scholarly journals 6. The distribution of atomic hydrogen in the inner parts of the Galaxy

1957 ◽  
Vol 4 ◽  
pp. 37-41
Author(s):  
M. Schmidt
Keyword(s):  
Radial Velocity ◽  
Atomic Hydrogen ◽  
Galactic Centre ◽  
The Sun ◽  
The Galaxy ◽  
Latitude Distribution ◽  
Inner Parts

The determination of the distribution of hydrogen from 21-cm. observations in parts of the Galaxy, which are nearer to the centre than the sun, is seriously handicapped by the fact that the observed radial velocity of the hydrogen clouds determines only the distance to the galactic centre. So two possible values of the distance to the sun correspond to one value of the frequency. We have used as a criterion to separate the contributions from the two regions the latitude distribution of the radiation.

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 The Arches cluster revisited

2019 ◽  
Vol 623 ◽  
pp. A84 ◽  
Author(s):  
J. S. Clark ◽  
M. E. Lohr ◽  
L. R. Patrick ◽  
F. Najarro
Keyword(s):  
Main Sequence ◽  
Mass Function ◽  
Initial Mass Function ◽  
Galactic Centre ◽  
Complete Dataset ◽  
Subsequent Determination ◽  
The Galaxy ◽  
First Time ◽  
Massive Clusters

The Arches is one of the youngest, densest and most massive clusters in the Galaxy. As such it provides a unique insight into the lifecycle of the most massive stars known and the formation and survival of such stellar aggregates in the extreme conditions of the Galactic Centre. In a previous study we presented an initial stellar census for the Arches and in this work we expand upon this, providing new and revised classifications for ∼30% of the 105 spectroscopically identified cluster members as well as distinguishing potential massive runaways. The results of this survey emphasise the homogeneity and co-evality of the Arches and confirm the absence of H-free Wolf-Rayets of WC sub-type and predicted luminosities. The increased depth of our complete dataset also provides significantly better constraints on the main sequence population; with the identification of O9.5 V stars for the first time we now spectroscopically sample stars with initial masses ranging from ∼16 M⊙ to ≥120 M⊙. Indeed, following from our expanded stellar census we might expect ≳50 stars within the Arches to have been born with masses ≳60 M⊙, while all 105 spectroscopically confirmed cluster members are massive enough to leave relativistic remnants upon their demise. Moreover the well defined observational properties of the main sequence cohort will be critical to the construction of an extinction law appropriate for the Galactic Centre and consequently the quantitative analysis of the Arches population and subsequent determination of the cluster initial mass function.

Coravel Radial-Velocity Curves for Cepheids in the Large Magellanic Cloud

1984 ◽  
Vol 88 ◽  
pp. 375-380
Author(s):  
M. Imbert ◽  
J. Andersen ◽  
A. Ardeberg ◽  
C. Bardin ◽  
W. Benz ◽  
...  
Keyword(s):  
Comparative Study ◽  
Radial Velocity ◽  
Stellar Evolution ◽  
Large Magellanic Cloud ◽  
Magellanic Clouds ◽  
Independent Determination ◽  
Fundamental Information ◽  
The Galaxy ◽  
Cepheid Variables

Radii and luminosities for Cepheid variables provide fundamental information on stellar evolution. Such data, obtained by the Baade-Wesselink method, are available and have been used for a number of galactic Cepheids. It is of particular interest to obtain corresponding data for Cepheids in the Magellanic Clouds. Firstly, this allows a comparative study of stellar evolution between the Galaxy and the Magellanic Clouds. Secondly, it provides data for an independent determination of the distance to the Magellanic Clouds.Radial-velocity observations have been made for a total of around 20 Cepheid variables in both the LMC and the SMC. All measurements were made with the photoelectric scanner CORAVEL attached to the Cassegrain focus of the Danish 1.54-m telescope at European Southern Observatory, La Silla, Chile. Observations were made from January 1981 through October 1983. The accuracy of individual radial-velocity observations is of the order of 1 km s−1. The B magnitudes of the six Cepheids presented range from 13.0 to 15.5.

scholarly journals A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes

1970 ◽  
Vol 38 ◽  
pp. 232-235
Author(s):  
W. Becker ◽  
R. Fenkart
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Gradients ◽  
The Sun ◽  
Main Sequence Stars

The Basel Observatory program of the determination of disc- and halo-density gradients for different intervals of absolute magnitude comprises in addition to Milky Way fields several directions, all pointing to Selected Areas near a plane perpendicular to the galactic equator and passing through the sun and the galactic centre. It was started with SA 51 (Becker, 1965) and continued with Sa 57, 54 and 141 (Fenkart, 1967, 1968, 1969).

A CO Survey of the Southern Galactic Plane

1981 ◽  
Vol 4 (2) ◽  
pp. 243-247 ◽  
Author(s):  
W. H. McCutcheon ◽  
B. J. Robinson ◽  
J. B. Whiteoak
Keyword(s):  
Northern Hemisphere ◽  
Atomic Hydrogen ◽  
Molecular Hydrogen ◽  
Large Scale ◽  
Galactic Plane ◽  
Galactic Centre ◽  
Hydrogen Distribution ◽  
Millimetre Wave ◽  
The Galaxy ◽  
Wave Emission

Millimetre-wave emission from the CO molecule has proven to be an extremely useful probe of the cold, dense clouds of molecular hydrogen in the Galaxy. Previous studies of the large-scale distribution of CO in the galactic plane (Scoville and Solomon 1975; Burton et al. 1975; Bash and Peters 1976; Burton and Gordon 1978; Solomon et al. 1979b; Cohen et al. 1980) have all been of the northern hemisphere and primarily at longitudes 0° ≤ l ≥ 80°. These studies have revealed the striking characteristic that the CO, and by implication molecular hydrogen clouds, are concentrated in a ring extending from 4 to 8 kpc from the galactic centre. This is in sharp contrast to the atomic hydrogen distribution, which is fairly constant over the extended region from 4 to 13 kpc but correlates well with other Population I indicators.

scholarly journals A method for mapping the aliphatic hydrocarbon content of interstellar dust towards the Galactic Centre

2020 ◽  
Vol 493 (1) ◽  
pp. 1109-1119
Author(s):  
B Günay ◽  
M G Burton ◽  
M Afşar ◽  
T W Schmidt
Keyword(s):  
Interstellar Dust ◽  
Elemental Carbon ◽  
Total Carbon ◽  
Galactic Centre ◽  
Absorption Feature ◽  
Ir Camera ◽  
Carbon Abundance ◽  
The Galaxy ◽  
Aliphatic Carbon

ABSTRACT In the interstellar medium, the cosmic elemental carbon abundance includes the total carbon in both gas and solid phases. The aim of the study was to trial a new method for measuring the amount and distribution of aliphatic carbon within interstellar dust over wide fields of view of our Galaxy. This method is based on the measurement of the 3.4-$\mu$m absorption feature from aliphatic carbonaceous matter. This can readily be achieved for single sources using infrared (IR) spectrometers. However, making such measurements over wide fields requires an imaging IR camera, equipped with narrow-band filters that are able to sample the spectrum. While this cannot produce as good a determination of the spectra, the technique can be applied to potentially tens to hundreds of sources simultaneously, over the field of view of the camera. We examined this method for a field in the centre of the Galaxy, and produced a map showing the variation of 3.4-$\mu$m optical depth across it.

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.

Developing an astrophysical line list for Keck/Nirspec observations of red giants in the Galactic centre

2017 ◽  
Vol 13 (S334) ◽  
pp. 372-373 ◽  
Author(s):  
B. Thorsbro ◽  
N. Ryde ◽  
R. M. Rich ◽  
M. Schultheis ◽  
T. K. Fritz ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Wavelength Region ◽  
Galactic Centre ◽  
Red Giants ◽  
The Sun ◽  
Galactic Chemical Evolution ◽  
Line List ◽  
Stellar Spectroscopy ◽  
Near Ir ◽  
The Galaxy

AbstractA major avenue in the study of the Galaxy is the investigation of stellar populations and Galactic chemical evolution by stellar spectroscopy. Due to the dust obscuration, stars in the centre of the Galaxy can only be observed in the near-IR wavelength region. However, existing line lists in this wavelength region are demonstratively not of good enough quality for use in stellar spectroscopy. In response to this, we have developed an empirical astrophysical line list in the K-band based on modelling against the Sun and testing against Arcturus. Of ca. 700 identified interesting lines about 570 lines have been assigned empirically determined values.

scholarly journals Planetary nebulae in the central region of the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 41-45 ◽  
Author(s):  
L. Perek
Keyword(s):  
Central Region ◽  
Surface Brightness ◽  
Large Scale ◽  
Direct Determination ◽  
Planetary Nebulae ◽  
Galactic Centre ◽  
Large Numbers ◽  
The Galaxy ◽  
Objective Prism

Planetary nebulae are convenient objects for studying the large-scale structure of the Galaxy. Firstly, they are easily recognized up to considerable distances on plates taken through an objective prism, and secondly, methods have been devised by various authors to determine their distances from two observable quantities: angular diameter and surface brightness. The importance of the subsystem of planetary nebulae has been accentuated especially by the discoveries by Minkowski and Haro of large numbers of planetaries in the direction of the galactic centre. The distribution of planetaries on the sphere suggests that they are connected with the galactic nucleus, but no direct determination of their distances, which would either confirm or contradict this statement, is available. The most serious obstacle in studying the subsystem of planetaries is the lack of observing data. The aim of the reported paper (Perek 1963) is to give a tentative outline of the distribution of planetaries in space based on extensive new observing material.

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.

Sign in / Sign up

Export Citation Format

Share Document