Max Planck Institute for Astronomy - Annual Report 2005
Max Planck Institute for Astronomy - Annual Report 2005
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)