GraF Integral Field and Long Slit Spectroscopy with the ESO 3.6m/ADONIS/SHARP system

We present the test results of the GraF instrument built at Grenoble for spectro-imaging at high angular resolution with the ESO 3.6m/ADONIS and the 256x256 pixels SHARP camera. The instrument is operated in the 1.2 2.5 μm spectral range. It uses a Fabry-Perot interferometer (FPI) cross-dispersed with a grating, and provides the integral field spectroscopic capability, projecting on the detector several simultaneous monochromatic images of the field (windows). The necessity of such a capability for spectroscopy at high angular resolution is stressed and illustrated on test astronomical data and their deconvolution. The instrument provides 17 windows of 0.5" by 9" in the J band, 10 windows of 0.9" by 9" in the H band, and 8 windows of 1.5" by 12" in the K band, with the platescale of 0.035" in the J and H, and 0.05" in the K. The spectral resolution of windows is about 20000 in J, 10000 in H, and 7000 in K. The spectrum recorded in one exposure corresponds to the transmission pics of the FPI. The interorder space is covered in a sequence of exposures varying plate spacing of the FPI, providing a spectro-spatial cube of data equivalent to 18002 pixels. The instrument is easily modular. It converts to a classical long slit spectrograph, useful for observations of simple geometry objects such as binary stars, and to a direct imaging camera. This modularity proved to be very useful at the telescope, allowing to acquire in the same sequence the image, the long slit spectrum, and the {x, y, λ} map of the field. The measured limiting magnitudes in the spectroimaging mode, for S/N = 5 and the exposure time 1 min, are respectively J/H/K = 8.5/9.4/9.3; in 5 min one gets J/H/K = 10.4/12.5/10.0. In the long slit mode, in 30 min exposure and with a high dispersion grating (300 mm-1, R = 4000), one gets J/H/K = 12.1/12.9/11.5. With the low dispersion grating (35 mm-1, R = 800) , available for the J and H bands, the limiting magnitudes are J/H = 14.5/15.4. The detector flat-field response, the instrumental thermal background, the pointspread function and the deconvolution results are presented and discussed. The instrument potential is illustrated by the data and astrophysical results obtained on a tight binary GU CMa and on the exploding star Eta Car. _______________________________________