All Figures

Figure 1: Positions of HD 283572, EK Dra and 31 Com in the H-R diagram. We have superimposed pre-main-sequence (dashed lines) and post-main-sequence (solid lines) tracks for the mass values reported in the plot. The evolutionary models are those of Ventura et al. (1998b,a), except for the 2 pre-M.S. track, for which we have used the model of Siess et al. (2000). All tracks are calculated for solar photospheric abundances.

Open with DEXTER


In the text

	Figure 2: Background-subtracted PN light curves of HD 283572 ( upper), EK Dra ( middle) and 31 Com ( lower), in the 0.2-10 keV band and with time bins of 200 s. The vertical lines in the light curve of EK Dra mark the time interval of the flare, excluded from the analysis of the quiescent emission.
Open with DEXTER


In the text

	Figure 3: EPIC PN spectra of HD 283572, EK Dra and 31 Com with their best-fit model spectra (the parameters of the models are listed in Table 3). The spectra of 31 Com and HD 283572, with their relevant best-fit models, have been shifted by -0.5 and +0.5 dex for clarity.
Open with DEXTER


In the text

	Figure 4: Co-added RGS spectra of HD 283572 ( upper), EK Dra ( middle) and 31 Com ( lower) with the identification of the most prominent lines; the bin size is 0.02 Å.
Open with DEXTER


In the text

	Figure 5: Distributions of emission measure derived from RGS data. Values without error bars are not statistically constrained by the MCMC algorithm. Note the different ordinate scale in the plot of EK Dra with respect to those of HD 283572 and 31 Com.
Open with DEXTER


In the text

	Figure 6: Comparison between observed fluxes and the fluxes predicted with the EMD model, for lines used in the EM reconstruction of EK Dra; Fe: open diamonds, Ne: triangles, Mg: open squares, Si: filled diamond, Ni: filled circle, O: filled squares, N: asterisk, C: open circle.
Open with DEXTER


In the text

	Figure 7: Model spectra compared to the original RGS spectra.
Open with DEXTER


In the text

	Figure 8: Element-to-iron abundance ratios, relative to the solar photospheric values (Grevesse et al. 1992), for HD 283572 (squares), EK Dra (triangles) and 31 Com (diamonds). The elements are ordered by increasing FIP.
Open with DEXTER


In the text

	Figure 9: Emission measure distribution of EK Dra reconstructed in this work using RGS data and the MCMC algorithm (solid line) and the smoothed solution whose shape is proportional to T3 for T<107 K and to T-1.3 for T>107 K (dashed line).
Open with DEXTER


In the text

	Figure 10: Comparison between observed fluxes and the fluxes predicted with the smoothed (dashed line in Fig. 9), for lines used in the EMD analysis of EK Dra; Fe: open diamonds, Ne: triangles, Mg: open squares, Si: filled diamond, Ni: filled circle, O: filled squares, N: asterisk, C: open circle.
Open with DEXTER


In the text

	Figure 11: Emission measure distributions of the coronal plasma of the quiet Sun (Peres et al. 2000, from /SXT data), Bootis (Laming & Drake 1999, from ASCA/EUVE data), EK Dra, 31 Com and HD 283572 (this work). For each of the three active stars, only the constrained part of the is shown.
Open with DEXTER


In the text

Figure A.1: EPIC PN spectrum of EK Dra (crosses) and the model spectrum derived from the reconstructed (solid line); the dashed line is the model spectrum obtained in the case of a distribution equal to the reconstructed one up to , but with a flatter hot tail drawn with the dashed line in the inset; the model spectrum shown with the dotted line, instead, is relevant to a steeper decrease of the hot tail.


In the text

Figure B.1: The upper panel shows the light curve of the flare on EK Dra, in the 0.3-10 keV band of the EPIC PN, obtained by subtracting the average quiescent emission from the total light curve in Fig. 2. The vertical lines mark the phases of the flare. The middle and the lower panels show the time evolution of the temperature and the emission measure, respectively. Filled symbols are relevant to the model with variable global metallicity, open symbols to the model with z = 0.83 solar.


In the text