Title: Pr
1Site 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
2South Pole 1979
3Main 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
4Altitude level
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10ConcordiAstro 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
11Wind 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)
12Concordiastro 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
13The experiments
14Estimating 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
15DIMM 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)
16Estimating isoplanatic angle
Principle scintillation measurement with a
circular 10cm diameter pupil with 4 cm central
obstruction
Ziad et al., 2000, Appl. Opt. 39, 30
17Balloons
In-situ soundings to obtain the turbulent
energy profile Cn2(h)
(Borgnino et al., 1979, AA 79, 184)
18Inflating the Balloon
In winter
In summer
19Preparing the sond
20Launching the balloon
In winter
In summer
21Summer turbulence conditions
22November 2003 amazing days
Wow ! Excellent !
! Values not corrected from z and exposure time
(10 ms)
23Summer seeing statistics
(based on 2 summer campaigns)
0.54
3
N data 31597 Std deviation 0.39
Mean seeing (arcsec) 0.66 Seeing max 5.22
Median seeing 0.54 Seeing min 0.08
24Seeing 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
25Isoplanatic 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
26Comparison 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 ?
27Night seeing at Dome C
SODAR MASS Travouillon et al
28Towards the winter
- summer seeing 0.54 arcsec
- AASTINO results 0.27 arcsec in autumn
We were very confident for the winter !
29First winterover
10 Feb Deparure of the last plane
Karim Agabi The winter astronomer
30Remote-controlling (useful at 70C)
Data acquisition
Concordia labo
300 m
Wi-Fi LANFiber optics connection
To the mast (700 m)
31About the weather
36 days
74 days
Statistics 2005 about 85 2006
systematic, visual, measurements about 80 in
summer, 90 in April
32Autumn seeing
33Some vertical profiles
Everything is in the surface layer !
Seeing in altitude lt0.4 arcsec
Ground seeing gt1 arcsec
34How high is the surface layer ?
35Estimating 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
36Surface layer
R.D. Marks, et al. 1999, AA
37Optical/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
38Comparison 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
39ECMWF (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)
40- 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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43- 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
44 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)
45Atmospheric 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
46Auroras
47Instruments 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
48Future 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)
-
49Observability