The Dynamical State of the Serpens South Filamentary Infrared Dark Cloud

We present the results of N_2H^+ (J = 1-0) observations toward Serpens South, the nearest cluster-forming, infrared dark cloud. The physical quantities are derived by fitting the hyperfine structure of N_2H^+. The Herschel and 1.1 mm continuum maps show that a parsec-scale filament fragments into three clumps with radii of 0.1-0.2 pc and masses of 40-230 M_☉. We find that the clumps contain smaller-scale (~0.04 pc) structures, i.e., dense cores. We identify 70 cores by applying CLUMPFIND to the N_2H^+ data cube. In the central cluster-forming clump, the excitation temperature and line-width tend to be large, presumably due to protostellar outflow feedback and stellar radiation. However, for all the clumps, the virial ratios are evaluated to be 0.1-0.3, indicating that the internal motions play only a minor role in the clump support. The clumps exhibit no free fall but exhibit low-velocity infall, and thus the clumps should be supported by additional forces. The most promising force is the globally ordered magnetic field observed toward this region. We propose that the Serpens South filament was close to magnetically critical and ambipolar diffusion triggered the cluster formation. We find that the northern clump, which shows no active star formation, has a mass and radius comparable to the central cluster-forming clump and is therefore a likely candidate of a pre-protocluster clump. The initial condition for cluster formation is likely to be a magnetically supported clump of cold, quiescent gas. This appears to contradict the accretion-driven turbulence scenario, for which the turbulence in the clumps is maintained by the accretion flow

Clustered Star Formation in Magnetic Clouds: Properties of Dense Cores Formed in Outflow-Driven Turbulence

We investigate the physical properties of dense cores formed in turbulent, magnetized, parsec-scale clumps of molecular clouds, using three-dimensional numerical simulations that include protostellar outflow feedback. The dense cores are identified in the simulated density data cube through a clumpfind algorithm. We find that the core velocity dispersion does not show any clear dependence on the core size, in contrast to Larson's linewidth-size relation, but consistent with recent observations. In the absence of a magnetic field, the majority of the cores have supersonic velocity dispersions. A moderately-strong magnetic field reduces the dispersion to a subsonic or at most transonic value typically. Most of the cores are out of virial equilibrium, with the external pressure dominating the self-gravity. The implication is that the core evolution is largely controlled by the outflow-driven turbulence. Even an initially-weak magnetic field can retard star formation significantly, because the field is amplified by the outflow-driven turbulence to an equipartition strength, with the distorted field component dominating the uniform one. In contrast, for a moderately-strong field, the uniform component remains dominant. Such a difference in the magnetic structure is evident in our simulated polarization maps of dust thermal emission; it provides a handle on the field strength. Recent polarization measurements show that the field lines in cluster-forming clumps are spatially well-ordered. It is indicative of a moderately-strong, dynamically important, field which, in combination with outflow feedback, can keep the rate of star formation in embedded clusters at the observationally-inferred, relatively-slow rate of several percent per free-fall time.Comment: 49 pages, 16 figures accepted by The Astrophysical Journa

Evidence For Cloud-Cloud Collision and Parsec-Scale Stellar Feedback Within the L1641-N Region

We present high spatial resolution $^{12}$CO ($J=1-0$) images taken by the Nobeyama 45m telescope toward a $48' \times 48'$ area including the L1641-N cluster. The effective spatial resolution of the maps is $21"$, corresponding to 0.04 pc at a distance of 400 pc. A recent 1.1 mm dust continuum map reveals that the dense gas is concentrated in several thin filaments. We find that a few dust filaments are located at the parts where $^{12}$CO ($J=1-0$) emission drops sharply. Furthermore, the filaments have two-components with different velocities. The velocity difference between the two-components is about 3 km s$^{-1}$, corresponding to a Mach number of 10, significantly larger than the local turbulent velocity in the cloud. These facts imply that the collision of the two components (hereafter, the cloud-cloud collision) possibly contributed to the formation of these filaments. Since the two components appear to overlap toward the filaments on the plane of the sky, the collision may have occurred almost along the line of sight. Star formation in the L1641-N cluster was probably triggered by such a collision. We also find several parsec-scale CO shells whose centers are close to either the L1641-N cluster or V 380 Ori cluster. We propose that these shells were created by multiple winds and/or outflows from cluster YSOs, i.e., "protocluster winds." One exceptional dust filament located at the western cloud edge lies along a shell; it is presumably a part of the expanding shell. Both the cloud-cloud collision and protocluster winds are likely to influence the cloud structure and kinematics in this region.Comment: 44 pages, 12 figures, submitted to Ap

Abstract Approximation of Involute Curves for CAD-System Processing

In numerous instances, accurate algorithms for approximating the original geometry is required. One typical example is a circle involute curve which represents the underlying geometry behind a gear tooth. The circle involute curves are by definition transcendental and cannot be expressed by algebraic equations, and hence it cannot be directly incorporated into commercial CAD systems. In this paper an approximation algorithm for circle involute curves in terms of polynomial functions is developed. The circle involute curve is approximated using a Chebyshev approximation formula [11], which enables us to represent the involute in terms of polynomials, and hence as a Bézier curve. In comparison with the current B-spline approximation algorithms for circle involute curves, the proposed method is found to be more accurate and compact, and induces fewer oscillations