SINFONI Overview

SINFONI is a near-infrared (1.1 - 2.45 μm) integral field spectrograph fed by an adaptive optics module. The spectrograph operates with 4 gratings (J, H, K, H+K) providing a spectral resolution around 2000, 3000, 4000 in J, H, K, respectively, and 1500 in H+K - each wavelength band fitting fully on the 2048 pixels of the Hawaii 2RG (2kx2k) detector in the dispersion direction. The SINFONI field of view on the sky is sliced into 32 slices. The pre-slit optics allows to chose the width of the slices. The choices are 250mas, 100mas and 25mas, leading to field of views on the sky of 8"x8", 3"x3", or 0.8"x0.8" respectively. Each one of the 32 slitlets is imaged onto 64 pixels of the detector. Thus one obtains 32x64 spectra of the imaged region on the sky.

SINFONI can be used without adaptive optics guide stars, in which case the AO module just acts as relay optics and the spatial resolution is dictated by the natural seeing. The full power of the instrument is, of cause, achieved when as adaptive optics guide star is available. For best correction, the star should be brighter then R ~ 11 mag. However, the AO can work (and will provide moderate image quality improvement) with stars as faint as R ~ 17 mag in the best seeing conditions. Ideally, the AO guide star should be as close as possible to the scientific target (if not the science target itself), and usually closer than 10". Depending on the atmospheric conditions (atmospheric coherence length) the AO guide star could be chosen as far as 30" for the AO system to still provide a mild improvement of the encircled energy.

As of Period 79 the AO module of SINFONI can be fed by an artificial sodium laser guide star (LGS) which is positioned on sky on top of the science target allowing for high-order AO corrections. A natural guide star is still required to correct for the tip-tilt motions, which are not sensed by the LGS. This tip-tilt star (TTS) has to be in the V magnitude range 12-17 and can be as far away as 60" from the science target, however, with decreasing performance with increasing distance. At 40" distance about half the Strehl ratio is achieved as compared to having the TTS on-axis with the LGS (in K band). The TTS must be specified in the target list of the Phase 1 proposal using the ESOFORM proposal template.

As of Period 84 SINFONI is offering a new LGS mode with no TTS, the so-called Seeing Enhancer mode (SE mode).

As of Period 78 SINFONI is available in the Rapid Response Mode (RRM) in the NGS and noAO mode.

Instrument Performance

The following table gives the limiting magnitudes for continuum sources such as to reach a S/N integrated over the typical size of the point spread function in one hour of integration time.

These values were calculated for a visual seeing of 0.8" which would provide infrared seeing values of 0.67", 0.63", 0.59" and 0.61" at the central wavelength of the J, H, K and H+K grating respectively. For the closed loop adaptive optics observations with natural guide stars we have assumed a guide star at a distance of 10" with a photometric brightness of R = 12 and B-R = 1.5 magnitudes. We encourage the use of the exposure time calculator for more detailed estimates.

Brightness Limits

To avoid saturation of the detector and detector persistence which would affect the subsequent observations of faint sources, no objects with J, H, K magnitudes <6mag must be visible in a field of view of 15" arround the AO guide star and/or the target.

Sky Subtraction

The users should note, that sky offset fields are mandatory for observations in the 25 and 100mas scales. The coresponding overheads have to be taken into account when estimating the required time for the execution of the observation program. Typically 50% (33%) of the time is spent on sky fields if NDIT_sky = NDIT_target (NDIT_sky = 1/2 NDIT_target)

Image Reconstruction

In visitor mode, both the raw image and a reconstructed image can be visualized on a real-time display. For the reconstructed image, a wavelength range can be selected in order to allow an easier visualization of emission line objects. The brightest OH lines are automatically suppressed by the software.

Calibrations

Observations of telluric standard stars at an airmass within +-0.1 and +-2hrs of the science observations will be offered as part of the SINFONI calibration plan for all modes available (i.e., for all combinations of image scales and gratings). Dark, internal flat-field, and wavelength calibrations are also part of the SINFONI calibration plan and are taken during daytime. Observation time to obtain special calibrations such as observations of PSF reference stars to test the AO performance must be requested in the proposal.

Modes which are not offered

Observation modes and techniques which are not offered in are the sky spider and spectral dithering.