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.

Time-domain statistical studies of mid-infrared and submm variability in nearby star-forming regions show that at least half of all protostars are variable. In this study, we present a statistical analysis of the mid-infrared variability of Young Stellar Objects (YSOs) in the distant, massive star-forming region W51, based on data from the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) All-Sky Survey. From a catalog of 81 protostars, 527 disk objects, and 37,687 other sources, including diskless pre-main sequence stars (Class III) and likely evolved contaminants such as AGB stars (collectively labeled as PMS+E), we identified significant variability in both the 3.4 μm(W1) and 4.6 μm(W2) bands. Due to the large distance (∼5.4 kpc) and high extinction of W51, our sample primarily includes intermediate- to high-mass YSOs (≥2 M⊙), in contrast to nearby star-forming regions such as Taurus or the Gould Belt, which are dominated by low-mass stars (≤1M⊙). This mass bias may affect the observed variability characteristics and their interpretation. Specifically, 11.1% of protostars, 7.6% of Disk objects, and 0.6% of PMS+E sources exhibited secular variability in the W2, while 8.6% of protostars, 2.3% of Disk objects, and 0.5% of PMS+E sources exhibited stochastic variability. Similar trends were observed in the W1 band. Both the fraction and amplitude of variability increase toward earlier evolutionary stages. Protostars exhibit predominantly stochastic variability with high amplitudes, likely driven by dynamic accretion, and extinction changes. In contrast, disk objects show more secular variability, including linear, curved, and periodic patterns, possibly caused by moderate accretion changes or geometric modulation in the inner disk. Analysis of brightness and color changes revealed that protostars typically become redder as they brighten, while disk objects show more complex behavior: they appear roughly balanced in W1 but more often become bluer in W2. These trends are consistent with enhanced dust emission or extinction in protostars, and reduced extinction or accretion-induced hotspot modulation in disk objects. These trends reflect the distinct physical mechanisms at play across evolutionary stages and demonstrate that mid-infrared variability provides useful insight into the accretion and disk evolution processes in young stars.

생태계 내에서 일어나는 모든 현상은 매우 느리고 긴 시간에 걸쳐서 이루어진다. 그렇기에 생태계 내에서 일어나는 현상을 이해하고 연구하기 위해 장기생태연구가 필요하다. 현재 우리나라의 소나무는 단일 수종으로 가장 넓게 분포하 고 있으나 기후변화 및 음수로의 천이과정 등 다양한 요인에 의하여 변화가 예상된다. 변화과정에 대한 모니터링은 생태계 과정의 이해와 임분관리 등에 있어서 매우 중요한 부분을 차지하므로 장기생태모니터링구에 대한 매목조사와 변화상 분석을 실시하였다. 국가장기생태연구의 조사지로 구축된 지리산 소나무림(100m × 100m)을 대상으로 격년별 (2017년, 2019년, 2021년, 2023년) 4회 매목조사를 실시하였고, 매목조사자료를 바탕으로 밀도, 흉고단면적, 중요치, 직경급 분포, 수간건강상태, 고사율, 이입률 등의 분석을 실시하였다. 소나무개체군의 밀도는 6년 동안 292본/㏊에서 272본/㏊으로 6.8% 가량 감소하였고, 특히 비목나무는 6년 동안 161본/㏊에서 46본/㏊으로 71.4% 가량 크게 감소하였 다. 흉고단면적(㎡/㏊)은 비목나무를 제외한 모든 수종이 증가하였고 이에 따라 중요치는 비목나무만 감소하고 이외 모든 수종은 증가하거나 유지되는 경향으로 나타났다. 직경급 분포에서 전제 구성종은 10㎝ 미만의 직경급이 가장 높은 역 J자형을 보이고 소나무는 30-40㎝의 직경급의 개체목이 가장 많은 정규분포형을 보였다. 소나무의 수간건강상 태에서 AS가 2017년에 76.1%(252본/㏊)로 가장 높게 나타났지만 AL과 DF의 증가로 인해 2023년에 ㏊당 63.4%(210 본/㏊)로 12.8%(42본/㏊)감소하였다. 소나무의 6년간 연평균고사율은 1.18%, 연평균이입률은 진계목이 발생하지 않아 나타나지 않았다. 그러나 비목나무의 6년간 연평균고사율은 19.75%로 높게 나타났다. 지리산 소나무림의 소나무 개체 군 밀도는 감소하나 흉고단면적, 중요치는 유지되어 양호한 생육상태인 것으로 나타났지만 진계목이 발생하지 않았고 이는 소나무가 양수의 특성에 기인된 것으로 판단되었다. 앞으로 소나무개체군, 비목나무개체군, 삼나무개체군, 굴참나 무개체군 등 개체군 변화에 대한 지속적인 후속 연구가 필요할 것으로 판단되었다.

We present the combined 2.5–30 μm spectra of four protostars acquired with the infrared camera and the infrared spectrograph on board the AKARI and Spitzer space telescopes, respectively. To analyze the ice absorption features in the 8–22 μm, we first performed a continuum determination process on mid-infrared spectra and applied a method to subtract the silicate absorption. We conducted a global fitting process to the absorption features in the combined infrared spectra using the experimental ice absorbance data to identify the intrinsic absorption of each ice component. We first derived the H2O ice column densities of both stretch and libration modes at 3.05 μm and 13.6 μm simultaneously. We also identified the absorption features containing NH3, CH3OH, CO2, and CO and decomposed their mixed components and compared their ice abundances at different evolutionary stages of the protostars. We explored possible absorptions of the organic ice species such as HCOOH, CH3CHO, and CH3CH2OH in the mid-infrared ranges. The ice analysis method developed in this study can be applied to the ice spectra obtained by the James Webb Space Telescope.

느티나무(Zelkova) 속은 전세계적으로 대부분 멸종위기종으로 발표되고 있어 그 보전가치가 높으며, 우리나라 자생 종인 느티나무(Zelkova serrata)는 준위협종(Near Threatened, NT)으로 발표되고 있다. 따라서, 본 연구는 2018년부터 2023년까지 총 125개소의 느티나무림을 대상으로 식생유형과 층위구조를 파악함으로써 느티나무 자생지 보전을 위한 생태적 천이경향을 구명하고자 수행되었다. 종조성에 따른 유형분류 결과, 총 4개의 식생단위와 7개의 종군유형으로 분류되었다. 느티나무군락군은 비목나무군락(소나무군, 개서어나무군), 참식나무군락으로 분류되었다. 각 식생단위의 층위별 중요치를 분석하여 느티나무림의 천이경향을 분석해본 결과, 느티나무림은 ◯1 느티나무 우점군락으로 당분간 유지되는 유형, ◯2 고로쇠나무 중심 군락으로의 천이가 예상되는 유형, ◯3 참식나무와 소사나무 혼합군락으로의 천이가 예상되는 유형의 총 3가지 천이유형으로 나타났다. 따라서, 느티나무의 체계적 보전을 위해서는 임분의 수직적 구조를 고려한 천이유형별 관리방안 마련이 필요할 것으로 판단된다.

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.