花輪 知幸

Context. Recent observations suggest that planet formation starts early, in protostellar disks of ≤10⁵ yr, which are characterized by strong interactions with the environment, such as through accretion streamers and molecular outflows. Aims. To investigate the impact of such phenomena on the physical and chemical properties of a disk, it is key to understand what chemistry planets inherit from their natal environment. Methods. In the context of the ALMA large program Fifty AU Study of the chemistry in the disk/envelope system of solar-like protostars (FAUST), we present observations on scales from ∼1500 au to ∼60 au of H₂CO, HDCO, and D₂CO toward the young planet-forming disk IRS 63. Results. The H₂CO probes the gas in the disk as well as in a large scale streamer (∼1500 au) impacting onto the southeast disk side. We detected for the first time deuterated formaldehyde, HDCO and D₂CO, in a planet-forming disk and HDCO in the streamer that is feeding it. These detections allowed us to estimate the deuterium fractionation of H₂CO in the disk: [HDCO]/[H₂CO] ∼ 0.1 − 0.3 and [D₂CO]/[H₂CO] ∼ 0.1. Interestingly, while HDCO follows the H₂CO distribution in the disk and in the streamer, the distribution of D₂CO is highly asymmetric, with a peak of the emission (and [D]/[H] ratio) in the southeast disk side, where the streamer crashes onto the disk. In addition, D₂CO was detected in two spots along the blue- and redshifted outflow. This suggests that (i) in the disk, HDCO formation is dominated by gas-phase reactions in a manner similar to H₂CO, while (ii) D₂CO is mainly formed on the grain mantles during the prestellar phase and/or in the disk itself and is at present released in the gas phase in the shocks driven by the streamer and the outflow. Conclusions. These findings testify to the key role of streamers in the buildup of the disk concerning both the final mass available for planet formation and its chemical composition.

Abstract The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS 4A protobinary system. This analysis is based on ALMA observations of SiO(5–4), H2CO(30, 3–20, 3), and HDCO(41, 4–31, 3) with a spatial resolution of ∼150 au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS 4A1 and IRAS 4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS 4A1 exhibit extensions of 10″ and 13″ with position angles (PA) of 0○ and -12○, respectively, while those of IRAS 4A2 are more extended, spanning 18″ and 25″ with PAs of 29○ and 26○. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH₃OH, H₂CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H₂CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H₂ column density of ∼7 × 10²¹ cm⁻², a mass of ∼9 × 10⁻³ M_⊙, and a lower limit on the dust spectral index of 1.4. Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.

Abstract Characterizing the physical properties of dust grains in a protoplanetary disk is critical to comprehending the planet formation process. Our study presents Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution observations of the young protoplanetary disk around DG Tau at a 1.3 mm dust continuum. The observations, with a spatial resolution of ≈0.″04, or ≈5 au, revealed a geometrically thin and smooth disk without substantial substructures, suggesting that the disk retains the initial conditions of the planet formation. To further analyze the distributions of dust surface density, temperature, and grain size, we conducted a multiband analysis with several dust models, incorporating ALMA archival data of the 0.87 and 3.1 mm dust polarization. The results showed that the Toomre Q parameter is ≲2 at a 20 au radius, assuming a dust-to-gas mass ratio of 0.01. This implies that a higher dust-to-gas mass ratio is necessary to stabilize the disk. The grain sizes depend on the dust models, and for the DSHARP compact dust, they were found to be smaller than ∼400 μm in the inner region (r ≲ 20 au) while exceeding larger than 3 mm in the outer part. Radiative transfer calculations show that the dust scale height is lower than at least one-third of the gas scale height. These distributions of dust enrichment, grain sizes, and weak turbulence strength may have significant implications for the formation of planetesimals through mechanisms such as streaming instability. We also discuss the CO snowline effect and collisional fragmentation in dust coagulation for the origin of the dust size distribution.

<jats:p><jats:italic>Aims.</jats:italic> Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the build-up of chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance.</jats:p> <jats:p><jats:italic>Methods.</jats:italic> We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disc has previously been detected.</jats:p> <jats:p><jats:italic>Results.</jats:italic> Twelve methanol lines have been detected with upper energies in the [45–537] K range along with one <jats:sup>13</jats:sup>CH<jats:sub>3</jats:sub>OH transition and one methyl formate (CH<jats:sub><jats:sc>3</jats:sc></jats:sub>OCHO) line blended with one of the methanol transitions. The methanol emission is compact (FWHM ~ 0.5″) and encompasses both protostars, which are separated by only 0.2″ (28 au). In addition, the overall methanol line emission presents three velocity components, which are not spatially resolved by our observations. Nonetheless, a detailed analysis of the spatial origin of these three components suggests that they are associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A radiative transfer analysis of the methanol lines gives a kinetic temperature of [100–140] K, an H<jats:sub>2</jats:sub> volume density of 10<jats:sup>6</jats:sup>–10<jats:sup>7</jats:sup> cm<jats:sup>−3</jats:sup> and column density of a few 10<jats:sup>18</jats:sup> cm<jats:sup>−2</jats:sup> in all three components with a source size of ~0.15″. Thus, this hot and dense gas is highly enriched in methanol with an abundance as high as 10<jats:sup>−5</jats:sup>. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects.</jats:p> <jats:p><jats:italic>Conclusions.</jats:italic> Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have investigated the protostellar disk around a Class 0/I protostar, L1527 IRS, using multiwavelength observations of the dust continuum emission at <jats:italic>λ</jats:italic> = 0.87, 2.1, 3.3, and 6.8 mm, obtained by the Atacama Large Millimeter/submillimeter Array and the Jansky Very Large Array (VLA). Our observations achieved a spatial resolution of 3–13 au and revealed an edge-on disk structure with a size of ∼80–100 au. The emission at 0.87 and 2.1 mm is found to be optically thick, within a projected disk radius of <jats:italic>r</jats:italic> <jats:sub>proj</jats:sub> ≲ 50 au. The emission at 3.3 and 6.8 mm shows that the power-law index of the dust opacity (<jats:italic>β</jats:italic>) is <jats:italic>β</jats:italic> ∼ 1.7 around <jats:italic>r</jats:italic> <jats:sub>proj</jats:sub> ∼ 50 au, suggesting that grain growth has not yet begun. The dust temperature (<jats:italic>T</jats:italic> <jats:sub>dust</jats:sub>) shows a steep decrease with <jats:italic>T</jats:italic> <jats:sub>dust</jats:sub> ∝ <jats:italic>r</jats:italic> <jats:sub>proj</jats:sub> <jats:sup>−2</jats:sup> outside the VLA clumps previously identified at <jats:italic>r</jats:italic> <jats:sub>proj</jats:sub> ∼ 20 au. Furthermore, the disk is gravitationally unstable at <jats:italic>r</jats:italic> <jats:sub>proj</jats:sub> ∼ 20 au, as indicated by a Toomre <jats:italic>Q</jats:italic> parameter value of <jats:italic>Q</jats:italic> ≲ 1.0. These results suggest that the VLA clumps are formed via gravitational instability, which creates a shadow on the outside of the substructure, resulting in the sudden drop in temperature. The derived dust masses for the VLA clumps are ≳0.1 <jats:italic>M</jats:italic> <jats:sub>J</jats:sub>. Thus, we suggest that Class 0/I disks can be massive enough to be gravitationally unstable, which may be the origin of gas giant planets in a 20 au radius. Furthermore, the protostellar disks could be cold due to shadowing.</jats:p>

<BR /> Aims: Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the build-up of chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance. <BR /> Methods: We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disc has previously been detected. <BR /> Results: Twelve methanol lines have been detected with upper energies in the [45-537] K range along with one ¹³CH₃OH transition and one methyl formate (CH₃OCHO) line blended with one of the methanol transitions. The methanol emission is compact (FWHM ~ 0.5″) and encompasses both protostars, which are separated by only 0.2″ (28 au). In addition, the overall methanol line emission presents three velocity components, which are not spatially resolved by our observations. Nonetheless, a detailed analysis of the spatial origin of these three components suggests that they are associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A radiative transfer analysis of the methanol lines gives a kinetic temperature of [100-140] K, an H₂ volume density of 10⁶-10⁷ cm⁻³ and column density of a few 10¹⁸ cm⁻² in all three components with a source size of ~0.15″. Thus, this hot and dense gas is highly enriched in methanol with an abundance as high as 10⁻⁵. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects. <BR /> Conclusions: Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis....

<jats:title>ABSTRACT</jats:title> <jats:p>The ALMA (Atacama Large Millimeter Array) interferometer, with its unprecedented combination of high sensitivity and high angular resolution, allows for (sub-)mm wavelength mapping of protostellar systems at Solar system scales. Astrochemistry has benefitted from imaging interstellar complex organic molecules in these jet–disc systems. Here, we report the first detection of methanol (CH3OH) and methyl formate (HCOOCH3) emission towards the triple protostellar system VLA1623−2417 A1+A2+B, obtained in the context of the ALMA Large Programme FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar-like protostars). Compact methanol emission is detected in lines from Eu = 45 K up to 61 K and 537 K towards components A1 and B, respectively. Large velocity gradient analysis of the CH3OH lines towards VLA1623−2417 B indicates a size of 0.11–0.34 arcsec (14–45 au), a column density $N_{\rm CH_3OH}$ = 1016–1017 cm−2, kinetic temperature ≥ 170 K, and volume density ≥ 108 cm−3. A local thermodynamic equilibrium approach is used for VLA1623−2417 A1, given the limited Eu range, and yields Trot ≤ 135 K. The methanol emission around both VLA1623−2417 A1 and B shows velocity gradients along the main axis of each disc. Although the axial geometry of the two discs is similar, the observed velocity gradients are reversed. The CH3OH spectra from B show two broad (4–5 km s−1) peaks, which are red- and blueshifted by ∼ 6–7 km s−1 from the systemic velocity. Assuming a chemically enriched ring within the accretion disc, close to the centrifugal barrier, its radius is calculated to be 33 au. The methanol spectra towards A1 are somewhat narrower (∼ 4 km s−1), implying a radius of 12–24 au.</jats:p>

Abstract The chemical diversity of low-mass protostellar sources has so far been recognized, and environmental effects are invoked as its origin. In this context, observations of isolated protostellar sources without the influence of nearby objects are of particular importance. Here, we report the chemical and physical structures of the low-mass Class 0 protostellar source IRAS 16544−1604 in the Bok globule CB 68, based on 1.3 mm Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of ∼70 au that were conducted as part of the large program FAUST. Three interstellar saturated complex organic molecules (iCOMs), CH₃OH, HCOOCH₃, and CH₃OCH₃, are detected toward the protostar. The rotation temperature and the emitting region size for CH₃OH are derived to be 131 ± 11 K and ∼10 au, respectively. The detection of iCOMs in close proximity to the protostar indicates that CB 68 harbors a hot corino. The kinematic structure of the C¹⁸O, CH₃OH, and OCS lines is explained by an infalling–rotating envelope model, and the protostellar mass and the radius of the centrifugal barrier are estimated to be 0.08–0.30 M_⊙ and &lt;30 au, respectively. The small radius of the centrifugal barrier seems to be related to the small emitting region of iCOMs. In addition, we detect emission lines of c-C₃H₂ and CCH associated with the protostar, revealing a warm carbon-chain chemistry on a 1000 au scale. We therefore find that the chemical structure of CB 68 is described by a hybrid chemistry. The molecular abundances are discussed in comparison with those in other hot corino sources and reported chemical models.

<jats:title>Abstract</jats:title> <jats:p>TMC-1A is a protostellar source harboring a young protostar, IRAS 04365+2353, and shows highly asymmetric features of a few 100 au scale in its molecular emission lines. Blueshifted emission is much stronger in the CS (<jats:italic>J</jats:italic> = 5–4) line than redshifted emission. This asymmetry can be explained if the gas accretion is episodic and takes the form of cloudlet capture, given that the cloudlet is approaching toward us. The gravity of the protostar transforms the cloudlet into a stream and changes its velocity along the flow. The emission from the cloudlet should be blueshifted before the periastron, while it should be redshifted after the periastron. If a major part of cloudlet has not reached the periastron, the former should be dominant. We perform hydrodynamical simulations to examine the validity of the scenario. Our numerical simulations can reproduce the observed asymmetry if the orbit of the cloudlet is inclined to the disk plane. The inclination can explain the slow infall velocity observed in the C<jats:sup>18</jats:sup>O (<jats:italic>J</jats:italic> = 2–1) line emission. Such episodic accretion may occur in various protostellar cores since actual clouds could have inhomogeneous density distributions. We also discuss the implication of the cloudlet capture on observations of related objects.</jats:p>

<title>Abstract</title> We report a study of the low-mass Class 0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H¹³CO⁺ (<italic>J</italic> = 3–2), CS (<italic>J</italic> = 5–4), and CCH (<italic>N</italic> = 3–2) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circumbinary VLA 1623A disk, as well as the VLA 1623B disk. We found that the minor axis of the circumbinary disk of VLA 1623A is misaligned by about 12° with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be 5–16 au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circumbinary disk. The origin of its opposite gradient is also discussed.

We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and (CO)-O-18 line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s(-1) over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.

<title>ABSTRACT</title> The study of hot corinos in solar-like protostars has been so far mostly limited to the Class 0 phase, hampering our understanding of their origin and evolution. In addition, recent evidence suggests that planet formation starts already during Class I phase, which therefore represents a crucial step in the future planetary system chemical composition. Hence, the study of hot corinos in Class I protostars has become of paramount importance. Here, we report the discovery of a hot corino towards the prototypical Class I protostar L1551 IRS5, obtained within the ALMA (Atacama Large Millimeter/submillimeter Array) Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar-like protostars). We detected several lines from methanol and its isotopologues (13CH3OH and CH2DOH), methyl formate, and ethanol. Lines are bright towards the north component of the IRS5 binary system, and a possible second hot corino may be associated with the south component. The methanol lines' non-LTE analysis constrains the gas temperature (∼100 K), density (≥1.5 × 108 cm−3), and emitting size (∼10 au in radius). All CH3OH and 13CH3OH lines are optically thick, preventing a reliable measure of the deuteration. The methyl formate and ethanol relative abundances are compatible with those measured in Class 0 hot corinos. Thus, based on this work, little chemical evolution from Class 0 to I hot corinos occurs.

© 2019. The American Astronomical Society. All rights reserved. We examine the linear stability of a filamentary cloud permeated by a perpendicular magnetic field. The initial magnetic field is assumed to be uniform and perpendicular to the cloud axis. The model cloud is assumed to have a Plummer-like density profile and to be supported against self-gravity by turbulence. The effects of turbulence are taken into account by enhancing the effective pressure of a low-density gas. We derive the effective pressure as a function of density from the condition of hydrostatic balance. It is shown that the model cloud is more unstable against radial collapse when the radial density slope is shallower. When the magnetic field is relatively weak, radial collapse is suppressed. If the displacement vanishes in a region very far from the cloud axis, the model cloud is stabilized completely by a relatively weak magnetic field. If rearrangement of the magnetic flux tubes is permitted, the model cloud is unstable even when the magnetic field is extremely strong. The stability depends on the outer boundary condition as in the case of an isothermal cloud. The growth rate of the rearrangement mode is smaller when the radial density slope is shallower.

Numerical simulations of binary star formation suffer from serious mismatch with observations. Equal mass binaries are abundant in numerical simulations while also unequal mass binaries are commonly observed. The discrepancy should be due to errors in the numerical simulations. In this paper we discuss the evaluation of the Coriolis force as a source of errors in the numerical simulations. Simulations of an accreting young binary is often performed in the frame co-rotating with the binary. We demonstrate that the specific angular momentum changes spuriously at a shock front, if it is evaluated either solely with the density and velocity at the cell center. We show that the spurious change is erased out if a half of it is evaluated from the numerical flux on the cell surface. We name this method of evaluating the Coriolis force HH type since a half is evaluated from the numerical mass flux and the other half is from the momentum density in the cell. We prove that simulations conserve the momentum measured in the rest frame only when HH type Coriolis force is adopted. The numerical error is serious around shock waves since the difference between the numerical mass flux and momentum density is large there. The shock waves drive gas accretion through angular momentum transfer and should be simulated accurately.

We examine the linear stability of an isothermal filamentary cloud permeated by a perpendicular magnetic field. Our model cloud is assumed to be supported by gas pressure against self-gravity in the unperturbed state. For simplicity, the density distribution is assumed to be symmetric around the axis. Also for simplicity, the initial magnetic field is assumed to be uniform, and turbulence is not taken into account. The perturbation equation is formulated to be an eigenvalue problem. The growth rate is obtained as a function of the wavenumber for fragmentation along the axis and the magnetic field strength. The growth rate depends critically on the outer boundary. If the displacement vanishes in regions very far from the cloud axis (fixed boundary), cloud fragmentation is suppressed by a moderate magnetic field, which means the plasma beta is below 1.67 on the cloud axis. If the displacement is constant along the magnetic field in regions very far from the cloud, the cloud is unstable even when the magnetic field is infinitely strong. The cloud is deformed by circulation in the plane perpendicular to the magnetic field. The unstable mode is not likely to induce dynamical collapse, since it is excited even when the whole cloud is magnetically subcritical. For both boundary conditions, the magnetic field increases the wavelength of the most unstable mode. We find that the magnetic force suppresses compression perpendicular to the magnetic field especially in regions of low density.

We have resolved for the first time the radial and vertical structures of the almost edge-on envelope/disc system of the low-mass Class 0 protostar L1527. For that, we have used Atacama Large Millimetre/submillimetre Array (ALMA) observations with a spatial resolution of 0.25 x 0.13 arcsec(2) and 0.37 x 0.23 arcsec(2) at 0.8 and 1.2 mm, respectively. The L1527 dust continuum emission has a deconvolved size of 78 x 21 au(2), and shows a flared disc-like structure. A thin infalling-rotating envelope is seen in the CCH emission outward of about 150 au, and its thickness is increased by a factor of 2 inward of it. This radius lies between the centrifugal radius (200 au) and the centrifugal barrier of the infalling-rotating envelope (100 au). The gas stagnates in front of the centrifugal barrier and moves towards vertical directions. SO emission is concentrated around and inside the centrifugal barrier. The rotation speed of the SO emitting gas is found to be decelerated around the centrifugal barrier. A part of the angular momentum could be extracted by the gas that moves away from the mid-plane around the centrifugal barrier. If this is the case, the centrifugal barrier would be related to the launching mechanism of low-velocity outflows, such as disc winds.

We investigate the dust distribution in the crescent disk around HD 142527 based on the continuum emission at 890 mu m obtained by ALMA Cycle 0. The map is divided into 18 azimuthal sectors, and the radial intensity profile in each sector is reproduced with a two-dimensional diskmodel. Ourmodel takes account of scattering and inclination of the disk as well as the azimuthal dependence in intensity. When the dust is assumed to have the conventional composition and a maximum size of 1mm, the northwestern region (PA = 291 degrees-351 degrees) cannot be reproduced. This is because the model intensity becomes insensitive to the increase in surface density due to heavy self-scattering, reaching its ceilingmuch lower than the observed intensity. The ceiling depends on the position angle, PA. When the scattering opacity is reduced by a factor of 10, the intensity distribution is reproduced successfully in all the sectors, including those in the northwestern region. The best-fitting model parameters depend little on the scattering opacity in the southern region where the disk is optically thin. The contrast ratio of dust surface densities along PA is derived to be about 40, much smaller than the value in the case of conventional opacities (70-130). These results strongly suggest that the albedo is lower than that considered for some reason, at least in the northwestern region.

We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, (CO)-O-18 (3-2), (CO)-C-13 (3-2), SO (7(8)-6(7)), and CS (7-6) emission. At 0.'' 18 (= 25 au) resolution, similar to 4 times higher than that of our Cycle 0 observations, the circumbinary disk (CBD) as seen in the 0.9 mm emission is shown to be composed of a northern and a southern spiral arm, with the southern arm connecting to the circumstellar disk (CSD) around Source B. The western parts of the spiral arms are brighter than the eastern parts, suggesting the presence of an m = 1 spiral mode. In the (CO)-O-18 emission, the infall gas motions in the interarm regions and the outward gas motions in the arms are identified. These observed features are well reproduced with our numerical simulations, where gravitational torques from the binary system impart angular momenta to the spiral-arm regions and extract angular momenta from the interarm regions. Chemical differentiation of the CBD is seen in the four molecular species. Our Cycle 2 observations have also resolved the CSDs around the individual protostars, and the beam-deconvolved sizes are 0.'' 29 x 0.'' 19. (=40 x 26 au) (P.A = 144 degrees) and 0.'' 26 x 0.'' 20 (=36 x 27 au) (P. A = 147 degrees) for Sources A and B, respectively. The position and inclination angles of these CSDs are misaligned with those of the CBD. The (CO)-O-18 emission traces the Keplerian rotation of the misaligned disk around Source A.

We analyse the cosmic ray magnetohydrodynamic (CR MHD) equations to improve the numerical simulations. We propose to solve them in the fully conservation form, which is equivalent to the conventional CR MHD equations. In the fully conservation form, the CR energy equation is replaced with the CR 'number' conservation, where the CR number density is defined as the three-fourths power of the CR energy density. The former contains an extra source term, while latter does not. An approximate Riemann solver is derived from the CR MHD equations in the fully conservation form. Based on the analysis, we propose a numerical scheme of which solutions satisfy the Rankine-Hugoniot relation at any shock. We demonstrate that it reproduces the Riemann solution derived by Pfrommer et al. for a 1D CR hydrodynamic shock tube problem. We compare the solution with those obtained by solving the CR energy equation. The latter solutions deviate from the Riemann solution seriously, when the CR pressure dominates over the gas pressure in the post-shocked gas. The former solutions converge to the Riemann solution and are of the second-order accuracy in space and time. Our numerical examples include an expansion of high-pressure sphere in a magnetized medium. Fast and slow shocks are sharply resolved in the example. We also discuss possible extension of the CR MHD equations to evaluate the average CR energy.

We present observations at 7 mm that fully resolve the two circumstellar disks and a reanalysis of archival observations at 3.5 cm that resolve along their major axes the two ionized jets of the Class I binary protostellar system L1551NE. We show that the two circumstellar disks are better fit by a shallow inner and steep outer power law than a truncated power law. The two disks have very different transition radii between their inner and outer regions of similar to 18.6 au and similar to 8.9 au, respectively. Assuming that they are intrinsically circular and geometrically thin, we find that the two circumstellar disks are parallel with each other and orthogonal in projection to their respective ionized jets. Furthermore, the two disks are closely aligned if not parallel with their circumbinary disk. Over an interval of similar to 10 yr, source B (possessing the circumsecondary disk) has moved northward with respect to and likely away from source A, indicating an orbital motion in the same direction as the rotational motion of their circumbinary disk. All the aforementioned elements therefore share the same axis for their angular momentum, indicating that L1551NE is a product of rotationally driven fragmentation of its parental core. Assuming a circular orbit, the relative disk sizes are compatible with theoretical predictions for tidal truncation by a binary system having a mass ratio of similar to 0.2, in agreement with the reported relative separations of the two protostars from the center of their circumbinary disk. The transition radii of both disks, however, are a factor of greater than or similar to 1.5 smaller than their predicted tidally truncated radii.

Both bulk rotation and local turbulence have been widely suggested to drive the fragmentation in collapsing cores that produces multiple star systems. Even when the two mechanisms predict different alignments for stellar spins and orbits, subsequent internal or external interactions can drive multiple systems toward or away from alignment, thus masking their formation processes. Here, we demonstrate that the geometrical and dynamical relationship between a binary system and its surrounding bulk envelope provide the crucial distinction between fragmentation models. We find that the circumstellar disks of the binary protostellar system L1551 IRS 5 are closely parallel, not just with each other but also with their surrounding flattened envelope. Measurements of the relative proper motion of the binary components spanning nearly 30 years indicate an orbital motion related to that of the envelope rotation. Eliminating orbital solutions whereby the circumstellar disks would be tidally truncated to sizes smaller than observed, the remaining solutions favor a circular or low-eccentricity orbit tilted by up to similar to 25 degrees from the circumstellar disks. Turbulence-driven fragmentation can generate local angular momentum to produce a coplanar binary system, but this would have no particular relationship to the system's surrounding envelope. Instead, the observed properties conform with predictions for rotationally driven fragmentation. If the fragments were produced at different heights or on opposite sides of the mid-plane in the flattened central region of a rotating core, the resulting protostars would then exhibit circumstellar disks parallel with the surrounding envelope but tilted from the orbital plane, as is observed.

Protoplanetary disks are circumstellar disks of gas and dust, from which planets may eventually form or be in the process of forming. Recent direct imaging of them has enabled us to derive the density and temperature distributions. Interestingly they often show quite different features depending on the wavelength observed. The near-infrared emission is dominated by scattering of stellar light while the mm-and submm-wave emissions are dominated by thermal dust emission. Thus, the near-infrared emission traces a low density surface layer where stellar light is scattered toward us. The mm-and submm-wave emission trace the high density part of the disk near the mid plane. In order to explain the wavelength dependent images, we have constructed a passive disk model for HL Tau and HD142527. The former shows concentric rings in the ALMA image while the latter shows a highly asymmetric arc. Our models are based on the multi-color radiation transfer calculation. It takes account of radiation ranging from 100 nm to 3.16 mm. We used the M1 model to solve the radiative equilibrium. Our model gives some constraints on the optical properties of the dust.

We examine the two-fluid cosmic-ray magnetohydrodynamic (CR MHD) equations to take account of the dynamical effects of cosmic rays (CRs) in the simplest form. For simplicity we assume that the pressure of the CRs is proportional to the energy density, P-cr = (gamma(cr)-1) E-cr, where gamma(cr) denotes the adiabatic index of CRs. We find the fully conservative form of the CR MHD equations and derive the Rankine-Hugoniot relation for a shock. One component of the CR MHD equations describes conservation of total number of CRs where the number density is defined as rho(cr) = P-cr(1/gamma cr) . We also find the Riemann solution, which provides us approximate Riemann fluxes fluxes for numerical solutions. We have also identified origin of spurious oscillation originating from the pressure balance mode across which the CR pressure has a jump while the total pressure is continuous. We propose the two step method to solve the CR MHD equations. We use 1D shock tube problems to compare our method with others.

We have constructed two types of analytical models for an isothermal filamentary cloud supported mainly by magnetic tension. The first one describes an isolated cloud while the second considers filamentary clouds spaced periodically. Both models assume that the filamentary clouds are highly flattened. The former is proved to be the asymptotic limit of the latter in which each filamentary cloud is much thinner than the distance to the neighboring filaments. We show that these models reproduce the main features of the 2D equilibrium model of Tomisaka for a filamentary cloud threaded by a perpendicular magnetic field. It is also shown that the critical mass to flux ratio is M/Phi = (2 pi root G)(-1), where M, Phi and G denote the cloud mass, the total magnetic flux of the cloud, and the gravitational constant, respectively. This upper bound coincides with that for an axisymmetric cloud supported by poloidal magnetic fields. We apply the variational principle for studying the Jeans instability of the first model. Our model cloud is unstable against fragmentation as well as the filamentary clouds threaded by a longitudinal magnetic field. The fastest growing mode has a wavelength several times longer than the cloud diameter. The second model describes quasi-static evolution of a filamentary molecular cloud by ambipolar diffusion.

There has been few significant detections of linear polarization of sub-mm continuum from protoplanetary disks. Polarization from star-forming cores has been interpreted as thermal emission from dust grains aligned with magnetic fields. Thus, the mechanism of polarization from protoplanetary disks has also been expected to be the aligned grains. In this work, however, we show that dust scattering accounts for the sub-mm polarization of protoplanetary disks. We use 3D-radiative transfer calculations to evaluate the polarization of a lopsided protoplanetary disk. As a result, we find that the polarization by dust scattering is detectable by ALMA Band 7 polarization observations. If the maximum dust grain size is 100 mu m, the polarization by dust scattering is 2.5 % at the peak of the polarized intensity. If the polarization is detected, it will be a direct evidence of grain growth.

HD142527 is a Herbig Fe star accompanied by a disk with ring-like structure. We derive the distributions of dust and gas separately by model fitting and discuss the spatial variation of gas-to-dust mass ratio in the disk. The radial distribution of dust is well approximated by a Gaussian function, while the gas is roughly followed by a power-law distribution between 110 and 400 AU in radius, which is significantly more extended than dust. G/d may reach the order of unity at the northern peak.

We present our ALMA Cycle 0 result of a protostellar binary system L1551 NE, and discuss our future Cycle 2 observation.

We report an ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, (CO)-O-18 (3-2), and (CO)-C-13 (3-2) lines at a similar to 1.6 times higher resolution and a similar to 6 times higher sensitivity than those of our previous SubMillimeter Array (SMA) observations, which revealed a r similar to 300 AU scale circumbinary disk in Keplerian rotation. The 0.9 mm continuum shows two opposing U-shaped brightenings in the circumbinary disk and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.

We show our recent observational results of L1551 NE, an archetypal binary protostellar system, in the 0.9-mm dust continuum emission and the C-18 (J=3-2) emission with the SubMillimeter Array (SMA). The SMA results show firm evidence for a Keplerian circumbinary disk, circumstellar disks, and an inner clearing in the circumbinary disk, in L1551 NE. We demonstrate that future observations of L1551 NE with Atacama Large Millimeter and submillimeter Array (ALMA) have the potential to unveil the theoretically-predicted "accretion streams" that channel material from the circumbinary disk to the individual circumstellar disks.

Protoplanetary disks are ubiquitously observed around young solar-mass stars and are considered to be not only natural by-products of stellar evolution but also precursors of planet formation. If a forming star has close companions, the protoplanetary disk may be seriously influenced. It is important to consider this effect because most stars form as multiples. Thus, studies of protoplanetary disks in multiple systems are essential to describe the general processes of star and planet formation. We present the direct image of an interacting binary protoplanetary system. We obtained an infrared image of a young multiple circumstellar disk system, SR24, with the Subaru 8.2-m Telescope. Both circumprimary and circumsecondary disks are clearly resolved with a 0.1 arcsecond resolution. The binary system exhibits a bridge of infrared emission connecting the two disks and a long spiral arm extending from the circumprimary disk. A spiral arm would suggest that the SRN system rotates counter-clockwise. The orbital period of the binary is 15,000 yr. Numerical simulations reveal that the bridge corresponds to gas flow and a shock wave caused by the collision of gas rotating around the primary and secondary stars. The simulations also show that fresh material streams along the spiral arm, confirming the theoretical proposal that gas is replenished from a circum-multiple reservoir. These results reveal the mechanism of interacting protoplanetary disks in young multiple systems. Furthermore, our observations provide the first direct image that enables a comparison with theoretical models of mass accretion in binary systems. The observations of this binary system provide a great opportunity to test and refine theoretical models of star and planet formation in binary systems.

We discuss the stability of hydrodynamical shock against perturbations which distort the wave front. First we restrict ourselves to the case in which the flow is isothermal and one-dimensional in the steady state. It is proven that such a steady shock is stable against two-dimensional perturbations when the gas is decelerated just behind the shock front. Next we demonstrate that the conventional numerical scheme fails to simulate the physically stable flow when the shock is strong and the front is inclined with the numerical cell boundary. It is also demonstrated that the numerical instability cannot be removed by the upwind flux of the first order accuracy in space. The instability looks quite similar to the wiggle instability appearing in the hydrodynamical simulations of spiral galaxies. The similarity suggests that the wiggle instability may also be of numerical origin. The numerical instability is suppressed if we add extra numerical diffusion in the direction tangential to the shock front. Otherwise the numerical simulation suffers from spurious vortex and excess free energy in the post shocked flow. This instability is ascribed to the digitized error that the shock front is not straight but zigzagged in numerical simulations.

A new computational scheme is developed to study gas accretion from a circumbinary disk. The scheme decomposes the gas velocity into two components one of which denotes the Keplerian rotation and the other of which does the deviation from it. This scheme enables us to solve the centrifugal balance of a gas disk against gravity with better accuracy, since the former inertia force cancels the gravity. It is applied to circumbinary disk rotating around binary of which primary and secondary has mass ratio, 1.4:0.95. The gravity is reduced artificially softened only in small circular regions around the primary and secondary. The radii are 7% of the binary separation and much smaller than those in the previous grid based simulations. Seven models are constructed to study dependence on the gas temperature and the initial inner radius of the disk. The gas accretion shows both fast and slow time variations while the binary is assumed to have a circular orbit. The time variation is due to oscillation of spiral arms in the circumbinary disk. The masses of primary and secondary disks increase while oscillating appreciably. The mass accretion rate tends to be higher for the primary disk although the secondary disk has a higher accretion rate in certain periods. The accretion rates onto the two components are similar within the fluctuations in late times, i.e., after the binary rotates more than 20 times. The primary disk is perturbed intensely by the impact of gas flow so that the outer part is removed. The secondary disk is quiet in most of time on the contrary. Both the primary and secondary disks have traveling spiral waves which transfer angular momentum within them.