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

108 CHAPTER 8. SYSTEMATIC STUDY OF YSO FLARES= 1.1±0.4 % and 0.7±0.2 % for class II and III). Also, there is a relation that lower mass sourcesshow lower flare rate (∼5 %). However, this would be merely due to lower quiescent flux ( ∼ = lowerluminosity) for lower mass sources (Figure 7.8 left), hence it is still controversial whether the flarerate is affected by the stellar mass or not. In the last row of Table 8.1, we show the data of sourcespreviously revealed as binary systems (Simon et al., 1995; Haisch et al., 2002); A-22, A-23/A-24(see §6.3.2 and §6.3.3), A-41, A-78, A-82, BF-46, BF-61, and BF-96. Although the flare rate ofbinary sources is significantly larger than the others like the Taurus-Auriga-Perseus sources (Stelzeret al., 2000), the effect of the flare detection sensitivity can not be negligible; the quiescent flux ofthe binary sources is ∼4–10 times larger than the others.Table 8.1: Flare rate sorted by several physical parametersParameter range N * N † F ¯τ ‡ r τ¯‡ d F § log[Flux(Q)] ‖(ks) (ks) (%)– Class –Class I 8 8 3.4±0.8 11.6±3.0 15.0±1.1 −13.2Class II 63 36 6.2±1.4 7.9±1.0 8.0±0.2 −13.6Class III+III c 27 16 10.1±6.5 11.5±3.9 12.6±1.1 −13.6(3.1±0.6) (6.9±0.8) (5.0±0.1)– Age (Myr) –t ≤ 0.1 11 11 3.6±0.6 29.2±12.1 32.8±3.6 −13.2(3.7±0.8) (8.6±2.0) (10.9±0.7)0.1 < t ≤ 0.5 20 15 7.9±2.4 9.4±1.6 13.0±0.6 −13.30.5 < t 12 7 17.8±10.8 5.4±1.6 13.5±2.4 −13.4(8.2±6.3) (4.0±1.0) (6.6±1.4)– Mass (M ⊙ ) –M ≤ 0.2 11 4 3.3±1.2 9.7±3.7 4.7±0.7 −14.20.2 < M ≤ 0.4 23 20 8.4±2.2 11.4±3.1 17.2±0.7 −13.1(8.7±2.3) (8.5±2.5) (14.8±0.7)0.4 < M 9 9 9.3±6.7 28.7±15.8 38.0±5.7 −12.9(2.5±0.5) (6.2±2.2) (7.4±0.8)– Binarity –Binary # 9 9 8.4±6.0 8.9±1.6 17.3±2.1 −12.9(2.5±0.4) (8.3±1.7) (10.8±0.6)Others 102 57 4.9±0.8 11.9±2.6 9.8±0.2 −13.7(4.9±0.9) (7.9±0.9) (7.2±0.1)* The number of X-ray sources.† The number of detected flares (§5.5).‡ Mean values of τ r and τ d . Parentheses indicate the mean values when we exclude the flares withunusually long timescales (A-2, A-63, and BF-96).§ Flare rate defined by Eq.(8.1) (Stelzer et al., 2000). Parentheses indicate the mean values whenwe exclude the flares with unusually long timescales (A-2, A-63, and BF-96).‖ Mean value of quiescent X-ray flux (ergs s −1 cm −2 ).# Sources previously revealed as binary systems (Simon et al., 1995; Haisch et al., 2002).