Interstellar Deuterium Research Articles

Ultraviolet observations of cool stars. V - The local density of interstellar matter

A high-resolution Copernicus observation of the chromospheric Ly-alpha emission line of the nearby (3.3 pc) K dwarf epsilon Eri sets limits on the velocity, the velocity dispersion, and the density of atomic hydrogen in the local interstellar medium. Analysis shows that the interstellar Ly-alpha absorption is on the flat portion of the curve of growth. An upper limit of 0.12 per cu cm is derived for the atomic-hydrogen density. The value of this density is 0.08 (plus or minus 0.04 per cu cm if the velocity-dispersion parameter is 9 km/s, corresponding to a temperature of 5000 K. Also, the interstellar deuterium Ly-alpha line may be present in the spectrum.

Relativistic spaceflight and the catalytic nuclear ramjet

The interstellar ramjet concept allows us, at least hypothetically, to get around the mass-ratio limit inherent with relativistic fuel-carrying rockets. The required ramjet energy must be extracted from the nuclear reserves of the interstellar hydrogen (interstellar deuterium is too scarce). Unfortunately, the usual PPI chain for converting hydrogen to helium is hopelessly slow due to the minute weak interaction cross section of the reaction p + p → 2 D + e + + v at essentially any energy. It is shown here that this problem can be avoided, in principle, by exploiting a proton burning catalytic cycle. The best known catalytic cycle is the CNO Bi-Cycle occurring in sufficiently hot main sequence stars. The catalyst “fuel” may be carried on board the ship since it is not depleted, and the ultimate source of energy is the interstellar hydrogen. It is shown that with potentially realistic parameters the energy requirements for a ramjet accelerating at 1 g to near luminal velocities can be met with either the “hot” CNO Bi-Cycle or the Ne-Na cycle. Some of the formidable technological problems associated with a conventional heavy ion fusion reactor are briefly discussed. It is not absolutely necessary that a conventional plasma reactor model be used; for example a laser fusion reactor or a large scale Migma-type reactor (if technologically possible) might be employed. The problem of interstellar drag is considered and a model is suggested in which the incident proton's kinetic energy is stored in the electric field between charged grids and returned to the exhaust particles after the relevant nuclear reactions are completed. Such a combination of electric and magnetic fields would make less severe other suggested limitations to the ramjet's performance. The problem of ionizing the interstellar medium directly in front of the ramjet when operating in non-HII regions of space is also discussed. It is shown that laser ionization is energetically possible for interstellar number densities ≳10 cm −3; however, since the laser also tends to sweep the interstellar matter out of the ramjet's path, more quantitative study is necessary before the method can be considered feasible at any density. The possibility of using a thin stripper foil, placed over the intake cross section, to ionize the interstellar medium is suggested. This method has the advantage of efficiently ionizing the interstellar matter independent of density.

Further observations at the interstellar deuterium frequency

view Abstract Citations (18) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Further observations at the interstellar deuterium frequency. Pasachoff, J. M. ; Cesarsky, D. A. Abstract Two sets of Sgr A observations of neutral deuterium in the direction of the galactic center are reported. A wider bandwidth was used in the second set with no significant reduction of overall noise levels. The line-peak temperature of the merged data from both years yields an upper limit for the D/H ratio of 0.00035; if the absorption is the deuterium line, this ratio will be between the above value and 0.00002. These values continue to imply cosmic densities insufficient to close the universe. Publication: The Astrophysical Journal Pub Date: October 1974 DOI: 10.1086/153128 Bibcode: 1974ApJ...193...65P Keywords: Absorption Spectra; Deuterium; Galactic Nuclei; Interstellar Gas; Neutral Particles; Astronomical Spectroscopy; Cosmology; Interstellar Extinction; Line Spectra; Astrophysics full text sources ADS |

Interstellar Deuterium: the Hyperfine Structure of DCN

view Abstract Citations (44) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Deuterium: the Hyperfine Structure of DCN Wilson, R. W. ; Penzias, A. A. ; Jefferts, K. B. ; Solomon, P. M. Abstract The hyperfine structure of emission from deuterated hydrocyanic acid, DCN, in the J = lA) line at 72.4 GHz has been observed in the Orion cloud. The observed intensities of the three components are in agreement with theoretical line strengths. A comparison with observations of H13C'4N and H12C15N leads to the extraordinary result, D/H = 6 X lO- in hydrocyanic acid located in the Orion Nebula molecular cloud; this is 40 times greater than D/H in terrestrial water and cannot be accounted for by any known process of nucleosynthesis. It is suggested that enrichment of the deuterated molecule takes place through chemical fractionation. Subject headings: abundances - hyperfine structure - molecules, interstellar - Orion Nebula - spectra, radio Publication: The Astrophysical Journal Pub Date: February 1973 DOI: 10.1086/181127 Bibcode: 1973ApJ...179L.107W full text sources ADS |

Cosmological Element Production

Two recent observations appear to have provided critical information about the past history of the universe. The thermal character of the microwave background radiation suggests that the universe has expanded from a state of high temperature and density, and places constraints on such a big-bang cosmology. The observations of very weak helium lines in the spectra of certain stars in the halo of our galaxy are possibly due to a low primeval abundance of this element. However, the simplest model of a big-bang cosmology leads to much higher helium abundances, such as are observed in the solar system and in many stars. The production of helium can be reduced either by altering the early expansion rate or by introducing degenerate electron neutrinos. Observations of interstellar and intergalactic deuterium and He(4), and possibly even He(3) and Li(7), are needed to test the various models.

15. Detection of the spectral line of deuterium from the centre of the Galaxy on the wave-length of 91·6 cm.

As was shown by I. S. Shklovsky, a radio spectral line from interstellar deuterium on λD = 91·6 cm. (fD = 327·38424 Mc./s.) may be expected [1]. According to Shklovsky the difference between the effective temperature Teff in this line and outside it must be of the order of 1/500 Teff in the direction of the galactic centre, if the concentration of deuterium equals 10−3 that of hydrogen. In this case, contrary to the emission by hydrogen, an absorption line is expected. As Teff equals about 300° the depth should be of the order of 0·6°.