scholarly journals The Influence of the Local Bubble on the Ionization of the Local Interstellar Cloud

1997 ◽  
Vol 166 ◽  
pp. 305-308
Author(s):  
Jonathan D. Slavin ◽  
Priscilla C. Frisch
Keyword(s):  
Interstellar Cloud ◽  
Diffuse Emission ◽  
Ionization State ◽  
Interstellar Gas ◽  
Local Bubble ◽  
X Ray ◽  
Hot Gas ◽  
Local Interstellar Cloud ◽  
Ionization Sources ◽  
X Ray Background

AbstractThe ionization of the the Local Interstellar Cloud (LIC) is quite unusual compared with most warm (T ~ 104 K) interstellar gas. Hydrogen and helium are both partially ionized with helium surprisingly more ionized than hydrogen. Directly observed ionization sources including nearby stellar EUV sources and the diffuse emission of the Soft X-ray Background (SXRB), do not provide enough ionization and heating to account for both the ionization state and temperature of the LIC. We propose that an evaporative boundary between the LIC and the hot gas of the Local Bubble can provide the necessary ionizing radiation. Results of detailed models of the emission from the interface are presented and shown to be adequate to explain the observations.

scholarly journals Observations of the Local Interstellar Cloud

1997 ◽  
Vol 166 ◽  
pp. 17-28
Author(s):  
R. Lallement
Keyword(s):  
Magnetic Field ◽  
Interstellar Cloud ◽  
Local Magnetic Field ◽  
Thermal Pressure ◽  
Local Bubble ◽  
Hot Gas ◽  
Local Interstellar Cloud ◽  
Nearby Stars ◽  
Local Cloud ◽  
The Magnetic Field

AbstractConstraints on the ambient (circumsolar) interstellar medium can be derived from observations of interstellar neutrals or their derivatives in the heliosphere. New results have been recently obtained which, when combined with optical and UV observations of the nearby stars (HST-GHRS, EUVE), remove long-standing contradictions and allow us to infer for our local cloud, pressure, ionization and limits on the magnetic field. The electron density in the circumsolar gas is found to be between 0.04 and 0.15 cm−3. Its total thermal pressure is within the interval 1700 – 2600 cm−3 K. If the local magnetic field is nearly perpendicular to the interstellar wind flow, which is likely, then its intensity is smaller than 3.6 μG. Our Sun is located very close to the edge of the local cloud (the volume of gas which has the same physical properties as the circumsolar gas), while there are at least 5 other cloudlets within 10 pc. Abundances vary from cloudlet to cloudlet. How they are located and whether they are separated by tenuous gas or shock discontinuities is not clear yet. Semi-hot (105 K) gas has been detected in absorption towards nearby stars (Wood et al, 1996), which probably originates in the “H walls” surrounding our heliosphere and other asterospheres. This shows that semi-hot gas is not necessarily linked with cloud interfaces with the hot gas of the Local Bubble.

scholarly journals The Evaporation of Nearby Clouds and the Soft X-ray Background

1997 ◽  
Vol 166 ◽  
pp. 169-172
Author(s):  
Jonathan D. Slavin
Keyword(s):  
Solar System ◽  
Thermal Conduction ◽  
Low Density ◽  
Local Bubble ◽  
X Ray ◽  
Hot Gas ◽  
Single Temperature ◽  
Temperature Equilibrium ◽  
X Ray Background ◽  
The One

AbstractIn recent years the nature of the low density clouds within the Local Bubble has been increasingly well characterized. These clouds, including the one which surrounds the solar system, are embedded in the hot gas and therefore should be evaporating via thermal conduction. If several evaporation fronts exist within the Local Bubble, the emissivity and spectrum of the hot gas is significantly different from a single temperature, equilibrium ionization plasma. We explore models in which the the temperature, density and ionization in the hot gas are influenced by cloud evaporation and compare the results with the observed Soft X-ray Background.

scholarly journals GRADES: A New Instrument for Spectroscopy of the Local Hot Gas

1997 ◽  
Vol 166 ◽  
pp. 91-94
Author(s):  
M. Hurwitz ◽  
C. McKee ◽  
J. Edelstein ◽  
J. Vallerga ◽  
P. Jelinsky ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Diffuse Emission ◽  
Local Component ◽  
X Ray ◽  
Hot Gas ◽  
New Instrument ◽  
Order Of Magnitude ◽  
Competing Models ◽  
Grating Array ◽  
X Ray Background

AbstractCompeting models for the origin of the local component of the diffuse X-ray background span more than an order of magnitude in temperature. We propose to test these models with a new instrument, the GRating Array Diffuse EUV Spectrometer (GRADES), which is sensitive to diffuse emission in the 90 – 260 Å bandpass, and offers a peak spectral resolution of about λ/127.

scholarly journals Local Contributions to the 0.6 keV Diffuse X-Ray Background

1984 ◽  
Vol 81 ◽  
pp. 215-218 ◽  
Author(s):  
David N. Burrows
Keyword(s):  
Galactic Latitude ◽  
The Sun ◽  
X Rays ◽  
Diffuse Emission ◽  
General Direction ◽  
X Ray ◽  
Hot Gas ◽  
X Ray Background

The intensity of the X-ray background between 0.5 and 1.0 keV has surprisingly little dependence on galactic latitude. Possible mechanisms for the production of these X-rays include extragalactic emission and emission from dM stars, both of which should be strongly dependent on galactic latitude, and diffuse emission from hot gas (T ≃ 3 x 106 K) surrounding the Sun. These mechanisms can be distinguished by the presence or absence of absorption by gas within a few hundred parsecs of the Sun. We use X-ray data from the HEA0-1 LED detectors and HI data from the recent Crawford Hill 21 cm survey to place limits on the 0.6 keV intensity originating within 300 pc of the Sun in the general direction of (l,b) = (150°, -30°).

scholarly journals The Soft X-Ray Background

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.

scholarly journals Fluctuations in the Diffuse Soft X-ray Background; Probably of Galactic Halo Origin

1997 ◽  
Vol 166 ◽  
pp. 333-336
Author(s):  
T.J. Sumner ◽  
S.D. Sidher ◽  
J.J. Quenby ◽  
M. Hernandez ◽  
A. Mian ◽  
...  
Keyword(s):  
Galactic Halo ◽  
Emission Measure ◽  
Local Bubble ◽  
Spherical Distribution ◽  
X Ray ◽  
Hot Gas ◽  
Galactic Emission ◽  
Global Trend ◽  
Background Data ◽  
X Ray Background

AbstractSoft X-ray background data from the ROSATPSPC have been fitted by a model including emission from the local bubble, embedded hot gas within the disk, hot gas in the Galactic halo and extra-galactic emission, together with local and disk absorption. In all directions a halo component at 106.2 K (0.2 keV) is required for an acceptable fit. The halo emission measure shows spatial variability and the global trend suggests a disk-like planar rather than more extended spherical distribution. New values for the emission measure within the local bubble are derived.

scholarly journals X-Ray Emission from Expanding Shells in NGC 3077

2004 ◽  
Vol 217 ◽  
pp. 310-311
Author(s):  
Jürgen Ott ◽  
Crystal L. Martin ◽  
Fabian Walter
Keyword(s):  
Thermal Emission ◽  
Dwarf Galaxy ◽  
Point Sources ◽  
Starburst Galaxy ◽  
Interstellar Gas ◽  
X Ray ◽  
Hot Gas ◽  
Hα Emission ◽  
Emission Models ◽  
Expanding Shells

Deep Chandra observations of NGC 3077, a starburst dwarf galaxy in the M81 triplet, resolve the X-ray emission from several supershells. The emission is brightest in the cavities defined by expanding shells detected previously in Hα emission. Thermal emission models fitted to the data imply temperatures ranging from 1.3 to 4.9 × 106 K. The total 0.3–6.0 keV X-ray luminosity is 2 − 5 × 1039ergs−1 (depending on the selected thermal plasma model). Most (85%) of the X-ray luminosity in NGC 3077 comes from the hot interstellar gas; the remainder comes from six X-ray point sources. The radial density profile of the hot gas is not as steep as that expected in a freely expanding wind (e.g., as seen in the neighboring starburst galaxy M 82) implying that the hot gas is still confined by the Hα shells.

scholarly journals Modeling the Local Bubble

1997 ◽  
Vol 166 ◽  
pp. 121-131 ◽  
Author(s):  
Donald P. Cox
Keyword(s):  
Solar System ◽  
Facial Expressions ◽  
Simplified Model ◽  
Observational Constraints ◽  
Local Bubble ◽  
Interstellar Absorption ◽  
Modeling Effort ◽  
X Ray ◽  
Idealized Modeling ◽  
X Ray Background

AbstractModeling the Local Bubble is one of those activities fraught with danger. It is very easy to be too naive, to fail to consider the dependence of the model on assumptions about the nearby ambient state, or the likelihood of such a structure. It is similarly easy to become so caught up in the details of the vicinity that it is unclear where to begin a necessarily idealized modeling effort. And finally, it is important to remember that the data we have may in some cases be lying to us, and that we have not yet learned to read their facial expressions quite carefully enough.That said, I’ve tried in this paper to be helpful to those who may wish to take the risks. I surveyed the very most basic stories that the data seem to tell, and pointed out the standard coincidences that may be telling us a lot about what is happening, but may turn out once again to have been just coincidences. I’ve described 5 distinct conceptions that in one flavor or another pretty well survey the collection of mental images that have so far been carried by those who’ve attempted models. One may be right, or something entirely different may be more appropriate. It’s at least vital to realize that a conception comes first, followed by a simplified model of details. I’ve also included a long list of questions directed at observers. Some have partial answers, some one wouldn’t know today quite how to approach. But it is a list that students of the soft x-ray background, interstellar absorption lines, possible instrumentation, and the heliosphere may wish to review from time to time, just to see whether they can figure out how to be more helpful. There is another list for modelers, things the models must address, however-so-flimsily if necessary, because there are strong observational constraints (and stronger ones coming) on what can and cannot be present in the local ISM. To that I’ve added a few remarks concerning x-ray emission coming from beyond the Local Bubble, and another few on how x-ray emission from within the solar system might be contaminating what we see. That last bit is new, exciting, and possibly wrong, but it is an example of the ongoing wariness I believe one has to take toward the facts in the case. By the way, Dieter, it really was a great meeting.

scholarly journals Observations of Highly-Ionized Interstellar Iron

1984 ◽  
Vol 81 ◽  
pp. 189-191
Author(s):  
L.M. Hobbs
Keyword(s):  
Radial Velocity ◽  
Absorption Line ◽  
Equivalent Width ◽  
Column Density ◽  
Light Path ◽  
Interstellar Gas ◽  
X Ray ◽  
X Ray Background ◽  
Multi Phase ◽  
No Absorption

AbstractThe spectra of 24 stars, including 5 at distances d < 200 pc, have been observed in the regions of the coronal [Fe X] λ6375 and [Fe XIV] λ5303 lines at detection limits near an equivalent width of 1 mÅ in the best cases. In general agreement with predictions based on a multi-phase model of the interstellar medium, no absorption which can be attributed to Fe X or Fe XIV ions in hot interstellar gas emitting the soft x-ray background is seen in any of these spectra, except for two. Toward λ Cephei an absorption line near λ6375 is measured with an equivalent width of 8.1 ± 2 mÅ, a width corresponding to 20 ± 5 km s-1 or a temperature T ≤ (0.5 ± 0.25) x 106 °K, and, if it is caused by Fe X ions, a radial velocity of -355 km s-1. On that hypothesis, the hot interstellar gas constitutes at least 63% of the column density of gas along this light path.

scholarly journals The Soft X-ray Background Spectrum from DXS

1997 ◽  
Vol 166 ◽  
pp. 83-90 ◽  
Author(s):  
W.T. Sanders ◽  
R.J. Edgar ◽  
D.A. Liedahl ◽  
J.P. Morgenthaler
Keyword(s):  
Galactic Plane ◽  
Emission Lines ◽  
Background Spectrum ◽  
Local Bubble ◽  
X Ray ◽  
Hot Plasma ◽  
Solar Abundances ◽  
Ionic Emission ◽  
X Ray Background ◽  
Ionization Balance

AbstractThe Diffuse X-ray Spectrometer (DXS) obtained spectra of the low energy X-ray (44 – 83 Å) diffuse background near the galactic plane from galactic longitudes 150° ≲ l ≲ 300° with ≲ 3 Å spectral resolution and ~ 15° angular resolution. Thus, DXS measured X-ray spectra that arise almost entirely from within the Local Bubble. The DXS spectra show emission lines and emission-line blends, indicating that the source of the X-ray emission is thermal – hot plasma in the Local Bubble. The measured spectra are not consistent with those predicted by standard coronal models, either with solar abundances or depleted abundances, over the temperature range 105 – 107 K. The measured spectra are also inconsistent with the predictions of various non-equilibrium models. A nearly acceptable fit to DXS spectra can be achieved using a hybrid model that combines the Raymond & Smith ionization balance calculation with recently calculated (by DAL) ionic emission lines.

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