arXiv subjects

Kenji Furuya

Publications and source records attributed to Kenji Furuya.

97 records · Page 6Linked to original sources

arXiv2014

ALMA Observations of the IRDC Clump G34.43+00.24 MM3: 278 GHz Class I Methanol Masers

We have observed a molecular clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the CH3OH J_K=9_{-1}--8_0 E, 5_0-4_0 E, and 5_{-1}-4_{-1} E lines at sub-arcsecond resolution by using the Atacama Large Millimeter/submillimeter Array. By comparing the CH3OH J_K=9_{-1}-8_0 E emission with the CH3OH 5_0-4_0 E and 5_{-1}-4_{-1} E emission, we have found that the CH3OH J_K=9_{-1}-8_0 E emission is masing. We have clearly shown that the CH3OH J_K=9_{-1}-8_0 masers arise from the post shocked gas in the interacting regions between the outflows and ambient dense gas. Toward the strongest peak of the CH3OH maser emission, SiO J=6-5 emission is very weak. This indicates that the CH3OH maser emission traces relatively old shocks or weak shocks.

astro-ph.SR↗

arXiv2014

Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry

We study the influence of the turbulent transport on ice chemistry in protoplanetary disks, focusing on carbon and nitrogen bearing molecules. Chemical rate equations are solved with the diffusion term, mimicking the turbulent mixing in the vertical direction. Turbulence can bring ice-coated dust grains from the midplane to the warm irradiated disk surface, and the ice mantles are reprocessed by photoreactions, thermal desorption, and surface reactions. The upward transport decreases the abundance of methanol and ammonia ices at r < 30 AU, because warm dust temperature prohibits their reformation on grain surfaces. This reprocessing could explain the smaller abundances of carbon and nitrogen bearing molecules in cometary coma than those in low-mass protostellar envelopes. We also show the effect of mixing on the synthesis of complex organic molecules (COMs) are two ways: (1) transport of ices from the midplane to the disk surface and (2) transport of atomic hydrogen from the surface to the midplane. The former enhances the COMs formation in the disk surface, while the latter suppresses it in the midplane. Then, when mixing is strong, COMs are predominantly formed in the disk surface, while their parent molecules are (re)formed in the midplane. This cycle expands the COMs distribution both vertically and radially outward compared with that in the non-turbulent model. We derive the timescale of the sink mechanism by which CO and N2 are converted to less volatile molecules to be depleted from the gas phase, and find that the vertical mixing suppresses this mechanism in the inner disks.

astro-ph.EP↗

arXiv2013

Water in Protoplanetary Disks: Deuteration and Turbulent Mixing

We investigate water and deuterated water chemistry in turbulent protoplanetary disks. Chemical rate equations are solved with the diffusion term, mimicking turbulent mixing in vertical direction. Water near the midplane is transported to the disk atmosphere by turbulence and destroyed by photoreactions to produce atomic oxygen, while the atomic oxygen is transported to the midplane and reforms water and/or other molecules. We find that this cycle significantly decreases column densities of water ice at r < 30 AU, where dust temperatures are too high to reform water ice effectively. The radial extent of such region depends on the desorption energy of atomic hydrogen. Our model indicates that water ice could be deficient even outside the sublimation radius. Outside this radius, the cycle decreases the D/H ratio of water ice from 2x10^-2, which is set by the collapsing core model, to 10^-4-10^-2 in 10^6 yr, without significantly decreasing the water ice column density. The resultant D/H ratios depend on the strength of mixing and the radial distance from the central star. Our finding suggests that the D/H ratio of cometary water (10^-3-10^-4) could be established (i.e. cometary water could be formed) in the solar nebula, even if the D/H ratio of water ice delivered to the disk was very high (10^-2).

astro-ph.GA↗

arXiv2013

ALMA Observations of the IRDC Clump G34.43+00.24 MM3: Hot Core and Molecular Outflows

We have observed a cluster forming clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the 1.3 mm continuum and the CH3OH, CS, 13CS, SiO, CH3CH2CN, and HCOOCH3 lines with the Atacama Large Millimeter/submillimeter Array and in K-band with the Keck telescope. We have found a young outflow toward the center of this clump in the SiO, CS, and CH3OH lines. This outflow is likely driven by a protostar embedded in a hot core, which is traced by the CH3CH2CN, HCOOCH3, 13CS, and high excitation CH3OH lines. The size of the hot core is about 800 x 300 AU in spite of its low mass (<1.1 M_sun), suggesting a high accretion rate or the presence of multiple star system harboring a few hot corinos. The outflow is highly collimated, and the dynamical timescale is estimated to be less than 740 yr. In addition, we have also detected extended emission of SiO, CS, and CH3OH, which is not associated with the hot core and the outflow. This emission may be related to past star formation activity in the clump. Although G34.43+00.24 MM3 is surrounded by a dark feature in infrared, it has already experienced active formation of low-mass stars in an early stage of clump evolution.

astro-ph.SR↗

arXiv2012

Chemistry in the First Hydrostatic Core Stage By Adopting Three-Dimensional Radiation Hydrodynamic Simulations

We investigate molecular evolution from a molecular cloud core to a first hydrostatic core in three spatial dimensions. We perform a radiation hydrodynamic simulation in order to trace fluid parcels, in which molecular evolution is investigated, using a gas-phase and grain-surface chemical reaction network. We derive spatial distributions of molecular abundances and column densities in the core harboring the first core. We find that the total of gas and ice abundances of many species in a cold era (10 K) remain unaltered until the temperature reaches ~500 K. The gas abundances in the warm envelope and the outer layer of the first core (T < 500 K) are mainly determined via the sublimation of ice-mantle species. Above 500 K, the abundant molecules, such as H2CO, start to be destroyed, and simple molecules, such as CO, H2O and N2 are reformed. On the other hand, some molecules are effectively formed at high temperature; carbon-chains, such as C2H2 and cyanopolyynes, are formed at the temperature of >700 K. We also find that large organic molecules, such as CH3OH and HCOOCH3, are associated with the first core (r < 10 AU). Although the abundances of these molecules in the first core stage are comparable or less than in the protostellar stage (hot corino), reflecting the lower luminosity of the central object, their column densities in our model are comparable to the observed values toward the prototypical hot corino, IRAS 16293-2422. We propose that these large organic molecules can be good tracers of the first cores.

astro-ph.SR↗

arXiv2012

DNC/HNC Ratio of Massive Clumps in Early Evolutionary Stages of High-Mass Star Formation

We have observed the HN13C J=1-0 and DNC J=1-0 lines toward 18 massive clumps, including infrared dark clouds (IRDCs) and high-mass protostellar objects (HMPOs), by using the Nobeyama Radio Observatory 45 m telescope. We have found that the HN13C emission is stronger than the DNC emission toward all the observed sources. The averaged DNC/HNC ratio is indeed lower toward the observed high-mass sources (0.009\pm0.005) than toward the low-mass starless and star-forming cores (0.06). The kinetic temperature derived from the NH3 (J, K) = (1, 1) and (2, 2) line intensities is higher toward the observed high-mass sources than toward the low-mass cores. However the DNC/HNC ratio of some IRDCs involving the Spitzer 24 μm sources is found to be lower than that of HMPOs, although the kinetic temperature of the IRDCs is lower than that of the HMPOs. This implies that the DNC/HNC ratio does not depend only on the current kinetic temperature. With the aid of chemical model simulations, we discuss how the DNC/HNC ratio decreases after the birth of protostars. We suggest that the DNC/HNC ratio in star-forming cores depends on the physical conditions and history in their starless-core phase, such as its duration time and the gas kinetic temperature.

astro-ph.SR↗

arXiv2011

Carbon Isotope and Isotopomer Fractionation in Cold Dense Cloud Cores

We construct the gas-grain chemical network model which includes carbon isotopes (12C and 13C) with an emphasis on isotopomer-exchange reactions. Temporal variations of molecular abundances, the carbon isotope ratios (12CX/13CX) and the isotopomer ratios (12C13CX/13C12CX) of CCH and CCS in cold dense cloud cores are investigated by numerical calculations. We confirm that the isotope ratios of molecules, both in the gas phase and grain surfaces, are significantly different depending on whether the molecule is formed from the carbon atom (ion) or the CO molecule. Molecules formed from carbon atoms have the CX/13CX ratios greater than the elemental abundance ratio of [12C/13C]. On the other hand, molecules formed from CO molecules have the CX/13CX ratios smaller than the [12C/13C] ratio. We reproduce the observed C13CH/13CCH ratio in TMC-1, if the isotopomer exchange reaction, 13CCH + H <-> C13CH + H + 8.1 K, proceeds with the forward rate coefficient kf > 10^-11 cm3 s-1. However, the C13CS/13CCS ratio is lower than that observed in TMC-1. We then assume the isotopomer exchange reaction catalyzed by the H atom, 13CCS + H <-> C13CS + H + 17.4 K. In the model with this reaction, we reproduce the observed C13CS/13CCS, CCS/C13CS and CCS/13CCS ratio simultaneously.

astro-ph.SR↗