Engineering topics

Jenkins, E. B.

Publications and source records attributed to Jenkins, E. B..

At least 37 records · Page 2

NASA NTRS1983

A survey of ultraviolet interstellar absorption lines

A telescope-spectrometer on the Copernicus spacecraft made possible the measurement of many ultraviolet absorption lines produced by the interstellar gas. The present survey provides data on ultraviolet absorption lines in the spectra of 88 early-type stars. The stars observed are divided into four classes, including reddened stars, unreddened bright stars, moderately reddened bright stars, and unreddened and moderately reddened faint stars. Data are presented for equivalent width, W, radial velocity V, and rms line width, D, taking into account some 10 to 20 lines of N I, O I, Si II, P II, S II, Cl I, Cl II, Mn II, Fe II, Ni II, Cu II, and H2. The data are based on multiple scans for each line. Attention is given to details of observations, the data reduction procedure, and the computation of equivalent width, mean velocity, and velocity dispersion.

Bohlin, R. C.↗

NASA NTRS1983

Interstellar abundances of oxygen and nitrogen

Neutral nitrogen and oxygen column densities or limits are derived for 53 path lengths through the diffuse interstellar medium and compared with column densities of neutral hydrogen. For neither N nor O is a systematic increase of depletion found as reddening increases. The value found for forbidden O/N is 8, and the abundances of N and O are both between 40% and 70% of the solar values. Implications of these results for models of interstellar grains are briefly discussed.

York, D. G.↗

NASA NTRS1983

Changes in interstellar atomic abundances from the galactic plane to the halo

A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron. Previously announced in STAR as N82-33310

Jenkins, E. B.↗

NASA NTRS1982

Fabry-Perot/CCD observations of /S III/ and /S II/ emissions from the Jupiter plasma torus

Explore the source record for details and available documents.

Roesler, F. L.↗

NASA NTRS1982

Changes in interstellar atomic abundances from the galactic plane to the halo

Jenkins, E. B.↗

NASA NTRS1981

A compressed cloud in the Vela supernova remnant

Strong interstellar absorption lines of C I, arising from the two excited fine-structure levels, are found in IUE observations of HD 72350 (type B4 III). An analysis of the excited-level populations of C I gives local temperature and pressure limits, and auxiliary data on the limit of column density for excited O I and the carbon ionization help to establish that (1) the local temperature is within the limits of 25-100 K, and (2) the pressure/Boltzmann's constant ratio is at least 10 to the 4.3/cu cm K, despite its small size. This high-pressure cloud is discussed in terms of shock compression by the Vela supernova blast wave, along with the relationship of this kind of cloud compression to star formation and to the origin of the characteristic filamentary emission arcs seen in Vela and other supernova remnants

Jenkins, E. B.↗

NASA NTRS1981

Observations of the interstellar medium with IUE

Limitations of the International Ultraviolet Explorer (IUE) are discussed, as well as improved powers of research in these areas: (1) Si and C IV doublet absorptions in the high dispersion stellar spectra of distant stars; (2) observation of spectra outside the galactic plans; (3) high velocity gas.

Jenkins, E. B.↗

NASA NTRS1981

A compressed cloud in the Vela supernova remnant

To elucidate the nature of the interstellar medium in the vicinity of the Vela supernova remnants (SNR) an extensive study with the International Ultraviolet Explorer of interstellar absorption lines toward 35 stars in the vicinity of the Vela SNR was undertaken. Observations of interstellar absorption, in particular of CI, towards one of these stars, HD 72350 (type B4 III), is of particular interest.

Jenkins, E. B.↗

NASA NTRS1981

Observations of the plasma torus of Jupiter with a Fabry-Perot/charge-coupled device /CCD/ imaging spectrometer

A description is presented of the use of a CCD imaging spectrometer which has been employed at a 2.1 m telescope to obtain monochromatic images in the red and near infrared. The system studied was Jupiter's plasma torus which circles the planet with radial extent about 5 RJ and 7 RJ (RJ is the radius of Jupiter). In ground based measurements the torus has been observed in the forbidden emission lines of S(plus) at 6716 A and 6731 A and S(plus plus) at 9531 A. Attention is given to aspects of instrumentation, observations, and performance. It is felt that the particular significance of the obtained results from the instrumental point of view is the demonstration that the CCD is an excellent detector for monochromatic imaging in the near infrared out to at least 10830 A and that pixel binning before readout can produce significantly improved S/N ratios for the study of faint, diffuse sources in cases where readout noise is dominant.

Roesler, F. L.↗

NASA NTRS1981

Echelle spectroscopy with a charge-coupled device /CCD/

The recent availability of large format CCD's with high quantum efficiency makes it possible to achieve significant advances in high dispersion astronomical spectroscopy. An echelle CCD combination excels or equals other techniques presently available, and offers the advantage of complete spectral coverage of several thousand Angstroms in a single exposure. Attention is given to experiments which were conducted with a CCD camera head and an echelle spectrograph on a 4-meter telescope. It was found possible to achieve a signal-to-noise ratio of 150/1 on a 13th magnitude star at 6000 A in a two-hour exposure at 0.16 A/pixel, limited primarily by photon statistics. For fainter objects, readout noise is the limiting factor in precision. For 20 electron rms readout noise, an S/N = 15/1 at 18th magnitude is expected, all other things being equal.

York, D. G.↗

NASA NTRS1980

The abundance of CO in diffuse interstellar clouds - An ultraviolet survey

CO was detected in 17 directions and its upper limits were estimated in 21 directions by a UV survey carried out with the Copernicus satellite in the C-X 1088 A and E-X 1076 A lines toward 48 bright stars. The CO column densities range from 10 to the 12th to 10 to the 17th/sq cm and correlate with C I and H2. The tendency of the C I/CO ratio to be about 10 follows the ratio of particular atomic and molecular cross-sections and the physical parameters of interstellar clouds. Finally, the connection between UV observations in diffuse clouds and radio observations of (C-13)O in dark clouds is discussed.

Federman, S. R.↗

NASA NTRS1980

Copernicus observations of C I and CO in diffuse interstellar clouds

Copernicus was used to observe absorption lines of C I in its ground state and excited fine structure levels and CO toward 29 stars. We use the C I data to infer densities and pressures within the observed clouds, and because our results are of higher precision than previous work, much more precise estimates of the physical conditions in clouds are obtained. In agreement with previous work, the interstellar thermal pressure appears to be variable, with most clouds having values of p/k between 1000/cu cm K and 10,000/cu cm K, but there are some clouds with p/k as high as 100,000/cu cm K. Our results are consistent with the view that the interstellar thermal pressure is so variable that the gas undergoes continuous dynamic evolution. Our observations provide useful constraints on the physical processes on the surfaces of grains. In particular, we find that grains are efficient catalysts of interstellar H2 in the sense that at least half of the hydrogen atoms that strike grains come off as part of H2. Results place strong constraints on models for the formation and destruction of interstellar CO. In many clouds, an order of magnitude less CO than predicted in some models was found.

Jenkins, E. B.↗

NASA NTRS1980

Interstellar depletions and far-ultraviolet extinction in the Rho Ophiuchi cloud

Copernicus ultraviolet data on six stars embedded in the well-studied Rho Ophiuchi cloud complex have been analyzed for interstellar abundances, densities, and far-ultraviolet extinction parameters, in an effort to determine how interstellar depletions depend on physical conditions. While there are variations within the cloud in the overall depletions, the pattern of depletions from element to element is constant for all six lines of sight. A picture is suggested in which the cloud core has a small velocity dispersion or is either so strongly depleted or so dense (hence not ionized) that the lines of first ions of heavy elements do not arise there, but rather form in a less-dense or less-depleted outer region. The cloud as a whole has substantial depletions, average to low far-ultraviolet extinction, and a low ratio of molecular to atomic hydrogen.

Snow, T. P., Jr.↗

NASA NTRS1980

Interstellar gas in the Gum Nebula

A survey of the interstellar gas near the Gum Nebula by optical observation of 67 stars at Ca II, 42 stars at Na I, and 14 stars in the UV with the Copernicus satellite provided radial velocities and column densities for all resolved absorption components. Velocity dispersions for gas in the Gum Nebula are not significantly larger than in the general interstellar medium; the ionization structure is predominantly that of an H II region with moderately high ionization. Denser, more highly ionized clouds are concentrated toward the Gum Nebula; these clouds do not show the anomalously high ionization observed in the Vela remnant clouds.

Wallerstein, G.↗

NASA NTRS1979

O VI absorption in interstellar cloud surfaces

The velocity profiles of O VI absorption lines of 24 stars, observed in early Copernicus surveys, have been compared with the line profiles of Si III (1206.51 A) and N II (1083.99 A). The velocity structures of the O VI lines appear to be correlated with those of the material in the lower ionization stages. It is argued that the O VI absorption arises in the coronal gas of the conductive interface between hot gas, responsible for extended, soft X-ray emission, and cooler interstellar clouds. The velocity broadening of both sets of lines is attributed to motions of the cloud surfaces induced by pressure fluctuations in the interstellar medium.

Cowie, L. L.↗

NASA NTRS1979

A survey of interstellar C I - Insights on carbon abundances, UV grain albedos, and pressures in the interstellar medium

Interstellar atomic carbon has been sampled over 33 different paths with visual extinctions ranging from about 0.15 to 1.5 mag. The trend of C I vs different forms of hydrogen is found to be steep and somewhat erratic. It is concluded that the observed behavior can be explained by strong differences in the responses of C I, H I, and H2 equilibria to physical conditions, together with marked variations of these conditions within different interstellar clouds.

Jenkins, E. B.↗

NASA NTRS1978

Coronal gas in the Galaxy. II - A statistical analysis of O VI absorptions

This paper deals with general inferences about the low-density phase of interstellar gas having temperatures well above 200,000 K (the 'coronal gas') which can be drawn from O VI absorption data for 72 stars. Attention is given to the behavior of radial velocities, possible evidence for circumstellar O VI, the space distribution of the O VI gas, crowding of normal interstellar gas, and temperature distributions for the coronal gas. A model is adopted in which the coronal gas is contained within randomly distributed and nonoverlapping parcels, each with a size, pressure, and internal temperature distribution that do not vary markedly from one unit to the next. It is shown that the one-dimensional velocity dispersion for O VI regions (26 km/s) is substantially higher than the value for ordinary interstellar clouds (6.4 km/s).

Jenkins, E. B.↗

NASA NTRS1978

Coronal gas in the Galaxy. I - A new survey of interstellar O VI

Ultraviolet spectra of 40 O- and B-type stars have been intensively scanned in the vicinity of the O VI transitions at 1032 and 1038 A with the Copernicus satellite. This survey of the high-temperature (log T about 5.5) phase of interstellar gas is an extension of the earlier observations of interstellar O VI by Jenkins and Meloy (1974), bringing the total coverage up to 72 stars. Except for a few distant stars, the overall quality of the present data surpasses that of the earlier work. Plots of absorption optical depths versus radial velocity are presented for both transitions in each star. Total column densities (or their upper limits), velocity centroids, and velocity widths have been extracted from the profiles and tabulated, with the results of Jenkins and Meloy (1974) included. Qualitatively, the highly variable O VI densities and velocities seem to exhibit no systematic patterns or regional trends; there is no recognizable correlation in the behavior of coronal gas with pronounced features of galactic structure.

Jenkins, E. B.↗