Shigehisa Takakuwa - Academia.edu (original) (raw)

Papers by Shigehisa Takakuwa

We have analyzed ALMA Cycle 5 data in Band 4 toward three low-mass young stellar objects (YSOs), ... more We have analyzed ALMA Cycle 5 data in Band 4 toward three low-mass young stellar objects (YSOs), IRAS 03235+3004 (hereafter IRAS 03235), IRAS 03245+3002 (IRAS 03245), and IRAS 03271+3013 (IRAS 03271), in the Perseus region. The HC_3N (J=16-15; E_up/k = 59.4 K) line has been detected in all of the target sources, while four CH_3OH lines (E_up/k = 15.4-36.3 K) have been detected only in IRAS 03245. Sizes of the HC_3N distributions (∼ 2930-3230 au) in IRAS 03235 and IRAS 03245 are similar to those of the carbon-chain species in the warm carbon chain chemistry (WCCC) source L1527. The size of the CH_3OH emission in IRAS 03245 is ∼ 1760 au, which is slightly smaller than that of HC_3N in this source. We compare the CH_3OH/HC_3N abundance ratios observed in these sources with predictions of chemical models. We confirm that the observed ratio in IRAS 03245 agrees with the modeled values at temperatures around 30–35 K, which supports the HC_3N formation by the WCCC mechanism. In this temper...

With the ASTE telescope, we have made observations of three low-mass protostellar envelopes aroun... more With the ASTE telescope, we have made observations of three low-mass protostellar envelopes around L483, B335, and L723 in the submillimeter CS (J=7--6) and HCN (J=4--3) lines. We detected both the CS and HCN lines toward all the targets, and the typical CS intensity (∼ 1.0 K in T_B) is twice higher than that of the HCN line. Mapping observations of L483 in these lines have shown that the submillimeter emissions in the low-mass protostellar envelope are resolved, exhibit a western extension from the central protostar, and that the deconvolved size is ∼ 5500 AU × 3700 AU (P.A. = 78^∘) in the HCN emission. The extent of the submillimeter emissions in L483 implies the presence of higher-temperature (≳ 40 K) gas at 4000 AU away from the central protostar, which suggests that we need to take 2-dimensional radiative transfer models with a flattened disklike envelope and bipolar cavity into account to explain the temperature structure inside the low-mass protostellar envelope. The position...

The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and i... more The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and it is still embedded in a protostellar envelope with a size of thousands of au. In this work, we study the gas kinematics in the envelope and its possible influence on the embedded disk. We present our new ALMA cycle 3 observational results of HL Tau in the 13CO (2-1) and C18O (2-1) emission at resolutions of 0.8" (110 au), and we compare the observed velocity pattern with models of different kinds of gas motions. Both the 13CO and C18O emission lines show a central compact component with a size of 2" (280 au), which traces the protoplanetary disk. The disk is clearly resolved and shows a Keplerian motion, from which the protostellar mass of HL Tau is estimated to be 1.8+/-0.3 M_, assuming the inclination angle of the disk to be 47 deg from the plane of the sky. The 13CO emission shows two arc structures with sizes of 1000-2000 au and masses of 3E-3 M_ connected to the central d...

We have imaged the circumstellar envelope around the binary protostar L1551 IRS 5 in CS (J=7-6) a... more We have imaged the circumstellar envelope around the binary protostar L1551 IRS 5 in CS (J=7-6) and 343 GHz continuum emission at ~ 3 arcsec resolution using the Submillimeter Array. The continuum emission shows an elongated structure (~ 220 x 100 AU) around the binary perpendicular to the axis of the associated radio jet. The CS emission extends over ~ 400 AU, appears approximately circularly symmetric, and shows a velocity gradient from southeast (blueshifted) to northwest (redshifted). The direction of the velocity gradient is different from that observed in C18O (J=1-0). This may be because rotation is more dominant in the CS envelope than the C18O envelope, in which both infall and rotation exist. The CS emission may be divided into two velocity components: (1) a "high" velocity disk-like structure surrounding the protostar, +-1.0 - 1.5 km s-1 from the systemic velocity, and (2) a "low" velocity structure, located southwest of the protostar, < 1.0 km s -1...

With the Submillimeter Array (SMA) we have made high angular-resolution (∼ 1 ′′ = 160 AU) observa... more With the Submillimeter Array (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 15 N, 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 of Source A in the SouthEast and Source B in the NorthWest with a separation of ∼5 ′′. The optically-thin HC 15 N (4-3) emission taken with the SMA has revealed a compact (∼ 500 AU) flattened structure (P.A. =-16 •) associated with Source A. This compact structure 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, although the P.A. of the compact structure (=-45 •) seen in the HCN emission is slightly different from that of the HC 15 N emission. A toy model consisting of a flattened structure with radial infall towards a 1 M ⊙ central star reproduces the HCN/HC 15 N position-velocity diagram along the minor axis of the HC 15 N emission. In the extended envelope there is also a NorthEast

We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the... more We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), 13CO (3-2), SO (7_8-6_7), and the CS (7-6) emission. At 0.18" (= 25 AU) resolution, ~4-times higher than that of our Cycle 0 observations, the circumbinary disk as seen in the 0.9-mm emission is shown to be comprised of a northern and a southern spiral arm, with the southern arm connecting to the circumstellar disk 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 C18O emission, the infall gas motions in the inter-arm 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 inter-arm regions. Chemical differentiation of the circumbinary disk i...

We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm c... more We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SMA observations, which revealed a r ~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 ob...

We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs) L1521F-IRS and IRAM 0... more We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs) L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines with the Nobeyama 45 m telescope. Towards L1521F-IRS, carbon-chain lines of CH3CCH (50-40), C4H (17/2-15/2), and C3H2 (212-101) are 1.5 - 3.5 times stronger than those towards IRAM 04191+1522, and the abundances of the carbon-chain molecules towards L1521F-IRS are 2 to 5 times higher than those towards IRAM 04191+1522. Mapping observations of these carbon-chain molecular lines show that in L1521F the peak positions of these carbon-chain molecular lines are different from each other and there is no emission peak towards the VeLLO position, while in IRAM 04191+1522 these carbon-chain lines are as weak as the detection limits except for the C3H2 line. The observed chemical differentiation between L1521F and IRAM 04191+1522 suggests that the evolutionary stage of L1521F-IRS is younger than that of IRAM 04191+1522, consistent with the exte...

We present SubMillimeter-Array observations of a Keplerian disk around the Class I protobinary sy... more We present SubMillimeter-Array observations of a Keplerian disk around the Class I protobinary system L1551 NE in 335 GHz continuum emission and submillimeter line emission in 13CO (J=3-2) and C18O (J=3-2) at a resolution of ~120 x 80 AU. The 335-GHz dust-continuum image shows a strong central peak closely coincident with the binary protostars and likely corresponding to circumstellar disks, surrounded by a ~600 x 300 AU feature elongated approximately perpendicular to the [Fe II] jet from the southern protostellar component suggestive of a circumbinary disk. The 13CO and C18O images confirm that the circumbinary continuum feature is indeed a rotating disk; furthermore, the C18O channel maps can be well modeled by a geometrically-thin disk exhibiting Keplerian rotation. We estimate a mass for the circumbinary disk of ~0.03-0.12 Msun, compared with an enclosed mass of ~0.8 Msun that is dominated by the protobinary system. Compared with several other Class I protostars known to exhibi...

We report the discovery of an extremely young protostar, SMM11, located in the associated submill... more We report the discovery of an extremely young protostar, SMM11, located in the associated submillimeter condensation SMM11 in the Serpens Main cluster using the Atacama Large Millimeter/submillimeter Array (ALMA) during its Cycle 3 at 1.3 mm and an angular resolution of ~0.5"~210 AU. SMM11 is a Class 0 protostar without any counterpart at 70 um or shorter wavelengths. The ALMA observations show 1.3 mm continuum emission associated with a collimated 12CO bipolar outflow. Spitzer and Herschel data show that SMM11 is extremely cold (T_bol=26 K) and faint (L_bol<~0.9 Lsun). We estimate the inclination angle of the outflow to be ~80 deg, almost parallel to the plane of the sky, from simple fitting using wind-driven-shell model. The continuum visibilities consist of Gaussian and power-law components, suggesting a spherical envelope with a radius of ~600 AU around the protostar. The estimated low C18O abundance, X(C18O)=1.5-3x10^-10, is also consistent with its youth. The high outf...

We have made mapping observations of L1551 IRS 5, L1551NE, L723, and L43 and single-point observa... more We have made mapping observations of L1551 IRS 5, L1551NE, L723, and L43 and single-point observations of IRAS 16293-2422 in the submillimeter CS (J = 7-6) and HCN (J = 4-3) lines with ASTE. Including our previous ASTE observations of L483 and B335, we found a clear linear correlation between the source bolometric luminosities and the total integrated intensities of the submillimeter lines (I_CS ~L_bol^0.92). The combined ASTE + SMA CS (7-6) image of L1551 IRS 5 exhibits an extended (~2000 AU) component tracing the associated reflection nebula at the west and southwest, as well as a compact (< 500 AU) component centered on the protostellar position. The emission peaks of the CS and HCN emissions in L1551 NE are not located at the protostellar position but offset (~1400 AU) toward the associated reflection nebula at the west. With the statistical analyses, we confirmed the opposite velocity gradients of the CS (7-6) emission to those of the millimeter lines along the outflow direc...

We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum observations toward one ... more We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum observations toward one of the strongest mm-wave sources in OMC-3, MMS 7, with the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the NMA, we detected centrally-condensed 3.3 mm dust-continuum emission which coincides with the MIR source and the free-free jet. Our combined H13CO+ observations have revealed a disk-like envelope. The size and the mass of the disk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively. The combined map also shows that the outer portion of the disk-like envelope has a fan-shaped structure which delineates the rim of the CO(1-0) outflow observed with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0) emission show that the velocity field in the disk-like envelope is composed of a dispersing gas motion and a possible rigid-like rotation. The mass dispersing rate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies th...

With the ASTE telescope, we have made observations of three low-mass protostellar envelopes aroun... more With the ASTE telescope, we have made observations of three low-mass protostellar envelopes around L483, B335, and L723 in the submillimeter CS (J=7–6) and HCN (J=4–3) lines. We detected both the CS and HCN lines toward all the targets, and the typical CS intensity ( ∼ 1.0 K in TB) is twice higher than that of the HCN line. Mapping observations of L483 in these lines have shown that the submillimeter emissions in the low-mass protostellar envelope are resolved, exhibit a western extension from the central protostar, and that the deconvolved size is ∼ 5500 AU × 3700 AU (P.A. = 78 ◦ ) in the HCN emission. The extent of the submillimeter emissions in L483 implies the presence of higher-temperature (> ∼ 40 K) gas at 4000 AU away from the central protostar, which suggests that we need to take 2-dimensional radiative transfer models with a flattened disklike envelope and bipolar cavity into account to explain the temperature structure inside the low-mass protostellar envelope. The posi...

We have mapped the proto-binary source IRAS 16293–2422 in CO 2–1, 13 CO 2–1, and CO 3–2 with the ... more We have mapped the proto-binary source IRAS 16293–2422 in CO 2–1, 13 CO 2–1, and CO 3–2 with the Submillimeter Array (SMA). The maps with resolution of 1. ′ ′ 5–5 ′ ′ reveal a single small scale (∼3000 AU) bipolar molecular outflow along the east-west direction. We found that the blueshifted emission of this small scale outflow mainly extends to the east and the redshifted emission to the west from the position of IRAS 16293A. A comparison with the morphology of the large scale outflows previously observed by single-dish telescopes at millimeter wavelengths suggests that the small scale outflow may be the inner part of the large scale (∼15000 AU) E–W outflow. On the other hand, there is no clear counterpart of the large scale NE–SW outflow in our SMA maps. Comparing analytical models to the data suggests that the morphology and kinematics of the small scale outflow can be explained by a wide-angle wind with an inclination angle of ∼30 ◦ –40 ◦ with respect to the plane of the sky. Th...

We have investigated the evolution and distribution of molecules in collapsing prestellar cores v... more We have investigated the evolution and distribution of molecules in collapsing prestellar cores via numerical chemical models, adopting the Larson-Penston solution and its delayed analogues to study collapse. Molecular abundances and distributions in a collapsing core are determined by the balance among the dynamical, chemical and adsorption time scales. When the central density nH of a prestellar core with the Larson-Penston flow rises to 3 × 10 6 cm −3, the CCS and CO column densities are calculated to show central holes of radius 7000 AU and 4000 AU, respectively, while the column density of N2H + is centrally peaked. These predictions are consistent with observations of L1544. If the dynamical time scale of the core is larger than that of the Larson-Penston solution owing to magnetic fields, rotation, or turbulence, the column densities of CO and CCS are smaller, and their holes are larger than in the Larson-Penston core with the same central gas density. On the other hand, N2H ...

We have analyzed Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 4 Band 6 data toward t... more We have analyzed Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in the Ophiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9 is irradiated by a nearby bright Herbig Be star. Molecular lines from cyclic-C3H2 (c-C3H2), H2CO, CH3OH, CO, CO, and DCO have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5, c-C3H2 is enhanced at the west side, relative to the IR source, whereas H2CO and CH3OH are abundant at the east side. In the field of Oph-emb9, moment 0 maps of the c-C3H2 lines show a peak at the eastern edge of the field of view, which is irradiated by the Herbig Be star. Moment 0 maps of CH3OH and H2CO show peaks farther from the bright star. We derive the N(cC3H2)/N(CH3OH) column density ratios at the peak positions of c-C3H2 and CH3OH near each YSO, which are identified based on their moment 0 maps. T...

arXiv: Astrophysics of Galaxies, 2017

We report our current SMA and ALMA studies of disk and planet formation around protostars. We hav... more We report our current SMA and ALMA studies of disk and planet formation around protostars. We have revealed that rgtrsimr \gtrsimrgtrsim100 AU scale disks in Keplerian rotation are ubiquitous around Class I sources. These Class I Keplerian disks are often embedded in rotating and infalling protostellar envelopes. The infalling speeds of the protostellar envelopes are typically sim\simsim 3-times smaller than the free-fall velocities, and the rotational profiles follow the r−1r^{-1}r−1 profile, that is, rotation with the conserved specific angular momentum. Our latest high-resolution ($\sim$0$\farcs$5) ALMA studies, as well as the other studies in the literature, have unveiled that rsimr \simrsim100-AU scale Keplerian disks are also present in several Class 0 protostars, while in the other Class 0 sources the inferred upper limits of the Keplerian disks are very small ($r \lessim$20 AU). Our recent data analyses of the ALMA long baseline data of the Class I-II source HL Tau have revealed gaps in molecular gas...

We have analyzed ALMA Cycle 5 data in Band 4 toward three low-mass young stellar objects (YSOs), ... more We have analyzed ALMA Cycle 5 data in Band 4 toward three low-mass young stellar objects (YSOs), IRAS 03235+3004 (hereafter IRAS 03235), IRAS 03245+3002 (IRAS 03245), and IRAS 03271+3013 (IRAS 03271), in the Perseus region. The HC_3N (J=16-15; E_up/k = 59.4 K) line has been detected in all of the target sources, while four CH_3OH lines (E_up/k = 15.4-36.3 K) have been detected only in IRAS 03245. Sizes of the HC_3N distributions (∼ 2930-3230 au) in IRAS 03235 and IRAS 03245 are similar to those of the carbon-chain species in the warm carbon chain chemistry (WCCC) source L1527. The size of the CH_3OH emission in IRAS 03245 is ∼ 1760 au, which is slightly smaller than that of HC_3N in this source. We compare the CH_3OH/HC_3N abundance ratios observed in these sources with predictions of chemical models. We confirm that the observed ratio in IRAS 03245 agrees with the modeled values at temperatures around 30–35 K, which supports the HC_3N formation by the WCCC mechanism. In this temper...

With the ASTE telescope, we have made observations of three low-mass protostellar envelopes aroun... more With the ASTE telescope, we have made observations of three low-mass protostellar envelopes around L483, B335, and L723 in the submillimeter CS (J=7--6) and HCN (J=4--3) lines. We detected both the CS and HCN lines toward all the targets, and the typical CS intensity (∼ 1.0 K in T_B) is twice higher than that of the HCN line. Mapping observations of L483 in these lines have shown that the submillimeter emissions in the low-mass protostellar envelope are resolved, exhibit a western extension from the central protostar, and that the deconvolved size is ∼ 5500 AU × 3700 AU (P.A. = 78^∘) in the HCN emission. The extent of the submillimeter emissions in L483 implies the presence of higher-temperature (≳ 40 K) gas at 4000 AU away from the central protostar, which suggests that we need to take 2-dimensional radiative transfer models with a flattened disklike envelope and bipolar cavity into account to explain the temperature structure inside the low-mass protostellar envelope. The position...

The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and i... more The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and it is still embedded in a protostellar envelope with a size of thousands of au. In this work, we study the gas kinematics in the envelope and its possible influence on the embedded disk. We present our new ALMA cycle 3 observational results of HL Tau in the 13CO (2-1) and C18O (2-1) emission at resolutions of 0.8" (110 au), and we compare the observed velocity pattern with models of different kinds of gas motions. Both the 13CO and C18O emission lines show a central compact component with a size of 2" (280 au), which traces the protoplanetary disk. The disk is clearly resolved and shows a Keplerian motion, from which the protostellar mass of HL Tau is estimated to be 1.8+/-0.3 M_, assuming the inclination angle of the disk to be 47 deg from the plane of the sky. The 13CO emission shows two arc structures with sizes of 1000-2000 au and masses of 3E-3 M_ connected to the central d...

We have imaged the circumstellar envelope around the binary protostar L1551 IRS 5 in CS (J=7-6) a... more We have imaged the circumstellar envelope around the binary protostar L1551 IRS 5 in CS (J=7-6) and 343 GHz continuum emission at ~ 3 arcsec resolution using the Submillimeter Array. The continuum emission shows an elongated structure (~ 220 x 100 AU) around the binary perpendicular to the axis of the associated radio jet. The CS emission extends over ~ 400 AU, appears approximately circularly symmetric, and shows a velocity gradient from southeast (blueshifted) to northwest (redshifted). The direction of the velocity gradient is different from that observed in C18O (J=1-0). This may be because rotation is more dominant in the CS envelope than the C18O envelope, in which both infall and rotation exist. The CS emission may be divided into two velocity components: (1) a "high" velocity disk-like structure surrounding the protostar, +-1.0 - 1.5 km s-1 from the systemic velocity, and (2) a "low" velocity structure, located southwest of the protostar, < 1.0 km s -1...

With the Submillimeter Array (SMA) we have made high angular-resolution (∼ 1 ′′ = 160 AU) observa... more With the Submillimeter Array (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 15 N, 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 of Source A in the SouthEast and Source B in the NorthWest with a separation of ∼5 ′′. The optically-thin HC 15 N (4-3) emission taken with the SMA has revealed a compact (∼ 500 AU) flattened structure (P.A. =-16 •) associated with Source A. This compact structure 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, although the P.A. of the compact structure (=-45 •) seen in the HCN emission is slightly different from that of the HC 15 N emission. A toy model consisting of a flattened structure with radial infall towards a 1 M ⊙ central star reproduces the HCN/HC 15 N position-velocity diagram along the minor axis of the HC 15 N emission. In the extended envelope there is also a NorthEast

We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the... more We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), 13CO (3-2), SO (7_8-6_7), and the CS (7-6) emission. At 0.18" (= 25 AU) resolution, ~4-times higher than that of our Cycle 0 observations, the circumbinary disk as seen in the 0.9-mm emission is shown to be comprised of a northern and a southern spiral arm, with the southern arm connecting to the circumstellar disk 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 C18O emission, the infall gas motions in the inter-arm 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 inter-arm regions. Chemical differentiation of the circumbinary disk i...

We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm c... more We report the ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SMA observations, which revealed a r ~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 ob...

We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs) L1521F-IRS and IRAM 0... more We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs) L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines with the Nobeyama 45 m telescope. Towards L1521F-IRS, carbon-chain lines of CH3CCH (50-40), C4H (17/2-15/2), and C3H2 (212-101) are 1.5 - 3.5 times stronger than those towards IRAM 04191+1522, and the abundances of the carbon-chain molecules towards L1521F-IRS are 2 to 5 times higher than those towards IRAM 04191+1522. Mapping observations of these carbon-chain molecular lines show that in L1521F the peak positions of these carbon-chain molecular lines are different from each other and there is no emission peak towards the VeLLO position, while in IRAM 04191+1522 these carbon-chain lines are as weak as the detection limits except for the C3H2 line. The observed chemical differentiation between L1521F and IRAM 04191+1522 suggests that the evolutionary stage of L1521F-IRS is younger than that of IRAM 04191+1522, consistent with the exte...

We present SubMillimeter-Array observations of a Keplerian disk around the Class I protobinary sy... more We present SubMillimeter-Array observations of a Keplerian disk around the Class I protobinary system L1551 NE in 335 GHz continuum emission and submillimeter line emission in 13CO (J=3-2) and C18O (J=3-2) at a resolution of ~120 x 80 AU. The 335-GHz dust-continuum image shows a strong central peak closely coincident with the binary protostars and likely corresponding to circumstellar disks, surrounded by a ~600 x 300 AU feature elongated approximately perpendicular to the [Fe II] jet from the southern protostellar component suggestive of a circumbinary disk. The 13CO and C18O images confirm that the circumbinary continuum feature is indeed a rotating disk; furthermore, the C18O channel maps can be well modeled by a geometrically-thin disk exhibiting Keplerian rotation. We estimate a mass for the circumbinary disk of ~0.03-0.12 Msun, compared with an enclosed mass of ~0.8 Msun that is dominated by the protobinary system. Compared with several other Class I protostars known to exhibi...

We report the discovery of an extremely young protostar, SMM11, located in the associated submill... more We report the discovery of an extremely young protostar, SMM11, located in the associated submillimeter condensation SMM11 in the Serpens Main cluster using the Atacama Large Millimeter/submillimeter Array (ALMA) during its Cycle 3 at 1.3 mm and an angular resolution of ~0.5"~210 AU. SMM11 is a Class 0 protostar without any counterpart at 70 um or shorter wavelengths. The ALMA observations show 1.3 mm continuum emission associated with a collimated 12CO bipolar outflow. Spitzer and Herschel data show that SMM11 is extremely cold (T_bol=26 K) and faint (L_bol<~0.9 Lsun). We estimate the inclination angle of the outflow to be ~80 deg, almost parallel to the plane of the sky, from simple fitting using wind-driven-shell model. The continuum visibilities consist of Gaussian and power-law components, suggesting a spherical envelope with a radius of ~600 AU around the protostar. The estimated low C18O abundance, X(C18O)=1.5-3x10^-10, is also consistent with its youth. The high outf...

We have made mapping observations of L1551 IRS 5, L1551NE, L723, and L43 and single-point observa... more We have made mapping observations of L1551 IRS 5, L1551NE, L723, and L43 and single-point observations of IRAS 16293-2422 in the submillimeter CS (J = 7-6) and HCN (J = 4-3) lines with ASTE. Including our previous ASTE observations of L483 and B335, we found a clear linear correlation between the source bolometric luminosities and the total integrated intensities of the submillimeter lines (I_CS ~L_bol^0.92). The combined ASTE + SMA CS (7-6) image of L1551 IRS 5 exhibits an extended (~2000 AU) component tracing the associated reflection nebula at the west and southwest, as well as a compact (< 500 AU) component centered on the protostellar position. The emission peaks of the CS and HCN emissions in L1551 NE are not located at the protostellar position but offset (~1400 AU) toward the associated reflection nebula at the west. With the statistical analyses, we confirmed the opposite velocity gradients of the CS (7-6) emission to those of the millimeter lines along the outflow direc...

We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum observations toward one ... more We report the results of H13CO+(1-0), CO(1-0), and 3.3 mm dust continuum observations toward one of the strongest mm-wave sources in OMC-3, MMS 7, with the Nobeyama Millimeter Array (NMA) and the Nobeyama 45 m telescope. With the NMA, we detected centrally-condensed 3.3 mm dust-continuum emission which coincides with the MIR source and the free-free jet. Our combined H13CO+ observations have revealed a disk-like envelope. The size and the mass of the disk-like envelope are 0.15 times 0.11 pc and 5.1 - 9.1 M_sun, respectively. The combined map also shows that the outer portion of the disk-like envelope has a fan-shaped structure which delineates the rim of the CO(1-0) outflow observed with the NMA. The position-velocity (P-V) diagrams in the H13CO+ (1-0) emission show that the velocity field in the disk-like envelope is composed of a dispersing gas motion and a possible rigid-like rotation. The mass dispersing rate is estimated to be (3.4 - 6.0) times 10^-5 M_sun/yr, which implies th...

With the ASTE telescope, we have made observations of three low-mass protostellar envelopes aroun... more With the ASTE telescope, we have made observations of three low-mass protostellar envelopes around L483, B335, and L723 in the submillimeter CS (J=7–6) and HCN (J=4–3) lines. We detected both the CS and HCN lines toward all the targets, and the typical CS intensity ( ∼ 1.0 K in TB) is twice higher than that of the HCN line. Mapping observations of L483 in these lines have shown that the submillimeter emissions in the low-mass protostellar envelope are resolved, exhibit a western extension from the central protostar, and that the deconvolved size is ∼ 5500 AU × 3700 AU (P.A. = 78 ◦ ) in the HCN emission. The extent of the submillimeter emissions in L483 implies the presence of higher-temperature (> ∼ 40 K) gas at 4000 AU away from the central protostar, which suggests that we need to take 2-dimensional radiative transfer models with a flattened disklike envelope and bipolar cavity into account to explain the temperature structure inside the low-mass protostellar envelope. The posi...

We have mapped the proto-binary source IRAS 16293–2422 in CO 2–1, 13 CO 2–1, and CO 3–2 with the ... more We have mapped the proto-binary source IRAS 16293–2422 in CO 2–1, 13 CO 2–1, and CO 3–2 with the Submillimeter Array (SMA). The maps with resolution of 1. ′ ′ 5–5 ′ ′ reveal a single small scale (∼3000 AU) bipolar molecular outflow along the east-west direction. We found that the blueshifted emission of this small scale outflow mainly extends to the east and the redshifted emission to the west from the position of IRAS 16293A. A comparison with the morphology of the large scale outflows previously observed by single-dish telescopes at millimeter wavelengths suggests that the small scale outflow may be the inner part of the large scale (∼15000 AU) E–W outflow. On the other hand, there is no clear counterpart of the large scale NE–SW outflow in our SMA maps. Comparing analytical models to the data suggests that the morphology and kinematics of the small scale outflow can be explained by a wide-angle wind with an inclination angle of ∼30 ◦ –40 ◦ with respect to the plane of the sky. Th...

We have investigated the evolution and distribution of molecules in collapsing prestellar cores v... more We have investigated the evolution and distribution of molecules in collapsing prestellar cores via numerical chemical models, adopting the Larson-Penston solution and its delayed analogues to study collapse. Molecular abundances and distributions in a collapsing core are determined by the balance among the dynamical, chemical and adsorption time scales. When the central density nH of a prestellar core with the Larson-Penston flow rises to 3 × 10 6 cm −3, the CCS and CO column densities are calculated to show central holes of radius 7000 AU and 4000 AU, respectively, while the column density of N2H + is centrally peaked. These predictions are consistent with observations of L1544. If the dynamical time scale of the core is larger than that of the Larson-Penston solution owing to magnetic fields, rotation, or turbulence, the column densities of CO and CCS are smaller, and their holes are larger than in the Larson-Penston core with the same central gas density. On the other hand, N2H ...

We have analyzed Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 4 Band 6 data toward t... more We have analyzed Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in the Ophiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9 is irradiated by a nearby bright Herbig Be star. Molecular lines from cyclic-C3H2 (c-C3H2), H2CO, CH3OH, CO, CO, and DCO have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5, c-C3H2 is enhanced at the west side, relative to the IR source, whereas H2CO and CH3OH are abundant at the east side. In the field of Oph-emb9, moment 0 maps of the c-C3H2 lines show a peak at the eastern edge of the field of view, which is irradiated by the Herbig Be star. Moment 0 maps of CH3OH and H2CO show peaks farther from the bright star. We derive the N(cC3H2)/N(CH3OH) column density ratios at the peak positions of c-C3H2 and CH3OH near each YSO, which are identified based on their moment 0 maps. T...

arXiv: Astrophysics of Galaxies, 2017

We report our current SMA and ALMA studies of disk and planet formation around protostars. We hav... more We report our current SMA and ALMA studies of disk and planet formation around protostars. We have revealed that rgtrsimr \gtrsimrgtrsim100 AU scale disks in Keplerian rotation are ubiquitous around Class I sources. These Class I Keplerian disks are often embedded in rotating and infalling protostellar envelopes. The infalling speeds of the protostellar envelopes are typically sim\simsim 3-times smaller than the free-fall velocities, and the rotational profiles follow the r−1r^{-1}r−1 profile, that is, rotation with the conserved specific angular momentum. Our latest high-resolution ($\sim$0$\farcs$5) ALMA studies, as well as the other studies in the literature, have unveiled that rsimr \simrsim100-AU scale Keplerian disks are also present in several Class 0 protostars, while in the other Class 0 sources the inferred upper limits of the Keplerian disks are very small ($r \lessim$20 AU). Our recent data analyses of the ALMA long baseline data of the Class I-II source HL Tau have revealed gaps in molecular gas...