scholarly journals Spiral arms in the protoplanetary disc HD100453 detected with ALMA: evidence for binary–disc interaction and a vertical temperature gradient

2019 ◽  
Vol 491 (1) ◽  
pp. 1335-1347 ◽  
Author(s):  
G P Rosotti ◽  
M Benisty ◽  
A Juhász ◽  
R Teague ◽  
C Clarke ◽  
...  
Keyword(s):  
High Resolution ◽  
Pitch Angle ◽  
Scattered Light ◽  
Vertical Temperature ◽  
Spiral Arms ◽  
Resolution Imaging ◽  
The Difference ◽  
Hydrodynamical Simulations ◽  
The One ◽  
Spiral Arm

ABSTRACT Scattered light high-resolution imaging of the protoplanetary disc orbiting HD100453 shows two symmetric spiral arms, possibly launched by an external stellar companion. In this paper, we present new, sensitive high-resolution (∼30 mas) Band 7 ALMA observations of this source. This is the first source where we find counterparts in the sub-mm continuum to both scattered light spirals. The CO J = 3–2 emission line also shows two spiral arms; in this case, they can be traced over a more extended radial range, indicating that the southern spiral arm connects to the companion position. This is clear evidence that the companion is responsible for launching the spirals. The pitch angle of the submillimetre continuum spirals (∼6°) is lower than the one in scattered light (∼16°). We show that hydrodynamical simulations of binary–disc interaction can account for the difference in pitch angle only if one takes into account that the mid-plane is colder than the upper layers of the disc, as expected for the case of externally irradiated discs.

scholarly journals Interarm islands in the Milky Way – the one near the Cygnus spiral arm

2020 ◽  
Vol 494 (1) ◽  
pp. 1134-1142
Author(s):  
Jacques P Vallée
Keyword(s):  
Observational Data ◽  
Milky Way ◽  
Young Stars ◽  
H Ii Regions ◽  
Spiral Arms ◽  
The Galaxy ◽  
The One ◽  
Loop 2 ◽  
Perseus Arm ◽  
Spiral Arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

scholarly journals Substructure within galactic spiral arms as derived from studies at 21 cm

1959 ◽  
Vol 9 ◽  
pp. 355-359
Author(s):  
R. D. Davies
Keyword(s):  
Fine Structure ◽  
High Resolution ◽  
Velocity Dispersion ◽  
Detailed Structure ◽  
Hydrogen Line ◽  
Spiral Arms ◽  
Frequency Structure ◽  
Galactic Spiral ◽  
Spiral Arm

Detailed structure within the spiral arms of our Galaxy is suggested by hydrogen-line spectra taken with high resolution in frequency [1]. The spectra show much detail in each maximum (spiral arm). It is not clear, however, if this frequency structure refers to fine structure in depth or in velocity dispersion or in both. Fine structure in position and depth has been inferred from 21-cm drift curves taken across the nearby spiral arms. The results of three investigations will be discussed. Two have been published in some detail [2, 3] and will only be summarized here.

scholarly journals A Precise Algorithm for Computing Sun Position on a Satellite

2019 ◽  
Author(s):  
Tao Zheng ◽  
Fei Zheng ◽  
Xi Rui ◽  
Xiang Ji
Keyword(s):  
Coordinate System ◽  
High Precision ◽  
Pitch Angle ◽  
Azimuth Angle ◽  
Maximum Deviation ◽  
The Sun ◽  
Solar Concentrator ◽  
The Difference ◽  
The One ◽  
Right Ascension

To meet the high precision sun tracking needs of a space deployable membrane solar concentrator and other equipment, an existing algorithm for accurately computing the sun position is improved. Firstly, compared with other theories, the VSOP (variation seculaires des orbits planetaires) 87 theory is selected and adopted to obtain the sun position in the second equatorial coordinate system. Comparing the results with data of the astronomical almanac from 2015, it is found that the deviation of the apparent right ascension does not exceed 0.17 arc seconds, while that of the apparent declination does not exceed 1.2 arc seconds. Then, to eliminate the difference in the direction of the sun position with respect to the satellite caused by the size of the satellite’s orbit, a translation transform is introduced in the proposed algorithm. Finally, the proposed algorithm is applied to the orbit of the satellite designated by SJ-4 (shijian-4). Under the condition that both of the existing and improved algorithms adopt the VSOP87 theory to compute sun position in the second equatorial coordinate system, the maximum deviation of the azimuth angle on the SJ-4 is 35.19 arc seconds and the one of pitch angle is 19.93 arc seconds, when the deviation is computed by subtracting the results given by both algorithms. In summary, the proposed algorithm is more accurate than the existing one.

scholarly journals Spiral arms and instability within the AFGL 4176 mm1 disc

2020 ◽  
Vol 634 ◽  
pp. L11 ◽  
Author(s):  
Katharine G. Johnston ◽  
Melvin G. Hoare ◽  
Henrik Beuther ◽  
Rolf Kuiper ◽  
Nathaniel Dylan Kee ◽  
...  
Keyword(s):  
High Resolution ◽  
Velocity Field ◽  
Pitch Angle ◽  
Local Thermodynamic Equilibrium ◽  
High Mass ◽  
Archimedean Spiral ◽  
Multiple Systems ◽  
High Fraction ◽  
Significant Structure ◽  
Spiral Arm

We present high-resolution (30 mas or 130 au at 4.2 kpc) Atacama Large Millimeter/submillimeter Array observations at 1.2 mm of the disc around the forming O-type star AFGL 4176 mm1. The disc (AFGL 4176 mm1-main) has a radius of ∼1000 au and contains significant structure, most notably a spiral arm on its redshifted side. We fitted the observed spiral with logarithmic and Archimedean spiral models. We find that both models can describe its structure, but the Archimedean spiral with a varying pitch angle fits its morphology marginally better. As well as signatures of rotation across the disc, we observe gas arcs in CH3CN that connect to other millimetre continuum sources in the field, supporting the picture of interactions within a small cluster around AFGL 4176 mm1-main. Using local thermodynamic equilibrium modelling of the CH3CN K-ladder, we determine the temperature and velocity field across the disc, and thus produce a map of the Toomre stability parameter. Our results indicate that the outer disc is gravitationally unstable and has already fragmented or is likely to fragment in the future, possibly producing further companions. These observations provide evidence that disc fragmentation is one possible pathway towards explaining the high fraction of multiple systems around high-mass stars.

scholarly journals ALMA study of the HD 100453 AB system and the tidal interaction of the companion with the disk

2019 ◽  
Vol 624 ◽  
pp. A33 ◽  
Author(s):  
G. van der Plas ◽  
F. Ménard ◽  
J.-F. Gonzalez ◽  
S. Perez ◽  
L. Rodet ◽  
...  
Keyword(s):  
Scattered Light ◽  
Gravitational Interaction ◽  
Position Angle ◽  
Continuum Emission ◽  
Spiral Arms ◽  
Particle Hydrodynamics ◽  
Planar Orbit ◽  
Good Laboratory ◽  
Low Mass ◽  
Spiral Arm

Context. The complex system HD 100453 AB with a ring-like circumprimary disk and two spiral arms, one of which is pointing to the secondary, is a good laboratory in which to test spiral formation theories. Aims. We aim to resolve the dust and gas distribution in the disk around HD 100453 A and to quantify the interaction of HD 100453 B with the circumprimary disk. Methods. Using ALMA band 6 dust continuum and CO isotopologue observations we have studied the HD 100453 AB system with a spatial resolution of 0′′.09 × 0′′.17 at 234 GHz. We used smoothed particle hydrodynamics (SPH) simulations and orbital fitting to investigate the tidal influence of the companion on the disk. Results. We resolve the continuum emission around HD 100453 A into a disk between 0′′.22 and 0′′.40 with an inclination of 29.5° and a position angle of 151.0°, an unresolved inner disk, and excess mm emission cospatial with the northern spiral arm which was previously detected using scattered light observations. We also detect CO emission from 7 au (well within the disk cavity) out to 1′′.10, overlapping with HD 100453 B at least in projection. The outer CO disk position angle (PA) and inclination differ by up to 10° from the values found for the inner CO disk and the dust continuum emission, which we interpret as due to gravitational interaction with HD 100453 B. Both the spatial extent of the CO disk and the detection of mm emission at the same location as the northern spiral arm are in disagreement with the previously proposed near co-planar orbit of HD 100453 B. Conclusions. We conclude that HD 100453 B has an orbit that is significantly misaligned with the circumprimary disk. Because it is unclear whether such an orbit can explain the observed system geometry we highlight an alternative scenario that explains all detected disk features where another, (yet) undetected, low mass close companion within the disk cavity, shepherds a misaligned inner disk whose slowly precessing shadows excite the spiral arms.

scholarly journals The Bell Laboratories CO Survey: Star Formation in Spiral Arms

1987 ◽  
Vol 115 ◽  
pp. 495-499
Author(s):  
A. A. Stark ◽  
J. Bally ◽  
G. R. Knapp ◽  
A. Krahnert ◽  
A. A. Penzias ◽  
...  
Keyword(s):  
Star Formation ◽  
Survey Data ◽  
Noise Level ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Giant Molecular Clouds ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
The Difference ◽  
Spiral Arm

We present a galactic survey which to date consists of 47,000 positions covering −3° < l < 122°, −1° < b < 1°, observed in the J= 1→ 0 line of 13CO to an rms noise level of 0.15 K in 0.68 km s−1 channels, using the 7 m antenna at Crawford Hill. Maps made from the survey data show a clear difference between spiral arm and interarm regions. The signature of spiral structure on kiloparsec scales is the presence in galactic survey data of voids in l, b, v space which contain many times fewer Giant Molecular Clouds (GMCs) than do adjacent regions of similar size. The difference between arm and interarm regions in the inner galaxy is manifested only in the GMCs — small clouds are present throughout. These results are based on catalogs of clouds and their estimated sizes in 13CO. We suggest that GMCs are formed as interstellar gas enters a spiral arm, and that they break up into small molecular or atomic clouds as the gas leaves the arm.

scholarly journals Spatial and velocity offsets of Galactic masers from the centres of spiral arms

2019 ◽  
Vol 489 (2) ◽  
pp. 2819-2829 ◽  
Author(s):  
Jacques P Vallée
Keyword(s):  
Star Formation ◽  
Pitch Angle ◽  
Milky Way ◽  
Galactic Centre ◽  
Spiral Arms ◽  
Corotation Radius ◽  
Pattern Speed ◽  
Spiral Model ◽  
Spiral Arm ◽  
Co Gas

ABSTRACT Some theories about the spiral arms of galaxies predict an offset between different tracers of star formation. Our goal in this paper is to find such an offset between the observed locations of radio masers and the locations of the arms, using a recent four-arm model fitted to the CO 1–0 gas. Our method is to compare a recent global four-arm spiral model (as fitted to the arms’ tangents in the observed broad CO 1–0 gas) with the recent results for the trigonometric distances of radio masers, for the main arms (Cygnus–Norma, Perseus, Sagittarius–Carina, Scutum and Norma). Our results indicate that most radio masers are near the inner edge of each spiral arm (towards the Galactic Centre). These masers are offset from the model arm (where the broad CO 1–0 molecular region resides), by 0.34 ± 0.06 kpc inward. In radial velocity space, the median offset between masers and the CO-fitted model is around 10 ± 1 km s–1. Based on the fact that the masers are observed here to be radially inward of the broad CO gas in the Cygnus arm at 15 kpc along the Galactic meridian, the corotation radius of the Milky Way disc is >15 kpc distant from the Galactic Centre and the density wave’s angular pattern speed is <15 km s–1 kpc–1. The pitch angle of the arm should be measured using many arm tracers, and located on both sides of the Galactic meridian, to ensure better precision and to avoid a bias pertinent to a single tracer.

scholarly journals Stellar metallicity variations across spiral arms in disk galaxies with multiple populations

2018 ◽  
Vol 611 ◽  
pp. L2 ◽  
Author(s):  
S. Khoperskov ◽  
P. Di Matteo ◽  
M. Haywood ◽  
F. Combes
Keyword(s):  
High Resolution ◽  
Spiral Galaxy ◽  
Spiral Galaxies ◽  
Stellar Populations ◽  
Disk Galaxies ◽  
Model Composite ◽  
Spiral Arms ◽  
Radial Migration ◽  
The Mean ◽  
Spiral Arm

This Letter studies the formation of azimuthal metallicity variations in the disks of spiral galaxies in the absence of initial radial metallicity gradients. Using high-resolution N-body simulations, we model composite stellar discs, made of kinematically cold and hot stellar populations, and study their response to spiral arm perturbations. We find that, as expected, disk populations with different kinematics respond differently to a spiral perturbation, with the tendency for dynamically cooler populations to show a larger fractional contribution to spiral arms than dynamically hotter populations. By assuming a relation between kinematics and metallicity, namely the hotter the population, the more metal-poor it is, this differential response to the spiral arm perturbations naturally leads to azimuthal variations in the mean metallicity of stars in the simulated disk. Thus, azimuthal variations in the mean metallicity of stars across a spiral galaxy are not necessarily a consequence of the reshaping, by radial migration, of an initial radial metallicity gradient. They indeed arise naturally also in stellar disks which have initially only a negative vertical metallicity gradient.

scholarly journals Are the spiral arms in the MWC 758 protoplanetary disc driven by a companion inside the cavity?

2020 ◽  
Vol 498 (1) ◽  
pp. 639-650 ◽  
Author(s):  
Josh Calcino ◽  
Valentin Christiaens ◽  
Daniel J Price ◽  
Christophe Pinte ◽  
Tamara M Davis ◽  
...  
Keyword(s):  
Spiral Structure ◽  
Scattered Light ◽  
Three Dimensional ◽  
Molecular Line ◽  
Spiral Arms ◽  
North West ◽  
The North ◽  
Structure Detection ◽  
Double Spiral ◽  
Spiral Arm

ABSTRACT Spiral arms in protoplanetary discs are thought to be linked to the presence of companions. We test the hypothesis that the double spiral arm morphology observed in the transition disc MWC 758 can be generated by an ≈10MJup companion on an eccentric orbit internal to the spiral arms. Previous studies on MWC 758 have assumed an external companion. We compare simulated observations from three-dimensional hydrodynamics simulations of disc–companion interaction to scattered light, infrared and CO molecular line observations, taking into account observational biases. The inner companion hypothesis is found to explain the double spiral arms, as well as several additional features seen in MWC 758 – the arc in the north-west, substructures inside the spiral arms, the cavity in CO isotopologues, and the twist in the kinematics. Testable predictions include detection of fainter spiral structure, detection of a point source south-southeast of the primary, and proper motion of the spiral arms.

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