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Sample records for absorption interstellar zones

  1. VAPID: Voigt Absorption-Profile [Interstellar] Dabbler

    NASA Astrophysics Data System (ADS)

    Howarth, Ian D.

    2015-06-01

    VAPID (Voigt Absorption Profile [Interstellar] Dabbler) models interstellar absorption lines. It predicts profiles and optimizes model parameters by least-squares fitting to observed spectra. VAPID allows cloud parameters to be optimized with respect to several different data set simultaneously; those data sets may include observations of different transitions of a given species, and may have different S/N ratios and resolutions.

  2. O VI absorption in interstellar cloud surfaces

    NASA Technical Reports Server (NTRS)

    Cowie, L. L.; Jenkins, E. B.; Songaila, A.; York, D. G.

    1979-01-01

    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.

  3. Interstellar Medium Absorption Profile Spectrograph (IMAPS)

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.

    1985-01-01

    The design and fabrication of an objective-grating echelle spectrograph to fly on sounding rockets and record spectra of stars from approximately 920 to 1120A with a resolving power lambda/delta lambda = 200,000 is discussed. The scientific purpose of the program is to observe, with ten times better velocity resolution than before, the plentiful absorption lines in this spectral region produced by atoms, ions and molecules in the interstellar medium. In addition, an important technical goal is to develop and flight-quality a new ultraviolet, photon-counting image sensor which has a windowless, opaque photocathode and a CCD bombarded directly by the accelerated photoelectrons. Except for some initial difficulties with the performance of CCDs, the development of the payload instrument is relatively straightforward and our overall design goals are satisfied. The first flight occurred in late 1984, but no data were obtained because of an inrush of air degraded the instrument's vacuum and caused the detector's high voltage to arc. A second flight in early 1985 was a complete success and obtained a spectrum of pi Sco. Data from this mission are currently being reduced; quick-look versions of the spectra indicate that excellent results will be obtained. Currently, the payload is being reconfigured to fly on a Spartan mission in 1988.

  4. SEARCHING FOR NAPHTHALENE CATION ABSORPTION IN THE INTERSTELLAR MEDIUM

    SciTech Connect

    Searles, Justin M.; Destree, Joshua D.; Snow, Theodore P.; Salama, Farid; York, Donald G.; Dahlstrom, Julie E-mail: destree@colorado.edu E-mail: Farid.Salama@nasa.gov E-mail: jdahlstrom1@carthage.edu

    2011-05-01

    Interstellar naphthalene cations (C{sub 10}H{sup +}{sub 8}) have been proposed by a study to be the carriers of a small number of diffuse interstellar bands (DIBs). Using an archive of high signal-to-noise spectra obtained at the Apache Point Observatory, we used two methods to test the hypothesis. Both methods failed to detect significant absorption at lab wavelengths of interstellar spectra with laboratory spectra. We thereby conclude that C{sub 10}H{sup +}{sub 8} is not a DIB carrier in typical reddened sight lines.

  5. A survey with Copernicus of interstellar O VI absorption

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.; Meloy, D. A.

    1974-01-01

    The presence of broad, shallow absorptions caused by O VI ions were revealed from UV spectra observations recorded by the Copernicus satellite for thirty-two stars. A table lists survey data on the stars observed for which values of the O VI column densities or their upper limits are extracted. Interstellar rather than circumstellar origin is evident from observation of the lack of correspondence between radical velocities of the stars and those of the O VI profiles. The presence of a low-density high-temperature phase of interstellar gas produced by supernova explosions is suggested.

  6. Interstellar absorption lines in the galaxy NGC 1705

    SciTech Connect

    York, D.G.; Caulet, A.; Rybski, P.M.; Gallagher, J.S.; Blades, J.C. Lowell Observatory, Flagstaff, AZ Space Telescope Science Institute, Baltimore, MD )

    1990-03-01

    The possibility is considered, and shown to be plausible, that the strong C IV and Si IV absorption lines in low-resolution ultraviolet spectra of gas-rich dwarf galaxies are primarily interstellar, not stellar as has been supposed. The argument is based on analogies with H II regions in the Local Group, on low-resolution equivalent width measurements of gas-rich dwarf galaxies from the literature and on high-resolution UV spectra of NGC 1705. 48 refs.

  7. Interstellar absorption lines in the galaxy NGC 1705

    NASA Technical Reports Server (NTRS)

    York, Donald G.; Caulet, Adeline; Rybski, Paul M.; Gallagher, John S.; Blades, J. Chris

    1990-01-01

    The possibility is considered, and shown to be plausible, that the strong C IV and Si IV absorption lines in low-resolution ultraviolet spectra of gas-rich dwarf galaxies are primarily interstellar, not stellar as has been supposed. The argument is based on analogies with H II regions in the Local Group, on low-resolution equivalent width measurements of gas-rich dwarf galaxies from the literature and on high-resolution UV spectra of NGC 1705.

  8. Interstellar MG II Absorption Lines from Low-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bowen, David V.; Blades, J. Chris; Pettini, Max

    1995-08-01

    We have used the GHRS aboard HST to search for interstellar Mg II 2796, 2803 absorption from the disks and halos of 17 low-redshift galaxies, using as probes QSOs and extragalactic supernovae whose sight lines pass close to, or through, intervening galaxies. The galaxies studied are of diverse morphological type, reside in different environments, and lie at separations of p' ≃ 2-113 h-1 kpc from a QSO line of sight. Ten of 11 galaxies at separations 31-113 h-1 kpc show no absorption to equivalent width limits of W(λ2796) <40-90 mÅ, which corresponds to N(Mg II) ≃1-4 × 1012 cm-2. Six galaxies lie at p' ≤ 9 kpc, and of these, four (NGC 4319, the LMC, M81, and the Milky Way) show absorption. Two early-type galaxies (NGC 1380 and Leo I) show no absorption at p' < 9 kpc: these nondetections are surprising because the separations are small and point to the possibility that the existence of extended absorbing halos may be a function of galaxy type. All of the galaxies which produce absorption are plausibly members of interacting systems. For absorbing galaxies probed below 9 kpc, the sight line passes within the optical radius of the galaxy, where the interstellar medium (ISM) is expected to have a high covering factor, and we do not attribute the absorption to the interactions. However, we do find that the environment of the absorbing galaxies affects the characteristics of the absorption detected the strength of lines, the complexity of line components, the ionization state of the gas and we warn of the dangers inherent in constructing models of generic halos based on statistical properties of QSO absorption-line surveys. Our data suggest that the covering factor of Mg II absorption is high for galaxies within ≍10 kpc, but very small beyond ≍30 h-1 kpc, a result consistent with the size found of Mg II halos deduced for galaxies at redshifts z > 0.2. The low-redshift galaxies observed in this study which show Mg II absorption are probably drawn from the same

  9. INTERSTELLAR SILICATE DUST IN FIVE QUASAR ABSORPTION SYSTEMS

    SciTech Connect

    Kulkarni, Varsha P.; Torres-Garcia, Legna M.; Som, Debopam; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni

    2011-01-01

    We report on a study of interstellar silicate dust in five quasar absorption systems at 0.44 < z{sub abs} < 1.31 toward quasars Q0235+164, 3C196, Q0852+3435, Q0937+5628, and Q1203+0634, using data from the Infrared Spectrograph on board the Spitzer Space Telescope. In the absorbers toward Q0235+164, 3C196, Q0852+3435, and Q0937+5628, the 9.7 {mu}m silicate feature is detected in absorption at {approx}5{sigma}-10{sigma} significance, with rest-frame equivalent widths of {approx}0.2-0.5 {mu}m. For Q1203+0634, the noisy data allow us to make only a 3.6{sigma} detection of absorption at 10 {mu}m. Fits to the redshifted 9.7 {mu}m features with four possible template profiles indicate that the laboratory amorphous olivine profile generally provides the best fit, with inferred peak optical depths of {tau}{sub 9.7} {approx} 0.08-0.18. For three of the quasars with optical spectra available from the Sloan Digital Sky Survey, the Large Magellanic Cloud supershell extinction curve provides the best formal fits, with E(B - V) of 0.34-0.54 mag. A 2175 A extinction bump at the absorber redshift (known to exist in Q0235+164) appears to be present at >2.8{sigma} level in Q0852+3435, >2.5{sigma} level in Q1203+0634, and marginally at nearly 2{sigma} level in Q0937+5628. We briefly explore possible correlations between {tau}{sub 9.7} and the color excess, the strength of the 2175 A bump, and the metallicity (which appears to be relatively high for these absorbers, in the range of {approx}>0.1 solar to supersolar). While our measurements are consistent with a linear relation between {tau}{sub 9.7} and E(B - V), the {tau}{sub 9.7}/E(B - V) ratios for these quasar absorbers appear to be higher than those for diffuse interstellar clouds in the Milky Way, closer to values observed for the Galactic center. Some of these quasar sightlines may trace regions in the bulges of the galaxies responsible for the absorption systems.

  10. Observations of interstellar helium with a gas absorption cell - Implications for the structure of the local interstellar medium

    NASA Technical Reports Server (NTRS)

    Freeman, J.; Paresce, F.; Bowyer, S.; Lampton, M.

    1980-01-01

    A photometer sensitive at the 584 A line of He 1, incorporating a helium gas resonance absorption cell, was flown on the Apollo-Soyuz Test Project in July 1975. The instrument observed much of the night-time sky, and returned 42 min of usable data. The data were analyzed by fitting to a model of resonant scattering of solar 584 A flux from nearby interstellar helium. Good model fits were obtained for an interstellar gas bulk velocity vector pointing toward alpha = 72 deg, delta = +15 deg, with speed 20 km/s, with interstellar medium temperatures from 5000 to 20,000 K and with neutral interstellar helium density (8.9 plus or minus 10 to the -3rd/cu cm). In the context of theoretical studies of the interstellar medium by McKee and Ostriker (1977), the results may indicate that the sun lies in the warm, partially ionized periphery of a cold interstellar cloud, surrounded by a high-temperature gas heated by old supernova remnants.

  11. The interstellar absorption-line spectrum of Mu Ophiuchi

    NASA Technical Reports Server (NTRS)

    Cardelli, J.; Boehm-Vitense, E.

    1982-01-01

    UV interstellar lines have been measured on high-resolution, long- and short-wavelength IUE spectra of the B8 V star Mu Oph. Column densities for the observed atoms and ions have been determined as well as turbulent velocities. The interstellar spectrum of Mu Oph is similar to the ones for Rho Oph and Zeta Oph. The ionization equilibria of several elements give consistent limits for the electron density. The C I line arising from different fine-structure levels are studied to yield estimates on the physical conditions in the cloud. Relative depletion of elements in the cloud seen in the interstellar spectrum of Mu Oph follows the same pattern as seen in the interstellar spectra of Zeta Oph and six other stars in the Rho Oph cloud complex.

  12. Interstellar molecules. [detection from Copernicus satellite UV absorption data

    NASA Technical Reports Server (NTRS)

    Drake, J. F.

    1974-01-01

    The Princeton equipment on the Copernicus satellite provides the means to study interstellar molecules between the satellite and stars from 20 to 1000 pc distant. The study is limited to stars relatively unobscured by dust which strongly attenuates the ultraviolet continuum flux used as a source to probe the interstellar medium. Of the 14 molecules searched for only three have been detected including molecular hydrogen, molecular HD, and carbon monoxide.

  13. Interstellar Silicate Dust Grain Properties in Distant Galaxies Probed by Quasar Absorption Systems

    NASA Astrophysics Data System (ADS)

    Aller, Monique C.; Kulkarni, Varsha P.; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni; Som, Debopam

    2015-01-01

    Dust grains are a fundamental component of the interstellar medium, and significantly impact many of the physical processes driving galaxy evolution, including star formation, and the heating, cooling and ionization of interstellar material. Using the absorption features produced by dust in the spectra of luminous background quasars, it is possible to study the properties of extragalactic interstellar dust grains. We will present results from an ongoing program utilizing existing Spitzer Space Telescope infrared quasar spectra to probe silicate dust grain properties in z<1.4 quasar absorption systems. In combination with complementary ground-based data on associated gas-phase metal absorption lines, we explore connections between the interstellar dust and gas in the quasar absorption systems. Our project yields clear detections of the 10 micron silicate dust absorption feature in the studied systems, as well as detections of the 18 micron silicate dust absorption feature in sources with adequate spectral coverage. Based on measured variations in the breath, peak wavelength, and substructure of the 10 micron absorption features, there appear to be differences in the silicate dust grain properties from system-to-system. We also show indications of trends between the gas-phase metal properties, such as metallicity and gas velocity spread, with the silicate dust grain absorption properties. Support for this work is provided by NASA through an award issued by JPL/Caltech and through NASA grant NNX14AG74G, and from National Science Foundation grants AST-0908890 and AST-1108830 to the University of South Carolina.

  14. Observationally determined Fe II oscillator strengths. [interstellar and quasar absorption spectra

    NASA Technical Reports Server (NTRS)

    Van Steenberg, M.; Shull, J. M.; Seab, C. G.

    1983-01-01

    Absorption oscillator strengths for 21 Fe II resonance lines, have been determined using a curve-of-growth analysis of interstellar data from the Copernicus and International Ultraviolet Explorer (IUE) satellites. In addition to slight changes in strengths of the far-UV lines, new f-values are reported for wavelength 1608.45, a prominent line in interstellar and quasar absorption spectra, and for wavelength 2260.08, a weak, newly identified linen in IUE interstellar spectra. An upper limit on the strength of the undetected line at 2366.867 A (UV multiplet 2) is set. Using revised oscillator strengths, Fe II column densities toward 13 OB stars are derived. The interstellar depletions, (Fe/H), relative to solar values range between factors of 10 and 120.

  15. Interstellar absorption in the Mg II resonance line k2 and h2 emissions

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, E.

    1981-01-01

    High-resolution (0.2 A) IUE spectra for the long wavelength range (1800-3000 A) have been studied. It is shown that narrow interstellar Mg II lines are seen in the center of the k2 and h2 emissions from nearby stars with large rotational velocities. For all observed stars, the radial velocity of the central k3 absorption component in the rest system of the star is strongly correlated with the mirror image of the radial velocity of the stars; this shows that a major fraction if not all of the k3 absorption is due to interstellar absorption in the solar neighborhood. The violet to red asymmetry of the k2 emission also correlates with the radial velocities of the star; this shows that the shift of k3 is due to the velocity shift of the local interstellar cloud with respect to the star.

  16. Ultraviolet spectra of quenched carbonaceous composite derivatives: Comparison to the '217 nanometer' interstellar absorption feature

    NASA Technical Reports Server (NTRS)

    Sakata, Akira; Wada, Setsuko; Tokunaga, Alan T.; Narisawa, Takatoshi; Nakagawa, Hidehiro; Ono, Hiroshi

    1994-01-01

    QCCs (quenched carbonaceous composite) are amorphus carbonaceous material formed from a hydrocarbon plasma. We present the UV-visible spectra of 'filmy QCC; (obtained outside of the beam ejected from the hydrocarbon plasma) and 'dark QCC' (obtained very near to the beam) for comparison to the stellar extinction curve. When filmy QCC is heated to 500-700 C (thermally altered), the wavelength of the absorption maximum increases form 204 nm to 220-222 nm. The dark QCC has an absorption maximum at 217-222 nm. In addition, the thermally altered filmy QCC has a slope change at about 500 nm which resmbles that in the interstellar extinction curve. The resemblance of the extinction curve of the QCCs to that of the interstellar medium suggests that QCC derivatives may be representative of the type of interstellar material that produces the 217 nm interstellar medium feature. The peak extinction of the dark QCC is higher than the average interstellar extinction curve while that of the thermally altered filmy QCC is lower, so that a mixture of dark and thermally altered filmy QCC can match the peak extinction observed in the interstellar medium. It is shown from electron micrographs that most of the thermally altered flimy QCC is in the form of small grainy structure less than 4 nm in diameter. This shows that the structure unit causing the 217-222 nm feature in QCC is very small.

  17. Interstellar dust grain composition from high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, Lia

    2016-06-01

    X-ray light is sufficient to excite electrons from n=1 (K-shell) and n=2 (L-shell) energy levels of neutral interstellar metals, causing a sharp increase in the absorption cross-section. Near the ionization energy, the shape of the photoelectric absorption edge depends strongly on whether the atom is isolated or bound in molecules or minerals (dust). With high resolution X-ray spectroscopy, we can directly measure the state of metals and the mineral composition of dust in the interstellar medium. In addition, the scattering contribution to the X-ray extinction cross-section can be used to gauge grain size, shape, and filling factor. In order to fully take advantage of major advances in high resolution X-ray spectroscopy, lab measurements of X-ray absorption fine structure (XAFS) from suspected interstellar minerals are required. Optical constants derived from the absorption measurements can be used with Mie scattering or anomalous diffraction theory in order to model the full extinction cross-sections from the interstellar medium. Much like quasar spectra are used to probe other intergalactic gas, absorption spectroscopy of Galactic X-ray binaries and bright stars will yield key insights to the mineralogy and evolution of dust grains in the Milky Way.

  18. Absorption Reveals and Hydrogen Addition Explains New Interstellar Aldehydes: Propenal and Propanal

    NASA Technical Reports Server (NTRS)

    Hollis, J. M.; Jewell, P. R.; Lovas, F. J.; Remijan, A.; Mollendal, H.

    2004-01-01

    New interstellar molecules propenal (CH2CHCHO) and propanal (CH3CH2CHO) have been detected largely in absorption toward the star-forming region Sagittarius B2(N) by means of rotational transitions observed with the 100-m Green Bank Telescope (GBT) operating in the range of 18 GHz (lambda approximately 1.7 cm) to 26 GHz (lambda approximately 1.2 cm). The GBT was also used to observe the previously reported interstellar aldehyde propynal (HC2CHO) in Sagittarius B2(N) which is known for large molecules believed to form on interstellar grains. The presence of these three interstellar aldehydes toward Sagittarius B2(N) strongly suggests that simple hydrogen addition on interstellar grains accounts for successively larger molecular species: from propynal to propenal and from propenal to propanal. Energy sources within Sagittarius B2(N) likely permit the hydrogen addition reactions on grain surfaces to proceed. This work demonstrates that successive hydrogen addition is probably an important chemistry route in the formation of a number of complex interstellar molecules. We also searched for but did not detect the three-carbon sugar glyceraldehyde (CH2OHCHOHCHO).

  19. The interstellar deuterium-to-hydrogen ratio - A reevaluation of Lyman absorption-line measurements

    NASA Technical Reports Server (NTRS)

    Mccullough, Peter R.

    1992-01-01

    The D/H ratio in the local interstellar medium is evaluated based upon previously published measurements of Lyman absorption lines together with the hypothesis that the D/H ratio is constant. A unique value for the D/H ratio of 1.5 (+/- 0.2) x 10 exp -5 by number is shown to be consistent with all published determinations made with the Copernicus and the International Ultraviolet Explorer satellites. The possibility that the D/H ratio may vary substantially in the local interstellar medium is considered and found to be unnecessary.

  20. The velocity distribution of interstellar gas observed in strong UV absorption lines

    NASA Technical Reports Server (NTRS)

    Cowie, L. L.; York, D. G.

    1978-01-01

    Observations of three strong interstellar UV absorption lines of N I (1199 A), N II (1083 A), and Si III (1206 A) in 47 stars of widely varying distance and a variety of spectral types are analyzed to obtain a velocity distribution function for the interstellar gas. A technique based on the maximum and minimum velocities observed along a line of sight is adopted because of heavy line blending, and results are discussed for both power-law and exponential distribution functions. The expected distribution of radiative-phase supernova remnants (SNRs) in the interstellar medium is calculated as a function of SNR birthrate and of the interstellar density in which they evolve. The results are combined with observed distance estimates, and it is shown that an interstellar density in excess of 0.1 per cu cm would be required to keep the SNRs sufficiently confined so that their cross sections are consistent with the observed number of components. The alternative possibility is considered that SNRs do not enter the radiative phase before escaping from the Galaxy or colliding with neighboring remnants.

  1. Mapping the Local Interstellar Medium Using High-Resolution UV Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Malamut, Craig; Redfield, S.; Linsky, J.

    2013-01-01

    Observations using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope have provided high-resolution near ultraviolet spectra showing MgII, FeII and MnII absorption in the local interstellar medium (LISM). The sample includes sight lines towards over 30 stars within 100 parsecs and across a wide range of spectral types. Observations span the entire sky, probing previously unobserved regions of the LISM. The heavy ions studied in this survey produce narrow absorption features that make possible the identification of multiple interstellar components. Our simultaneous fits of the MgII, FeII, and MnII doublets reveal anywhere from one to six individual absorption components in a particular sight line, where the number of absorbers roughly correlates with the length of the sight line. The simultaneous fitting procedure reduces the systematic errors involved in continuum placement and number of absorbers. Already, sight lines show evidence of previously unidentified clouds within the Local Bubble. These measurements will be added to a growing data set of 81 near UV sight lines. The increase in the number of sight lines will test and improve a three dimensional kinematic model of the local interstellar medium. With an improved understanding of the LISM's kinematical structure, it will be possible to distinguish blended components within the absorption features of lighter ions. Specifically, the MAST Archive contains FUV observations of interstellar absorption by low mass ions (DI, CII, NI, OI) along the the same sight lines. The combination of these data will constrain properties of the LISM such as temperature, turbulence, ionization, abundances and depletions. We acknowledge support for this project through NASA HST Grant GO-11568 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555, and a student research fellowship from the

  2. Ultraviolet observations of interstellar absorption lines toward SN 1987A

    NASA Technical Reports Server (NTRS)

    Savage, Blair D.; Jenkins, Edward B.; Joseph, Charles L.; De Boer, Klass S.

    1989-01-01

    High-dispersion IUE echelle spectra of SN 1987A were averaged in order to obtain UV absorption-line profiles of the highest possible quality in the direction of SN 1987A. The profiles for Si IV and C IV are quite similar and have much less structure than the Al III profile. On relating column densities, while the C IV and Si IV ratio is relatively constant over the 0-100 km/s velocity range, the C IV to Al III and Si IV to Al III ratios vary by nearly a factor of 10. This suggests that the C IV and Si IV along this sight line in the Galaxy and its halo may have a common origin which differs from that for Al III.

  3. Ultraviolet absorption by interstellar gas at large distances from the galactic plane

    NASA Technical Reports Server (NTRS)

    Savage, B. D.; De Boer, K. S.

    1981-01-01

    Eighteen high-dispersion IUE spectra of six stars in the Large Magellanic Cloud, three stars in the Small Magellanic Cloud, and two foreground stars were analyzed. Fourteen spectra cover the wavelengths 1150-2000 A, and four cover 1900-3200 A; the velocity resolution is about 25 km/s. All the Magellanic Cloud spectra exhibit very strong interstellar absorption lines due to a wide range of ionization stages at galactic velocities and at velocities associated with the IMC or SMC. The observational results are related to current theoretical ideas about the origin and physical state of gaseous galactic halos; the analysis is restricted to the Milky Way absorption features.

  4. A survey of local interstellar hydrogen from OAO-2 observations of Lyman alpha absorption

    NASA Technical Reports Server (NTRS)

    Savage, B. D.; Jenkins, E. B.

    1972-01-01

    The Wisconsin far ultraviolet spectrometer aboard OAO-2 observed the wavelength region near 1216 A for 69 stars of spectral type B2 or earlier. From the strength of the observed interstellar L sub alpha absorption, atomic hydrogen column densities were derived over distances averaging 300 pc away from the sun. The OAO data were compared to synthetic ultraviolet spectra, originally derived from earlier higher resolution rocket observations, which were computer processed to simulate the effects of absorption by different amounts of hydrogen followed by the instrumental blending.

  5. Interstellar X-Ray Absorption Spectroscopy of the Crab Pulsar with the LETGS

    NASA Technical Reports Server (NTRS)

    Paerels, Frits; Weisskopf, Martin C.; Tennant, Allyn F.; ODell, Stephen L.; Swartz, Douglas A.; Kahn, Steven M.; Behar, Ehud; Becker, Werner; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    We study the interstellar X-ray absorption along the line of sight to the Crab Pulsar. The Crab was observed with the Low Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory, and the pulsar, a point source, produces a full resolution spectrum. The continuum spectrum appears smooth, and we compare its parameters with other measurements of the pulsar spectrum. The spectrum clearly shows absorption edges due to interstellar Ne, Fe, and O. The O edge shows spectral structure that is probably due to O bound in molecules or dust. We search for near-edge structure (EXAFS) in the O absorption spectrum. The Fe L absorption spectrum is largely due to a set of unresolved discrete n=2-3 transitions in neutral or near-neutral Fe, and we analyze it using a new set of dedicated atomic structure calculations, which provide absolute cross sections. In addition to being interesting in its own right, the ISM absorption needs to be understood in quantitative detail in order to derive spectroscopic constraints on possible soft thermal radiation from the pulsar.

  6. An IUE survey of interstellar H I Ly alpha absorption. 1: Column densities

    NASA Technical Reports Server (NTRS)

    Diplas, Athanassios; Savage, Blair D.

    1994-01-01

    We measure Galactic interstellar neutral hydrogen column densities by analyzing archival interstellar Ly alpha absorption line data toward 554 B2 and hotter stars observed at high resolution with the IUE satellite. This study more than doubles the number of lines of sight with measures of N(H I) based on Ly alpha. We have included the scattered light background correction algorithm of Bianchi and Bohlin in our data reduction. We use the correlation between the Balmer discontinuity (c sub 1) index and the stellar Ly alpha absorption in order to assess the effects of stellar Ly alpha contamination. Approximately 40% of the B stars with measured (c sub 1) index, exhibit serious stellar Ly alpha contamination. One table contains the derived values of the interstellar N(H I) for 393 stars with at most small amounts of stellar contamination. Another lists the observed values of total N(H I) for 161 stars with suspected stellar Ly alpha contamination and/or uncertain stellar parameters.

  7. Direct measurement of interstellar extinction toward young stars using atomic hydrogen Lyα absorption

    SciTech Connect

    McJunkin, Matthew; France, Kevin; Brown, Alexander; Schneider, P. C.; Herczeg, Gregory J.; Hillenbrand, Lynne; Schindhelm, Eric; Edwards, Suzan

    2014-01-10

    Interstellar reddening corrections are necessary to reconstruct the intrinsic spectral energy distributions (SEDs) of accreting protostellar systems. The stellar SED determines the heating and chemical processes that can occur in circumstellar disks. Measurement of neutral hydrogen absorption against broad Lyα emission profiles in young stars can be used to obtain the total H I column density (N(H I)) along the line of sight. We measure N(H I) with new and archival ultraviolet observations from the Hubble Space Telescope (HST) of 31 classical T Tauri and Herbig Ae/Be stars. The H I column densities range from log{sub 10}(N(H I)) ≈19.6-21.1, with corresponding visual extinctions of A{sub V} =0.02-0.72 mag, assuming an R{sub V} of 3.1. We find that the majority of the H I absorption along the line of sight likely comes from interstellar rather than circumstellar material. Extinctions derived from new HST blue-optical spectral analyses, previous IR and optical measurements, and new X-ray column densities on average overestimate the interstellar extinction toward young stars compared to the N(H I) values by ∼0.6 mag. We discuss possible explanations for this discrepancy in the context of a protoplanetary disk geometry.

  8. A new X-ray Absorption Model for the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Gatuzz, E.; Kallman, T.; García, J.; Gorczyca, T.; Mendoza, C.

    2014-07-01

    Absorption from the interstellar medium (ISM) affects every X-ray observation. Its effects are usually removed or studied using models which assume that the gas is neutral. However, spectra show that ions are present in most or many lines of sight. We present a model for interstellar X-ray absorption, which we call ismabs, that includes both ions and neutral elements and which uses the most accurate atomic data available for abundant elements. We have benchmarked ismabs using high-resolution spectra from X-ray binary sources obtained with the High Energy Transmission Grating Spectrometer (HETGS) on the Chandra X-ray observatory. The oxygen and neon K edge absorption regions as well as the iron L edge absorption region have been studied in detail. Although the neutral component is dominant in these spectra, the inclusion of ions leads to better fits to observed data, compared with previous work which only included neutral elements. The use of ismabs allows the determination of column densities of abundant elements, and their mean ionization states. Ismabs is fast and has relatively few free parameters. It has been developed for use with common X-ray spectral fitting packages such as XSPEC or ISIS.

  9. The silicate absorption profile in the interstellar medium towards the heavily obscured nucleus of NGC 4418

    NASA Astrophysics Data System (ADS)

    Roche, P. F.; Alonso-Herrero, A.; Gonzalez-Martin, O.

    2015-05-01

    The 9.7-μm silicate absorption profile in the interstellar medium (ISM) provides important information on the physical and chemical composition of interstellar dust grains. Measurements in the Milky Way have shown that the profile in the diffuse ISM is very similar to the amorphous silicate profiles found in circumstellar dust shells around late M stars, and narrower than the silicate profile in denser star-forming regions. Here, we investigate the silicate absorption profile towards the very heavily obscured nucleus of NGC 4418, the galaxy with the deepest known silicate absorption feature, and compare it to the profiles seen in the Milky Way. Comparison between the 8-13 μm spectrum obtained with Thermal-Region Camera Spectrograph on Gemini and the larger aperture spectrum obtained from the Spitzer archive indicates that the former isolates the nuclear emission, while Spitzer detects low surface brightness circumnuclear diffuse emission in addition. The silicate absorption profile towards the nucleus is very similar to that in the diffuse ISM in the Milky Way with no evidence of spectral structure from crystalline silicates or silicon carbide grains.

  10. Connecting the Interstellar Gas and Dust Properties in Distant Galaxies Using Quasar Absorption Systems

    NASA Astrophysics Data System (ADS)

    Aller, Monique Christine; Kulkarni, Varsha P.; York, Donald; Welty, Daniel; Vladilo, Giovanni; Som, Debopam; Lackey, Kyle; Dwek, Eli

    2015-08-01

    Gas and dust grains are fundamental components of the interstellar medium and significantly impact many of the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of the interstellar material. Quasar absorption systems (QASs), which trace intervening galaxies along the sightlines to luminous quasars, provide a valuable tool to directly study the properties of the interstellar gas and dust in distant, normal galaxies. We have established the presence of silicate dust grains in at least some gas-rich QASs, and find that they exist at higher optical depths than expected for diffuse gas in the Milky Way. Differences in the absorption feature shapes additionally suggest variations in the silicate dust grain properties, such as in the level of grain crystallinity, from system-to-system. Recent studies of QASs also find trends in both the gas and dust properties, such as correlations in metallicity with redshift and dust depletions. We present results from a study of the gas and dust properties of QASs with adequate archival IR data to probe the silicate dust grain properties. We discuss our measurements of gas-phase element abundances based on archival high-resolution optical spectra. We also discuss our measurements of the strengths of the 10 and 18 micron silicate dust absorption features in the QASs, and constraints on the grain properties (e.g., composition, shape, crystallinity) based on fitted silicate profile templates. We investigate correlations between absorption redshift, gas metallicity, metal depletions, and silicate dust abundance, which will yield valuable insights into the star formation history. Support is provided by NASA through grant NNX14AG74G and by an award issued by JPL/Caltech, and from US-NSF grants AST-0908890 and AST-1108830 to the U. of S. Carolina.

  11. Probing Interstellar Silicate Dust Grain Properties in Quasar Absorption Systems at Redshifts z<1.4

    NASA Astrophysics Data System (ADS)

    Aller, M.; Kulkarni, V. P.; York, D. G.; Welty, D. E.; Vladilo, G.; Som, D.

    Absorption lines in the spectra of distant quasars whose sightlines serendipitously pass through foreground galaxies provide a valuable tool to simultaneously probe the dust and gas compositions of the interstellar medium (ISM) in galaxies. In particular, the damped and sub-damped Lyman- α (DLA/sub-DLA) absorbers trace gas-rich galaxies, independent of the intrinsic luminosities or star-formation rates of the associated galaxy stellar populations. The first evidence of silicate dust in a quasar absorption system was provided through our detection of the 10 µ m silicate feature in the z=0.52 DLA absorber toward the quasar AO 0235+164. We present results from 2 follow-up programs using archival Spitzer Space Telescope infrared spectra to study the interstellar silicate dust grain properties in a total of 13 quasar absorption systems at 0.1 < z < 1.4. We find clear detections of the 10 µ m silicate feature in the quasar absorption systems studied. In addition, we also detect the 18 µ m silicate feature in the sources with adequate spectral coverage. We find variations in the breadth, peak wavelength, and substructure of the 10 µ m interstellar silicate absorption features among the absorbers. This suggests that the silicate dust grain properties in these distant galaxies may differ relative to one another, and relative to those in the Milky Way. We also find suggestions in several sources, based on comparisons with laboratory-derived profiles from the literature, that the silicate dust grains may be significantly more crystalline than those in the amorphous Milky Way ISM. This is particularly evident in the z=0.89 absorber toward the quasar PKS 1830-211, where substructure near 10 µ m is consistent with a crystalline olivine composition. If confirmed, these grain property variations may have implications for both dust and galaxy evolution over the past 9 Gyrs, and for the commonly-made assumption that highredshift dust is similar to local dust. We also discuss

  12. The η Car Campaign with UVES at the ESO VLT II. Interstellar and circumstellar absorption lines

    NASA Astrophysics Data System (ADS)

    Weis, K.; Bomans, D. J.; Stahl, O.; Davidson, K.; Humphreys, R. M.; Gull, T. R.

    2005-09-01

    We monitored η Car and the Homunculus using the ESO VLT UVES spectrograph between 2002 and 2004 (see Weis et al., this proceedings). In these high dispersion spectra practically all interstellar absorption features known in the 3000 Å to 10000 Å regime are present (e.g. 4 Ti II lines, 3 Fe I lines, the Ca I line, both Na I doublets, the two K I doublets, and the Ca II doublets, several molecular lines, and a number of diffuse interstellar bands). Near-UV STIS spectra show many low ionization absorption lines (e.g. Gull et al., this proceedings), but there are several differences in the velocity structure and line strengths between these lines of sight, e.g. we do not detect multiple absorption components between -350 to -550 km s-1 in the UVES spectra. Changes over time are present in e.g. the Ca II lines, with small column density changes in the (probably interstellar) +80 km s-1 component and large changes in the -510 km s-1 component, which is most probably located in the outer shell of the Homunculus (see e.g. Nielsen et al., this proceedings). Similar changes in the Ti II 3384 Å component at -147 km s-1 are present, too. With the data set, we not only follow the temporal evolution of the circumstellar absorption components (presumably originating near η Car and in the Homunculus) before, during and after the event, but also search for changes along our long-slits centered on the star and on FOS4. Indeed, the -147 km s-1 component of the Ti II 3384 Å lines shows line strength variations over the southeast lobe of the Homunculus. A preliminary search for very high velocity absorption lines from the outer ejected using only one of our spectra already yielded a possible detection at -1500 km s-1. Clearly a detailed analysis of the absorption lines in the UVES data will provide many new insights into the structure and physics of η Car's ejecta.

  13. Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption Toward 3C 273

    NASA Technical Reports Server (NTRS)

    Sembach, Kenneth R.; Howk, J. Christopher; Savage, Blair D.; Shull, J. Michael; Oegerle, William R.; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    We present Far Ultraviolet Spectroscopic Explorer observations of the molecular, neutral atomic, weakly ionized, and highly ionized components of the interstellar and intergalactic material toward the quasar 3C273. We identify Ly-beta absorption in eight of the known intergalactic Ly-alpha absorbers along the sight line with the rest-frame equivalent widths W(sub r)(Ly-alpha) > 50 micro-angstroms. Refined estimates of the H(I) column densities and Doppler parameters (b) of the clouds are presented. We find a range of b = 16-46 km/s. We detect multiple H(I) lines (Ly-beta - Ly-theta) in the 1590 km/s Virgo absorber and estimate logN(H(I)) = 15.85 +/- 0.10, ten times more H(I) than all of the other absorbers along the sight line combined. The Doppler width of this absorber, b = 16 km/s, implies T < 15,000 K. We detect O(VI) absorption at 1015 km/s at the 2-3(sigma) level that may be associated with hot, X-ray emitting gas in the Virgo Cluster. We detect weak C(III) and O(VI) absorption in the IGM at z=0.12007; this absorber is predominantly ionized and has N(H+)/N(H(I)) > 4000/Z, where Z is the metallicity. Strong Galactic interstellar O(VI) is present between -100 and +100 km/s with an additional high-velocity wing containing about 13% of the total O(VI) between +100 and +240 km/s. The Galactic O(VI), N(V), and C(IV) lines have similar shapes, with roughly constant ratios across the -100 to +100 km/s velocity range. The high velocity O(VI) wing is not detected in other species. Much of the interstellar high ion absorption probably occurs within a highly fragmented medium within the Loop IV remnant or in the outer cavity walls of the remnant. Multiple hot gas production mechanisms are required. The broad O(VI) absorption wing likely traces the expulsion of hot gas out of the Galactic disk into the halo. A flux limit of 5.4 x 10(epx -16) erg/sq cm/s on the amount of diffuse O(VI) emission present = 3.5' off the 3C273 sight line combined with the observed O(VI) column

  14. Oxygen, neon, and iron X-ray absorption in the local interstellar medium

    NASA Astrophysics Data System (ADS)

    Gatuzz, Efraín; García, Javier A.; Kallman, Timothy R.; Mendoza, Claudio

    2016-04-01

    Aims: We present a detailed study of X-ray absorption in the local interstellar medium by analyzing the X-ray spectra of 24 galactic sources obtained with the Chandra High Energy Transmission Grating Spectrometer and the XMM-Newton Reflection Grating Spectrometer. Methods: By modeling the continuum with a simple broken power-law and by implementing the new ISMabs X-ray absorption model, we have estimated the total H, O, Ne, and Fe column densities towards the observed sources. Results: We have determined the absorbing material distribution as a function of source distance and galactic latitude-longitude. Conclusions: Direct estimates of the fractions of neutrally, singly, and doubly ionized species of O, Ne, and Fe reveal the dominance of the cold component, thus indicating an overall low degree of ionization. Our results are expected to be sensitive to the model used to describe the continuum in all sources.

  15. Mapping atomic and diffuse interstellar band absorption across the Magellanic Clouds and the Milky Way

    NASA Astrophysics Data System (ADS)

    Bailey, Mandy; van Loon, Jacco Th.; Sarre, Peter J.; Beckman, John E.

    2015-12-01

    Diffuse interstellar bands (DIBs) trace warm neutral and weakly ionized diffuse interstellar medium (ISM). Here we present a dedicated, high signal-to-noise spectroscopic survey of two of the strongest DIBs, at 5780 and 5797 Å, in optical spectra of 666 early-type stars in the Small and Large Magellanic Clouds, along with measurements of the atomic Na I D and Ca II K lines. The resulting maps show for the first time the distribution of DIB carriers across large swathes of galaxies, as well as the foreground Milky Way ISM. We confirm the association of the 5797 Å DIB with neutral gas, and the 5780 Å DIB with more translucent gas, generally tracing the star-forming regions within the Magellanic Clouds. Likewise, the Na I D line traces the denser ISM whereas the Ca II K line traces the more diffuse, warmer gas. The Ca II K line has an additional component at ˜200-220 km s-1 seen towards both Magellanic Clouds; this may be associated with a pan-Magellanic halo. Both the atomic lines and DIBs show sub-pc-scale structure in the Galactic foreground absorption; the 5780 and 5797 Å DIBs show very little correlation on these small scales, as do the Ca II K and Na I D lines. This suggests that good correlations between the 5780 and 5797 Å DIBs, or between Ca II K and Na I D, arise from the superposition of multiple interstellar structures. Similarity in behaviour between DIBs and Na I in the Small Magellanic Cloud (SMC), Large Magellanic Cloud (LMC) and Milky Way suggests the abundance of DIB carriers scales in proportion to metallicity.

  16. ISMabs: A COMPREHENSIVE X-RAY ABSORPTION MODEL FOR THE INTERSTELLAR MEDIUM

    SciTech Connect

    Gatuzz, E.; Mendoza, C.; García, J.; Kallman, T. R.; Gorczyca, T. W. E-mail: claudio@ivic.gob.ve E-mail: timothy.r.kallman@nasa.gov

    2015-02-10

    We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS, and SHERPA.

  17. Anomalously Broad Diffuse Interstellar Bands and Excited CH+ Absorption in the Spectrum of Herschel 36

    NASA Astrophysics Data System (ADS)

    York, D. G.; Dahlstrom, J.; Welty, D. E.; Oka, T.; Hobbs, L. M.; Johnson, S.; Friedman, S. D.; Jiang, Z.; Rachford, B. L.; Snow, T. P.; Sherman, R.; Sonnentrucker, P.

    2014-02-01

    Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.

  18. ISMabs: A Comprehensive X-Ray Absorption Model for the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Gatuzz, E.; García, J.; Kallman, T. R.; Mendoza, C.; Gorczyca, T. W.

    2015-02-01

    We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS, and SHERPA.

  19. Spatial and temporal variations in interstellar absorption towards HD 72127AB

    NASA Astrophysics Data System (ADS)

    Welty, Daniel E.; Simon, Thuso; Hobbs, L. M.

    2008-07-01

    New optical spectra of CaII and NaI towards HD 72127AB provide additional evidence for both spatial and temporal variations in the complex interstellar absorption along the two sightlines; archival ultraviolet spectra yield information on the abundances, depletions and physical conditions in the gas towards HD 72127A. Similarities in the strengths of various tracers of interstellar material in the two lines of sight suggest that the total hydrogen column densities (N ~ 2.5 × 1020cm-2) and the depletions and ionization in the main components at low local standard of rest (LSR) velocities also are similar. Towards HD 72127A, the main components are relatively cool (T <~ 900 K), but with depletions resembling those found in warm, diffuse disc clouds; the generally weaker components at higher velocities have much milder depletions, more like those found in halo clouds. Several trace neutral species - CaI, CrI and FeI - are much stronger towards HD 72127B, however. The column density of CrI, for example, is about 30 times the value determined towards ζ Oph (the only previous detection of that species in the ISM). Dielectronic recombination in warmer gas (T >~ 5000 K) may be largely responsible for the enhanced abundances of those trace neutral species towards HD 72127B. If the main components towards HD 72127AB are associated with material in the Vela supernova remnant, the differences in abundances and physical conditions occur on scales of about 1100 au. Based on observations collected at the European Southern Observatory, Chile, under programme 72.C-0682, and on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Visiting observer, European Southern Observatory. ‡ E-mail: welty@oddjob.uchicago.edu (DEW); thuso@unm.edu (TS); hobbs@yerkes.uchicago.edu (LMH)

  20. The Mid-Infrared Absorption Spectra of Neutral PAHs in Dense Interstellar Clouds

    NASA Technical Reports Server (NTRS)

    Bernstein, M. P.; Sandford, S. A.; Allamandola, L. J.

    2005-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are common throughout the universe and are expected to be present in dense interstellar clouds. In these environments, some P.4Hs may be present in the gas phase, but most should be frozen into ice mantles or adsorbed onto dust grains and their spectral features are expected to be seen in absorption. Here we extend our previous work on the infrared spectral properties of the small PAH naphthalene (C10H8) in several media to include the full mid-infrared laboratory spectra of 11 other PAHs and related aromatic species frozen in H2O ices. These include the molecules 1,2-dihydronaphthalene, anthracene, 9,1O-dihydroanthracene, phenanthrene, pyrene, benzo[e]pyrene, perylene, benzo(k)fluoranthene, pentacene, benzo[ghi]perylene, and coronene. These results demonstrate that PAHs and related molecules, as a class, show the same spectral behaviors as naphthalene when incorporated into H2O-rich matrices. When compared to the spectra of these same molecules isolated in inert matrices (e.g., Ar or N2), the absorption bands produced when they are frozen in H2O matrices are broader (factors of 3-10), show small position shifts in either direction (usually < 4/cm, always < 10/cm), and show variable changes in relative band strengths (typically factors of 1-3). There is no evidence of systematic increases or decreases in the absolute strengths of the bands of these molecules when they are incorporated in H2O matrices. In H2O-rich ices, their absorption bands are relatively insensitive to concentration over the range of 10 < H2O/PAH < 200): The absorption bands of these molecules are also insensitive to temperature over the 10 K < T < 125 K range, although the spectra can show dramatic changes as the ices are warmed through the temperature range in which amorphous H2O ice converts to its cubic and hexagonal crystalline forms (T > 125 Kj. Given the small observed band shifts cause by H2O, the current database of spectra from Ar matrix

  1. Optical studies of interstellar material in low density regions of the Galaxy. I - A survey of interstellar Na I and Ca II absorption toward 57 distant stars

    NASA Technical Reports Server (NTRS)

    Sembach, K. R.; Danks, A. C.; Savage, B. D.

    1993-01-01

    We present high-resolution spectra of the Na I D and Ca II K lines toward 57 late-O and early-B stars along extended (d greater than 1 kpc) low-density paths through the Milky Way disk and halo. The sight lines preferentially sample diffuse gas in the interstellar medium (ISM) along interarm, Galactic center, and high latitude directions. We measure equivalent widths, apparent column densities, and absorption component structure. The Ca II to Na I ratios presented as a function of velocity for each sight line exhibit variations due to elemental depletion, ionization, and density enhancements. Absorption along high latitude sight lines is kinematically simpler than it is along interarm and Galactic center sight lines. Galactic rotation noticeably broadens the absorption profiles of distant stars located in these latter directions. Along several sight lines, we see Ca II absorption at velocities corresponding to large distances (/z/ about 1 kpc) from the Galactic plane. The effects of differences in the Ca II and Na I scale heights and nonzero velocity dispersions are readily apparent in the data. Brief notes are given for several sight lines with interesting absorption properties.

  2. The Role of Polycyclic Aromatic Hydrocarbons in Dense Cloud Absorption Features: The Last Major Unanswered Question in Interstellar Ice Spectroscopy

    NASA Astrophysics Data System (ADS)

    Chiar, Jean

    Interstellar dust plays a vital role in the star formation process and the eventual formation of planetary systems including our own. Ice mantles are an important component of the dust: reactions involving simple ices can create more complex (and astrobiologically interesting) molecules, and ices sublimated back into the gas phase influence the gas- phase chemistry. Although polycyclic aromatic hydrocarbons (PAHs) are commonly thought to be very abundant interstellar species and, as such, are likely to be important components of interstellar ices, their contribution to the infrared spectra and chemistry of ices in dense molecular clouds is an open question. This program makes extensive use of three major NASA-funded databases: the Spitzer archive, the 2MASS archive, and the NASA Ames PAH database in order to answer the last major unanswered question in interstellar ice spectroscopy: what role do PAHs play in contributing to unidentified absorption features observed in dense cloud spectra. PAHs are observed to be present and abundant in nearly all phases of the galactic and extragalactic interstellar medium. The evidence for the ubiquity of interstellar PAHs is the widespread well-known family of prominent emission bands at 3.28, 6.2, 7.7, 8.6, and 11.2 micron. To date, these PAH bands have been most easily detected in regions where individual gas phase PAH molecules (neutrals and ions) become highly vibrationally excited by the ambient radiation field. While PAHs and closely related aromatic materials should be present throughout dense interstellar regions, PAH emission is quenched in cold dark dense clouds. Also, in these regions, most PAHs should efficiently condense out onto dust grains, either as "pure" solids or as "guest molecules" in icy grain mantles, much as is the case for most other interstellar molecules. Thus, in dense molecular clouds, condensed PAHs will give rise to IR absorption bands rather than emission features. While PAH absorption has been

  3. Method for processing seismic data to identify anomalous absorption zones

    DOEpatents

    Taner, M. Turhan

    2006-01-03

    A method is disclosed for identifying zones anomalously absorptive of seismic energy. The method includes jointly time-frequency decomposing seismic traces, low frequency bandpass filtering the decomposed traces to determine a general trend of mean frequency and bandwidth of the seismic traces, and high frequency bandpass filtering the decomposed traces to determine local variations in the mean frequency and bandwidth of the seismic traces. Anomalous zones are determined where there is difference between the general trend and the local variations.

  4. [C II] absorption and emission in the diffuse interstellar medium across the Galactic plane

    NASA Astrophysics Data System (ADS)

    Gerin, M.; Ruaud, M.; Goicoechea, J. R.; Gusdorf, A.; Godard, B.; de Luca, M.; Falgarone, E.; Goldsmith, P.; Lis, D. C.; Menten, K. M.; Neufeld, D.; Phillips, T. G.; Liszt, H.

    2015-01-01

    Aims: Ionized carbon is the main gas-phase reservoir of carbon in the neutral diffuse interstellar medium (ISM) and its 158 μm fine structure transition [C ii] is the most important cooling line of the diffuse ISM. We combine [C ii] absorption and emission spectroscopy to gain an improved understanding of physical conditions in the different phases of the ISM. Methods: We present high-resolution [C ii] spectra obtained with the Herschel/HIFI instrument towards bright dust continuum regions in the Galactic plane, probing simultaneously the diffuse gas along the line of sight and the background high-mass star forming regions. These data are complemented by single pointings in the 492 and 809 GHz fine structure lines of atomic carbon and by medium spectral resolution spectral maps of the fine structure lines of atomic oxygen at 63 and 145 μm with Herschel/PACS. Results: We show that the presence of foreground absorption may completely cancel the emission from the background source in medium spectral resolution PACS data and that high spectral resolution spectra are needed to interpret the [C ii] and [O i] emission and the [C ii]/FIR ratio. This phenomenon may explain part of the [C ii]/FIR deficit seen in external luminous infrared galaxies where the bright emission from the nuclear regions may be partially canceled by absorption from diffuse gas in the foreground. The C+ and C excitation in the diffuse gas is consistent with a median pressure of ~5900 K cm-3 for a mean kinetic temperature of ~100 K. A few higher pressure regions are detected along the lines of sight, as emission features in both fine structure lines of atomic carbon. The knowledge of the gas density allows us to determine the filling factor of the absorbing gas along the selected lines of sight. The derived median value of the filling factor is 2.4%, in good agreement with the properties of the Galactic cold neutral medium. The mean excitation temperature is used to derive the average cooling due

  5. Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption

    NASA Astrophysics Data System (ADS)

    McEvoy, Catherine M.; Smoker, Jonathan V.; Dufton, Philip L.; Smith, Keith T.; Kennedy, Michael B.; Keenan, Francis P.; Lambert, David L.; Welty, Daniel E.; Lauroesch, James T.

    2015-08-01

    The structure and properties of the diffuse interstellar medium (ISM) on small scales, sub-au to 1 pc, are poorly understood. We compare interstellar absorption lines, observed towards a selection of O- and B-type stars at two or more epochs, to search for variations over time caused by the transverse motion of each star combined with changes in the structure in the foreground ISM. Two sets of data were used: 83 VLT/UVES spectra with approximately 6 yr between epochs and 21 McDonald observatory 2.7-m telescope echelle spectra with 6-20 yr between epochs, over a range of scales from ˜0-360 au. The interstellar absorption lines observed at the two epochs were subtracted and searched for any residuals due to changes in the foreground ISM. Of the 104 sightlines investigated with typically five or more components in Na I D, possible temporal variation was identified in five UVES spectra (six components), in Ca II, Ca I and/or Na I absorption lines. The variations detected range from 7 per cent to a factor of 3.6 in column density. No variation was found in any other interstellar species. Most sightlines show no variation, with 3σ upper limits to changes of the order 0.1-0.3 dex in Ca II and Na I. These variations observed imply that fine-scale structure is present in the ISM, but at the resolution available in this study, is not very common at visible wavelengths. A determination of the electron densities and lower limits to the total number density of a sample of the sightlines implies that there is no striking difference between these parameters in sightlines with, and sightlines without, varying components.

  6. Hot gas in the interstellar medium: A reanalysis of O VI absorption data

    NASA Technical Reports Server (NTRS)

    Shelton, R. L.; Cox, D. P.

    1994-01-01

    The Copernicus O(+5) column densities toward 72 stars provide a rare and valuable tracer of 10(exp 5.5) K gas in the interstellar medium. The original analysis of the data by Jenkins provided important clues about the distribution of interstellar O(+5) ions, but our understanding of the local interstellar medium has since grown substantially. We revisit that work, including the possibility that local hot gas may contribute a significant O(+5) column density to most lines of sight. Our reanalysis also includes slight improvements in the statistics and was found to be reliable when tested on simulated data sets. In the end, we come to conclusions about the distribution of interstellar O(+5) ions that differ considerably from those of the original analysis. With our reanalysis, some theoretical models now show promise. For example, our Local Bubble column density compares favorably with the estimated quantity of O(+5) within the remnant of an ancient local explosion. Similarly, our mean O(+5) column density per feature in more distant regions is like that found in models of hot interstellar bubbles from either stellar winds or ancient supernova explosions in a warm diffuse interstellar environment, suggesting that the hot gas in interstellar space may exist primarily within discrete regions of modest volume occupation rather than in a continuous and pervasive phase.

  7. A new perspective on the interstellar cloud surrounding the Sun from UV absorption line results

    NASA Astrophysics Data System (ADS)

    Gry, Cecile; Jenkins, Edward B.

    2015-01-01

    We offer a new, more inclusive, picture of the local interstellar medium, where it is composed of a single, monolithic cloud that surrounds the Sun in all directions. Our study of velocities based on Mg II and Fe II ultraviolet absorption lines indicates that the cloud has an average motion consistent with the velocity vector of gas impacting the heliosphere and does not behave like a rigid body: gas within the cloud is being differentially decelerated in the direction of motion, and the cloud is expanding in directions perpendicular to this flow, much like the squashing of a balloon. The outer boundary of the cloud is in average 10 pc away from us but is highly irregular, being only a few parsecs away in some directions, with possibly a few extensions up to 20 pc. Average H I volume densities vary between 0.03 and 0.1 cm3 over different sight lines. Metals appear to be significantly depleted onto grains, and there is a steady increase in this effect from the rear of the cloud to the apex of motion. There is no evidence that changes in the ionizing radiation influence the apparent abundances. Additional, secondary velocity components are detected in 60% of the sight lines. Almost all of them appear to be interior to the volume holding the gas that we identify with the main cloud. Half of the sight lines exhibit a secondary component moving at about - 7.2 km/s with respect to the main component, which may be the signature of an implosive shock propagating toward the cloud's interior.

  8. Sodium Absorption Systems toward SN Ia 2014J Originate on Interstellar Scales

    NASA Astrophysics Data System (ADS)

    Maeda, K.; Tajitsu, A.; Kawabata, K. S.; Foley, R. J.; Honda, S.; Moritani, Y.; Tanaka, M.; Hashimoto, O.; Ishigaki, M.; Simon, J. D.; Phillips, M. M.; Yamanaka, M.; Nogami, D.; Arai, A.; Aoki, W.; Nomoto, K.; Milisavljevic, D.; Mazzali, P. A.; Soderberg, A. M.; Schramm, M.; Sato, B.; Harakawa, H.; Morrell, N.; Arimoto, N.

    2016-01-01

    Na i D absorbing systems toward Type Ia supernovae (SNe Ia) have been intensively studied over the last decade with the aim of finding circumstellar material (CSM), which is an indirect probe of the progenitor system. However, it is difficult to deconvolve CSM components from non-variable, and often dominant, components created by interstellar material (ISM). We present a series of high-resolution spectra of SN Ia 2014J from before maximum brightness to ≳250 days after maximum brightness. The late-time spectrum provides unique information for determining the origin of the Na i D absorption systems. The deep late-time observation allows us to probe the environment around the SN at a large scale, extending to ≳40 pc. We find that a spectrum of diffuse light in the vicinity, but not directly in the line of sight, of the SN has absorbing systems nearly identical to those obtained for the “pure” SN line of sight. Therefore, basically all Na i D systems seen toward SN 2014J must originate from foreground material that extends to at least ∼40 pc in projection and none at the CSM scale. A fluctuation in the column densities at a scale of ∼20 pc is also identified. After subtracting the diffuse, “background” spectrum, the late-time Na i D profile along the SN line of sight is consistent with profiles near maximum brightness. The lack of variability on a ∼1 year timescale is consistent with the ISM interpretation for the gas. Based on data collected at the Subaru Telescope and Okayama 1.88 m Telescope, which are operated by the National Astronomical Observatory of Japan, and at the Gunma 1.5 m Telescope operated by the Gunma Astronomical Observatory.

  9. Probing X-Ray Absorption and Optical Extinction in the Interstellar Medium Using Chandra Observations of Supernova Remnants

    NASA Astrophysics Data System (ADS)

    Foight, Dillon R.; Güver, Tolga; Özel, Feryal; Slane, Patrick O.

    2016-07-01

    We present a comprehensive study of interstellar X-ray extinction using the extensive Chandra supernova remnant (SNR) archive and use our results to refine the empirical relation between the hydrogen column density and optical extinction. In our analysis, we make use of the large, uniform data sample to assess various systematic uncertainties in the measurement of the interstellar X-ray absorption. Specifically, we address systematic uncertainties that originate from (i) the emission models used to fit SNR spectra; (ii) the spatial variations within individual remnants; (iii) the physical conditions of the remnant such as composition, temperature, and non-equilibrium regions; and (iv) the model used for the absorption of X-rays in the interstellar medium. Using a Bayesian framework to quantify these systematic uncertainties, and combining the resulting hydrogen column density measurements with the measurements of optical extinction toward the same remnants, we find the empirical relation N H = (2.87 ± 0.12) × 1021 A V cm‑2, which is significantly higher than the previous measurements.

  10. Observations of Interstellar Formamide: Availability of a Prebiotic Precursor in the Galactic Habitable Zone

    PubMed Central

    Adande, Gilles R.; Woolf, Neville J.

    2013-01-01

    Abstract We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×1012 to 9.1×1013 cm−2, with rotational temperatures of 70–177 K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10−11 to 1×10−10. It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ∼0.1 mol/km2/yr or 0.18 mmol/m2 in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH2CHO could have been available for such chemistry. Key Words: Formamide—Astrobiology—Radioastronomy—ISM—Comets—Meteorites. Astrobiology 13, 439–453. PMID:23654214

  11. Observations of interstellar formamide: availability of a prebiotic precursor in the galactic habitable zone.

    PubMed

    Adande, Gilles R; Woolf, Neville J; Ziurys, Lucy M

    2013-05-01

    We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×10(12) to 9.1×10(13) cm(-2), with rotational temperatures of 70-177 K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10(-11) to 1×10(-10). It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ~0.1 mol/km(2)/yr or 0.18 mmol/m(2) in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH2CHO could have been available for such chemistry. PMID:23654214

  12. Modeling the Oxygen K Absorption in the Interstellar Medium: An XMM-Newton View of Sco X-1

    NASA Technical Reports Server (NTRS)

    Garcia, J.; Ramirez, J. M.; Kallman, T. R.; Witthoeft, M.; Bautista, M. A.; Mendoza, C.; Palmeri, P.; Quinet, P.

    2011-01-01

    We investigate the absorption structure of the oxygen in the interstellar medium by analyzing XMM-Newton observations of the low mass X-ray binary Sco X-1. We use simple models based on the O I atomic cross section from different sources to fit the data and evaluate the impact of the atomic data in the interpretation of astrophysical observations. We show that relatively small differences in the atomic calculations can yield spurious results. We also show that the most complete and accurate set of atomic cross sections successfully reproduce the observed data in the 21 - 24.5 Angstrom wavelength region of the spectrum. Our fits indicate that the absorption is mainly due to neutral gas with an ionization parameter of Epsilon = 10(exp -4) erg/sq cm, and an oxygen column density of N(sub O) approx. = 8-10 x 10(exp 17)/sq cm. Our models are able to reproduce both the K edge and the K(alpha) absorption line from O I, which are the two main features in this region. We find no conclusive evidence for absorption by other than atomic oxygen.

  13. Modeling the Oxygen K Absorption in the Interstellar Medium: An XMM-Newton View of Sco X-1

    NASA Astrophysics Data System (ADS)

    García, J.; Ramírez, J. M.; Kallman, T. R.; Witthoeft, M.; Bautista, M. A.; Mendoza, C.; Palmeri, P.; Quinet, P.

    2011-04-01

    We investigate the X-ray absorption structure of oxygen in the interstellar medium by analyzing XMM - Newton observations of the low-mass X-ray binary Sco X-1. Simple models based on the O I atomic photoabsorption cross section from different sources are used to fit the data and evaluate the impact of the atomic data on the interpretation of the observations. We show that relatively small differences in the atomic calculations can yield spurious results, and that the most complete and accurate set of atomic cross sections successfully reproduce the observed data in the 21.0-24.5 Å wavelength region of the spectrum. Our fits indicate that the absorption is mainly due to neutral gas with an ionization parameter of ξ = 10-4 erg cm s-1 and an oxygen column density of N O ≈ (8-10) × 1017 cm-2. The models are able to reproduce both the K edge and the Kα absorption line from O I which are the two main features in this region. We find no conclusive evidence for absorption by anything other than atomic oxygen.

  14. Calcium H&K and sodium D absorption induced by the interstellar and circumgalactic media of the Milky Way

    NASA Astrophysics Data System (ADS)

    Murga, Maria; Zhu, Guangtun; Ménard, Brice; Lan, Ting-Wen

    2015-09-01

    We map out calcium II and sodium I absorption (Fraunhofer H, K & D lines) induced by both the interstellar medium and the circumgalactic medium of the Milky Way. Our measurements cover more than 9000 deg2 and make use of about 300 000 extragalactic spectra from the Sloan Digital Sky Survey. We present absorption maps for these two species and then compare their distributions to those of neutral hydrogen and dust. We show that the abundance of Na I with respect to neutral hydrogen stays roughly constant in different environments, while that of Ca II decreases with hydrogen column density. Studying how these tracers vary as a function of velocity, we show that, on average, the NNaI/NCaII ratio decreases at higher velocity with respect to the local standard of rest, similar to the local Routly-Spitzer effect but seen on Galactic scale. We show that it is likely caused by higher gas/dust density at lower velocity. Finally, we show that Galactic Ca II and Na I absorption needs to be taken into account for precision photometry and, more importantly, for photometric redshift estimation with star-forming galaxies. Our maps of Ca II and Na I absorption are publicly available.

  15. MODELING THE OXYGEN K ABSORPTION IN THE INTERSTELLAR MEDIUM: AN XMM-NEWTON VIEW OF Sco X-1

    SciTech Connect

    GarcIa, J.; Bautista, M. A.; RamIrez, J. M.; Kallman, T. R.; Witthoeft, M.; Mendoza, C.; Palmeri, P.; Quinet, P. E-mail: manuel.bautista@wmich.edu E-mail: michael.c.witthoeft@nasa.gov E-mail: claudio@ivic.gob.v E-mail: quinet@umh.ac.be

    2011-04-10

    We investigate the X-ray absorption structure of oxygen in the interstellar medium by analyzing XMM - Newton observations of the low-mass X-ray binary Sco X-1. Simple models based on the O I atomic photoabsorption cross section from different sources are used to fit the data and evaluate the impact of the atomic data on the interpretation of the observations. We show that relatively small differences in the atomic calculations can yield spurious results, and that the most complete and accurate set of atomic cross sections successfully reproduce the observed data in the 21.0-24.5 A wavelength region of the spectrum. Our fits indicate that the absorption is mainly due to neutral gas with an ionization parameter of {xi} = 10{sup -4} erg cm s{sup -1} and an oxygen column density of N{sub O} {approx} (8-10) x 10{sup 17} cm{sup -2}. The models are able to reproduce both the K edge and the K{alpha} absorption line from O I which are the two main features in this region. We find no conclusive evidence for absorption by anything other than atomic oxygen.

  16. INTERSTELLAR ANALOGS FROM DEFECTIVE CARBON NANOSTRUCTURES ACCOUNT FOR INTERSTELLAR EXTINCTION

    SciTech Connect

    Tan, Zhenquan; Abe, Hiroya; Sato, Kazuyoshi; Ohara, Satoshi; Chihara, Hiroki; Koike, Chiyoe; Kaneko, Kenji

    2010-11-15

    Because interstellar dust is closely related to the evolution of matter in the galactic environment and many other astrophysical phenomena, the laboratory synthesis of interstellar dust analogs has received significant attention over the past decade. To simulate the ultraviolet (UV) interstellar extinction feature at 217.5 nm originating from carbonaceous interstellar dust, many reports focused on the UV absorption properties of laboratory-synthesized interstellar dust analogs. However, no general relation has been established between UV interstellar extinction and artificial interstellar dust analogs. Here, we show that defective carbon nanostructures prepared by high-energy collisions exhibit a UV absorption feature at 220 nm which we suggest accounts for the UV interstellar extinction at 217.5 nm. The morphology of some carbon nanostructures is similar to that of nanocarbons discovered in the Allende meteorite. The similarity between the absorption feature of the defective carbon nanostructures and UV interstellar extinction indicates a strong correlation between the defective carbon nanostructures and interstellar dust.

  17. Interstellar condensed (icy) amino acids and precursors: theoretical absorption and circular dichroism under UV and soft X-ray irradiation

    NASA Astrophysics Data System (ADS)

    Da Pieve, F.; Avendaño-Franco, G.; De Proft, F.; Geerlings, P.

    2014-05-01

    The photophysics of interstellar ices and condensed molecules adsorbed on grains is of primary importance for studies on the origin of the specific handedness of complex organic molecules delivered to the early Earth and of the homochirality of the building blocks of life. Here, we present quantum mechanical calculations based on time-dependent density functional theory for the absorption and circular dichroism (CD) of isovaline and its chiral precursor 5-ethyl-5-methylhydantoin, both observed in meteoritic findings. The systems are considered in their geometrical conformation as extracted from a full solid (icy) matrix, as a shortcut to understand the behaviour of molecules with fixed orientation, and/or taking into account the full solid matrix. In the context of a possible `condensation-warming plus hydrolysis-recondensation' process, we obtain that: (i) for low-energy excitations, the `condensed' precursor has a stronger CD with respect to the amino acid, suggesting that the handedness of the latter could be biased by asymmetric photolysis of the precursor in cold environments; (ii) enantiomeric excess could in principle be induced more efficiently in both systems for excitation at higher energies (VUV). X-ray absorption near-edge spectroscopy and related CD results could serve as support for future experiments on ionization channels.

  18. Physical properties of the interstellar medium using high-resolution Chandra spectra: O K-edge absorption

    SciTech Connect

    Gatuzz, E.; Mendoza, C.; García, J.; Kallman, T. R.; Bautista, M. A.; Gorczyca, T. W. E-mail: claudio@ivic.gob.ve E-mail: manuel.bautista@wmich.edu E-mail: timothy.r.kallman@nasa.gov

    2014-08-01

    Chandra high-resolution spectra toward eight low-mass Galactic binaries have been analyzed with a photoionization model that is capable of determining the physical state of the interstellar medium. Particular attention is given to the accuracy of the atomic data. Hydrogen column densities are derived with a broadband fit that takes into account pileup effects, and in general are in good agreement with previous results. The dominant features in the oxygen-edge region are O I and O II Kα absorption lines whose simultaneous fits lead to average values of the ionization parameter of log ξ = –2.90 and oxygen abundance of A{sub O} = 0.70. The latter is given relative to the standard by Grevesse and Sauval, but rescaling with the revision by Asplund et al. would lead to an average abundance value fairly close to solar. The low average oxygen column density (N{sub O} = 9.2 × 10{sup 17} cm{sup –2}) suggests a correlation with the low ionization parameters, the latter also being in evidence in the column density ratios N(O II)/N(O I) and N(O III)/N(O I) that are estimated to be less than 0.1. We do not find conclusive evidence for absorption by any other compound but atomic oxygen in our oxygen-edge region analysis.

  19. Interstellar photoelectric absorption cross sections, 0.03-10 keV

    NASA Technical Reports Server (NTRS)

    Morrison, R.; Mccammon, D.

    1983-01-01

    An effective absorption cross section per hydrogen atom has been calculated as a function of energy in the 0.03-10 keV range using the most recent atomic cross section and cosmic abundance data. Coefficients of a piecewise polynomial fit to the numerical results are given to allow convenient application in automated calculations.

  20. Interstellar formaldehyde. I - The collisional pumping mechanism for anomalous 6-centimeter absorption.

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.

    1972-01-01

    Investigation of the quantum mechanics of the collisional pumping process which Townes and Cheung (1969) propose as the cause of 'anomalous' formaldehyde absorption in diffuse dark nebulae discussed by Palmer et al. (1969). Quantum effects are taken into account in an attempt to determine whether such nebulae are likely to provide the physical conditions required for the collisional pumping process.

  1. A survey of interstellar HI from L alpha absorption measurements 2

    NASA Technical Reports Server (NTRS)

    Bohlin, R. C.; Savage, B. D.; Drake, J. F.

    1977-01-01

    The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars. The distance to 10 stars exceeds 2 kpc and 34 stars lie beyond 1 kpc. Stars with color excess E(B-V) up to 0.5 mag are observed. The value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag). For stars with accurate E(B-V), the deviations from this mean are generally less than a factor of 1.5. A notable exception is the dark cloud star, rho Oph. A reduction in visual reddening efficiency for the grains that are larger than normal in the rho Oph dark cloud probably explains this result. The conversion of atomic hydrogen into molecular form in dense clouds was observed in the gas to E(B-V) correlation plots. The best estimate for the mean total gas density for clouds and the intercloud medium, as a whole, in the solar neighborhood and in the plane of the galaxy is 1.15 atoms per cu. cm; those for the atomic gas and molecular gas alone are 0.86 atoms per cu cm and 0.143 molecules per cu cm respectively. For the intercloud medium, where molecular hydrogen is a negligible fraction of the total gas, atomic gas density was found to equal 0.16 atoms per cu cm with a Gaussian scale height perpendicular to the plane of about 350 pc, as derived from high latitude stars.

  2. FUSE Observations of O VI Absorption in the Local Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Oegerle, W. R.; Jenkins, E. B.; Shelton, R. L.; Bowen, D. V.; Fisher, Richard R. (Technical Monitor)

    2000-01-01

    We report the results of an initial Far Ultraviolet Spectroscopic Explorer (FUSE) survey of O VI Lambda 1032 absorption along the lines of sight to eleven nearby white dwarfs, ten of which are within the Local Bubble (LB; d < or approximately equal 100 pc). A goal of this survey is to investigate the possible formation of O VI in the conductive interfaces between cool (about 10(exp 4) K) clouds immersed in the presumably hot (10(exp 6) K) gas within the LB. This mechanism is often invoked to explain the widespread presence of 0 VI throughout the Galactic disk. We find no 0 VI absorption toward two stars, and the column densities along three additional sight lines are quite low; N(O VI) about 5 x 10(exp 13)/sq cm. In several directions, we observe rather broad, shallow absorption with N(O VI) about 1 - 2 x 10(exp 13)/sq cm. Models of conductive interfaces predict narrow profiles with N(OVI) > or about equal to 10(exp 13)/sq cm per interface, in the absence of a significant transverse magnetic field. Hence, our observations of weak 0 VI absorption indicate that conduction is being quenched, possibly by non-radial magnetic fields. Alternatively, the gas within the LB may not be hot. Breitschwerdt & Schmutzler have proposed a model for the LB in which an explosive event within a dense cloud created rapid expansion and adiabatic cooling, resulting in a cavity containing gas with a kinetic temperature of T about 50,000 K, but with an ionization state characteristic of much hotter gas. This model has a number of attractive features, but appears to predict significantly more O VI than we observe.

  3. Study of interstellar molecular clouds using formaldehyde absorption toward extragalactic radio sources

    SciTech Connect

    Araya, E. D.; Andreev, N.; Dieter-Conklin, N.; Goss, W. M.

    2014-04-01

    We present new Very Large Array 6 cm H{sub 2}CO observations toward four extragalactic radio continuum sources (B0212+735, 3C 111, NRAO 150, and BL Lac) to explore the structure of foreground Galactic clouds as revealed by absorption variability. This project adds a new epoch in the monitoring observations of the sources reported by Marscher and collaborators in the mid-1990s. Our new observations confirm the monotonic increase in H{sub 2}CO absorption strength toward NRAO 150. We do not detect significant variability of our 2009 spectra with respect to the 1994 spectra of 3C111, B0212+735, and BL Lac; however, we find significant variability of the 3C111 2009 spectrum with respect to archive observations conducted in 1991 and 1992. Our analysis supports that changes in absorption lines could be caused by chemical and/or geometrical gradients in the foreground clouds and not necessarily by small-scale (∼10 AU) high-density molecular clumps within the clouds.

  4. INTERSTELLAR SODIUM AND CALCIUM ABSORPTION TOWARD SN 2011dh IN M51

    SciTech Connect

    Ritchey, Adam M.; Wallerstein, George E-mail: wall@astro.washington.edu

    2012-03-20

    We present high-resolution echelle observations of SN 2011dh, which exploded in the nearby, nearly face-on spiral galaxy M51. Our data, acquired on three nights when the supernova was near maximum brightness, reveal multiple absorption components in Na I D and Ca II H and K, which we identify with gaseous material in the Galactic disk or low halo and in the disk and halo of M51. The M51 components span a velocity range of over 140 km s{sup -1}, extending well beyond the range exhibited by H I 21 cm emission at the position of the supernova. Since none of the prominent Na I or Ca II components appear to coincide with the peak in H I emission, the supernova may lie just in front of the bulk of the H I disk. The Na I/Ca II ratios for the components with the most extreme positive and negative velocities relative to the disk are {approx}1.0, similar to those for more quiescent components, suggesting that the absorption originates in relatively cool gas. Production scenarios involving a galactic fountain and/or tidal interactions between M51 and its companion would be consistent with these results. The overall weakness of Na I D absorption in the direction of SN 2011dh confirms a low foreground and host galaxy extinction for the supernova.

  5. Interstellar absorption lines toward NGC 2264 and AFGL 2591 - Abundances of H2, H3(+), and CO

    NASA Technical Reports Server (NTRS)

    Black, John H.; Van Dishoek, Ewine F.; Willner, Steven P.; Woods, R. Claude

    1990-01-01

    Interstellar absorption-line spectroscopy of NGC 2264 is reported which shows that the CO molecule has a column density of 5 x 10 to the 18th/sq cm and a rotational excitation temperature of 28 K. A direct upper limit on the H2 column density implies that at least 6 percent of a solar carbon abundance is in the form of CO. The upper limit on the H3(+) abundance implies that the cosmic-ray ionization rate is of the order of 10 to the -16th/s or less. The H3(+) upper limit, together with a previous radio detection of H2D(+) emission, implies either an enormous overabundance of the deuterated molecule or else that most of the radio emission comes from clouds not located directly between use and the infrared source. Observations of the sources AFGL 2591 and NGC 2024 IRS2 indicate that upper limits on H3(+) imply cosmic ray ionization rates of less than 3 and 60 x 10 to the -17th/s, respectively.

  6. Photoionization Modeling of Oxygen K Absorption in the Interstellar Medium: The Chandra Grating Spectra of XTE J1817-330

    NASA Technical Reports Server (NTRS)

    Gatuzz, E.; Garcia, J.; Menodza, C.; Kallman, T. R.; Witthoeft, M.; Lohfink, A.; Bautista, M. A.; Palmeri, P.; Quinet, P.

    2013-01-01

    We present detailed analyses of oxygen K absorption in the interstellar medium (ISM) using four high-resolution Chandra spectra towards the X-ray low-mass binary XTE J1817-330. The 11-25 A broadband is described with a simple absorption model that takes into account the pileup effect and results in an estimate of the hydrogen column density. The oxygen K-edge region (21-25 A) is fitted with the physical warmabs model, which is based on a photoionization model grid generated with the XSTAR code with the most up-to-date atomic database. This approach allows a benchmark of the atomic data which involves wavelength shifts of both the K lines and photoionization cross sections in order to fit the observed spectra accurately. As a result we obtain: a column density of N(sub H) = 1.38 +/- 0.01 x 10(exp 21) cm(exp -2); ionization parameter of log xi = .2.70 +/- 0.023; oxygen abundance of A(sub O) = 0.689(exp +0.015./-0.010); and ionization fractions of O I/O = 0.911, O II/O = 0.077, and O III/O = 0.012 that are in good agreement with previous studies. Since the oxygen abundance in warmabs is given relative to the solar standard of Grevesse and Sauval (1998), a rescaling with the revision by Asplund et al. (2009) yields A(sub O) = 0.952(exp +0.020/-0.013, a value close to solar that reinforces the new standard. We identify several atomic absorption lines.K-alpha , K-beta, and K-gamma in O I and O II; and K-alpha in O III, O VI, and O VII--last two probably residing in the neighborhood of the source rather than in the ISM. This is the first firm detection of oxygen K resonances with principal quantum numbers n greater than 2 associated to ISM cold absorption.

  7. Photoionization Modeling of Oxygen K Absorption in the Interstellar Medium:. [The Chandra Grating Spectra of XTE J1817-330

    NASA Technical Reports Server (NTRS)

    Gatuzz, E.; Garcia, J.; Mendoza, C.; Kallman, T. R.; Witthoeft, M.; Lohfink, A.; Bautista, M. A.; Palmeri, P.; Quinet, P.

    2013-01-01

    We present detailed analyses of oxygen K absorption in the interstellar medium (ISM) using four high-resolution Chandra spectra toward the X-ray low-mass binary XTE J1817-330. The 11-25 Angstrom broadband is described with a simple absorption model that takes into account the pile-up effect and results in an estimate of the hydrogen column density. The oxygen K-edge region (21-25 Angstroms) is fitted with the physical warmabs model, which is based on a photoionization model grid generated with the xstar code with the most up-to-date atomic database. This approach allows a benchmark of the atomic data which involves wavelength shifts of both the K lines and photoionization cross sections in order to fit the observed spectra accurately. As a result we obtain a column density of N(sub H) = 1.38 +/- 0.01 × 10(exp 21) cm(exp -2); an ionization parameter of log xi = -2.70 +/- 0.023; an oxygen abundance of A(sub O) = 0.689 (+0.015/-0.010); and ionization fractions of O(sub I)/O = 0.911, O(sub II)/O = 0.077, and O(sub III)/O = 0.012 that are in good agreement with results from previous studies. Since the oxygen abundance in warmabs is given relative to the solar standard of Grevesse & Sauval, a rescaling with the revision by Asplund et al. yields A(sub O) = 0.952(+0.020/-0.013), a value close to solar that reinforces the new standard.We identify several atomic absorption lines-K(alpha), K(beta), and K(gamma) in O(sub I) and O(sub II) and K(alpha) in O(sub III), O(sub VI), and O(sub VII)-the last two probably residing in the neighborhood of the source rather than in the ISM. This is the first firm detection of oxygen K resonances with principal quantum numbers n greater than 2 associated with ISM cold absorption.

  8. PHOTOIONIZATION MODELING OF OXYGEN K ABSORPTION IN THE INTERSTELLAR MEDIUM: THE CHANDRA GRATING SPECTRA OF XTE J1817-330

    SciTech Connect

    Gatuzz, E.; Mendoza, C.; Garcia, J.; Lohfink, A.; Kallman, T. R.; Witthoeft, M.; Bautista, M. A.; Palmeri, P.; Quinet, P. E-mail: claudio@ivic.gob.ve E-mail: alohfink@astro.umd.edu E-mail: michael.c.witthoeft@nasa.gov E-mail: palmeri@umons.ac.be

    2013-05-01

    We present detailed analyses of oxygen K absorption in the interstellar medium (ISM) using four high-resolution Chandra spectra toward the X-ray low-mass binary XTE J1817-330. The 11-25 A broadband is described with a simple absorption model that takes into account the pile-up effect and results in an estimate of the hydrogen column density. The oxygen K-edge region (21-25 A) is fitted with the physical warmabs model, which is based on a photoionization model grid generated with the XSTAR code with the most up-to-date atomic database. This approach allows a benchmark of the atomic data which involves wavelength shifts of both the K lines and photoionization cross sections in order to fit the observed spectra accurately. As a result we obtain a column density of N{sub H} = 1.38 {+-} 0.01 Multiplication-Sign 10{sup 21} cm{sup -2}; an ionization parameter of log {xi} = -2.70 {+-} 0.023; an oxygen abundance of A{sub O}= 0.689{sup +0.015}{sub -0.010}; and ionization fractions of O I/O = 0.911, O II/O = 0.077, and O III/O = 0.012 that are in good agreement with results from previous studies. Since the oxygen abundance in warmabs is given relative to the solar standard of Grevesse and Sauval, a rescaling with the revision by Asplund et al. yields A{sub O}=0.952{sup +0.020}{sub -0.013}, a value close to solar that reinforces the new standard. We identify several atomic absorption lines-K{alpha}, K{beta}, and K{gamma} in O I and O II and K{alpha} in O III, O VI, and O VII-the last two probably residing in the neighborhood of the source rather than in the ISM. This is the first firm detection of oxygen K resonances with principal quantum numbers n > 2 associated with ISM cold absorption.

  9. Absorption at 11 μm in the interstellar medium and embedded sources: evidence for crystalline silicates

    NASA Astrophysics Data System (ADS)

    Wright, Christopher M.; Do Duy, Tho; Lawson, Warrick

    2016-04-01

    An absorption feature is occasionally reported around 11 μm in astronomical spectra, including those of forming stars. Candidate carriers include water ice, polycyclic aromatic hydrocarbons, silicon carbide, crystalline silicates or even carbonates. All are known constituents of cosmic dust in one or more types of environments, though not necessarily together. In this paper, we present new ground-based 8-13 μm spectra of one evolved star, several embedded young stellar objects and a background source lying behind a large column of the interstellar medium (ISM) towards the Galactic Centre. Our observations, obtained at a spectral resolution of ˜100, are compared with previous lower resolution data, as well as data obtained with the Infrared Space Observatory (ISO) on these and other targets. By presenting a subset of a larger sample, our aim is to establish the reality of the feature and subsequently speculate on its carrier. All evidence points towards crystalline silicate. For instance, the 11 μm band profile is well matched with the emissivity of crystalline olivine. Furthermore, the apparent association of the absorption feature with a sharp polarization signature in the spectrum of two previously reported cases suggests a carrier with a relatively high band strength compared to amorphous silicates. If true, this would either set back the evolutionary stage in which silicates are crystallized, either to the embedded phase or even before within the ISM, or else the silicates ejected from the outflows of evolved stars retain some of their crystalline identity during their long residence in the ISM.

  10. A compilation of electronic transitions in the CO molecule and the interpretation of some puzzling interstellar absorption features

    NASA Astrophysics Data System (ADS)

    Morton, Donald C.; Noreau, Louis

    1994-11-01

    This compilation lists wavenumbers, wavelengths, and oscillator strengths for 1589 electronic transitions of (12)C(16)O, (13)C(16)O, (12)C(18)O, and (13)C(18)O between 1000 and 1545 A. These are the transitions from J double prime = 0 to 6 and v double prime = 0 of the ground term which are most likely to appear as interstellar absorption lines in spectra observed with the Hubble Space Telescope and other instruments in space. We include a derivation of the formulae relating transition probabilities, lifetimes, line strengths, and oscillator strengths for individual rovibronic transitions and whole bands. The compilation contains all the known spin-permitted bands A1Pi - X1Sigma+, B1Sigma+ - X1Sigma+, C1Sigma+ - X1Sigma+, E1Pi - X1Sigma+, and F1Sigma+ - X1Sigma+, as well as the spin-forbidden a'3Sigma+ - X1Sigma+, d3delta - X1Sigma+ and e3Sigma- - X1Sigma+ bands which are enhanced by perturbations of A1Pi on certain of their upper levels. Oscillator strengths are quoted for each rovibronic transition, taking account of the mixing of the triplet states with A1 Pi, v' = 0 to 6. A separate finding list orders the stronger transitions with J double prime less than or equal to 3 by wavelength. Comparison of the compiled data with existing UV observations of HD 27778, zeta Oph, and 20 Aql shows how the a' - X, d - X, and e - X bands that borrow oscillator strength from A - X can account for several puzzling absorption features. Finally, we include some suggestions for further study with spectrographs in the laboratory and in space.

  11. Determination of the habitable zone through planetary atmospheric absorption analysis

    NASA Astrophysics Data System (ADS)

    Poffo, D. A.; Caranti, G. M.; Comes, R. A.

    2014-03-01

    The so-called Habitable Zone (HZ) is a region around a star where a planet without atmosphere and considered as a black body, is subjected to a radiative flux appropriate to maintain liquid water on its surface. The location of this region is closely related to the physical properties of the star and in particular with its luminosity. It is important to note that being a planet within the HZ region is a necessary condition but may not be a sufficient one to be habitable. The concept of Planetary Habitability means that not only orbital conditions must be satisfied, but also that the planet itself must be able to develop and maintain a biosphere (Porto de Mello et al. 2006). This paper aims to determine the planetary HZ for a planet with similar conditions than the Earth, i.e. having an atmosphere, using a simple model based on the interactions between the star radiation and the radiation emitted by the planet with the atmosphere. The absorption spectrum for the proposed atmospheric chemical composition is calculated as a function of temperature by means of the HITRAN database. Another important factor taken into account in this model is cloud cover. Clouds act as "traps" to the long wave radiation emitted by the surface of the planet, resulting in an additional warming contributing to the greenhouse effect, but at the same time, reflect solar radiation back into space (albedo), producing surface cooling (Porto de Mello 2010). Taken these effects into account on a global level, we find a relationship between the orbital location of the planet and the average surface temperature that allows us to extend the habitable limits proposed by Kasting et al (1993).

  12. Absorption variability as a probe of the multiphase interstellar media surrounding active galaxies

    NASA Astrophysics Data System (ADS)

    Macquart, Jean-Pierre; Tingay, Steven

    2016-08-01

    We examine a model for the variable free-free and neutral hydrogen absorption inferred towards the cores of some compact radio galaxies in which a spatially fluctuating medium drifts in front of the source. We relate the absorption-induced intensity fluctuations to the statistics of the underlying opacity fluctuations. We investigate models in which the absorbing medium consists of either discrete clouds or a power-law spectrum of opacity fluctuations. We examine the variability characteristics of a medium comprised of Gaussian-shaped clouds in which the neutral and ionized matter are co-located, and in which the clouds comprise spherical constant-density neutral cores enveloped by ionized sheaths. The cross-power spectrum indicates the spatial relationship between neutral and ionized matter, and distinguishes the two models, with power in the Gaussian model declining as a featureless power-law, but that in the ionized sheath model oscillating between positive and negative values. We show how comparison of the HI and free-free power spectra reveals information on the ionization and neutral fractions of the medium. The background source acts as a low-pass filter of the underlying opacity power spectrum, which limits temporal fluctuations to frequencies $\\omega < \\dot{\\theta}_v / \\theta_{\\rm src}$, where $\\dot{\\theta}_v$ is the angular drift speed of the matter in front of the source, and it quenches the observability of opacity structures on scales smaller than the source size $\\theta_{\\rm src}$. For drift speeds of $\\sim 10^3\\,$km s$^{-1}$ and source brightness temperatures $\\sim 10^{12}\\,$K, this limitation confines temporal opacity fluctuations to timescales of order several months to decades.

  13. Absorption variability as a probe of the multiphase interstellar media surrounding active galaxies

    NASA Astrophysics Data System (ADS)

    Macquart, Jean-Pierre; Tingay, Steven

    2016-08-01

    We examine a model for the variable free-free and neutral hydrogen absorption inferred towards the cores of some compact radio galaxies in which a spatially fluctuating medium drifts in front of the source. We relate the absorption-induced intensity fluctuations to the statistics of the underlying opacity fluctuations. We investigate models in which the absorbing medium consists of either discrete clouds or a power-law spectrum of opacity fluctuations. We examine the variability characteristics of a medium comprised of Gaussian-shaped clouds in which the neutral and ionized matter are co-located, and in which the clouds comprise spherical constant-density neutral cores enveloped by ionized sheaths. The cross-power spectrum indicates the spatial relationship between neutral and ionized matter, and distinguishes the two models, with power in the Gaussian model declining as a featureless power-law, but that in the ionized sheath model oscillating between positive and negative values. We show how comparison of the H I and free-free power spectra reveals information on the ionization and neutral fractions of the medium. The background source acts as a low-pass filter of the underlying opacity power spectrum, which limits temporal fluctuations to frequencies ω ≲ dot{θ }_v/θ _src, where dot{θ }_v is the angular drift speed of the matter in front of the source, and it quenches the observability of opacity structures on scales smaller than the source size θsrc. For drift speeds of ˜103 km s-1 and source brightness temperatures ˜1012 K, this limitation confines temporal opacity fluctuations to time-scales of order several months to decades.

  14. The Zone of Inertia: Absorptive Capacity and Organizational Change

    ERIC Educational Resources Information Center

    Godkin, Lynn

    2010-01-01

    Purpose: The purpose of this paper is to describe how interruptions in organizational learning effect institutional absorptive capacity and contribute to organizational inertia. Design/methodology/approach: An exploratory model is presented as a heuristic to describe how interruptions in organizational learning affect absorptive capacity.…

  15. DDT_ldecin_2: Unraveling the enigmatic nature of the turbulent interaction zone between the circumstellar and interstellar medium around the well-known supergiant Beteleuse

    NASA Astrophysics Data System (ADS)

    Decin, L.

    2011-01-01

    Evolved stars are the birthplaces of the interstellar gas and solid dust particles. Such stars lose mass through a stellar wind, which is slow and dusty for cool giants and supergiants, or through impressive supernova explo- sions. However, recent observations with the PACS and SPIRE photometers reveal that the encounter between these slow and dusty winds and the interstellar medium is as spectacular as supernova explosions: multiple arcs, bar-like structures and different kind of instabilities (Rayleigh-Taylor and Kelvin-Helmholtz) are detected. The most outstanding example concerns the well-known supergiant Betelgeuse. However, with the current set of Herschel observations, it is impossible to dene the exact physical mechanism causing the observed infrared emission. We propose to obtain PACS [O I] and HIFI [C II] spectroscopic observations at different pointings in the turbulent wind interaction zone around Betelgeuse. The proposed DDT observations would only take 3.1 hr and would give the astronomical community the rst possibility to study spectroscopically the different dynam- ical and chemical processes partaking in the interaction zone between circumstellar and interstellar material. The derived spectroscopic information will be valuable to the whole community in preparation of OT2.

  16. The Copernicus observations - Interstellar or circumstellar material. [UV spectra of early stars

    NASA Technical Reports Server (NTRS)

    Steigman, G.; Strittmatter, P. A.; Williams, R. E.

    1975-01-01

    It is suggested that the sharp absorption lines observed in the ultraviolet spectra of early-type stars by the Copernicus satellite may be entirely accounted for by the circumstellar material in the H II regions and associated transition zones around the observed stars. If this interpretation is correct, the Copernicus results yield little information on the state of any interstellar (as opposed to circumstellar) gas and, in particular, shed little light on the degree of element depletion in interstellar space.

  17. XMM-Newton/Reflection Grating Spectrometer detection of the missing interstellar O VII Kα absorption line in the spectrum of Cyg X-2

    NASA Astrophysics Data System (ADS)

    Cabot, Samuel H. C.; Wang, Q. Daniel; Yao, Yangsen

    2013-05-01

    The hot interstellar medium is an important part of the Galactic ecosystem and can be effectively characterized through X-ray absorption line spectroscopy. However, in a study of the hot medium using the accreting neutron star X-ray binary, Cyg X-2, as a background light source, a mystery came about when the putatively strong O VII Kα line was not detected in Chandra grating observations, while other normally weaker lines such as O VII Kβ as well as O VI and O VIII Kα are clearly present. We have investigated the grating spectra of Cyg X-2 from 10 XMM-Newton observations, in search of the missing line. We detect it consistently in nine of these observations, but the line is absent in the remaining one observation or is inconsistent with the detection in others at a ˜4σ confidence level. This absence of the line resembles that seen in the Chandra observations. Similarly, the O VI Kα line is found to disappear occasionally, but not in concert with the variation of the O VII Kα line. All these variations are most likely due to the presence of changing O VII and O VI Kα emission lines of Cyg X-2, which are blurred together with the absorption ones in the X-ray spectra. A re-examination of the Chandra grating data indeed shows evidence for a narrow emission line slightly off the O VI Kα absorption line. We further show that narrow N V emission lines with varying centroids and fluxes are present in far-ultraviolet spectra from the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. These results provide new constraints on the accretion around the neutron star and on the X-ray-heating of the stellar companion. The understanding of these physical processes is also important to the fidelity of using such local X-ray binaries for interstellar absorption line spectroscopy.

  18. Photochemistry of interstellar molecules

    NASA Technical Reports Server (NTRS)

    Stief, L. J.

    1971-01-01

    The photochemistry of two diatomic and eight polyatomic molecules is discussed quantitatively. For an interstellar molecule, the lifetime against photodecomposition depends upon the absorption cross section, the quantum yield or probability of dissociation following photon absorption, and the interstellar radiation field. The constant energy density of Habing is used for the unobserved regions of interstellar radiation field, and the field in obscuring clouds is estimated by combining the constant flux with the observed interstellar extinction curve covering the visible and ultraviolet regions. Lifetimes against photodecomposition in the unobscured regions and as a function of increasing optical thickness in obscuring clouds are calculated for the ten species. The results show that, except for CO, all the molecules have comparable lifetimes of less than one hundred years. Thus they can exist only in dense clouds and can never have been exposed to the unobscured radiation. The calculations further show that the lifetimes in clouds of moderate opacity are of the order of one million years.

  19. Computational Interstellar Chemistry

    NASA Astrophysics Data System (ADS)

    Hirata, So; Fan, Peng-Dong; Head-Gordon, Martin; Kamiya, Muneaki; Keçeli, Murat; Lee, Timothy J.; Shiozaki, Toru; Szczepanski, Jan; Vala, Martin; Valeev, Edward F.; Yagi, Kiyoshi

    Computational applications of electronic and vibrational many-body theories are increasingly indispensable in interpreting and, in some instances, predicting the spectra of gas-phase molecular species of importance in interstellar chemistry as well as in atmospheric and combustion chemistry. This chapter briefly reviews our methodological developments of electronic and vibrational many-body theories that are particularly useful for these gas-phase molecular problems. Their applications to anharmonic vibrational frequencies of triatomic and tetratomic interstellar molecules and to electronic absorption spectra of the radical ions of polycyclic aromatic hydrocarbons, which are ubiquitous in the interstellar medium, are also discussed.

  20. Interstellar matter research with the Copernicus satellite

    NASA Technical Reports Server (NTRS)

    Spitzer, L., Jr.

    1976-01-01

    The use of the Copernicus satellite in an investigation of interstellar matter makes it possible to study absorption lines in the ultraviolet range which cannot be observed on the ground because of atmospheric absorption effects. A brief description is given of the satellite and the instrument used in the reported studies of interstellar matter. The results of the studies are discussed, giving attention to interstellar molecular hydrogen, the chemical composition of the interstellar gas, the coronal gas between the stars, and the interstellar abundance ratio of deuterium to hydrogen.

  1. Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules

    NASA Astrophysics Data System (ADS)

    Cruz-Diaz, G. A.; Muñoz Caro, G. M.; Chen, Y.-J.; Yih, T.-S.

    2014-02-01

    Context. Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K are covered by ice mantles. A nonthermal desorption mechanism is invoked to explain the presence of gas-phase molecules in these environments, such as the photodesorption induced by irradiation of ice due to secondary ultraviolet photons. To quantify the effects of ice photoprocessing, an estimate of the photon absorption in ice mantles is required. In a recent work, we reported the vacuum-ultraviolet (VUV) absorption cross sections of nonpolar molecules in the solid phase. Aims: The aim was to estimate the VUV-absorption cross sections of nonpolar molecular ice components, including CH4, CO2, N2, and O2. Methods: The column densities of the ice samples deposited at 8 K were measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. Results: We found that, as expected, solid N2 has the lowest VUV-absorption cross section, which about three orders of magnitude lower than that of other species such as O2, which is also homonuclear. Methane (CH4) ice presents a high absorption near Ly-α (121.6 nm) and does not absorb below 148 nm. Estimating the ice absorption cross sections is essential for models of ice photoprocessing and allows estimating the ice photodesorption rates as the number of photodesorbed molecules per absorbed photon in the ice. Data can be found at http://ghosst.osug.fr/

  2. Moderate-resolution spectroscopy of the lensed quasar 2237 + 0305 - A search for CA II absorption due to the interstellar medium in the foreground lensing galaxy

    NASA Astrophysics Data System (ADS)

    Hintzen, Paul; Maran, Stephen P.; Michalitsianos, Andrew G.; Foltz, Craig B.; Chaffee, Frederic H., Jr.; Kafatos, Minas

    1990-01-01

    The gravitational lens system 2237+0305 consists of a low-redshift barred spiral galaxy (z = 0.0394) centered on a more distant quasar (z = 1.695). Because the lensing galaxy is nearly face on, spectroscopy of the background quasar affords a unique opportunity to study the interstellar medium in the galaxy's center and . We report moderate-resolution spectroscopy of QSO2237+0305 yielding a 3σ upper limit of 72 mÅ for the rest equivalent width of Ca II K absorption due to gas in the intervening galaxy. Since gas in the Milky Way "thick disk" typically produces 220 mÅ Ca II lines along lines of sight at high galactic latitude, while our line of sight to QSO 2237+0305 is effectively the weighted mean of four lines of sight, each of which transects an entire halo diameter in the lensing galaxy rather than just a radius, our Ca II upper limit argues against the presence of such a thick disk near the center of the lensing galaxy. Also, published studies indicate that at 8200 Å, QSO 2237+0305 suffers roughly 0.5 mag of extinction due to the leasing galaxy. Assuming a normal gas-to-dust ratio and allowing for various sources of uncertainty, this absorption estimate combined with our Ca II K upper limit implies that calcium is depleted with respect to hydrogen by at least 2.7-3.7 dex, compared to solar abundances. This depletion is similar to the more extreme cases seen in our own galaxy, and higher-dispersion observations may further decrease the upper limit on Ca II absorption.

  3. Interstellar molecules

    NASA Astrophysics Data System (ADS)

    Smith, D.

    1987-09-01

    Some 70 different molecular species have so far been detected variously in diffuse interstellar clouds, dense interstellar clouds, and circumstellar shells. Only simple (diatomic and triatomic) species exist in diffuse clouds because of the penetration of destructive UV radiations, whereas more complex (polyatomic) molecules survive in dense clouds as a result of the shielding against this UV radiation provided by dust grains. A current list of interstellar molecules is given together with a few other molecular species that have so far been detected only in circumstellar shells. Also listed are those interstellar species that contain rare isotopes of several elements. The gas phase ion chemistry is outlined via which the observed molecules are synthesized, and the process by which enrichment of the rare isotopes occurs in some interstellar molecules is described.

  4. Interstellar H3+

    PubMed Central

    Oka, Takeshi

    2006-01-01

    Protonated molecular hydrogen, H3+, is the simplest polyatomic molecule. It is the most abundantly produced interstellar molecule, next only to H2, although its steady state concentration is low because of its extremely high chemical reactivity. H3+ is a strong acid (proton donor) and initiates chains of ion-molecule reactions in interstellar space thus leading to formation of complex molecules. Here, I summarize the understandings on this fundamental species in interstellar space obtained from our infrared observations since its discovery in 1996 and discuss the recent observations and analyses of H3+ in the Central Molecular Zone near the Galatic center that led to a revelation of a vast amount of warm and diffuse gas existing in the region. PMID:16894171

  5. Laboratory Astrochemistry: Interstellar PAHs

    NASA Technical Reports Server (NTRS)

    Salama, Farid; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are now considered to be an important and ubiquitous component of the organic material in space. PAHs are found in a large variety of extraterrestrial materials such as interplanetary dust particles (IDPs) and meteoritic materials. PAHs are also good candidates to account for the infrared emission bands (UIRs) and the diffuse interstellar optical absorption bands (DIBs) detected in various regions of the interstellar medium. The recent observations made with the Infrared Space Observatory (ISO) have confirmed the ubiquitous nature of the UIR bands and their carriers. PAHs are thought to form through chemical reactions in the outflow from carbon-rich stars in a process similar to soot formation. Once injected in the interstellar medium, PAHs are further processed by the interstellar radiation field, interstellar shocks and energetic particles. A major, dedicated, laboratory effort has been undertaken to measure the physical and chemical characteristics of these complex molecules and their ions under experimental conditions that mimic the interstellar conditions. These measurements require collision-free conditions where the molecules and ions are cold and chemically isolated. The spectroscopy of PAHs under controlled conditions represents an essential diagnostic tool to study the evolution of extraterrestrial PAHs. The Astrochemistry Laboratory program will be discussed through its multiple aspects: (1) objectives, (2) approach and techniques adopted, (3) adaptability to the nature of the problem(s), and (4) results and implications for astronomy as well as for molecular spectroscopy. A review of the data generated through laboratory simulations of space environments and the role these data have played in our current understanding of the properties of interstellar PAHs will be presented. The discussion will also introduce the newest generation of laboratory experiments that are currently being developed in order to provide a

  6. Interstellar Optics

    NASA Technical Reports Server (NTRS)

    Gwinn, C. R.; Britton, M. C.; Reynolds, J. E.; Jauncey, D. L.; King, E. A.; McCulloch, P. M.; Lovell, J. E. J.; Preston, R. A.

    1998-01-01

    We discuss the effects of finite source size on the diffraction pattern produced by scattering in a thin screen, particularly as applied to radio-wave scattering, by density fluctuations in the interstellar plasma.

  7. ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. I. OBSERVATIONS OF ROTATIONALLY EXCITED CH AND CH{sup +} ABSORPTION AND STRONG, EXTENDED REDWARD WINGS ON SEVERAL DIBs

    SciTech Connect

    Dahlstrom, Julie; York, Donald G.; Welty, Daniel E.; Oka, Takeshi; Johnson, Sean; Jiang Zihao; Sherman, Reid; Hobbs, L. M.; Friedman, Scott D.; Sonnentrucker, Paule; Rachford, Brian L.; Snow, Theodore P.

    2013-08-10

    Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 A are found in absorption along the line of sight to Herschel 36, the star illuminating the bright Hourglass region of the H II region Messier 8. Interstellar absorption from excited CH{sup +} in the J = 1 level and from excited CH in the J = 3/2 level is also seen. To our knowledge, neither those excited molecular lines nor such strongly extended DIBs have previously been seen in absorption from interstellar gas. These unusual features appear to arise in a small region near Herschel 36 which contains most of the neutral interstellar material in the sight line. The CH{sup +} and CH in that region are radiatively excited by strong far-IR radiation from the adjacent infrared source Her 36 SE. Similarly, the broadening of the DIBs toward Herschel 36 may be due to radiative pumping of closely spaced high-J rotational levels of relatively small, polar carrier molecules. If this picture of excited rotational states for the DIB carriers is correct and applicable to most DIBs, the 2.7 K cosmic microwave background may set the minimum widths (about 0.35 A) of known DIBs, with molecular processes and/or local radiation fields producing the larger widths found for the broader DIBs. Despite the intense local UV radiation field within the cluster NGC 6530, no previously undetected DIBs stronger than 10 mA in equivalent width are found in the optical spectrum of Herschel 36, suggesting that neither dissociation nor ionization of the carriers of the known DIBs by this intense field creates new carriers with easily detectable DIB-like features. Possibly related profile anomalies for several other DIBs are noted.

  8. Characteristics of the local interstellar hydrogen determined from PROGNOZ 5 and 6 interplanetary Lyman-alpha line profile measurements with a hydrogen absorption cell

    NASA Astrophysics Data System (ADS)

    Bertaux, J. L.; Lallement, R.; Kurt, V. G.; Mironova, E. N.

    1985-09-01

    The flow of interstellar H atoms in the solar system was observed through resonance scattering of solar Lyman-alpha protons with two Lyman-alpha photometers on the Prognoz 5 and 6 satellites. Data collected at five different locations in the solar system were compared with a model of the interstellar H flow, modified by solar interaction. Five parameters describing atomic hydrogen of the local interstellar medium and two parameters describing the solar interaction were derived simultaneously to give a good fit of the upwind hemisphere. The solar Lyman-alpha flux at line center was determined along with the ionization rate of H atoms.

  9. Interstellar PAH Analogs in the Laboratory: Comparison with Astronomical Data

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2005-01-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the near-UV and visible range. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high-sensitivity spectroscopy and directly compared to the astronomical data. Preliminary conclusions from the comparison of the laboratory data with astronomical observations will also be presented.

  10. Astrochemistry: Fullerene solves an interstellar puzzle

    NASA Astrophysics Data System (ADS)

    Ehrenfreund, Pascale; Foing, Bernard

    2015-07-01

    Laboratory measurements confirm that a 'buckyball' ion is responsible for two near-infrared absorption features found in spectra of the interstellar medium, casting light on a century-old astrochemical mystery. See Letter p.322

  11. Interstellar grains

    NASA Technical Reports Server (NTRS)

    Snow, T. P.

    1986-01-01

    There are few aspects of interstellar grains that can be unambiguously defined. Very little can be said that is independent of models or presuppositions; hence issues are raised and questions categorized, rather than providing definitive answers. The questions are issues fall into three general areas; the general physical and chemical nature of the grains; the processes by which they are formed and destroyed; and future observational approaches.

  12. Interstellar grains within interstellar grains

    NASA Technical Reports Server (NTRS)

    Bernatowicz, Thomas J.; Amari, Sachiko; Zinner, Ernst K.; Lewis, Roy S.

    1991-01-01

    Five interstellar graphite spherules extracted from the Murchison carbonaceous meteorite are studied. The isotopic and elemental compositions of individual particles are investigated with the help of an ion microprobe, and this analysis is augmented with structural studies of ultrathin sections of the grain interiors by transmission electron microscopy. As a result, the following procedure for the formation of the interstellar graphite spherule bearing TiC crystals is inferred: (1) high-temperature nucleation and rapid growth of the graphitic carbon spherule in the atmosphere of a carbon-rich star, (2) nucleation and growth of TiC crystals during continued growth of the graphitic spherule and the accretion of TiC onto the spherule, (3) quenching of the graphite growth process by depletion of C or by isolation of the spherule before other grain types could condense.

  13. Regional Climate Zone Modeling of a Commercial Absorption Heat Pump Hot Water Heater Part 1: Southern and South Central Climate Zones

    SciTech Connect

    Geoghegan, Patrick J; Shen, Bo; Keinath, Christopher M.; Garrabrant, Michael A.

    2016-01-01

    Commercial hot water heating accounts for approximately 0.78 Quads of primary energy use with 0.44 Quads of this amount from natural gas fired heaters. An ammonia-water based commercial absorption system, if fully deployed, could achieve a high level of savings, much higher than would be possible by conversion to the high efficiency nonheat-pump gas fired alternatives. In comparison with air source electric heat pumps, the absorption system is able to maintain higher coefficients of performance in colder climates. The ammonia-water system also has the advantage of zero Ozone Depletion Potential and low Global Warming Potential. A thermodynamic model of a single effect ammonia-water absorption system for commercial space and water heating was developed, and its performance was investigated for a range of ambient and return water temperatures. This allowed for the development of a performance map which was then used in a building energy modeling software. Modeling of two commercial water heating systems was performed; one using an absorption heat pump and another using a condensing gas storage system. The energy and financial savings were investigated for a range of locations and climate zones in the southern and south central United States. A follow up paper will analyze northern and north/central regions. Results showed that the system using an absorption heat pump offers significant savings.

  14. Laboratory Astrochemistry: Interstellar PAH Analogs

    NASA Technical Reports Server (NTRS)

    Salama, Farid; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are now considered to be an important and ubiquitous component of the organic material in space. PAHs are found in a large variety of extraterrestrial materials such as interplanetary dust particles (IDPs) and meteoritic materials. PAHs are also good candidates to account for the infrared emission bands (UIRs) and the diffuse interstellar optical absorption bands (DIBs) detected in various regions of the interstellar medium. The recent observations made with the Infrared Space Observatory (ISO) have confirmed the ubiquitous nature of the UIR bands and their carriers. PAHs are though to form through chemical reactions in the outflow from carbon-rich stars in a process similar to soot formation. Once injected in the interstellar medium, PAHs are further processed by the interstellar radiation field, interstellar shocks and energetic particles. A major, dedicated, laboratory effort has been undertaken over the past years to measure the physical and chemical characteristics of these complex molecules and their ions under experimental conditions that mimic the interstellar conditions. These measurements require collision-free conditions where the molecules and ions are cold and chemically isolated. The spectroscopy of PAHs under controlled conditions represents an essential diagnostic tool to study the evolution of extraterrestrial PAHs. The Astrochemistry Laboratory program will be discussed through its multiple aspects: objectives, approach and techniques adopted, adaptability to the nature of the problem(s), results and implications for astronomy as well as for molecular spectroscopy. A review of the data generated through laboratory simulations of space environments and the role these data have played in our current understanding of the properties of interstellar PAHs will be presented. The discussion will also introduce the newest generation of laboratory experiments that are currently being developed in order to provide a

  15. Interstellar Alcohols

    NASA Technical Reports Server (NTRS)

    Charnley, S. B.; Kress, M. E.; Tielens, A. G. G. M.; Millar, T. J.

    1995-01-01

    We have investigated the gas-phase chemistry in dense cores where ice mantles containing ethanol and other alcohols have been evaporated. Model calculations show that methanol, ethanol, propanol, and butanol drive a chemistry leading to the formation of several large ethers and esters. Of these molecules, methyl ethyl ether (CH3OC2H5) and diethyl ether (C2H5)2O attain the highest abundances and should be present in detectable quantities within cores rich in ethanol and methanol. Gas-phase reactions act to destroy evaporated ethanol and a low observed abundance of gas-phase C,H,OH does not rule out a high solid-phase abundance. Grain surface formation mechanisms and other possible gas-phase reactions driven by alcohols are discussed, as are observing strategies for the detection of these large interstellar molecules.

  16. [New methodic approach to hygienic evaluation of electromagnetic energy absorption in near-field zone of irradiation source].

    PubMed

    Perov, S Yu; Bogachova, E V; Belaya, O V

    2015-01-01

    Nowadays, essential objective of hygienic evaluation of electromagnetic energy absorption of mobile radio-frequency devices is specification of new approach with consideration of russian and international regulation principles. This approach enables to ealuate correctly users' actual exposure conditions and consider energy absorption by human in near-field zone of the irradiation source. The work is aimed to study applicability of hypothesis on possible relations between magnetic part of electromagnetic field and specific absorbed capacity. This hypothesis is considered a basis for designing a new methodic approach to hygienic evaluation of individual mobile communication devices in near-field zone of the source. Analysis of the data obtained demonstrates that visible difference between suggested and classic methods decreases with higher frequency. Every studied source in its near-field zone can be characterized by optimal conditions for the suggested method usage with error less than 2 dB. The study results on relations between decreasing electromagnetic energy and specific absorbed capacity value make possible further improvement of methods controlling electromagnetic field levels in assessment of personal mobile radio communication devices. PMID:26470479

  17. Interstellar Mg II and C IV absorption by 1 1/2 galaxies along the sightline to MrK 205

    NASA Technical Reports Server (NTRS)

    Bowen, David V.; Blades, J. Chris

    1993-01-01

    The first results of our HST survey designed to search for Mg 2 and C 4 absorption lines from the disks and halos of low-redshift galaxies using background QSO's and supernovae as probes are presented. Our survey utilizes the high resolution of the Goddard High Resolution Spectrograph enabling us to calculate the column densities and doppler parameters of individual components within an absorption complex, and hence determine the physical conditions of the absorbing gas. Observing the complexity of the absorption line profiles i.e., the velocity distribution and total velocity extent of the constituent components, offers an important description of the kinematics of the absorbing gas, and hence an understanding of its origin. Focus is on one sight line in particular, that towards Mrk 205, which passes 3-5 kpc from the intervening galaxy NGC 4319. Mg 2 and C 4 absorption from both local Milky Way halo gas and from NGC 4319 is detected.

  18. The absorption chiller in large scale solar pond cooling design with condenser heat rejection in the upper convecting zone

    SciTech Connect

    Tsilingiris, P.T. )

    1992-07-01

    The possibility of using solar ponds as low-cost solar collectors combined with commercial absorption chillers in large scale solar cooling design is investigated. The analysis is based on the combination of a steady-state solar pond mathematical model with the operational characteristics of a commercial absorption chiller, assuming condenser heat rejection in the upper convecting zone (U.C.Z.). The numerical solution of the nonlinear equations involved leads to results which relate the chiller capacity with pond design and environmental parameters, which are also employed for the investigation of the optimum pond size for a minimum capital cost. The derived cost per cooling kW for a 350 kW chiller ranges from about 300 to 500 $/kW cooling. This is almost an order of magnitude lower than using a solar collector field of evacuated tube type.

  19. Interstellar isomers

    NASA Technical Reports Server (NTRS)

    Defrees, D.; Mclean, D.; Herbst, E.

    1986-01-01

    Both observational and theoretical studies of molecular clouds are hindered by many difficulties. One way to partially circumvent the difficulties of characterizing the chemistry within these objects is to study the relative abundances of isomers which are synthesized from a common set of precursors. Unfortunately, only one such system has been confirmed, the HCN/HNC pair of isomers. While the basic outlines of its chemistry have been known for some years, there are still many aspects of the chemistry which are unclear. Another potential pair of isomers is HCO+/HOC+; HCO+ is an abundant instellar molecule and a tentative identification of HOC+ has been made in Sgr B2. This identification is being challenged, however, based on theoretical and laboratory evidence that HOC+ reacts with H2. Another potential pair of interstellar isomers is methyl cyanide (CH3CN, acetonitrile) and methyl isocyanide (CH3NC). The cyanide is well known, however the isocyanide has yet to be observed despite theoretical predictions that appreciable quantities should be present.

  20. O VI IN THE LOCAL INTERSTELLAR MEDIUM

    SciTech Connect

    Barstow, M. A.; Boyce, D. D.; Barstow, J. K.; Forbes, A. E.; Preval, S.; Welsh, B. Y.; Lallement, R.

    2010-11-10

    We report the results of a search for O VI absorption in the spectra of 80 hot DA white dwarfs observed by the FUSE satellite. We have carried out a detailed analysis of the radial velocities of interstellar and (where present) stellar absorption lines for the entire sample of stars. In approximately 35% of cases (where photospheric material is detected), the velocity differences between the interstellar and photospheric components were beneath the resolution of the FUSE spectrographs. Therefore, in 65% of these stars the interstellar and photospheric contributions could be separated and the nature of the O VI component unambiguously determined. Furthermore, in other examples, where the spectra were of a high signal-to-noise, no photospheric material was found and any O VI detected was assumed to be interstellar. Building on the earlier work of Oegerle et al. and Savage and Lehner, we have increased the number of detections of interstellar O VI and, for the first time, compared their locations with both the soft X-ray background emission and new detailed maps of the distribution of neutral gas within the local interstellar medium. We find no strong evidence to support a spatial correlation between O VI and SXRB emission. In all but a few cases, the interstellar O VI was located at or beyond the boundaries of the local cavity. Hence, any T {approx} 300,000 K gas responsible for the O VI absorption may reside at the interface between the cavity and surrounding medium or in that medium itself. Consequently, it appears that there is much less O VI-bearing gas than previously stated within the inner rarefied regions of the local interstellar cavity.

  1. Stimulated Mid-Infrared Luminescence Experiment: Contribution to the Study of Pre-Earthquake Phenomena and UV Absorption by Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Freund, Friedemann; Freund, Minoru M.; Tsay, Si-Chee; Ouzounov, Dimitar

    2004-01-01

    The work performed under this proposal is based on the experimentally supported observation - or inference - that a small fraction of the oxygen anions in silicate minerals in igneous and high-grade metamorphic rocks on Earth may not be in the usual 2- oxidation state, O(sup 2-), but in a higher oxidation state, as O(sup -). If this is true, the same would likely apply to the fine dust that fills the diffuse interstellar medium. An (sup -) in a matrix of O(sup 2-) represents a defect electron in the valence band, also known as positive hole or p-hole for short. When two O(sup -) combine, they undergo spin-pairing and form a positive hole pair, PHP. Chemically speaking a PHP is a peroxy bond. In an oxide matrix a peroxy bond takes the form of a peroxy anion, O2(sup 2-). In a silicate matrix it probably exists in the form of peroxy links between adjacent [SiO4] tetrahedral, O3Si00\\SiO3. From a physics perspective a PHP is an electrically inactive point defect, which contains dormant electronic charge carriers. When the peroxy bond breaks, p-hole charge carriers are released. These p-holes are diffusively mobile and spread through the O 2p-dominated valence band of the otherwise insulating mineral matrix.

  2. Effects of Fusion Zone Size and Failure Mode on Peak Load and Energy Absorption of Advanced High Strength Steel Spot Welds under Lap Shear Loading Conditions

    SciTech Connect

    Sun, Xin; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2008-06-01

    This paper examines the effects of fusion zone size on failure modes, static strength and energy absorption of resistance spot welds (RSW) of advanced high strength steels (AHSS) under lap shear loading condition. DP800 and TRIP800 spot welds are considered. The main failure modes for spot welds are nugget pullout and interfacial fracture. Partial interfacial fracture is also observed. Static weld strength tests using lap shear samples were performed on the joint populations with various fusion zone sizes. The resulted peak load and energy absorption levels associated with each failure mode were studied for all the weld populations using statistical data analysis tools. The results in this study show that AHSS spot welds with conventionally required fusion zone size of can not produce nugget pullout mode for both the DP800 and TRIP800 welds under lap shear loading. Moreover, failure mode has strong influence on weld peak load and energy absorption for all the DP800 welds and the TRIP800 small welds: welds failed in pullout mode have statistically higher strength and energy absorption than those failed in interfacial fracture mode. For TRIP800 welds above the critical fusion zone level, the influence of weld failure modes on peak load and energy absorption diminishes. Scatter plots of peak load and energy absorption versus weld fusion zone size were then constructed, and the results indicate that fusion zone size is the most critical factor in weld quality in terms of peak load and energy absorption for both DP800 and TRIP800 spot welds.

  3. A Type Stars as Probes of the Local Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Ferrero, R. F.; Ferlet, R.; Vidal-Madjar, A.

    1984-01-01

    With the aim to sample the Local Interstellar Medium (LISM), it was proposed to use A stars as targets. The Mg II UV lines seem to be the best interstellar absorption candidates. Several hundreths of A stars can be reached within 100 pc. First preliminary results (20 lines of sight) are presented, based on previous Copernicus and actual IUE observations.

  4. Interstellar Dust: Contributed Papers

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M. (Editor); Allamandola, Louis J. (Editor)

    1989-01-01

    A coherent picture of the dust composition and its physical characteristics in the various phases of the interstellar medium was the central theme. Topics addressed included: dust in diffuse interstellar medium; overidentified infrared emission features; dust in dense clouds; dust in galaxies; optical properties of dust grains; interstellar dust models; interstellar dust and the solar system; dust formation and destruction; UV, visible, and IR observations of interstellar extinction; and quantum-statistical calculations of IR emission from highly vibrationally excited polycyclic aromatic hydrocarbon (PAH) molecules.

  5. Ionization in nearby interstellar gas

    NASA Technical Reports Server (NTRS)

    Frisch, P. C.; Welty, D. E.; York, D. G.; Fowler, J. R.

    1990-01-01

    Due to dielectric recombination, neutral magnesium represents an important tracer for the warm low-density gas around the solar system. New Mg I 2852 absorption-line data from IUE are presented, including detections in a few stars within 40 pc of the sun. The absence of detectable Mg I in Alpha CMa and other stars sets limits on the combined size and electron density of the interstellar cloud which gives rise to the local interstellar wind. For a cloud radius greater than 1 pc and density of 0.1/cu cm, the local cloud has a low fractional ionization, n(e)/n(tot) less than 0.05, if magnesium is undepleted, equilibrium conditions prevail, the cloud temperature is 11,750 K, and 80 percent of the magnesium in the sightline is Mg II.

  6. Iron-absorption band analysis for the discrimination of iron-rich zones

    NASA Technical Reports Server (NTRS)

    Rowan, L. C. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. Study has concentrated on the two primary aspects of the project, structural analysis through evaluation of lineaments and circular features and spectral analyses through digital computer-processing techniques. Several previously unrecognized lineaments are mapped which may be the surface manifestations of major fault or fracture zones. Two of these, the Walker Lane and the Midas Trench lineament system, transect the predominantly NNE-NNW-trending moutain ranges for more than 500 km. Correlation of major lineaments with productive mining districts implies a genetic relationship, the 50 circular or elliptical features delineated suggest a related role for Tertiary volcanism. Color-ratio composites have been used to identify limonitic zones and to discriminate mafic and felsic rock by combing diazo color transparencies of three different ratios. EROS Data Center scene identification number for color composite in this report is ER 1 CC 500. Refinement of enhancement procedures for the ratio images is progressing. Fieldwork in coordination with both spectral and structural analyses is underway.

  7. Interstellar and Cometary Dust

    NASA Technical Reports Server (NTRS)

    Mathis, John S.

    1997-01-01

    'Interstellar dust' forms a continuum of materials with differing properties which I divide into three classes on the basis of observations: (a) diffuse dust, in the low-density interstellar medium; (b) outer-cloud dust, observed in stars close enough to the outer edges of molecular clouds to be observed in the optical and ultraviolet regions of the spectrum, and (c) inner-cloud dust, deep within the cores of molecular clouds, and observed only in the infrared by means of absorption bands of C-H, C=O, 0-H, C(triple bond)N, etc. There is a surprising regularity of the extinction laws between diffuse- and outer-cloud dust. The entire mean extinction law from infrared through the observable ultraviolet spectrum can be characterized by a single parameter. There are real deviations from this mean law, larger than observational uncertainties, but they are much smaller than differences of the mean laws in diffuse- and outer-cloud dust. This fact shows that there are processes which operate over the entire distribution of grain sizes, and which change size distributions extremely efficiently. There is no evidence for mantles on grains in local diffuse and outer-cloud dust. The only published spectra of the star VI Cyg 12, the best candidate for showing mantles, does not show the 3.4 micro-m band which appreciable mantles would produce. Grains are larger in outer-cloud dust than diffuse dust because of coagulation, not accretion of extensive mantles. Core-mantle grains favored by J. M. Greenberg and collaborators, and composite grains of Mathis and Whiffen (1989), are discussed more extensively (naturally, I prefer the latter). The composite grains are fluffy and consist of silicates, amorphous carbon, and some graphite in the same grain. Grains deep within molecular clouds but before any processing within the solar system are presumably formed from the accretion of icy mantles on and within the coagulated outer-cloud grains. They should contain a mineral

  8. Beyond Clausius-Mossotti - Wave propagation on a polarizable point lattice and the discrete dipole approximation. [electromagnetic scattering and absorption by interstellar grains

    NASA Technical Reports Server (NTRS)

    Draine, B. T.; Goodman, Jeremy

    1993-01-01

    We derive the dispersion relation for electromagnetic waves propagating on a lattice of polarizable points. From this dispersion relation we obtain a prescription for choosing dipole polarizabilities so that an infinite lattice with finite lattice spacing will mimic a continuum with dielectric constant. The discrete dipole approximation is used to calculate scattering and absorption by a finite target by replacing the target with an array of point dipoles. We compare different prescriptions for determining the dipole polarizabilities. We show that the most accurate results are obtained when the lattice dispersion relation is used to set the polarizabilities.

  9. Ion-absorption band analysis for the discrimination of iron-rich zones. [Nevada

    NASA Technical Reports Server (NTRS)

    Rowan, L. C. (Principal Investigator); Wetlaufer, P. H.

    1974-01-01

    The author has identified the following significant results. A technique which combines digital computer processing and color composition was devised for detecting hydrothermally altered areas and for discriminating among many rock types in an area in south-central Nevada. Subtle spectral reflectance differences among the rock types are enhanced by ratioing and contrast-stretching MSS radiance values for form ratio images which subsequently are displayed in color-ratio composites. Landform analysis of Nevada shows that linear features compiled without respect to length results in approximately 25 percent coincidence with mapped faults. About 80 percent of the major lineaments coincides with mapped faults, and substantial extension of locally mapped faults is commonly indicated. Seven major lineament systems appear to be old zones of crustal weakness which have provided preferred conduits for rising magma through periodic reactivation.

  10. On the detection of rubidium in diffuse interstellar clouds

    NASA Technical Reports Server (NTRS)

    Federman, S. R.; Sneden, C.; Schempp, W. V.; Smith, W. H.

    1985-01-01

    A search for absorption from neutral rubidium at 7800 A was conducted. No evidence for absorption to a 3 sigma limit of less than 1.5 mA was seen in the diffuse interstellar gas toward the stars omicron Persei, zeta Persei, and zeta Ophiuchi. Present results do not confirm the detection by Jura and Smith (1981) toward zeta Oph. A possible reason for the discrepancy is presented. In light of the present measurements, the abundance of interstellar rubidium in reconsidered.

  11. Iron absorption band analysis for the discrimination of iron rich zones

    NASA Technical Reports Server (NTRS)

    Rowan, L. C. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. A lineament study of the Nevada test site is near completion. Two base maps (1:500,000) have been prepared, one of band 7 lineaments and the other of band 5 lineaments. In general, more lineaments and more faults are seen on band 5. About 45% of the lineaments appear to be faults and contacts, the others being predominantly streams, roads, railway tracks, and mountain crests. About 25% of the lineaments are unidentified so far. Special attention is being given to unmapped extensions of faults, groups of unmapped lineaments, and known mineralized areas and alteration zones. Earthquake epicenters recorded from 1869 to 1963 have been plotted on the two base maps. Preliminary examination as yet indicates no basic correlation with the lineaments. Attempts are being made to subtract bands optically, using an I2S viewer, an enlarger, and a data color viewer. Success has been limited so far due to technical difficulties, mainly vignetting and poor light sources, within the machines. Some vegetation and rock type differences, however, have been discerned.

  12. Iron-absorption band analysis for the discrimination of iron-rich zones

    NASA Technical Reports Server (NTRS)

    Rowan, L. C. (Principal Investigator)

    1973-01-01

    The author has identified the following significant results. Lineament analysis of the area was initiated on individual images and then expanded areally by the use of mosaics at the 1:1,000,000 scale. Principal trends are NE, NW, NNE-NNW, and ENE. Several previously unrecognized lineaments are mapped which may be the surface manifestations of major fault or fracture zones. Three lineaments are especially noteworthy. Two of these, the Walker Lane and the Midas Trench lineament system, transect the prediominantly NNE-NNW trending mountain ranges for more than 500 km. A third major lineament, formed by the alinement of several topographic escarpments 10-20 km long, is orthogonal to the Midas Trench lineament. This lineament is marked by a distinct positive magnetic anomaly for approximately 200 km. Further visual analysis of ERTS-1 images has resulted in the delineation of 50 circular or elliptical features which are presumed to be volcanic or intrusive centers. A comparison with the 78 Tertiary volcanic centers mapped in the study area in 1970 indicates some good agreement between the proposed and known volcanic centers. The coincidence of some major lineaments and productive ore bodies implies a genetic relationship.

  13. Interstellar grain chemistry and organic molecules

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Sandford, S. A.

    1990-01-01

    The detection of prominant infrared absorption bands at 3250, 2170, 2138, 1670 and 1470 cm(-1) (3.08, 4.61, 4.677, 5.99 and 6.80 micron m) associated with molecular clouds show that mixed molecular (icy) grain mantles are an important component of the interstellar dust in the dense interstellar medium. These ices, which contain many organic molecules, may also be the production site of the more complex organic grain mantles detected in the diffuse interstellar medium. Theoretical calculations employing gas phase as well as grain surface reactions predict that the ices should be dominated only by the simple molecules H2O, H2CO, N2, CO, O2, NH3, CH4, possibly CH3OH, and their deuterated counterparts. However, spectroscopic observations in the 2500 to 1250 cm(-1)(4 to 8 micron m) range show substantial variation from source reactions alone. By comparing these astronomical spectra with the spectra of laboratory-produced analogs of interstellar ices, one can determine the composition and abundance of the materials frozen on the grains in dense clouds. Experiments are described in which the chemical evolution of an interstellar ice analog is determined during irradiation and subsequent warm-up. Particular attention is paid to the types of moderately complex organic materials produced during these experiments which are likely to be present in interstellar grains and cometary ices.

  14. Interstellar grain chemistry and organic molecules

    NASA Astrophysics Data System (ADS)

    Allamandola, L. J.; Sandford, S. A.

    1990-04-01

    The detection of prominant infrared absorption bands at 3250, 2170, 2138, 1670 and 1470 cm(-1) (3.08, 4.61, 4.677, 5.99 and 6.80 micron m) associated with molecular clouds show that mixed molecular (icy) grain mantles are an important component of the interstellar dust in the dense interstellar medium. These ices, which contain many organic molecules, may also be the production site of the more complex organic grain mantles detected in the diffuse interstellar medium. Theoretical calculations employing gas phase as well as grain surface reactions predict that the ices should be dominated only by the simple molecules H2O, H2CO, N2, CO, O2, NH3, CH4, possibly CH3OH, and their deuterated counterparts. However, spectroscopic observations in the 2500 to 1250 cm(-1)(4 to 8 micron m) range show substantial variation from source reactions alone. By comparing these astronomical spectra with the spectra of laboratory-produced analogs of interstellar ices, one can determine the composition and abundance of the materials frozen on the grains in dense clouds. Experiments are described in which the chemical evolution of an interstellar ice analog is determined during irradiation and subsequent warm-up. Particular attention is paid to the types of moderately complex organic materials produced during these experiments which are likely to be present in interstellar grains and cometary ices.

  15. The hydrogen coverage of interstellar PAHs

    NASA Technical Reports Server (NTRS)

    Barker, J. R.; Cohen, M.; Tielens, Alexander G. G. M.; Allamandola, Louis J.; Barker, J. R.; Barker, J. R.

    1986-01-01

    The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a UV photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense UV fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments.

  16. The hydrogen coverage of interstellar PAHs

    NASA Technical Reports Server (NTRS)

    Tielens, A. G. G. M.; Allamandola, L. J.; Barker, J. R.; Cohen, M.

    1987-01-01

    The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a UV photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense UV fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments.

  17. Erratum: "Photoionization Modeling of Oxygen K Absorption in the Interstellar Medium, the Chandra Grating Spectra of XTE J1817-330" (2013, Apj, 768, 60)

    NASA Technical Reports Server (NTRS)

    Gatuzz, E.; Garcia, J.; Mendoza, C.; Kallman, Timothy R.; Witthoeft, Michael C.; Lohfink, A.; Bautista, M. A.; Palmeri, P.; Quinet, P.

    2013-01-01

    In the published version of this paper, there are some minor inaccuracies in the absorption-line wavelengths listed in Table 4 as a result of a faulty reduction procedure of the Obs6615 spectrum. The shifts have been detected in a comparison with the wavelengths listed for this spectrum in the Chandra Transmission Grating Catalog and Archive (TGCat8). They are due to incorrect centroid positions of the zero-order image in both reductions as determined by the tgdetect utility which, when disentangled, yield the improved line positions of the amended Table 4 given below. It must also be pointed out that other quantitative findings of the original paper: 1. Table 5, p. 9: the column density (NH), ionization parameter, oxygen abundance of the warmabs model and the normalization and photon index of the power-law model; 2. Table 6, p. 9: the hydrogen column density of the warmabs fit; 3. Table 7, p. 9: the present oxygen equivalent widths of XTE J1817-330; and 4. Table 8, p. 10: the present oxygen column densities of XTE J1817-330 derived from both the curve of growth and warmabs model fit have been revised in the new light and are, within the estimated uncertainty ranges, in good accord with the new rendering.

  18. Processing Mechanisms for Interstellar Ices: Connections to the Solar System

    NASA Technical Reports Server (NTRS)

    Pendleton, Y. J.; Cuzzi, Jeffrey N. (Technical Monitor)

    1995-01-01

    The organic component of the interstellar medium, which has revealed itself through the ubiquitous 3.4 micrometers hydrocarbon absorption feature, is widespread throughout the disk of our galaxy and has been attributed to dust grains residing in the diffuse interstellar medium. The absorption band positions near 3.4 micrometers are characteristic of C-H stretching vibrations in the -CH3 and -CH2- groups of saturated aliphatic hydrocarbons associated with perturbing chemical groups. The production of complex molecules is thought to occur within dense molecular clouds when ice-mantled grains are processed by various energetic mechanisms. Studies of the processing of interstellar ices and the subsequent production of organic residues have relevance to studies of ices in the solar system, because primitive, icy solar system bodies such as those in the Kuiper belt are likely reservoirs of organic material, either preserved from the interstellar medium or produced in situ. Connections between the interstellar medium and the early solar nebula have long been a source of interest. A comparison of the interstellar organics and the Murchison meteorite illustrates the importance of probing the interstellar connection to the solar system, because although the carbonaceous meteorites are undoubtedly highly processed, they do retain specific interstellar signatures (such as diamonds, SiC grains, graphite and enriched D/H). The organic component, while not proven interstellar, has a remarkable similarity to the interstellar organics observed in over a dozen sightlines through our galaxy. This paper compares spectra from laboratory organics produced through the processing of interstellar ice analog materials with the high resolution infrared observations of the interstellar medium in order to investigate the mechanisms (such as ion bombardment, plasma processing, and UV photolysis) that may be producing the organics in the ISM.

  19. Organic molecules in translucent interstellar clouds.

    PubMed

    Krełowski, Jacek

    2014-09-01

    Absorption spectra of translucent interstellar clouds contain many known molecular bands of CN, CH+, CH, OH, OH(+), NH, C2 and C3. Moreover, one can observe more than 400 unidentified absorption features, known as diffuse interstellar bands (DIBs), commonly believed to be carried by complex, carbon-bearing molecules. DIBs have been observed in extragalactic sources as well. High S/N spectra allow to determine precisely the corresponding column densities of the identified molecules, rotational temperatures which differ significantly from object to object in cases of centrosymmetric molecular species, and even the (12)C/(13)C abundance ratio. Despite many laboratory based studies of possible DIB carriers, it has not been possible to unambiguously link these bands to specific species. An identification of DIBs would substantially contribute to our understanding of chemical processes in the diffuse interstellar medium. The presence of substructures inside DIB profiles supports the idea that DIBs are very likely features of gas phase molecules. So far only three out of more than 400 DIBs have been linked to specific molecules but none of these links was confirmed beyond doubt. A DIB identification clearly requires a close cooperation between observers and experimentalists. The review presents the state-of-the-art of the investigations of the chemistry of interstellar translucent clouds i.e. how far our observations are sufficient to allow some hints concerning the chemistry of, the most common in the Galaxy, translucent interstellar clouds, likely situated quite far from the sources of radiation (stars). PMID:25467771

  20. The violent interstellar medium

    NASA Technical Reports Server (NTRS)

    Mccray, R.; Snow, T. P., Jr.

    1979-01-01

    Observational evidence for high-velocity and high-temperature interstellar gas is reviewed. The physical processes that characterize this gas are described, including the ionization and emissivity of coronal gas, the behavior and appearance of high-velocity shocks, and interfaces between coronal gas and cooler interstellar gas. Hydrodynamical models for the action of supernova explosions and stellar winds on the interstellar medium are examined, and recent attempts to synthesize all the processes considered into a global model for the interstellar medium are discussed.

  1. Observations of interstellar zinc

    NASA Technical Reports Server (NTRS)

    Jura, M.; York, D.

    1981-01-01

    The International Ultraviolet Explorer observations of interstellar zinc toward 10 stars are examined. It is found that zinc is at most only slightly depleted in the interstellar medium; its abundance may serve as a tracer of the true metallicity in the gas. The local interstellar medium has abundances that apparently are homogeneous to within a factor of two, when integrated over paths of about 500 pc, and this result is important for understanding the history of nucleosynthesis in the solar neighborhood. The intrinsic errors in detecting weak interstellar lines are analyzed and suggestions are made as to how this error limit may be lowered to 5 mA per target observation.

  2. Complex Organics in Interstellar Space

    NASA Astrophysics Data System (ADS)

    Foing, B.; Ehrenfreund, P.; Ruiterkamp, R.; Cox, N.

    There are signatures of large organic molecules in the interstellar medium, from the ultraviolet to the infrared. Some infrared emission bands, which have been ascribed to families of large aromatic compounds are not specific for individual identification (and for discriminating free floating PAH molecules from loosely bound aromatics in amorphous carbon compounds). Red fluorescence and FUV absorption have also been ascribed to these aromatic compounds. Electronic transitions in the visible are a key to identify free gas phase molecules. The origin of Diffuse Interstellar Bands (Herbig 1995), more than 300 in recent surveys (O' Tuairisg et al 2000) is still a mystery. However the measurements of sub-structures rotational contours in DIBs (Ehrenfreund Foing 1996) indicate large molecules such as chains (12-18C), rings, 50 C PAHs or fullerenes. The distribution of DIB widths permit to estimate a distribution of size of molecular carriers. The environment properties of DIB carriers also indicate ionisation potentials similar to those of cations of large carbonaceous molecules, such as large PAHs or fullerenes (Sonnentrucker et al 1997). The correlation studies of DIBS also indicate different carriers for the strong DIBs observed in the visible (Cami et al 1997). DIBS are weakened in the in the low-metallicity Magellanic clouds (Ehrenfreund et al 2002, Cox et al 2004). The detection of near IR bands at 9577 and 9632 A coinciding with laboratory transitions of C60+ (Foing, Ehrenfreund 1994, 1997, Galatzudinov et al 2000 ) suggest that significant interstellar carbon could reside in complex fullerene type compounds. These results indicate that many different large and complex organic molecules can form and survive in the very harsh interstellar environments. A follow up interdisciplinary work is required between astronomical observations, laboratory matrix and gas phase spectroscopy, theoretical work and modelling, and active experiments in space to study the formation

  3. NASA's IBEX Observes Interstellar Matter

    NASA Video Gallery

    The Interstellar Boundary Explorer (IBEX) has directly sampled multiple heavy elements from the Local Interstellar Cloud for the first time. It turns out that this interstellar material is not like...

  4. L(alpha)-induced two-photon absorption of visible light emitted from an O-type star by H2(+) ions located near the surface of the Stromgren sphere surrounding the star: A possible explanation for the diffuse interstellar absorption bands (DIDs)

    NASA Technical Reports Server (NTRS)

    Glownia, James H.; Sorokin, Peter P.

    1994-01-01

    In this paper, a new model is proposed to account for the DIB's (Diffuse Interstellar Bands). In this model, the DIB's result from a non-linear effect: resonantly-enhanced two-photon absorption of H(2+) ions located near the surface of the Stromgren sphere that surrounds an O- or B- type star. The strong light that is required to 'drive' the two-photon transition is provided by L(alpha) light emerging from the Stromgren sphere that bounds the H II region surrounding the star. A value of approximately 100 micro W/sq cm is estimated for the L(alpha) flux at the Stromgren radius, R(s), of a strong (O5) star. It is shown that a c.w. L(alpha) flux of this intensity should be sufficient to induce a few percent absorption for visible light radiated by the same star at a frequency (omega2) that completes an allowed two-photon transition, provided (1) the L(alpha) radiation happens to be nearly resonant with the frequency of a fully-allowed absorber transition that effectively represents the first step in the two-photon transition, and (2) an effective column density approximately 10(sup18)/sq cm of the absorber is present near the Stromgren sphere radius, R(sub s).

  5. Effects of Fusion Zone Size and Failure Mode on Peak Load and Energy Absorption of Advanced High Strength Steel Spot Welds

    SciTech Connect

    Sun, Xin; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2007-01-01

    This paper examines the effects of fusion zone size on failure modes, static strength and energy absorption of resistance spot welds (RSW) of advanced high strength steels (AHSS). DP800 and TRIP800 spot welds are considered. The main failure modes for spot welds are nugget pullout and interfacial fracture. Partial interfacial fracture is also observed. The critical fusion zone sizes to ensure nugget pull-out failure mode are developed for both DP800 and TRIP800 using limit load based analytical model and micro-hardness measurements of the weld cross sections. Static weld strength tests using cross tension samples were performed on the joint populations with controlled fusion zone sizes. The resulted peak load and energy absorption levels associated with each failure mode were studied for all the weld populations using statistical data analysis tools. The results in this study show that AHSS spot welds with fusion zone size of can not produce nugget pullout mode for both the DP800 and TRIP800 materials examined. The critical fusion zone size for nugget pullout shall be derived for individual materials based on different base metal properties as well as different heat affected zone (HAZ) and weld properties resulted from different welding parameters.

  6. Is interstellar archeology possible?

    NASA Astrophysics Data System (ADS)

    Carrigan, Richard A.

    2012-09-01

    Searching for signatures of cosmic-scale archeological artifacts such as Dyson spheres is an interesting alternative to conventional radio SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archeology or sometimes cosmic archeology. A variety of interstellar archeology signatures is discussed including non-natural planetary atmospheric constituents, stellar doping, Dyson spheres, as well as signatures of stellar, and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is reviewed in the discussion of galactic signatures. These potential interstellar archeological signatures are classified using the Kardashev scale. A modified Drake equation is introduced. With few exceptions interstellar archeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.

  7. The Organic Component of Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Pendleton, Yvonne

    2003-01-01

    The distribution, chemical structure, and formation of organic matter in the interstellar medium are important to our understanding of the overall evolution of dust. The exchange of dust between the dense and diffuse interstellar medium, and the effects of processing on dust within dense clouds will affect the inventory of material available for incorporation into newly forming star and planetary systems. Observational ground-based studies have confirmed the widespread distribution of the 3.4 pm absorption band attributed to aliphatic hydrocarbons in the diffuse interstellar medium of our own galaxy, and in the dusty spectra of a few nearby galaxies, while space based observations from IS0 probed the signatures of corresponding mid-infrared features. Laboratory experiments which utilize both thermal processes and energetic processing by high energy photons and cosmic rays, produce candidate materials which offer close matches to the observed diffuse interstellar medium and extragalactic hydrocarbon absorption features. Through an analysis of the 4000 to 1000 cm (2.5 to 10 micrometers) region of the spectrum of diffuse interstellar medium (DISM) dust compared with the spectra of thirteen chemical entities produced in the laboratory which serve as analogs to the interstellar material, significant constraints have been placed on the applicability of proposed candidate materials to explain the interstellar features. The results indicate that the organic refractory material in the diffuse interstellar medium is predominantly hydrocarbon in nature, possessing little nitrogen or oxygen, with the carbon distributed between the aromatic and aliphatic forms. Long alkane chains H3C-(CH2),- with n much greater than 4 or 5 are not major constituents of this material. Comparisons to laboratory analogs indicate the DISM organic material resembles plasma processed pure hydrocarbon residues much more so than energetically processed ice residues. This result is consistent with a

  8. Laboratory Studies of Interstellar PAH Analogs

    NASA Technical Reports Server (NTRS)

    Salama, Farid; DeVincenzi, Donald (Technical Monitor)

    2000-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are now considered to be an important and ubiquitous component of the organic material in space. PAHs are found in a large variety of extraterrestrial materials such as interplanetary dust particles (IDPs) and meteoritic materials. PAHs are also good candidates to account for the infrared emission bands (UIRs) and the diffuse interstellar optical absorption bands (DIBs) detected in various regions of the interstellar medium. The recent observations made with the Infrared Space Observatory (ISO) have confirmed the ubiquitous nature of the UIR bands and their carriers. PAHs are though to form through chemical reactions in the outflow from carbon-rich stars in a process similar to soot formation. Once injected in the interstellar medium, PAHs are further processed by the interstellar radiation field, interstellar shocks and energetic particles. A major, dedicated, laboratory effort has been undertaken over the past years to measure the physical and chemical characteristics of these complex molecules and their ions under experimental conditions that mimic the interstellar conditions. These measurements require collision-free conditions where the molecules and ions are cold and chemically isolated. The spectroscopy of PAHs under controlled conditions represents an essential diagnostic tool to study the evolution of extraterrestrial PAHs. The Astrochemistry Laboratory program will be discussed through its multiple aspects: objectives, approach and techniques adopted, adaptability to the nature of the problem(s), results and implications for astronomy as well as for molecular spectroscopy. A review of the data generated through laboratory simulations of space environments and the role these data have played in our current understanding of the properties of interstellar PAHs will be presented. The discussion will also introduce the newest generation of laboratory experiments that are currently being developed in order to provide a

  9. Molecular Spectroscopy in Astrophysics: Interstellar PAHs

    NASA Technical Reports Server (NTRS)

    Salama, Farid; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Polycyclic aromatic hydrocarbons (PAHs) are now considered to be an important and ubiquitous component of the organic material in space. PAHs are found in a large variety of extraterrestrial materials such as interplanetary dust particles (IDPs) and meteoritic materials. PAHs are also good candidates to account for the infrared emission bands (UIRs) and the diffuse interstellar optical absorption bands (DIBs) detected in various regions of the interstellar medium. The recent observations made with the Infrared Space Observatory (ISO) have confirmed the ubiquitous nature of the UIR bands and their carriers. PAHs are thought to form through chemical reactions in the outflow from carbon-rich stars in a process similar to soot formation. Once injected in the interstellar medium, PAHs are further processed by the interstellar radiation field, interstellar shocks and energetic particles. A long-term laboratory effort has been undertaken to measure the physical and chemical characteristics of these carbon molecules and their ions under experimental conditions that mimic the interstellar conditions. These measurements require collision-free conditions where the molecules and ions are cold and chemically isolated. The spectroscopy of PAHs under controlled conditions represents an essential diagnostic tool to study the evolution of extraterrestrial PAHs. The laboratory results will be discussed as well as the implications for astronomy and for molecular spectroscopy. A review of the data generated through laboratory simulations of space environments and the role these data have played in our current understanding of the properties of interstellar PAHs will be presented. We will also present the new generation of laboratory experiments that are currently being developed in order to provide a closer simulation of space environments and a better support to space missions.

  10. Interstellar fullerene compounds and diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Omont, Alain

    2016-05-01

    Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed and new findings suggest that these fullerenes may possibly form from polycyclic aromatic hydrocarbons (PAHs) in the ISM. Moreover, the first confirmed identification of two strong diffuse interstellar bands (DIBs) with the fullerene, C60+, connects the long standing suggestion that various fullerenes could be DIB carriers. These new discoveries justify reassessing the overall importance of interstellar fullerene compounds, including fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerene compounds is complex. In addition to fullerene formation in grain shattering, fullerene formation from fully dehydrogenated PAHs in diffuse interstellar clouds could perhaps transform a significant percentage of the tail of low-mass PAH distribution into fullerenes including EEHFs. But many uncertain processes make it extremely difficult to assess their expected abundance, composition and size distribution, except for the substantial abundance measured for C60+. EEHFs share many properties with pure fullerenes, such as C60, as regards stability, formation/destruction and chemical processes, as well as many basic spectral features. Because DIBs are ubiquitous in all lines of sight in the ISM, we address several questions about the interstellar importance of various EEHFs, especially as possible carriers of diffuse interstellar bands. Specifically, we discuss basic interstellar properties and the likely contributions of fullerenes of various sizes and their charged counterparts such as C60+, and then in turn: 1) metallofullerenes; 2) heterofullerenes; 3) fulleranes; 4) fullerene-PAH compounds; 5) H2@C60. From this reassessment of the literature and from combining it with known DIB line identifications, we conclude that the general landscape of interstellar fullerene compounds is probably much richer than heretofore realized

  11. Presolar/Interstellar Materials

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.; DeVincenzi, Donald (Technical Monitor)

    2002-01-01

    This talk will review much of our current understanding of the origins, nature, and evolution of materials in circumstellar and interstellar space. I will begin by familiarizing the audience with some of the nomenclature associated the field, reviewing the lifecycle of dust in space, and pointing out where the speakers that follow will address portions of the lifecycle in greater detail. I will then address the different techniques used to study interstellar materials, paying particular attention to (i) telescopic remote sensing of the dust currently in interstellar space, (ii) laboratory studies of individual interstellar grains found in meteorites and other extraterrestrial materials, and (iii) laboratory simulation experiments. To complete the talk, I will focus on the nature of interstellar organic compounds as a particular example of how these disparate techniques can be used to improve our understanding of interstellar matter. While interstellar organics will be addressed in general, particular attention will be made to that portion of the organic inventory that may play a role in the origin and evolution of life on planetary surfaces.

  12. The Interstellar Medium Surrounding the Sun

    NASA Astrophysics Data System (ADS)

    Frisch, Priscilla C.; Redfield, Seth; Slavin, Jonathan D.

    2011-09-01

    The Solar System is embedded in a flow of low-density, warm, and partially ionized interstellar material that has been sampled directly by in situ measurements of interstellar neutral gas and dust in the heliosphere. Absorption line data reveal that this interstellar gas is part of a larger cluster of local interstellar clouds, which is spatially and kinematically divided into additional small-scale structures indicating ongoing interactions. An origin for the clouds that is related to star formation in the Scorpius-Centaurus OB association is suggested by the dynamic characteristics of the flow. Variable depletions observed within the local interstellar medium (ISM) suggest an inhomogeneous Galactic environment, with shocks that destroy grains in some regions. Although photoionization models of the circumheliospheric ISM do an excellent job of reproducing the observed properties of the surrounding ISM, the unknown characteristics of the very low-density hot plasma filling the Local Bubble introduces uncertainty about the source of ionization and nature of cloud boundaries. Recent observations of small cold clouds provide new insight into the processes affecting the local ISM. A fuller understanding of the local ISM can provide insights into the past and future Galactic environment of the Sun, and deeper knowledge of the astrospheres of nearby stars.

  13. Instrumentation for interstellar exploration

    NASA Astrophysics Data System (ADS)

    Gruntman, M.

    The time has arrived for designing, building, and instrumenting a spacecraft for a dedicated foray into interstellar space surrounding our star, the Sun. This region was probed in the past by remote techniques and it will be explored in situ by the Interstellar Probe mission. The mission will significantly advance our understanding of the nature of the local interstellar medium and explore the distant frontier of the solar system by revealing the details of the interaction between the Sun and Galaxy. This mission will also be an important practical step toward interstellar flight of the future. Reaching interstellar space in reasonable time requires high escape velocities and will likely be enabled by non-chemical propulsion such as nuclear-powered electric propulsion or solar sailing. Unusually high spacecraft velocities, enormous distances from the Sun, and non-chemical propulsion will significantly influence the design of the mission, spacecraft and scientific instrumentation. We will review measurement objectives of the first mission into interstellar space and outline constrains on the instrumentation. Measurement of particles, fields, and dust in the interstellar medium will be complemented by search for complex molecules and remote sensing capabilities in various spectral bands. A "look" back at our solar system will also be a glimpse of wh at a flyby mission of the distant future would encounter in approaching another star. The instrumentation for interstellar exploration presents numerous challenges. Mass, telemetry, and power constraints would place a premium on miniaturization and autonom . There are, however,y physical limits on how small the sensors could be. New instrument concepts may be required to achieve the desired measurement capabilities under the stringent constraints of a realistic interstellar mission.

  14. Instrumentation for interstellar exploration

    NASA Astrophysics Data System (ADS)

    Gruntman, Mike

    2004-01-01

    The time has arrived for designing, building, and instrumenting a spacecraft for a dedicated foray into the galactic environment surrounding our star, the sun. This region was probed in the past by remote techniques and it will be explored in situ by the NASA's planned Interstellar Probe mission. The mission will significantly advance our understanding of the nature of the local interstellar medium and explore the distant frontier of the solar system by revealing the details of the interaction between the sun and the Galaxy. This mission will also be an important practical step toward interstellar flight of the future. Reaching interstellar space in reasonable time requires high escape velocities and will likely be enabled by non-chemical propulsion such as nuclear-powered electric propulsion or solar sailing. Unusually high spacecraft velocities, enormous distances from the Sun, and non-chemical propulsion will significantly influence design of the mission, spacecraft, and scientific instrumentation. We will review measurement objectives of the first dedicated mission into interstellar space and outline constraints on the instrumentation. Measurement of particles, fields, and dust in the interstellar medium will be complemented by search for complex organic molecules and remote sensing capabilities in various spectral bands. A "look" back at our solar system will also be a glimpse of what a truly-interstellar mission of the distant future would encounter in approaching a target star. The instrumentation for interstellar exploration presents numerous challenges. Mass, telemetry, and power constraints would place a premium on miniaturization and autonomy. There are, however, physical limits on how small the sensors could be. New instrument concepts may be required to achieve the desired measurement capabilities under the stringent constraints of a realistic interstellar mission.

  15. Interstellar Dust - A Review

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2012-01-01

    The study of the formation and the destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic materials. Although dust with all its components plays an important role in the evolution of interstellar physics and chemistry and in the formation of organic materials, little is known on the formation and destruction processes of carbonaceous dust. Laboratory experiments that are performed under conditions that simulate interstellar and circumstellar environments to provide information on the nature, the size and the structure of interstellar dust particles, the growth and the destruction processes of interstellar dust and the resulting budget of extraterrestrial organic molecules. A review of the properties of dust and of the laboratory experiments that are conducted to study the formation processes of dust grains from molecular precursors will be given.

  16. Interstellar shock waves

    NASA Technical Reports Server (NTRS)

    Mckee, C. F.; Hollenbach, D. J.

    1980-01-01

    The structure of interstellar shocks driven by supernova remnants and by expanding H II regions around early-type stars is discussed. Jump conditions are examined, along with shock fronts, post-shock relaxation layers, collisional shocks, collisionless shocks, nonradiative shocks, radiative atomic shocks, and shock models of observed nebulae. Effects of shock waves on interstellar molecules are examined, with reference to the chemistry behind shock fronts, infrared and vibrational-rotational cooling by molecules, and observations of shocked molecules. Some current problems and applications of the study of interstellar shocks are summarized, including the initiation of star formation by radiative shock waves, interstellar masers, the stability of shocks, particle acceleration in shocks, and shocks in galactic nuclei.

  17. Probing the diffuse interstellar medium with diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Theodorus van Loon, Jacco; Bailey, Mandy; Farhang, Amin; Javadi, Atefeh; Khosroshahi, Habib

    2015-08-01

    For a century already, a large number of absorption bands have been known at optical wavelengths, called the diffuse interstellar bands (DIBs). While their carriers remain unidentified, the relative strengths of these bands in various environments make them interesting new probes of the diffuse interstellar medium (ISM). We present the results from two large, dedicated campaigns to map the ISM using DIBs measured in the high signal-to-noise spectra of hundreds of early-type stars: [1] in and around the Local Bubble using ESO's New Technology Telescope and the Isaac Newton Telescope, and [2] across both Magellanic Clouds using the Very Large Telescope and the Anglo-Australian Telescope. We discuss the implications for the structure and dynamics of the ISM, as well as the constraints these maps place on the nature of the carriers of the DIBs. Partial results have appeared in the recent literature (van Loon et al. 2013; Farhang et al. 2015a,b; Bailey, PhD thesis 2014) with the remainder being prepared for publication now.

  18. HERSCHEL OBSERVATIONS OF INTERSTELLAR CHLORONIUM

    SciTech Connect

    Neufeld, David A.; Indriolo, Nick; Roueff, Evelyne; Le Bourlot, Jacques; Le Petit, Franck; Snell, Ronald L.; Lis, Dariusz; Monje, Raquel; Phillips, Thomas G.; Benz, Arnold O.; Bruderer, Simon; Black, John H.; Larsson, Bengt; De Luca, Massimo; Gerin, Maryvonne; Goldsmith, Paul F.; Gupta, Harshal; Melnick, Gary J.; Menten, Karl M.; Nagy, Zsofia; and others

    2012-03-20

    Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed para-chloronium (H{sub 2}Cl{sup +}) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight lines to the bright submillimeter continuum sources Sgr A (+50 km s{sup -1} cloud) and W31C. Both the para-H{sup 35}{sub 2}Cl{sup +} and para-H{sup 37}{sub 2}Cl{sup +} isotopologues were detected, through observations of their 1{sub 11}-0{sub 00} transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio (OPR) of 3, the observed optical depths imply that chloronium accounts for {approx}4%-12% of chlorine nuclei in the gas phase. We detected interstellar chloronium emission from two sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion South condensation. For an assumed OPR of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of {approx}2 Multiplication-Sign 10{sup 13} cm{sup -2} and {approx}1.2 Multiplication-Sign 10{sup 13} cm{sup -2}, respectively, for chloronium in these two sources. We obtained upper limits on the para-H{sup 35}{sub 2}Cl{sup +} line strengths toward H{sub 2} Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL 2591. The chloronium abundances inferred in this study are typically at least a factor {approx}10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine. Several explanations for this discrepancy were investigated, but none has proven satisfactory, and thus the large observed abundances of chloronium remain puzzling.

  19. Interstellar magnesium abundances

    NASA Technical Reports Server (NTRS)

    Murray, M. J.; Dufton, P. L.; Hibbert, A.; York, D. G.

    1984-01-01

    An improved evaluation of the Mg II 1240 A doublet oscillator strength is used in conjunction with recently published Copernicus observations to derive accurate Mg II column densities toward 74 stars. These imply an average of 40 percent of interstellar magnesium is in the gaseous phase. Magnesium depletion is examined as a function of various interstellar extinction and density parameters, and the results are briefly discussed in terms of current depletion theories.

  20. Interstellar Propulsion Concepts Assessment

    NASA Technical Reports Server (NTRS)

    Forward, Robert L.

    2000-01-01

    NASA is investigating the feasibility of conducting extra-solar and interstellar missions over the next 10 to 50 years. An assessment of technologies supporting these near and far term objectives is required. To help meet these objectives the Principal Investigator assessed the feasibility of candidate propulsion systems for the proposed 'Interstellar Probe', a mission to send a spacecraft to the Heliopause at 250 AU and beyond.

  1. Interstellar organic chemistry.

    NASA Technical Reports Server (NTRS)

    Sagan, C.

    1972-01-01

    Most of the interstellar organic molecules have been found in the large radio source Sagittarius B2 toward the galactic center, and in such regions as W51 and the IR source in the Orion nebula. Questions of the reliability of molecular identifications are discussed together with aspects of organic synthesis in condensing clouds, degradational origin, synthesis on grains, UV natural selection, interstellar biology, and contributions to planetary biology.

  2. Observations of interstellar zinc

    NASA Technical Reports Server (NTRS)

    York, D. G.; Jura, M.

    1982-01-01

    IUE observations toward 10 stars have shown that zinc is not depleted in the interstellar medium by more than a factor of two, suggesting that its abundance may serve as a tracer of the true metallicity in the gas. A result pertinent to the history of nucleosynthesis in the solar neighborhood is that the local interstellar medium has abundances that appear to be homogeneous to within a factor of two, when integrated over paths of about 500 pc.

  3. Interstellar chemistry - Polycyanoacetylene formation

    NASA Technical Reports Server (NTRS)

    Langer, W. D.; Schloerb, F. P.; Snell, R. L.; Young, J. S.

    1981-01-01

    It is argued that interstellar polycyanoacetylenes are formed not on dust grains by catalytic buildup or by dissociation of longer molecules, but rather by gas phase ion-molecule reactions. The primary evidence for this view is the detection of deuterated cyanoacetylene in an interstellar cloud. It is also argued that the relative abundance of successive homologs of polycyanoacetylenes rules out the grain catalysis theory.

  4. Discovery of interstellar rubidium

    NASA Technical Reports Server (NTRS)

    Jura, M.; Smith, W. H.

    1981-01-01

    Interstellar rubidium is detected through observations of the resonance line of Rb I at 7800 A towards zeta Oph. The abundance ratio of rubidium to potassium is estimated to be approximately solar, and if rubidium is generally found to have an abundance similar to potassium, it is indicated that the local interstellar medium is well mixed with a wide variety of the products of nucleosynthesis.

  5. Stellar and interstellar K lines - Gamma Pegasi and iota Herculis.

    NASA Technical Reports Server (NTRS)

    Hobbs, L. M.

    1973-01-01

    High-resolution scans show that the relatively strong (about 90 mA) K lines of Ca II in the early B stars gamma-Peg and iota-Her are almost entirely stellar in origin, although the latter case includes a small interstellar contribution. Such stellar lines can be of great importance in augmenting the interstellar absorption, up through the earliest of the B stars.

  6. Local interstellar medium and gamma-ray astronomy

    NASA Technical Reports Server (NTRS)

    Lebrun, F.; Paul, J.

    1985-01-01

    The recent improvement of the calibration of the galaxy counts used as an interstellar absorption tracer modifies significantly the picture of the local interstellar medium (ISM). Consequently, previous analyses of the gamma ray emission from the local ISM involving galaxy counts have to be revised. The implications regarding the cosmic ray (CR) density in the local ISM are considered and in particular within Loop I, a nearby supernova remnant (SNR).

  7. STIS Observations of Interstellar C I

    NASA Astrophysics Data System (ADS)

    Jenkins, E. B.

    2000-05-01

    In the interstellar medium, the excited fine-structure levels in the ground electronic state of neutral carbon can be populated by collisions with other atoms and electrons. In turn, the levels are depopulated by spontaneous radiative decays. The balance between these processes allows us to solve for the physical conditions in the C I-bearing clouds by measuring the relative populations in the three levels. For the most part, the thermal pressure of the gas p/k is the primary parameter that establishes the level populations. In an effort to sample p/k in different places, a survey of the UV spectra of 21 stars is underway using the highest resolution mode of the STIS instrument on HST. Most of the target stars are in the HST Continuous Viewing Zone (CVZ), which means that galactic longitudes 120+/- 20 and 300+/- 20 degrees are most heavily sampled. For each star, nine multiplets of C I between 1189 and 1656 Angstroms are recorded at a resolving power λ /Δ λ of about 200,000, revealing the details of the narrow C I velocity components in the absorption profiles. A special analysis technique developed for this survey can be used to unscramble the overlapping features within the multiplets (a different pattern in each case), so that the velocity profiles for the three levels can be derived without implementing tedious, trial-and-error model fitting procedures. Also, we can derive the relative strengths of the different multiplets and the lines within each multiplet. The survey is about half complete, and the conclusions derived so far about the distribution of thermal pressures will be presented. This research is supported by NASA contract NAG5-30110.

  8. Interstellar medium. Pseudo-three-dimensional maps of the diffuse interstellar band at 862 nm.

    PubMed

    Kos, Janez; Zwitter, Tomaž; Wyse, Rosemary; Bienaymé, Olivier; Binney, James; Bland-Hawthorn, Joss; Freeman, Kenneth; Gibson, Brad K; Gilmore, Gerry; Grebel, Eva K; Helmi, Amina; Kordopatis, Georges; Munari, Ulisse; Navarro, Julio; Parker, Quentin; Reid, Warren A; Seabroke, George; Sharma, Sanjib; Siebert, Arnaud; Siviero, Alessandro; Steinmetz, Matthias; Watson, Fred G; Williams, Mary E K

    2014-08-15

    The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research. PMID:25124434

  9. Copernicus observations of interstellar matter in the direction of HR 1099

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Weiler, E. J.

    1978-01-01

    Results are reported for high-resolution Copernicus U1 and V2 scans of the bright RS CVn spectroscopic binary HR 1099. The observations reveal strong UV emission lines at L-alpha and Mg II h and k from the stars as well as interstellar H I and D I L-alpha absorption lines and interstellar Mg II h and k absorption in the direction of the binary system. Column densities, bulk velocities, and temperatures are derived for the interstellar features. A comparison of the derived number density of interstellar H I with data for the nearby star Epsilon Eri indicates an inhomogeneous distribution of interstellar hydrogen along the line of sight. The range of values obtained for the D/H ratio is shown to be consistent with results of other studies. A depletion factor of at least 5 with respect to the solar abundance is estimated for the interstellar magnesium.

  10. Pathway to the identification of C60+ in diffuse interstellar clouds.

    PubMed

    Maier, John P; Campbell, Ewen K

    2016-09-13

    The origin of the attenuation of starlight in diffuse clouds in interstellar space at specific wavelengths ranging from the visible to the near-infrared has been unknown since the first astronomical observations around a century ago. The absorption features, termed the diffuse interstellar bands, have subsequently been the subject of much research. Earlier this year four of these interstellar bands were shown to be due to the absorption by cold, gas phase [Formula: see text] molecules. This discovery provides the first answer to the problem of the diffuse interstellar bands and leads naturally to fascinating questions regarding the role of fullerenes and derivatives in interstellar chemistry. Here, we review the identification process placing special emphasis on the laboratory studies which have enabled spectroscopic measurement of large cations cooled to temperatures prevailing in the interstellar medium.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501976

  11. Waves in Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Kamaya, H.

    1998-03-01

    Many hydrodynamical researches have been developed. Especially, analysis of the compressible flow is significantly improved by interstellar physicists. To obtain sufficient appreciation, we should not analyze only the effect of self-gravity of the system but also consider the property of inhomogeneity of the interstellar medium. I stress that another hydrodynamical approach is appreciated. That is the multi-phase-flow method. In the astrophysical context, there are few preliminary works of it. I intend to develop it in more suitable method for the interstellar physics. This dissertation is only the first step for me. But, fundamental properties of the multi-phase-flow are presented, considering the effect of compressibility, self-(and/or mutual) gravity, and friction between two phases. All of these properties are generally important to examine the origin, destruction and the global distribution of interstellar medium. My motivation is trying to delve into the global properties of the interstellar medium. The method of multi-phase-flow has great advantage for my aim, and its usefulness has been shown in this thesis.

  12. Interstellar Antifreeze: Ethylene Glycol

    NASA Astrophysics Data System (ADS)

    Hollis, J. M.; Lovas, F. J.; Jewell, P. R.; Coudert, L. H.

    2002-05-01

    Interstellar ethylene glycol (HOCH2CH2OH) has been detected in emission toward the Galactic center source Sagittarius B2(N-LMH) by means of several millimeter-wave rotational torsional transitions of its lowest energy conformer. The types and kinds of molecules found to date in interstellar clouds suggest a chemistry that favors aldehydes and their corresponding reduced alcohols-e.g., formaldehyde (H2CO)/methanol (CH3OH), acetaldehyde (CH3CHO)/ethanol (CH3CH2OH). Similarly, ethylene glycol is the reduced alcohol of glycolaldehyde (CH2OHCHO), which has also been detected toward Sgr B2(N-LMH). While there is no consensus as to how any such large complex molecules are formed in the interstellar clouds, atomic hydrogen (H) and carbon monoxide (CO) could form formaldehyde on grain surfaces, but such surface chemistry beyond that point is uncertain. However, laboratory experiments have shown that the gas-phase reaction of atomic hydrogen (H) and solid-phase CO at 10-20 K can produce formaldehyde and methanol and that alcohols and other complex molecules can be synthesized from cometary ice analogs when subject to ionizing radiation at 15 K. Thus, the presence of aldehyde/reduced alcohol pairs in interstellar clouds implies that such molecules are a product of a low-temperature chemistry on grain surfaces or in grain ice mantles. This work suggests that aldehydes and their corresponding reduced alcohols provide unique observational constraints on the formation of complex interstellar molecules.

  13. Interstellar Antifreeze: Ethylene Glycol

    NASA Technical Reports Server (NTRS)

    Hollis, J. M.; Lovas, F. J.; Jewell, P. R.; Coudert, L. H.

    2002-01-01

    Interstellar ethylene glycol (HOCH2CH2,OH) has been detected in emission toward the Galactic center source Sagittarius B2(N-LMH) by means of several millimeter-wave rotational torsional transitions of its lowest energy conformer. The types and kinds of molecules found to date in interstellar clouds suggest a chemistry that favors aldehydes and their corresponding reduced alcohols-e.g., formaldehyde (H2CO)/methanol (CH3OH), acetaldehyde (CH3CHO)/ethanol (CH3CH2OH). Similarly, ethylene glycol is the reduced alcohol of glycolaldehyde (CH2OHCHO), which has also been detected toward Sgr B2(N-LMH). While there is no consensus as to how any such large complex molecules are formed in the interstellar clouds, atomic hydrogen (H) and carbon monoxide (CO) could form formaldehyde on grain surfaces, but such surface chemistry beyond that point is uncertain. However, laboratory experiments have shown that the gas-phase reaction of atomic hydrogen (H) and solid-phase CO at 10-20 K can produce formaldehyde and methanol and that alcohols and other complex molecules can be synthesized from cometary ice analogs when subject to ionizing radiation at 15 K. Thus, the presence of aldehyde/ reduced alcohol pairs in interstellar clouds implies that such molecules are a product of a low-temperature chemistry on grain surfaces or in grain ice mantles. This work suggests that aldehydes and their corresponding reduced alcohols provide unique observational constraints on the formation of complex interstellar molecules.

  14. PAH Clusters and the Interstellar Infrared Emission Bands

    NASA Astrophysics Data System (ADS)

    Ricca, Alessandra; Roser, Joseph

    2016-06-01

    Polycyclic aromatic hydrocarbons (or PAHs) are the leading candidate for the emitters of the interstellar aromatic infrared emission bands. Some aspects of these emission bands indicate a contribution from PAH clusters. To better assess this contribution, we measured infrared absorption spectra of a series of homogeneous and heterogeneous PAH clusters using matrix isolation spectroscopy in solid argon and we performed theoretical calculations. The spectral shifts observed in the absorption spectra as a function of the PAH concentration can be related to preferred cluster structures forming in the argon matrix. Based upon our results, we predict that the large PAHs present in the interstellar medium are likely to have clusters with redshifted absorption bands in the C–H out-of-plane bending region. These clusters could contribute to a well-known red-shading observed in the profile of the interstellar 11.2 micron emission band.

  15. The interstellar gas experiment

    NASA Technical Reports Server (NTRS)

    Lind, D. L.; Geiss, J.; Buehler, F.; Eugster, O.

    1992-01-01

    The Interstellar Gas Experiment (IGE) exposed thin metallic foils to collect neutral interstellar gas particles. These particles penetrate the solar system due to their motion relative to the sun. Thus, it is possible to entrap them in the collecting foils along with precipitating magnetospheric and perhaps some ambient atmospheric particles. For the entire duration of the Long Duration Exposure Facility (LDEF) mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. In the mass spectroscopic analysis of the noble gas component of these particles, we have detected the isotopes of He-3, He-4, Ne-20, and Ne-22. In the foil analyses carried out so far, we find a distribution of particle arrival directions which shows that a significant part of the trapped particles are indeed interstellar atoms. The analysis needed to subtract the competing fluxes of magnetospheric and atmospheric particles is still in progress.

  16. Interstellar Deuterium Chemistry

    NASA Technical Reports Server (NTRS)

    Sandford, S. A.

    2003-01-01

    The presence of isotopic anomalies is the most unequivocal demonstration that meteoritic material contains circumstellar or interstellar components. In the case of organic compounds in meteorites and interplanetary dust particles (IDPs), the most useful isotopic tracer of interstellar components has been deuterium (D) excesses. In some cases these enrichments are seen in bulk meteoritic materials, but D enrichments have also been observed in meteoritic subfractions and even within specific classes of molecular species, such as amino and carboxylic acids. These anomalies are not thought to be the result of nucleosynthetic processes, but are instead ascribed to chemical and physical processes occurring in the interstellar medium (ISM). The traditional explanation of these D excesses has been to invoke the presence of materials made in the ISM by low temperature gas phase ion-molecule reactions. Indeed, the DM ratios seen in the simple interstellar gas phase molecules in cold dense clouds amenable to measurement using radio spectral techniques are generally considerably higher than the values seen in enriched Solar System materials. However, the true linkage between the DM ratios in interstellar and meteoritic materials is obscured by several effects. First, current observations of D enrichment in the ISM have been made of only a few simple molecules, molecules that are not the main carriers of D in Solar System materials. Second, some of the interstellar D enrichment is likely to reside on labile moieties that will have exchanged to some degree with more isotopically normal material during incorporation into the warm protosolar nebula, parent body processing, delivery, recovery, and analysis. Third, ion-molecule reactions represent only one of at least four processes that can produce strong D-H fractionation in the ISM.

  17. Time-dependent interstellar chemistry

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.

    1985-01-01

    Some current problems in interstellar chemistry are considered in the context of time-dependent calculations. The limitations of steady-state models of interstellar gas-phase chemistry are discussed, and attempts to chemically date interstellar clouds are reviewed. The importance of studying the physical and chemical properties of interstellar dust is emphasized. Finally, the results of a series of studies of collapsing clouds are described.

  18. Small-scale structure in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Meyer, David M.

    1990-01-01

    The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linear separations ranging from 5700 to 700 Au. Except for Kappa CrA, the strengths of the interstellar absorption lines toward both components of these binaries agree to within 10 percent. In the case of Kappa CrA, the optically thin interstellar Mg I and Mn II lines are about 50 percent stronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolution observations of interstellar Ca II show that this difference is concentrated in the main interstellar component at V(LSR) = 9 + or - 2 km/s. Interestingly, this velocity corresponds to an intervening cloud that may be associated with the prominent Loop I shell in the local ISM. Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, the line strength variations indicate that this cloud has structure on scales of 2800 AU or less.

  19. The Interstellar Medium in External Galaxies: Summaries of contributed papers

    NASA Technical Reports Server (NTRS)

    Hollenbach, David J. (Editor); Thronson, Harley A., Jr. (Editor)

    1990-01-01

    The Second Wyoming Conference entitled, The Interstellar Medium in External Galaxies, was held on July 3 to 7, 1989, to discuss the current understanding of the interstellar medium in external galaxies and to analyze the basic physical processes underlying interstellar phenomena. The papers covered a broad range of research on the gas and dust in external galaxies and focused on such topics as the distribution and morphology of the atomic, molecular, and dust components; the dynamics of the gas and the role of the magnetic field in the dynamics; elemental abundances and gas depletions in the atomic and ionized components; cooling flows; star formation; the correlation of the nonthermal radio continuum with the cool component of the interstellar medium; the origin and effect of hot galactic halos; the absorption line systems seen in distant quasars; and the effect of galactic collisions.

  20. Detection of organic matter in interstellar grains.

    PubMed

    Pendleton, Y J

    1997-06-01

    Star formation and the subsequent evolution of planetary systems occurs in dense molecular clouds, which are comprised, in part, of interstellar dust grains gathered from the diffuse interstellar medium (DISM). Radio observations of the interstellar medium reveal the presence of organic molecules in the gas phase and infrared observational studies provide details concerning the solid-state features in dust grains. In particular, a series of absorption bands have been observed near 3.4 microns (approximately 2940 cm-1) towards bright infrared objects which are seen through large column densities of interstellar dust. Comparisons of organic residues, produced under a variety of laboratory conditions, to the diffuse interstellar medium observations have shown that aliphatic hydrocarbon grains are responsible for the spectral absorption features observed near 3.4 microns (approximately 2940 cm-1). These hydrocarbons appear to carry the -CH2- and -CH3 functional groups in the abundance ratio CH2/CH3 approximately 2.5, and the amount of carbon tied up in this component is greater than 4% of the cosmic carbon available. On a galactic scale, the strength of the 3.4 microns band does not scale linearly with visual extinction, but instead increases more rapidly for objects near the Galactic Center. A similar trend is noted in the strength of the Si-O absorption band near 9.7 microns. The similar behavior of the C-H and Si-O stretching bands suggests that these two components may be coupled, perhaps in the form of grains with silicate cores and refractory organic mantles. The ubiquity of the hydrocarbon features seen in the near infrared near 3.4 microns throughout out Galaxy and in other galaxies demonstrates the widespread availability of such material for incorporation into the many newly forming planetary systems. The similarity of the 3.4 microns features in any organic material with aliphatic hydrocarbons underscores the need for complete astronomical observational

  1. Interstellar Panspermia Reconsidered

    NASA Astrophysics Data System (ADS)

    Zubrin, R.

    The absence of free-living microorganisms simpler than bacteria on Earth is evidence that life did not originate on Earth, but immigrated. The question then arises as to whether life was imported from a point of origin in our solar system, most likely Mars, of whether the solar system was seeded from interstellar sources. The search for fossil or extant prebacterial organisms (prebacteria) on Mars can resolve this question. However, to understand the likelihood of interstellar panspermia, we also need to consider whether the Earth itself has served as an efficient source for the spread of microorganisms. Close encounters with other stars due to random stellar motion occur with a frequency of 1/20 Myr, in fair agreement with the observed frequency of major impact events and mass extinctions. Such events are estimated to eject unsterilized material into interstellar space at a time-averaged rate of 10 tonnes per year. A number of mechanisms for the interstellar dissemination of bacteria along with this material are considered. It is shown that transmission of microbial life from one solar system to another is highly probable.

  2. Prebiologically Important Interstellar Molecules

    NASA Astrophysics Data System (ADS)

    Kuan, Y.-J.; Huang, H.-C.; Charnley, S. B.; Tseng, W.-L.; Snyder, L. E.; Ehrenfreund, P.; Kisiel, Z.; Thorwirth, S.; Bohn, R. K.; Wilson, T. L.

    2004-06-01

    Understanding the organic chemistry of molecular clouds, particularly the formation of biologically important molecules, is fundamental to the study of the processes which lead to the origin, evolution and distribution of life in the Galaxy. Determining the level of molecular complexity attainable in the clouds, and the nature of the complex organic material available to protostellar disks and the planetary systems that form from them, requires an understanding of the possible chemical pathways and is therefore a central question in astrochemistry. We have thus searched for prebiologically important molecules in the hot molecular cloud cores: Sgr B2(N-LMH), W51 e1/e2 and Orion-KL. Among the molecules searched: Pyrimidine is the unsubstituted ring analogue for three of the DNA and RNA bases. 2H-Azirine and Aziridine are azaheterocyclic compounds. And Glycine is the simplest amino acid. Detections of these interstellar organic molecular species will thus have important implications for Astrobiology. Our preliminary results indicate a tentative detection of interstellar glycine. If confirmed, this will be the first detection of an amino acid in interstellar space and will greatly strengthen the thesis that interstellar organic molecules could have played a pivotal role in the prebiotic chemistry of the early Earth.

  3. Molecules in interstellar clouds

    NASA Astrophysics Data System (ADS)

    Irvine, W. M.; Hjalmarson, A.; Rydbeck, O. E. H.

    The physical conditions and chemical compositions of the gas in interstellar clouds are reviewed in light of the importance of interstellar clouds for star formation and the origin of life. The Orion A region is discussed as an example of a giant molecular cloud where massive stars are being formed, and it is pointed out that conditions in the core of the cloud, with a kinetic temperature of about 75 K and a density of 100,000-1,000,000 molecules/cu cm, may support gas phase ion-molecule chemistry. The Taurus Molecular Clouds are then considered as examples of cold, dark, relatively dense interstellar clouds which may be the birthplaces of solar-type stars and which have been found to contain the heaviest interstellar molecules yet discovered. The molecular species identified in each of these regions are tabulated, including such building blocks of biological monomers as H2O, NH3, H2CO, CO, H2S, CH3CN and H2, and more complex species such as HCOOCH3 and CH3CH2CN.

  4. The Voyager Interstellar Mission.

    PubMed

    Rudd, R P; Hall, J C; Spradlin, G L

    1997-01-01

    The Voyager Interstellar Mission began on January 1, 1990, with the primary objective being to characterize the interplanetary medium beyond Neptune and to search for the transition region between the interplanetary medium and the interstellar medium. At the start of this mission, the two Voyager spacecraft had already been in flight for over twelve years, having successfully returned a wealth of scientific information about the planetary systems of Jupiter, Saturn, Uranus, and Neptune, and the interplanetary medium between Earth and Neptune. The two spacecraft have the potential to continue returning science data until around the year 2020. With this extended operating lifetime, there is a high likelihood of one of the two spacecraft penetrating the termination shock and possibly the heliopause boundary, and entering interstellar space before that time. This paper describes the Voyager Interstellar Mission--the mission objectives, the spacecraft and science payload, the mission operations system used to support operations, and the mission operations strategy being used to maximize science data return even in the event of certain potential spacecraft subsystem failures. The implementation of automated analysis tools to offset and enable reduced flight team staffing levels is also discussed. PMID:11540770

  5. Evolution of Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Allamandola, Lou J.; DeVincenzi, Donald L. (Technical Monitor)

    1998-01-01

    During the past two decades observations combined with laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the raw materials from which planets, comets and stars form. Most interstellar material is concentrated in large molecular clouds where simple molecules are formed by dust-grain and gas-phase reactions. Gaseous species striking the cold (10K) dust stick, forming an icy grain mantle. This accretion, coupled with UV photolysis, produces a complex chemical mixture containing volatile, non-volatile, and isotopically fractionated species. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, H2, and perhaps some NH3 and H2CO, as well as more complex species. The evidence for these compounds, as well as carbon-rich materials, will be reviewed and the possible connections with comets and meteorites will be presented in the first part of the talk . The second part of the presentation will focus on interstellar/precometary ice photochemical evolution and the species likely to be found in comets. The chemical composition and photochemical evolution of realistic interstellar/pre-cometary ice analogs will be discussed. Ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and more complex molecules. When ices representative of interstellar grains and comets are exposed to UV radiation at low temperature a series of moderately complex organic molecules are formed in the ice including: CH3CH2OH (ethanol), HC(=O)NH2 (formamide), CH3C(=O)NH2 (acetamide), and R-C=N (nitriles). Several of these are already known to be in the interstellar medium, and their presence indicates the importance of grain processing. After warming to room temperature an organic residue remains. This is composed primarily of hexamethylenetetramine (HMT, C6H12N4), with lesser amounts of polyoxymethylene-related species (POMs), amides, and ketones. This is in sharp contrast to the organic residues produced by

  6. Search for interstellar adenine

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Sandip K.; Majumdar, Liton; Das, Ankan; Chakrabarti, Sonali

    2015-05-01

    It is long debated if pre-biotic molecules are indeed present in the interstellar medium. Despite substantial works pointing to their existence, pre-biotic molecules are yet to be discovered with a complete confidence. In this paper, our main aim is to study the chemical evolution of interstellar adenine under various circumstances. We prepare a large gas-grain chemical network by considering various pathways for the formation of adenine. Majumdar et al. (New Astron. 20:15, 2013) proposed that in the absence of adenine detection, one could try to trace two precursors of adenine, namely, HCCN and NH2CN. Recently Merz et al. (J. Phys. Chem. A 118:3637-3644, 2014), proposed another route for the formation of adenine in interstellar condition. They proposed two more precursor molecules. But it was not verified by any accurate gas-grain chemical model. Neither was it known if the production rate would be high or low. Our paper fills this important gap. We include this new pathways to find that the contribution through this pathways for the formation of Adenine is the most dominant one in the context of interstellar medium. We propose that observers may look for the two precursors (C3NH and HNCNH) in the interstellar media which are equally important for predicting abundances of adenine. We perform quantum chemical calculations to find out spectral properties of adenine and its two new precursor molecules in infrared, ultraviolet and sub-millimeter region. Our present study would be useful for predicting abundance of adenine.

  7. The diffuse interstellar bands - a brief review

    NASA Astrophysics Data System (ADS)

    Geballe, T. R.

    2016-07-01

    The diffuse interstellar bands, or DIBs, are a large set of absorption features, mostly at optical and near infrared wavelengths, that are found in the spectra of reddened stars and other objects. They arise in interstellar gas and are observed toward numerous objects in our galaxy as well as in other galaxies. Although long thought to be associated with carbon-bearing molecules, none of them had been conclusively identified until last year, when several nearinfrared DIBs were matched to the laboratory spectrum of singly ionized buckminsterfullerene (C60 +). This development appears to have begun to solve what is perhaps the greatest unsolved mystery in astronomical spectroscopy. Also recently, new DIBs have been discovered at infrared wavelengths and are the longest wavelength DIBs ever found. I present the general characteristics of the DIBs and their history, emphasizing recent developments.

  8. Interstellar C3 toward HD 210121

    NASA Astrophysics Data System (ADS)

    Roueff, E.; Felenbok, P.; Black, J. H.; Gry, C.

    2002-03-01

    We report the detection of the 405 nm band of interstellar C3 in absorption toward HD 210121. The abundance of triatomic carbon is approximately 1/17 of that of diatomic carbon in the same diffuse molecular cloud. Rotational levels of C3 up to J=14 are seen in this cloud. The rotational excitation of C3 in the interstellar medium may reflect a competition between inelastic collisions, formation and destruction of the molecule, and radiative pumping in the far-infrared. The abundance of C3 is compared with chemical models. Attention is called to molecular properties that need to be better determined. Based on observations collected at the European Southern Observatory, Paranal, Chile [ESO VLT-UT2 No 65.I-0526(A)].

  9. Discovery of Interstellar Hydrogen Fluoride

    NASA Technical Reports Server (NTRS)

    Neufeld, David A.; Zmuidzinas, Jonas; Schilke, Peter; Phillips, Thomas G.

    1997-01-01

    We report the first detection of interstellar hydrogen fluoride. Using the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO), we have detected the 121.6973 micron J = 2-1 line of HF in absorption toward the far-infrared continuum source Sagittarius B2. The detection is statistically significant at the 13 sigma level. On the basis of our model for the excitation of HF in Sgr B2, the observed line equivalent width of 1.0 nm implies a hydrogen fluoride abundance of about 3 x 10 (exp -10) relative to H, If the elemental abundance of fluorine in Sgr B2 is the same as that in the solar system, then HF accounts for about 2% of the total number of fluorine nuclei. We expect hydrogen fluoride to be the dominant reservoir of gas-phase fluorine in Sgr B2, because it is formed rapidly in exothermic reactions of atomic fluorine with either water or molecular hydrogen; thus, the measured HF abundance suggests a substantial depletion of fluorine onto dust grains. Similar conclusions regarding depletion have previously been reached for the case of chlorine in dense interstellar clouds. We also find evidence at a lower level of statistical significance (about 5 sigma) for an emission feature at the expected position of the 4(sub 32)-4(sub 23) 121.7219 micron line of water. The emission-line equivalent width of 0.5 mm for the water feature is consistent with the water abundance of 5 x 10(exp -6) relative to H, that has been inferred previously from observations of the hot core of Sgr B2.

  10. Discovery of Interstellar Hydrogen Fluoride

    NASA Technical Reports Server (NTRS)

    Neufeld, David A.; Zmuidzinas, Jonas; Schilke, Peter; Phillips, Thomas G.

    1997-01-01

    We report the first detection of interstellar hydrogen fluoride. Using the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO), we have detected the 121.6973 micron J = 2-1 line of HF in absorption toward the far-infrared continuum source Sagittarius B2. The detection is statistically significant at the 13 sigma level. On the basis of our model for the excitation of HF in Sgr B2, the observed line equivalent width of 1.0 nm implies a hydrogen fluoride abundance of approximately 3 x 10(exp -10) relative to H2. If the elemental abundance of fluorine in Sgr B2 is the same as that in the solar system, then HF accounts for approximately 2% of the total number of fluorine nuclei. We expect hydrogen fluoride to be the dominant reservoir of gas-phase fluorine in Sgr B2, because it is formed rapidly in exothermic reactions of atomic fluorine with either water or molecular hydrogen; thus, the measured HF abundance suggests a substantial depletion of fluorine onto dust grains. Similar conclusions regarding depletion have previously been reached for the case of chlorine in dense interstellar clouds. We also find evidence at a lower level of statistical significance (approximately 5 sigma) for an emission feature at the expected position of the 4(sub 32)-4(sub 23) 121.7219 micron line of water. The emission-line equivalent width of 0.5 nm for the water feature is consistent with the water abundance of 5 x 10(exp -6) relative to H2 that has been inferred previously from observations of the hot core of Sgr B2.

  11. Ubiquitous Argonium, ArH^+, in the Diffuse Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Schilke, P.; Müller, Holger S. P.; Comito, C.; Sanchez-Monge, A.; Neufeld, D. A.; Indriolo, Nick; Bergin, Edwin; Lis, D. C.; Gerin, Maryvonne; Black, J. H.; Wolfire, M. G.; Pearson, John; Menten, Karl; Winkel, B.

    2014-06-01

    ArH^+ is isoelectronic with HCl. The J = 1 - 0 and 2 - 1 transitions of 36ArH^+ near 617.5 and 1234.6 GHz, respectively, have been identified very recently as emission lines in spectra obtained with Herschel toward the Crab Nebula supernova remnant. On Earth, 40Ar is by far the most abundant isotope, being almost exclusively formed by the radioactive decay of 40K. However, 36Ar is the dominant isotope in the Universe. In the course of unbiased line surveys of the massive and very luminous Galactic Center star-forming regions Sagittarius B2(M) and (N) with the high-resolution instrument HIFI on board of Herschel, we detected the J = 1 - 0 transition of 36ArH^+ as a moderately strong absorption line initially associated with an unidentified carrier. In both cases, the absorption feature is unique in its appearance at all velocity components associated with diffuse foreground molecular clouds, together with its conspicuous absence at velocities related to the denser sources themselves. Model calculations are able to reproduce the derived ArH^+ column densities and suggest that argonium resides in the largely atomic, diffuse interstellar medium with a molecular fraction of no more than ˜10-4. The 38ArH^+ isotopolog was also detected. Subsequent observations toward the continuum sources W51, W49, W31C, and G34.3+0.1 resulted in unequivocal detections of 36ArH^+ absorption. Hence, argonium is a good probe of the transition zone between atomic and molecular gas, in particular in combination with OH^+ and H_2O^+, whose abundances peak at a molecular fraction of ˜0.1. Moreover, argonium is a good indicator of an enhanced cosmic ray ionization rate. Therefore, it may be prominent toward, e.g., active galactic nuclei (AGNs) in addition to supernova remnants. M. J. Barlow et al., Science 342 (2013) 1343. H. S. P. Müller et al., Proceedings of the IAU Symposium 297, 2013, "The Diffuse Interstellar Bands", Eds. J. Cami & N. Cox.

  12. Observations of the interstellar gas with the Copernicus satellite

    NASA Technical Reports Server (NTRS)

    Morton, D. C.

    1975-01-01

    Results are reviewed for Copernicus far-UV measurements of the absorption lines of H I, D I, H2, and heavier elements in the interstellar gas. Column densities along several lines of sight, as estimated from Ly-alpha absorption-line profiles, confirm that wide differences in the gas density are present in various directions. The measurement of interstellar D I implies an open universe unless alternate sources for this nuclide are found. Analysis of reddened stars for which the line of sight passes through one or more interstellar clouds indicates a depletion of several heavy elements in the gas. It is suggested that the depleted elements may be present in grains rather than molecules and that the intercloud medium may consist primarily of H II with a few small H I clouds.

  13. Local Interstellar Medium. International Astronomical Union Colloquium No. 81

    NASA Technical Reports Server (NTRS)

    Kondo, Y. (Editor); Bruhweiler, F. C. (Editor); Savage, B. D. (Editor)

    1984-01-01

    Helium and hydrogen backscattering; ultraviolet and EUV absorption spectra; optical extinction and polarization; hot gases; soft X-ray observations; infrared and millimeter wavelengths; radio wavelengths and theoretical models of the interstellar matter within about 150 parsecs of the Sun were examined.

  14. The Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M.

    1995-01-01

    The Interstellar Medium (ISM) forms an integral part of the lifecycle of stars and the galaxy. Stars are formed by gravitational contraction of interstellar clouds. Over their life, stars return much of their mass to the ISM through winds and supernova explosions, resulting in a slow enrichment in heavy elements. Understanding the origin and evolution of the ISM is a key problem within astrophysics. The KAO has made many important contributions to studies of the interstellar medium both on the macro and on the micro scale. In this overview, I will concentrate on two breakthroughs in the last decade in which KAO observations have played a major role: (1) the importance of large Polycyclic Aromatic Hydrocarbon (PAH) molecules for the ISM (section 3) and (2) the study of Photodissociation Regions (PDRs) as an analog for the diffuse ISM at large (section 4). Appropriately, the micro and macro problem are intricately interwoven in these problems. Finally, section 5 reviews the origin of the (CII) emission observed by COBE.

  15. The Local Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Redfield, S.

    2006-09-01

    The Local Interstellar Medium (LISM) is a unique environment that presents an opportunity to study general interstellar phenomena in great detail and in three dimensions. In particular, high resolution optical and ultraviolet spectroscopy have proven to be powerful tools for addressing fundamental questions concerning the physical conditions and three-dimensional (3D) morphology of this local material. After reviewing our current understanding of the structure of gas in the solar neighborhood, I will discuss the influence that the LISM can have on stellar and planetary systems, including LISM dust deposition onto planetary atmospheres and the modulation of galactic cosmic rays through the astrosphere --- the balancing interface between the outward pressure of the magnetized stellar wind and the inward pressure of the surrounding interstellar medium. On Earth, galactic cosmic rays may play a role as contributors to ozone layer chemistry, planetary electrical discharge frequency, biological mutation rates, and climate. Since the LISM shares the same volume as practically all known extrasolar planets, the prototypical debris disks systems, and nearby low-mass star-formation sites, it will be important to understand the structures of the LISM and how they may influence planetary atmospheres.

  16. Innovative interstellar explorer

    NASA Astrophysics Data System (ADS)

    McNutt, R.; Innovative Interstellar Explorer Team

    Fundamental scientific questions about the interaction of the Sun with the interstellar medium can only be answered with in situ measurements. The problem is the development of a probe that can provide the required measurements and can reach a heliocentric distance of at least 200 astronomical units (AU) in 15 years or less, an average speed almost four times the 3.6 AU/yr speed of Voyager 1. The Innovative Interstellar Explorer (IIE) and its use of Radioisotope Electric Propulsion (REP) is now being studied under a NASA Vision Mission grant to enable such a mission. Speed is provided by a high-energy launch using current launch vehicle technology followed by long-term, low-thrust, continuous acceleration. The latter is provided by a kilowatt-class ion thruster running off of electricity provided by advanced Stirling radioisotope generators (SRGs) powered by Pu-238. While subject to mass and power limitations for the instruments on board, such an approach relies on known General Purpose Heat Source (GPHS) Pu-238 technology and current launch vehicles for speed, both of which require little new development and have well-known regulatory requirements for launch. In addition, this approach avoids the intrinsically large masses associated with nuclear fission reactors and incorporates launch of all nuclear material directly into an Earth-escape trajectory. We discuss the ongoing trade studies and development of this approach to an Interstellar Probe

  17. Interstellar Grain Surface Chemistry

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M.; Cuzzi, Jeffrey N. (Technical Monitor)

    1995-01-01

    Chemistry on grain surfaces plays an Important role in the formation of interstellar Ices, It can also influence the composition of the gas phase through outgassing near luminous, newly formed stars. This paper reviews the chemical processes taking place on Interstellar grain surfaces with the emphasis on those transforming CO into other hydrocarbons. At low, molecular cloud temperatures (approximately equal to 10K), physisorption processes dominate interstellar grain surface chemistry and GO is largely hydrogenated through reactions with atomic H and oxidized through reactions with atomic O. The former will lead to the formation of H2CO and CH3OH ices, while the latter results in CO2 ice. The observational evidence for these ices in molecular clouds will be discussed. Very close to protostars, the gas and grain temperatures are much higher (approximately equal to 500K) and chemisorption processes, including catalytic surface reactions, becomes important. This will be illustrated based upon our studies of the Fischer-Tropsch Synthesis of CH4 from CO on metallic surfaces. Likely, this process has played an important role in the early solar nebula. Observational consequences will be pointed out.

  18. The effect of temperature and pressure on optical absorption spectra of transition zone minerals - Implications for the radiative conductivity of the Earth's interior

    NASA Astrophysics Data System (ADS)

    Thomas, S.; Jacobsen, S. D.; Bina, C. R.; Goncharov, A. F.; Frost, D. J.; McCammon, C. A.

    2010-12-01

    Optical absorption spectra of high-pressure minerals can be used as indirect tools to calculate radiative conductivities of the Earth’s interior [e.g., 1]. Recent high-pressure studies imply that e.g. ringwoodite, γ-(Mg,Fe)2SiO4, does not become opaque in the near infrared and visible region, as previously assumed, but remains transparent to 21.5 GPa [2]. Therefore, it has been concluded that radiative heat transfer does not necessarily become blocked at high pressures of the mantle and ferromagnesian minerals actually might contribute to the heat flow in the Earth’s interior [2]. However, experimental results on temperature effects on radiative heat transfer are not available. We studied the effect of both, pressure and temperature, on the optical absorption of hydrous Fe-bearing ringwoodite, γ-(Mg,Fe)2SiO4, and hydrous Fe-bearing wadsleyite, β-(Mg,Fe)2SiO4, which are the main components of the Earth’s transition zone. Gem-quality single-crystals were synthesized at 18 GPa and 1400 °C in a 5000t multianvil apparatus. Crystals were analyzed by Mössbauer and Raman spectroscopy, electron microprobe analysis and single-crystal X-ray diffraction. For optical absorption measurements in the IR - VIS - UV spectral range (400 - 50000 cm-1) 50 µm sized single-crystals of ringwoodite and wadsleyite were double polished to thicknesses of 13 µm and 18 µm, respectively, and loaded in resistively heated diamond-anvil cells with argon as pressure medium. After taking measurements at high pressure and room temperature, ringwoodite was studied at 26 GPa up to 650 °C and wadsleyite spectra were recorded at 16 GPa up to 450 °C. At ambient pressure the absorption spectrum of ringwoodite reveals a crystal field band (Fe2+) at 12075 cm-1, an intervalence charge transfer band (Fe2+ to Fe3+) at 16491 cm-1, and an absorption edge due to ligand-metal charge transfer close to 30000 cm-1. The wadsleyite spectrum is characterized by a similar absorption edge in the VIS-UV range

  19. Infra-red absorption lines by molecules in grain mantles

    NASA Astrophysics Data System (ADS)

    Hagen, W.; Allamandola, L. J.; Greenberg, J. M.

    1980-06-01

    The laboratory spectrum of a solid mixture of H2O, CO, CH3OH, and NH3 at a temperature of 10 K reproduces the shape and peak positions of interstellar features. It is shown that the broad absorption features evident in the MIR spectra of some astronomical objects associated with interstellar dust can be explained by absorptions of molecules in grain mantles.

  20. Thermalization of Interstellar CO

    NASA Astrophysics Data System (ADS)

    Oka, Takeshi; Xiao, Han; Lynch, Phillip

    2009-06-01

    Unlike radio emission of CO, infrared absorption of CO give column densities in each rotational level directly when weak transitions like overtone bands or ^{13}CO or C^{18}O isotope bands are used. This allows more straightforward determination of temperature (T) and density (n) of the environment than the large velocity gradient (LVG) model used to determine them from antenna temperatures of radio emission. In order to facilitate such determination, we have solved the steady state linear simultaneous equations for thermalization of CO and calculated population ratios of rotational levels as a function of T and n as we did for H_3^+. We thus get two-dimensional graph of column density ratios, for example, N(J=1)/N(J=0) and N(J=2)/N(J=0) as a function of T and n or variation of it when other population ratios are used. As for H_3^+ we can invert the graph to obtain graphs of T versus n as functions of population ratios which is more convenient to apply to observed data. We use rate constants of collision-induced transitions between CO and ortho- and para-H_2 theoretically calculated by Fowler and Wernli et al. which have been compiled and extended by Schöier et al. As the first approximation, only spontaneous emissions are considered and other radiative effects such as induced emission and absorption are ignored. The results are applied to CO column densities observed toward the Galactic center, that is, CO in the three spiral arms, 3-kpc (Norma), 4.5-kpc (Scutum), and local arms (Sagittarius), and in the Central Molecular Zone. T. Oka and E. Epp, ApJ, 613, 349 (2004) M. Goto, Usuda, Nagata, Geballe, McCall, Indriolo, Suto, Henning, Morong, and Oka, ApJ, 688, 306 (2008) D. R. Fowler, J. Phys. B: At. Mol. Opt. Phys. 34, 2731 (2001) M. Wernli, P. Valiron, A. Faure, L. Wiesenfeld, P. Jankowski, and K. Szalewicz, A & A, 446, 367 (2006) F. L. Schöier, F. F. S. van der Tak, E. F. van Dishoeck, and J. H. Black, A & A, 432, 369 (2005)

  1. PAHs and the Diffuse Interstellar Bands. What have we Learned from the New Generation of Laboratory and Observational Studies?

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2005-01-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones, An extensive laboratory program has been developed at NASA Ames to characterize the physical and chemical properties of PAHs in astrophysical environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-W and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong V W radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral

  2. Non-equilibrium processes in interstellar molecules

    NASA Technical Reports Server (NTRS)

    Strelnitskiy, V. S.

    1979-01-01

    The types of nonequilibrium emission and absorption by interstellar molecules are summarized. The observed brightness emission temperatures of compact OH and H2O sources are discussed using the concept of maser amplification. A single thermodynamic approach was used in which masers and anti-masers are considered as heat engines for the theoretical interpretation of the cosmic maser and anti-maser phenomena. The requirements for different models of pumping are formulated and a classification is suggested for the mechanisms of pumping, according to the source and discharge of energy.

  3. The Nature of Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Huss, G. R.

    2003-01-01

    The STARDUST mission is designed to collect dust the coma of comet Wild 2 and to collect interstellar dust on a second set of collectors. We have a reasonable idea of what to expect from the comet dust collection because the research community has been studying interplanetary dust particles for many years. It is less clear what we should expect from the interstellar dust. This presentation discusses what we might expect to find on the STARDUST interstellar dust collector.

  4. Properties of interstellar dust in reflection nebulae

    NASA Technical Reports Server (NTRS)

    Sellgren, Kristin

    1988-01-01

    Observations of interstellar dust in reflection nebulae are the closest analog in the interstellar medium to studies of cometary dust in our solar system. The presence of a bright star near the reflection nebula dust provides the opportunity to study both the reflection and emission characteristics of interstellar dust. At 0.1 to 1 micrometer, the reflection nebula emission is due to starlight scattered by dust. The albedo and scattering phase function of the dust is determined from observations of the scattered light. At 50 to 200 micrometers, thermal emission from the dust in equilibrium with the stellar radiation field is observed. The derived dust temperature determines the relative values of the absorption coefficient of the dust at wavelengths where the stellar energy is absorbed and at far infrared wavelengths where the absorbed energy is reradiated. These emission mechanisms directly relate to those seen in the near and mid infrared spectra of comets. In a reflection nebula the dust is observed at much larger distances from the star than in our solar system, so that the equilibrium dust temperature is 50 K rather than 300 K. Thus, in reflection nebulae, thermal emission from dust is emitted at 50 to 200 micrometer.

  5. The Abundance of Interstellar Fluorine

    NASA Technical Reports Server (NTRS)

    Lauroesch, James T.

    2005-01-01

    The primary objective of this program was to obtain FUSE observations of the interstellar absorption lines of F I at 951 and 954 Angstroms to derive the abundance of fluorine toward the star HD 164816. The nucleosynthetic source(s) of fluorine are still a matter of debate - the present day abundance of fluorine can potentially constrain models for pulsationally driven dredge-up in asymptotic giant branch stars. An accurate measure for the depletion behavior of fluorine will determine whether it may be detectable in QSO absorption line systems - an unambiguous detection of fluorine at suitably high redshifts would provide the best evidence to date for the neutrino process in massive stars. Furthermore, due to its extreme reactivity, measurement of the gas-phase interstellar fluorine abundance is important for models of grain chemistry. Despite the importance of measuring the interstellar fluorine abundance, at the time of our proposal only one previous detection has been made due to the low relative abundance of fluorine, the lack of lines outside the far-UV, and the blending of the available F I transitions with lines of Hz. The star HD 164816 is associated with the Lagoon nebula (M8), and at a distance of approximately 1.5 kpc probes both distant and local gas. Beginning April 8th, 2004 FUSE FP-Split observations of the star HD 164816 were obtained for this program. This data became available in the FUSE data archive May 21, 2004, and these observations were then downloaded and we began our analysis. Our analysis procedure has involved (1) fitting stellar models to the FUSE spectra, (2) using the multiple lines of Hz and N I at other wavelengths in the FUSE bandpass to derive column densities for the lines of H2 and N I which are blended with the F I features at 951 and 954 angstroms (3) the measurement of the column densities of F I and the species O I and C1 I which are important species for the dis-entangling of dust and nucleosynthetic effects. As discussed in

  6. Gas Phase Spectroscopy of Cold PAH Ions: Contribution to the Interstellar Extinction and the Diffuse Interstellar Bands

    NASA Technical Reports Server (NTRS)

    Biennier, L.; Salama, F.; Allamandola, L. J.; Scherer, J. J.; OKeefe, A.

    2002-01-01

    Polycyclic Aromatic Hydrocarbon molecules (PAHs) are ubiquitous in the interstellar medium (ISM) and constitute the building blocks of interstellar dust grains. Despite their inferred important role in mediating the energetic and chemical processes in thc ISM, their exact contribution to the interstellar extinction, and in particular to the diffuse interstellar bands (DIBs) remains unclear. The DIBs are spectral absorption features observed in the line of sight of stars that are obscured by diffuse interstellar clouds. More than 200 bands have been reported to date spanning from the near UV to the near IR with bandwidths ranging from 0.4 to 40 Angstroms (Tielens & Snow 1995). The present consensus is that the DIBs arise from free flying, gas-phase, organic molecules and/or ions that are abundant under the typical conditions reigning in the diffuse ISM. PAHs have been proposed as possible carriers (Allamandola et al. 1985; Leger & DHendecourt 1985). The PAH hypothesis is consistent with the cosmic abundance of Carbon and Hydrogen and with the required photostability of the DIB carriers against the strong VUV radiation field in the diffuse interstellar clouds. A significant fraction of PAHs is expected to be ionized in the diffuse ISM.

  7. Interstellar clouds and molecular hydrogen

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1977-01-01

    Data obtained from the Copernicus Orbiting Astronomical Observatory, launched in 1972 and still obtaining information, are used in a discussion of the interstellar medium. The Copernicus instruments have facilitated direct estimates for the density and temperature of individual interstellar clouds, and improved the ability to determine where along the line of sight a cloud lies with respect to background stars. The physical characteristics of hydrogen molecules are considered, with attention to the formation and destruction of interstellar hydrogen. The differences between 'thin' clouds, in which molecular hydrogen is optically thin, and 'thick' clouds are examined. Several features of the interstellar medium are described.

  8. Stardust Interstellar Preliminary Examination

    NASA Astrophysics Data System (ADS)

    Westphal, A.; Stardust Interstellar Preliminary Examation Team: http://www. ssl. berkeley. edu/~westphal/ISPE/

    2011-12-01

    A. J. Westphal, C. Allen, A. Ansari, S. Bajt, R. S. Bastien, H. A. Bechtel, J. Borg, F. E. Brenker, J. Bridges, D. E. Brownlee, M. Burchell, M. Burghammer, A. L. Butterworth, A. M. Davis, P. Cloetens, C. Floss, G. Flynn, D. Frank, Z. Gainsforth, E. Grün, P. R. Heck, J. K. Hillier, P. Hoppe, G. Huss, J. Huth, B. Hvide, A. Kearsley, A. J. King, B. Lai, J. Leitner, L. Lemelle, H. Leroux, R. Lettieri, W. Marchant, L. R. Nittler, R. Ogliore, F. Postberg, M. C. Price, S. A. Sandford, J.-A. Sans Tresseras, T. Schoonjans, S. Schmitz, G. Silversmit, A. Simionovici, V. A. Solé, R. Srama, T. Stephan, V. Sterken, J. Stodolna, R. M. Stroud, S. Sutton, M. Trieloff, P. Tsou, A. Tsuchiyama, T. Tyliszczak, B. Vekemans, L. Vincze, D. Zevin, M. E. Zolensky, >29,000 Stardust@home dusters ISPE author affiliations are at http://www.ssl.berkeley.edu/~westphal/ISPE/. In 2000 and 2002, a ~0.1m2 array of aerogel tiles and alumi-num foils onboard the Stardust spacecraft was exposed to the interstellar dust (ISD) stream for an integrated time of 200 days. The exposure took place in interplanetary space, beyond the orbit of Mars, and thus was free of the ubiquitous orbital debris in low-earth orbit that precludes effective searches for interstellar dust there. Despite the long exposure of the Stardust collector, <<100 ISD particles are expected to have been captured. The particles are thought to be ~1μm or less in size, and the total ISD collection is probably <10-6 by mass of the collection of cometary dust parti-cles captured in the Stardust cometary dust collector from the coma of the Jupiter-family comet Wild 2. Thus, although the first solid sample from the local interstellar medium is clearly of high interest, the diminutive size of the particles and the low numbers of particles present daunting challenges. Nevertheless, six recent developments have made a Preliminary Examination (PE) of this sample practical: (1) rapid automated digital optical scanning microscopy for three

  9. Interstellar Dust Instrumentation

    NASA Astrophysics Data System (ADS)

    Sternovsky, Zoltan; Gruen, E.; Horanyi, M.; Drake, K.; Collette, A.; Kempf, S.; Srama, R.; Postberg, F.; Krueger, H.; Auer, S.

    2010-10-01

    Interstellar grains traversing the inner planetary system have been identified by the Ulysses dust detector. Space dust detectors on other missions confirmed this finding. Analysis of the Stardust collectors is under way to search for and analyze such exotic grains. Interstellar dust particles can be detected and analyzed in the near-Earth space environment. New instrumentation has been developed to determine the origin of dust particles and their elemental composition. A Dust Telescope is a combination of a Dust Trajectory Sensor (DTS, Rev. Sci. Instrum. 79, 084501, 2008) together with a high mass resolution mass analyzer for the chemical composition of dust particles in space. Dust particles' trajectories are determined by the measurement of induced electric signals when a charged grain flies through a position sensitive electrode system. A modern DTS can measure dust particles as small as 0.2 micron in radius and dust speeds up to 100 km/s. Large area chemical analyzers of 0.1 m2 sensitive area have been tested at a dust accelerator and it was demonstrated that they have sufficient mass resolution to resolve ions with atomic mass number up to >100 (Earth, Moon and Planets, DOI: 10.1007/s11038-005-9040-z, 2005; Rev. Sci. Instrum. 78, 014501, 2007). The advanced Dust Telescope is capable of identifying interstellar and interplanetary grains, and measuring their mass, velocity vector, charge, elemental and isotopic compositions. An Active Dust Collector combines a DTS with an aerogel or other dust collector materials, e.g. like the ones used on the Stardust mission. The combination of a DTS with a dust collector provides not only individual trajectories of the collected particles but also their impact time and position on the collector which proves essential in finding collected sub-micron sized grains on the collector.

  10. Innovative interstellar explorer

    NASA Astrophysics Data System (ADS)

    McNutt, Ralph L.; Gold, Robert E.; Krimigis, Tom; Roelof, Edmond C.; Gruntman, Mike; Gloeckler, George; Koehn, Patrick L.; Kurth, William S.; Oleson, Steven R.; Fiehler, Douglas I.; Horanyi, Mihaly; Mewaldt, Richard A.; Leary, James C.; Anderson, Brian J.

    2006-09-01

    An interstellar ``precursor'' mission has been under discussion in the scientific community for at least 30 years. Fundamental scientific questions about the interaction of the Sun with the interstellar medium can only be answered with in situ measurements that such a mission can provide. The Innovative Interstellar Explorer (IIE) and its use of Radioisotope Electric Propulsion (REP) is being studied under a NASA ``Vision Mission'' grant. Speed is provided by a combination of a high-energy launch, using current launch vehicle technology, a Jupiter gravity assist, and long-term, low-thrust, continuous acceleration provided by an ion thruster running off electricity provided by advanced radioisotope electric generators. A payload of ten instruments with an aggregate mass of ~35 kg and requiring ~30 W has been carefully chosen to address the compelling science questions. The nominal 20-day launch window opens on 22 October 2014 followed by a Jupiter gravity assist on 5 February 2016. The REP system accelerates the spacecraft to a ``burnout'' speed of 7.8 AU per year at 104 AU on 13 October 2032 (Voyager 1's current speed is ~3.6 AU/yr). The spacecraft will return at least 500 bits per second from at least 200 AU ~30 years after launch. Additional (backup) launch opportunities occur every 13 months to early 2018. In addition to addressing basic heliospheric science, the mission will ensure continued information on the far-heliospheric galactic cosmic ray population after the Voyagers have fallen silent and as the era of human Mars exploration begins.

  11. Interstellar and Circumstellar Fullerenes

    NASA Astrophysics Data System (ADS)

    Bernard-Salas, J.; Cami, J.; Jones, A.; Peeters, E.; Micelotta, E.; Otsuka, M.; Sloan, G. C.; Kemper, F.; Groenewegen, M.

    Fullerenes are a particularly stable class of carbon molecules in the shape of a hollow sphere or ellipsoid that might be formed in the outflows of carbon stars. Once injected into the interstellar medium (ISM), these stable species survive and are thus likely to be widespread in the Galaxy where they contribute to interstellar extinction, heating processes, and complex chemical reactions. In recent years, the fullerene species C60 (and to a lesser extent C70 ) have been detected in a wide variety of circumstellar and interstellar environments showing that when conditions are favourable, fullerenes are formed efficiently. Fullerenes are the first and only large aromatics firmly identified in space. The detection of fullerenes is thus crucial to provide clues as to the key chemical pathways leading to the formation of large complex organic molecules in space, and offers a great diagnostic tool to describe the environment in which they reside. Since fullerenes share many physical properties with PAHs, understanding how fullerenes form, evolve and respond to their physical environment will yield important insights into one of the largest reservoirs of organic material in space. In spite of all these detections, many questions remain about precisely which members of the fullerene family are present in space, how they form and evolve, and what their excitation mechanism is. We present here an overview of what we know from astronomical observations of fullerenes in these different environments, and discuss current thinking about the excitation process. We highlight the various formation mechanisms that have been proposed, discuss the physical conditions conducive to the formation and/or detection of fullerenes in carbon stars, and their possible connection to PAHs, HACs and other dust features.

  12. Interstellar abundance and depletion studies along Galactic sightlines

    NASA Astrophysics Data System (ADS)

    Haris, U.; Murthy, Jayant; Sofia, Ulysses

    2016-07-01

    The Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) has enhanced our understanding many aspects of interstellar medium of our galaxy. The wavelength coverage of FUSE and HST is of great astrophysical importance. We use FUSE and HST data for interstellar abundances studies of some important atomic species, such as sulphur and silicon. We report the newly derived column densities by measuring the equivalent widths of several ultraviolet absorption lines. Comparisons of observed depletions and grain properties with existing dust models will be discussed.

  13. The interstellar medium and the soft X-ray background

    NASA Technical Reports Server (NTRS)

    Snowden, S. L.

    1996-01-01

    The soft X-ray background (SXRB) surface brightness provides data to study the approximately 10(exp 6) K plasma of the local interstellar medium of our Galaxy. Various studies were carried out in order to search for negative correlation, or shadowing, of the SXRB, and were coupled with interstellar medium absorption line studies. The purpose was to determine whether the distances to the shadowing material will lead to a three dimensional mapping of the X-ray emitting, and X-ray absorbing components.

  14. The interstellar carbon abundance. II - Rho Ophiuchi and Beta Scorpii

    NASA Technical Reports Server (NTRS)

    Welty, D. E.; York, D. G.; Hobbs, L. M.

    1986-01-01

    A procedure designed to obtain increased sensitivity from high-dispersion IUE spectra by using a flat-field spectrum to remove nonrandom noise due to the response pattern of the SEC vidicon detector is described. Application of this procedure to spectra of Rho Oph and Beta(1) Sco near the spin-forbidden interstellar 2325 line of C II yields 2 sigma upper limits on absorption of W (lambda) not greater than about 4 mA. The resulting depletion of carbon from the interstellar gas toward Rho Oph exceeds a factor of 1.4.

  15. The Interstellar Heliopause Probe

    NASA Astrophysics Data System (ADS)

    Lyngvi, A.; Falkner, P.; Peacock, A.

    The Interstellar Heliopause Probe (IHP) is one of four Technology Reference Missions (TRM) introduced by the Planetary Exploration Studies Section of the Science Payload & Advanced Concepts Office (SCI-A) at ESA. The overall purpose of the TRMs is to focus the development of strategically important technologies of likely relevance to future science missions. This is accomplished through the study of several technologically demanding and scientifically interesting missions, which are currently not part of the ESA science programme. The TRM baseline uses small satellites (< 200kg), with highly miniaturized and highly integrated payload suites. The motivation for this is to use low resource spacecraft in a phased approach, which will reduce the risk and cost, compared to a single, high resource mission. Equipped with a Highly Integrated Payload Suite (HIPS) the IHP will answer scientific questions concerning the nature of the interstellar medium, how the interstellar medium affects our solar system and how the solar system impacts the interstellar medium. The HIPS, which is a standard element in all TRMs miniaturize through resource reduction, by using miniaturized components and sensors, and by sharing common structures and payload functionality. To achieve the scientific requirements of the mission the spacecraft is to leave the solar system as close to the heliosphere nose as possible and reach a distance of 200 AU from the Sun within 25 years. The requirement of all TRMs is to use a Souyz-Fregat version 2B or equivalent low cost launch vehicle. With this constraint no current propulsion system is capable of delivering the necessary mass to the final destination. Technologies are therefore needed to enable this mission. The current alternatives are using nuclear propulsion, either with radioisotope or reactor power system or solar sailing. All these alternatives are currently being investigated. Other challenges exist as well such as designing a communication link

  16. Visualizing Interstellar's Wormhole

    NASA Astrophysics Data System (ADS)

    James, Oliver; von Tunzelmann, Eugénie; Franklin, Paul; Thorne, Kip S.

    2015-06-01

    Christopher Nolan's science fiction movie Interstellar offers a variety of opportunities for students in elementary courses on general relativity theory. This paper describes such opportunities, including: (i) At the motivational level, the manner in which elementary relativity concepts underlie the wormhole visualizations seen in the movie; (ii) At the briefest computational level, instructive calculations with simple but intriguing wormhole metrics, including, e.g., constructing embedding diagrams for the three-parameter wormhole that was used by our visual effects team and Christopher Nolan in scoping out possible wormhole geometries for the movie; (iii) Combining the proper reference frame of a camera with solutions of the geodesic equation, to construct a light-ray-tracing map backward in time from a camera's local sky to a wormhole's two celestial spheres; (iv) Implementing this map, for example, in Mathematica, Maple or Matlab, and using that implementation to construct images of what a camera sees when near or inside a wormhole; (v) With the student's implementation, exploring how the wormhole's three parameters influence what the camera sees—which is precisely how Christopher Nolan, using our implementation, chose the parameters for Interstellar's wormhole; (vi) Using the student's implementation, exploring the wormhole's Einstein ring and particularly the peculiar motions of star images near the ring, and exploring what it looks like to travel through a wormhole.

  17. Interstellar Travel without 'Magic'

    NASA Astrophysics Data System (ADS)

    Woodcock, G.

    The possibility of interstellar space travel has become a popular subject. Distances of light years are an entirely new realm for human space travel. New means of propulsion are needed. Speculation about propulsion has included "magic", space warps, faster-than-light travel, known physics such as antimatter for which no practical implementation is known and also physics for which current research offers at least a hint of implementation, i.e. fusion. Performance estimates are presented for the latter and used to create vehicle concepts. Fusion propulsion will mean travel times of hundreds of years, so we adopt the "space colony" concepts of O'Neill as a ship design that could support a small civilization indefinitely; this provides the technical means. Economic reasoning is presented, arguing that development and production of "space colony" habitats for relief of Earth's population, with addition of fusion engines, will lead to vessels that can go interstellar. Scenarios are presented and a speculative estimate of a timetable is given.

  18. Interstellar Cloud Collisions

    NASA Astrophysics Data System (ADS)

    Lattanzio, J. C.; Monaghan, J. J.; Pongracic, H.; Schwarz, M. P.

    1985-07-01

    We describe the results of a three-dimensional numerical simulation of isothermal interstellar clouds in the absence of magnetic fields. A wide variety of high and low Mach number, head-on and off-centre collisions of clouds with mass ratios 1, 2.5, 5.0 and 10.1 have been studied. The results show that a necessary, but not sufficient, condition for the gravitational instability of a substantial fraction of the matter is that the initial clouds should be either marginally stable or unstable according to the usual Jeans criterion. The collisions, in general, do not result in one or more clouds. Instead we find, in most cases, that the matter disperses in an irregular way. The calculations therefore suggest that if the initial state of the interstellar medium is one of cool dense clouds in a hotter more tenuous background, collisions will rapidly mix the medium rather than produce a steady-state spectrum of cool clouds.

  19. An interstellar precursor mission

    NASA Technical Reports Server (NTRS)

    Jaffe, L. D.; Ivie, C.; Lewis, J. C.; Lipes, R.; Norton, H. N.; Stearns, J. W.; Stimpson, L. D.; Weissman, P.

    1980-01-01

    A mission out of the planetary system, launched about the year 2000, could provide valuable scientific data as well as test some of the technology for a later mission to another star. Primary scientific objectives for the precursor mission concern characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low-energy cosmic rays, interplanetary gas distribution, and the mass of the solar system. Secondary objectives include investigation of Pluto. The mission should extend to 400-1000 AU from the sun. A heliocentric hyperbolic escape velocity of 50-100 km/sec or more is needed to attain this distance within a reasonable mission duration (20-50 years). The trajectory should be toward the incoming interstellar gas. For a year 2000 launch, a Pluto encounter and orbiter can be included. A second mission targeted parallel to the solar axis would also be worthwhile. The mission duration is 20 years, with an extended mission to a total of 50 years. A system using one or two stages of nuclear electric propulsion (NEP) was selected as a possible baseline. The most promising alternatives are ultralight solar sails or laser sailing, with the lasers in earth orbit, for example. The NEP baseline design allows the option of carrying a Pluto orbiter as a daughter spacecraft.

  20. Graphene, the Ultimate Interstellar Solar Sail Material?

    NASA Astrophysics Data System (ADS)

    Matloff, G. L.

    Graphene (a carbon molecular monolayer) is a wonder material of great interest to materials researchers. Its molecular-layer thickness, finite fractional absorption, high melting point, and impermeability to gases coupled with the fact that doped materials, additives and multiple layers increase both fractional absorption and reflectivity indicates that it may be a superior material for application in solar-photon sailing. This paper first reviews relevant graphene physical and optical properties and then investigates the kinematics of interstellar solar sails constructed using this material. Two sail configurations are considered: thin-film probes and hollow-bodies sails. It is shown that graphene sail performance may be superior to that of beryllium sails. Less intense perihelion passes and accelerations may allow transit times to Alpha Centauri approximating a millennium. Future research should consider the interaction of graphene sails with the space environment and large-scale fabrication techniques.

  1. Polycyclic Aromatic Hydrocarbons in Interstellar Medium Dust

    NASA Astrophysics Data System (ADS)

    Malsberger, Rosalie; Chiar, J. E.; Tielens, A. G. G. M.; Sloan, G. C.

    2009-01-01

    We obtained spectra from the Spitzer Space Telescope Infrared Spectrometer (IRS) of lines of sight that probe large columns of diffuse interstellar medium (ISM) dust (PID 3616, J. Chiar). An absorption feature at 6.2 μm, that we attribute to polycyclic aromatic hydrocarbons (PAHs) in the cold ISM, is detected in nine of our spectra. PAHs are normally observed in emission near an exciting source, rather than in the cold ISM dust, however, Schutte et al. (1998, A&A, 337, 261) found the 6.2 μm absorption feature in spectra of WC-type Wolf-Rayet stars that probed moderate columns of diffuse ISM dust. However, it was later shown by Chiar et al. (2001, ApJ, 550, 207) that the feature could be attributed to circumstellar dust around these objects. A low limit was set on lack of detection in the diffuse ISM. Our new Spitzer spectra provide the first indisputable detections of the 6.2 μm PAH absorption feature toward stars that are not associated with circumstellar dust. Based on our nine detections and twenty detection limits, a positive correlation is suggested between the optical depth of the 6.2 μm absorption feature and visual extinction. If verified (with higher signal-to-noise data), this relationship would imply that PAHs are widespread components of cold ISM dust, similar to the well-known aliphatic hydrocarbons that peak at 3.4 μm. Assuming an elemental carbon abundance of C/H=3.7 x 10-4, we estimate that 30 to 40% of the interstellar carbon can be tied up in PAH dust. Future high signal-to-noise observations with SOFIA and/or the James Webb Space Telescope will be crucial to verify the nature and distribution of PAHs in cold ISM dust. This material is based upon work supported by the National Science Foundation under Grant No. 0552751.

  2. Detection of interstellar boron in front of kappa Orionus

    NASA Technical Reports Server (NTRS)

    Meneguzzi, M.; York, D. G.

    1980-01-01

    The detection of interstellar boron in the direction of kappa Ori, obtained with the Copernicus satellite telescope by observing the B II 1362.46-A resonance line is reported. A B/H concentration ratio of (1.5 + or - 0.7) x 10 to the -10th (2 standard deviation error bar) is obtained. The main uncertainty lies in the determination of the continuum of the star in that wavelength region, dominated by a broad stellar absorption feature. The value inferred for B/H in the interstellar medium is consistent with the solar and stellar values, believed to be the galactic value, and with the theory of the production of B by cosmic rays in the interstellar medium.

  3. NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS

    SciTech Connect

    Bzowski, M.; Kubiak, M. A.; Sokol, J. M.; Hlond, M.; Moebius, E.; Bochsler, P.; Leonard, T.; Heirtzler, D.; Kucharek, H.; Schwadron, N. A.; Crew, G. B.; Fuselier, S. A.; McComas, D. J.

    2012-02-01

    Because of its high ionization potential and weak interaction with hydrogen, neutral interstellar helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. This second most abundant species provides some of the best information on the characteristics of the interstellar gas in the local interstellar cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local interstellar flow vector obtained from studies of interstellar absorption: the newly established flow direction is ecliptic longitude 79.{sup 0}2, latitude -5.{sup 0}1, the velocity is {approx}22.8 km s{sup -1}, and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the interstellar magnetic field, and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of interstellar plasma and strength of interstellar magnetic field.

  4. Synchrotron FTIR Examination of Interplanetary Dust Particles: An Effort to Determine the Compounds and Minerals in Interstellar and Circumstellar Dust

    NASA Technical Reports Server (NTRS)

    Flynn, G. J.; Keller, L. P.

    2002-01-01

    Some interplanetary dust particles (IDPs), collected by NASA from the Earth's stratosphere, are the most primitive extraterrestrial material available for laboratory analysis. Many exhibit isotopic anomalies in H, N, and O, suggesting they contain preserved interstellar matter. We report the preliminary results of a comparison of the infrared absorption spectra of subunits of the IDPs with astronomical spectra of interstellar grains.

  5. An interstellar precursor mission

    NASA Technical Reports Server (NTRS)

    Jaffe, L. D.; Ivie, C.; Lewis, J. C.; Lipes, R. G.; Norton, H. N.; Stearns, J. W.; Stimpson, L.; Weissman, P.

    1977-01-01

    A mission out of the planetary system, with launch about the year 2000, could provide valuable scientific data as well as test some of the technology for a later mission to another star. Primary scientific objectives for the precursor mission concern characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low energy cosmic rays, interplanetary gas distribution, and mass of the solar system. Secondary objectives include investigation of Pluto. Candidate science instruments are suggested. Individual spacecraft systems for the mission were considered, technology requirements and problem areas noted, and a number of recommendations made for technology study and advanced development. The most critical technology needs include attainment of 50-yr spacecraft lifetime and development of a long-life NEP system.

  6. Interstellar sulfur chemistry

    NASA Technical Reports Server (NTRS)

    Prasad, S. S.; Huntress, W. T., Jr.

    1980-01-01

    The results of a chemical model of SO, CS, and OCS chemistry in dense clouds are summarized. The results are obtained from a theoretical study of sulfur chemistry in dense interstellar clouds using a large-scale time-dependent model of gas-phase chemistry. Among the results are the following: (1) owing to activation energy, the reaction of CS with O atoms is efficient as a loss mechanism of CS during the early phases of cloud evolution or in hot and oxygen-rich sources such as the KL nebula; (2) if sulfur is not abnormally depleted in dense clouds, then the observed abundances of SO, SO2, H2S, CS, OCS, H2CS, and SiS indicate that sulfur is mostly atomic in dense clouds; and (3) OCS is stable against reactions with neutral atoms and radicals in dense clouds.

  7. Interstellar carbon in meteorites

    NASA Technical Reports Server (NTRS)

    Swart, P. K.; Grady, M. M.; Pillinger, C. T.; Lewis, R. S.; Anders, E.

    1983-01-01

    The Murchison and Allende chondrites contain up to 5 parts per million carbon that is enriched in carbon-13 by up to +1100 per mil (the ratio of carbon-12 to carbon-13 is approximately 42, compared to 88 to 93 for terrestrial carbon). This 'heavy' carbon is associated with neon-22 and with anomalous krypton and xenon showing the signature of the s-process (neutron capture on a slow time scale). It apparently represents interstellar grains ejected from late-type stars. A second anomalous xenon component ('CCFXe') is associated with a distinctive, light carbon (depleted in carbon-13 by 38 per mil), which, however, falls within the terrestrial range and hence may be of either local or exotic origin.

  8. Very Small Interstellar Spacecraft

    NASA Astrophysics Data System (ADS)

    Peck, Mason A.

    2007-02-01

    This paper considers lower limits of length scale in spacecraft: interstellar vehicles consisting of little more material than found in a typical integrated-circuit chip. Some fundamental scaling principles are introduced to show how the dynamics of the very small can be used to realize interstellar travel with minimal advancements in technology. Our recent study for the NASA Institute for Advanced Concepts provides an example: the use of the Lorentz force that acts on electrically charged spacecraft traveling through planetary and stellar magnetospheres. Schaffer and Burns, among others, have used Cassini and Voyager imagery to show that this interaction is responsible for some of the resonances in the orbital dynamics of dust in Jupiter's and Saturn's rings. The Lorentz force turns out to vary in inverse proportion to the square of this characteristic length scale, making it a more effective means of propelling tiny spacecraft than solar sailing. Performance estimates, some insight into plasma interactions, and some hardware concepts are offered. The mission architectures considered here involve the use of these propellantless propulsion techniques for acceleration within our solar system and deceleration near the destination. Performance estimates, some insight into plasma interactions, and some hardware concepts are offered. The mission architectures considered here involve the use of these propellantless propulsion techniques for acceleration within our solar system and deceleration near the destination. We might envision a large number of such satellites with intermittent, bursty communications set up as a one-dimensional network to relay signals across great distances using only the power likely from such small spacecraft. Conveying imagery in this fashion may require a long time because of limited power, but the prospect of imaging another star system close-up ought to be worth the wait.

  9. SOLAR RADIATION PRESSURE AND LOCAL INTERSTELLAR MEDIUM FLOW PARAMETERS FROM INTERSTELLAR BOUNDARY EXPLORER LOW ENERGY HYDROGEN MEASUREMENTS

    SciTech Connect

    Schwadron, N. A.; Moebius, E.; Kucharek, H.; Lee, M. A.; French, J.; Saul, L.; Wurz, P.; Bzowski, M.; Fuselier, S. A.; Livadiotis, G.; McComas, D. J.; Frisch, P.; Gruntman, M.; Mueller, H. R.

    2013-10-01

    Neutral hydrogen atoms that travel into the heliosphere from the local interstellar medium (LISM) experience strong effects due to charge exchange and radiation pressure from resonant absorption and re-emission of Lyα. The radiation pressure roughly compensates for the solar gravity. As a result, interstellar hydrogen atoms move along trajectories that are quite different than those of heavier interstellar species such as helium and oxygen, which experience relatively weak radiation pressure. Charge exchange leads to the loss of primary neutrals from the LISM and the addition of new secondary neutrals from the heliosheath. IBEX observations show clear effects of radiation pressure in a large longitudinal shift in the peak of interstellar hydrogen compared with that of interstellar helium. Here, we compare results from the Lee et al. interstellar neutral model with IBEX-Lo hydrogen observations to describe the distribution of hydrogen near 1 AU and provide new estimates of the solar radiation pressure. We find over the period analyzed from 2009 to 2011 that radiation pressure divided by the gravitational force (μ) has increased slightly from μ = 0.94 ± 0.04 in 2009 to μ = 1.01 ± 0.05 in 2011. We have also derived the speed, temperature, source longitude, and latitude of the neutral H atoms and find that these parameters are roughly consistent with those of interstellar He, particularly when considering the filtration effects that act on H in the outer heliosheath. Thus, our analysis shows that over the period from 2009 to 2011, we observe signatures of neutral H consistent with the primary distribution of atoms from the LISM and a radiation pressure that increases in the early rise of solar activity.

  10. Ultraviolet observations of cool stars. VII - Local interstellar hydrogen and deuterium Lyman-alpha

    NASA Technical Reports Server (NTRS)

    Mcclintock, W.; Henry, R. C.; Linsky, J. L.; Moos, H. W.

    1978-01-01

    High-resolution Copernicus spectra of Epsilon Eri and Epsilon Ind containing interstellar hydrogen and deuterium L-alpha absorption lines are presented, reduced, and analyzed. Parameters of the interstellar hydrogen and deuterium toward these two stars are derived independently, without any assumptions concerning the D/H ratio. Copernicus spectra of Alpha Aur and Alpha Cen A are reanalyzed, and limits on the D/H number-density ratio consistent with the data for all four stars are considered. A comparison of the present estimates for the parameters of the local interstellar medium with those obtained by other techniques shows that there is no compelling evidence for significant variations in the hydrogen density and D/H ratio in the local interstellar medium. On this basis the hypothesis of an approaching local interstellar cloud proposed by Vidal-Madjar et al. (1978) is rejected

  11. Four Interstellar Dust Candidates from the Stardust Interstellar Dust Collector

    NASA Technical Reports Server (NTRS)

    Westphal, A. J.; Allen, C.; Bajt, S.; Bechtel, H. A.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.; Butterworth, A. L.; Cloetens, P.; Davis, A. M.; Floss, C.; Flynn, G. J.; Fougeray, P.; Frank, D.; Gainsforth, Z.; Grun, E.; Heck, P. R.; Jillier, J. K.; Hoppe, P.; Howard, L.; Hudson, B.; Huss, G. R.

    2011-01-01

    In January 2006, the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were approx. 0.1 sq m in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 sq m/day. The Stardust Interstellar Preliminary Examination (ISPE) is a consortium-based project to characterize the collection using nondestructive techniques. The goals and restrictions of the ISPE are described . A summary of analytical techniques is described.

  12. Discovery of Interstellar Heavy Water

    NASA Astrophysics Data System (ADS)

    Butner, H. M.; Charnley, S. B.; Ceccarelli, C.; Rodgers, S. D.; Pardo, J. R.; Parise, B.; Cernicharo, J.; Davis, G. R.

    2007-04-01

    We report the discovery of doubly deuterated water (D2O, heavy water) in the interstellar medium. Using the James Clerk Maxwell Telescope and the Caltech Submillimeter Observatory 10 m telescope, we detected the 110-101 transition of para-D2O at 316.7998 GHz in both absorption and emission toward the protostellar binary system IRAS 16293-2422. Assuming that the D2O exists primarily in the warm regions where water ices have been evaporated (i.e., in a ``hot corino'' environment), we determine a total column density of N(D2O) of 1.0×1013 cm-2 and a fractional abundance of D2O/H2=1.7×10-10. The derived column density ratios for IRAS 16293-2422 are D2O/HDO=1.7×10-3 and D2O/H2O=5×10-5 for the hot corino gas. Steady state models of water ice formation, either in the gas phase or on grains, predict D2O/HDO ratios that are about 4 times larger than that derived from our observations. For water formation on grain surfaces to be a viable explanation, a larger H2O abundance than that measured in IRAS 16293-2422 is required. Alternatively, the observed D2O/HDO ratio could be indicative of gas-phase water chemistry prior to a chemical steady state being attained, such as would have occurred during the formation of this source. Future observations with the Herschel Space Observatory satellite will be important for settling this issue.

  13. The diffuse interstellar bands: a tracer for organics in the diffuse interstellar medium?

    NASA Technical Reports Server (NTRS)

    Salama, F.

    1998-01-01

    The diffuse interstellar bands (DIBs) are absorption bands seen in the spectra of stars obscured by interstellar dust. DIBs are recognized as a tracer for free, organic molecules in the diffuse interstellar medium (ISM). The potential molecular carriers for the DIBs are discussed with an emphasis on neutral and ionized polycyclic aromatic hydrocarbons (PAHs) for which the most focused effort has been made to date. From the combined astronomical, laboratory and theoretical study, it is concluded that a distribution of free neutral and ionized complex organics (PAHs, fullerenes, unsaturated hydrocarbons) represents the most promising class of candidates to account for the DIBs. The case for aromatic hydrocarbons appears particularly strong. The implied widespread distribution of complex organics in the diffuse ISM bears profound implications for our understanding of the chemical complexity of the ISM, the evolution of prebiotic molecules and its impact on the origin and the evolution of life on early Earth through the exogenous delivery (cometary encounters and metoritic bombardments) of prebiotic organics.

  14. Theoretical Modeling of Interstellar Chemistry

    NASA Technical Reports Server (NTRS)

    Charnley, Steven

    2009-01-01

    The chemistry of complex interstellar organic molecules will be described. Gas phase processes that may build large carbon-chain species in cold molecular clouds will be summarized. Catalytic reactions on grain surfaces can lead to a large variety of organic species, and models of molecule formation by atom additions to multiply-bonded molecules will be presented. The subsequent desorption of these mixed molecular ices can initiate a distinctive organic chemistry in hot molecular cores. The general ion-molecule pathways leading to even larger organics will be outlined. The predictions of this theory will be compared with observations to show how possible organic formation pathways in the interstellar medium may be constrained. In particular, the success of the theory in explaining trends in the known interstellar organics, in predicting recently-detected interstellar molecules, and, just as importantly, non-detections, will be discussed.

  15. First detection of [N II] 205 μm absorption in interstellar gas. Herschel-HIFI observations towards W 31C, W 49N, W 51, and G34.3+0.1

    NASA Astrophysics Data System (ADS)

    Persson, C. M.; Gerin, M.; Mookerjea, B.; Black, J. H.; Olberg, M.; Goicoechea, J. R.; Hassel, G. E.; Falgarone, E.; Levrier, F.; Menten, K. M.; Pety, J.

    2014-08-01

    We present high resolution [N ii] 205 μm (3P1 - 3P0) spectra obtained with Herschel-HIFI towards a small sample of far-infrared bright star forming regions in the Galactic plane: W 31C (G10.6-0.4), W 49N (G43.2-0.1), W 51 (G49.5-0.4), and G34.3+0.1. All sources display an emission line profile associated directly with the H ii regions themselves. For the first time we also detect absorption of the [N ii] 205 μm line by extended low-density foreground material towards W 31C and W 49N over a wide range of velocities. We attribute this absorption to the warm ionised medium (WIM) and find N(N+) ≈ 1.5 × 1017 cm-2 towards both sources. This is in agreement with recent Herschel-HIFI observations of [C ii] 158 μm, also observed in absorption in the same sight-lines, if ≈7-10% of all C+ ions exist in the WIM on average. Using an abundance ratio of [N] / [H] = 6.76 × 10-5 in the gas phase we find that the mean electron and proton volume densities are ~0.1-0.3 cm-3 assuming a WIM volume filling fraction of 0.1-0.4 with a corresponding line-of-sight filling fraction of 0.46-0.74. A low density and a high WIM filling fraction are also supported by RADEX modelling of the [N ii] 205 μm absorption and emission together with visible emission lines attributed mainly to the WIM. The detection of the 205 μm line in absorption emphasises the importance of a high spectral resolution, and also offers a new tool for investigation of the WIM. Appendix A is available in electronic form at http://www.aanda.orgHerschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  16. A new model of composite interstellar grains

    NASA Astrophysics Data System (ADS)

    Voshchinnikov, N. V.; Il'in, V. B.; Henning, Th.; Dubkova, D. N.

    The approach to model composite interstellar dust grains using the exact solution to the light scattering problem for multi-layered spheras suggested by Voshchinnikov & Mathis (1999) is further developed. Heterogeneous scatterers are represented by particles with very large numof shells each including a homogeneous layer per material considered (here amorphous carbon, astronomical silicate and vacuum). It is demonstrated that the scattering characteristics (cross-sections, albedo, asymmetry factor, etc.) well converge with the increase of the number of shells (layers) and each of the characteristics has the same limit independent of the layer order in the shells. The limit obviously corresponds to composite particles consisting of several well mixed materials. However, our results indicate that layered particles with even a few shells (layers) have the characteristics close enough to these limits. The applicability of the effective medium theory (EMT) mostly utilized earlier to approximate inhomogeneous interstellar grains is examined on the base of the model. It is shown that the used EMT rules generally have the accuracy of several percents in the whole range of particle sizes provided the porosity does not exceed about 50%. For larger porosity, the rules give wrong results. Using the model we reanalyze basics of interpretation of various manifestations of cosmic dust --- interstellar extinction, scattered radiation, infrared radiation, radiation pressure, etc. It is found that an increase of porosity typically leads to the increase of cross-sections, albedo and the sweeping efficiency of small grains as well as to the decrease of dust temperature and the strength of infrared bands (the EMT fails to produce these effects). We also conclude that pure iron even in negligible amount (<˜1 % by the volume fractis unlikely to form a layer on or inside a grain because of peculiar absorption of radiation by such particles. As an example of the potential of the model, it

  17. Detection of Interstellar Urea

    NASA Astrophysics Data System (ADS)

    Kuo, Hsin-Lun; Remijan, Anthony J.; Snyder, Lewis E.; Looney, Leslie W.; Friedel, Douglas N.; Lovas, Francis J.; McCall, Benjamin J.; Hollis, Jan M.

    2010-11-01

    Urea, a molecule discovered in human urine by H. M. Rouelle in 1773, has a significant role in prebiotic chemistry. Previous BIMA observations have suggested that interstellar urea [(NH2)2CO] is a compact hot core molecule such as other large molecules (e.g. methyl formate and acetic acid). We have conducted an extensive search for urea toward the high mass hot molecular core Sgr B2(N-LMH) using BIMA, CARMA and the IRAM 30 m. Because the spectral lines of heavy molecules like urea tend to be weak and hot cores display lines from a wide range of molecules, it is necessary to detect a number of urea lines and apply sophisticated statistical tests before having confidence in an identification. The 1 mm resolution of CARMA enables favorable coupling of the source size and synthesized beam size, which was found to be essential for the detection of weak signals. We have detected a total of 65 spectral lines (32 molecular transitions and 33 unidentified transitions), most of which are narrower than the SEST survey (Nummelin et al. 1998) due to the small synthesized beam (2.5" x 2") of CARMA. It significantly resolves out the contamination by extended emission and reveals the eight weak urea lines that were previously blended with nearby transitions. Our analysis indicates that these lines are likely to be urea since the resulting observed line frequencies are coincident with a set of overlapping connecting urea lines, and the observed line intensities are consistent with the expected line strengths of urea. In addition, we have developed a new statistical approach to examine the spatial correlation between the observed lines by applying the Student's t test to the high resolution channel maps obtained from CARMA. The t test shows consistent spatial distributions from all eight candidate lines, suggesting a common molecular origin, urea. Our t test method could have a broad impact on the next generation of arrays, such as ALMA, because the new arrays will require a method

  18. Photoluminescence by Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Vijh, U. P.

    2005-12-01

    In this dissertation talk, I will report on our study of interstellar dust through the process of photoluminescence (PL). We present the discovery of a new band of dust PL, blue luminescence (BL) with λ peak ˜ 370 nm in the proto-planetary nebula known as the Red Rectangle (RR). We attribute this to fluorescence by small, 3-4-ringed polycyclic aromatic hydrocarbon (PAH) molecules. Further analysis reveals additional independent evidence for the presence of small PAHs in this nebula. Detection of BL using long-slit spectroscopic observations in other ordinary reflection nebulae suggests that the BL carrier is an ubiquitous component of the ISM and is not restricted to the particular environment of the RR. We present the spatial distribution of the BL in these nebulae and find that the BL is spatially correlated with IR emission structures attributed to aromatic emission features (AEFs), attributed to PAHs. The carrier of the dust-associated photoluminescence process causing the extended red emission (ERE), known now for over twenty five years, remains unidentified. We constrain the character of the ERE carrier by determining the wavelengths of the radiation that initiates the ERE -- λ < 118 nm. We note that under interstellar conditions most PAH molecules are ionized to the di-cation stage by photons with E > 10.5 eV and that the electronic energy level structure of PAH di-cations is consistent with fluorescence in the wavelength band of the ERE. I will also present first results from ongoing work: Using narrow-band imaging, we present the optical detection of the circum-binary disk of the RR in the light of the BL, and show that the morphology of the BL and ERE emissions in the RR nebula are almost mutually exclusive. It is very suggestive to attribute them to different ionization stages of the same family of carriers such as PAH molecules. Financial support for this study was provided through NSF Grant AST0307307 to The University of Toledo.

  19. Photoluminescence by Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Vijh, U. P.

    2005-08-01

    In this dissertation, we report on our study of interstellar dust through the process of photoluminescence (PL). We present the discovery of a new band of dust PL, blue luminescence (BL) with λpeak˜370 nm in the proto-planetary nebula known as the Red Rectangle (RR). We attribute this to fluorescence by small, 3-4-ringed polycyclic aromatic hydrocarbon (PAH) molecules. Further analysis reveals additional independent evidence for the presence of small PAHs in this nebula. Detection of BL using long-slit spectroscopic observations in other ordinary reflection nebulae suggests that the BL carrier is an ubiquitous component of the ISM and is not restricted to the particular environment of the RR. We present the spatial distribution of the BL in these nebulae and find that the BL is spatially correlated with IR emission structures attributed to aromatic emission features (AEFs), attributed to PAHs. The carrier of the dust-associated photoluminescence process causing the extended red emission (ERE), known now for over twenty five years, remains unidentified. We constrain the character of the ERE carrier by determining the wavelengths of the radiation that initiates the ERE -- λ < 118 nm. We note that under interstellar conditions most PAH molecules are ionized to the di-cation stage by photons with E > 10.5 eV and that the electronic energy level structure of PAH di-cations is consistent with fluorescence in the wavelength band of the ERE. In the last few chapters of the dissertation we present first results from ongoing work: i) Using narrow-band imaging, we present the optical detection of the circum-binary disk of the RR in the light of the BL, and show that the morphology of the BL and ERE emissions in the RR nebula are almost mutually exclusive. It is very suggestive to attribute them to different ionization stages of the same family of carriers such as PAH molecules. ii) We also present a pure spectrum of the BL free of scattered light, resolved into seven

  20. The Interstellar Conspiracy

    NASA Technical Reports Server (NTRS)

    Johnson, Les; Matloff, Gregory L.

    2005-01-01

    If we were designing a human-carrying starship that could be launched in the not-too-distant future, it would almost certainly not use a warp drive to instantaneously bounce around the universe, as is done in Isaac Asimov's classic Foundation series or in episodes of Star Trek or Star Wars. Sadly, those starships that seem to be within technological reach could not even travel at high relativistic speeds, as does the interstellar ramjet in Poul Anderson's Tau Zero. Warp-speeds seem to be well outside the realm of currently understood physical law; proton-fusing ramjets may never be technologically feasible. Perhaps fortunately in our terrorist-plagued world, the economics of antimatter may never be attractive for large-scale starship propulsion. But interstellar travel will be possible within a few centuries, although it will certainly not be as fast as we might prefer. If humans learn how to hibernate, perhaps we will sleep our way to the stars, as do the crew in A. E. van Vogt's Far Centaurus. However, as discussed in a landmark paper in The Journal of the British Interplanetary Society, the most feasible approach to transporting a small human population to the planets (if any) of Alpha Centauri is the worldship. Such craft have often been featured in science fiction. See for example Arthur C. Clarke's Rendezvous with Rama, and Robert A. Heinlein's Orphans of the Sky. Worldships are essentially mobile versions of the O Neill free-space habitats. Constructed mostly from lunar and/or asteroidal materials, these solar-powered, multi-kilometer-dimension structures could house 10,000 to 100,000 humans in Earth-approximating environments. Artificial gravity would be provided by habitat rotation, and cosmic ray shielding would be provided by passive methods, such as habitat atmosphere and mass shielding, or magnetic fields. A late 21st century space-habitat venture might support itself economically by constructing large solar-powered satellites to beam energy back to

  1. PROSPECTS FOR THE DETECTION OF INTERSTELLAR CYANOVINYLIDENE

    SciTech Connect

    Kolos, Robert; Gronowski, Marcin; Dobrowolski, Jan Cz.

    2009-08-10

    Prospects for the presence and detection of interstellar cyanovinylidene, CC(H)CN, a Y-shaped isomer of cyanoacetylene, are discussed. It is proposed that CC(H)CN can arise in interstellar clouds as one of the HC{sub 3}NH{sup +} + e {sup -} dissociative recombination products, by rearrangements of the neutral chain radical HC{sub 3}NH into branched species HCCC(H)N, CC(H)C(H)N, and/or HCC(H)CN, and by the subsequent elimination of a hydrogen atom. It is deduced that the abundance of cyanovinylidene in molecular clouds should be confined between the abundances of its chain isomers HNCCC and HCNCC. Quantum chemical predictions regarding cyanovinylidene geometry, ground-state rotational constants, centrifugal distortion constants, spin-orbit coupling, IR absorption spectroscopy, and electric dipole moment are given. The spectroscopically observed molecules formyl cyanide, NC{sub 2}(H)O, and propynal, HC{sub 3}(H)O, with structures qualitatively resembling cyanovinylidene, served to prove the adequacy of the calculational procedures employed.

  2. On Ion Clusters in the Interstellar Gas

    NASA Technical Reports Server (NTRS)

    Donn, Bertram

    1960-01-01

    In a recent paper V.I. Krassovsky (1958) predicts the occurrence of clusters of large numbers of atoms and molecules around ions in the interstellar gas. He then proposes a number of physicochemical processes that would be considerably enhanced by the high particle density in such clusters. In particular, he suggests that absorption by negative ions formed in the clusters would account for the interstellar extinction without any necessity for the presence of grains. Because of the important consequences that ion clusters could have, it is necessary to examine their occurrence more fully. This note re-examines the formation of ion clusters in space and shows that even ion-molecule pairs are essentially non-existent. Ion clusters have been considered by Bloom and Margenau (1952) from the same point of view as that used by Krassovsky, whose basic reference (Joffe and Semenov 1933) unfortunately is not available. A different approach has been used by Eyring, Hirschfelder, and Taylor (1936) following the methods of chemical equilibrium. Both the references cited here enable one to conclude that clustering is negligible. Therefore, the treatment of Eyring et al. is more appropriate than the method of Bloom and Margenau, which depends on the statistical equilibrium of an atmosphere in a force field.

  3. Interstellar Clouds Near the Sun, III

    NASA Astrophysics Data System (ADS)

    Frisch, Priscilla C.

    We propose to continue a study of interstellar sight-lines with low total column densities in order to determine the nature (temperature, density, fractional ionization) of the low density gas near the Sun and within the interior of the local superbubble. IUE data, combined with previous Copernicus observations, can be used to delimit the filling factor of nearby low density warm gas, and by default restrict the filling factor of 10^6 K plasma. In the proposed program, observations of MgI and ZnII(and in one region CIV) are combined with cloud maps and ground-based NaI observations (from a separate program) to restrict gas temperature, spatial and electron densities. The Welty et al. (1986) technique for removing fixed pattern noise through observations of a template star (used to flat-field the target stars on a pixel-by-pixel basis) is used to enable 3sigma absorption line detections at the 6-9 mA level, depending on the number of exposures involved. The ultimate goal of both the IUE and ground-based program is to map out the local interstellar medium. Apart from the intrinsic interest of this problem, it will help define regions where ultraviolet sources can be observed with FUSE/Lyman at lambda<912 A.

  4. Desorption from interstellar grains

    NASA Technical Reports Server (NTRS)

    Leger, A.; Jura, M.; Omont, A.

    1985-01-01

    Different desorption mechanisms from interstellar grains are considered to resolve the conflict between the observed presence of gaseous species in molecular clouds and their expected depletion onto grains. The physics of desorption is discussed with particular reference to the process of grain heating and the specific heat of the dust material. Impulsive heating by X-rays and cosmic rays is addressed. Spot heating of the grains by cosmic rays and how this can lead to desorption of mantles from very large grains is considered. It is concluded that CO depletion on grains will be small in regions with A(V) less than five from the cloud surface and n(H) less than 10,000, in agreement with observations and in contrast to expectations from pure thermal equilibrium. Even in very dense and obscured regions and in the absence of internal ultraviolet sources, the classical evaporation of CO or N2 and O2-rich mantles by cosmic rays is important.

  5. Neutral gas and diffuse interstellar bands in the LMC

    NASA Technical Reports Server (NTRS)

    Danks, Anthony C.; Penprase, Brian

    1994-01-01

    Tracing the dynamics of the neutral gas and observing diffuse interstellar bands in the LMC (Large Magellanic Cloud) was the focus of this study. The S/N values, a Quartz lamp exposure, a T horium Argon Comparision lamp exposure, and spectral plots for each star observed were taken. The stars observed were selected to sample the 30 Dor vicinty. NaI absorption profiles are included.

  6. Stardust interstellar preliminary examination (ISPE).

    SciTech Connect

    Westphal, A.J.; Allen, C.; Bajt, S.; Basset, R.; Flynn, G.L.; Sutton, S.

    2009-03-23

    The Stardust Interstellar Preliminary Examination (ISPE) is a three-year effort to characterize the Stardust interstellar dust collection and collector using non-destructive techniques. We summarize the status of the ISPE. In January 2006 the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were {approx}0.1 m{sup 2} in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m{sup 2}-day during two periods before the cometary encounter. The Stardust Interstellar Preliminary Examination (ISPE) is a three-year effort to characterize the collection using nondestructive techniques. The goals and restrictions of the ISPE are described in Westphal et al. The ISPE consists of six interdependent projects: (1) Candidate identification through automated digital microscopy and a massively distributed, calibrated search; (2) Candidate extraction and photodocumentation; (3) Characterization of candidates through synchrotron-based Fourier-Tranform Infrared Spectroscopy (FTIR), Scanning X-Ray Fluoresence Microscopy (SXRF), and Scanning Transmission X-ray Microscopy (STXM); (4) Search for and analysis of craters in foils through FESEM scanning, Auger Spectroscopy and synchrotron-based Photoemission Electron Microscopy (PEEM); (5) Modeling of interstellar dust transport in the solar system; and (6) Laboratory simulations of hypervelocity dust impacts into the collecting media.

  7. Editorial: Interstellar Boundary Explorer (IBEX): Direct Sampling of the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    McComas, D. J.

    2012-02-01

    absorption (Redfield & Linsky 2008). Bzowski et al. also show evidence for a previously unknown and unanticipated secondary population of helium. Together, the Möbius et al. (2012) and Bzowski et al. (2012) results provide a new interstellar flow direction and a significantly lower velocity of the incoming gas and therefore significantly lower dynamic pressure on the heliosphere, which translates into a heliospheric interaction that is even less dominated by the external dynamic pressure and clearly lies squarely in the middle ground of astrospheres dominated by the external magnetic and dynamic pressures (McComas et al. 2009b). On another topic, Bochsler et al. (2012) report the first direct measurements of interstellar Ne and estimate the interstellar Ne/O abundance ratio, showing a gas-phase Ne/O ratio for the LISM of 0.27 ± 0.10. This value agrees with results obtained from pickup ion observations (Gloeckler & Geiss 2004; Gloeckler & Fisk 2007) and is significantly larger than the solar abundance ratio, indicating that the LISM is different than the Sun's formation region and/or that a substantial portion of the O in the LISM is tied up (and thus "hidden") in grains and/or ices. Finally, Saul et al. (2012) provide the first detailed analysis of the new interstellar H measurements from IBEX. These authors confirm that the arrival direction of interstellar H is offset from that of He. They further show a variation in the strength of the radiation pressure and thus a change in the apparent arrival direction of H penetrating to 1 AU between the first two years of IBEX observations; these results are consistent with solar cycle variations in the radiation pressure, which works opposite to the Sun's gravitational force to effect the penetration of H into the inner heliosphere. Together, these six studies provide the first detailed analyses of the multi-component local interstellar medium—a medium that both effects us by bounding and interacting with our heliosphere, and a

  8. Interstellar clouds containing optically thin H2

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1975-01-01

    The theory of Black and Delgarno that the relative populations of the excited rotational levels of H2 can be understood in terms of cascading following absorption in the Lyman and Werner bands is employed to infer the gas densities and radiation fields within diffuse interstellar clouds containing H2 that is optically thin in those bands. The procedure is described for computing the populations of the different rotation levels, the relative distribution among the different rotation levels of newly formed H2 is determined on the basis of five simplified models, and the rate of H2 formation is estimated. The results are applied to delta Ori, two components of iota Ori, the second components of rho Leo and zeta Ori, tau Sco, gamma Vel, and zeta Pup. The inferred parameters are summarized for each cloud.

  9. The mass spectrum of interstellar clouds

    NASA Technical Reports Server (NTRS)

    Dickey, John M.; Garwood, Robert W.

    1989-01-01

    The abundances of diffuse clouds and molecular clouds in the inner Galaxy and at the solar circle are compared. Using results of recent low-latitude 21 cm absorption studies, the number of diffuse clouds per kiloparsec along the line of sight is derived as a function of the cloud column density, under two assumptions relating cloud densities and temperatures. The density of clouds is derived as a function of cloud mass. The results are consistent with a single, continuous mass spectrum for interstellar clouds from less than 1 solar mass to 1,000,000 solar masses, with perhaps a change of slope at masses where the atomic and molecular mass fractions are roughly equal.

  10. Interstellar Electron Density Spectra

    NASA Astrophysics Data System (ADS)

    Lambert, Hendrick Clark

    This study concerns the investigation of the form of the wavenumber spectrum of the Galactic electron density fluctuations through an examination of the scattering of the radio pulses emitted by pulsars as they propagate through the diffuse ionized interstellar gas. A widely used model for the electron density spectrum is based on the simple power-law: Pne(q)∝ q-β, where β = 11/3 is usually assumed, corresponding to Kolmogorov's turbulence spectrum. The simple Kolmogorov model provides satisfactory agreement for observations along many lines of sight; however, major inconsistencies remain. The inconsistencies suggest that an increase in the ratio of the power between the high (10-8[ m]-1≤ q<=10-7[ m]-1) and low (10-13[ m]-1≤ q<=10-12[ m]-1) wavenumbers is needed. This enhancement in the ratio can in turn be achieved by either including an inner scale, corresponding to a dissipation scale for the turbulent cascade, in the Kolmogorov spectrum or by considering steeper spectra. Spectra with spectral exponents β > 4 have been in general rejected based on observations of pulsar refractive scintillations. The special case of β = 4 has been given little attention and is analyzed in detail. Physically, this 'β = 4' model corresponds to the random distribution, both in location and orientation, of discrete objects with relatively sharp boundaries across the line of sight. An outer scale is included in the model to account for the average size of such objects. We compare the predictions of the inner-scale and β = 4 models both with published observations and observations we made as part of this investigation. We conclude that the form of the wavenumber spectrum is dependent on the line of sight. We propose a composite spectrum featuring a uniform background turbulence in presence of randomly distributed discrete objects, as modeled by the β = model.

  11. Interstellar Sweat Equity

    NASA Astrophysics Data System (ADS)

    Cohen, M. H.; Becker, R. E.; O'Donnell, D. J.; Brody, A. R.

    So, you have just launched aboard the Starship, headed to an exoplanet light years from Earth. You will spend the rest of your natural life on this journey in the expectation and hope that your grandchildren will arrive safely, land, and build a new settlement. You will need to govern the community onboard the Starship. This system of governance must meet unique requirements for participation, representation, and decision-making. On a spaceship that can fly and operate by itself, what will the crewmembers do for their generations in transit? Certainly, they will train and train again to practice the skills they will need upon arrival at a new world. However, this vicarious practice neither suffices to prepare the future pioneers for their destiny at a new star nor will it provide them with the satisfaction in their own work. To hone the crewmembers' inventive and technical skills, to challenge and prepare them for pioneering, the crew would build and expand the interstellar ship in transit. This transstellar ``sweat equity'' gives a stake in the enterprise to all the people, providing meaningful and useful activity to the new generations of crewmembers. They build all the new segments of the vessel from raw materials - including atmosphere - stored on board. Construction of new pressure shell modules would be one option, but they also reconstruct or fill-in existing pressurized volumes. The crew makes new life support system components and develops new agricultural modules in anticipation of their future needs. Upon arrival at the new star or planet, the crew shall apply these robustly developed skills and self-sufficient spirit to their new home.

  12. Identification of More Interstellar C60+ Bands

    NASA Astrophysics Data System (ADS)

    Walker, G. A. H.; Bohlender, D. A.; Maier, J. P.; Campbell, E. K.

    2015-10-01

    Based on gas-phase laboratory spectra at 6 K, Campbell et al. confirmed that the diffuse interstellar bands (DIBs) at 9632.7 and 9577.5 Å are due to absorption by the fullerene ion {{{C}}}60+. They also reported the detection of two other, weaker bands at 9428.5 and 9365.9 Å. These lie in spectral regions heavily contaminated by telluric water vapor lines. We acquired CFHT ESPaDOnS spectra of HD 183143 close to the zenith and chopped with a nearby standard to correct for the telluric line absorption which enabled us to detect a DIB at 9365.9 Å of relative width and strength comparable to the laboratory absorption. There is a DIB of similar strength and FWHM at 9362.5 Å. A stellar emission feature at 9429 Å prevented detection of the 9428.5 Å band. However, a CFHT archival spectrum of HD 169454, where emission is absent at 9429 Å, clearly shows the 9428.5 Å DIB with the expected strength and width. These results further confirm {{{C}}}60+ as a DIB carrier. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

  13. "CHON" particles: The interstellar component of cometary dust

    NASA Technical Reports Server (NTRS)

    Lien, David J.

    1998-01-01

    Interstellar dust is characterized by strong absorption in the ultraviolet and the mid-IR. Current models of interstellar dust are based on three chemically distinct components: a form of carbon (usually graphite), a silicate, and a blend of polycyclic aromatic hydrocarbons or other carbonaceous material. Previous work using effective medium theories to understand the optical properties of cometary dust suggested that an amalgam of materials could reproduce the observed interstellar and cometary dust features. Recently, Lawler and Brownlee (1992) re-analyzed the PIA and PUMA-1 data sets from the Giotto flyby of P/Halley and discovered that the so-called "CHON" particles were actually composed of a blend of carbon-bearing and silicon-bearing materials. Based on effective medium theories, the absorption spectrum of such a material would display the spectral features of each of the components - strong UV absorption from the carbonaceous component and strong absorption in the IR from the silicate component. To test this idea, vapor-deposited samples were created using two different deposition techniques: sputtering with an argon RF magnetron and deposition from an argon plasma torch. Two different compositions were tested: a blend of graphite and silica in a 7:1 ratio and an amalgam of materials whose approximate composition matches the "CHON"-silicate abundances for the uncompressed PIA data set of Lawler and Brownlee: graphite, iron oxide, magnesium oxide, ammonium sulfate, calcium carbonate, and silica in mass ratios of 6:4.3:4:2.2:1:9. The samples were finely ground and pressed into 2" diameter disks using a 40 ton press. In all, four different experiments were performed: one with each of the compositions (C:SiO and "CHON") in both the RF magnetron and the plasma torch chambers. The RF magnetron created a uniform dark thin film on the substrate surface, and the plasma torch created a coating of small (<100 micron) diameter grey particles. The spectra of all four

  14. On the Virial Theorem for Interstellar Medium

    SciTech Connect

    Ryutov, D

    2007-09-24

    An attempt has been made to derive a version of the virial integral that would describe average properties of the interstellar medium (ISM). It is suggested to eliminate the (large) contribution of stellar matter by introducing 'exclusion zones' surrounding stars. Such an approach leads to the appearance of several types of additional surface integrals in the general expression. Their contribution depends on the rate of energy and matter exchange between the stars and ISM. If this exchange is weak, one can obtain a desired virial integral for ISM. However, the presence of intermittent large-scale energetic events significantly constrains the applicability of the virial theorem. If valid, the derived virial integral is dominated by cold molecular/atomic clouds, with only minor contribution of the global magnetic field and low-density warm part.

  15. Some O I oscillator strengths and the interstellar abundance of oxygen

    NASA Technical Reports Server (NTRS)

    Zeippen, C. J.; Seaton, M. J.; Morton, D. C.

    1977-01-01

    Calculated and experimental oscillator strengths for the O I intersystem line at 1356 A and for other O I lines of interest in interstellar absorption-line studies are discussed. Attention is given to experimental f-values for the lines at 1302, 1305, and 1306 A, previous work on the f-values for the lines at 1356 and 1359 A, wave-function expansion, and calculations for permitted as well as intercombination lines. Copernicus observations of several interstellar absorption lines due to O I, C II, P II, and Ni II toward Zeta Oph are reported, equivalent widths are determined, and a curve-of-growth analysis is performed for the O I absorption lines. Oscillator strengths are recommended for the far-UV resonance lines of O I, and it is concluded that the oxygen in the interstellar H I regions toward Zeta Oph is depleted by 45% to 69%.

  16. Interstellar gas, dust and diffuse bands in the SMC

    NASA Astrophysics Data System (ADS)

    Cox, N. L. J.; Cordiner, M. A.; Ehrenfreund, P.; Kaper, L.; Sarre, P. J.; Foing, B. H.; Spaans, M.; Cami, J.; Sofia, U. J.; Clayton, G. C.; Gordon, K. D.; Salama, F.

    2007-08-01

    Aims:In order to gain new insight into the unidentified identity of the diffuse interstellar band (DIB) carriers, this paper describes research into possible links between the shape of the interstellar extinction curve (including the 2175 Å bump and far-UV rise), the presence or absence of DIBs, and physical and chemical conditions of the diffuse interstellar medium (gas and dust) in the Small Magellanic Cloud (SMC). Methods: We searched for DIB absorption features in VLT/UVES spectra of early-type stars in the SMC whose reddened lines-of-sight probe the diffuse interstellar medium of the SMC. Apparent column density profiles of interstellar atomic species (Na i, K i, Ca ii and Ti ii) are constructed to provide information on the distribution and conditions of the interstellar gas. Results: The characteristics of eight DIBs detected toward the SMC wing target AzV 456 are studied and upper limits are derived for the DIB equivalent widths toward the SMC stars AzV 398, AzV 214, AzV 18, AzV 65 and Sk 191. The amount of reddening is derived for these SMC sightlines, and, using RV and the H i column density, converted into a gas-to-dust ratio. From the atomic column density ratios we infer an indication of the strength of the interstellar radiation field, the titanium depletion level and a relative measure of turbulence/quiescence. The presence or absence of DIBs appears to be related to the shape of the extinction curve, in particular with respect to the presence or absence of the 2175 Å feature. Our measurements indicate that the DIB characteristics depend on the local physical conditions and chemical composition of the interstellar medium of the SMC, which apparently determine the rate of formation (and/or) destruction of the DIB carriers. The UV radiation field (via photoionisation and photo-destruction) and the metallicity (i.e. carbon abundance) are important factors in determining diffuse band strengths which can differ greatly both between and within galaxies

  17. Anomalous Oxygen and Krypton Abundances in Interstellar Gas

    NASA Technical Reports Server (NTRS)

    Meyer, David M.

    2004-01-01

    The primary objective of this program was to obtain FUSE observations of the interstellar H2 absorption toward a sample of stars observed with the HST STIS spectrograph as part of the ISM SNAP Survey. This Survey was designed to produce a database of high quality, high resolution W spectra from which interstellar gas-phase elemental abundances could be derived for large portions of the Galaxy. In particular, oxygen and krypton were chosen as excellent tracers for measuring the homogeneity of the interstellar gas due to their weak depletion into dust grains. The gas-phase 0 and Kr abundances relative to total hydrogen column density had previously been shown with HST GHRS measurements to be essentially constant in the local Milky Way. One of the main motivations of the ISM SNAP Survey was to determine if this constancy held at greater distances and in denser sightlines (where depletion into dust could be a possibility). The initial ISM SNAP STIS observations indicated a number of sightlines with unusual 0 and Kr abundances relative to the measured H I column densities. Since the appropriate benchmark for accurate abundance comparisons is the total hydrogen column density (H I plus H2), FUSE observations of interstellar H2 were carried out in these sightlines in order to determine if they represent cases of true abundance anomalies.

  18. Surface science studies of ethene containing model interstellar ices

    NASA Astrophysics Data System (ADS)

    Puletti, F.; Whelan, M.; Brown, W. A.

    2011-05-01

    The formation of saturated hydrocarbons in the interstellar medium (ISM) is difficult to explain only by taking into account gas phase reactions. This is mostly due to the fact that carbonium ions only react with H_2 to make unsaturated hydrocarbons, and hence no viable route to saturated hydrocarbons has been postulated to date. It is therefore likely that saturation processes occur via surface reactions that take place on interstellar dust grains. One of the species of interest in this family of reactions is C_2H_4 (ethene) which is an intermediate in several molecular formation routes (e.g. C_2H_2 → C_2H_6). To help to understand some of the surface processes involving ethene, a study of ethene deposited on a dust grain analogue surface (highly oriented pyrolytic graphite) held under ultra-high vacuum at 20 K has been performed. The adsorption and desorption of ethene has been studied both in water-free and water-dominated model interstellar ices. A combination of temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) have been used to identify the adsorbed and trapped species and to determine the kinetics of the desorption processes. In all cases, ethene is found to physisorb on the carbonaceous surface. As expected water has a very strong influence on the desorption of ethene, as previously observed for other model interstellar ice systems.

  19. High Resolution Laboratory Spectroscopy: Unraveling the Secrets of Interstellar Chemistry

    NASA Astrophysics Data System (ADS)

    Ziurys, Lucy M.

    2008-05-01

    At present, over 140 different chemical compounds have been identified in interstellar and circumstellar gas. Such observations have offered a unique avenue by which to probe the cold, dense regions in our Galaxy and in external galaxies. Because these molecules are primarily present in colder material, they are usually studied at high spectral resolutions (1 part in 106-107) via their pure rotational transitions, which typically occur at millimeter and sub-millimeter wavelengths. Such studies cannot be carried out, however, without the input of high resolution laboratory spectroscopy. Such measurements provide the "fingerprint” spectral pattern critical for accurate astronomical identifications. Because of the complexity of current interstellar spectra and the propensity of unidentified features, precise laboratory data are essential. Current methods employed in the laboratory for high resolution measurements include millimeter/sub-mm direct absorption, velocity modulation, and Fourier transform microwave spectroscopy (FTMW). Each of these experimental techniques has certain unique advantages, which will be discussed. Also of importance are the synthetic methods utilized to create the radicals, ions, and other transient species typically found in interstellar space. Such molecules are generated in DC and AC glow discharges, pulsed supersonic jet expansions, and using Broida-type ovens. In addition, spectral analyses can be quite complex, in particular if there are low lying excited torsional or electronic states, or if molecular inversion is present. Recent laboratory results for potential interstellar species will also be presented, in particular those for negative ions, phosphorus-bearing radicals, and organic "prebiotic” species.

  20. Silicon chemistry in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Langer, William D.; Glassgold, A. E.

    1990-01-01

    A new model of interstellar silicon chemistry is presented that explains the lack of SiO detections in cold clouds and contains an exponential temperature dependence for the SiO abundance. A key aspect of the model is the sensitivity of SiO production by neutral silicon reactions to density and temperature, which arises from the dependence of the rate coefficients on the population of the excited fine-structure levels of the silicon atom. As part of the explanation of the lack of SiO detections at low temperatures and densities, the model also emphasizes the small efficiencies of the production routes and the correspondingly long times needed to reach equilibrium. Measurements of the abundance of SiO, in conjunction with theory, can provide information on the physical properties of interstellar clouds such as the abundance of oxygen bearing molecules and the depletion of interstellar silicon.

  1. An Interstellar Sail before 2020?

    NASA Astrophysics Data System (ADS)

    Matloff, G. L.; Johnson, L.

    In 2017, NASA plans to launch the Near Earth Asteroid (NEA) Scout, a solar-photon-sail propelled probe to rendezvous with one or more near-Earth asteroids. According to a publication describing early design parameters, the spacecraft mass is 12 kg and the square sail has an area of 83 square meters. This craft, like many other NASA science missions, will likely remain functional after the completion of its primary mission. This paper investigates options for application of this spacecraft during its extended mission as an Interstellar Trailblazer. As well as kinematics, thermal aspects and the communications challenges are discussed. Although interstellar velocities for this craft will not be high and engineering the pre-perihelion trajectory will be challenging, an extended demonstration mission of this type would certainly spur interest in the development of true interstellar sails. As of December 2014, the design of this spacecraft continues to evolve. The performance estimates presented here may be overly conservative.

  2. Interstellar Isotopes: Prospects with ALMA

    NASA Technical Reports Server (NTRS)

    Charnley Steven B.

    2010-01-01

    Cold molecular clouds are natural environments for the enrichment of interstellar molecules in the heavy isotopes of H, C, N and O. Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets, that may trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. Models of the fractionation chemistry of H, C, N and O in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred, make several predictions that can be tested in the near future by molecular line observations. The range of fractionation ratios expected in different interstellar molecules will be discussed and the capabilities of ALMA for testing these models (e.g. in observing doubly-substituted isotopologues) will be outlined.

  3. Interrelationships between interstellar and interplanetary grains

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.

    1986-01-01

    The relationship between solar system dust (SSD) and interstellar dust particles (ISMD) is being reconsidered because of the discovery of isotopic anomalies in meteorites. Meteoritic, circumstellar/meteoritic, interstellar/meteoritic, planetary, and cometary data are reviewed.

  4. Interstellar Initiative Web Page Design

    NASA Technical Reports Server (NTRS)

    Mehta, Alkesh

    1999-01-01

    This summer at NASA/MSFC, I have contributed to two projects: Interstellar Initiative Web Page Design and Lenz's Law Relative Motion Demonstration. In the Web Design Project, I worked on an Outline. The Web Design Outline was developed to provide a foundation for a Hierarchy Tree Structure. The Outline would help design a Website information base for future and near-term missions. The Website would give in-depth information on Propulsion Systems and Interstellar Travel. The Lenz's Law Relative Motion Demonstrator is discussed in this volume by Russell Lee.

  5. Experimental interstellar organic chemistry - Preliminary findings

    NASA Technical Reports Server (NTRS)

    Khare, B. N.; Sagan, C.

    1973-01-01

    Review of the results of some explicit experimental simulation of interstellar organic chemistry consisting in low-temperature high-vacuum UV irradiation of condensed simple gases known or suspected to be present in the interstellar medium. The results include the finding that acetonitrile may be present in the interstellar medium. The implication of this and other findings are discussed.

  6. On the question of interstellar travel

    NASA Technical Reports Server (NTRS)

    Wolfe, J. H.

    1985-01-01

    Arguments are presented which show that motives for interstellar travel by advanced technological civilizations based on an extrapolation of earth's history may be quite invalid. In addition, it is proposed that interstellar travel is so enormously expensive and perhaps so hazardous, that advanced civilizations do not engage in such practices because of the ease of information transfer via interstellar communication.

  7. Interstellar Aldehydes and their corresponding Reduced Alcohols: Interstellar Propanol?

    NASA Astrophysics Data System (ADS)

    Etim, Emmanuel; Chakrabarti, Sandip Kumar; Das, Ankan; Gorai, Prasanta; Arunan, Elangannan

    2016-07-01

    There is a well-defined trend of aldehydes and their corresponding reduced alcohols among the known interstellar molecules; methanal (CH_2O) and methanol (CH_3OH); ethenone (C_2H_2O) and vinyl alcohol (CH_2CHOH); ethanal (C_2H_4O) and ethanol(C_2H_5OH); glycolaldehyde (C_2H_4O_2) and ethylene glycol(C_2H_6O_2). The reduced alcohol of propanal (CH_3CH_2CHO) which is propanol (CH_3CH_2CH_2OH) has not yet been observed but its isomer; ethyl methyl ether (CH_3CH_2OCH_3) is a known interstellar molecule. In this article, different studies are carried out in investigating the trend between aldehydes and their corresponding reduced alcohols and the deviation from the trend. Kinetically and with respect to the formation route, alcohols could have been produced from their corresponding reduced aldehydes via two successive hydrogen additions. This is plausible because of (a) the unquestionable high abundance of hydrogen, (b) presence of energy sources within some of the molecular clouds and (c) the ease at which successive hydrogen addition reaction occurs. In terms of stability, the observed alcohols are thermodynamically favorable as compared to their isomers. Regarding the formation process, the hydrogen addition reactions are believed to proceed on the surface of the interstellar grains which leads to the effect of interstellar hydrogen bonding. From the studies, propanol and propan-2-ol are found to be more strongly attached to the surface of the interstellar dust grains which affects its overall gas phase abundance as compared to its isomer ethyl methyl ether which has been observed.

  8. The Speed Limit for Graphene Interstellar Photon Sails

    NASA Astrophysics Data System (ADS)

    Matloff, G. L.

    Graphene, a two-dimensional carbon molecular monolayer, has properties that may render it very useful for application to interstellar solar photon sailing. These include very low areal mass thickness, high melting point, high impermeability to fill gas in a hollow-body sail configuration, and high tensile strength. With appropriate "additives," graphene has a finite reflectance to sunlight and sunlight absorption of 40% or higher. Here, we evaluate the probably unobtainable ultimate performance of this material. It is assumed that absorption can be raised to 95% and reflectance to 5% without increasing areal mass thickness over the graphene value of 7.4 * 10-7 kg/m2. It is also assumed that the only limitations on perihelion distance are thermal; spaceenvironment effects and possible variation of optical properties with temperature are ignored. To evaluate ultimate performance, an initially parabolic solar orbit with a ~0.01 AU perihelion is assumed. A thin-film probe with the payload integrated with the sail can achieve an interstellar cruise velocity of ~0.046c in the highly unlikely event that accelerations of ~6,000g can be tolerated. Regardless of the final velocity, graphene "Starwisps" might see application in interstellar particle-beam propulsion.

  9. The interstellar tunnel of neutral-free gas toward Beta Canis Majoris

    NASA Technical Reports Server (NTRS)

    Welsh, Barry Y.

    1991-01-01

    Using high-resolution sodium absorption observations of early-type stars to determine the distribution of neutral interstellar gas in the direction of the star Beta CMa, the contours of a large feature in the local interstellar medium, some 50 pc in diameter and 300 pc long, that appears to be virtually free of neutral gas have been mapped. This rarefied 'interstellar tunnel' is an extension of a region of very low gas density surrounding the sun called the Local Bubble, which may well have been formed by the interaction of expanding interstellar cavities produced by multiple supernova events. This large region of unusually low gas density will be a prime area for study in the soft X-ray and EUV spectral regions.

  10. Isotopic Fractionation in Interstellar Chemistry

    NASA Technical Reports Server (NTRS)

    Charnley, Steven

    2009-01-01

    Isotopically fractionated material is found in many solar system objects, including meteorites and comets. It is thought, in some cases, to trace interstellar material that was incorporated into the solar sys tem without undergoing significant processing. In this poster, we sho w the results of several models of the nitrogen, oxygen, and carbon f ractionation in proto-stellar cores.

  11. Term Projects on Interstellar Comets

    ERIC Educational Resources Information Center

    Mack, John E.

    1975-01-01

    Presents two calculations of the probability of detection of an interstellar comet, under the hypothesis that such comets would escape from comet clouds similar to that believed to surround the sun. Proposes three problems, each of which would be a reasonable term project for a motivated undergraduate. (Author/MLH)

  12. Erratum: Interstellar Abundance Standards Revisited

    NASA Astrophysics Data System (ADS)

    Sofia, U. J.; Meyer, D. M.

    2001-09-01

    In the Letter ``Interstellar Abundance Standards Revisited'' by U. J. Sofia and D. M. Meyer (ApJ, 554, L221 [2001]), Table 2 and its footnotes contain several typographical errors. The corrected table is shown below. We note that the solar reference standard now implies a positive abundance of nitrogen in halo dust.

  13. Stardust Interstellar Preliminary Examination (ISPE)

    NASA Technical Reports Server (NTRS)

    Westphal, A. J.; Allen, C.; Bajt, S.; Basset, R.; Bastien, R.; Bechtel, H.; Bleuet, P.; Borg, J.; Brenker F.; Bridges, J.

    2009-01-01

    In January 2006 the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, C omet 81P/Wild2, and a collector dedicated to the capture and return o f contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the co llecting area) and aluminum foils. The Stardust Interstellar Dust Col lector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2-) day during two periods before the co metary encounter. The Stardust Interstellar Preliminary Examination ( ISPE) is a three-year effort to characterize the collection using no ndestructive techniques. The ISPE consists of six interdependent proj ects: (1) Candidate identification through automated digital microsco py and a massively distributed, calibrated search (2) Candidate extr action and photodocumentation (3) Characterization of candidates thro ugh synchrotronbased FourierTranform Infrared Spectroscopy (FTIR), S canning XRay Fluoresence Microscopy (SXRF), and Scanning Transmission Xray Microscopy (STXM) (4) Search for and analysis of craters in f oils through FESEM scanning, Auger Spectroscopy and synchrotronbased Photoemission Electron Microscopy (PEEM) (5) Modeling of interstell ar dust transport in the solar system (6) Laboratory simulations of h ypervelocity dust impacts into the collecting media

  14. Constraining the Properties of Cold Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    Spraggs, Mary Elizabeth; Gibson, Steven J.

    2016-01-01

    Since the interstellar medium (ISM) plays an integral role in star formation and galactic structure, it is important to understand the evolution of clouds over time, including the processes of cooling and condensation that lead to the formation of new stars. This work aims to constrain and better understand the physical properties of the cold ISM by utilizing large surveys of neutral atomic hydrogen (HI) 21cm spectral line emission and absorption, carbon monoxide (CO) 2.6mm line emission, and multi-band infrared dust thermal continuum emission. We identify areas where the gas may be cooling and forming molecules using HI self-absorption (HISA), in which cold foreground HI absorbs radiation from warmer background HI emission.We are developing an algorithm that uses total gas column densities inferred from Planck and other FIR/sub-mm data in parallel with CO and HISA spectral line data to determine the gas temperature, density, molecular abundance, and other properties as functions of position. We can then map these properties to study their variation throughout an individual cloud as well as any dependencies on location or environment within the Galaxy.Funding for this work was provided by the National Science Foundation, the NASA Kentucky Space Grant Consortium, the WKU Ogden College of Science and Engineering, and the Carol Martin Gatton Academy for Mathematics and Science in Kentucky.

  15. Accurate Modeling of X-ray Extinction by Interstellar Grains

    NASA Astrophysics Data System (ADS)

    Hoffman, John; Draine, B. T.

    2016-02-01

    Interstellar abundance determinations from fits to X-ray absorption edges often rely on the incorrect assumption that scattering is insignificant and can be ignored. We show instead that scattering contributes significantly to the attenuation of X-rays for realistic dust grain size distributions and substantially modifies the spectrum near absorption edges of elements present in grains. The dust attenuation modules used in major X-ray spectral fitting programs do not take this into account. We show that the consequences of neglecting scattering on the determination of interstellar elemental abundances are modest; however, scattering (along with uncertainties in the grain size distribution) must be taken into account when near-edge extinction fine structure is used to infer dust mineralogy. We advertise the benefits and accuracy of anomalous diffraction theory for both X-ray halo analysis and near edge absorption studies. We present an open source Fortran suite, General Geometry Anomalous Diffraction Theory (GGADT), that calculates X-ray absorption, scattering, and differential scattering cross sections for grains of arbitrary geometry and composition.

  16. The Sun's dusty interstellar environment

    NASA Astrophysics Data System (ADS)

    Sterken, Veerle

    2016-07-01

    The Sun's dusty interstellar environment Interstellar dust from our immediate interstellar neighborhood travels through the solar system at speeds of ca. 26 km/s: the relative speed of the solar system with respect to the local interstellar cloud. On its way, its trajectories are altered by several forces like the solar radiation pressure force and Lorentz force. The latter is due to the charged dust particles that fly through the interplanetary magnetic field. These trajectories differ per particle type and size and lead to varying fluxes and directions of the flow inside of the solar system that depend on location but also on phase in the solar cycle. Hence, these fluxes and directions depend strongly on the configuration of the inner regions and outer regions of the heliosphere. Several missions have measured this dust in the solar system directly. The Ulysses dust detector data encompasses 16 years of intestellar dust fluxes and approximate directions, Stardust captured returned to Earth a few of these particles sucessfully, and finally the Cassini dust detector allowed for compositional information to be obtained from the impacts on the instrument. In this talk, we give an overview of the current status of interstellar dust research through the measurements made inside of the solar system, and we put them in perspective to the knowledge obtained from more classical astronomical means. In special, we focus on the interaction of the dust with the interplanetary magnetic field, and on what we learn about the dust (and the fields) by comparing the available dust data to computer simulations of dust trajectories. Finally, we synthesize the different methods of observation, their results, and give a preview on new research opportunities in the coming year(s).

  17. The Interstellar Abundance of Lead: Experimental Oscillator Strengths for Pb II λ1203 and λ1433 and New Detections of Pb II in the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Ritchey, Adam Michael; Heidarian, Negar; Irving, Richard E.; Federman, Steven R.; Ellis, David G.; Cheng, Song; Curtis, Larry J.; Furman, W. A.

    2015-08-01

    Accurate gas-phase abundances of ions in the interstellar medium may be obtained through the analysis of interstellar absorption lines, but only if the oscillator strengths (f-values) of the relevant transitions are well known. For dominant ions, comparison of the gas-phase abundance with the appropriate solar reference abundance yields the degree to which the element is incorporated into interstellar dust grains. Singly-ionized lead is the dominant form of this element in the neutral interstellar medium. However, while Pb II has several strong resonance lines in the ultraviolet, the f-values for these transitions are uncertain. Here, we present the first experimentally determined oscillator strengths for the Pb II transitions at 1203.6 Å and 1433.9 Å, obtained from lifetime measurements made using beam-foil techniques. We also present new detections of these lines in the interstellar medium from an analysis of archival spectra acquired by the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. Notably, our observations of the Pb II λ1203 line represent the first detection of this transition in interstellar gas. Our experimental f-values for the Pb II λ1203 and λ1433 transitions are consistent with recent theoretical results, including our own relativistic calculations, but are significantly smaller than previous values based on older calculations. For the Pb II λ1433 line, in particular, our new f-value yields an increase in the interstellar abundance of Pb of 0.43 dex over estimates based on the f-value listed by Morton. With our revised f-values, and with our new detections of Pb II λ1203 and λ1433, we find that the depletion of Pb onto interstellar grains is not nearly as severe as previously thought, and is very similar to the depletions seen for elements such as Zn and Sn, which have similar condensation temperatures.

  18. Ultraviolet observations of cool stars. VIII - Interstellar matter toward Procyon

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Henry, R. C.; Moos, H. W.; Linsky, J. L.

    1978-01-01

    The profile of the chromospheric L-alpha emission line of the F5 IV-V star Procyon (Alpha CMi, d = 3.5 pc) has been measured using the high-resolution Princeton spectrometer aboard NASA's Copernicus satellite. L-alpha absorption lines of interstellar deuterium and hydrogen are distinctly present. The average number density of interstellar hydrogen along the line of sight is found to be 0.11 + or - 0.02 per cu cm, similar to the densities that have been found in the directions of the stars Epsilon Eri, Epsilon Ind, and Alpha Cen A. These stars are all within 3.5 pc of the earth. The ratio of deuterium to hydrogen in the direction of Procyon is found to be 1.3 (+1.2, -0.5) x 10 to the -5th.

  19. Variable interstellar lines in spectra of HD 73882

    NASA Astrophysics Data System (ADS)

    Galazutdinov, G.; Krełowski, J.; Beletsky, Y.; Valyavin, G.

    2013-11-01

    We report a detection of variability in interstellar absorption lines of Cai at 4227 Å and Fei at 3860 Å in very high signal-to-noise ratio (>1000) UVES and MIKE spectra of HD 73882 (NX Vel) carried out with the aid of 8-m telescope UT2 at Paranal and 6.5-m Magellan Telescope Clay at Las Campanas Observatory, Chile. The spectra, acquired in 2006 January and 2012 January, respectively, clearly show that the intensity and profile shapes of the Cai and Fei lines had dramatically changed within the 6 year period. Other interstellar features, observed along the same line of sight, do not demonstrate strong changes. It is likely that a high velocity CaFe cloud obscured the star between the two observations.

  20. A survey of interstellar neutral potassium. I - Abundances and physical conditions in clouds toward 188 early-type stars

    NASA Technical Reports Server (NTRS)

    Chaffee, F. H., Jr.; White, R. E.

    1982-01-01

    Observations of interstellar absorption in the resonance doublet 7664, 7698 A of neutral potassium toward 188 early-type stars at a spectral resolution of 8 km/s are reported. The 7664 A line is successfully separated from nearly coincident telluric O2 absorption for all but a few of the 165 stars for which K I absorption is detected, making possible an abundance analysis by the doublet ratio method. The relationships between the potassium abundances and other atomic abundances, the abundance of molecular hydrogen, and interstellar reddening are investigated.

  1. The interstellar C3 chain molecule in different interstellar environments

    NASA Astrophysics Data System (ADS)

    Galazutdinov, G.; Pětlewski, A.; Musaev, F.; Moutou, C.; Lo Curto, G.; Krelowski, J.

    2002-12-01

    We present an analysis of spectra of six stars taken with high resolution (R=220 000). The stars are reddened by molecular clouds that differ by the relative strength of the 5797 and 5780 diffuse interstellar bands (DIBs). The high signal-to-noise ratio of the spectra (S/N ~ 700-1000) shows that the abundance of the linear molecule C3 with respect to EB-V varies considerably from one star to an other. There is no correlation with EB-V. The strong variations in the abundance of C3 must therefore be caused by another circumstance. We point out that this may be the case: from an analysis of the interstellar potassium lines in the same spectra we conclude large differences in the state of ionization produced by interstellar photons with energies below the ionization potential of hydrogen. The ratio of the abundances of C3 and C2 varies considerably in different directions, even when the ratio between the strengths of various DIBs remains approximately constant. Based on data collected at the ESO 3.6 m telescope operated on La Silla Observatory, Chile.

  2. Interstellar dust. Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft.

    PubMed

    Westphal, Andrew J; Stroud, Rhonda M; Bechtel, Hans A; Brenker, Frank E; Butterworth, Anna L; Flynn, George J; Frank, David R; Gainsforth, Zack; Hillier, Jon K; Postberg, Frank; Simionovici, Alexandre S; Sterken, Veerle J; Nittler, Larry R; Allen, Carlton; Anderson, David; Ansari, Asna; Bajt, Saša; Bastien, Ron K; Bassim, Nabil; Bridges, John; Brownlee, Donald E; Burchell, Mark; Burghammer, Manfred; Changela, Hitesh; Cloetens, Peter; Davis, Andrew M; Doll, Ryan; Floss, Christine; Grün, Eberhard; Heck, Philipp R; Hoppe, Peter; Hudson, Bruce; Huth, Joachim; Kearsley, Anton; King, Ashley J; Lai, Barry; Leitner, Jan; Lemelle, Laurence; Leonard, Ariel; Leroux, Hugues; Lettieri, Robert; Marchant, William; Ogliore, Ryan; Ong, Wei Jia; Price, Mark C; Sandford, Scott A; Sans Tresseras, Juan-Angel; Schmitz, Sylvia; Schoonjans, Tom; Schreiber, Kate; Silversmit, Geert; Solé, Vicente A; Srama, Ralf; Stadermann, Frank; Stephan, Thomas; Stodolna, Julien; Sutton, Stephen; Trieloff, Mario; Tsou, Peter; Tyliszczak, Tolek; Vekemans, Bart; Vincze, Laszlo; Von Korff, Joshua; Wordsworth, Naomi; Zevin, Daniel; Zolensky, Michael E

    2014-08-15

    Seven particles captured by the Stardust Interstellar Dust Collector and returned to Earth for laboratory analysis have features consistent with an origin in the contemporary interstellar dust stream. More than 50 spacecraft debris particles were also identified. The interstellar dust candidates are readily distinguished from debris impacts on the basis of elemental composition and/or impact trajectory. The seven candidate interstellar particles are diverse in elemental composition, crystal structure, and size. The presence of crystalline grains and multiple iron-bearing phases, including sulfide, in some particles indicates that individual interstellar particles diverge from any one representative model of interstellar dust inferred from astronomical observations and theory. PMID:25124433

  3. The violet interstellar medium associated with the Carina Nebula

    NASA Technical Reports Server (NTRS)

    Pettini, M.; Laurent, C.; Paul, J. A.

    1982-01-01

    The interstellar spectrum of HD 93205, an 03V star in the cluster Tr16, located inside the most active part of the Great Carina Nebula was analyzed using data extracted directly from raw IUE images. From the analysis of 67 lines of 25 atoms, ions and molecules, up to six discrete absorption components spanning a maximum velocity range of approximately 375 km 5/1 were identified. The component structure for different species is tabulated and sample absorption lines, indicating at the top the positions of the six components, labelled A to F are shown. Ion column densities appropriate to each component which can be resolved in at least one line were derived by constructing empirical curves of growth and by fitting the observations with corresponding theoretical absorption line profiles. The most important results concerning each component are discussed.

  4. Evolutionary models of interstellar chemistry

    NASA Technical Reports Server (NTRS)

    Prasad, Sheo S.

    1987-01-01

    The goal of evolutionary models of interstellar chemistry is to understand how interstellar clouds came to be the way they are, how they will change with time, and to place them in an evolutionary sequence with other celestial objects such as stars. An improved Mark II version of an earlier model of chemistry in dynamically evolving clouds is presented. The Mark II model suggests that the conventional elemental C/O ratio less than one can explain the observed abundances of CI and the nondetection of O2 in dense clouds. Coupled chemical-dynamical models seem to have the potential to generate many observable discriminators of the evolutionary tracks. This is exciting, because, in general, purely dynamical models do not yield enough verifiable discriminators of the predicted tracks.

  5. Interstellar organic matter in meteorites

    NASA Technical Reports Server (NTRS)

    Yang, J.; Epstein, S.

    1983-01-01

    Deuterium-enriched hydrogen is present in organic matter in such meteorites as noncarbonaceous chondrites. The majority of the unequilibrated primitive meteorites contain hydrogen whose D/H ratios are greater than 0.0003, requiring enrichment (relative to cosmic hydrogen) by isotope exchange reactions taking place below 150 K. The D/H values presented are the lower limits for the organic compounds derived from interstellar molecules, since all processes subsequent to their formation, including terrestrial contamination, decrease their D/H ratios. In contrast, the D/H ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites analyzed. The C-13/C-12 ratios of organic matter, irrespective of D/H ratio, lie well within those observed for the earth. Present findings suggest that other interstellar material, in addition to organic matter, is preserved and is present in high D/H ratio meteorites.

  6. One Kilogram Interstellar Colony Mission

    NASA Astrophysics Data System (ADS)

    Mole, A.

    Small interstellar colony probes based on nanotechnology will become possible long before giant multi-generation ships become affordable. A beam generator and magnetic sail can accelerate a one kg probe to .1 c, braking via the interstellar field can decelerate it, and the field in a distant solar system can allow it to maneuver to an extrasolar planet. A heat shield is used for landing and nanobots emerge to build ever-larger robots and construct colony infrastructure. Humans can then be generated from genomes stored as data in computer memory. Technology is evolving towards these capabilities and should reach the required level in fifty years. The plan appears to be affordable, with the principal cost being the beam generator, estimated at $17 billion.

  7. The Properties of the local Interstellar Medium and the Interaction of the Stellar Winds of epsilon Indi and lambda Andromedae with the Interstellar Environment

    NASA Technical Reports Server (NTRS)

    Wood, Brian E.; Alexander, William R.; Linsky, Jeffrey L.

    1996-01-01

    We present new observations of the Ly alpha lines of Epsilon Indi (K5 5) and A Andromedae (G8 4-3 + ?) These data were obtained by the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. Analysis of the interstellar H 1 and D 1 absorption lines reveals that the velocities and temperatures inferred from the H 1 lines are inconsistent with the parameters inferred from the D 1 lines, unless the H 1 absorption is assumed to be produced by two absorption components. One absorption component is produced by interstellar material. For both lines of sight observed, the velocity of this component is consistent with the velocity predicted by the local flow vector. For the Epsilon Indi data, the large velocity separation between the stellar emission and the interstellar absorption allows us to measure the H 1 column density independent of the shape of the intrinsic stellar Ly alpha profile. This approach permits us to quote an accurate column density and to assess its uncertainty with far more confidence than in previous analyses, for which the errors were dominated by uncertainties in the assumed stellar profiles.

  8. Silicon chemistry in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Langer, William D.; Glassgold, A. E.

    1989-01-01

    Interstellar SiO was discovered shortly after CO but it has been detected mainly in high density and high temperature regions associated with outflow sources. A new model of interstellar silicon chemistry that explains the lack of SiO detections in cold clouds is presented which contains an exponential temperature dependence for the SiO abundance. A key aspect of the model is the sensitivity of SiO production by neutral silicon reactions to density and temperature, which arises from the dependence of the rate coefficients on the population of the excited fine structure levels of the silicon atom. This effect was originally pointed out in the context of neutral reactions of carbon and oxygen by Graff, who noted that the leading term in neutral atom-molecule interactions involves the quadrupole moment of the atom. Similar to the case of carbon, the requirement that Si has a quadrupole moment requires population of the J = 1 level, which lies 111K above the J = 0 ground state and has a critical density n(cr) equal to or greater than 10(6)/cu cm. The SiO abundance then has a temperature dependence proportional to exp(-111/T) and a quadratic density dependence for n less than n(cr). As part of the explanation of the lack of SiO detections at low temperatures and densities, this model also emphasizes the small efficiencies of the production routes and the correspondingly long times needed to reach equilibrium. Measurements of the abundance of SiO, in conjunction with theory, can provide information on the physical properties of interstellar clouds such as the abundances of oxygen bearing molecules and the depletion of interstellar silicon.

  9. Cost considerations for interstellar missions

    NASA Astrophysics Data System (ADS)

    Andrews, Dana G.

    This paper examines the technical and economic feasibility of interstellar exploration. Three candidate interstellar propulsion systems are evaluated with respect to technical viability and compared on an estimated cost basis. Two of the systems, the laser-propelled lightsail (LPL) and the particle-beam propelled magsail (PBPM), appear to be technically feasible and capable supporting one-way probes to nearby star systems within the lifetime of the principal investigators, if enough energy is available. The third propulsion system, the antimatter rocket, requires additional proof of concept demonstrations before its feasibility can be evaluated. Computer simulations of the acceleration and deceleration interactions of LPL and PBPM were completed and spacecraft configurations optimized for minimum energy usage are noted. The optimum LPL transfers about ten percent of the laser beam energy into kinetic energy of the spacecraft while the optimum PBPM transfers about thirty percent. Since particle beam generators are roughly twice as energy efficient as large lasers, the PBPM propulsion system requires roughly one-sixth the busbar electrical energy a LPL system would require to launch an identical payload. The total beam energy requirement for an interstellar probe mission is roughly 10 20 joules, which would require the complete fissioning of one thousand tons of Uranium assuming thirty-five percent powerplant efficiency. This is roughly equivalent to a recurring cost per flight of 3.0 Billion dollars in reactor grade enriched uranium using today's prices. Therefore, interstellar flight is an expensive proposition, but not unaffordable, if the nonrecurring costs of building the powerplant can be minimized.

  10. Representing culture in interstellar messages

    NASA Astrophysics Data System (ADS)

    Vakoch, Douglas A.

    2008-09-01

    As scholars involved with the Search for Extraterrestrial Intelligence (SETI) have contemplated how we might portray humankind in any messages sent to civilizations beyond Earth, one of the challenges they face is adequately representing the diversity of human cultures. For example, in a 2003 workshop in Paris sponsored by the SETI Institute, the International Academy of Astronautics (IAA) SETI Permanent Study Group, the International Society for the Arts, Sciences and Technology (ISAST), and the John Templeton Foundation, a varied group of artists, scientists, and scholars from the humanities considered how to encode notions of altruism in interstellar messages . Though the group represented 10 countries, most were from Europe and North America, leading to the group's recommendation that subsequent discussions on the topic should include more globally representative perspectives. As a result, the IAA Study Group on Interstellar Message Construction and the SETI Institute sponsored a follow-up workshop in Santa Fe, New Mexico, USA in February 2005. The Santa Fe workshop brought together scholars from a range of disciplines including anthropology, archaeology, chemistry, communication science, philosophy, and psychology. Participants included scholars familiar with interstellar message design as well as specialists in cross-cultural research who had participated in the Symposium on Altruism in Cross-cultural Perspective, held just prior to the workshop during the annual conference of the Society for Cross-cultural Research . The workshop included discussion of how cultural understandings of altruism can complement and critique the more biologically based models of altruism proposed for interstellar messages at the 2003 Paris workshop. This paper, written by the chair of both the Paris and Santa Fe workshops, will explore the challenges of communicating concepts of altruism that draw on both biological

  11. RUBIDIUM IN THE INTERSTELLAR MEDIUM

    SciTech Connect

    Walker, Kyle M.; Federman, S. R.; Knauth, David C.; Lambert, David L. E-mail: steven.federman@utoledo.ed E-mail: dll@astro.as.utexas.ed

    2009-11-20

    We present observations of interstellar rubidium toward o Per, zeta Per, AE Aur, HD 147889, chi Oph, zeta Oph, and 20 Aql. Theory suggests that stable {sup 85}Rb and long-lived {sup 87}Rb are produced predominantly by high-mass stars, through a combination of the weak s- and r-processes. The {sup 85}Rb/{sup 87}Rb ratio was determined from measurements of the Rb I line at 7800 A and was compared to the solar system meteoritic ratio of 2.59. Within 1sigma uncertainties, all directions except HD 147889 have Rb isotope ratios consistent with the solar system value. The ratio toward HD 147889 is much lower than the meteoritic value and similar to that toward rho Oph A; both lines of sight probe the Rho Ophiuchus Molecular Cloud. The earlier result was attributed to a deficit of r-processed {sup 85}Rb. Our larger sample suggests instead that {sup 87}Rb is enhanced in these two lines of sight. When the total elemental abundance of Rb is compared to the K elemental abundance, the interstellar Rb/K ratio is significantly lower than the meteoritic ratio for all the sight lines in this study. Available interstellar samples for other s- and r- process elements are used to help interpret these results.

  12. Copernicus observations of interstellar absorption at Lyman alpha

    NASA Technical Reports Server (NTRS)

    Bohlin, R. C.

    1975-01-01

    Column densities NH of atomic hydrogen have been derived for 40 OB stars from spectral scans at Lyman alpha obtained by the Copernicus (OAO-3) satellite. The stars are all between 60 and 1100 pc away with a range of mean densities n sub H of 0.01 to 2.5 atoms cm-3. The gas to color-excess ratio in clouds varies from 1 to 3 times the mean outside of clouds. The presence of molecular hydrogen correlates with E(B-V), but the best tracer for H2 is atomic hydrogen. The mean density of the gas for all 40 stars is much smaller than the mean of 0.7 atoms cm-3 obtained from 21-cm observations, because the brightest stars with less than average amounts of matter in the line of sight were selected for observation.

  13. DETERMINING INTERSTELLAR CARBON ABUNDANCES FROM STRONG-LINE TRANSITIONS

    SciTech Connect

    Sofia, U. J.; Parvathi, V. S.; Babu, B. R. S.; Murthy, J.

    2011-01-15

    Carbon is arguably the most important element in the interstellar medium, yet its abundance in gas and dust is poorly understood due to a paucity of data. We explore the possibility of substantially increasing our knowledge of interstellar carbon by applying and assessing a new method for determining the column density of the dominant ion of interstellar carbon in diffuse neutral lines of sight. The method relies on profile fitting of the strong transition of C II at 1334 A in spectra continuum normalized with stellar models. We apply our method to six sight lines for which the carbon abundance has previously been determined with a weak intersystem absorption transition. Our strong-line method consistently shows a significantly lower gas-phase C abundance than the measurements from the weak lines. This result implies that more carbon could reside in dust than was previously thought. This has implications for dust models, which often suffer from a lack of sufficient carbon to plausibly explain extinction. There is no immediately clear explanation for the difference found between the strong- and weak-line C II determinations, but there are indications that the results from the method presented here have advantages over the weak-line column densities. If this is the case, then the reported oscillator strength for the C II transition at 2325 A may be too small. Our findings further suggest that damping wings modeled with a single absorption component may not produce accurate abundances. This problem could affect a large number of H I abundances determined through absorption line analysis that are reported in the literature.

  14. Green Bank Telescope Detection of New Interstellar Aldehydes: Propenal and Propanal

    NASA Astrophysics Data System (ADS)

    Hollis, J. M.; Jewell, P. R.; Lovas, F. J.; Remijan, A.; Møllendal, H.

    2004-07-01

    The new interstellar molecules propenal (CH2CHCHO) and propanal (CH3CH2CHO) have been detected largely in absorption toward the star-forming region Sagittarius B2(N) by means of rotational transitions observed with the 100 m Green Bank Telescope (GBT) operating in the range from 18 GHz (λ~1.7 cm) to 26 GHz (λ~1.2 cm). The GBT was also used to observe the previously reported interstellar aldehyde propynal (HC2CHO) in Sagittarius B2(N), which is a known source of large molecules presumably formed on interstellar grains. The presence of these three interstellar aldehydes toward Sagittarius B2(N) strongly suggests that simple hydrogen addition on interstellar grains accounts for successively larger molecular species: from propynal to propenal and from propenal to propanal. Energy sources within Sagittarius B2(N) likely permit the hydrogen addition reactions on grain surfaces to proceed. This work demonstrates that successive hydrogen addition is probably an important chemistry route in the formation of a number of complex interstellar molecules. We also searched for but did not detect the three-carbon sugar glyceraldehyde (CH2OHCHOHCHO).

  15. Intersystem transitions of interstellar carbon monoxide toward zeta Ophiuchi

    NASA Technical Reports Server (NTRS)

    Federman, S. R.; Cardelli, Jason A.; Sheffer, Yaron; Lambert, David L.; Morton, D. C.

    1994-01-01

    Absorption from seven intersystem (triplet-singlet) transitions of interstellar (12)CO were detected in ultraviolet spectra of zeta Oph. The observed equivalent widths are approximately consistent with the transitions' predicted f-values and the (12) CO column density derived from the weakest of the observed A-X bands. These unsaturated intersystem transitions provide the opportunity to measure the (12)CO column density for heavily reddened (dense) sight lines. Laboratory measurements of oscillator strengths more precise than available ones will be needed to derive accurate column densities.

  16. Studies of Interstellar and Circumstellar Magnetic Field with Aligned Atoms

    NASA Astrophysics Data System (ADS)

    Lazarian, A.; Yan, H.

    2004-12-01

    Population of levels of the hyperfine and fine split ground state of an atom is affected by radiative transitions induced by anisotropic radiation flux. Such aligned atoms precess in the external magnetic field and this affects properties of polarized radiation arising from both scattering and absorption by atoms. As the result the degree of light polarization depends on the direction of the magnetic field. This provides a new tool for studies of astrophysical magnetic fields using optical and UV polarimetry. We provide calculations for several atoms and ions that can be used to study magnetic fields in interplanetary medium, interstellar medius, circumstellar regions and quasars.

  17. Astrophysics. Volume 2 - Interstellar matter and galaxies

    NASA Astrophysics Data System (ADS)

    Bowers, Richard L.; Deeming, Terry

    The astrophysics of interstellar matter, galaxies, and cosmology is presented in an intermediate-level college textbook. Chapters are devoted to interstellar matter, interstellar dust grains, gaseous nebulae, hydrodynamics, the virial theorem, star formation, supersonic flow and shock waves, diffuse supernova remnants, the expanding universe, galaxies, dynamics of stellar systems, axially symmetric galaxies, spiral structure, and galactic evolution. Diagrams, graphs, photographs, and problems are provided.

  18. Ultraviolet interstellar polarization observed with the Hubble Space Telescope

    NASA Technical Reports Server (NTRS)

    Somerville, W. B.; Allen, R. G.; Carnochan, D. J.; He, Lida; Mcnally, D.; Martin, P. G.; Morgan, D. H.; Nandy, K.; Walsh, J. R.; Whittet, D. C. B.

    1994-01-01

    We have used the Faint Object Spectrograph of the Hubble Space Telescope to observe interstellar linear polarization from 1300 to 3300 A in two stars with well-studied interstellar polarization at visible wavelenths. The wavelength dependence of linear polarization declines smoothly with decreasing wavelength and is devoid of structure associated with the prominent 2175 A absorption bump in the interstellar extinction curve. The data for one star (HD 161056) are consistent with an extrapolation based on the Serkowski formula of a fit to the ground-based polariztion; the other star (HD 7252) shows excess (super-Serkowski) polarization relative to the extrapolation. Out of a total of 10 stars now studied by means of spectropolarimetry in the satellite ultraviolet, including eight obseved with the Wisconsin Ultraviolet Photopolarimeter, five (those of longest lambda (sub max)) show Serkowski behavior, and four others show super-Serkowski behavior; only one (HD 197770) shows evidence for polarization associated with the 2175 A bump. These results place important constraints on the nature of the bump feature.

  19. The Origin and Evolution of Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Dwek, Eli; Houches, Les

    2006-01-01

    In this lecture I will discuss the many different manifestation of interstellar dust, and current dust models that satisfy interstellar extinction, diffuse infrared emission, and interstellar abundances constraints. Dust is made predominantly in AGB stars and Type I1 supernovae, and I will present observational evidence for the presence of dust in these sources. I will then present chemical evolution models that follow the abundance of dust which is determined by the combined processes of formation, destruction by interstellar shock waves, and accretion in molecular clouds. The model will be applied to the evolution of PAHs and the evolution of dust in the high-redshift galaxy (z=6.42) JD11.

  20. Laboratory Needs for Interstellar Ice Studies

    NASA Astrophysics Data System (ADS)

    Boogert, Abraham C. A.

    2012-05-01

    A large fraction of the molecules in dense interstellar and circumstellar environments is stored in icy grain mantles. The mantles are formed by a complex interplay between chemical and physical processes. Key questions on the accretion and desorption processes and the chemistry on the grain surfaces and within the icy mantles can only be answered by laboratory experiments. Recent infrared (2-30 micron) spectroscopic surveys of large samples of Young Stellar Objects (YSOs) and background stars tracing quiescent cloud material have shown that the ice band profiles and depths vary considerably as a function of environment. Using laboratory spectra in the identification process, it is clear that a rather complex mixture of simple species (CH3OH, CO2, H2O, CO) exists even in the quiescent cloud phase. Variations of the local physical conditions (CO freeze out) and time scales (CH3OH formation) appear to be key factors in the observed variations. Sublimation and thermal processing dominate as YSOs heat their environments. The identification of several ice absorption features is still disputed. I will outline laboratory work (e.g., on salts, PAHs, and aliphatic hydrocarbons) needed to further constrain the ice band identification as well as the thermal and chemical history of the carriers. Such experiments will also be essential to interpret future high spectral resolution SOFIA and JWST observations.

  1. Fluorescent excitation of interstellar H2

    NASA Technical Reports Server (NTRS)

    Black, John H.; Van Dishoeck, Ewine F.

    1987-01-01

    The infrared emission spectrum of H2 excited by ultraviolet absorption, followed by fluorescence, was investigated using comprehensive models of interstellar clouds for computing the spectrum and to assess the effects on the intensity to various cloud properties, such as density, size, temperature, and the intensity of the UV radiation field. It is shown that the absolute H2 IR line intensities depend primarily on the density of the cloud and the strength of the incident UV radiation, and to a much lesser exent on the temperature of the gas, the total thickness of the cloud, and the optical properties of the grains. A variety of recent observational results are discussed with reference to theoretical models. It is shown that the rich H2 emission spectrum of the reflection nebula NGC 2023 can be reproduced by a model with density of about 10,000/cu cm, temperature of about 80 K, and UV flux approximately 300 times that of the Galactic background starlight.

  2. MATRIICES - Mass Analytical Tool for Reactions in Interstellar ICES

    NASA Astrophysics Data System (ADS)

    Isokoski, K.; Bossa, J. B.; Linnartz, H.

    2011-05-01

    The formation of complex organic molecules (COMs) observed in the inter- and circumstellar medium (ISCM) is driven by a complex chemical network yet to be fully characterized. Interstellar dust grains and the surrounding ice mantles, subject to atom bombardment, UV irradiation, and thermal processing, are believed to provide catalytic sites for such chemistry. However, the solid state chemical processes and the level of complexity reachable under astronomical conditions remain poorly understood. The conventional laboratory techniques used to characterize the solid state reaction pathways - RAIRS (Reflection Absorption IR Spectroscopy) and TPD (Temperature-Programmed Desorption) - are suitable for the analysis of reactions in ices made of relatively small molecules. For more complex ices comprising a series of different components as relevant to the interstellar medium, spectral overlapping prohibits unambiguous identification of reaction schemes, and these techniques start to fail. Therefore, we have constructed a new and innovative experimental set up for the study of complex interstellar ices featuring a highly sensitive and unambiguous detection method. MATRIICES (Mass Analytical Tool for Reactions in Interstellar ICES) combines Laser Ablation technique with a molecular beam experiment and Time-Of-Flight Mass Spectrometry (LA-TOF-MS) to sample and analyze the ice analogues in situ, at native temperatures, under clean ultra-high vacuum conditions. The method allows direct sampling and analysis of the ice constituents in real time, by using a pulsed UV ablation laser (355-nm Nd:YAG) to vaporize the products in a MALDI-TOF like detection scheme. The ablated material is caught in a synchronously pulsed molecular beam of inert carrier gas (He) from a supersonic valve, and analysed in a Reflectron Time-of-Flight Mass Spectrometer. The detection limit of the method is expected to exceed that of the regular surface techniques substantially. The ultimate goal is to fully

  3. THE CHEMISTRY OF INTERSTELLAR MOLECULES CONTAINING THE HALOGEN ELEMENTS

    SciTech Connect

    Neufeld, David A.; Wolfire, Mark G. E-mail: mwolfire@astro.umd.ed

    2009-12-01

    Although they are only minor constituents of the interstellar medium, halogen-containing molecules are of special interest because of their unique thermochemistry. Here, we present a theoretical study of the chemistry of interstellar molecules containing the halogen elements chlorine and fluorine. We have modeled both diffuse and dense molecular clouds, making use of updated estimates for the rates of several key chemical processes. We present predictions for the abundances of the three halogen molecules that have been detected to date in the interstellar medium: HF, CF{sup +}, and HCl. As in our previous study of fluorine-bearing interstellar molecules, we predict HF to be the dominant gas-phase reservoir of fluorine within both diffuse and dense molecular clouds; we expect the Herschel Space Observatory to detect widespread absorption in the HF J = 1 - 0 transition. Our updated model now overpredicts the CF{sup +} abundance by a factor approx>10 relative to observations of the Orion Bar; this discrepancy has widened because we now adopt a laboratory measurement of the CF{sup +} dissociative recombination rate that is smaller than the estimate we adopted previously. This disagreement suggests that the reaction of C{sup +} with HF proceeds more slowly than the capture rate assumed in our model; a laboratory measurement of this reaction rate would be very desirable. Our model predicts diffuse cloud HCl abundances that are similar to those predicted previously and detected tentatively toward zeta Oph. Two additional species are potentially detectable from photodissociation regions: the H{sub 2}Cl{sup +}, and HCl{sup +} molecular ions. Ortho-H{sub 2}Cl{sup +} has its lowest-lying transition in the millimeter spectral region observable from the ground, and the lowest rotational transition of HCl{sup +} is observable with Herschel's HIFI instrument.

  4. INTERSTELLAR ABUNDANCES TOWARD X Per, REVISITED

    SciTech Connect

    Valencic, Lynne A.; Smith, Randall K.

    2013-06-10

    The nearby X-ray binary X Per (HD 24534) provides a useful beacon with which to examine dust grain types and measure elemental abundances in the local interstellar medium (ISM). The absorption features of O, Fe, Mg, and Si along this line of sight were measured using spectra from the Chandra X-Ray Observatory's LETG/ACIS-S and XMM-Newton's RGS instruments, and the Spex software package. The spectra were fit with dust analogs measured in the laboratory. The O, Mg, and Si abundances were compared to those from standard references, and the O abundance was compared to that along lines of sight toward other X-ray binaries. The results are as follows. First, it was found that a combination of MgSiO{sub 3} (enstatite) and Mg{sub 1.6}Fe{sub 0.4}SiO{sub 4} (olivine) provided the best fit to the O K edge, with N(MgSiO{sub 3})/N(Mg{sub 1.6}Fe{sub 0.4}SiO{sub 4}) = 3.4. Second, the Fe L edge could be fit with models that included metallic iron, but it was not well described by the laboratory spectra currently available. Third, the total abundances of O, Mg, and Si were in very good agreement with that of recently re-analyzed B stars, suggesting that they are good indicators of abundances in the local ISM, and the depletions were also in agreement with expected values for the diffuse ISM. Finally, the O abundances found from X-ray binary absorption spectra show a similar correlation with Galactocentric distances as seen in other objects.

  5. Deuterium enrichment of interstellar dusts

    NASA Astrophysics Data System (ADS)

    Das, Ankan; Chakrabarti, Sandip Kumar; Majumdar, Liton; Sahu, Dipen

    2016-07-01

    High abundance of some abundant and simple interstellar species could be explained by considering the chemistry that occurs on interstellar dusts. Because of its simplicity, the rate equation method is widely used to study the surface chemistry. However, because the recombination efficiency for the formation of any surface species is highly dependent on various physical and chemical parameters, the Monte Carlo method is best suited for addressing the randomness of the processes. We carry out Monte-Carlo simulation to study deuterium enrichment of interstellar grain mantle under various physical conditions. Based on the physical properties, various types of clouds are considered. We find that in diffuse cloud regions, very strong radiation fields persists and hardly a few layers of surface species are formed. In translucent cloud regions with a moderate radiation field, significant number of layers would be produced and surface coverage is mainly dominated by photo-dissociation products such as, C, CH_3, CH_2D, OH and OD. In the intermediate dense cloud regions (having number density of total hydrogen nuclei in all forms ˜2 × 10^4 cm^{-3}), water and methanol along with their deuterated derivatives are efficiently formed. For much higher density regions (˜10^6 cm^{-3}), water and methanol productions are suppressed but surface coverage of CO, CO_2, O_2, O_3 are dramatically increased. We find a very high degree of fractionation of water and methanol. Observational results support a high fractionation of methanol but surprisingly water fractionation is found to be low. This is in contradiction with our model results indicating alternative routes for de-fractionation of water.

  6. Charge transfer reactions in multiply charged ion-atom collisions. [in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    Charge-transfer reactions in collisions between highly charged ions and neutral atoms of hydrogen and/or helium may be rapid at thermal energies. If these reactions are rapid, they will suppress highly charged ions in H I regions and guarantee that the observed absorption features from such ions cannot originate in the interstellar gas. A discussion of such charge-transfer reactions is presented and compared with the available experimental data. The possible implications of these reactions for observations of the interstellar medium, H II regions, and planetary nebulae are outlined.

  7. A search for interstellar pyrimidine

    NASA Astrophysics Data System (ADS)

    Kuan, Yi-Jehng; Yan, Chi-Hung; Charnley, Steven B.; Kisiel, Zbigniew; Ehrenfreund, Pascale; Huang, Hui-Chun

    2003-10-01

    We have searched three hot molecular cores for submillimetre emission from the nucleic acid building block pyrimidine. We obtain upper limits to the total pyrimidine (beam-averaged) column densities towards Sgr B2(N), Orion KL and W51 e1/e2 of 1.7 × 1014, 2.4 × 1014 and 3.4 × 1014 cm-2, respectively. The associated upper limits to the pyrimidine fractional abundances lie in the range (0.3-3) × 10-10. Implications of this result for interstellar organic chemistry, and for the prospects of detecting nitrogen heterocycles in general, are discussed briefly.

  8. 3D distribution of interstellar medium in the Galaxy: Preparation for analysis of Gaia observations

    NASA Astrophysics Data System (ADS)

    Puspitarini, Lucky; Lallement, Rosine

    2015-09-01

    Accurate and detailed three-dimensional (3D) maps of Galactic interstellar medium (ISM) are still lacking. One way to obtain such 3D descriptions is to record a large set of individual absorption or reddening measurements toward target stars located at various known distances and directions. The inversion of these measurements using a tomographic method can produce spatial distribution of the ISM. Until recently absorption data were very limited and distances to the target stars are still uncertain, but the situation will greatly improve thanks to current and future massive stellar surveys from ground, and to Gaia mission. To prepare absorption data for inversion from a huge number of stellar spectra, automated tools are needed. We have developed various spectral analysis tools adapted to different type of spectra, early- or late- type star. We also have used diffuse interstellar bands (DIBs) to trace IS structures and kinematics. Although we do not know yet their carriers, they can be a promising tool to trace distant interstellar clouds or Galactic arms. We present some examples of the interstellar fitting and show the potentiality of DIBs in tracing the ISM. We will also briefly show and comment the latest 3D map of the local ISM which reveal nearby cloud complexes and cavities.

  9. 3D distribution of interstellar medium in the Galaxy: Preparation for analysis of Gaia observations

    SciTech Connect

    Puspitarini, Lucky; Lallement, Rosine

    2015-09-30

    Accurate and detailed three-dimensional (3D) maps of Galactic interstellar medium (ISM) are still lacking. One way to obtain such 3D descriptions is to record a large set of individual absorption or reddening measurements toward target stars located at various known distances and directions. The inversion of these measurements using a tomographic method can produce spatial distribution of the ISM. Until recently absorption data were very limited and distances to the target stars are still uncertain, but the situation will greatly improve thanks to current and future massive stellar surveys from ground, and to Gaia mission. To prepare absorption data for inversion from a huge number of stellar spectra, automated tools are needed. We have developed various spectral analysis tools adapted to different type of spectra, early- or late- type star. We also have used diffuse interstellar bands (DIBs) to trace IS structures and kinematics. Although we do not know yet their carriers, they can be a promising tool to trace distant interstellar clouds or Galactic arms. We present some examples of the interstellar fitting and show the potentiality of DIBs in tracing the ISM. We will also briefly show and comment the latest 3D map of the local ISM which reveal nearby cloud complexes and cavities.

  10. Infrared spectra of interstellar deuteronated PAHs

    NASA Astrophysics Data System (ADS)

    Buragohain, Mridusmita; Pathak, Amit; Sarre, Peter

    2015-08-01

    Polycyclic Aromatic Hydrocarbon (PAH) molecules have emerged as a potential constituent of the ISM that emit strong features at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.7 μm with weaker and blended features in the 3-20μm region. These features are proposed to arise from the vibrational relaxation of PAH molecules on absorption of background UV photons (Tielens 2008). These IR features have been observed towards almost all types of astronomical objects; say H II regions, photodissociation regions, reflection nebulae, planetary nebulae, young star forming regions, external galaxies, etc. A recent observation has proposed that interstellar PAHs are major reservoir for interstellar deuterium (D) (Peeters et al. 2004). According to the `deuterium depletion model' as suggested by Draine (2006), some of the Ds formed in the big bang are depleted in PAHs, which can account for the present value of D/H in the ISM. Hence, study of deuterated PAHs (PADs) is essential in order to measure D/H in the ISM.In this work, we consider another probable category of the large PAH family, i.e. Deuteronated PAHs (DPAH+). Onaka et al. have proposed a D/H ratio which is an order of magnitude smaller than the proposed value of D/H by Draine suggesting that if Ds are depleted in PAHs, they might be accommodated in large PAHs (Onaka et al. 2014). This work reports a `Density Functional Theory' calculation of large deuteronated PAHs (coronene, ovalene, circumcoronene and circumcircumcoronene) to determine the expected region of emission features and to find a D/H ratio that is comparable to the observational results. We present a detailed analysis of the IR spectra of these molecules and discuss the possible astrophysical implications.ReferencesDraine B. T. 2006, in ASP Conf. Ser. 348, Proc. Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE, ed. G. Sonneborn, H. Moos, B-G Andersson (San Francisco, CA:ASP) 58Onaka T., Mori T. I., Sakon I., Ohsawa R., Kaneda H., Okada Y., Tanaka M

  11. Interstellar PAH in the Laboratory and in Space. What have we Learned from the New Generation of Laboratory and Observational Studies?

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2005-01-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-UV and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong VUV radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in

  12. Probing the Diffuse Interstellar Medium at AU Scales

    NASA Astrophysics Data System (ADS)

    Lauroesch, J. T.; Meyer, D. M.

    2002-12-01

    Recently, there have been a number of serendipitous discoveries of temporal variations in interstellar absorption lines indicative of significant structure on AU scales. In an effort to better quantify the fraction of gas in these smallest scale structures, we have obtained multi-epoch, high spectral resolution observations of interstellar NaI, CaII, CH, CH+, and CN absorption lines toward a number of stars using the KPNO Coude Feed telescope. Our NaI survey has followed 27 stars for 2 to 7 years, and probed scales of 1-40 AU. To date, we have identified no variable components for the 11 stars in our sample with projected motions of less than 10 AU, while we have identified at least 3 variable components toward the 16 stars with projected motions greater than 10 AU. Following the suggestion by Pan, Federman, and Welty (2001, ApJ, 558, L105) that CN may be a particularly useful tracer of density variations, we have begun to search for temporal fluctuations in the strength of the CN lines. So far we have found no compelling evidence for temporal variations in any sightline, although our sample size is still small. For example, we have recently obtained very high S/N ratio spectra towards the star zeta Oph, and find no variations in the strength of the R(0), R(1), and P(1) lines of the 3874 CN (0,0) band at the 0.1 mA level. The corresponding limits on the variation in the column densities depend upon the details of the component model, but suggest that the total CN column has changed by less than 5 percent over a period of 10 years, or a projected motion of approximately 40 AU. We will discuss these results in the context of interstellar turbulence models for the formation of small scale structure.

  13. A prelude to interstellar flight

    NASA Technical Reports Server (NTRS)

    Jaffe, L. D.; Norton, H. N.

    1980-01-01

    A 20 to 50 year interstellar precursor mission extending 400 to 1000 AU from the solar system is outlined as a means of bringing out and solving engineering problems inherent in a star mission, and of studying the heliopause, the interstellar medium, and cosmic rays outside the heliosphere. Solar or laser sailing combined with a 500 kWe nuclear-electric propulsion system using fission would achieve a heliocentric excess velocity of 100km/s for the 32,000 kg spacecraft having a Shuttle derivative as a launch vehicle, and containing a Pluto flyby or separate orbiter powered by radioiosotope thermoelectric generators. X-band transmission using 40 w of power, a 15 m diameter spacecraft antenna and a 100 m receiving antenna on earth and providing 100 b/s is proposed, but a rate of 2 to 4 kb/s via 500 to 1000 w of power using the K-band and a 300 m diameter receiving antenna located on an Orbiting Deep Space Relay Station is also considered.

  14. Optical interstellar lines toward 18 stars of low reddening. III

    NASA Technical Reports Server (NTRS)

    Hobbs, L. M.

    1978-01-01

    Photoelectric scans of the interstellar D-line of Na I and the K-line of Ca II are compared with those of H I and H sub 2. Three general conclusions are drawn from the observations: (1) normal Na I/H ratios are found in 14 of the 18 cases studied, most likely due to absorption in cool, dense clouds; (2) low Na I/H ratios are observed in the direction of Gamma-Pegasus and Mu-Scorpio, implying that absorption occurs in clouds of warm (over 100 K) gas, or through extended paths of cool gas with low ionization; and (3) the absence of Na I, H I, and H sub 2 lines toward Nu-Scorpio and Sigma-Sagittarius indicates that little neutral gas is present along these light paths.

  15. The cloudy state of interstellar matter

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.

    1978-01-01

    The expression 'cloudy state' is used to describe the state of the diffuse interstellar matter, with emphasis on its denser and more opaque regions. Questions of morphology with respect to the Galaxy are examined, taking into account neutral hydrogen, molecular regions, H II regions, infrared sources and masers, coronal gas in the Galaxy, and the major components of the interstellar medium. Aspects of dynamics are also considered, giving attention to the two-phase interstellar medium, the three-phase interstellar medium, the density-wave compression of clouds, and problems related to the concept of collapsing clouds. Developments concerning chemistry are explored. Radioactive chronologies are discussed along with isotopic anomalies and aspects of interstellar chemistry.

  16. THE STRUCTURE, ORIGIN, AND EVOLUTION OF INTERSTELLAR HYDROCARBON GRAINS

    SciTech Connect

    Chiar, J. E.; Ricca, A.; Tielens, A. G. G. M.; Adamson, A. J. E-mail: Alessandra.Ricca@1.nasa.gov E-mail: aadamson@gemini.edu

    2013-06-10

    Many materials have been considered for the carrier of the hydrocarbon absorption bands observed in the diffuse interstellar medium (ISM). In order to refine the model for ISM hydrocarbon grains, we analyze the observed aromatic (3.28, 6.2 {mu}m) and aliphatic (3.4 {mu}m) hydrocarbon absorption features in the diffuse ISM along the line of sight toward the Galactic center Quintuplet Cluster. Observationally, sp {sup 2} bonds can be measured in astronomical spectra using the 6.2 {mu}m CC aromatic stretch feature, whereas the 3.4 {mu}m aliphatic feature can be used to quantify the fraction of sp {sup 3} bonds. The fractional abundance of these components allows us to place the Galactic diffuse ISM hydrocarbons on a ternary phase diagram. We conclude that the Galactic hydrocarbon dust has, on average, a low H/C ratio and sp {sup 3} content and is highly aromatic. We have placed the results of our analysis within the context of the evolution of carbon dust in the ISM. We argue that interstellar carbon dust consists of a large core of aromatic carbon surrounded by a thin mantle of hydrogenated amorphous carbon (a-C:H), a structure that is a natural consequence of the processing of stardust grains in the ISM.

  17. Anthracene clusters and the interstellar infrared emission features

    SciTech Connect

    Roser, J. E.; Ricca, A.; Allamandola, L. J.

    2014-03-10

    The unidentified infrared bands are ubiquitous in the interstellar medium and typically attributed to emission from neutral and ionized polycyclic aromatic hydrocarbons (or PAHs). The contribution of neutral PAH clusters to these bands has been impossible to determine due to a paucity of infrared spectral data. Here we investigated neutral clusters of the three-ring PAH anthracene using FTIR absorption spectroscopy of anthracene matrix-isolated at varying concentrations in solid argon. In order to determine likely cluster structures of the embedded molecules, we also calculated theoretical absorption spectra for the anthracene monomer through hexamer using density functional theory with a dispersion correction (DFT-D). The DFT-D calculations have been calibrated for the anthracene dimer using the second-order Møller-Plesset approach. Because there is some support for the hypothesis that three or four-ring PAHs are present in the Red Rectangle nebula, we discuss the application of our results to this nebula in particular as well as to the interstellar infrared emission in general.

  18. MAGNETIC NANOPARTICLES IN THE INTERSTELLAR MEDIUM: EMISSION SPECTRUM AND POLARIZATION

    SciTech Connect

    Draine, B. T.; Hensley, Brandon

    2013-03-10

    The presence of ferromagnetic or ferrimagnetic nanoparticles in the interstellar medium would give rise to magnetic dipole radiation at microwave and submillimeter frequencies. Such grains may account for the strong millimeter-wavelength emission observed from a number of low-metallicity galaxies, including the Small Magellanic Cloud. We calculate the absorption and scattering cross sections for such grains, with particular attention to metallic Fe, magnetite Fe{sub 3}O{sub 4}, and maghemite {gamma}-Fe{sub 2}O{sub 3}, all potentially present in the interstellar medium. The rate of Davis-Greenstein alignment by magnetic dissipation is also estimated. We determine the temperature of free-flying magnetic grains heated by starlight and calculate the polarization of the magnetic dipole emission from both free-fliers and inclusions. For inclusions, the magnetic dipole emission is expected to be polarized orthogonally relative to the normal electric dipole radiation. Magnetic dipole radiation will contribute significantly to the 20-40 GHz anomalous microwave emission only if a large fraction of the Fe is in metallic Fe iron nanoparticles with extreme elongations. Finally, we present self-consistent dielectric functions for metallic Fe, magnetite Fe{sub 3}O{sub 4}, and maghemite {gamma}-Fe{sub 2}O{sub 3}, enabling calculation of absorption and scattering cross sections from microwave to X-ray wavelengths.

  19. A SENSITIVE SPECTRAL SURVEY OF INTERSTELLAR FEATURES IN THE NEAR-UV [3050-3700 Å

    SciTech Connect

    Bhatt, N. H.; Cami, J. E-mail: jcami@uwo.ca

    2015-02-01

    We present a comprehensive and sensitive unbiased survey of interstellar features in the near-UV range (3050-3700 Å). We combined a large number of VLT/UVES archival observations of a sample of highly reddened early-type stars—typical diffuse interstellar band targets—and unreddened standards. We stacked the individual observations to obtain a reddened ''superspectrum'' in the interstellar rest frame with a signal-to-noise ratio exceeding 1500. We compared this to the analogous geocentric and stellar rest frame superspectra as well as to an unreddened superspectrum to find interstellar absorption features. We find 30 known features (11 atomic and 19 molecular) and tentatively detect up to 7 new interstellar absorption lines of unknown origin. Our survey is sensitive to narrow and weak features; telluric residuals preclude us from detecting broader features. For each sightline, we measured fundamental parameters (radial velocities, line widths, and equivalent widths) of the detected interstellar features. We also revisit upper limits for the column densities of small, neutral polycyclic aromatic hydrocarbon molecules that have strong transitions in this wavelength range.

  20. A Tale of Two Mysteries in Interstellar Astrophysics: The 2175 Å Extinction Bump and Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Xiang, F. Y.; Li, Aigen; Zhong, J. X.

    2011-06-01

    The diffuse interstellar bands (DIBs) are ubiquitous absorption spectral features arising from the tenuous material in the space between stars—the interstellar medium (ISM). Since their first detection nearly nine decades ago, over 400 DIBs have been observed in the visible and near-infrared wavelength range in both the Milky Way and external galaxies, both nearby and distant. However, the identity of the species responsible for these bands remains as one of the most enigmatic mysteries in astrophysics. An equally mysterious interstellar spectral signature is the 2175 Å extinction bump, the strongest absorption feature observed in the ISM. Its carrier also remains unclear since its first detection 46 years ago. Polycyclic aromatic hydrocarbon (PAH) molecules have long been proposed as a candidate for DIBs as their electronic transitions occur in the wavelength range where DIBs are often found. In recent years, the 2175 Å extinction bump is also often attributed to the π-π* transition in PAHs. If PAHs are indeed responsible for both the 2175 Å extinction feature and DIBs, their strengths may correlate. We perform an extensive literature search for lines of sight for which both the 2175 Å extinction feature and DIBs have been measured. Unfortunately, we found no correlation between the strength of the 2175 Å feature and the equivalent widths of the strongest DIBs. A possible explanation might be that DIBs are produced by small free gas-phase PAH molecules and ions, while the 2175 Å bump is mainly from large PAHs or PAH clusters in condensed phase so that there is no tight correlation between DIBs and the 2175 Å bump.

  1. A TALE OF TWO MYSTERIES IN INTERSTELLAR ASTROPHYSICS: THE 2175 A EXTINCTION BUMP AND DIFFUSE INTERSTELLAR BANDS

    SciTech Connect

    Xiang, F. Y.; Zhong, J. X.; Li Aigen E-mail: lia@missouri.edu

    2011-06-01

    The diffuse interstellar bands (DIBs) are ubiquitous absorption spectral features arising from the tenuous material in the space between stars-the interstellar medium (ISM). Since their first detection nearly nine decades ago, over 400 DIBs have been observed in the visible and near-infrared wavelength range in both the Milky Way and external galaxies, both nearby and distant. However, the identity of the species responsible for these bands remains as one of the most enigmatic mysteries in astrophysics. An equally mysterious interstellar spectral signature is the 2175 A extinction bump, the strongest absorption feature observed in the ISM. Its carrier also remains unclear since its first detection 46 years ago. Polycyclic aromatic hydrocarbon (PAH) molecules have long been proposed as a candidate for DIBs as their electronic transitions occur in the wavelength range where DIBs are often found. In recent years, the 2175 A extinction bump is also often attributed to the {pi}-{pi}* transition in PAHs. If PAHs are indeed responsible for both the 2175 A extinction feature and DIBs, their strengths may correlate. We perform an extensive literature search for lines of sight for which both the 2175 A extinction feature and DIBs have been measured. Unfortunately, we found no correlation between the strength of the 2175 A feature and the equivalent widths of the strongest DIBs. A possible explanation might be that DIBs are produced by small free gas-phase PAH molecules and ions, while the 2175 A bump is mainly from large PAHs or PAH clusters in condensed phase so that there is no tight correlation between DIBs and the 2175 A bump.

  2. The diffuse interstellar cloud toward HD 179406 (20 Aquilae)

    NASA Technical Reports Server (NTRS)

    Hanson, Margaret M.; Snow, Theodore P.; Black, John H.

    1992-01-01

    An analysis of the diffuse interstellar cloud complex in front of HD 179406 (20 Aql) is presented. Along this sight line, multispectral absortion- and emission-line studies have uncovered at least three distinct velocity components due to individual clouds. A dominant velocity component is seen in both the absorption and emission-line data sets at 3 +/- 1 km/s. It is argued that the cloud associated with this velocity component is responsible for most of the atomic and all of the molecular gas in front of 20 Aql. The present chemical and physical analysis of the cloud combines the diagnostic tools of radio emission-line data with those of UV and optical absorption data. Using non-LTE models to synthesize the observed absorption profiles, (C-12)O and (C-13)O column densities along this line of sight are determined. The (C-12)O/(C-13)O abundance ratio was found to be 50 +/- 15, similar to that found by Wannier et al. toward Zeta Oph. The physical conditions of the cloud have been investigated using ultraviolet absorption lines. Measurements indicate that the dominant absorption cloud has a gas pressure similar to that found in the local diffuse molecular cloud in Ophiuchus with nT = 20,000/cu cm K.

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

    NASA Technical Reports Server (NTRS)

    Mcclintock, W.; Henry, R. C.; Moos, H. W.; Linsky, J. L.

    1976-01-01

    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.

  4. Accurate oscillator strengths for ultraviolet lines of Ar I - Implications for interstellar material

    NASA Technical Reports Server (NTRS)

    Federman, S. R.; Beideck, D. J.; Schectman, R. M.; York, D. G.

    1992-01-01

    Analysis of absorption from interstellar Ar I in lightly reddened lines of sight provides information on the warm and hot components of the interstellar medium near the sun. The details of the analysis are limited by the quality of the atomic data. Accurate oscillator strengths for the Ar I lines at 1048 and 1067 A and the astrophysical implications are presented. From lifetimes measured with beam-foil spectroscopy, an f-value for 1048 A of 0.257 +/- 0.013 is obtained. Through the use of a semiempirical formalism for treating singlet-triplet mixing, an oscillator strength of 0.064 +/- 0.003 is derived for 1067 A. Because of the accuracy of the results, the conclusions of York and colleagues from spectra taken with the Copernicus satellite are strengthened. In particular, for interstellar gas in the solar neighborhood, argon has a solar abundance, and the warm, neutral material is not pervasive.

  5. Polarimetry of the Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Sandford, Scott; Witteborn, Fred C. (Technical Monitor)

    1995-01-01

    The talk will review what is known about the composition of ices and organics in the dense and diffuse interstellar media (ISM). Mixed molecular ices make up a significant fraction of the solid materials in dense molecular clouds and it is now known that thermal and radiation processing of these ices results in the production of more complex organic species, some of which may survive transport into forming stellar systems and the diffuse ISM. Molecular species identified in interstellar ices include H2O, CH3OH, CO, CH4, CO2, and somewhat surprisingly, H2. Theoretical and laboratory studies of the processing of interstellar analog ices containing these species indicate that species like HCO, H2CO, CH3, and NH3 are readily made and should also be present. The irradiation of mixed molecular ices containing these species, when followed by warming, leads to the production of a large variety of more complex species, including ethanol (CH3CH2OH), formamide (HC(=O)NH2), acetamide (CH3C(=O)NH2), nitriles or isonitriles (R-CN or R-NC hexamethylenetetramine (HMT; C6H12N4), a number of polymeric species related to polyoxymethylene [POM,(-CH2O-)n], and ketones {R-C(=O)-R'}. Spectral studies of dust in the diffuse ISM indicate the presence of fairly complex organics, some of which may be related to the organics produced in dense molecular clouds. Spectral comparisons indicate that the diffuse ISM organics may be quite similar to meteoritic kerogens, i.e. they may consist largely of aromatic moieties interlinked by short aliphatic bridges. Interestingly, recent evidence indicates that the galactic distribution of this material closely matches that of silicates, but does not correlate directly with visual extinction. This implies that a large fraction of the visual extinction is caused by a material other than these organics and silicates and that this other material has a significantly different distribution within the galaxy.

  6. On the nature of absorption features toward nearby stars

    NASA Astrophysics Data System (ADS)

    Kohl, S.; Czesla, S.; Schmitt, J. H. M. M.

    2016-06-01

    Context. Diffuse interstellar absorption bands (DIBs) of largely unknown chemical origin are regularly observed primarily in distant early-type stars. More recently, detections in nearby late-type stars have also been claimed. These stars' spectra are dominated by stellar absorption lines. Specifically, strong interstellar atomic and DIB absorption has been reported in τ Boo. Aims: We test these claims by studying the strength of interstellar absorption in high-resolution TIGRE spectra of the nearby stars τ Boo, HD 33608, and α CrB. Methods: We focus our analysis on a strong DIB located at 5780.61 Å and on the absorption of interstellar Na. First, we carry out a differential analysis by comparing the spectra of the highly similar F-stars, τ Boo and HD 33608, whose light, however, samples different lines of sight. To obtain absolute values for the DIB absorption, we compare the observed spectra of τ Boo, HD 33608, and α CrB to PHOENIX models and carry out basic spectral modeling based on Voigt line profiles. Results: The intercomparison between τ Boo and HD 33608 reveals that the difference in the line depth is 6.85 ± 1.48 mÅ at the DIB location which is, however, unlikely to be caused by DIB absorption. The comparison between PHOENIX models and observed spectra yields an upper limit of 34.0 ± 0.3 mÅ for any additional interstellar absorption in τ Boo; similar results are obtained for HD 33608 and α CrB. For all objects we derive unrealistically large values for the radial velocity of any presumed interstellar clouds. In τ Boo we find Na D absorption with an equivalent width of 0.65 ± 0.07 mÅ and 2.3 ± 0.1 mÅ in the D2 and D1 lines. For the other Na, absorption of the same magnitude could only be detected in the D2 line. Our comparisons between model and data show that the interstellar absorption toward τ Boo is not abnormally high. Conclusions: We find no significant DIB absorption in any of our target stars. Any differences between modeled and

  7. Evolution of interstellar dust and stardust in the solar neighbourhood

    NASA Astrophysics Data System (ADS)

    Zhukovska, S.; Gail, H.-P.; Trieloff, M.

    2008-02-01

    Aims:We studied the evolution of the abundance in interstellar dust species that originate in stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way. We determined from this the input of dust material to the Solar System. Methods: A one-zone chemical evolution model of the Milky Way for the elemental composition of the disk combined with an evolution model for its interstellar dust component similar to that of Dwek (1998) is developed. The dust model considers dust-mass return from AGB stars as calculated from synthetic AGB models combined with models for dust condensation in stellar outflows. Supernova dust formation is included in a simple parametrised form that is gauged by observed abundances of presolar dust grains with a supernova origin. For dust growth in the ISM, a simple method is developed for coupling this with disk and dust evolution models. Results: A chemical evolution model of the solar neighbourhood in the Milky Way is calculated, which forms the basis for calculating a model of the evolution of the interstellar dust population at the galactocentric radius of the Milky Way. The model successfully passes all standard tests for the reliability of such models. In particular the abundance evolution of the important dust-forming elements is compared with observational results for the metallicity-dependent evolution of the abundances for G-type stars from the solar neighbourhood. It is found that the new tables of Nomoto et al. (2006) for the heavy element production give much better results for the abundance evolution of these important elements than the widely used tables of Woosley & Weaver (1995). The time evolution for the abundance of the following dust species is followed in the model: silicate, carbon, silicon carbide, and iron dust from AGB stars and from supernovae, as well as silicate, carbon, and iron dust grown in molecular clouds. It is shown that the interstellar dust population is

  8. Investigation of ultraviolet interstellar extinction

    NASA Technical Reports Server (NTRS)

    Payne, C.; Haramundanis, K. L.

    1973-01-01

    Results concerning interstellar extinction in the ultraviolet are reported. These results were initially obtained by using data from main-sequence stars and were extended to include supergiants and emission stars. The principal finding of the analysis of ultraviolet extinction is not only that it is wavelength dependent, but that if changes with galactic longitude in the U3 passband (lambda sub eff = 1621 A); it does not change significantly in the U2 passband (lambda sub eff = 2308 A). Where data are available in the U4 passband (lambda sub eff = 1537 A), they confirm the rapid rise of extinction in the ultraviolet found by other investigators. However, in all cases, emission stars must be used with great caution. It is important to realize that while extinction continues to rise toward shorter wavelengths in the ultraviolet, including the shortest ultraviolet wavelengths measured (1100 A), it no longer plays an important role in the X-ray region (50 A).

  9. From interstellar dust to comets

    NASA Technical Reports Server (NTRS)

    Greenberg, J. M.

    1989-01-01

    The bulk and microstructure of comet nuclei are derived from the morphological structure and chemical composition of submicron sized interstellar dust grains which have undergone cold aggregation in the pre-solar nebula. The evolutionary picture of dust which is emerging is a cyclic one in which the particles, before being destroyed or going into solar system bodies, find themselves during their 5 billion year lifetime alternately in diffuse clouds and in molecular clouds. A small silicate core captured within a molecular cloud accretes various ices and gradually builds up an inner mantle of organic refractory material which has been produced by photoprocessing of the volatile ices. Clumps of grains form, and then clumps of clumps, and so on, until finally we reach the size of the comet nucleus.

  10. Identification of interstellar methanol lines

    NASA Astrophysics Data System (ADS)

    Sutton, E. C.; Herbst, Eric

    1988-10-01

    The extended internal axis method Hamiltonian of Herbst et al. has been employed to study the rotational spectrum of methanol out to high values of the rotational quantum number J. For 12CH3OH the available laboratory data, consisting of 783 lines out to J = 22, have been fitted with a Hamiltonian containing 32 free parameters. For 13CH3OH a Hamiltonian with 23 free parameters is sufficient for fitting 455 lines, also out to J = 22. Frequency predictions based on these fits have permitted the identification of a number of previously unidentified interstellar lines from OMC-1. The majority of these are b-type R-branch transitions of 12CH3OH.

  11. Organic Model of Interstellar Grains

    NASA Astrophysics Data System (ADS)

    Yabushita, S.; Inagaki, T.; Kawabe, T.; Wada, K.

    1987-04-01

    Extinction efficiency of grains is calculated from the Mie formula on the premise that the grains are of organic composition. The optical constants adopted for the calculations are those of E. coli, polystyrene and bovine albumin. The grain radius a is assumed to obey a distribution of the form N(a) ∝ a-α and the value of α is chosen so as to make the calculated extinction curve match the observed interstellar extinction curve. Although the calculated curve gives a reasonably good fit to the observed extinction curve for wavelengths less than 2100 Å, at longer wavelength regions, agreement is poor. It is concluded that another component is required for the organic model to be viable.

  12. Interstellar extinction in the ultraviolet

    NASA Technical Reports Server (NTRS)

    Bless, R. C.; Savage, B. D.

    1972-01-01

    Interstellar extinction curves over the region 3600-1100 A for 17 stars are presented. The observations were made by the two Wisconsin spectrometers onboard the OAO-2 with spectral resolutions of 10 A and 20 A. The extinction curves generally show a pronounced maximum at 2175 plus or minus 25 A, a broad minimum in the region 1800-1350 A, and finally a rapid rise to the far ultraviolet. Large extinction variations from star to star are found, especially in the far ultraviolet; however, with only two possible exceptions in this sample, the wavelength at the maximum of the extinction bump is essentially constant. These data are combined with visual and infrared observations to display the extinction behavior over a range in wavelength of about a factor of 20.

  13. Inward Radial Mixing of Interstellar Water Ices in the Solar Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Vacher, Lionel G.; Marrocchi, Yves; Verdier-Paoletti, Maximilien J.; Villeneuve, Johan; Gounelle, Matthieu

    2016-08-01

    The very wide diversity of asteroid compositions in the main belt suggests significant material transport in the solar protoplanetary disk and hints at the presence of interstellar ices in hydrated bodies. However, only a few quantitative estimations of the contribution of interstellar ice in the inner solar system have been reported, leading to considerable uncertainty about the extent of radial inward mixing in the solar protoplanetary disk 4.56 Ga ago. We show that the pristine CM chondrite Paris contains primary Ca-carbonates whose O-isotopic compositions require an 8%–35% contribution from interstellar water. The presence of interstellar water in Paris is confirmed by its bulk D/H isotopic composition that shows significant D enrichment (D/H = (167 ± 0.2) × 10‑6) relative to the mean D/H of CM chondrites ((145 ± 3) × 10‑6) and the putative D/H of local CM water ((82 ± 1.5) × 10‑6). These results imply that (i) efficient radial mixing of interstellar ices occurred from the outer zone of the solar protoplanetary disk inward and that (ii) chondrites accreted water ice grains from increasing heliocentric distances in the solar protoplanetary disk.

  14. Speckles in interstellar radio-wave scattering

    NASA Technical Reports Server (NTRS)

    Desai, K. M.; Gwinn, C. R.; Reynolds, J.; King, E. A.; Jauncey, D.; Nicholson, G.; Flanagan, C.; Preston, R. A.; Jones, D. L.

    1991-01-01

    Observations of speckles in the scattering disk of the Vela pulsar are presented and speckle techniques for studying and circumventing scattering of radio waves by the turbulent interstellar plasma are discussed. The speckle pattern contains, in a hologrammatic fashion, complete information on the structure of the radio source as well as the distribution of the scattering material. Speckle observations of interstellar scattering of radio waves are difficult because of their characteristically short timescales and narrow bandwidths. Here, first observations are presented, taken at 13 cm wavelength with elements of the SHEVE VLBI network, of speckles in interstellar scattering.

  15. Chemical abundances in cold, dark interstellar clouds

    NASA Technical Reports Server (NTRS)

    Irvine, William M.; Kaifu, Norio; Ohishi, Masatoshi

    1991-01-01

    Current tabulations are presented of the entire range of known interstellar molecules, giving attention to that subset which has been identified in the cold, dark interstellar clouds out of which the sun has been suggested to have formed. The molecular abundances of two such clouds, Taurus Molecular Cloud 1 and Lynd's 134N, exhibit prepossessing chemical differences despite considerable physical similarities. This discrepancy may be accounted for by the two clouds' differing evolutionary stages. Two novel classes of interstellar molecules are noted: sulfur-terminated carbon chains and silicon-terminated ones.

  16. Global observations of the interstellar interaction from the Interstellar Boundary Explorer (IBEX).

    PubMed

    McComas, D J; Allegrini, F; Bochsler, P; Bzowski, M; Christian, E R; Crew, G B; DeMajistre, R; Fahr, H; Fichtner, H; Frisch, P C; Funsten, H O; Fuselier, S A; Gloeckler, G; Gruntman, M; Heerikhuisen, J; Izmodenov, V; Janzen, P; Knappenberger, P; Krimigis, S; Kucharek, H; Lee, M; Livadiotis, G; Livi, S; MacDowall, R J; Mitchell, D; Möbius, E; Moore, T; Pogorelov, N V; Reisenfeld, D; Roelof, E; Saul, L; Schwadron, N A; Valek, P W; Vanderspek, R; Wurz, P; Zank, G P

    2009-11-13

    The Sun moves through the local interstellar medium, continuously emitting ionized, supersonic solar wind plasma and carving out a cavity in interstellar space called the heliosphere. The recently launched Interstellar Boundary Explorer (IBEX) spacecraft has completed its first all-sky maps of the interstellar interaction at the edge of the heliosphere by imaging energetic neutral atoms (ENAs) emanating from this region. We found a bright ribbon of ENA emission, unpredicted by prior models or theories, that may be ordered by the local interstellar magnetic field interacting with the heliosphere. This ribbon is superposed on globally distributed flux variations ordered by both the solar wind structure and the direction of motion through the interstellar medium. Our results indicate that the external galactic environment strongly imprints the heliosphere. PMID:19833923

  17. "Dark" Atomic Gas in the Diffuse Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Reach, William T.; Heiles, Carl; Bernard, Jean-Philippe

    2015-08-01

    Far-infrared and gamma-ray surveys indicate there are significantly more nucleons in the diffuse interstellar medium than are traced by HI and CO emission. We are using the Arecibo Observatory to complement Planck observations, testing hypotheses for the origin of "dark gas" associated with the far-infrared and gamma rays. The "dark gas" is really the far-infrared emission in excess over what can be explained by dust mixed with atomic gas traced by the 21-cm line in the GALFA survey. First we test the hypothesis that the excess is molecular gas, by measuring OH absorption toward selected radio sources. Next, we are observing HI absorption, because cold atomic gas is optically thick and does not emit as readily in the 21-cm line, but it can be seen in absorption against radio continuum sources. We will observe radio sources near clouds with far-infrared emission measured by Planck to be in excess of the high-resolution HI observations from the Arecibo GALFA HI survey. We will also test another hypothesis that the ”dark gas” is molecular by observing OH absorption toward the brightest sources.

  18. The Identification of Complex Organic Molecules in the Interstellar Medium: Using Lasers and Matrix Isolation Spectroscopy to Simulate the Interstellar Environment

    NASA Technical Reports Server (NTRS)

    Stone, Bradley M.

    1998-01-01

    The Astrochemistry Group at NASA Ames Research Center is interested in the identification of large organic molecules in the interstellar medium Many smaller organic species (e.g. hydrocarbons, alcohols, etc.) have been previously identified by their radiofrequency signature due to molecular rotations. However, this becomes increasingly difficult to observe as the size of the molecule increases. Our group in interested in the identification of the carriers of the Diffuse Interstellar Bands (absorption features observed throughout the visible and near-infrared in the spectra of stars, due to species in the interstellar medium). Polycyclic Aromatic Hydrocarbons (PAHs) and related molecules are thought to be good candidates for these carriers. Laboratory experiments am performed at Ames to simulate the interstellar environment, and to compare spectra obtained from molecules in the laboratory to those derived astronomically. We are also interested in PAHs with respect to their possible connection to the UIR (Unidentified infrared) and ERE (Extended Red Emission) bands - emission features found to emanate from particular regions of our galaxy (e.g. Orion nebula, Red Rectangle, etc.). An old, "tried and proven spectroscopic technique, matrix isolation spectroscopy creates molecular conditions ideal for performing laboratory astrophysics.

  19. Interstellar Polycyclic Aromatic Compounds and Astrophysics

    NASA Technical Reports Server (NTRS)

    Hudgins, Douglas M.; DeVincenzi, Donald (Technical Monitor)

    2001-01-01

    Over the past fifteen years, thanks to significant, parallel advancements in observational, experimental, and theoretical techniques, tremendous strides have been made in our understanding of the role polycyclic aromatic compounds (PAC) in the interstellar medium (ISM). Twenty years ago, the notion of an abundant population of large, carbon rich molecules in the ISM was considered preposterous. Today, the unmistakable spectroscopic signatures of PAC - shockingly large molecules by previous interstellar chemistry standards - are recognized throughout the Universe. In this paper, we will examine the interstellar PAC model and its importance to astrophysics, including: (1) the evidence which led to inception of the model; (2) the ensuing laboratory and theoretical studies of the fundamental spectroscopic properties of PAC by which the model has been refined and extended; and (3) a few examples of how the model is being exploited to derive insight into the nature of the interstellar PAC population.

  20. Deuterium Abundance in the Local Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Ferlet, R.; Gry, C.; Vidal-Madjar, A.

    1984-01-01

    The present situation of deuterium abundance evaluation in interstellar space is discussed, and it is shown that it should be or = .00001 by studying in more detail lambda the Sco line of sight and by observing two NaI interstellar components toward that star, it can be shown that the D/H evaluation made toward lambda Sco is in fact related to the local interstellar medium (less than 10 pc from the Sun). Because this evaluation is also or = .00001 it is in striking contrast with the one made toward alpha Aur (D/H or = .000018 confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.

  1. Interstellar and interplanetary solids in the laboratory

    NASA Astrophysics Data System (ADS)

    Dartois, E.; Alata, I.; Engrand, C.; Brunetto, R.; Duprat, J.; Pinot, T.; Quirico, E.; Remusat, L.; Bardin, N.; Briani, G.; Mostefaoui, S.; Morinaud, G.; Crane, B.; Szwec, N.; Delauche, L.; Jamme, F.; Sandt, C.; Dumas, P.

    2015-01-01

    The composition of the interstellar matter is driven by environmental parameters (e.g. elemental abundance, density, reactant nature, radiations, temperature, time scales) and results also from external interstellar medium physico-chemical conditions. Astrochemists must rely on remote observations to monitor and analyze the com­position of interstellar solids. These observations give essentially access to the molecular functionality of the solids, rarely elemental composition constraints and isotopic fractionation only in the gas phase. Astrochemists bring additional information from the study of analogues produced in the laboratory, placed in simulated space environments. Planetologists and cosmochemists can have access and spectroscopically examine collected extra-terrestrial material directly in the laboratory. Observations of the diffuse interstellar medium (DISM) and molecular clouds (MC) set constraints on the composition of organic solids and large molecules, that! can then be compared with collected extraterrestrial materials analyses, to shed light on their possible links.

  2. Cosmocultural Evolution: Cosmic Motivation for Interstellar Travel?

    NASA Astrophysics Data System (ADS)

    Lupisella, M.

    Motivations for interstellar travel can vary widely from practical survival motivations to wider-ranging moral obligations to future generations. But it may also be fruitful to explore what, if any, "cosmic" relevance there may be regarding interstellar travel. Cosmocultural evolution can be defined as the coevolution of cosmos and culture, with cultural evolution playing an important and perhaps critical role in the overall evolution of the universe. Strong versions of cosmocultural evolution might suggest that cultural evolution may have unlimited potential as a cosmic force. In such a worldview, the advancement of cultural beings throughout the universe could have significant cosmic relevance, perhaps providing additional motivation for interstellar travel. This paper will explore some potential philosophical and policy implications for interstellar travel of a cosmocultural evolutionary perspective and other related concepts, including some from a recent NASA book, Cosmos and Culture: Cultural Evolution in a Cosmic Context.

  3. Comets, interstellar clouds and star clusters

    NASA Technical Reports Server (NTRS)

    Donn, B.

    1976-01-01

    The association of comets with star formation in clusters is elaborated. This hypothesis is also used to explain origin and evaluation of the Oort cloud, the composition of comets, and relationships between cometary and interstellar molecules.

  4. Interstellar material in the solar system

    NASA Technical Reports Server (NTRS)

    Wood, J. A.

    1986-01-01

    All the substance of the Earth and other terrestrial planets once existed in the form of interstellar grains and gas. A major aspect of solar system formation (and undoubtedly of star formation generally) is the complex series of processes that converted infalling interstellar grains into planets. A cryptic record of these processes is preserved in certain samples of planetary materials, such as chondritic meteorites, that were preserved in a relatively unchanged form since the beginning. It is to be expected that some of these primitive materials might contain or even consist of preserved presolar interstellar grains. The identification and study of such grains, the ancestors of our planetary system, is a matter of intense interest. Types of primitive material accessible or potentially accessible, and component of or relationship to presolar interstellar grains are discussed.

  5. Observations of interstellar Ne at 1 AU

    NASA Astrophysics Data System (ADS)

    Drews, Christian; Berger, Lars; Wimmer-Schweingruber, Robert F.; Galvin, Antoinette B.; Klecker, Berndt; Möbius, Eberhard

    2010-05-01

    Interstellar pickup ions are produced by ionization of interstellar neutral atoms which can penetrate the heliosphere unimpeded through the heliopause. The relative motion of the interstellar medium in respect to the heliosphere causes them to drift towards the sun with v=26km/s where they are gradually ionized by solar radiation and charge exchange with solar protons. Once ionized, the new born ions are "picked up" by the solar wind magnetic field and carried outwards. Accordingly interstellar neutrals of high First Ionization Potentials (FIP) or rather low ionization probability, e.g. helium and neon, are not significantly depleted in the vicinity of the sun and can be observed by spacecraft like STEREO A and B. Signatures of other pickup ions, e.g. carbon, nitrogen, and oxygen must be due to an inner source because corresponding interstellar neutrals are ionized much further away from the sun. Processes which could lead to an inner source of pickup ions are not fully understood but are possibly connected to re-ionization of neutralized solar wind ions that are trapped in small dust particles orbiting the sun. Associated with the different source regions of interstellar and inner-source PUIs is the formation of the so-called focusing cone. Due to solar gravitation interstellar atoms are focused behind the sun in respect to the direction from which they arrived. This focusing effect can be (and has been) observed for He+ in form of an enhanced pickup He+ flux once a year for an earth-bound spacecraft and every 346 and 388 days for STEREO A and B respectively. On the contrary focusing of inner-source pickup ions is not observed nor expected due to their lower FIP. STEREO PLASTIC's big geometric factor and the current unusual prolonged solar minimum allows for the first time investigation of these rare pickup ions with unprecedented quality. Within the framework of our analysis we were able to identify signatures of inner-source carbon, nitrogen, and oxygen as well

  6. The Enigmatic Diffuse Interstellar Bands: A Reservoir of Organic Material

    NASA Astrophysics Data System (ADS)

    McCall, Benjamin

    2008-05-01

    The diffuse interstellar medium of our galaxy contains about 3 billion solar masses of atomic hydrogen, or ˜3x10^66 H atoms. The inventory of identified heavy-atom-containing molecules in diffuse clouds includes CH, CH^+, NH, OH, C2, CN, C2H, and C3H2, and totals to roughly ˜10^59 in number. However, a ubiquitous set of optical absorption lines known as the diffuse interstellar bands (DIBs) belies the likely presence of ˜10^58 large organic molecules that have yet to be identified. The first of the DIBs were observed in 1919, but despite many decades of intensive efforts by laboratory spectroscopists and astronomers the identities of the molecular carriers of the DIBs remain a mystery. After reviewing the history of the DIBs, I will discuss some preliminary results from a large-scale DIBs observing campaign that was conducted on over 119 nights between 1999 and 2003, using the 3.5-meter telescope at the Apache Point Observatory. This survey, undertaken by a collaboration led by Don York at the University of Chicago, has produced high-resolution, high signal-to-noise ratio spectra of over 160 stars, spanning the entire optical region from 3600--10200 å. In particular, I will focus on two ongoing efforts. The first is the generation of a comprehensive spectral atlas of the DIBs based on four heavily reddened sightlines; this atlas will be of great use to spectroscopists who wish to compare their laboratory spectra to interstellar spectra (in hopes of finding a match!). The second is the search for correlations among the different DIBs, and especially the search for sets of DIBs that always have the same relative intensities in different sightlines. Such sets would represent the electronic spectra of individual molecular carriers of the DIBs, and could provide hints about which species should be considered for additional laboratory spectroscopic studies.

  7. The physics of interstellar shock waves

    NASA Technical Reports Server (NTRS)

    Shull, J. Michael; Draine, Bruce T.

    1987-01-01

    This review discusses the observations and theoretical models of interstellar shock waves, in both diffuse cloud and molecular cloud environments. It summarizes the relevant gas dynamics, atomic, molecular and grain processes, radiative transfer, and physics of radiative and magnetic precursors in shock models. It then describes the importance of shocks for observations, diagnostics, and global interstellar dynamics. It concludes with current research problems and data needs for atomic, molecular and grain physics.

  8. The Diffuse Interstellar Bands: Contributed papers

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M. (Editor)

    1994-01-01

    Drawing a coherent picture of the observational characteristics of the Diffuse Interstellar Bands (DIB's) and the physical and chemical properties of its proposed carriers was the focus of this NASA sponsored conference. Information relating to absoption spectra, diffuse radiation carriers, carbon compounds, stellar composition, and interstellar extinction involving T-Tauri stars, Reflection Nebulae, Red Giants, and accretion discs are discussed from those papers presented at the conference, which are included in this analytic.

  9. Cosmic ray studies with an Interstellar Probe

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Stone, E. C.

    1990-01-01

    Among the NASA mission concepts that have been suggested for the 21st century is an Interstellar Probe that might be accelerated to a velocity of about 10 to 20 AU/yr, allowing it to leave the heliosphere, ultimately reaching a radial distance of about 500 to 1000 AU in about 50 years. Previous studies of such a mission, and its potential significance for cosmic ray studies, both within the heliosphere, and beyond, in interstellar space are discussed.

  10. The interstellar gas experiment: Analysis in progress

    NASA Technical Reports Server (NTRS)

    Buehler, F.; Lind, D. L.; Geiss, J.; Eugster, O.

    1992-01-01

    The interstellar gas experiment (IGE) exposed thin metallic foils in order to collect neutral interstellar particles which penetrate the solar system due to their motion relative to the sun. These atoms were entrapped in the collecting foils along with precipitating magnetospheric ions and with ambient atmospheric atoms. For the entire duration of the LDEF mission, seven of the foils collected particles arriving from seven different directions as seen from the spacecraft. In the mass spectrometric analysis of the trapped noble gas component, we detected the He-3, He-4, Ne-20, and Ne-22 isotopes. In order to infer the isotopic ratios in the interstellar medium from the measured concentrations found in the foil piece, several lines of investigation had to be initiated. The flux of incident noble gas atoms from the ambient atmosphere was estimated by detailed calculations. The contributions proved to be negligible, supporting the experimental evidence. Foil and machine backgrounds for the four isotopes which were measured had to be assessed individually. While this was easy for He-4, spurious foil background of He-3 had to be monitored carefully by analyzing unflown foil pieces. Trapped Ne concentrations are not far above the background. During the flight, a stuck electrical relay precluded the foil-trays from sequencing as designed. Therefore, we could not use the seasonal variation of the direction of the incoming interstellar atoms to make the distinction between interstellar and magnetospheric components of the trapped particles. Instead, we had to try the method of stepwise heating to extract the interstellar component at lower temperatures than we use to extract the magnetospheric component (the interstellars hit the foil with lower energies than most of the magnetospherics). New limiting values for the isotopic composition of the interstellar medium, unavailable yet from any other method of measurement, are emerging from this analysis.

  11. A new interstellar molecule - Tricarbon monoxide

    NASA Technical Reports Server (NTRS)

    Matthews, H. E.; Irvine, W. M.; Friberg, P.; Brown, R. D.; Godfrey, P. D.

    1984-01-01

    The C3O molecule, whose pure rotational spectrum has only recently been studied in the laboratory, has been detected in the cold, dark interstellar Taurus Molecular Cloud 1. Since C3O is the first interstelar carbon chain molecule to contain oxygen, its existence places an important new constraint on chemical schemes for cold interstellar clouds. The abundance of C3O can be understood in terms of purely gas-phase ion-molecule chemistry.

  12. Reaction dynamics and the interstellar environment

    NASA Technical Reports Server (NTRS)

    Polanyi, J. C.

    1973-01-01

    Following a brief outline of the 'normal' equilibrium reaction rate laws, the theme of thermal disequilibrium in interstellar space and the related topic of detailed rate constants are more extensively discussed. Comment is made concerning the two principal techniques that are currently being used to explore the dynamical details of an increasing range of chemical reactions in the laboratory, since it is considered that these techniques suggest ways in which the understanding of the chemistry of interstellar space may be extended.

  13. A Heliosphere Buffeted by Interstellar Turbulence?

    NASA Astrophysics Data System (ADS)

    Jokipii, J. R.; Giacalone, J.

    2014-12-01

    Recent observations from IBEX combined with previous measurements from other sources suggest new, local, effects of interstellar turbulence. Observations of various interstellar parameters such as the magnetic field, fluid velocity and electron density, over large spatial scales, have revealed a broadband Kolmogorov spectrum of interstellar turbulence which pervades most of interstellar space. The outer scale (or coherence scale of this turbulence) is found to be approximately 10^19 cm and the inner cutoff scale is less than 1000 km. The root-mean-square relative fluctuation in the fluid and the magnetic-field parameters is of order unity. If this turbulence exists at the heliosphere, the root-mean-square relative fluctuations at 100 (heliospheric) AU scales is approximately 0.1. The recently published value for the change In observed velocity direction for the interstellar flow relative to the heliosphere (Frisch, etal, 2014)is consistent with this. Similarly, interpreting the width of the IBEX ribbon in terms of a fluctuating magnetic field also is in agreement with this picture. Observations of TeV cosmic rays can also be explained. Potential effects of these fluctuations in the interstellar medium on the heliosphere will be discussed. Reference: Frisch, etal, Science, 341, 480

  14. Topics in the physics of interstellar clouds

    SciTech Connect

    Roberge, W.G.

    1981-01-01

    Physical and chemical processes in interstellar clouds are discussed in six papers. In Collision-Induced Dissociation of H/sub 2/ and CO Molecules, the destruction of molecular hydrogen and carbon monoxide in shock-heated clouds is examined. Below a certain density n., radiative stabilization greatly reduces the dissociation rates with substantial consequences for the thermal and chemical evolution of the shocked gas. In The Penetration of Diffuse Ultraviolet Radiation into Interstellar Clouds, it is shown that the solution of the radiative transfer equation for coherent, nonconservative, anisotropic scattering of photons of dust grains can be expressed analytically, with arbitrary accuracy, by means of the spherical harmonics method. In Photoionization and Photodissociation in Diffuse Interstellar Clouds, this method is used to explore the dependence of photodestruction rates inside diffuse, plane parallel clouds to assumptions about the grain scattering properties. In The Calculation of Steady State Models of Diffuse Interstellar Clouds, a model of the xi Ophiuchi cloud is calculated including an accurate treatment of line and continuum radiative transfer. The abundances of certain molecules, including H/sub 2/ and OH, are sensitive to the radiative transfer calculation and models of diffuse clouds calculated with approximate treatments of radiative transfer may require substantial revision. In Cooling by C/sup +/ Ions in Interstellar Clouds, processes that determine the production and propagation of cooling radiation are examined and their effects on cooling rates in interstellar clouds are discussed.

  15. Quenched carbonaceous composite. III - Comparison to the 3.29 micron interstellar emission feature

    NASA Technical Reports Server (NTRS)

    Sakata, A.; Wada, S.; Onaka, T.; Tokunaga, A. T.

    1990-01-01

    Laboratory data are presented showing that oxidized f-QCC, after heating to 500 C, has a 3.29 micron absorption feature that matches precisely the wavelength of the 3.29 micron interstellar emission feature. In addition, the width of the f-QCC (filmy quenched carbonaceous composite) feature is close to that of the 3.29 micron emission feature observed in NGC 7027, Orion, and IRAS 21282 + 5050. Laboratory spectra of polycyclic aromatic hydrocarbons (PAHs) were also obtained, and comparison of the f-QCC and PAH absorption spectra to that of the 3.29 micron emission feature indicates that the f-QCC provides a much better match. It is thus suggested that f-QCC is representative of the class of material giving rise to the emission features in the interstellar medium.

  16. Photoprocessing of astrophysical ice analogs using the Interstellar Astrochemistry Chamber

    NASA Astrophysics Data System (ADS)

    Cruz-Díaz, G. A.; Martín-Doménech, R.; Muñoz Caro, G. M.

    2015-01-01

    UV-photodesorption is a plausible non-thermal desorption process in dark clouds, which is required to explain the presence of molecules in the gas phase. Models of ice photoprocessing depend on the vacuum ultraviolet (VUV) absorption cross section of the ice. In the past, gas phase cross section values were used as an approximation due to the lack of reported VUV-absorption cross sections of most molecules present in interstellar ice mantles (with the exception of H2O, CO2, and NH3). ISAC is an ultra-high-vacuum (UHV) set-up where pure ices composed of H2O, CO, CO2, CH3OH, NH3, CH4, H2S, N2, and O2 were deposited at 8 K. The column density of the ice samples was measured in situ by infrared spectroscopy in transmittance. VUV-absorption spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. We provide VUV-absorption cross sections of the reported molecular ices. H2S presents the highest absorption in the 120-160 nm range, while solid N2 has the lowest VUV-absorption cross section, which is about three orders of magnitude lower than that of other species. Isotopic effects were studied for D2O, 13CO2, CD3OD, and 15N2. Our method allows fast and readily available VUV spectroscopy of ices without the need of using a synchrotron beamline. Photodesorption rates of pure ices, expressed in molecules per absorbed photon, can be derived from our data.

  17. [Effect of Charge-Transfer Complex on Ultraviolet-Visible (UV-Vis) Absorption Property of Chromophoric Dissolved Organic Matter (CDOM) in Waters of Typical Water-Level Fluctuation Zones of the Three Gorges Reservoir Areas].

    PubMed

    Jiang, Tao; Liang, Jian; Zhang, Mu-xue; Wang, Ding-yong; Wei, Shi-qiang; Lu, Song

    2016-02-15

    As an important fraction of dissolved organic matter (DOM), chromophoric dissolved organic matter (CDOM) plays a key role in decision of the optical properties and photogeochemistry of DOM, and further affects pollutant fate and global carbon cycle. These optical properties are ascribed to two chromophoric systems including superposition of individual chromophores and charge-transfer (CT) complexation between electron donor (e.g., phenols and indoles) and acceptor (e.g., quinones and other oxidized aromatics) in DOM structures. Thus in this study, based on the "double-chromophoric system" model, DOM samples from four typical water-level fluctuation zones of Three Gorges Reservoir (TGR) areas were selected, to investigate the effect and contribution of charge-transfer complex to ultraviolet-visible (UV-Vis) absorption property of CDOM. Using NaBH, reduction method, original featureless absorption curve was classified into two independent curves caused by individual chromophoric group, which were derived from a simple superposition of independent chromophore and charge-transfer complex, respectively. Also, the changes in curve properties and specific parameters before and after NaBH4 reduction were compared. The results showed that in all DOM samples from the four sites of TGR, more than 35% of absorption was attributed from CT complex. Shibaozhai of Zhongxian and Zhenxi of Fuling showed the highest proportion ( > 50%). It suggested that the role of CT complex in CDOM property could not be neglected. After removal of CT complex, absorption curve showed blue-shift and CDOM concentration [a (355)] decreased significantly. Meanwhile, because of deforming of bonds by reduction, DOM structures became more dispersive and the molecular size was decreased, resulting in the lower spectral slope (S) observed, which evidentially supported that the supermolecular association structure of DOM was self-assembled through CT complex. Meanwhile, deceasing hydrophobic components led

  18. Interstellar dust from the Milky Way to the Magellanic Clouds

    NASA Technical Reports Server (NTRS)

    Pei, Yichuan C.

    1992-01-01

    Interstellar dust in the Magellanic Clouds, with a weak or nearly absent 2175 A extinction feature, may be of interest in studies of galaxies in early stages of chemical evolution. To this inquiry, we extend the graphite-silicate grain model, introduced by Mathis, Rumpl, and Nordsieck and developed by Draine and Lee (1984) from the Milky Way to the Magellanic Clouds. We find that the empirical extinction curves in the Large and Small Magellanic Clouds can be reproduced by adjusting only the relative abundances of graphite and silicate grains, while leaving all other model properties fixed to those appropriate for the Galactic extinction curve. Using the graphite-silicate models, we calculate the absorption and scattering optical depths, the mass-density ratio of interstellar dust to neutral hydrogen, and the Kramers-Kronig relation for all three galaxies. We also present a fitting function for the three extinction curves, valid not only over the observed range of wavelengths but also over the full range as predicted by the models. All the quantities we derived here are independent of the dust-to-gas ratios in the Milky Way and the Magellanic Clouds, and can be applied to other galaxies if they contain Galactic or Magellanic-type dust.

  19. The Properties of Single Interstellar Clouds Cycle 2

    NASA Astrophysics Data System (ADS)

    Hobbs, Lewis

    1991-07-01

    IN THIS CONTINUATION PROPOSAL, WE PROPOSE TO USE THE ECHELLEAND 160M GRATINGS OF THE HIGH RESOLUTION SPECTROGRAPH TO OBSERVE THE PZROFILES OF INTERSTELLAR ABSORPTION LINES, DURING THE SECOND YEAR OF A TWO-YEAR PROGRAM. IN THE TWO CYCLES TOGETHER, THE COLUMN DENSITES OF 17 NEUTRAL OR IONIZED FORMS OF THE ELEMENTS C,N,O,Mg,Si,P,S,Fe, AND Zn WILL BE MEASURED IN THE APPROXIMATELY 100 INDIVIDUAL INTERSTELLAR CLOUDS ALONG THE LIGHT PATHS TO 12 BRIGHT, BROAD-LINED STARS OF EARLY SPECTRAL TYPE WITHIN 1 KPC OF THE SUN. THE PRIMARY PURPOSE OF THE OBSERVATIONS IS TO DETERMINE MORE ACCURATELY THAN WAS HITHERTO POSSIBLE THE FUNDAMENTAL PHYSICAL PROPERTIES OF THE RESOLVED CLOUDS, INCLUDING LINEAR SIZE, TEMPERATURE, TOTAL DENSITY, FRACTIONAL IONIZATION AND THE RELATIVE ABUNDANCES OF THE 9 SELECTED ELEMENTS. THIS SECOND-YEAR PROGRAM CONSISTS OF ECH-B AND G160M OBSERVATIONS OF EACH OF 4 STARS AT 21 OR MORE WAVELENGTHS, AND OF A SUBSET OF THESE OBSERVATIONS FOR A FIFTH STAR, PI SCO. PROGRAMS 2251 AND 3993 SHOULD BE CONSULTED FOR DETAILS OF THE PREVIOUS OBSERVATIONS OBTAINED DURING CYCLE 1.

  20. The Properties of Single Interstellar Clouds: Modified Cycle 1 Observations

    NASA Astrophysics Data System (ADS)

    Hobbs, Lewis

    1990-12-01

    WE PROPOSE TO USE THE ECHELLE AND 160M GRATINGS OF THE HIGH RESOLUTION SPECTROGRAPH OVER A TWO-YEAR PERIOD TO OBSERVE THE PROFILES OF INTERSTELLAR ABSORPTION LINES. THE COLUMN DENSITES OF 18 NEUTRAL OR IONIZED FORMS OF THE ELEMENTS C,N,O,Mg,Si,P,S,Fe, AND Zn WILL BE MEASURED IN THE APPROXIMATELY 100 INDIVIDUAL INTERSTELLAR CLOUDS ALONG THE LIGHT PATHS TO 18 BRIGHT, BROAD-LINED STARS OF EARLY SPECTRAL TYPE WITHIN 1 KPC OF THE SUN. THE PRIMARY PURPOSE OF THE OBSERVATIONS IS TO DETERMINE MORE ACCURATELY THAN WAS HITHERTO POSSIBLE THE FUNDAMENTAL PHYSICAL PROPERTIES OF THE RESOLVED CLOUDS, INCLUDING LINEAR SIZE, TEMPERATURE, TOTAL DENSITY, FRACTIONAL IONIZATION AND THE RELATIVE ABUNDANCES OF THE 9 SELECTED ELEMENTS. THE REST OF THIS OBSERVING PROGRAM IS CONTAINED IN APPROVED PROPOSAL ID = 3993; THE PROGRAM ENUMERATED HERE CONSISTS OF THAT PART OF OUR ORIGINAL PROGRAM, ID = 2251, WHICH REQUIRED MODIFICATION IN ORDER TO BE CARRIED OUT USING ONLY SIDE 2 OF THE GHRS. THIS PROGRAM THEREFORE CONSISTS OF ECH-B AND G160M OBSERVATIONS OF EACH OF 8 STARS AT 14 OR MORE WAVELENGTHS. PROGRAMS 2251 AND 3993 SHOULD BE CONSULTED FOR ADDITIONAL DETAILS.

  1. Investigation of claims for interstellar organisms and complex organic molecules

    NASA Astrophysics Data System (ADS)

    Davies, Robert E.; Delluva, Adelaide M.; Koch, Robert H.

    1984-10-01

    For many years, Hoyle, Wickramasinghe and their associates have examined interstellar (IS) absorption features in the ultraviolet, visible and infrared and `identified' them with a variety of organic structures or organisms. Among these there have been generalized, pre-biotic molecules1, polyoxymethylene whiskers2, polysaccharides and hydrocarbons3,4, tryptophan (and inferentially proteins)5-all claimed to be coatings on IS grains. In other cases, the grains1,6 have been described as 10-100% alkanes, alkenes, alkynes or aromatics by mass. In extensions of these claims, the grains are supposed to be microorganisms (such as viruses and bacteria7, algae8, siliceous cells similar to diatoms9, yeasts10 or other eukaryotic cells11) in whole or in part. Finally, a case has been advanced for possible interstellar and interplanetary insects11. The `identifications' in these and many other publications call into question the intrinsic origin of Earth life itself12,13 and the uniqueness and validity of darwinian evolution11. We now report on ultraviolet spectra of specimens of the types cited by these workers and compare our results with infrared and ultraviolet data published previously. We conclude that the identifications claimed by Hoyle, Wickramasinghe and their colleagues are unwarranted.

  2. The physical properties of the interstellar cloud around the heliosphere

    NASA Astrophysics Data System (ADS)

    Gry, C.

    2015-12-01

    A new interpretation of interstellar absorption lines in the spectra of nearby stars indicates that the medium surrounding the Sun can be regarded as a single, coherent cloud if we relax the assumption that a cloud behaves like a rigid body. This outlook permits us to construct a comprehensive picture of the local interstellar cloud and reveals that it departs from homogeneity in a number of aspects and physical properties: - This local cloud undergoes a deformation related to a compression in the direction of motion and an expansion in perpendicular directions, much like a squashed balloon. - The metal abundances decrease steadily from the rear to the head of the cloud, and this phenomenon does not appear to be related to ionization effects. - The cloud average HI density, estimated toward a number of nearby stars around which an astrophere is detected in Lyman alpha, varies from 0.03 to 0.1 cm-3. The cloud outer boundary inferred from the average density and column densities is very irregular with an average distance to the Sun of 9 +/- 7 pc. - The electron density and the cloud temperature can be derived from the combination of the ionization equilibrium of MgI and the excitation of CII in a restricted number of sightlines where column density is such that MgI and CII* features are strong enough to be detectable without saturating MgII. We present a few additional targets from which we examine the physical conditions inside the cloud.

  3. Characterization of Interstellar Organic Molecules

    SciTech Connect

    Gencaga, Deniz; Knuth, Kevin H.; Carbon, Duane F.

    2008-11-06

    Understanding the origins of life has been one of the greatest dreams throughout history. It is now known that star-forming regions contain complex organic molecules, known as Polycyclic Aromatic Hydrocarbons (PAHs), each of which has particular infrared spectral characteristics. By understanding which PAH species are found in specific star-forming regions, we can better understand the biochemistry that takes place in interstellar clouds. Identifying and classifying PAHs is not an easy task: we can only observe a single superposition of PAH spectra at any given astrophysical site, with the PAH species perhaps numbering in the hundreds or even thousands. This is a challenging source separation problem since we have only one observation composed of numerous mixed sources. However, it is made easier with the help of a library of hundreds of PAH spectra. In order to separate PAH molecules from their mixture, we need to identify the specific species and their unique concentrations that would provide the given mixture. We develop a Bayesian approach for this problem where sources are separated from their mixture by Metropolis Hastings algorithm. Separated PAH concentrations are provided with their error bars, illustrating the uncertainties involved in the estimation process. The approach is demonstrated on synthetic spectral mixtures using spectral resolutions from the Infrared Space Observatory (ISO). Performance of the method is tested for different noise levels.

  4. High-resolution ultra-violet observations of the interstellar diffuse clouds toward Mu Columbae

    NASA Technical Reports Server (NTRS)

    Sofia, Ulysses J.; Savage, Blair D.; Cardelli, Jason A.

    1993-01-01

    Data obtained from the Goddard High Resolution spectrograph (GHRS) are used to study differences in gas-phase abundances of ions occurring in the diffuse neutral clouds toward mu Col. The sight-line characteristics determined in previous studies are reviewed and results for the cloud velocities, absorption equivalent widths, ion column densities, and depletions are presented. It is found that interstellar features from four distinct absorption regions with low-ionization gas are apparent in the GHRS data at heliocentric velocities of 23, 41, 53, and 62 km/s. Absorption by Mg II, Si II, and possibly Al II also occurs over the heliocentric velocity range from -17 to 0 km/s. The presence of stronger Si III absorption over this velocity region indicates that the absorption arises from an ionized gas region.

  5. Diffuse interstellar bands versus known atomic and molecular species in the interstellar medium of M82 toward SN 2014J

    SciTech Connect

    Welty, Daniel E.; York, Donald G.; Ritchey, Adam M.; Dahlstrom, Julie A.

    2014-09-10

    We discuss the absorption due to various constituents of the interstellar medium (ISM) of M82 seen in moderately high-resolution, high signal-to-noise ratio optical spectra of SN 2014J. Complex absorption from M82 is seen, at velocities 45 ≲ v {sub LSR} ≲ 260 km s{sup –1}, for Na I, K I, Ca I, Ca II, CH, CH{sup +}, and CN; many of the diffuse interstellar bands (DIBs) are also detected. Comparisons of the column densities of the atomic and molecular species and the equivalent widths of the DIBs reveal both similarities and differences in relative abundances, compared to trends seen in the ISM of our Galaxy and the Magellanic Clouds. Of the 10 relatively strong DIBs considered here, 6 (including λ5780.5) have strengths within ±20% of the mean values seen in the local Galactic ISM, for comparable N(K I); 2 are weaker by 20%-45% and 2 (including λ5797.1) are stronger by 25%-40%. Weaker than 'expected' DIBs (relative to N(K I), N(Na I), and E(B – V)) in some Galactic sight lines and toward several other extragalactic supernovae appear to be associated with strong CN absorption and/or significant molecular fractions. While the N(CH)/N(K I) and N(CN)/N(CH) ratios seen toward SN 2014J are similar to those found in the local Galactic ISM, the combination of high N(CH{sup +})/N(CH) and high W(5797.1)/W(5780.5) ratios has not been seen elsewhere. The centroids of many of the M82 DIBs are shifted relative to the envelope of the K I profile—likely due to component-to-component variations in W(DIB)/N(K I) that may reflect the molecular content of the individual components. We compare estimates for the host galaxy reddening E(B – V) and visual extinction A {sub V} derived from the various interstellar species with the values estimated from optical and near-IR photometry of SN 2014J.

  6. Complex Organics from Laboratory Simulated Interstellar Ices

    NASA Technical Reports Server (NTRS)

    Dworkin, J. P.

    2003-01-01

    Many of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. The low temperatures of these ices (T < 50 K) preclude most chemical reactions, but photolysis can drive reactions that produce a suite of new species, many of which are complex organics. We study the UV and proton radiation processing of interstellar ice analogs to explore links between interstellar chemistry, the organics in comets and meteorites, and the origin of life on Earth. The high D/H ratios in some interstellar species, and the knowledge that many of the organics in primitive meteorites are D-enriched, suggest that such links are plausible. Once identified, these species may serve as markers of interstellar heritage of cometary dust and meteorites. Of particular interest are our findings that UV photolysis of interstellar ice analogs produce molecules of importance in current living organisms, including quinones, amphiphiles, and amino acids. Quinones are essential in vital metabolic roles such as electron transport. Studies show that quinones should be made wherever polycyclic aromatic hydrocarbons are photolyzed in interstellar ices. In the case of anthracene-containing ices, we have observed the production of 9-anthrone and 9,10 anthraquinone, both of which have been observed in the Murchison meteorite. Amphiphiles are also made when mixed molecular ices are photolyzed. These amphiphiles self-assemble into fluorescent vesicles when placed in liquid water, as do Murchison extracts. Both have the ability to trap an ionic dye. Photolysis of plausible ices can also produce alanine, serine, and glycine as well as a number of small alcohols and amines. Flash heating of the room temperature residue generated by such experiments generates mass spectral distributions similar to those of IDPs. The detection of high D/H ratios in some interstellar molecular species, and the knowledge that many of the organics, such as hydroxy and amino acids, in primitive meteorites are D

  7. MAPPING THE INTERSTELLAR MEDIUM WITH NEAR-INFRARED DIFFUSE INTERSTELLAR BANDS

    SciTech Connect

    Zasowski, G.; Ménard, B.; Bizyaev, D.; García-Hernández, D. A.; Pérez, A. E. García; Majewski, S. R.; Hayden, M. R.; Holtzman, J.; Kinemuchi, K.; Johnson, J. A.; Wilson, J. C.; Nidever, D. L.; Shetrone, M.

    2015-01-01

    We map the distribution and properties of the Milky Way's interstellar medium as traced by diffuse interstellar bands (DIBs) detected in near-infrared stellar spectra from the SDSS-III/APOGEE survey. Focusing exclusively on the strongest DIB in the H band, at λ ∼ 1.527 μm, we present a projected map of the DIB absorption field in the Galactic plane, using a set of about 60,000 sightlines that reach up to 15 kpc from the Sun and probe up to 30 mag of visual extinction. The strength of this DIB is linearly correlated with dust reddening over three orders of magnitude in both DIB equivalent width (W {sub DIB}) and extinction, with a power law index of 1.01 ± 0.01, a mean relationship of W {sub DIB}/A{sub V} = 0.1 Å mag{sup –1} and a dispersion of ∼0.05 Å mag{sup –1} at extinctions characteristic of the Galactic midplane. These properties establish this DIB as a powerful, independent probe of dust extinction over a wide range of A{sub V} values. The subset of about 14,000 robustly detected DIB features have a W {sub DIB} distribution that follows an exponential trend. We empirically determine the intrinsic rest wavelength of this transition to be λ{sub 0} = 15 272.42 Å  and use it to calculate absolute radial velocities of the carrier, which display the kinematical signature of the rotating Galactic disk. We probe the DIB carrier distribution in three dimensions and show that it can be characterized by an exponential disk model with a scale height of about 100 pc and a scale length of about 5 kpc. Finally, we show that the DIB distribution also traces large-scale Galactic structures, including the Galactic long bar and the warp of the outer disk.

  8. Laboratory confirmation of C60(+) as the carrier of two diffuse interstellar bands.

    PubMed

    Campbell, E K; Holz, M; Gerlich, D; Maier, J P

    2015-07-16

    The diffuse interstellar bands are absorption lines seen towards reddened stars. None of the molecules responsible for these bands have been conclusively identified. Two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from C60(+) molecules (ref. 3), on the basis of the proximity of these wavelengths to the absorption bands of C60(+) measured in a neon matrix. Confirmation of this assignment requires the gas-phase spectrum of C60(+). Here we report laboratory spectroscopy of C60(+) in the gas phase, cooled to 5.8 kelvin. The absorption spectrum has maxima at 9,632.7 ± 0.1 ångströms and 9,577.5 ± 0.1 ångströms, and the full widths at half-maximum of these bands are 2.2 ± 0.2 ångströms and 2.5 ± 0.2 ångströms, respectively. We conclude that we have positively identified the diffuse interstellar bands at 9,632 ångströms and 9,577 ångströms as arising from C60(+) in the interstellar medium. PMID:26178962

  9. The 5-8 Micron Infrared Spectrum of the Galactic Center and the Composition of Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Tielens, A. G. G. M.; Wooden, D. H.; Allamandola, L. J.; Bregman, J.; Witteborn, F. C.; Cuzzi, Jeffery N. (Technical Monitor)

    1995-01-01

    Interstellar dust is an important component of the interstellar medium which dominates the opacity and, hence, regulates radiative transfer, molecule formation, and thermal balance of the ISM. Much of our knowledge on the composition of interstellar dust results from infrared spect,oscopy. The extinction along the line of sight towards the galactic center is believed to be dominated by dust in the diffuse ISM. Because of the high extinction and high IR flux, IR spectra of galactic center sources have been a prime sampling ground for the characteristics of interstellar dust. We have obtained 5-8 micrometer spectra of the galactic center using the KAO. These spectra show absorption features at 5.5, 5.8, 6.1, and 6.8 micrometers. Together with features in the 3 micrometer region previously observed by us using the IRTF, these features are compared to laboratory spectra of candidate materials. We conclude that the 3.0 and 6.1 micrometer feature are carried by H2O, likely in the form of water of hydration in interstellar silicates. The 3.4, 5.5, 5.8, and 6.8 micrometer features are due to CH2, CH3 and C=O stretching and deformation modes in a hydrocarbon grain component. Comparing derived dust abundances, we conclude that silicates dominate the interstellar dust volume. Hydrocarbon and (small) graphite grains contribute each about 0.1. The remainder of the interstellar dust volume does not show strong IR absorption features and is likely in the form of large graphite, amorphous, carbon, or diamond grains.

  10. Statistical time-dependent model for the interstellar gas

    NASA Technical Reports Server (NTRS)

    Gerola, H.; Kafatos, M.; Mccray, R.

    1974-01-01

    We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.

  11. Low intensity H-beta emission from the interstellar medium

    NASA Technical Reports Server (NTRS)

    Reynolds, R. J.

    1972-01-01

    Pulsar pulse dispersions and low-frequency absorption of galactic and extragalactic radio sources strongly suggest that the interstellar medium is much more ionized than previously assumed. The search was confined to directions near pulsars because of the additional information provided by the dispersion measure which gives the total number of electrons along the line of sight to the pulsar. Of the four directions in which observations were made, an emission line appears to be present in at least two and possibly three directions. The data are shown from a low galactic latitude direction near the Crab Nebula pulsar. The observing direction was about 9 arcmin off the Crab with the field of view of about 1.5 arcmin. The number of counts was plotted versus the local standard of rest velocity and local standard wavelength of H-beta.

  12. Organic chemistry and biology of the interstellar medium

    NASA Technical Reports Server (NTRS)

    Sagan, C.

    1973-01-01

    Interstellar organic chemistry is discussed as the field of study emerging from the discovery of microwave lines of formaldehyde and of hydrogen cyanide in the interstellar medium. The reliability of molecular identifications and comparisons of interstellar and cometary compounds are considered, along with the degradational origin of simple organics. It is pointed out that the contribution of interstellar organic chemistry to problems in biology is not substantive but analogical. The interstellar medium reveals the operation of chemical processes which, on earth and perhaps on vast numbers of planets throughout the universe, led to the origin of life, but the actual molecules of the interstellar medium are unlikely to play any significant biological role.

  13. Summer School on Interstellar Processes: Abstracts of contributed papers

    NASA Technical Reports Server (NTRS)

    Hollenbach, D. J. (Editor); Thronson, H. A., Jr. (Editor)

    1986-01-01

    The Summer School on Interstellar Processes was held to discuss the current understanding of the interstellar medium and to analyze the basic physical processes underlying interstellar phenomena. Extended abstracts of the contributed papers given at the meeting are presented. Many of the papers concerned the local structure and kinematics of the interstellar medium and focused on such objects as star formation regions, molecular clouds, HII regions, reflection nebulae, planetary nebulae, supernova remnants, and shock waves. Other papers studied the galactic-scale structure of the interstellar medium either in the Milky Way or other galaxies. Some emphasis was given to observations of interstellar grains and

  14. Supernova-driven interstellar turbulence

    NASA Astrophysics Data System (ADS)

    Joung, M. K. Ryan

    To study how supernova feedback structures the turbulent interstellar medium, we construct 3D models of vertically stratified gas stirred by discrete supernova explosions, including vertical gravitational field and parametrized heating and cooling. The models reproduce many observed characteristics of the Galaxy such as global circulation of gas (i.e., galactic fountain) and the existence of cold dense clouds in the galactic disk. Global quantities of the model such as warm and hot gas filling factors in the midplane, mass fraction of thermally unstable gas, and the averaged vertical density profile are compared directly with existing observations, and shown to be broadly consistent. We find that energy injection occurs over a broad range of scales. There is no single effective driving scale, unlike the usual assumption for idealized models of incompressible turbulence. However, >90% of the total kinetic energy is contained in wavelengths shortward of 200 pc. The shape of the kinetic energy spectrum differs substantially from that of the velocity power spectrum, which implies that the velocity structure varies with the gas density. Velocity structure functions demonstrate that the phenomenological theory proposed by Boldyrev is applicable to the medium. We show that it can be misleading to predict physical properties such as the stellar initial mass junction based on numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. Supernova-driven turbulence inhibits star formation globally rather than triggering it. Feedback from massive stars is perhaps the least understood aspect of the current scenario of large-scale structure formation. Many recent observations on both galactic and cosmological scales require

  15. Excitation of interstellar hydrogen chloride

    NASA Technical Reports Server (NTRS)

    Neufild, David A.; Green, Sheldon

    1994-01-01

    We have computed new rate coefficients for the collisional excitation of HCl by He, in the close-coupled formalism and using an interaction potential determined recently by Willey, Choong, & DeLucia. Results have been obtained for temperatures between 10 K and 300 K. With the use of the infinite order sudden approximation, we have derived approximate expressions of general applicability which may be used to estimate how the rate constant for a transition (J to J prime) is apportioned among the various hyperfine states F prime of the final state J prime. Using these new rate coefficients, we have obtained predictions for the HCl rotational line strengths expected from a dense clump of interstellar gas, as a function of the HCl fractional abundance. Over a wide range of HCl abundances, we have found that the line luminosities are proportional to abundance(exp 2/3), a general result which can be explained using a simple analytical approximation. Our model for the excitation of HCl within a dense molecular cloud core indicates that the J = 1 goes to 0 line strengths measured by Blake, Keene, & Phillips toward the Orion Molecular Cloud (OMC-1) imply a fractional abundance n(HCl)/n(H2) approximately 2 x 10(exp -9), a value which amounts to only approximately 0.3% of the cosmic abundance of chlorine nuclei. Given a fractional abundance of 2 x 10(exp -9), the contribution of HCl emission to the total radiative cooling of a dense clump is small. For Orion, we predict a flux approximately 10(exp -19) W/sq cm for the HCl J = 3 goes to 2 line near 159.8 micrometers, suggesting that the strength of this line could be measured using the Infrared Space Observatory.

  16. The Physical Character of Small-Scale Interstellar Structures

    NASA Technical Reports Server (NTRS)

    Lauroesch, James T.

    2005-01-01

    The primary objective of this program was to obtain FUSE observations of the multiple interstellar absorption lines of H2 toward the members of 3 resolvable binary/multiple star systems to explore the physical conditions in known interstellar small-scale structures. Each of the selected systems was meant to address a different aspect of the models for the origin of these structures: 1) The stars HD 32039/40 were meant to probe a temporally varying component which probed a cloud with an inferred size of tens to a few hundreds of AU. The goal was to see if there was any significant H2 associated with this component; 2) The star HD 36408B and its companion HD 36408A (observed as part of FUSE GTO program P119) show significant spatial and temporal (proper motion induced) Na I column variations in a strong, relatively isolated component, as well as a relatively simple component structure. The key goal here was to identify any differences in H2 or C I excitation between the sightlines, and to measure the physical conditions (primarily density and temperature) in the temporally varying component; 3) The stars HD 206267C and HD 206267D are highly reddened sightlines which showed significant variations in K I and molecular absorption lines in multiple velocity components. Coupled with FUSE GTO observations of HD 206267A (program P116), the goal was to study the variations in H2 along sightlines which are significantly more distant, with larger separations, and with greater extinctions than the other selected binary systems.

  17. Green Bank Telescope Observations of Interstellar Glycolaldehyde: Low Temperature Sugar

    NASA Technical Reports Server (NTRS)

    Hollis, J. M.; Jewell, P. R.; Lovas, F. J.; Remijan, A.

    2004-01-01

    Interstellar glycolaldehyde (CH20HCHO) has been detected with the 100-m Green Bank Telescope (GBT) toward the star-forming region Sagittarius B2(N) by means of the 1(sub 10)-1(sub 01),2(sub 11)-2(sub 02),3(sub 12)-3(sub 0), and 4(sub 13)-4(sub 04) rotational transitions at 13.48, 15.18, 17.98, and 22.14 GHz, respectively. An analysis of these four high signal- to-noise rotational transitions yields a glycolaldehyde state temperature of 8 K. Previously reported emission line detections of glycolaldehyde with the NRAO 12-m telescope at mm-wavelengths (71 GHz to 103 GHz) are characterized by a state temperature of -50 K. By comparison the GBT detections are surprisingly strong and seen in emission at 13.48 GHz, emission and absorption at 15.18 GHz, and absorption at 17.98 GHz and 22.14 GHz. We attribute the strong absorption observed by the GBT at the higher frequencies to the correspondingly smaller GBT beams coupling better to the continuum source(s) in Sagittarius B2(N). A possible model for the two-temperature regions of glycolaldehyde is discussed.

  18. Prospective of Photon Propulsion for Interstellar Flight

    NASA Astrophysics Data System (ADS)

    Bae, Young K.

    Mastering photon propulsion is proposed to be the key to overcoming the limit of the current propulsion technology based on conventional rocketry and potentially opening a new space era. A perspective on photon propulsion is presented here to elucidate that interstellar manned roundtrip flight could be achievable in a century within a frame of exiting scientific principles, once the required existing technologies are further developed. It is shown that the developmental pathway towards the interstellar flight demands not only technological breakthroughs, but consistent long-term world-scale economic interest and investment. Such interest and investment will result from positive financial returns from routine interstellar commutes that can transport highly valuable commodities in a profitable manner. The Photonic Railway, a permanent energy-efficient transportation structure based on the Beamed-Laser Propulsion (BLP) by Forward and the Photonic Laser Thruster (PLT) by the author, is proposed to enable such routine interstellar commutes via Spacetrains. A four-phased evolutionary developmental pathway towards the Interstellar Photonic Railway is proposed. Each phase poses evolutionary, yet daunting, technological and financial challenges that need to be overcome within each time frame of 20 _ 30 years, and is projected to generate multitudes of applications that would lead to sustainable reinvestment into its development. If successfully developed, the Photonic Railway would bring about a quantum leap in the human economic and social interests in space from explorations to terraforming, mining, colonization, and permanent habitation in exoplanets.

  19. A Laboratory Route to Interstellar Ice

    NASA Astrophysics Data System (ADS)

    van Broekhuizen, Fleur Antoinette

    2005-06-01

    The formation of snow and ice has always intrigued humans and challenged them to study these phenomena. Every snowflake has its own unique history of formation, but no two are alike. Like snow-crystals, interstellar ices consist predominantly of water (H2O), but also contain significant fractions of other molecules such as carbon monoxide (CO), carbon dioxide (CO2), and methanol (CH3OH), and traces of dinitrogen (N2) and ammonia (NH3). The presence, or absence, of a molecule in the ice strongly depends on the environmental conditions. Vice versa, these molecules have an influence on their environment as well. Hence, the chemical composition and the structure of interstellar ices are thought to contain valuable information about the past and the future of interstellar regions, and it is for this reason that interstellar ices are simulated and studied under laboratory conditions. The present thesis contains a study of laboratory analogs of interstellar ices and presents a newly developed apparatus that provides a novel laboratory route to investigate the properties of these ices in more detail than has previously been possible.

  20. Composition, structure and chemistry of interstellar dust

    NASA Technical Reports Server (NTRS)

    Tielens, Alexander G. G. M.; Allamandola, Louis J.

    1986-01-01

    The observational constraints on the composition of the interstellar dust are analyzed. The dust in the diffuse interstellar medium consists of a mixture of stardust (amorphous silicates, amorphous carbon, polycyclic aromatic hydrocarbons, and graphite) and interstellar medium dust (organic refractory material). Stardust seems to dominate in the local diffuse interstellar medium. Inside molecular clouds, however, icy grain mantles are also important. The structural differences between crystalline and amorphous materials, which lead to differences in the optical properties, are discussed. The astrophysical consequences are briefly examined. The physical principles of grain surface chemistry are discussed and applied to the formation of molecular hydrogen and icy grain mantles inside dense molecular clouds. Transformation of these icy grain mantles into the organic refractory dust component observed in the diffuse interstellar medium requires ultraviolet sources inside molecular clouds as well as radical diffusion promoted by transient heating of the mantle. The latter process also returns a considerable fraction of the molecules in the grain mantle to the gas phase.

  1. Innovative Interstellar Explorer (I2E)

    NASA Astrophysics Data System (ADS)

    McNutt, R. L.; Gold, R. E.; Krimigis, T.; Roelof, E. C.; Gruntman, M.; Gloeckler, G.; Koehn, P. L.; Kurth, W. S.; Oleson, S. R.; Fiehler, D. I.; Horanyi, M.; Mewaldt, R. A.; Leary, J. C.; Anderson, B. J.

    2005-12-01

    An interstellar "precursor" mission has been under discussion in the scientific community for almost 30 years. Fundamental scientific questions about the interaction of the Sun with the interstellar medium and the nature of the very local interstellar medium (VLISM) itself can only be answered with the in situ measurements from a probe penetrating into interstellar space. The problem is the development of a probe that can provide the required measurements and can reach a heliocentric distance of at least 200 astronomical units (AU) in a "reasonable" time. High-performance radioisotope power systems (RPSs) are enabling for our approach: The Innovative Interstellar Explorer (IIE) and its use of Radioisotope Electric Propulsion (REP) is being studied under a NASA "Vision Mission" grant. Speed is provided by a combination of a high-energy launch, a Jupiter gravity assist, and long-term, low-thrust, continuous acceleration provided by a kilowatt-class ion thruster running off electricity provided by an RPS. Such an approach relies upon known technology for most subsystems and upon current launch vehicles for speed. A payload of nine instruments with an aggregate mass of about 35 kg and requiring 30 W has been carefully chosen to address the compelling science questions. We describe the mission and system that can reach 200 AU in a 30-year flight time.

  2. Communicating Concepts about Altruism in Interstellar Messages

    NASA Astrophysics Data System (ADS)

    Vakoch, Douglas A.

    2002-01-01

    This project identifies key principles of altruism that can be translated into interstellar messages for communication with extraterrestrial intelligence. The message contents will focus specifically on the evolution of altruism, drawing on recent insights in evolutionary biology, with particular emphasis on sociobiological accounts of kin selection and reciprocal altruism. This focus on altruism for message contents has several advantages. First, the subject can be translated into interstellar messages both via an existing formal interstellar language and via pictorial messages. For example, aspects of reciprocal altruism can be described through mathematical modeling, such as game theoretic approaches, which in turn can be described readily in the interstellar language Lincos. Second, concentrating on altruism as a message content may facilitate communications with extraterrestrial intelligence. Some scientists have argued that humans may be expected to communicate something about their moral status and development in an exchange with extraterrestrials. One of the most salient ways that terrestrial and extraterrestrial civilizations might be expected to evaluate one another is in terms of ethical motivations. Indeed, current search strategies assume some measure of altruism on the part of transmitting civilizations; with no guarantee of a response, the other civilization would be providing information to us with no direct payoff. Thus, concepts about altruism provide an appropriate content for interstellar messages, because the concepts themselves might be understood by extraterrestrial civilizations.

  3. Interstellar H2 toward HD 147888

    NASA Astrophysics Data System (ADS)

    Gnaciński, P.

    2013-01-01

    The ultraviolet and far-ultraviolet spectra of HD 147888 allows the H2 vibrational level ν = 0 to be accessed along with higher vibrational levels of the ground H2 electronic level. The large number of H2 absorption lines in the HST spectra allows column densities to be determined even from a noisy spectra. We have determined column densities of the H2 molecule on vibrational levels ν = 0-5 and rotational levels J = 0-6 using the profile fitting method. No variations in the column densities of H2 on vibrationally excited levels were observed from 2000 through 2009. The ortho to para H2 ratio (O/P)* for the excited vibrational states ν = 1-4 equals to 1.13. For the lowest vibrational state ν = 0 and rotational level J = 1 the ortho to para H2 ratio is only 0.15. The temperature of ortho-para thermodynamical equilibrium is TOP = 42 ± 3 K. The measurements of H2 column densities on excited vibrational levels (from the HST spectra) leads to constraints on the radiation field in photon-dominated region (PDR) models of the interstellar cloud towards HD 147888. The Meudon PDR model locates the cloud 0.62 pc from the star. The modeled hydrogen cloud density (89-336 cm-3) agrees with independent density estimations based on the C2 molecule and the chemical model. The observed (O/P)J = 1 and (O/P)* H2 ratios cannot be explained by a simple model. Based on observations made with the NASA/ESA Hubble Space Telescope and with NASA/Johns Hopkins University Far Ultraviolet Spectroscopic Explorer, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Support for FUSE data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts.

  4. The abundant elements in interstellar dust

    NASA Technical Reports Server (NTRS)

    Sofia, Ulysses J.; Cardelli, Jason A.; Savage, Blair D.

    1994-01-01

    We explore the incorporation of the cosmically abundant species O, C, N, Mg, Si, Fe, and S into interstellar dust. Column densities based on Goddard High Resolution Spectrograph 3.5 km/s resolution measurements from the literature for eight individual absorbing regions toward five lines of sight are used. Corrections are applied as needed in order to account for recent improvements in oscillator strengths. In order to acquire the most accurate column densities, and check on the accuracy of the oscillator strengths, we compare column densities based on the very strong Lorentzian damped lines of C II, O I, N I, and Mg II with results for the weak lines of these species, and confirm the previously determined f-values for O I lambda 1335, C II lambda 2325, and N I lambda lambda 1159, 1160. New empirical f-values of 1.25 x 10(exp -3) and 6.25 x 10(exp -4), respectively, are derived for the Mg II weak doublet at 1239 and 1240 A. Assuming a cosmic reference abundance based on solar and B star values, we derive depletions and dust-phase abundances which suggest that more than 70% of the available Mg and Fe is incorporated into dust-grain cores, whereas only 35% of the silicon is. This implies that oxides are important constituents of the grain core population. Mg and Fe atoms are mantled onto grain cores in a ratio of 1.8 to 1, whereas approximately 4.0 Si atoms are in the mantle per Fe atom. Since Si is not expected to accrete onto silicate or graphite grains, other grain cores, perhaps oxides and/or metallic Fe, may provide mantling sites for this species. The abundances of Fe and Mg in mantles would imply that graphite grains must have a substantial coating unless oxides provide significant mantling sites for these species. The abundance of O and N in the dust phase as implied by the solar reference abundance values are difficult to reconcile with the fact that these elements are not expected to participate in mantle formation, and the 3.1 micrometer H2O ice feature is

  5. CAN NEUTRAL AND IONIZED POLYCYCLIC AROMATIC HYDROCARBONS BE CARRIERS OF THE ULTRAVIOLET EXTINCTION BUMP AND THE DIFFUSE INTERSTELLAR BANDS?

    SciTech Connect

    Steglich, M.; Huisken, F.; Bouwman, J.; Henning, Th.

    2011-11-20

    Up to now, no laboratory-based study has investigated polycyclic aromatic hydrocarbon (PAH) species as potential carriers of both the diffuse interstellar bands (DIBs) and the 2175 A UV bump. We examined the proposed correlation between these two features by applying experimental and theoretical techniques on two specific medium-sized/large PAHs (dibenzorubicene C{sub 30}H{sub 14} and hexabenzocoronene C{sub 42}H{sub 18}) in their neutral and cationic states. It was already shown that mixtures of sufficiently large, neutral PAHs can partly or even completely account for the UV bump. We investigated how the absorption bands are altered upon ionization of these molecules by interstellar UV photons. The experimental studies presented here were realized by performing matrix isolation spectroscopy with subsequent far-UV irradiation. The main effects were found to be a broadening of the absorption bands in the UV combined with slight redshifts. The position of the complete {pi}-{pi}* absorption structure around 217.5 nm, however, remains more or less unchanged, which could explain the observed position invariance of the interstellar bump for different lines of sight. This favors the assignment of this feature to the interstellar PAH population. As far as the DIBs are concerned, neither our investigations nor the laboratory studies carried out by other research groups support a possible connection with this class of molecules. Instead, there are reasonable arguments that neutral and singly ionized cationic PAHs cannot be held responsible for the DIBs.

  6. Copernicus observations of C I and CO in diffuse interstellar clouds

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.; Jura, M.; Loewenstein, M.

    1980-01-01

    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.

  7. Meteorite nanoparticles as models for interstellar grains: synthesis and preliminary characterisation.

    PubMed

    Mautner, M N; Abdelsayed, V; El-Shall, M S; Thrower, J D; Green, S D; Collings, M P; McCoustra, M R S

    2006-01-01

    Dust particles and their interaction with gases play important roles in star formation and in solar nebulae. Appropriate model dust grains are needed for the laboratory simulation of gas-grain interactions. Nanoparticles formed from carbonaceous meteorites may be particularly suitable, as these particles are formed from materials that were formed originally from interstellar/nebula dust. Extending our previous studies with grounded meteorite powders, we demonstrate here the production of nanoparticles formed from meteorites using the laser desorption/controlled condensation method developed in our laboratory. The product nanoparticle aggregates have porous, web-like morphologies similar to interstellar dust grains, indicating that they can present large specific surface areas for gas/grain interactions. In this paper, we present polarisation modulation reflection-absorption infrared spectra (PM-RAIRS) of supported thin films and compare these spectra with the known silicate bands in the spectra of interstellar dust recorded during the ISO mission. We also report an ultrahigh vacuum (UHV) temperature programmed desorption (TPD) study of the adsorption of CO on the supported nanoparticle films. The latter allow us to estimate the CO binding energy on the meteorite nanoparticles as 13.5 +/- 3.0 kJ mol(-1), cf. a value of 9.8 +/- 0.2 kJ mol(-1) for CO binding to a water ice substrate. Such thermochemical data can be useful for computational modelling of gas-grain interactions under the diverse conditions in interstellar clouds and solar nebulae. PMID:17191444

  8. New Maps of the 3-D Distribution of Cold and Warm Interstellar Gas within 500pc

    NASA Astrophysics Data System (ADS)

    Welsh, Barry; Lallement, R.; Vergely, J.

    2006-12-01

    We present preliminary maps of the 3-D spatial distribution of cold (T <1000K) neutral and warm (T 5000K) partially ionized interstellar gas as traced by the NaI and CaII absorption lines observed towards stars with distances < 500pc from the Sun. These maps have been constructed from high-resolution (R 80,000) spectral data collected towards 1600 sight-lines, with the 3-D local gas density distribution being calculated from an inversion of the derived column density values. Our new maps, which trace the gas density within a 1kpc 3-D data cube surrounding the Sun, clearly show the neutral boundaries to several interstellar cavities that surround our own Local Bubble region (e.g. Loop I) and also reveal several adjacent interstellar tunnels and chimneys. Our final goal is to obtain maps based on 2000 interstellar sight-line measurements, and these data will be a valuable tool in solving several anomalies linked to the distribution of local gas such as the puzzling distribution of D-to-H values as measured within 1kpc by the NASA FUSE satellite.

  9. HERSCHEL/HIFI DISCOVERY OF HCL{sup +} IN THE INTERSTELLAR MEDIUM

    SciTech Connect

    De Luca, M.; Gerin, M.; Falgarone, E.; Gupta, H.; Drouin, B. J.; Pearson, J. C.; Neufeld, D.; Teyssier, D.; Lis, D. C.; Monje, R.; Phillips, T. G.; Goicoechea, J. R.; Godard, B.; Bell, T. A.; Coutens, A.

    2012-06-01

    The radical ion HCl{sup +}, a key intermediate in the chlorine chemistry of the interstellar gas, has been identified for the first time in the interstellar medium with the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared. The ground-state rotational transition of H{sup 35}Cl{sup +}, {sup 2}{Pi}{sub 3/2} J = 5/2-3/2, showing {Lambda}-doubling and hyperfine structure, is detected in absorption toward the Galactic star-forming regions W31C (G10.6-0.4) and W49N. The complex interstellar absorption features are modeled by convolving in velocity space the opacity profiles of other molecular tracers toward the same sources with the fine and hyperfine structure of HCl{sup +}. This structure is derived from a combined analysis of optical data from the literature and new laboratory measurements of pure rotational transitions, reported in the accompanying Letter by Gupta et al. The models reproduce well the interstellar absorption, and the frequencies inferred from the astronomical observations are in exact agreement with those calculated using spectroscopic constants derived from the laboratory data. The detection of H{sup 37}Cl{sup +} toward W31C, with a column density consistent with the expected {sup 35}Cl/{sup 37}Cl isotopic ratio, provides additional evidence for the identification. A comparison with the chemically related molecules HCl and H{sub 2}Cl{sup +} yields an abundance ratio of unity with both species (HCl{sup +} : H{sub 2}Cl{sup +} : HCl {approx} 1). These observations also yield the unexpected result that HCl{sup +} accounts for 3%-5% of the gas-phase chlorine toward W49N and W31C, values several times larger than the maximum fraction ({approx}1%) predicted by chemical models.

  10. Positron annihilation in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Guessoum, Nidhal; Ramaty, Reuven; Lingenfelter, Richard E.

    1991-01-01

    Positronium formation and annihilation are studied in a model for the interstellar medium consisting of cold cloud cores, warm partially ionized cloud envelopes, and hot intercloud gas. The gamma-ray spectra resulting from positron annihilation in these components of the interstellar medium are calculated. The spectra from the individual components are then combined, using two limiting assumptions for the propagation of the positrons, namely, that the positrons propagate freely throughout the interstellar medium, and that the positrons are excluded from the cold cloud cores. In the first case, the bulk of the positrons annihilate in the cloud cores and the annihilation line exhibits broad wings resulting from the annihilation of positronium formed by charge exchange in flight. In the second case, the positrons annihilate mainly in the warm envelopes, and the line wings are suppressed.

  11. Observations of interstellar chlorine and phosphorus

    NASA Technical Reports Server (NTRS)

    Jura, M.; York, D. G.

    1978-01-01

    Copernicus observations of interstellar Cl I, Cl II, and P II UV lines toward 10 stars are reported. Column densities are estimated for each species, and upper limits are computed for HCl column densities. Derivation of the gas-phase abundances of chlorine and phosphorus indicates that the averages of both the chlorine and the phosphorus logarithmic abundances relative to hydrogen are between 5.0 and 5.1. It is suggested that interstellar chlorine may be depleted by about a factor of 3 relative to the solar abundance and that interstellar phosphorus is depleted by a factor of 2 to 3. The results are shown to support the prediction that chlorine is ionized in regions containing primarily atomic oxygen and is neutral in regions where there is a significant amount of molecular hydrogen. The photoionization rate of neutral chlorine toward 15 Mon is estimated, and it is concluded that most chlorine is contained within the gas phase.

  12. PAH in the laboratory and interstellar space

    NASA Technical Reports Server (NTRS)

    Wdowiak, Thomas J.; Flickinger, Gregory C.; Boyd, David A.

    1989-01-01

    The theory that polycyclic aromatic hydrocarbons (PAHs) are a constituent of the interstellar medium, and a source of the IR emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3 microns is being studied using PAH containing acid insoluble residue of the Orgueil CI meteorite and coal tar. FTIR spectra of Orgueil PAH material that has undergone thermal treatment, and a solvent insoluble fraction of coal tar that has been exposed to hydrogen plasma are presented. The UV excided luminescence spectrum of a solvent soluble coal tar film is also shown. Comparison of the lab measurements with observations appears to support the interstellar PAH theory, and shows the process of dehydrogenation expected to take place in the interstellar medium.

  13. Long-Term Perspectives on Interstellar Flight

    NASA Astrophysics Data System (ADS)

    Michaud, M. A. G.

    Realizing interstellar travel by machines or living beings will require not only scientific and technological progress, but also a shared secular belief among a determined minority that this enterprise is important for the human future. Their efforts may have to extend beyond individual human lifetimes. Historical perspectives, on both the past and the future, are proposed. Interstellar probes could be a more thorough way of searching for alien forms of life and intelligence in nearby systems, particularly if there were intelligent beings there who did not employ technologies our astronomical observing devices can detect from here. Perspectives on the ethical, policy, and design issues of such close encounters with alien life and intelligence are presented. Ways of accelerating the coming of interstellar probes are suggested.

  14. On an Interstellar Origin for N-15 Fractionation in Meteorites

    NASA Technical Reports Server (NTRS)

    Charnley, S. B.; Rodgers, S. D.

    2001-01-01

    We have shown that interstellar chemistry could produce much larger N-15/N-14 fractionation in specific interstellar molecules than previously thought. Additional information is contained in the original extended abstract.

  15. Interstellar Travel. (Latest citations from the Aerospace Database)

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The bibliography contains citations concerning travel between the stars. Topics include cost considerations, hyperspace navigation, exploration, and propulsion systems for vehicles to be used in interstellar travel. Human factor issues and social aspects of interstellar travel are also discussed.

  16. The Dissipation Range of Interstellar Turbulence

    NASA Astrophysics Data System (ADS)

    Spangler, Steven R.; Buffo, J. J.

    2013-06-01

    Turbulence may play an important role in a number of interstellar processes. One of these is heating of the interstellar gas, as the turbulent energy is dissipated and changed into thermal energy of the gas, or at least other forms of energy. There have been very promising recent results on the mechanism for dissipation of turbulence in the Solar Wind (Howes et al, Phys. Plasm. 18, 102305, 2011). In the Solar Wind, the dissipation arises because small-scale irregularities develop properties of kinetic Alfven waves, and apparently damp like kinetic Alfven waves. A property of kinetic Alfven waves is that they become significantly compressive on size scales of order the ion Larmor radius. Much is known about the plasma properties of ionized components of interstellar medium such as HII regions and the Diffuse Ionized Gas (DIG) phase, including information on the turbulence in these media. The technique of radio wave scintillations can yield properties of HII region and DIG turbulence on scales of order the ion Larmor radius, which we refer to as the dissipation scale. In this paper, we collect results from a number of published radio scattering measurements of interstellar turbulence on the dissipation scale. These studies show evidence for a spectral break on the dissipation scale, but no evidence for enhanced compressibility of the fluctuations. The simplest explanation of our result is that turbulence in the ionized interstellar medium does not possess properties of kinetic Alfven waves. This could point to an important difference with Solar Wind turbulence. New observations, particularly with the Very Long Baseline Array (VLBA) could yield much better measurements of the power spectrum of interstellar turbulence in the dissipation range. This research was supported at the University of Iowa by grants AST09-07911 and ATM09-56901 from the National Science Foundation.

  17. The origin of extended interstellar shells around Wolf-Rayet stars having bright optical ring nebulae

    NASA Technical Reports Server (NTRS)

    Nichols, J. S.; Fesen, R. A.

    1994-01-01

    Investigations of the interstellar environment around Wolf-Rayet (WR) stars have lead to the discovery of extended shells of gas and dust 50-100 pc in diameter in the lines of sight toward three WR stars. In this paper, several origins for these extended shells are discussed. While positional coincidences cannot be excluded, the locations of the WR stars near the projected centers of the shells, the detection of only shortward-shifted, high-velocity UV absorption line components in their IUE spectra, plus commonality of some WR star properties which are rare in the general WR star population suggest some casual connections between the WR stars and formation of interstellar shells. To access whether the high-velocity UV interstellar absorption lines are a frequent phenomenon related to WR stellar winds, we present a survey of such features in all WR stars observed with IUE through 1991. Of 35 stars studied, only four are found to have components with velocity displacements greater than 45 km/s which are not attributable to previously identified OB association superbubbles. The means a surprising 82% of non-OB association WR stars show no evidence of high-velocity gas in their lines of sight at IUE's spectral resolution, suggesting that high-velocity interstellar absorption lines are not a common consequence of Wolf-Rayet star stellar winds alone. We review the properties of three WR stars (HD 50896, HD 96548, and HD 192163) which may reside inside extended interstellar shells and find that they are similar in terms of spectral class (WN5-8), presence of an optical ring nebula, and reported photometric variability. Evaluation of possible origins of the extended shells suggests these three stars are in a post X-ray binary stage of high-mass binary star evolution. If this is correct, then the large interstellar shells detected might be evidence of either supernova remnant shells generated by the explosion of the binary's primary star, or non-conservative mass transfer

  18. Studies of solid carbon dioxide in interstellar ice analogs subject to thermal processing

    NASA Astrophysics Data System (ADS)

    White, Douglas W.

    2010-09-01

    Solid CO2 has been detected in many lines of sight in the interstellar medium from infrared observatories. Spectral profiles from space-based observatories have suggested that CO2 on icy grain mantles is mixed with other common molecules such as H2O and CH 3OH in interstellar regions and that thermal annealing has occurred. The vibrational mode at 658 cm-1 (15.2 mum) is suspected to be a powerful diagnostic tool as to the composition of species on icy grain mantles as well as thermal histories. However, previous studies have not systematically investigated ice composition and temperature. Laboratory spectra of interstellar ice analogs have been created in this study order to better understand the physical properties of solid CO2 in these interstellar environments. Existing databases of ice composition studies and effects of ice thermal history were updated in this study to include a more systematic approach. The 658 cm-1 (15.2 mum) bending mode feature of CO2 is examined here and the subsequent astrophysical implications stated. In the first set of experiments, 47 mixtures of H2O,CH3OH, andCO2 were slowly warmed and mid-infrared absorption spectra were recorded at 5K intervals. The second set of experiments involved examining the CO2 bending mode feature of 10 different CO2-containing ice mixtures at different temperatures where ice segregation was suspected. In these experiments, the ice mixtures were slowly heated to the desired temperature for increasing time intervals before cooling down and recording mid-IR absorption spectra. These studies may be used to analyze IR data from space-based observatories such as the Spitzer Space Telescope Infrared Spectrograph as well other future IR observations of the interstellar medium. Finally, mass spectroscopy measurements were taken from temperature programmed desorption (TPD) experiments performed on several binary mixtures of H2O + CO2 and CH 3OH + CO2. Physical properties such as desorption energy of CO2 can be

  19. Diffuse interstellar bands in reflection nebulae

    NASA Technical Reports Server (NTRS)

    Fischer, O.; Henning, Thomas; Pfau, Werner; Stognienko, R.

    1994-01-01

    A Monte Carlo code for radiation transport calculations is used to compare the profiles of the lambda lambda 5780 and 6613 Angstrom diffuse interstellar bands in the transmitted and the reflected light of a star embedded within an optically thin dust cloud. In addition, the behavior of polarization across the bands were calculated. The wavelength dependent complex indices of refraction across the bands were derived from the embedded cavity model. In view of the existence of different families of diffuse interstellar bands the question of other parameters of influence is addressed in short.

  20. Electron energy loss spectrometry of interstellar diamonds

    NASA Technical Reports Server (NTRS)

    Bernatowicz, Thomas J.; Gibbons, Patrick C.; Lewis, Roy S.

    1990-01-01

    The results are reported of electron energy loss spectra (EELS) measurements on diamond residues from carbonaceous meteorites designed to elucidate the structure and composition of interstellar diamonds. Dynamic effective medium theory is used to model the dielectric properties of the diamonds and in particular to synthesize the observed spectra as mixtures of diamond and various pi-bonded carbons. The results are shown to be quantitatively consistent with the idea that diamonds and their surfaces are the only contributors to the electron energy loss spectra of the diamond residues and that these peculiar spectra are the result of the exceptionally small grain size and large specific surface area of the interstellar diamonds.

  1. Radio searches for additional interstellar molecules

    NASA Technical Reports Server (NTRS)

    Hollis, J. M.; Suenram, R. D.; Lovas, F. J.; Snyder, L. E.

    1983-01-01

    Observations in the 2-mm wavelength range are reported which yield new interstellar molecular transitions of NH2CHO, SO2, H2CCO, U150820.5, and U150850.0 toward Sgr B2, and SO2, CH2CHCN, HCOOCH3, and U153513.0 toward Orion A. The first interstellar searches for HOCl, CH3CH2CCH, and CH3SiH3 were conducted, but these species were not detected. During these observations limits were also obtained on 2-mm wave transitions of N2O and NaOH toward several galactic sources of molecular emission.

  2. Chemical abundances in cold, dark interstellar clouds.

    PubMed

    Irvine, W M; Ohishi, M; Kaifu, N

    1991-05-01

    The Sun may well have formed in the type of interstellar cloud currently referred to as a cold, dark cloud. We present current tabulations of the totality of known interstellar molecules and of the subset which have been identified in cold clouds. Molecular abundances are given for two such clouds which show interesting chemical differences in spite of strong physical similarities, Taurus Molecular Cloud 1 (TMC-1) and Lynd's 134N (L134N, also referred to as L183). These regions may be at different evolutionary stages. PMID:11542208

  3. Indirect observation of unobservable interstellar molecules

    NASA Technical Reports Server (NTRS)

    Herbst, E.; Green, S.; Thaddeus, P.; Klemperer, W.

    1977-01-01

    It is suggested that the abundances of neutral non-polar interstellar molecules unobservable by radio astronomy can be systematically determined by radio observation of the protonated ions. As an example, observed N2H(+) column densities are analyzed to infer molecular nitrogen abundances in dense interstellar clouds. The chemistries and expected densities of the protonated ions of O2, C2, CO2, C2H2 and CH4 are then discussed. Microwave transition frequencies fo HCO2(+) and C2H3(+) are estimated, and a preliminary astronomical search for HCO2(+) is described.

  4. The Light Cage Limit to Interstellar Expansion

    NASA Astrophysics Data System (ADS)

    McInnes, C. R.

    It has long been argued that an advanced space-faring civilisation must be gradualists who evolve and migrate within the limits imposed by resources and whose culture avoids conflict and exploitation. However, it is argued here that a relatively young civilisation which develops a set of technologies which enable it to engage in economic interstellar travel is unlikely to constrain its activities in this way and will experience rapid economic expansion and growth. In such a scenario the speed of light imposes a fundamental limit to the distance over which the civilisation can expand, providing a possible mechanism whereby interstellar expansion is self-limiting and possibly self-terminating.

  5. Newly detected molecules in dense interstellar clouds

    NASA Technical Reports Server (NTRS)

    Irvine, William M.; Ziurys, L. M.; Avery, L. W.; Matthews, H. E.; Friberg, P.

    1988-01-01

    The last year or so has seen the identification of several new interstellar molecules, including C2S, C3S, C5H, C6H, and (probably) HC2CHO in the cold, dark cloud TMC-1, and the discovery of the first interstellar phosphorus-containing molecule, PN, in the Orion 'plateau' source. Further interesting results include the observations of (C-13))3H2 and C3HD, and the first detection of HCOOH (formic acid) in a (C-13)3H2 cold cloud.

  6. The size distribution of interstellar grains

    NASA Technical Reports Server (NTRS)

    Witt, Adolf N.

    1987-01-01

    Three major areas involving interstellar grains were investigated. First, studies were performed of scattering in reflection nebulae with the goal of deriving scattering characteristics of dust grains such as the albedo and the phase function asymmetry throughout the visible and the ultraviolet. Secondly, studies were performed of the wavelength dependence of interstellar extinction designed to demonstrate the wide range of grain size distributions naturally occurring in individual clouds in different parts of the galaxy. And thirdly, studies were also performed of the ultraviolet powered emission of dust grains in the 0.5 to 1.0 micron wavelength range in reflection nebulae. Findings considered of major importance are highlighted.

  7. The 2140 cm(exp -1) (4.673 Microns) Solid CO Band: The Case for Interstellar O2 and N2 and the Photochemistry of Non-Polar Interstellar Ice Analogs

    NASA Technical Reports Server (NTRS)

    Elsila, Jamie; Allamandola, Louis J.; Sandford, Scott A.; Witteborn, Fred C. (Technical Monitor)

    1996-01-01

    The infrared spectra of CO frozen in non-polar ices containing N2, CO2, O2, and H2O, and the ultraviolet photochemistry of these interstellar/precometary ice analogs are reported. The spectra are used to test the hypothesis that the narrow 2140/cm (4.673 micrometer) interstellar absorption feature attributed to solid CO might be produced by CO frozen in ices containing non-polar species such as N2 and O2. It is shown that mixed molecular ices containing CO, N2, O2, and CO2 provide a very good match to the interstellar band at all temperatures between 12 and 30 K both before and after photolysis. The optical constants (real and imaginary parts of the index of refraction) in the region of the solid CO feature are reported for several of these ices.

  8. Comets, carbonaceous chondrites, and interstellar clouds: Condensation of carbon

    NASA Technical Reports Server (NTRS)

    Field, G. B.

    1979-01-01

    Comets, carbonaceous chondrites, and interstellar clouds are discussed in relation to information on interstellar dust. The formation and presence of carbon in stars, comets, and meteorites is investigated. The existence of graphite in the interstellar medium, though it is predicted from thermodynamic calculations, is questioned and the form of carbon contained in comets is considered.

  9. Interstellar silicate dust in the z = 0.685 absorber toward TXS 0218+357

    SciTech Connect

    Aller, Monique C.; Kulkarni, Varsha P.; Liger, Nicholas; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni

    2014-04-10

    We report the detection of interstellar silicate dust in the z {sub abs} = 0.685 absorber along the sightline toward the gravitationally lensed blazar TXS 0218+357. Using Spitzer Space Telescope Infrared Spectrograph data, we detect the 10 μm silicate absorption feature with a detection significance of 10.7σ. We fit laboratory-derived silicate dust profile templates obtained from the literature to the observed 10 μm absorption feature and find that the best single-mineral fit is obtained using an amorphous olivine template with a measured peak optical depth of τ{sub 10} = 0.49 ± 0.02, which rises to τ{sub 10} ∼ 0.67 ± 0.04 if the covering factor is taken into account. We also detected the 18 μm silicate absorption feature in our data with a >3σ significance. Due to the proximity of the 18 μm absorption feature to the edge of our covered spectral range, and associated uncertainty about the shape of the quasar continuum normalization near 18 μm, we do not independently fit this feature. We find, however, that the shape and depth of the 18 μm silicate absorption are well matched to the amorphous olivine template prediction, given the optical depth inferred for the 10 μm feature. The measured 10 μm peak optical depth in this absorber is significantly higher than those found in previously studied quasar absorption systems. However, the reddening, 21 cm absorption, and velocity spread of Mg II are not outliers relative to other studied absorption systems. This high optical depth may be evidence for variations in dust grain properties in the interstellar medium between this and the previously studied high redshift galaxies.

  10. Ice in space: surface science investigations of the thermal desorption of model interstellar ices on dust grain analogue surfaces.

    PubMed

    Burke, Daren J; Brown, Wendy A

    2010-06-21

    More than 140 different molecules have been identified in the interstellar medium (ISM) to date. Dust grain particles are also found in the ISM, and some of these molecules freeze out at the cold temperatures (10-20 K) to form molecular ices. Understanding the adsorption and desorption of these ices is crucially important in understanding the processes that lead to star and planet formation, and may even help to lead to an understanding of the origin of life itself. High sensitivity surface science techniques, including temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS), are being increasingly used to investigate the interactions between dust grains and interstellar ices. This perspective provides an overview of the current level of understanding of the adsorption and desorption of astrophysically relevant molecules from a range of dust grain analogue surfaces. Whilst the focus of this review is on interstellar ices, the results discussed are equally valid to discussions of cometary and planetary ices. PMID:20520900

  11. The Mg II h and k interstellar lines in the spectrum of the G-type giant HD 156854

    NASA Technical Reports Server (NTRS)

    Gurzadian, G. A.; Cholakian, V. G.; Kondo, Y.; Shore, Steven N.; Terzian, Yervant

    1990-01-01

    The results of the measurements and analysis of the IUE observations of the 2800 Mg II doublet in the spectrum of HD 156854, a G9 III star, are presented. The relative power of the magnesium chromosphere, R(Mg) = 0.00001, is in agreement with the known data for giants of the same class. The emission profiles of this doublet present absorption cores, which are of interstellar origin. Taking into account the interstellar depletion of Mg, the derived density of interstellar hydrogen is n(H) = 0.001/cu cm, which agrees with the conclusion (Paresce 1984) about the possibility of large hydrogen concentrations in some directions of the Galaxy far from the sun.

  12. The violent interstellar medium associated with the Carina nebula. I - The line of sight toward HD 93205

    NASA Astrophysics Data System (ADS)

    Laurent, C.; Paul, J. A.; Pettini, M.

    1982-09-01

    Four high velocity and two low velocity components have been identified by the analysis of interstellar absorption lines in high resolution spectra of HD 93205. The chemical composition and physical conditions of the different regions are discussed in light of UV, optical and radio observations, and the two main high velocity components are found to show different relative abundance patterns. Among the two low velocity components, one has been identified with the normal interstellar material in the disk of the Galaxy between the sun and the Carina nebula. Column densities of interstellar C IV and Si IV have been measured in this component, free from contamination by circumstellar material. The other low velocity component has been identified with the approaching part of the expanding ionized nebula around the Carina OB associations, and consists of a dense H II region in which the two O I fine structure lines originate.

  13. An interstellar cloud density from Copernicus observations of CO in the spectrum of Zeta Ophiuchi

    NASA Technical Reports Server (NTRS)

    Smith, A. M.; Stecher, T. P.; Krishna Swamy, K. S.

    1978-01-01

    Interstellar CO absorption bands in Copernicus spectra of Zeta Oph have been studied. Absorption profiles, computed under the assumption that excitation is due to collisions with H2 molecules and interaction with the 3-K background radiation field, were fitted to the reduced data of nine bands. When a gas kinetic temperature of 56 K is assumed, the best-fit condition implies a hydrogen-nucleus density of 120 per cu cm, a CO column density of 1.2 by 10 to the 15th power per sq cm, and a radial-velocity dispersion of 0.9 km/s. The relevance of these results to existing ideas concerning the Zeta Oph interstellar clouds is discussed. It is suggested that the strongest interstellar component is not circumstellar in origin but is instead part of a supernova remnant. Simple calculations are made to establish the plausibility of the supernova-remnant identification. This suggestion is also supported by Heiles's (1976) 21-cm pictures.

  14. Stardust Interstellar Preliminary Examination II: Curating the interstellar dust collector, picokeystones, and sources of impact tracks

    NASA Astrophysics Data System (ADS)

    Frank, David R.; Westphal, Andrew J.; Zolensky, Michael E.; Gainsforth, Zack; Butterworth, Anna L.; Bastien, Ronald K.; Allen, Carlton; Anderson, David; Ansari, Asna; Bajt, Sasa; Bassim, Nabil; Bechtel, Hans A.; Borg, Janet; Brenker, Frank E.; Bridges, John; Brownlee, Donald E.; Burchell, Mark; Burghammer, Manfred; Changela, Hitesh; Cloetens, Peter; Davis, Andrew M.; Doll, Ryan; Floss, Christine; Flynn, George; Grün, Eberhard; Heck, Philipp R.; Hillier, Jon K.; Hoppe, Peter; Hudson, Bruce; Huth, Joachim; Hvide, Brit; Kearsley, Anton; King, Ashley J.; Lai, Barry; Leitner, Jan; Lemelle, Laurence; Leroux, Hugues; Leonard, Ariel; Lettieri, Robert; Marchant, William; Nittler, Larry R.; Ogliore, Ryan; Ong, Wei Ja; Postberg, Frank; Price, Mark C.; Sandford, Scott A.; Tresseras, Juan-Angel Sans; Schmitz, Sylvia; Schoonjans, Tom; Silversmit, Geert; Simionovici, Alexandre S.; Solé, Vicente A.; Srama, Ralf; Stephan, Thomas; Sterken, Veerle J.; Stodolna, Julien; Stroud, Rhonda M.; Sutton, Steven; Trieloff, Mario; Tsou, Peter; Tsuchiyama, Akira; Tyliszczak, Tolek; Vekemans, Bart; Vincze, Laszlo; Korff, Joshua Von; Wordsworth, Naomi; Zevin, Daniel

    2014-09-01

    We discuss the inherent difficulties that arise during "ground truth" characterization of the Stardust interstellar dust collector. The challenge of identifying contemporary interstellar dust impact tracks in aerogel is described within the context of background spacecraft secondaries and possible interplanetary dust particles and β-meteoroids. In addition, the extraction of microscopic dust embedded in aerogel is technically challenging. Specifically, we provide a detailed description of the sample preparation techniques developed to address the unique goals and restrictions of the Interstellar Preliminary Exam. These sample preparation requirements and the scarcity of candidate interstellar impact tracks exacerbate the difficulties. We also illustrate the role of initial optical imaging with critically important examples, and summarize the overall processing of the collection to date.

  15. Stardust Interstellar Preliminary Examination II: Curating the Interstellar Dust Collector, Picokeystones, and Sources of Impact Tracks

    NASA Technical Reports Server (NTRS)

    Frank, David R.; Westphal, Andrew J.; Zolensky, Michael E.; Gainsforth, Zack; Butterworth, Anna L.; Bastien, Ronald K.; Allen, Carlton; Anderson, David; Bechtel, Hans A.; Sandford, Scott A.

    2013-01-01

    We discuss the inherent difficulties that arise during "ground truth" characterization of the Stardust interstellar dust collector. The challenge of identifying contemporary interstellar dust impact tracks in aerogel is described within the context of background spacecraft secondaries and possible interplanetary dust particles and beta-meteoroids. In addition, the extraction of microscopic dust embedded in aerogel is technically challenging. Specifically, we provide a detailed description of the sample preparation techniques developed to address the unique goals and restrictions of the Interstellar Preliminary Exam. These sample preparation requirements and the scarcity of candidate interstellar impact tracks exacerbate the difficulties. We also illustrate the role of initial optical imaging with critically important examples, and summarize the overall processing of the collection to date.

  16. Exploring the central molecular zone of the Galaxy using spectroscopy of H3+ and CO.

    PubMed

    Geballe, T R

    2012-11-13

    The central 400 parsecs of the Milky Way, a region known as the central molecular zone (CMZ), contains interstellar gas in a wide range of physical environments, from ultra-hot, rarified and highly ionized to warm, dense and molecular. The combination of infrared spectroscopy of H(3)(+) and CO is a powerful way to determine the basic properties of molecular interstellar gas, because the abundance ratio of H(3)(+) to CO in 'dense' clouds is quite different from that in 'diffuse' clouds. Moreover, the energy-level structure and the radiative properties of H(3)(+) combined with the unusually warm temperatures of molecular gas in the CMZ make H(3)(+) a unique probe of the physical conditions there. This paper describes how, using infrared absorption spectroscopy of H(3)(+) and CO, it has been discovered that a large fraction of the volume of the CMZ is filled with warm, diffuse and partially molecular gas moving at speeds of up to approximately 200 km s(-1) and that the mean cosmic ray ionization rate in the CMZ exceeds by roughly an order of magnitude values found in diffuse molecular clouds elsewhere in the Galaxy. PMID:23028162

  17. Complex Chemistry on Interstellar Grains

    NASA Astrophysics Data System (ADS)

    Widicus Weaver, Susanna L.; Kelley, Matthew J.; Blake, Geoffrey A.

    Early interstellar chemical models considered complex molecule formation on grains [Allen & Robinson (1977)], but current models assume that simple molecules form on grains and subsequent gas phase ion-molecule reactions produce the more complex species [Ruffle & Herbst (2001), Charnley (2001)]. It has been shown, however, that gas phase ion-molecule reactions are insufficient for the production of such complex organic species as ethanol (CH3CH2OH) and methyl formate (CH3OCHO) [Horn et al. (2004)]. Organics such as acetaldehyde (CH3CHO), ethanol, methyl formate, acetic acid (CH3COOH), and glycolaldehyde (CH2OHCHO) have also been detected in high abundance in regions of grain mantle disruption or evaporation, indicating that these species are formed on grain surfaces [see Chengalur & Kanekar (2003), Bottinelli et al. (2004), Hollis et al. (2001)]. The mechanisms for complex molecule production on grains are clearly much more important, and much more complex, than has been recognized. Recent observational studies of these types of species have offered insight into the mechanisms for their possible grain surface synthesis. The relative hot core abundances of the 2C structural isomers methyl formate, acetic acid, and glycolaldehyde (52:2:1, respectively [Hollis et al. (2001)]) indicate that if they form on grains it is not from kinetically-controlled single-atom addition reactions. Likewise, the 3C aldose sugar, glyceraldehyde (CH2OHCHOHCHO), was not detected in Sgr B2(N-LMH) [Hollis et al. (2004)] while the 3C ketose sugar, dihydroxyacetone (CO(CH2OH)2) was detected in this source [Widicus Weaver & Blake (2005)]. Chemical pathways favoring the more stable carbonates over acids and aldehydes are required to explain these results. Interestingly, all of these species can be formed from reactions involving the abundant grain mantle constituents CO, HCOOH, and CH3OH and their radical precursors. A model has been developed to investigate this type of chemical network, and

  18. A search for interstellar nitrous oxide

    NASA Technical Reports Server (NTRS)

    Wilson, W. J.; Snyder, L. E.

    1981-01-01

    An extensive search for interstellar nitrous oxide (N2O) has been made at two different frequencies, 75.4 and 100.5 GHz, in a number of molecular sources. No N2O signal was detected; however, a number of other spectral lines including two new transitions of methyl formate and several new unidentified lines were measured.

  19. INTERSTELLAR MAGNETIC FIELD SURROUNDING THE HELIOPAUSE

    SciTech Connect

    Whang, Y. C.

    2010-02-20

    This paper presents a three-dimensional analytical solution, in the limit of very low plasma beta-ratio, for the distortion of the interstellar magnetic field surrounding the heliopause. The solution is obtained using a line dipole method that is the integration of point dipole along a semi-infinite line; it represents the magnetic field caused by the presence of the heliopause. The solution allows the variation of the undisturbed magnetic field at any inclination angle. The heliosphere is considered as having blunt-nosed geometry on the upwind side and it asymptotically approaches a cylindrical geometry having an open exit for the continuous outflow of the solar wind on the downwind side. The heliopause is treated as a magnetohydrodynamic tangential discontinuity; the interstellar magnetic field lines at the boundary are tangential to the heliopause. The interstellar magnetic field is substantially distorted due to the presence of the heliopause. The solution shows the draping of the field lines around the heliopause. The magnetic field strength varies substantially near the surface of the heliopause. The effect on the magnetic field due to the presence of the heliopause penetrates very deep into the interstellar space; the depth of penetration is of the same order of magnitude as the scale length of the heliosphere.

  20. A Fission-Powered Interstellar Precursor Mission

    SciTech Connect

    Lenard, R.X.; Lipinski, R.J.; West, J.L.; Wright, S.A.

    1998-10-28

    An 'interstellar precursor mission' lays the groundwork for eventual interstellar exploration by studying the interstellar medium and by stretching technologies that have potential application for eventual interstellar exploration. The numerous scientific goals for such a mission include generating a 3-D stellar map of our galaxy, studying Kuiper-belt and Oort cloud objects, and observing distant objects using the sun's gravitational lens as the primary of an enormous telescope. System equations are developed for a space tug which propels a 2500-kg scientific payload to 550 astronomical units in about 20 years. The tug to transport this payload uses electric propulsion with an Isp of 15,000 seconds and a fission reactor with a closed Brayton cycle to genemte the electricity. The optimal configuration may be to thrust for only about 6 years and then coast for the remaining 14 pars. This spacecraft does not require any physics breakthroughs or major advances in technology. The fission power syslem can be engineered and built by drawing upon known technologies developed for relatgd systems over the past 40 years. The tug system would eventually reach 1000 a.u in 33 years, and would have adequate power to relay large amounts of data throughout its journey.

  1. Diffuse Interstellar Bands: Past and Present

    NASA Astrophysics Data System (ADS)

    Snow, T. P.

    2014-02-01

    The diffuse interstellar bands (DIBs) have come to the fore as an important mystery. This paper presents the history of DIB discovery and research; their importance; a summary of their properties; constraints on proposed identifications; a survey of DIB papers (including graduate student's theses); and a web site that lists DIBs paper from 1922 to 2011 (to be extended to the present).

  2. THE AGE OF THE LOCAL INTERSTELLAR BUBBLE

    SciTech Connect

    Abt, Helmut A.

    2011-05-15

    The Local Interstellar Bubble is an irregular region from 50 to 150 pc from the Sun in which the interstellar gas density is 10{sup -2}-10{sup -3} of that outside the bubble and the interstellar temperature is 10{sup 6} K. Evidently most of the gas was swept out by one or more supernovae. I explored the stellar contents and ages of the region from visual double stars, spectroscopic doubles, single stars, open clusters, emission regions, X-ray stars, planetary nebulae, and pulsars. The bubble has three sub-regions. The region toward the galactic center has stars as early as O9.5 V and with ages of 2-4 M yr. It also has a pulsar (PSRJ1856-3754) with a spin-down age of 3.76 Myr. That pulsar is likely to be the remnant of the supernova that drove away most of the gas. The central lobe has stars as early as B7 V and therefore an age of about 160 Myr or less. The Pleiades lobe has stars as early as B3 and therefore an age of about 50 Myr. There are no obvious pulsars that resulted from the supernovae that cleared out those areas. As found previously by Welsh and Lallement, the bubble has five B stars along its perimeter that show high-temperature ions of O VI and C II along their lines of sight, confirming its high interstellar temperature.

  3. A Rigorous Attempt to Verify Interstellar Glycine

    NASA Technical Reports Server (NTRS)

    Snyder, L. E.; Lovas, F. J.; Hollis, J. M.; Friedel, D. N.; Jewell, P. R.; Remijan, A.; Ilyushin, V. V.; Alekseev, E. A.; Dyubko, S. F.

    2004-01-01

    In 2003, Kuan, Charnley, and co-workers reported the detection of interstellar glycine (NH2CH2COOH) based on observations of 27 lines in 19 different spectral bands in one or more of the sources Sgr BP(N-LMH), Orion KL, and W51 e1/e2. They supported their detection report with rotational temperature diagrams for all three sources. In this paper, we present essential criteria which can be used in a straightforward analysis technique to confirm the identity of an interstellar asymmetric rotor such as glycine. We use new laboratory measurements of glycine as a basis for applying this analysis technique, both to our previously unpublished 12 m telescope data and to the previously published SEST data of Nummelin and colleagues. We conclude that key lines necessary for an interstellar glycine identification have not yet been found. We identify several common molecular candidates that should be examined further as more likely carriers of the lines reported as glycine. Finally, we illustrate that rotational temperature diagrams used without the support of correct spectroscopic assignments are not a reliable tool for the identification of interstellar molecules. Subject headings: ISM: abundances - ISM: clouds - ISM: individual (Sagittarius B2[N-

  4. Interstellar polarization in an irregularly fluctuating medium

    NASA Technical Reports Server (NTRS)

    Nee, S. F.; Jokipii, J. R.

    1979-01-01

    The interstellar polarization of starlight for an irregularly fluctuating medium is analyzed statistically. A general formulation is presented for the case in which the propagation distance s is larger than the coherence scale of the fluctuations. One specific result for randomly changing field direction is that the linear polarization saturates at a value which can be much less than unity, in agreement with observations.

  5. Revisiting Ulysses Observations of Interstellar Helium

    NASA Astrophysics Data System (ADS)

    Wood, Brian E.; Müller, Hans-Reinhard; Witte, Manfred

    2015-03-01

    We report the results of a comprehensive reanalysis of Ulysses observations of interstellar He atoms flowing through the solar system, the goal being to reassess the interstellar He flow vector and to search for evidence of variability in this vector. We find no evidence that the He beam seen by Ulysses changes at all from 1994-2007. The direction of flow changes by no more than ~0.°3 and the speed by no more than ~0.3 km s-1. A global fit to all acceptable He beam maps from 1994-2007 yields the following He flow parameters: V ISM = 26.08 ± 0.21 km s-1, λ = 75.54 ± 0.°19, β = -5.44 ± 0.°24, and T = 7260 ± 270 K where λ and β are the ecliptic longitude and latitude direction in J2000 coordinates. The flow vector is consistent with the original analysis of the Ulysses team, but our temperature is significantly higher. The higher temperature somewhat mitigates a discrepancy that exists in the He flow parameters measured by Ulysses and the Interstellar Boundary Explorer, but does not resolve it entirely. Using a novel technique to infer photoionization loss rates directly from Ulysses data, we estimate a density of n He = 0.0196 ± 0.0033 cm-3 in the interstellar medium.

  6. A fission-powered interstellar precursor mission

    SciTech Connect

    Lipinski, Ronald J.; Lenard, Roger X.; Wright, Steven A. West, John L.

    1999-01-01

    An {open_quotes}interstellar precursor mission{close_quotes} lays the groundwork for eventual interstellar exploration by studying the interstellar medium and by stretching technologies that have potential application for eventual interstellar exploration. The numerous scientific goals for such a mission include generating a 3-D stellar map of our galaxy, studying Kuiper-belt and Oort cloud objects, and observing distant objects using the sun{close_quote}s gravitational lens as the primary of an enormous telescope. System equations are developed for a space tug which propels a 2500-kg scientific payload to 550 astronomical units in about 20 years. The tug to transport this payload uses electric propulsion with an lsp of 15,000 seconds and a fission reactor with a closed Brayton cycle to generate the electricity. The optimal configuration may be to thrust for only about 6 years and then coast for the remaining 14 years. This spacecraft does not require any physics breakthroughs or major advances in technology. The fission power system can be engineered and built by drawing upon known technologies developed for related systems over the past 40 years. The tug system would eventually reach 1000 a.u in 33 years, and would have adequate power to relay large amounts of data throughout its journey. {copyright} {ital 1999 American Institute of Physics.}

  7. Legal challenges in realizing interstellar initiatives

    NASA Astrophysics Data System (ADS)

    Hodge, Suzanne M.; Osmond, Elizabeth B.; Urrutia, Manuel C.

    Legal aspects of interstellar exploration and travel are examined. The concept of a space management and legal infrastructure is discussed. Attention is given to space law applicable to social customs, birth, citizenship, ownership, the right to protect one's property and life through insurance, commercial endeavors, colonial government, law and order, space debris, hazardous wastes, and burial and inheritance.

  8. Interstellar Carbon Chains: Is Thermodynamics the Key?

    NASA Astrophysics Data System (ADS)

    Etim, Emmanuel; Chakrabarti, Sandip Kumar; Das, Ankan; Gorai, Prasanta; Arunan, Elangannan

    2016-07-01

    In an effort to further our interest in understanding basic chemistry of interstellar molecules, we carry out here an extensive investigation of the stabilities of interstellar carbon chains; C_n, H_2C_n, HC_nN and C_nX (X=N, O, Si, S, H, P, H^-, N^-). These sets of molecules account for about 20% of all the known interstellar and circumstellar molecules. Their high abundances therefore demand a serious attention. High level ab initio quantum chemical simulations are employed to accurately estimate enthalpy of formation, chemical reactivity indices; global hardness and softness; and other chemical parameters of these molecules. Chemical modeling of the abundances of these molecular species has also been performed. Of the 89 molecules considered from these groups, 47 have been astronomically observed, these observed molecules are found to be more stable with respect to other members of the group. Of the 47 observed molecules, 60% are odd number carbon chains. The reason for the high abundance of odd numbered carbon chains can easily be seen from the fact that they are more stable than the corresponding even number carbon chains. This further confirms the dominance of thermodynamics in interstellar formation processes as described in the Energy, Stability and Abundance (ESA) relationship. The next possible carbon chain molecule for astronomical observation in each group is proposed. The effect of kinetics in the formation processes of these carbon chains is shown to be largely dominated by thermodynamics.

  9. Elemental nitrogen partitioning in dense interstellar clouds

    PubMed Central

    Daranlot, Julien; Hincelin, Ugo; Bergeat, Astrid; Costes, Michel; Loison, Jean-Christophe; Wakelam, Valentine; Hickson, Kevin M.

    2012-01-01

    Many chemical models of dense interstellar clouds predict that the majority of gas-phase elemental nitrogen should be present as N2, with an abundance approximately five orders of magnitude less than that of hydrogen. As a homonuclear diatomic molecule, N2 is difficult to detect spectroscopically through infrared or millimeter-wavelength transitions. Therefore, its abundance is often inferred indirectly through its reaction product N2H+. Two main formation mechanisms, each involving two radical-radical reactions, are the source of N2 in such environments. Here we report measurements of the low temperature rate constants for one of these processes, the N + CN reaction, down to 56 K. The measured rate constants for this reaction, and those recently determined for two other reactions implicated in N2 formation, are tested using a gas-grain model employing a critically evaluated chemical network. We show that the amount of interstellar nitrogen present as N2 depends on the competition between its gas-phase formation and the depletion of atomic nitrogen onto grains. As the reactions controlling N2 formation are inefficient, we argue that N2 does not represent the main reservoir species for interstellar nitrogen. Instead, elevated abundances of more labile forms of nitrogen such as NH3 should be present on interstellar ices, promoting the eventual formation of nitrogen-bearing organic molecules. PMID:22689957

  10. Stardust Interstellar Preliminary Examination III: Infrared spectroscopic analysis of interstellar dust candidates

    NASA Astrophysics Data System (ADS)

    Bechtel, Hans A.; Flynn, George J.; Allen, Carlton; Anderson, David; Ansari, Asna; Bajt, SašA.; Bastien, Ron K.; Bassim, Nabil; Borg, Janet; Brenker, Frank E.; Bridges, John; Brownlee, Donald E.; Burchell, Mark; Burghammer, Manfred; Butterworth, Anna L.; Changela, Hitesh; Cloetens, Peter; Davis, Andrew M.; Doll, Ryan; Floss, Christine; Frank, David R.; Gainsforth, Zack; Grün, Eberhard; Heck, Philipp R.; Hillier, Jon K.; Hoppe, Peter; Hudson, Bruce; Huth, Joachim; Hvide, Brit; Kearsley, Anton; King, Ashley J.; Lai, Barry; Leitner, Jan; Lemelle, Laurence; Leroux, Hugues; Leonard, Ariel; Lettieri, Robert; Marchant, William; Nittler, Larry R.; Ogliore, Ryan; Ong, Wei Ja; Postberg, Frank; Price, Mark C.; Sandford, Scott A.; Tresseras, Juan-Angel Sans; Schmitz, Sylvia; Schoonjans, Tom; Silversmit, Geert; Simionovici, Alexandre S.; Solé, Vicente A.; Srama, Ralf; Stadermann, Frank J.; Stephan, Thomas; Sterken, Veerle J.; Stodolna, Julien; Stroud, Rhonda M.; Sutton, Steven; Trieloff, Mario; Tsou, Peter; Tsuchiyama, Akira; Tyliszczak, Tolek; Vekemans, Bart; Vincze, Laszlo; von Korff, Joshua; Westphal, Andrew J.; Wordsworth, Naomi; Zevin, Daniel; Zolensky, Michael E.

    2014-09-01

    Under the auspices of the Stardust Interstellar Preliminary Examination, picokeystones extracted from the Stardust Interstellar Dust Collector were examined with synchrotron Fourier transform infrared (FTIR) microscopy to establish whether they contained extraterrestrial organic material. The picokeystones were found to be contaminated with varying concentrations and speciation of organics in the native aerogel, which hindered the search for organics in the interstellar dust candidates. Furthermore, examination of the picokeystones prior to and post X-ray microprobe analyses yielded evidence of beam damage in the form of organic deposition or modification, particularly with hard X-ray synchrotron X-ray fluorescence. From these results, it is clear that considerable care must be taken to interpret any organics that might be in interstellar dust particles. For the interstellar candidates examined thus far, however, there is no clear evidence of extraterrestrial organics associated with the track and/or terminal particles. However, we detected organic matter associated with the terminal particle in Track 37, likely a secondary impact from the Al-deck of the sample return capsule, demonstrating the ability of synchrotron FTIR to detect organic matter in small particles within picokeystones from the Stardust interstellar dust collector.

  11. Properties of Interstellar Dust in the MBM 18-19 Cloud Complex

    NASA Astrophysics Data System (ADS)

    Chaplin, V. H.; Larson, K. A.; Gerakines, P. A.

    2004-12-01

    Studies of the interactions of starlight with materials present in the interstellar medium reveal much about the properties of interstellar dust grains - the main source of scattering and absorption of starlight. Here, we present a study of dust in lines of sight that pass through the interstellar cloud complex MBM 18-19. Data for 238 stars were collected from the SIMBAD Astronomical Database, the OASIS archive of the Infrared Processing and Analysis Center (IPAC), and the recently released database from the 2-Micron All-Sky Survey (2MASS) for infrared luminosity data. Comparisons of infrared colors have shown evidence for at least 20 newly forming star systems, or Young Stellar Objects (YSOs). Through examination of the amount of reddening due to interstellar dust, we determined that the distance to the cloud is 80 ± 20 parsecs. A useful indicator of interstellar dust grain properties is the ratio (RV) of total extinction of visible light to the reddening in each line of sight. Large values of RV signify large dust grains in a particular line of sight, and larger grains are usually found deep within the cloud where total extinction is large. In our study, we find only slight evidence for a systematic increase in RV with increasing extinction. We have also studied other methods of determining RV, with the limited results. From the data, we have produced detailed maps of extinction and RV in the region of the MBM 18-19 cloud complex. We acknowledge support from the National Science Foundation (NSF)- Research Experiences for Undergraduates (REU)- site award to the University of Alabama at Birmingham (UAB) under Grant No. DMR-0243640

  12. Effects of mechanical interaction between the interstellar medium and comets

    SciTech Connect

    Stern, S.A.

    1986-11-01

    The present treatment of the mechanical interaction of Oort Cloud comets with the interstellar medium gives attention to the importance of the accretion of interstellar material onto comets, as well as to the erosion of cometary surfaces by impacting interstellar grains and the consequences of these interactions. Scaling analyses indicate that collisions with interstellar grains can furnish a potent evolutionary mechanism in the modification of cometary surfaces; this factor may also contribute a substantial number of low mass particulated to the interstellar medium. 48 references.

  13. Far Ultraviolet Spectroscopic Explorer Measurements of Interstellar Fluorine

    NASA Astrophysics Data System (ADS)

    Federman, S. R.; Sheffer, Yaron; Lambert, David L.; Smith, V. V.

    2005-02-01

    The source of fluorine is not well understood, although core-collapse supernovae, Wolf-Rayet stars, and asymptotic giant branch stars have been suggested. A search for evidence of the ν-process during Type II supernovae is presented. Absorption from interstellar F I is seen in spectra of HD 208440 and HD 209339A acquired with the Far Ultraviolet Spectroscopic Explorer. In order to extract the column density for F I from the line at 954 Å, absorption from H2 has to be modeled and then removed. Our analysis indicates that for H2 column densities less than about 3×1020 cm-2, the amount of F I can be determined from λ954. For these two sight lines, there is no clear indication for enhanced F abundances resulting from the ν-process in a region shaped by past supernovae. Based on observations made with the NASA/CNES/CSA Far Ultraviolet Spectroscopic Explorer (FUSE), which is operated for NASA by the Johns Hopkins University under NASA contract NAS 5-32985.

  14. The interstellar D1 line at high resolution

    NASA Technical Reports Server (NTRS)

    Hobbs, L. M.; Welty, D. E.

    1990-01-01

    Observations at a resolving power or a velocity resolution are reported of the interstellar D(sub 1) line of Na I in the spectra of gamma Cas, delta Ori, epsilon Ori, pi Sco, delta Cyg, and alpha Cyg. An echelle grating was used in a double-pass configuration with a CCD detector in the coude spectrograph of the 2.7 m reflector at McDonald Observatory. At least 42 kinematically distinct clouds are detected along the light paths to the five more distant stars, in addition to a single cloud seen toward delta Cyg. The absorption lines arising in 13 of the clouds are sufficiently narrow and unblended to reveal clearly resolved hyperfine structure components split by 1.05 km/s. An additional 13 clouds apparently show comparably narrow, but more strongly blended, lines. For each individual cloud, upper limits T(sub max) and (v sub t)(sub max) on the temperature and the turbulent velocity, respectively, are derived by fitting the observed lines with theoretical absorption profiles.

  15. ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) - Merging Observations and Laboratory Data

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2016-01-01

    The Diffuse Interstellar Bands (DIBs) are a set of 500 absorption bands that are detected in the spectra of stars with interstellar clouds in the line of sight. DIBs are found from the NUV to the NIR in the spectra of reddened stars spanning different interstellar environments in our local, and in other galaxies. DIB carriers are a significant part of the interstellar chemical inventory. They are stable and ubiquitous in a broad variety of environments and play a unique role in interstellar physics/chemistry. It has long been realized that the solving of the DIB problem requires a strong synergy between astronomical observations, laboratory astrophysics, and astrophysical modeling of line-of-sights. PAHs are among the molecular species that have been proposed as DIB carriers. We will present an assessment of the PAH-DIB model in view of the progress and the advances that have been achieved over the past years through a series of studies involving astronomical observations of DIBs, laboratory simulation of interstellar analogs for neutrals and ionized PAHs, theoretical calculations of PAH spectra and the modelization of diffuse and translucent interstellar clouds. We will present a summary of what has been learned from these complementary studies, the constraints that can now be derived for the PAHs as DIB carriers in the context of the PAH-DIB model and how these constraints can be applied to the EDIBLES project. The spectra of several neutral and ionized PAHs isolated in the gas phase at low temperature have been measured in the laboratory under experimental conditions that mimic interstellar conditions and are compared with an extensive set of astronomical spectra of reddened, early type stars. The comparisons of astronomical and laboratory data provide upper limits for the abundances of specific neutral PAH molecules and ions along specific lines-of-sight. Something that is not attainable from infrared observations alone. We present the characteristics of the

  16. Quenched Carbonaceous Composite: a laboratory analog for carbonaceous material in the interstellar medium.

    PubMed

    Tokunaga, A T; Wada, S

    1997-01-01

    We review the properties of Quenched Carbonaceous Composite (QCC), a residue produced from a hydrocarbon plasma, and the properties of its derivatives. A. Sakata and his colleagues have shown that QCC has a 220 nm absorption band, visible fluorescence matching the extended red emission seen in reflection nebulae, and infrared absorption bands that correspond to the infrared emission features in reflection nebulae, HII regions, and planetary nebulae. These properties make QCC a strong candidate material as a laboratory analog to the carbonaceous material in the interstellar medium. QCC is distinguished from the PAH hypothesis in that (1) it is a condensate composed of aromatic and aliphatic molecules, as well as radicals; (2) it exhibits a 220 nm absorption that is very similar in wavelength to the 217 nm absorption in the interstellar medium; (3) it exhibits visible fluorescence consistent with that seen in reflection nebulae; and (4) the bands at 7.7 and 8.6 microns are caused by ketone bands in oxidized QCC. The aromatic component in QCC is thought to be typically 1-4 rings, with the majority being about 1-2 rings. PMID:11541327

  17. Connecting The Interstellar Gas And Dust Properties Of Distant Galaxies

    NASA Astrophysics Data System (ADS)

    Kulkarni, Varsha

    The properties of interstellar gas and dust in distant galaxies are fundamental parameters in constraining galaxy evolution models. Quasar absorption systems (QASs), which trace intervening galaxies along the sightlines to luminous background quasars, provide invaluable tools to directly study gas and dust in distant normal galaxies. Recent studies of QASs have found interesting trends in both gas and dust properties, such as correlations in metallicity with redshift and dust depletions. Our Spitzer spectroscopic studies also indicate that silicate dust grains are present in QASs, and in fact, at a level higher than expected for diffuse gas in the Milky Way. Moreover, the silicate dust grains in these distant galaxies may be substantially more crystalline than those in the Milky Way interstellar medium. We now propose a comprehensive study of the gas and dust properties of all QASs with strong Ly-alpha and/or metal absorption lines that have adequate archival IR data to probe the study of dust. Our analysis will include data primarily from the NASA-supported Spitzer, Herschel, HST, and Keck Observatory archives, along with a small amount of VLT/SDSS archival data. Our specific goals are as follows: (1) We will measure a large range of metal absorption lines in high-resolution quasar spectra from Keck, HST, and VLT archives to uniformly determine the metallicity, dust depletions, ionization, and star formation rates in the foreground QASs. In particular, we will study the variations in these quantities with gas velocity, using Voigt profile fitting techniques to determine the velocity structure. This analysis will also allow us to quantify the kinematics of the absorbing gas. (2) We will use archival Spitzer IRS quasar spectra to search for and measure the strengths of the 10 and 18 micron silicate dust absorption features for a much larger sample of QASs than previously studied. (3) We will fit the observed silicate absorption features in the Spitzer archival

  18. Triangulation of the Interstellar Magnetic Field

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Richardson, J. D.; Burlaga, L. F.; McComas, D. J.; Moebius, E.

    2015-11-01

    Determining the direction of the local interstellar magnetic field (LISMF) is important for understanding the heliosphere’s global structure, the properties of the interstellar medium, and the propagation of cosmic rays in the local galactic medium. Measurements of interstellar neutral atoms by Ulysses for He and by SOHO/SWAN for H provided some of the first observational insights into the LISMF direction. Because secondary neutral H is partially deflected by the interstellar flow in the outer heliosheath and this deflection is influenced by the LISMF, the relative deflection of H versus He provides a plane—the so-called B-V plane in which the LISMF direction should lie. Interstellar Boundary Explorer (IBEX) subsequently discovered a ribbon, the center of which is conjectured to be the LISMF direction. The most recent He velocity measurements from IBEX and those from Ulysses yield a B-V plane with uncertainty limits that contain the centers of the IBEX ribbon at 0.7-2.7 keV. The possibility that Voyager 1 has moved into the outer heliosheath now suggests that Voyager 1's direct observations provide another independent determination of the LISMF. We show that LISMF direction measured by Voyager 1 is >40° off from the IBEX ribbon center and the B-V plane. Taking into account the temporal gradient of the field direction measured by Voyager 1, we extrapolate to a field direction that passes directly through the IBEX ribbon center (0.7-2.7 keV) and the B-V plane, allowing us to triangulate the LISMF direction and estimate the gradient scale size of the magnetic field.

  19. Triangulation of the Interstellar Magnetic Field

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Richardson, J. D.; Burlaga, L. F.; McComas, D. J.; Moebius, E.

    2015-11-01

    Determining the direction of the local interstellar magnetic field (LISMF) is important for understanding the heliosphere’s global structure, the properties of the interstellar medium, and the propagation of cosmic rays in the local galactic medium. Measurements of interstellar neutral atoms by Ulysses for He and by SOHO/SWAN for H provided some of the first observational insights into the LISMF direction. Because secondary neutral H is partially deflected by the interstellar flow in the outer heliosheath and this deflection is influenced by the LISMF, the relative deflection of H versus He provides a plane—the so-called B–V plane in which the LISMF direction should lie. Interstellar Boundary Explorer (IBEX) subsequently discovered a ribbon, the center of which is conjectured to be the LISMF direction. The most recent He velocity measurements from IBEX and those from Ulysses yield a B–V plane with uncertainty limits that contain the centers of the IBEX ribbon at 0.7–2.7 keV. The possibility that Voyager 1 has moved into the outer heliosheath now suggests that Voyager 1's direct observations provide another independent determination of the LISMF. We show that LISMF direction measured by Voyager 1 is >40° off from the IBEX ribbon center and the B–V plane. Taking into account the temporal gradient of the field direction measured by Voyager 1, we extrapolate to a field direction that passes directly through the IBEX ribbon center (0.7–2.7 keV) and the B–V plane, allowing us to triangulate the LISMF direction and estimate the gradient scale size of the magnetic field.

  20. Interstellar gas phase abundance of carbon, oxygen, nitrogen, copper, gallium, germanium, and krypton toward Zeta Ophiuchi

    NASA Technical Reports Server (NTRS)

    Cardelli, Jason A.; Savage, Blair D.; Ebbets, Dennis C.

    1991-01-01

    An analysis of weak (less than 10 mA) UV interstellar absorption line data obtained for the line of sight to the O9.5 IV star Zeta Oph is presented. Measurements of weak semiforbidden lines of N I, O I, Cu II, and a new UV detection of Na I are reported along with a small upper limit for C II. Interstellar detections of Ga II, Ge II, and Kr I are also presented. Ga, Ge, and Kr represent the heaviest elements detected in the ISM. A comparison of the derived column densities to cosmic abundances shows Ga to be depleted by about -1.2 dex while Ge is overabundant by +0.2 dex. Assuming Kr to be undepleted, a logarithmic cosmic abundance of Kr/H = 2.95 is obtained on the scale where H = 12.00.

  1. PROBING THE LOCAL BUBBLE WITH DIFFUSE INTERSTELLAR BANDS. III. THE NORTHERN HEMISPHERE DATA AND CATALOG

    SciTech Connect

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; Van Loon, Jacco Th.

    2015-02-01

    We present new high signal-to-noise ratio (S/N) observations of the diffuse interstellar bands (DIBs) in the Local Bubble and its surroundings. We observed 432 sightlines and obtain the equivalent widths of the λ5780 and λ5797 Å DIBs up to a distance of ∼200 pc. All of the observations were carried out using the Intermediate Dispersion Spectrograph on the 2.5 m Isaac Newton Telescope, during three years, to reach a minimum S/N of ∼2000. All of the λ5780 and λ5797 absorptions are presented in this paper and we tabulate the observed values of the interstellar parameters, λ5780, λ5797, Na ID{sub 1}, and Na ID{sub 2}, including the uncertainties.

  2. Probing the Local Bubble with Diffuse Interstellar Bands. III. The Northern Hemisphere Data and Catalog

    NASA Astrophysics Data System (ADS)

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; van Loon, Jacco Th.

    2015-02-01

    We present new high signal-to-noise ratio (S/N) observations of the diffuse interstellar bands (DIBs) in the Local Bubble and its surroundings. We observed 432 sightlines and obtain the equivalent widths of the λ5780 and λ5797 Å DIBs up to a distance of ~200 pc. All of the observations were carried out using the Intermediate Dispersion Spectrograph on the 2.5 m Isaac Newton Telescope, during three years, to reach a minimum S/N of ~2000. All of the λ5780 and λ5797 absorptions are presented in this paper and we tabulate the observed values of the interstellar parameters, λ5780, λ5797, Na ID1, and Na ID2, including the uncertainties.

  3. Atoms in carbon cages as a source of interstellar diffuse lines

    NASA Technical Reports Server (NTRS)

    Ballester, J. L.; Antoniewicz, P. R.; Smoluchowski, R.

    1990-01-01

    A model to describe the resonance absorption lines of various atoms trapped in closed carbon cages is presented. These systems may be responsible for some of the as yet unexplained diffuse interstellar bands. Model potentials for possible atom-C60 systems are obtained and used to calculate the resonance lines. The trapped atoms considered are O, N, Si, Mg, Al, Na, and S, and in all cases the resonance lines are shifted toward the red as compared to the isolated atoms. The calculated wavelengths are compared to the range of wavelengths observed for the diffuse interstellar bands, and good agreement is found for Mg and Si resonance lines. Other lines may be caused by other than resonance transitions or by trapped molecules. The oscillator strengths and the abundances are evaluated and compared with observation. Mechanisms to explain the observed band width of the lines and the existence of certain correlated pairs of lines are discussed.

  4. Theoretical models of interstellar shocks. I - Radiative transfer and UV precursors

    NASA Technical Reports Server (NTRS)

    Shull, J. M.; Mckee, C. F.

    1979-01-01

    Theoretical models of interstellar radiative shocks are constructed, with special attention to the transfer of ionizing radiation. These models are 'self-consistent' in the sense that the emergent ionizing radiation (the UV precursor) is coupled with the ionization state of H, He, and the metals in the preshock gas. For shock velocities of at least 110 km/s the shocks generate sufficient UV radiation for complete preionization of H and He, the latter to He(+). At lower velocities the preionization can be much smaller, with important consequences for the cooling function, the shock structure, and the emission. For models with shock velocities of 40 to 130 km/s the intensities of the strongest emission lines in the UV, optical, and infrared are tabulated, as well as postshock column densities of metal ions potentially observable by UV absorption spectroscopy. Possible applications to supernova remnants and high-velocity interstellar gas are assessed.

  5. The extinction toward the galactic center from observations of interstellar lines

    NASA Technical Reports Server (NTRS)

    Federman, S. R.; Evans, N. J., II

    1981-01-01

    H2CO absorption observations against Sgr A are used to select the molecular material lying in front of the galactic center, and an analysis similar to that of Blitz and Shu (1980) is carried out. The ratio of visual extinction to equivalent width of the 6 cm line of H2CO is found to be similar for several nearby interstellar clouds. By considering only the molecular components in front of the infrared cluster, the estimate for the extinction is decreased to 15-46 mag. These results are consistent with those from infrared observations toward the galactic center. Extinction estimates based on other interstellar species are also considered. Atomic gas is seen as contributing less than 10 mag of extinction.

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

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.

    1982-01-01

    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.

  7. VizieR Online Data Catalog: Interstellar extinction curves of OB stars (Wegner 2002)

    NASA Astrophysics Data System (ADS)

    Wegner, W.

    2003-02-01

    The paper presents a collection of 436 extinction curves covering the whole available range of wavelengths from satellite UV to near-IR. The data were taken from the ANS photometric catalogue (Cat. ) and from the compilations of IR photometric measurements. The data curves have been obtained with the aid of "artificial standards" Papaj et al. (1993A&A...273..575P) and Wegner (1994MNRAS.270..229W, 1995, Interstellar Absorption Structures in the Direction of Nearby OB stars, Wyd. Uczelniane WSP, Bydgoszcz, p. 1-383). The visual magnitudes and spectral classifications of O and B type stars with EB-V>=0.05 were taken from the SIMBAD database. The curves are given in the form of plots and tables E{lambda}-V/EB-V versus 1/{lambda}. The observed variety of extinction laws among slightly reddened stars is apparently due to the various physical parameters of interstellar clouds. (3 data files).

  8. Cholesterol absorption.

    PubMed

    Ostlund, Richard E

    2002-03-01

    Cholesterol absorption is a key regulatory point in human lipid metabolism because it determines the amount of endogenous biliary as well as dietary cholesterol that is retained, thereby influencing whole body cholesterol balance. Plant sterols (phytosterols) and the drug ezetimibe reduce cholesterol absorption and low-density lipoprotein cholesterol in clinical trials, complementing the statin drugs, which inhibit cholesterol biosynthesis. The mechanism of cholesterol absorption is not completely known but involves the genes ABC1, ABCG5, and ABCG8, which are members of the ATP-binding cassette protein family and appear to remove unwanted cholesterol and phytosterols from the enterocyte. ABC1 is upregulated by the liver X (LXR) and retinoid X (RXR) nuclear receptors. Acylcholesterol acytransferase-2 is an intestinal enzyme that esterifies absorbed cholesterol and increases cholesterol absorption when dietary intake is high. New clinical treatments based on better understanding of absorption physiology are likely to substantially improve clinical cholesterol management in the future. PMID:17033296

  9. The 2140 cm-1 (4.673 microns) Solid CO Band: The Case for Interstellar O2 and N2 and the Photochemistry of Nonpolar Interstellar Ice Analogs

    NASA Astrophysics Data System (ADS)

    Elsila, Jamie; Allamandola, Louis J.; Sandford, Scott A.

    1997-04-01

    The infrared spectra of CO frozen in nonpolar ices containing N2, CO2, O2, and H2O and the UV photochemistry of these interstellar/precometary ice analogs are reported. The spectra are used to test the hypothesis that the narrow 2140 cm-1 (4.673 μm) interstellar absorption feature attributed to solid CO might be produced by CO frozen in ices containing nonpolar species such as N2 and O2. It is shown that mixed molecular ices containing CO, N2, O2, and CO2 provide a good match to the interstellar band at all temperatures between 12 and 30 K both before and after photolysis. The optical constants (real and imaginary parts of the index of refraction) in the region of the solid CO feature are reported for several of these ices. The N2 and O2 absorptions at 2328 cm-1 (4.296 μm) and 1549 cm-1 (6.456 μm), respectively, are also shown. The best matches between the narrow interstellar band and the feature in the laboratory spectra of nonpolar ices are for samples which contain comparable amounts of N2, O2, CO2, and CO. Co-adding the CO band from an N2:O2:CO2:CO=1:5:1/2:1 ice with that of an H2O:CO = 20:1 ice provides an excellent fit across the entire interstellar CO feature. The four-component, nonpolar ice accounts for the narrow 2140 cm-1 portion of the feature which is associated with quiescent regions of dense molecular clouds. Using this mixture, and applying the most recent cosmic abundance values, we derive that between 15% and 70% of the available interstellar N is in the form of frozen N2 along several lines of sight toward background stars. This is reduced to a range of 1%-30% for embedded objects with lines of sight more dominated by warmer grains. The cosmic abundance of O tied up in frozen O2 lies in the 10%-45% range toward background sources, and it is between 1% and 20% toward embedded objects. The amount of oxygen tied up in CO and CO2 frozen in nonpolar ices can be as much as 2%-10% toward background sources and on the order of 0.2%-5% for embedded

  10. The 2140 cm-1 (4.673 microns) solid CO band: the case for interstellar O2 and N2 and the photochemistry of nonpolar interstellar ice analogs

    NASA Technical Reports Server (NTRS)

    Elsila, J.; Allamandola, L. J.; Sandford, S. A.

    1997-01-01

    The infrared spectra of CO frozen in nonpolar ices containing N2, CO2, O2, and H2O and the UV photochemistry of these interstellar/precometary ice analogs are reported. The spectra are used to test the hypothesis that the narrow 2140 cm-1 (4.673 microns) interstellar absorption feature attributed to solid CO might be produced by CO frozen in ices containing nonpolar species such as N2 and O2. It is shown that mixed molecular ices containing CO, N2, O2, and CO2 provide a good match to the interstellar band at all temperatures between 12 and 30 K both before and after photolysis. The optical constants (real and imaginary parts of the index of refraction) in the region of the solid CO feature are reported for several of these ices. The N2 and O2 absorptions at 2328 cm-1 (4.296 microns) and 1549 cm-1 (6.456 microns), respectively, are also shown. The best matches between the narrow interstellar band and the feature in the laboratory spectra of nonpolar ices are for samples which contain comparable amounts of N2, O2, CO2, and CO. Co-adding the CO band from an N2:O2:CO2:CO = 1:5:1/2:1 ice with that of an H2O:CO = 20:1 ice provides an excellent fit across the entire interstellar CO feature. The four-component, nonpolar ice accounts for the narrow 2140 cm-1 portion of the feature which is associated with quiescent regions of dense molecular clouds. Using this mixture, and applying the most recent cosmic abundance values, we derive that between 15% and 70% of the available interstellar N is in the form of frozen N2 along several lines of sight toward background stars. This is reduced to a range of 1%-30% for embedded objects with lines of sight more dominated by warmer grains. The cosmic abundance of O tied up in frozen O2 lies in the 10%-45% range toward background sources, and it is between 1% and 20% toward embedded objects. The amount of oxygen tied up in CO and CO2 frozen in nonpolar ices can be as much as 2%-10% toward background sources and on the order of 0

  11. The 2140 cm-1 (4.673 microns) solid CO band: the case for interstellar O2 and N2 and the photochemistry of nonpolar interstellar ice analogs.

    PubMed

    Elsila, J; Allamandola, L J; Sandford, S A

    1997-04-20

    The infrared spectra of CO frozen in nonpolar ices containing N2, CO2, O2, and H2O and the UV photochemistry of these interstellar/precometary ice analogs are reported. The spectra are used to test the hypothesis that the narrow 2140 cm-1 (4.673 microns) interstellar absorption feature attributed to solid CO might be produced by CO frozen in ices containing nonpolar species such as N2 and O2. It is shown that mixed molecular ices containing CO, N2, O2, and CO2 provide a good match to the interstellar band at all temperatures between 12 and 30 K both before and after photolysis. The optical constants (real and imaginary parts of the index of refraction) in the region of the solid CO feature are reported for several of these ices. The N2 and O2 absorptions at 2328 cm-1 (4.296 microns) and 1549 cm-1 (6.456 microns), respectively, are also shown. The best matches between the narrow interstellar band and the feature in the laboratory spectra of nonpolar ices are for samples which contain comparable amounts of N2, O2, CO2, and CO. Co-adding the CO band from an N2:O2:CO2:CO = 1:5:1/2:1 ice with that of an H2O:CO = 20:1 ice provides an excellent fit across the entire interstellar CO feature. The four-component, nonpolar ice accounts for the narrow 2140 cm-1 portion of the feature which is associated with quiescent regions of dense molecular clouds. Using this mixture, and applying the most recent cosmic abundance values, we derive that between 15% and 70% of the available interstellar N is in the form of frozen N2 along several lines of sight toward background stars. This is reduced to a range of 1%-30% for embedded objects with lines of sight more dominated by warmer grains. The cosmic abundance of O tied up in frozen O2 lies in the 10%-45% range toward background sources, and it is between 1% and 20% toward embedded objects. The amount of oxygen tied up in CO and CO2 frozen in nonpolar ices can be as much as 2%-10% toward background sources and on the order of 0

  12. Probing model interstellar grain surfaces with small molecules

    NASA Astrophysics Data System (ADS)

    Collings, M. P.; Frankland, V. L.; Lasne, J.; Marchione, D.; Rosu-Finsen, A.; McCoustra, M. R. S.

    2015-05-01

    Temperature-programmed desorption and reflection-absorption infrared spectroscopy have been used to explore the interaction of oxygen (O2), nitrogen (N2), carbon monoxide (CO) and water (H2O) with an amorphous silica film as a demonstration of the detailed characterization of the silicate surfaces that might be present in the interstellar medium. The simple diatomic adsorbates are found to wet the silica surface and exhibit first-order desorption kinetics in the regime up to monolayer coverage. Beyond that, they exhibit zero-order kinetics as might be expected for sublimation of bulk solids. Water, in contrast, does not wet the silica surface and exhibits zero-order desorption kinetics at all coverages consistent with the formation of an islanded structure. Kinetic parameters for use in astrophysical modelling were obtained by inversion of the experimental data at sub-monolayer coverages and by comparison with models in the multilayer regime. Spectroscopic studies in the sub-monolayer regime show that the C-O stretching mode is at around 2137 cm-1 (5.43 μm), a position consistent with a linear surface-CO interaction, and is inhomogenously broadened as resulting from the heterogeneity of the surface. These studies also reveal, for the first time, direct evidence for the thermal activation of diffusion, and hence de-wetting, of H2O on the silica surface. Astrophysical implications of these findings could account for a part of the missing oxygen budget in dense interstellar clouds, and suggest that studies of the sub-monolayer adsorption of these simple molecules might be a useful probe of surface chemistry on more complex silicate materials.

  13. Plasma processing of interstellar PAHs into solar system kerogen

    NASA Technical Reports Server (NTRS)

    Wdowiak, T. J.; Lee, W.; Cronin, J.; Beegle, L. W.; Robinson, M. S.

    1995-01-01

    Processes resulting in the formation of hydrocarbons of carbonaceous chondrites and the identity of the interstellar molecular precursors involved are an objective of investigations into the origin of the solar system and perhaps even life on earth. We have combined the resources and experience of an astronomer and physicists doing laboratory simulations with those of a chemical expert in the analysis of meteoritic hydrocarbons, in a project that investigated the conversion of polycyclic aromatic hydrocarbons (PAHs) formed in stellar atmospheres into alkanes found in meteorites. Plasma hydrogenation has been found in the University of Alabama at Birmingham Astrophysics Laboratory to produce from the precursor PAH naphthalene, a new material having an IR absorption spectrum (Lee, W. and Wdowiak, T.J., Astrophys. J. 417, L49-L51, 1993) remarkably similar to that obtained at Arizona State University of the benzene-methanol extract of the Murchison meteorite (Cronin, J.R. and Pizzarello, S., Geochim. Cosmochim. Acta 54, 2859-2868, 1990). There are astrophysical and meteoritic arguments for PAH species from extra-solar sources being incorporated into the solar nebula, where plasma hydrogenation is highly plausible. Conversion of PAHs into alkanes could also have occurred in the interstellar medium. The synthesis of laboratory analogs of meteoritic hydrocarbons through plasma hydrogenation of PAH species is underway, as is chemical analysis of those analogs. The objective is to clarify this heretofore uninvestigated process and to understand its role during the origin of the solar system as a mechanism of production of hydrocarbon species now found in meteorites. Results have been obtained in the form of time-of-flight spectroscopy and chemical analysis of the lab analog prepared from naphthalene.

  14. The VLT-FLAMES Tarantula Survey. IX. The interstellar medium seen through diffuse interstellar bands and neutral sodium&

    NASA Astrophysics Data System (ADS)

    van Loon, J. Th.; Bailey, M.; Tatton, B. L.; Maíz Apellániz, J.; Crowther, P. A.; de Koter, A.; Evans, C. J.; Hénault-Brunet, V.; Howarth, I. D.; Richter, P.; Sana, H.; Simón-Díaz, S.; Taylor, W.; Walborn, N. R.

    2013-02-01

    Context. The Tarantula Nebula (a.k.a. 30 Dor) is a spectacular star-forming region in the Large Magellanic Cloud (LMC), seen through gas in the Galactic disc and halo. Diffuse interstellar bands (DIBs) offer a unique probe of the diffuse, cool-warm gas in these regions. Aims: The aim is to use DIBs as diagnostics of the local interstellar conditions, whilst at the same time deriving properties of the yet-unknown carriers of these enigmatic spectral features. Methods: Spectra of over 800 early-type stars from the Very Large Telescope Flames Tarantula Survey (VFTS) were analysed. Maps were created, separately, for the Galactic and LMC absorption in the DIBs at 4428 and 6614 Å and - in a smaller region near the central cluster R 136 - neutral sodium (the Na i D doublet); we also measured the DIBs at 5780 and 5797 Å. Results: The maps show strong 4428 and 6614 Å DIBs in the quiescent cloud complex to the south of 30 Dor but weak absorption in the harsher environments to the north (bubbles) and near the OB associations. The Na maps show at least five kinematic components in the LMC and a shell-like structure surrounding R 136, and small-scale structure in the Milky Way. The strengths of the 4428, 5780, 5797 and 6614 Å DIBs are correlated, also with Na absorption and visual extinction. The strong 4428 Å DIB is present already at low Na column density but the 6614, 5780 and 5797 Å DIBs start to be detectable at subsequently larger Na column densities. Conclusions: The carriers of the 4428, 6614, 5780 and 5797 Å DIBs are increasingly prone to removal from irradiated gas. The relative strength of the 5780 and 5797 Å DIBs clearly confirm the Tarantula Nebula as well as Galactic high-latitude gas to represent a harsh radiation environment. The resilience of the 4428 Å DIB suggests its carrier is large, compact and neutral. Structure is detected in the distribution of cool-warm gas on scales between one and >100 pc in the LMC and as little as 0.01 pc in the Sun

  15. Probing the Origin and Evolution of Interstellar and Protoplanetary Biogenic Molecules:A Comprehensive Survey of Interstellar Ices with SPHEREx

    NASA Astrophysics Data System (ADS)

    Melnick, Gary J.; SPHEREx Science Team

    2016-01-01

    Many of the most important building blocks of life are locked in interstellar and protoplanetary ices. Examples include H2O, CO, CO2, and CH3OH, among others. There is growing evidence that in some environments, such as within the cores of dense molecular clouds and the mid-plane of protoplanetary disks, the amounts of these species in ices far exceeds that in the gas phase. As a result, collisions between ice-bearing bodies and newly forming planets are thought to be a major means of delivering these key species to young planets. There currently exist fewer than 250 ice absorption spectra toward Galactic molecular clouds, which is insufficient to reliably trace the ice content of clouds through the various stages of collapse to star and planet formation, or assess the effects of their environments and physical conditions, such as cloud density, internal temperature, presence or absence of embedded sources, external UV and X-ray radiation, gas-phase composition, or cosmic-ray ionization rate, on the ice composition for clouds at similar evolutionary stages. Ultimately, our goal is to understand how these findings connect to our own Solar System.SPHEREx, which is a mission in NASA's Small Explorer (SMEX) program that was selected for a Phase A study in July 2015, will be a game changer for the study of interstellar, circumstellar, and protoplanetary disk ices. SPHEREx will obtain spectra over the entire sky in the optical and near-IR, including the 2.5 to 4.8 micron region, which contains the above biogenic ice features. SPHEREx will detect millions of potential background continuum point sources already catalogued by NASA's Wide-field Infrared Survey Explorer (WISE) at 3.4 and 4.6 microns for which there is evidence for intervening gas and dust based on the 2MASS+WISE colors with sufficient sensitivity to yield ice absorption spectra with SNR ≥ 100 per spectral resolution element. The resulting > 100-fold increase in the number of high-quality ice absorption

  16. Far Ultraviolet Spectroscopic Explorer (FUSE) observations of emitting and absorbing gas in the Local Interstellar Chimney

    NASA Astrophysics Data System (ADS)

    Welsh, B. Y.; Sallmen, S.; Sfeir, D.; Shelton, R. L.; Lallement, R.

    2002-11-01

    We present Far Ultraviolet Spectroscopic Explorer (FUSE) satellite measurements of the absorption and emission characteristics of interstellar gas associated with the Local Interstellar Chimney, which is an extension of the rarefied Local Bubble cavity that extends outward from the galactic disk towards the lower galactic halo. Far ultraviolet (FUV) diffuse background emission has been detected in the high ionization line of O VI (lambda 1032 Å) for two lines-of-sight (l = 162.7deg, b = +57.0deg) and (l = 156.3deg, b = +57.8deg) at emission levels of 2500+/-700 photons cm-2 s-1 sr-1 (LU) and 3300+/-1100 LU respectively. These levels of O VI emission are very similar to those found for four other lines-of-sight sampled thus far by the FUSE satellite, implying a fairly constant level of average O VI surface brightness emission at high galactic latitudes of about 2700 LU with a standard deviation of 450 LU. These emission-line data are supplemented by FUV interstellar absorption line measurements taken towards the hot DA white dwarf star, REJ 1032+532 (l = 157.5deg, b = +53.2deg), whose distance of 116 pc places it within the Local Bubble region. No high ionization interstellar O VI lambda 1032 Å absorption has been detected (N(O VI) < 13.0 cm-2), which is consistent with the non-detections of interstellar C IV and Si IV absorption reported towards this star by Holberg et al. (\\cite{holberg99a}). Taken together, our FUV absorption and emission data may be explained by a scenario in which the O VI emission and absorption lines are both formed at the conductive interface of the neutral boundary to the Local Bubble. For the presently sampled sight-lines we have found no correlation between the OVI emission line intensity and the associated 0.25 keV soft X-ray background flux as measured in the R1 and R2 bands by the ROSAT satellite. The OVI line intensities also show no correlation with the soft X-ray background flux attributable to emission from the million degree K

  17. Interstellar Probe: The Next Step To Flight

    NASA Astrophysics Data System (ADS)

    McNutt, Ralph; Zurbuchen, Thomas H.

    2016-07-01

    In the years following the discovery of the solar wind, the term "heliosphere" was coined and defined as "the region of interplanetary space where the solar wind is flowing supersonically." In June 1971, with the development of the Pioneer probes to Jupiter and beyond well underway, a session of the American Astronautical Society meeting considered scientific exploration reaching beyond the solar system and into the interstellar medium. Despite many discussions, studies, and meetings since, the most recent held under the auspices of the Keck Institute for Space Studies (8-11 September 2014 and 13-15 January 2015), such missions have been relegated to the '"future" due to the large distances and solar system escape speeds contemplated for their execution. In the meantime, the Voyager Interstellar Mission (VIM), consisting of the twin Voyager spacecraft almost 40 years since their respective launches, are making inroads into this region beyond the termination shock of the solar wind, a new region of the solid bodies of the solar system has been opened by the New Horizons flyby of the Pluto system, and the Cassini Ion and Neutral CAmera (INCA) and Interstellar Boundary Explorer (IBEX) have remotely sensed neutral atoms that have provided significant clues to the global structure of the interaction of the solar wind and interstellar medium. It is now time for a dedicated mission to the regime beyond the solar system to explore our galactic environment. A first, near-term implementation can be carried out with the near-current flight system technology. What is also clear is that the high speeds required will limit the spacecraft to a relatively small mass of no more than ~500 kg, regardless of the propulsion details. The recent success of the New Horizons mission at the Pluto system illustrates that with modern technologies, such spacecraft sizes can still accommodate the means to produce paradigm-shifting science, providing for a compelling scientific mission. The

  18. New observations of interstellar organic molecules

    NASA Technical Reports Server (NTRS)

    Irvine, W. M.; Friberg, P.; Matthews, H. E.; Minh, Y. C.; Ziurys, L. M.

    1990-01-01

    Discussed here are new observations of 3-carbon-containing interstellar molecules which play an important role in the chemistry of dense molecular clouds: protonated carbon dioxide, formic acid, and propynal. In 1984 a new oxide of carbon, C3O, was discovered in the interstellar medium (Matthews et al. 1984; Brown et al. 1985). Theoretical models suggest that C3O is produced by dissociative electron recombination with the ion H3C3O+. Although no laboratory data for the branching ratios of such a recombination exist, it seemed to us likely that additional products would include H2C3O. This molecule has more than one isomeric form, but one stable species is propynal (HC2CHO), which had been suggested as a possible interstellar molecule by Winnewisser (1973). In observations at the National Radio Astronomy Observatory 43 m telescope in Green Bank earlier this year, researchers detected a line in the cold cloud TMC-1 which they assign to the 2(0,2)-1(0,1) transition of propynal. The observed line agrees with the laboratory frequency to well within the experimental uncertainty a few parts in 10 to the 7th power. Researchers sought and failed to detect the corresponding 2(1,1)-1(1,0) line, which is understandable given the presence of both a and b components of the electric dipole moment in propynal. The b type transitions will drain population from energy levels with K(sub p) does not equal 0 into the K(sub p) equal 0 stack. If the researchers' assignment is correct, this is the first interstellar detection of propynal. Assuming typical rotational temperatures for TMC-1 and that the line is optically thin, the column density determined is about 5 times 10 to the 12th power cm to the -2nd power, or about three times that for C3O. Formic acid (HCOOH) was the first organic acid to be observed in the interstellar medium, in the Galactic center source Sgr B2. The only other interstellar detection has been recently made in the giant molecular cloud in Orion. As part of the

  19. The local interstellar medium. VII - The local interstellar wind and interstellar material in front of the nearby star Alpha Ophiuchi

    NASA Technical Reports Server (NTRS)

    Frisch, P. C.; York, D. G.; Fowler, J. R.

    1987-01-01

    IUE observations of Mg I 2852.127 A are used to search for warm interstellar gas in the direction of Alpha Oph. The data on Mg I are first presented, and Mg I as a diagnostic of warm gas is discussed. A cool H I feature found in the direction of Alpha Oph, and which is evidently the origin of most of the observed optical and ultraviolet lines, is discussed, and the cloud geometry is examined.

  20. Organic Synthesis in Simulated Interstellar Ice Analogs

    NASA Technical Reports Server (NTRS)

    Dworkin, Jason P.; Bernstein, Max P.; Sandford, Scott A.; Allamandola, Louis J.; Deamer, David W.; Elsila, Jamie; Zare, Richard N.; DeVincenzi, Donald (Technical Monitor)

    2001-01-01

    Comets and carbonaceous micrometeorites may have been significant sources of organic compounds on the early Earth. Ices on grains in interstellar dense molecular clouds contain a variety of simple molecules as well as aromatic molecules of various sizes. While in these clouds the icy grains are processed by ultraviolet light and cosmic radiation which produces more complex organic molecules. ID We have run laboratory simulations to identify the types of molecules which could have been generated photolytically in pre-cometary ices. Experiments were conducted by forming various realistic interstellar mixed-molecular ices with and without polycyclic aromatic hydrocarbons (PAHs) at approx. 10 K under high vacuum irradiated with LTV light from a hydrogen plasma lamp: The residue that remained after warming to room temperature was analyzed by HPLC, and by laser desorption mass spectrometry. The residue contains several classes of compounds which may be of prebiotic significance.

  1. Organic Synthesis in Simulated Interstellar Ice Analogs

    NASA Technical Reports Server (NTRS)

    Dworkin, Jason P.; Bernstein, Max P.; Sandford, Scott A.; Allamandola, Louis J.; Deamer, David W.; Elsila, Jamie; Zare, Richard N.

    2001-01-01

    Comets and carbonaceous micrometeorites may have been significant sources of organic compounds on the early Earth. Ices on grains in interstellar dense molecular clouds contain a variety of simple molecules as well as aromatic molecules of various sizes. While in these clouds the icy grains are processed by ultraviolet light and cosmic radiation which produces more complex organic molecules. We have run laboratory simulations to identify the types of molecules which could have been generated photolytically in pre-cometary ices. Experiments were conducted by forming various realistic interstellar mixed-molecular ices with and without polycyclic aromatic hydrocarbons (PAHs) at approx. 10 K under high vacuum irradiated with UV light from a hydrogen plasma lamp. The residue that remained after warming to room temperature was analyzed by HPLC, and by laser desorption mass spectrometry. The residue contains several classes of compounds which may be of prebiotic significance.

  2. Ionized interstellar froth in irregular galaxies

    NASA Technical Reports Server (NTRS)

    Hunter, Deidre A.; Gallagher, John S., III

    1990-01-01

    The warm interstellar medium of galaxies is a complicated place. It is often full of holes, neutral and ionized loops and shells, and diffuse ionized gas. Deep H alpha images of Magellanic-type irregular galaxies also reveal complex spatial structures consisting of loops and filaments in the interstellar gas outside of the boundaries of traditional HII regions. Researchers refer to these ionized structures as froth. Such structures could mark paths over which newly produced heavy elements are dispersed in irregular galaxies, and they could be the signatures of a feedback process related to star formation. In order to investigate the physical nature of the froth, researchers obtained narrow-band images and high and low dispersion spectra from Kitt Peak National Observatory (KPNO) and deep blue-passband plates from the Canada-France-Hawaii Observatory (CFHO).

  3. Galactic civilizations: Population dynamics and interstellar diffusion

    NASA Technical Reports Server (NTRS)

    Newman, W. I.; Sagan, C.

    1978-01-01

    The interstellar diffusion of galactic civilizations is reexamined by potential theory; both numerical and analytical solutions are derived for the nonlinear partial differential equations which specify a range of relevant models, drawn from blast wave physics, soil science, and, especially, population biology. An essential feature of these models is that, for all civilizations, population growth must be limited by the carrying capacity of the environment. Dispersal is fundamentally a diffusion process; a density-dependent diffusivity describes interstellar emigration. Two models are considered: the first describing zero population growth (ZPG), and the second which also includes local growth and saturation of a planetary population, and for which an asymptotic traveling wave solution is found.

  4. Polycyclic aromatic hydrocarbons in interstellar chemistry

    SciTech Connect

    Lepp, S.; Dalgarno, A.

    1988-01-01

    Interstellar chemistry modifications resulting form the presence of large molecules such as polycyclic aromatic hydrocarbons (PAHs) are investigated. For abundances of PAH relative to hydrogen of greater than 10 to the -8th, free electrons attach to PAH molecules to yield PAH(-) ions, and qualitative interstellar chemistry changes are shown to result as atomic and molecular ions undergo nondestructive mutual neutralization reactions with these negative ions. An increase in the steady state abundances of carbon-bearing molecules is also noted. For a PAH abundance ratio relative to hydrogen of 10 to the -7th, the equilibrium densities of C3H2 and neutral atomic C are found to be enhanced by two orders of magnitude. 18 references.

  5. Human factors issues for interstellar spacecraft

    NASA Technical Reports Server (NTRS)

    Cohen, Marc M.; Brody, Adam R.

    1991-01-01

    Developments in research on space human factors are reviewed in the context of a self-sustaining interstellar spacecraft based on the notion of traveling space settlements. Assumptions about interstellar travel are set forth addressing costs, mission durations, and the need for multigenerational space colonies. The model of human motivation by Maslow (1970) is examined and directly related to the design of space habitat architecture. Human-factors technology issues encompass the human-machine interface, crew selection and training, and the development of spaceship infrastructure during transtellar flight. A scenario for feasible instellar travel is based on a speed of 0.5c, a timeframe of about 100 yr, and an expandable multigenerational crew of about 100 members. Crew training is identified as a critical human-factors issue requiring the development of perceptual and cognitive aids such as expert systems and virtual reality.

  6. Icarus Institute for Interstellar Sciences (IIS)

    NASA Astrophysics Data System (ADS)

    Cress, B.

    2012-09-01

    In this paper, a vision for a proposed interstellar research center, to be developed in the United States, will be presented. The major focus will be on an innovative approach to the planning and achieving a new sustainable world class facility devoted to the technologies and various science missions of multi-disciplined teams reaching for the stars. The project will provide the personnel, feature sets, facilities and equipment needed to initiate and support an aggressive program of advanced interstellar vehicle and propulsion design and implementation. Also shared will be personal insights and economic considerations gained during prior planning for a private research institute in Nevada, home to more than 300 international scientists. The views expressed in this discussion paper are the personal views of the author and not necessarily representing the entire Icarus team.

  7. Isotope Fractionation in the Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Charnley, Steven

    2011-01-01

    Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with ALMA.

  8. Interstellar molecules - Formation in solar nebulae

    NASA Technical Reports Server (NTRS)

    Anders, E.

    1973-01-01

    Herbig's (1970) hypothesis that solar nebulae might be the principal source of interstellar grains and molecules is investigated. The investigation includes the determination of physical and chemical conditions in the early solar system. The production of organic compounds in the solar nebula is studied, and the compounds in meteorites are compared with those obtained in Miller-Urey and Fischer-Tropsch-type (FTT) reactions, taking into consideration aliphatic hydrocarbons, aromatic hydrocarbons, purines, pyrimidines, amino acids, porphyrins, and aspects of carbon-isotope fractionation. It is found that FTT reactions account reasonably well for all well-established features of organic matter in meteorites investigated. The distribution of compounds produced by FTT reactions is compared with the distribution of interstellar molecules. Biological implications of the results are considered.

  9. Complex Molecules in the Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Sandford, Scott

    1996-01-01

    A brief review of the current state of knowledge concerning the composition of complex molecules in the interstellar medium (ISM) is given. The materials in interstellar dense molecular clouds is also discussed. As well as the formation of stars and planetary systems. A concentration on solids are addressed, because they contain a major fraction of the heavier elements in these clouds and because these materials are the most likely to survive incorporation into new planetary systems and participate in the subsequent formation and evolution of life. However, dense clouds are not well-defined, long-lived entities but are dynamic objects that are formed from materials in the diffuse ISM and destroyed on time scales of 10(exp 6)-10(exp 8) years. As a result, materials in space are probably constantly being mixed between the dense ISM and the more diffuse intercloud ISM, and some discussion of the materials found in the diffuse ISM is also merited.

  10. A search for interstellar H3O+.

    PubMed

    Wootten, A; Boulanger, F; Bogey, M; Combes, F; Encrenaz, P J; Gerin, M; Ziurys, L

    1986-01-01

    The P (2,1) line of H3O+, the hydroxonium ion, a key species in ion-molecule chemistry, has been sought in the interstellar medium and in Halley's Comet. In OMC1 and SgrB2, a line was detected which may possibly be attributed to H3O+. Verification of this identification must be accomplished through observation of the P(3,2) line at 364 GHz, or detection of isotopic variants. If we were to assume that the detected line arises from H3O+, we can deduce a fractional abundance X(H3O+) in OMC1 and SgrB2 of approximately 10(-9) and a production rate in Comet Halley of Q(H3O+) 10(28)s-1. These results would place H3O+ among the more abundant molecular ions in the interstellar gas in agreement with theoretical predictions. PMID:11542067

  11. Local Interstellar Magnetic Field Determined from the Interstellar Boundary Explorer Ribbon

    NASA Astrophysics Data System (ADS)

    Zirnstein, E. J.; Heerikhuisen, J.; Funsten, H. O.; Livadiotis, G.; McComas, D. J.; Pogorelov, N. V.

    2016-02-01

    The solar wind emanating from the Sun interacts with the local interstellar medium (LISM), forming the heliosphere. Hydrogen energetic neutral atoms (ENAs) produced by the solar-interstellar interaction carry important information about plasma properties from the boundaries of the heliosphere, and are currently being measured by NASA's Interstellar Boundary Explorer (IBEX). IBEX observations show the existence of a “ribbon” of intense ENA emission projecting a circle on the celestial sphere that is centered near the local interstellar magnetic field (ISMF) vector. Here we show that the source of the IBEX ribbon as a function of ENA energy outside the heliosphere, uniquely coupled to the draping of the ISMF around the heliopause, can be used to precisely determine the magnitude (2.93 ± 0.08 μG) and direction (227.°28 ± 0.°69, 34.°62 ± 0.°45 in ecliptic longitude and latitude) of the pristine ISMF far (∼1000 AU) from the Sun. We find that the ISMF vector is offset from the ribbon center by ∼8.°3 toward the direction of motion of the heliosphere through the LISM, and their vectors form a plane that is consistent with the direction of deflected interstellar neutral hydrogen, thought to be controlled by the ISMF. Our results yield draped ISMF properties close to that observed by Voyager 1, the only spacecraft to directly measure the ISMF close to the heliosphere, and give predictions of the pristine ISMF that Voyager 1 has yet to sample.

  12. Collisional excitation of interstellar methyl cyanide

    NASA Technical Reports Server (NTRS)

    Green, Sheldon

    1986-01-01

    Theoretical calculations are used to determine the collisional excitation rates of methyl cyanide under interstellar molecular cloud conditions. The required Q(L,M) as a function of kinetic temperature were determined by averaging fixed energy IOS (infinite order sudden) results over appropriate Boltzmann distributions of collision energies. At a kinetic temperature of 40 K, rates within a K ladder were found to be accurate to generally better than about 30 percent.

  13. TAU as Tao. [interstellar spacecraft performance

    NASA Technical Reports Server (NTRS)

    Lyman, P. T.; Reid, M. S.

    1989-01-01

    This paper discusses the feasibility of building and launching a truly deep-space spacecraft mission that will penetrate near interstellar space to a depth of one thousand astronomical units (TAU) within a flight time of 50 years. Particular attention is given to the mission profile and to its communications system, power system, and propulsion system. Results of experimental studies indicate that, with advanced technology, reasonable trip times can be achieved and adequate science information can be brought to earth.

  14. Diffuse Interstellar Bands: Families and Correlations

    NASA Astrophysics Data System (ADS)

    Krełowski, J.

    2014-02-01

    The term ``families of diffuse bands'' (DIBs) appeared in 1986/87 when my collaborators: Gordon A.H. Walker, Bengt E. Westerlund and I found that the strength ratio of the major DIBs 5780 and 5797 is heavily variable. We proved that at the same E(B-V) the DIB intensities may vary by as much as a factor of three or more. A similar result was published by Karl Josafatsson and Ted Snow soon after. A decade later, we proved (with Chris Sneden) that certain DIB strength ratios seem to be related to intensities of the known features of simple molecular species; this led to the introduction of the so called σ and ζ type interstellar clouds. The former are characterized by very weak molecular features (but broad DIBs - very strong) while the latter by rather strong bands of simple radicals and weak broad DIBs. Currently we face a bunch of questions: are the DIB intensities related to those of certain molecular species, e.g. C2 as suggested by Lew Hobbs' and Ted Snow's group? Do the DIB profiles, found to be complex by Peter Sarre, depend on e.g. the rotational temperatures of simple, linear carbon species? Do the DIB profiles depend on the irradiation of interstellar clouds by nearby stars? The relative DIB strengths as well as those of the simple radicals seem to be related to the shapes of interstellar extinction curves. We thus face three players in the interstellar translucent clouds: dust particles, simple radicals and the DIB carriers. Apparently, their mutual relations depend on local physical parameters of intervening clouds; these relations are not clear yet.

  15. Stellar sources of the interstellar medium

    NASA Astrophysics Data System (ADS)

    Thielemann, F.-K.; Argast, D.; Brachwitz, F.; Martinez-Pinedo, G.; Oechslin, R.; Rauscher, T.; Hix, W. R.; Liebendörfer, M.; Mezzacappa, A.; Höflich, P.; Iwamoto, K.; Nomoto, K.; Schatz, H.; Wiescher, M. C.; Kratz, K.-L.; Pfeiffer, B.; Rosswog, S.

    With the exception of the Big Bang, responsible for 1,2 H, 3,4 He, and 7 Li, stars act as sources for the composition of the interstellar medium. Cosmic rays are related to the latter and very probably due to acceleration of the mixed interstellar medium by shock waves from supernova remnants. Thus, the understanding of the abundance evolution in the interstellar medium and especially the enrichment of heavy elements, as a function of space and time, is essential. It reflects the history of star formation and the lifetimes of the diverse contributing stellar objects. Therefore, the understanding of the endpoints of stellar evolution is essential as well. These are mainly planetary nebulae and type II/Ib/Ic supernovae as evolutionary endpoints of single stars, but also events in binary systems can contribute, like e.g. supernovae of type Ia, novae and possibly X-ray bursts and neutron star or neutron star - black hole mergers. Despite many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies) is not existing, yet. Their fingerprints, however, seen either in spectra, lightcurves, radioactivities/decay gamma-rays or in galactic evolution, can help to constrain the composition of their ejecta and related model uncertainties.

  16. Design for minimum energy in interstellar communication

    NASA Astrophysics Data System (ADS)

    Messerschmitt, David G.

    2015-02-01

    Microwave digital communication at interstellar distances is the foundation of extraterrestrial civilization (SETI and METI) communication of information-bearing signals. Large distances demand large transmitted power and/or large antennas, while the propagation is transparent over a wide bandwidth. Recognizing a fundamental tradeoff, reduced energy delivered to the receiver at the expense of wide bandwidth (the opposite of terrestrial objectives) is advantageous. Wide bandwidth also results in simpler design and implementation, allowing circumvention of dispersion and scattering arising in the interstellar medium and motion effects and obviating any related processing. The minimum energy delivered to the receiver per bit of information is determined by cosmic microwave background alone. By mapping a single bit onto a carrier burst, the Morse code invented for the telegraph in 1836 comes closer to this minimum energy than approaches used in modern terrestrial radio. Rather than the terrestrial approach of adding phases and amplitudes increases information capacity while minimizing bandwidth, adding multiple time-frequency locations for carrier bursts increases capacity while minimizing energy per information bit. The resulting location code is simple and yet can approach the minimum energy as bandwidth is expanded. It is consistent with easy discovery, since carrier bursts are energetic and straightforward modifications to post-detection pattern recognition can identify burst patterns. Time and frequency coherence constraints leading to simple signal discovery are addressed, and observations of the interstellar medium by transmitter and receiver constrain the burst parameters and limit the search scope.

  17. Interstellar and Planetary Analogs in the Laboratory

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2013-01-01

    We present and discuss the unique capabilities of the laboratory facility, COSmIC, that was developed at NASA Ames to investigate the interaction of ionizing radiation (UV, charged particles) with molecular species (neutral molecules, radicals and ions) and carbonaceous grains in the Solar System and in the Interstellar Medium (ISM). COSmIC stands for Cosmic Simulation Chamber, a laboratory chamber where interstellar and planetary analogs are generated, processed and analyzed. It is composed of a pulsed discharge nozzle (PDN) expansion that generates a free jet supersonic expansion in a plasma cavity coupled to two ultrahigh-sensitivity, complementary in situ diagnostics: a cavity ring down spectroscopy (CRDS) system for photonic detection and a Reflectron time-of-flight mass spectrometer (ReTOF-MS) for mass detection. This setup allows the study of molecules, ions and solids under the low temperature and high vacuum conditions that are required to simulate some interstellar, circumstellar and planetary physical environments providing new fundamental insights on the molecular level into the processes that are critical to the chemistry in the ISM, circumstellar and planet forming regions, and on icy objects in the Solar System. Recent laboratory results that were obtained using COSmIC will be discussed, in particular the progress that have been achieved in monitoring in the laboratory the formation of solid particles from their gas-phase molecular precursors in environments as varied as circumstellar outflow and planetary atmospheres.

  18. A survey of interstellar molecular hydrogen. I

    NASA Technical Reports Server (NTRS)

    Savage, B. D.; Drake, J. F.; Budich, W.; Bohlin, R. C.

    1977-01-01

    Data from the Copernicus satellite's ultraviolet telescope were used to survey column densities of atomic and molecular hydrogen from a large sample of early-type stars; these data have bearing on an eventual understanding of diffuse and dense interstellar clouds. Column densities are derived by fitting damping profiles to the observed spectra, most of which exhibit strong damping lines in the lower rotational levels surveyed. Plots of dust column density, fractional abundance of molecular hydrogen, and the logarithm of fractional abundance versus total gas column density are given for many of the stars; stars with abnormally large or small hydrogen column densities, as well as some distant stars at high galactic latitudes, are considered. Equilibrium and nonequilibrium theories accounting for the abundance of interstellar hydrogen are compared, and support is found in the data for an account which balances hydrogen formation on interstellar grains with destruction through photodissociation. Overall averages for atomic and molecular hydrogen levels in the galactic plane are also calculated.

  19. Thermal phases of interstellar and quasar gas

    NASA Technical Reports Server (NTRS)

    Lepp, S.; Mccray, R.; Shull, J. M.; Woods, D. T.; Kallman, T.

    1985-01-01

    Interstellar gas may be in a variety of thermal phases, depending on how it is heated and ionized; here a unified picture of the equation of state of interstellar and quasar gas is presented for a variety of such mechanisms over a broad range of temperatures, densities, and column densities of absorbing matter. It is found that for select ranges of gas pressure, photoionizing flux, and heating, three thermally stable phases are allowed: coronal gas (T above 100,000 K); warm gas (T about 10,000 K); and cold gas (T less than 100 K). With attenuation of ultraviolet and X-ray radiation, the cold phase may undergo a transition to molecules. In quasar broad-line clouds, this transition occurs at column density N(H) = about 10 to the 23rd/sq cm and could result in warm molecular cores and observable emission from H2 and OH. The underlying atomic physics behind each of these phase transitions and their relevance to interstellar matter and quasars are discussed.

  20. Theoretical studies in interstellar cloud chemistry

    NASA Technical Reports Server (NTRS)

    Chiu, Y. T.; Prasad, S. S.

    1993-01-01

    This final report represents the completion of the three tasks under the purchase order no. SCPDE5620,1,2F. Chemical composition of gravitationally contracting, but otherwise quiescent, interstellar clouds and of interstellar clouds traversed by high velocity shocks, were modeled in a comprehensive manner that represents a significant progress in modeling these objects. The evolutionary chemical modeling, done under this NASA contract, represents a notable advance over the 'classical' fixed condition equilibrium models because the evolutionary models consider not only the chemical processes but also the dynamical processes by which the dark interstellar clouds may have assumed their present state. The shock calculations, being reported here, are important because they extend the limited chemical composition derivable from dynamical calculations for the total density and temperature structures behind the shock front. In order to be tractable, the dynamical calculations must severely simplify the chemistry. The present shock calculations take the shock profiles from the dynamical calculations and derive chemical composition in a comprehensive manner. The results of the present modeling study are still to be analyzed with reference to astronomical observational data and other contemporary model predictions. As far as humanly possible, this analysis will be continued with CRE's (Creative Research Enterprises's) IR&D resources, until a sponsor is found.

  1. Closing Remarks: A Charter for Interstellar Studies

    NASA Astrophysics Data System (ADS)

    Gilster, Paul A.

    2007-02-01

    Multidisciplinary by necessity, interstellar studies attack a seemingly intractable problem from numerous angles, many of which were on display at the Princeton conference. The past year has seen work that firms up our knowledge of the nearest interstellar target, the triple star system Alpha Centauri. Learning that the Centauri A and B stars may well support terrestrial style worlds, we push ahead into an era of breakthrough investigations in exoplanet detection and imaging. The treatment of the Centauri developments illustrates the changes that online capabilities bring to research, offering new venues and providing for vigorous debate via preprint archives, weblogs and self-archiving by researchers. These tools also hone our skills at presenting the public case for interstellar research to a lay audience often indifferent to both space-related activities and the possibility of long-term planning. We must continue to press the case for vigorous exploration and use these new online capabilities to re-energize an all too jaded public.

  2. Low Frequency Interstellar Scattering and Pulsar Observations

    NASA Technical Reports Server (NTRS)

    Cordes, James M.

    1992-01-01

    Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities.

  3. Formation of water in the interstellar medium

    NASA Astrophysics Data System (ADS)

    Vidali, Gianfranco; Jing, Dapeng; He, Jiao

    2012-07-01

    The formation of water in the interstellar medium is an important topic of research nowadays because water plays key roles in the cooling of collapsing clouds and, while condensed in ices that cover dust grains, in the formation and storage of molecules of biogenic interest. Furthermore, how water interacts with grains is of importance in understanding the delivery of water to planetary bodies. Water formation occurs largely on dust grains. In the last couple of years, a few laboratories have explored the network of reactions that lead to the formation of water on grain analogs. There are three main branches of this network^1: hydrogenation of O_2, hydrogenation of O_3, and O+H reactions. In our laboratory we studied the formation of water on amorphous silicate films by the interaction of hydrogen and oxygen atoms^2. We will also present measurements of the diffusion of oxygen atoms on amorphous silicate surfaces. Financial support from the NSF Astronomy and Astrophysics Division (grant No. 0908108) is gratefully acknowledged. We like to thank Dr. Brucato and his team (Astrophysical Observatory of Arcetri, Italy) for providing the samples. Tielens, A. G. G. M., & Hagen, W. 1982 ``Model calculations of the molecular composition of interstellar grain mantles'' Astron.& Astrophys., 114, 245. Jing, D., He, J., Brucato, J., De Sio, A., Tozzetti, L. & Vidali, G. 2011 ``On water formation in the interstellar medium: laboratory study of the O+D reaction on surfaces'' Astrophys.J., 741, L9.

  4. H3+ in the diffuse interstellar medium.

    PubMed

    Liszt, Harvey S

    2006-11-15

    Three forms of solely hydrogen-bearing molecules--H2, HD and H3+--are observed in diffuse or optically transparent interstellar clouds. Although no comprehensive theory exists for the diffuse interstellar medium or its chemistry, the abundances of these species can generally be accommodated locally within the existing static equilibrium frameworks for heating/cooling, H2-formation on large grains, etc. with one modification demanded equally by observations of HD and H3+, i.e. a pervasive low-level source of H and H2 ionization ca 10 times faster than the usual cosmic ray ionization rate zetaH = 10(-17) s(-1) per free H-atom. We discuss this situation with reference to observation and time-dependent modelling of H2 and H3+ formation. While not wishing to appear ungrateful for the success of what are very simplistic notions of the interstellar medium, we point out several reasons not to feel smug. The equilibrium conditions which foster high H2 and H3+ abundances are very slow to appear and these same simple ideas of static equilibrium cannot explain any, but a few, of the simplest of the trace species, which are ubiquitously embedded in H2-bearing diffuse gases. PMID:17015375

  5. Solving the Mysteries of Interstellar Dust Composition in the Milky Way

    NASA Astrophysics Data System (ADS)

    Chiar, Jean; Egan, Michael; Sloan, G. C.; Tielens, Alexander

    2004-09-01

    Interstellar dust is ubiquitous, yet its precise composition is still widely debated. Spitzer's Infrared Spectrometer provides the sensitivity to study previously unattainable lines of sight throughout the plane of the Milky Way. In this proposal, we seek to study the hydrocarbon and silicate dust components of the interstellar medium for 56 lines of sight spanning visual extinctions from 6.6 to 32.2 magnitudes across a range of Galactic longitudes and latitudes. Specifically, we will measure the hydrocarbon absorption features at 6.9 and 7.3 micron, and the silicate absorption features at 9.7 and 18.5 micron. The ratio of the hydrocarbon and silicate features provides a direct handle on the hydrocarbon to silicate dust volume. It has been previously been noted that the optical depth to visual extinction ratio is distinct for lines of sight within the Solar neighborhood compared to the Galactic Center. Thus, these features will also be related to their visual extinction and Galactic location to test whether location has an effect on the optical depth to Av ratio. Finally, the silicate mineralogy can be assessed by studying the ratio of the 9.7 to 18.5 micron absorption features, whose relative strengths have been shown to be indicative of olivine-rich or pyroxene-rich silicates. In order to obtain sufficient sampling of both Galactic location and visual extinction, we will observe 56 lines of sight requiring a total of 16.3 hours.

  6. A Catalog of 1.5273 um Diffuse Interstellar Bands Based on APOGEE Hot Telluric Calibrators

    NASA Astrophysics Data System (ADS)

    Elyajouri, M.; Monreal-Ibero, A.; Remy, Q.; Lallement, R.

    2016-08-01

    High resolution stellar spectroscopic surveys provide massive amounts of diffuse interstellar bands (DIBs) measurements. Data can be used to study the distribution of the DIB carriers and those environmental conditions that favor their formation. In parallel, recent studies have also proved that DIBs extracted from stellar spectra constitute new tools for building the 3D structure of the Galactic interstellar medium (ISM). The amount of details on the structure depends directly on the quantity of available lines of sight. Therefore there is a need to construct databases of high-quality DIB measurements as large as possible. We aim at providing the community with a catalog of high-quality measurements of the 1.5273 μm DIB toward a large fraction of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) hot stars observed to correct for the telluric absorption and not used for ISM studies so far. This catalog would complement the extensive database recently extracted from the APOGEE observations and used for 3D ISM mapping. We devised a method to fit the stellar continuum of the hot calibration stars and extracted the DIB from the normalized spectrum. Severe selection criteria based on the absorption characteristics are applied to the results. In particular limiting constraints on the DIB widths and Doppler shifts are deduced from the H i 21 cm measurements, following a new technique of decomposition of the emission spectra. From ∼16,000 available hot telluric spectra we have extracted ∼6700 DIB measurements and their associated uncertainties. The statistical properties of the extracted absorptions are examined and our selection criteria are shown to provide a robust dataset. The resulting catalog contains the DIB total equivalent widths, central wavelengths and widths. We briefly illustrate its potential use for the stellar and interstellar communities.

  7. A Catalog of 1.5273 um Diffuse Interstellar Bands Based on APOGEE Hot Telluric Calibrators

    NASA Astrophysics Data System (ADS)

    Elyajouri, M.; Monreal-Ibero, A.; Remy, Q.; Lallement, R.

    2016-08-01

    High resolution stellar spectroscopic surveys provide massive amounts of diffuse interstellar bands (DIBs) measurements. Data can be used to study the distribution of the DIB carriers and those environmental conditions that favor their formation. In parallel, recent studies have also proved that DIBs extracted from stellar spectra constitute new tools for building the 3D structure of the Galactic interstellar medium (ISM). The amount of details on the structure depends directly on the quantity of available lines of sight. Therefore there is a need to construct databases of high-quality DIB measurements as large as possible. We aim at providing the community with a catalog of high-quality measurements of the 1.5273 μm DIB toward a large fraction of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) hot stars observed to correct for the telluric absorption and not used for ISM studies so far. This catalog would complement the extensive database recently extracted from the APOGEE observations and used for 3D ISM mapping. We devised a method to fit the stellar continuum of the hot calibration stars and extracted the DIB from the normalized spectrum. Severe selection criteria based on the absorption characteristics are applied to the results. In particular limiting constraints on the DIB widths and Doppler shifts are deduced from the H i 21 cm measurements, following a new technique of decomposition of the emission spectra. From ˜16,000 available hot telluric spectra we have extracted ˜6700 DIB measurements and their associated uncertainties. The statistical properties of the extracted absorptions are examined and our selection criteria are shown to provide a robust dataset. The resulting catalog contains the DIB total equivalent widths, central wavelengths and widths. We briefly illustrate its potential use for the stellar and interstellar communities.

  8. Interstellar dust spectra between 2.5 and 3.3 microns - A search for hydrated silicates

    NASA Technical Reports Server (NTRS)

    Knacke, R. F.; Mccorkle, S.; Puetter, R. C.; Erickson, E.

    1985-01-01

    Spectra in the 2.5-3.3 micron wavelength region of VI Cyg 12, AFGL 2205, and AFGL 2885 were obtained in a search for bound water, hydroxyl groups, and hydrated minerals in interstellar dust. No new absorption bands were found. Comparison of expected strengths of bands of serpentine and chlorite-like minerals with the data suggests that less than 25 percent and 50 percent, respectively, of the silicate in the grains is composed of these materials.

  9. FORMATION AND IDENTIFICATION OF INTERSTELLAR MOLECULE LINEAR C{sub 5}H FROM PHOTOLYSIS OF METHANE DISPERSED IN SOLID NEON

    SciTech Connect

    Wu Yujong; Chen Huifen; Hsu Shengchuan; Lin Mengyeh; Chou Shenglung; Cheng Bingming; Camacho, Cristopher; Witek, Henryk A.; Ogilvie, J. F.

    2009-08-10

    Photolysis of methane dispersed (1/1000) in solid Ne at 3 K with vacuum-ultraviolet light from a synchrotron produced infrared absorption lines of several products, including new lines at 3319.3 and 1955.5 cm{sup -1}. Based on experiments with isotopic labeling and results of quantum-chemical calculations, these lines are assigned to the C-H stretching and C=C stretching modes, respectively, of interstellar molecule linear C{sub 5}H radicals.

  10. THE INTERSTELLAR MEDIUM AND FEEDBACK IN THE PROGENITORS OF THE COMPACT PASSIVE GALAXIES AT z ∼ 2

    SciTech Connect

    Williams, Christina C.; Giavalisco, Mauro; Lee, Bomee; Tundo, Elena; Mobasher, Bahram; Nayyeri, Hooshang; Ferguson, Henry C.; Koekemoer, Anton; Grogin, Norman; Trump, Jonathan R.; Cassata, Paolo; Dekel, Avishai; Guo, Yicheng; Pentericci, Laura; Castellano, Marco; Fontana, Adriano; Grazian, Andrea; Bell, Eric F.; Finkelstein, Steven L.; and others

    2015-02-10

    Quenched galaxies at z > 2 are nearly all very compact relative to z ∼ 0, suggesting a physical connection between high stellar density and efficient, rapid cessation of star-formation. We present rest-frame UV spectra of Lyman-break galaxies (LBGs) at z ∼ 3 selected to be candidate progenitors of the quenched galaxies at z ∼ 2 based on their compact rest-frame-optical sizes and high Σ{sub SFR}. We compare their UV properties to those of more extended LBGs of similar mass and star-formation rate (non-candidates). We find that candidate progenitors have faster bulk interstellar medium (ISM) gas velocities and higher equivalent widths of interstellar absorption lines, implying larger velocity spread among absorbing clouds. Candidates deviate from the relationship between equivalent widths of Lyα and interstellar absorption lines in that their Lyα emission remains strong despite high interstellar absorption, possibly indicating that the neutral H I fraction is patchy, such that Lyα photons can escape. We detect stronger C IV P-Cygni features (emission and absorption) and He II emission in candidates, indicative of larger populations of metal-rich Wolf-Rayet stars compared to non-candidates. The faster bulk motions, broader spread of gas velocity, and Lyα properties of candidates are consistent with their ISM being subject to more energetic feedback than non-candidates. Together with their larger metallicity (implying more evolved star-formation activity) this leads us to propose, if speculatively, that they are likely to quench sooner than non-candidates, supporting the validity of selection criteria used to identify them as progenitors of z ∼ 2 passive galaxies. We propose that massive, compact galaxies undergo more rapid growth of their stellar mass content, perhaps because the gas accretion mechanisms are different, and quench sooner than normally sized LBGs at these (early) epochs.

  11. Time Dependent Density Functional Theory Calculations of Large Compact PAH Cations: Implications for the Diffuse Interstellar Bands

    NASA Technical Reports Server (NTRS)

    Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)

    2002-01-01

    We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

  12. The structure of the time-dependent interstellar shocks and grain destruction in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Mckee, Christopher F.; Hollenbach, David J.; Seab, Gregory C.; Tielens, A. G. G. M.

    1987-01-01

    A new theoretical analysis of the structure of interstellar shocks and the grain dynamics of these shocks is presented. The basic hydrodynamic equations for J-shocks in interstellar gas are given in which shock-driving pressure is allowed to be weakly time-dependent and the grains are treated as a separate two-dimensional fluid. Specific equations for the grain dynamics in the cooling postshock gas are derived. An analytic theory for the propagation of a shock driven into an interstellar cloud by the blast wave of a supernova remnant which sweeps over the cloud is developed. An improved calculation of the grain charge in postshock gas is described, giving a simple analytic approximation for the results. The consequences of including these processes in the numerical code of Seab and Shull (1983) are addressed, including the effect of realistic magnetic fields in low-density gas.

  13. Helium atoms in interstellar and interplanetary media, part 3: Temperature and velocity of interstellar wind

    NASA Astrophysics Data System (ADS)

    Kurt, V. G.; Mironova, Y. N.; Berto, Z. L.; Dalode, F.

    1984-10-01

    The distribution of intensities over the celestial sphere in the neutral helium line ar lambda=584 A which is obtained from background radiation observations on the Prognoz-6 satellite with a 4 channel photometer was used to find the temperature and magnitude of the velocity vector of the interstellar wind. The direction of motin of the interstellar medium relative to the sun was determined from the same observations. Interaction of neutral helium in the interstellar medium with the gravitational field of the sun and resonant scattering on intereplanetary helium are calculated. The temperature and velocity of the model which best agree with the results were determined separately for each of six measurement sessions onboard the satellite. The average temperature was 11,600 K, velocity 25.3 km/s. It is found that the mean density of helium in space near the sun is be 0.018 cm -3.

  14. Interstellar bubbles. II - Structure and evolution. [stellar wind interaction with interstellar gas

    NASA Technical Reports Server (NTRS)

    Weaver, R.; Mccray, R.; Castor, J.; Moore, R.; Shapiro, P.

    1977-01-01

    The detailed structure of the interaction of a strong stellar wind with the interstellar medium is presented. First, an adiabatic similarity solution is given which is applicable at early times. Second, a similarity solution is derived which includes the effects of thermal conduction between the hot (about 1 million K) interior and the cold shell of swept-up interstellar matter. This solution is then modified to include the effects of radiative energy losses. The evolution of an interstellar bubble is calculated, including the radiative losses. The quantitative results for the outer-shell radius and velocity and the column density of highly ionized species such as O VI are within a factor 2 of the approximate results of Castor, McCray, and Weaver (1975). The effect of stellar motion on the structure of a bubble, the hydrodynamic stability of the outer shell, and the observable properties of the hot region and the outer shell are discussed.

  15. The Ingenious Theory of Interstellar Trade

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, Arun; Ganapathy, Rohan M.

    This paper extends interplanetary trade theory to an interstellar setting. It is chiefly concerned with the following question: How should interest charges on goods in transit be computed when the goods travel at speeds close to the actual speed of light? This is a problem because the time taken in transit will appear less to an observer travelling with the goods than to a stationary observer. An innovative and ingenious solution is derived from the economic theory, and two useless but TRUE theorems are proved. The interstellar trade would happen in such a way that two time frames must be considered namely that of the stationary observer whose time runs faster compared to the time frame of the observer in transit The interest in a given trade is purely based on the time taken for the debtor to pay the amount, once the goods have been delivered by the seller. But, in case of interstellar trade, the interest to be calculated in between two time frames would lead to the question of which time frame to be considered and moreover, the time taken for the goods to reach the destination is signicantly prolonged compared to the interplanetary trade, which means, even the slightest variations in the interest rate would be magnied. Apart from this, various new factors arise while calculating the interest. The factors include the time value of money, and the risk of variation in demand for goods, the risk of interspace accidents causing loss of the goods and the rate of perish-ability in case of organic goods. The first two factors considered, for which the time frame of the stationary observer is considered and the factors such as the risk of accidents and the rate of perish-ability of the goods are considered based on the time frame of the observer in transit's point of view. The reasons for such considerations and various assumptions on these concepts are dealt in this paper. The theorems that are formulated in this paper would provide the interstellar traders a basic

  16. New Large Interstellar Molecules Detected with the GBT

    NASA Technical Reports Server (NTRS)

    Hollis, Jan M.

    2005-01-01

    At present, more than 135 different molecules have been identified in interstellar clouds. The newest instrument in the interstellar molecule search arsenal is the recently commissioned Green Bank Telescope (GBT). In 2004, the large aldehydes propenal (CH2CHCHO) and propanal (CH3CH2CHO) were the first new interstellar molecules discovered with the GBT. At the same time, the GBT was used to observe interstellar glycolaldehyde (CH2OHCHO), which is the simplest possible aldehyde sugar; interstellar ethylene glycol (HOCH2CH2OH), which is the sugar alcohol of glycolaldehyde; and interstellar methylcyanodiacetylene (CH3C5N). These new GBT observations suggest that successive atomic addition reactions are common in the formation of larger related species. The observations will be presented and discussed.

  17. Interstellar dust on the eve of Herschel and Planck

    NASA Astrophysics Data System (ADS)

    Miville-Deschênes, M.-A.

    2008-11-01

    In this contribution I review some of the key scientific questions that animate the interstellar dust community a few months before the launch of Herschel and Planck. Great progress have been made in the past 25 years on the subject of interstellar dust using infrared observations from space. With the advent of sub-millimeter and millimeter observations with Herschel and Planck, new scientific challenges are coming and exciting discoveries are to be expected. In particular Herschel and Planck will bring key information 1) on the growth process of dust grains, the first step toward the formation of planetesimals, 2) on the structure of the interstellar medium and its link with interstellar turbulence, 3) on the physical conditions of the Galactic halo clouds which are thought to have some cold dust, 4) on the properties of the interstellar magnetic field and 5) on the interstellar PAHs using their spinning dust emission in the millimeter.

  18. Seasonal Solar Thermal Absorption Energy Storage Development.

    PubMed

    Daguenet-Frick, Xavier; Gantenbein, Paul; Rommel, Mathias; Fumey, Benjamin; Weber, Robert; Gooneseker, Kanishka; Williamson, Tommy

    2015-01-01

    This article describes a thermochemical seasonal storage with emphasis on the development of a reaction zone for an absorption/desorption unit. The heat and mass exchanges are modelled and the design of a suitable reaction zone is explained. A tube bundle concept is retained for the heat and mass exchangers and the units are manufactured and commissioned. Furthermore, experimental results of both absorption and desorption processes are presented and the exchanged power is compared to the results of the simulations. PMID:26842331

  19. DIFFUSE ATOMIC AND MOLECULAR GAS IN THE INTERSTELLAR MEDIUM OF M82 TOWARD SN 2014J

    SciTech Connect

    Ritchey, Adam M.; Welty, Daniel E.; York, Donald G.; Dahlstrom, Julie A.

    2015-02-01

    We present a comprehensive analysis of interstellar absorption lines seen in moderately high resolution, high signal-to-noise ratio optical spectra of SN 2014J in M82. Our observations were acquired over the course of six nights, covering the period from ∼6 days before to ∼30 days after the supernova reached its maximum B-band brightness. We examine complex absorption from Na I, Ca II, K I, Ca I, CH{sup +}, CH, and CN, arising primarily from diffuse gas in the interstellar medium (ISM) of M82. We detect Li I absorption over a range in velocity consistent with that exhibited by the strongest Na I and K I components associated with M82; this is the first detection of interstellar Li in a galaxy outside of the Local Group. There are no significant temporal variations in the absorption-line profiles over the 37 days sampled by our observations. The relative abundances of the various interstellar species detected reveal that the ISM of M82 probed by SN 2014J consists of a mixture of diffuse atomic and molecular clouds characterized by a wide range of physical/environmental conditions. Decreasing N(Na I)/N(Ca II) ratios and increasing N(Ca I)/N(K I) ratios with increasing velocity are indicative of reduced depletion in the higher-velocity material. Significant component-to-component scatter in the N(Na I)/N(Ca II) and N(Ca I)/N(Ca II) ratios may be due to variations in the local ionization conditions. An apparent anti-correlation between the N(CH{sup +})/N(CH) and N(Ca I)/N(Ca II) ratios can be understood in terms of an opposite dependence on gas density and radiation field strength, while the overall high CH{sup +} abundance may be indicative of enhanced turbulence in the ISM of M82. The Li abundance also seems to be enhanced in M82, which supports the conclusions of recent gamma-ray emission studies that the cosmic-ray acceleration processes are greatly enhanced in this starburst galaxy.

  20. Diffuse interstellar clouds as a chemical laboratory - The chemistry of diatomic carbon species

    NASA Technical Reports Server (NTRS)

    Federman, S. R.; Huntress, W. T., Jr.

    1989-01-01

    The chemistry of C2, CH, and CO in diffuse interstellar clouds is analyzed and compared to absorption line measurements toward background stars. Analytical expressions in terms of column densities are derived for the rate equations. The results indicate that in clouds with 4 mag of visual extinction, the abundance of C+ has to decrease by a factor of about 15 from the value traditionally used for clouds with 1 mag of extinction. The rate coefficients for the reactions C+ + CH - C2+ + H and C+ + H2 - CH2+ + h-nu need to be reduced from previous estimates. Chemical arguments are presented for the revised rate coefficients.

  1. Laboratory investigations of irradiated acetonitrile-containing ices on an interstellar dust analog

    SciTech Connect

    Abdulgalil, Ali G. M.; Marchione, Demian; Rosu-Finsen, Alexander; Collings, Mark P.; McCoustra, Martin R. S.

    2012-07-15

    Reflection-absorption infrared spectroscopy is used to study the impact of low-energy electron irradiation of acetonitrile-containing ices, under conditions close to those in the dense star-forming regions in the interstellar medium. Both the incident electron energy and the surface coverage were varied. The experiments reveal that solid acetonitrile is desorbed from its ultrathin solid films with a cross section of the order of 10{sup -17} cm{sup 2}. Evidence is presented for a significantly larger desorption cross section for acetonitrile molecules at the water-ice interface, similar to that previously observed for the benzene-water system.

  2. SUB-PARSEC STRUCTURE OF INTERSTELLAR H{sub 2}CO CLOUDS

    SciTech Connect

    Dieter-Conklin, Nan

    2010-08-15

    Data derived from the absorption of background sources by H{sub 2}CO clouds show that there are smaller cells within the extended clouds. A cell that is found in many clouds extends about 0.5 pc with a velocity dispersion of about 1 km s{sup -1}. Larger features, in general, have higher dispersion while those of smaller dimension (tens of AU) have lower dispersion (0.5-0.7 km s{sup -1}). These data should be considered in models of the dynamics of interstellar clouds.

  3. Unusual relative strengths of the diffuse interstellar bands in some interstellar dust clouds

    NASA Technical Reports Server (NTRS)

    Krelowski, J.; Walker, G. A. H.

    1986-01-01

    Some of the diffuse interstellar features (DIBs) in the spectra of certain stars at high galactic latitudes (1 is greater than 15 degrees) are unusually weak or absent while others have the strength expected for their color excess. In some cases the stars are probably reddened by single interstellar clouds. There appear to be three families of DIBs. The effects of these families are examined. The existance of the three families implies that at least three agents cause the DIBs and that the proportions of the agents or the physical conditions giving rise to the DIBs can vary from cloud to cloud.

  4. Reconstructing our Interstellar Past: A Look at the Small Scale Structure in the Direction of the Historical Solar Trajectory

    NASA Astrophysics Data System (ADS)

    Redfield, S.; Scalo, J.; Smith, D. S.

    2007-07-01

    The properties of our nearby interstellar medium (NISM) out to ˜500 pc, including density, temperature, and velocity, provide a sample of the range and timing of environments that have been encountered by our solar system. These conditions influence the structure of the heliosphere, which modulates the flux of Galactic cosmic rays and interstellar gas and dust that reach the Earth. There is a long tradition of speculation focused on the effects of the ISM on heliospheric modulation of cosmic rays and interstellar hydrogen on atmospheric chemistry, cloud cover, glaciation episodes, and exogenous mutation, but the intensity and timing of such variations has never been established empirically, even in a statistical sense. The present work is aimed at evaluating the impact of small scale low column density structures in the NISM, using analysis of absorption line features toward early type stars, on the intensity and timing of heliospheric variations, and at placing these structures, invisible by most other techniques of tracing interstellar structure, in the overall dynamics of the interstellar medium. We present high spectral resolution observations of 49 stars within 10 degrees of the direction of the historical solar trajectory. This densely packed collection of sightlines provides an opportunity to (1) study small-scale structure in the shell separating the Local Bubble from the more distant NISM, (2) enable a rough reconstruction of the interstellar density profile, and hence cosmic ray flux history, encountered by the Solar System in the past 40 million years, and (3) clarify the prevalence of small column density fluctuations in the NISM.

  5. The distribution of neutral hydrogen in the interstellar medium. 1: The data

    NASA Technical Reports Server (NTRS)

    Fruscione, Antonella; Hawkins, Isabel; Jelinsky, Patrick; Wiercigroch, Alexandria

    1994-01-01

    We compile, from the existing literature, the largest sample to date (842 data points) of hydrogen column density measurements, N(H I), of the gas in the interstellar medium. We include only results obtained from absorption measurements toward individual stars (594 in our sample) in an effort to construct a three-dimensional picture of the interstellar gas. We derive hydrogen column densities toward a fraction of the stars in the sample from published column density measurements of metal ions. A three-dimensional physical model derived from this data set will be presented in a companion paper. The observed stars span distances from a few parsecs to a few thousand parsecs, and more than half of the sample serves to describe the local interstellar medium within a few hundred parsecs of the Sun. Hydrogen column densities range from 10(exp 17) to 10(exp 22)/sq cm. We describe here the various observational methods used to estimate the hydrogen column densities and present the table with the stellar and hydrogen column density data. The provided table is intended as a global reference work, not to introduce new results.

  6. Investigation of Carbonaceous Interstellar Dust Analogues by Infrared Spectroscopy: Effects of Energetic Processing

    NASA Astrophysics Data System (ADS)

    Maté, Belén; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Victor Jose

    2015-06-01

    Carbonaceous compounds, both solids and gas-phase molecules, are found in very diverse astronomical media. A significant amount of the elemental carbon is found in small dust grains. This carbonaceous dust, mostly formed in the last stages of evolution of C-rich stars, is the carrier of characteristic IR absorption bands revealing the presence of aliphatic, aromatic and olefinic functional groups in variable proportions. Among the various candidate materials investigated as possible carriers of these bands, hydrogenated amorphous carbon (a-C:H) has led to the best agreement with the observations. Carbonaceous grains are processed by H atoms, UV radiation, cosmic rays and interstellar shocks in their passage from asymptotic giant branch stars to planetary nebulae and to the diffuse interstellar medium. The mechanisms of a-C:H production and evolution in astronomical media are presently a subject of intensive investigation. In this work we present a study of the stability of carbonaceous dust analogues generated in He+CH_4 radiofrequency discharges. In order to simulate the processing of dust in the interstellar environments, the samples have been subjected to electron bombardment, UV irradiation, and both He and H_2 plasma processing. IR spectroscopy is employed to monitor the changes in the structure and composition of the carbonaceous films. A.G.G.M. Tielens. Rev. Mod. Phys., 85, 1021 (2013) J.E. Chiar, A.G.G.M. Tielens, A.J. Adamson and A. Ricca. Astrophys. J., 770, 78 (2013)

  7. Laboratory Rotational Spectroscopy of the Interstellar Diatomic Hydride Ion SH+ (X 3Σ-)

    NASA Astrophysics Data System (ADS)

    Halfen, DeWayne; Ziurys, Lucy M.

    2016-06-01

    Diatomic hydride are among the most common molecular species in the interstellar medium (ISM). The low molecular mass and thus moments of inertia cause their rotational spectra to lie principally in the submillimeter and far-infrared regions. Diatomic hydrides, both neutral (MH) and ionic (MH+) forms, are also basic building blocks of interstellar chemistry. In ionic form, they may be the “hidden” carriers of refractory elements in dense gas. They are therefore extremely good targets for space-borne and airborne platforms such as Herschel, SOFIA, and SAFIR. However, in order to detect these species in the ISM, their rotational spectra must first be measured in the laboratory. To date, there is very little high resolution data available for many hydride species, in particular the ionic form. Using submillimeter/THz direct absorption methods in the Ziurys laboratory, spectra of the interstellar diatomic hydride SH+ (X 3Σ-) have been recorded. Recent work has concerned measurement of all three fine structure components of the fundamental rotational transition N = 1 ← 0 in the range 345 - 683 GHz. SH+ was generated from H2S and argon in an AC discharge. The data have been analyzed, and spectroscopic constants for this species have been refined. SH+ is found in Photon Dominated Regions (PDRs) and X-ray Dominated Regions (XDRs) and is thought to trace energetic processes in the ISM. These current measurements confirm recent observations of this species at submillimeter/THz wavelengths with ALMA and other ground-based telescopes.

  8. The orientation of the local interstellar magnetic field.

    PubMed

    Opher, M; Stone, E C; Gombosi, T I

    2007-05-11

    The orientation of the local interstellar magnetic field introduces asymmetries in the heliosphere that affect the location of heliospheric radio emissions and the streaming direction of ions from the termination shock of the solar wind. We combined observations of radio emissions and energetic particle streaming with extensive three-dimensional magnetohydrodynamic computer simulations of magnetic field draping over the heliopause to show that the plane of the local interstellar field is approximately 60 degrees to 90 degrees from the galactic plane. This finding suggests that the field orientation in the Local Interstellar Cloud differs from that of a larger-scale interstellar magnetic field thought to parallel the galactic plane. PMID:17495167

  9. DESPOTIC - a new software library to Derive the Energetics and SPectra of Optically Thick Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark R.

    2014-01-01

    I describe DESPOTIC, a code to Derive the Energetics and SPectra of Optically Thick Interstellar Clouds. DESPOTIC represents such clouds using a one-zone model, and can calculate line luminosities, line cooling rates, and in restricted cases line profiles using an escape probability formalism. It also includes approximate treatments of the dominant heating, cooling and chemical processes for the cold interstellar medium, including cosmic ray and X-ray heating, grain photoelectric heating, heating of the dust by infrared and ultraviolet radiation, thermal cooling of the dust, collisional energy exchange between dust and gas, and a simple network for carbon chemistry. Based on these heating, cooling and chemical rates, DESPOTIC can calculate clouds' equilibrium gas and dust temperatures, equilibrium carbon chemical state and time-dependent thermal and chemical evolution. The software is intended to allow rapid and interactive calculation of clouds' characteristic temperatures, identification of their dominant heating and cooling mechanisms and prediction of their observable spectra across a wide range of interstellar environments. DESPOTIC is implemented as a PYTHON package, and is released under the GNU General Public License.

  10. New Ultraviolet Extinction Curves for Interstellar Dust in M31

    NASA Astrophysics Data System (ADS)

    Clayton, Geoffrey C.; Gordon, Karl D.; Bianchi, Luciana C.; Massa, Derck L.; Fitzpatrick, Edward L.; Bohlin, R. C.; Wolff, Michael J.

    2015-12-01

    New low-resolution UV spectra of a sample of reddened OB stars in M31 were obtained with the Hubble Space Telescope/STIS to study the wavelength dependence of interstellar extinction and the nature of the underlying dust grain populations. Extinction curves were constructed for four reddened sightlines in M31 paired with closely matching stellar atmosphere models. The new curves have a much higher signal-to-noise ratio than previous studies. Direct measurements of N(H i) were made using the Lyα absorption lines enabling gas-to-dust ratios to be calculated. The sightlines have a range in galactocentric distance of 5-14 kpc and represent dust from regions of different metallicities and gas-to-dust ratios. The metallicities sampled range from solar to 1.5 solar. The measured curves show similarity to those seen in the Milky Way and the Large Magellanic Cloud. The Maximum Entropy Method was used to investigate the dust composition and size distribution for the sightlines observed in this program, finding that the extinction curves can be produced with the available carbon and silicon abundances if the metallicity is super-solar. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained by the Space Telescope Science Institute, and from the data archive at STScI. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  11. Turbulent mixing layers in the interstellar medium of galaxies

    NASA Technical Reports Server (NTRS)

    Slavin, J. D.; Shull, J. M.; Begelman, M. C.

    1993-01-01

    We propose that turbulent mixing layers are common in the interstellar medium (ISM). Injection of kinetic energy into the ISM by supernovae and stellar winds, in combination with density and temperature inhomogeneities, results in shear flows. Such flows will become turbulent due to the high Reynolds number (low viscosity) of the ISM plasma. These turbulent boundary layers will be particularly interesting where the shear flow occurs at boundaries of hot (approximately 10(exp 6) K) and cold or warm (10(exp 2) - 10(exp 4) K) gas. Mixing will occur in such layers producing intermediate-temperature gas at T is approximately equal to 10(exp 5.0) - 10(exp 5.5) that radiates strongly in the optical, ultraviolet, and EUV. We have modeled these layers under the assumptions of rapid mixing down to the atomic level and steady flow. By including the effects of non-equilibrium ionization and self-photoionization of the gas as it cools after mixing, we predict the intensities of numerous optical, infrared, and ultraviolet emission lines, as well as absorption column densities of C 4, N 5, Si 4, and O 6.

  12. Angular motion of a PAH molecule in interstellar environment

    NASA Technical Reports Server (NTRS)

    Rouan, D.; Leger, Alain; Omont, A.; Giard, Martin

    1989-01-01

    Polycyclic aromatic hydrocarbon (PAH) molecules have recently been proposed as an important and hitherto undetected component of the Interstellar Medium (ISM). The theory was based on an explanation of the Unidentified IR Emission Bands by Leger et al. It has already led to a verified prediction on extended galactic and extragalactic emissions measured by IRAS, or by a recent balloon borne experiment. The physics that rules the motion of such molecules in the ISM was studied, taking into account their coupling with the ambient gas, the radiation field (absorption and emission) and the static magnetic field. This is important for many implications of the PAH theory such as the radio emission by these molecules or the expected polarization of their IR emission. A reflection nebulae is considered where the situation is rather well known. Every day life of a mean PAH molecule in such a region is as follows: every 3 hrs a UV photon is absorbed heating the molecule to a thousand degs; the temperature decay due to cooling by IR emission follows then within a few seconds. A collision with a molecule of gas occurs typically once a week, while an H atom is ejected or captured at the same rate. A typical cooling cycle after a heat impulse is given. The PAH molecules studied as representative of the family has typically 50 atoms, a radius of 4.5 A, is circular and has a molecular mass of M = 300; its permanent dipole moment is 3 Debye.

  13. The EUV background, the interstellar medium, and ROSAT

    NASA Astrophysics Data System (ADS)

    Walker, H. J.; Harris, A. W.; Sumner, T. J.; Brebner, G. C.; Barstow, M. A.; Willingale, R.

    An overview is presented of work done by the UK Interstellar Medium/Diffuse Emission Rosat Special Interest Group to survey the sky in the X-ray/EUV wavelength region, and to perform Guest Observer pointed observations. The emphasis is placed on the results obtained with the Wide Field Camera (WFC). Surveys in the X-ray region, such as that in the B band by McCammon et al. (1983), show that less diffuse soft X-ray/EUV emission is detected from near the galactic plane than is detected from near the Galactic poles. A general anticorrelation of soft X-ray/EUV background (SXRB) emission with N(H) is found, as well as residual emission in the Galactic plane. X-ray intensity variations do not show the large energy dependence predicted by photoelectric absorption. Consideration is given to a model proposed by Snowden et al. (1990), in which the hot gas displaced the cool HI gas in the local cavity and the variations in the SXRB intensity were due to variations in the extent of the emission volume.

  14. Atomic and Molecular Data for Interstellar Studies: A Status Report

    NASA Technical Reports Server (NTRS)

    Federman, Steven R.; Cardelli, Jason A.

    1996-01-01

    Most interstellar species have a large fraction of their electronic transitions at far ultraviolet wavelengths. Observations at these wavelengths reveal spectra rich in absorption lines seen against the continuum of a background source, such as a hot star in our Galaxy, a supernova in a nearby galaxy, or even a bright nucleus in an active galaxy. Most of the observations continue to be made with space-borne instruments, but recent work includes measurements of extragalactic material at large redshifts obtained at high resolution with large ground-based telescopes (e.g., the Keck Telescope). The combination of precise experimental oscillator strengths, large-scale computations, and astronomical spectra with high signal-to-noise ratios are yielding a set of self-consistent-values that span a range in strength in excess of 100 for more and more species. The large range is important for studies involving the different environments probed by the various background sources. This review highlights recent work on the atomic species. Si II, S I, and Fe II, and on the molecules, CO and C2.

  15. Probing the interstellar medium with pulsars on AU scales

    NASA Technical Reports Server (NTRS)

    Frail, Dale A.; Weisberg, Joel M.; Cordes, James M.; Mathers, Corey

    1994-01-01

    We present a new technique, multiepoch observations of 21 cm absorption against high-velocity pulsars, to probe the properties of the cold neutral hydrogen gas (H I) in the interstellar medium (ISM) at AU scales. In three epochs, over a 1.7 yr interval, we find evidence for significant opacity variations toward all of the pulsars in our sample. Small-scale structure in the ISM is detected on a range of scales from 5 AU to 100 AU, over a wide range of distances (50-2600 pc), opacities (tau(sub max) = 0.1 - 2.5) and directions (anticenter, interarm, high latitude, and local ISM). It appears that small-scale structure is a general property of the ISM and is not confined to special lines of sight. A significant fraction (10%-15%) of the cold H I gas is in this form. These opacity variations do not show any strong correlations with such parameters as transverse distance or integrated opacity, and there is no obvious relation between these structures and those seen in the ionized phase of the ISM.

  16. The Abundances of Solid N2 and Gaseous CO2 in Interstellar Dense Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.; Bernstein, Max P.; Allamandola, Louis J.; Goorvitch, David; Teixeira, Teresa C. V. S.; DeVincenzi, D. (Technical Monitor)

    2000-01-01

    We present 2338-2322 per centimeter (4.277-4.307 micrometer) infrared spectra of a number of N2-containing mixed molecular ices and demonstrate that the strength of the infrared "forbidden" band due to the N=N stretch near 2328 per centimeter (4.295 micrometer) is extremely sensitive to the composition of the ice. The strength of the 2328 per centimeter N2 fundamental is significantly enhanced relative to that of pure N2 ice when NH3, H2O, or CO2 are present, but is largely unaffected by the presence of CO, CH4 or O2. We use the laboratory data in coil junction with ISO data that probes several lines-of-sight through dense molecular clouds to place limits on the abundance of interstellar solid phase N2 and the composition of the ices. Deriving upper limits is complicated by the presence of overlapping absorptions due to CO2 gas in the clouds and, in some cases, to photospheric CO in the background star. These upper limits are just beginning to be low enough to constrain interstellar grain models and the composition of possible N2-bearing interstellar ices. We outline the search criteria that will need to be met if solid interstellar N2 is to be detected in the future. We also discuss some of the implications of the presence of warm CO2 gas along the lines-of-sight to embedded protostars and demonstrate that its presence may help resolve certain puzzles associated with the previously derived gas/solid CO2 ratios and the relative abundances of polar and nonpolar ices towards these objects. Finally, we briefly comment on the possible implications of these results for the interpretation of N2 detections on outer solar system bodies.

  17. New Methods for Studying Interstellar Continuum and Spectral Polarization

    NASA Astrophysics Data System (ADS)

    Messinger, David W.

    Polarization studies have been shown to provide information about the aligned component of interstellar dust particles. These particles are aligned with respect to the local magnetic field and as such, models of polarization observations provide morphological information in addition to the determination of grain characteristics. Continuum polarization in molecular clouds observed to have a change in the polarization position angle indicates a region with at least two distinct components in the line of sight. A slab model is developed using the Stokes parameters to separate the competing effects of these multiple components and investigate the properties of the ``clump'' within the larger cloud complex. This model is applied to two lines of sight in the Taurus Molecular Cloud toward HD 29647 and HD 283809. For this model, a third line of sight, toward HD 283812, is used to probe the ``standard'' properties of the larger cloud. It is shown that within these clumps, the average aligned grain size is larger than in the overall cloud complex. The degree of alignment toward HD 29647 is higher than toward HD 283809, but both ``clumps'' show a dramatic change in polarization position angle. It is hypothesized that this change in the local magnetic field direction is a remnant of, or reason for, the collapse of the material in the region of TMC-1. Spectropolarization provides further constraints on the aligned grain population in the line of sight compared when with spectroscopy studies. A model is developed to study these two datasets, absorption and polarization, simultaneously for the water-ice absorption feature at ~3.1 μm in particular. This model investigates the individual grain population properties through a multiple slab structure. The grain sizes, shapes, mantle thicknesses, compositions, and alignment characteristics are all parameters in the model. The water-ice mantle is modeled with a Lorentz oscillator model to simplify the process and remove any

  18. Probing the Local Bubble with Diffuse Interstellar Bands (DIBs)

    NASA Astrophysics Data System (ADS)

    van Loon, Jacco Th.; Farhang, A.; Javadi, A.; Bailey, M.; Khosroshahi, H. G.

    The Sun lies in the middle of an enormous cavity of a million degree gas, known as the Local Bubble. The Local Bubble is surrounded by a wall of denser neutral and ionized gas. The Local Bubble extends around 100 pc in the plane of Galaxy and hundreds of parsecs vertically, but absorption-line surveys of neutral sodium and singly-ionized calcium have revealed a highly irregular structure and the presence of neutral clouds within an otherwise tenuous and hot gas. We have undertaken an all-sky, European-Iranian survey of the Local Bubble in the absorption of a number of diffuse interstellar bands (DIBs) to offer a novel view of our neighbourhood. Our dedicated campaigns with ESO's New Technology Telescope and the ING's Isaac Newton Telescope comprise high signal-to-noise, medium-resolution spectra, concentrating on the 5780 and 5797 Å bands which trace ionized/irradiated and neutral/shielded environments, respectively; their carriers are unknown but likely to be large carbonaceous molecules. With about 660 sightlines towards early-type stars distributed over distances up to about 200 pc, our data allow us to reconstruct the first ever 3D DIB map of the Local Bubble, which we present here. While we confirm our expectations that the 5780 Å DIB is relatively strong compared to the 5797 Å DIB in hot/irradiated regions such as which prevail within the Local Bubble and its walls, and the opposite is true for cooler/shielded regions beyond the confines of the Local Bubble, we unexpectedly also detect DIB cloudlets inside of the Local Bubble. These results reveal new insight into the structure of the Local Bubble, as well as helping constrain our understanding of the carriers of the DIBs.

  19. Analysis of "Midnight" Tracks in the Stardust Interstellar Dust Collector: Possible Discovery of a Contemporary Interstellar Dust Grain

    NASA Technical Reports Server (NTRS)

    Westphal, A. J.; Allen, C.; Bajit, S.; Bastien, R.; Bechtel, H.; Bleuet, P.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.; Butterworth, A. L.; Cloetens, P.; Cody, G.; Ferrior, T.; Floss, C.; Flynn, G. J.; Frank, D.; Gainsforth, Z.; Grun, E.; Hoppe, P.; Hudson, B.; Kearsley, A.; Lai, B.

    2010-01-01

    In January 2006, the Stardust sample return capsule returned to Earth bearing the first solid samples from a primitive solar system body, Comet 81P/Wild2, and a collector dedicated to the capture and return of contemporary interstellar dust. Both collectors were approximately 0.1m(exp 2) in area and were composed of aerogel tiles (85% of the collecting area) and aluminum foils. The Stardust Interstellar Dust Collector (SIDC) was exposed to the interstellar dust stream for a total exposure factor of 20 m(exp 2) day. The Stardust Interstellar Preliminary Examination (ISPE) is a three-year effort to characterize the collection using nondestructive techniques.

  20. Solar lens mission concept for interstellar exploration

    NASA Astrophysics Data System (ADS)

    Brashears, Travis; Lubin, Philip; Turyshev, Slava; Shao, Michael; Zhang, Qicheng

    2015-09-01

    The long standing approach to space travel has been to incorporate massive on-board electronics, probes and propellants to achieve space exploration. This approach has led to many great achievements in science, but will never help to explore the interstellar medium. Fortunately, a paradigm shift is upon us in how a spacecraft is constructed and propelled. This paper describes a mission concept to get to our Sun's Gravity Lens at 550AU in less than 10 years. It will be done by using DE-STAR, a scalable solar-powered phased-array laser in Earth Orbit, as a directed energy photon drive of low-mass wafersats. [1] [2] [3] [4] [5] With recent technologies a complete mission can be placed on a wafer including, power from an embedded radio nuclear thermal generator (RTG), PV, laser communications, imaging, photon thrusters for attitude control and other sensors. As one example, a futuristic 200 MW laser array consisting of 1 - 10 kw meter scale sub elements with a 100m baseline can propel a 10 gram wafer scale spacecraft with a 3m laser sail to 60AU/Year. Directed energy propulsion of low-mass spacecraft gives us an opportunity to capture images of Alpha Centauri and its planets, detailed imaging of the cosmic microwave background, set up interstellar communications by using gravity lenses around nearby stars to boost signals from interstellar probes, and much more. This system offers a very large range of missions allowing hundreds of wafer scale payload launches per day to reach this cosmological data reservoir. Directed Energy Propulsion is the only current technology that can provide a near-term path to utilize our Sun's Gravity Lens.