Dust Cores Research Articles

Pleistocene people and environments

Human Evolution In the past few decades, hundreds of hominin fossils have been recovered from well-dated sites in East Africa. In addition, early representatives from far outside Africa have been found in Asia and Europe. Recently, discoveries at Malapa in South Africa and at Dmanisi in western Asia have brought important new fossils and archaeological residues to light. Analyses of local stratigraphy, windblown dust, sea and lake cores, and stable isotopic analyses have improved the reconstruction of ancient environments inhabited by early humans. Anton et al. review recent evidence and arguments about the evolution of early Homo , arguing that habitat instability and fragmentation imposed an important selective force. Science , this issue p. [10.1126/science.1236828][1] [1]: /lookup/doi/10.1126/science.1236828

Shaping a high-mass star-forming cluster through stellar feedback

Context: NGC 7538 IRS 1-3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact H$_{\rm II}$ regions, molecular outflows, and masers. In such a complex environment, important interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region. Aims: We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1-3 region to investigate the role of the different forces interplaying in the formation and evolution of high-mass star-forming clusters. Methods: We perform SMA high angular resolution observations at 880 $\mu$m with the compact configuration. We develop the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. We develop the "mass balance" analysis to quantify the stability against gravitational collapse accounting for all the energetics at core scales. Results: We detect 14 dust cores from 3.5 $M_{\odot}$ to 37 $M_{\odot}$ arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large scale velocity gradients in H$^{13}$CO$^+$ 4-3 and C$^{17}$O 3-2, and magnetic field segments well aligned to the dust main axis. The velocity gradient is well reproduced by a spiral arm expanding at 9 km s$^{-1}$ with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable with the spiral arm kinetic energy, which is dominant over gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. ... (Full abstract in the pdf version)

MASSIVE QUIESCENT CORES IN ORION. V. THE INTERNAL STRUCTURES AND PHYSICAL AND CHEMICAL PROPERTIES OF TWO EXTREMELY DENSE CORES

We present a high-resolution $1.5"$ observational study towards two massive dust-and-gas cores, ORI8nw\_2 and ORI2\_6 in Orion Molecular Cloud using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). In both regions the 3.2 mm continuum emission reveals a dense and compact dust core of 1 to 3 solar masses. The cores are estimated to have number densities more than $10^9$ cm$^{-3}$, which are among the highest volume density ever published for the star-forming cores. In both regions the ${\rm N_2H^+}$ shows multiple gas clumps which are spatially displaced from the dense gas traced by the 3.2 mm continuum as well as the ${\rm HCO^+}$. The ${\rm N_2H^+}$ clumps in ORI8nw\_2 are gravitationally unbound. The clumps have masses comparable to the thermal Jeans mass, and are separated with intervals comparable with the Jeans length, thus likely result from thermal Jeans fragmentation. The fragmentation may have prohibited the high-mass star formation in the two cores which originally have larger total masses. In both regions the abundance ratio of ${\rm [N_2H^+]/[HCO^+]}$ appears to be higher than those in infrared dark clouds as a result of CO depletion. The extreme high central density in these Orion cores implies a very small Jeans scale ($<500$ AU). To further reveal the evolution of such dense cores requires higher resolution and sensitivity.

Magnetic Property of Iron-Dust Cores With Mixture of Ferromagnetic Ferrite Powder and Alumina Powder

Iron-dust cores are produced from insulated iron particles by using the powder metallurgy pressure forming process. These dust cores are suitable for small motor cores because of their high shape flexibility; however, the iron loss of iron-dust cores is larger than conventional laminated cores. Generally, the insulation material between the iron particles degrades the magnetic property of the core. In this paper, the magnetic property of the iron-dust core in which the resin, which is usually used as insulation material, is replaced by the soft magnetic Mn-Zn ferrite or alumina is examined. We have found that the iron-dust core mixed with alumina particles shows higher space factor, 10% lower iron loss, and 30% higher permeability. Contrary to expectation, the magnetic properties of the iron-dust core deteriorate by mixing with soft magnetic Mn-Zn ferrite.

Investigation of Carbonyl Iron Powder for Development of Power Inductors for High Frequency

SUMMARYWe have investigated carbonyl iron powder (CIP) for the development of a low‐loss power inductor at about 1 MHz. Significant differences were observed for the coercivity between two kinds of CIP, nonreduction CIP and reduction CIP. In order to investigate the origin of the significant differences of coercivity, we studied two kinds of CIP. It was shown that nonreduction CIP with low coercivity is an Fe‐based nanocrystalline soft magnetic material with a high saturation magnetization. We were able to produce a low‐loss dust core using a low‐coercivity CIP at about 1 MHz. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(9): 46–52, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11408

A spectral line survey of the starless and proto-stellar cores detected by BLAST toward the Vela-D molecular cloud

We present a 3-mm and 1.3-cm spectral line survey conducted with the Mopra 22-m and Parkes 64-m radio telescopes of a sample of 40 cold dust cores, previously observed with BLAST, including both starless and proto-stellar sources. 20 objects were also mapped using molecular tracers of dense gas. To trace the dense gas we used the molecular species NH3, N2H+, HNC, HCO+, H13CO+, HCN and H13CN, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes. The selected cores have a wide variety of morphological types and also show physical and chemical variations, which may be associated to different evolutionary phases. We find evidence of systematic motions in both starless and proto-stellar cores and we detect line wings in many of the proto-stellar cores. Our observations probe linear distances in the sources >~0.1pc, and are thus sensitive mainly to molecular gas in the envelope of the cores. In this region we do find that, for example, the radial profile of the N2H+(1-0) emission falls off more quickly than that of C-bearing molecules such as HNC(1-0), HCO+(1-0) and HCN(1-0). We also analyze the correlation between several physical and chemical parameters and the dynamics of the cores. Depending on the assumptions made to estimate the virial mass, we find that many starless cores have masses below the self-gravitating threshold, whereas most of the proto-stellar cores have masses which are near or above the self-gravitating critical value. An analysis of the median properties of the starless and proto-stellar cores suggests that the transition from the pre- to the proto-stellar phase is relatively fast, leaving the core envelopes with almost unchanged physical parameters.

CO depletion in the Gould Belt clouds

We present a statistical comparison of CO depletion in a set of local molecular clouds within the Gould Belt using Sub-millimetre Common User Bolometer Array (SCUBA) and Heterodyne Array Receiver Programme (HARP) data. This is the most wide-ranging study of depletion thus far within the Gould Belt. We estimate CO column densities assuming local thermodynamic equilibrium and, for a selection of sources, using the radiative transfer code RADEX in order to compare the two column density estimation methods. High levels of depletion are seen in the centres of several dust cores in all the clouds. We find that in the gas surrounding protostars, levels of depletion are somewhat lower than for starless cores with the exception of a few highly depleted protostellar cores in Serpens and NGC 2024. There is a tentative correlation between core mass and core depletion, particularly in Taurus and Serpens. Taurus has, on average, the highest levels of depletion. Ophiuchus has low average levels of depletion which could perhaps be related to the anomalous dust grain size distribution observed in this cloud. High levels of depletion are often seen around the edges of regions of optical emission (Orion) or in more evolved or less dynamic regions such as the bowl of L1495 in Taurus and the north-western region of Serpens.

The JCMT Legacy Survey of the Gould Belt: mapping 13CO and C18O in Orion A

The Gould Belt Legacy Survey will map star-forming regions within 500 pc, using HARP (Heterodyne Array Receiver Programme), SCUBA-2 (Submillimetre Common-User Bolometer Array 2) and POL-2 (Polarimeter 2) on the James Clerk Maxwell Telescope (JCMT). This paper describes HARP observations of the J = 3-2 transitions of 13CO and C18O towards Orion A. The 1500-resolution observations cover 5 pc of the Orion filament, including OMC1 (inc. BN-KL and Orion Bar), OMC 2/3 and OMC 4, and allow a comparative study of the molecular gas properties throughout the star-forming cloud. The filament shows a velocity gradient of ~1 km/s /pc between OMC 1, 2 and 3, and high velocity emission is detected in both isotopologues. The Orion Nebula and Bar have the largest masses and line widths, and dominate the mass and energetics of the high velocity material. Compact, spatially resolved emission from CH3CN, 13CH3OH, SO, HCOOCH3, C2H5OH, CH3CHO and CH3OCHO is detected towards the Orion Hot Core. The cloud is warm, with a median excitation temperature of ~24 K; the Orion Bar has the highest excitation temperature gas, at >80 K. The C18O excitation temperature correlates well with the dust temperature (to within 40%). The C18O emission is optically thin, and the 13CO emission is marginally optically thick; despite its high mass, OMC 1 shows the lowest opacities. A virial analysis indicates that Orion A is too massive for thermal or turbulent support, but is consistent with a model of a filamentary cloud that is threaded by helical magnetic fields. The variation of physical conditions across the cloud is reflected in the physical characteristics of the dust cores....continued

高絶縁ダストコアの開発とSMD インダクタへの応用

高絶縁ダストコアの開発とSMD インダクタへの応用

Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines

We have mapped 20 molecular lines in the Central Molecular Zone (CMZ) around the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth UNSW-MOPS digital filter bank, obtaining \sim 2 km/s spectral and \sim 40 arcsec spatial resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+, SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+ molecules. The area covered is Galactic longitude -0.7 to 1.8 deg. and latitude -0.3 to 0.2 deg., including the bright dust cores around Sgr A, Sgr B2, Sgr C and G1.6-0.025. We present images from this study and conduct a principal component analysis on the integrated emission from the brightest 8 lines. This is dominated by the first component, showing that the large-scale distribution of all molecules are very similar. We examine the line ratios and optical depths in selected apertures around the bright dust cores, as well as for the complete mapped region of the CMZ. We highlight the behaviour of the bright HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues of these species, and compare the behaviour with that found in extra-galactic sources where the emission is unresolved spatially. We also find that the isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing red-shifted velocity in some locations. Line luminosities are also calculated and compared to that of CO, as well as to line luminosities determined for external galaxies.

Characteristics of Fe-Si-B-P-Cu Nanocrystalline Soft Magnetic Alloy Powders With High Bs

Nanocrystalline soft magnetic alloy powders produced by heat treating amorphous powders are expected to improve properties and miniaturize dust cores because of their low coercive force Hc and high saturation magnetic flux density Bs. By water atomization process, we successfully obtained quenched Fe-Si-B-P-Cu alloy powders with spherical particle shape. The obtained powders have different average particle sizes of 2.0, 3.0, 5.0, and 8.5 μm. After annealing at 723 K, the as-quenched alloy powders are crystallized and Bs of the nanocrystalline alloy powders with Fe83.3Si4B8P4Cu0.7 and Fe84.8Si2B10P2Cu1.2 exhibit high Bs of 1.72 and 1.76 T, respectively. Core loss characteristics of the dust cores are found to be dependent on amorphous stability of the as-quenched powders. Thus, the Fe83.3Si4B8P4Cu0.7 nanocrystalline alloy powder with an average particle size of 3.0 μm exhibits the best core loss of 1461 kW/m3 (Bm = 50 mT, f=300 kHz).

HIERARCHICAL FRAGMENTATION AND JET-LIKE OUTFLOWS IN IRDC G28.34+0.06: A GROWING MASSIVE PROTOSTAR CLUSTER

We present Submillimeter Array (SMA) \lambda = 0.88mm observations of an infrared dark cloud (IRDC) G28.34+0.06. Located in the quiescent southern part of the G28.34 cloud, the region of interest is a massive ($>10^3$\,\msun) molecular clump P1 with a luminosity of $\sim 10^3$ \lsun, where our previous SMA observations at 1.3mm have revealed a string of five dust cores of 22-64 \msun\ along the 1 pc IR-dark filament. The cores are well aligned at a position angle of 48 degrees and regularly spaced at an average projected separation of 0.16 pc. The new high-resolution, high-sensitivity 0.88\,mm image further resolves the five cores into ten compact condensations of 1.4-10.6 \msun, with sizes a few thousands AU. The spatial structure at clump ($\sim 1$ pc) and core ($\sim 0.1$ pc) scales indicates a hierarchical fragmentation. While the clump fragmentation is consistent with a cylindrical collapse, the observed fragment masses are much larger than the expected thermal Jeans masses. All the cores are driving CO(3-2) outflows up to 38 km/s, majority of which are bipolar, jet-like outflows. The moderate luminosity of the P1 clump sets a limit on the mass of protostars of 3-7 \msun. Because of the large reservoir of dense molecular gas in the immediate medium and ongoing accretion as evident by the jet-like outflows, we speculate that P1 will grow and eventually form a massive star cluster. This study provides a first glimpse of massive, clustered star formation that currently undergoes through an intermediate-mass stage.

A numerical simulation of a ‘Super-Earth’ core delivery from ∼100 to ∼8 au

We use SPH simulations with an approximate radiative cooling prescription to model evolution of a massive and large ($\sim 100$ AU) very young protoplanetary disc. We also model dust growth and gas-grain dynamics with a second fluid approach. It is found that the disc fragments onto a large number of $\sim 10$ Jupiter mass clumps that cool and contract slowly. Some of the clumps evolve onto eccentric orbits delivering them into the inner tens of AU, where they are disrupted by tidal forces from the star. Dust grows and sediments inside the clumps, displaying a very strong segregation, with the largest particles forming dense cores in the centres. The density of the dust cores may exceed that of the gas and is limited only by the numerical constraints, indicating that these cores should collapse into rocky planetary cores. One particular giant planet embryo migrates inward close enough to be disrupted at about 10 AU, leaving a self-bound solid core of about 7.5 $\mearth$ mass on a low eccentricity orbit at a radius of $\sim$ 8 AU. These simulations support the recent suggestions that terrestrial and giant planets may be the remnants of tidally disrupted giant planet embryos.

IRDC G030.88+00.13: A TALE OF TWO MASSIVE CLUMPS

Massive stars (M $\gsim 10$ \msun) form from collapse of parsec-scale molecular clumps. How molecular clumps fragment to give rise to massive stars in a cluster with a distribution of masses is unclear. We search for cold cores that may lead to future formation of massive stars in a massive ($> 10^3$ \msun), low luminosity ($4.6 \times 10^2$ \lsun) infrared dark cloud (IRDC) G030.88+00.13. The \nh3 data from VLA and GBT reveal that the extinction feature seen in the infrared consists of two distinctive clumps along the same line of sight: The C1 clump at 97 \kms-1 coincides with the extinction in the Spitzer 8 and 24 $\mu$m. Therefore, it is responsible for the majority of the IRDC. The C2 clump at 107 \kms-1 is more compact and has a peak temperature of 45 K. Compact dust cores and \h2O masers revealed in the SMA and VLA observations are mostly associated with C2, and none is within the IRDC in C1. The luminosity indicates that neither the C1 nor C2 clump has yet to form massive protostars. But C1 might be at a precluster forming stage. The simulated observations rule out 0.1pc cold cores with masses above 8 \msun\ within the IRDC. The core masses in C1 and C2, and those in high-mass protostellar objects suggest an evolutionary trend that the mass of cold cores increases over time. Based on our findings, we propose an empirical picture of massive star formation that protostellar cores and the embedded protostars undergo simultaneous mass growth during the protostellar evolution.

Hot HCN around young massive stars at 0.1′′ resolution

Massive stars form deeply embedded in dense molecular gas, which they stir and heat up and ionize. During an early phase, the ionization is confined to hypercompact HII regions, and the stellar radiation is entirely absorbed by dust, giving rise to a hot molecular core. To investigate the innermost structure of such high-mass star-forming regions, we observed vibrationally excited HCN (via the direct $\ell$-type transition of v2=1, $\Delta J$=0, J=13, which lies 1400 K above ground) toward the massive hot molecular cores G10.47+0.03, SgrB2-N, and SgrB2-M with the Very Large Array (VLA) at 7 mm, reaching a resolution of about 1000 AU (0.1"). We detect the line both in emission and in absorption against HII regions. The latter allows to derive lower limits on the column densities of hot HCN, which are several times $10^{19}$ cm$^{-2}$. We see indication of expansion motions in G10.47+0.03 and detect velocity components in SgrB2-M at 50, 60, and 70 km/s relative to the Local Standard of Rest. The emission originates in regions of less than 0.1 pc diameter around the hypercompact HII regions G10.47+0.03 B1 and SgrB2-N K2, and reaches brightness temperatures of more than 200 K. Using the three-dimensional radiative transfer code RADMC-3D, we model the sources as dense dust cores heated by stars in the HII regions, and derive masses of hot (>300 K) molecular gas of more than 100 solar masses (for an HCN fractional abundance of 10$^{-5}$), challenging current simulations of massive star formation. Heating only by the stars in the HII regions is sufficient to produce such large quantities of hot molecular gas, provided that dust is optically thick to its own radiation, leading to high temperatures through diffusion of radiation.

INFALL AND OUTFLOW MOTIONS IN THE HIGH-MASS STAR-FORMING COMPLEX G9.62+0.19

We present the results of a high resolution study with the Submillimeter Array towards the massive star forming complex G9.62+0.19. Three sub-mm cores are detected in this region. The masses are 13, 30 and 165 M$_{\sun}$ for the northern, middle and southern dust cores, respectively. Infall motions are found with HCN (4-3) and CS (7-6) lines at the middle core (G9.62+0.19 E). The infall rate is $4.3\times10^{-3}~M_{\odot}\cdot$yr$^{-1}$. In the southern core, a bipolar-outflow with a total mass about 26 M$_{\sun}$ and a mass-loss rate of $3.6\times10^{-5}~M_{\odot}\cdot$yr$^{-1}$ is revealed in SO ($8_{7}-7_{7}$) line wing emission. CS (7-6) and HCN (4-3) lines trace higher velocity gas than SO ($8_{7}-7_{7}$). G9.62+0.19 F is confirmed to be the driving source of the outflow. We also analyze the abundances of CS, SO and HCN along the redshifted outflow lobes. The mass-velocity diagrams of the outflow lobes can be well fitted by a single power law. The evolutionary sequence of the cm/mm cores in this region are also analyzed. The results support that UC~H{\sc ii} regions have a higher blue excess than their precursors.

Internal Proper Motions of Methanol Masers at 6.7 GHz in Massive Star-Forming Region Onsala 1

We present the internal proper motions of 6.7 GHz methanol masers in a massive star-forming region, Onsala 1 (ON 1), measured using the Japanese very long baseline interferometry network (JVN) at three epochs spanning 778 days. The methanol masers were clearly distinct from water masers. The methanol masers surrounded an ultra-compact (UC) H II region, and their distribution was similar to that of hydroxyl masers. The internal motions of the methanol masers were clearly detected; they show outward motions in roughly the north–south direction with a relative velocity of $\sim\ $5 km s$^{-1}$. Their motion is similar to that of hydroxyl masers, which showed expansion at $\sim\ $5 km s$^{-1}$, and these two types of masers seem to trace the expanding UC H II region. Another possibility is that the methanol masers are associated with a molecular outflow observed by H$^{13}$CO$^{+}$ and SiO lines, because the direction and velocity of the methanol masers were similar to those of the molecular lines. Regarding the relative phases of water and methanol masers in the evolutionary stage of massive young stellar objects, we found that the former was earlier than the latter in ON 1 by comparing the sites associated with the masers. The water masers were associated with dust emission at submillimeter wavelengths, whereas the methanol masers were associated with an UC H II region at centimeter wavelengths, which appears at a later evolutionary phase than the dust core.

INFALL AND OUTFLOW DETECTIONS IN A MASSIVE CORE JCMT 18354–0649S

We present a high-resolution study of a massive dense core JCMT 18354-0649S with the Submillimeter Array. The core is mapped with continuum emission at 1.3 mm, and molecular lines including CH$_{3}$OH ($5_{23}$-$4_{13}$) and HCN (3-2). The dust core detected in the compact configuration has a mass of $47 M_{\odot}$ and a diameter of $2\arcsec$ (0.06 pc), which is further resolved into three condensations with a total mass of $42 M_{\odot}$ under higher spatial resolution. The HCN (3-2) line exhibits asymmetric profile consistent with infall signature. The infall rate is estimated to be $2.0\times10^{-3} M_{\odot}\cdot$yr$^{-1}$. The high velocity HCN (3-2) line wings present an outflow with three lobes. Their total mass is $12 M_{\odot}$ and total momentum is $121 M_{\odot}\cdot$km s$^{-1}$, respectively. Analysis shows that the N-bearing molecules especially HCN can trace both inflow and outflow.

Research of Carbonyl Iron Powder for Development of the Power Inductor for High Frequency

We have investigated the carbonyl iron powder (CIP) for development of the low-loss power inductor at about 1 MHz. Significant differences were observed for the coercivity between two kinds of CIP (Non-reduction CIP and Reduction CIP). In order to investigate the origin of significant differences for the coercivity, we have studied two kinds of CIP. As a result, it was shown that Non-reduction CIP with low-coercivity is Fe-based nanocrystalline soft magnetic material with high saturation magnetization. We could produce a low-loss dust core using low coercivity CIP at about 1 MHz.

THE MAGNETIC FIELD IN THE NGC 2024 FIR 5 DENSE CORE

We used the Submillimeter Array (SMA) to observe the thermal polarized dust emission from the protostellar source NGC 2024 FIR 5. The polarized emission outlines a partial hourglass morphology for the plane-of-sky component of the core magnetic field. Our data are consistent with previous BIMA maps, and the overall magnetic field geometries obtained with both instruments are similar. We resolve the main core into two components, FIR 5A and FIR 5B. A possible explanation for the asymmetrical field lies in depolarization effects due to the lack of internal heating from FIR 5B source, which may be in a prestellar evolutionary state. The field strength was estimated to be 2.2 mG, in agreement with previous BIMA data. We discuss the influence of a nearby H{\sc ii} region over the field lines at scales of $\sim 0.01$ pc. Although the hot component is probably compressing the molecular gas where the dust core is embedded, it is unlikely that the radiation pressure exceeds the magnetic tension. Finally, a complex outflow morphology is observed in CO (3 $\rightarrow$ 2) maps. Unlike previous maps, several features associated with dust condensations other than FIR 5 are detected.