X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi ...

6.3. OTHER T TAURI STARS 77quasi-periodic flares from YLW15A (Tsuboi et al., 2000). We hence make and fit the time slicedspectra of A-79 as shown in Figure 6.14, however no significant sign of increase of kT is found atthe second flare but it keeps almost constant of 3–4 keV (phases 3–5 in Figure 6.14), which is asharp contrast to the case of YLW15A (Figure 2 in Tsuboi et al., 2000).6.3.7 BF-10 – WL22The X-ray spectrum of a class II BF-10 = WL22 exhibitsclear line structure at ∼3.2 and ∼3.9 keV (Figure 6.15).The line energies correspond to He-like Ca and Ar. Wehence relax the abundances of these elements to be freeand fit it by the MEKAL model. The best-fit < kT >and N H are 2.1 keV and 12×10 22 cm −2 , respectively (Table5.2), while the abundances of Ar and Ca are 2.7 +8.3−2.7and 5.0 +7.9−4.1 solar. Thus Ca is extremely overabundant,although the mechanism is an open question.Fig. 6.15.— Spectrum of BF10 = WL22. Theupper panel shows data points (crosses) and thebest-fit MEKAL model (solid line), while thelower panel shows residuals from the best-fitmodel. The line structure at ∼3.2 keV and ∼3.9keV is due to He-like Ar and Ca.Fig. 6.14.— (top) Light curve and(middle and bottom) time evolution ofkT and EM of A-79 = GY195.