Entity

Time filter

Source Type


Sylwester B.,Polish Academy of Sciences | Phillips K.J.H.,University College London | Sylwester J.,Polish Academy of Sciences | Kuznetsov V.D.,Institute of Terrestrial Magnetism and Radiowave Propagation IZMIRAN
Astrophysical Journal | Year: 2011

The abundance of chlorine is determined from X-ray spectra obtained with the RESIK instrument on CORONAS-F during solar flares between 2002 and 2003. Using weak lines of He-like Cl, Cl XVI, between 4.44 and 4.50 , and with temperatures and emission measures from GOES on an isothermal assumption, we obtained A(Cl) = 5.75 0.26 on a scale A(H) = 12. The uncertainty reflects an approximately a factor of two scatter in measured line fluxes. Nevertheless, our value represents what is probably the best solar determination yet obtained. It is higher by factors of 1.8 and 2.7 than Cl abundance estimates from an infrared sunspot spectrum and nearby H II regions. The constancy of the RESIK abundance values over a large range of flares (GOES class from below C1 to X1) argues for any fractionation that may be present in the low solar atmosphere to be independent of the degree of solar activity. © 2011. The American Astronomical Society. All rights reserved. Source


Sylwester J.,Polish Academy of Sciences | Sylwester B.,Polish Academy of Sciences | Phillips K.J.H.,University College London | Kuznetsov V.D.,Institute of Terrestrial Magnetism and Radiowave Propagation IZMIRAN
Astrophysical Journal | Year: 2010

The abundance of potassium is derived from X-ray lines observed during flares by the RESIK instrument on the solar mission CORONAS-F between 3.53 Å and 3.57 Å. The lines include those emitted by He-like K and Li-like K dielectronic satellites, which have been synthesized using the CHIANTI atomic code and newly calculated atomic data. There is good agreement between observed and synthesized spectra, and the theoretical behavior of the spectra with varying temperature estimated from the ratio of the two GOES channels is correctly predicted. The observed fluxes of the He-like K resonance line per unit emission measure give log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a factor 2.9. This is higher than photospheric abundance estimates by a factor 5.5, a slightly greater enhancement than for other elements with first ionization potential (FIP) less than ∼ 10 eV. There is, then, the possibility that enrichment of low-FIP elements in coronal plasmas depends weakly on the value of the FIP which for K is extremely low (4.34 eV). Our work also suggests that fractionation of elements to form the FIP effect occurs in the low chromosphere rather than higher up, as in some models. © 2010. The American Astronomical Society. All rights reserved.. Source


Phillips K.J.H.,University College London | Sylwester J.,Polish Academy of Sciences | Sylwester B.,Polish Academy of Sciences | Kuznetsov V.D.,Institute of Terrestrial Magnetism and Radiowave Propagation IZMIRAN
Astrophysical Journal | Year: 2010

The solar X-ray continuum emission at five wavelengths between 3.495 and 4.220 for 19 flares in a 7-month period in 2002-2003 was observed by the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami) crystal spectrometer on CORONAS-F. In this wavelength region, free-free and free-bound emissions have comparable fluxes. With a pulse-height analyzer having settings close to optimal, the fluorescence background was removed so that RESIK measured true solar continuum in these bands with an uncertainty in the absolute calibration of ±20%. With an isothermal assumption, and temperature and emission measure derived from the ratio of the two GOES channels, the observed continuum emission normalized to an emission measure of 1048cm-3 was compared with theoretical continua using the CHIANTI atomic code. The accuracy of the RESIK measurements allows photospheric and coronal abundance sets, important for the free-bound continuum, to be discriminated. It is found that there is agreement to about 25% of the measured continua with those calculated from CHIANTI assuming coronal abundances in which Mg, Si, and Fe abundances are four times photospheric. © 2010 The American Astronomical Society. Source


Sylwester J.,Polish Academy of Sciences | Sylwester B.,Polish Academy of Sciences | Phillips K.J.H.,University College London | Kuznetsov V.D.,Institute of Terrestrial Magnetism and Radiowave Propagation IZMIRAN
Astrophysical Journal | Year: 2010

Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at 3.949 Å and 3.733 Å, respectively, with the RESIK X-ray spectrometer on the CORONAS-F spacecraft, together with temperatures and emission measures from the two channels of GOES, have been analyzed to obtain the abundance of Ar in flare plasmas in the solar corona. The line fluxes per unit emission measure show a temperature dependence like that predicted from theory and lead to spectroscopically determined values for the absolute Ar abundance, A(Ar) = 6.44 ± 0.07 (Ar XVII) and 6.49 ± 0.16 (Ar XVIII), which are in agreement to within uncertainties. The weighted mean is 6.45 ± 0.06, which is between two recent compilations of the solar Ar abundance and suggests that the photospheric and coronal abundances of Ar are very similar. © 2010. The American Astronomical Society. Source


Sylwester J.,Polish Academy of Sciences | Sylwester B.,Polish Academy of Sciences | Phillips K.J.H.,University College London | Kuznetsov V.D.,Institute of Terrestrial Magnetism and Radiowave Propagation IZMIRAN
Astrophysical Journal | Year: 2012

The RESIK instrument on CORONAS-F spacecraft observed several sulfur X-ray lines in three of its four channels covering the wavelength range 3.8-6.1 Å during solar flares. The fluxes are analyzed to give the sulfur abundance. Data are chosen for when the instrument parameters were optimized. The measured fluxes of the S XV 1s 2-1s4p (w4) line at 4.089 Å gives A(S) = 7.16 ± 0.17 (abundances on a logarithmic scale with A(H) = 12) which we consider to be the most reliable. Estimates from other lines range from 7.13 to 7.24. The preferred S abundance estimate is very close to recent photospheric abundance estimates and to quiet-Sun solar wind and meteoritic abundances. This implies no fractionation of sulfur by processes tending to enhance the coronal abundance from the photospheric that depend on the first ionization potential (FIP), or that sulfur, though its FIP has an intermediate value of 10.36 eV, acts like a "high-FIP" element. © 2012. The American Astronomical Society. All rights reserved.. Source

Discover hidden collaborations