INAF­ Osservatorio Astrofisico di Arcetri
Firenze, Italy
First Results from IBIS: Photospheric and Chromospheric
Structure and Dynamics
Katja Janßen
Gianna Cauzzi, Ambretta Falchi
JENAM­ Conference
The many scales in the universe
13. September 2004
Data Characteristics
Investigated Line: Fe I 7090 Å
The data consists of 2­dim Spectrograms (80'
'
diameter), scanned in wavelengths (with a stepwidths of 26 mÅ) => Datacube with two spatial and one spectral axis
The FPIs are mounted in collimated beam:
=> Blueshift of wavelength over the FOV (max. 60 mÅ, at imagerim) Complete dataset shows a timeseries of 30 min (with 30 s interval)
Photo of IBIS at the Dunn Solar Telescope, two big boxes contain the FPIs, between them the filterwheel is seen.
Data Reduction
We do:
Cut imagesize to 50'
'
x 50'
'
Bin by a factor of 2 => Pixelsize: 0.16'
'
This is done to speed up the calculations.
Flatfield and Dark correction The flatfield scan contains the spectral line as the data. This spectral information has to be deleted, in order not to cancel the line in the data with the flatfielding. This is done by dividing the flatfield scan by an average flatfield profile (adding up the blueshift­corrected profiles), for each pixel shifted to the wavelengths of its original profile. Image Motion Images in one scan are correlated and shifted in x,y. For each wavelength position also the blueshift map is shifted and saved. Blueshift of Wavelength
The correction of the wavelength shifts is not applied directly, in order to avoid interpolations. Instead the blueshift is taken care of with the velocity calculations. Data Reduction
We get:
Continuum Images
Center of Gravity Velocities
Bisector Velocities
Line Core Velocities
FWHM of the Line
To the timeseries we apply:
Image Tracking Correlation of scans
p­mode Filter
Masks
Segmentation Algorithms
Granular mask: A variable threshold in a box of 1.8'
'
square locates granules
=> “locally high mountains”
Intergranular mask: Skeleton, that finds midpoints between granules, enlarges these lines with darker points, again finds midpoints... (Berrilli,1998)
=> “valleys between mountains”
Turbulence
FWHM of 7090.4 Å line
granules and intergranules are clearly distinguished
=> masks do good job slightly bigger FWHM in intergranules => higher turbulence in intergranules, as they are even colder than granules (confirms e.g. Puschmann 2003)
Turbulence
Unfiltered and P­mode filtered FWHMs
=> influence of oscillations?
Bisectors
Bisector Velocities
Seperated for Granules and Intergranules
Filtered for 5­min oscillations
=> Same kind of shape for
granular and intergranular bisectors.
(unlike Hanslmeier 2000)
Slightly straighter bisector
over intergranules.
(like Maltagliati 2000)
Still, small patches of bisectors show a broad variety of shapes.
Future
Outlook:
First polarimeter tests with IBIS in October 2004 Investigation of turbulence at granule borders
Tracking of bisectors from center to border of granules Comparison of line parameters with simulations
Thanks
for listening!
Katja Janßen is a member of the European Solar Magnetism Network (ESMN) supported by the EC through the RTN programme.
Unfiltered Bisectors
Bisector Velocities
Granules and Intergranules
Not Filtered for
5­min oscillations
Cores
Core Velocity in 7090.4 Å line
Filtered for p­modes