The 95% C.I. upper limits of g_ae × g_aγ as a function of ALP mass m_a for the combined analysis of all 18 stars for the energy range 20 − 2000 keV. The solid blue line shows the upper limit for t_cc = 6900 yr, assuming a representative value of B_T = 1.4 μG. The solid purple line shows the upper limit for the most conservative (B_T = 0.4 μG and t_cc = 1.55 × 10⁵ yr) and the green line for the most optimistic case (B_T = 3.0 μG and t_cc = 3.6 yr). Note that the limits for the extended energy range are identical to the ones shown in Fig. 8 as the ALP spectrum peaks around 500 keV or below.