Magnetic Fields in the Horsehead Nebula Hwang, Jihye; Pattle, Kate; Parsons, Harriet ...
The Astronomical journal,
05/2023, Volume:
165, Issue:
5
Journal Article
Peer reviewed
Open access
Abstract
We present the first polarized dust emission measurements of the Horsehead Nebula, obtained using the POL-2 polarimeter on the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera on ...the James Clerk Maxwell Telescope. The Horsehead Nebula contains two submillimeter sources: a photodissociation region (PDR; SMM1) and a starless core (SMM2). We see well-ordered magnetic fields in both sources. We estimated plane-of-sky magnetic field strengths of 56 ± 9 and 129 ± 21
μ
G in SMM1 and SMM2, respectively, and obtained mass-to-flux ratios and Alfvén Mach numbers of less than 0.6, suggesting that the magnetic field can resist gravitational collapse and that magnetic pressure exceeds internal turbulent pressure in these sources. In SMM2, the kinetic and gravitational energies are comparable to one another, but less than the magnetic energy. We suggest a schematic view of the overall magnetic field structure in the Horsehead Nebula. Magnetic field lines in SMM1 appear to have been compressed and reordered during the formation of the PDR, while the likely more-embedded SMM2 may have inherited its field from that of the pre-shock molecular cloud. The magnetic fields appear to currently play an important role in supporting both sources.
Abstract We develop a physical framework for interpreting complex circumstellar patterns whorled around asymptotic giant branch (AGB) stars by investigating stable, coplanar triple systems using ...hydrodynamic and particle simulations. The introduction of a close tertiary body causes an additional periodic variation in the orbital velocity and trajectory of the AGB star. As a result, the circumstellar outflow builds a fine non-Archimedean spiral pattern superimposed upon the Archimedean spiral produced by the outer binary alone. This fine spiral can be approximated by off-centered circular rings that become tangent to each other at the location of the Archimedean spiral. The superimposed fine pattern fades out relatively quickly as a function of distance from the center of the system, in contrast to the dominant Archimedean spiral pattern, which presents a much slower fractional density decrease with radius. The different rates of radial decrease of the density contrast in the two superimposed patterns, coupled with their different time and spatial scales, lead to an apparent, but illusory radial change in the observed pattern interval, as has been reported, for example, in CW Leo. The function describing the detailed radial dependence of the expansion velocity is different in the two patterns, which may be used to distinguish them. The shape of the circumstellar whorled pattern is further explored as a function of the orbital eccentricity and the inner companion’s mass. Although this study is confined to stable, coplanar triple systems, the results are likely applicable to moderately noncoplanar systems and open interesting avenues for studying noncoplanar systems.
We determine the magnetic field strength in the OMC 1 region of the Orion A filament via a new implementation of the Chandrasekhar-Fermi method using observations performed as part of the James Clerk ...Maxwell Telescope (JCMT) B-Fields In Star-forming Region Observations (BISTRO) survey with the POL-2 instrument. We combine BISTRO data with archival SCUBA-2 and HARP observations to find a plane-of-sky magnetic field strength in OMC 1 of mG, where mG represents a predominantly systematic uncertainty. We develop a new method for measuring angular dispersion, analogous to unsharp masking. We find a magnetic energy density of J m−3 in OMC 1, comparable both to the gravitational potential energy density of OMC 1 (∼10−7 J m−3) and to the energy density in the Orion BN/KL outflow (∼10−7 J m−3). We find that neither the Alfvén velocity in OMC 1 nor the velocity of the super-Alfvénic outflow ejecta is sufficiently large for the BN/KL outflow to have caused large-scale distortion of the local magnetic field in the ∼500 yr lifetime of the outflow. Hence, we propose that the hourglass field morphology in OMC 1 is caused by the distortion of a primordial cylindrically symmetric magnetic field by the gravitational fragmentation of the filament and/or the gravitational interaction of the BN/KL and S clumps. We find that OMC 1 is currently in or near magnetically supported equilibrium, and that the current large-scale morphology of the BN/KL outflow is regulated by the geometry of the magnetic field in OMC 1, and not vice versa.
Abstract
We present the results of molecular line observations performed toward the NGC 2068 and NGC 2071 regions of the Orion B cloud as the TRAO-FUNS project to study the roles of the filamentary ...structure in the formation of dense cores and stars in the clouds. Gaussian decomposition for the C
18
O spectra with multiple velocity components and the application of a friends-of-friends algorithm for the decomposed components allowed us to identify a few tens of velocity-coherent filaments. We also identified 48 dense cores from the observations of N
2
H
+
using a core finding tool, FellWalker. We performed a virial analysis for these filaments and dense cores, finding that the filaments with N
2
H
+
dense core are thermally supercritical, and the filaments with a larger ratio between the line mass and the thermal critical line mass tend to have more dense cores. We investigated the contribution of the nonthermal motions in dense cores and filaments, showing the dense cores are mostly in transonic/subsonic motions while their natal filaments are mostly in supersonic motions. This may indicate that gas turbulent motions in the filaments have been dissipated at the core scale to form the dense cores there. The filaments with (dynamically evolved) dense cores in infalling motions or with NH
2
D bright (or chemically evolved) dense cores are all found to be gravitationally critical. Therefore, the criticality of the filament is thought to provide a key condition for its fragmentation, the formation of dense cores, and their kinematical and chemical evolution.
We investigate the time-evolution of the mass distribution of pre-stellar cores (PSCs) and their transition to the initial stellar mass function (IMF) in the central parts of a molecular cloud (MC) ...under the assumption that the coalescence of cores is important. Our aim is to explain the observed shallow IMF in dense stellar clusters such as the Arches cluster. The initial distributions of PSCs at various distances from the MC centre are those of gravitationally unstable cores resulting from the gravo-turbulent fragmentation of the MC. As time evolves, there is a competition between the rates of coalescence and collapse of the PSCs. Whenever the local rate of collapse is larger than the rate of coalescence in a given mass bin, cores are collapsed into stars. With appropriate parameters, we find that the coalescence–collapse model reproduces very well all the observed characteristics of the Arches stellar cluster IMF: namely, the slopes at high- and low-mass ends and the peculiar bump observed at ∼ 5–6M⊙. Our results suggest that today's IMF of the Arches cluster is very similar to the primordial one and is little affected by the mass segregation due to dynamical effects.
This paper describes the design and analysis of a 42-kW (14 kV, 3 A) high-voltage power supply for a 30-kW industrial magnetron drive. The design is based on a series resonant converter in ...discontinuous conduction mode (DCM) to take advantage of both the superior arc protection stemming from the current source characteristics and the high power density owing to the use of parasitic elements such as the leakage inductance in the high-voltage transformer. The detailed design procedure for the resonant tank and high-voltage transformer with respect to the input and output specifications is described on the basis of a simplified analysis of the DCM series resonant converter. Special considerations for designing high-power high-voltage power supplies are provided, such as series stacking of diodes for a voltage doubling rectifier and insulation between each winding of the high-voltage transformer. In addition, a comparative study using theoretical equations, simulation, and experimental results was carried out. This study yielded the output voltage and current characteristics at different switching frequencies and verified the advantages of this topology, such as arc protection without an additional protection circuit and high efficiency due to zero-current or zero-voltage switching. Moreover, the parallel operation of two converters with phase shifted gating signal is proposed to reduce the output current ripple and increase power capability for higher power magnetron drive. Additionally, the design considerations of two auxiliary power supplies (a filament power supply: 15 V, 150 A and a magnet power supply: 50 V, 5 A) are also provided and optimized for effective driving industrial magnetron. Finally, the developed power supply was tested with a 30-kW industrial magnetron, and the results prove the reliability and robustness of the proposed scheme.
Turbulent flows are ubiquitous in astrophysical environments, and understanding density structures and their statistics in turbulent media is of great importance in astrophysics. In this Letter, we ...study the density power spectra Pr of transonic and supersonic turbulent flows through one- and three-dimensional simulations of driven, isothermal hydrodynamic turbulence with rms Mach numbers in the range 1 M sub(rms) 10. From one-dimensional experiments we find that the slope of the density power spectra becomes gradually shallower as the rms Mach number increases. This is because the density distribution is transformed from the profile with discontinuities having Pr 8 k super(-2) for M sub(rms) 61 to the profile with peaks having Pr 8 k super(0) for M sub(rms) >> 1. We also find that the same trend is carried to three dimensions; that is, the density power spectrum flattens as the Mach number increases. But the density power spectrum of the flow with M sub(rms) 6 1 has a Kolmogorov slope. The flattening is a consequence of the dominant density structures of filaments and sheets. Observations have claimed different slopes of density power spectra for electron density and cold H I gas in the interstellar medium. We argue that while the Kolmogorov spectrum for electron density reflects the transonic turbulence of M sub(rms) 6 1 in the warm ionized medium, the shallower spectrum of cold H I gas reflects the supersonic turbulence of M sub(rms) 6 a few in the cold neutral medium.
Copyright, a right exclusively granted to authors based on the originality of their work, is an essential institution for the establishment of modern literature. As a basic right guaranteeing the ...existence of professional writers of modern literature, copyright is quintessential to the status of authors as actors of modern literature. Writers in colonial Korea lacked a clear grasp of the modern yet discriminatory political systems of copyright and publication law. Under circumstances demanding self-censorship, writers were unable to actively demand copyright protection, as they lacked pride in their work and sold it at low prices as a way out of poverty. Under colonial rule, the importance of a writer's economic rights through acknowledging the originality of their literary work was overlooked, while pangwon (publication right) was universally used by publishers as an exclusive sales right for publication. The social status of writers was established through social developments that secured revenue for authors, such as the establishment of standards for manuscript rates and restrictive royalty payments. However, since "copyright" was not politically, economically, or legally guaranteed throughout the development of modern literature, writers had to find solace in the idea that members of their profession inevitably had to endure poverty. web URL: http://www.ekoreajournal.net/issue/view_pop.htm?Idx=3744
Research summary
Do former star performers become superior managers? If so, why? Using performance data from a professional sports league, this study finds that organizational performance is greater ...under star‐performers‐turned‐managers (SPTMs) than other managers. We develop a typology of six causal mechanisms by which SPTMs might affect organizational performance, and we indirectly test for each of them using data from a professional sports league. Our results indicate that SPTMs outperform other managers, and that this benefit is due to their role modeling and their superior ability to train and incentivize subordinates.
Managerial summary
Organizations are often, but not always, led by managers who previously achieved outstanding performance in an individual contributor role. Do such star‐performers‐turned‐managers (SPTMs) benefit an organization's performance more than other managers? If so, why? Our statistical analysis finds that National Basketball Association (NBA) teams managed by head coaches who had previously been All‐Star NBA players win games more often than other NBA teams, and also that this effect is due to a combination of SPTMs serving as a role model for their players, as well as training and incentivizing their players better.
Abstract
We investigate the effect of star formation on turbulence in the Orion A and Ophiuchus clouds using principal component analysis (PCA). We measure the properties of turbulence by applying ...PCA on the spectral maps in
13
CO, C
18
O, HCO
+
J
= 1–0, and CS
J
= 2–1. First, the scaling relations derived from PCA of the
13
CO maps show that the velocity difference (
δv
) for a given spatial scale (
L
) is the highest in the integral-shaped filament (ISF) and L1688, where the most active star formation occurs in the two clouds. The
δv
increases with the number density and total bolometric luminosity of the protostars in the subregions. Second, in the ISF and L1688 regions, the
δv
of C
18
O, HCO
+
, and CS are generally higher than that of
13
CO, which implies that the dense gas is more turbulent than the diffuse gas in the star-forming regions; stars form in dense gas, and dynamical activities associated with star formation, such as jets and outflows, can provide energy into the surrounding gas to enhance turbulent motions.
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