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Language: Japanese
Abstract: Chemical composition around young stellar objects (YSOs) is an essential tool to investigate physical conditions and the history of star formation. Approximately 300 molecules have been detected in the interstellar medium so far. Some of them are categorized into complex organic molecules (COMs), and others are called carbon-chain molecules, which account for ~40% of the interstellar molecules. In this talk, I will present our recent work on chemistry on COMs and carbon-chain species around massive YSOs using ALMA. One topic is a study to investigate the formation processes of NH2CHO, a possible prebiotic molecule, using the ALMA Band 6 data toward 30 high-mass star-forming regions called the DIHCA project. Another topic is research to investigate chemical differentiation among carbon-chain species and nitrogen- and oxygen-bearing COMs using ALMA Band 3 data. We have proposed new carbon-chain chemistry around massive YSOs which we name Hot Carbon-Chain Chemistry (HCCC).
Language: Japanese
Abstract: The mystery of the fast-rotating atmosphere on Venus is well known as the name of the super-rotation. At the cloud top altitude of ~70 km, the super-rotation reaches 100 ms-1 and many types of atmospheric waves are found as periodical signals in winds and temperatures. Planetary-scale waves are one of the important clues that maintain the super-rotation by transporting angular momentum and heat. Imai et al. [2016] implemented long-term monitoring of the rotation period of planetary-scale UV features using a ground-based telescope. Two significant periodicities, at 5.1 and 3.5 days, should be manifestations of these planetary-scale waves (Rossby wave and Kelvin wave, respectively), which were subjected to temporal variations within several months. However, the temporal evolution of these variations remained largely unknown. On 7 December 2015, the Japanese Venus Climate Orbiter named Akatsuki successfully inserted the Venus orbit, and its exploration is still ongoing. The periodicities in the UV brightness and winds derived from cloud-tracking were analyzed throughout the entire observation, and dramatic evolutions of planetary-scale waves were revealed [Imai et al., 2019]. One of the prominent events was observed from June to October 2017, where a 5-day Rossby wave consisting of equatorially symmetric planetary-scale vortices with zonal wavenumber 1 had been captured. At the same time, planetary-scale temperature deviations associated with the 5-day wave were reconstructed for the first time from the Longwave Infrared Camera (LIR) images. By using cloud-tracked winds and brightness temperature measurements, angular momentum and heat fluxes induced by the 5-day wave were quantitatively estimated. While the origin of transient waves is still unclear, the poleward heat transport suggests that they can be related to upward propagating Rossby waves and/or baroclinic instability waves in the lower cloud layer. In this talk, I would like to introduce our research with the "history" of myself involved in planetary exploration missions based on my background in ground-based observations.
Language: Japanese
Abstract: Machine learning has been successfully applied in varied field but whether it is a viable tool for determining the distance to molecular clouds in the Galaxy is an open question. In the Galaxy, the kinematic distance is commonly employed as the distance to a molecular cloud. However, there is a problem in that for the inner Galaxy, two different solutions, the “Near" solution, and the “Far" solution, can be derived simultaneously. We attempted to construct a two-class ( “Near” or “Far” ) inference model using a Convolutional Neural Network (CNN), a form of deep learning that can capture spatial features generally. In this study, we used the CO dataset toward the 1st quadrant of the Galactic plane obtained with the Nobeyama 45-m radio telescope (l = 62-10 degree, |b| < 1 degree). In the model, we applied the three-dimensional distribution (position-position-velocity) of the 12CO (J=1-0) emissions as the main input. The dataset with “Near” or “Far” annotation was made from the HII region catalog of the infrared astronomy satellite WISE to train the model. As a result, we could construct a CNN model with a 76% accuracy rate on the training dataset. By using the model, we determined the distance to molecular clouds identified by the CLUMPFIND algorithm. We found that the mass of the molecular clouds with a distance of < 16.3 kpc identified in the 12CO data follows a power-law distribution with an index of about from -1.5 to -2.3 in the mass range of M >1000 Msun. In particular, the slope was shallow in the arm region and the bar-end region. Also, the detailed molecular gas distribution of the Galaxy as seen from the Galactic North pole was determined. In addition, we obtained a result that approximately 450 cloud-cloud collision events are expected to be included in the data.
Language: English
Abstract: The discovery of complex organic molecules (COMs) in solar-type protostars highlights the extensive chemical evolution at the onset of planet formation. These molecules, which are potential precursors to pre-biotic molecules, are also found in comets that contain the most pristine matter in the solar system. In recent years, the increasing detection of COMs by interferometric sub-mm/mm observations, such as ALMA and VLA, suggest a common presence of COMs in the early stage of star formation. However, the formation pathways of COMs and whether most protostars undergo similar chemical evolution remain open questions with incomplete observational constraints. It is thought that COMs form in the ice mantles on dust grains followed by thermal sublimation near protostars, but direct observational constraints are scarce. While ALMA provides sub-100 au resolution, a resolution necessary to resolve sites of planet formation, to characterize gaseous COMs in nearby embedded protostars, measurements of chemical composition in ices had been limited by low-resolution and limited sensitivity spectroscopy until JWST, which can probe ices at a spatial scale comparable to that by ALMA with unprecedented sensitivity. In this talk, I will highlight the frontier of complex chemistry from observations of COMs in both gas- and ice-phase. Particularly, I will discuss the recent JWST results on ice in protostellar environments, especially focusing on the latest results of the CORINOS program. We have found potential signatures of icy COMs in a young embedded protostar. I will also discuss the prospects of a holistic chemical analysis of both ice and gas in the era of JWST and ALMA.
Language: English
Abstract: The James Clerk Maxwell Telescope (JCMT) has been monitoring eight nearby low-mass star-forming regions in the Gould Belt at submillimetre wavelengths for over six years to search for and quantify the time dependent brightness variability of the resident deeply embedded protostars. Secular variability is common among these protostars; greater than 25% of the sample show measurable long-term brightness changes and 10% show burst behaviour lasting months to years. We interpret this secular variability as reflecting changes in the mass accretion rate from the disk to the protostar, as predicted by theoretical models of (proto)stellar assembly. For a subset of our sample we have contemporaneous mid-IR light-curves which allow additional constraints on the conditions responsible for the brightness variations, confirming that the submillimetre variability is driven by changes in the dust temperature profile of the envelope. Furthermore, we have combined, for one source, single dish and interferometric sub-mm monitoring, which has allowed us to unambiguously recover a time lag in the variability at larger angular scales and use the results to confirm the envelope structure surrounding the embedded protostar. More recently, we have added somewhat more distant intermediate mass regions to our JCMT monitoring and collaborated with the Maser Monitoring Organization (M2O) in follow-up of more massive protostar candidate variables.
