May 31 2008 Prasentation 1

Making and Observationof the Tohoku Univ. Antarctica DIMM

Hirofumi OKITA Astronomical Institute

Tohoku Univ. (B4)

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Contents・ Introduction・ DIMM・ Theory・ Tohoku DIMM・ Observation・ Result・ Future work

Antarctica 40cm Telescope with the DIMM

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The case of the grand base observation, wavefront from the star is not parallel.

→It is important to choice Good Seeing Site.

Introduction (1)→The Seeing is defined as FWHM of stars at long time exposure.

In Space, star’s FWHM is “Rayleigh limit”.

So the star size is not “Rayleigh limit”, but expanded image by the air turbulence.

But…

Rayleigh limit

Actuallyseeing

Subaru Telescope

0.06"

0.3"

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Antarctica

Introduction (2) 　

Cord

DryIR Background is very low, and NIR transimittance is very high

Many fine daysGood seeing

Calm weatherDowndraft

Dome C（ Alt.3250m）　　～ 0.54”

The last window to the Universe

→

→

Dome Fuji（ Alt.3810m）　≦ 0.5” ??

http://en.wikipedia.org/wiki/Showa_Base

However, the site testing at Dome Fuji has not been done yet.

I made the DIMM, and want to get actually seeing size.

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DIMM

Convert them into seeing value

“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

↓

↓

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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 　→

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Theory (2)Change the angle of arrival fluctuation　　 = Change in position of stars

Relationship between

Zenith angle correction・・・

It calculates…

D・・・ Aperture Diameterd・・・ separation two aperture

→From We obtain Seeing size. 　　　　　

and FWHM

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DIMM HardwareUnlike 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 　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]

Wat-100N (Watec Co., Ltd.)Min. 0.001 lx, and Exp. time/gain/gammaManually changeable

Expose time: 1/1000s

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DIMM SoftwareSoftware was Developed by Dr. Motohara ( Research Associate, University of Tokyo)

Dr.Motohara and UT-DIMM

His SoftwareFrom His software we can get analyzed data (seeing size [arcsec]) but zenith angle is not corrected, so I made zenith angle correction software.

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ObservationJan 13 2008 Measurement of Pixel sizeJan 16 2008 Observation at SendaiFeb 10 2008 Observation at Rikubetsu ( Hokkaido, the North island of Japan) Feb 14 2008 Observation at Rikubetsu

Star

Saturn

Movies

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Result (1)

Sendai

Jan 16 2008 Observation at Sendai

Average 2.09”Median 2.03”

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Result (2)

Rikubetsu

Feb 10 2008 Observation at Rikubetsu

Average 1.49”Median 1.48”

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Result (3)

Rikubetsu

Feb 16 2008 Observation at Rikubetsu

Average 2.81”Median 2.79”

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Future Work

More Observationchange in a day change in a season

Comparison with Hiroshima Univ. DIMMCheck the Value is reasonable

Cold TestCameraAD converterPC ,etc.

We observe more and more at Sendai,and get knowhow and technique.

2010 　 Observation at Dome Fuji

Hiroshima Univ. DIMM

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