Line of Sight H and He Ionization Fractions in the Local Interstellar Medium

1997 ◽  
pp. 285-288
Author(s):  
P. D. Dobbie ◽  
M. A. Barstow
Keyword(s):  
Interstellar Medium ◽  
Line Of Sight ◽  
Local Interstellar Medium

scholarly journals The Deuterium Abundance in the Local Interstellar Medium

1992 ◽  
Vol 9 ◽  
pp. 455-458
Author(s):  
Jeffrey L. Linsky
Keyword(s):  
Binary System ◽  
Interstellar Medium ◽  
Line Of Sight ◽  
High Signal ◽  
Local Interstellar Medium ◽  
Signal Noise ◽  
Spectroscopic Binary

AbstractAccurate measurements of the interstellar deuterium/hydrogen ratio along different lines of sight are needed to test predictions of contemporary cosmologies. I describe our GHRS observations of the Lyman-α, 2600 Å and 2800 Å spectral regions for the spectroscopic binary system Capella, obtained with 3.57 km s resolution and high signal/noise. We are now analyzing these data to infer the column densities of H I, D I, Mg II, and Fe II along this 13 pc line of sight.

scholarly journals The Interstellar and Circumstellar Environment of White Dwarfs

1997 ◽  
Vol 166 ◽  
pp. 69-74
Author(s):  
M.A. Barstow ◽  
P.D. Dobbie ◽  
J.B. Holberg
Keyword(s):  
Interstellar Medium ◽  
White Dwarfs ◽  
Column Density ◽  
Line Of Sight ◽  
Local Distribution ◽  
Local Interstellar Medium ◽  
Weighted Mean ◽  
Ionization Fraction ◽  
Absorbing Material ◽  
Circumstellar Environment

AbstractWe have studied the EUV spectra of 13 DA white dwarfs, observed by the EUVE satellite, paying attention to the possible sources of absorbing material along the lines-of-sight in both the local interstellar medium and in the photospheres of the stars themselves. The range of interstellar column densities seen are consistent with our previous understanding of the local distribution of material. Absorption from interstellar He II is found in the direction of five stars, allowing us to measure directly the He ionization fraction and estimate, indirectly, that of H. The weighted mean ionization fractions along these lines-of-sight are 0.27 ± 0.04 and 0.35 ± 0.1 respectively. Where He II is directly detected, the observed ionization fractions are not correlated with direction or with the volume/column density of material along the line-of-sight. Furthermore, the limits on the amount of He II established in all other directions completely encompass the range of observed values. Indeed, all the data can be consistent with more or less constant He and H ionization fractions throughout the local ISM. However, observation of very hot DA stars, indicating higher He II columns, might contradict this picture if the material is not photospheric or circumstellar.

Goddard high-resolution spectrograph observations of the local interstellar medium and the deuterium/hydrogen ratio along the line of sight toward Capella

1993 ◽  
Vol 402 ◽  
pp. 694 ◽  
Author(s):  
Jeffrey L. Linsky ◽  
Alexander Brown ◽  
Ken Gayley ◽  
Athanassios Diplas ◽  
Blair D. Savage ◽  
...  
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Line Of Sight ◽  
Local Interstellar Medium

scholarly journals Dust towards the Galactic Centre

1989 ◽  
Vol 135 ◽  
pp. 47-54
Author(s):  
D. K. Aitken
Keyword(s):  
Interstellar Medium ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Dust Grains ◽  
Local Interstellar Medium ◽  
Dust Extinction ◽  
Polarized Emission ◽  
Central Regions

The observed infrared properties of dust extinction along the line of site to the Galactic Centre are compared with those in the local interstellar medium. Further constraints on the nature of the dust grains are provided by polarimetric observations, which also lead to information on the stratification of the material along the line of sight. Finally some implications of the large polarized emission seen from the central regions are discussed.

scholarly journals A Study of the Interstellar Medium Towards the Unidentified Dark TeV γ-Ray Sources HESS J1614–518 and HESS J1616–508

2017 ◽  
Vol 34 ◽  
Author(s):  
J. C. Lau ◽  
G. Rowell ◽  
F. Voisin ◽  
C. Braiding ◽  
M. Burton ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Galactic Plane ◽  
Convincing Evidence ◽  
Line Of Sight ◽  
Transition Line ◽  
Dense Gas ◽  
Local Interstellar Medium ◽  
Electron Volt ◽  
Γ Ray ◽  
Atomic Gas

AbstractHESS J1614–518 and HESS J1616–508 are two tera-electron volt γ-ray sources that are not firmly associated with any known counterparts at other wavelengths. We investigate the distribution of interstellar medium towards the tera-electron volt γ-ray sources using results from a 7-mm-wavelength Mopra study, the Mopra Southern Galactic Plane CO Survey, the Millimetre Astronomer’s Legacy Team-45 GHz survey and [C i] data from the HEAT telescope. Data in the CO(1–0) transition lines reveal diffuse gas overlapping the two tera-electron volt sources at several velocities along the line of sight, while observations in the CS(1–0) transition line reveal several interesting dense gas features. To account for the diffuse atomic gas, archival H i data was taken from the Southern Galactic Plane Survey. The observations reveal gas components with masses ~103 to 105 M⊙ and with densities ~102 to 103 cm−3 overlapping the two tera-electron volt sources. Several origin scenarios potentially associated with the tera-electron volt γ-ray sources are discussed in light of the distribution of the local interstellar medium. We find no strong convincing evidence linking any counterpart with HESS J1614–518 or HESS J1616–508.

scholarly journals Deuterium Abundance in the Local Interstellar Medium

1984 ◽  
Vol 81 ◽  
pp. 84-88
Author(s):  
R. Ferlet ◽  
C. Gry ◽  
A. Vidal-Madjar
Keyword(s):  
Interstellar Medium ◽  
Present Situation ◽  
Line Of Sight ◽  
Interstellar Space ◽  
The Sun ◽  
Local Interstellar Medium ◽  
The One

AbstractWe underline the present situation of deuterium abundance evaluation in interstellar space and show that it should be < 10-5. Studiing in more detail the λ Sco line of sight and having observed two Nal interstellar components toward that star, we can show that the D/H evaluation made toward λ Sco is in fact related to the local interstellar medium (less than 10 pc from the sun). Because this evaluation is also < 10-5 it is in stricking contrast with the one made toward α Aur (D/H > 1.8 10-5 ) confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.

Kinematical Structure of the Local Interstellar Medium: The Galactic Center Hemisphere

1997 ◽  
Vol 484 (2) ◽  
pp. 761-778 ◽  
Author(s):  
Ricardo Genova ◽  
John E. Beckman ◽  
Stuart Bowyer ◽  
Thomas Spicer
Keyword(s):  
Interstellar Medium ◽  
Galactic Center ◽  
Local Interstellar Medium

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

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