内山 瑞穂

<jats:title>Abstract</jats:title> <jats:p>We followed up the massive young stellar object S255-NIRS3 (= S255-IRS1b) during its recent accretion outburst event in the $K_{\rm s}$ band with Kanata/HONIR for four years after its burst and obtained a long-term light curve. This is the most complete near-infrared light curve of the S255-NIRS3 burst event that has ever been presented. The light curve showed a steep increase reaching a peak flux that was 3.4 mag brighter than the quiescent phase and then a relatively moderate year-scale fading until the last observation, similar to that of the accretion burst events such as EXors found in lower-mass young stellar objects. The behavior of the $K_{\rm s}$-band light curve is similar to that observed in 6.7 GHz class II methanol maser emission, with a sudden increase followed by moderate year-scale fading. However, the maser emission peaks appear 30–50 d earlier than that of the $K_{\rm s}$ band emission. The similarities confirmed that the origins of the maser emission and the $K_{\rm s}$-band continuum emission are common, as previously shown from other infrared and radio observations by Stecklum et al. (2016, Astronomer’s Telegram, 8732), Caratti o Garatti et al. (2017b, Nature Phys., 13, 276), and Moscadelli et al. (2017, A&amp;A, 600, L8). However, the differences in energy transfer paths, such as the exciting/emitting/scattering structures, may cause the delay in the flux-peak dates.</jats:p>

We report the restraint deformation and the corrosion protection of gold deposited aluminum mirrors for mid-infrared instruments. To evaluate the deformation of the aluminum mirrors by thermal shrinkage, monitoring measurement of the surface of a mirror has been carried out in the cooling cycles from the room temperature to 100 K. The result showed that the effect of the deformation was reduced to one fourth if the mirror was screwed with spring washers. We have explored an effective way to prevent the mirror from being galvanically corroded. A number of samples have been prepared by changing the coating conditions, such as inserting an insulation layer, making a multi-layer and over-coating water blocking layer, or carrying out precision cleaning before coating. Precision cleaning before the deposition and protecting coat with SiO over the gold layer seemed to be effective in blocking corrosion of the aluminum. The SiO over-coated mirror has survived the cooling test for the mid-infrared use and approximately 1 percent decrease in the reflectance has been detected at 6-25 microns compared to gold deposited mirror without coating.