Preliminary seeing data and isoplanatic angles in 2003-2004
| The fourth summer campaign
of the Concordiastro program is currently on process. Karim Agabi, Eric
Aristidi, Eric Fossat (LUAN, Univ. of Nice, France)
and Tony Travouillon (University of New South Wales, Sydney) are at Dome
C since November 13. Seeing measurements started earlier than last year,
with an average temperature 10° lower (see thermometer !). Thus the
conditions were closest to what can be expected in winter. |
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Concordiastro platform around the 20 November 2003, with two telescopes
Seeing Data
First
seeing time-series are very very good. Data are not fully processed yet,
but the raw seeing values obtained on the two first days (21 and 22 Nov)
shows stable seeing between 0.2 and 0.5 arcsec. These values are not corrected
for zenithal angle (the star Canopus has zenithal angle varying from 33°
to 63°). After the beginning of December, seeing statistics
seem comparable to what we obtained last year. Hereafter is a typical 24h
seeing profile taken on December 11th, 2003. It exhibits a minimum
in the mid-afternoon, when the temperature gradient near the surface is almost
zero.
Temporal autocorrelation of differential positions of the twin images at DIMM's focus have been computed. When the seeing is good (e.g. <0.5 arcsec), they show exponential decay near the origin whith time constant of the order of 1 second. This is the correlation time of the differential tilt. These large values might suggest large coherence time of the wavefront. Same processing when seeing is bad shows nothing at the scale of our temporal sampling (1 image each 13 ms).
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| Raw seeing curve on 21 Nov 2003 |
Raw seeing curve on 22 Nov 2003 |
Raw seeing curve on 11 Dec 2003 |
Daily averaged (raw) seeing |
Temporal correlations
Temporal autocorrelation of differential positions of the twin images at DIMM's focus have been computed. When the seeing is good (e.g. <0.5 arcsec), they show exponential decay near the origin whith time constant of the order of 1 second. This is the correlation time of the differential tilt. These large values might suggest large coherence time of the wavefront. Same processing when seeing is bad shows nothing at the scale of our temporal sampling (1 image each 13 ms).
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| Temporal autocorrelation of differential
positions of the star's image. This has been computed on one time-series
of 9600 short-exposure frames. Exposure time is 10ms. Seeing was 0.4 arcsec. |
Isoplanatic angle data
The
isoplanatic angle is measured through the stellar scintillation with a telescope
equipped with a special mask (circular aperture of 10 cm diameter, with
a central obstruction of 4cm). This mask has been built here and the measurements
begun on January 5th. Some data are presented in figure hereafter. The first
day, only a 30mn data set, but it was a first trial. The values are corrected
from exposure time and zenithal angle.
Large values were obtained so far, up to 16 arc sec and even more... For comparison Paranal is about 2 arc sec.
Large values were obtained so far, up to 16 arc sec and even more... For comparison Paranal is about 2 arc sec.
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| First values on 5 Jan 2004 |
Time series on 8 Jan 2004 |
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