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SHARK-NIR is an instrument which provides direct imaging, coronagraphic imaging, dual band imaging and low resolution spectroscopy in Y, J and H bands, taking advantage of the outstanding performance of the Large Binocular Telescope AO systems. Binocular observations will be provided used in combination with SHARK-VIS (operating in V band) and LMIRCam of LBTI (operating from K to M bands), in a way to exploit coronagraphic simultaneous observations in three different wavelengths.
A wide variety of coronagraphic techniques have been implemented in SHARK-NIR, ranging from conventional ones such as the Gaussian Lyot, to others quite robust to misalignments such as the Shaped Pupil, to eventually techniques more demanding in term of stability during the observation, as the Four Quadrant; the latter is giving in theory and simulations outstanding contrast, and it is supported in term of stability by the SHARK-NIR internal fast tip-tilt loop and local NCPA correction, which should ensure the necessary stability allowing this technique to operate at its best.
The main science case is of course exoplanets search and characterization and young stellar systems, jets and disks characterization, although the LBT AO extreme performance, allowing to reach excellent correction even at very faint magnitudes, may open to science previously difficult to be achieved, as for example AGN and QSO morphological studies.
The institutes participating to the SHARK-NIR consortium which designed and built the instrument are Istituto Nazionale di Astro Fisica (INAF, Italy), the Max Planck Institute for Astronomy (MPIA, Heidelberg, Germany) and University of Arizona/Steward Observatory (UoA/SO, Tucson, Az, USA). We report here about the SHARK-NIR status, that should achieve first light at LBT before the end of 2022.
The Multi-conjugate adaptive Optics Relay For ELT Observations (MORFEO), formerly MAORY, is the Multi-conjugate Adaptive Optics (MCAO) relay for the Extremely Large Telescope (ELT). The instrument provides the MCAO correction to two instruments at the ELT Nasmyth platform. One first light instrument fed by MORFEO is the Multi-AO Imaging Camera for Deep Observations (MICADO) that will provide imaging, astrometric, spectroscopic and coronographic observing modes. A second generation instrument, still to be defined, will occupy the other port of MORFEO. The delivered MCAO-corrected Field of View (FoV) of MORFEO is 2 arcmin. In this paper we present the possible fine optical alignment and recollimation strategies to bring the relay optics within the diffraction-limited performances.
More than one MORFEO fine Optical Alignment (MOA) strategy is currently under study in the development of the instrument towards its final design review. Given the complexity and the size of this new generation instrument diversifying and enlarging the set of possible techniques for the system alignment is an effective and more robust approach. As the Alignment Integration Verification (AIV) phase will develop the different strategies will be deployed and tested to possibly spot the best method (if any) among the others which will then be kept as back-up alternatives. One technique relies on the metrology of out-of-focus PSF images as proxy of the system pupil to detect the main optical aberrations in the instrument. This method has been proposed by Tokovinin & Heathcote [1] for a 2-mirror telescope. The challenge to be faced with MORFEO is given by the large number of optical elements and the related pseudo wavefront sensing limitations. Other techniques under study involve the use of wavefront sensing, phase diversity techniques and aberrations spotting using the MORFEO deformable mirrors. The MOA is meant to be performed both at the first AIV operations and at the periodic recollimations of the system during its nominal operation lifetime. The paper reports the results of a preliminary set of simulations carried out using a OpticStudio-Matlab simulator for the Donut technique.
Initially proposed as an instrument covering also the K-band, the current design foresees a camera working from Y to H bands, exploiting in this way the synergy with other LBT instruments such as LBTI, which is actually covering wavelengths greater than L' band, and it will be soon upgraded to work also in K band. SHARK-NIR has been undergoing the conceptual design review at the end of 2015 and it has been approved to proceed to the final design phase, receiving the green light for successive construction and installation at LBT.
The current design is significantly more flexible than the previous one, having an additional intermediate pupil plane that will allow the usage of coronagraphic techniques very efficient in term of contrast and vicinity to the star, increasing the instrument coronagraphic performance. The latter is necessary to properly exploit the search of giant exo-planets, which is the main science case and the driver for the technical choices of SHARK-NIR. We also emphasize that the LBT AO SOUL upgrade will further improve the AO performance, making possible to extend the exo-planet search to target fainter than normally achieved by other 8-m class telescopes, and opening in this way to other very interesting scientific scenarios, such as the characterization of AGN and Quasars (normally too faint to be observed) and increasing considerably the sample of disks and jets to be studied.
Finally, we emphasize that SHARK-NIR will offer XAO direct imaging capability on a FoV of about 15"x15", and a simple coronagraphic spectroscopic mode offering spectral resolution ranging from few hundreds to few thousands. This article presents the current instrument design, together with the milestones for its installation at LBT.
This concept was only merely described and functionally tested in the framework of MAD, and subsequently, with a holographic diffuser. The latter produce a sort of random distribution of the light coming out from the pupil plane, leading to sort of inefficient modulation, as most of the rays are focused in the central region of the light diffused by such device. The bi-dimensional original grating is, in contrast, producing a well defined deterministic distribution of the light onto a specifically shaped pattern. A crude option has been already discussed as a possibility, and it is here generalized to holographic plates leading to various distribution of lights, including a circle whose diameter would match the required modulation pattern, or more cost effective approaches like the one of a square pattern. These holographic diffusers would exhibit also zero-th and high order patterns and the actual size of the equivalent modulation would be linearly wavelength dependent, leading to colour effects that requires a careful handling in order to properly choose the right amount of equivalent modulation.
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