Solar Physics

, Volume 291, Issue 3, pp 779–789 | Cite as

New Observations of Balmer Continuum Flux in Solar Flares

Instrument Description and First Results
Article

Abstract

Increase in the Balmer continuum radiation during solar flares was predicted by various authors, but has never been firmly confirmed observationally using ground-based slit spectrographs. Here we describe a new post-focal instrument, the image selector, with which the Balmer continuum flux can be measured from the whole flare area, in analogy to successful detections of flaring dMe stars. The system was developed and put into operation at the horizontal solar telescope HSFA2 of the Ondřejov Observatory. We measure the total flux by a fast spectrometer from a limited but well-defined region on the solar disk. Using a system of diaphragms, the disturbing contribution of a bright solar disk can be eliminated as much as possible. Light curves of the measured flux in the spectral range 350 – 440 nm are processed, together with the \(\mathrm{H}\upalpha\) images of the flaring area delimited by the appropriate diaphragm. The spectral flux data are flat-fielded, calibrated, and processed to be compared with model predictions. Our analysis of the data proves that the described device is sufficiently sensitive to detect variations in the Balmer continuum during solar flares. Assuming that the Balmer-continuum kernels have at least a similar size as those visible in \(\mathrm{H}\upalpha\), we find the flux increase in the Balmer continuum to reach 230 – 550 % of the quiet continuum during the observed X-class flare. We also found temporal changes in the Balmer continuum flux starting well before the onset of the flare in \(\mathrm{H}\upalpha\).

Keywords

Flares, spectrum Flares, white, light Spectrum, continuum 

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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Astronomical InstituteAcademy of Sciences of the Czech RepublicOndřejovCzech Republic
  2. 2.Faculty of Mathematics and PhysicsCharles UniversityPraha 8Czech Republic

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