High spatial resolution observations of a small δ spot

Carsten Denker, Haimin Wang

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12 Scopus citations


The Big Bear Solar Observatory (BBSO) has a long tradition of flare observations. In this paper, we would like to direct the reader's attention to observations of a small δ spot that produced a moderate flare activity characterized by 18 C-class and 2 M-class flares. Active region NOAA 8076 (BBSO 3877) was one of the first active regions in the new solar cycle 23. We present for the first time high spatial resolution white-light observations obtained on 1997 August 31 with the speckle masking technique to study mechanisms that trigger flares. Almost diffraction-limited speckle reconstructions revealed the complex and highly dynamical behavior of a small emerging δ configuration in the central part of NOAA 8076. We found strong shear flows and indications of strong transverse fields in the small δ spot. The flare-producing mechanism for this small activity complex was very similar to that of the outstanding flare-producing region NOAA 5395 of 1989 March however, on a completely opposite spatial scale. As an important by-product, the speckle-interferometric techniques provided information about the seeing quality at a site. We used the spectral ratio technique to estimate the Fried parameter r0. We measured a maximum Fried parameter of r0max = 10.3 cm and an average Fried parameter of r0 = 9.0 ± 0.7 cm in which the standard deviation reflects the temporal variations of the seeing, indicating good seeing conditions during our observations.

Original languageEnglish (US)
Pages (from-to)493-497
Number of pages5
JournalAstrophysical Journal
Issue number1 PART I
StatePublished - 1998

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Sun: Activity
  • Sun: Flares
  • Sun: Magnetic fields
  • Techniques: Image processing
  • Techniques: Interferometric


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