Tracing the water snowline in low-mass young stellar objects (YSOs) is important because dust grain growth is promoted and the chemical composition varies at the water snowline, which influences planet formation and its properties. In protostellar envelopes, the water snowline can be estimated as a function of luminosity using a relation derived from radiative transfer models, and these predictions are consistent with observations. However, accurately estimating the water snowline in protoplanetary disks requires new relations that account for the disk structure. We present the relations between luminosity and water snowline using the dust continuum radiative transfer models with various density structures. We adopt two-dimensional density structures for an envelope-only model (Model E), an envelope+disk+cavity model (Model E+D), and a protoplanetary disk model (Model PPD). The relations between the water snowline, where Tdust = 100 K, and the total luminosity, ranging 0.1–1,000 L⊙, are well fitted by a power-law relation, Rsnow = a × (L/L⊙)p au. The factor a decreases with increasing disk density, while the power index p has values around 0.5 in all models. As the disk becomes denser, the water snowline forms at smaller radii even at the same luminosity, since dense dust hinders photon propagation. We also explore the effect of viscous heating on the water snowline. In Model PPD with viscous heating, the water snowline shifts outward by a few au up to 15 au, increasing the factor a and decreasing the power index p. In Model E+D with lower disk mass, the effect of viscous heating is negligible, indicating that the disk mass controls the effect. The discrepancy between our models and direct observations provides insights into the recent outburst event and the presence of a disk structure in low-mass YSOs.

본 연구에서는 광체꽃벌속의 미기록종 Ceratina iwatai Yasumatsu, 1936을 한국에서 처음으로 보고한다. 본 종의 기재, 분포정보, 그리고 삽화를 제공한다.

Hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) are isomers with similar chemical properties. However, HNC can be converted into other molecules by reactions with atomic hydrogen (H) and atomic oxygen (O), resulting in a variation of the HCN/HNC abundance ratio. These reaction rates are sensitive to gas temperature, resulting in different abundance ratios in different temperature environments. The emission of HCN and HNC was found to distribute along ring structures in the protoplanetary disk of V883 Ori. HCN exhibits a multi-ring structure consisting of inner and outer rings. The outer ring represents a genuine chemical structure, whereas the inner ring appears to display such characteristics due to the high dust continuum optical depth at the center. However, HNC is entirely depleted in the warmer inner ring, while its line intensity is similar to that of HCN in the colder outer ring. In this study, we present a chemical calculation that reproduces the observed HCN/HNC abundance ratio in the inner and outer rings. This calculation suggests that the distinct emission distribution between HCN and HNC results from a currently ongoing outburst in V883 Ori. The sublimation of HCN and HNC from grain surfaces and the conversion of HNC to HCN determine their chemical distribution in the heated, warm inner disk.