arXiv subjects

Y. -J. Kuan

Publications and source records attributed to Y. -J. Kuan.

At least 19 recordsLinked to original sources

arXiv2026

A Multi-Wavelength Study of Comet C/2022 E3 (ZTF): Complementary ALMA and JWST Investigations of Water and Methanol in Cometary Comae

Long-period comets, which are often considered to be representative of material in the protoplanetary disk that formed the Solar System, are ideal to investigate the question of chemical inheritance in astronomy. Determining the chemistry of comets, both individually and as a population, has become of great importance in comparative studies against sources representative of evolutionary precursors to planetary systems. Contemporaneous observations of long-period comet C/2022 E3 (ZTF) were obtained with the JWST and the Atacama Large Millimeter/submillimeter Array (ALMA) in early 2023 March. This work focuses on \ce{CH3OH} measurements from both ALMA and JWST as well as \ce{H2O} measurements from JWST. Radiative transfer modeling of \ce{CH3OH} and \ce{H2O} was performed to investigate spatial variations in rotational temperature, column density, and production rates, as well as a comparison of derived values between the two telescopes. Most of the spatial distributions of the modeled values are centrally peaked, and the modeled values from JWST are all within the error bars of the average values from ALMA. C/2022 E3 (ZTF) also displays an enhancement in modeled rotational temperature in the anti-Sunward direction that is shown to be statistically significant. Based on non-LTE radiative transfer modeling, the declining \ce{H2O} rotational temperatures as a function of nucleocentric distance observed by JWST can be explained primarily as a result of rotational line cooling. The values derived in this work are in general agreement with single-dish millimeter-wave observations.

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arXiv2025

A D/H Ratio Consistent with Earth's Water in Halley-type Comet 12P from ALMA HDO Mapping

Isotopic measurements of Solar System bodies provide a primary paradigm within which to understand the origins and histories of planetary materials. The D/H ratio in particular, helps reveal the relationship between (and heritage of) different H$_2$O reservoirs within the Solar System. Here we present interferometric maps of water (H$_2$O) and semiheavy water (HDO) in the gas-phase coma of a comet (Halley-type comet 12P/Pons-Brooks), obtained using the Atacama Large Millimeter/submillimeter Array (ALMA). The maps are consistent with outgassing of both H$_2$O and HDO directly from the nucleus, and imply a coma D/H ratio (for water) of $(1.71 \pm 0.44)\times10^{-4}$. This is at the lower end of the range of previously-observed values in comets, and is consistent with D/H in Earth's ocean water. Our results suggest a possible common heritage between a component of the Oort cloud's water ice reservoir, and the water that was delivered to the young Earth during the early history of the Solar System.

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arXiv2024

CHIMPS2: $^{13}$CO $J = 3 \to 2$ emission in the Central Molecular Zone

We present the initial data for the ($J = 3 \to 2$) transition of $^{13}$CO obtained from the Central Molecular Zone (CMZ) of the Milky Way as part of the CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). Covering $359^\circ \leq l \leq 1^\circ$ and $|b| \leq 0.5^\circ$ with an angular resolution of 19 arcsec, velocity resolution of 1 km s$^{-1}$, and rms $T_A^* = 0.59$ K at these resolutions, our observations unveil the complex structure of the CMZ molecular gas in improved detail. Complemented by the $^{12}$CO CHIMPS2 data, we estimate a median optical depth of $τ_{13} = 0.087$. The preliminary analysis yields a median $^{13}$CO column density range equal to $N(^{13}\text{CO})= 2$--$5 \times 10^{18}$ cm$^{-2}$, median H$_2$ column density equal to $N(\text{H}_2)= 4 \times 10^{22}$ cm$^{-2}$ to $1 \times 10^{23}$ cm$^{-2}$. We derive $N(\text{H}_2)$-based total mass estimates of $M(\text{H}_2)= 2$--$6 \times 10^7\, M_{\odot}$, in agreement with previous studies. We analyze the relationship between the integrated intensity of $^{13}$CO and the surface density of compact sources identified by Herschel Hi-GAL, and find that younger Hi-GAL sources detected at 500 $μ$m but not at 70 $μ$m follow the dense gas of the CMZ more closely than those that are bright at 70 $μ$m. The latter, actively star-forming sources, appear to be more associated with material in the foreground spiral arms.

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arXiv2024

ALMA Spectroscopy of Europa: A Search for Active Plumes

The subsurface ocean of Europa is a high priority target in the search for extraterrestrial life, but direct investigations are hindered by the presence of a thick, exterior ice shell. Here we present spectral line and continuum maps of Europa obtained over four epochs in May-June 2021 using the Atacama Large Millimeter/submillimeter Array (ALMA), to search for molecular emission from atmospheric plumes, with the aim of investigating subsurface processes. Using a 3D physical model, we obtained upper limits for the plume abundances of HCN, H$_2$CO, SO$_2$ and CH$_3$OH. If active plume(s) were present, they contained very low abundances of these molecules. Assuming a total gas production rate of $10^{29}$ s$^{-1}$, our H$_2$CO abundance upper limit of $<0.016$\% is more than an order of magnitude less than measured in the Enceladus plume by the Cassini spacecraft, implying a possible chemical difference between the plume source materials for these two icy moons.

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arXiv2022

A SUBLIME 3D Model for Cometary Coma Emission: the Hypervolatile-Rich Comet C/2016 R2 (PanSTARRS)

The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H2O and N2+/H2O ratios}, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high resolution, spatially, spectrally and temporally resolved CO observations using the James Clerk Maxwell Telescope (JCMT) and Submillimeter Array (SMA) to elucidate the outgassing behaviour of C/2016 R2. Results are analyzed using a new, time-dependent, three dimensional radiative transfer code (SUBLIME), incorporating for the first time, accurate state-to-state collisional rate coefficients for the CO--CO system. The total CO production rate was found to be in the range $(3.8-7.6)\times10^{28}$ s$^{-1}$ between 2018-01-13 and 2018-02-01, with a mean value of $(5.3\pm0.6)\times10^{28}$ s$^{-1}$ at r_H = 2.8-2.9 au. The emission is concentrated in a near-sunward jet, with an outflow velocity $0.51\pm0.01$ km/s, compared to $0.25\pm0.01$ km/s in the ambient (and night-side) coma. Evidence was also found for an extended source of CO emission, possibly due to icy grain sublimation around $1.2\times10^5$ km from the nucleus. Based on the coma molecular abundances, we propose that the nucleus ices of C/2016 R2 can be divided into a rapidly sublimating apolar phase, rich in CO, CO2, N2 and CH3OH, and a predominantly frozen (or less abundant), polar phase containing more H2O, CH4, H2CO and HCN.

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arXiv2021

The Nearby Evolved Stars Survey II: Constructing a volume-limited sample and first results from the James Clerk Maxwell Telescope

The Nearby Evolved Stars Survey (NESS) is a volume-complete sample of $\sim$850 Galactic evolved stars within 3\,kpc at (sub-)mm wavelengths, observed in the CO $J = $ (2$-$1) and (3$-$2) rotational lines, and the sub-mm continuum, using the James Clark Maxwell Telescope and Atacama Pathfinder Experiment. NESS consists of five tiers, based on distances and dust-production rate (DPR). We define a new metric for estimating the distances to evolved stars and compare its results to \emph{Gaia} EDR3. Replicating other studies, the most-evolved, highly enshrouded objects in the Galactic Plane dominate the dust returned by our sources, and we initially estimate a total DPR of $4.7\times 10^{-5}$ M$_\odot$ yr$^{-1}$ from our sample. Our sub-mm fluxes are systematically higher and spectral indices are typically shallower than dust models typically predict. The 450/850 $μ$m spectral indices are consistent with the blackbody Rayleigh--Jeans regime, suggesting a large fraction of evolved stars have unexpectedly large envelopes of cold dust.

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arXiv2020

CHIMPS2: Survey description and $^{12}$CO emission in the Galactic Centre

The latest generation of Galactic-plane surveys is enhancing our ability to study the effects of galactic environment upon the process of star formation. We present the first data from CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). CHIMPS2 is a survey that will observe the Inner Galaxy, the Central Molecular Zone (CMZ), and a section of the Outer Galaxy in $^{12}$CO, $^{13}$CO, and C$^{18}$O $(J = 3\rightarrow2)$ emission with the Heterodyne Array Receiver Program on the James Clerk Maxwell Telescope (JCMT). The first CHIMPS2 data presented here are a first look towards the CMZ in $^{12}$CO J = 3$\rightarrow$2 and cover $-3^{\circ}\leq\,\ell\,\leq\,5^{\circ}$ and $\mid$b$\mid \leq 0.5^{\circ}$ with angular resolution of 15 arcsec, velocity resolution of 1 km s$^{-1}$, and rms $ΔT_A ^\ast =$ 0.58 K at these resolutions. Such high-resolution observations of the CMZ will be a valuable data set for future studies, whilst complementing the existing Galactic Plane surveys, such as SEDIGISM, the Herschel infrared Galactic Plane Survey, and ATLASGAL. In this paper, we discuss the survey plan, the current observations and data, as well as presenting position-position maps of the region. The position-velocity maps detect foreground spiral arms in both absorption and emission.

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arXiv2020

Unusually High CO Abundance of the First Active Interstellar Comet

Comets spend most of their lives at large distances from any star, during which time their interior compositions remain relatively unaltered. Cometary observations can therefore provide direct insight into the chemistry that occurred during their birth at the time of planet formation. To-date, there have been no confirmed observations of parent volatiles (gases released directly from the nucleus) of a comet from any planetary system other than our own. Here we present high-resolution, interferometric observations of 2I/Borisov, the first confirmed interstellar comet, obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) on 15th-16th December 2019. Our observations reveal emission from hydrogen cyanide (HCN), and carbon monoxide (CO), coincident with the expected position of 2I/Borisov's nucleus, with production rates Q(HCN)=$(7.0\pm1.1)\times10^{23}$ s$^{-1}$ and Q(CO)=$(4.4\pm0.7)\times10^{26}$ s$^{-1}$. While the HCN abundance relative to water (0.06-0.16%) appears similar to that of typical, previously observed comets in our Solar System, the abundance of CO (35-105%) is among the highest observed in any comet within 2 au of the Sun. This shows that 2I/Borisov must have formed in a relatively CO-rich environment - probably beyond the CO ice-line in the very cold, outer regions of a distant protoplanetary accretion disk, as part of a population of small, icy bodies analogous to our Solar System's own proto-Kuiper Belt.

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arXiv2019

ALMA Autocorrelation Spectroscopy of Comets: The HCN/H^13CN ratio in C/2012 S1 (ISON)

The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful tool for high-resolution mapping of comets, but the main interferometer (comprised of 50x12-m antennas) is insensitive to the largest coma scales due to a lack of very short baselines. In this work, we present a new technique employing ALMA autocorrelation data (obtained simultaneously with the interferometric observations), effectively treating the entire 12-m array as a collection of single-dish telescopes. Using combined autocorrelation spectra from 28 active antennas, we recovered extended HCN coma emission from comet C/2012 S1 (ISON), resulting in a fourteen-fold increase in detected line brightness compared with the interferometer. This resulted in the first detection of rotational emission from H^13CN in this comet. Using a detailed coma radiative transfer model accounting for optical depth and non-LTE excitation effects, we obtained an H^12CN/H^13CN ratio of 88+-18, which matches the terrestrial value of 89, consistent with a lack of isotopic fractionation in HCN during comet formation in the protosolar accretion disk. The possibility of future discoveries in extended sources using autocorrelation spectroscopy from the main ALMA array is thus demonstrated.

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arXiv2017

Deep K-band observations of TMC-1 with the Green Bank Telescope: Detection of HC7O, non-detection of HC11N, and a search for new organic molecules

The 100 m Robert C. Byrd Green Bank Telescope K-band (KFPA) receiver was used to perform a high-sensitivity search for rotational emission lines from complex organic molecules in the cold interstellar medium towards TMC-1 (cyanopolyyne peak), focussing on the identification of new carbon-chain-bearing species as well as molecules of possible prebiotic relevance. We report a detection of the carbon-chain oxide species HC$_7$O and derive a column density of $(7.8\pm0.9)\times10^{11}$~cm$^{-2}$. This species is theorized to form as a result of associative electron detachment reactions between oxygen atoms and C$_7$H$^-$, and/or reaction of C$_6$H$_2$$^+$ with CO (followed by dissociative electron recombination). Upper limits are given for the related HC$_6$O, C$_6$O and C$_7$O molecules. In addition, we obtained the first detections of emission from individual $^{13}$C isotopologues of HC$_7$N, and derive abundance ratios HC$_7$N/HCCC$^{13}$CCCCN = $110\pm16$ and HC$_7$N/HCCCC$^{13}$CCCN = $96\pm 11$, indicative of significant $^{13}$C depletion in this species relative to the local interstellar elemental $^{12}$C/$^{13}$C ratio of 60-70. The observed spectral region covered two transitions of HC$_{11}$N, but emission from this species was not detected, and the corresponding column density upper limit is $7.4\times10^{10}$ cm$^{-2}$ (at 95% confidence). This is significantly lower than the value of $2.8\times10^{11}$ cm$^{-2}$ previously claimed by Bell et al. (1997) and confirms the recent non-detection of HC$_{11}$N in TMC-1 by Loomis et al. (2016). Upper limits were also obtained for the column densities of malononitrile and the nitrogen heterocycles quinoline, isoquinoline and pyrimidine.

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arXiv2017

ALMA mapping of rapid gas and dust variations in comet C/2012 S1 (ISON): new insights into the origin of cometary HNC

Observations of the sungrazing comet C/2012 S1 (ISON) were carried out using the Atacama Large Millimeter/submillimeter Array (ALMA) at a heliocentric distance of 0.58-0.54 AU (pre-perihelion) on 2013 November 16-17. Temporally resolved measurements of the coma distributions of HNC, CH$_3$OH, H$_2$CO and dust were obtained over the course of about an hour on each day. During the period UT 10:10-11:00 on Nov. 16, the comet displayed a remarkable drop in activity, manifested as a $>42$% decline in the molecular line and continuum fluxes. The H$_2$CO observations are consistent with an abrupt, $\approx50$% reduction in the cometary gas production rate soon after the start of our observations. On Nov. 17, the total observed fluxes remained relatively constant during a similar period, but strong variations in the morphology of the HNC distribution were detected as a function of time, indicative of a clumpy, intermittent outflow for this species. Our observations suggest that at least part of the detected HNC originated from degradation of nitrogen-rich organic refractory material, released intermittently from confined regions of the nucleus. By contrast, the distributions of CH$_3$OH and H$_2$CO during the Nov. 17 observations were relatively uniform, consistent with isotropic outflow and stable activity levels for these species. These results highlight a large degree of variability in the production of gas and dust from comet ISON during its pre-perihelion outburst, consistent with repeated disruption of the nucleus interspersed with periods of relative quiescence.

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arXiv2017

Thermal physics of the inner coma: ALMA studies of the methanol distribution and excitation in comet C/2012 K1 (PanSTARRS)

We present spatially and spectrally-resolved observations of CH$_3$OH emission from comet C/2012 K1 (PanSTARRS) using The Atacama Large Millimeter/submillimeter Array (ALMA) on 2014 June 28-29. Two-dimensional maps of the line-of-sight average rotational temperature ($T_{rot}$) were derived, covering spatial scales $0.3''-1.8''$ (corresponding to sky-projected distances $ρ\sim500$-2500 km). The CH$_3$OH column density distributions are consistent with isotropic, uniform outflow from the nucleus, with no evidence for extended sources of CH$_3$OH in the coma. The $T_{rot}(ρ)$ radial profiles show a significant drop within a few thousand kilometers of the nucleus, falling from about 60 K to 20 K between $ρ=0$ and 2500 km on June 28, whereas on June 29, $T_{rot}$ fell from about 120 K to 40 K between $ρ=$ 0 km and 1000 km. The observed $T_{rot}$ behavior is interpreted primarily as a result of variations in the coma kinetic temperature due to adiabatic cooling of the outflowing gas, as well as radiative cooling of the CH$_3$OH rotational levels. Our excitation model shows that radiative cooling is more important for the $J=7-6$ transitions (at 338 GHz) than for the $K=3-2$ transitions (at 252 GHz), resulting in a strongly sub-thermal distribution of levels in the $J=7-6$ band at $ρ\gtrsim1000$ km. For both bands, the observed temperature drop with distance is less steep than predicted by standard coma theoretical models, which suggests the presence of a significant source of heating in addition to the photolytic heat sources usually considered.

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arXiv2016

Measuring the Distribution and Excitation of Cometary CH3OH Using ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA) was used to obtain measurements of spatially and spectrally resolved CH$_3$OH emission from comet C/2012 K1 (PanSTARRS) on 28-29 June 2014. Detection of 12-14 emission lines of CH$_3$OH on each day permitted the derivation of spatially-resolved rotational temperature profiles (averaged along the line of sight), for the innermost 5000 km of the coma. On each day, the CH$_3$OH distribution was centrally peaked and approximately consistent with spherically symmetric, uniform outflow. The azimuthally-averaged CH$_3$OH rotational temperature ($T_{rot}$) as a function of sky-projected nucleocentric distance ($ρ$), fell by about 40 K between $ρ=0$ and 2500 km on 28 June, whereas on 29 June, $T_{rot}$ fell by about 50 K between $ρ=$0 km and 1500 km. A remarkable ($\sim50$ K) rise in $T_{rot}$ at $ρ=$1500-2500 km on 29 June was not present on 28 June. The observed variations in CH$_3$OH rotational temperature are interpreted primarily as a result of variations in the coma kinetic temperature due to adiabatic cooling, and heating through Solar irradiation, but collisional and radiative non-LTE excitation processes also play a role.

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arXiv2015

Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA

We report the first spectroscopic detection of ethyl cyanide (C$_2$H$_5$CN) in Titan's atmosphere, obtained using spectrally and spatially resolved observations of multiple emission lines with the Atacama Large Millimeter/submillimeter array (ALMA). The presence of C$_2$H$_5$CN in Titan's ionosphere was previously inferred from Cassini ion mass spectrometry measurements of C$_2$H$_5$CNH$^+$. Here we report the detection of 27 rotational lines from C$_2$H$_5$CN (in 19 separate emission features detected at $>3σ$ confidence), in the frequency range 222-241 GHz. Simultaneous detections of multiple emission lines from HC$_3$N, CH$_3$CN and CH$_3$CCH were also obtained. In contrast to HC$_3$N, CH$_3$CN and CH$_3$CCH, which peak in Titan's northern (spring) hemisphere, the emission from C$_2$H$_5$CN is found to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly different chemistry for this species, consistent with a relatively short chemical lifetime for C$_2$H$_5$CN. Radiative transfer models show that most of the C$_2$H$_5$CN is concentrated at altitudes 300-600 km, suggesting production predominantly in the mesosphere and above. Vertical column densities are found to be in the range (2-5)$\times10^{14}$ cm$^{-2}$.

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arXiv2014

ALMA measurements of the HNC and HC$_3$N distributions in Titan's atmosphere

We present spectrally and spatially-resolved maps of HNC and HC$_3$N emission from Titan's atmosphere, obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) on 2013 November 17. These maps show anisotropic spatial distributions for both molecules, with resolved emission peaks in Titan's northern and southern hemispheres. The HC$_3$N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titan's photochemistry and atmospheric circulation. Differences between the spectrally-integrated flux distributions of HNC and HC$_3$N show that these species are not co-spatial. The observed spectral line shapes are consistent with HNC being concentrated predominantly in the mesosphere and above (at altitudes $z\gtrsim 400$ km), whereas HC$_3$N is abundant at a broader range of altitudes ($z\approx70$-600 km). From spatial variations in the HC$_3$N line profile, the locations of the HC$_3$N emission peaks are shown to be variable as a function of altitude. The peaks in the integrated emission from HNC and the line core (upper-atmosphere) component of HC$_3$N (at $z\gtrsim300$ km) are found to be asymmetric with respect to Titan's polar axis, indicating that the mesosphere may be more longitudinally-variable than previously thought. The spatially-integrated HNC and HC$_3$N spectra are modeled using the NEMESIS planetary atmosphere code and the resulting best-fitting disk-averaged vertical mixing ratio (VMR) profiles are found to be in reasonable agreement with previous measurements for these species. Vertical column densities of the best-fitting gradient models for HNC and HC$_3$N are $1.9\times10^{13}$ cm$^{-2}$ and $2.3\times10^{14}$ cm$^{-2}$, respectively.

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arXiv2014

Mapping the release of volatiles in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array

Results are presented from the first cometary observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), including measurements of the spatially-resolved distributions of HCN, HNC, H$_2$CO and dust within the comae of two comets: C/2012 F6 (Lemmon) and C/2012 S1 (ISON), observed at heliocentric distances of 1.5 AU and 0.54 AU, respectively. These observations (with angular resolution $\approx0.5''$), reveal an unprecedented level of detail in the distributions of these fundamental cometary molecules, and demonstrate the power of ALMA for quantitative measurements of the distributions of molecules and dust in the inner comae of typical bright comets. In both comets, HCN is found to originate from (or within a few hundred km of) the nucleus, with a spatial distribution largely consistent with spherically-symmetric, uniform outflow. By contrast, the HNC distributions are clumpy and asymmetrical, with peaks at cometocentric radii $\sim$500-1000~km, consistent with release of HNC in collimated outflow(s). Compared to HCN, the H$_2$CO distribution in comet Lemmon is very extended. The interferometric visibility amplitudes are consistent with coma production of H$_2$CO and HNC from unidentified precursor material(s) in both comets. Adopting a Haser model, the H$_2$CO parent scale-length is found to be a few thousand km in Lemmon and only a few hundred km in ISON, consistent with destruction of the precursor by photolysis or thermal degradation at a rate which scales in proportion to the Solar radiation flux.

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arXiv2014

Ground-based Multiwavelength Observations of Comet 103P/Hartley 2

The Jupiter-family comet 103P/Hartley 2 (103P) was the target of the NASA EPOXI mission. In support of this mission, we conducted observations from radio to submillimeter wavelengths of comet 103P in the three weeks preceding the spacecraft rendezvous on UT 2010 November 4.58. This time period included the passage at perihelion and the closest approach of the comet to the Earth. Here we report detections of HCN, H2CO, CS, and OH and upper limits for HNC and DCN towards 103P, using the Arizona Radio Observatory Kitt Peak 12m telescope (ARO 12m) and submillimeter telescope (SMT), the James Clerk Maxwell Telescope (JCMT) and the Greenbank Telescope (GBT). The water production rate, QH2O = (0.67 - 1.07) x 10^28 s^-1, was determined from the GBT OH data. From the average abundance ratios of HCN and H2CO relative to water (0.13 +/- 0.03 % and 0.14 +/- 0.03 %, respectively), we conclude that H2CO is depleted and HCN is normal with respect to typically-observed cometary mixing ratios. However, the abundance ratio of HCN with water shows a large diversity with time. Using the JCMT data we measured an upper limit for the DCN/HCN ratio <0.01. Consecutive observations of ortho- H2CO and para-H2CO on November 2 (from data obtained at the JCMT), allowed us to derive an ortho : para ratio (OPR) ~ 2.12 +/- 0.59 (1sigma), corresponding to Tspin > 8 K (2sigma).

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arXiv2007

Arcsecond-Resolution Submillimeter HCN Imaging of the Binary Protostar IRAS 16293-2422

(Abridged) With the SMA we have made high angular-resolution (~1" = 160 AU) observations of the protobinary system IRAS 16293-2422 in the J = 4-3 lines of HCN and HC^15N, and in the continuum at 354.5 GHz. The HCN (4-3) line was also observed using the JCMT to supply missing short spacing information. Submillimeter continuum emission is detected from the individual binary components with a separation of ~5". The HC^15N (4-3) emission has revealed a compact (~500 AU) flattened structure (P.A. = -16 degree) associated with Source A, and shows a velocity gradient along the projected minor axis, which can be interpreted as an infalling gas motion. Our HCN image including the short-spacing information shows an extended (~3000 AU) circumbinary envelope as well as the compact structure associated with Source A. A toy model consisting of a flattened structure with radial infall towards a 1 Msun central star reproduces the HCN/HC^15N position-velocity diagram along the minor axis of the HC^15N emission. In the extended envelope there is also a North-East (Blue) to South-West (Red) velocity gradient across the binary alignment, which is likely to reflect gas motion in the swept-up dense gas associated with the molecular outflow from Source A. At Source B, there is only a weak compact structure with much narrower line widths (~2 km/s) seen in the optically-thin HC^15N emission than that at Source A (>10 km/s), and there is no clearly defined bipolar molecular outflow associated with Source B. These results imply the different evolutionary stages between Source A and B in the common circumbinary envelope.

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