Static and dynamic measurements of the altitude of solar structures with the Secchi telescopes of STEREO-A and STEREO-B SOHO 20 Gent august 27, 31: 2007 Caltech November, Guy ARTZNER Institut d’Astrophysique Spatiale Bâtiment 121 F Orsay ftp://ftp.ias.u-psud.fr/gartzner/ftp_projet/SECCHI UMR8617 CNRS - Université Paris XI Orsay The STEREO/SECCHI data used here are produced by an international consortium of the Naval Research Laboratory (USA), Lockheed Martin Solar and Astrophysics Lab (USA), NASA Goddard Space Flight Center (USA) Rutherford Appleton Laboratory (UK), University of Birmingham (UK), Max-Planck-Institut für Sonnensystemforschung(Germany), Centre Spatiale de Liege (Belgium), Institut d'Optique Théorique et Appliqueé (France), Institut d'Astrophysique Spatiale (France). The USA institutions were funded by NASA; the UK institutions by Particle Physics and Astronomy Research Council (PPARC); the German institutions by Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR); the Belgian institutions by Belgian Science Policy Office; the French institutions by Centre National d’Etudes Spatiales (CNES) and the Centre National de la Recherche Scientifique (CNRS). The NRL effort was also supported by the USAF Space Test Program and the Office of Naval Research.

a1 July,15, h 36m STEREO_A 1320x1320 from 2048x2048 compression factor: 27

a2 July,15, h 36m STEREO_B 1320x1320 subset from 2048x2048 original image; compression factor: 27.

b Map of the X component of the homologous points vector between A and B; -5 to pixels calibration scale; 7x7 correlation window,5x15 exploration zone; The correlation is performed for one point out of two points on each axis, using the MEDICIS program available at CNES.

c a cut in the preceding slide

d Map of the X component of the homologous points vector between A and B, after substraction of a spherical model for the solar surface; -5 to + 5 pixels calibration scale;

e Map of the X component of the homologous points vector between A and B, after substraction of a spherical model for the solar surface and averaging over 18 STEREO pairs from 0h06mn to 02h56mn +1,5 to +2,5 pixels calibration scale

f a cut in the preceding slide

Precision of geometrical altitude measurements : results When comparing the original STEREO-A and STEREO-B images, a1 and a2, with the raw altitudes map b, we note that the filamentary structures do somehow appear in the altitude map, whereas the bright regions do not appear. The raw altitudes are measured towards the observer, with respect to the plane firstly perpendicular to the line of sight of STEREO-A and secondly going throuh the Sun’s center. Substracting from the raw altitudes a spherical model of the solar surfaces indicates more clearly, map d, the altitudes of filament structures. Averaging over 18 pairs from 0h 06m to 02h 56m helps in order to lower the noise arising from the fact that the data suffer from a high (27) compression factor. This is the reason why the range of the calibration scale of map e amounts to a quantity, 1 pixel, small with respect to the range, 200 pixels, of the raw measurements. The depth of the central shallow structure appearing in dark blue color in map e amounts to 0.3 pixel, according to the cut f. It appears that these shallow structures, « dimples on the Sun», observed on July, 14 and July, 15, match the active regions of views a1 and a2 and follow the solar rotation. We feel that further investigations are needed in order to be sure that the observed active regions are located below the average solar surface. If this is actually the case, the estimated depth is of the order of km (solar radius) x 0.3 pixel (slide f )/200 pixel (slide c )= thousand kilometers

Temporal evolution of measured altitudes : sanity checks Slides g to l relate to a two-days sequence of 4094 stereo pairs on May 9 and 10, 2007, at a 40 time seconds cadence. The global solar convexity effect on the X residuals amounts to 80 pixels. We measure the time evolution of the average residual X shift between homologous points on STEREO-A and STEREO-B. When considering quiet, filament free areas, we note a good stability of measurements on view h. The rms value amounts to a few 10**-3 pixel. The general shape of the X residuals, view g, is somehow distorded, despite adjustments of the three parameters A to B enlargment, A roll and B roll, in order to match the A and B images. As the asymetry of view g is clearly observers’s dependent, we have to investigate further parameters, differential distorsion between Secchi-A and Secchi-b telescopes or some flaw in images processing, in order to reduce the size of this asymetry. By contrast the model for the Y residuals is easily handled as these residuals are identically equal to zero if we neglect the small perspective effect arising from the different distances of STEREO-A and B to the Sun. The alignment between A and B images is adjusted by translations amounting to an integer number of pixels, in order to avoid interpolation problems already present in the rotations needed in order to compensate for the roll angle between the X axis of each image and the line between the two spacecrafts. We understand that the fact that the average values for quiet, filament free zones in the next slides have a value different from zero arise from the fact that the images are aligned within half a pixel. We estimate that the average values for two different zones in the same time sequence have a small (0.001 to.01 pixel) but significant value, arise from the interpolations performed..

Temporal evolution of measured altitudes : results from X measurements We compare on the west end of a filament and on a neighbouring quiet filament-free zone the time evolution of the average X residual, view i. We note that: - the altitude of the reference zone remains stable, at a constant height with respect to the global reference obtained on the whole hemisphere; we attribute to minor imperfections of the measurements the fact that this constant height is not equal to zero; - the altitude of the filament zone is higher than the altitude of the reference zone; - the altitude of the considered zone of the filament has a pronounced time evolution, especially around and seconds from the beginning of the sequence. With a 40 seconds cadence, we observe 1000s to 3000s intervals between consecutive peaks. We obtain similar results on another filamentary zone, view k.

Temporal evolution of measured altitudes : results from Y measurements : We compare on the west end of a filament and on a neighbouring quiet filament-free zone the time evolution of the average Y residual, view j. When comparing X and Y measurements, view i and j, we note that the results are anticorrelated. This is due to the fact that the observed zone is situated below the symetry plane containing the center of the Sun, STEREO-A and STEREO-B. When performing the same measurements closer to this symetry plane, we obtain a lower anticorrelation between views k and l. We presently do further investigations in order to possibly obtain similar altitude measurements immediatly before the disappearance of a filament.

g One of 4094 X residuals maps obtained at 40seconds cadence on may 9-10, to +5 pixels range of the calibration scale; 80 pixel range for the raw X displacments.

h y axis (pixels): average X residuals from two small 50x20 quiet filament free zones, lower left corners [420,200,] et [420,150] x axis: 0 to seconds (May 9, 2007, 0h 06m to 10h 44m)

i y axis (pixels): average X residuals from two small 50x20 zones, west end of a filament and reference zone, lower left corners [420,200] et [420,180] x axis: 0 to seconds (May 9, 2007, 0h 06m to 10h 44m)

j y axis (pixels): average Y residuals from two small 50x20 zones, west end of a filament and reference zone, lower left corners [420,200] et [420,180] x axis: 0 to seconds (May 9, 2007, 0h 06m to 10h 44m ?)

k y axis (pixels): average X residuals from two small 50x30 zones, center of a filament and reference zone, lower left corners [520,260] and [420,260]. x axis: 0 to seconds (May 9, 2007, 0h 06m to 10h 44m )

l y axis (pixels): average Y residuals from two small 50x30 zones, center of a filament and reference zone, lower left corners [520,260] and [420,260]. x axis: 0 to seconds (May 9, 2007, 0h 06m to 10h 44m )

October 6, 2007 STEREO- A EUVI 304A intensity scale [100,20000]

October 6, 2007 STEREO -B EUVI 304A intensity scale [100,20000]

October 6, A 5 parameters automatic adjustement with StereoPhotoMaker Most of the field of view behind the window; circular ring in the window; central disk in front of the window.

October 6, A 5 parameters automatic adjustement with StereoPhotoMaker « upper » part of the circular ring located in the window.

STEREO-A + STEREO-B mapped to STEREO-A = flat view

STEREO-A + STEREO-B mapped to STEREO-A = flat view: filamentary structure (North)

STEREO-A + STEREO-B mapped to STEREO-A = flat view: filamentary structure (South)

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of view for structure #1in the map of the X residuals

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of view for reference structure #1in the map of the X residuals

October 6,2007: STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular field of view #1 abscissa: seconds ordinates: EUVI pixels.02 pixel full scale vs.01

October 6,2007 STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular reference field of view #1 abscissa: seconds ordinates: EUVI pixels.01 pixel full scale (vs.02)

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of viewfor structure #2 in the map of the X residuals

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of view for reference structure #2 in the map of the X residuals

October 6, 2007 STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular field of view #2 abscissa: seconds ordinates: EUVI pixels.12 pixel full scale vs.012

October 6, 2007 STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular reference field of view #2 abscissa: seconds ordinates: EUVI pixels.012 pixel full scale (vs..12)

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of viewfor structure #3 in the map of the X residuals

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of view for reference structure #3 in the map of the X residuals

October 6, 2007 STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular field of view #3 abscissa: seconds ordinates: EUVI pixels.40 pixel full scale vs.015

October 6, 2007 STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular reference field of view #3 abscissa: seconds ordinates: EUVI pixels.015 pixel full scale (vs..40)

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of viewfor structure #4 in the map of the X residuals

STEREO-A + STEREO-B mapped to STEREO-A = flat view: rectangular field of view for reference structure #4 in the map of the X residuals

October 6, STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular field of view #4 abscissa: seconds ordinates: EUVI pixels.20 pixel full scale (vs.03)

October 6, 2007 STEREO-A + STEREO-B mapped to STEREO-A = flat view: time evolution of average X residual in the rectangular reference field of view #4 abscissa: seconds ordinates: EUVI pixels.030 pixel full scale (vs..20)