FRIDA@IAC

FRIDA Concept:

FRIDA (inFRared Imager and Dissector for Adaptive optics) is the first instrument for the Adaptive Optics system of the 10.4 m Gran Telescopio de Canarias GTC
It has two observation modes:

× Near-IR imaging

× Near-IR integral field spectroscopy

with three different plate scales:

× Coarse (0.040 arcsec/pixel)

× Mediun (0.020 arcsec/pixel)
× Fine (0.010 arcsec/pixel)

FRIDA is optimized in the 1.1 - 2.4 µm range, in both imaging and integral field mode.

FRIDA Summary:

Operation modes	Imaging and Integral field spectroscopy
Working Wavelength	0.9 - 2.5 µm (optimized 1.1 - 2.4 µm)
Detector	Hawaii RG 2048x2048 pix
Location	Nasmyth platform, at the output focus of GTC Adaprive Optics system
Imaging mode
Scales	0.010 arcsec/pixel 0.020 arcsec/pixel 0.040 arcsec/pixel
FoV	~20x20 arcsec² ~40x40 arcsec²
Integral field mode
Format	30 slices with 66 pixels/slice in the spatial direction and 2 pixels per resolution element in the spectral direction. The format Nyquist samples both spatial and spectral direction.
Slice Scales (spectral direction X spatial direction)	0.020 x 0.010 arcsec per slice X arcsec per pixel 0.040 x 0.020 arcsec per slice X arcsec per pixel 0.080 x 0.040 arcsec per slice X arcsec per pixel
FoV	~0.60 x 0.66 arcsec² ~1.20 x 1.32 arcsec² ~2.40 x 2.64 arcsec²
Spectral resolution	R~ 1300 for the H+K grating R~ 4000 in Z, J, H amd bands R~ 20,000 (goal 30,000) in selectable windows in the 1.4 - 2.4 µm range

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FRIDA Observation Modes:

Imaging Mode:

(Image from Marin-Franch, Lenorzer, Herrero & Najarro, 2007)

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Integral Field Spectroscopy (IFS):

(Image from Marin-Franch, Lenorzer, Herrero & Najarro, 2007)

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Adaptive Optics:

FRIDA will be installed at the Nasmyth A platform behind the output focus of the GTC adaptive optic system (GTCAO.

GTCAO will routinely deliver subarcsec resolutions down to the GTC diffraction limit, this being about 4 times that provided by HST at the same IR wavelengths. FRIDA is designed to fully exploit these resolutions in its two observation modes: direct imaging and integral field spectroscopy, both working in the 0.9 -2.5 um range.

Two unique capabilities of FRIDA with respect to current or planned 2D spectrographs are: 1) its high spectral resolution mode, 20,000; 2) its separate imaging mode which will allow the observer very fast switch to the integral-field-spectroscopy - mode. The combination will allow the user a fast selection of the field of interest for follow up spectroscopy, and facilitate a fast acquisition in the small FoV of the integral field unit.

GTCAO is a Shack-Hartmann-based wave-front sensor working with natural guide stars at optical wavelengths. For a median seeing, 0.65 arcsec, at the GTC site, it is expected to provide an on-axis Strehl ratio of 0.60 in K-band, with guide stars of m_R= 6-12, down to ~ 0.30 for m_R = 15. Measurements of the isoplanatic angle at La Palma Observatory indicate a degradation of the Strehl in K-band to ~10 % when the natural guide star is at 30 arcsec from the science target.

FRIDA Nyquist sample the diffraction limit of GTC in J-, H- and K-bands in its imaging mode, in K-band in its integral field mode, and partially in H- and J-bands in the integral field mode.
The integral field mode is provided with three spectral resolution sets: ~200 km/s, allowing two atmospheric bands to be observed at once; ~ 75 km/s, to cover only one band at a time; and ~15 km/s to cover selectable regions in the 1.4 -2.5 µm range.

FRIDA design is being optimised in the 1.1 - 2.4 um range, in both imaging and integral field mode. Its ultimate performance is foreseen in the K-band where GTCAO is also expected to achieve maximum atmosphere correction. In this case, FRIDA will deliver images and spectra with spatial resolutions close to GTC diffraction limit at 2 um, FWHM ~ 44 mas, with maximized image contrast and high throughput for point-like sources

An advantage of FRIDA with respect to akin instruments is that it does not rotate - the rotated field will be provided by the GTCAO system. This will translate into a highly stable instrument with minimum flexure, and an accurately-calibrated distortion pattern.

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