DOT tomography of the solar atmosphereLeenaarts, J. and Wedenmeyer-Böhm, S. 2005 A&A 431, 681

Comments on the optimization of high resolution Fabry-Pérot filtergraphsSharmer, G. B. 2006 A&A 447, 1111

Speaker: S. KamioSolar Seminar 2006.02.27

Dutch open telescope

• 45cm diameter with open design• High resolution (0.2") image by Speckle reconstruction• Ongoing projects

BBSO/NST(1.6m), GREGOR(1.5m), ATST(4m), DOT++(1.4m)

G-band image

• bright points in the intergranular lanesmagnetic flux

Movies available at http://dot.astro.uu.nl/(79" x 63")

Reversed granulation

dark intergranular-lane (G-band) bright cell-boundary (Ca II H)

Simulations

• CO5BOLD code(Wedenmeyer 2003)radiation + hydrodynamicsnon-magnetic

• 140x140x200 grids• Synthesize Ca II H spectra

with SPANSAT(396.0-396.8nm)

• blue continuum (396.0nm)in stead of G-band

5600km

5600km1400km

1710km

photosphere

Results

• simulation reproducesactual contrast

• Not all dark intergranular lanes show bright in Ca II H

blue continuum Ca II H core

Obs

Calc

Calc + smear

Brightness distribution

• solid curves are derived from simulations.

• solid curve 2 (smear with realistic Airy function) is close to the observation

Fourior analysis

• Phase differenceG-band -- Ca II H

• Power spectrain good agreement

Obs

Simulation

Conclusions

• High resolution G-band and Ca II H images were obtained with DOT

• Results of non-magnetic hydrodynamics simulations agree well with observations

• Reversed granulation (i.e. dark intergranular lane and Ca II H brightening) can be explained by non-magnetic process

Fabry-Pérot interferometer (FPI)

• Basic parametersReflectivity: R and cavity distance: d

• Benefithigh transmission, rapid tuning, no-polarization,spectral resolution 2x105

• ShortcomingsTelecentric optics, wings of transmission profile

R

/

FPI systems

• VTT/TESOS (Kentischer et al. 1998)Triple FPI

• THEMIS/IPM (Cavallini 1998)UBF + FPI

• THEMIS/IBS (Cavallini et al. 2003)dual FPI

• IMAX/SUNRISE (Martinez-Pillet 2004)• ATST ?

Calculation

• 2 FPI system

• Parameters: d1, d2, R1, and R2

• Estimate parasitic light, ghost intensity, and FWHM

• Cavity error < 2 nm

d1 d2

R1 R2

Paracitic light level

R=83%

R=89%

R=94%

Results

• Item

Conclusion

• Cavity ratio has a significant impact on FPI system performance

• Homogeneity can be achieved by lowering reflectivity of small cavity FPI

• Optimal setupLow resolution & low reflectivity +high resolution & high reflectivity (cavity ratio 0.3-0.4)

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