HAWK-I Overview

HAWK-I is a near-infrared (0.85-2.5 μm ) wide-field imager. It is being offered for the first time in Period 81. The instrument is cryogenic (120 K, detectors at 80 K) and has a full reflective design. The light passes four mirrors and two filter wheels before hitting a mosaic of four Hawaii 2RG 2048 * 2048 pixels detectors. The final F-ratio is F/4.36 ( 1 arcsec on the sky corresponds to 169 μm on the detector).

Imaging mode

The two filter wheels of six positions each host ten filters: Y(Z), J, H, K (identical to the VISTA filters), as well as 6 narrow band filters (Br_γ , CH4, H2 and three cosmological filters at 1.061, 1.187, and 2.090 μm ). The Field of View of HAWK-I on the sky is 7.5 arcmin * 7.5 arcmin, covered by the mosaic of the four Hawaii-2RG chips. The four detectors are separated by a cross-shaped gap of ~ 15 arcsec. The pixel scale is 0.1064 arcsec/pix with negligible distortions (< 0.3 %) across the field of view. The image quality is seeing limited down to at least 0.4 arcsec seeing (i.e., 0.3 arcsec measured in K).

HAWK-I Field of View

Limiting magnitudes

Typical limiting magnitudes of HAWK-I (S/N of 5 on a point source, 3600s integration on source) under average conditions (0.8 arcsec seeing, 1.2 airmass) are:

HAWK-I limiting magnitude examples

Filter	Limiting mag	Limiting mag
	[Vega]	[AB]
J	23.9	24.8
H	22.5	23.9
K	22.3	24.2

The read-out noise is around 5 electrons, while the dark current of the instrument is around 2 electrons/pix/s. For a more detailed exposure time calculation, in particular for narrow band filters, we encourage you to use the exposure time calculator .