Eight new astrometry results of 6.7 GHz CH3OH and 22 GHz H2O masers in the Perseus arm

2017 ◽  
Vol 13 (S336) ◽  
pp. 168-171 ◽  
Author(s):  
Nobuyuki Sakai ◽  
Keyword(s):  
Pitch Angle ◽  
Three Dimensional ◽  
Weighted Mean ◽  
Large Sample ◽  
Small Pitch ◽  
Trigonometric Parallaxes ◽  
Perseus Arm ◽  
Spiral Arm ◽  
Interior Side

AbstractWe report astrometric results for seven 6.7 GHz CH3OH and one 22 GHz H2O masers in the Perseus arm with VLBA and VERA observations. Among the eight sources, we succeeded in obtaining trigonometric parallaxes for all sources, except G098.03+1.44 at 6.7 GHz band. By combining our results with previous astrometry results (Choi et al. 2014), we determined an arm width of 0.41 kpc and a pitch angle of 8.2 ± 2.5 deg for the Perseus arm. By using a large sample of the Perseus arm (26 sources), we examined the three-dimensional, non-circular motions (defined as U, V and W) of sources in the Perseus arm as a function of the distance (D) perpendicular to the arm. Interestingly, we found a weighted mean of <U > = 12.7 ± 1.2 km s−1 for 14 sources with D < 0 kpc (i.e. sources on the interior side of the arm) and <U > = −0.3 ± 1.5 km s−1 for 12 sources with D > 0 kpc (i.e. sources exterior to the arm). These findings might be the first observational indication of the ”damping phase of a spiral arm” suggested by the non-steady spiral arm model of Baba et al. (2013). The small pitch angle of the Perseus arm (< 10 deg) also supports the damping phase, based on ”pitch angle vs. arm amplitude” relation shown in Grøsbol et al. (2004).

scholarly journals Spiral structure of the Galaxy Derived from the Hat Creek survey of neutral hydrogen

1970 ◽  
Vol 38 ◽  
pp. 126-139 ◽  
Author(s):  
H. Weaver
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
The Sun ◽  
General Picture ◽  
Contour Maps ◽  
The Galaxy ◽  
External Galaxies ◽  
Perseus Arm ◽  
Spiral Arm

The extensive Hat Creek survey of neutral hydrogen combined with southern observations provides the basis for a new discussion of the spiral structure of the galaxy. The purpose of this investigation is to provide a general picture of the galaxy. It is found that the pitch of the spiral arms is approximately 12°.5 and that there are many spurs and interarm features as we observe in external galaxies.The sun is not located in a major spiral arm, but rather in a spur or offshoot originating near or at the Sagittarius arm, which is a major structure in the galaxy. The young stars in the general vicinity of the sun delineate this spur, not a major arm structure. The stars and the gas are in agreement in indicating a large pitch angle (20°–25°) for this local structure, which differs from the smaller pitch angle for the arms which form the system as a whole.In the presentation a computer-produced movie of the galaxy based on Hat Creek hydrogen contour maps similar to those in Figure 1 was shown. It was used to illustrate generally the complexity of the gas structure and, in particular, to show (i) observational aspects of the spur in which the sun is located and (ii) the point of origin of the so-called Perseus arm.

scholarly journals The Dark Matter Halo Density Profile, Spiral Arm Morphology, and Supermassive Black Hole Mass of M33

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Marc S. Seigar
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Density Profile ◽  
Pitch Angle ◽  
Rotation Curve ◽  
Dark Matter Halo ◽  
Black Hole Mass ◽  
Supermassive Black Hole ◽  
Virial Mass ◽  
Spiral Arm

We investigate the dark matter halo density profile of M33. We find that the HI rotation curve of M33 is best described by an NFW dark matter halo density profile model, with a halo concentration of and a virial mass of . We go on to use the NFW concentration of M33, along with the values derived for other galaxies (as found in the literature), to show that correlates with both spiral arm pitch angle and supermassive black hole mass.

Testing the Correlation between Spiral Arm Pitch Angle and Central Black Hole Mass

2010 ◽  
Author(s):  
Douglas W. Shields ◽  
J. Adam Hughes ◽  
Scott R. Barrows ◽  
Ben Davis ◽  
Daniel Kennefick ◽  
...  
Keyword(s):  
Black Hole ◽  
Pitch Angle ◽  
Black Hole Mass ◽  
Central Black Hole ◽  
Spiral Arm

Large- and small-scale vortical motions in a shear layer perturbed by tabs

1999 ◽  
Vol 382 ◽  
pp. 307-329 ◽  
Author(s):  
JUDITH K. FOSS ◽  
K. B. M. Q. ZAMAN
Keyword(s):  
Shear Layer ◽  
Pitch Angle ◽  
Large Scale ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Small Scale ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Cross Sectional ◽  
Scale Population

The large- and small-scale vortical motions produced by ‘delta tabs’ in a two-stream shear layer have been studied experimentally. An increase in mixing was observed when the base of the triangular shaped tab was affixed to the trailing edge of the splitter plate and the apex was pitched at some angle with respect to the flow axis. Such an arrangement produced a pair of counter-rotating streamwise vortices. Hot-wire measurements detailed the velocity, time-averaged vorticity (Ωx) and small-scale turbulence features in the three-dimensional space downstream of the tabs. The small-scale structures, whose scale corresponds to that of the peak in the dissipation spectrum, were identified and counted using the peak-valley-counting technique. The optimal pitch angle, θ, for a single tab and the optimal spanwise spacing, S, for a multiple tab array were identified. Since the goal was to increase mixing, the optimal tab configuration was determined from two properties of the flow field: (i) the large-scale motions with the maximum Ωx, and (ii) the largest number of small-scale motions in a given time period. The peak streamwise vorticity magnitude [mid ]Ωx−max[mid ] was found to have a unique relationship with the tab pitch angle. Furthermore, for all cases examined, the overall small-scale population was found to correlate directly with [mid ]Ωx−max[mid ]. Both quantities peaked at θ≈±45°. It is interesting to note that the peak magnitude of the corresponding circulation in the cross-sectional plane occurred for θ≈±90°. For an array of tabs, the two quantities also depended on the tab spacing. An array of contiguous tabs acted as a solid deflector producing the weakest streamwise vortices and the least small-scale population. For the measurement range covered, the optimal spacing was found to be S≈1.5 tab widths.

Pattern generation and motion control of a vortex-like paramagnetic nanoparticle swarm

2018 ◽  
Vol 37 (8) ◽  
pp. 912-930 ◽  
Author(s):  
Jiangfan Yu ◽  
Lidong Yang ◽  
Li Zhang
Keyword(s):  
Magnetic Field ◽  
Targeted Delivery ◽  
Pitch Angle ◽  
Dynamic Equilibrium ◽  
Equilibrium Structure ◽  
Pattern Generation ◽  
Analytical Models ◽  
Generation Process ◽  
Rotating Magnetic Fields ◽  
Small Pitch

Controlling a swarm of microrobots with external fields is one of the major challenges for untethered microrobots. In this work, we present a new method to generate a vortex-like paramagnetic nanoparticle swarm (VPNS) from dispersed nanoparticles with a diameter of 500 nm, using rotating magnetic fields. The VPNS exhibits a dynamic-equilibrium structure, in which the nanoparticles perform synchronized motions. The mechanisms of the pattern-generation process are analyzed, simulated, and validated by experiments. By tuning the rotating frequency of the input magnetic field, the pattern of a VPNS changes accordingly. Analytical models for estimating the areal change of the pattern are proposed, and they have good agreement with the experimental data. Moreover, reversible merging and splitting of vortex-like swarms are demonstrated and investigated. Serving as a mobile robotic end-effector, a VPNS is capable of making locomotion by tuning the pitch angle of the actuating rotating field. With a small pitch angle, e.g. 2°, the whole swarm moves as an entity, and the shape of the pattern remains intact. In addition, the trapping forces of VPNSs are verified, showing the critical input parameters of the magnetic field that affect the morphology of the swarm. Finally, we demonstrate that VPNSs pass through curved and branched channels with high positioning precision, and the access rates for targeted delivery are over 90%, which are significantly higher than those in the cases of particle swarms moving with tumbling motions.

Short helical antenna with extremely small pitch angle

2006 ◽  
Vol 49 (1) ◽  
pp. 17-19
Author(s):  
Ze-Hai Wu ◽  
Edward K. N. Yung
Keyword(s):  
Pitch Angle ◽  
Helical Antenna ◽  
Small Pitch

Heat Transfer for Laminar Flow in Spiral Ducts of Rectangular Cross Section

2005 ◽  
Vol 127 (3) ◽  
pp. 352-356 ◽  
Author(s):  
Michael W. Egner ◽  
Louis C. Burmeister
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Aspect Ratios ◽  
Small Pitch

Laminar flow and heat transfer in three-dimensional spiral ducts of rectangular cross section with aspect ratios of 1, 4, and 8 were determined by making use of the FLUENT computational fluid dynamics program. The peripherally averaged Nusselt number is presented as a function of distance from the inlet and of the Dean number. Fully developed values of the Nusselt number for a constant-radius-of-curvature duct, either toroidal or helical with small pitch, can be used to predict those quantities for the spiral duct in postentry regions. These results are applicable to spiral-plate heat exchangers.

Perseus arm - a new perspective on star formation and spiral structure in our home galaxy

2021 ◽  
Author(s):  
M Wienen ◽  
C M Brunt ◽  
C L Dobbs ◽  
D Colombo
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Milky Way ◽  
Velocity Structure ◽  
Data Cube ◽  
High Angular Resolution ◽  
Molecular Gas ◽  
Linear Scale ◽  
Perseus Arm ◽  
Spiral Arm

Abstract Expansion of (sub)millimetre capabilities to high angular resolution offered with interferometers allows to resolve giant molecular clouds (GMCs) in nearby galaxies. This enables us to place the Milky Way in the context of other galaxies to advance our understanding of star formation in our own Galaxy. We thus remap 12CO (1 - 0) data along the Perseus spiral arm in the outer Milky Way to a fixed physical resolution and present the first spiral arm data cube at a common distance as it would be seen by an observer outside the Milky Way. To achieve this goal we calibrated the longitude-velocity structure of 12CO gas of the outer Perseus arm based on trigonometric distances and maser velocities provided by the BeSSeL survey. The molecular gas data were convolved to the same spatial resolution along the whole spiral arm and regridded on to a linear scale map with the coordinate system transformed to the spiral arm reference frame. We determined the width of the Perseus spiral arm to be 7.8 ± 0.2 km s−1 around the kinematic arm centre. To study the large scale structure we derived the 12CO gas mass surface density distribution of velocities shifted to the kinematic arm centre and arm length. This yields a variation of the gas mass surface density along the arm length and a compression of molecular gas mass at linear scale. We determined a thickness of ∼63 pc on average for the Perseus spiral arm and a centroid of the molecular layer of 8.7 pc.

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