<i>FUSE</i>Observations of the Loop I/Local Bubble Interaction Region

Sallmen, S.; Korpela, E. J.; Yamashita, Hideaki

doi:10.1086/588802

Cited by 9 publications

(7 citation statements)

References 31 publications

(39 reference statements)

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“…We also tried two-slab models, representing the LB and Loop I boundaries, but the two slabs could not be separated effectively, perhaps because the density of the LB is similar to that of the ambient medium and thus the present models are not able to discriminate the shell of the LB from the ambient medium. Sallmen et al (2008) analyzed the results of the FUV observations made by the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite towards a single direction (l, b) = (277 • , 9 • ) at the boundary of the interaction zone. By comparing the O VI and C III intensities of two other neighboring directions across the boundary of the interaction zone, one just outside the interaction zone and the other inside the interaction zone, they were able to discriminate the contributions of Loop I from those of the LB, by considering the fact that the interaction zone with a neutral hydrogen column density of N(H I) ∼ 4 × 10 20 cm −2 makes a shadowing effect on the two FUV lines.…”

Section: Modeling and Discussionmentioning

confidence: 99%

Far-Ultraviolet Observations of the Spica Nebula and the Interaction Zone

Choi

Kang

Seon

et al. 2013

ApJ

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We report the analysis results of far ultraviolet (FUV) observations, made for a broad region around α Vir (Spica) including the interaction zone of Loop I and the Local Bubble. Whole region was optically thin and a general correlation was seen between the FUV continuum intensity and the dust extinction, except in the neighborhood of the bright central star, indicating the dust scattering nature of the FUV continuum. We performed Monte-Carlo radiative transfer simulations to obtain the optical parameters related to the dust scattering as well as the geometrical structure of the region. The albedo and asymmetry factor were found to be 0.38±0.06 and 0.46±0.06, respectively, in good agreement with the Milky Way dust grain models. The distance to and the thickness of the interaction zone were estimated to be 70 +4 −8 pc and 40 +8 −10 pc, respectively. The diffuse FUV continuum in the northern region above Spica was mostly the result of scattering of the starlight from Spica, while that in the southern region was mainly due to the background stars. The C IV λλ1548, 1551 emission was found throughout the whole region, in contrast to the Si II* λ1532 emission which was bright only within the H II region. This indicates that the C IV line arises mostly at the shell boundaries of the bubbles, with a larger portion likely from the Loop I than from the Local Bubble side, whereas the Si II* line is from the photoionized Spica nebula.

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Section: Modeling and Discussionmentioning

confidence: 99%

Far-Ultraviolet Observations of the Spica Nebula and the Interaction Zone

Choi

Kang

Seon

et al. 2013

ApJ

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“…Several efforts have been made to build a tridimensional view of the LC, mainly by using Na I observations in the direction of nearby stars, which is a suitable tracer of the neutral gas (Welsh et al 1994;Sfeir et al 1999;Lallement et al 2003;Vergely et al 2010). Information on the shape and size of this structure can also be inferred from ultraviolet interstellar absorption lines (Frisch 1981;Frisch & York 1983;Paresce 1984;Centurion & Vladilo 1991;Welsh et al 1994;Redfield & Linsky 2000;Sallmen et al 2008;Welsh & Lallement 2005), interstellar reddening (Franco 1990;Corradi et al 1997Corradi et al , 2004Frisch 2007;Reis & Corradi 2008;Vergely et al 2010, Reis et al 2010 and interstellar polarization (Tinbergen 1982;Reiz & Franco 1998;Heiles 1998Heiles , 2000Leroy 1999). The overall shape of the LC suggests that it is being compressed due to the expansion of the neighboring bubbles, with a narrower dimension along the Galactic Plane (GP), and probably opened in the direction of the Galactic halo.…”

Section: Introductionmentioning

confidence: 99%

Optical Polarization Mapping Toward the Interface Between the Local Cavity and Loop I

Santos

Corradi

Reis

2011

ApJ

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The Sun is located inside an extremely low density and quite irregular volume of the interstellar medium, known as the Local Cavity (LC). It has been widely believed that some kind of interaction could be occurring between the LC and Loop I, a nearby superbubble seen in the direction of the Galactic Center. As a result of such interaction, a wall of neutral and dense material, surrounded by a ring shaped feature, would be formed at the interaction zone. Evidence of this structure was previously observed by analyzing the soft X-ray emission in the direction of Loop I. Our goal is to investigate the distance of the proposed annular region and map the geometry of the Galactic magnetic field in these directions. On that account, we have conducted an optical polarization survey to 878 stars from the Hipparcos catalogue. Our results suggest that the structure is highly twisted and fragmented, showing very discrepant distances along the annular region: ≈ 100 pc to the left side and 250 pc to the right side, independently confirming the indication from a previous photometric analysis. In addition, the polarization vectors' orientation pattern along the ring also shows a widely different behavior toward both sides of the studied feature, running parallel to the ring contour in the left side and showing no relation to its direction in the right side. Altogether, these evidence suggest a highly irregular nature, casting some doubt on the existence of a unique large-scale ring-like structure.

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“…Highly ionized species such as C IV, N V, and O VI are often used as tracers for diffuse gas within the temperature range of (1 − 3) × 10 5 K. These high ions are found by absorption line measurements in various places in the universe, including the disk (Bowen et al 2008;Sallmen et al 2008;Savage et al 2001a;Savage & Massa 1987;Cowie et al 1981;Jenkins 1978a,b) and the halo of the Milky Way (Ganguly et al 2005;Savage et al 2003;Zsargó et al 2003;Sterling et al 2002;Savage et al 2001bSavage et al , 1997Sembach et al 1997;Savage & Sembach 1994;Sembach & Savage 1992). The emission lines of these high ions are also found in the Galaxy (Shelton et al 2001(Shelton et al , 2007Dixon et al 2006;Korpela et al 2006;Welsh et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Turbulent Mixing Layers With Non-Equilibrium Ionization Calculations

Kwak

Shelton

2010

ApJ

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Highly ionized species such as C IV, N V, and O VI, are commonly observed in diffuse gas in various places in the universe, such as in our Galaxy's disk and halo, high velocity clouds (HVCs), external galaxies, and the intergalactic medium. These ions are often used to trace hot gas whose temperature is a few times 10 5 K. One possible mechanism for producing high ions is turbulent mixing of cool gas (such as that in a high or intermediate velocity cloud) with hotter (a few times 10 6 K) gas in locations where these gases slide past each other. By using hydrodynamic simulations with radiative cooling and non-equilibrium ionization (NEI) calculations, we investigate the physical properties of turbulent mixing layers and the production of high ions (C IV, N V, and O VI). We find that most of the mixing occurs on the hot side of the hot/cool interface, where denser cool gas is entrained and mixed into the hotter, more diffuse gas. Our simulations reveal that the mixed region separates into a tepid zone containing radiatively cooled, C IV-rich gas and a hotter zone which is rich in C IV, N V, and O VI. The hotter zone contains a mixture of low and intermediate ions contributed by the cool gas and intermediate and high-stage ions contributed by the hot gas. Mixing occurs faster than ionization or recombination, making the mixed gas a better source of C IV, N V, and O VI in our NEI simulations than in our collisional ionization equilibrium (CIE) simulations. In addition, the gas radiatively cools faster than the ions recombine, which also allows large numbers of C IV, N V, and O VI ions to linger in the NEI simulations. For these reasons, our NEI calculations predict more C IV, N V, and O VI than our CIE calculations predict. We also simulate various initial configurations and find that more C IV is produced when the shear speed is smaller or the hot gas has a higher temperature. We find no significant differences between simulations having different perturbation amplitudes in the initial boundary between the hot and cool gas. We discuss the results of our simulations, compare with observations of the Galactic halo and highly ionized HVCs, and compare with other models, including other turbulent mixing calculations. The ratios of C IV to N V and N V to O VI are in reasonable agreement with the averages calculated from observations of the halo. There is a great deal of variation from sightline to sightline and with time in our simulations. Such spatial and temporal variation may explain some of the variation seen among observations.

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FUSEObservations of the Loop I/Local Bubble Interaction Region

Cited by 9 publications

References 31 publications

Far-Ultraviolet Observations of the Spica Nebula and the Interaction Zone

Far-Ultraviolet Observations of the Spica Nebula and the Interaction Zone

Optical Polarization Mapping Toward the Interface Between the Local Cavity and Loop I

Numerical Study of Turbulent Mixing Layers With Non-Equilibrium Ionization Calculations

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