scholarly journals Spiral structure and distribution of stellar associations in NGC 6946

1970 ◽  
Vol 38 ◽  
pp. 87-90
Author(s):  
E. Ye. Khachikian ◽  
K. A. Sahakian
Keyword(s):  
Spiral Structure ◽  
Absolute Magnitude ◽  
Colour Index ◽  
Spiral Arms ◽  
Ngc 6946 ◽  
Stellar Associations

The associations of NGC 6946 outline its spiral arms. There is no relation between the colour or magnitude of the associations and their distance from the centre. Their mean absolute magnitude is −11m.1 and their mean colour index near zero.

Dynamical imprint of interstellar gas on persistence of spiral structure in galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 296-297
Author(s):  
Soumavo Ghosh ◽  
Chanda J. Jog
Keyword(s):  
Time Scale ◽  
Spiral Structure ◽  
Density Wave ◽  
Disk Galaxies ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
Pattern Speed

AbstractThe persistence of the spiral structure in disk galaxies has long been debated. In this work, we investigate the dynamical influence of interstellar gas on the persistence of the spiral arms in disk galaxies. We show that the gas helps the spiral arms to survive for longer time-scale (~ a few Gyr). Also, we show that the addition of gas in calculation is necessary for getting a stable density wave corresponding to the observed pattern speed of the spiral arms.

scholarly journals A Spiral-Like Disk of Ionized Gas in IC 1459: Signature of a Merging Collision?

1990 ◽  
Vol 124 ◽  
pp. 215-219
Author(s):  
Paul Goudfrooij ◽  
H.U. Nørgaard-Nielsen ◽  
H.E. Jørgensen ◽  
L. Hansen ◽  
T. de Jong
Keyword(s):  
Spiral Structure ◽  
Elliptical Galaxy ◽  
Broad Band ◽  
Major Axis ◽  
Colour Index ◽  
Line Flux ◽  
Ionized Gas ◽  
The Galaxy ◽  
Merger Event ◽  
Stellar Body

AbstractWe report the discovery of a large (15 kpc diameter) Hα+[NII] emission-line disk in the elliptical galaxy IC 1459, showing weak spiral structure. The line flux peaks strongly at the nucleus and is more concentrated than the stellar continuum. The major axis of the disk of ionized gas coincides with that of the stellar body of the galaxy. The mass of the ionized gas is estimated to be ~ 1 105 M⊙, less than 1% of the total mass of gas present in IC 1459. The total gas mass of 4 107 M⊙ has been estimated from the dust mass derived from a broad-band colour index image and the IRAS data. We speculate that the presence of dust and gas in IC 1459 is a signature of a merger event.

The Hertzsprung-Russell diagram

1961 ◽  
Vol 260 (1301) ◽  
pp. 175-182
Keyword(s):  
Surface Brightness ◽  
Absolute Magnitude ◽  
Black Body ◽  
Colour Index ◽  
Similar Material ◽  
Initial Composition ◽  
Evolutionary Time ◽  
Horizontal Scale ◽  
Bolometric Correction ◽  
Stellar Masses

The theory of stellar evolution aims at predicting the luminosity L and radius R of a star as a function of its mass M , its initial composition, and its age. As the time scales are so long, comparison with observation must necessarily be indirect. A convenient method is to select clusters of stars, all born from similar material and at times close together compared with the evolutionary time scale, leaving just the mass as a parameter. However, the paucity of well-determined stellar masses forces us to eliminate the mass between the ( M, L ) and ( M, R ) relations. The ( L, R ) relation is studied indirectly by introducing the effective temperature T e , defined by L = (¼ acT 4 e ) (4 πR 2 ), where c is the velocity of light, and a the stefan-Boltzmann constant. Thus T e is the temperature of a black body having the same surface brightness as the star. The theorist’s ‘Hertzsprung-Russell diagram’ is a plot of log T e on a horizontal scale, increasing to the left, against log ( L/L ʘ ), where L ʘ is the solar luminosity. The observer’s diagram is a plot of V , the absolute magnitude in the visual waveband, against the colour index ( B ─ V ), where B is the blue magnitude. The transformation of one diagram into the other by means of the bolometric correction and the T e , ( B ─ V relation is still subject to considerable uncertainties at the extremes of high and low T e .

scholarly journals The spiral structure of our Milky Way

2012 ◽  
Vol 8 (S292) ◽  
pp. 106-106
Author(s):  
L. G. Hou ◽  
J. L. Han
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Hii Regions ◽  
Giant Molecular Clouds ◽  
Constant Weight ◽  
Spiral Arms ◽  
Flat Rotation Curve ◽  
Methanol Masers ◽  
The Masses ◽  
Excitation Parameters

AbstractThe spiral structure of our Milky Way has not yet been well outlined. HII regions, giant molecular clouds (GMCs) and 6.7-GHz methanol masers are primary tracers for spiral arms. We collect and update the database of these tracers which has been used in Hou et al. (2009) for the spiral arms.The new database consists of ∼ 2000 HII regions, ∼ 1300 GMCs and ∼ 800 methanol masers (6.7 GHz). If the photometric or trigonometric distance for any tracer is available from the literature, we will adopt it. Otherwise, we have to use the kinematic distance. We modify the VLSR according to the newly determined solar motions (U0 = 10.27 km s−1, V0 = 15.32 km s−1 and W0 = 7.74 km s−1, Schönrich et al. 2010), then calculate the kinematic distances with a flat rotation curve (R0 = 8.3 kpc, θ0 = 239 km s−1, Brunthaler et al. 2011). Very important step is that we weight tracers according to the excitation parameters of HII regions or the masses of GMCs, and a constant weight for masers. All three kinds of tracers are used together to outline the spiral structure (Fig. 1). A contour and gray map is constructed after we made a Gaussian extension for the tracers with the amplitude of weighting parameter.

scholarly journals Spiral structure of our Galaxy and of other galaxies

1970 ◽  
Vol 38 ◽  
pp. 15-17 ◽  
Author(s):  
B.A. Vorontsov-Velyaminov
Keyword(s):  
Spiral Structure ◽  
The State ◽  
Spiral Arms

Time and again Dr. B. Bok publishes his reviews on the state of optical searches of the spiral arms in our Galaxy. A great optimist at the beginning, concerning the agreement of different results, he became later more critical in his conclusions. But in his paper of 1967 he claims anew, as well established, that we can trace the spiral arms up to a distance of 14000 pc from the centre.

scholarly journals Some Comments on Radio Observations of Spiral Arms

1978 ◽  
Vol 77 ◽  
pp. 97-104 ◽  
Author(s):  
W.W. Shane ◽  
J. Bystedt
Keyword(s):  
Spiral Structure ◽  
Physical Models ◽  
Dynamical Process ◽  
Radio Observations ◽  
Spiral Arms ◽  
Theoretical Developments

If we view spiral structure in galaxies as a manifestation of some dynamical process which we wish to understand, then the observer can distinguish two facets of the problems. In the first place he must consider the observable consequences suggested by theoretical developments. In the second place he must endeavour to interpret the available observations in terms of realistic physical models, where such models may require detailed information beyond that required for an understanding of spiral structure as a dynamical phenomenon. We shall consider these two aspects in turn.

scholarly journals Outer spiral structure in disk galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 123-123
Author(s):  
P.A. Patsis
Keyword(s):  
Periodic Orbits ◽  
Spiral Galaxies ◽  
Spiral Structure ◽  
Disk Galaxies ◽  
Spiral Arms ◽  
Chaotic Orbits ◽  
Grand Design ◽  
Pattern Speed ◽  
Spiral Structures ◽  
Barred Spiral Galaxies

AbstractIn several grand design barred-spiral galaxies it is observed a second, fainter, outer set of spiral arms. Typical examples of objects of this morphology can be considered NGC 1566 and NGC 5248. I suggest that such an overall structure can be the result of two dynamical mechanisms acting in the disc. The bar and both spiral systems rotate with the same pattern speed. The inner spiral is reinforced by regular orbits trapped around the stable, elliptical, periodic orbits of the central family, while the outer system of spiral arms is supported by chaotic orbits. Chaotic orbits are also responsible for a rhomboidal area surrounding the inner barred-spiral region. In general there is a discontinuity between the two spiral structures at the corotation region.

scholarly journals The Spiral Structure in the Solar Neighborhood

2021 ◽  
Vol 8 ◽  
Author(s):  
L. G. Hou
Keyword(s):  
Spiral Structure ◽  
Open Clusters ◽  
Solar Neighborhood ◽  
High Mass ◽  
Mass Star ◽  
Giant Molecular Clouds ◽  
Star Formation Region ◽  
Spiral Arms ◽  
Different Types ◽  
Better Than

The spiral structure in the solar neighborhood is an important issue in astronomy. In the past few years, there has been significant progress in observation. The distances for a large number of good spiral tracers, i.e., giant molecular clouds, high-mass star-formation region masers, HII regions, O-type stars, and young open clusters, have been accurately estimated, making it possible to depict the detailed properties of nearby spiral arms. In this work, we first give an overview about the research status for the Galaxy’s spiral structure based on different types of tracers. Then the objects with distance uncertainties better than 15% and <0.5 kpc are collected and combined together to depict the spiral structure in the solar neighborhood. Five segments related with the Perseus, Local, Sagittarius-Carina, Scutum-Centaurus, and Norma arms are traced. With the large dataset, the parameters of the nearby arm segments are fitted and updated. Besides the dominant spiral arms, some substructures probably related to arm spurs or feathers are also noticed and discussed.

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