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        Information from the European Southern Observatory

ESO Press Release 06/03

27 March 2003

For immediate release
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"First Light" for HARPS at La Silla

Part 1 of 2

Advanced Planet-Hunting Spectrograph Passes First Tests With Flying
Colours

Summary

The initial commissioning period of the new HARPS spectrograph (High
Accuracy Radial Velocity Planet Searcher) of the 3.6-m telescope at
the ESO La Silla Observatory has been successfully accomplished in
the period February 11 - 27, 2003.

This new instrument is optimized to detect planets in orbit around
other stars ("exoplanets") by means of accurate (radial) velocity
measurements with an unequalled precision of 1 meter per second. This
high sensitivity makes it possible to detect variations in the motion
of a star at this level, caused by the gravitational pull of one or
more orbiting planets, even relatively small ones.

"First Light" occurred on February 11, 2003, during the first night
of tests. The instrument worked flawlessly and was fine-tuned during
subsequent nights, achieving the predicted performance already during
this first test run.

The measurement of accurate stellar radial velocities is a very
efficient way to search for planets around other stars. More than one
hundred extrasolar planets have so far been detected, providing an
increasingly clear picture of a great diversity of exoplanetary
systems.

However, current technical limitations have so far prevented the
discovery around solar-type stars of exoplanets that are much less
massive than Saturn, the second-largest planet in the solar system.
HARPS will break through this barrier and will carry this fundamental
exploration towards detection of exoplanets with masses like Uranus
and Neptune. 

Moreover, in the case of low-mass stars - like Proxima Centauri, cf.
ESO PR 05/03 - HARPS will have the unique capability to detect big
"telluric" planets with only a few times the mass of the Earth.

The HARPS instrument is being offered to the research community in
the ESO member countries, already from October 2003.

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The HARPS Spectrograph

ESO PR Photo 08a/03

ESO PR Photo 08b/03

Captions: PR Photo 08a/03 and PR Photo 08b/03 show the HARPS
spectrograph during laboratory tests. The vacuum tank is open so that
some of the high-precision components inside can be seen. On PR Photo
08a/03, the large optical grating by which the incoming stellar light
is dispersed is visible on the top of the bench; it measures 200 x
800 mm. 


HARPS is a unique fiber-fed "echelle" spectrograph able to record at
once the visible range of a stellar spectrum (wavelengths from 380 -
690 nm) with very high spectral resolving power (better than
R =3D 100,000). Any light losses inside the instrument caused by
reflections of the starlight in the various optical components
(mirrors and gratings), have been minimised and HARPS therefore works
very efficiently.
 
First observations

ESO PR Photo 08c/03

ESO PR Photo 08d/03

Captions: PR Photo 08c/03 displays a HARPS untreated ("raw") exposure
of the star HD100623, of the comparatively cool stellar spectral type
K0V. The frame shows the complete image as recorded with the 4000 x
4000 pixel CCD detector in the focal plane of the spectrograph. The
horizontal white lines correspond to the stellar spectrum, divided
into 70 adjacent spectral bands which together cover the entire
visible wavelength range from 380 to 690 nm. Some of the stellar
absorption lines are seen as dark horizontal features; they are the
spectral signatures of various chemical elements in the star's upper
layers ("atmosphere"). Bright emission lines from the heavy element
thorium are visible between the bands - they are exposed by a lamp in
the spectrograph to calibrate the wavelengths. This allows measuring
any instrumental drift, thereby guaranteeing the exceedingly high
precision that qualifies HARPS. PR Photo 08d/03 displays a small part
of the spectrum of the star HD100623 following on-line data
extraction (in astronomical terminology: "reduction") of the previous
raw frame, shown in PR Photo 08c/03. Several deep absorption lines
are clearly visible. 


During the first commissioning period in February 2003, the high
efficiency of HARPS was clearly demonstrated by observations of a
G6V-type star of magnitude 8. This star is similar to, but slightly
less heavy than our Sun and about 5 times fainter than the faintest
stars visible with the unaided eye. During an exposure lasting only
one minute, a signal-to-noise ratio (S/N) of 45 per pixel was
achieved - this allows to determine the star's radial velocity with
an uncertainty of only ~1 m/s!. For comparison, the velocity of a
briskly walking person is about 2 m/s. A main performance goal of the
HARPS instrument has therefore been reached, already at this early
moment.

This result also demonstrates an impressive gain in efficiency of no
less than about 75 times as compared to that achievable with its
predecessor CORALIE. That instrument has been operating very
successfully at the 1.2-m Swiss Leonard Euler telescope at La Silla
and has discovered several exoplanets during the past years, see for
instance ESO Press Releases (PR 18/98, PR 13/00 and PR 07/01). In
practice, this means that this new planet searcher at La Silla can
now investigate many more stars in a given observing time and
consequently with much increased probability for success. 

Extraordinary stability

ESO PR Photo 08e/03

Caption: PR Photo 08e/03 is a powerful demonstration of the
extraordinary stability of the HARPS spectrograph. It plots the
instrumentally induced velocity change, as measured during one night
(9 consecutive hours) in the commissioning period. The drift of the
instrument is determined by computing the exact position of the
Thorium emission lines. As can be seen, the drift is of the order of
1 m/s during 9 hours and is measured with an accuracy of only 20
cm/s.

 - Continued -

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