An Expanding Ring of Interstellar Gas with Center Close to the Sun

We illustrate a method for estimating the vertical position of the Sun above the Galactic plane by γ-ray observations. Photons of γ-ray wavelengths are particularly well suited for geometrical and kinematic studies of the Milky Way because they are not subject to extinction by interstellar gas or dust. Here, we use the radioactive decay line of 26Al at 1.809 MeV to perform maximum likelihood fits to data from the spectrometer SPI on board the INTEGRAL satellite as a proof-of-concept study. Our simple analytic 3D emissivity models are line-of-sight integrated, and varied as a function of the Sun’s vertical position, given a known distance to the Galactic centre. We find a vertical position of the Sun of z0 = 15 ± 17 pc above the Galactic plane, consistent with previous studies, finding z0 in a range between 5 and 29 pc. Even though the sensitivity of current MeV instruments is several orders of magnitude below that of telescopes for other wavelengths, this result reveals once more the disregarded capability of soft γ-ray telescopes. We further investigate possible biases in estimating the vertical extent of γ-ray emission if the Sun’s position is set incorrectly, and find that the larger the true extent, the less is it affected by the observer position. In the case of 26Al with an exponential scale height of 150 pc (700 pc) in the inner (full) Galaxy, this may lead to misestimates of up to 25%.

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Can Galactic GMCs be Identified from l-v Diagrams?

Highlights of Astronomy ◽

10.1017/s1539299600008455 ◽

1989 ◽

Vol 8 ◽

pp. 587-588

Author(s):

David S. Adler ◽

William W. Roberts

Keyword(s):

Numerical Simulations ◽

Spiral Galaxy ◽

Molecular Cloud ◽

Cloud System ◽

The Sun ◽

Interstellar Gas ◽

The Past ◽

The Galaxy

Identifying the spiral nature of the distribution of gas in the Galaxy has been a subject of much research in the past thirty years. The position of the sun in the disk of the Galaxy presents us with a problem of perspective: how does one identify the cloud system from within the system? Longitude-velocity (l-v) diagrams have been used to try to determine the distribution of interstellar gas, but problems inherent in the methods have been pointed out previously (Burton 1971). Recent Galactic CO surveys have been used in attempts to map the distribution of molecular cloud complexes in the disk of the Galaxy (Dame, et al. 1986). Here, we use numerical simulations of the molecular cloud system in a spiral galaxy to consider the following question: to what extent can concentrations of emission in the l-v diagram (LVCs) be considered complexes of gas in the disk of the Galaxy (GMCs)?

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The Soft X-Ray Background

Highlights of Astronomy ◽

10.1017/s1539299600005827 ◽

1983 ◽

Vol 6 ◽

pp. 681-687

Author(s):

W. Kraushaar ◽

D. Burrows ◽

D. McCammon ◽

W. Sanders

Keyword(s):

The Sun ◽

Diffuse Emission ◽

Energy Bands ◽

Interstellar Gas ◽

Energy Data ◽

X Ray ◽

X Ray Background ◽

Require Emission

AbstractMaps in three energy bands from the recently-completed Wisconsin survey of the soft X-ray sky are presented. The lowest energy data require emission, almost certainly from hot interstellar gas, from regions within 100 pc of the sun. The data do not require diffuse emission from beyond the neutral galactic gas but are compatible with such emission under certain assumptions.

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Trapped orbits and solar-neighbourhood kinematics

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1103 ◽

2020 ◽

Vol 495 (1) ◽

pp. 895-904 ◽

Cited By ~ 5

Author(s):

James Binney

Keyword(s):

Quantitative Measure ◽

Velocity Space ◽

The Sun ◽

Interstellar Gas ◽

Gas Trapping ◽

Constants Of Motion ◽

Pattern Speed ◽

Star Density ◽

Pattern Speeds ◽

Lindblad Resonance

ABSTRACT Torus mapping yields constants of motion for stars trapped at a resonance. Each such constant of motion yields a system of contours in velocity space at the Sun and neighbouring points. If Jeans’ theorem applied to resonantly trapped orbits, the density of stars in velocity space would be equal at all intersections of any two contours. A quantitative measure of the violation of this principle is defined and used to assess various pattern speeds for a model of the bar recently fitted to observations of interstellar gas. Trapping at corotation of a bar with pattern speed near $36\, \mathrm{Gyr}^{-1}$ is favoured and trapping at the outer Lindblad resonance is disfavoured. As one moves around the Sun the structure of velocity space varies quite rapidly, both as regards the observed star density and the zones of trapped orbits. The data seem consistent with trapping at corotation.

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Nearby Molecular Hydrogen

International Astronomical Union Colloquium ◽

10.1017/s0252921100098377 ◽

1984 ◽

Vol 81 ◽

pp. 276-279

Author(s):

F. Lebrun

Keyword(s):

Interstellar Medium ◽

Molecular Mass ◽

Molecular Cloud ◽

Molecular Hydrogen ◽

Large Scale ◽

Gamma Ray ◽

The Sun ◽

Local Interstellar Medium ◽

Interstellar Gas ◽

Co Observations

AbstractIf the gas-to-dust ratio is sufficiently uniform throughout the local interstellar medium, galaxy counts may provide a useful probe of the large scale structure of the interstellar gas. This idea substantiated by gamma-ray observations has led to the discovery of nearby molecular cloud complexes. The reddening studies indicate that one of them lies between 80 and 140 pc from the sun. From CO observations, its molecular mass is estimated to be a few 103 M⊙.

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2. Gas between the stars

Astrophysics: A Very Short Introduction ◽

10.1093/actrade/9780198752851.003.0002 ◽

2016 ◽

pp. 11-21

Author(s):

James Binney

Keyword(s):

Chemical Composition ◽

Ultraviolet Light ◽

Crucial Role ◽

Red Light ◽

The Sun ◽

Dust Grains ◽

Interstellar Gas ◽

Interstellar Absorption ◽

Pass Through ◽

Ultraviolet Photons

The space between stars is taken up by gas—mostly hydrogen and helium—which manifests itself in many ways, the most important being the absorption of starlight. ‘Gas between the stars’ describes interstellar absorption and the reddening of stars—when dust grains in the gas absorb blue and ultraviolet light, but let red light from the Sun pass through. These dust grains play a crucial role in regulating the temperature, density, and chemical composition of the gas. This composition of interstellar gas hinges on the balance between the destructive power of ultraviolet photons and the catalytic action of dust grains.

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From Planetoids to Planets

Highlights of Astronomy ◽

10.1017/s1539299600009205 ◽

1992 ◽

Vol 9 ◽

pp. 367-374

Author(s):

P. Barge ◽

R. Pellat

Keyword(s):

Time Scale ◽

Model Building ◽

Time Constraint ◽

Common Origin ◽

The Other ◽

The Sun ◽

Solar Mass ◽

Interstellar Gas ◽

Starting Point ◽

Previous Step

A common origin of the sun and the planets from the collapse of interstellar gas is now widely accepted. Regardless of how stars form, which is considered as the previous step of the whole story, the starting point is a flattened rotating cloud containing a mixture of dusts and gas (the so called Kant-Laplace Nebula). On the other hand the observations of young solar-mass stars show with increasing evidence that the gas is dispersed away on a time scale less than 107 years and this provides us with a clear time constraint for model building since the formation of the giant gaseous planets have to take place on a shorter time scale.

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The total deuterium abundance in the local Galactic disk: decisions and implications

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310003868 ◽

2009 ◽

Vol 5 (S268) ◽

pp. 53-58

Author(s):

Jeffrey L. Linsky

Keyword(s):

Gas Phase ◽

Time Scales ◽

Chemical Evolution ◽

Galactic Disk ◽

Mixing Time ◽

Stellar Winds ◽

The Sun ◽

Galactic Chemical Evolution ◽

Interstellar Gas ◽

Wide Range

AbstractAnalyses of FUSE spacecraft spectra have provided measurements of D/H in the gas phase of the interstellar medium for many lines of sight extending to several kpc from the Sun. These measurements, together with the earlier Copernicus, HST, and IMAPS data, show a wide range of D/H values that have challenged both observers and chemical evolution modellers. I believe that the best explanation for the diverse D/H measurements is that deuterium can be sequestered on to carbonaceous grains and PAH molecules and thereby removed from the interstellar gas. Grain destruction can raise the gas phase D/H value to approximately the total D/H value. Supernovae and stellar winds, however, can decrease the total D/H value along lines of sight on time scales less than mixing time scales. I will summarize the theoretical and observational arguments for this model and estimate the most likely range for the total D/H in the local Galactic disk. This range in total D/H presents a constraint on realistic Galactic chemical evolution models or the primordial value of D/H or both.

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Chromospheric activity as a function of age in main-sequence stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900053146 ◽

1966 ◽

Vol 24 ◽

pp. 40-43

Author(s):

O. C. Wilson ◽

A. Skumanich

Keyword(s):

Main Sequence ◽

The Sun ◽

Main Sequence Stars ◽

Tentative Conclusion ◽

Chromospheric Activity ◽

General Field ◽

Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

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