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News Article | December 29, 2015

Takeshi Sakai, Assistant Professor, Graduate School of Informatics and Engineering, discusses recent work. "I am using the Atacama Large Millimeter/Submillimeter Array (ALMA) facilities in Chile to study the formation of stars," says Sakai. "In particular I am looking at 'high-mass' stars formed in clusters that are approximately 10,000 light years from the Earth. High mass stars play an important role in the evolution of galaxies and ultimately hold the secrets of the origins of life on Earth." Interest in the formation of stars in clusters stems from research that indicates that 70-90% of stars in our galaxy are born in clusters. In contrast to high mass stars, there is much more knowledge about low mass stars because at 400 light years away, they are located much closer to Earth and more readily accessible with telescopes. The radio telescopes at ALMA are located at approximately 5000 m above sea level in Atacama, Chile, where the air is dry with minimal absorption of weak infra-red signature signals of the chemical composition of the clusters where high mass stars are born. "Our telescopes enable us to map the evolution of the chemical compositions of molecular clouds," explains Sakai. "So we are able to detect the very early stages of star formation by looking for changes in the chemical species of molecular clouds." For example, the core of a diffuse cloud may be composed of only ionized carbon but chemical spectra of a dense cloud will show signals from carbon monoxide/ammonia, and complex organic molecules when a star is formed. In their experiments, Sakai uses the strategy of narrowing down possible targets using single dish telescopes such as those at the Nobeyama Radio Observatory (NRO) in Nagano Prefecture, Japan, and then use the 66 telescopes at ALMA for detailed analysis of these promising targets. Needless to say astrophysics is a time consuming area of research, where it can take two to three years for data collection. "I collaborate with groups in other countries to write proposals for machine time on all the telescopes we want to use," says Sakai. "In the case of ALMA we usually get a few hours each year." In research recent Sakai and an international team recently discovered a very young star of about 1000 years old [1,3] and observations of methanol masers in a molecular clump indicating the existence of a star-forming region [2]. "We hope this research will increase our knowledge of the formation of galaxies and ultimately shed light on the origin of life of Earth." More information: [1] Takeshi Sakai, ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: DNC/HNC RATIO, Astrophysical Journal, 803:70 (9pp), (2015) [3] Takeshi Sakai, ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: HOT CORE AND MOLECULAR OUTFLOWS, Astrophysical Journal Letters, 775:L31 (6pp), (2013)

Asaki Y.,Japan Aerospace Exploration Agency | Asaki Y.,Graduate University for Advanced Studies | Deguchi S.,Nobeyama Radio Observatory | Imai H.,Kagoshima University | And 3 more authors.
Astrophysical Journal | Year: 2010

We have conducted Very Long Baseline Array phase-referencing monitoring of H2O masers around the red supergiant, S Persei, for six years.We have fitted maser motions to a simple expanding-shell model with a common annual parallax and stellar proper motion, and obtained the annual parallax as 0.413 ± 0.017 mas and the stellar proper motion as (-0.49±0.23 mas yr-1, -1.19±0.20 mas yr-1) in right ascension and declination, respectively. The obtained annual parallax corresponds to the trigonometric distance of 2.42+0.11 -0.09 kpc. Assuming a Galactocentric distance of the Sun of 8.5 kpc, the circular rotational velocity of the local standard of rest at a distance of the Sun of 220 km s-1, and a flat Galactic rotation curve, S Persei is suggested to have a non-circular motion deviating from the Galactic circular rotation for 15 km s-1, which is mainly dominated by the anti-rotation direction component of 12.9 ± 2.9 km s-1. This red supergiant is thought to belong to the OB association, Per OB1, so that this non-circular motion is representative of a motion of the OB association in the MilkyWay. This non-circular motion is somewhat larger than that explained by the standard density-wave theory for a spiral galaxy and is attributed to either a cluster shuffling of the OB association, or to non-linear interactions between non-stationary spiral arms and multi-phase interstellar media. The latter comes from a new view of a spiral arm formation in the Milky Way suggested by recent large N-body/smoothed particle hydrodynamics numerical simulations. © 2010. The American Astronomical Society. All rights reserved.

Higuchi A.E.,Joint ALMA Observatory | Higuchi A.E.,Japan National Astronomical Observatory | Higuchi A.E.,Ibaraki University | Chibueze J.O.,Japan National Astronomical Observatory | And 4 more authors.
Astronomical Journal | Year: 2014

We present the results of the sulfur monoxide, SO, line emission observations of G0.253+0.016 with the Atacama Large Millimeter/Submillimeter Array at an angular resolution of 1.″7. The dense and massive molecular cloud of G0.253+0.016 is highly sub-structured, yet it shows no obvious signs of cluster formation. We found three outstanding features of the cloud from the SO emission, namely, shell structure with a radius of 1.3 pc, large velocity gradients of 20 km s-1 pc-1 with the cloud, and cores with large velocity dispersions (30-40 km s-1) around the shell structure. We suggest that these large-velocity dispersion cores will form high-mass stars in the future. In an attempt to explore the formation scenario of the dense cloud, we compared our results with numerical simulations; therefore, we propose that G0.253+0.016 may have formed due to a cloud-cloud collision process. © 2014. The American Astronomical Society. All rights reserved.

Tsukagoshi T.,Ibaraki University | Momose M.,Ibaraki University | Saito M.,Nobeyama Radio Observatory | Kitamura Y.,Japan Aerospace Exploration Agency | And 2 more authors.
Astrophysical Journal Letters | Year: 2015

We performed single point [C i] 3P1-3P0 and CO J = 4-3 observations toward three T Tauri stars (TTSs), DM Tau, LkCa 15, and TW Hya, using the Atacama Large Millimeter/submillimeter Array Band 8 qualification model receiver installed on the Atacama Submillimeter Telescope Experiment. Two protostars (PSs) in the Taurus L1551 region, L1551 IRS 5 and HL Tau, were also observed. We successfully detected [C i] emission from the protoplanetary disk around DM Tau as well as the protostellar targets. The spectral profile of the [C i] emission from the protoplanetary disk is marginally single-peaked, suggesting that atomic carbon (C) extends toward the outermost disk. The detected [C i] emission is optically thin and the column densities of C are estimated to be ≲1016 and ∼1017 cm-2 for the TTS targets and the PSs, respectively. We found a clear difference in the total mass ratio of C to dust, M(C)/M(dust), between the TTSs and protostellar targets; the M(C)/M(dust) ratio of the TTSs is one order of magnitude smaller than that of the PSs. The decrease of the estimated M(C)/M(dust) ratios for the disk sources is consistent with a theoretical prediction that the atomic C can survive only in the near surface layer of the disk and C+/C/CO transition occurs deeper into the disk midplane. © 2015. The American Astronomical Society. All rights reserved..

Higuchi A.E.,Japan National Astronomical Observatory | Kurono Y.,Japan National Astronomical Observatory | Saito M.,Japan National Astronomical Observatory | Kawabe R.,Nobeyama Radio Observatory
Astrophysical Journal | Year: 2010

We report the H13CO+ (J = 1-0) survey observations toward embedded clusters obtained using the Nobeyama 45 m telescope, which were performed to follow up our previous study in the C18O survey with a dense gas tracer. Our aim is to address the evolution of cluster-forming clumps. We observed the same 14 clusters in C18O, which are located at distances from 0.3 to 2.1 kpc with a 27″ resolution (corresponding to the Jeans length for most of our targets) in H13CO+. We detected the 13 clumps in H13CO+ line emission and obtained the physical parameters of the clumps with radii of 0.24-0.75 pc, masses of 100-1400 M⊙, and velocity widths in FWHM of 1.5-4.0 km s-1. The mean density is ∼3.9 × 104 cm -3 and the equivalent Jeans length is ∼0.13 pc at 20 K. We classified the H13CO+ clumps into three types, type A, type B, and type C according to the relative locations of the H 13CO+ clumps and the clusters (see our previous study). Our classification represents an evolutionary trend of cluster-forming clumps because dense clumps are expected to be converted into stellar constituents, or dispersed by stellar activities. We found a similar, but clearer trend than our previous results, for derived star formation efficiencies to increase from type A to C in the H13CO+ data, and for the dense gas regions within the clumps traced by H13CO+ to be sensitive to the physical evolution of the clump-cluster systems. In addition, we found that 4 out of 13 H13CO+ clumps, which we named "Distinct Velocity Structure Objects" (DVSOs), have distinct velocity gradients at their central parts, i.e., at the location of the embedded clusters. Assuming that the velocity gradients represent the rigid-like rotation of the clumps, we calculated the virial parameter of the H13CO+ clumps by taking into account the contribution of the rotation and found that the DVSOs tend to be gravitationally unbound. In order to explain the above physical properties for DVSOs in a consistent way, we propose a clump-clump collision model as a possible mechanism for triggering the formation of clusters. © 2010. The American Astronomical Society.

Yoshida A.,Tokyo Institute of Technology | Kitamura Y.,Japan Aerospace Exploration Agency | Shimajiri Y.,University of Tokyo | Shimajiri Y.,Nobeyama Radio Observatory | And 2 more authors.
Astrophysical Journal | Year: 2010

We have carried out mapping observations of the entire L1551 molecular cloud with about 2 pc × 2 pc size in the 12CO(1-0) line with the Nobeyama 45 m radio telescope at the high effective resolution of 22″ (corresponding to 0.017 pc at the distance of 160 pc), and analyzed the 12CO data together with the 13CO(1-0) and C 18O(1-0) data from the Nobeyama Radio Observatory database. We derived the new non-thermal line width-size relations, σNT ∝ Lγ , for the three molecular lines, corrected for the effect of optical depth and the line-of-sight integration. To investigate the characteristic of the intrinsic turbulence, the effects of the outflows were removed. The derived relations are (σNT/km s-1) = (0.18 ± 0.010)(L/pc)0.45±0.095, (0.20 ± 0.020)(L/pc)0.48±0.091, and (0.22 ± 0.050) (L/pc) 0.54±0.21 for the 12CO, 13CO, and C 18O lines, respectively, suggesting that the line width-size relation of the turbulence very weakly depends on our observed molecular lines, i.e., the relation does not change between the density ranges of 10 2-103 and 103-104 cm-3. In addition, the relations indicate that incompressible turbulence is dominant at the scales smaller than 0.6 pc in L1551. The power spectrum indices converted from the relations, however, seem to be larger than that of the Kolmogorov spectrum for incompressible flow. The disagreement could be explained by the anisotropy in the turbulent velocity field in L1551, as expected in MHD turbulence. Actually, the autocorrelation functions of the centroid velocity fluctuations show larger correlation along the direction of the magnetic field measured for the whole Taurus cloud, which is consistent with the results of numerical simulations for incompressible MHD flow. © 2010. The American Astronomical Society. All rights reserved.

Nakamura F.,Japan National Astronomical Observatory | Nakamura F.,Nobeyama Radio Observatory | Li Z.-Y.,University of Virginia
Astrophysical Journal | Year: 2014

Protostellar outflows have been shown theoretically to be capable of maintaining supersonic turbulence in cluster-forming clumps and keeping the star formation rate per free-fall time as low as a few percent. We aim to test two basic predictions of this outflow-regulated cluster formation model, namely, (1) the clump should be close to virial equilibrium and (2) the turbulence dissipation rate should be balanced by the outflow momentum injection rate, using recent outflow surveys toward eight nearby cluster-forming clumps (B59, L1551, L1641N, Serpens Main Cloud, Serpens South, ρ Oph, IC 348, and NGC 1333). We find, for almost all sources, that the clumps are close to virial equilibrium and the outflow momentum injection rate exceeds the turbulence momentum dissipation rate. In addition, the outflow kinetic energy is significantly smaller than the clump gravitational energy for intermediate and massive clumps with M cl ≳ a few × 102 M ⊙, suggesting that the outflow feedback is not enough to disperse the clump as a whole. The number of observed protostars also indicates that the star formation rate per free-fall time is as small as a few percent for all clumps. These observationally based results strengthen the case for outflow-regulated cluster formation. © 2014. The American Astronomical Society. All rights reserved.

Sawada T.,Joint ALMA Office | Sawada T.,NAOJ Chile Observatory | Sawada T.,Nobeyama Radio Observatory | Hasegawa T.,Joint ALMA Office | And 6 more authors.
Astrophysical Journal | Year: 2012

We have carried out survey observations toward the Galactic plane at l 38° in the 12CO and 13CO J = 1-0 lines using the Nobeyama Radio Observatory 45m telescope. A wide area (08 × 08) was mapped with high spatial resolution (17″). The line of sight samples the gas in both the Sagittarius arm and the interarm regions. The present observations reveal how the structure and physical conditions vary across a spiral arm. We classify the molecular gas in the line of sight into two distinct components based on its appearance: the bright and compact B component and the fainter and diffuse (i.e., more extended) D component. The B component is predominantly seen at the spiral arm velocities, while the D component dominates at the interarm velocities and is also found at the spiral arm velocities. We introduce the brightness distribution function and the brightness distribution index (BDI, which indicates the dominance of the B component) in order to quantify the map's appearance. The radial velocities of BDI peaks coincide with those of high 12CO J = 3-2/12CO J = 1-0 intensity ratio (i.e., warm gas) and H II regions, and tend to be offset from the line brightness peaks at lower velocities (i.e., presumably downstream side of the arm). Our observations reveal that the gas structure at small scales changes across a spiral arm: bright and spatially confined structures develop in a spiral arm, leading to star formation at the downstream side, while extended emission dominates in the interarm region. © 2012. The American Astronomical Society. All rights reserved..

Nimori M.,Hokkaido University | Habe A.,Hokkaido University | Sorai K.,Hokkaido University | Watanabe Y.,University of Tokyo | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2MASS data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than 104M⊙ (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholz & McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The star formation efficiency in the bar region is ̃60 per cent of the spiral arm region. This trend is consistent with observations of barred galaxies. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Bezrukov D.A.,Ventspils International Radio Astronomy Center | Ryabov B.I.,Ventspils International Radio Astronomy Center | Shibasaki K.,Nobeyama Radio Observatory
Baltic Astronomy | Year: 2012

On the base of the 17 GHz radio maps of the Sun taken with the Nobeyama Radio Heliograph we estimate plasma parameters in the specific region of the sunspot atmosphere in the active region AR 11312. This region of the sunspot atmosphere is characterized by the depletion in coronal emission (soft X-ray and EUV lines) and the reduced absorption in the a chromospheric line (HeI 1.083 μm). In the ordinary normal mode of 17 GHz emission the corresponding dark patch has the largest visibility near the central solar meridian. We infer that the reduced coronal plasma density of about 5 × 108 cm -3 is the characteristic feature of the dark patch.

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