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Site testing at Dome C recent results
CONCORDIASTRO Project E. Aristidi, A. Agabi, E.
Fossat, T. Travouillon, M. Azouit, J. Vernin, A.
Ziad, F. Martin, Sadibekova T.
www-luan.unice.fr/Concordia
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South Pole 1979
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Main characteristics of the site
1. Altitude gt 3000 m 2. Slope lt 1/1000 3. Snow lt
5g/cm/year 4. Limit for auroras2 5. Limit of
visibility fo geostationary satelites
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Altitude level
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ConcordiAstro site testing 3 experiments
To obtain a complete astronomical qualification
of the site from the turbulence side
? Goal
DIMM/GSM Step 1 seeing Step 2 q0, L0, t0
Mast Monitor the ground layer Cn2
Balloons Step 1 PTU Step 2
Cn2
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Wind Speed Profiles
Altitude (Km)
Altitude (Km)
Altitude (Km)
Wind Speed Profiles at Paranal ESO Chili (1992)
Wind Speed Profiles at Gemini NOAO Chili (1998)
Wind Speed Profiles at Dome C (Dec 2000)
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Concordiastro 4 (1) summer campaigns
Who Stay Balloon Telescope
1995 J. Vernin 1 week 5 (1) 0
2000-01 A Agabi JM Clausse 1 week 6 (1) 0
2001-02 A Agabi J Dubourg 6 weeks 34 1
2002-03 A Agabi E Aristidi T. Travouillon 5 weeks 61 1
2003-04 A Agabi E Aristidi E Fossat T. Travouillon 3 months 96 2
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The experiments
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Estimating the seeing Differential Image Motion
Monitor
Glass prism

• Celestron 11 d28 cm, f 2.8 m, tube in
  INVAR
• 2 holes mask on pupil
• diam. D6 cm sep. B20 cm
• glass prism deviation30  arcsec
• CCD max sensitivity500 nm pixel size10
  microns
• thermostated at 20C

Overall cost 30 k
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DIMM Principle
The transverse (st2) and longitudinal (sl2)
variances of the spots position difference gives
two estimates of the seeing e.
Assuming Kolmogorov turbulence (infinite outer
scale), we have (Tokovinin, 2002, PASP 114, 1156)
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Estimating isoplanatic angle
Principle scintillation measurement with a
circular 10cm diameter pupil with 4 cm central
obstruction
Ziad et al., 2000, Appl. Opt. 39, 30
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Balloons
In-situ soundings to obtain the turbulent
energy profile Cn2(h)
(Borgnino et al., 1979, AA 79, 184)
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Inflating the Balloon
In winter
In summer
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Preparing the sond
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Launching the balloon
In winter
In summer
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Summer turbulence conditions
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November 2003 amazing days
Wow ! Excellent !
! Values not corrected from z and exposure time
(10 ms)
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Summer seeing statistics
(based on 2 summer campaigns)
0.54
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N data 31597 Std deviation 0.39
Mean seeing (arcsec) 0.66 Seeing max 5.22
Median seeing 0.54 Seeing min 0.08
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Seeing as function of time
Good seeing when surface layer temperature
gradient vanishes
No temp. gradient
Temp. Gradient (6/100m)
(Aristidi et al., AA 2005)

• Good news for solar astronomy
• seeing below 0.5 almost every day at tea time
  during 6h

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Isoplanatic angle statistics
N data 6328
Mean (arcsec) 6.8
Median 6.8
Std dev 2.4
Max 17.1
Min 0.7
6.8
6.8
Maidanak 2.47 Ziad et al. 2000
Oukaimeden 1.58 Ziad et al. 2000
South Pole 3.23 Marks et al. 1999
Paranal 1.91 Ziad et al. 2000
La Silla 1.25 Ziad et al. 2000
Pachon 2.71 Ziad et al. 2000
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Comparison with other sites
Site Seeing Isoplan. angle
Paranal 0.66 1.91
La Silla 0.87 1.25
Maidanak 0.70 2.47
South Pole 1.74 3.23
Dome C (summer) 0.54 6.8
The best site of the world ?
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Night seeing at Dome C

SODAR MASS Travouillon et al
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Towards the winter

• summer seeing 0.54 arcsec

• AASTINO results 0.27 arcsec in autumn

We were very confident for the winter !
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First winterover
10 Feb Deparure of the last plane
Karim Agabi The winter astronomer
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Remote-controlling (useful at 70C)
Data acquisition
Concordia labo
300 m
Wi-Fi LANFiber optics connection
To the mast (700 m)
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About the weather
36 days
74 days
Statistics 2005 about 85 2006
systematic, visual, measurements about 80 in
summer, 90 in April
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Autumn seeing
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Some vertical profiles
Everything is in the surface layer !
Seeing in altitude lt0.4 arcsec
Ground seeing gt1 arcsec
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How high is the surface layer ?
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Estimating turbulence parametersfrom balloon
Cn2(h) profiles
Cn2(h)
wind speed
h1

• Parameters can be computed from Cn2(h) and the
  wind profile v(h)
• Changing h1 compute parameters that would be
  observed at alt. h1

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Surface layer

• South Pole 220m

R.D. Marks, et al. 1999, AA

• Dome C 30m

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Optical/interferometric parameters
Integrated from h8m
Balloons (10) Dimms (March- May 05)
Seeing (arcs) 1.6 1.2
t0 (ms) 7.0
q0 (arcs) 5.3 3.6
Integrated from h 30m
s
AASTINO 2004 data
0.27
7.9
5.7
Balloons
Seeing (arcs) 0.4
t0 (ms) 11.2
q0 (arcs) 5.3
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Comparison with other sites
Site e q (arcs) t (ms) Lo(m)
La Silla 0.9 1.3 1.5 25
Paranal 0.9 1.9 3.0 24
Pachon 0.9 2.7 3.0 28
Maidanak 0.7 2.5 6.6 28
Mauna Kea 0.8 2.9 2.4 18
San Pedro 0.7 2 1.2 27
South Pole 1.9 3.2
Dome C (0) 1.6 5.3 7 10
Hgt 30m 0.4 5.3 11.2
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ECMWF (European Center for Medium range Weather
Forecast) http//www.ecmwf.int

• 60 pressure levels from surface 655mB to 0.1 mB
  
• 0h, 6h, 12h, 18h UT
• Parameters 
• pressure (mB),
• temperature (oC),
• relative humidity (),
• zonal et meridian wind speed projections (m/s)

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• Two types of sondes, RS80 and RS90 (more precise
  on the humidity and temperature parameters)
• Examples of the comparison between ECMWF analysis
  and balloons measurements
• RS80
• 
  ____
  balloons data
• 
  ____
  model
• 
  
• 
  
  RS90

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• Differences Model Data
• RS80 168 used balloons
• RS90 48 used balloons
• Temperature rms 1.5 - 3 ºC for RS80
• 1
  - 1.5 ºC for RS90
• Relative humidity rms 1 - 10 for RS80
• 
  1 - 2 for RS90
• Wind speed rms ? 1m/s at all altitudes
  (figure).
• Optical turbulence forecast ?
• Turbulence temperature gradient wind
• Turbulence above Dome C can be produced mostly
  at
• Tropause
• Ground layer

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Tropause (4-6km
above ground) - In summer inversion
of the temperature gradient -
No tropopause in winter!!!
Average monthly wind speed (m/s) at  
  200mB     250mB    
 300mB_________________________________________
January   6.57     8.15       9.91
February   10.26   14.18     15.89 March    
  9.39   10.88     12.21 April       10.47
  10.94     12.01 May         12.60   12.95  
  13.54 June       12.93   13.93     14.21
July       12.94   13.45     13.68 August    
17.56   17.84     16.70 September   12.69  
13.64     13.56 October   10.85   10.65    
10.76 November   12.08   13.46     14.89
December     6.40     8.66   11.21
- The Coherence time of the wavefront is defined
by (Roddier, 1981)
?o 1/Vo where Vo is velocity of
the turbulence - And SarazinTokovin (2001)
proposed an expression for Vo which related to
metrological variables only
Vo Max(0.4V200Mb)
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Atmospheric turbulence modelH. Gallee, M. Swain

• Instantaneous (snap shot) profiles show strong
  and fast boundary layer seeing nearly always
  present over Antarctic ice sheets.
• Models predicts large improvement in seeing and
  coherence time above boundary layer.
• Model predicts Dome C has 1.16 average seeing at
  8 m elevation.
• Dome C boundary layer most probable elevation is
  22 m.
• Good agreement between model and observations for
  elevations below 1000 m.

For best results, place telescope above blue line
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Auroras
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Instruments for the next winter
2006 - 2007
Increase the statistics over more than one year

• SSS
• Photometer (v)
• MOSP
• DIMM
• GSM
• Pistonscope
• Mast

q0, t0, e
Cn²(z), V(z)
Extinction coefficient
Cn²(z), L0(z)
e
L0, t0, e
sopd, qopd
Cn²(hi), up to 40m
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Future instruments

• AIRBUS (Near IR sky brightness)
• IRAIT (80 cm IR telescope, general user)
• A-STEP (40 cm telescope 30x30 photometer)
• ICE-T (2x80 cm wide-field photometer)
• MYKERINOS (Prototype interferometer 3x40 cm)

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Observability