | +-2% RMS in respect to 2MASS in J,H,Ks |
| photometric calibration | +-2% RMS internally |
| sky concentration/ illumination | <5% absolute, can be corrected down to <2% |
| detector | 16 Raytheon VIRGO HgCdTe arrays, sensitive over 0.84 to 2.5 micron, high quantum efficiency, large numer of hot pixels, some dead areas on detector 1 |
The system characterization and the optimization of the calibration strategy
will be continued during the science verification and later phases.
