arXiv subjects

Pavel Kotrč

Publications and source records attributed to Pavel Kotrč.

3 recordsLinked to original sources

arXiv2017

Suppression of Hydrogen Emission in an X-class White-light Solar Flare

We present unique NUV observations of a well-observed X-class flare from NOAA 12087 obtained at Ondřejov Observatory. The flare shows a strong white-light continuum but no detectable emission in the higher Balmer and Lyman lines. RHESSI and Fermi observations indicate an extremely hard X-ray spectrum and gamma-ray emission. We use the RADYN radiative hydrodynamic code to perform two type of simulations. One where an energy of 3 x 10^11 erg/cm^2/s is deposited by an electron beam with a spectral index of ~3 and a second where the same energy is applied directly to the photosphere. The combination of observations and simulations allow us to conclude that the white-light emission and the suppression or complete lack of hydrogen emission lines is best explained by a model where the dominant energy deposition layer is located in the lower layers of the solar atmosphere rather than the chromosphere.

astro-ph.SR↗

arXiv2015

KAPPA: A Package for Synthesis of optically thin spectra for the non-Maxwellian kappa-distributions based on the CHIANTI database

The non-Maxwellian $κ$-distributions have been detected in the solar transition region and flares. These distributions are characterized by a high-energy tail and a near-Maxwellian core and are known to have significant impact on the resulting optically thin spectra arising from collisionally dominated astrophysical plasmas. We developed the KAPPA package (http://kappa.asu.cas.cz) for synthesis of such line and continuum spectra. The package is based on the freely available CHIANTI database and software, and can be used in a similar manner. Ionization and recombination rates together with the ionization equilibria are provided for a range of $κ$ values. Distribution-averaged collision strengths for excitation are obtained by an approximate method for all transitions in all ions available within CHIANTI. The validity of this approximate method is tested by comparison with direct calculations. Typical precisions of better than 5% are found, with all cases being within 10%. Tools for calculation of synthetic line and continuum intensities are provided and described. Examples of the synthetic spectra and SDO/AIA responses to emission for the $κ$-distributions are given.

astro-ph.SR↗

arXiv2011

Oscillations of Prominences Observed by MSDP and HSFA Telescopes

Results of an oscillation analysis of two solar quiescent prominences (QPs) observed with two quite different telescopes and spectrographs are presented. For the QP of 23 September 2009 we used data from the Multi-channel Subtractive Double Pass Spectrograph (MSDP) installed in Białków Observatory which provides Hα two dimensional spectra with a higher spatial resolution but with a smaller spectral resolution. The other QP was observed on 20 August 2010 with the Ondřejov Multichannel Spectrograph (HSFA-2) in 5 spectral lines and the slit-jaw imaging system simultaneously. Doppler velocity was analyzed in the both the QPs. In addition, using MSDP possibilities, for the QP of 23 September 2009 we analyzed also movements in the plane of sky. In both the QPs we found oscillations with a small amplitude (less than 0.3 km/s) and with a medium period (approx. a dozen of minutes) which occurred simultaneously. We discuss results reported by other authors.

astro-ph.SR↗