Shark-Vis
the visible-band high-contrast imager of the Large Binocular Telescope
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instrument overview
instrument overview
Shark-Vis is the visible-band (400-950 nm) high-contrast and coronagraphic instrument of the Large Binocular Telescope (LBT). Mounted on the 8.2m DX telescope of LBT and fed by the LBT extreme Adaptive Optics system SOUL, it provides high-angular-resolution and high-contrast capabilities in the visible band, delivering quasi diffraction-limited images with angular resolutions of the order of 20 milliarcsec.
SHARK-VIS provides both wide-band and narrow-band image capabilities and adopts a fast-imaging approach, using short DITs to limit the PSF smearing due to atmospheric AO residuals and telescope jitter. The instrument focal plane is always tracking the telescope pupil, hence derotation is performed post-facto, by processing the acquired stream of consecutive images.
Because the SOUL wavefront sensor operates in the optical, SHARK-VIS always shares part of the visible light with the AO system. Available input dichroics allow the observer to split the light between the two systems in different ways, so as to optimize both the AO performance and the scientific observations.
Shark-Vis is a PI-instrument designed and built at INAF-Osservatorio Astronomico di Roma.
observing modes
observing modes
FAST IMAGING: used for bright targets, for which the PSF peak in the observation filter is above 1000 adu/ms. The typical DIT in these cases is 0.1ms - 10ms, which allows us to freeze jitter and speckles for a complex post processing image reconstruction. This modality achieves the maximum resolution level, very close to the diffraction limit (λ/D~16 mas in the R band). This mode is suggested for bright targets (mag R < 8-9) and for a small field of view of about 1-2 arcsec.
STABILIZED IMAGING: used for targets for which the PSF peak in the observation filter is lower than 1000 adu/ms. The typical DIT in these cases is 10ms - 10s. In this regime SHARK-VIS can employ its Automatic Beam Stabilization unit (ABS) that helps to mitigate the PSF residual jitter from 20-15 mas to 5-6 mas. The ABS is driven by using some of the light sent into the instrument, which is selected with an internal splitter (guide cube); a number of different splitters are available for this task (see next section). Although using the ABS removes part of the light from the science path, this mode delivers better results than direct imaging for fainter sources. This mode is suggested for faint sources and high-contrast targets.
STABILIZED CORONAGRAPHIC IMAGING: Lyot masks (IWA 55, 100, 200, 300 mas) are available; however, this mode offered on a best-effort basis, as this setup has not yet been fully validated given the limited Strehl ratio achievable in visible bands. The use of the coronagraphs must be discussed and agreed upon with the SHARK-VIS team during the proposal preparation.
DUAL BAND IMAGING in Hα: this mode employs the SHARK-VIS internal PRISMATRON beam splitter, which allows the observer to simultaneously acquire with a single exposure the target in two filters: Hα (1nm) and surrounding continuum (10nm). This mode is recommended for Hα-emitting targets that require high-contrast.
specifications
specifications
wide-band filters: B Bessel, V Bessel, R Bessel, g Sloan, r Sloan, i Sloan, z Sloan
narrow-band filters (central wavelength, width in nm): [OIII] (500.7, 3), [OI] (630.3, 2), Hα (656.3, 5), Hα (656.3, 1), Cnt (647, 10), [SII] (672.4, 3),
prismatron (dual-band splitter + filters): channel 1 Hα (656.3, 1), 90% of the light + channel 2 Hα (656.3, 10) 10% of the light
field of view: (maximum) 10"x10"
pixel scales: 6.5 mas/pixel, 4.3 mas/pixel (1.5x magnification mode)
coronagraphs: IWA 55 mas (1.2" FoV diameter), IWA 100 mas (1.2" FoV diameter), IWA 200 mas (2.4" FoV diameter), IWA 300 mas (4.8" FoV diameter)
General scheme of the SHARK-VIS light optical path. The picture shows in particular the setup for stabilized imaging for optimized observations in the Hα filter with the ABS system.
how to access the instrument
how to access the instrument
Access to the instrument can be obtained through standard calls for proposals of the LBT partners or DDT proposals. However, Shark-Vis is a PI instrument, so the proponents must contact the instrument team in advance (see contacts). This allows the instrument team to verify the feasibility of the proposed observations, to select the most suitable setup, to estimate the expected performance, and to check for possible target conflicts with ongoing programs of the SHARK-VIS scientific team.
contacts
contacts
To contact the team send an email to: sharkvis.oaroma -at- inaf.it
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