The oxygen I depletion in the diffuse interstellar medium
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De Boer, K. S.↗
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Mechanical heating of the interstellar medium. II - The phase properties and structural control
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Cox, D. P.↗
On the transport and propagation of cosmic rays in galaxies. I - Solution of the steady-state transport equation for cosmic ray nucleons, momentum spectra and heating of the interstellar medium
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Lerche, I.↗
Absorption Line Studies and the Distribution of Neutral Gas in the Local Interstellar Medium
Previous published absorption line studies performed at ultraviolet and visual wavelengths are combined with new ultraviolet data in order to map out the distribution of HI within 150 pc of the Sun. Newly presented data for distances less than 50 pc further support the local cloud model as presented by Bruhweiler (1982). The Sun is embedded, near the edge of a diffuse cloud with total column density 2 x 10 to the 19th power/sq cm. Most observed directions within 50 pc away from the cloud body reveal trace amounts of gas (N)HI) approximately 10 to the 18th power/sq cm presumably arising in the outer skin of the local cloud. At greater distances (50 approximately or d approximately or 150 pc) most directions show significant absorption with N(HI) 10(19)/sq cm. Two directions, one toward the northern galactic pole (NGP), the other toward beta CMa exhibit unusually low HI column densities out to distances of 150 to 200 pc. However, substantial amounts of gas N(HI) 10 to the 19th power/sq cm, are seen toward the NGP at greater distances. The implicatons of these results on astronomy at wavelengths shortward of 912A are discussed.
Bruhweiler, F. C.↗
Probe of the Nearby Interstellar Medium by the Vacant Line of Sight to Beta Cma
The line of sight to Beta CM a was probed by Copernicus observations. This particular line of sight is remarkable for the low mean densities. The density was found to be bar N sub H approximately .002/cu cm. Two separate regions were distinguished: (1) A local nearby HI region extends over a few parsecs from the Sun with a density of the order of 0.1/cu cm and a temperature of 11000 to 12500 K; (2) An HII region lies somewhere beyond the HI region and is spread over about 60pc. Its total hydrogen mean density is of the same order as the HI region, i.e., of approximately 0.1 cu cm and it contains only elements in low ionization state. All the ata are coherent with the picture of a cloud in ionization equilibrium at T approximately 23000 deg K.
Gry, C.↗
The flux of secondary anti-deuterons and antihelium produced in the interstellar medium
Several measurements were performed to find antiprotons in the primary cosmic radiation. Because it is difficult to get completely separated secondarily produced antiprotons from primary ones, calculations based on accelerator results were performed for the flux of secondarily produced anti-deuterons and antihelium.
Allkofer, O. C.↗
Density fluctuations in the interstellar medium: Evidence for anisotropic magnetogasdynamic turbulence. I - Model and astrophysical sites
A self-consistent theoretical model of turbulent fluctuations in a compressible electrically conducting gas is developed in order to quantitatively study a turbulent fluid origin for the small spiral scale density fluctuations observed by Armstrong et al. (1981). A heuristic description of turbulent flows in compressible fluids is offered as an analogy for the small-scale turbulent velocity and magnetic field variations which derive density variations in the presence of a strong local magnetic field.
Higdon, J. C.↗
The bird: A pressure-confined explosion in the interstellar medium
The non-thermal radio continuum source G5.3-1.0, mapped at 20 cm with the Very Large Array (VLA) by Becker and Helfand, has an unusual bird-like shape. In order to determine possible interaction of this source with adjacent cold gas, we have mapped this region in the J=1-0 line of CO using the AT and T Bell Laboratories 7m antenna and the FCRAO 14m antenna. The map shown contains 1859 spectra sampled on a 1.5 arcminute grid; each spectrum has an rms noise of 0.2 K in 1 MHz channels. There are several molecular clouds at different velocities along the line of sight. The outer regions of a previously unknown Giant Molecular Cloud (GMC) at l=4.7 deg., b=-0.85 deg., v=200 km s(-1) appears to be interacting with G5.3-10: the molecular cloud has a bird-shaped hole at the position of the continuum source, except that the brightest continuum point (the bird's head) appears to be embedded in the cloud. The velocity of this GMC indicates it is within 2 kpc of the galactic center. The morphology suggests that a supernova or other explosive event occurred near the outside of the GMC, in a region where (n) is approximately 300 cm(-3), and expanded into a region of lower density and pressure. The pressures, densities, and velocity gradients of molecular clouds near the galactic center are on average higher than those of clouds near the Sun. We therefore expect that Type II supernovae near the galactic center would be distorted by their interactions with their parent molecular clouds.
Lane, A. P.↗
Planetary nebulae and the interstellar medium
In addition to available published data on planetary nebulae (PN), some 40 objects largely concentrated towards the galactic center and anticenter regions were included. All were observed with the Lick 3(sup m) telescope and image tube scanner. Abundances of C, N, O, Ne, Cl, and Ar were determined by a procedure in which theoretical models were used to obtain ionization correction factors (ICF). Of the 106 PN, 66 are N-rich and 40 are N-poor. There appear to be no significant differences between the average compositions in the solar neighborhood and the average taken over the entire observable portion of the galaxy.
Aller, L. H.↗
Mass return to the interstellar medium from highly-evolved carbon stars
Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated.
Latter, W. B.↗
The local interstellar medium. IV - The line of sight to Upsilon Scorpii
Profile fitting of Copernicus UV absorption lines separates out four components in the line of sight to Upsilon Sco. Velocities for three of the components, including the two components associated with major H I and H II regions, are in excellent agreement with the corresponding components in the nearby line of sight to Lambda Sco. The velocity of the remaining component is between the velocities of the two remaining Lambda Sco components. Column densities of the various ionization stages of C, N, Si, S, and Ar in the major H I and H II regions are in reasonable agreement with those determined from the Lambda Sco observations, with four notable exceptions. In Upsilon Sco there is more N II and substantially less S III in the H I component and significantly less N I and Si III in the H II component.
Eder, D. C.↗
The interstellar medium in the central 1 kiloparsec of M82
The spatial distribution of the 158 micron forbidden C II emission in the central 1 kiloparsec of the infrared galaxy M82 is discussed, and the detection of two fine-structure lines of forbidden O I and forbidden O III at 146 and 52 microns is reported. Within 500 pc of the nucleus, the far-infrared emission lines contain about 200 million solar luminosities. The neutral gas in the inner disk is in dense, relatively small clouds, thin filaments, or sheets of very low volume filling factor, associated with a lower density ionized medium of moderately high filling factor. Within 500 pc of the nucleus, about 30 million solar masses is contained in H II regions and 30 million solar masses in photodissociation regions. There is a component of ionized and neutral gas near LSR of roughly 150 km/s centered near the compact radio source 41.9 + 58 and elongated along the minor axis of M82. The gas is especially dense in this region and appears to be associated with X-ray emission and the inner H-alpha filaments.
Lugten, J. B.↗
The C-12/C-13 isotope ratio of the interstellar medium in the neighborhood of the sun
Data from observations of Xi Per, P Cyg, 20 Tau, and 23 Tau, obtained at 4232 and 3957 A using a coude spectrograph and a 1872-element reticon on the 3-m Shane telescope at Lick Observatory during 1984-1985, are combined with data on Zeta Oph (Hawkins et al., 1985) and used to estimate the C isotope ratio of the ISM near the sun. The results are presented in extensive tables and graphs and characterized in detail. The (C-12)H(+)/(C-13)H(+) abundance ratios toward the five stars are found to agree to within 12 percent and shown to be representative of the C-12/C-13 ratios in the gas, strongly indicating that the local ISM is homogeneous. The difference between the ISM ratio (43 + or - 4) and the solar-system value (89) is attributed to the chemical evolution of the ISM in the 4.9 Gyr since the formation of the sun.
Hawkins, Isabel↗
The interstellar medium toward SN 1987A
High-resolution spectra of SN 1987A obtained with the IUE satellite show absorption features from the disk and halo of the Galaxy and the LMC. A rich variety of elements and ionization states is found, including allowed resonance lines of abundant elements with ionization states ranging from C I and O I to Al III, Si IV, and C IV. The Si IV and C IV absorption at LMC velocities is unusually strong toward the supernova as compared to most other stars in the LMC and SMC. The origin of these lines is discussed.
Dupree, A. K.↗
A model for the interaction between stars and gas in the interstellar medium
A model for the ISM is considered in which stars lose mass and heat the gas while the gas can form into stars. Three scale-free models are calculated, and in each case the star formation instability leads to a network of dense filaments that surround hotter, more rarefied gas, all of which are close to pressure equilibrium. Depending upon the star formation and cooling laws adopted, the stars are located either in the middle of a bubble or along the inside edge of a dense filament. When a model for the ISM with a cooling curve appropriate for gas of cosmic abundance and a star formation rate proportional to the local gas density is used, the star formation instability is found to grow at temperatures below about 10,000 K. A network structure develops in which most of the mass is in neutral filaments. Newly formed stars lie adjacent to the filaments and create pressure forces that lead to filament motion.
Chiang, Wei-Hwan↗
'Infrared cirrus' - New light on the interstellar medium
The observational data on 'infared cirrus', considered here to be emission from tenuous dust clouds scattered throughout the ISM, are reviewed. The morphology of individual clouds and of the global distribution of infared cirrus is addressed, as well as the energy distribution. Some of the implications of the results for the ISM are summarized, and prospects for future cirrus measurements are briefly addressed.
Hauser, Michael G.↗
Shock-associated plasma density fluctuations in the interstellar medium
Theories of diffuse shock acceleration of the cosmic rays that predict that there should be regions of intense Alfven waves both upstream and downstream of the shock front are considered. Observations of similar waves near solar system shock waves show that they produce substantial density fluctuations. Such density fluctuations might produce observable scattering of radio waves. Observations which searched for angular broadening or blurring of radio sources whose lines of sight pass close to or through supernova remnants are discussed. No definite cases of remnant-associated scattering are detected. However, the source CL 4, which is viewed through the Cygnus Loop supernova remnant, may be such an object and merits further observation.
Spangler, S. R.↗
Supernova remnants and the interstellar medium - Constraints from cosmic-ray acceleration
The reacceleration rate of cosmic rays by supernova (SN) remnants is calculated and expressed in terms of the parameters determining the cosmic ray model and the SN expansion. It is shown that the constraint on reacceleration derived from the B/C data leads to constraint on the expansion of SN remnants in the ISM and on the effective density of ISM. The effect of cloud evaporation is estimated and the expansion rate of supernova remnants, cosmic ray reacceleration, and the state of the ISM are solved for simultaneously. In the resulting self-consistent solution, SN remnants produce a reacceleration rate and an effective acceleration shock strength which is consistent with the values indicated by the cosmic ray data.
Wandel, A.↗