DOT specials

NB: during lengthy downloads you may only see the QuickTime logo.  Recipes for dowloading directly from the repositories are given under DOT showpieces.

General explanation:
       The light in spectral lines in the solar spectrum escapes at different heights in the solar atmosphere, higher at wavelengths in which the gas is less transparent.  The DOT takes images simultaneously in blue and red continuum windows and in the blue G band (many lines from CH molecules), one of the two resonance lines of Ca II (violet, once-ionized calcium atoms, strongest lines in the visible solar spectrum), and the Balmer Halpha line (red, excited neutral hydrogen atoms, most enigmatic line in the solar spectrum).
       The continua and the G band show the photospheric solar surface covered by convective granules and tiny bright magnetic elements between these.  The latter are best visible in the G band.  Sunspots show a dark umbra surrounded by a filamentary penumbra.  The strong Ca II H line samples the low chromosphere, a few hundred kilometers higher up.  At that height the granulation appears reversedly, acoustic shocks abound, and the magnetic elements appear considerably brighter.  The Halpha line shows fibrils in the high chromosphere that lie at a few thousand kilometer height and are obviously controlled by magnetic fields.
       The fibrils demonstrate that solar magnetic fields have a much more complex structure than the Earth's magnetic field, which is approximately a simple North-South dipole like a bar magnet.  The photospheric fields visible as tiny bright points in the G band are mostly vertical but can flip in polarity (upward or inward field direction) over small horizontal distances.  The chromospheric fields mapped by Halpha fibrils connect these photospheric "footpoints" like a dome ("magnetic canopy").  These connections evolve while the footpoints move and emergence of opposite fields causes magnetic reconnection.  The latter is one important heating mechanism; waves running along the field lines are another.  The complexity of solar magnetic fields governs much of the solar activity, including the Sun's spectacular outbursts which arise when the field topology gets overloaded and shorts in electric currents.  The ejecta sometimes hit the Earth.
       Tomographic multi-layer slicing with the DOT helps to unravel the field's secrets by connecting the chromospheric structure and dynamics to the photospheric footpoints.  The multi-layer DOT movies vividly illustrate the dynamical behaviour of the magnetic features.  They show solar fine structure so sharply thanks to the combination of the outstanding wind-swept observing conditions ("seeing") at La Palma, the wind-flushed open structure of the DOT, the excellent DOT optics and mechanical stability, and the consistent application of numerical speckle reconstruction through which each image is corrected for the degradation by the remaining atmospheric seeing above the DOT.
       More detail is given in Rutten et al. 2004, and under course material and lesmateriaal at the author's website.

Aug 1, 2010:   a demonstration movie comparing the two different modes of speckle reconstruction employed at the DOT: full speckle restoration versus "Keller - von der Lühe" two-channel restoration. The movie is available at 1 fps play rate as 2005-10-19-QS-hac-speckledemo.avi and, both in the DOT movie album, while the original 24 fps movie is 2005-10-19-QS-hac-speckledemo.mpg in the DOT mpg directory.  See DOT speckle modes for explanation.

April 12, 2007:   the sun gets awfully quiet towards the close of Cycle 23.  This quiet-sun mosaic blinker steps through blue continuum, G band, red continuum, Ca II H wing, Ca II H core, Halpha wing, and Halpha Doppler.  In such quiet areas the Halpha chromosphere is not filled with long parallel fibrils but shows smaller-scale and highly dynamical patterning.

September 23, 2006:   This mosaic blinker steps through G band, Ca II H core, and Halpha core for a small active region with a small spot.  Even at such modest activity the Halpha chromosphere is organised in extended fibrilar patterns outlining the magnetic field. The separate mosaics are available in the DOT image album.  A smaller subfield is followed with time in this four-panel movie.

Autumn 2006:   DOT sunflowers adorned the back cover of the Nederlands Tijdschrift voor Natuurkunde.

July 8, 2005:   another beautiful DOT active region morph.  Active region AR10786, field 182 x 133 arcsec.  It shifts from G band via Ca II H to Halpha.  The Earth inset shows the scale.  And here is a synchronous quartet movie showing part of this active region a day earlier simultaneously in the G band, Ca II H wing, Halpha line center, and Halpha Dopplershift.

September 29, 2004:   the newly-installed Halpha filter produced a beautiful three-level image-mosaic morph of active region AR10675:
       monochrome morph        false-color morph
It sequentially shows the photosphere sampled in the G band, the low chromosphere sampled simultaneously in Ca II H, and the high chromosphere sampled simultaneously in Halpha.  A simple version served as Astronomy Picture of the Day and was pictured in the Frankfurter Allgemeine. The coloring is false, just to make a nice display - except for the Earth, indeed a magnificent blue-white-redbrown jewel of a planet. As scientists, we prefer the monochrome versions which give a more precise rendering of the solar scene. 

June 8, 2004:   the DOT recorded the first Venus transit in 122 years in splendid movies including detailed egress ones.  See DOT and the 2004 Venus transit.

November 2, 2003:   the DOT observed the spectacular active region AR10486 two days before it sent off the largest flare ever recorded. Here is a false-colour morph (9.2 MByte) of simultaneously taken image mosaics at different wavelengths, from red continuum (red) via G band (colored green here) to Ca II H (blue) and back to red.  A monochrome version with different panels for the four wavelengths (scales in arcsec) is available here (0.5 MB) and also at full resolution (7862 x 7862 px;  6 MB).  A surge sent off by AR10486 two hours before the big flare was also registered with the DOT.  It is shown in this extreme-limb Ca II H movie and was analysed in this A&A paper.

August 9, 2003:   a beautiful three-hour double sunspot movie combines the chromospheric Ca II H view at left with the synchronous photospheric G-band view at right. It very clearly shows the inward migration of small bright features along the penumbral filaments and the outward migration of bright magnetic features across the moat around the sunspot.  Also available as separate movies plus the companion blue continuum movie in the DOT database.

June 18, 2003:   a short near-limb Ca II H movie showing "straws'', with a companion four-panel movie showing the same scene also in the blue continuum, G band, and the wing of Ca II H.  The solar limb is at bottom left.  The straws are very long, very slender structures that stick more or less upright out of the chromospheric network and display rapid swaying motions.

June 6, 2003. A remarkable photosphere-chromosphere fade-over which morphs a photospheric (G band) mosaic of active region AR10375 into the overlying low-chromosphere (Ca II H) scene, co-spatially and simultaneously.  The field measures 250 x 220 arcsec (1 arcsec is about 725 km on the sun).  The smallest axis ticks measure 1 arcsec. A scaled photograph of the Earth is inserted at the upper right to show the geometrical scale.  Three-by-three pixel summation was applied to make the field fit your screen; the actual resolution is three times higher.  There are substantial changes in magnetic field topology between photosphere and chromosphere.  Actually, the DOT took four simultaneous mosaics, also in blue continuum and the continuum near Halpha; here is the corresponding four-wavelength morph sequence with the red-continuum contrast steepened to resemble the G-band image. Here is a mosaic with the four images in four panels (scales in arcsec).

May 2, 2003:   a quadruple movie of a quiet region near the solar center combines the photospheric view in the G band and blue and red contina with the chromospheric Ca II H view at the lower left.  There is some fairly dense network.  All four movies are synchronous and have been Fourier-filtered to remove acoustic oscillations (removing all features that move with apparent supersonic speed over the solar surface).  The four movies are separately available in the DOT database.

December 8, 2002:   a one-hour synchronous double movie the first tomographic one taken with the DOT. It features disk-center G-band and Ca II H simultaneously and co-spatially.  The lefthand movie is from the low photosphere and show granulation plus tiny magnetic elements.  The righthand movie from the high photosphere shows the magnetic network, inversed granulation, and rapidly-changing wave patterns.  The seeing was only fair but the speckle restoration produces quite good quality.  Results from an elaborate analysis are given in Rutten, de Wijn & Sütterlin, A&A 416, 333 and compared to a numerical simulation in Leenaarts & Wedemeyer-Böhm, A&A 431, 687.

July 3, 2002:   a 143 x 118 arcsec G-band mosaic of active region AR10019

October 17, 2001:   a double movie using two cameras to register the G band and nearby continuum simultaneously.  Thanks to the strictly synchronous speckle burst registration, these images can be pairwise subtracted to separate the hydrodynamically dominated granules and the magnetically dominated G-band bright points from each other.  These data were analysed in Nisenson, van Ballegooijen, de Wijn & Sütterlin, Ap. J. 587, 458, 2003.

April 2, 2001:   a mosaic of active region AR9393 shows the largest sunspot group of the past solar activity cycle. Here is a plain image version with a photograph of the Earth inserted as scale indicator (upper right corner), and here is a large 4300 x 2500 pixel poster version to print at large size for wall decoration.

April 1, 2001:   sixty-minute sunspot movie of AR9407 which illustrates the large field of the new DOT cameras. Here is a scaled-down jpeg image taken from the movie, and here is an annotated copy of the same image (also as pdf file from Sütterlin, A&A 374, 21, 2001). The corner inset displays intergranular magnetic elements at high spatial resolution.

February 23, 2000:   this sunspot movie was posted as Astronomy Picture of the Day. It was taken with the simple video camera that initially served to test the viability of the DOT's open principle - indeed superbly demonstrated by this movie. Here is a snapshot image from the movie.

Rob Rutten 2017-11-19