scholarly journals A New Value for the Rotation Speed of the Spiral Structure

1977 ◽  
Vol 45 ◽  
pp. 293-296 ◽  
Author(s):  
J. Palouš
Keyword(s):  
Surface Density ◽  
Galactic Center ◽  
Local Density ◽  
Outer Part ◽  
Density Variation ◽  
The Sun ◽  
Basic Model ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Nearby Stars

The basic model of our Galaxy, like the Schmidt (1965) model, obeys the density law ρ(R) for the Galaxy based on divers evidence, less or better known from observation. The interpretation of the interstellar hydrogen radio profiles yields the rotation curve and the run of the force component in the radial direction. The Oort constants A, B known from radial velocities and proper motions of nearby stars, the distance from the Sun to the galactic center Roestablished from the distances of RR Lyrae stars, the local density and density gradients in the vicinity of the Sun, known from the star counts, are involved in this basic model of the Galaxy. The r.m.s. velocity component in the z direction yields the approximate mass distribution in this direction. The model surface density is computed by integrating the density along the z direction in the model. The local surface density in the Schmidt model is 114 solar masses per pc2; it depends rather strongly on the assumed density variation in the outer part of the Galaxy.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

scholarly journals Pulsars as a galactic population

1979 ◽  
Vol 84 ◽  
pp. 119-123
Author(s):  
Joseph H. Taylor
Keyword(s):  
Carbon Monoxide ◽  
Statistical Analysis ◽  
Supernova Remnants ◽  
Galactic Center ◽  
Hii Regions ◽  
The Sun ◽  
Disk Thickness ◽  
Galactic Population ◽  
The Galaxy

Recent pulsar surveys have increased the number of known pulsars to well over 300, and many of them lie at distances of several kpc or more from the sun. The distribution of pulsars with respect to distance from the galactic center is similar to other population I material such as HII regions, supernova remnants, and carbon monoxide gas, but the disk thickness of the pulsar distribution is rather greater, with <|z|>≈350 pc. Statistical analysis suggests that the total number of active pulsars in the Galaxy is a half million or more, and because kinematic arguments require the active lifetimes of pulsars to be ≲5×106 years, it follows that the birthrate required to maintain the observed population is one pulsar every ∼10 years (or less) in the Galaxy.

scholarly journals Probing the structure of the Galactic disk through open clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 482-482
Author(s):  
Xiaoying Pang ◽  
Chenggang Shu
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Age Distribution ◽  
Outer Part ◽  
Simulation Models ◽  
Open Clusters ◽  
Galactocentric Distance ◽  
Distance Measurements ◽  
The Galaxy

AbstractThe WEBDA database of open clusters (hereafter OCs) in the Galaxy contains 970 OCs, of which 911 have age determinations, 920 have distance measurements, and 911 have color-excess data. Base on the statistical analysis of global properties of open clusters, we investigate disk properties such as the height above the Galactic plane. We find that old open clusters (age ≥ 1 Gyr) are preferentially located far from the Galactic plane with 〈|z|〉~394.5 pc. They lie in the outer part of the Galactic disk. The young open clusters are distributed in the Galactic plane almost symmetrically with respect to the Sun, with a scale height perpendicular to the Galactic plane of 50.5 pc. The age distribution of open clusters can be fit approximately with a two-component exponential decay function: one component has an age scale factor of 225.2 Myr, and the other consists of longer-lived clusters with an age scale of 1.8 Gyr, which are smaller than those derived by Janes & Phelps (1994) of 200 Myr and 4 Gyr for the young and old OCs, respectively. As a consequence of completeness effects, the observed radial distribution of OCs with respect to Galactocentric distance does not follow the expected exponential profile. Instead, it falls off both for regions external to the solar circle and more sharply towards the Galactic Center, which is probably due to giant molecular cloud disruption in the center. We simulate the effects of completeness, assuming that the observed distribution of the number of OCs with a given number of stars above the background is representative of the intrinsic distribution of OCs throughout the Galaxy. Two simulation models are considered, in which the intrinsic number of the observable stars are distributed (i) assuming the actual positions of the OCs in the sample, and (ii) random selection of OC positions. As a result, we derive completeness-corrected radial distributions which agree with an exponential disk throughout the observed Galactocentric distance in the range of 5–15 kpc, with scale lengths in the range of 1.6–2.8 kpc.

scholarly journals RR Lyrae stars as probes of the Milky Way structure and formation

2015 ◽  
Vol 11 (S317) ◽  
pp. 116-119
Author(s):  
Pawel Pietrukowicz ◽  
Keyword(s):  
Galactic Center ◽  
Variable Stars ◽  
Wide Field ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
The Galaxy ◽  
First Results ◽  
Formation And Evolution ◽  
Lyrae Stars ◽  
Distance Indicators

AbstractRR Lyrae stars being distance indicators and tracers of old population serve as excellent probes of the structure, formation, and evolution of our Galaxy. Thousands of them are being discovered in ongoing wide-field surveys. The OGLE project conducts the Galaxy Variability Survey with the aim to detect and analyze variable stars, in particular of RRab type, toward the Galactic bulge and disk, covering a total area of 3000 deg2. Observations in these directions also allow detecting background halo variables and unique studies of their properties and distribution at distances from the Galactic Center to even 40 kpc. In this contribution, we present the first results on the spatial distribution of the observed RRab stars, their metallicity distribution, the presence of multiple populations, and relations with the old bulge. We also show the most recent results from the analysis of RR Lyrae stars of the Sgr dwarf spheroidal galaxy, including its center, the globular cluster M54.

The Rotation Curve from A-F Supergiants

1996 ◽  
Vol 169 ◽  
pp. 703-706
Author(s):  
D. M. Peterson ◽  
D. Slowik
Keyword(s):  
Total Mass ◽  
Rotation Curve ◽  
Galactic Center ◽  
Galactic Rotation ◽  
The Sun ◽  
Critical Information ◽  
New Class ◽  
The Galaxy ◽  
Local Distance

The Galactic rotation law provides critical information for estimating the distribution of mass in the Galaxy, for tying the distance of the Sun from the Galactic center to local distance scales, and, if determined over large enough distances, for estimating the total mass of the system and the amount of nonluminous matter present. Interior to the Sun velocities are well defined by observations of the ISM, particularly HI. These techniques are not available for points exterior to the Sun and we must rely on observations of velocities of objects whose distances can be estimated. Notable among these are the Cepheids (Pont et al 1994) and the combination of CO velocities and OB cluster distances (Brand & Blitz 1993) where the two are found to coexist. Adding a new class of objects, particularly bright, relatively common objects to this effort is of importance.

scholarly journals The spiral potential of the Milky Way

2018 ◽  
Vol 619 ◽  
pp. A50 ◽  
Author(s):  
P. Grosbøl ◽  
G. Carraro
Keyword(s):  
Radial Velocity ◽  
Galactic Center ◽  
Galactic Plane ◽  
Small Mass ◽  
The Sun ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Best Fit ◽  
Armed Spiral

Context. The location of young sources in the Galaxy suggests a four-armed spiral structure, whereas tangential points of spiral arms observed in the integrated light at infrared and radio wavelengths indicate that only two arms are massive. Aims. Variable extinction in the Galactic plane and high light-to-mass ratios of young sources make it difficult to judge the total mass associated with the arms outlined by such tracers. The current objective is to estimate the mass associated with the Sagittarius arm by means of the kinematics of the stars across it. Methods. Spectra of 1726 candidate B- and A-type stars within 3◦ of the Galactic center (GC) were obtained with the FLAMES instrument at the VLT with a resolution of ≈6000 in the spectral range of 396–457 nm. Radial velocities were derived by least-squares fits of the spectra to synthetic ones. The final sample was limited to 1507 stars with either Gaia DR2 parallaxes or main-sequence B-type stars having reliable spectroscopic distances. Results. The solar peculiar motion in the direction of the GC relative to the local standard of rest (LSR) was estimated to U⊙ = 10.7 ± 1.3kms−1. The variation in the median radial velocity relative to the LSR as a function of distance from the sun shows a gradual increase from slightly negative values near the sun to almost 5 km s−1 at a distance of around 4 kpc. A sinusoidal function with an amplitude of 3.4 ± 1.3kms−1 and a maximum at 4.0 ± 0.6 kpc inside the sun is the best fit to the data. A positive median radial velocity relative to the LSR around 1.8 kpc, the expected distance to the Sagittarius arm, can be excluded at a 99% level of confidence. A marginal peak detected at this distance may be associated with stellar streams in the star-forming regions, but it is too narrow to be associated with a major arm feature. Conclusions. A comparison with test-particle simulations in a fixed galactic potential with an imposed spiral pattern shows the best agreement with a two-armed spiral potential having the Scutum–Crux arm as the next major inner arm. A relative radial forcing dFr ≈ 1.5% and a pattern speed in the range of 20–30 km s−1 kpc−1 yield the best fit. The lack of a positive velocity perturbation in the region around the Sagittarius arm excludes it from being a major arm. Thus, the main spiral potential of the Galaxy is two-armed, while the Sagittarius arm is an inter-arm feature with only a small mass perturbation associated with it.

Approaches of stars to the Sun

1999 ◽  
Vol 173 ◽  
pp. 345-352 ◽  
Author(s):  
P.A. Dybczyński ◽  
P. Kankiewicz
Keyword(s):  
Minimum Distance ◽  
Galactic Disk ◽  
Equations Of Motion ◽  
Oort Cloud ◽  
The Sun ◽  
The Past ◽  
Straight Line ◽  
The Galaxy ◽  
Hipparcos Catalogue ◽  
Nearby Stars

AbstractClose approaches of stars to the Solar System perturb comets from the Oort cloud so that they pass into the planetary system − the gravitational impulse changes the distribution of observable comets. This paper presents the results of calculations of the motion of stars in the solar neighbourhood in the past and future. The main results for each star are: the time of the encounter and the minimum distance between the Sun and the star. They are calculated using three different methods: a straight line motion model, a model with a Sun − star Keplerian interaction, and the numerical integration of the equations of motion with galactic perturbations included. In the last case, two models of the Galactic potential are used: a simplified potential of the Galactic disk and the more complex potential of the Galaxy by Dauphole and Colin. Coordinates and velocities of nearby stars are taken from several different catalogues: the Gliese catalogue, the Hipparcos catalogue, and the Barbier-Brossat catalogue of Radial Velocities.

scholarly journals The distribution of H II regions

1970 ◽  
Vol 38 ◽  
pp. 107-121
Author(s):  
P. G. Mezger
Keyword(s):  
Surface Density ◽  
Interstellar Dust ◽  
Large Scale ◽  
Galactic Center ◽  
Neutral Hydrogen ◽  
Optical Observations ◽  
H Ii Regions ◽  
The Sun ◽  
Radio Recombination Line ◽  
Actual Space

The distribution of optically observed H II regions and OB stars with galactic longitude indicates that it is primarily determined by extinction by interstellar dust. Thus optical observations can, at the best, reveal the local structure in the vicinity of the sun. Radio observations, on the other hand, are not affected by dust. Thus the distribution of galactic radio sources, which peaks in the northern part at about lII = 17°.5, must be related to the large-scale structure of our Galaxy. Two radio recombination line surveys of the northern and southern sky yield kinematic distances. If only the ‘giant H II regions’ are retained, the following distribution is obtained: (1) Only 5 giant H II regions are found within the 4 kpc arm. (2) The bulk of the giant H II regions is concentrated in a ring between 4 and 6 kpc from the galactic center. (3) There are other concentrations of giant H II regions indicating the existence of the Sagittarius and Perseus arm. (4) The three features revealed by optical observations of H II regions in the vicinity of the sun cannot be matched with the large-scale distribution outlined by giant H II regions. This is particularly true for the so-called Orion arm. (5) At distances beyond 13 kpc from the galactic center virtually no giant H II regions are found. (6) The surface density of giant H II regions attains its maximum between 4 and 8 kpc; the surface density of neutral hydrogen (H I) attains its maximum between 11 and 15 kpc, but the actual space density of H I in the region 4 to 8 kpc may still be rather high.

scholarly journals Composition of matter in the heliosphere

2008 ◽  
Vol 4 (S257) ◽  
pp. 17-28 ◽  
Author(s):  
Peter Bochsler
Keyword(s):  
Solar Wind ◽  
Solar System ◽  
Galactic Center ◽  
Compositional Data ◽  
The Other ◽  
The Sun ◽  
Pickup Ions ◽  
Solar Composition ◽  
The Galaxy ◽  
State Composition

AbstractThe Sun is by far the largest reservoir of matter in the solar system and contains more than 99% of the mass of the solar system. Theories on the formation of the solar system maintain that the gravitational collapse is very efficient and that typically not more than one tenth from the solar nebula is lost during the formation process. Consequently, the Sun can be considered as a representative sample of interstellar matter taken from a well mixed reservoir 4.6 Gy ago, at about 8 kpc from the galactic center. At the same time, the Sun is also a faithful witness of the composition of matter at the beginning of the evolution of the solar system and the formation of planets, asteroids, and comets. Knowledge on the solar composition and a fair account of the related uncertainties is relevant for many fields in astrophysics, planetary sciences, cosmo- and geochemistry. Apart from the basic interest in the chemical evolution of the galaxy and the solar system, compositional studies have also led to many applications in space research, i.e., it has helped to distinguish between different components of diffuse heliospheric matter. The elemental, isotopic, and charge state composition of heliospheric particles (solar wind, interstellar neutrals, pickup ions) has been used for a multitude of applications, such as tracing the source material, constraining parameters for models of the acceleration processes, and of the transport through the interplanetary medium. It is important to realize, that the two mainstream applications, as outlined above – geochemistry and cosmochemistry on one side, and tracing of heliospheric processes on the other side – are not independent of each other. Understanding the physical processes, e.g., of the fractionation of the solar wind, is crucial for the interpretation of compositional data; on the other hand, reliable information on the source composition is the basis for putting constraints on models of the solar wind fractionation.

A statistical study of the distribution of y-ray sources

1981 ◽  
Vol 301 (1462) ◽  
pp. 529-531 ◽  
Keyword(s):  
Surface Density ◽  
Statistical Study ◽  
Galactic Plane ◽  
The Sun ◽  
The Galaxy ◽  
Latitude Distribution

Data from the COS-B satellite have enabled discrete sources of cosmic y-rays to be identified. We wish to estimate the contribution that such sources make to the y-ray luminosity of the Galaxy (see Protheroe et al . 1979; Rothenflug & Caraveo 1980). Since only the brightest, and hence relatively near, sources are known, only the contribution of sources to the local y-ray emissivity can be determined from them. The distances to most of the sources in the second COS-B catalogue (Hermsen 1980) are not known so that neither their mean luminosity, nor their surface density, on the galactic plane can be determined accurately. The latitude distribution of sources indicates that their distance from the Sun, r , is much greater than their distance from the galactic plane, z . We can therefore calculate the product without knowing the distances of the sources.

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