In this page are listed the main characteristics of the imaging mode and the filters of the instrument.
This is intended as a quick reference. A detailed description of HAWK-I can be found in the user's manual

GRAAL+HAWK-I GLAO mode

In P102 HAWK-I started to offer the Ground Layer Adaptive Optic  (GLAO) mode of the VLT Adaptive Optics Facility (AOF) via the GRAAL adaptive optics module, offering an AO corrected 7.5'x7.5' field of view. GRAAL is a module of the Adaptive Optics Facility (AOF) at UT4. GRAAL uses the 4 LGS system and the deformable secondary mirror to correct the turbulent atmospheric at ground layer for HAWK-I. The GRAAL+HAWK-I GLAO is operated in the Tip-Tilt free mode.

GRAAL focal plane illustration. The 4LGS rotate with respect to the FoV and the lasers are side-launched.

GRAAL GLAO Performance

The GRAAL GLAO performance depends on the ratio of the turbulence in the ground layer, also known as the ground layer fraction (GLF). At the GLF of 70%, GRAAL can improve a factor of 1.5 on the FWHM.  Please find the following  plot on the FWHM gain in Ks-band.

FWHM gain in Ks-band in function of the DIMM seeing and the ground layer fraction measured in TTS-free mode.

To achieve the expected image quality for the science goal, the user should refer to the ETC to find out the turbulence category to request to reach the required performance.  

Imaging mode: characteristics and sensitivity

The detectors

HAWK-I Detectors definition

Characteristics of the four detectors Detector Parameter Q1 Q2 Q3 Q4 Detector numbering #66 #78 #79 #88 Gain [e-/ADU] 1.705 1.870 1.735 2.110 Operating temperature 75K, controlled to 1mK Dark current [e-/s] (at 75K) between 0.10 & 0.15 Read noise* (DCR) ~ 12 e- Read noise* (NDR) ~ 5 e- Linear range (1%) 60.000e- (~30.000 ADUs) Saturation level between 40.000 & 50.000 ADUs

*: The RON depends on the number of non-destructive samples during the integration.
DCR (Double-Correlated Read) refers to two samples, i.e. minimum DIT ~ 1.25s.
NDR (Non-Destructive Read) refers to > 10 samples, i.e. DIT > 10s

The gap

There is a small mis-alignment between the detectors. Quadrants 2,3 & 4 are tilted with respect to quadrant 1 by 0.13, 0.04 & 0.03degrees respectively.

Details of the gap between detectors

List of filters offered for HAWK-I

Click on the filter name to retrieve the transmission curve Filter Name Central Wavelength (μm) Width (μm) Transmission (%) Y 1.021 0.101 92 J 1.258 0.154 88 H 1.620 0.289 95 Ks (1) 2.146 0.324 82 Ks (2) 2.146 0.324 82 CH4 1.575 0.112 90 H2 2.124 0.030 90 Brγ 2.165 0.030 77 NB1060 1.061 0.009 70 NB1190(3) 1.186 0.012 75 NB0984(4) 0.984 0.005 60 NB2090 2.095 0.020 81 (1) Filter used from Aug 2007 until Dec 3, 2007. Showed some structure for the Nov 2007 Science Verification run.(2) New Ks filter, used starting Jan 2008. (3) Not offered from P90, to be inserted during P93. (4) Visitor filter, please consult for usage. To be removed during P93.

Plot of filters efficiency