南極サイト調査用DIMM(シーイング測定装置)の開発と

Making and Observation
of the Tohoku Univ.
Antarctica DIMM
Hirofumi OKITA
Astronomical Institute
Tohoku Univ. (B4)
May 31 2008 Prasentation
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Contents
・Introduction
・DIMM
・Theory
・Tohoku DIMM
・Observation
・Result
・Future work
Antarctica 40cm Telescope with the DIMM
May 31 2008 Prasentation
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Introduction (1)
→The Seeing is defined as FWHM of stars at long time exposure.
In Space, star’s FWHM is “Rayleigh limit”.
Rayleigh Actually
limit
seeing
Subaru
Telescope
0.06"
0.3"
But…
The case of the grand base observation, wavefront from the
star is not parallel.
So the star size is not “Rayleigh limit”, but expanded image by
the air turbulence.
→It is important to choice Good Seeing Site.
May 31 2008 Prasentation
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Introduction (2)
Antarctica
Cord
→
Dry
The last window to the Universe
IR Background is very low, and NIR transimittance is very high
Calm weather
Downdraft
→
Many fine days
Good seeing
Dome C（Alt.3250m）～0.54”
Dome Fuji（Alt.3810m） ≦0.5” ??
However, the site testing at Dome Fuji has
not been done yet.
I made the DIMM, and want to get
actually seeing size.
May 31 2008 Prasentation
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http://en.wikipedia.org/wiki/Showa_Base
DIMM
“Classical” DIMM(Differential Image Motiron Monitor) has 2 apature.
Star light
↓
The phase shifts by air turbulence
↓
DIMM
↓
Image of two stars
↓
Measurement of relative position
↓
Convert them into seeing value
May 31 2008 Prasentation
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Theory (1)
Star light at Space・・・Parallel
↓
Air turbulence・・・wavefront
・・・phase error
Angle of arrival fluctuation・・・
・・・Covariance of α
・・・Covariance of φ
・・・Phas structure function
Kolmogorov turbulence →
May 31 2008 Prasentation
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Theory (2)
Change the angle of arrival
fluctuation
= Change in position of
stars
Relationship between
and FWHM
Zenith angle correction・・・
It calculates…
D・・・Aperture Diameter
d・・・separation two aperture
May 31 2008 Prasentation
→From
We obtain Seeing size.
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DIMM Hardware
Unlike a “classical” DIMM,
Tohoku DIMM is “Four aperture DIMM”
to get more information of a turbulence layer.
Antarctica 40cm Telescope
Aperture
400mm
Focal length
5190mm
DIMM
Wat-100N (Watec Co., Ltd.)
Min. 0.001 lx, and
Exp. time/gain/gamma
Manually changeable
Expose time: 1/1000s
May 31 2008 Prasentation
Separation of
diagonal apertures d
250[mm]
Aperture diameter D
74mm[mm]
Apex angle of Wedge
prism
30[arcsec]
Pixel size
Horizontal
0.3903[arcsec/pix]
Vertical
0.4553[arcsec/pix]
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DIMM Software
Software was Developed by Dr. Motohara ( Research
Associate, University of Tokyo)
Dr.Motohara and UT-DIMM
His Software
From His software we can get analyzed data
(seeing size [arcsec]) but zenith angle is not
corrected, so I made zenith angle correction
software.
May 31 2008 Prasentation
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Observation
Jan 13 2008 Measurement of Pixel size
Jan 16 2008 Observation at Sendai
Feb 10 2008 Observation at Rikubetsu ( Hokkaido, the North island
of Japan)
Feb 14 2008 Observation at Rikubetsu
Movies
Star
Saturn
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Result (1)
Jan 16 2008 Observation at Sendai
Sendai
Average 2.09”
Median 2.03”
May 31 2008 Prasentation
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Result (2)
Feb 10 2008 Observation at Rikubetsu
Rikubetsu
Average 1.49”
Median 1.48”
May 31 2008 Prasentation
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Result (3)
Feb 16 2008 Observation at Rikubetsu
Rikubetsu
Average 2.81”
Median 2.79”
May 31 2008 Prasentation
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Future Work
More Observation
change in a day
change in a season
Comparison with Hiroshima Univ. DIMM
Check the Value is reasonable
Cold Test
Camera
AD converter
PC ,etc.
Hiroshima Univ. DIMM
We observe more and more at Sendai,
and get knowhow and technique.
↓
2010 Observation at Dome Fuji
May 31 2008 Prasentation
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