8/6/2019 Spie2008 ADC Poster

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Roberto Lpez Lpez, Ariadna Calcines Rosario

rll@iac.es azcr@iac.es Instituto de AstroCanarias

ADC

SPIE 2008. MARSEILLE, FRANCE

lineation and workshop teams of

CONCLUSIONS

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(1) Original image, elongation is in zenithal orientation. Separation between prisms is zero and angle is in nominal horizontal pprisms the elongation rotates.(3) Increasing separation between prisms the elongation decreases. (4) At appropiate separatio

mounting the elongation practically disappears. These are pre-processed images so that the seeing does ahalo rounding the star. Total field in each image is less than 10 arcsec. (May 23,2008).

Sequencial images, V-band, for a HR7557 star (a-AQL) to 30 degrees from zenith.

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A Oscoz & FastCam Team, . FastCam: a new lucky imaging instrument for medium-sized telescopes, SPIE, Marseille, Jun2008. Filippenko, A.V., The importance of Atmospheric differential refraction in spectrophotometry, Pub. Astron

1982, v94, p715-721. Roland J. Sarlot, Donald W. McCarthy A Cryogenic, 1-5 Micron Atmospheric Dispersion Corrector for Astronomical Adaptive Optics, Proceedings of SPIE Vol. 4441 (2001). Avila, G., Rupprecht, G., Atmospheric

FORS focal reducers at the ESO VLT. Avila, G., Manescau, A., Pascini, L. ESPRESSO Concept Study Telescope Interfaces,Doc. Nr.: VLT-TRE-ESO-13520-4241 Issue: 0.3, 31-05-2007.

In this poster an Atmospheric Dispersion Corrector (ADC) developed for the FastCam project is presented. FastCam is a system based on lucky imaging techniques for high spatial resolutio

the Instituto de Astrofisica de Canarias (IAC). The use of a system to correct the atmospheres effects is necessary to obtain a good optics quality in order to satisfy science requirements.

One ADC has been designed to be implemented and intended to correct that atmospherical effect at the 4.2m William Herchel Telescope (Roque de los Muchachos Obs

Palma) for zenithal distances larger than 15 degrees, mainly in I band. Two alternatives are shown, one of them in prefocus configuration and another in collimated beam

Fastcam is an ambicious instrument designed and developed by the Instituto de Astrofsica de Canarias and the

Universidad Politcnica de Cartagena that has reached the diffraction limit in the telescopes: TCS, NOT, WHT. Theprincipal investigator is the Doctor Rafael Rebolo. For WHT (4.5m) and atmospheric corrector is needed. The ADC

has been designed for WHT though it can be implemented in other telescopes.

(2.5m)

TCS (Fig. 9) Carlos Snchez

Telescope (Izaa, Tenerife).

The next tests of the ADC willtake place in this telescope in

September 2008

NOT (Fig. 10) Nordic Optical

Telescope (Roque de los

Muchachos, La Palma). TheADC has been tested in May

2008 (as can be seen in the

picture), in order to test the pre-focus design.

ADC (fig.11) The atmospherical dispersion corr

ADC with two BK7 prisms of 25 tilted 15 eachseparation between prisms is variable and both

implementedin a rotator to compensate the orientation of the object during the night.

T (Figs.5,6,7,8) William Herschel Telescope (Roque de los Muchachos, La Palma) The ADC

implemented in May 2008 and the results are shown in figs.1,2,3,4.

(4.2m)

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This configuration is optimal for telescopes with a lab in

Nasmyth focus. This is the case of WHT.

This also allows stability which is important for the image in the focal plane. In our configuration

he variable separation between the prisms allows to correct zenithal distances until 45 in

band and 34 degrees in V band.

When the prisms are in contact(Fig.13) any correction is produced.

With different separa-tions (Fig.14)

higher dispersions can be solved, ascan be seen in this figure all thewavelengths focus in the focal plane.

The (Fig. 15) spot diagram shows

the dispersion effect for three wave-

lengths in I band. Attending to the

figure, blue and red wavelengths donot come in the Airy disc.The

(Fig.16) spot diagram presents the

incident rays of the system in the

focal plane once they have beencorrected. The ADC

otating them. The result is a good optics quality with aberrations under the diffraction circle soat they do not affect.

solves the problem by moving the prisms and

An atmospheric dispersion corrector placed in a collimated

beam offers advantages respect to the pre-focus

configuration. The most significant is the generality of this

system to be implemented in other instruments. The mainproblem is howto correct many collimated

beams every one with adifferent angle.The study of a tilting

system for the WHT which

has a small field results

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18g.17 Optical layout of tilting prisms in collimated beam.g.18 Correction of atmospheric dispersion equivalent to 45

grees of zenithal distance tilting only one prism.

s possible to optimize the aberration tilting the second one

ore o less appropriate but it shows lacks for greater fields.

prism, but the relatives movements are complicated for use with several values of Z.

AtmosphericDi s

persion

Corrector

The future of FastCam is foreseen to(Fig.19)working as a single instrumen

images from each 1.8m segment and

after to increase the deep in magnitu

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dered a multi-instrument dividing the

each one going to a individual FastC

(FASTCAM6, Fig.20) reaching more deep obtained in WHT. All of these c

have an ADC. Prefocus seems more

FastCam-6 but no for FastCam-Seg.

tCam is going to be integrated as common use instrument in 1.5m TCS in Teide Observatory. Given the space disposable, a classical double bi-prism will be implemented. We will develop the best combination

each the diffraction limit as normal use to V band.The designs have used available material from IAC lab, so that was a restriction. Also, we are working in the extension to infrared J, H and K bands. The detect

ectivity) is at moment most important constrain in this line, but we are going to try a system in next months. Any ADC will be necessary in this case, because IR bands do not show atmospheric dispersion at thscope.ADCs develop-ment are coming more and more important due to the increasing of the resolution required by new instruments what are in designing for the new generation of large telescopes. The know

erstanding of all type of correctors will be a necessary task in order to can obtain the best system for every instrument.

(10m)

0 0.5 1 1.5 2 2.5

x 104

0

1000

2000

3000

4000

5000

6000Image motionin prefocus ADC

Separation betweenprism (m)

Displacementofimagecentroid(m)

One inconvenience of this system is that moving

one prism the position of the centroid in the focal

plane also changes.This deviation has been mea-sured in lab.A f/11 imaging system is reproduced

(Fig.23) in order to get the measurement of image

displacement by one millimeter steps for a total

separation between prisms of 24 millimeters.Thesame has been done for ADC in collimated beam

(Fig.26).

Fig.24 Representation of displacement of image centroid against separa

prisms, both in m.Circles are experimental positions over a detector fo

values of separation between prisms. Line is the theoretical value for theBut it was needed to reduce slightly the angle of each prism in order to a

rimental data, verifying a 24.6 angle.

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Fig.25 Lab images. Dispersion sprism and obtained correction inc

between prisms of the ADC

For the design in

collimated beamthe prisms are

over 360 rotators

(Fig.27) and

displacement isdue to the angle.

Special thanks to: