LUCAS experiment: Observations of Earthshine in Antarctica

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LUCAS experimentObservations of Earthshine in
Antarctica

• Danielle BRIOT (Paris-Meudon Observatory)

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• Main collaborators
• Eric Aristidi (LUAN, Nice)
• Luc Arnold (Obs. Haute-Provence)
• Jérome Berthier (Obs.Paris-Meudon)
• Danielle Briot (Obs.Paris-Meudon)
• Eric Fossat (LUAN, Nice)
• Stéphane Jacquemoud (IPGP, Paris)
• Pierre Riaud (Obs. Paris-Meudon)
• Jean Schneider (Obs. Paris-Meudon)
• and the winterover observers in Antarctica
  Karim Agabi, Eric Aristidi, Erick Bondoux and
  Zalpha Challita.

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 Restrictions  of Earthshine observations

• As it is well known, at mean or low latitudes,
  Earthshine observations are are observations of
  twilight just after the sunset or just before
  the sunrise. So observations can only be made
  during a short time.
• And roughly speaking, for one telescope, only two
  enlighted parts of Earth can be facing the Moon
  
• either the part located at the West of the
  observing telescope for evening observations
  (begginning of the lunar cycle),
• or the part of Earth located at the East of the
  observing telescope for morning observations
  (last days of the lunar cycle).

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New perspectives

• However, there other possibilities.
• From an idea of Jean Schneider (2002), if
  observations are made from a site located at a
  high latitude, conditions of Earthshine
  observations are different.
• From six to eight times in a year, around
  equinoxes, Earthshine can be observed during
  several hours, and even in very high latitude
  places during a 24 hour duration (total
  nycthemere).
• During these long observing times, and due to the
  terrestrial rotation, several  landscapes 
  alternately face the Moon.
• Actually, Antarctica offers a very good
  opportunity for this kind of observations.

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The Concordia station

• The Concordia station is a French-Italian base
  for scientific research, among them astrophysics,
  located at Dome C in Antarctica.
• Latitude -7506 South
• Longitude 12323 East
• Altitude 3220 m on a plateau
• Mean temperature - 54C
• Lowest temperature - 81.9C

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The Concordia station

• Dome C is located (3220 m altitude) on
  sub-horizontal ice ground with no crevasses.
• There is no local fauna or flora.
• The distance is around 1100 km from the French
  base Dumont dUrville (Terre Adélie) and around
  1200 km from Terra Nova bay where is established
  the Italian station Mario Zucchelli, behind the
  Transantarctic mountain range.

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Dome C location
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Antarctic Continent
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Observational qualities of the Dome C site (1)

• The Dome C is a very good site for astronomy,
  maybe the best in the world.
• Many testing instruments have been operated
  during the last years, and specially during the
  last five years.
• It is an extremely clear site
• instrumentation has given lower limits of 74 -
  80 to the percentage of clear skies, and recent
  estimates put this number to a remarquable 96
  over a 5 month period.

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Observational qualities of the Dome C site (2)

• As well as having one of the lowest average wind
  speed ever recorded at an existing or potential
  observatory, Dome C also has an extremely stable
  upper atmosphere and a very low inversion layer.
• The atmosphere is divided in two regions (i) a
  36 m high surface layer responsible for 87 of
  turbulence and (ii) a very stable free atmosphere
  above with a median seeing of 0.360.19 arcsec at
  an elevation of h 30m.

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Preliminary observations at Concordia

• Checking the feasability of Earthshine
  observations considering the darkness of the sky
  was the first point. Is the sky enough dark to
  allow observations of Earthshine ?
• The first tests have been planned during the
  first winterover campaign in 2005, by Karim
  Agabi. However, bad weather conditions did not
  allow some conclusive observations.
• In 2006, photographic tests made by Eric Aristidi
  showed that Earthshine observations can be
  possible.

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• Then, we decide to make observations to observe
  Vegetation Red Edge and biomarkers during the
  southern winter of 2008.
• It was first necessary to collect some funds
•  and then to design and construct a special
  instrumentation for Earthshine spectroscopic
  observations in the extreme conditions
  corresponding to Concordia station.
• It was a rather tight schedule !

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LUCAS technology

• Special instrumentation for Earthshine
  observations
• The telescope is a Celestron 8
• Diametre 203 mm
• The spectrograph was designed by Luc Arnold and
  Pierre Riaud and built at the Haute-Provence
  Observatory.
• Grating 300t/mm
• CCD Camera Audine -
• Detector KAF 402 ME

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3D assembly diagram of LUCAS
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LUCAS instrumentation during testing at the
Haute-Provence Observatory
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LUCAS technology

• Acquisition and storage of observational data
  will be provided by a computer located in a
   igloo  at around twenty meters of the
  telescope.
• Testings carried out at the Haute-Provence
  observatory validated the instrumentation.
• The mean temperature being - 54C and the extreme
  temperature being - 81.9C, all the instruments
  (telescope, camera, spectrograph and all
  acquisition system) have been to be
   antarctised  that is to say specially adapted
  for very cold conditions.
• And Luc Arnold has written a very detailed
  handbook intented for winterover observers.

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Position of the slit on the lunar surface The
observing slit is to be positionned  first on
both the lighted crescent and the sky,  and
then on both the Earthshine and the sky.
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Example of conditions of astronomical
observations at the Concordia station
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• Before their departure, winterover observers made
  testing of observations at the Haute-Provence
  observatory.
• And the instrumentation was carried to the Dome
  C.
• Since the Haute-Provence Observatory (South of
  France) the way is
• Plouzané (Institut Paul Emile Victor, in the
  western part of France),
• Roissy (Paris airport),
•  Hong-Kong (China),
• Hobart (Australia),
•  Dumont-dUrville (Antarctica)
•  and finally attained the Concordia station at
  Dome C.

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Current situation

• The LUCAS instrumentation arrived at Concordia
  last week, on the 9th of January.
• And first observations are planned for the
  beginning of March 2008 (Southern autumn).
• We have to note that LUCAS takes place among the
  first  purely  astrophysical experiments at the
  Dome C site.

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General schedule

• January 2008 March 2008
• Conveying and installation of instruments at
  Concordia testing in real conditions.
• March 2008 September 2008
• First campaign of observations of Earthshine
  reception of data
• Preparation of the 2009 observation campaign
  buying of a new mounting conveying and
  installation at Concordia.
• October 2008 Décember 2009
• Analysis and interpretation of data first
  publications and communications in scientific
  meetings.
• Second campaign of Earthshine observations
  reception and analysis of data.