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Max Planck Institute for Astronomy - Annual Report 2005

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102 IV. Instrumental Development<br />

IV.6 Differential Delay Lines <strong>for</strong> Prima<br />

Within a few years, the high-precision astrometric facility<br />

Prima (Phase Referenced Imaging and Microarcsecond<br />

Astrometry) will be available at the Very Large<br />

Telescope Interferometer (VLTI) of the European Southern<br />

Observatory.<br />

PriMa will be equipped with Differential Delay Lines<br />

(DDL), in order to per<strong>for</strong>m high-precision astrometry<br />

at the 10 microarcsecond level. This precision enables<br />

the detection of extrasolar planets using the astrometric<br />

method, which is complementary to the radial velocity<br />

technique. In particular, the precise astrometry method<br />

can be used to search <strong>for</strong> planets around stars which are<br />

not suitable <strong>for</strong> the radial-velocity planet search programs.<br />

Astrometry allows a characterization of extrasolar<br />

planetary systems, because the mass of the planets can be<br />

determined by this technique.<br />

During the astrometric observations with PriMa, two<br />

stars will be observed simultaneously in a larger field of<br />

view (1 arc minute in diameter). If one of the stars is used<br />

as a reference, perturbations caused by atmospheric turbulence<br />

can be compensated <strong>for</strong> the other object in real<br />

time, leading to an increase in angular resolution and to<br />

a higher sensitivity.<br />

The MPIA Heidelberg, Geneva Observatory and<br />

Leiden Observatory are cooperating in a consortium that<br />

has agreed with Eso to build and deliver the Differential<br />

Delay Lines <strong>for</strong> PriMa, and then to carry out an astro-<br />

Fig. IV.6.1: Result of a Finite Element Analysis of the de<strong>for</strong>mation<br />

by gravity <strong>for</strong>ces and <strong>for</strong>ces by the magnetic mount. The<br />

maximum de<strong>for</strong>mation is 149 nm (red).<br />

0.149<br />

0.132<br />

0.116<br />

0.099<br />

0.083<br />

0.066<br />

0.050<br />

0.033<br />

0.017<br />

0<br />

Total de<strong>for</strong>mation [�m]<br />

x<br />

10 cm<br />

y<br />

z<br />

Fig. IV.6.2: Optics of PRIMA DDL on a kinematic mount and<br />

subplates <strong>for</strong> adjustment.<br />

metric planet search program at the VLTI with the auxiliary<br />

telescopes in the near-infrared K-band.<br />

In the DDL project, the MPIA is primarily involved in<br />

the development of a high-precision, movable cat's eye<br />

telescope with an aperture of 20 cm driven by a linear<br />

motion mechanism and placed in a vacuum, the delay<br />

lines will compensate optical path differences of up to<br />

12 cm with nanometer accuracy, corresponding to an<br />

accuracy of one part in 10 8 .<br />

In addition to this instrumentation project, the MPIA<br />

is also participating in the development of the astrometric<br />

operation software (AOS) and scientific preparatory<br />

programs <strong>for</strong> the astrometric observations. The MPIA is<br />

the leading partner in the preparatory observations <strong>for</strong> the<br />

planet search project with PriMa.<br />

The PriMa-DDL and AOS projects have successfully<br />

passed the preliminary design review, which was held at<br />

Eso Garching in June <strong>2005</strong>. The final design review is<br />

<strong>for</strong>eseen <strong>for</strong> July 2006.<br />

(Harald Baumeister, Peter Bizenberger,<br />

Uwe Graser, Thomas Henning (Co-PI),<br />

Ralf Launhardt (Project Scientist,<br />

PM Optomechanics),<br />

Ralf-Rainer Rohloff,<br />

Johny Setiawan, Karl Wagner.<br />

Partners: Observatoire de Geneve,<br />

Sterrewacht Leiden)

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