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/slitlets. The pre-slit optics allows 3 choices of the slice height. The choices are 250mas, 100mas and 25mas, leading to field of views on the sky of 8"x8", 3"x3", and 0.8"x0.8" respectively. Each one of the 32 slitlets is imaged onto 64 pixels of the detector. Thus one obtains 64x32 spectra of the imaged region on the sky.

SINFONI can be used without adaptive optics guide stars -- the noAO mode -- 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 a Natural Guide Star is available (NGS). For best correction, the star should be brighter than R ~ 11 mag. However, the AO can work (and will provide moderate improvement in image quality) with stars as faint as R ~ 17 mag in the best atmospheric conditions (good seeing and high coherence time or length). 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" from the target for the AO system to still provide a mild improvement of the encircled energy.

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

Since Period 79 the AO module of SINFONI can be fed by an artificial sodium laser guide star (LGS) which is positioned on sky in front 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 the performance decreases with increasing distance. At 40" distance, about half the Strehl ratio (in the K band) is achieved as compared to having the TTS on the same axis as the LGS. The TTS must be specified in the target list of the Phase 1 proposal.

Since Period 84 SINFONI offers a new LGS mode with no TTS, the so-called Seeing Enhancer mode (SE mode). This still offers an improvement in image quality over natural seeing, for targets without a suitably bright TTS nearby.

Since Period 92 the old LGS system PARSEC has been replaced by a newer, more powerful system called PARLA, which is available for most nights of the year.

Since Period 93 SINFONI offers the Pupil-tracking mode (see below).

Instrument Performance

The following table gives the limiting magnitudes for continuum point sources such as to reach a S/N=5 per spectral pixel, integrated spatially over the typical size of the point spread function, with one hour of integration time.

Field of View Spatial Scale Mode Limiting Magnitudes
8"x8" 125x250mas noAO J=20.2 H=19.9 K=17.9 H+K=19.6
3"x3" 50x100mas NGS J=19.4 H=19.6 K=18.8 H+K=19.8
0.8"x0.8" 12.5x 25mas NGS J=17.8 H=18.7 K=18.3 H+K=19.2

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 wavelengths of the J, H, K and H+K gratings respectively. For 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. The user should use the exposure time calculator for more detailed estimates.

Brightness and Persistence Limits

Although the saturation level of the detector is 45000 AUDs, SINFONI observations must keep below about 1/6 of that to avoid detector persistence which leaves an imprint of the observed object on the detector. Detector persistence would affect the subsequent observations of faint sources, and can take days to disappear, therefore this must be avoided.

The current detector persistence limits are 6000, 7000, 8000 and 7000 ADUs per (detector) pixel for J, H, K and H+K respectively. This usually means no objects with J, H, K magnitudes < 6mag must be visible within a field of view of 15" arround the AO guide star and/or the target. However, brighter objects are possible (while keeping within the persistence limits) but this requires using the fast acquistion template, as well as obtaining a waiver. The observation may also need to be done as the last observation of the night to avoid affecting other programs. Please refer to the User Manual for details, and use the ETC to predict the peak flux level of your target.

Sky Subtraction

The users should note that that sky offset fields are usually necessary for observations in the 25 and 100mas scales due to the small FOVs. 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).

Detector setup and readout overheads

The minimum DIT is 0.83s and the maxium is 3600s. The overhead for every detector setup (NDITxDIT) is about 18 seconds while in addition the readout time for each DIT is about 4 seconds. This means SINFONI is efficient for faint sources with long DITS, but the overheads can be huge of bright sources requiring short DITs. Please refer to the User Manul for more information. 

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

Observation of a telluric standard star at an airmass within +/- 0.2 and +/- 2hrs of the science observation is 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 PSF reference stars to test the AO performance must be requested in the proposal.

Pupil Tracking mode

Since period 93 the Pupil Trackng mode is offered for both visitor and service observations, for NGS only. For information please refer to the User Manual.

Modes which are not offered

Observation modes and techniques which are not offered are:

  • Sky Spider
  • Spectral Dithering.