WorldWideScience

Sample records for surrounding interstellar gas

  1. The Interstellar Cloud Surrounding the Solar System

    Science.gov (United States)

    Frisch, P. C.

    Ultraviolet spectral data of nearby stars indicate that the cloud surrounding the solar system has an average neutral density n(HI)~0.1 cm-3, temperature ~6800 K, and turbulence ~1.7 km/s. Comparisons between the anomalous cosmic ray data and ultraviolet data suggest that the electron density is in the range n(e-)~0.22 to 0.44 cm-3. This cloud is flowing past the Sun from a position centered in the Norma-Lupis region. The cloud properties are consistent with interstellar gas which originated as material evaporated from the surfaces of embedded clouds in the Scorpius-Centaurus Association, and which was then displaced towards the Sun by a supernova event about 4 Myrs ago. The Sun and surrounding cloud velocities are nearly perpendicular in space, and this cloud is sweeping past the Sun. The morphology of this cloud can be reconstructed by assuming that the cloud moves in a direction parallel to the surface normal. With this assumption, the Sun entered the surrounding cloud 2000 to 8000 years ago, and is now about 0.05 to 0.16 pc from the cloud surface. Prior to its recent entry into the surrounding cloud complex, the Sun was embedded in a region of space with average density lower than 0.0002 cm-3. If a denser cloud velocity component seen towards alpha Cen A,B is real, it will encounter the solar system within 50,000 yr. The nearby magnetic field seen upwind has a spatial orientation that is parallel to the cloud surface. The nearby star Sirius is viewed through the wake of the solar system, but this direction also samples the hypothetical cloud interface. Comparisons of anomalous cosmic ray and interstellar absorption line data suggest that trace elements in the surrounding cloud are in ionization equilibrium. Data towards nearby white dwarfs indicate partial helium ionization, N(N(HI)(/N(HeI)>~13.7, which is consistent with pickup ion data within the solar system if less than 40% hydrogen ionization occurs in the heliopause region. However, the white dwarfs may

  2. The interstellar cloud surrounding the Sun: a new perspective

    Science.gov (United States)

    Gry, Cécile; Jenkins, Edward B.

    2014-07-01

    Aims: We offer a new, simpler picture of the local interstellar medium, made of a single continuous cloud enveloping the Sun. This new outlook enables the description of a diffuse cloud from within and brings to light some unexpected properties. Methods: We re-examine the kinematics and abundances of the local interstellar gas, as revealed by the published results for the ultraviolet absorption lines of Mg II, Fe II, and H I. Results: In contrast to previous representations, our new picture of the local interstellar medium consists of a single, monolithic cloud that surrounds the Sun in all directions and accounts for most of the matter present in the first 50 parsecs around the Sun. The cloud fills the space around us out to about 9 pc in most directions, although its boundary is very irregular with possibly a few extensions up to 20 pc. The cloud 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 a squashed balloon. Average H I volume densities inside the cloud vary between 0.03 and 0.1 cm-3 over different directions. Metals appear to be significantly depleted onto grains, and there is a steady increase in depletion 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. Secondary absorption components are detected in 60% of the sight lines. Almost all of them appear to be interior to the volume occupied by the main cloud. Half of the sight lines exhibit a secondary component moving at about -7.2 km s-1 with respect to the main component, which may be the signature of a shock propagating toward the cloud's interior.

  3. The interstellar cloud surrounding the Sun -- a new perspective

    CERN Document Server

    Gry, Cecile

    2014-01-01

    Aims: We offer a new, simpler picture of the local interstellar medium around the Sun (LISM) made of a single continuous cloud enveloping the Sun. This new outlook enables the description of a diffuse cloud from within and brings to light some unexpected properties. Methods: We re-examine the kinematics and abundances of the local interstellar medium, as revealed by the published results for the ultraviolet absorption lines of MgII, FeII and HI. Results: In contrast to previous representations, our new picture of the LISM consists of a single, monolithic cloud that surrounds the Sun in all directions and accounts for most of the matter present in the first 50 parsecs around the Sun. The cloud fills the space around us out to about 9 pc in most directions, although its boundary is very irregular with possibly a few extensions up to 20 pc. The cloud 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 per...

  4. Ionization in nearby interstellar gas

    Science.gov (United States)

    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.

  5. Ionization in nearby interstellar gas

    Energy Technology Data Exchange (ETDEWEB)

    Frisch, P.C.; Welty, D.E.; York, D.G.; Fowler, J.R. (Chicago Univ., IL (USA) New Mexico State Univ., Las Cruces (USA))

    1990-07-01

    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. 85 refs.

  6. Sh2-205: I. The surrounding interstellar medium

    CERN Document Server

    Romero, G A

    2008-01-01

    We present a study of the HII region Sh2-205 and its environs, based on data obtained from the CGPS, 12CO observations, and MSX data. We find that Sh2-205 can be separated in three independent optical structures: SH149.25--0.0, SH 148.83-0.67, and LBN 148.11-0.45. The derived spectral indices show the thermal nature of SH 148.83--0.67 and LBN 148.11--0.45. The morphology of SH 148.83--0.67, both in the optical and radio data, along with the energetic requ irements indicate that this feature is an interstellar bubble powered by the UV photons of HD 24431 (O9 III). LBN 148.11--0.45 has the morphology of a classic al HII region and their ionizing sources remain uncertain. Dust and molecular gas are found related to LBN 148.11-0.45.Particularly, a photodissociation region is detected at the interface between the ionized and molecular regions. If the proposed exciting star HD 24094 were an O8--O9 type star, as suggested by its near-infrared colors, its UV photon flux would be enough to explain the ionization of th...

  7. Interstellar gas in the Gum Nebula

    Science.gov (United States)

    Wallerstein, G.; Jenkins, E. B.; Silk, J.

    1980-01-01

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

  8. The interplay between the young stellar super cluster Westerlund 1, and the surrounding interstellar medium

    Directory of Open Access Journals (Sweden)

    Carrasco L.

    2012-02-01

    Full Text Available We analyze the multi-band (CO, HI and Spitzer maps, large-scale (150 pc gaseous structure around Westerlund 1, the most massive known superstar cluster in the Milky Way, with the intention of exploring the effect of feedback from massive stars in this young (age < 5 Myr cluster on the surrounding interstellar medium. We find no traces of the parental molecular cloud in the immediate vicinity of the cluster, instead this volume is partially filled by HI gas. On the other hand, there are two giant molecular clouds, both moving away from the cluster at 5–10 km s−1, at distances of around 50–150 pc. There are several ultra-compact HII regions associated with these giant molecular clouds. All these events suggest that the cluster has played an important role in re-structuring the ISM, in the form of ejecting the molecular gas, as well as triggering secondary star formation.

  9. Turbulence and the ionization of interstellar gas

    Science.gov (United States)

    Hill, Alex S.

    2015-08-01

    Turbulence is widely observed in the ionized gas in the interstellar media of star-forming galaxies. Observations in the Milky Way indicate emission from that the warm ionized medium -- ionized gas far from massive stars, the most likely source of the ionization -- has a lognormal intensity distribution. This and other measurements indicate that the gas is well-described as a transonic turbulent fluid. Such a fluid can be produced by feedback from supernovae in the Galaxy. Understanding of this turbulence has also led to a natural explanation for a long-standing puzzle: how do ionizing photons travel through the largely-neutral interstellar medium and produce the ionization? In the turbulent gas, low-density pathways allow ionizing photons to propagate for kiloparsecs, with implications for radiative energy transport in star-forming galaxies.

  10. Interstellar Gas and a Dark Disk

    Science.gov (United States)

    Kramer, Eric David; Randall, Lisa

    2016-10-01

    We introduce a potentially powerful method for constraining or discovering a thin dark matter disk in the Milky Way. The method relies on the relationship between the midplane densities and scale heights of interstellar gas being determined by the gravitational potential, which is sensitive to the presence of a dark disk. We show how to use the interstellar gas parameters to set a bound on a dark disk and discuss the constraints suggested by the current data. However, current measurements for these parameters are discordant, with the uncertainty in the constraint being dominated by the molecular hydrogen midplane density measurement, as well as by the atomic hydrogen velocity dispersion measurement. Magnetic fields and cosmic ray pressure, which are expected to play a role, are uncertain as well. The current models and data are inadequate to determine the disk's existence, but taken at face value, may favor its existence depending on the gas parameters used.

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

    Science.gov (United States)

    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.

  12. Properties of interstellar wind leading to shape morphology of the dust surrounding HD 61005

    Science.gov (United States)

    Pástor, P.

    2017-08-01

    Aims: A structure formed by dust particles ejected from the debris ring around HD 61005 is observed in the scattered light. The main aim here is to constrain interstellar wind parameters that lead to shape morphology in the vicinity of HD 61005 using currently available observational data for the debris ring. Methods: Equation of motion of 2 × 105 dust particles ejected from the debris ring under the action of the electromagnetic radiation, stellar wind, and interstellar wind is solved. A two-dimensional (2D) grid is placed in a given direction for accumulation of the light scattered on the dust particles in order to determine the shape morphology. The interaction of the interstellar wind and the stellar wind is considered. Results: Groups of unknown properties of the interstellar wind that create the observed morphology are determined. A relation between number densities of gas components in the interstellar wind and its relative velocity is found. Variations of the shape morphology caused by the interaction with the interstellar clouds of various temperatures are studied. When the interstellar wind velocity is tilted from debris ring axis a simple relation between the properties of the interstellar wind and an angle between the line of sight and the interstellar wind velocity exists. Dust particles that are most significantly influenced by stellar radiation move on the boundary of observed structure. Conclusions: Observed structure at HD 61005 can be explained as a result of dust particles moving under the action of the interstellar wind. Required number densities or velocities of the interstellar wind are much higher than that of the interstellar wind entering the solar system.

  13. Two-component model of the interaction of an interstellar cloud with surrounding hot plasma

    OpenAIRE

    Provornikova, E. A.; Izmodenov, V. V.; Lallement, R.

    2011-01-01

    We present a two-component gasdynamic model of an interstellar cloud embedded in a hot plasma. It is assumed that the cloud consists of atomic hydrogen gas, interstellar plasma is quasineutral. Hydrogen atoms and plasma protons interact through a charge exchange process. Magnetic felds and radiative processes are ignored in the model. The influence of heat conduction within plasma on the interaction between a cloud and plasma is studied. We consider the extreme case and assume that hot plasma...

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

    CERN Document Server

    Gry, Cecile

    2014-01-01

    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 cm-3 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...

  15. Using IBEX data to constrain the heliosphere's large-scale structure: interstellar neutral gas and the Warm Breeze

    Science.gov (United States)

    Bzowski, Maciej; McComas, David; Galli, Andre; Kucharek, Harald; Wurz, Peter; Sokol, Justyna M.; Schwadron, Nathan; Heirtzler, David M.; Kubiak, M. Marzena A.; Möbius, Eberhard; Fuselier, Stephen; Swaczyna, Paweł; Leonard, Trevor; Park, Jeewoo

    2016-07-01

    The large-scale structure of the heliosphere is governed by the interaction of the partly ionized, magnetized interstellar gas and the magnetized, fully ionized solar wind, structured in heliolatitude. Determining factors of this interaction are the density and flow velocity of interstellar gas relative to the Sun, the Mach number of this flow and the strength and inclination of the interstellar magnetic field to the flow vector at the interstellar side, and the magnitude of dynamic pressure of solar wind and the strength of its embedded magnetic field at the solar side. As a result of charge exchange interactions operating in the boundary region between the heliosphere and interstellar matter, a new population of neutral atoms is created, in addition to the population of unperturbed interstellar neutral gas. Both of these populations penetrate deep inside the heliosphere, where they can be sampled by the first space probe dedicated to observations of the heliosphere and its immediate surroundings by means of neutral atoms: the Interstellar Boundary Explorer (IBEX). Due to distortion of the heliosphere from axial symmetry, the secondary population of interstellar neutrals, created via charge exchange between the plasma flowing past the heliopause and the unperturbed pristine neutral interstellar gas, appears to be coming from a different direction than the unperturbed interstellar neutral flow. These two directions should be coplanar with the plane defined by the local interstellar magnetic field and the flow direction of the unperturbed gas. IBEX provides an unprecedented opportunity to study and interpret these relations. The IBEX science team have recently accomplished important milestones in researching the primary and secondary populations of interstellar gas and their relation to the local interstellar magnetic fields. First, the temperature and velocity vector of the inflowing interstellar neutral gas has been determined with unprecedented robustness based

  16. The Ionization of Nearby Interstellar Gas

    CERN Document Server

    Slavin, J D; Slavin, Jonathan D.; Frisch, Priscilla C.

    2002-01-01

    We present new calculations of the photoionization of interstellar matter within ~5 pc of the Sun (which we refer to as the Local Cloud Complex or LCC) by directly observed radiation sources including nearby hot stars and the diffuse emission of the Soft X-ray Background (SXRB). In addition, we model the important, unobserved EUV emission both from the hot gas responsible for the SXRB and from a possible evaporative boundary between the LCC and the hot gas. We carry out radiative transfer calculations and show that these radiation sources can provide the ionization and heating of the cloud required to match a variety of observations. The ionization predicted in our models shows good agreement with pickup ion results, interstellar absorption line data towards epsilon CMa, and EUV opacity measurements of nearby white dwarf stars. Including the radiation from the conductive boundary improves agreement with data on the temperature and electron density in the cloud. The presence of dust in the cloud, or at least d...

  17. Two-component model of the interaction of an interstellar cloud with surrounding hot plasma

    CERN Document Server

    Provornikova, E A; Lallement, R

    2011-01-01

    We present a two-component gasdynamic model of an interstellar cloud embedded in a hot plasma. It is assumed that the cloud consists of atomic hydrogen gas, interstellar plasma is quasineutral. Hydrogen atoms and plasma protons interact through a charge exchange process. Magnetic felds and radiative processes are ignored in the model. The influence of heat conduction within plasma on the interaction between a cloud and plasma is studied. We consider the extreme case and assume that hot plasma electrons instantly heat the plasma in the interaction region and that plasma flow can be described as isothermal. Using the two-component model of the interaction of cold neutral cloud and hot plasma, we estimate the lifetime of interstellar clouds. We focus on the clouds typical for the cluster of local interstellar clouds embedded in the hot Local Bubble and give an estimate of the lifetime of the Local interstellar cloud where the Sun currently travels. The charge transfer between highly charged plasma ions and neutr...

  18. Radio observations of Supernova Remnants and the surrounding molecular gas

    CERN Document Server

    Dubner, G

    2011-01-01

    Supernova Remnants (SNRs) are believed to be the main source of Galactic cosmic rays (CR). The strong SNR shocks provide ideal acceleration sites for particles of at least 10^14 eV/nucleon. Radio continuum studies of SNRs carried out with good sensitivity and high angular resolution convey information about three main aspects of the SNRs: morphology, polarization and spectrum. Based on this information it is possible to localize sites of higher compression and particle acceleration as well as the orientation and degree of order of the magnetic fields, and in some cases even its intensity. All this information, when complemented with the study of the distribution and kinematics of the surrounding interstellar gas, results in a very useful dataset to investigate the role of SNRs as cosmic ray accelerators. In this presentation, I analyze the radio observations of SNRs and surrounding molecular clouds, showing the contribution of these studies to the understanding of the role of SNRs as factories of CRs.

  19. Star Formation in Turbulent Interstellar Gas

    CERN Document Server

    Klessen, R S

    2003-01-01

    Understanding the star formation process is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay between gravity and magnetostatic support, modulated by ambipolar diffusion. Recently, however, both observational and numerical work has begun to suggest that supersonic interstellar turbulence rather than magnetic fields controls star formation. Supersonic turbulence can provide support against gravitational collapse on global scales, while at the same time it produces localized density enhancements that allow for collapse on small scales. The efficiency and timescale of stellar birth in Galactic molecular clouds strongly depend on the properties of the interstellar turbulent velocity field, with slow, inefficient, isolated star formation being a hallmark of turbulent support, and fast, efficient, clustered star formation occurring in its absence.

  20. The Interstellar Boundary Explorer (IBEX): Tracing the Interaction between the Heliosphere and Surrounding Interstellar Material with Energetic Neutral Atoms

    CERN Document Server

    Frisch, Priscilla C

    2010-01-01

    The Interstellar Boundary Explorer (IBEX) mission is exploring the frontiers of the heliosphere where energetic neutral atoms (ENAs) are formed from charge exchange between interstellar neutral hydrogen atoms and solar wind ions and pickup ions. The geography of this frontier is dominated by an unexpected nearly complete arc of ENA emission, now known as the IBEX 'Ribbon'. While there is no consensus agreement on the Ribbon formation mechanism, it seems certain this feature is seen for sightlines that are perpendicular to the interstellar magnetic field as it drapes over the heliosphere. At the lowest energies, IBEX also measures the flow of interstellar H, He, and O atoms through the inner heliosphere. The asymmetric helium profile suggests that a secondary flow of helium is present, such as would be expected if some fraction of helium is lost through charge exchange in the heliosheath regions. The detailed spectra characterized by the ENAs provide time-tagged samples of the energy distributions of the under...

  1. Hydrostatic equilibrium of interstellar gas and magnetic fields in the 6 kpc region of the galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fuchs, B.; Spreckels, H.; Thielheim, K.O.

    1980-01-01

    A two-component gas model is applied to the vertical hydrogen distribution in the 6 kpc region of the Galaxy. Galactic gravitational field and interstellar magnetic field determination of the dynamics of interstellar gas is reviewed.

  2. Observing the Interstellar Neutral He Gas Flow with a Variable IBEX Pointing Strategy

    Science.gov (United States)

    Leonard, T.; Moebius, E.; Bzowski, M.; Fuselier, S. A.; Heirtzler, D.; Kubiak, M. A.; Kucharek, H.; Lee, M. A.; McComas, D. J.; Schwadron, N.; Wurz, P.

    2015-12-01

    The Interstellar Neutral (ISN) gas flow can be observed at Earth's orbit due to the motion of the solar system relative to the surrounding interstellar gas. Since He is minimally influenced by ionization and charge exchange, the ISN He flow provides a sample of the pristine interstellar environment. The Interstellar Boundary Explorer (IBEX) has observed the ISN gas flow over the past 7 years from a highly elliptical orbit around the Earth. IBEX is a Sun-pointing spinning spacecraft with energetic neutral atom (ENA) detectors observing perpendicular to the spacecraft spin axis. Due to the Earth's orbital motion around the Sun, it is necessary for IBEX to perform spin axis pointing maneuvers every few days to maintain a sunward pointed spin axis. The IBEX operations team has successfully pointed the spin axis in a variety of latitude orientations during the mission, including in the ecliptic during the 2012 and 2013 seasons, about 5 degrees below the ecliptic during the 2014 season, and recently about 5 degrees above the ecliptic during the 2015 season, as well as optimizing observations with the spin axis pointed along the Earth-Sun line. These observations include a growing number of measurements near the perihelion of the interstellar atom trajectories, which allow for an improved determination of the ISN He bulk flow longitude at Earth orbit. Combining these bulk flow measurements with an analytical model (Lee et al. 2012 ApJS, 198, 10) based upon orbital mechanics improves the knowledge of the narrow ISN parameter tube, obtained with IBEX, which couples the interstellar inflow longitude, latitude, speed, and temperature.

  3. Tholins - Organic chemistry of interstellar grains and gas

    Science.gov (United States)

    Sagan, C.; Khare, B. N.

    1979-01-01

    The paper discusses tholins, defined as complex organic solids formed by the interaction of energy - for example, UV light or spark discharge - with various mixtures of cosmically abundant gases - CH4, C2H6, NH3, H2O, HCHO, and H2S. It is suggested that tholins occur in the interstellar medium and are responsible for some of the properties of the interstellar grains and gas. Additional occurrences of tholins are considered. Tholins have been produced experimentally; 50 or so pyrolytic fragments of the brown, sometimes sticky substances have been identified by gas chromatography-mass spectrometry, and the incidence of these fragments in tholins produced by different procedures is reported.

  4. A Survey of Interstellar Gas Inside the 3 KPC Arm

    Science.gov (United States)

    Massa, Derck L.

    We are requesting 5 US1 shifts to obtain high dispersion spectra Of B stars in the direction of the 3 kpc arm. The interstellar absorption along these lines of sight will be compared to models for the absorbing gas in order to determine whether additional absorption is present inside the 3 kpc arm. This information will help to distinguish between the two competing theories for the formation of the arm.

  5. Evidence for the Heating of Atomic Interstellar Gas by PAHs

    CERN Document Server

    Helou, G; Hollenbach, D J; Dale, D A; Contursi, A; Helou, George; Malhotra, Sangeeta; Hollenbach, David J.; Dale, Daniel A.; Contursi, Alessandra

    2001-01-01

    We report a strong correlation between the [CII] 158 micron cooling line and the mid-infrared flux in the 5-10 micron range in a wide variety of star-forming galaxies. The mid-infrared flux is dominated by Aromatic Feature Emission (AFE), which is thought to arise from large polycyclic aromatic hydrocarbon molecules or `PAHs' and generally associated with the smallest interstellar grains. The [CII] line is the dominant gas coolant in most regions of atomic interstellar gas, and therefore reflects the heating input to the gas. The ratio of these two quantities, [CII]/AFE, remains nearly constant with the ratio of the IRAS 60 micron band flux to the 100 micron band flux, R(60/100). This is in contrast to the drop in the [CII]/FIR ratio with increasing R(60/100), which signal higher dust temperatures and more intense radiation fields. We interpret the stable [CII]/AFE ratio as evidence that gas heating is dominated by the PAHs or small grains which are also AFE carriers over a wide range of conditions. The trend...

  6. Variations between Dust and Gas in the Diffuse Interstellar Medium

    CERN Document Server

    Reach, William T; Bernard, Jean-Philippe

    2015-01-01

    Using the Planck far-infrared and Arecibo GALFA 21-cm line surveys, we identified a set of isolated interstellar clouds (approximately degree-sized on the sky and comprising 100 solar masses) and assessed the ratio of gas mass to dust mass. Significant variations of the gas-to-dust ratio are found both from cloud to cloud and within regions of individual clouds; within the clouds, the atomic gas per unit dust decreases by more than a factor of 3 compared to the standard gas-to-dust ratio. Three hypotheses are considered. First, the apparently low gas-to-dust ratio could be due to molecular gas. Comparing to Planck CO maps, the brightest clouds have a H2/CO ratio comparable to galactic plane clouds, but a strong lower limit is placed on the ratio for other clouds, such that the required amount of molecular gas is far higher than would be expected based on the CO upper limits. Second, we consider self-absorbed 21-cm lines and find the optical depth must be approximately 3, significantly higher than found from s...

  7. A dirty window diffuse and translucent molecular gas in the interstellar medium

    CERN Document Server

    Magnani, Loris

    2017-01-01

    This book provides an introduction to the physics of interstellar gas in the Galaxy. It deals with the diffuse interstellar medium which supplies a complex environment for exploring the neutral gas content of a galaxy like the Milky Way and the techniques necessary for studying this non-stellar component. After an initial exposition of the phases of the interstellar medium and the role of gas in a spiral galaxy, the authors discuss the transition from atomic to molecular gas. They then consider basic radiative transfer and molecular spectroscopy with particular emphasis on the molecules useful for studying low-density molecular gas. Observational techniques for investigating the gas and the dust component of the diffuse interstellar medium throughout the electromagnetic spectrum are explored emphasizing results from the recent Herschel and Planck missions. A brief exposition on dust in the diffuse interstellar medium is followed by a discussion of molecular clouds in general and high-latitude molecular clouds...

  8. COS-B gamma-ray sources and interstellar gas

    Science.gov (United States)

    Pollock, A. M. T.; Bennett, K.; Bignami, G. F.; Bloemen, J. B. G. M.; Buccheri, R.; Caraveo, P. A.; Hermsen, W.; Kanbach, G.; Lebrun, F.; Mayer-Hasselwander, H. A.

    1985-01-01

    Of the gamma-radiation observed above 100 MeV only a few percent is due to the catalogued sources which are viewed against intense background mission from the Galactic plane. There has been considerable recent success in modelling the Galactic plane emission as the interactions of cosmic rays with atomic and molecular interstellar gas; Bloemen, et al., demonstrate that large angular scale features of the observations are well reproduced in this way. By extending the analysis to small angular scales, which of the eCG sources might be due to conventional levels of cosmic rays within clumps of gas are shown and which cannot be so explained. With the use of a more sophisticated model the results presented improve and extend those of an earlier report. So far only the data above 300 MeV is used where the instrument's angular resolution is at its best.

  9. Observations of interstellar helium with a gas absorption cell - Limits on the bulk velocity of the interstellar medium

    Science.gov (United States)

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

    1976-01-01

    Results are reported for observations of solar 584-A flux resonantly scattered by the 1s(2)-1s2p transition of neutral interstellar helium. A photometer equipped with a helium gas-absorption cell and flown aboard a sounding rocket to a peak altitude of 185 km was employed to observe the sky in Perseus. The data reduction procedure is described, including subtraction of the terrestrial atmospheric background, calculation of the solar flux, and reduction of the number density of scatters to a function of phase-space parameters of the local interstellar medium. The ratio of 584-A fluxes observed with the gas cell full and empty is computed and compared with numerical models of the interstellar-helium flow through the solar system. The results show that the bulk speed of the distant interstellar medium with respect to the sun is unlikely to be less than 10 to 15 km/s, at the 2-sigma level. Since this value is inconsistent with results obtained from Lyman-alpha observations, it is suggested that either the total ionization rate for helium is variable or present models of the behavior of the local interstellar medium need further refinement.

  10. Connecting The Interstellar Gas And Dust Properties Of Distant Galaxies

    Science.gov (United States)

    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

  11. Hot Gas in the Diffuse Interstellar Medium: The Soft X-ray Background

    Science.gov (United States)

    Sanders, Wilton

    1996-05-01

    The immediate solar neighborhood, the nearest 100 pc or so, is filled with hot low-density gas that has a substantial thermal pressure and is a dominant factor in the energy budget of the local interstellar medium. This gas produces substantial soft thermal soft x-ray emission below 1/4 keV, but is difficult to observe outside the soft x-ray band. Sounding rocket and satellite all-sky surveys in several broad x-ray energy bands provided the general picture of this million-degree gas surrounding the solar system, extending perhaps as far as 100 pc in the galactic plane and roughly twice that far out of the plane, and showing no signs of being absorbed by intervening neutral gas. ROSAT observations of "shadows" in the diffuse x-ray background have subsequently determined the spatial locations of this hot gas along a few lines of sight: closer than 65 pc in some low galactic latitude directions, farther than several hundred pc in some high galactic latitude directions. Other large regions of hot gas are seen nearby, within a few hundred parsecs, but the galactic filling factor of the hot gas is unknown. DXS obsrvations of the spectra of the diffuse soft x-ray background confirm that the emission in the plane is thermal, but the spectrum of the hot gas is not fit by standard thermal equilibrium models. The temperature distribution, emission measure, ionization distributions, and metallicity of the hot gas are unknown. This talk emphasizes a few of the things that are clear about the hot ISM, and discusses a few of the most puzzling problems in our understanding of the nature of the diffuse hot gas. New instruments with hig spectral resolution will make it possible to address some of these problems.

  12. Rotation of the Warm Molecular Gas Surrounding Ultracompact HII Regions

    CERN Document Server

    Klaassen, P D; Keto, E R; Zhang, Q

    2009-01-01

    We present molecular line and 1.4 mm continuum observations towards five massive star forming regions at arcsecond resolution using the Submillimeter Array (SMA). We find that the warm molecular gas surrounding each HII region (as traced by SO_2 and OCS) appears to be undergoing bulk rotation. From the molecular line emission and thermal component of the continuum emission, we independently derived gas masses for each region which are consistent with each other. From the free-free component of the continuum emission we estimate the minimum stellar mass required to power the HII region and find that this mass, when added to the derived gas mass, is a significant fraction of the dynamical mass for that region.

  13. Gas-Grain Models for Interstellar Anion Chemistry

    Science.gov (United States)

    Cordiner, M. A.; Charnely, S. B.

    2012-01-01

    Long-chain hydrocarbon anions C(sub n) H(-) (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n(sub H2) approx > / cubic cm). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C6H(-) anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O, and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment

  14. Gas-Grain Models for Interstellar Anion Chemistry

    Science.gov (United States)

    Cordiner, M. A.; Charnely, S. B.

    2012-01-01

    Long-chain hydrocarbon anions C(sub n) H(-) (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n(sub H2) approx > / cubic cm). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C6H(-) anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O, and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment

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

    NARCIS (Netherlands)

    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.

    2007-01-01

    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

  16. High-velocity interstellar gas in the lines of sight to the Wolf-Rayet stars HD 97152 and HD 96548

    Science.gov (United States)

    Nichols-Bohlin, Joy; Fesen, Robert A.

    1990-01-01

    The interstellar medium was studied in the direction to the WR stars HD 96548 and HD 97152, and the results are reported. New observational data on the UV spectra of several field stars near both these WR stars are presented. The high-velocity gas seen in the spectra of these stars suggests that the detected expanding interstellar gas structure consists of two OB cluster supershells. The presence of high-velocity absorption components in one of five field star spectra in the direction of the more isolated WR star HD 96548 suggests that this expanding gas does not originate from the optical ring nebula RCW 58 surrounding HD 96548, as previously believed, but instead indicates the detection of a previously unknown expanding interstellar shell in this line of sight.

  17. PAHs molecules and heating of the interstellar gas

    Science.gov (United States)

    Verstraete, Laurent; Leger, Alain; Dhendecourt, Louis B.; Dutuit, O.; Defourneau, D.

    1989-01-01

    Until now it has remained difficult to account for the rather high temperatures seen in many diffuse interstellar clouds. Various heating mechanisms have been considered: photoionization of minor species, ionization of H by cosmic rays, and photoelectric effect on small grains. Yet all these processes are either too weak or efficient under too restricting conditions to balance the observed cooling rates. A major heat source is thus still missing in the thermal balance of the diffuse gas. Using photoionization cross sections measured in the lab, it was shown that in order to balance the observed cooling rates in cold diffuse clouds (T approx. 80 K) the PAHs would have to contain 15 percent of the cosmic abundance of carbon. This value does not contradict the former estimation of 6 percent deduced from the IR emission bands since this latter is to be taken as a lower limit. Further, it was estimated that the contribution to the heating rate due to PAH's in a warm HI cloud, assuming the same PAH abundance as for a cold HI cloud, would represent a significant fraction of the value required to keep the medium in thermal balance. Thus, photoionization of PAHs might well be a major heat source for the cold and warm HI media.

  18. The influence of variations of elemental composition on the thermal properties of interstellar gas

    Science.gov (United States)

    Vasiliev, E. O.; Shchekinov, Yu. A.

    2016-10-01

    The mixing of metals and redistribution of the relative abundances of chemical elements in the interstellar medium often takes place on a timescale that exceeds the characteristic timescales for many other processes, such as ionization and the establishment of thermal equilibrium. Under these conditions, different regions of interstellar gas can have different thermal, chemical, and spectral properties. The paper considers the ionization kinetics and thermal regime of interstellar gas with variations in the relative elemental abundances. The thermal properties and observational (spectral) characteristics are most sensitive to variations of the relative abundance of carbon, oxygen, neon, and iron. The dynamic consequences of such variations are considered.

  19. Variations between Dust and Gas in the Diffuse Interstellar Medium. 2. Search for Cold Gas

    CERN Document Server

    Reach, William T; Bernard, Jean-Philippe

    2016-01-01

    The content of interstellar clouds, in particular the inventory of diffuse molecular gas, remains uncertain. We identified a sample of isolated clouds, approximately 100 solar masses in size, and used the dust content to estimate the total amount of gas. In Paper 1, the total inferred gas content was found significantly larger than that seen in 21-cm emission measurements of H~I. In this paper we test the hypothesis that the apparent excess `dark' gas is cold H~I, which would be evident in absorption but not in emission due to line saturation. The results show there is not enough 21-cm absorption toward the clouds to explain the total amount of `dark' gas.

  20. Variations between Dust and Gas in the Diffuse Interstellar Medium. II. Search for Cold Gas

    Science.gov (United States)

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

    2017-01-01

    The content of interstellar clouds, in particular the inventory of diffuse molecular gas, remains uncertain. We identified a sample of isolated clouds, approximately 100 M⊙ in size, and used the dust content to estimate the total amount of gas. In Paper I, the total inferred gas content was found significantly larger than that seen in 21 cm emission measurements of H i. In this paper we test the hypothesis that the apparent excess “dark” gas is cold H i, which would be evident in absorption but not in emission due to line saturation. The results show that there is not enough 21 cm absorption toward the clouds to explain the total amount of “dark” gas.

  1. Dense Ionized and Neutral Gas Surrounding Sgr A*

    CERN Document Server

    Shukla, Hemant; Scoville, N Z

    2004-01-01

    We present high resolution H41a hydrogen recombination line observations of the 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO Millimeter Array with an angular resolution of 7" x 3" and velocity resolution of 13 km/s. New observations of H31a, H35a, H41a, and H44a lines were obtained using the NRAO 12-m telescope, and their relative line strengths are interpreted in terms of various emission mechanisms. These are the most extensive and most sensitive observations of recombination line to date. Observations of HCO+ (1 - 0) transition at 89 GHz are also obtained simultaneously with a 40% improved angular resolution and 4-15 times improved sensitivity over previous observations, and the distribution and kinematics of the dense molecular gas in the circumnuclear disk (CND) are mapped and compared with those of the ionized gas. The line brightness ratios of the hydrogen recombination lines are consistent with purely spontaneous emission from 7000 K gas with n_e = 20,000 cm$^{-3}$ near LTE condition...

  2. Efficient simulations of gas-grain chemistry in interstellar clouds

    CERN Document Server

    Lipshtat, A; Lipshtat, Azi; Biham, Ofer

    2004-01-01

    Chemical reactions on dust grains are of crucial importance in interstellar chemistry because they produce molecular hydrogen and various organic molecules. Due to the submicron size of the grains and the low flux, the surface populations of reactive species are small and strongly fluctuate. Under these conditions rate equations fail and the master equation is needed for modeling these reactions. However, the number of equations in the master equation grows exponentially with the number of reactive species, severely limiting its feasibility. Here we present a method which dramatically reduces the number of equations, thus enabling the incorporation of the master equation in models of interstellar chemistry.

  3. Numerical simulations of compressively driven interstellar turbulence: I. Isothermal gas

    CERN Document Server

    Schmidt, Wolfram; Hupp, Markus; Kern, Sebastian; Niemeyer, Jens C

    2008-01-01

    We performed numerical simulations of supersonic isothermal turbulence driven by mostly compressive large-scale forcing, using both a static grid and adaptive mesh refinement with an effective resolution N=768^3. After a transient phase dominated by shocks, turbulence evolves into a steady state with an RMS Mach number about 2.5, in which cloud-like structures of over-dense gas are surrounded by highly rarefied gas. The index of the turbulence energy spectrum function beta = 2.0 in the shock-dominated phase. As the flow approaches statistical equilibrium, the spectrum flattens, with beta = 1.9. For the scaling exponent of the root mean square velocity fluctuation, we obtain gamma = 0.43 from the velocity structure functions of second order. These results are well within the range of observed scaling properties for the velocity dispersion in molecular clouds. Calculating structure functions of order p=1,...,5, we find for all scaling exponents significant deviations from the Kolmogorov-Burgers model proposed b...

  4. Studies of dust and gas in the interstellar medium of the Milky Way

    NARCIS (Netherlands)

    Salgado Cambiazo, Francisco Javier

    2015-01-01

    This thesis focus on the study of the Interstellar Medium (ISM) of the Milky Way and consists of two parts: in the first one we present a study of the dust properties in HII regions and their surrounding PDRs. We focus our studies on two compact HII regions: W3(A) and the Orion Nebula (Chapters 2 an

  5. A detailed investigation of proposed gas-phase syntheses of ammonia in dense interstellar clouds

    Science.gov (United States)

    Herbst, Eric; Defrees, D. J.; Mclean, A. D.

    1987-01-01

    The initial reactions of the Herbst and Klemperer (1973) and the Dalgarno (1974) schemes (I and II, respectively) for the gas-phase synthesis of ammonia in dense interstellar clouds were investigated. The rate of the slightly endothermic reaction between N(+) and H2 to yield NH(+) and H (scheme I) under interstellar conditions was reinvestigated under thermal and nonthermal conditions based on laboratory data. It was found that the relative importance of this reaction in synthesizing ammonia is determined by how the laboratory data at low temperature are interpreted. On the other hand, the exothermic reaction between N and H3(+) to form NH2(+) + H (scheme II) was calculated to possess significant activation energy and, therefore, to have a negligible rate coefficient under interstellar conditions. Consequently, this reaction cannot take place appreciably in interstellar clouds.

  6. Low-Mach-number turbulence in interstellar gas revealed by radio polarization gradients

    CERN Document Server

    Gaensler, Bryan M; Burkhart, Blakesley; Newton-McGee, Katherine J; Ekers, Ronald D; Lazarian, Alex; McClure-Griffiths, Naomi M; Robishaw, Timothy; Dickey, John M; Green, Anne J; 10.1038/nature10446

    2011-01-01

    The interstellar medium of the Milky Way is multi-phase, magnetized and turbulent. Turbulence in the interstellar medium produces a global cascade of random gas motions, spanning scales ranging from 100 parsecs to 1000 kilometres. Fundamental parameters of interstellar turbulence such as the sonic Mach number (the speed of sound) have been difficult to determine because observations have lacked the sensitivity and resolution to directly image the small-scale structure associated with turbulent motion. Observations of linear polarization and Faraday rotation in radio emission from the Milky Way have identified unusual polarized structures that often have no counterparts in the total radiation intensity or at other wavelengths, and whose physical significance has been unclear. Here we report that the gradient of the Stokes vector (Q,U), where Q and U are parameters describing the polarization state of radiation, provides an image of magnetized turbulence in diffuse ionized gas, manifested as a complex filamenta...

  7. Interstellar PAHs

    Science.gov (United States)

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

    2000-01-01

    Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in two closely related areas: observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at and the notion of abundant, gas phase, polycyclic aromatic hydrocarbons (PAHs) anywhere in the interstellar medium (ISM) considered impossible. Today the dust composition of the diffuse and dense ISM is reasonably well constrained and the spectroscopic case for interstellar PAHs, shockingly large molecules by early interstellar chemistry standards, is very strong.

  8. Dust as interstellar catalyst - II. How chemical desorption impacts the gas

    CERN Document Server

    Cazaux, S; Dulieu, F; Hocuk, S

    2015-01-01

    Context. Interstellar dust particles, which represent 1% of the total mass, are recognized to be very powerful interstellar catalysts in star-forming regions. The presence of dust can have a strong impact on the chemical composition of molecular clouds. While observations show that many species that formed onto dust grains populate the gas phase, the process that transforms solid state into gas phase remains unclear. Aims. The aim of this paper is to consider the chemical desorption process, i.e. the process that releases solid species into the gas phase, in astrochemical models. These models allow determining the chemical composition of star-forming environments with an accurate treatment of the solid-phase chemistry. Methods. In paper I we derived a formula based on experimental studies with which we quantified the efficiencies of the chemical desorption process. Here we extend these results to astrophysical conditions. Results. The simulations of astrophysical environments show that the abundances of gas-p...

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

    Science.gov (United States)

    Aller, Monique C.; Dwek, Eliahu; Kulkarni, Varsha P.; York, Donald G.; Welty, Daniel E.; Vladilo, Giovanni; Som, Debopam; Lackey, Kyle; Dwek, Eli; Beiranvand, Nassim; hide

    2016-01-01

    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. 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 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 silicate dust abundance, reddening, and gas metallicity, which will yield valuable insights into the history of star formation and chemical enrichment in galaxies.

  10. The nearby interstellar medium toward α Leo. UV observations and modeling of a warm cloud within hot gas

    Science.gov (United States)

    Gry, Cecile; Jenkins, Edward B.

    2017-02-01

    Aims: Our aim is to characterize the conditions in the nearest interstellar cloud. Methods: We analyze interstellar absorption features in the full UV spectrum of the nearby (d = 24 pc) B8 IVn star α Leo (Regulus). Observations were obtained with STIS at high resolution and high signal-to-noise ratio by the HST ASTRAL Treasury program. We derive column densities for many key atomic species and interpret their partial ionizations. Results: The gas in front of α Leo exhibits two absorption components. The main one is kinematically identified as the local interstellar cloud (LIC) that surrounds the Sun. The second component is shifted by +5.6 km s-1 relative to the main component, in agreement with results for other lines of sight in this region of the sky, and shares its ionization and physical conditions. The excitation of the C II fine-structure levels and the ratio of Mg I to Mg II reveal a temperature T = 6500 (+750, -600) K and electron density n(e) = 0.11 (+0.025, -0.03) cm-3. Our investigation of the ionization balance yields the ion fractions for 10 different atoms and indicates that about 1/3 of the hydrogen atoms are ionized. Metals are significantly depleted onto grains, with sulfur showing [S/H] -0.27. N(H I) = 1.9 (+0.9, -0.6) × 1018 cm-3, which indicates that this partly neutral gas occupies only 2 to 8 parsecs (about 13%) of the space toward the star, with the remaining volume being filled with a hot gas that emits soft X-rays. We do not detect any absorption features from the highly ionized species that could be produced in an interface between the warm medium and the surrounding hot gas, possibly because of non-equilibrium conditions or a particular magnetic field orientation that reduces thermal conduction. Finally, the radial velocity of the LIC agrees with that of the Local Leo Cold Cloud, indicating that they may be physically related.

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

    Science.gov (United States)

    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.

  12. Interstellar neutral flow characteristics, composition, and interaction with the heliosphere - neutral gas and pickup ion analysis from ongoing observations and perspectives for IMAP

    Science.gov (United States)

    Moebius, E.; Bzowski, M.; Drews, C.; Frisch, P. C.; Fuselier, S. A.; Galli, A.; Gloeckler, G.; Kubiak, M. A.; Kucharek, H.; Lee, M. A.; Leonard, T.; McComas, D. J.; Park, J.; Schwadron, N.; Swaczyna, P.; Sokol, J. M.; Wood, B. E.; Wurz, P.

    2015-12-01

    The Sun's motion relative to the surrounding interstellar medium leads to an interstellar neutral (ISN) wind through the heliosphere that is moderately depleted by ionization. This situation allows remote sensing of the ISN through resonant scattering of solar UV and in-situ sampling, first via pickup ions (PUI) and most recently with direct neutral atom imaging. PUI observations have revealed the gravitational focusing cone of interstellar He and Ne as well as the composition of high ionization potential elements. After the first direct ISN He observations with Ulysses GAS, the Interstellar Boundary Explorer (IBEX) observes with high collecting power the ISN flow trajectories very close to their perihelion in Earth's orbit for H, He, O, and Ne from December through March. Meanwhile, IBEX has recorded seven years of ISN observations, with changing solar activity and varying viewing strategies. These recurring and remarkably repeatable observations allow us to consolidate the derived physical parameters and some key compositional aspects of the interstellar medium. IBEX observations provide a very precise relation between ISN flow longitude and speed via the hyperbolic trajectory equation, but with larger uncertainties separately for longitude and speed. Recent concerted studies have led to a velocity vector that is consistent between IBEX and Ulysses, with a substantially higher temperature than found previously. The fact that the IBEX He and O ISN observations contain a substantial secondary neutral contribution adds complexity to the quantitative analysis of the physical interstellar medium parameters. However, their discovery also provides invaluable insight into the interstellar plasma interaction in the outer heliosheath, which is shaped strongly by the interstellar magnetic field. The longitude range of the IBEX observations limits the precision of the ISN velocity vector. The IBEX collection power and its sensitivity to the Earth's magnetosphere limit

  13. TANGO I: Interstellar medium in nearby radio galaxies. Molecular gas

    Science.gov (United States)

    Ocaña Flaquer, B.; Leon, S.; Combes, F.; Lim, J.

    2010-07-01

    Context. Powerful radio-AGN are hosted by massive elliptical galaxies that are usually very poor in molecular gas. Nevertheless, gas is needed at their very center to feed the nuclear activity. Aims: We study the molecular gas properties (i.e., mass, kinematics, distribution, origin) of these objects, and compare them with results for other known samples. Methods: At the IRAM-30m telescope, we performed a survey of the CO(1-0) and CO(2-1) emission from the most powerful radio galaxies of the Local Universe, selected only on the basis of their radio continuum fluxes. Results: The main result of our survey is that the molecular gas content of these galaxies is very low compared to spiral or FIR-selected galaxies. The median value of the molecular gas mass, including detections and upper limits, is 2.2 × 108 M⊙. When separated into FR-I and FR-II types, a difference in their H2 masses is found. The median value of FR-I galaxies is about 1.9 × 108 M⊙ and higher for FR-II galaxies, at about 4.5 × 108 M⊙. Which is probably entirely because of a Malmquist bias. Our results contrast with those of previous surveys, whose targets were mainly selected by means of their FIR emission, implying that we measure higher observed masses of molecular gas. Moreover, the shape of CO spectra suggest that a central molecular gas disk exists in 30% of these radio galaxies, a lower rate than in other active galaxy samples. Conclusions: We find a low level of molecular gas in our sample of radio-selected AGNs, indicating that galaxies do not need much molecular gas to host an AGN. The presence of a molecular gas disk in some galaxies and the wide range of molecular gas masses may be indicative of different origins for the gas, which we can not exclude at present (e.g., minor/major mergers, stellar mass loss, or accretion). Appendices and Figure 15 are only available in electronic form at http://www.aanda.org

  14. Is the interstellar gas of starburst galaxies well mixed?

    CERN Document Server

    Lebouteiller, V; Lebouteiller, Vianney; Kunth, Daniel

    2004-01-01

    The extent to which the ISM in galaxies is well mixed is not yet settled. Measured metal abundances in the diffuse neutral gas of star--forming gas--rich dwarf galaxies are deficient with respect to that of the ionized gas. The reasons, if real, are not clear and need to be based on firm grounds. Far-UV spectroscopy of giant HII regions such as NGC604 in the spiral galaxy M33 using FUSE allows us to investigate possible systematic errors in the metallicity derivation. We still find underabundances of nitrogen, oxygen, argon, and iron in the neutral phase by a factor of~6. This could either be explained by the presence of less chemically evolved gas pockets in the sightlines or by dense clouds out of which HIIregions form. Those could be more metallic than the diffuse medium.

  15. The nearby interstellar medium towards alpha Leo -- UV observations and modeling of a warm cloud within hot gas

    CERN Document Server

    Gry, Cecile

    2016-01-01

    We analyze interstellar absorption features in the full UV spectrum of the nearby (d = 24 pc) B8 IVn star alpha Leo (Regulus) obtained at high resolution and high S/N by the HST ASTRAL Treasury program. We derive column densities for many key atomic species and interpret their partial ionizations. The gas in front of alpha Leo exhibits two absorption components, one of which coincides in velocity with the local interstellar cloud (LIC) that surrounds the Sun. The second, smaller, component is shifted by +5.6 km/s relative to the main component, in agreement with results for other lines of sight in this region of the sky. The excitation of the C II fine-structure levels and the ratio of Mg I to Mg II reveal a temperature T = 6500 (+750,-600)K and electron density n(e) = 0.11 (+0.025,-0.03) cm^-3. Our investigation of the ionization balance of all the available species indicates that about 1/3 of the hydrogen atoms are ionized and that metals are significantly depleted onto grains. We infer that N(H I) = 1.9 (+...

  16. Interstellar Ices

    CERN Document Server

    Boogert, A C A

    2003-01-01

    Currently ~36 different absorption bands have been detected in the infrared spectra of cold, dense interstellar and circumstellar environments. These are attributed to the vibrational transitions of ~17 different molecules frozen on dust grains. We review identification issues and summarize the techniques required to extract information on the physical and chemical evolution of these ices. Both laboratory simulations and line of sight studies are essential. Examples are given for ice bands observed toward high mass protostars, fields stars and recent work on ices in disks surrounding low mass protostars. A number of clear trends have emerged in recent years. One prominent ice component consists of an intimate mixture between H2O, CH3OH and CO2 molecules. Apparently a stable balance exists between low temperature hydrogenation and oxidation reactions on grain surfaces. In contrast, an equally prominent ice component, consisting almost entirely of CO, must have accreted directly from the gas phase. Thermal proc...

  17. Resolution and Kinematics of Molecular Gas Surrounding the Cloverleaf Quasar at z=2.6 Using the Gravitational Lens

    CERN Document Server

    Yun, M S; Carrasco, J J; Blandford, R D

    1997-01-01

    Gravitational lenses have long been advertised as primitive telescopes, capable of magnifying cosmologically distant sources (Zwicky 1937). In this Letter, we present new 0''.9 resolution CO (7-6) observations of the z=2.56 Cloverleaf quasar (H 1413+117) and spatially resolved images. By modeling the gravitational lens, we infer a size scale of 0''.3 (~1 kpc) for the molecular gas structure surrounding the quasar, and the gas has a kinematic structure roughly consistent with a rotating disk. The observed properties of the CO emitting gas are similar to the nuclear starburst complexes found in the infrared luminous galaxies in the local universe, and metal enrichment by vigorous star formation within this massive nuclear gas complex can explain the abundance of carbon and oxygen in the interstellar medium of this system observed when the universe was only a few billion years old. Obtaining corresponding details in an unlensed object at similar distances would be well beyond the reach of current instruments, an...

  18. The Local Interstellar Medium

    CERN Document Server

    Redfield, S

    2006-01-01

    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 cl...

  19. Diffuse Atomic and Molecular Gas in the Interstellar Medium of M82 toward SN 2014J

    CERN Document Server

    Ritchey, Adam M; Dahlstrom, Julie A; York, Donald G

    2014-01-01

    We present a comprehensive analysis of interstellar absorption lines seen in moderately-high resolution, high S/N ratio optical spectra of SN 2014J in M82. Our observations were acquired over the course of six nights, covering the period from ~7 days before to ~29 days after the supernova reached its maximum V-band brightness. Complex interstellar absorption is observed from Na I, Ca II, K I, Ca I, CH+, CH, and CN, much of which arises from gas in the interstellar medium of M82, although absorption features associated with the Galactic disk and halo are also observed. 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 observed atomic and molecular species reveal that the ISM of M82...

  20. 16 Years of Ulysses Interstellar Dust Measurements in the Solar System: I. Mass Distribution and Gas-to-Dust Mass Ratio

    CERN Document Server

    Krüger, Harald; Gruen, Eberhard; Sterken, Veerle J

    2015-01-01

    In the early 1990s, contemporary interstellar dust (ISD) penetrating deep into the heliosphere was identified with the in-situ dust detector on board the Ulysses spacecraft. Between 1992 and the end of 2007 Ulysses monitored the ISD stream. The interstellar grains act as tracers of the physical conditions in the local interstellar medium surrounding our solar system. Earlier analyses of the Ulysses ISD data measured between 1992 and 1998 implied the existence of 'big' ISD grains [up to 10^-13kg]. The derived gas-to-dust-mass ratio was smaller than the one derived from astronomical observations, implying a concentration of ISD in the very local interstellar medium. We analyse the entire data set from 16 yr of Ulysses ISD measurements in interplanetary space. This paper concentrates on the overall mass distribution of ISD. An accompanying paper investigates time-variable phenomena in the Ulysses ISD data, and in a third paper we present the results from dynamical modelling of the ISD flow applied to Ulysses. We...

  1. Exploring the gas-phase spectroscopy of interstellar PAH and dust analogs: Astrophysical applications

    Science.gov (United States)

    Biennier, Ludovic; Salama, Farid; Allamandola, Lou; Gupta, Manish; O'Keefe, Anthony; Scherer, James J.

    We present and discuss the gas-phase electronic absorption spectra of selected ionized polycyclic aromatic hydrocarbons (PAHs) measured in the UV-Visible-NIR range in an astrophysically relevant environment. This type of measurements provides data on PAHs and nanometer-sized particles that can now be directly compared to astronomical spectra of the UV interstellar (IS) extinction curve and of the diffuse interstellar bands (DIBs). 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. This source combines a pulsed slit supersonic free jet expansion of argon seeded with PAHs (Salama, F., Allamandola, L. J. & Scherer, J. J., `Pulsed discharge nozzle cavity ringdown spectroscopy of cold PAH ions', J. Chem Phys.;in press) that have been pre-selected from Matrix Isolation Spectroscopy (MIS) studies. The absorption spectrum of the Pyrene cation (C16H10+) has also been measured. These experiments provide unique information on the spectra of free, large carbon-containing molecules and ions in the gas phase. The electronic bands measured for this selection of PAH ions are all found to be intrinsically broad (>˜20 cm-1). The laboratory data are compared with recent astronomical spectra of large DIBs. Preliminary results also show that carbon nanoparticles (˜2 nm size) are formed during the short residence time of the precursors in the plasma. This finding holds great potential for the spectroscopy of nanoparticles isolated in the gas-phase in an interstellar-like environment and for understanding the formation process of interstellar grains.

  2. The Interstellar Gas Dust Streams and Seeds of Life

    Science.gov (United States)

    Oleg, Khavroshkin; Vladislav, Tsyplakov

    Gas dust Streams from Double Stars & Lunar Seismicity. The time series of seismic events were generated as follows: on the ordinate axis the peak amplitudes of events in standard units, on abscissa axis - seismogram durations of the same moonquakes and subsequent time intervals between them were used. Spectrum of the series disclosed time picks on hidden cosmological periodicities of lunar seismicity. A part of results (picks) presents orbital periods of double stars nearest to the Solar system. The explanation of that results is existing gas-dust streams from binary stars systems and interacting of it with lunar surface. Information content of the Nakamura`s Catalog of moonquakes is very rich: from solar-earth tides to clustering among the meteoroid streams [1, 2]. The histograms from meteoroid impacts seismic data revealed the seismic wave responses of the Moon to solar oscillations and the action on the lunar surface by dust-gas plasma of meteoroid streams [3]. The time series of seismic events were generated as follows: on an axis of ordinates - the peak amplitudes of events in standard units, on an abscissa - seismogram durations of the same moonquakes and subsequent time intervals between them were put aside [4]. Spectrum of the series of meteoroid streams seismicity disclosed time picks on orbital periods some planets and their satellites and solar oscillations [4, 5]. The research of peculiarities of histogram envelopes [3] and comparative common analysis solar bursts data and mass meteoroid distribution are confirmed [3, 4] and revealed Forbush`s effect for gas-dust plasma [6]. Hidden astrophysical periodicities of lunar seismicity were obtained early from an analysis of time series [7] which were similarity to series [4]. The path of results of [7] is presented in the Table where picks presents orbital periods of double stars nearest to the Solar system. Hypothesis for explanation of the Table results is existing gas-dust streams from binary stars near

  3. Spatial distribution of interstellar dust in the Sun vicinity, comparison with neutral sodium-bearing gas

    CERN Document Server

    Vergely, Jean-Luc; Lallement, Rosine; Raimond, Severine

    2010-01-01

    3D tomography of the interstellar dust and gas may be useful in many respects, from the physical and chemical evolution of the ISM itself to foreground decontamination of the CMB, or various studies of the environments of specific objects. Our goal here is to bring more precise information on the distance to nearby interstellar dust and gas clouds within 250 pc. We apply the best available calibration methods to a carefully screened set of stellar Stromgren photometry data for targets possessing a Hipparcos parallax and spectral type classification. We combine the derived interstellar extinctions and the parallax distances for about 6,000 stars to build a 3D tomography of the local dust. We use an inversion method based on a regularized Bayesian approach and a least squares criterion. We obtain 3D maps of the opacity and the distance to the main dust-bearing clouds with 250 pc. We calculate the integrated extinction between the Sun and the cube boundary and compare with the total galactic extinction derived f...

  4. Spatial distribution of interstellar dust in the Sun's vicinity. Comparison with neutral sodium-bearing gas

    Science.gov (United States)

    Vergely, J.-L.; Valette, B.; Lallement, R.; Raimond, S.

    2010-07-01

    Aims: 3D tomography of the interstellar dust and gas may be useful in many respects, from the physical and chemical evolution of the interstellar medium itself to foreground decontamination of the cosmic microwave background, or various studies of the environments of specific objects. However, while spectral data cubes of the galactic emission become increasingly precise, the information on the distance to the emitting regions has not progressed as well and relies essentially on the galactic rotation curve. Our goal here is to bring more precise information on the distance to nearby interstellar dust and gas clouds within 250 pc. Methods: We apply the best available calibration methods to a carefully screened set of stellar Strömgren photometry data for targets possessing a Hipparcos parallax and spectral type classification. We combine the derived interstellar extinctions and the parallax distances for about 6000 stars to build a 3D tomography of the local dust. We use an inversion method based on a regularized Bayesian approach and a least squares criterion, optimized for this specific data set. We apply the same inversion technique to a totally independent set of neutral sodium absorption data available for about 1700 target stars. Results: We obtain 3D maps of the opacity and the distance to the main dust-bearing clouds within 250 pc and identify in those maps well-known dark clouds and high galactic more diffuse entities. We calculate the integrated extinction between the Sun and the cube boundary and compare this with the total galactic extinction derived from infrared 2D maps. The two quantities reach similar values at high latitudes, as expected if the local dust content is satisfyingly reproduced and the dust is closer than 250 pc. Those maps show a larger high latitude dust opacity in the North compared to the South, reinforcing earlier evidences. Interestingly the gas maps do not show the same asymmetry, suggesting a polar asymmetry of the dust to gas

  5. ISO observations of the Galactic center Interstellar Medium: ionized gas

    CERN Document Server

    Rodríguez-Fernández, N J

    2004-01-01

    (Abridged) We present fine structure and recombination lines observations of the ionized gas toward a sample of 18 sources located within 300 pc of the center of the Galaxy (GC). The fine structure lines from [NII] and [SIII] have been detected in 16 sources. In 10 sources we have even detected the [OIII] 88 $\\mu$m line. The measured N, S and Ne abundances are similar to those measured in the HII regions in the 5-kpc ring and in the nuclei of starburst galaxies. The fine structure lines ratios measured for all the sources can be explained by photo-ionization with an effective temperature of 32000-37000 K and an ionization parameter, $U$, of $-1>\\log U > -3$. The highest excitation is found in the Radio Arc region but there must be more ionizing sources distributed over the Galactic center than the known clusters of massive stars. Most of the clouds are located far from the prominent continuum complexes (Sgr C, B ...). However, it is possible that the clouds are ionized by escaped photons from those complexes....

  6. Structure and Evolution of Interstellar Gas in Flattened, Rotating Elliptical Galaxies

    Science.gov (United States)

    Brighenti, Fabrizio; Mathews, William G.

    1996-10-01

    We study the time-dependent evolution of interstellar gas in a family of elliptical galaxies having identical masses and central densities but various ellipticities and total angular momenta. Dark halos are assumed to be flattened in the same manner as the stars. Normal mass loss from evolving galactic stars is sufficient to account for the amount of hot interstellar gas observed. Gas ejected from stars shares the random motions of the stars and the bulk stellar velocity relative to the local interstellar medium; the ejected gas thermalizes to a temperature similar to the virial temperature of the stellar system. The random stellar motions and galactic rotation are found by solving Jeans's equations in cylindrical geometry. For a sequence of galaxies differing only in degree of flattening-E0, E2, and E4-we find that the X-ray images and luminosities are not very different. As the hot interstellar gas loses energy by radiation, it cools to the very center of these nonrotating galaxies regardless of flattening. The X-ray surface brightness is generally slightly steeper than the optical surface brightness of starlight. However, when a small but typical galactic rotation is introduced, the evolution of the interstellar medium is radically altered. The average X- ray surface brightness {SIGMA}_X_ is lower in the galactic center compared to nonrotating galaxies. This lower {SIGMA}_X_ can be achieved without invoking an ad hoc mass dropout from the hot gas. As the gas cools in rotating galaxies, it is deposited in a large disk comparable in size to the effective radius. Alter evolving for several gigayears, most of the new gas in the cooling flow is constrained by angular momentum conservation to arrive at the outer edge of the disk, Causing a local enhancement in the X-ray surface brightness. This results in flattened inner X-ray surface brightness contours that have peanut shapes when viewed nearly perpendicular to the axis of galactic rotation. As gas approaches the

  7. Instellar Gas Experiment (IGE): Testing interstellar gas particles to provide information on the processes of nucleosynthesis in the big bang stars and supernova

    Science.gov (United States)

    Lind, Don

    1985-01-01

    The Interstellar Gas Experiment (IGE) is designed to collect particles of the interstellar gas - a wind of interstellar media particles moving in the vicinity of the solar system. These particles will be returned to earth where the isotopic ratios of the noble gases among these particles will be measured. IGE was designed and programmed to expose 7 sets of six copper-beryllium metallic collecting foils to the flux of neutral interstellar gas particles which penetrate the heliosphere to the vicinity of the earth's orbit. These particles are trapped in the collecting foils and will be returned to earth for mass-spectrographic analysis when Long Duration Exposure Facility (LDEF) on which IGE was launched, is recovered.

  8. Recovering Interstellar Gas Properties with Hi Spectral Lines: A Comparison between Synthetic Spectra and 21-SPONGE

    Science.gov (United States)

    Murray, Claire E.; Stanimirović, Snežana; Kim, Chang-Goo; Ostriker, Eve C.; Lindner, Robert R.; Heiles, Carl; Dickey, John M.; Babler, Brian

    2017-03-01

    We analyze synthetic neutral hydrogen (H i) absorption and emission spectral lines from a high-resolution, three-dimensional hydrodynamical simulation to quantify how well observational methods recover the physical properties of interstellar gas. We present a new method for uniformly decomposing H i spectral lines and estimating the properties of associated gas using the Autonomous Gaussian Decomposition (AGD) algorithm. We find that H i spectral lines recover physical structures in the simulation with excellent completeness at high Galactic latitude, and this completeness declines with decreasing latitude due to strong velocity-blending of spectral lines. The temperature and column density inferred from our decomposition and radiative transfer method agree with the simulated values within a factor of Large Array using AGD. We find more components per line of sight in 21-SPONGE than in synthetic spectra, which reflects insufficient simulated gas scale heights and the limitations of local box simulations. In addition, we find a significant population of low-optical depth, broad absorption components in the synthetic data which are not seen in 21-SPONGE. This population is not obvious in integrated or per-channel diagnostics, and reflects the benefit of studying velocity-resolved components. The discrepant components correspond to the highest spin temperatures (1000< {T}s< 4000 {{K}}), which are not seen in 21-SPONGE despite sufficient observational sensitivity. We demonstrate that our analysis method is a powerful tool for diagnosing neutral interstellar medium conditions, and future work is needed to improve observational statistics and implementation of simulated physics.

  9. The interstellar medium in Andromeda's dwarf spheroidal galaxies - II. Multiphase gas content and ISM conditions

    Science.gov (United States)

    De Looze, Ilse; Baes, Maarten; Cormier, Diane; Kaneko, Hiroyuki; Kuno, Nario; Young, Lisa; Bendo, George J.; Boquien, Médéric; Fritz, Jacopo; Gentile, Gianfranco; Kennicutt, Robert C.; Madden, Suzanne C.; Smith, Matthew W. L.; Wilson, Christine D.

    2017-03-01

    We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC 147, NGC 185 and NGC 205). Ancillary H I, CO, Spitzer Infrared Spectrograph spectra, Hα and X-ray observations are combined to trace the atomic, cold and warm molecular, ionized and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [C I] observations of NGC 205 to revise its molecular gas content. We derive total gas masses of Mg = 1.9-5.5 × 105 M⊙ for NGC 185 and Mg = 8.6-25.0 × 105 M⊙ for NGC 205. Non-detections combine to an upper limit on the gas mass of Mg ≤ 0.3-2.2 × 105 M⊙ for NGC 147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR ∼ 37-107 and 48-139 are also considerably lower compared to the expected GDR ∼ 370 and 520 for the low metal abundances in NGC 185 (0.36 Z⊙) and NGC 205 (0.25 Z⊙), respectively. To simultaneously account for the gas deficiency and low gas-to-dust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (∼1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC 147, NGC 185 and NGC 205.

  10. DIFFUSE ATOMIC AND MOLECULAR GAS IN THE INTERSTELLAR MEDIUM OF M82 TOWARD SN 2014J

    Energy Technology Data Exchange (ETDEWEB)

    Ritchey, Adam M. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Welty, Daniel E.; York, Donald G. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 (United States); Dahlstrom, Julie A., E-mail: aritchey@astro.washington.edu [Department of Physics and Astronomy, Carthage College, 2001 Alford Park Dr., Kenosha, WI 53140 (United States)

    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.

  11. Diffuse Atomic and Molecular Gas in the Interstellar Medium of M82 toward SN 2014J

    Science.gov (United States)

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

    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+, 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+)/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+ 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.

  12. Evaluation of Changes and Stability on the Surroundings Adjacent to Exhaust-Gas Emitting Port

    Institute of Scientific and Technical Information of China (English)

    AO Yong'an; Marc A. Rosen; WANG Yueren

    2011-01-01

    The exergy and entropy changes of the surroundings adjacent to exhaust-gas emitting ports, and the probable effects on the atmosphere, are investigated and the current stable state changing point of atmosphere is determined and compared in the paper. The potential of doing work is described and the effects of the amount of exhaust gas on the atmosphere are studied through exergy and entropy change functions. The exergy change function accounts for the flow direction of the exhaust gas without local wind. It appears that exergy can be used as a state function to describe the change, the stability and the order of a system.

  13. Gamma ray astronomy and the origin of the light nuclei. [cosmic ray and interstellar gas reactions

    Science.gov (United States)

    Reeves, H.

    1978-01-01

    Nuclear reactions induced by the collisions of the protons and alphas of the galactic cosmic ray with heavy nuclei of the interstellar gas are responsible for the continuous production of the light elements lithium, beryllium, and boron in the galaxy. To better than one order of magnitude, the observed ratios of these abundances to hydrogen abundance and the nuclidic abundance ratios between themselves are accounted for by simply considering the effect of fast protons and alphas with a flux and an energy spectrum as observed in galactic cosmic rays, for a period comparable with the life of our galaxy. The role of gamma ray astronomy in solving problems that occur when accurate agreement is sought with increasingly accurate data is discussed.

  14. Test studies of gas flow in rock and coal surrounding a mined coal seam

    Institute of Scientific and Technical Information of China (English)

    Lv Youchang

    2012-01-01

    An analysis of the variation rule of abutment pressure at the mining working face in a single coal seam and the mechanical behavior of surrounding rock during stoping is presented.Consideration of the elastic and plastic deformation zones that develop during the mining process allowed the determination of a relationship between horizontal stress and vertical stress.Based on this,a confined pressure unloading test was conducted by the use of the "gas-containing coal thermo-fluid-solid coupling 3-axis servo seepage" experimental apparatus.Thus,gas flow patterns in the elastic and plastic zones were derived from an experimental point of view.Darcy's law and the Klinkenberg effect were used to derive a gas flow equation for the elastic and plastic stress fields.The study of gas flow phenomena at the working face during coal mining is of great importance for the study of gas migration and enrichment oatterns.

  15. The Smooth MgII gas distribution through the interstellar/extra-planar/halo interface

    CERN Document Server

    Kacprzak, Glenn G; Churchill, Christopher W; Ryan-Weber, Emma V; Nielsen, Nikole M

    2013-01-01

    We report the first measurements of MgII absorption systems associated with spectroscopically confirmed z~0.1 star-forming galaxies at projected distances of D<6kpc. We demonstrate the data are consistent with the well known anti-correlation between rest-frame MgII equivalent width, Wr(2796), and impact parameter, D, represented by a single log-linear relation derived by Nielsen et al. (MAGIICAT) that converges to ~2A at D=0kpc. Incorporating MAGIICAT, we find that the halo gas covering fraction is unity below D~25kpc. We also report that our D<6kpc absorbers are consistent with the Wr(2796) distributions of the Milky Way interstellar medium (ISM) and ISM+halo. In addition, quasar sight-lines of intermediate redshift galaxies with 6gas and not the ISM. As inferred by the Milky Way and our new data, the gas profiles of galaxies can be fit by a ...

  16. Supernova Feedback and the Hot Gas Filling Fraction of the Interstellar Medium

    CERN Document Server

    Li, Miao; Cen, Renyue; Bryan, Greg L; Naab, Thorsten

    2015-01-01

    Supernovae are the most energetic among stellar feedback processes, and are crucial for regulating the interstellar medium (ISM) and launching galactic winds. We explore how supernova remnants (SNRs) create a multiphase medium by performing high resolution, 3D hydrodynamical simulations at various SN rates, $S$, and ISM average densities, $n$. We find that the evolution of a SNR in a self-consistently generated three-phase ISM is qualitatively different from that in a uniform or a two-phase warm/cold medium. By traveling faster and further in the cooling-inefficient hot phase, the spatial-temporal domain of a SNR is enlarged by $>10^{2.5}$ in a hot-dominated multiphase medium (HDMM) compared to the uniform case. We then examine the resultant ISM as we vary $n$ and $S$, finding that a steady state can only be achieved when the hot gas volume fraction \\fvh $\\lesssim 0.6\\pm 0.1$. Above that, overlapping SNRs render connecting topology of the hot gas, and such a HDMM is subjected to thermal runaway with growing p...

  17. THE SMOOTH Mg II GAS DISTRIBUTION THROUGH THE INTERSTELLAR/EXTRA-PLANAR/HALO INTERFACE

    Energy Technology Data Exchange (ETDEWEB)

    Kacprzak, Glenn G.; Cooke, Jeff; Ryan-Weber, Emma V. [Swinburne University of Technology, VIC 3122 (Australia); Churchill, Christopher W.; Nielsen, Nikole M., E-mail: gkacprzak@astro.swin.edu.au [New Mexico State University, Las Cruces, NM 88003 (United States)

    2013-11-01

    We report the first measurements of Mg II absorption systems associated with spectroscopically confirmed z ∼ 0.1 star-forming galaxies at projected distances of D < 6 kpc. We demonstrate that the data are consistent with the well-known anti-correlation between rest-frame Mg II equivalent width, W{sub r} (2796), and impact parameter, D, represented by a single log-linear relation derived by Nielsen et al. (MAGIICAT) that converges to ∼2 Å at D = 0 kpc. Incorporating MAGIICAT, we find that the halo gas covering fraction is unity below D ∼ 25 kpc. We also report that our D < 6 kpc absorbers are consistent with the W{sub r} (2796) distributions of the Milky Way interstellar medium (ISM) and ISM+halo. In addition, quasar sight lines of intermediate redshift galaxies with 6 < D < 25 kpc have an equivalent width distribution similar to that of the Milky Way halo, implying that beyond ∼6 kpc, quasar sight lines are likely probing halo gas and not the ISM. As inferred by the Milky Way and our new data, the gas profiles of galaxies can be fit by a single log-linear W{sub r} (2796)-D relation out to large scales across a variety of gas-phase conditions and is maintained through the halo/extra-planar/ISM interfaces, which is remarkable considering their kinematic complexity. These low-redshift, small impact parameter absorption systems are the first steps to bridge the gap between quasar absorption-line studies and H I observations of the circumgalactic medium.

  18. Chemical Complementarity between the Gas Phase of the Interstellar Medium and the Rocky Material of Our Planetary System

    CERN Document Server

    Wang, Haiyang

    2016-01-01

    We compare the elemental depletions in the gas phase of the interstellar medium (ISM) with the elemental depletions in the rocky material of our Solar System. Our analysis finds a high degree of chemical complementarity: elements depleted in the gas phase of the ISM are enriched in the rocky material of our Solar System, and vice versa. This chemical complementarity reveals the generic connections between interstellar dust and rocky planetary material. We use an inheritance model to explain the formation of primordial grains in the solar nebula. The primary dust grains inherited from the ISM, in combination with the secondary ones condensed from the solar nebula, constitute the primordial rocky material of our planetary system, from which terrestrial planets are formed through the effects of the progressive accretion and sublimation. The semi-major-axis-dependence of the chemical composition of rocky planetary material is also observed by comparing elemental depletions in the Earth, CI chondrites and other ty...

  19. Some insights into formamide formation through gas-phase reactions in the interstellar medium

    Energy Technology Data Exchange (ETDEWEB)

    Redondo, Pilar; Barrientos, Carmen; Largo, Antonio, E-mail: predondo@qf.uva.es [Computational Chemistry Group, Departamento de Química Física, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid (Spain)

    2014-01-10

    We study the viability of different gas-phase ion-molecule reactions that could produce precursors of formamide in the interstellar medium. We analyze different reactions between cations containing a nitrogen atom (NH{sub 3}{sup +}, NH{sub 4}{sup +}, NH{sub 3}OH{sup +}, and NH{sub 2}OH{sup +}) and neutral molecules having one carbonyl group (H{sub 2}CO and HCOOH). First, we report a theoretical estimation of the reaction enthalpies for the proposed processes. Second, for more favorable reactions, from a thermodynamic point of view, we perform a theoretical study of the potential energy surface. In particular, the more exothermic processes correspond to the reactions of ionized and protonated hydroxylamine with formaldehyde. In addition, a neutral-neutral reaction has also been considered. The analysis of the potential energy surfaces corresponding to these reactions shows that these processes present a net activation barrier and that they cannot be considered as a source of formamide in space.

  20. Analytical methods for measuring the parameters of interstellar gas using methanol observations

    Science.gov (United States)

    Kalenskii, S. V.; Kurtz, S.

    2016-08-01

    The excitation of methanol in the absence of external radiation is analyzed, and LTE methods for probing interstellar gas considered. It is shown that rotation diagrams correctly estimate the gas kinetic temperature only if they are constructed using lines whose upper levels are located in the same K-ladders, such as the J 0- J -1 E lines at 157 GHz, the J 1- J 0 E lines at 165 GHz, and the J 2- J 1 E lines at 25 GHz. The gas density must be no less than 107 cm-3. Rotation diagrams constructed from lines with different K values for their upper levels (e.g., 2 K -1 K at 96 GHz, 3 K -2 K at 145 GHz, 5 K -4 K at 241 GHz) significantly underestimate the temperature, but enable estimation of the density. In addition, diagrams based on the 2 K -1 K lines can be used to estimate the methanol column density within a factor of about two to five. It is suggested that rotation diagrams should be used in the following manner. First, two rotation diagrams should be constructed, one from the lines at 96, 145, or 241 GHz, and another from the lines at 157, 165, or 25 GHz. The former diagram is used to estimate the gas density. If the density is about 107 cm-3 or higher, the latter diagram reproduces the temperature fairly well. If the density is around 106 cm-3, the temperature obtained from the latter diagram should be multiplied by a factor of 1.5-2. If the density is about 105 cm-3 or lower, then the latter diagram yields a temperature that is lower than the kinetic temperature by a factor of three or more, and should be used only as a lower limit for the kinetic temperature. The errors in the methanol column density determined from the integrated intensity of a single line can be more than an order of magnitude, even when the gas temperature is well known. However, if the J 0-( J - 1)0 E lines, as well as the J 1-( J - 1)1 A + or A - lines are used, the relative error in the column density is no more than a factor of a few.

  1. Interstellar Cloud Formation through Aggregation of Cold Blobs in a Two-Phase Gas Mixture

    Science.gov (United States)

    Kamaya, Hideyuki

    1997-05-01

    We propose a new formation scenario for interstellar clouds through the aggregation of dense cold blobs (phase II [PII]), which drift in a diffuse warm medium (phase I [PI]). We examine how important it is that there exist numerous PII blobs when the properties of such a two-phase flow are studied. First, we solve a one-dimensional shock-tube problem and find that the shock wave in the mixture is considerably damped because of the drag force between the two phases. This is because the PII blobs are left behind the shock front, since their inertia is larger than that of PI, thus suppressing large spatial variations of PI gas via the drag force. The PII blobs thus play the role of anchors. Therefore, mass aggregation by shocks may be ineffective in a two-phase medium. However, the PII blobs can still aggregate through a kind of fluid dynamical instability. We next suppose that the PI gas is accelerated upward by shocks against downward gravity, while the PII blobs are at rest because of balance between the drag force due to PI and gravity. If we put a positive perturbation in the number density of PII blobs, the upward PI flow above the perturbation is decelerated by the enhanced drag force, and the velocity difference between PI and PII is thereby reduced. Then the PII blobs above the perturbation are accelerated downward, since the gravity on PII now dominates the reduced drag force. As a result, the blobs will fall onto this perturbed region, and this region becomes denser and denser. This is the mechanism of the instability. Therefore, we expect efficient cloud formation by this instability in spiral arms, even when galactic shocks are extremely damped.

  2. Kinematics of Interstellar Gas in Nearby UV-selected Galaxies Measured with HST STIS Spectroscopy

    Science.gov (United States)

    Schwartz, C. M.; Martin, C. L.; Chandar, R.; Leitherer, C.; Heckman, T. M.; Oey, M. S.

    2006-08-01

    We measure Doppler shifts of interstellar absorption lines in HST STIS spectra of individual star clusters in nearby UV-selected galaxies. Values for systemic velocities, which are needed to quantify outflow speeds, are taken from the literature and verified with stellar lines. We detect outflowing gas in 8 of 17 galaxies via low-ionization lines (e.g., C II, Si II, Al II), which trace cold and/or warm gas. The starbursts in our sample are intermediate in luminosity (and mass) to dwarf galaxies and luminous infrared galaxies (LIRGs), and we confirm that their outflow speeds (ranging from -100 to nearly -520 km s-1, with an accuracy of ~80 km s-1) are intermediate to those previously measured in dwarf starbursts and LIRGs. We do not detect the outflow in high-ionization lines (such as C IV or Si IV); higher quality data will be needed to empirically establish how velocities vary with the ionization state of the outflow. We do verify that the low-ionization UV lines and optical Na I doublet give roughly consistent outflow velocities, solidifying an important link between studies of galactic winds at low and high redshift. To obtain a higher signal-to-noise ratio (S/N), we create a local average composite spectrum and compare it to the high-z Lyman break composite spectrum. It is surprising that the low-ionization lines show similar outflow velocities in the two samples. We attribute this to a combination of weighting toward higher luminosities in the local composite, as well as both samples being, on average, brighter than the ``turnover'' luminosity in the v-SFR relation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-9036.

  3. The D/H Ratio in Interstellar Gas toward G191-B2B

    Science.gov (United States)

    Sahu, M. S.; Landsman, W.; Bruhweiler, F. C.; Gull, T. R.; Bowers, C. A.; Lindler, D.; Feggans, K.; Barstow, M. A.; Hubeny, I.; Holberg, J. B.

    1999-10-01

    Recent analysis of Goddard High-Resolution Spectrograph (GHRS) echelle spectra suggests ~30% variations in the D/H abundance ratio along the line of sight to the nearby (69 pc) hot white dwarf (WD) G191-B2B (Vidal-Madjar et al.). Variations in the D/H ratio on such short length scales imply nonuniform production/destruction of deuterium and an inefficient mixing of gas in the local interstellar medium (LISM). We reinvestigate the question of the spatial variation of the local D/H abundance using both archival GHRS spectra and new echelle spectra of G191-B2B obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The STIS spectra were obtained in the high-resolution (E140H) mode and cover the wavelength region ranging from 1140 to 1700 Å. Our analysis uses stratified line-blanketed non-LTE model atmosphere calculations to determine the shape of the intrinsic WD Lyα profile and to estimate the WD photospheric contamination of the interstellar lines. Although three velocity components were reported previously toward G191-B2B, we deduce only two velocity components. The first component is at vhel~8.6 km s-1, and the second is at vhel~19.3 km s-1, which we identify with the local interstellar cloud (LIC). From the STIS data, we derive D/H = 1.60+0.39-0.27×10-5 for the LIC component and D/H>1.26×10-5 for the 8.6 km s-1 component (uncertainties denote 2σ or 95% confidence limits). The derived D/H values in both components are consistent with (D/H)LIC = (1.5+/-0.1)×10-5, which was determined by Linsky in 1998. The STIS data provide no evidence for local or component-to-component variation in the D/H ratio. Our reanalysis of the GHRS data gives essentially the same results as Vidal-Madjar et al., despite using two velocity components for the profile fitting (vs. three by Vidal-Madjar et al.) and a more physically realistic WD Lyα profile for G191-B2B. The GHRS data indicate a component-to-component variation as well as a

  4. Heat Dissipation from Suspended Carbon Nanotubes to their Surrounding Gas Environment

    Science.gov (United States)

    Hsu, I. Kai; Pettes, Michael T.; Aykol, Mehmet; Shi, Li; Cronin, Stephen

    2011-03-01

    The assistance of gas molecules to dissipate heat in 5- μ m-long, electrical heated suspended carbon nanotubes (CNTs) is observed by comparing the G band Raman phonon temperature profiles measured in different gas environments and in vacuum. The measurement results show that 50-60% of the heat generated in the CNT is carried away by its surrounding gas molecules. By analyzing the temperature profiles investigated in different gases, the thermal boundary conductance (TBC) between the gas molecules and the CNT can also be extracted. We find the TBC to be higher in carbon dioxide than in nitrogen, argon and helium. Moreover, we report another optical method to explore the heat spreading behavior on a longer suspended CNTs in air, in which one laser is used as a heat source while another laser is used as a local temperature probe. A fin-shape thermal transport model is applied to fit the exponentially decaying temperature profiles measured away from the heat source. These results yield a heat decay length and TBC for air to be around 6.5 μ m and 3 × 105 W/ m 2 K, respectively. I Kai Hsu et al. Journal of Applied Physics 2010, 108, (084307).

  5. GAS PHASE SYNTHESIS OF (ISO)QUINOLINE AND ITS ROLE IN THE FORMATION OF NUCLEOBASES IN THE INTERSTELLAR MEDIUM

    Energy Technology Data Exchange (ETDEWEB)

    Parker, Dorian S. N.; Kaiser, Ralf I. [Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Kostko, Oleg; Troy, Tyler P.; Ahmed, Musahid [Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Mebel, Alexander M. [Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199 (United States); Tielens, Alexander G. G. M. [Leiden Observatory, University of Leiden, Leiden (Netherlands)

    2015-04-20

    Nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) have been proposed to play a key role in the astrochemical evolution of the interstellar medium, yet the formation mechanisms of even their simplest prototypes—quinoline and isoquinoline—remain elusive. Here, we reveal a novel concept that under high temperature conditions representing circumstellar envelopes of carbon stars, (iso)quinoline can be synthesized via the reaction of pyridyl radicals with two acetylene molecules. The facile gas phase formation of (iso)quinoline in circumstellar envelopes defines a hitherto elusive reaction class synthesizing aromatic structures with embedded nitrogen atoms that are essential building blocks in contemporary biological-structural motifs. Once ejected from circumstellar shells and incorporated into icy interstellar grains in cold molecular clouds, these NPAHs can be functionalized by photo processing forming nucleobase-type structures as sampled in the Murchison meteorite.

  6. The interstellar medium in Andromeda's dwarf spheroidal galaxies: II. Multi-phase gas content and ISM conditions

    CERN Document Server

    De Looze, Ilse; Cormier, Diane; Kaneko, Hiroyuki; Kuno, Nario; Young, Lisa; Bendo, George J; Boquien, Mederic; Fritz, Jacopo; Gentile, Gianfranco; Kennicutt, Robert C; Madden, Suzanne C; Smith, Matthew W L; Wilson, Christine D

    2016-01-01

    We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC147, NGC185 and NGC205). Ancillary HI, CO, Spitzer IRS spectra, H{\\alpha} and X-ray observations are combined to trace the atomic, cold and warm molecular, ionised and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [CI] observations of NGC205 to revise its molecular gas content. We derive total gas masses of M_gas = 1.9-5.5x10^5 Msun for NGC185 and M_gas = 8.6-25.0x10^5 Msun for NGC205. Non-detections combine to an upper limit on the gas mass of M_gas =< 0.3-2.2x10^5 Msun for NGC147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR~37-107 and GDR~48-139 are also considerably lower compared to the expected GDR~370 and GDR~520 for the low metal abundances in NGC 1...

  7. Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC 612 (PKS 0131-36)

    NARCIS (Netherlands)

    Emonts, B. H. C.; Morganti, R.; Oosterloo, T. A.; Holt, J.; Tadhunter, C. N.; van der Hulst, J. M.; Ojha, R.; Sadler, E. M.

    2008-01-01

    We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC612, which hosts one of the nearest powerful radio sources (PKS 0131-36). Using the Australia Telescope Compact Array, we detect MHI = 1.8 x 10(9) M(circle dot) of HI emission-line gas that is

  8. Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC 612 (PKS 0131-36)

    NARCIS (Netherlands)

    Emonts, B. H. C.; Morganti, R.; Oosterloo, T. A.; Holt, J.; Tadhunter, C. N.; van der Hulst, J. M.; Ojha, R.; Sadler, E. M.

    2008-01-01

    We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC612, which hosts one of the nearest powerful radio sources (PKS 0131-36). Using the Australia Telescope Compact Array, we detect MHI = 1.8 x 10(9) M(circle dot) of HI emission-line gas that is

  9. Radiation-pressure-driven dust waves inside bursting interstellar bubbles

    NARCIS (Netherlands)

    Ochsendorf, B.B.; Verdolini, S.; Cox, N.L.J.; Berné, O.; Kaper, L.; Tielens, A.G.G.M.

    2014-01-01

    Massive stars drive the evolution of the interstellar medium through their radiative and mechanical energy input. After their birth, they form "bubbles" of hot gas surrounded by a dense shell. Traditionally, the formation of bubbles is explained through the input of a powerful stellar wind, even tho

  10. Ubiquitous argonium (ArH$^+$) in the diffuse interstellar medium -- a molecular tracer of almost purely atomic gas

    CERN Document Server

    Schilke, Peter; Mueller, Holger S P; Comito, Claudia; Bergin, Edwin A; Lis, Dariusz C; Gerin, Maryvonne; Black, John H; Wolfit, Mark; Indriolo, Nick; Pearson, John C; Menten, Karl M; Winkel, Benjamin; Sanchez-Monge, Alvaro; Moeller, Thomas; Godard, Benjamin; Falgarone, Edith

    2014-01-01

    We describe the assignment of a previously unidentified interstellar absorption line to ArH$^+$ and discuss its relevance in the context of hydride absorption in diffuse gas with a low H$_2$ fraction. The column densities along several lines of sight are determined and discussd in the framework of chemical models. The column densities of ArH$^+$ are compared to those of other species, tracing interstellar medium (ISM) components with different H$_2$ abundances. Chemical models are constructed, taking UV radiation and cosmic ray ionization into account. Due to the detection of two isotopologues, $^{36}$ArH$^+$ and $^{38}$ArH$^+$, we are confident about the carrier assignment to ArH$^+$. NeH$^+$ is not detected with a limit of [NeH$^+$]/[ArH$^+$] $\\le$ 0.1. The derived column densities agree well with the predictions of chemical models. ArH$^+$ is a unique tracer of gas with a fractional H$_2$ abundance of $10^{-4}- 10^{-3}$ and shows little correlation with H$_2$O$^+$, which traces gas with a fractional H$_2$ ...

  11. Neutral interstellar helium parameters based on Ulysses/GAS and IBEX-Lo observations: what are the reasons for the differences?

    CERN Document Server

    Katushkina, Olga A; Wood, Brain E; McMulin, Donald R

    2014-01-01

    Recent analysis of the interstellar helium fluxes measured in 2009-2010 at Earth orbit by the Interstellar Boundary Explorer (IBEX) has suggested that the interstellar velocity (both direction and magnitude) is inconsistent with that derived previously from Ulysses/GAS observations made in the period from 1990 to 2002 at 1.5-5.5 AU from the Sun. Both results are model-dependent and models that were used in the analyses are different. In this paper, we perform an analysis of the Uysses/GAS and IBEX-Lo data using our state-of-the-art 3D time-dependent kinetic model of interstellar atoms in the heliosphere. For the first time we analyze Ulysses/GAS data from year 2007, the closest available Ulysses/GAS observations in time to the IBEX observations. We show that the interstellar velocity derived from the Ulysses 2007 data is consistent with previous Ulysses results and does not agree with the velocity derived from IBEX. This conclusion is very robust since, as is shown in the paper, it does not depend on the ioni...

  12. Helium Ionization in the Diffuse Ionized Gas Surrounding UCH ii Regions

    Science.gov (United States)

    Anish Roshi, D.; Churchwell, E.; Anderson, L. D.

    2017-04-01

    We present measurements of the singly ionized helium-to-hydrogen ratio ({n}{{He}+}/{n}{{{H}}+}) toward diffuse gas surrounding three ultracompact H ii (UCH ii) regions: G10.15-0.34, G23.46-0.20, and G29.96-0.02. We observe radio recombination lines of hydrogen and helium near 5 GHz using the GBT to measure the {n}{{He}+}/{n}{{{H}}+} ratio. The measurements are motivated by the low helium ionization observed in the warm ionized medium and in the inner Galaxy diffuse ionized regions. Our data indicate that the helium is not uniformly ionized in the three observed sources. Helium lines are not detected toward a few observed positions in sources G10.15-0.34 and G23.46-0.20, and the upper limits of the {n}{{He}+}/{n}{{{H}}+} ratio obtained are 0.03 and 0.05, respectively. The selected sources harbor stars of type O6 or hotter as indicated by helium line detection toward the bright radio continuum emission from the sources with mean {n}{{He}+}/{n}{{{H}}+} value 0.06 ± 0.02. Our data thus show that helium in diffuse gas located a few parsecs away from the young massive stars embedded in the observed regions is not fully ionized. We investigate the origin of the nonuniform helium ionization and rule out the possibilities (a) that the helium is doubly ionized in the observed regions and (b) that the low {n}{{He}+}/{n}{{{H}}+} values are due to additional hydrogen ionizing radiation produced by accreting low-mass stars. We find that selective absorption of ionizing photons by dust can result in low helium ionization but needs further investigation to develop a self-consistent model for dust in H ii regions.

  13. Time-Domain TeraHertz Spectroscopy and Observational Probes of Prebiotic Interstellar Gas and Ice Chemistry

    Science.gov (United States)

    McGuire, Brett A.

    2015-01-01

    Despite the detection of amino acids in meteoritic and cometary samples, our understanding of the formation of such molecules remains incomplete, because we do not yet fully understand the interplay between chemical reactions occurring within interstellar ices, and the gas-phase chemistry which seeds and enriches them. My dissertation work takes a holistic view of the system, approaching the topic by studying both fundamental spectroscopic and physical properties of astrochemical ices, as well as chemical evolutionary processes in the gas-phase ISM. I'll discuss my work to confirm the detection of l-C3H+, a potentially key intermediate in interstellar carbon chemistry, as well as the first detection of HNCNH, a potential DNA nucleobase precursor, which must be formed in ices. I'll also present the design and construction of, and initial spectroscopic work with, a time-domain spectrometer built to study astrochemical ices in the largely unexplored TerHertz (far-Infrared) region of the spectrum, and its application to astronomical observations.

  14. Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)

    CERN Document Server

    Persson, C M; Cernicharo, J; Goicoechea, J R; Hassel, G E; Herbst, E; Gerin, M; De Luca, M; Bell, T A; Coutens, A; Falgarone, E; Goldsmith, P F; Gupta, H; Kazmierczak, M; Lis, D C; Mookerjea, B; Neufeld, D A; Pearson, J; Phillips, T G; Sonnentrucker, P; Stutzki, J; Vastel, C; Yu, S; Boulanger, F; Dartois, E; Encrenaz, P; Geballe, T R; Giesen, T; Godard, B; Gry, C; Hennebelle, P; Hily-Blant, P; Joblin, C; Kolos, R; Krelowski, J; Martin-Pintado, J; Menten, K; Monje, R; Perault, M; Plume, R; Salez, M; Schlemmer, S; Schmidt, M; Teyssier, D; Peron, I; Cais, P; Gaufre, P; Cros, A; Ravera, L; Morris, P; Lord, S; Planesas, P

    2010-01-01

    The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N=1-0, J=2-1 and ortho-NH2 1_1,1-0_0,0. We also observed ortho-NH3 1_0-0_0, and 2_0-1_0, para-NH3 2_1-1_1, and searched unsuccessfully for NH+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11-54 km/s are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6*10^-9, 3*10^-9, and 3*10^-9 for NH, NH2, and NH3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry...

  15. Optical IFU observations of gas pillars surrounding the super star cluster NGC 3603

    CERN Document Server

    Westmoquette, M S; Ercolano, B; Smith, L J

    2013-01-01

    We present optical integral field unit (IFU) observations of two gas pillars surrounding the Galactic young massive star cluster NGC 3603. The high S/N and spectral resolution of these data have allowed us to accurately quantify the H-alpha, [NII] and [SII] emission line shapes, and we find a mixture of broad (FWHM~70-100 km/s) and narrow (10000 cm-3. In one pillar we found that these high densities are only found in the narrow component, implying it must originate from deeper within the pillar than the broad component. From this, together with our kinematical data, we conclude that the narrow component traces a photoevaporation flow, and that the TML forms at the interface with the hot wind. On the pillar surfaces we find a consistent offset in radial velocity between the narrow (brighter) components of H-alpha and [NII] of ~5-8 km/s, for which we were unable to find a satisfactory explanation. We urge the theoretical community to simulate mechanical and radiative cloud interactions in more detail to address...

  16. Gas-phase Reactions of Polycyclic Aromatic Hydrocarbon Anions with Molecules of Interstellar Relevance

    Science.gov (United States)

    Demarais, Nicholas J.; Yang, Zhibo; Martinez, Oscar; Wehres, Nadine; Snow, Theodore P.; Bierbaum, Veronica M.

    2012-02-01

    We have studied reactions of small dehydrogenated polycyclic aromatic hydrocarbon anions with neutral species of interstellar relevance. Reaction rate constants are measured at 300 K for the reactions of phenide (C6H- 5), naphthalenide (C10H- 7), and anthracenide (C14H- 9) with atomic H, H2, and D2 using a flowing afterglow-selected ion flow tube instrument. Reaction rate constants of phenide with neutral molecules (CO, O2, CO2, N2O, C2H2, CH3OH, CH3CN, (CH3)2CO, CH3CHO, CH3Cl, and (CH3CH2)2O) are also measured under the same conditions. Experimental measurements are accompanied by ab initio calculations to provide insight into reaction pathways and enthalpies. Our measured reaction rate constants should prove useful in the modeling of astrophysical environments, particularly when applied to dense regions of the interstellar and circumstellar medium.

  17. Interstellar Dust Close to the Sun

    CERN Document Server

    Frisch, Priscilla C

    2012-01-01

    The low density interstellar medium (ISM) close to the Sun and inside of the heliosphere provides a unique laboratory for studying interstellar dust grains. Grain characteristics in the nearby ISM are obtained from observations of interstellar gas and dust inside of the heliosphere and the interstellar gas towards nearby stars. Comparison between the gas composition and solar abundances suggests that grains are dominated by olivines and possibly some form of iron oxide. Measurements of the interstellar Ne/O ratio by the Interstellar Boundary Explorer spacecraft indicate that a high fraction of interstellar oxygen in the ISM must be depleted onto dust grains. Local interstellar abundances are consistent with grain destruction in ~150 km/s interstellar shocks, provided that the carbonaceous component is hydrogenated amorphous carbon and carbon abundances are correct. Variations in relative abundances of refractories in gas suggest variations in the history of grain destruction in nearby ISM. The large observed ...

  18. High-resolution extreme ultraviolet spectroscopy of G191-B2B: structure of the stellar photosphere and the surrounding interstellar medium

    Science.gov (United States)

    Barstow, M. A.; Cruddace, R. G.; Kowalski, M. P.; Bannister, N. P.; Yentis, D.; Lapington, J. S.; Tandy, J. A.; Hubeny, I.; Schuh, S.; Dreizler, S.; Barbee, T. W.

    2005-10-01

    We have continued our detailed analysis of the high-resolution (R= 4000) spectroscopic observation of the DA white dwarf G191-B2B, obtained by the Joint Astrophysical Plasmadynamic Experiment (J-PEX) normal incidence sounding rocket-borne telescope, comparing the observed data with theoretical predictions for both homogeneous and stratified atmosphere structures. We find that the former models give the best agreement over the narrow waveband covered by J-PEX, in conflict with what is expected from previous studies of the lower resolution but broader wavelength coverage Extreme Ultraviolet Explorer spectra. We discuss the possible limitations of the atomic data and our understanding of the stellar atmospheres that might give rise to this inconsistency. In our earlier study, we obtained an unusually high ionization fraction for the ionized HeII present along the line of sight to the star. In the present paper, we obtain a better fit when we assume, as suggested by Space Telescope Imaging Spectrograph results, that this HeII resides in two separate components. When one of these is assigned to the local interstellar cloud, the implied He ionization fraction is consistent with measurements along other lines of sight. However, the resolving power and signal-to-noise available from the instrument configuration used in this first successful J-PEX flight are not sufficient to clearly identify and prove the existence of the two components.

  19. VALES - III. The calibration between the dust continuum and interstellar gas content of star-forming galaxies

    Science.gov (United States)

    Hughes, T. M.; Ibar, E.; Villanueva, V.; Aravena, M.; Baes, M.; Bourne, N.; Cooray, A.; Davies, L. J. M.; Driver, S.; Dunne, L.; Dye, S.; Eales, S.; Furlanetto, C.; Herrera-Camus, R.; Ivison, R. J.; van Kampen, E.; Lara-López, M. A.; Maddox, S.; Michałowski, M. J.; Oteo, I.; Smith, D.; Smith, M. W. L.; Valiante, E.; van der Werf, P.; Viaene, S.; Xue, Y. Q.

    2017-06-01

    We present the calibration between the dust continuum luminosity and interstellar gas content obtained from the Valparaíso ALMA Line Emission Survey (VALES) sample of 67 main-sequence star-forming galaxies at 0.02 Assembly survey. Adopting αCO = 6.5 (K km s-1 pc2)-1, the average ratio of L_{ν _{850}}/MH2 = (6.4 ± 1.4)× 1019 erg s-1 Hz-1 M_{⊙}^{-1}, in excellent agreement with literature values. We obtain a linear fit of log _{10} ({M}_{H2}/{M_{⊙}}) = (0.92± 0.02) log _{10} (L_{ν _{850}}/{erg s^{-1} Hz^{-1}})-(17.31± 0.59). We provide relations between L_{ν _{850}}, MH2 and MISM when combining the VALES and literature samples, and adopting a Galactic αCO value.

  20. Peptide bond formation through gas-phase reactions in the interstellar medium: formamide and acetamide as prototypes

    Energy Technology Data Exchange (ETDEWEB)

    Redondo, Pilar; Barrientos, Carmen; Largo, Antonio, E-mail: predondo@qf.uva.es [Computational Chemistry Group, Departamento de Química Física, Facultad de Ciencias, Universidad de Valladolid, E-47011 Valladolid (Spain)

    2014-09-20

    A theoretical study of the reactions of NH{sub 4}{sup +} with formaldehyde and CH{sub 5}{sup +} with formamide is carried out. The viability of these gas-phase ion-molecule reactions as possible sources of formamide and acetamide under the conditions of interstellar medium is evaluated. We report a theoretical estimation of the reaction enthalpies and an analysis of their potential energy surfaces. Formation of protonated formamide from the reaction between ammonium cation and formaldehyde is an exothermic process, but all the channels located on the potential energy surface leading to this product present net activation energies. For the reaction between methanium and formamide, different products are possible from a thermodynamic point of view. An analysis of its potential energy surface showed that formation of protonated acetamide and amino acetaldehyde takes place through barrier-free paths. Therefore, this reaction could be a feasible source of acetamide and amino acetaldehyde in space.

  1. Numerical simulation of free surface incompressible liquid flows surrounded by compressible gas

    Science.gov (United States)

    Caboussat, A.; Picasso, M.; Rappaz, J.

    2005-03-01

    A numerical model for the three-dimensional simulation of liquid-gas flows with free surfaces is presented. The incompressible Navier-Stokes equations are assumed to hold in the liquid domain. In the gas domain, the velocity is disregarded, the pressure is supposed to be constant in each connected component of the gas domain and follows the ideal gas law. The gas pressure is imposed as a normal force on the liquid-gas interface. An implicit splitting scheme is used to decouple the physical phenomena. Given the gas pressure on the interface, the method described in [J. Comput Phys. 155 (1999) 439; Int. J. Numer. Meth. Fluids 42(7) (2003) 697] is used to track the liquid domain and to compute the velocity and pressure fields in the liquid. Then the connected components of the gas domain are found using an original numbering algorithm. Finally, the gas pressure is updated from the ideal gas law in each connected component of gas. The implementation is validated in the frame of mould filling. Numerical results in two and three space dimensions show that the effect of pressure in the bubbles of gas trapped by the liquid cannot be neglected.

  2. Efficient Simulations of Interstellar Gas-Grain Chemistry Using Moment Equations

    CERN Document Server

    Barzel, B

    2007-01-01

    Networks of reactions on dust grain surfaces play a crucial role in the chemistry of interstellar clouds, leading to the formation of molecular hydrogen in diffuse clouds as well as various organic molecules in dense molecular clouds. Due to the sub-micron size of the grains and the low flux, the population of reactive species per grain may be very small and strongly fluctuating. Under these conditions rate equations fail and the simulation of surface-reaction networks requires stochastic methods such as the master equation. However, the master equation becomes infeasible for complex networks because the number of equations proliferates exponentially. Here we introduce a method based on moment equations for the simulation of reaction networks on small grains. The number of equations is reduced to just one equation per reactive specie and one equation per reaction. Nevertheless, the method provides accurate results, which are in excellent agreement with the master equation. The method is demonstrated for the m...

  3. Molecular gas and triggered star formation surrounding Wolf-Rayet stars

    CERN Document Server

    Liu, Tie; Zhang, Huawei

    2012-01-01

    The environments surrounding nine Wolf-Rayet stars were studied in molecular emission. Expanding shells were detected surrounding these WR stars (see left panels of Figure 1). The average masses and radii of the molecular cores surrounding these WR stars anti-correlate with the WR stellar wind velocities (middle panels of Figure 1), indicating the WR stars has great impact on their environments. The number density of Young Stellar Objects (YSOs) is enhanced in the molecular shells at $\\sim$5 arcmin from the central WR star (lower-right panel of Figure 1). Through detailed studies of the molecular shells and YSOs, we find strong evidences of triggered star formation in the fragmented molecular shells (\\cite[Liu et al. 2010]{liu_etal12}

  4. INTERSTELLAR TURBULENCE

    Directory of Open Access Journals (Sweden)

    D. Falceta-Gonçalves

    2011-01-01

    Full Text Available The Interstellar Medium (ISM is a complex, multi-phase system, where the history of the stars occurs. The processes of birth and death of stars are strongly coupled to the dynamics of the ISM. The observed chaotic and diffusive motions of the gas characterize its turbulent nature. Understanding turbulence is crucial for understanding the star-formation process and the energy-mass feedback from evolved stars. Magnetic fields, threading the ISM, are also observed, making this effort even more difficult. In this work, I briefly review the main observations and the characterization of turbulence from these observable quantities. Following on, I provide a review of the physics of magnetized turbulence. Finally, I will show the main results from theoretical and numerical simulations, which can be used to reconstruct observable quantities, and compare these predictions to the observations.

  5. Laboratory Studies of Stabilities of Heterocyclic Aromatic Molecules: Suggested Gas Phase Ion-Molecule Routes to Production in Interstellar Gas Clouds

    Science.gov (United States)

    Adams, Nigel G.; Fondren, L. Dalila; McLain, Jason L.; Jackson, Doug M.

    2006-01-01

    Several ring compounds have been detected in interstellar gas clouds, ISC, including the aromatic, benzene. Polycyclic aromatic hydrocarbons, PAHs, have been implicated as carriers of diffuse interstellar bands (DIBs) and unidentified infrared (UIR) bands. Heterocyclic aromatic rings of intermediate size containing nitrogen, possibly PreLife molecules, were included in early searches but were not detected and a recent search for Pyrimidine was unsuccessful. Our laboratory investigations of routes to such molecules could establish their existence in ISC and suggest conditions under which their concentrations would be maximized thus aiding the searches. The stability of such ring compounds (C5H5N, C4H4N2, C5H11N and C4H8O2) has been tested in the laboratory using charge transfer excitation in ion-molecule reactions. The fragmentation paths, including production of C4H4(+), C3H3N(+) and HCN, suggest reverse routes to the parent molecules, which are presently under laboratory investigation as production sources.

  6. The interstellar gas seen in the mid- and far-infrared: The promise of SPICA Space Telescope

    CERN Document Server

    Goicoechea, Javier R

    2009-01-01

    The mid- and far-IR spectral ranges are critical windows to characterize the physical and chemical processes that transform the interstellar gas and dust into stars and planets. Sources in the earliest phases of star formation and in the latest stages of stellar evolution release most of their energy at these wavelengths. Besides, the mid- and far-IR ranges provide key spectral diagnostics of the gas chemistry (water, light hydrides, organic species ...), of the prevailing physical conditions (H2, atomic fine structure lines...), and of the dust mineral and ice composition that can not be observed from ground-based telescopes. With the launch of JAXA's SPICA telescope, uninterrupted studies in the mid- and far-IR will be possible since ESA's Infrared Space Observatory (1995). In particular, SAFARI will provide full access to the 34-210um waveband through several detector arrays and flexible observing modes (from broadband photometry to medium resolution spectroscopy with R~3,000 at 63um), and reaching very hi...

  7. Impact of oil and gas field in sugar cane condition using landsat 8 in Indramayu area and its surrounding, West Java province, Republic of Indonesia

    Science.gov (United States)

    Muji Susantoro, Tri; Wikantika, Ketut; Saskia Puspitasari, Alia; Saepuloh, Asep

    2017-01-01

    This study tried to monitor sugar cane condition surrounding of oil and gas field area. The spectral approaches were conducted for mapping sugar cane stress. As an initial stage Landsat-8 was corrected radiometrically and geometrically. Radiometric correction is an important stages for spectral approaching. Then all pixel values were transformed to the surface reflectance. Several vegetation indices were calculated to monitor vegetation stress surrounding of oil and gas field. NDVI, EVI, DVI, GVI, GRVI, GDVI and GNDVI were applied for generating tentative sugar cane stress images. The results indicated that sugar cane surrounding of oil and gas field has been influenced by oil and gas field.

  8. Mm/submm Study of Gas-Phase Photoproducts from Methanol Interstellar Ice Analogues

    Science.gov (United States)

    Mesko, AJ; Smith, Houston Hartwell; Milam, Stefanie N.; Widicus Weaver, Susanna L.

    2016-06-01

    Icy grain reactions have gained quite the popularity in the astrochemistry community to explain the formation of complex organic molecules. Through temperature programmed desorption and photolysis experiments we use rotational spectroscopy to measure the gas-phase products of icy grain reactions. Previous results include testing detection limits of the system by temperature programmed desorption of methanol and water ices, photochemistry of gas-phase methanol, and detection of photodesorbed water from a pure water ice surface. Current work that will be discussed focuses on the detection of gas-phase CO and other photoproducts from an ice surface.

  9. Gas Properties and Implications for Galactic Star Formation in Numerical Models of the Turbulent, Multiphase Interstellar Medium

    Science.gov (United States)

    Koyama, Hiroshi; Ostriker, Eve C.

    2009-03-01

    Using numerical simulations of galactic disks that resolve scales from ~1 to several hundred pc, we investigate dynamical properties of the multiphase interstellar medium (ISM) in which turbulence is driven by feedback from star formation. We focus on effects of H II regions by implementing a recipe for intense heating confined within dense, self-gravitating regions. Our models are two dimensional, representing radial-vertical slices through the disk, and include sheared background rotation of the gas, vertical stratification, heating and cooling to yield temperatures T ~ 10 - 104 K, and conduction that resolves thermal instabilities on our numerical grid. Each simulation evolves to reach a quasi-steady state, for which we analyze the time-averaged properties of the gas. In our suite of models, three parameters (the gas surface density Σ, the stellar volume density ρ*, and the local angular rotation rate Ω) are separately controlled in order to explore environmental dependences. Among other statistical measures, we evaluate turbulent amplitudes, virial ratios, Toomre Q parameters including turbulence, and the mass fractions at different densities. We find that the dense gas (n>100 cm-3) has turbulence levels similar to those observed in giant molecular clouds and virial ratios ~1-2. Our models show that the Toomre Q parameter in the dense gas evolves to values near unity; this demonstrates self-regulation via turbulent feedback. We also test how the surface star formation rate ΣSFR depends on Σ, ρ*, and Ω. Under the assumption that the star formation rate (SFR) is proportional to the amount of gas at densities above a threshold n th divided by the free-fall time at that threshold, we find that ΣSFR vprop Σ1+p with 1 + p~ 1.2-1.4 when n th = 102 or 103 cm-3, consistent with observed Kennicutt-Schmidt relations. Estimates of SFRs based on large-scale properties (the orbital time, the Jeans time, or the free-fall time at the mean density within a scale height

  10. Upgrade of PARC2D to include real gas effects. [computer program for flowfield surrounding aeroassist flight experiment

    Science.gov (United States)

    Saladino, Anthony; Praharaj, Sarat C.; Collins, Frank G.; Seaford, C. Mark

    1990-01-01

    This paper presents a description of the changes and additions to the perfect gas PARC2D code to include chemical equilibrium effects, resulting in a code called PARCEQ2D. The work developed out of a need to have the capability of more accurately representing the flowfield surrounding the aeroassist flight experiment (AFE) vehicle. Use is made of the partition function of statistical mechanics in the evaluation of the thermochemical properties. This approach will allow the PARC code to be extended to thermal nonequilibrium when this task is undertaken in the future. The transport properties follow from formulae from the kinetic theory of gases. Results are presented for a two-dimensional AFE that compare perfect gas and real gas solutions at flight conditions, showing vast differences between the two cases.

  11. Interstellar processes; Proceedings of the Symposium, Grand Teton National Park, WY, July 1-7, 1986

    Science.gov (United States)

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

    1987-01-01

    The conference presents papers on the Milky Way as a galaxy; observations of components of the interstellar medium; interstellar magnetic properties; interstellar processes on a galactic scale; dynamical processes in interstellar clouds; interstellar dust grains; interstellar chemical processes; and heating, cooling, and radiative processes. Attention is given to H2 in the Galaxy, hot interstellar gas in the Galactic disk and halo, interstellar magnetic fields, cloud formation and destruction, theoretical approaches to interstellar turbulence, and infrared absorption and emission characteristics of interstellar PAHs. Other topics include gas phase chemical processes in molecular clouds, the chemical evolution of galaxies, and the atomic and molecular physics of interstellar heating and cooling.

  12. Production of secondary particles and nuclei in cosmic rays collisions with the interstellar gas using the FLUKA code

    Science.gov (United States)

    Mazziotta, M. N.; Cerutti, F.; Ferrari, A.; Gaggero, D.; Loparco, F.; Sala, P. R.

    2016-08-01

    The measured fluxes of secondary particles produced by the interactions of Cosmic Rays (CRs) with the astronomical environment play a crucial role in understanding the physics of CR transport. In this work we present a comprehensive calculation of the secondary hadron, lepton, gamma-ray and neutrino yields produced by the inelastic interactions between several species of stable or long-lived cosmic rays projectiles (p, D, T, 3He, 4He, 6Li, 7Li, 9Be, 10Be, 10B, 11B, 12C, 13C, 14C, 14N, 15N, 16O, 17O, 18O, 20Ne, 24Mg and 28Si) and different target gas nuclei (p, 4He, 12C, 14N, 16O, 20Ne, 24Mg, 28Si and 40Ar). The yields are calculated using FLUKA, a simulation package designed to compute the energy distributions of secondary products with large accuracy in a wide energy range. The present results provide, for the first time, a complete and self-consistent set of all the relevant inclusive cross sections regarding the whole spectrum of secondary products in nuclear collisions. We cover, for the projectiles, a kinetic energy range extending from 0.1 GeV/n up to 100 TeV/n in the lab frame. In order to show the importance of our results for multi-messenger studies about the physics of CR propagation, we evaluate the propagated spectra of Galactic secondary nuclei, leptons, and gamma rays produced by the interactions of CRs with the interstellar gas, exploiting the numerical codes DRAGON and GammaSky. We show that, adopting our cross section database, we are able to provide a good fit of a complete sample of CR observables, including: leptonic and hadronic spectra measured at Earth, the local interstellar spectra measured by Voyager, and the gamma-ray emissivities from Fermi-LAT collaboration. We also show a set of gamma-ray and neutrino full-sky maps and spectra.

  13. Propagation mechanisms of guided streamers in plasma jets: the influence of electronegativity of the surrounding gas

    Science.gov (United States)

    Schmidt-Bleker, Ansgar; Norberg, Seth A.; Winter, Jörn; Johnsen, Eric; Reuter, S.; Weltmann, K. D.; Kushner, Mark J.

    2015-06-01

    Atmospheric pressure plasma jets for biomedical applications are often sustained in He with small amounts of, for example, O2 impurities and typically propagate into ambient air. The resulting poorly controlled generation of reactive species has motivated the use of gas shields to control the interaction of the plasma plume with the ambient gas. The use of different gases in the shield yields different behavior in the plasma plume. In this paper, we discuss results from experimental and computational investigations of He plasma jets having attaching and non-attaching gas shields. We found that negative ion formation in the He-air mixing region significantly affects the ionization wave dynamics and promotes the propagation of negative guided streamers through an electrostatic focusing mechanism. Results from standard and phase resolved optical emission spectroscopy ratios of emission from states of N2 and He imply different electric fields in the plasma plume depending on the composition of the shielding gas. These effects are attributed to the conductivity in the transition region between the plasma plume and the shield gas, and the immobile charge represented by negative ions. The lower conductivity in the attaching mixtures enables more extended penetration of the electric field whereas the negative ions aid in focusing the electrons towards the axis.

  14. ASTRO-H White Paper - High Resolution Spectroscopy of Interstellar and Circumgalactic Gas in the Milky Way and Other Galaxies

    CERN Document Server

    Paerels, F; Anabuki, N; Costantini, E; de Vries, C; Fujimoto, R; Hornschemeier, A; Iizuka, R; Kilbourne, C; Konami, S; LaMassa, S; Loewenstein, M; McCammon, D; Matsushita, K; McNamara, B; Mitsuishi, I; Nagino, R; Nakagawa, T; Porter, S; Sakai, K; Smith, R K; Takei, Y; Tsuru, T; Uchiyama, H; Yamaguchi, H; Yamauchi, S

    2014-01-01

    We describe the potential of high resolution imaging spectroscopy with the SXS on ASTRO-H to advance our understanding of the interstellar- and circumgalactic media of our own Galaxy, and other galaxies. Topics to be addressed range from absorption spectroscopy of dust in the Galactic interstellar medium, to observations to constrain the total mass-, metal-, and energy flow out of starburst galaxies.

  15. Gas-grain Modeling of Isocyanic Acid (HNCO), Cyanic Acid (HOCN), Fulminic Acid (HCNO), and Isofulminic Acid (HONC) in Assorted Interstellar Environments

    Science.gov (United States)

    Quan, Donghui; Herbst, Eric; Osamura, Yoshihiro; Roueff, Evelyne

    2010-12-01

    Isocyanic acid (HNCO) is a well-known interstellar molecule. Evidence also exists for the presence of two of its metastable isomers in the interstellar medium: HCNO (fulminic acid) and HOCN (cyanic acid). Fulminic acid has been detected toward cold and lukewarm sources, while cyanic acid has been detected both in these sources and in warm sources in the Galactic Center. Gas-phase models can reproduce the abundances of the isomers in cold sources, but overproduce HCNO in the Galactic Center. Here we present a detailed study of a gas-grain model that contains these three isomers, plus a fourth isomer, isofulminic acid (HONC), for four types of sources: hot cores, the warm envelopes of hot cores, lukewarm corinos, and cold cores. The current model is partially able to rationalize the abundances of HNCO, HOCN, and HCNO in cold and warm sources. Predictions for HONC in all environments are also made.

  16. Effect of surrounding gas condition on surface integrity in micro-drilling of SiC by ns pulsed laser

    Science.gov (United States)

    Okamoto, Yasuhiro; Asako, Kiichi; Nishi, Norio; Sakagawa, Tomokazu; Okada, Akira

    2015-06-01

    The influence of the surrounding gas conditions on the surface integrity in the micro-drilling of silicon carbide was experimentally investigated using ns pulsed laser of 266 nm wavelength. Moreover, micro-machining characteristics were observed using high-speed shutter and video cameras in the micro-drilling of silicon carbide. The size and intensity of the laser-induced plasma were larger, and the plasma affected area was larger and deeper in argon than that in air. Although the intensity of the plasma was lower in helium than that in other gases, the surface around the drilled hole was roughened by the spread of the plasma in the vicinity of the drilled hole. Debris was removed along the flow field generated by laser shot in the opposite direction to the laser irradiation. The gas flow behavior and the spectrum and intensity of the laser-induced plasma were influenced by the surrounding gas type and pressure. The appearance of plasma generation affected the surface integrity at the circumference of the drilled hole, and the surface integrity was improved by reducing the pressure.

  17. Digital tabulation of stratigraphic data from oil and gas wells in Cuyama Valley and surrounding areas, central California

    Science.gov (United States)

    Sweetkind, Donald S.; Bova, Shiera C.; Langenheim, V.E.; Shumaker, Lauren E.; Scheirer, Daniel S.

    2013-01-01

    Stratigraphic information from 391 oil and gas exploration wells from Cuyama Valley, California, and surrounding areas are herein compiled in digital form from reports that were released originally in paper form. The Cuyama Basin is located within the southeasternmost part of the Coast Ranges and north of the western Transverse Ranges, west of the San Andreas fault. Knowledge of the location and elevation of stratigraphic tops of formations throughout the basin is a first step toward understanding depositional trends and the structural evolution of the basin through time, and helps in understanding the slip history and partitioning of slip on San Andreas and related faults.

  18. Investigations of Flare Gas Emissions in Taq Taq Oil Field on the Surrounding Land

    Directory of Open Access Journals (Sweden)

    Jafar A. Ali

    2014-11-01

    Full Text Available Environmental pollution caused by oil takes many different forms; one of the most damaging sources is simply the combustion of oil products, such as a well flare burn-off. This paper presents the results of a survey of the agriculture lands around the Taq Taq Oil Production Company. The aim of the survey was to determine the potential contamination caused by the gas emissions from the well flares. Taq Taq field is located in the Kurdistan Region of Iraq, 60 km north of the giant Kirkuk oil field, 85 km south-east of Erbil and 120 km north-west of Suleimani. Samples of soil were collected from several locations around the site and analyzed to determine the content of Polycyclic Aromatic Hydrocarbons PAH present. A gas chromatography linked to a mass spectrometry (GCMS machine was used for these measurements. The PAH contamination at each location of soil was determined and the 16-PAHs, as listed in the US Environmental Protection Agency (EPA documentation were investigated. The average content of total PAH in all samples of the agricultural soil was 0.654 mg·kg-1 with the concentrations ranging from 0.310 to 0.869 mg·kg-1. It was found that the PAH concentrations decreased with increasing distance from the TTOPCO oil field, indicating that pollution was evident, the area close to the field being more affected by the gas pollution.

  19. Diffuse Interstellar Bands: How Are They Related to Known Gas-Phase Constituents of the ISM?

    OpenAIRE

    Welty, Daniel E.

    2013-01-01

    In this brief review of recent work relating the DIBs to other gas-phase constituents of the ISM, we explore correlations between DIB equivalent widths and the column densities of various atomic and molecular species, drawn from a large database constructed for that purpose. The tightness and slopes of the correlations can provide information on how the DIBs might be related to those species (physically, chemically, spatially) and on various properties of the DIB carriers. Deviations from the...

  20. Wide-Area Interference Spectroscopy of the Ionized Gas Surrounding the OCL-352 (IC-1805) Stellar Association

    Science.gov (United States)

    Solomos, Nikolaos

    We investigated the global kinematics of the giant ionized shell IC1805 centred a (l,b)=(134.7deg,+0.92deg)at a distance of -2.3 Kpc and surrounding the Ocl352, within Cassiopeia OB6 stellar association. Fabry-Perot interference spectroscopy data in the light of [SIII]9530.9A have been used to obtain the radial velocity field of the IC1795/IC1805 (W3/W4) region as a means to probe the large scale gas motions around Cass Ocl-352. The observations are discussed and interpreted in conjuction with radioastronomical and optical data available. A new empirical model is proposed to account for the complex kinematical structure of the region. As was suggested by Solomos (Ph.D Thesis, 1991)the region is a leaking HII shell with the ionized gas flowing to the North escaping from the galactic plane.

  1. Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150

    CERN Document Server

    Pety, Jérôme; Liszt, Harvey S

    2008-01-01

    To understand the environment and extended structure of the host galactic gas whose molecular absorption line chemistry, we previously observed along the microscopic line of sight to the blazar/radiocontinuum source NRAO150 (aka B0355+508), we used the IRAM 30m Telescope and Plateau de Bure Interferometer to make two series of images of the host gas: i) 22.5 arcsec resolution single-dish maps of 12CO J=1-0 and 2-1 emission over a 220 arcsec by 220 arcsec field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of 12CO J=1-0 emission at 5.8 arcsec resolution over a 90 arcsec-diameter region. CO components that are observed in absorption at a moderate optical depth (0.5) and are undetected in emission at 1 arcmin resolution toward NRAO 150 remain undetected at 6 arcsec resolution. This implies that they are not a previously-hidden large-scale molecular component revealed in absorption, but they do highlight the robustness of the chemistry into regions where the density and column density are to...

  2. Ripping Apart at the Seams: The Network of Stripped Gas Surrounding M86

    CERN Document Server

    Ehlert, S; Simionescu, A; Allen, S W; Kenney, J D P; Million, E; Finoguenov, A

    2012-01-01

    We present a new study of the Virgo Cluster galaxies M86, M84, NGC 4338, and NGC 4438 using a mosaic of five separate pointings with XMM-Newton. Our observations allow for robust measurements of the temperature and metallicity structure of each galaxy along with the entire ~ 1 degree region between these galaxies. When combined with multiwavelength observations, the data suggest that all four of these galaxies are undergoing ram pressure stripping by the Intracluster Medium (ICM). The manner in which the stripped gas trailing the galaxies interacts with the ICM, however, is observably distinct. Consistent with previous observations, M86 is observed to have a long tail of ~ 1 keV gas trailing to the north-west for distances of ~ 100-150 kpc. However, a new site of ~ 0.6 keV thermal emission is observed to span to the east of M86 in the direction of the disturbed spiral galaxy NGC 4438. This region is spatially coincident with filaments of H-alpha emission, likely originating in a recent collision between the t...

  3. IONIZED GAS IN THE FIRST 10 kpc OF THE INTERSTELLAR GALACTIC HALO: METAL ION FRACTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Howk, J. Christopher [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Consiglio, S. Michelle, E-mail: jhowk@nd.edu, E-mail: smconsiglio@ucla.edu [Current address: Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, CA 90095 (United States)

    2012-11-10

    We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high-resolution ultraviolet absorption-line spectroscopy of post-asymptotic giant branch stars in the globular clusters Messier 3 [(l, b) = (42.{sup 0}2, +78.{sup 0}7), d = 10.2 kpc, and z = 10.0 kpc] and Messier 5 [(l, b) = (3.{sup 0}9, +46.{sup 0}8), d = 7.5 kpc, and z = +5.3 kpc] with the Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure, or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H I. These clusters also house millisecond pulsars, whose dispersion measures give an electron column density from which we infer the H II column in these directions. We find fractions of S{sup +2} in the WIM for the M 3 and M 5 sight lines x(S{sup +2}) {identical_to} N(S{sup +2})/N(S) = 0.33 {+-} 0.07 and 0.47 {+-} 0.09, respectively, with variations perhaps related to location. With negligible quantities of the higher ionization states, we conclude that S{sup +} and S{sup +2} account for all of the S in the WIM. We extend the methodology to study the ion fractions in the warm and hot ionized gas of the Milky Way, including the high ions Si{sup +3}, C{sup +3}, N{sup +4}, and O{sup +5}. The vast majority of the Galactic ionized gas is warm (T {approx} 10{sup 4} K) and photoionized (the WIM) or very hot (T > 4 Multiplication-Sign 10{sup 5} K) and collisionally ionized. The common tracer of ionized gas beyond the Milky Way, O{sup +5}, traces <1% of the total ionized gas mass of the Milky Way.

  4. Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC 612 (PKS 0131-36)

    CERN Document Server

    Emonts, B H C; Oosterloo, T A; Holt, J; Tadhunter, C N; Van der Hulst, J M; Ojha, R; Sadler, E M

    2008-01-01

    We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131-36). Using the Australia Telescope Compact Array, we detect M_HI = 1.8 x 10^9 M_sun of HI emission-line gas that is distributed in a 140 kpc wide disc-like structure along the optical disc and dust-lane of NGC 612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850 km/s, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The HI disc in NGC 612 suggests that the total mass enclosed by the system is M_enc ~ 2.9 x 10^12 sin^-2(i) M_sun, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC 612, indicating that ...

  5. A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium

    CERN Document Server

    Jenkins, Edward B

    2009-01-01

    A study of gas-phase element abundances reported in the literature for 17 different elements sampled over 243 sight lines in the local part of our Galaxy reveals that the depletions into solid form (dust grains) are extremely well characterized by trends that employ only three kinds of parameters. One is an index that describes the overall level of depletion applicable to the gas in any particular sight line, and the other two represent linear coefficients that describe how to derive each element's depletion from this sight-line parameter. The information from this study reveals the relative proportions of different elements that are incorporated into dust at different stages of grain growth. An extremely simple scheme is proposed for deriving the dust contents and metallicities of absorption-line systems that are seen in the spectra of distant quasars or the optical afterglows of gamma-ray bursts. Contrary to presently accepted thinking, the elements sulfur and krypton appear to show measurable changes in th...

  6. Environmental assessment survey of the vegetation surrounding a Lower Wilcox Group coal gas well site

    Science.gov (United States)

    McCoy, John W.

    2004-01-01

    This environmental assessment was conducted to examine the impacts on vegetation of the drilling and operation of a coal gas well located along Hwy 134 about 5 miles (8 km) east of Fairbanks, La. The drill site is 85 meters north of Hwy 134 and operations at the well were performed by EnerVest Operating LLC. The site (privately owned) was formerly a mixed hardwood/pine forest that was clear-cut in 1998 and planted with loblolly pine. Once completed, the well site, with its associated pipeline covered about 1,560 m2 (11.5 percent of the survey area). This survey was conducted in coordination with Peter D. Warwick, Research Geologist, U.S. Geological Survey, and Jim York, contract geologist for EnerVest Operating, LLC.

  7. Chemical composition of interstellar dust

    Science.gov (United States)

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

    Study of chemical evolution of interstellar medium is well recognized to be a challenging task. Interstellar medium (ISM) is a rich reservoir of complex molecules. So far, around 180 gas phase molecules and around 20 molecular species on the interstellar dust have been detected in various regions of ISM, especially in regions of star formation. In last decade, it was well established that gas phase reactions alone cannot explain molecular abundances in ISM. Chemical reactions which occur on interstellar dust grains are essential to explain formation of several molecules especially hydrogenated species including simplest and most abundant molecule H2. Interstellar grains provide surface for accreted species to meet and react. Therefore, an understanding of formation of molecules on grain surfaces is of prime importance. We concentrate mainly on water, methanol, carbon dioxide, which constitute nearly 90% of the grain mantle. These molecules are detected on grain surface due to their strong absorption bands arising out of multiple vibrational modes. Water is the most abundant species (with a surface coverage >60% ) on a grain in dense interstellar medium. CO2 is second most abundant molecule in interstellar medium with an abundance of around 20% with respect to H2O. However, this can vary from cloud to cloud. In clouds like W 33A it could be even less than 5% of water abundance. The next most abundant molecule is CO, which is well studied ice with an abundance varying between 2%\\ to 15% of water. Methanol (CH3OH) is also very abundant having abundance 2% to 30% of water. Measurement of water deuterium fractionation is a relevant tool for understanding mechanisms of water formation and evolution from prestellar phase to formation of planets and comets. We are also considering deuterated species in our simulation. We use Monte Carlo method (considering multilayer regime) to mimic the exact scenario. We study chemical evolution of interstellar grain mantle by varying

  8. Diffuse Interstellar Bands: How Are They Related to Known Gas-Phase Constituents of the ISM?

    CERN Document Server

    Welty, Daniel E

    2013-01-01

    In this brief review of recent work relating the DIBs to other gas-phase constituents of the ISM, we explore correlations between DIB equivalent widths and the column densities of various atomic and molecular species, drawn from a large database constructed for that purpose. The tightness and slopes of the correlations can provide information on how the DIBs might be related to those species (physically, chemically, spatially) and on various properties of the DIB carriers. Deviations from the mean relationships can reveal dependences of DIB strengths on other parameters, regional variations in DIB behavior, and individual sight lines where unusual environmental conditions affect the DIBs. Variations in DIB profiles (e.g., wings, substructure) and relative strengths may be related to differences in physical conditions inferred from atomic and/or molecular absorption lines.

  9. Diffuse Interstellar Bands: How are they related to known Gas-Phase Constituents of the ISM?

    Science.gov (United States)

    Welty, D. E.

    2014-02-01

    In this brief review of recent work relating the DIBs to other gas-phase constituents of the ISM, we explore correlations between DIB equivalent widths and the column densities of various atomic and molecular species, drawn from a large database constructed for that purpose. The tightness and slopes of the correlations can provide information on how the DIBs might be related to those species (physically, chemically, spatially) and on various properties of the DIB carriers. Deviations from the mean relationships can reveal dependences of DIB strengths on other parameters, regional variations in DIB behavior, and individual sight lines where unusual environmental conditions affect the DIBs. Variations in DIB profiles (e.g., wings, substructure) and relative strengths may be related to differences in physical conditions inferred from atomic and/or molecular absorption lines.

  10. CO/H2, C/CO, OH/CO, and OH/O2 in dense interstellar gas: from high ionization to low metallicity

    Science.gov (United States)

    Bialy, Shmuel; Sternberg, Amiel

    2015-07-01

    We present numerical computations and analytic scaling relations for interstellar ion-molecule gas-phase chemistry down to very low metallicities (10-3 × solar), and/or up to high driving ionization rates. Relevant environments include the cool interstellar medium (ISM) in low-metallicity dwarf galaxies, early enriched clouds at the reionization and Pop-II star formation era, and in dense cold gas exposed to intense X-ray or cosmic ray sources. We focus on the behaviour for H2, CO, CH, OH, H2O and O2, at gas temperatures ˜100 K, characteristic of a cooled ISM at low metallicities. We consider shielded or partially shielded one-zone gas parcels, and solve the gas-phase chemical rate equations for the steady-state `metal-molecule abundances for a wide range of ionization parameters, ζ/n, and metallicties, Z '. We find that the OH abundances are always maximal near the H-to-H2 conversion points, and that large OH abundances persist at very low metallicities even when the hydrogen is predominantly atomic. We study the OH/O2, C/CO and OH/CO abundance ratios, from large to small, as functions of ζ/n and Z '. Much of the cold dense ISM for the Pop-II generation may have been OH-dominated and atomic rather than CO-dominated and molecular.

  11. Imaging galactic diffuse gas: bright, turbulent CO surrounding the line of sight to NRAO150

    Science.gov (United States)

    Pety, J.; Lucas, R.; Liszt, H. S.

    2008-10-01

    Aims: To understand the environment and extended structure of the host galactic gas whose molecular absorption line chemistry, we previously observed along the microscopic line of sight to the blazar/radiocontinuum source NRAO150 (aka B0355+508). Methods: We used the IRAM 30 m Telescope and Plateau de Bure Interferometer to make two series of images of the host gas: i) 22.5'' resolution single-dish maps of 12CO J = 1-0 and 2-1 emission over a 220'' by 220'' field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of 12CO J = 1-0 emission at 5.8'' resolution over a 90''-diameter region. Results: At 22.5'' resolution, the CO J = 1-0 emission toward NRAO150 is 30-100% brighter at some velocities than seen previously with 1' resolution, and there are some modest systematic velocity gradients over the 220'' field. Of the five CO components seen in the absorption spectra, the weakest ones are absent in emission toward NRAO150 but appear more strongly at the edges of the region mapped in emission. The overall spatial variations in the strongly emitting gas have Poisson statistics with rms fluctuations about equal to the mean emission level in the line wings and much of the line cores. The J = 2-1/J = 1-0 line ratios calculated pixel-by-pixel cluster around 0.7. At 6'' resolution, disparity between the absorption and emission profiles of the stronger components has been largely ameliorated. The 12CO J = 1-0 emission exhibits i) remarkably bright peaks, {T}_mb = 12-13 K, even as 4'' from NRAO150; ii) smaller relative levels of spatial fluctuation in the line cores, but a very broad range of possible intensities at every velocity; and iii) striking kinematics whereby the monotonic velocity shifts and supersonically broadened lines in 22.5'' spectra are decomposed into much stronger velocity gradients and abrupt velocity reversals of intense but narrow, probably subsonic, line cores. Conclusions: CO components that are observed in absorption at a moderate

  12. Chemical models of interstellar gas-grain processes. II - The effect of grain-catalysed methane on gas phase evolution

    Science.gov (United States)

    Brown, Paul D.; Charnley, S. B.

    1991-01-01

    The effects on gas phase chemistry which result from the continuous desorption of methane molecules from grain surfaces are studied. Significant and sustained enhancements in the abundances of several complex hydrocarbon molecules are found, in good agreement with their observed values in TMC-1. The overall agreement is, however, just as good for the case of zero CH4 desorption efficiency. It is thus impossible to determine from the models whether or not the grain-surface production of methane is responsible for the observed abundances of some hydrocarbon molecules.

  13. Gas in Galaxies

    OpenAIRE

    Bland-Hawthorn, J.; Reynolds, R. J.

    2000-01-01

    The interstellar medium (ISM) can be thought of as the galactic atmosphere which fills the space between stars. When clouds within the ISM collapse, stars are born. When the stars die, they return their matter to the surrounding gas. Therefore the ISM plays a vital role in galactic evolution. The medium includes starlight, gas, dust, planets, comets, asteroids, fast moving charged particles (cosmic rays) and magnetic fields. The gas can be further divided into hot, warm and cold components, e...

  14. DUST AND GAS IN THE MAGELLANIC CLOUDS FROM THE HERITAGE HERSCHEL KEY PROJECT. II. GAS-TO-DUST RATIO VARIATIONS ACROSS INTERSTELLAR MEDIUM PHASES

    Energy Technology Data Exchange (ETDEWEB)

    Roman-Duval, Julia; Gordon, Karl D.; Meixner, Margaret [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bot, Caroline [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l' université, F-67000 Strasbourg (France); Bolatto, Alberto; Jameson, Katherine [Department of Astronomy, Lab for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Hughes, Annie; Hony, Sacha [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Wong, Tony [University of Illinois at Urbana-Champaign, 1002 W. Green St., Urbana, IL 61801 (United States); Babler, Brian [Department of Astronomy, University of Wisconsin, 475 North Charter St., Madison, WI 53706 (United States); Bernard, Jean-Philippe [CNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse Cedex 4 (France); Clayton, Geoffrey C. [Louisiana State University, Department of Physics and Astronomy, 233-A Nicholson Hall, Tower Dr., Baton Rouge, LA 70803-4001 (United States); Fukui, Yasuo [Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Galametz, Maud [European Southern Observatory, Karl-Schwarzschild-Str 2, D-85748 Garching (Germany); Galliano, Frederic; Lebouteiller, Vianney; Lee, Min-Young [CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Glover, Simon [Zentrum für Astronomie, Institut für Theoretische Astrophysik, Universität Heidelberg, Albert-Ueberle Strasse 2, D-69120 Heidelberg (Germany); Israel, Frank [Sterrewacht Leiden, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Li, Aigen, E-mail: duval@stsci.edu [314 Physics Building, Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); and others

    2014-12-20

    The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), H I 21 cm, CO, and Hα observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380{sub −130}{sup +250} ± 3 in the LMC, and 1200{sub −420}{sup +1600} ± 120 in the SMC, not including helium. The atomic-to-molecular transition is located at dust surface densities of 0.05 M {sub ☉} pc{sup –2} in the LMC and 0.03 M {sub ☉} pc{sup –2} in the SMC, corresponding to A {sub V} ∼ 0.4 and 0.2, respectively. We investigate the range of CO-to-H{sub 2} conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on X {sub CO} to be 6 × 10{sup 20} cm{sup –2} K{sup –1} km{sup –1} s in the LMC (Z = 0.5 Z {sub ☉}) at 15 pc resolution, and 4 × 10{sup 21} cm{sup –2} K{sup –1} km{sup –1} s in the SMC (Z = 0.2 Z {sub ☉}) at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor ∼2, even after accounting for the effects of CO-dark H{sub 2} in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H{sub 2}. Within the expected 5-20 times Galactic X {sub CO} range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further modeling

  15. Interstellar Extinction

    Science.gov (United States)

    Gontcharov, G. A.

    2016-12-01

    This review describes our current understanding of interstellar extinction. This differ substantially from the ideas of the 20th century. With infrared surveys of hundreds of millions of stars over the entire sky, such as 2MASS, SPITZER-IRAC, and WISE, we have looked at the densest and most rarefied regions of the interstellar medium at distances of a few kpc from the Sun. Observations at infrared and microwave wavelengths, where the bulk of the interstellar dust absorbs and radiates, have brought us closer to an understanding of the distribution of the dust particles on scales of the Galaxy and the universe. We are in the midst of a scientific revolution in our understanding of the interstellar medium and dust. Progress in, and the key results of, this revolution are still difficult to predict. Nevertheless, (a) a physically justified model has been developed for the spatial distribution of absorbing material over the nearest few kiloparsecs, including the Gould belt as a dust container, which gives an accurate estimate of the extinction for any object just by its galactic coordinates. It is also clear that (b) the interstellar medium contains roughly half the mass of matter in the galactic vicinity of the solar system (the other half is made up of stars, their remnants, and dark matter) and (c) the interstellar medium and, especially, dust, differ substantially in different regions of space and deep space cannot be understood by only studying near space.

  16. Interstellar Antifreeze: Ethylene Glycol

    Science.gov (United States)

    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.

  17. Molecular Ro-vibrational Collision Rates for Infrared Modeling of Warm Interstellar Gas from Full-dimensional Quantum Calculations

    Science.gov (United States)

    Stancil, Phillip

    We propose to compute accurate collisional excitation rate coefficients for rovibrational transitions of CS, SiO, SO, NO, H_2O, and HCN due to H_2, He, or H impact. This extends our previous grant which focused on 3- and 4-atom systems to 4- and 5-atom collision complexes, with dynamics to be performed on 6-9 dimensional potential energy surfaces (PESs). This work, which uses fully quantum mechanical methods for inelastic scattering and incorporates full-dimensional PESs, pushes beyond the state-of-the-art for such calculations, as recently established by our group for rovibrational transitions in CO-H_2 in 6D. Many of the required PESs will be computed as part of this project using ab initio theory and basis sets of the highest level feasible and particular attention will be given to the long range form of the PESs. The completion of the project will result in 6 new global PESs and state-to-state rate coefficients for a large range of initial rovibrational levels for temperatures between 1 and 3000 K. The chosen collision systems correspond to cases where data are limited or lacking, are important coolants or diagnostics, and result in observable emission features in the infrared (IR). The final project results will be important for the analysis of a variety of interstellar and extragalactic environments in which the local conditions of gas density, radiation field, and/or shocks drive the level populations out of equilibrium. In such cases, collisional excitation data are critical to the accurate prediction and interpretation of observed molecular IR emission lines in protoplanetary disks, star-forming regions, planetary nebulae, embedded protostars, photodissociation regions, etc. The use of the proposed collisional excitation data will lead to deeper examination and understanding of the properties of many astrophysical environments, hence elevating the scientific return from the upcoming JWST, as well as from current (SOFIA, Herschel, HST) and past IR missions

  18. Physical processes in the interstellar medium

    CERN Document Server

    Spitzer, Lyman

    2008-01-01

    Physical Processes in the Interstellar Medium discusses the nature of interstellar matter, with a strong emphasis on basic physical principles, and summarizes the present state of knowledge about the interstellar medium by providing the latest observational data. Physics and chemistry of the interstellar medium are treated, with frequent references to observational results. The overall equilibrium and dynamical state of the interstellar gas are described, with discussions of explosions produced by star birth and star death and the initial phases of cloud collapse leading to star formation.

  19. Time-Domain TeraHertz Spectroscopy and Observational Probes of Prebiotic Interstellar Gas and Ice Chemistry

    Science.gov (United States)

    McGuire, Brett Andrew

    ruled out a gas-phase route to the synthesis of the simplest amino acid in the ISM. A molecular mystery in the case of the carrier of a series of transitions was resolved using observational data toward a large number of sources, confirming the identity of this important carbon-chemistry intermediate B11244 as l-C3H+ and identifying it in at least two new environments. Finally, the doubly-nitrogenated molecule carbodiimide HNCNH was identified in the ISM for the first time through maser emission features in the centimeter-wavelength regime. In the laboratory, a TeraHertz Time-Domain Spectrometer was constructed to obtain the experimental spectra necessary to search for solid-phase species in the ISM in the THz region of the spectrum. These investigations have shown a striking dependence on large-scale, long-range (i.e. lattice) structure of the ices on the spectra they present in the THz. A database of molecular spectra has been started, and both the simplest and most abundant ice species, which have already been identified, as well as a number of more complex species, have been studied. The exquisite sensitivity of the THz spectra to both the structure and thermal history of these ices may lead to better probes of complex chemical and dynamical evolution in interstellar environments.

  20. VALES: II. The physical conditions of interstellar gas in normal star-forming galaxies up to z=0.2 revealed by ALMA

    CERN Document Server

    Hughes, T M; Villanueva, V; Aravena, M; Baes, M; Bourne, N; Cooray, A; Dunne, L; Dye, S; Eales, S; Furlanetto, C; Herrera-Camus, R; Ivison, R J; van Kampen, E; Lara-López, M A; Maddox, S J; Michałowski, M J; Smith, M W L; Valiante, E; van der Werf, P; Xue, Y Q

    2016-01-01

    We use new Band-3 CO(1-0) observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the physical conditions in the interstellar gas of a sample of 27 dusty main-sequence star-forming galaxies at 0.035$\\sigma$ in 26 sources. We find an average [CII] to CO(1-0) luminosity ratio of 3500$\\pm$1200 for our sample that is consistent with previous studies. Using the [CII], CO and FIR measurements as diagnostics of the physical conditions of the interstellar medium, we compare these observations to the predictions of a photodissociation region (PDR) model to determine the gas density, surface temperature, pressure, and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$, normalised to the Habing Field. The majority of our sample exhibit hydrogen densities of 4 < $\\log n/\\mathrm{cm}^{3}$ < 5.5 and experience an incident FUV radiation field with strengths of 2 < $\\log G_0$ < 3 when adopting standard adjustments. A comparison to galaxy samples at differen...

  1. Interstellar Gas and X-rays toward the Young Supernova Remnant RCW 86; Pursuit to the Origin of the Thermal and Non-thermal X-ray

    CERN Document Server

    Sano, H; Furukawa, N; Mruganka, K; Fukuda, T; Yoshiike, S; Nishimura, A; Ohama, A; Torii, K; Kuwahara, T; Okuda, T; Yamamoto, H; Tachihara, K; Reynoso, E M; Fukui, Y

    2016-01-01

    We have analyzed the atomic and molecular gas using the 21 cm HI and 2.6/1.3 mm CO emissions toward the TeV $\\gamma$-ray supernova remnant (SNR) RCW 86 in order to identify the interstellar medium interacting with the shock waves of the SNR. We have found intensity depression in HI at a velocity range of $-46$-$-28$ km s$^{-1}$ toward the SNR, suggesting a cavity of the interstellar medium. The HI cavity corresponds with the X-ray shell consisting of thermal and non-thermal emission. The thermal X-rays are coincident with the edge of the HI distribution which indicates strong density gradient, while the non-thermal X-rays are found toward the less dense inner part of the HI cavity. The most significant non-thermal X-rays are seen toward the southwestern part of the shell where HI gas includes the dense and cold component. We also identified CO clouds which are likely interacting with the SNR shock waves in the same velocity range with HI whereas the CO clouds are distributed only in a limited part of the SNR ...

  2. Void induced molecule c23h12++ could reproduce the infrared spectrum (3 to 20 micron) of interstellar gas and dust

    CERN Document Server

    Ota, Norio

    2014-01-01

    In order to find out a selected number of molecules to reproduce the infrared spectrum of interstellar gas and dust, model coronene molecules with void and charge have been computed using density functional theory. Among them, a single void induced cation C23H12++ have successfully reproduced a wide range spectrum from 3 to 20 micron of typical interstellar gas and dust. Well known astronoically observed emission peaks are 3.3, 6.2, 7.6, 7.8, 8.6, 11.2, 12.7, 13.5 and 14.3 micro meter. Whereas, calculated peaks of C23H12++ were 3.2, 6.4, 7.6, 7.8, 8.6, 11.4, 12.9, 13.5, and 14.4 micron meter. It should be noted that a single kind of molecule could reproduce very well not depending on the decomposition method using many polycyclic aromatic hydrocarbon (PAH) data. Such coincidence suggested that some astronomical chemical evolution may select a particular PAH. Molecular sructure of C23H12++ was dramatically deformed by the Jahn-Teller effect. There is a featured carbon skeleton having two pentagons connected to...

  3. Interstellar holography

    NARCIS (Netherlands)

    Walker, M. A.; Koopmans, L. V. E.; Stinebring, D. R.; van Straten, W.

    2008-01-01

    The dynamic spectrum of a radio pulsar is an in-line digital hologram of the ionized interstellar medium. It has previously been demonstrated that such holograms permit image reconstruction, in the sense that one can determine an approximation to the complex electric field values as a function of Do

  4. Laboratory spectroscopic studies of interstellar ice analogues

    OpenAIRE

    Puletti, F

    2014-01-01

    In recent years, the molecular chemistry in interstellar environments has proven to be far more complex than was initially expected. We live in a molecular universe that is rich with molecules formed both in the gas phase and on the surface of interstellar icy dust grains. Two important classes of interstellar molecules are sulphur-bearing species and complex organic molecules, i.e., molecules containing carbon and containing more than 6 atoms. The former are relevant because of their potenti...

  5. Physics of the interstellar and intergalactic medium

    CERN Document Server

    Draine, Bruce T

    2010-01-01

    This is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium--the gas and dust, as well as the electromagnetic radiation, cosmic rays, and magnetic and gravitational fields, present between the stars in a galaxy and also between galaxies themselves. Topics include radiative processes across the electromagnetic spectrum; radiative transfer; ionization; heating and cooling; astrochemistry; interstellar dust; fluid dynamics, including ionization fronts and shock waves; cosmic rays; distribution and evolution of the interstellar medium

  6. Interstellar gas towards the TeV gamma-ray sources HESS J1640-465 and HESS J1641-463

    CERN Document Server

    Lau, J C; Burton, M G; Fukui, Y; Aharonian, F A; Oya, I; Vink, J; Ohm, S; Casanova, S

    2016-01-01

    We present a detailed analysis of the interstellar medium towards the TeV $\\gamma$-ray sources HESS J1640$-$465 and HESS J1641$-$463 using results from the Mopra Southern Galactic Plane CO Survey and from a Mopra 7 mm-wavelength study. The $\\gamma$-ray sources are positionally coincident with two supernova remnants G338.3$-$0.0 and G338.5+0.1 respectively. A bright complex of HII regions connect the two SNRs and TeV objects. Observations in the CO(1-0) transition lines reveal substantial amounts of diffuse gas positionally coincident with the $\\gamma$-ray sources at multiple velocities along the line of sight, while 7 mm observations in CS, SiO, HC$_{3}$N and CH$_{3}$OH transition lines reveal regions of dense, shocked gas. Archival HI data from the Southern Galactic Plane Survey was used to account for the diffuse atomic gas. Physical parameters of the gas towards the TeV sources were calculated from the data. We find that for a hadronic origin for the $\\gamma$-ray emission, the cosmic-ray enhancement rates ...

  7. Interstellar gas towards the TeV γ-ray sources HESS J1640-465 and HESS J1641-463

    Science.gov (United States)

    Lau, J. C.; Rowell, G.; Burton, M. G.; Fukui, Y.; Aharonian, F. A.; Oya, I.; Vink, J.; Ohm, S.; Casanova, S.

    2017-01-01

    We present a detailed analysis of the interstellar medium towards the tera electron volt (TeV) γ-ray sources HESS J1640-465 and HESS J1641-463 using results from the Mopra Southern Galactic Plane CO Survey and from a Mopra 7 mm-wavelength study. The γ-ray sources are positionally coincident with two supernova remnants (SNRs) G338.3-0.0 and G338.5+0.1, respectively. A bright complex of H II regions connect the two SNRs and TeV objects. Observations in the CO(1-0) transition lines reveal substantial amounts of diffuse gas positionally coincident with the γ-ray sources at multiple velocities along the line of sight, while 7 mm observations in CS, SiO, HC3N and CH3OH transition lines reveal regions of dense, shocked gas. Archival H I data from the Southern Galactic Plane Survey was used to account for the diffuse atomic gas. Physical parameters of the gas towards the TeV sources were calculated from the data. We find that for a hadronic origin for the γ-ray emission, the cosmic ray enhancement rates are ˜103 and 102 times the local solar value for HESS J1640-465 and HESS J1641-463, respectively.

  8. The alpha Centauri Line of Sight: D/H Ratio, Physical Properties of Local Interstellar Gas, and Measurement of Heated Hydrogen (The 'Hydrogen Wall') Near the Heliopause

    Science.gov (United States)

    Linsky, Jeffrey L.; Wood, Brian E.

    1996-01-01

    We analyze high-resolution spectra of the nearby (1.34 pc) stars alpha Cen A (G2 V) and alpha Cen B (K1 V), which were obtained with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. The observations consist of echelle spectra of the Mg II 2800 A and Fe II 2599 A resonance lines and the Lyman-alpha lines of hydrogen and deuterium. The interstellar gas has a velocity (v = - 18.0 +/- 0.2 km/s) consistent with the local flow vector proposed for this line of sight by Lailement & Berlin (1992). The temperature and nonthermal velocity inferred from the Fe II, Mg II, and D I line profiles are T = 5400 +/- 500 K and xi = 1.20 +/- 0.25 km/s, respectively. However, single-component fits to the H I Lyman-alpha lines yield a Doppler parameter (b(sub HI) = 11.80 km/s) that implies a significantly warmer temperature of 8350 K, and the velocity of the H I absorption (v = - 15.8 +/- 0.2 km/s) is redshifted by about 2.2 km/s with respect to the Fe II, Mg II, and D I lines. The one-component model of the interstellar gas suggests natural logarithm N base HI = 18.03 +/- 0.01 and D/H = (5.7 +/- 0.2) x 10(exp -6) . These parameters lead to a good fit to the observed spectra, but this model does not explain the higher temperature and redshift of H I relative to the other interstellar lines. The most sensible way to resolve the discrepancy between H(I) and the other lines is to add a second absorption component to the H(I) lines. This second component is hotter (T approx. equals 30,000 K), is redshifted relative to the primary component by 2-4 km/s, and has a column density too low to be detected in the Fe(II), Mg(II), and D(I) lines. We propose that the gas responsible for this component is located near the heliopause, consisting of the heated H I gas from the interstellar medium that is compressed by the solar wind. This so-called 'hydrogen wall' is predicted by recent multifluid gasdynamical models of the interstellar gas and solar wind interaction. Our data

  9. Electronic Spectroscopy of Organic Cations in Gas-Phase at 6 K:IDENTIFICATION of C60/^+ in the Interstellar Medium

    Science.gov (United States)

    Maier, John P.

    2016-06-01

    After the discovery of C60, the question of its relevance to the diffuse interstellar bands was raised. In 1987 H. W. Kroto wrote: ``The present observations indicate that C60 might survive in the general interstellar medium (probably as the ion C60/^+)''. In 1994 two diffuse interstellar bands (DIBs) at 9632 and 9577 Å/ were detected and proposed to be the absorption features of C60/^+. This was based on the proximity of these wavelengths to the two prominent absorption bands of C60/^+ measured by us in a neon matrix in 1993. Confirmation of the assignment required the gas phase spectrum of C60/^+ and has taken 20 years. The approach which succeeded confines C60/^+ ions in a radiofrequency trap, cools them by collisions with high density helium allowing formation of the weakly bound C60/^+--He complexes below 10 K. The photofragmentation spectrum of this mass-selected complex is then recorded using a cw laser. In order to infer the position of the absorption features of the bare C60/^+ ion, measurements on C60/^+--He_2 were also made. The spectra show that the presence of a helium atom shifts the absorptions by less than 0.2 Å, much less than the accuracy of the astronomical measurements. The two absorption features in the laboratory have band maxima at 9632.7(1) and 9577.5(1) Å, exactly the DIB wavelengths, and the widths and relative intensities agree. This leads to the first definite identification of now five bands among the five hundred or so DIBs known and proves the presence of gaseous C60/^+ in the interstellar medium. The absorption of cold C70/^+ has also been obtained by this approach. In addition the electronic spectra of a number of cations of astrophysical interest ranging from those of carbon chains including oxygen to larger polycyclic aromatic hydrocarbon could be measured in the gas phase at around 10 K in the ion trap but using an excitation-dissociation approach. The implications of these laboratory spectra in relation to the diffuse

  10. Two-Dimensional MHD Numerical Simulations of Magnetic Reconnection Triggered by A Supernova Shock in Interstellar Medium, Generation of X-Ray Gas in Galaxy

    CERN Document Server

    Tanuma, S; Kudoh, T; Shibata, K; Tanuma, Syuniti; Yokoyama, Takaaki; Kudoh, Takahiro; Shibata, Kazunari

    2001-01-01

    We examine the magnetic reconnection triggered by a supernova (or a point explosion) in interstellar medium, by performing two-dimensional resistive magnetohydrodynamic (MHD) numerical simulations with high spatial resolution. We found that the magnetic reconnection starts long after a supernova shock (fast-mode MHD shock) passes a current sheet. The current sheet evolves as follows: (i) Tearing-mode instability is excited by the supernova shock, and the current sheet becomes thin in its nonlinear stage. (ii) The current-sheet thinning is saturated when the current-sheet thickness becomes comparable to that of Sweet-Parker current sheet. After that, Sweet-Parker type reconnection starts, and the current-sheet length increases. (iii) ``Secondary tearing-mode instability'' occurs in the thin Sweet-Parker current sheet. (iv) As a result, further current-sheet thinning occurs and anomalous resistivity sets in, because gas density decreases in the current sheet. Petschek type reconnection starts and heats interste...

  11. Averaged resonant equations for non-gravitational effects without a spherical symmetry and their application for an interstellar gas flow

    CERN Document Server

    Pastor, P

    2013-01-01

    Within the framework of the circular restricted three body problem we investigate the motion of a dust particle captured into a mean motion resonance with a planet under the action of non-gravitational effects. From equations of motion in a near-canonical form averaged resonant equations are derived. The averaged resonant equations describe secular variations of the particle orbit in the mean motion resonance. The secular variations of the particle orbit caused by the non-gravitational effects can depend on the orientation of the orbit in space. The averaged resonant equations are derived with this dependence taken into account. We also present an alternative way how the averaged resonant equations can be derived. We applied derived theory for the case when non-gravitational effects are the Poynting-Robertson effect, radial stellar wind and interstellar wind. Obtained analytical and numerical results are in excellent agreement in the Solar system. We found that types of orbits correspond to libration centers ...

  12. The small scale structure of the interstellar medium in the Orion association: The flotsam of star formation

    Science.gov (United States)

    Sonneborn, G.; Shore, S. N.; Brown, D. N.

    1988-01-01

    The small scale dynamics and structure of the interstellar medium of the Orion OB1b, c association was studied using IUE high dispersion SWP and LWR/LWP spectra. The area surveyed centers on the Belt and encompasses the Orion Cloak. The dynamics and abundances of the ionized and warm neutral gas surrounding the central parts of the association are determined using 35 B stars. Results are compared with the picture of the Orion interstellar medium gained using COPERNICUS, especially for the structure and dynamics of the Orion Cloak.

  13. CO/H$_2$, C/CO, OH/CO, and OH/O$_2$ in Dense Interstellar Gas: From High Ionization to Low Metallicity

    CERN Document Server

    Bialy, Shmuel

    2014-01-01

    We present numerical computations and analytic scaling relations for cold-gas, ionization-driven interstellar ion-molecule chemistry, down to the very low metallicities (< 10$^{-3}$ solar) associated with the Pop-III to Pop-II star transition and the early enrichment reionization epoch. We focus on the behavior for H$_2$, CO, CH, OH, H$_2$O and O$_2$. We consider shielded or partially shielded one-zone gas parcels, and solve the chemical rate equations for steady-state conditions for a wide range of ionization parameters, $\\zeta/n$, and metallicties, $Z'$. We find that the OH abundances are always maximal at the H-to-H$_2$ conversion points, and that large OH abundances persist at very low metallicities even when the hydrogen is predominantly atomic. We study the OH/O$_2$, C/CO and OH/CO abundance ratios, from large to small, as functions of $\\zeta/n$ and $Z'$. Cold dense star-forming clouds for the Pop-II generation may have been OH-dominated and atomic rather than CO-dominated and molecular.

  14. Transparency, consultation and conflict: Assessing the micro-level risks surrounding the drive to develop Peru's Amazonian oil and gas resources

    DEFF Research Database (Denmark)

    Haselip, James Arthur

    2011-01-01

    Since the 1990s, successive Governments in Peru have sought to expand the exploration and production of the country's oil and gas resources. This economic agenda poses significant opportunities and risks which are usually considered at the macro-level and framed by debates regarding the so......-called “natural resource curse”. While risks such as “Dutch disease” are important to consider, a worrying set of short-term issues surrounds the impacts of rapid changes brought on by oil and gas industrial development at the micro-level, namely, those that affect local communities and the environment....... In the case of Peru, this is especially relevant to the vast areas of ecologically sensitive and previously under-developed Amazonia that are now under concession to oil and gas companies. Low levels of industry transparency combined with a lack of uniform free, prior and informed consent are exacerbating...

  15. Influence of surrounding gas, composition and pressure on plasma plume dynamics of nanosecond pulsed laser-induced aluminum plasmas

    Directory of Open Access Journals (Sweden)

    Mahmoud S. Dawood

    2015-10-01

    Full Text Available In this article, we present a comprehensive study of the plume dynamics of plasmas generated by laser ablation of an aluminum target. The effect of both ambient gas composition (helium, nitrogen or argon and pressure (from ∼5 × 10−7 Torr up to atmosphere is studied. The time- and space- resolved observation of the plasma plume are performed from spectrally integrated images using an intensified Charge Coupled Device (iCCD camera. The iCCD images show that the ambient gas does not significantly influence the plume as long as the gas pressure is lower than 20 Torr and the time delay below 300 ns. However, for pressures higher than 20 Torr, the effect of the ambient gas becomes important, the shortest plasma plume length being observed when the gas mass species is highest. On the other hand, space- and time- resolved emission spectroscopy of aluminum ions at λ = 281.6 nm are used to determine the Time-Of-Flight (TOF profiles. The effect of the ambient gas on the TOF profiles and therefore on the propagation velocity of Al ions is discussed. A correlation between the plasma plume expansion velocity deduced from the iCCD images and that estimated from the TOF profiles is presented. The observed differences are attributed mainly to the different physical mechanisms governing the two diagnostic techniques.

  16. New Neutral Interstellar Helium Flow Parameters Based on IBEX-Lo Observations

    Science.gov (United States)

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

    2011-12-01

    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 (LIC). The Interstellar Boundary Explorer is the second mission to directly detect NISHe (after Ulysses) and the first to directly detect other interstellar neutrals. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. This code includes motion of the spacecraft and the Earth relative to the incident NISHe in the inner heliosphere and accounts for both major and minor interactions between NISHe and its surrounding medium. The interactions include gravitational attraction by the Sun and losses by solar photoionization, electron impact ionization, and charge exchange with solar wind protons and alphas. 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 previously undetected secondary population of neutral helium, likely produced by interaction of helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous results: the newly-established flow direction is ecliptic longitude 79.2°, latitude -5.1°, velocity 22.8 km/s. 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 (the plane that contains the inflow vectors of hydrogen and helium in the inner heliosphere) compared to prior results from Ulysses. A different orientation of this plane

  17. Hydrocarbon and Carbon Dioxide Fluxes from Natural Gas Well Pad Soils and Surrounding Soils in Eastern Utah.

    Science.gov (United States)

    Lyman, Seth N; Watkins, Cody; Jones, Colleen; Mansfield, Marc L; McKinley, Michael; Kenney, Donna; Evans, Jordan

    2017-09-07

    We measured fluxes of methane, non-methane hydrocarbons, and carbon dioxide from natural gas well pad soils and from nearby undisturbed soils in eastern Utah. Methane fluxes varied from less than zero to more than 38 g m-2 h-1. Fluxes from well pad soils were almost always greater than from undisturbed soils. Fluxes were greater from locations with higher concentrations of total combustible gas in soil and were inversely correlated with distance from well heads. Several lines of evidence show that the majority of emission fluxes (about 70%) were primarily due to subsurface sources of raw gas that migrated to the atmosphere, with the remainder likely caused primarily by re-emission of spilled liquid hydrocarbons. Total hydrocarbon fluxes during summer were only 39 (16, 97)% as high as during winter, likely because soil bacteria consumed the majority of hydrocarbons during summer months. We estimate that natural gas well pad soils account for 4.6×10-4 (1.6×10-4, 1.6×10-3)% of total emissions of hydrocarbons from the oil and gas industry in Utah's Uinta Basin. Our undisturbed soil flux measurements were not adequate to quantify rates of natural hydrocarbon seepage in the Uinta Basin.

  18. Planck intermediate results. XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck

    CERN Document Server

    Planck,; Ade, P A R; Aghanim, N; Aniano, G; Arnaud, M; Ashdown, M; Aumont, J; Baccigalupi, C; Banday, A J; Barreiro, R B; Bartolo, N; Battaner, E; Benabed, K; Benoit-Levy, A; Bernard, J -P; Bersanelli, M; Bielewicz, P; Bonaldi, A; Bonavera, L; Bond, J R; Borrill, J; Bouchet, F R; Boulanger, F; Burigana, C; Butler, R C; Calabrese, E; Cardoso, J -F; Casandjian, J M; Catalano, A; Chamballu, A; Chiang, H C; Christensen, P R; Colombo, L P L; Combet, C; Couchot, F; Crill, B P; Curto, A; Cuttaia, F; Danese, L; Davies, R D; Davis, R J; de Bernardis, P; de Rosa, A; de Zotti, G; Delabrouille, J; Desert, F -X; Dickinson, C; Diego, J M; Digel, S W; Dole, H; Donzelli, S; Dore, O; Douspis, M; Ducout, A; Dupac, X; Efstathiou, G; Elsner, F; Ensslin, T A; Eriksen, H K; Falgarone, E; Finelli, F; Forni, O; Frailis, M; Fraisse, A A; Franceschi, E; Frejsel, A; Fukui, Y; Galeotta, S; Galli, S; Ganga, K; Ghosh, T; Giard, M; Gjerlow, E; Gonzalez-Nuevo, J; Gorski, K M; Gregorio, A; Grenier, I A; Gruppuso, A; Hansen, F K; Hanson, D; Harrison, D L; Henrot-Versille, S; Hernandez-Monteagudo, C; Herranz, D; Hildebrandt, S R; Hivon, E; Holmes, W A; Hovest, W; Huffenberger, K M; Hurier, G; Jaffe, A H; Jaffe, T R; Jones, W C; Keihanen, E; Keskitalo, R; Kisner, T S; Kneissl, R; Knoche, J; Kunz, M; Kurki-Suonio, H; Lagache, G; Lamarre, J -M; Lasenby, A; Lattanzi, M; Lawrence, C R; Leonardi, R; Levrier, F; Liguori, M; Lilje, P B; Linden-Vornle, M; Lopez-Caniego, M; Lubin, P M; Macias-Perez, J F; Maffei, B; Maino, D; Mandolesi, N; Maris, M; Marshall, D J; Martin, P G; Martinez-Gonzalez, E; Masi, S; Matarrese, S; Mazzotta, P; Melchiorri, A; Mendes, L; Mennella, A; Migliaccio, M; Miville-Deschenes, M -A; Moneti, A; Montier, L; Morgante, G; Mortlock, D; Munshi, D; Murphy, J A; Naselsky, P; Natoli, P; Norgaard-Nielsen, H U; Novikov, D; Novikov, I; Oxborrow, C A; Pagano, L; Pajot, F; Paladini, R; Paoletti, D; Pasian, F; Perdereau, O; Perotto, L; Perrotta, F; Pettorino, V; Piacentini, F; Piat, M; Plaszczynski, S; Pointecouteau, E; Polenta, G; Popa, L; Pratt, G W; Prunet, S; Puget, J -L; Rachen, J P; Reach, W T; Rebolo, R; Reinecke, M; Remazeilles, M; Renault, C; Ristorcelli, I; Rocha, G; Roudier, G; Rusholme, B; Sandri, M; Santos, D; Scott, D; Spencer, L D; Stolyarov, V; Strong, A W; Sudiwala, R; Sunyaev, R; Sutton, D; Suur-Uski, A -S; Sygnet, J -F; Tauber, J A; Terenzi, L; Tibaldo, L; Toffolatti, L; Tomasi, M; Tristram, M; Tucci, M; Umana, G; Valenziano, L; Valiviita, J; Van Tent, B; Vielva, P; Villa, F; Wade, L A; Wandelt, B D; Wehus, I K; Yvon, D; Zacchei, A; Zonca, A

    2014-01-01

    Shortened abstract: Observations of the nearby Chamaeleon clouds in gamma rays with the Fermi Large Area Telescope and in thermal dust emission with Planck and IRAS have been used with the HI and CO radio data to (i) map the gas column densities in the different phases and at the dark neutral medium (DNM) transition between the HI-bright and CO-bright media; (ii) constrain the CO-to-$H_2$ conversion factor, $X_{CO}$; (iii) probe the dust properties per gas nucleon in each gas phase and spatially across the clouds. We have separated clouds in velocity in HI and CO emission and modelled the 0.4-100 GeV intensity, the dust optical depth at 353 GHz, the thermal radiance of the large grains, and an estimate of the dust extinction empirically corrected for the starlight intensity, $A_{VQ}$. The gamma-ray emissivity spectra confirm that the GeV-TeV cosmic rays uniformly permeate all gas phases up to the CO cores. The dust and cosmic rays reveal large amounts of DNM gas, with comparable spatial distributions and twic...

  19. Theory of interstellar medium diagnostics

    Science.gov (United States)

    Fahr, H. J.

    1983-01-01

    The theoretical interpretation of observed interplanetary resonance luminescence patterns is used as one of the must promising methods to determine the state of the local interstellar medium (LISM). However, these methods lead to discrepant results that would be hard to understand in the framework of any physical LISM scenario. Assuming that the observational data are reliable, two possibilities which could help to resolve these discrepancies are discussed: (1) the current modeling of resonance luminescence patterns is unsatisfactory and has to be improved, and (2) the extrapolated interstellar parameters are not indicative of the unperturbed LISM state, but rather designate an intermediate state attained in the outer regions of the solar system. It is shown that a quantitative treatment of the neutral gas-plasma interaction effects in the interface between the heliospheric and the interstellar plasmas is of major importance for the correct understanding of the whole complex.

  20. Interstellar gas towards CTB 37A and the TeV gamma-ray source HESS J1714-385

    Science.gov (United States)

    Maxted, Nigel I.; Rowell, Gavin P.; Dawson, Bruce R.; Burton, Michael G.; Fukui, Yasuo; Walsh, Andrew; Kawamura, Akiko; Horachi, Hirotaka; Sano, Hidetoshi; Yoshiike, Satoshi; Fukuda, Tatsuya

    2013-09-01

    Observations of dense molecular gas towards the supernova remnants CTB 37A (G348.5+0.1) and G348.5-0.0 were carried out using the Mopra and Nanten2 radio telescopes. We present CO(2-1) and CS(1-0) emission maps of a region encompassing the CTB 37A TeV gamma-ray emission, HESS J1714-385, revealing regions of dense gas within associated molecular clouds. Some gas displays good overlap with gamma-ray emission, consistent with hadronic gamma-ray emission scenarios. Masses of gas towards the HESS J1714-385 TeV gamma-ray emission region were estimated, and were of the order of 103-104 M⊙. In the case of a purely hadronic origin for the gamma-ray emission, the cosmic ray flux enhancement is ˜80-1100 times the local solar value. This enhancement factor and other considerations allow a discussion of the age of CTB 37A, which is consistent with ˜104 yr.

  1. Interstellar gas towards CTB 37A and the TeV gamma-ray source HESS J1714-385

    CERN Document Server

    Maxted, Nigel I; Dawson, Bruce R; Burton, Michael G; Fukui, Yasuo; Walsh, Andrew; Kawamura, Akiko; Horachi, Hirotaka; Sano, Hidetoshi; Yoshiike, Satoshi; Fukuda, Tatsuya

    2013-01-01

    Observations of dense molecular gas towards the supernova remnants CTB 37A (G348.5+0.1) and G348.5-0.0 were carried out using the Mopra and Nanten2 radio telescopes. We present CO(2-1) and CS(1-0) emission maps of a region encompassing the CTB 37A TeV gamma-ray emission, HESS J1714-385, revealing regions of dense gas within associated molecular clouds. Some gas displays good overlap with gamma-ray emission, consistent with hadronic gamma-ray emission scenarios. Masses of gas towards the HESS J1714-385 TeV gamma-ray emission region were estimated, and were of the order of 10^3-10^4 solar masses. In the case of a purely hadronic origin for the gamma-ray emission, the cosmic ray flux enhancement is ~80-1100 times the local solar value. This enhancement factor and other considerations allow a discussion of the age of CTB 37A, which is consistent with ~10^4 yr.

  2. Nitrogen hydrides in interstellar gas II. Analysis of Herschel/HIFI observations towards W49N and G10.6-0.4 (W31C)

    CERN Document Server

    Persson, C M; Mookerjea, B; Olofsson, A O H; Black, J H; Gerin, M; Herbst, E; Bell, T A; Coutens, A; Godard, B; Goicoechea, J R; Hassel, G E; Hily-Blant, P; Menten, K M; Muller, H S P; Pearson, J C; Yu, S; 10.1051/0004-6361/201118686

    2012-01-01

    We have used the Herschel-HIFI instrument to observe interstellar nitrogen hydrides along the sight-lines towards W49N and G10.6-0.4 in order to elucidate the production pathways leading to nitrogen-bearing species in diffuse gas. All detections show absorption by foreground material over a wide range of velocities, as well as absorption associated directly with the hot-core source itself. As in the previously published observations towards G10.6-0.4, the NH, NH2 and NH3 spectra towards W49N show strikingly similar and non-saturated absorption features. We decompose the absorption of the foreground material towards W49N into different velocity components in order to investigate whether the relative abundances vary among the velocity components, and, in addition, we re-analyse the absorption lines towards G10.6-0.4 in the same manner. Abundances, with respect to molecular hydrogen, in each velocity component are estimated using CH. The analysis points to a co-existence of the nitrogen hydrides in diffuse or tr...

  3. A detailed study of non-thermal X-ray properties and interstellar gas toward the \\gamma-ray supernova remnant RX J1713.7-3946

    CERN Document Server

    Sano, H; Yoshiike, S; Sato, J; Horachi, H; Kuwahara, T; Torii, K; Hayakawa, T; Tanaka, T; Matsumoto, H; Inoue, T; Yamazaki, R; Inutsuka, S; Kawamura, A; Yamamoto, H; Okuda, T; Tachihara, K; Mizuno, N; Onishi, T; Mizuno, A; Acero, F; Fukui, Y

    2014-01-01

    We have carried out a spectral analysis of the Suzaku X-ray data in the 0.4-12 keV range toward the shell-type very-high-energy {\\gamma}-ray supernova remnant RX J1713.7-3946. The aims of this analysis are to estimate detailed X-rays spectral properties at a high angular resolution up to 2 arcmin, and to compare them with the interstellar matter. The X-ray spectrum is non-thermal and used to calculate absorbing column density, photon index, and absorption-corrected X-ray flux. The photon index varies significantly from 2.1 to 2.9. The hardest spectra are found in six positions at around 6-8 pc from the center, in two compact regions around dense molecular cloud cores as well as toward four extended diffuse regions with no molecular gas. We present an interpretation that diffusive shock acceleration with little turbulence realizes a high cut-off energy and the hardest spectra in the diffuse regions, where the shock speed is probably as high as ~6000 km s-1 and a gyro-factor is larger than 1. On the other hand,...

  4. Thermodynamics and Charging of Interstellar Iron Nanoparticles

    Science.gov (United States)

    Hensley, Brandon S.; Draine, B. T.

    2017-01-01

    Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of ≃4.5 Å, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges, particularly in regions with high gas temperatures and ionization fractions. If ≳10% of the interstellar iron is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.

  5. Thermodynamics and Charging of Interstellar Iron Nanoparticles

    CERN Document Server

    Hensley, Brandon S

    2016-01-01

    Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of $\\simeq 4.5\\,$\\AA, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges particularly in regions with high gas temperatures and ionization fractions. If $\\gtrsim 10\\%$ of the interstellar iron is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.

  6. Effects of shock waves in the interstellar medium

    Science.gov (United States)

    Petriella, Alberto

    2013-12-01

    In this Thesis, we study the effects on the interstellar medium of shock waves produced by massive stars during different stages of their evolution. We investigate the interaction between HII regions, interstellar bubbles, and supernova remnants and the surrounding medium and we analize the star forming activity to establish if they can trigger star formation around them. We study the distribution of the molecular gas around the supernova remnants G20.0-0.2 and G24.7+0.6 and we find molecular clouds probably shocked by the remnants. These clouds host star forming regions, which suggest a connection between the birth of the new stars and the expansion of the supernova remnants. We analyze the distribution of the interstellar medium around three HII regions (an HII region complex near the supernova remnant G18.8+0.3 and the HII regions N65 and G35.673-0.847) and we find shells of molecular material swept up by their front shocks. These shells show signs of star forming activity probably triggered by the expanding HII regions. Lastly, we find evidence of the interaction between the stellar winds of the LBV stars G24.73+0.69 and G26.47+0.02 and the surrounding molecular gas. The data used in this Thesis were obtained through dedicated observations of several molecular transitions with the Atacama Submillimeter Telescope Experiment (ASTE) and through the calibration of unpublished archival observations of the Chandra X-ray telescope and the VLA interferometer. Additional data were extracted from public surveys in the radio, infrared, millimeter and submillimeter bands.

  7. A SUBSTANTIAL MASS OF COOL, METAL-ENRICHED GAS SURROUNDING THE PROGENITORS OF MODERN-DAY ELLIPTICALS

    Energy Technology Data Exchange (ETDEWEB)

    Prochaska, J. Xavier [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Hennawi, Joseph F. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69115 Heidelberg (Germany); Simcoe, Robert A. [MIT-Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

    2013-01-10

    The hosts of luminous z {approx} 2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circumgalactic medium (CGM) of these massive, dark matter halos (M{sub DM} {approx} 10{sup 12.5} M{sub Sun }) should be dominated by a T {approx} 10{sup 7} K virialized plasma. We test this hypothesis with observations of 74 close-projected quasar pairs, using spectra of the background QSO to characterize the CGM of the foreground one. Surprisingly, our measurements reveal a cool (T Almost-Equal-To 10{sup 4} K), massive (M{sub CGM} > 10{sup 10} M{sub Sun }), and metal-enriched (Z {approx}> 0.1 Z{sub Sun }) medium extending to at least the expected virial radius (r{sub vir} = 160 kpc). The average equivalent widths of H I Ly{alpha} (W-bar{sub Ly{alpha}}= 2.1{+-}0.15 A for impact parameters R < 200 kpc) and C II 1334 (W-bar{sub 1334}= 0.7{+-}0.1) exceed the corresponding CGM measurements of these transitions from all galaxy populations studied previously. Furthermore, we conservatively estimate that the quasar CGM has a 64{sup +6}{sub -7}% covering fraction of optically thick gas (N{sub HI} > 10{sup 17.2} cm{sup -2}) within r{sub vir}; this covering factor is twice that of the contemporaneous Lyman break galaxy population. This unexpected reservoir of cool gas is rarely detected 'down-the-barrel' to quasars, and hence it is likely that our background sight lines intercept gas that is shadowed from the quasar ionizing radiation by the same obscuring medium often invoked in models of active galactic nucleus unification. Because the high-z halos inhabited by quasars predate modern groups and clusters, these observations are also relevant to the formation and enrichment history of the intragroup/intracluster medium.

  8. Beyond Science and Hysteria: Reality and Perceptions of Environmental Justice Concerns Surrounding Marcellus and Utica Shale Gas Development

    Directory of Open Access Journals (Sweden)

    Ann M. Eisenberg

    2016-01-01

    This Article argues that a nuanced characterization of the HF controversy should include a more robust discussion of both environmental justice and discourse in order to account for the inordinate burden residents of Appalachia have historically borne in fossil fuel production.  Part I examines relevant regional economic and social dynamics, including the natural resource curse, Appalachia’s unique vulnerabilities, efforts to portray opponents of shale gas development as “anti-science,” and the environmental justice movement’s relationship to extractive industries.  Part II reviews the use of modern HF technology and applicable legal frameworks in West Virginia, Pennsylvania, Ohio, and New York.  Part III argues that across Ohio, Pennsylvania, and West Virginia, environmental justice issues have arisen from shale gas development, including problems stemming from information asymmetries, power asymmetries, and limited access to justice.  In Part IV, the Article argues that the “anti-science” portrayal of shale gas opponents is unjustified, and that such “discourse-framing” obfuscates the actual costs and limitations on benefits of HF use, and thus, becomes an environmental justice issue itself.  Part IV also argues that environmental justice concerns shaped public sentiment in New York, and that the resulting “moral outrage” added to New York’s policy decision to ban HF altogether.  In Part V, the Article suggests that ideas which transcend the study of “moral outrage”/risk assessment and environmental justice advocacy may offer a way forward.

  9. Enormous Disc of Cool Gas Surrounding the Nearby Powerful Radio Galaxy NGC 612 (PKS 0131-36)

    Science.gov (United States)

    2008-05-22

    with a small overlap region Figure 1. Radio continuum map (contours) – constructed from the 750C array data – overlaid on to an optical SDSS image...optical SDSS image (grey-scale). Contour levels H I: 0.8, 1.1, 1.5, 1.9, 2.8, 4.0, 5.1, 6.5, 7.8 ×1019 cm−2. Left: HI absorption profile against the...I gas stretches 219 kpc toward the south-west. This H I tail has no identi- fiable counterpart in the optical Sloan Digital Sky Survey ( SDSS ) image

  10. Revealing the Large-Scale Structures of Interstellar Gas Associated with the Magellanic SNR N132D

    CERN Document Server

    Sano, H; Yoshiike, S; Fukuda, T; Tachihara, K; Inutsuka, S; Kawamura, A; Fujii, K; Mizuno, N; Inoue, T; Onishi, T; Acero, F; Vink, J

    2015-01-01

    We report preliminary results of large-scale distribution toward the Magellanic supernova remnant N132D using Mopra and Chandra archival datasets. We identified a cavity-like CO structure along the X-ray shell toward the southern half of it. The total mass of associating molecular gas is $\\sim10^4 M_\\odot$, which is smaller than the previous study by an order of magnitude. Further observations using ALMA, ASTE, and Mopra will reveal the detailed spatial structures and its physical conditions.

  11. The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution

    CERN Document Server

    Fedele, D; Acke, B; van der Plas, G; Van Boekel, R; Wittkowski, M; Henning, T; Bouwman, J; Meeus, G; Rafanelli, P

    2008-01-01

    [Abridged] We present the first direct comparison of the distribution of the gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10 micron emission, in the protoplanetary disk around three intermediate-mass stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained with VLTI/MIDI. Simple geometrical models are used to compare the dust emission to high-resolution optical spectra in the 6300 AA [OI] line of the same targets. The disks around HD 101412 and HD 135344 B appear strongly flared in the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10 micron emission is rather compact (< 2 AU) while the [OI] brightness profile shows a double peaked structure. The inner peak is strongest and is consistent with the location of the dust, the outer peak is fainter and is located at 5-10 AU. Spatially extended PAH emission is found in both disks. The disk around HD 179218 is flared in the dust. The 10 micron emission emerges from a double ring-like str...

  12. Theory and technique of permeability enhancement and coal mine gas extraction by fracture network stimulation of surrounding beds and coal beds

    Directory of Open Access Journals (Sweden)

    Ma Geng

    2014-12-01

    Full Text Available The existing reservoir stimulating technologies are only applicable to hard coal but helpless for soft coal, which is one of the main factors hindering the CBM industrialization in China. Therefore, it is urgent to develop a universal stimulating technology which can increase the permeability in various coal reservoirs. Theoretical analysis and field tests were used to systematically analyze the mechanical mechanisms causing the formation of various levels and types of fractures, such as radial tensile fractures, peripheral tensile fractures, and shear fractures in hydraulic fracturing, and reveal the mechanism of permeability enhancement by fracture network stimulating in surrounding beds and coal reservoirs. The results show that multi-staged perforation fracturing of horizontal wells, hydraulic-jet staged fracturing, four-variation hydraulic fracturing and some auxiliary measures are effective technical approaches to fracture network stimulation, especially the four-variation hydraulic fracturing can stimulate the fracture network in vertical and cluster wells. It is concluded that the fracture network stimulating technology for surrounding beds has significant advantages, such as safe drilling operation, strong stimulation effect, strong adaptability to stress-sensitive and velocity-sensitive beds, and is suitable for coal reservoirs of any structure. Except for the limitation in extremely water-sensitive and high water-yield surrounding beds, the technology can be universally used in all other beds. The successful industrial tests in surface coal bed methane and underground coal mines gas extraction prove that the theory and technical system of fracture network stimulating in surrounding beds and coal reservoirs, as a universally applicable measure, will play a role in the CBM development in China.

  13. Copernicus observations of interstellar matter toward the Orion OB1 association. I - Epsilon and Pi-5 Orionis

    Science.gov (United States)

    Shull, J. M.

    1979-01-01

    Copernicus UV data on interstellar lines toward Epsilon Ori and Pi-5 Ori are analyzed to study abundances and physical conditions in both low- and intermediate-velocity components. Clouds at -8 and +5 km/s (LSR) toward Epsilon Ori show typical depletions of Fe, Ti, Mg, and Si in dense (H number density about 100 per cu cm) gas. Low-column-density intermediate-velocity clouds toward both stars, with low densities (hydrogen number density less than 1 per cu cm) and near-cosmic Si abundances, are consistent with a widespread pattern of high-velocity gas over a 15-deg area surrounding the Orion region. Such activity may be attributed to the repeated action of supernovae in a patchy low-density region of interstellar gas.

  14. Study of the dense molecular gas surrounding the "Extended Green Object" G35.03+0.35

    CERN Document Server

    Paron, S; Petriella, A; Rubio, M; Giacani, E; Dubner, G

    2011-01-01

    We present the results of a new study of the molecular gas associated with the "extended green object" (EGO) G35.03+0.35. This object, very likely a massive young stellar object, is embedded in a molecular cloud at the border of an HII region. The observations were performed with the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO and 13CO J=3-2, HCO+ J=4-3, and CS J=7-6 lines with an angular resolution about 22". From the 12CO J=3-2 line we discovered outflowing activity of the massive young stellar object. We obtained a total mass and kinetic energy for the outflows of 30 M_sun and 3000 M_sun (km/s)^2 (6 x 10^{46} ergs), respectively. We discovered a HCO+ and CS clump towards the EGO G35.03+0.35. The detection of these molecular species supports the presence of molecular outflows and a dense molecular envelope with temperatures and densities above 40 K and 6 x 10^{6} cm^{-3}, respectively. Using public near- and mid-IR, and sub-mm data we investigated the spectral energy distribution confirmin...

  15. Interstellar Gas-phase Element Depletions in the Small Magellanic Cloud: A Guide to Correcting for Dust in QSO Absorption Line Systems

    Science.gov (United States)

    Jenkins, Edward B.; Wallerstein, George

    2017-04-01

    We present data on the gas-phase abundances for 9 different elements in the interstellar medium of the Small Magellanic Cloud (SMC), based on the strengths of ultraviolet absorption features over relevant velocities in the spectra of 18 stars within the SMC. From this information and the total abundances defined by the element fractions in young stars in the SMC, we construct a general interpretation on how these elements condense into solid form onto dust grains. As a group, the elements Si, S, Cr, Fe, Ni, and Zn exhibit depletion sequences similar to those in the local part of our Galaxy defined by Jenkins. The elements Mg and Ti deplete less rapidly in the SMC than in the Milky Way, and Mn depletes more rapidly. We speculate that these differences might be explained by the different chemical affinities to different existing grain substrates. For instance, there is evidence that the mass fractions of polycyclic aromatic hydrocarbons in the SMC are significantly lower than those in the Milky Way. We propose that the depletion sequences that we observed for the SMC may provide a better model for interpreting the element abundances in low-metallicity Damped Lyman Alpha (DLA) and sub-DLA absorption systems that are recorded in the spectra of distant quasars and gamma-ray burst afterglows. Based on observations with the NASA/ESA Hubble Space Telescope and additional data obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. These observations are associated with program nr. 13778.

  16. Production of secondary particles and nuclei in cosmic rays collisions with the interstellar gas using the FLUKA code

    CERN Document Server

    Mazziotta, M N; Ferrari, A; Gaggero, D; Loparco, F; Sala, P R

    2016-01-01

    The measured fluxes of secondary particles produced by the interactions of Cosmic Rays (CRs) with the astronomical environment play a crucial role in understanding the physics of CR transport. In this work we present a comprehensive calculation of the secondary hadron, lepton, gamma-ray and neutrino yields produced by the inelastic interactions between several species of stable or long-lived cosmic rays projectiles (p, D, T, 3He, 4He, 6Li, 7Li, 9Be, 10Be, 10B, 11B, 12C, 13C, 14C, 14N, 15N, 16O, 17O, 18O, 20Ne, 24Mg and 28Si) and different target gas nuclei (p, 4He, 12C, 14N, 16O, 20Ne, 24Mg, 28Si and 40Ar). The yields are calculated using FLUKA, a simulation package designed to compute the energy distributions of secondary products with large accuracy in a wide energy range. The present results provide, for the first time, a complete and self-consistent set of all the relevant inclusive cross sections regarding the whole spectrum of secondary products in nuclear collisions. We cover, for the projectiles, a ki...

  17. Impact of surrounding environment evolution on long-term gas flux measurements in a temperate mixed forest

    Science.gov (United States)

    Hurdebise, Quentin; Rixen, Toma; De Ligne, Anne; Vincke, Caroline; Heinesch, Bernard; Aubinet, Marc

    2016-04-01

    With the development of eddy covariance networks like Fluxnet, ICOS or NEON, long-term data series of carbon dioxide, water vapor and other gas exchanges between terrestrial ecosystems and atmosphere will become more and more numerous. However, long-term analyses of such exchanges require a good understanding of measurement conditions during the investigated period. Independently of climate drivers, measurements may indeed be influenced by measurement conditions themselves subjected to long-term variability due to vegetation growth or set-up changes. The present research refers to the Vielsalm Terrestrial Observatory (VTO) where fluxes of momentum, carbon dioxide, latent and sensible heat have been continuously measured by eddy covariance during twenty years. VTO is an ICOS site installed in a mixed forest (beech, silver fir, Douglas fir, Norway spruce) in the Belgian Ardennes. A multidisciplinary approach was developed in order to investigate the spatial and temporal evolution of several site characteristics: -displacement height (d) and relative measurement height (z-d) were determined using a spectral approach that compared observed and theoretical cospectra; -turbulence statistics were analyzed in the context of Monin-Obukhov similarity theory; -tree height during the measurement period was obtained by combining tree height inventories, a LIDAR survey and tree growth models; -measurement footprint was determined by using a footprint model. A good agreement was found between the three first approaches. Results show notably that z-d was subjected to both temporal and spatial evolution. Temporal evolution resulted from continuous tree growth as well as from a tower raise, achieved in 2009. Spatial evolution, due to canopy heterogeneity, was also observed. The impacts of these changes on measurements are investigated. In particular, it was shown that they affect measurement footprint, flux spectral corrections and flux quality. All these effects must be taken into

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

    Science.gov (United States)

    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.

  19. Interstellar Dust Inside and Outside the Heliosphere

    CERN Document Server

    Krueger, Harald

    2008-01-01

    In the early 1990s, after its Jupiter flyby, the Ulysses spacecraft identified interstellar dust in the solar system. Since then the in-situ dust detector on board Ulysses continuously monitored interstellar grains with masses up to 10e-13 kg, penetrating deep into the solar system. While Ulysses measured the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the in-situ dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the inner solar system is altered by the solar radiation pressure force, gravitational focussing and interaction of charged grains with the time varying interplanetary magnetic field. The grains act as tracers of the physical conditions in the local interstellar cloud (LIC). Our in-situ measurements imply the existence of a population of 'big' interstellar grains (up to 10e-13 kg) and a gas-to-dust-mass ratio i...

  20. Coupled gas flow/solid dynamics model for predicting the formation of fracture patterns in gas well simulation experiments. [Propellant mixture used instead of explosives to fracture rock surrounding borehole

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, L.M.; Swenson, D.V.; Cooper, P.W.

    1984-07-01

    A two-dimensional finite element model for predicting fracture patterns obtained in high energy gas fracture experiments is presented. In these experiments, a mixture of propellants is used instead of explosives to fracture the rock surrounding the borehole. The propellant mixture is chosen to tailor the pressure pulse so that multiple fractures emanate from the borehole. The model allows the fracture pattern and pressure pulse to be calculated for different combinations of propellant mixture, in situ stress conditions, and rock properties. The model calculates the amount of gas generated by the burning propellants using a burn rate given by a power law in pressure. By assuming that the gas behaves as a perfect gas and that the flow down the fractures is isothermal, the loss of gas from the borehole due to flow down the cracks is accounted for. The flow of gas down the cracks is included in an approximate manner by assuming self-similar pressure profiles along the fractures. Numerical examples are presented and compared to three different full-scale experiments. Results show a good correlation with the experimental data over a wide variety of test parameters. 9 reference, 10 figures, 3 tables.

  1. The VLT-FLAMES Tarantula Survey. IX. The interstellar medium seen through Diffuse Interstellar Bands and neutral sodium

    CERN Document Server

    van Loon, Jacco Th; Tatton, Benjamin L; Apellaniz, Jesus Maiz; Crowther, Paul A; de Koter, Alex; Evans, Christopher J; Henault-Brunet, Vincent; Howarth, Ian D; Richter, Philipp; Sana, Hugues; Simon-Diaz, Sergio; Taylor, William; Walborn, Nolan R

    2012-01-01

    The Tarantula Nebula (30 Dor) is a spectacular star-forming region in the Large Magellanic Cloud, seen through gas in the Galactic Disc and Halo. Diffuse Interstellar Bands offer a unique probe of the diffuse, cool-warm gas in these regions. 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. Spectra of over 800 early-type stars from the VLT Flames Tarantula Survey (VFTS) were analysed. Maps were created, separately, for the Galactic and LMC absorption in the DIBs at 4428 and 6614 Ang and - in a smaller region near the central cluster R136 - neutral sodium (Na I D); we also measured the DIBs at 5780 and 5797 Ang. The maps show strong 4428 and 6614 Ang 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 R136,...

  2. Grain Destruction in Interstellar Shocks

    OpenAIRE

    1995-01-01

    Interstellar shock waves can erode and destroy grains present in the shocked gas, primarily as the result of sputtering and grain-grain collisions. Uncertainties in current estimates of sputtering yields are reviewed. Results are presented for the simple case of sputtering of fast grains being stopped in cold gas. An upper limit is derived for sputtering of refractory grains in C-type MHD shocks: shock speeds $v_s \\gtrsim 50 \\kms$ are required for return of more than 30\\% of the silicate to t...

  3. PAHs in Translucent Interstellar Clouds

    Science.gov (United States)

    Salama, Farid; Galazutdinov, G.; Krelowski, J.; Biennier, L.; Beletsky, Y.; Song, I.

    2011-05-01

    We discuss the proposal of relating the origin of some of the diffuse interstellar bands (DIBs) to neutral polycyclic aromatic hydrocarbons (PAHs) present in translucent interstellar clouds. The spectra of several cold, isolated gas-phase PAHs have been measured in the laboratory under experimental conditions that mimic the interstellar conditions and are compared with an extensive set of astronomical spectra of reddened, early type stars. This comparison provides - for the first time - accurate upper limits for the abundances of specific PAH molecules along specific lines-of-sight. Something that is not attainable from IR observations alone. The comparison of these unique laboratory data with high resolution, high S/N ratio astronomical observations leads to two major findings: (1) a finding specific to the individual molecules that were probed in this study and, which leads to the clear and unambiguous conclusion that the abundance of these specific neutral PAHs must be very low in the individual translucent interstellar clouds that were probed in this survey (PAH features remain below the level of detection) and, (2) a general finding that neutral PAHs exhibit intrinsic band profiles that are similar to the profile of the narrow DIBs indicating that the carriers of the narrow DIBs must have close molecular structure and characteristics. This study is the first quantitative survey of neutral PAHs in the optical range and it opens the way for unambiguous quantitative searches of PAHs in a variety of interstellar and circumstellar environments. // Reference: F. Salama et al. (2011) ApJ. 728 (1), 154 // Acknowledgements: F.S. acknowledges the support of the NASA's Space Mission Directorate APRA Program. J.K. acknowledges the financial support of the Polish State (grant N203 012 32/1550). The authors are deeply grateful to the ESO archive as well as to the ESO staff members for their active support.

  4. Interstellar Fullerene Compounds and Diffuse Interstellar Bands

    CERN Document Server

    Omont, Alain

    2015-01-01

    Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed, especially with the first confirmed identification of two strong diffuse interstellar bands (DIBs) with C60+. This justifies reassesing the importance of interstellar fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerenes is complex. In addition to formation in shock shattering, fully dehydrogenated PAHs in diffuse interstellar (IS) clouds could perhaps efficiently transform into fullerenes including EEHFs. But it is extremely difficult to assess their expected abundance, composition and size distribution, except for C60+. As often suggested, EEHFs share many properties with C60, as regards stability, formation/destruction, chemical processes and many basic spectral features. We address the importance of various EEHFs as possible DIB carriers. Specifically, we discuss IS properties and the contributions of fullerenes of various sizes and charge su...

  5. Interstellar Molecules Their Laboratory and Interstellar Habitat

    CERN Document Server

    Yamada, Koichi M T

    2011-01-01

    This book deals with the astrophysics and spectroscopy of the interstellar molecules. In the introduction, overview and history of interstellar observations are described in order to help understanding how the modern astrophysics and molecular spectroscopy have been developed interactively. The recent progress in the study of this field, after the 4th Cologne-Bonn-Zermatt symposium 2003 is briefly summarized. Furthermore, the basic knowledge of molecular spectroscopy, which is essential to correctly comprehend the astrophysical observations, is presented in a compact form.

  6. A multifrequency study of the active star-forming complex NGC 6357 - I. Interstellar structures linked to the open cluster Pis 24

    Science.gov (United States)

    Cappa, C. E.; Barbá, R.; Duronea, N. U.; Vasquez, J.; Arnal, E. M.; Goss, W. M.; Fernández Lajús, E.

    2011-08-01

    We investigate the distribution of gas (ionized, neutral atomic and molecular) and interstellar dust in the complex star-forming region NGC 6357 with the goal of studying the interplay between the massive stars in the open cluster Pis 24 and the surrounding interstellar matter. Our study of the distribution of the ionized gas is based on narrow-band Hα, [S II]and [O III] images obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on radio continuum observations at 1465 MHz taken with the VLA with a synthesized beam of 40 arcsec. The distribution of the molecular gas is analysed using 12CO(1-0) data obtained with the NANTEN radiotelescope, Chile (angular resolution = 2.7 arcmin). The interstellar dust distribution was studied using mid-infrared data from the GLIMPSE survey and far-infrared observations from IRAS. NGC 6357 consists of a large ionized shell and a number of smaller optical nebulosities. The optical, radio continuum, and near- and mid-IR images delineate the distributions of the ionized gas and interstellar dust in the H II regions and in previously unknown wind-blown bubbles linked to the massive stars in Pis 24 revealing surrounding photodissociation regions. The CO line observations allowed us to identify the molecular counterparts of the ionized structures in the complex and to confirm the presence of photodissociation regions. The action of the WR star HD 157504 on the surrounding gas was also investigated. The molecular mass in the complex is estimated to be (4 ± 2) × 105 M⊙. The mean electron densities derived from the radio data suggest electron densities >200 cm-3, indicating that NGC 6357 is a complex formed in a region of high ambient density. The known massive stars in Pis 24 and a number of newly inferred massive stars are mainly responsible for the excitation and photodissociation of the parental molecular cloud.

  7. Observational astrochemistry: The quest for interstellar molecules

    Directory of Open Access Journals (Sweden)

    Guélin M.

    2012-01-01

    Full Text Available Over 160 molecular species, not counting isotopologues, have been identified in circumstellar envelopes and interstellar clouds. These species have revealed a wealth of familiar, as much as exotic molecules and in complex organic (and silicon compounds, that was fully unexpected in view of the harshness of surrounding conditions: vanishingly low densities, extreme temperatures and intense embedding UV radiation. They illustrate the diversity of astrochemistry and show robust prebiotic molecules may be. In this lecture, we review the quest for interstellar molecules and show how tributary it is from theoretical ideas and technology developments. A. A. Penzias, who discovered interstellar CO and the 2.7 K Cosmic Background radiation, used to joke that astronomical research is easy: the great questions have largely been formulated; one only has to wait until technological progress makes it possible to answer.

  8. Interstellar grain chemistry and organic molecules

    Science.gov (United States)

    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.

  9. Is interstellar archeology possible?

    Science.gov (United States)

    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.

  10. Complex Organics from Laboratory Simulated Interstellar Ices

    Science.gov (United States)

    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 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-enriched provides evidence for a connection between intact organic material in the interstellar medium and in meteorites. Thus, some of the

  11. Interstellar molecular clouds

    Science.gov (United States)

    Bally, J.

    1986-04-01

    The physical properties of the molecular phase of the interstellar medium are studied with regard to star formation and the structure of the Galaxy. Most observations of molecular clouds are made with single-dish, high-surface precision radio telescopes, with the best resolution attainable at 0.2 to 1 arcmin; the smallest structures that can be resolved are of order 10 to the 17th cm in diameter. It is now believed that: (1) most of the mass of the Galaxy is in the form of giant molecular clouds; (2) the largest clouds and those responsible for most massive star formation are concentrated in spiral arms; (3) the molecular clouds are the sites of perpetual star formation, and are significant in the chemical evolution of the Galaxy; (4) giant molecular clouds determine the evolution of the kinematic properties of galactic disk stars; (5) the total gas content is diminishing with time; and (6) most clouds have supersonic internal motions and do not form stars on a free-fall time scale. It is concluded that though progress has been made, more advanced instruments are needed to inspect the processes operating within stellar nurseries and to study the distribution of the molecular clouds in more distant galaxies. Instruments presently under construction which are designed to meet these ends are presented.

  12. Interstellar Solid Hydrogen

    CERN Document Server

    Lin, Ching Yeh; Walker, Mark A

    2011-01-01

    We consider the possibility that solid molecular hydrogen is present in interstellar space. If so cosmic-rays and energetic photons cause ionisation in the solid leading to the formation of H6+. This ion is not produced by gas-phase reactions and its radiative transitions therefore provide a signature of solid H2 in the astrophysical context. The vibrational transitions of H6+ are yet to be observed in the laboratory, but we have characterised them in a quantum-theoretical treatment of the molecule; our calculations include anharmonic corrections, which are large. Here we report on those calculations and compare our results with astronomical data. In addition to the H6+ isotopomer, we focus on the deuterated species (HD)3+ which is expected to dominate at low ionisation rates as a result of isotopic condensation reactions. We can reliably predict the frequencies of the fundamental bands for five modes of vibration. For (HD)3+ all of these are found to lie close to some of the strongest of the pervasive mid-in...

  13. Progress on the Study of Atomic and Molecular Gas in Interstellar Medium%星系中分子气体和原子气体的研究进展

    Institute of Scientific and Technical Information of China (English)

    富坚

    2012-01-01

    Molecular gas (mainly H2 molecule) and atomic gas (mainly HI atom) are very important baryonic components in interstellar medium, and they play significant roles in various kinds of physical processes in galaxies, including gas cooling and infall, star formation, metal producing, supernova reheating and feedback. It is generally considered that stars form in giant molecular clouds, and atomic gas is the reservoir of the molecular clouds. In recent years, observations give more and more results on molecular and atomic gas with the development of observational technology. Atomic gas component in nearby galaxies at low redshift is observed through 21 cm radio emission by neutral hydrogen atoms. 21 cm HI surveys provide a lot of information about the neutral gas components in galaxies at low redshift. Some famous HI survey in recent years are HIPASS, HIJASS, WSRT, ALFALFA, THINGS etc. For galaxies at redshift higher than 0.2, people usually use DLA absorbers to observe the HI gas components indirectly. Because of the symmetric structure, molecular hydrogen H2 components cannot be directly observed, and the molecular gas is observed through carbon monoxide or some other molecules as tracers. Some famous CO observations in recent years are FCRAO, COLD GASS, BIMA SONG, HERACLES. Based on these observations, people get the H2 properties for the local galaxies including the H2 mass functions at z = 0, the surface density profiles of molecular gas etc. Combining with the star formation rate observations of these galaxies, some astronomers find that the star formation rate correlates with the molecular components more tightly than total cold gas components. With the advance of observational studies along this line, more and more galaxy formation models have include the molecular and neutral gas components. There are mainly two aspects on the transition of these two components. One is on the transition between atomic and molecular gas in ISM, and the other is the semi

  14. Physics and chemistry of interstellar ice

    NARCIS (Netherlands)

    Guss (née Isokoski), Karoliina Marja-Riita

    2013-01-01

    The importance of ice in the interstellar medium is indisputable. Gas phase reactions relying on three-body collisions are exceedingly rare in the sparse medium between the stars. On solid surfaces, atoms and molecules can reside and rove the surface until a reaction takes place. Upon reaction, the

  15. Impacts from Partial Removal of Decommissioned Oil and Gas Platforms on Fish Biomass and Production on the Remaining Platform Structure and Surrounding Shell Mounds.

    Directory of Open Access Journals (Sweden)

    Jeremy T Claisse

    Full Text Available When oil and gas platforms become obsolete they go through a decommissioning process. This may include partial removal (from the surface to 26 m depth or complete removal of the platform structure. While complete removal would likely eliminate most of the existing fish biomass and associated secondary production, we find that the potential impacts of partial removal would likely be limited on all but one platform off the coast of California. On average 80% of fish biomass and 86% of secondary fish production would be retained after partial removal, with above 90% retention expected for both metrics on many platforms. Partial removal would likely result in the loss of fish biomass and production for species typically found residing in the shallow portions of the platform structure. However, these fishes generally represent a small proportion of the fishes associated with these platforms. More characteristic of platform fauna are the primarily deeper-dwelling rockfishes (genus Sebastes. "Shell mounds" are biogenic reefs that surround some of these platforms resulting from an accumulation of mollusk shells that have fallen from the shallow areas of the platforms mostly above the depth of partial removal. We found that shell mounds are moderately productive fish habitats, similar to or greater than natural rocky reefs in the region at comparable depths. The complexity and areal extent of these biogenic habitats, and the associated fish biomass and production, will likely be reduced after either partial or complete platform removal. Habitat augmentation by placing the partially removed platform superstructure or some other additional habitat enrichment material (e.g., rock boulders on the seafloor adjacent to the base of partially removed platforms provides additional options to enhance fish production, potentially mitigating reductions in shell mound habitat.

  16. The interaction of the solar wind with the interstellar medium

    Science.gov (United States)

    Axford, W. I.

    1972-01-01

    The expected characteristics of the solar wind, extrapolated from the vicinity of the earth are described. Several models are examined for the interaction of the solar wind with the interstellar plasma and magnetic field. Various aspects of the penetration of neutral interstellar gas into the solar wind are considered. The dynamic effects of the neutral gas on the solar wind are described. Problems associated with the interaction of cosmic rays with the solar wind are discussed.

  17. Radical routes to interstellar glycolaldehyde. The possibility of stereoselectivity in gas-phase polymerization reactions involving CH(2)O and ˙CH(2)OH.

    Science.gov (United States)

    Wang, Tianfang; Bowie, John H

    2010-10-21

    A previous report that the interstellar molecule glycolaldehyde (HOCH(2)CHO) can be made from hydroxymethylene (HOCH:) and formaldehyde has been revisited at the CCSD(T)/6-311++G(3df,2p)//MP2/6-311++G(3df,2p) level of theory. This reaction competes with the formation of acetic acid and methylformate, molecules which have also been detected in interstellar clouds. Other possible modes of formation of glycolaldehyde by radical/radical reactions have been shown to be viable theoretically as follows: HO˙+˙CH2CHO -->HOCH2CHO [ΔG(Γ)(298K)=-303kJ mol⁻¹] HOCH2˙+˙CHO-->HOCH2CHO (-259kJ mol⁻¹). The species in these two processes are known interstellar molecules. Key radicals ˙CH(2)CHO and ˙CH(2)OH in these sequences have been shown to be stable for the microsecond duration of neutralization/reionization experiments in the dual collision cells of a VG ZAB 2HF mass spectrometer. The polymerization reaction HOCH(2)CH˙OH + nCH(2)O → HOCH(2)[CH(OH)](n)˙CHOH (n = 1 to 3) has been studied theoretically and shown to be energetically feasible, as is the cyclization reaction of HOCH(2)[(CH(2)OH)(4)]˙CHOH (in the presence of one molecule of water at the reacting centre) to form glucose. The probability of such a reaction sequence is small even if polymerization were to occur in interstellar ice containing a significant concentration of CH(2)O. The large number of stereoisomers produced by such a reaction sequence makes the formation of a particular sugar, again for example glucose, an inefficient synthesis. The possibility of stereoselectivity occurring during the polymerization was investigated for two diastereoisomers of HOCH(2)[(CHOH)](2)˙CHOH. No significant difference was found in the transition state energies for addition of CH(2)O to these two diastereoisomers, but a barrier difference of 12 kJ mol(-1) was found for the H transfer reactions ˙OCH(2)[(CHOH)](2)CH(2)OH → HOCH(2)[(CHOH)(2)˙CHOH of the two diastereoisomers.

  18. The galactic interstellar medium

    CERN Document Server

    Burton, WB; Genzel, R

    1992-01-01

    This volume contains the papers of three extended lectures addressing advanced topics in astronomy and astrophysics. The topics discussed include the most recent observational data on interstellar matter outside our galaxy and the physics and chemistry of molecular clouds.

  19. Diffuse interstellar absorption bands

    Institute of Scientific and Technical Information of China (English)

    XIANG FuYuan; LIANG ShunLin; LI AiGen

    2009-01-01

    The diffuse interstellar bands (DIBs) are a large number of absorption bands that are superposed on the interstellar extinction curve and are of interstellar origin. Since the discovery of the first two DIBs in the 1920s, the exact nature of DIBs still remains unclear. This article reviews the history of the detec-tions of DIBs in the Milky Way and external galaxies, the major observational characteristics of DIBs, the correlations or anti-correlations among DIBs or between DIBs and other interstellar features (e.g. the prominent 2175 Angstrom extinction bump and the far-ultraviolet extinction rise), and the proposed candidate carriers. Whether they are also present in circumstellar environments is also discussed.

  20. Diffuse interstellar absorption bands

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The diffuse interstellar bands(DIBs) are a large number of absorption bands that are superposed on the interstellar extinction curve and are of interstellar origin. Since the discovery of the first two DIBs in the 1920s,the exact nature of DIBs still remains unclear. This article reviews the history of the detections of DIBs in the Milky Way and external galaxies,the major observational characteristics of DIBs,the correlations or anti-correlations among DIBs or between DIBs and other interstellar features(e.g. the prominent 2175 Angstrom extinction bump and the far-ultraviolet extinction rise),and the proposed candidate carriers. Whether they are also present in circumstellar environments is also discussed.

  1. Interstellar water chemistry: from laboratory to observations

    CERN Document Server

    van Dishoeck, Ewine F; Neufeld, David A

    2013-01-01

    Water is observed throughout the universe, from diffuse interstellar clouds to protoplanetary disks around young stars, and from comets in our own solar system and exoplanetary atmospheres to galaxies at high redshifts. This review summarizes the spectroscopy and excitation of water in interstellar space as well as the basic chemical processes that form and destroy water under interstellar conditions. Three major routes to water formation are identified: low temperature ion-molecule chemistry, high-temperature neutral-neutral chemistry and gas-ice chemistry. The rate coefficients of several important processes entering the networks are discussed in detail; several of them have been determined only in the last decade through laboratory experiments and theoretical calculations. Astronomical examples of each of the different chemical routes are presented using data from powerful new telescopes, in particular the Herschel Space Observatory. Basic chemical physics studies remain critically important to analyze ast...

  2. Interstellar organic chemistry.

    Science.gov (United States)

    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.

  3. Interstellar organic chemistry.

    Science.gov (United States)

    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.

  4. GAS-PHASE SYNTHESIS OF PRECURSORS OF INTERSTELLAR GLYCINE: A COMPUTATIONAL STUDY OF THE REACTIONS OF ACETIC ACID WITH HYDROXYLAMINE AND ITS IONIZED AND PROTONATED DERIVATIVES

    Energy Technology Data Exchange (ETDEWEB)

    Barrientos, Carmen; Redondo, Pilar; Largo, Laura; Rayon, Victor M.; Largo, Antonio, E-mail: alargo@qf.uva.es [Departamento de Quimica Fisica y Quimica Inorganica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid (Spain)

    2012-04-01

    A computational study of the reactions of hydroxylamine and its ionized and protonated derivatives with acetic acid is provided. The reaction of neutral hydroxylamine with acetic acid, despite being clearly exothermic, involves a very large energy barrier. The reaction of ionized hydroxylamine with acetic acid is also clearly exothermic, but again a significant energy barrier is found (around 24 kcal mol{sup -1} at the CCSD(T) level). The reaction of the most stable protonated isomer of hydroxylamine, NH{sub 3}OH{sup +}, with acetic acid also involves a high barrier (more than 27 kcal mol{sup -1} at the CCSD(T) level). Only the higher energy isomer, NH{sub 2}OH{sup +}{sub 2}, leads to a sensibly lower energy barrier (about 2.3 kcal mol{sup -1} at the CCSD(T) level). Nevertheless, an estimate of the reaction coefficient at low temperatures such as those reigning in the interstellar medium gives very low values. Therefore, it seems that precursors of interstellar glycine could not be efficiently produced from the reactions of hydroxylamine-derived ions with acetic acid.

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

    Science.gov (United States)

    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.

  6. Neutral interstellar helium parameters based on IBEX-Lo observations and test particle calculations

    CERN Document Server

    Bzowski, M; Moebius, E; Bochsler, P; Leonard, T; Heirtzler, D; Kucharek, H; Sokol, J M; Hlond, M; Crew, G B; Schwadron, N A; Fuselier, S A; McComas, D J; 10.1088/0067--0049/198/2/12

    2012-01-01

    Neutral Interstellar Helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. It 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 agr...

  7. On the Critical Ionization Velocity Effect in Interstellar Space and Possible Detection of Related Continuum Emission

    CERN Document Server

    Verschuur, Gerrit L

    2007-01-01

    Interstellar neutral hydrogen (HI) emission spectra manifest several families of linewidths whose numerical values (34, 13 & 6 km/s) appear to be related to the critical ionization velocities (CIVs) of the most abundant interstellar atomic species. Extended new analysis of HI emission profiles shows that the 34 km/s wide component, probably corresponding to the CIV for helium, is pervasive. The 34 km/s wide linewidth family is found in low-velocity (local) neutral hydrogen (HI) profiles as well as in the so-called high-velocity clouds. In addition, published studies of HI linewidths found in the Magellanic Stream, Very-High-Velocity Clouds, and Compact High-Velocity Clouds, all of which are believed to be intergalactic, have noted that typical values are of the same order. If the critical ionization velocity effect does play a role in interstellar space it may be expected to produce locally enhanced electron densities where rapidly moving neutral gas masses interact with surrounding plasma. Evidence is pr...

  8. Probing the Local Bubble with Diffuse Interstellar Bands (DIBs)

    CERN Document Server

    van Loon, Jacco Th; Javadi, Atefeh; Bailey, Mandy; Khosroshahi, Habib

    2015-01-01

    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 \\AA\\ bands which trace ionized/irradiated and neutral/shielded environments, respectively; their carriers are unknown but likely to be large carbonaceous molecules. With about 660 s...

  9. Laboratory Astrochemistry: Interstellar PAHs

    Science.gov (United States)

    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

  10. HERSCHEL OBSERVATIONS OF INTERSTELLAR CHLORONIUM

    Energy Technology Data Exchange (ETDEWEB)

    Neufeld, David A.; Indriolo, Nick [Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218 (United States); Roueff, Evelyne; Le Bourlot, Jacques; Le Petit, Franck [Observatoire de Paris-Meudon, LUTH UMR 8102, 5 Pl. Jules Janssen, F-92195 Meudon Cedex (France); Snell, Ronald L. [Astronomy Department, University of Massachusetts at Amherst, Amherst, MA 01003 (United States); Lis, Dariusz; Monje, Raquel; Phillips, Thomas G. [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Benz, Arnold O. [Institute of Astronomy, ETH Zurich, 8092 Zurich (Switzerland); Bruderer, Simon [Max Planck Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching (Germany); Black, John H.; Larsson, Bengt [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala (Sweden); De Luca, Massimo; Gerin, Maryvonne [LERMA, UMR 8112 du CNRS, Observatoire de Paris, Ecole Normale Superieure, UPMC and UCP (France); Goldsmith, Paul F.; Gupta, Harshal [JPL, California Institute of Technology, Pasadena, CA (United States); Melnick, Gary J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Menten, Karl M. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Nagy, Zsofia [Kapteyn Astronomical Institute University of Groningen, Groningen (Netherlands); 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.

  11. Filtration of interstellar hydrogen in the two-shock heliospheric interface Inferences on the local interstellar electron density

    CERN Document Server

    Izmodenov, V V; Lallement, R; Glöckler, G; Baranov, V B; Malama, Y G

    1998-01-01

    The solar system is moving through the partially ionized local interstellar cloud (LIC). The ionized matter of the LIC interacts with the expanding solar wind forming the heliospheric interface. The neutral component (interstellar atoms) penetrates through the heliospheric interface into the heliosphere, where it is measured directly "in situ" as pick-up ions and neutral atoms (and as anomalous cosmic rays) or indirectly through resonant scattering of solar Ly-alpha. When crossing the heliospheric interface, interstellar atoms interact with the plasma component through charge exchange. This interaction leads to changes of both neutral gas and plasma properties. The heliospheric interface is also the source of radio emissions which have been detected by the Voyager since 1983. In this paper, we have used a kinetic model of the flow of the interstellar atoms with updated values of velocity, temperature, and density of the circumsolar interstellar hydrogen and calculated how all quantities which are directly ass...

  12. Abundances and Depletions of Interstellar Oxygen

    Science.gov (United States)

    Jensen, A. G.; Rachford, B. L.; Snow, T. P.

    2003-12-01

    We extend previous work on interstellar oxygen abundances with the addition of data from the Far Ultraviolet Spectroscopic Explorer (FUSE). We report on the abundance of interstellar neutral oxygen (OI) for several sightlines, using data from FUSE, the International Spectroscopic Explorer (IUE), and the Hubble Space Telescope (HST). OI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines, and subsequently fitting those to a curve of growth. The column densities of our best-constrained sightlines show a ratio of O/H that agrees with the current best solar value if dust is considered. We do not see evidence of enhanced depletion of gas-phase oxygen that is systematically variable with respect to the physical parameters of different environments (e.g., reddening or molecular fraction). The column densities of our less well-constrained sightlines show some scatter in O/H, but many agree with the solar value to within errors. We discuss these results in the context of deriving the best methods for determining interstellar abundances, the unresolved question of the best value for O/H in the interstellar medium (ISM), the O/H ratio observed in Galactic stars, and the depletion of gas-phase oxygen onto dust grains. Financial support for this research has been provided by the National Science Foundation GK-12 Program and NASA contract NAS 5-32985.

  13. Herschel observations of interstellar chloronium

    CERN Document Server

    Neufeld, David A; Snell, Ronald L; Lis, Dariusz; Benz, Arnold O; Bruderer, Simon; Black, John H; De Luca, Massimo; Gerin, Maryvonne; Goldsmith, Paul F; Gupta, Harshal; Indriolo, Nick; Bourlot, Jacques Le; Petit, Franck Le; Larsson, Bengt; Melnick, Gary J; Menten, Karl M; Monje, Raquel; Nagy, Zsofia; Phillips, Thomas G; Sandqvist, Aage; Sonnentrucker, Paule; van der Tak, Floris; Wolfire, Mark G

    2012-01-01

    Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared (HIFI), we have observed para-chloronium (H2Cl+) 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 cloud) and W31C. Both the para-H2-35Cl+ and para-H2-37Cl+ isotopologues were detected, through observations of their 1(11)-0(00) transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio of 3, the observed optical depths imply that chloronium accounts for ~ 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 ortho-to-para ratio of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of ~ 2.0E+13 cm-2 and ~ 1.2E+13 cm-2, respect...

  14. Ionization of Interstellar Hydrogen Beyond the Termination Shock

    Science.gov (United States)

    Gruntman, Mike

    2016-11-01

    Models of solar wind interaction with the surrounding interstellar medium usually disregard ionization of interstellar hydrogen atoms beyond the solar wind termination shock. If and when included, the effects of ionization in the heliospheric interface region are often obscured by complexities of the interaction. This work assesses the importance of interstellar hydrogen ionization in the heliosheath. Photoionization could be accounted for in a straightforward way. In contrast, electron impact ionization is largely unknown because of poorly understood energy transfer to electrons at the termination shock and beyond. We first estimate the effect of photoionization and then use it as a yardstick to assess the role of electron impact ionization. The physical estimates show that ionization of interstellar hydrogen may lead to significant mass loading in the inner heliosheath which would slow down plasma flowing toward the heliotail and deplete populations of nonthermal protons, with the corresponding effect on heliospheric fluxes of energetic neutral atoms.

  15. Interstellar and circumstellar fullerenes

    CERN Document Server

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

    2014-01-01

    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, understand...

  16. Multiphase turbulent interstellar medium: some recent results from radio astronomy

    CERN Document Server

    Roy, Nirupam

    2015-01-01

    The radio frequency 1.4 GHz transition of the atomic hydrogen is one of the important tracers of the diffuse neutral interstellar medium. Radio astronomical observations of this transition, using either a single dish telescope or an array interferometer, reveal different properties of the interstellar medium. Such observations are particularly useful to study the multiphase nature and turbulence in the interstellar gas. Observations with multiple radio telescopes have recently been used to study these two closely related aspects in greater detail. Using various observational techniques, the density and the velocity fluctuations in the Galactic interstellar medium was found to have a Kolmogorov-like power law power spectra. The observed power law scaling of the turbulent velocity dispersion with the length scale can be used to derive the true temperature distribution of the medium. Observations from a large ongoing atomic hydrogen absorption line survey have also been used to study the distribution of gas at d...

  17. Star-forming regions at the periphery of the supershell surrounding the Cyg OB1 association. I. The star cluster vdB 130 and its ambient gas and dust medium

    CERN Document Server

    Sitnik, T G; Lozinskaya, T A; Moiseev, A V; Rastorguev, A S; Tatarnikov, A M; Tatarnikova, A A; Wiebe, D S; Zabolotskikh, M V

    2015-01-01

    Stellar population and the interstellar gas-dust medium in the vicinity of the open star cluster vdB 130 are analysed using optical observations taken with the 6-m telescope of the SAO RAS and the 125-cm telescope of the SAI MSU along with the data of Spitzer and Herschel. Based on proper motions and BV and JHKs 2MASS photometric data, we select additional 36 stars as probable cluster members. Some stars in vdB 130 are classified as B stars. Our estimates of minimum colour excess, apparent distance modulus and the distance are consistent with young age (from 5 to 10 Myrs) of the cluster vdB 130. We suppose the large deviations from the conventional extinction law in the cluster direction, with $R_V$ ~ 4 - 5. The cluster vdB 130 appears to be physically related to the supershell around Cyg OB1, a cometary CO cloud, ionized gas, and regions of infrared emission. There are a few regions of bright mid-infrared emission in the vicinity of vdB 130. The largest of them is also visible on H-alpha and [SII] emission m...

  18. The interstellar formation and spectra of the noble gas, proton-bound HeHHe+, HeHNe+ and HeHAr+ complexes

    Science.gov (United States)

    Stephan, Cody J.; Fortenberry, Ryan C.

    2017-07-01

    The sheer interstellar abundance of helium makes any bound molecules or complexes containing it of potential interest for astrophysical observation. This work utilizes high-level and trusted quantum chemical techniques to predict the rotational, vibrational and rovibrational traits of HeHHe+, HeHNe+ and HeHAr+. The first two are shown to be strongly bound, while HeHAr+ is shown to be more of a van der Waals complex of argonium with a helium atom. In any case, the formation of HeHHe+ through reactions of HeH+ with HeH3+ is exothermic. HeHHe+ exhibits the quintessentially bright proton-shuttle motion present in all proton-bound complexes in the 7.4 micron range making it a possible target for telescopic observation at the mid-/far-Infrared crossover point and a possible tracer for the as-of-yet unobserved helium hydride cation. Furthermore, a similar mode in HeHNe+ can be observed to the blue of this close to 6.9 microns. The brightest mode of HeHAr+ is dimmed due the reduced interaction of the helium atom with the central proton, but this fundamental frequency can be found slightly to the red of the Ar-H stretch in the astrophysically detected argonium cation.

  19. The Possibility of Forming Propargyl Alcohol in the Interstellar Medium

    Science.gov (United States)

    Gorai, Prasanta; Das, Ankan; Majumdar, Liton; Chakrabarti, Sandip Kumar; Sivaraman, Bhalamurugan; Herbst, Eric

    2017-03-01

    Propargyl alcohol (HC2CH2OH, PA) has yet to be observed in the interstellar medium (ISM) although one of its stable isomers, propenal (CH2CHCHO), has already been detected in Sagittarius B2(N) with the 100-meter Green Bank Telescope in the frequency range 18 - 26 GHz. In this paper, we investigate the formation of propargyl alcohol along with one of its deuterated isotopomers, HC2CH2OD (OD-PA), in a dense molecular cloud. Various pathways for the formation of PA in the gas and on ice mantles surrounding dust particles are discussed. We use a large gas-grain chemical network to study the chemical evolution of PA and its deuterated isotopomer. Our results suggest that gaseous HC2CH2OH can most likely be detected in hot cores or in collections of hot cores such as the star-forming region Sgr B2(N). A simple LTE (Local thermodynamic equilibrium) radiative transfer model is employed to check the possibility of detecting PA and OD-PA in the millimeter-wave regime. In addition, we have carried out quantum chemical calculations to compute the vibrational transition frequencies and intensities of these species in the infrared for perhaps future use in studies with the James Webb Space Telescope (JWST).

  20. Extra-Galactic Diffuse Interstellar Bands

    Science.gov (United States)

    Cox, N.; Ehrenfreund, Pascale; Kaper, Lex; Spaans, Marco; Foing, Bernard

    Diffuse Interstellar Bands (DIBs) have been observed ubiquitously along many sight-lines probing the interstellar medium of the Milky Way. Despite extensive efforts, their carrier(s) have not yet been identified, although they are very likely of a carbonaceous nature and reside in the gas phase. Possible candidates include, but are not limited to, polycyclic aromatic hydro- carbons (PAHs), fullerenes and carbon chains. To advance our understanding of DIB behaviour and thus DIB carrier properties we need to study environments inherently different from those observed in the Milky Way. Only recent advances in instrumentation and telescope capabilities are providing us with new exciting possibilities for extra-galactic DIB research. We present here a selection of our recent observational results for (extra)-galactic DIBs in the Local Group and beyond. In particular, DIBs in the Magellanic Clouds and in the spiral galaxy NGC1448. These first results show surprising similarities between certain DIB profiles as well as differences in DIB behaviour. Understanding diffuse cloud chemistry, in particular with respect to complex (carbonaceous) molecules, is crucial to any DIB carrier identification. In this respect, external galaxies offer a unique window as they exhibit local interstellar conditions (such as metallicity, UV-field and gas-to-dust ratio) very different from those observed in the Milky Way. We discuss briefly the effect of metallicity and the gas-to-dust ratio on the physi-chemical properties of diffuse clouds and the subsequent effects on the PAH charge state distribution and the DIB carriers.

  1. The Hot Interstellar Medium of Normal Elliptical Galaxies. I. A Chandra Gas Gallery and Comparison of X-ray and Optical Morphology

    CERN Document Server

    Diehl, S; Diehl, Steven; Statler, Thomas S.

    2006-01-01

    We present an X-ray analysis of 54 normal elliptical galaxies in the Chandra archive and isolate their hot gas component from the contaminating point source emission. This makes it possible to conduct, for the first time, a complete morphological analysis on the gas alone. A comparison with optical DSS images and published optical photometry shows that the hot gas morphology has surprisingly little in common with the shape of the stellar distribution. In particular, we observe no correlation between optical and X-ray ellipticity, as would be expected if the gas had settled into hydrostatic equilibrium with the underlying gravitational potential. In fact, the observed X-ray ellipticity exceeds the optical ellipticity in many cases. We exclude rotational support as the dominant factor to produce these high ellipticities. Instead, we find that the gas appears to be very disturbed and that the general perception of normal elliptical galaxies hosting calm, hydrostatic gas has to be revised. We conclude that, even ...

  2. SURVIVAL OF INTERSTELLAR MOLECULES TO PRESTELLAR DENSE CORE COLLAPSE AND EARLY PHASES OF DISK FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Hincelin, U. [Department of Chemistry, University of Virginia, Charlottesville, VA 22904 (United States); Wakelam, V.; Hersant, F.; Guilloteau, S. [University of Bordeaux, LAB, UMR 5804, F-33270 Floirac (France); Commerçon, B., E-mail: ugo.hincelin@virginia.edu [Laboratoire de radioastronomie, LERMA, Observatoire de Paris, Ecole Normale Supérieure (UMR 8112 CNRS), 24 rue Lhomond, F-75231 Paris Cedex 05 (France)

    2013-09-20

    An outstanding question of astrobiology is the link between the chemical composition of planets, comets, and other solar system bodies and the molecules formed in the interstellar medium. Understanding the chemical and physical evolution of the matter leading to the formation of protoplanetary disks is an important step for this. We provide some new clues to this long-standing problem using three-dimensional chemical simulations of the early phases of disk formation: we interfaced the full gas-grain chemical model Nautilus with the radiation-magnetohydrodynamic model RAMSES, for different configurations and intensities of the magnetic field. Our results show that the chemical content (gas and ices) is globally conserved during the collapsing process, from the parent molecular cloud to the young disk surrounding the first Larson core. A qualitative comparison with cometary composition suggests that comets are constituted of different phases, some molecules being direct tracers of interstellar chemistry, while others, including complex molecules, seem to have been formed in disks, where higher densities and temperatures allow for an active grain surface chemistry. The latter phase, and its connection with the formation of the first Larson core, remains to be modeled.

  3. Charge transfer reactions at interfaces between neutral gas and plasma: Dynamical effects and X-ray emission

    Science.gov (United States)

    Provornikova, E.; Izmodenov, V. V.; Lallement, R.

    2012-04-01

    Charge-transfer is the main process linking neutrals and charged particles in the interaction regions of neutral (or partly ionized) gas with a plasma. In this paper we illustrate the importance of charge-transfer with respect to the dynamics and the structure of neutral gas-plasma interfaces. We consider the following phenomena: (1) the heliospheric interface - region where the solar wind plasma interacts with the partly-ionized local interstellar medium (LISM) and (2) neutral interstellar clouds embedded in a hot, tenuous plasma such as the million degree gas that fills the so-called ``Local Bubble". In (1), we discuss several effects in the outer heliosphere caused by charge exchange of interstellar neutral atoms and plasma protons. In (2) we describe the role of charge exchange in the formation of a transition region between the cloud and the surrounding plasma based on a two-component model of the cloud-plasma interaction. In the model the cloud consists of relatively cold and dense atomic hydrogen gas, surrounded by hot, low density, fully ionized plasma. We discuss the structure of the cloud-plasma interface and the effect of charge exchange on the lifetime of interstellar clouds. Charge transfer between neutral atoms and minor ions in the plasma produces X-ray emission. Assuming standard abundances of minor ions in the hot gas surrounding the cold interstellar cloud, we estimate the X-ray emissivity consecutive to the charge transfer reactions. Our model shows that the charge-transfer X-ray emission from the neutral cloud-plasma interface may be comparable to the diffuse thermal X-ray emission from the million degree gas cavity itself.

  4. The 2014 KIDA network for interstellar chemistry

    CERN Document Server

    Wakelam, V; Herbst, E; Pavone, B; Bergeat, A; Béroff, K; Chabot, M; Faure, A; Galli, D; Geppert, W D; Gerlich, D; Gratier, P; Harada, N; Hickson, K M; Honvault, P; Klippenstein, S J; Picard, S D Le; Nyman, G; Ruaud, M; Schlemmer, S; Sims, I R; Talbi, D; Tennyson, J; Wester, R

    2015-01-01

    Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.

  5. Mapping the interstellar medium in galaxies with Herschel/SPIRE

    CERN Document Server

    Eales, S A; Wilson, C D; Bendo, G J; Cortese, L; Pohlen, M; Boselli, A; Gomez, H L; Auld, R; Baes, M; Barlow, M J; Bock, J J; Bradford, M; Buat, V; Castro-Rodriguez, N; Chanial, P; Charlot, S; Ciesla, L; Clements, D L; Cooray, A; Cormier, D; Davies, J I; Dwek, E; Elbaz, D; Galametz, M; Galliano, F; Gear, W K; Glenn, J; Griffin, M; Hony, S; Isaak, K G; Levenson, L R; Lu, N; Madden, S; O'Halloran, B; Okumura, K; Oliver, S; Page, M J; Panuzzo, P; Papageorgiou, A; Parkin, T J; Perez-Fournon, I; Rangwala, N; Rigby, E E; Roussel, H; Rykala, A; Sacchi, N; Sauvage, M; Schulz, B; Schirm, M R P; Spinoglio, L; Srinivasan, S; Stevens, J A; Symeonidis, M; Trichas, M; Vaccari, M; Vigroux, L; Wozniak, H; Wright, G S; Zeilinger, W W

    2010-01-01

    The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies.

  6. Interstellar hydrogen sulfide.

    Science.gov (United States)

    Thaddeus, P.; Kutner, M. L.; Penzias, A. A.; Wilson, R. W.; Jefferts, K. B.

    1972-01-01

    Hydrogen sulfide has been detected in seven Galactic sources by observation of a single line corresponding to the rotational transition from the 1(sub 10) to the 1(sub 01) levels at 168.7 GHz. The observations show that hydrogen sulfide is only a moderately common interstellar molecule comparable in abundance to H2CO and CS, but somewhat less abundant than HCN and much less abundant than CO.

  7. From Interstellar PAHs and Ices to the Origin of Life

    Science.gov (United States)

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

    2000-01-01

    Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to micron-sized cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In dense molecular clouds, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier interstellar chemistry standards, is widespread throughout the Universe. The first part of this lecture will describe how infrared studies of interstellar space, combined with laboratory simulations, have revealed the composition of interstellar ices (the building blocks of comets) and the high abundance and nature of interstellar PAHs. The laboratory database has now enabled us to gain insight into the identities, concentrations, and physical state of many interstellar materials. Within a dense molecular cloud, and especially in the solar nebula during the star and planet formation stage, the materials frozen into interstellar/precometary ices are photoprocessed by ultraviolet light, producing more complex molecules. The remainder of the presentation will focus on the photochemical evolution of these materials and the possible role of these compounds on the early Earth. As these materials are thought to be the building

  8. Discovery of Interstellar Hydrogen Fluoride

    Science.gov (United States)

    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.

  9. A cylindrical multiwire high-pressure gas proportional chamber surrounding a gaseous $_{2} target with a mylar separation foil $6 \\mu m thick

    CERN Document Server

    Gastaldi, Ugo; Averdung, H; Bailey, J; Beer, G A; Dreher, B; Erdman, K L; Klempt, E; Merle, K; Neubecker, K; Sabev, C; Schwenk, H; Wendling, R D; White, B L; Wodrich, R

    1978-01-01

    The characteristics and performances of a cylindrical multiwire proportional chamber built and used at CERN in experiment S142 for the study of the pp atom spectroscopy are presented. The chamber surrounds a high-pressure gaseous H/sub 2/ target, from which it is separated by a very thin window (6 mu m mylar foil). The active volume (90 cm long; 2 cm thick, internal diameter=30 cm) is divided into 36 equal and independent cells each covering 10 degrees in azimuth. At 4 abs. atm the detection efficiency for X-rays is higher than 20% in the whole energy range 1.5-15 keV. Typical resolutions are 35% fwhm for the 3 ke V Ar fluorescence line and 25% fwhm for the 5.5 keV /sup 54/Mn line. Working pressures from 0.5 to 16 abs. atm have been used. (8 refs).

  10. O VI Emission Imaging of a Galaxy with the Hubble Space Telescope: a Warm Gas Halo Surrounding the Intense Starburst SDSS J115630.63+500822.1

    CERN Document Server

    Hayes, Matthew; Östlin, Göran; Scarlata, Claudia; Lehnert, Matthew D; Mannerström-Jansson, Gustav

    2016-01-01

    We report results from a new HST study of the OVI 1032,1038\\AA\\ doublet in emission around intensely star-forming galaxies. The programme aims to characterize the energy balance in starburst galaxies and gas cooling in the difficult-to-map coronal temperature regime of 2-5 x $10^5$K. We present the first resolved image of gas emission in the OVI line. Our target, SDSS J1156+5008, is very compact in the continuum but displays OVI emission to radii of 23 kpc. The surface brightness profile is well fit by an exponential with a scale of 7.5kpc. This is ten times the size of the photoionized gas, and we estimate that 1/6 the total OVI luminosity comes from resonantly scattered continuum radiation. Spectroscopy - which closely resembles a stacked sample of archival spectra - confirms the OVI emission, and determines the column density and outflow velocity from blueshifted absorption. The combination of measurements enables several new calculations with few assumptions. The OVI regions fill only ~$10^{-3}$ of the vo...

  11. Planck intermediate results XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck

    DEFF Research Database (Denmark)

    Ade, P. A. R.; Aghanim, N.; Aniano, G.

    2015-01-01

    densities, NH, in the different gas phases, in particular at the dark neutral medium (DNM) transition between the H I-bright and CO-bright media; (ii) constrain the CO-to-H2 conversion factor, XCO; and (iii) probe the dust properties per gas nucleon in each phase and map their spatial variations across...... or equal to 0.9 and its mass often exceeds the one-third of the molecular mass expected by theory. The corrected A(VQ) extinction largely provides the best fit to the total gas traced by the γ rays. Nevertheless, we find evidence for a marked rise in AVQ/NH with increasing NH and molecular fraction......, and with decreasing dust temperature. The rise in τ353/NH is even steeper. We observe variations of lesser amplitude and orderliness for the specific power of the grains, except for a coherent decline by half in the CO cores. This combined information suggests grain evolution. We provide average values for the dust...

  12. Physical Processes of Interstellar Turbulence

    CERN Document Server

    Vazquez-Semadeni, Enrique

    2012-01-01

    I discuss the role of self-gravity and radiative heating and cooling in shaping the nature of the turbulence in the interstellar medium (ISM) of our galaxy. The heating and cooling cause it to be highly compressible, and, in some regimes of density and temperature, to become thermally unstable, tending to spontaneously segregate into warm/diffuse and cold/dense phases. On the other hand, turbulence is an inherently mixing process, tending to replenish the density and temperature ranges that would be forbidden under thermal processes alone. The turbulence in the ionized ISM appears to be transonic (i.e, with Mach numbers $\\Ms \\sim 1$), and thus to behave essentially incompressibly. However, in the neutral medium, thermal instability causes the sound speed of the gas to fluctuate by up to factors of $\\sim 30$, and thus the flow can be highly supersonic with respect to the dense/cold gas, although numerical simulations suggest that this behavior corresponds more to the ensemble of cold clumps than to the clumps'...

  13. Peru's Amazonian oil and gas industry: Risks, interests and the politics of grievance surrounding the development of block 76, Madre de Dios

    DEFF Research Database (Denmark)

    Haselip, James Arthur; Romera, B. Martinez

    2011-01-01

    investment in developing Amazonian oil and gas reserves. Specifically, this article aims to understand grievance-based conflict risk by documenting the positions and motivations of various organisations and local communities affected by exploration work conducted in block 76 overlapping the Amarakaeri...... Communal Reserve (ACR) in the region of Madre de Dios. An account is offered of how these positions have been steered and governed by a government-sanctioned management framework for the ACR, and by a limited and selected consultation process which lies at the heart of wider conflict over the large...

  14. A scenario for interstellar exploration and its financing

    CERN Document Server

    Bignami, Giovanni F

    2013-01-01

    This book develops a credible scenario for interstellar exploration and colonization. In so doing, it examines: • the present situation and prospects for interstellar exploration technologies; • where to go: the search for habitable planets; • the motivations for space travel and colonization; • the financial mechanisms required to fund such enterprises. The final section of the book analyzes the uncertainties surrounding the presented scenario. The purpose of building a scenario is not only to pinpoint future events but also to highlight the uncertainties that may propel the future in different directions. Interstellar travel and colonization requires a civilization in which human beings see themselves as inhabitants of a single planet and in which global governance of these processes is conducted on a cooperative basis. The key question is, then, whether our present civilization is ready for such an endeavor, reflecting the fact that the critical uncertainties are political and cultural in nature. I...

  15. Interstellar Pickup Ion Production in the Global Heliosphere and Heliosheath

    CERN Document Server

    Wu, Yihong; Guo, Xiaocheng

    2016-01-01

    Interstellar Pickup ions (PUIs) play a significant part in mediating the solar wind (SW) interaction with the interstellar medium. In this paper, we examine the details of spatial variation of the PUI velocity distribution function (VDF) in the SW by solving the PUI transport equation. We assume the PUI distribution is isotropic resulting from strong pitch-angle scattering by wave-particle interaction. A three-dimensional model combining the MHD treatment of the background SW and neutrals with a kinetic treatment of PUIs throughout the heliosphere and the surrounding local interstellar medium (LISM) has been developed. The model generates PUI power law tails via second-order Fermi process. We analyze how PUIs transform across the heliospheric termination shock (TS) and obtain the PUI phase space distribution in the inner heliosheath including continuing velocity diffusion. Our simulated PUI spectra are compared with observations made by New Horizons, Ulysses, Voyager 1, 2 and Cassini, and a satisfactory agree...

  16. Probing Interstellar Dust With Space-Based Coronagraphs

    CERN Document Server

    Turner, N J; Breckinridge, J B

    2008-01-01

    We show that space-based telescopes such as the proposed Terrestrial Planet Finder Coronagraph will be able to detect the light scattered by the interstellar grains along lines of sight passing near stars in our Galaxy. The relative flux of the scattered light within one arcsecond of a star at 100 pc in a uniform interstellar medium of 0.1 H atoms cm^-3 is about 10^-7. The halo increases in strength with the distance to the star and is unlikely to limit the coronagraphic detection of planets around the nearest stars. Grains passing within 100 AU of Sun-like stars are deflected by radiation, gravity and magnetic forces, leading to features in the scattered light that can potentially reveal the strength of the stellar wind, the orientation of the stellar magnetic field and the relative motion between the star and the surrounding interstellar medium.

  17. Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges

    CERN Document Server

    Wakelam, V; Herbst, E; Troe, J; Geppert, W; Linnartz, H; Oberg, K; Roueff, E; Agundez, M; Pernot, P; Cuppen, H M; Loison, J C; Talbi, D

    2010-01-01

    We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes -- ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination -- is reviewed. Emphasis is placed on those reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust p...

  18. The Relation between Interstellar Turbulence and Star Formation

    CERN Document Server

    Klessen, R S

    2004-01-01

    (ABBREVIATED) Understanding the formation of stars in galaxies is central to much of modern astrophysics. In this review the relation between interstellar turbulence and star formation is discussed. Supersonic turbulence can provide support against gravitational collapse on global scales, while at the same time it produces localized density enhancements that allow for collapse on small scales. The efficiency and timescale of stellar birth in Galactic gas clouds strongly depend on the properties of the interstellar turbulent velocity field, with slow, inefficient, isolated star formation being a hallmark of turbulent support, and fast, efficient, clustered star formation occurring in its absence. Star formation on scales of galaxies as a whole is expected to be controlled by the balance between gravity andturbulence, just like star formation on scales of individual interstellar gas clouds, but may be modulated by additional effects like cooling and differential rotation. The dominant mechanism for driving inte...

  19. Detection of organic matter in interstellar grains.

    Science.gov (United States)

    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

  20. Visualizing Interstellar's Wormhole

    Science.gov (United States)

    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.

  1. Potential formation of three pyrimidine bases in interstellar regions

    CERN Document Server

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

    2015-01-01

    Work on the chemical evolution of pre-biotic molecules remains incomplete since the major obstacle is the lack of adequate knowledge of rate coefficients of various reactions which take place in interstellar conditions. In this work, we study the possibility of forming three pyrimidine bases, namely, cytosine, uracil and thymine in interstellar regions. Our study reveals that the synthesis of uracil from cytosine and water is quite impossible under interstellar circumstances. For the synthesis of thymine, reaction between uracil and :CH2 is investigated. Since no other relevant pathways for the formation of uracil and thymine were available in the literature, we consider a large gas-grain chemical network to study the chemical evolution of cytosine in gas and ice phases. Our modeling result shows that cytosine would be produced in cold, dense interstellar conditions. However, presence of cytosine is yet to be established. We propose that a new molecule, namely, C4N3OH5 could be observable in the interstellar ...

  2. The interstellar medium in galaxies

    CERN Document Server

    1997-01-01

    It has been more than five decades ago that Henk van de Hulst predicted the observability of the 21-cm line of neutral hydrogen (HI ). Since then use of the 21-cm line has greatly improved our knowledge in many fields and has been used for galactic structure studies, studies of the interstellar medium (ISM) in the Milky Way and other galaxies, studies of the mass distribution of the Milky Way and other galaxies, studies of spiral struc­ ture, studies of high velocity gas in the Milky Way and other galaxies, for measuring distances using the Tully-Fisher relation etc. Regarding studies of the ISM, there have been a number of instrumen­ tal developments over the past decade: large CCD's became available on optical telescopes, radio synthesis offered sensitive imaging capabilities, not only in the classical 21-cm HI line but also in the mm-transitions of CO and other molecules, and X-ray imaging capabilities became available to measure the hot component of the ISM. These developments meant that Milky Way was n...

  3. Interstellar Clouds Near the Sun, III

    Science.gov (United States)

    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. Elemental nitrogen partitioning in dense interstellar clouds

    CERN Document Server

    Daranlot, Julien; 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 millimetre-wavelength transitions so 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 effect of 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 format...

  5. Supernova Feedback and Multiphase Interstellar Medium

    Science.gov (United States)

    Li, Miao; Ostriker, Jeremiah P.; Cen, Renyue; Bryan, Greg; Naab, Thorsten

    2015-01-01

    Without feedback, galaxies in cosmological simulations fail to generate outflows and tend to be too massive and too centrally concentrated, in contrast to the prominent disks observed ubiquitously in our universe. The nature of supernova (SN) feedback remains, however, highly uncertain, and most galaxy simulations so far adopt ad hoc models. Here we perform parsec-resolution simulations of a patch of the interstellar medium (ISM), and show that the unresolved multiphase gas in cosmological simulations can greatly affect the SN feedback by allowing blastwaves to travel in-between the clouds. We also show how ISM clumping varies with the mean gas density and SN rate encountered in real galactic environments. We emphasize that the inhomogeneity of the ISM must be considered in coarse-resolution simulations. We discuss how the gas pressure maintained by SN explosions can help to launch the galactic winds, and compare our results with the sub-grid models adopted in current cosmological simulations.

  6. Searches for interstellar molecules of potential prebiotic importance

    NARCIS (Netherlands)

    Kuan, Y.-J.; Charnley, S.B.; Huang, H.-C.; Kisiel, Z.; Ehrenfreund, P.; Tseng, W.-L.; Yan, C.-H.

    2004-01-01

    Interstellar chemistry leads to the formation of many prebiologically important molecules and is therefore of the fundamental interest to Astrobiology. Many organics can be produced in the gas phase where they can be detected. Molecules formed by reactions on the surfaces of dust grains are also bes

  7. Visualizing Interstellar's Wormhole

    CERN Document Server

    James, Oliver; Franklin, Paul; Thorne, Kip S

    2015-01-01

    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...

  8. Correcting the record on the analysis of IBEX and STEREO data regarding variations in the neutral interstellar wind

    CERN Document Server

    Frisch, P C; Drews, C; Leonard, T; Livadiotis, G; McComas, D J; Moebius, E; Schwadron, N A; Sokol, J M

    2015-01-01

    The journey of the Sun through space carries the solar system through a dynamic interstellar environment that is presently characterized by Mach 1 motion between the heliosphere and the surrounding interstellar medium (ISM). The interaction between the heliosphere and ISM is an evolving process due to the variable solar wind and to interstellar turbulence. Frisch et al. presented a meta-analysis of the historical data on the interstellar wind flowing through the heliosphere and concluded that temporal changes in the ecliptic longitude of the wind were statistically indicated by the data available in the refereed literature at the time of that writing. Lallement and Bertaux disagree with this result, and suggested, for instance, that a key instrumental response function of IBEX-Lo was incorrect and that the STEREO pickup ion data are unsuitable for diagnosing the flow of interstellar neutrals through the heliosphere. Here we show that temporal variations in the interstellar wind through the heliosphere are con...

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

    Science.gov (United States)

    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.

  10. Magnetic Fields in the Interstellar Medium

    Science.gov (United States)

    Clark, Susan

    2017-01-01

    The Milky Way is magnetized. Invisible magnetic fields thread the Galaxy on all scales and play a vital but still poorly understood role in regulating flows of gas in the interstellar medium and the formation of stars. I will present highlights from my thesis work on magnetic fields in the diffuse interstellar gas and in accretion disks. At high Galactic latitudes, diffuse neutral hydrogen is organized into an intricate network of slender linear features. I will show that these neutral hydrogen “fibers” are extremely well aligned with the ambient magnetic field as traced by both starlight polarization (Clark et al. 2014) and Planck 353 GHz polarized dust emission (Clark et al. 2015). The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. Because the orientation of neutral hydrogen is an independent predictor of the local dust polarization angle, our work provides a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination. Magnetic fields also drive accretion in astrophysical disks via the magnetorotational instability (MRI). I analytically derive the behavior of this instability in the weakly nonlinear regime and show that the saturated state of the instability depends on the geometry of the background magnetic field. The analytical model describes the behavior of the MRI in a Taylor-Couette flow, a set-up used by experimentalists in the ongoing quest to observe MRI in the laboratory (Clark & Oishi 2016a, 2016b).

  11. The interstellar medium towards the Ara OB1 region

    CERN Document Server

    Henderson, Christopher D; Hearnshaw, John B

    2008-01-01

    We present high resolution (R ~ 4 km/s) absorption measurements of the interstellar NaI and CaII lines measured towards 14 early-type stars of distance 123 pc - 1650 pc, located in the direction of the Ara OB1 stellar cluster. The line profiles can broadly be split into four distinct groupings of absorption component velocity, and we have attempted to identify an origin and distance to each of these interstellar features. For gas with absorption covering the velocity range -10 km/s < V_helio < +10 km/s, we can identify the absorbing medium with local gas belonging to the Lupus-Norma interstellar cavity located between 100 and 485 pc in this galactic direction. Gas with velocities spanning the range -20 km/s < V_helio < +20 km/s is detected towards stars with distances of 570-800 pc. We identify a wide-spread interstellar feature at V_helio ~ -15 km/s with the expanding HI shell called GSH 337+00-05, which is now placed at a distance of ~530 pc.

  12. Detection of interstellar $CH_{3}$

    CERN Document Server

    Feuchtgruber, H; Van Dishoeck, E F; Wright, C M

    2000-01-01

    Observations with the Short Wavelength Spectrometer (SWS) onboard the {\\it Infrared Space Observatory} (ISO) have led to the first detection of the methyl radical ${\\rm CH_3}$ in the interstellar medium. The $\

  13. Turbulence in the Interstellar Medium

    CERN Document Server

    Falceta-Goncalves, D; Falgarone, E; Chian, A C -L

    2014-01-01

    Turbulence is ubiquitous in the insterstellar medium and plays a major role in several processes such as the formation of dense structures and stars, the stability of molecular clouds, the amplification of magnetic fields, and the re-acceleration and diffusion of cosmic rays. Despite its importance, interstellar turbulence, alike turbulence in general, is far from being fully understood. In this review we present the basics of turbulence physics, focusing on the statistics of its structure and energy cascade. We explore the physics of compressible and incompressible turbulent flows, as well as magnetized cases. The most relevant observational techniques that provide quantitative insights of interstellar turbulence are also presented. We also discuss the main difficulties in developing a three-dimensional view of interstellar turbulence from these observations. Finally, we briefly present what could be the the main sources of turbulence in the interstellar medium.

  14. Practices Surrounding Event Photos

    NARCIS (Netherlands)

    Vyas, Dhaval; Nijholt, Antinus; van der Veer, Gerrit C.; Kotzé, P.; Marsden, G.; Lindgaard, G.; Wesson, J.; Winckler, M.

    Sharing photos through mobile devices has a great potential for creating shared experiences of social events between co-located as well as remote participants. In order to design novel event sharing tools, we need to develop indepth understanding of current practices surrounding these so called

  15. The Interstellar Conspiracy

    Science.gov (United States)

    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

  16. The 3D Dynamical Structure of the Supernova-Driven Interstellar Medium

    Science.gov (United States)

    Avillez, M. A.; Ballesteros-Paredes, J.; Mac Low, M.-M.

    2000-05-01

    Large scale modelling of the interstellar gas in the disk and halo has been carried out with a three-dimensional hydrodynamical code that uses adapted mesh refinement combined with message passing interface calls. The model includes a gravitational field provided by the stars in the disk, an ideal-gas equation of state, and an approximation for the cooling curve, assuming collisional ionization equilibrium. Supernovae are set up both isolated and in associations, in a manner compatible with observations. Once disrupted by the explosions, the disk never returns to its initial state, regardless of the initial vertical distribution of the disk gas, provided enough supernovae occur. Instead a thin HI disk forms in the Galactic plane, and, above and below, a thick inhomogeneous gas disk forms, with scale heights in HI of 500 pc and in HII of 1 kpc. The upper parts of the thick HII disk form the disk-halo interface, where a large scale fountain is set up by hot ionized gas escaping in a turbulent convective flow. The calculations also show the formation of HI clouds in both the disk and halo. These are dynamical objects with a two-phase structure composed of a cold core surrounded by warmer gas. The disk is populated by worms, bubbles, superbubbles and chimneys. Chimneys in the simulations have widths of approximately 120 pc. They inject high temperature gas directly from the Galactic disk into the halo, breaking through the warm neutral and ionized layers that compose the thick disk. Mushroom-shaped structures are also seen in the simulations, as have recently been observed. We identify them as tracers of buoyant flow in the thick disk

  17. Discovery of Interstellar CF+

    CERN Document Server

    Neufeld, D A; Menten, K M; Wolfire, M G; Black, J H; Schuller, F; Müller, H; Thorwirth, S; Gusten, R; Philipp, S

    2006-01-01

    We discuss the first astronomical detection of the CF+ (fluoromethylidynium) ion, obtained by observations of the J=1-0 (102.6 GHz), J=2-1 (205.2 GHz) and J=3-2 (307.7 GHz) rotational transitions toward the Orion Bar region. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few times 1.E-10 in UV-irradiated molecular regions where C+ is present. The CF+ ion is produced by exothermic reactions of C+ with HF. Because fluorine atoms can react exothermically with H2, HF is predicted to be the dominant reservoir of fluorine, not only in well-shielded regions but also in the surface layers of molecular clouds where the C+ abundance is large. The observed CF+ line intensities imply the presence of CF+ column densities of at least 1.E+12 cm-2 over a region of size at least ~ 1 arcmin, in good agreement with theoretical predictions. They provide support for our current theories of interstellar fluorine chemistry, whic...

  18. Stability of the interstellar hydrogen inflow longitude from 20 years of SOHO/SWAN observations

    CERN Document Server

    Koutroumpa, Dimitra; Katushkina, Olga; Lallement, Rosine; Bertaux, Jean-Loup; Schmidt, Walter

    2016-01-01

    Aims. A recent debate on the decade-long stability of the interstellar He flow vector, and in particular the flow longitude, has prompted us to check for any variability in the interstellar H flow vector as observed by the SWAN instrument on board SOHO. Methods. We used a simple model-independent method to determine the interstellar H flow longitude, based on the parallax effects induced on the Lyman-{\\alpha} intensity measured by SWAN following the satellite motion around the Sun. Results. Our results show that the interstellar H flow vector longitude does not vary significantly from an average value of 252.9$^{\\circ}$ $\\pm$ 1.4$^{\\circ}$ throughout the 20-year span of the SWAN dataset, further strengthening the arguments for the stability of the interstellar gas flow.

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

    Science.gov (United States)

    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

  20. Evidence for an interstellar dust filament in the outer heliosheath

    CERN Document Server

    Frisch, P C; Berdyugin, A; Funsten, H O; Magalhaes, A M; McComas, D J; Piirola, V; Schwadron, N A; Seriacopi, D B; Slavin, J D; Wiktorowicz, S J

    2015-01-01

    A recently discovered filament of polarized starlight that traces a coherent magnetic field is shown to have several properties that are consistent with an origin in the outer heliosheath of the heliosphere: (1) The magnetic field that provides the best fit to the polarization position angles is directed within 6.7+-11 degrees of the observed upwind direction of the flow of interstellar neutral helium gas through the heliosphere. (2) The magnetic field is ordered; the component of the variation of the polarization position angles that can be attributed to magnetic turbulence is small. (3) The axis of the elongated filament can be approximated by a line that defines an angle of 80+/-14 degrees with the plane that is formed by the interstellar magnetic field vector and the vector of the inflowing neutral gas (the "BV" plane). We propose that this polarization feature arises from aligned interstellar dust grains in the outer heliosheath where the interstellar plasma and magnetic field are deflected around the he...

  1. A study of the hot local interstellar medium

    Science.gov (United States)

    McLean, Ryan

    2000-10-01

    Material synthesized in stellar furnaces and supernova explosions recycles through a hot phase of the interstellar medium (ISM) before it condenses into new stellar systems. I have studied the hot phase of the interstellar medium using ISM absorption line spectra of hot gas. O VI, N V and C IV each have resonance absorption lines at ultraviolet wavelength and are the most cosmically abundant elements other than hydrogen and helium. Two sounding rocket experiments built at the University of Colorado observed hot gas in the interstellar medium of galaxies. The Hot Carbon Oxygen Nitrogen Echelle Spectrograph ( HotCONES) made observations of O VI, N V and C IV in the local interstellar medium and the Wadsworth High-resolution Instrument (WHI) observed O VI in both the ISM of our galaxy and in the ISM of the Large Magellanic Cloud. I have discovered evidence for O VI components moving at speeds of up to 750 km s-1 along the line of sight. These high velocity components may be indicative of an extended supernova remnant.

  2. The life cycle of the Interstellar Medium in other galaxies

    Science.gov (United States)

    Knapp, G. R.

    1995-01-01

    Gas in spiral galaxies cycles between the diffuse and dense phases as clouds collapse, form stars and are dispersed back into the ISM. Far infrared observations of continuum emission from interstellar dust and line emission from interstellar gas have revealed a wealth of information on the state of the ISM in galaxies of different morphological types. The analysis of these observations gives us information about the processes of star formation and about the evolution of the ISM. Star formation rates vary widely from galaxy to galaxy, with the rates in starburst galaxies being 10 - 100 times those in quiescent spiral galaxies. Far infrared spectroscopy of star-forming galaxies shows that the interstellar pressure increases with star formation rate. The structure of the interstellar medium in starburst galaxies is quite different from that of quiescent galaxies - much of the mass and volume are in HII regions and photodissociation regions. The size distribution of dust grains seems to depend on environment; small grains are abundant in the diffuse interstellar medium but not in dense molecular star forming regions. Quiescent spiral and elliptical galaxies contain a significant population of small grains, but starburst galaxies do not. Dwarf irregular galaxies also seem to contain few small grains; this may be the result of the higher UV flux in these galaxies. The star forming regions in dwarf irregulars also have a higher ratio of atomic to molecular gas than do those in the Galaxy. These results show that the ISM in galaxies of different morphological types reaches different equilibria, resulting in different modes of star formation and global galaxy evolution.

  3. Depolarization canals and interstellar turbulence

    Science.gov (United States)

    Fletcher, A.; Shukurov, A.

    Recent radio polarization observations have revealed a plethora of unexpected features in the polarized Galactic radio background that arise from propagation effects in the random (turbulent) interstellar medium. The canals are especially striking among them, a random network of very dark, narrow regions clearly visible in many directions against a bright polarized Galactic synchrotron background. There are no obvious physical structures in the ISM that may have caused the canals, and so they have been called Faraday ghosts. They evidently carry information about interstellar turbulence but only now is it becoming clear how this information can be extracted. Two theories for the origin of the canals have been proposed; both attribute the canals to Faraday rotation, but one invokes strong gradients in Faraday rotation in the sky plane (specifically, in a foreground Faraday screen) and the other only relies on line-of-sight effects (differential Faraday rotation). In this review we discuss the physical nature of the canals and how they can be used to explore statistical properties of interstellar turbulence. This opens studies of magnetized interstellar turbulence to new methods of analysis, such as contour statistics and related techniques of computational geometry and topology. In particular, we can hope to measure such elusive quantities as the Taylor microscale and the effective magnetic Reynolds number of interstellar MHD turbulence.

  4. IBEX views the global structure of the heliosphere influenced by the Interstellar Magnetic Field

    Science.gov (United States)

    Schwadron, Nathan

    The IBEX ribbon has been separated from the surrounding globally distributed flux (GDF), revealing ENA emission largely from the inner heliosheath. The line-of-sight (LOS) integrated pressure in the GDF is quite large, requiring that the interstellar magnetic field be sufficiently strong (e.g. 3 microG) to balance the pressure of the inner heliosheath. The LOS emissions from the GDF have revealed signatures of the nose of the heliosphere, and the heliotail, which has been examined carefully. The strong interstellar magnetic field has broad implications for the structure of the heliosphere and the existence or lack of a bow shock. These global heliospheric structures also filter primary interstellar neutral atoms and lead to creation of secondary atoms through charge-exchange in the outer heliosheath. IBEX observations of H atoms from the Local Interstellar Medium reveal remarkable signatures of both filtration and the secondary component likely reflecting influences of the interstellar magnetic field on the outer heliosheath. New determinations of the LISM velocity from neutral atom measurments and the LISM magnetic field direction from the IBEX ribbon are shown to be consistent with the interstellar modulation of TeV cosmic rays revealed in global anisotropy maps of Milagro, Asgamma and IceCube. Thus, IBEX observations reveal a new picture of heliospheric structures and interactions that are strongly influenced by the interstellar magnetic field.

  5. Interstellar Isotopes: Prospects with ALMA

    Science.gov (United States)

    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.

  6. Interstellar Initiative Web Page Design

    Science.gov (United States)

    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.

  7. The Warped Science of Interstellar

    CERN Document Server

    Luminet, Jean-Pierre

    2015-01-01

    The science fiction film, Interstellar, tells the story of a team of astronauts searching a distant galaxy for habitable planets to colonize. Interstellar's story draws heavily from contemporary science. The film makes reference to a range of topics, from established concepts such as fast-spinning black holes, accretion disks, tidal effects, and time dilation, to far more speculative ideas such as wormholes, time travel, additional space dimensions, and the theory of everything. The aim of this article is to decipher some of the scientific notions which support the framework of the movie.

  8. Infrared emission from interstellar PAHs

    Science.gov (United States)

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

    1987-01-01

    The mid-IR absorption and Raman spectra of polycyclic aromatic hydrocarbons (PAHs) and the mechanisms determining them are reviewed, and the implications for observations of similar emission spectra in interstellar clouds are considered. Topics addressed include the relationship between PAHs and amorphous C, the vibrational spectroscopy of PAHs, the molecular emission process, molecular anharmonicity, and the vibrational quasi-continuum. Extensive graphs, diagrams, and sample spectra are provided, and the interstellar emission bands are attributed to PAHs with 20-30 C atoms on the basis of the observed 3.3/3.4-micron intensity ratios.

  9. The formation of interstellar jets

    Science.gov (United States)

    Tenorio-Tagle, G.; Canto, J.; Rozyczka, M.

    1988-01-01

    The formation of interstellar jets by convergence of supersonic conical flows and the further dynamical evolution of these jets are investigated theoretically by means of numerical simulations. The results are presented in extensive graphs and characterized in detail. Strong radiative cooling is shown to result in jets with Mach numbers 2.5-29 propagating to lengths 50-100 times their original widths, with condensation of swept-up interstellar matter at Mach 5 or greater. The characteristics of so-called molecular outflows are well reproduced by the simulations of low-Mach-number and quasi-adiabatic jets.

  10. On the question of interstellar travel

    Science.gov (United States)

    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.

  11. Experimental interstellar organic chemistry - Preliminary findings

    Science.gov (United States)

    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.

  12. Experimental interstellar organic chemistry - Preliminary findings

    Science.gov (United States)

    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.

  13. Polycyclic Aromatic Hydrocarbons and the Diffuse Interstellar Bands: a Survey

    Science.gov (United States)

    Salama, F.; Galazutdinov, G. A.; Krelowski, J.; Allamandola, L. J.; Musaev, F. A.; DeVincenzi, Donald L. (Technical Monitor)

    1999-01-01

    We discuss the proposal relating the origin of some of the diffuse interstellar bands (DIBs) to neutral and ionized polycyclic aromatic hydrocarbons (PAHs) present in interstellar clouds. Laboratory spectra of several PAHs, isolated at low temperature in inert gas matrices, are compared with an extensive set of astronomical spectra of reddened, early type stars. From this comparison, it is concluded that PAN ions are good candidates to explain some of the DIBs. Unambiguous assignments are difficult, however, due to the shift in wavelengths and the band broadening induced in the laboratory spectra by the solid matrix. Definitive band assignments and, ultimately, the test of the of the proposal that PAH ions carry some of the DIB must await the availability of gas-phase measurements in the laboratory. The present assessment offers a guideline for future laboratory experiments by allowing the preselection of promising PAH molecules to be studied in jet expansions.

  14. Interaction of massive stars with their surroundings

    CERN Document Server

    Hensler, Gerhard

    2008-01-01

    Due to their short lifetimes but their enormous energy release in all stages of their lives massive stars are the major engines for the comic matter circuit. They affect not only their close environment but are also responsible to drive mass flows on galactic scales. Recent 2D models of radiation-driven and wind-blown HII regions are summarized which explore the impact of massive stars to the interstellar medium but find surprisingly small energy transfer efficiencies while an observable Carbon self-enrichment in the Wolf-Rayet phase is detected in the warm ionized gas. Finally, the focus is set on state-of-the-art modelling of HII regions and its present weaknesses with respect to uncertainties and simplifications but on a perspective of the requested art of their modelling in the 21st century.

  15. Formation of Cyanoformaldehyde in the interstellar space

    CERN Document Server

    Das, Ankan; Chakrabarti, Sandip K; Saha, Rajdeep; Chakrabarti, Sonali

    2013-01-01

    Cyanoformaldehyde (HCOCN) molecule has recently been suspected towards the Sagittarius B2(N) by the Green Bank telescope, though a confirmation of this observation has not yet been made. In and around a star forming region, this molecule could be formed by the exothermic reaction between two abundant interstellar species, H$_2$CO and CN. Till date, the reaction rate coefficient for the formation of this molecule is unknown. Educated guesses were used to explain the abundance of this molecule by chemical modeling. In this paper, we carried out quantum chemical calculations to find out empirical rate coefficients for the formation of HCOCN and different chemical properties during the formation of HCOCN molecules. Though HCOCN is stable against unimolecular decomposition, this gas phase molecule could be destroyed by many other means, like: ion-molecular reactions or by the effect of cosmic rays. Ion-molecular reaction rates are computed by using the capture theories. We have also included the obtained rate coef...

  16. SPIRE spectroscopy of the interstellar medium

    Science.gov (United States)

    Habart, E.; Dartois, E.; Abergel, A.; Baluteau, J.-P.; Naylor, D.; Polehampton, E.; Joblin, C.

    2010-12-01

    The SPIRE Fourier Transform Spectrometer on-board Herschel allows us, for the first time, to simultaneously measure the complete far-infrared spectrum from 194 to 671 μm. A wealth of rotational lines of CO (and its isotopologues), fine structure lines of C^0 and N^+, and emission lines from radicals and molecules has been observed towards several galactic regions and nearby galaxies. The strengths of the atomic and molecular lines place fundamental constraints on the physical conditions but also the chemistry of the interstellar medium. FTS mapping capabilities are also extremely powerful in characterizing the spatial morphology of the extended region and understand how the gas properties vary within the studied region. Here, we present a first analysis of SPIRE spectroscopic observations of the prototypical Orion Bar photodissociation region.

  17. Dynamical evolution and molecular abundances of interstellar clouds

    Science.gov (United States)

    Prasad, Sheo S.; Heere, Karen R.; Tarafdar, Shankar P.

    1991-01-01

    Dynamical models are presented that start with interstellar gas in an initial diffuse state and consider their gravitational collapse and the formation of dense cores. Frozen-in tangled magnetic fields are included to mimic forces that might oppose gravitational contraction and whose effectiveness may increase with increasing core densities. Results suggest the possibility that dense cloud cores may be dynamically evolving ephemeral objects, such that their lifespan at a given core density decreases as that density increases.

  18. The interstellar chemistry of H2C3O isomers

    Science.gov (United States)

    Loison, Jean-Christophe; Agúndez, Marcelino; Marcelino, Núria; Wakelam, Valentine; Hickson, Kevin M.; Cernicharo, José; Gerin, Maryvonne; Roueff, Evelyne; Guélin, Michel

    2016-01-01

    We present the detection of two H2C3O isomers, propynal and cyclopropenone, toward various starless cores and molecular clouds, together with upper limits for the third isomer propadienone. We review the processes controlling the abundances of H2C3O isomers in interstellar media showing that the reactions involved are gas-phase ones. We show that the abundances of these species are controlled by kinetic rather than thermodynamic effects. PMID:27013768

  19. The Distribution of Pressures in a Supernova-Driven Interstellar Medium. I. Magnetized Medium

    CERN Document Server

    MacLow, M M; Kim, J; Avillez, M A; Low, Mordecai-Mark Mac; Balsara, Dinshaw S.; Kim, Jongsoo; Avillez, Miguel A.

    2004-01-01

    Observations have suggested substantial departures from pressure equilibrium in the interstellar medium (ISM) in the plane of the Galaxy, even on scales under 50 pc. Nevertheless, multi-phase models of the ISM assume at least locally isobaric gas. The pressure then determines the density reached by gas cooling to stable thermal equilibrium. We use numerical models of the magnetized ISM to examine the consequences of supernova driving for interstellar pressures. In this paper we examine a (200 pc)^3 periodic domain threaded by magnetic fields. Individual parcels of gas at different pressures reach widely varying points on the thermal equilibrium curve: no unique set of phases is found, but rather a dynamically-determined continuum of densities and temperatures. A substantial fraction of the gas remains entirely out of thermal equilibrium. Our results appear consistent with observations of interstellar pressures. They also suggest that the high pressures observed in molecular clouds may be due to ram pressures ...

  20. Herschel observations of interstellar chloronium

    NARCIS (Netherlands)

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

    2012-01-01

    Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed parachloronium (H2Cl+) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight lines to the bright submillimeter continuum sourc

  1. Stardust Interstellar Preliminary Examination (ISPE)

    Science.gov (United States)

    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

  2. Moment equations for chemical reactions on interstellar dust grains

    CERN Document Server

    Lipshtat, A; Lipshtat, Azi; Biham, Ofer

    2003-01-01

    While most chemical reactions in the interstellar medium take place in the gas phase, those occurring on the surfaces of dust grains play an essential role. Chemical models based on rate equations including both gas phase and grain surface reactions have been used in order to simulate the formation of chemical complexity in interstellar clouds. For reactions in the gas phase and on large grains, rate equations, which are highly efficient to simulate, are an ideal tool. However, for small grains under low flux, the typical number of atoms or molecules of certain reactive species on a grain may go down to order one or less. In this case the discrete nature of the opulations of reactive species as well as the fluctuations become dominant, thus the mean-field approximation on which the rate equations are based does not apply. Recently, a master equation approach, that provides a good description of chemical reactions on interstellar dust grains, was proposed. Here we present a related approach based on moment equ...

  3. The interstellar abundances of tin and four other heavy elements

    Science.gov (United States)

    Hobbs, L. M.; Welty, D. E.; Morton, D. C.; Spitzer, L.; York, D. G.

    1993-01-01

    Spectra recorded at 1150-1600 A with an instrumental resolution near 16 km/s were obtained with the Goddard High-Resolution Spectrograph on board the HST. The gaseous interstellar abundances of five heavy elements along the light paths to 23 Ori, 15 Mon, 1 Sco, Pi Sco, and Pi Aqr were determined from the observations. The 1400.450 A line of Sn II was detected and identified toward three stars; at Z = 50, tin is the first element from the fifth row of the periodic table to be identified in the interstellar medium. One spectral line of each of Cu II (Z = 29) and Ga II (Z = 31), three lines of Ge II (Z = 32), and two lines of Kr I (Z = 36) were also detected toward some or all of the five stars. The depletions of these five heavy elements generally decrease monotonically with increasing atomic number toward each of the six stars, and tin is generally undepleted within the observational errors. The depletions of 26 elements from the interstellar gas in an average dense interstellar cloud appear to correlate with the elemental 'nebular' condensation temperatures more closely than with the first ionization potentials.

  4. The Sun's dusty interstellar environment

    Science.gov (United States)

    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).

  5. Constraining the Properties of Cold Interstellar Clouds

    Science.gov (United States)

    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.

  6. The stardust abundance in the local interstellar cloud at the birth of the Solar System

    Science.gov (United States)

    Hoppe, Peter; Leitner, Jan; Kodolányi, János

    2017-09-01

    Primitive Solar System materials, such as certain types of meteorites, interplanetary dust particles and cometary matter, contain small quantities of refractory dust grains that are older than our Solar System. These `presolar grains' condensed in the winds of evolved stars and in the ejecta of stellar explosions, and they were part of the interstellar gas and dust cloud from which our Solar System formed 4.57 billion years ago1. Interstellar dust is not only stardust but forms in the interstellar medium as well, predominantly as silicates, and, to a lesser extent, as carbonaceous dust and iron particles2. Presolar grains represent a sample of stardust, and their abundances in primitive Solar System materials can be used to constrain the fraction of stardust among interstellar dust. Here we show that the size distribution of presolar silicates follows that observationally derived for interstellar dust, at least in the diameter range 100-500 nm, that current estimates of presolar grain abundances (mass fractions) are at least a factor of 2 too low, and that several per cent of the interstellar dust in the interstellar cloud pre-dating our Solar System was stardust, making it a minor but still important ingredient of the starting material from which our Solar System formed.

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

    Science.gov (United States)

    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.

  8. A multiple system of high-mass YSOs surrounded by disks in NGC 7538 IRS1 . Gas dynamics on scales of 10-700 AU from CH3OH maser and NH3 thermal lines

    Science.gov (United States)

    Moscadelli, L.; Goddi, C.

    2014-06-01

    Context. It has been claimed that NGC 7538 IRS1 is a high-mass young stellar object (YSO) with 30 M⊙, surrounded by a rotating Keplerian disk, probed by a linear distribution of methanol masers. The YSO is also powering a strong compact Hii region or ionized wind, and is driving at least one molecular outflow. The axis orientations of the different structures (ionized gas, outflow, and disk) are, however, misaligned, which has led to the different competing models proposed to explain individual structures. Aims: We investigate the 3D kinematics and dynamics of circumstellar gas with very high linear resolution, from tens to 1500 AU, with the ultimate goal of building a comprehensive dynamical model for what is considered the best high-mass accretion disk candidate around an O-type young star in the northern hemisphere. Methods: We used high-angular resolution observations of 6.7 GHz CH3OH masers with the EVN, NH3 inversion lines with the JVLA B-Array, and radio continuum with the VLA A-Array. In particular, we employed four different observing epochs of EVN data at 6.7 GHz, spanning almost eight years, which enabled us to measure line-of-sight (l.o.s.) accelerations and proper motions of CH3OH masers, besides l.o.s. velocities and positions (as done in previous works). In addition, we imaged highly excited NH3 inversion lines, from (6,6) to (13,13), which enabled us to probe the hottest molecular gas very close to the exciting source(s). Results: We confirm previous results that five 6.7 GHz maser clusters (labeled from "A" to "E") are distributed over a region extended N-S across ≈1500 AU, and are associated with three components of the radio continuum emission. We propose that these maser clusters identify three individual high-mass YSOs in NGC 7538 IRS1, named IRS1a (associated with clusters "B" and "C"), IRS1b (associated with cluster "A"), and IRS1c (associated with cluster "E"). We find that the 6.7 GHz masers distribute along a line, with a regular

  9. Dust In Hell: Discovery Of Dust In Hot Gas Around Group-Centered Elliptical Galaxies

    Science.gov (United States)

    Temi, Pasquale; Brighenti, F.; Mathews, W. G.

    2007-05-01

    Observations with the Spitzer infrared telescope reveal extended internally produced dust in the hot gas (KT 1 KeV) atmospheres surrounding two optically normal galaxies, NGC 5044 and NGC 4636. We interpret this as a dusty buoyant outflow resulting from energy released by gas accretion onto supermassive black holes in the galaxy cores. Both galaxies have highly disturbed, transient activities in the hot gas and contain strong dust emission at 70 and 160 microns in excess of what expected from normal stellar mass loss. The 70 micron image is clearly extended. The lifetime of dust in hot (KT=1KeV) interstellar gas to destruction by sputtering (ion impacts), 10 million years, establishes the time when the dust first entered the hot gas. Remarkably, in NGC 5044 we observe interstellar PAH dust-molecular emission at 8 microns out to about 5 Kpc that is spatially coincident with extended Halpha+[NII] emission from warm gas. We propose that this dust comes from the destruction and heating of dusty disks in the nuclei of these galaxies, followed by buoyant transport. A simple calculation shows that dust-assisted cooling in outflowing buoyant gas in NGC 5044 can cool the gas within a few Kpc in about 10 million years, explaining the optical line emission observed.

  10. Depolarization canals and interstellar turbulence

    CERN Document Server

    Fletcher, A; Fletcher, Andrew; Shukurov, Anvar

    2006-01-01

    Recent radio polarization observations have revealed a plethora of unexpected features in the polarized Galactic radio background that arise from propagation effects in the random (turbulent) interstellar medium. The canals are especially striking among them, a random network of very dark, narrow regions clearly visible in many directions against a bright polarized Galactic synchrotron background. There are no obvious physical structures in the ISM that may have caused the canals, and so they have been called Faraday ghosts. They evidently carry information about interstellar turbulence but only now is it becoming clear how this information can be extracted. Two theories for the origin of the canals have been proposed; both attribute the canals to Faraday rotation, but one invokes strong gradients in Faraday rotation in the sky plane (specifically, in a foreground Faraday screen) and the other only relies on line-of-sight effects (differential Faraday rotation). In this review we discuss the physical nature o...

  11. Interstellar Grains: 50 Years On

    CERN Document Server

    Wickramasinghe, N Chandra

    2011-01-01

    Our understanding of the nature of interstellar grains has evolved considerably over the past half century with the present author and Fred Hoyle being intimately involved at several key stages of progress. The currently fashionable graphite-silicate-organic grain model has all its essential aspects unequivocally traceable to original peer-reviewed publications by the author and/or Fred Hoyle. The prevailing reluctance to accept these clear-cut priorities may be linked to our further work that argued for interstellar grains and organics to have a biological provenance - a position perceived as heretical. The biological model, however, continues to provide a powerful unifying hypothesis for a vast amount of otherwise disconnected and disparate astronomical data.

  12. One Kilogram Interstellar Colony Mission

    Science.gov (United States)

    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.

  13. A new interstellar component in the spectrum of HD 72127A

    Science.gov (United States)

    Hobbs, L. M.; Wallerstein, G.; Huu, E. M.

    1982-01-01

    New high dispersion observations are reported of the very strong, broad interstellar K line of Ca II in the spectrum of HD 72127A, a star located near a filament of the Vela supernova remnant. When compared with similar observations made in 1977, the new data reveal temporal variability of the interstellar absorption, as shown both by the presence of a new, sixth line component and by a 25% increase in the total equivalent width of the K line. All five Ca II components which were seen in both years show very large column-density ratios N(Ca II) /N(Na I) at least equal to 9, probably arising from anomalously large interstellar gas-phase abundances of Ca caused by disruption of interstellar grains. Marked differences in the structure of the K line between the two early-type components of this binary star, which are separated by only 3000 AU, are confirmed.

  14. Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains

    CERN Document Server

    Cuppen, H M

    2007-01-01

    Although still poorly understood, the chemistry that occurs on the surfaces of interstellar dust particles profoundly affects the growth of molecules in the interstellar medium. An important set of surface reactions produces icy mantles of many monolayers in cold and dense regions. The monolayers are dominated by water ice, but also contain CO, CO_{2}, and occasionally methanol as well as minor constituents. In this paper, the rate of production of water-ice dominated mantles is calculated for different physical conditions of interstellar clouds and for the first time images of the morphology of interstellar ices are presented. For this purpose, the continuous-time random-walk Monte Carlo simulation technique has been used. The visual extinction, density, and gas and grain temperatures are varied. It is shown that our stochastic approach can reproduce the important observation that ice mantles only grow in the denser regions.

  15. Representing culture in interstellar messages

    Science.gov (United States)

    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 art_science/2003>. 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 and cultural models.

  16. From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to the Origin of Life

    Science.gov (United States)

    Allamandola, Louis

    2004-01-01

    Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In the dense ISM, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the Universe. The first part of this talk will describe how infrared studies of interstellar space, combined with laboratory simulations, have revealed the composition of interstellar ices (the building blocks of comets) and the high abundance and nature of interstellar PAHs. The laboratory database has now enabled us to gain insight into the identities, abundances, and physical state of many interstellar materials. Within a dense molecular cloud, and especially in the presolar nebula, the materials frozen into the interstellar/precometary ices are photoprocessed by ultraviolet light and produce more complex molecules. The remainder of the presentation will focus on the photochemical evolution of these materials and the possible role of these compounds on the to the carbonaceous components of micrometeorites, they are likely to have been important sources of complex materials on the early

  17. H2-rich interstellar grain mantles: An equilibrium description

    Science.gov (United States)

    Dissly, Richard W.; Allen, Mark; Anicich, Vincent G.

    1994-01-01

    Experiments simulating the codeposition of molecular hydrogen and water ice on interstellar grains demonstrate that amorphous water ice at 12 K can incorporate a substantial amount of H2, up to a mole ratio of H2/H2O = 0.53. We find that the physical behavior of approximately 80% of the hydrogen can be explained satisfactorily in terms of an equilibrium population, thermodynamically governed by a wide distribution of binding site energies. Such a description predicts that gas phase accretion could lead to mole fractions of H2 in interstellar grain mantles of nearly 0.3; for the probable conditions of WL5 in the rho Ophiuchi cloud, an H2 mole fraction of between 0.05 and 0.3 is predicted, in possible agreement with the observed abundance reported by Sandford, Allamandola, & Geballe. Accretion of gas phase H2 onto grain mantles, rather than photochemical production of H2 within the ice, could be a general explanation for frozen H2 in interstellar ices. We speculate on the implications of such a composition for grain mantle chemistry and physics.

  18. Photodissociation of interstellar N2

    CERN Document Server

    Li, Xiaohu; Visser, Ruud; Ubachs, Wim; Lewis, Brenton R; Gibson, Stephen T; van Dishoeck, Ewine F

    2013-01-01

    Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks and the partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. The aim of this work is to gain a better understanding of the interstellar N2 photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. We simulated the full high-resolution line-by-line absorption + dissociation spectrum of N2 over the relevant 912-1000 \\AA\\ wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schr\\"odinger equation. The simulated N2 spectra were compared with the absorption spectra of H2, H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a ...

  19. The interaction of relativistic spacecrafts with the interstellar medium

    CERN Document Server

    Hoang, Thiem; Burkhart, Blakesley; Loeb, Abraham

    2016-01-01

    The Breakthrough Starshot initiative aims to launch a gram-scale spacecraft to a speed of $v\\sim 0.2$c, capable of reaching the nearest star system, $\\alpha$ Centauri, in about 20 years. However, a critical challenge for the initiative is the damage to the spacecraft by interstellar gas and dust during the journey. In this paper, we quantify the interaction of a relativistic spacecraft with gas and dust in the interstellar medium. For gas bombardment, we find that damage by track formation due to heavy elements is an important effect. We find that gas bombardment can potentially damage the surface of the spacecraft to a depth of $\\sim 0.1$ mm for quartz material after traversing a gas column of $N_{\\rm H}\\sim 2\\times 10^{18}\\rm cm^{-2}$ along the path to $\\alpha$ Centauri, whereas the effect is much weaker for graphite material. The effect of dust bombardment erodes the spacecraft surface and produces numerous craters due to explosive evaporation of surface atoms. For a spacecraft speed $v=0.2c$, we find that...

  20. Effects of turbulent dust grain motion to interstellar chemistry

    Science.gov (United States)

    Ge, J. X.; He, J. H.; Yan, H. R.

    2016-02-01

    Theoretical studies have revealed that dust grains are usually moving fast through the turbulent interstellar gas, which could have significant effects upon interstellar chemistry by modifying grain accretion. This effect is investigated in this work on the basis of numerical gas-grain chemical modelling. Major features of the grain motion effect in the typical environment of dark clouds (DC) can be summarized as follows: (1) decrease of gas-phase (both neutral and ionic) abundances and increase of surface abundances by up to 2-3 orders of magnitude; (2) shifts of the existing chemical jumps to earlier evolution ages for gas-phase species and to later ages for surface species by factors of about 10; (3) a few exceptional cases in which some species turn out to be insensitive to this effect and some other species can show opposite behaviours too. These effects usually begin to emerge from a typical DC model age of about 105 yr. The grain motion in a typical cold neutral medium (CNM) can help overcome the Coulomb repulsive barrier to enable effective accretion of cations on to positively charged grains. As a result, the grain motion greatly enhances the abundances of some gas-phase and surface species by factors up to 2-6 or more orders of magnitude in the CNM model. The grain motion effect in a typical molecular cloud (MC) is intermediate between that of the DC and CNM models, but with weaker strength. The grain motion is found to be important to consider in chemical simulations of typical interstellar medium.

  1. Consequences of the Solar System passage through dense interstellar clouds

    Directory of Open Access Journals (Sweden)

    A. G. Yeghikyan

    Full Text Available Several consequences of the passage of the solar system through dense interstellar molecular clouds are discussed. These clouds, dense (more than 100 cm-3, cold (10–50 K and extended (larger than 1 pc, are characterized by a gas-to-dust mass ratio of about 100, by a specific power grain size spectrum (grain radii usually cover the range 0.001–3 micron and by an average dust-to-gas number density ratio of about 10-12. Frequently these clouds contain small-scale (10–100 AU condensations with gas concentrations ranging up to 10 5 cm-3. At their casual passage over the solar system they exert pressures very much enhanced with respect to today’s standards. Under these conditions it will occur that the Earth is exposed directly to the interstellar flow. It is shown first that even close to the Sun, at 1 AU, the cloud’s matter is only partly ionized and should mainly interact with the solar wind by charge exchange processes. Dust particles of the cloud serve as a source of neutrals, generated by the solar UV irradiation of dust grains, causing the evaporation of icy materials. The release of neutral atoms from dust grains is then followed by strong influences on the solar wind plasma flow. The behavior of the neutral gas inflow parameters is investigated by a 2-D hydrodynamic approach to model the interaction processes. Because of a reduction of the heliospheric dimension down to 1 AU, direct influence of the cloud’s matter to the terrestrial environment and atmosphere could be envisaged.

    Key words. Interplanetary physics (heliopause and solar wind termination; interplanetary dust; interstellar gas

  2. Restructuring and destruction of hydrocarbon dust in the interstellar medium

    CERN Document Server

    Murga, M S; Wiebe, D S

    2016-01-01

    A model of key processes influencing the evolution of a hydrocarbon grain of an arbitrary size under astrophysical conditions corresponding to ionized hydrogen regions (HII regions) and supernova remnants is presented. The considered processes include aromatization and photodestruction, sputtering by electrons and ions, and shattering due to collisions between grains. The model can be used to simulate the grain size distribution and the aromatization degree during the evolution of HII regions and supernova remnants for a specified radiation field, relative velocity of gas and dust, etc. The contribution of various processes to the evolution of hydrocarbon dust grains for parameters typical for the interstellar medium of our Galaxy is presented. Small grains (less than 50 carbon atoms) should be fully aromatized in the general interstellar medium. If larger grains initially have an aliphatic structure, it is preserved to a substantial extent. Variations in the size distribution of the grains due to their mutua...

  3. Trans-cis molecular photoswitching in interstellar Space*

    Science.gov (United States)

    Cuadrado, S.; Goicoechea, J. R.; Roncero, O.; Aguado, A.; Tercero, B.; Cernicharo, J.

    2016-01-01

    As many organic molecules, formic acid (HCOOH) has two conformers (trans and cis). The energy barrier to internal conversion from trans to cis is much higher than the thermal energy available in molecular clouds. Thus, only the most stable conformer (trans) is expected to exist in detectable amounts. We report the first interstellar detection of cis-HCOOH. Its presence in ultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation region), with a low trans-to-cis abundance ratio of 2.8 ± 1.0, supports a photoswitching mechanism: a given conformer absorbs a stellar photon that radiatively excites the molecule to electronic states above the interconversion barrier. Subsequent fluorescent decay leaves the molecule in a different conformer form. This mechanism, which we specifically study with ab initio quantum calculations, was not considered in Space before but likely induces structural changes of a variety of interstellar molecules submitted to UV radiation. PMID:28003686

  4. The Origin of Radio Scintillation In the Local Interstellar Medium

    CERN Document Server

    Linsky, Jeffrey L; Redfield, Seth

    2007-01-01

    We study three quasar radio sources (B1257-326, B1519-273, and J1819+385) that show large amplitude intraday and annual scintillation variability produced by the Earth's motion relative to turbulent-scattering screens located within a few parsecs of the Sun. We find that the lines of sight to these sources pass through the edges of partially ionized warm interstellar clouds where two or more clouds may interact. From the gas flow vectors of these clouds, we find that the relative radial and transverse velocities of these clouds are large and could generate the turbulence that is responsible for the observed scintillation. For all three sight lines the flow velocities of nearby warm local interstellar clouds are consistent with the fits to the transverse flows of the radio scintillation signals.

  5. Trans-cis molecular photoswitching in interstellar Space

    CERN Document Server

    Cuadrado, S; Roncero, O; Aguado, A; Tercero, B; Cernicharo, J

    2016-01-01

    As many organic molecules, formic acid (HCOOH) has two conformers (trans and cis). The energy barrier to internal conversion from trans to cis is much higher than the thermal energy available in molecular clouds. Thus, only the most stable conformer (trans) is expected to exist in detectable amounts. We report the first interstellar detection of cis-HCOOH. Its presence in ultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation region), with a low trans-to-cis abundance ratio of 2.8+-1.0, supports a photoswitching mechanism: a given conformer absorbs a stellar photon that radiatively excites the molecule to electronic states above the interconversion barrier. Subsequent fluorescent decay leaves the molecule in a different conformer form. This mechanism, which we specifically study with ab initio quantum calculations, was not considered in Space before but likely induces structural changes of a variety of interstellar molecules submitted to UV radiation.

  6. The effect of selective desorption mechanisms during interstellar ice formation

    CERN Document Server

    Kalvans, Juris

    2015-01-01

    Major components of ices on interstellar grains in molecular clouds - water and carbon oxides - occur at various optical depths. This implies that selective desorption mechanisms are at work. An astrochemical model of a contracting low-mass molecular cloud core is presented. Ice was treated as consisting of the surface and three subsurface layers (sublayers). Photodesorption, reactive desorption, and indirect reactive desorption were investigated. The latter manifests itself through desorption from H+H reaction on grains. Desorption of shallow subsurface species was included. Modeling results suggest the existence of a "photon-dominated ice" during the early phases of core contraction. Subsurface ice is chemically processed by interstellar photons, which produces complex organic molecules. Desorption from the subsurface layer results in high COM gas-phase abundances at Av = 2.4...10mag. This may contribute towards an explanation for COM observations in dark cores. It was found that photodesorption mostly gove...

  7. Models of Veritcal Disturbances in the Interstellar Medium

    CERN Document Server

    Walters, M A; Walters, Michael A.; cox, Donald P.

    2000-01-01

    This paper describes some interesting properties of waves in, and oscillations of, the interstellar medium in the direction normal to the plane of the Galaxy. Our purpose is to examine possible reasons for four observed phenomena: the falling sky in the northern hemisphere; the apparent presence of clouds in absorption spectra when a sightline is occupied primarily only by warm intercloud gas; the peculiar structuring of spiral arms involving clumps, spurs, and feathering; and the existence of an abundance of high stage ions far off the plane of the Galaxy. We explored the reaction of the interstellar medium - in the vertical direction only - to large imposed disturbances (initial displacements, expansive velocities, and compressions), and to the introduction of small amplitude waves via oscillation of the midplane. Our findings included: 1) the anticipated growth in amplitude of high frequency waves with height; 2) the four lowest normal modes for the oscillation of the atmosphere as a whole, as functions of...

  8. Tsallis statistics as a tool for studying interstellar turbulence

    CERN Document Server

    Esquivel, A

    2009-01-01

    We used magnetohydrodynamic (MHD) simulations of interstellar turbulence to study the probability distribution functions (PDFs) of increments of density, velocity, and magnetic field. We found that the PDFs are well described by a Tsallis distribution, following the same general trends found in solar wind and Electron MHD studies. We found that the PDFs of density are different in subsonic and supersonic turbulence. In order to extend this work to ISM observations we studied maps of column density obtained from 3D MHD simulations. From the column density maps we found the parameters that fit to Tsallis distributions and demonstrated that these parameters vary with the Mach and Alfvenic Mach numbers of turbulence. This opens avenues for using Tsallis distributions to study the dynamical and magnetic states of interstellar gas.

  9. Interstellar Dust Models Towards Some IUE Stars

    Science.gov (United States)

    Katyal, N.; Gupta, R.; Vaidya, D. B.

    2013-12-01

    We study the extinction properties of the composite dust grains, consisting of host silicate spheroids and graphite as inclusions, using discrete dipole approximation (DDA). We calculate the extinction cross sections of the composite grains in the ultraviolet spectral region, 1200\\AA -3200\\AA and study the variation in extinction as a function of the volume fraction of the inclusions. We compare the model extinction curves with the observed interstellar extinction curves obtained from the data given by the International Ultraviolet Explorer (IUE) satellite. Our results for the composite grains show a distinct variation in the extinction efficiencies with the variation in the volume fraction of the inclusions. In particular, it is found that the wavelength of peak absorption at `2175\\AA' shifts towards the longer wavelength with the variation in the volume fraction of inclusions. We find that the composite grain models with the axial ratios viz. 1.33 and 2.0 fit the observed extinction reasonably well with a grain size distribution, a = 0.005-0.250$\\mu m$. Moreover, our results of the composite grains clearly indicate that the inhomogeneity in the grain structure, composition and the surrounding media modifies the extinction properties of the grains.

  10. The first step of interstellar chemistry revealed by Herschel/HIFI

    Science.gov (United States)

    Falgarone, E.; Gerin, M.; Godard, B.; de Luca, M.

    2010-12-01

    Absorption spectroscopy performed with Herschel/HIFI in the direction of bright star-forming regions of the inner Galaxy provides a new probe of the interstellar medium. The ground-state transition of several light hydrides are found to have large optical depths and are therefore sensitive tracers of gas components that are poorly known such as gas of low density containing only a small fraction of molecular hydrogen. The large observed abundances of HF, CH^+, OH^+, H_2O^+ among others, provide new clues on the processes leading to the incorporation of heavy elements into interstellar chemistry.

  11. Interstellar Extinction by Spheroidal Dust Grains

    OpenAIRE

    Gupta, Ranjan; Mukai, Tadashi; Vaidya, D. B.; Sen, Asoke K.; Okada, Yasuhiko

    2005-01-01

    Observations of interstellar extinction and polarization indicate that the interstellar medium consists of aligned non-spherical dust grains which show variation in the interstellar extinction curve for wavelengths ranging from NIR to UV. To model the extinction and polarization, one cannot use the Mie theory which assumes the grains as solid spheres. We have used a T-matrix based method for computing the extinction efficiencies of spheroidal silicate and graphite grains of different shapes (...

  12. Structure and Dynamics of the Interstellar Medium

    Science.gov (United States)

    Tenorio-Tagle, Guillermo; Moles, Mariano; Melnick, Jorge

    Here for the first time is a book that treats practically all aspects of modern research in interstellar matter astrophysics. 20 review articles and 40 carefully selected and refereed papers give a thorough overview of the field and convey the flavor of enthusiastic colloquium discussions to the reader. The book includes sections on: - Molecular clouds, star formation and HII regions - Mechanical energy sources - Discs, outflows, jets and HH objects - The Orion Nebula - The extragalactic interstellar medium - Interstellar matter at high galactic latitudes - The structure of the interstellar medium

  13. Clinical Application of Surrounding Puncture

    Institute of Scientific and Technical Information of China (English)

    GUO Yao-jie; HAN Chou-ping

    2003-01-01

    Surrounding puncture can stop pathogenic qi from spreading, consolidate the connection between local meridians and enrich local qi and blood, which can eventually supplement anti-pathogenic qi and remove pathogenic qi, and consequently remedy diseases. The author of this article summrized and analyzed the clinical application of surrounding puncture for the purpose of studying this technique and improving the therapeutic effect.

  14. An X-ray study of the supernova remnant G20.0-0.2 and its surroundings

    CERN Document Server

    Petriella, Alberto; Giacani, Elsa

    2013-01-01

    Aims: We study the supernova remnant G20.0-0.2 and its surroundings in order to look for the high energy counterpart of the radio nebula and to find evidence of interaction between the shock front and the interstellar medium. Methods: We used Chandra archival observations to analyze the X-ray emission from the supernova remnant. The surrounding gas was investigated using data extracted from the Galactic Ring Survey, the VLA Galactic Plane Survey, the Galactic Legacy Infrared Midplane Survey Extraordinaire, and the Bolocam Galactic Plane Survey. Results: G20.0-0.2 shows diffuse X-ray emission from the central region of the radio remnant. Although the current data do not allow us to distinguish between a thermal or non-thermal origin for the X-ray diffuse emission, based on the radio properties we suggest a synchrotron origin as the most favorable. The hard X-ray point source CXO J182807.4-113516 appears located at the geometrical center of the remnant and is a potential candidate to be the pulsar powering the ...

  15. Deuterium enrichment of interstellar dusts

    Science.gov (United States)

    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.

  16. A Search for Interstellar Pyrimidine

    CERN Document Server

    Kuan, Y J; Charnley, S B; Kisiel, Z; Ehrenfreund, P; Huang, H C; Kuan, Yi-Jehng; Yan, Chi-Hung; Charnley, Steven B.; Kisiel, Zbigniew; Ehrenfreund, Pascale; Huang, Hui-Chun

    2003-01-01

    We have searched three hot molecular cores for submillimeter 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 1.7E+14 cm^{-2}, 2.4E+14 cm^{-2} and 3.4E+14 cm^{-2}, respectively. The associated upper limits to the pyrimidine fractional abundances lie in the range (0.3-3)E-10. Implications of this result for interstellar organic chemistry, and for the prospects of detecting nitrogen heterocycles in general, are briefly discussed.

  17. Discovery of Interstellar Heavy Water

    OpenAIRE

    Butner, H. M.; Charnley, S. B.; Ceccarelli, C.; Rodgers, S.D.; Pardo Carrión, Juan Ramón; Parise, B.; Cernicharo, José; Davis, G. R.

    2007-01-01

    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 1_10–1_01 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 determi...

  18. Variable interstellar absorption toward HD 72127A. II - 1981-1988

    Science.gov (United States)

    Hobbs, L. M.; Ferlet, R.; Welty, D. E.; Wallerstein, G.

    1991-01-01

    The present study examines eight new echelle spectra of HD 72127A found between 1981 and 1988 near the Ca II K line, along with four similar spectra near the Na I D lines. In addition to the unrivaled intensity and width of this interstellar K line formed at a distance of not more than 500 pc, which were previously discovered by Thackeray (1974), the spectra show clearly the unique temporal variability of the interstellar absorption along this light path, which was reported in an earlier study by Hobbs et al. (1982). The new results strengthen further the hypothesis that the interstellar absorption toward this star occurs predominantly in the disturbed gas located within the SNR, in which the interstellar grains have been largely destroyed. The variable interstellar lines were found to consist of at least 120 components at the K line and of at least eight generally corresponding components at the D lines. The total column densities summed over all of these interstellar clouds varied irregularly by about 45 percent in five and about 38 percent in ten years, respectively.

  19. Probing Interstellar Silicate Dust in Quasar Absorption Systems at z<1.4

    Science.gov (United States)

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

    2013-01-01

    Interstellar dust plays a significant role in the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of interstellar material. While interstellar dust has been studied extensively in local galaxies, much less is known about the properties of dust grains in distant galaxies. One technique to study extragalactic interstellar dust is to look for absorption features produced by the dust in the spectra of background luminous objects, such as quasars. We will present results from an ongoing study of the interstellar silicate dust in several quasar absorption systems using infrared absorption spectra obtained with the Spitzer Space Telescope, and complementary ground-based data on associated gas-phase metal absorption lines. Based on the shape of the 10 micron silicate absorption feature, we find suggestions that the interstellar silicate dust grains in the distant universe may be significantly more crystalline in structure than those in our own Galaxy. If confirmed, this may have implications for both dust and galaxy evolution, and for assumptions about the similarity of dust properties at all epochs. Support for this work is provided by NASA through an award issued by JPL/Caltech. Additional support comes from National Science Foundation grants AST-0908890 and AST-1108830 to the University of South Carolina.

  20. Neutral interstellar He parameters in front of the heliosphere 1994--2007

    CERN Document Server

    Bzowski, M; Hlond, M; Sokol, J M; Banaszkiewicz, M; Witte, M

    2014-01-01

    Analysis of IBEX measurements of neutral interstellar He flux brought the inflow velocity vector different from the results of earlier analysis of observations from GAS/Ulysses. Recapitulation of results on the helium inflow direction from the past ~40 years suggested that the inflow direction may be changing with time. We reanalyze the old Ulysses data and reprocess them to increase the accuracy of the instrument pointing to investigate if the GAS observations support the hypothesis that the interstellar helium inflow direction is changing. We employ a similar analysis method as in the analysis of the IBEX data. We seek a parameter set that minimizes reduced chi-squared, using the Warsaw Test Particle Model for the interstellar He flux at Ulysses with a state of the art model of neutral He ionization in the heliosphere, and precisely reproducing the observation conditions. We also propose a supplementary method of constraining the parameters based on cross-correlations of parameters obtained from analysis of...

  1. Ultraviolet spectroscopy of the hot interstellar medium

    Science.gov (United States)

    Indebetouw, Remy

    I study the hot phase of the interstellar medium (ISM) in our Galaxy. The lithium-like ions of common metals are a powerful tracer of gas between the hot (106 K) and cooler (104 K) phases of the ISM, and are particularly sensitive to dynamical processes because gas at several 105 K cools very rapidly. These ions are usually produced in nonequilibrium processes such as shocks, evaporative interfaces, or rapidly cooling gas. There are two different approaches to studying the hot ISM via Li-like ions---analysis of the microphysics in a well-defined location in the Galaxy, and observation of a large part of the Galaxy searching for global trends. This thesis describes two experiments which follow these two approaches. Chapter 2 describes a sounding rocket experiment which could perform simultaneous ultra-high spectroscopy of C IV, N V, and O VI. In particular, it was to study the interface between the local bubble, a diffuse region of the Galaxy in which the Sun is located, and denser neighboring gas. I redesigned, integrated, and directed the flight of the payload, which in addition to its scientific goals was the first space demonstration of a low-order echelle spectrograph. Chapter 3 describes a survey of N V, O VI, and C IV in the Galactic halo using data from the Far Ultraviolet Spectroscopic Explorer and the Hubble Space Telescope. Searching for global trends, I found a general trend of higher ionization (lower N V/O VI column density ratio) at larger positive line-of-sight velocities. I modeled the various physical situations in which Li-like ions are produced, and found that the observed trend is qualitatively consistent with a cooling Galactic fountain flow which rises, cools, and recombines as it returns to the disk. The observed trend is also consistent with shocks moving towards the observer, and with observing through a conductive interface, looking from the hot gas into cooler gas. The latter geometry is consistent with the solar system being inside a hot

  2. Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data

    CERN Document Server

    Acero, F; Ajello, M; Albert, A; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bellazzini, R; Bissaldi, E; Bloom, E D; Bonino, R; Bottacini, E; Brandt, T J; Bregeon, J; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caragiulo, M; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Charles, E; Chekhtman, A; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Cuoco, A; Cutini, S; D'Ammando, F; de Angelis, A; de Palma, F; Desiante, R; Digel, S W; Di Venere, L; Drell, P S; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Franckowiak, A; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Guiriec, S; Hadasch, D; Harding, A K; Hayashi, K; Hays, E; Hewitt, J W; Hill, A B; Horan, D; Hou, X; Jogler, T; Jóhannesson, G; Kamae, T; Kuss, M; Landriu, D; Larsson, S; Latronico, L; Li, J; Li, L; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Maldera, S; Malyshev, D; Manfreda, A; Martin, P; Mayer, M; Mazziotta, M N; McEnery, J E; Michelson, P F; Mirabal, N; Mizuno, T; Monzani, M E; Morselli, A; Nuss, E; Ohsugi, T; Omodei, N; Orienti, M; Orlando, E; Ormes, J F; Paneque, D; Pesce-Rollins, M; Piron, F; Pivato, G; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Remy, Q; Renault, N; Sánchez-Conde, M; Schaal, M; Schulz, A; Sgrò, C; Siskind, E J; Spada, F; Spandre, G; Spinelli, P; Strong, A W; Suson, D J; Tajima, H; Takahashi, H; Thayer, J B; Thompson, D J; Tibaldo, L; Tinivella, M; Torres, D F; Tosti, G; Troja, E; Vianello, G; Werner, M; Wood, K S; Wood, M; Zaharijas, G; Zimmer, S

    2016-01-01

    Most of the celestial gamma rays detected by the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope originate from the interstellar medium when energetic cosmic rays interact with interstellar nucleons and photons. Conventional point and extended source studies rely on the modeling of this diffuse emission for accurate characterization. We describe here the development of the Galactic Interstellar Emission Model (GIEM) that is the standard adopted by the LAT Collaboration and is publicly available. The model is based on a linear combination of maps for interstellar gas column density in Galactocentric annuli and for the inverse Compton emission produced in the Galaxy. We also include in the GIEM large-scale structures like Loop I and the Fermi bubbles. The measured gas emissivity spectra confirm that the cosmic-ray proton density decreases with Galactocentric distance beyond 5 kpc from the Galactic Center. The measurements also suggest a softening of the proton spectrum with Galactocentric ...

  3. Photodissociation of OH in interstellar clouds

    NARCIS (Netherlands)

    Dishoeck, van E.F.; Dalgarno, A.

    1984-01-01

    Calculations are presented of the lifetime of OH against photodissociation by the interstellar radiation field as a function of depth into interstellar clouds containing grains of various scattering properties. The effectiveness of the different photodissociation channels changes with depth into a c

  4. The chemistry of interstellar HnO+ beyond the Galaxy

    CERN Document Server

    van der Tak, Floris

    2010-01-01

    The astrochemistry of the HnO+ (n=1..3) ions is important as the main gas-phase formation route for water, and as tracer of the interstellar ionization rate by cosmic rays and other processes. While interstellar H3O+ has been known since the early 1990's, interstellar OH+ and H2O+ have only recently been detected using the Herschel space observatory and also from the ground. This paper reviews detections of HnO+ toward external galaxies and compares with ground-based work. The similarities and differences of the HnO+ chemistry within the Galaxy and beyond are discussed. Special attention is given to the low H2O/H3O+ ratio in M82 of only 3.3, suggesting rapid H2O photodissociation, and the high apparent OH+ and H2O+ abundances in Mrk 231, suggesting radiative excitation and/or formation pumping. Photodissociation rates for H3O+ and collisional cross-sections for OH+ and H2O+ with H, He and electrons are needed to test these interpretations.

  5. Detection of interstellar hydrogen peroxide

    CERN Document Server

    Bergman, P; Liseau, R; Larsson, B; Olofsson, H; Menten, K M; Güsten, R

    2011-01-01

    The molecular species hydrogen peroxide, HOOH, is likely to be a key ingredient in the oxygen and water chemistry in the interstellar medium. Our aim with this investigation is to determine how abundant HOOH is in the cloud core {\\rho} Oph A. By observing several transitions of HOOH in the (sub)millimeter regime we seek to identify the molecule and also to determine the excitation conditions through a multilevel excitation analysis. We have detected three spectral lines toward the SM1 position of {\\rho} Oph A at velocity-corrected frequencies that coincide very closely with those measured from laboratory spectroscopy of HOOH. A fourth line was detected at the 4{\\sigma} level. We also found through mapping observations that the HOOH emission extends (about 0.05 pc) over the densest part of the {\\rho} Oph A cloud core. We derive an abundance of HOOH relative to that of H_2 in the SM1 core of about 1\\times10^(-10). To our knowledge, this is the first reported detection of HOOH in the interstellar medium.

  6. On the Nature of Interstellar Grains

    Science.gov (United States)

    Hoyle, F.; Wickramasinghe, C.

    Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, ~1040 g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals 1 μ-1 pigments. The strongest of the diffuse interstellar bands are provisionally assigned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The λ2200 Å interstellar absorption feature could be due to `degraded' cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths λ < 1800 Å could be due to scattering by virus particles.

  7. Realistic Detectability of Close Interstellar Comets

    CERN Document Server

    Cook, Nathaniel V; Granvik, Mikael; Stephens, Denise C

    2016-01-01

    During the planet formation process, billions of comets are created and ejected into interstellar space. The detection and characterization of such interstellar comets (also known as extra-solar planetesimals or extra-solar comets) would give us in situ information about the efficiency and properties of planet formation throughout the galaxy. However, no interstellar comets have ever been detected, despite the fact that their hyperbolic orbits would make them readily identifiable as unrelated to the solar system. Moro-Mart\\'in et al. 2009 have made a detailed and reasonable estimate of the properties of the interstellar comet population. We extend their estimates of detectability with a numerical model that allows us to consider "close" interstellar comets, e.g., those that come within the orbit of Jupiter. We include several constraints on a "detectable" object that allow for realistic estimates of the frequency of detections expected from the Large Synoptic Survey Telescope (LSST) and other surveys. The inf...

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

    CERN Document Server

    Macquart, Jean-Pierre

    2016-01-01

    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 th...

  9. Visual surround suppression in schizophrenia

    Directory of Open Access Journals (Sweden)

    Marc Samuel Tibber

    2013-02-01

    Full Text Available Compared to unaffected observers patients with schizophrenia show characteristic differences in visual perception, including a reduced susceptibility to the influence of context on judgements of contrast - a manifestation of weaker surround suppression. To examine the generality of this phenomenon we measured the ability of 24 individuals with schizophrenia to judge the luminance, contrast, orientation and size of targets embedded in contextual surrounds that would typically influence the target’s appearance. Individuals with schizophrenia demonstrated weaker surround suppression compared to matched controls for stimuli defined by contrast or size, but not for those defined by luminance or orientation. As perceived luminance is thought to be regulated at the earliest stages of visual processing our findings are consistent with a suppression deficit that is predominantly cortical in origin. In addition, we propose that preserved orientation surround suppression in schizophrenia may reflect the sparing of broadly tuned mechanisms of suppression. We attempt to reconcile these data with findings from previous studies.

  10. Educational Success and Surrounding Culture

    Science.gov (United States)

    Walters, Garrison

    2016-01-01

    The curriculum, instruction, and services we provide in schools, colleges, and universities matter a lot, but if we continue to ignore our students' "surrounding culture," progress toward a more educated nation will continue to be disappointing.

  11. Educational Success and Surrounding Culture

    Science.gov (United States)

    Walters, Garrison

    2016-01-01

    The curriculum, instruction, and services we provide in schools, colleges, and universities matter a lot, but if we continue to ignore our students' "surrounding culture," progress toward a more educated nation will continue to be disappointing.

  12. Multichannel spatial surround sound system

    Institute of Scientific and Technical Information of China (English)

    RAO Dan; XIE Bosun

    2004-01-01

    Based on the consideration of being compatible with 5.1 channel horizontal surround sound system, a spatial surround sound system is proposed. Theoretical and experimental results show that the system has a wide listening area. It can not only recreate stable image in the front and rear direction, but also eliminate the defect of poor lateral image of 5.1 channel system. The system can be used to reproduce special 3D sound effect and the spaciousness of hall.

  13. The determination of electron abundances in interstellar clouds

    Science.gov (United States)

    Wootten, A.; Snell, R.; Glassgold, A. E.

    1979-01-01

    An independent method is proposed for the determination of electron abundances in dense clouds based upon the abundance ratio of HCO(+) and CO. The method is derived from a simple application of gas phase ion molecule interstellar chemistry. It is noted that unlike the fractionation of deuterated molecules, it applies to warm as well as to cool clouds. The method is illustrated with the results of the recent abundance survey of Wooten et al. (1978). Finally, it is shown that in cases where deuterium enhancement is measured, an upper limit can be obtained for the cosmic ray ionization rate.

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

    Science.gov (United States)

    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.

  15. Interstellar hydroxyl near Sagittarius B2

    Energy Technology Data Exchange (ETDEWEB)

    Venger, A.; Gosachinskii, I.; Grachev, V.; Egorova, T.; Prozorov, V.; Ryzhkov, N.; Khersonskii, V.; Yudaeva, N.

    1981-05-01

    The 1665-, 1667-MHz OH absorption lines near the radio source Sgr B2 have been observed with the RATAN-600 radio telescope at 2'.2 x 47' x 5.4 km/sec resolution. Physical parameters are determined for the five OH clouds observed in this direction at positive radial velocities. Evidently only one of these clouds can have any connection with the Sgr B2 source; it is located at the edge of the gas envelope surrounding that source.

  16. Polarimetry of the Interstellar Medium

    Science.gov (United States)

    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.

  17. Planck intermediate results XXXIII. Signature of the magnetic field geometry of interstellar filaments in dust polarization maps

    DEFF Research Database (Denmark)

    Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.

    2016-01-01

    Planck observations at 353 GHz provide the first fully sampled maps of the polarized dust emission towards interstellar filaments and their backgrounds (i.e., the emission observed in the surroundings of the filaments). The data allow us to determine the intrinsic polarization properties of the f...

  18. Planck intermediate results XXXIII. Signature of the magnetic field geometry of interstellar filaments in dust polarization maps

    DEFF Research Database (Denmark)

    Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.;

    2016-01-01

    Planck observations at 353 GHz provide the first fully sampled maps of the polarized dust emission towards interstellar filaments and their backgrounds (i.e., the emission observed in the surroundings of the filaments). The data allow us to determine the intrinsic polarization properties of the f...

  19. The Sun's Journey Through the Local Interstellar Medium: The PaleoLISM and Paleoheliosphere

    CERN Document Server

    Frisch, P C

    2006-01-01

    Over the recent past, the galactic environment of the Sun has differed substantially from today. Sometime within the past ~130,000 years, and possibly as recent as ~56,000 years ago, the Sun entered the tenuous tepid partially ionized interstellar material now flowing past the Sun. Prior to that, the Sun was in the low density interior of the Local Bubble. As the Sun entered the local ISM flow, we passed briefly through an interface region of some type. The low column densities of the cloud now surrounding the solar system indicate that heliosphere boundary conditions will vary from opacity considerations alone as the Sun moves through the cloud. These variations in the interstellar material surrounding the Sun affected the paleoheliosphere.

  20. Polarized Emission from Interstellar Dust

    CERN Document Server

    Vaillancourt, J E

    2006-01-01

    Observations of far-infrared (FIR) and submillimeter (SMM) polarized emission are used to study magnetic fields and dust grains in dense regions of the interstellar medium (ISM). These observations place constraints on models of molecular clouds, star-formation, grain alignment mechanisms, and grain size, shape, and composition. The FIR/SMM polarization is strongly dependent on wavelength. We have attributed this wavelength dependence to sampling different grain populations at different temperatures. To date, most observations of polarized emission have been in the densest regions of the ISM. Extending these observations to regions of the diffuse ISM, and to microwave frequencies, will provide additional tests of grain and alignment models. An understanding of polarized microwave emission from dust is key to an accurate measurement of the polarization of the cosmic microwave background. The microwave polarization spectrum will put limits on the contributions to polarized emission from spinning dust and vibrat...

  1. Interstellar Grains: Effect of Inclusions on Extinction

    CERN Document Server

    Katyal, Nisha; Vaidya, D B

    2011-01-01

    A composite dust grain model which simultaneously explains the observed interstellar extinction, polarization, IR emission and the abundance constraints, is required. We present a composite grain model, which is made up of a host silicate oblate spheroid and graphite inclusions. The interstellar extinction curve is evaluated in the spectral region 3.4-0.1$\\mu m$ using the extinction efficiencies of the composite spheroidal grains for three axial ratios. Extinction curves are computed using the discrete dipole approximation (DDA). The model curves are subsequently compared with the average observed interstellar extinction curve and with an extinction curve derived from the IUE catalogue data.

  2. Interstellar grains: Effect of inclusions on extinction

    Science.gov (United States)

    Katyal, N.; Gupta, R.; Vaidya, D. B.

    2011-10-01

    A composite dust grain model which simultaneously explains the observed interstellar extinction, polarization, IR emission and the abundance constraints, is required. We present a composite grain model, which is made up of a host silicate oblate spheroid and graphite inclusions. The interstellar extinction curve is evaluated in the spectral region 3.4-0.1 μm using the extinction efficiencies of composite spheroidal grains for three axial ratios. Extinction curves are computed using the discrete dipole approximation (DDA). The model curves are subsequently compared with the average observed interstellar extinction curve and with an extinction curve derived from the IUE catalogue data.

  3. Gas Between the Stars: What Determines its Temperature?

    Indian Academy of Sciences (India)

    2016-11-01

    The interstellar gas in galaxies is heated by stellar radiationand cosmic rays and it also cools through radiation. We takea detailed look at these processes in order to understand thethermal state of equilibrium of the interstellar gas. This gasalso manifests itself in different ‘phases’– molecular, neutralatomic and ionized, each with its characteristic temperatureand density, which we attempt to understand.

  4. Discovery of Interstellar Anions in Cepheus and Auriga

    Science.gov (United States)

    Cordiner, M. A.; Charnely, S. B.; Buckle, J. V.; Walsh, C.

    2011-01-01

    We report the detection of microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H in the star-forming region LI251 A (in Cepheus), and the pre-stellar core LI512 (in Auriga). The carbon chain-bearing species C4H, HC3N, HC5N, HC7N, and C3S are also detected in large abundances. The observations of L1251A constitute the first detections of anions and long-chain polyynes and cyanopolyynes (with more than five carbon atoms) in the Cepheus Flare star-forming region, and the first detection of anions in the vicinity of a protostar outside of the Taurus molecular cloud complex, indicating a possible wider importance for anions in the chemistry of star formation. Rotational excitation temperatures have been derived from the HC3N hyperfine structure lines and are found to be 6.2 K for L1251A and 8.7 K for LI5l2. The anion-to-neutral ratios are 3.6% and 4.1%, respectively, which are within the range of values previously observed in the interstellar medium, and suggest a relative uniformity in the processes governing anion abundances in different dense interstellar clouds. This research contributes toward the growing body of evidence that carbon chain anions are relatively abundant in interstellar clouds throughout the Galaxy, but especially in the regions of relatively high density and high depletion surrounding pre-stellar cores and young, embedded protostars.

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

    Energy Technology Data Exchange (ETDEWEB)

    Chiar, J. E.; Ricca, A. [SETI Institute, Carl Sagan Center, 189 Bernardo Avenue, Mountain View, CA 94043 (United States); Tielens, A. G. G. M. [Leiden Observatory, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Adamson, A. J., E-mail: jchiar@seti.org, E-mail: Alessandra.Ricca@1.nasa.gov, E-mail: tielens@strw.leidenuniv.nl, E-mail: aadamson@gemini.edu [Gemini Observatory, Northern Operations Center, 670 North A' ohoku Place, Hilo, HI 96729 (United States)

    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.

  6. The Interstellar Medium in the Kepler Search Volume

    CERN Document Server

    Johnson, Marshall C; Jensen, Adam G

    2015-01-01

    The properties of the interstellar medium (ISM) surrounding a planetary system can impact planetary climate through a number of mechanisms, including changing the size of the astrosphere (one of the major shields for cosmic rays) as well as direct deposition of material into planetary atmospheres. In order to constrain the ambient ISM conditions for exoplanetary systems, we present observations of interstellar Na I and K I absorption towards seventeen early-type stars in the Kepler prime mission field of view. We identify 39 Na I and 8 K I velocity components, and attribute these to eleven ISM clouds. Six of these are detected towards more than one star, and for these clouds we put limits on the cloud properties, including distance and hydrogen number density. We identify one cloud with significant (>1.5 cm$^{-3}$) hydrogen number density located within the nominal ~100 pc boundary of the Local Bubble. We identify systems with confirmed planets within the Kepler field of view that could lie within these ISM c...

  7. Cosmocultural Evolution: Cosmic Motivation for Interstellar Travel?

    Science.gov (United States)

    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.

  8. Physical Processes in the Interstellar Medium

    CERN Document Server

    Klessen, Ralf S

    2014-01-01

    Interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ISM). Understanding its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. Galaxy formation and evolution, the formation of stars, cosmic nucleosynthesis, the origin of large complex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental building blocks of planets, all these processes are intimately coupled to the physics of the interstellar medium. However, despite its importance, its structure and evolution is still not fully understood. Observations reveal that the interstellar medium is highly turbulent, consists of different chemical phases, and is characterized by complex structure on all resolvable spatial and temporal scales. Our current numerical and theoretical models describe it as a strongly coupled system that is far from equilibrium and where th...

  9. Silicate Composition of the Interstellar Medium

    CERN Document Server

    Fogerty, Shane; Watson, Dan M; Sargent, Benjamin A; Koch, Ingrid

    2016-01-01

    The composition of silicate dust in the diffuse interstellar medium and in protoplanetary disks around young stars informs our understanding of the processing and evolution of the dust grains leading up to planet formation. Analysis of the well-known 9.7{\\mu}m feature indicates that small amorphous silicate grains represent a significant fraction of interstellar dust and are also major components of protoplanetary disks. However, this feature is typically modelled assuming amorphous silicate dust of olivine and pyroxene stoichiometries. Here, we analyze interstellar dust with models of silicate dust that include non-stoichiometric amorphous silicate grains. Modelling the optical depth along lines of sight toward the extinguished objects Cyg OB2 No. 12 and {\\zeta} Ophiuchi, we find evidence for interstellar amorphous silicate dust with stoichiometry intermediate between olivine and pyroxene, which we simply refer to as "polivene." Finally, we compare these results to models of silicate emission from the Trapez...

  10. On the Formation of CO2 and Other Interstellar Ices

    CERN Document Server

    Garrod, Robin T

    2011-01-01

    We investigate the formation and evolution of interstellar dust-grain ices under dark-cloud conditions, with a particular emphasis on CO2. We use a three-phase model (gas/surface/mantle) to simulate the coupled gas--grain chemistry, allowing the distinction of the chemically-active surface from the ice layers preserved in the mantle beneath. The model includes a treatment of the competition between barrier-mediated surface reactions and thermal-hopping processes. The results show excellent agreement with the observed behavior of CO2, CO and water ice in the interstellar medium. The reaction of the OH radical with CO is found to be efficient enough to account for CO2 ice production in dark clouds. At low visual extinctions, with dust temperatures ~12 K, CO2 is formed by direct diffusion and reaction of CO with OH; we associate the resultant CO2-rich ice with the observational polar CO2 signature. CH4 ice is well correlated with this component. At higher extinctions, with lower dust temperatures, CO is relative...

  11. Organic Chemistry in Interstellar Ices: Connection to the Comet Halley Results

    Science.gov (United States)

    Schutte, W. A.; Agarwal, V. K.; deGroot, M. S.; Greenberg, J. M.; McCain, P.; Ferris, J. P.; Briggs, R.

    1997-01-01

    Mass spectroscopic measurements on the gas and dust in the coma of Comet Halley revealed the presence of considerable amounts of organic species. Greenberg (1973) proposed that prior to the formation of the comet UV processing of the ice mantles on grains in dense clouds could lead to the formation of complex organic molecules. Theoretical predictions of the internal UV field in dense clouds as well as the discovery in interstellar ices of species like OCS and OCN- which have been formed in simulation experiments by photoprocessing of interstellar ice analogues point to the importance of such processing. We undertook a laboratory simulation study of the formation of organic molecules in interstellar ices and their possible relevance to the Comet Halley results.

  12. Observations of Interstellar Pickup Ions and their Suprathermal Tails in Interplanetary Space and in the Heliosheath

    Science.gov (United States)

    Gloeckler, George; Fisk, Len

    2014-10-01

    Since the invention of space-borne time-of-flight mass spectrometers in the late 1990s, distribution functions of singly charged interstellar pickup ions, produced primarily by charge exchange with the solar wind and by photoionization of the interstellar neutral gas, have been observed from 1 to ~5 AU in interplanetary space. Here we summarize observed characteristics of pickup ion spectra (primarily of H+ and He+) as well as of the pickup ion tails that are readily produced in Local Acceleration Regions in space, both at 1 AU and in the heliosheath, and briefly discuss the most likely mechanisms for producing interstellar pickup ions as well as their tails that in the heliosheath extend to high (~10 MeV/nuc) energies.

  13. Laboratory studies of polycyclic aromatic hydrocarbons: the search for interstellar candidates

    CERN Document Server

    Joblin, C; Simon, A; Mulas, G

    2009-01-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are considered as a major constituent of interstellar dust. They have been proposed as the carriers of the Aromatic Infrared Bands (AIBs) observed in emission in the mid-IR. They likely have a significant contribution to various features of the extinction curve such as the 220 nm bump,the far-UV rise and the diffuse interstellar bands. Emission bands are also expected in the far-IR, which are better fingerprints of molecular identity than the AIBs. They will be searched for with the Herschel Space Observatory. Rotational emission is also expected in the mm range for those molecules which carry significant dipole moments. Despite spectroscopic studies in the laboratory, no individual PAH species could be identified. This emphasises the need for an investigation on where interstellar PAHs come from and how they evolve due to environmental conditions: ionisation and dissociation upon UV irradiation, interactions with electrons, gas and dust. There is also evidence for PAH ...

  14. Physical Processes in the Interstellar Medium

    OpenAIRE

    2014-01-01

    Interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ISM). Understanding its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. Galaxy formation and evolution, the formation of stars, cosmic nucleosynthesis, the origin of large complex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental buil...

  15. Scouting the spectrum for interstellar travellers

    CERN Document Server

    Garcia-Escartin, Juan Carlos

    2012-01-01

    Advanced civilizations capable of interstellar travel, if they exist, are likely to have advanced propulsion methods. Spaceships moving at high speeds would leave a particular signature which could be detected from Earth. We propose a search based on the properties of light reflecting from objects travelling at relativistic speeds. Based on the same principles, we also propose a simple interstellar beacon with a solar sail.

  16. The hydrogen coverage of interstellar PAHs

    Science.gov (United States)

    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. Amino Acid Formation on Interstellar Dust Particles

    Science.gov (United States)

    Meierhenrich, U. J.; Munoz Caro, G. M.; Barbier, B.; Brack, A.; Thiemann, W.; Goesmann, F.; Rosenbauer, H.

    2003-04-01

    In the dense interstellar medium dust particles accrete ice layers of known molecular composition. In the diffuse interstellar medium these ice layers are subjected to energetic UV-irradiation. Here, photoreactions form complex organic molecules. The interstellar processes were recently successfully simulated in two laboratories. At NASA Ames Research Center three amino acids were detected in interstellar ice analogues [1], contemporaneously, our European team reported on the identification of 16 amino acids therein [2]. Amino acids are the molecular building blocks of proteins in living organisms. The identification of amino acids on the simulated icy surface of interstellar dust particles strongly supports the assumption that the precursor molecules of life were delivered from interstellar and interplanetary space via (micro-) meteorites and/or comets to the earyl Earth. The results shall be verified by the COSAC experiment onboard the ESA cometary mission Rosetta [3]. [1] M.P. Bernstein, J.P. Dworkin, S.A. Sandford, G.W. Cooper, L.J. Allamandola: itshape Nature \\upshape 416 (2002), 401-403. [2] G.M. Muñoz Caro, U.J. Meierhenrich, W.A. Schutte, B. Barbier, A. Arcones Sergovia, H. Rosenbauer, W.H.-P. Thiemann, A. Brack, J.M. Greenberg: itshape Nature \\upshape 416 (2002), 403-406. [3] U. Meierhenrich, W.H.-P. Thiemann, H. Rosenbauer: itshape Chirality \\upshape 11 (1999), 575-582.

  18. EXPERIMENTAL AND COMPUTATIONAL STUDIES OF THE FORMATION MECHANISM OF PROTONATED INTERSTELLAR DIAZINES

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhe-Chen; Cole, Callie A.; Bierbaum, Veronica M. [Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 (United States); Snow, Theodore P., E-mail: zhwa4666@colorado.edu [Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)

    2015-01-10

    Studies of interstellar chemistry have grown in number and complexity by both observations and laboratory measurements, and nitrogen-containing aromatics have been implicated as important interstellar molecules. In this paper, the gas-phase collision induced dissociation (CID) processes of protonated pyridazine (1,2-diazine), pyrimidine (1,3-diazine), and pyrazine (1,4-diazine) cations (C{sub 4}H{sub 5}N{sub 2} {sup +}) are investigated in detail both experimentally and theoretically. The major neutral loss for all three CID processes is HCN, leading to the formation of C{sub 3}H{sub 4}N{sup +} isomers; our density functional theory (DFT) calculations support and elucidate our experimental results. The formation of C{sub 3}H{sub 4}N{sup +} isomers from the reaction of abundant interstellar acrylonitrile (CH{sub 2}CHCN) and H{sup +}is also studied employing DFT calculations. Our results lead to a novel mechanism for interstellar protonated diazine formation from the consecutive reactions of CH{sub 2}CHCN+ H{sup +} + HCN. Moreover, our results motivate the continuing search for interstellar C{sub 3}H{sub 4}N{sup +} isomers as well as polycyclic aromatic N-containing hydrocarbons (PANHs)

  19. Interaction of the Local Interstellar Medium with the Heliosphere: Role of the Interior and Exterior Magnetic Fields

    Science.gov (United States)

    Barnes, Aaron; DeVincenzi, Donald (Technical Monitor)

    2000-01-01

    A complete model of the global interaction between the solar wind and the local interstellar medium must take account of interstellar neutral atoms, interstellar ionized gas, solar and galactic magnetic fields, galactic and anomalous cosmic rays. For now, however, in view of the many uncertainties about conditions in the interstellar medium, etc., all models must be regarded as highly idealized and incomplete. In the present review I concentrate on the role of magnetic fields of solar and interstellar origin. The former, the interior field, has negligible influence on the unshocked solar wind; the immediate post-shock solar wind is probably low-beta, so that the interior magnetic field is still unimportant, but this situation changes as the plasma flows through the heliosheath, and a ridge of strong magnetic field may form to separate materials of polar and equatorial origin. The exterior (interstellar) field is likely to play an important role in determining the global morphology of the system outside the termination shock. If the exterior field is strong enough, it can compress the heliosphere (although exterior neutral and/or ionized hydrogen may play the dominant role). Even if the interstellar magnetic field does not provide the dominant pressure, its orientation can substantially affect the configuration of the heliosphere, especially the location and orientation of the heliospheric discontinuities. The configurations can be quite different for the situations in which the field and flow are (a) aligned or (b) transverse. Obliquity of the field produces asymmetry in the geometry of the system; in particular the noses of heliopause and interstellar bow shock are shifted away from the interstellar flow direction, and in opposite directions, due to the asymmetric draping of the magnetic field.

  20. Non-thermal X-rays and interstellar gas toward the \\gamma-ray supernova remnant RX J1713.7-3946: Evidence for X-ray enhancement around CO and HI clumps

    CERN Document Server

    Sano, H; Torii, K; Fukuda, T; Yoshiike, S; Sato, J; Horachi, H; Kuwahara, T; Hayakawa, T; Matsumoto, H; Inoue, T; Yamazaki, R; Inutsuka, S; Kawamura, A; Yamamoto, H; Okuda, T; Mizuno, N; Onishi, T; Mizuno, A; Fukui, Y

    2013-01-01

    RX J1713.7-3946 is the most remarkable very-high-energy \\gamma-ray supernova remnant which emits synchrotron X-rays without thermal features. We made a comparative study of CO, HI and X-rays in order to better understand the relationship between the X-rays, and molecular and atomic gas. The results indicate that the X-rays are enhanced around the CO and HI clumps on a pc scale but decrease inside the clumps on a 0.1 pc scale. Magnetohydrodynamic numerical simulations of the shock interaction with molecular and atomic gas indicate that the interaction between the shock waves and the clumps excite turbulence which amplifies the magnetic field around the clumps. We suggest that the amplified magnetic field around the CO and HI clumps enhances the synchrotron X-rays and possibly the acceleration of cosmic-ray electrons.

  1. Dust as interstellar catalyst I. Quantifying the chemical desorption process

    CERN Document Server

    Minissale, M; Cazaux, S; Hocuk, S

    2015-01-01

    Context. The presence of dust in the interstellar medium has profound consequences on the chemical composition of regions where stars are forming. Recent observations show that many species formed onto dust are populating the gas phase, especially in cold environments where UV and CR induced photons do not account for such processes. Aims. The aim of this paper is to understand and quantify the process that releases solid species into the gas phase, the so-called chemical desorption process, so that an explicit formula can be derived that can be included into astrochemical models. Methods. We present a collection of experimental results of more than 10 reactive systems. For each reaction, different substrates such as oxidized graphite and compact amorphous water ice are used. We derive a formula to reproduce the efficiencies of the chemical desorption process, which considers the equipartition of the energy of newly formed products, followed by classical bounce on the surface. In part II we extend these resul...

  2. Photoionisation and Heating of a Supernova Driven, Turbulent, Interstellar Medium

    CERN Document Server

    Barnes, J E; Hill, Alex S; Haffner, L M

    2014-01-01

    The Diffuse Ionised Gas (DIG) in galaxies traces photoionisation feedback from massive stars. Through three dimensional photoionisation simulations, we study the propagation of ionising photons, photoionisation heating and the resulting distribution of ionised and neutral gas within snapshots of magnetohydrodynamic simulations of a supernova driven turbulent interstellar medium. We also investigate the impact of non-photoionisation heating on observed optical emission line ratios. Inclusion of a heating term which scales less steeply with electron density than photoionisation is required to produce diagnostic emission line ratios similar to those observed with the Wisconsin H{\\alpha} Mapper. Once such heating terms have been included, we are also able to produce temperatures similar to those inferred from observations of the DIG, with temperatures increasing to above 15000 K at heights |z| > 1 kpc. We find that ionising photons travel through low density regions close to the midplane of the simulations, while...

  3. Characterization of Interstellar Organic Molecules

    Science.gov (United States)

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

    2008-11-01

    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. Interstellar Transfer of Planetary Microbiota

    Science.gov (United States)

    Wallis, Max K.; Wickramasinghe, N. C.

    Panspermia theories require the transport of micro-organisms in a viable form from one astronomical location to another. The evidence of material ejection from planetary surfaces, of dynamical orbit evolution and of potential survival on landing is setting a firm basis for interplanetary panspermia. Pathways for interstellar panspermia are less clear. We compare the direct route, whereby life-bearing planetary ejecta exit the solar system and risk radiation hazards en route to nearby stellar systems, and an indirect route whereby ejecta hitch a ride within the shielded environment of comets of the Edgeworth- Kuiper Belt that are subsequently expelled from the solar system. We identify solutions to the delivery problem. Delivery to fully-fledged planetary systems of either the direct ejecta or the ejecta borne by comets depends on dynamical capture and is of very low efficiency. However, delivery into a proto-planetary disc of an early solar-type nebula and into pre-stellar molecular clouds is effective, because the solid grains efficiently sputter the incoming material in hypervelocity collisions. The total mass of terrestrial fertile material delivered to nearby pre-stellar systems as the solar system moves through the galaxy is from kilogrammes up to a tonne. Subject to further study of bio-viability under irradiation and fragmenting collisions, a few kg of original grains and sputtered fragments could be sufficient to seed the planetary system with a wide range of solar system micro-organisms.

  5. Rotational spectroscopy of interstellar PAHs

    CERN Document Server

    Ali-Haïmoud, Yacine

    2013-01-01

    Polycyclic aromatic hydrocarbons (PAHs) have long been part of the standard model of the interstellar medium, and are believed to play important roles in its physics and chemistry. Yet, up to now it has not been possible to identify any specific molecule among them. In this paper, a new observational avenue is suggested to detect individual PAHs, using their rotational line emission at radio frequencies. Previous PAH searches based on rotational spectroscopy have only targeted the bowl-shaped corannulene molecule, with the underlying assumption that other polar PAHs are triaxial and as a consequence their rotational emission is diluted over a very large number of lines and unusable for detection purposes. In this paper the rotational spectrum of quasi-symmetric PAHs is computed analytically, as a function of the level of triaxiality. It is shown that the asymmetry of planar, nitrogen-substituted symmetric PAHs is small enough that their rotational spectrum, when observed with a resolution of about a MHz, has ...

  6. Estimating interstellar extinction toward to elliptical galaxies and star clusters

    Science.gov (United States)

    Amores, E. B.; Lépine, J. R. D.

    2006-08-01

    The ability to estimate interstellar extinction is essential for color corrections and distance calculations of all sorts of astronomical objects being fundamental for galactic structure studies. We performed comparisons of interstellar extinction models by Amores & Lépine ( 2005). These models are based on the hypothesis that gas and dust are homogeneously mixed, and make use of the dust-to gas ratio. The gas density distribution used in the models is obtained from the gas large scale surveys: Berkeley and Parkes HI surveys and from the Columbia University CO survey. In the present work, we compared these models with extinction predictions of elliptical galaxies (gE) and star clusters. We used the similar sample of gE galaxies proposed by Burstein for the comparison between the extinction calculation methods of Burstein & Heiles (1978, 1982) and of Schlegel et al. (1998) extending the comparison to our models. We found rms differences equal to 0.0179 and 0.0189 mag respectively, in the comparison of the predictions of our "model A" with the two methods mentioned. The comparison takes into account the "zero points" introduced by Burstein. The correlation coefficient obtained in the comparison is around 0.85. These results bring to light that our models can be safely used for the estimation of extinction in our Galaxy for extragalactic work, as an alternative method to the BH and SFD predictions. In the comparison with the globular clusters we found rms differences equal to 0.32 and 0.30 for our models A and S, respectively. For the open clusters we made comparisons using different samples and the rms differences were around 0.25.

  7. Estimating interstellar extinction towards elliptical galaxies and star clusters.

    Science.gov (United States)

    de Amôres, E. B.; Lépine, J. R. D.

    The ability to estimate interstellar extinction is essential for color corrections and distance calculations of all sorts of astronomical objects being fundamental for galactic structure studies. We performed comparisons of interstellar extinction models by Amores & Lépine (2005) that are available at: http://www.astro.iag.usp.br/\\symbol{126}amores. These models are based on the hypothesis that gas and dust are homogeneously mixed, and make use of the dust-to gas ratio. The gas density distribution used in the models is obtained from the gas large scale surveys: Berkeley and Parkes HI surveys and from the Columbia University CO survey. In the present work, we compared these models with extinction predictions of elliptical galaxies (gE) and star clusters. We used the similar sample of gE galaxies proposed by Burstein for the comparison between the extinction calculation methods of Burstein & Heiles (1978, 1982) and of Schlegel et al. (1998) extending the comparison to our models. We found rms differences equal to 0.0179 and 0.0189 mag respectively, in the comparison of the predictions of our "model A" with the two methods mentioned. The comparison takes into account the "zero points" introduced by Burstein. The correlation coefficient obtained in the comparison is around 0.85. These results bring to light that our models can be safely used for the estimation of extinction in our Galaxy for extragalactic work, as an alternative method to the BH and SFD predictions. In the comparison with the globular clusters we found rms differences equal to 0.32 and 0.30 for our models A and S, respectively. For the open clusters we made comparisons using different samples and the rms differences were around 0.25.

  8. TEMPORAL VARIABILITY OF INTERSTELLAR Na I ABSORPTION TOWARD THE MONOCEROS LOOP

    Energy Technology Data Exchange (ETDEWEB)

    Dirks, Cody; Meyer, David M., E-mail: codydirks2017@u.northwestern.edu, E-mail: davemeyer@northwestern.edu [Center for Interdisciplinary Research and Exploration in Astrophysics, Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)

    2016-03-01

    We report the first evidence of temporal variability in the interstellar Na i absorption toward HD 47240, which lies behind the Monoceros Loop supernova remnant (SNR). Analysis of multi-epoch Kitt Peak coudé feed spectra from this sight line taken over an eight-year period reveals significant variation in both the observed column density and the central velocities of the high-velocity gas components in these spectra. Given the ∼1.3 mas yr{sup −1} proper motion of HD 47240 and an SNR distance of 1.6 kpc, this variation would imply ∼10 au fluctuations within the SNR shell. Similar variations have been previously reported in the Vela SNR, suggesting a connection between the expanding SNR gas and the observed variations. We speculate on the potential nature of the observed variations toward HD 47240 in the context of the expanding remnant gas interacting with the ambient interstellar medium.

  9. Visual Surround Suppression in Schizophrenia

    Science.gov (United States)

    Tibber, Marc S.; Anderson, Elaine J.; Bobin, Tracy; Antonova, Elena; Seabright, Alice; Wright, Bernice; Carlin, Patricia; Shergill, Sukhwinder S.; Dakin, Steven C.

    2013-01-01

    Compared to unaffected observers patients with schizophrenia (SZ) show characteristic differences in visual perception, including a reduced susceptibility to the influence of context on judgments of contrast – a manifestation of weaker surround suppression (SS). To examine the generality of this phenomenon we measured the ability of 24 individuals with SZ to judge the luminance, contrast, orientation, and size of targets embedded in contextual surrounds that would typically influence the target’s appearance. Individuals with SZ demonstrated weaker SS compared to matched controls for stimuli defined by contrast or size, but not for those defined by luminance or orientation. As perceived luminance is thought to be regulated at the earliest stages of visual processing our findings are consistent with a suppression deficit that is predominantly cortical in origin. In addition, we propose that preserved orientation SS in SZ may reflect the sparing of broadly tuned mechanisms of suppression. We attempt to reconcile these data with findings from previous studies. PMID:23450069

  10. Molecular Spectroscopy in Astrophysics: Interstellar PAHs

    Science.gov (United States)

    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.

  11. Organic chemistry and biology of the interstellar medium

    Science.gov (United States)

    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.

  12. Control of Formation of Lithological Reservoirs by Surrounding Mudstone

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Taking the Jiyang depression as an example, this paper discusses the control of the formation of lithological reservoir by surrounding rocks by integrated application of geological analysis, physical simulation, and the analysis of oil & gas accumulation mechanism. Geological statistical shows that the major burial depth and interval of lithological reservoirs in the Jiyang depression are related to the hydrocarbon generation in and expulsion from the Lower Tertiary source rocks and the time of the formation of most lithological reservoirs coincides with the peak of hydrocarbon generation and expulsion. The lithological traps located in the center of effective source rocks are propitious to high oil saturation than those located on the margin of effective source rocks. The hydrocarbon charge degree of the lithological reservoir has a positive correlation with the intensity of hydrocarbon expulsion from surrounding source rocks.Geological analyses and NMR experiments also show that the oil saturation of surrounding source rocks control the hydrocarbon potential of lithological traps, and a critical value for oil saturation of surrounding mudstone is required, that is, when the oil saturation of surrounding mudstone is lower than this critical value, no oil and gas accumulate in the lithological trap. The control of surrounding mudstone on the oil-bearing properties of lithological reservoirs is also analyzed by the mechanisms of hydrocarbon generation and expulsion as well as accumulation.

  13. Molecules in interstellar clouds. [physical and chemical conditions of star formation and biological evolution

    Science.gov (United States)

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

    1981-01-01

    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.

  14. EXPLORING THE POSSIBILITY OF O AND Ne CONTAMINATION IN ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM

    Energy Technology Data Exchange (ETDEWEB)

    Wood, Brian E. [Naval Research Laboratory, Space Science Division, Washington, DC 20375 (United States); Müller, Hans-Reinhard [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Bzowski, Maciej; Sokół, Justyna M. [Space Research Centre of the Polish Academy of Sciences, Ul. Bartycka 18 A, 00-716 Warsaw (Poland); Möbius, Eberhard [Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States); Witte, Manfred [Max-Planck-Institute for Solar System Research, Katlenburg-Lindau (Germany); McComas, David J., E-mail: brian.wood@nrl.navy.mil [Southwest Research Institute, San Antonio, TX 78228 (United States)

    2015-10-15

    We explore the possibility that interstellar O and Ne may be contributing to the particle signal from the GAS instrument on Ulysses, which is generally assumed to be entirely He. Motivating this study is the recognition that an interstellar temperature higher than any previously estimated from Ulysses data could potentially resolve a discrepancy between Ulysses He measurements and those from the Interstellar Boundary Explorer (IBEX). Contamination by O and Ne could lead to Ulysses temperature measurements that are too low. We estimate the degree of O and Ne contamination necessary to increase the inferred Ulysses temperature to 8500 K, which would be consistent with both the Ulysses and IBEX data given the same interstellar flow speed. We find that producing the desired effect requires a heavy element contamination level of ∼9% of the total Ulysses/GAS signal. However, this degree of heavy element contribution is about an order of magnitude higher than expected based on our best estimates of detection efficiencies, ISM abundances, and heliospheric survival probabilities, making it unlikely that heavy element contamination is significantly affecting temperatures derived from Ulysses data.

  15. High Resolution Mapping of Interstellar Clouds by Near--IR Scattering

    CERN Document Server

    Padoan, P; Pelkonen, V M; Padoan, Paolo; Juvela, Mika; Pelkonen, Veli-Matti

    2006-01-01

    We discuss the possibility of mapping interstellar clouds at unprecedentedly high spatial resolution by means of near-IR imaging of their scattered light. We calculate the scattering of the interstellar radiation field by a cloud model obtained from the simulation of a supersonic turbulent flow. Synthetic maps of scattered light are computed in the J, H and K bands and are found to allow an accurate estimate of column density, in the range of visual extinction between 1 and 20 magnitudes. We provide a formalism to convert the intensity of scattered light at these near-IR bands into a total gas column density. We also show that this new method of mapping interstellar clouds is within the capability of existing near-IR facilities, which can achieve a spatial resolution of up to ~ 0.1 arcsec. This opens new perspectives in the study of interstellar dust and gas structure on very small scales. The validity of the method has been recently demonstrated by the extraordinary images of the Perseus region obtained by F...

  16. Polysulfanes on interstellar grains as a possible reservoir of interstellar sulphur

    CERN Document Server

    Druard, C

    2012-01-01

    The form of depleted sulphur in dense clouds is still unknown. Until now, only two molecules, OCS and SO2, have been detected in interstellar ices but cannot account for the elemental abundance of sulphur observed in diffuse medium. Chemical models suggest that solid H2S is the main form of sulphur in denser sources but observational constraints exist that infirm this hypothesis. We have used the Nautilus gas-grain code in which new chemical reactions have been added, based on recent experiments of H2S ice irradiation with UV photons and high energy protons. In particular, we included the new species Sn, H2Sn and C2S. We found that at the low temperature observed in dense clouds, i.e. 10 K, these new molecules are not efficiently produced and our modifications of the network do not change the previous pre- dictions. At slightly higher temperature, 20 K in less dense clouds or in the proximity of protostars, H2S abundance on the surfaces is strongly decreased in favor of the polysulfanes H2S3. Such a result ca...

  17. Interstellar Dust in the Solar System

    CERN Document Server

    Krueger, Harald; Altobelli, Nicolas; Gruen, Eberhard

    2007-01-01

    The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse almost perpendicular to the ecliptic plane (inclination 79 deg, perihelion distance 1.3 AU, aphelion distance 5.4 AU) since it encountered Jupiter in 1992. The in-situ dust detector on board continuously measured interstellar dust grains with masses up to 10^-13 kg, penetrating deep into the solar system. The flow direction is close to the mean apex of the Sun's motion through the solar system and the grains act as tracers of the physical conditions in the local interstellar cloud (LIC). While Ulysses monitored the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the in-situ dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the inner solar system is altered by the solar radiation pressure force, gravitational focussing and interaction of charged gr...

  18. Prospective of Photon Propulsion for Interstellar Flight

    Science.gov (United States)

    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. O vi in the local interstellar medium

    CERN Document Server

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

    2010-01-01

    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. (2005) and Savage & Lehner (2006), we have increased the number of detections of interstellar O VI and, for the first time, compared their locations...

  20. Communicating Concepts about Altruism in Interstellar Messages

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  2. Interstellar iron and manganese - UV oscillator strengths and abundances

    Science.gov (United States)

    Lugger, P.; Barker, E.; York, D. G.; Oegerle, W.

    1982-01-01

    Observations of 16 UV resonance lines of Fe II and six of Mn II in five stars are used to derive new f-values for the lines of these species at wavelengths lower than 1300 A. Values of forbidden lines Fe/H and Mn/H are derived. These new values are used to reassess mean depletions and range of variations in depletions for several lines of sight. On an integrated line-of-sight basis, depletions of Fe and Mn show larger variations than P, Cl, or Zn. The mean local depletion forbidden line Fe/H is 1.65, in interstellar gas. One Fe II line, 2366.864 A, has never been detected. Its f-value is shown to be much lower than previously thought. This line is therefore not useful for interstellar studies at the present time. It is suggested that the true wavelength of 1142 A of Fe II, from UV multiplet 10, is 1142.285 A.

  3. Colliding interstellar bubbles in the direction of l=54{\\deg}

    CERN Document Server

    Zychova, Lenka

    2016-01-01

    Interstellar bubbles are structures in the interstellar medium with diameters of a few to tens of parsecs. Their progenitors are stellar winds, intense radiation of massive stars, or supernova explosions. Star formation and young stellar objects are commonly associated with these structures. We compare IR observations of bubbles N115, N116 and N117 with atomic, molecular and ionized gas in this region. While determining the dynamical properties of the bubbles, we also look into their ambient environment to understand their formation in a wider context. For finding bubbles in HI (VLA Galactic Plane Survey) and CO data (Galactic Ring Survey), we used their images from Galactic Legacy Infrared Mid-Plane Survey. We manually constructed masks based on the appearance of the bubbles in the IR images and applied it to the HI and CO data. We determined their kinematic distance, size, expansion velocity, mass, original density of the maternal cloud, age and energy input. We identified two systems of bubbles: the first,...

  4. Hydrogen isotope exchanges between water and methanol in interstellar ices

    CERN Document Server

    Faure, A; Theulé, P; Quirico, E; Schmitt, B

    2015-01-01

    The deuterium fractionation of gas-phase molecules in hot cores is believed to reflect the composition of interstellar ices. The deuteration of methanol is a major puzzle, however, because the isotopologue ratio [CH2DOH]/[CH3OD], which is predicted to be equal to 3 by standard grain chemistry models, is much larger (~20) in low-mass hot corinos and significantly lower (~1) in high-mass hot cores. This dichotomy in methanol deuteration between low-mass and massive protostars is currently not understood. In this study, we report a simplified rate equation model of the deuterium chemistry occurring in the icy mantles of interstellar grains. We apply this model to the chemistry of hot corinos and hot cores, with IRAS 16293-2422 and the Orion~KL Compact Ridge as prototypes, respectively. The chemistry is based on a statistical initial deuteration at low temperature followed by a warm-up phase during which thermal hydrogen/deuterium (H/D) exchanges occur between water and methanol. The exchange kinetics is incorpor...

  5. Interaction of planetary nebulae with the interstellar medium

    Science.gov (United States)

    Borkowski, Kazimierz J.; Sarazin, Craig L.; Soker, Noam

    1990-01-01

    The interaction of a moving planetary nebula (PN) with the interstellar medium is considered. The PN shell is compressed first in the direction of the stellar motion. This produces a dipole asymmetry in the surface brightness of the nebula, typically at a nebular density of about 40/cu cm if the nebula is located in the Galactic plane. In the later stages of the interaction, this part of the shell is significantly decelerated with respect to the central star, and the PN becomes strongly asymmetric in shape. This distortion and the subsequent stripping of the nebular gas away from the central star typically occurs at a low nebular density of about 6/cu cm. The morphology of PNs with central stars whose proper motions exceed 0.015 arcsec/yr was examined, and it was found that many of the extended nebulae are interacting with the interstellar medium (ISM). The sample doubles the number of known PNs interacting with the ISM. The morphology of nearby PNs was examined, and a number of strongly asymmetric nebuale were found.

  6. Trans-cis molecular photoswitching in interstellar space

    Science.gov (United States)

    Cuadrado, S.; Goicoechea, J. R.; Roncero, O.; Aguado, A.; Tercero, B.; Cernicharo, J.

    2016-11-01

    As many organic molecules, formic acid (HCOOH) has two conformers (trans and cis). The energy barrier to internal conversion from trans to cis is much higher than the thermal energy available in molecular clouds. Thus, only the most stable conformer (trans) is expected to exist in detectable amounts. We report the first interstellar detection of cis-HCOOH. Its presence in ultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation region), with a low trans-to-cis abundance ratio of 2.8 ± 1.0, supports a photoswitching mechanism: a given conformer absorbs a stellar photon that radiatively excites the molecule to electronic states above the interconversion barrier. Subsequent fluorescent decay leaves the molecule in a different conformer form. This mechanism, which we specifically study with ab initio quantum calculations, was not considered in Space before but likely induces structural changes of a variety of interstellar molecules submitted to UV radiation. This paper makes use of observations obtained with the IRAM-30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  7. Investigating nearby exoplanets via interstellar radar

    Science.gov (United States)

    Scheffer, Louis K.

    2014-01-01

    Interstellar radar is a potential intermediate step between passive observation of exoplanets and interstellar exploratory missions. Compared with passive observation, it has the traditional advantages of radar astronomy. It can measure surface characteristics, determine spin rates and axes, provide extremely accurate ranges, construct maps of planets, distinguish liquid from solid surfaces, find rings and moons, and penetrate clouds. It can do this even for planets close to the parent star. Compared with interstellar travel or probes, it also offers significant advantages. The technology required to build such a radar already exists, radar can return results within a human lifetime, and a single facility can investigate thousands of planetary systems. The cost, although too high for current implementation, is within the reach of Earth's economy.

  8. Long-Term Perspectives on Interstellar Flight

    Science.gov (United States)

    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.

  9. Model atmospheres - Tool for identifying interstellar features

    Science.gov (United States)

    Frisch, P. C.; Slojkowski, S. E.; Rodriguez-Bell, T.; York, D.

    1993-01-01

    Model atmosphere parameters are derived for 14 early A stars with rotation velocities, from optical spectra, in excess of 80 km/s. The models are compared with IUE observations of the stars in regions where interstellar lines are expected. In general, with the assumption of solar abundances, excellent fits are obtained in regions longward of 2580 A, and accurate interstellar equivalent widths can be derived using models to establish the continuum. The fits are poorer at shorter wavelengths, particularly at 2026-2062 A, where the stellar model parameters seem inadequate. Features indicating mass flows are evident in stars with known infrared excesses. In gamma TrA, variability in the Mg II lines is seen over the 5-year interval of these data, and also over timescales as short as 26 days. The present technique should be useful in systematic studies of episodic mass flows in A stars and for stellar abundance studies, as well as interstellar features.

  10. Investigating Nearby Exoplanets via Interstellar Radar

    CERN Document Server

    Scheffer, Louis K

    2013-01-01

    Interstellar radar is a potential intermediate step between passive observation of exoplanets and interstellar exploratory missions. Compared to passive observation, it has the traditional advantages of radar astronomy. It can measure surface characteristics, determine spin rates and axes, provide extremely accurate ranges, construct maps of planets, distinguish liquid from solid surfaces, find rings and moons, and penetrate clouds. It can do this even for planets close to the parent star. Compared to interstellar travel or probes, it also offers significant advantages. The technology required to build such a radar already exists, radar can return results within a human lifetime, and a single facility can investigate thousands of planetary systems. The cost, although high, is within the reach of Earth's economy, so it is cheaper as well.

  11. Gas Inflow and Metallicity Drops in Star-forming Galaxies

    CERN Document Server

    Ceverino, Daniel; Muñoz-Tuñon, Casiana; Dekel, Avishai; Elmegreen, Bruce G; Elmegreen, Debra M; Primack, Joel

    2015-01-01

    Gas inflow feeds galaxies with low metallicity gas from the cosmic web, sustaining star formation across the Hubble time. We make a connection between these inflows and metallicity inhomogeneities in star-forming galaxies, by using synthetic narrow-band images of the Halpha emission line from zoom-in AMR cosmological simulations of galaxies with stellar masses of $M \\simeq 10^9 $Msun at redshifts z=2-7. In $\\sim$50\\% of the cases at redshifts lower than 4, the gas inflow gives rise to star-forming, Halpha-bright, off-centre clumps. Most of these clumps have gas metallicities, weighted by Halpha luminosity, lower than the metallicity in the surrounding interstellar medium by $\\sim$0.3 dex, consistent with observations of chemical inhomogeneities at high and low redshifts. Due to metal mixing by shear and turbulence, these metallicity drops are dissolved in a few disc dynamical times. Therefore, they can be considered as evidence for rapid gas accretion coming from cosmological inflow of pristine gas.

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

    Science.gov (United States)

    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.

  13. HD/H2 as a Probe of the Roles of Gas, Dust, Light, Metallicity, and Cosmic Rays in Promoting the Growth of Molecular Hydrogen in the Diffuse Interstellar Medium

    Science.gov (United States)

    Liszt, H. S.

    2015-01-01

    We modeled recent observations of UV absorption of HD and {H_2} in the Milky Way and toward damped/subdamped Lyα systems at z = 0.18 and z >1.7. N(HD)/N({H_2}) ratios reflect the separate self-shieldings of HD and {H_2} and the coupling introduced by deuteration chemistry. Locally, observations are explained by diffuse molecular gas with 16 cm-3 1.7, N(HD) is comparable to the Galaxy but with 10 times smaller N({H_2}) and somewhat smaller N({H_2})/N(H I). Comparison of our Galaxy with the Magellanic Clouds shows that smaller {H_2}/H is expected at subsolar metallicity, and we show by modeling that HD/{H_2} increases with density at low metallicity, opposite to the Milky Way. Observations of HD would be explained with higher n(H) at low metallicity, but high-z systems have high HD/{H_2} at metallicity 0.04 shielding effects. The abrupt {H_2} transition to {H_2}/H ≈ 1%-10% occurs mostly from self-shielding, although it is assisted by extinction for n(H) <~ 16 cm-3. Interior {H_2} fractions are substantially increased by dust extinction below <~ 32 cm-3. At smaller n(H), ζ H , small increases in {H_2} triggered by dust extinction can trigger abrupt increases in N(HD).

  14. HD/H2 as a probe of the roles of gas, dust, light, metallicity and cosmic rays in promoting the growth of molecular hydrogen in the diffuse interstellar medium

    CERN Document Server

    Liszt, H S

    2014-01-01

    We modelled recent observations of UV absorption of HD and \\HH\\ in the Milky Way and toward damped/sub-damped Lyman alpha systems at z=0.18 and z $>$ 1.7. N(HD)/N(\\HH) ratios reflect the separate self-shieldings of HD and \\HH\\ and the coupling introduced by deuteration chemistry. Locally, observations are explained by diffuse molecular gas with $ 16 \\pccc \\la$ n(H) $\\la 128 \\pccc $ if the cosmic-ray ionization rate per H-nucleus \\zetaH $= 2\\times 10^{-16}\\ps$ as inferred from \\H3\\p\\ and OH\\p. The dominant influence on N(HD)/N(\\HH) is the cosmic-ray ionization rate with a much weaker downward dependence on n(H) at Solar metallicity, but dust-extinction can drive N(HD) higher as with N(\\HH). At z $>$ 1.7, N(HD) is comparable to the Galaxy but with 10x smaller N(\\HH) and somewhat smaller N(\\HH)/N(H I). Comparison of our Galaxy and the Magellanic Clouds shows that smaller \\HH/H is expected at sub-Solar metallicity and we show by modelling that HD/\\HH\\ increases with density at low metallicity, opposite to the Mil...

  15. Problems of Interplanetary and Interstellar Trade

    Science.gov (United States)

    Hickman, John

    2008-01-01

    If and when interplanetary and interstellar trade develops, it will be novel in two respects. First, the distances and time spans involved will reduce all or nearly all trade to the exchange of intangible goods. That threatens the possibility of conducting business in a genuinely common currency and of enforcing debt agreements, especially those involving sovereign debt. Second, interstellar trade suggests trade between humans and aliens. Cultural distance is a probable obstacle to initiating and sustaining such trade. Such exchange also threatens the release of new and potentially toxic memes.

  16. Water in the interstellar media of galaxies

    CERN Document Server

    van der Tak, Floris

    2015-01-01

    This paper reviews recent observations of water in Galactic interstellar clouds and nearby galactic nuclei. Two results are highlighted: (1) Multi-line H$_2$O mapping of the Orion Bar shows that the water chemistry in PDRs is driven by photodissociation and -desorption, unlike in star-forming regions. (2) High-resolution spectra of H$_2$O and its ions toward 5 starburst / AGN systems reveal low ionization rates, unlike as found from higher-excitation lines. We conclude that the chemistry of water strongly depends on radiation environment, and that the ionization rates of interstellar clouds decrease by at least 10 between galactic nuclei and disks.

  17. PROBING THE LOCAL BUBBLE WITH DIFFUSE INTERSTELLAR BANDS. III. THE NORTHERN HEMISPHERE DATA AND CATALOG

    Energy Technology Data Exchange (ETDEWEB)

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5746, Tehran (Iran, Islamic Republic of); Van Loon, Jacco Th., E-mail: a.farhang@ipm.ir [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom)

    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.

  18. Probing the Local Bubble with Diffuse Interstellar Bands. III. The Northern hemisphere data and catalog

    CERN Document Server

    Farhang, Amin; Javadi, Atefeh; van Loon, Jacco Th

    2014-01-01

    We present a new high signal-to-noise (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 $\\lambda$5780 and $\\lambda$5797 \\AA\\ DIBs up to distance of $\\sim$ 200 pc. All observations have been carried out by using Intermediate Dispersion Spectrograph (IDS) on 2.5 m Isaac Newton Telescope, during three years, to reach a minimum S/N ratio of $\\sim$ 2000. All $\\lambda$5780 and $\\lambda$5797 absorptions are presented in this paper and the observed values of interstellar parameter; $\\lambda$5780, $\\lambda$5797, Na I D lines including the uncertainties are tabulated.

  19. Organic molecules in ices and their release into the gas phase

    Science.gov (United States)

    Fayolle, Edith; Oberg, Karin I.; Garrod, Robin; van Dishoeck, Ewine; Rajappan, Mahesh; Bertin, Mathieu; Romanzin, Claire; Michaut, Xavier; Fillion, Jean-Hugues

    2015-08-01

    Organic molecules in the early stages of star formation are mainly produced in icy mantles surrounding interstellar dust grains. Identifying these complex organics and quantifying their abundance during the evolution of young stellar objects is of importance to understand the emergence of life. Simple molecules in ices, up to methanol in size, have been identified in the interstellar medium through their mid-IR vibrations, but band confusion prevents detections of more complex and less abundant organic molecules in interstellar ices. The presence of complex organics on grains can instead be indirectly inferred from observations of their rotational lines in the gas phase following ice sublimation.Thermal sublimation of protostellar ices occurs when icy grains flow toward a central protostar, resulting in the formation of a hot-core or a hot-corinos. The high degree of chemical complexity observed in these dense and warm regions can be the results of i) direct synthesis on the grains followed by desorption, but also to ii) the desorption of precursors from the ice followed by gas-phase chemistry. I will show how spatially resolved millimetric observations of hot cores and cooler protostellar environments, coupled to ice observations can help us pinpoint the ice or gas-phase origin of these organic species.Organic molecules have also recently been observed in cold environments where thermal desorption can be neglected. The presence of these cold molecules in the gas phase is most likely due to non-thermal desorption processes induced by, for e.g., photon-, electron-, cosmic-ray-irradiation, shock, exothermic reactions... I will present laboratory and observational efforts that push our current understanding of these non-thermal desorption processes and how they could be use to quantify the amount of organics in ices.

  20. Effects of turbulent dust grain motion to interstellar chemistry

    CERN Document Server

    Ge, J X; Yan, H R

    2015-01-01

    Theoretical studies have revealed that dust grains are usually moving fast through the turbulent interstellar gas, which could have significant effects upon molecular cloud chemistry by modifying grain accretion. This effect is investigated in this work on the basis of numerical gas-grain chemical modeling. Major features of the grain motion effect in the typical environment of dark clouds (DC) can be summarised as follows: 1) decrease of gas-phase (both neutral and ionic) abundances and increase of surface abundances by up to 2-3 orders of magnitude; 2) shifts of the existing chemical jumps to earlier evolution ages for gas-phase species and to later ages for surface species by factors of about ten; 3) a few exceptional cases in which some species turn out to be insensitive to this effect and some other species can show opposite behaviors too. These effects usually begin to emerge from a typical DC model age of about 10^5 yr. The grain motion in a typical cold neutral medium (CNM) can help overcome the Coulo...

  1. Scientists Toast the Discovery of Vinyl Alcohol in Interstellar Space

    Science.gov (United States)

    2001-10-01

    Astronomers using the National Science Foundation's 12 Meter Telescope at Kitt Peak, AZ, have discovered the complex organic molecule vinyl alcohol in an interstellar cloud of dust and gas near the center of the Milky Way Galaxy. The discovery of this long-sought compound could reveal tantalizing clues to the mysterious origin of complex organic molecules in space. Vinyl Alcohol and its fellow isomers "The discovery of vinyl alcohol is significant," said Barry Turner, a scientist at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Va., "because it gives us an important tool for understanding the formation of complex organic compounds in interstellar space. It may also help us better understand how life might arise elsewhere in the Cosmos." Vinyl alcohol is an important intermediary in many organic chemistry reactions on Earth, and the last of the three stable members of the C2H4O group of isomers (molecules with the same atoms, but in different arrangements) to be discovered in interstellar space. Turner and his colleague A. J. Apponi of the University of Arizona's Steward Observatory in Tucson detected the vinyl alcohol in Sagittarius B -- a massive molecular cloud located some 26,000 light-years from Earth near the center of our Galaxy. The astronomers were able to detect the specific radio signature of vinyl alcohol during the observational period of May and June of 2001. Their results have been accepted for publication in the Astrophysical Journal Letters. Of the approximately 125 molecules detected in interstellar space, scientists believe that most are formed by gas-phase chemistry, in which smaller molecules (and occasionally atoms) manage to "lock horns" when they collide in space. This process, though efficient at creating simple molecules, cannot explain how vinyl alcohol and other complex chemicals are formed in detectable amounts. For many years now, scientists have been searching for the right mechanism to explain how the building

  2. The Distribution of Pressures in a Supernova-Driven Interstellar Medium

    CERN Document Server

    MacLow, M M; Avillez, M A; Kim, J; Low, Mordecai-Mark Mac; Balsara, Dinshaw; Avillez, Miguel A.; Kim, Jongsoo

    2001-01-01

    Observations have suggested substantial departures from pressure equilibrium in the interstellar medium (ISM) in the plane of the Galaxy, even on scales under 50 pc. Nevertheless, multi-phase models of the ISM assume at least locally isobaric gas. The pressure then determines the density reached by gas cooling to stable thermal equilibrium. We use two different sets of numerical models of the ISM to examine the consequences of supernova driving for interstellar pressures. The first set of models is hydrodynamical, and uses adaptive mesh refinement to allow computation of a 1 x 1 x 20 kpc section of a stratified galactic disk. The second set of models is magnetohydrodynamical, using an independent code framework, and examines a 200 pc cubed periodic domain threaded by magnetic fields. Both of these models show broad pressure distributions with roughly log-normal functional forms produced by both shocks and rarefaction waves, rather than the power-law distributions predicted by previous work, with rather sharp ...

  3. Momentum Injection by Supernovae in the Interstellar Medium

    CERN Document Server

    Kim, Chang-Goo

    2014-01-01

    Supernova (SN) explosions deposit prodigious energy and momentum in their environments, with the former regulating multiphase thermal structure and the latter regulating turbulence and star formation rates in the interstellar medium (ISM). In contrast to the extensive efforts developing spherical models for SN remnant (SNR) evolution, systematic studies quantifying the impact of SNe in more realistic inhomogeneous ISM conditions have been lacking. Using three-dimensional hydrodynamic simulations with optically-thin radiative cooling, we investigate the dependence of radial momentum injection on both physical conditions (considering a range of mean density n=0.1-100) and numerical parameters. Our inhomogeneous simulations adopt two-phase background states that result from thermal instability in atomic gas. Although the SNR morphology becomes highly complex for inhomogeneous backgrounds, the radial momentum injection is remarkably insensitive to environmental details. For our two-phase simulations, the final mo...

  4. Shielding of CO from dissociating radiation in interstellar clouds

    Science.gov (United States)

    Glassgold, A. E.; Huggins, P. J.; Langer, W. D.

    1985-01-01

    The paper investigates the photodissociation of CO in interstellar clouds in the light of recent laboratory studies which suggest that line rather than continuum processes dominate its dissociation by ultraviolet radiation. Using a simple radiative transfer model, the shielding of representative dissociating bands is estimated, including self-shielding, mutual shielding between different isotopes, and near coincidences with strong lines of H2. Each of these processes materially affects the photodestruction rates of the various isotopic species in the transition regions of molecular clouds. These results are combined with an appropriate gas phase chemical model to determine how the abundances of the CO isotopes vary with depth into the cloud. It is found that self-shielding and mutual shielding cause significant variations in isotopic ratios. In addition, fractionation enhances species containing C-13. The relationship between the column densities of CO and H2 is found to vary for the different isotopes and to be sensitive to local conditions.

  5. Plasma Diagnostics of the Interstellar Medium with Radio Astronomy

    CERN Document Server

    Haverkorn, Marijke

    2013-01-01

    We discuss the degree to which radio propagation measurements diagnose conditions in the ionized gas of the interstellar medium (ISM). The "signal generators" of the radio waves of interest are extragalactic radio sources (quasars and radio galaxies), as well as Galactic sources, primarily pulsars. The polarized synchrotron radiation of the Galactic non-thermal radiation also serves to probe the ISM, including space between the emitting regions and the solar system. Radio propagation measurements provide unique information on turbulence in the ISM as well as the mean plasma properties such as density and magnetic field strength. Radio propagation observations can provide input to the major contemporary questions on the nature of ISM turbulence, such as its dissipation mechanisms and the processes responsible for generating the turbulence on large spatial scales. Measurements of the large scale Galactic magnetic field via Faraday rotation provide unique observational input to theories of the generation of the ...

  6. ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) - Merging Observations and Laboratory Data

    Science.gov (United States)

    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

  7. Laboratory formation of fullerenes from PAHs: Top-down interstellar chemistry

    OpenAIRE

    Zhen, Junfeng; Castellanos, Pablo; Paardekooper, Daniel M.; Linnartz, Harold; Tielens, Alexander G. G. M.

    2014-01-01

    Interstellar molecules are thought to build up in the shielded environment of molecular clouds or in the envelope of evolved stars. This follows many sequential reaction steps of atoms and simple molecules in the gas phase and/or on (icy) grain surfaces. However, these chemical routes are highly inefficient for larger species in the tenuous environment of space as many steps are involved and, indeed, models fail to explain the observed high abundances. This is definitely the case for the C$_{...

  8. Characteristics of and constraints on a secondary interstellar neutral stream

    Science.gov (United States)

    Collier, M. R.; Moore, T. E.; Simpson, D.; Roberts, A.; Szabo, A.; Fuselier, S. A.; Wurz, P.; Tsurutani, B. T.

    2003-04-01

    It has been recently proposed based on myriad data from IMAGE, ACE, ISEE-3, Wind, and SOHO that there may exist a secondary stream of neutral atoms entering the heliosphere from somewhere between 262 and 292 degrees ecliptic longitude, 10-40 degrees from the nominal upstream direction. Constraints may be placed on secondary stream properties using various data sets. For example, based on SOHO/SWAN data, rough estimates place an upper limit on the secondary stream density, assuming a bulk velocity of between 0 and 200 km/s, of about 0.001 cm{}-3. However, the presence of a strong suprathermal tail on the neutral population can yield high neutral fluxes of the order of 2x10{}^5/cm{}^2/s in spite of the low density. The presence of wave activity at 1 AU observed by ISEE-3 and Wind, as well as wave activity at 5 AU observed by Ulysses, may be related to this secondary stream as it "piles-up" around the hydrogen parabolic exclusion boundary near 1 AU, which will be present provided the force due to radiation pressure exceeds that due to gravity. Finally, we will examine various ideas about the origin of the secondary stream including asymmetries induced by the presence of a tilted interstellar magnetic field as well as possible charge exchange of the hot, 10{}^6 K, local bubble gas with the dense gas of our local cloud which may be observable due to the heliosphere's proximity to the edge of the local interstellar cloud in the direction of the Galactic center.

  9. The Voyager Journey to Interstellar Space

    Science.gov (United States)

    Stone, E. C.

    Launched in 1977 to explore Jupiter, Saturn, Uranus, and Neptune, the two Voyager spacecraft continued their journeys beyond the planets as they searched for the heliopause, the boundary between the solar wind and the local interstellar medium. After traveling more than 23 billion kilometers, Voyager 1 left the heliosphere on August 25, 2012, and began returning the first in-situ observations of local interstellar space. Voyager 1 found a wall of interstellar plasma beyond the heliopause with a density forty times greater than inside and an interstellar magnetic field that is compressed and wrapped around the outside. Voyager 1 also observed the energy spectrum of low energy galactic cosmic ray protons that are excluded from the heliosphere by solar modulation, finding a peak intensity at ˜30 MeV. that is ten times the maximum intensity at 1 AU that occurs at ˜300 MeV. An overview of the journey and the new aspects of the interaction of the sun and the nearby region of the Milky Way will be discussed.

  10. Bubbles and holes in the interstellar medium

    NARCIS (Netherlands)

    vanderHulst, JM; Skillman, ED

    1996-01-01

    Studies of the HI in nearby galaxies now clearly begin to show the effects of star formation on the interstellar medium. Holes, filaments, expanding motions and other anomalous velocity signatures are clearly apparent in sensitive observations of the HI in nearby galaxies. A global relation with the

  11. The composition of circumstellar and interstellar dust

    NARCIS (Netherlands)

    Tielens, AGGM; Woodward, CE; Biscay, MD; Shull, JM

    2001-01-01

    A large number of solid dust components have been identified through analysis of stardust recovered from meteorites, and analysis of IR observations of circumstellar shells and the interstellar medium. These include graphite, hydrogenated amorphous carbon, diamond, PAHs, silicon-, iron-, and titanin

  12. Infrared spectroscopy of interstellar apolar ice analogs

    NARCIS (Netherlands)

    Ehrenfreund, P; Boogert, ACA; Gerakines, PA; Tielens, AGGM; van Dishoeck, EF

    1997-01-01

    Apolar ices have been observed in several regions in dense clouds and are likely dominated by molecules such as CO, CO(2) and the infrared inactive molecules O(2) and N(2). Interstellar solid CO has been well characterized by ground-based high resolution measurements. Recent ISO results showed the u

  13. The photodissociation and chemistry of interstellar CO

    NARCIS (Netherlands)

    Dishoeck, van E.F.; Black, J.H.

    1988-01-01

    Recent work on the vacuum UV absorption spectrum of CO to the description of the photodissociation of interstellar CO and its principal isotopic varieties is discussed. The effects of line broadening, self-shielding, shielding by H and H2, and isotope-selective shielding are examined as functions of

  14. Far-infrared spectroscopy of interstellar dust

    NARCIS (Netherlands)

    Tielens, AGGM; Wilson, A

    2005-01-01

    The composition of interstellar dust is best studied using mid-infrared spectroscopy. Nevertheless, the far-infrared can make some unique contributions to this field. This includes studies on the Mg/Fe ratio and the temperature of crystalline silicates, the presence of carbonates, and the precense o

  15. A Rigorous Attempt to Verify Interstellar Glycine

    Science.gov (United States)

    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-

  16. The composition of circumstellar and interstellar dust

    NARCIS (Netherlands)

    Tielens, AGGM; Woodward, CE; Biscay, MD; Shull, JM

    2001-01-01

    A large number of solid dust components have been identified through analysis of stardust recovered from meteorites, and analysis of IR observations of circumstellar shells and the interstellar medium. These include graphite, hydrogenated amorphous carbon, diamond, PAHs, silicon-, iron-, and titanin

  17. Swift heavy ion irradiation of interstellar dust analogues. Small carbonaceous species released by cosmic rays

    Science.gov (United States)

    Dartois, E.; Chabot, M.; Pino, T.; Béroff, K.; Godard, M.; Severin, D.; Bender, M.; Trautmann, C.

    2017-03-01

    Context. Interstellar dust grain particles are immersed in vacuum ultraviolet (VUV) and cosmic ray radiation environments influencing their physicochemical composition. Owing to the energetic ionizing interactions, carbonaceous dust particles release fragments that have direct impact on the gas phase chemistry. Aims: The exposure of carbonaceous dust analogues to cosmic rays is simulated in the laboratory by irradiating films of hydrogenated amorphous carbon interstellar analogues with energetic ions. New species formed and released into the gas phase are explored. Methods: Thin carbonaceous interstellar dust analogues were irradiated with gold (950 MeV), xenon (630 MeV), and carbon (43 MeV) ions at the GSI UNILAC accelerator. The evolution of the dust analogues is monitored in situ as a function of fluence at 40, 100, and 300 K. Effects on the solid phase are studied by means of infrared spectroscopy complemented by simultaneously recording mass spectrometry of species released into the gas phase. Results: Specific species produced and released under the ion beam are analyzed. Cross sections derived from ion-solid interaction processes are implemented in an astrophysical context.

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

    Science.gov (United States)

    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.

  19. The Interstellar Neutral He haze in the heliosphere: what can we learn?

    CERN Document Server

    Sokół, Justyna M; Kubiak, M A; Swaczyna, P; Galli, A; Wurz, P; Möbius, E; Kucharek, H; Fuselier, S A; McComas, D J

    2015-01-01

    Neutral interstellar helium has been observed by the Interstellar Boundary Explorer (IBEX) since 2009 with a signal-to-noise ratio well above 1000. Because of the geometry of the observations, the signal observed from January to March each year is the easiest to identify. However, as we show via simulations, the portion of the signal in the range of intensities from 10^{-3} to 10^{-2} of the peak value, previously mostly left out from the analysis, may bring important information about the details of the distribution function of interstellar He gas in front of the heliosphere. In particular, these observations may inform us about possible departures of the parent interstellar He population from equilibrium. We compare the expected distribution of the signal for the canonical assumption of a single Maxwell-Boltzmann population with the distributions for a superposition of the Maxwell-Boltzmann primary population and the recently discovered Warm Breeze, and for a single primary population given by a kappa funct...

  20. Local Interstellar Hydrogen's Disappearance at 1 Au: Four Years of IBEX in the Rising Solar Cycle

    CERN Document Server

    Saul, Lukas; Fuselier, Stephen; Kubiak, Marzena; McComas, Dave; Möbius, Eberhard; Sokół, Justina; Rodríguez, Diego; Scheer, Juergen; Wurz, Peter

    2013-01-01

    NASA's Interstellar Boundary Explorer (IBEX) mission has recently opened a new window on the interstellar medium (ISM) by imaging neutral atoms. One "bright" feature in the sky is the interstellar wind flowing into the solar system. Composed of remnants of stellar explosions as well as primordial gas and plasma, the ISM is by no means uniform. The interaction of the local ISM with the solar wind shapes our heliospheric environment with hydrogen being the dominant component of the very local ISM. In this paper, we report on direct sampling of the neutral hydrogen of the local ISM over four years of IBEX observations. The hydrogen wind observed at 1 AU has decreased and nearly disappeared as the solar activity has increased over the last four years; the signal at 1 AU has dropped off in 2012 by a factor of ~8 to near background levels. The longitudinal offset has also increased with time presumably due to greater radiation pressure deflecting the interstellar wind. We present longitudinal and latitudinal arriva...

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

    Science.gov (United States)

    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.

  2. The Interstellar Line of Sight to the Interacting Galaxy NGC 5195

    CERN Document Server

    Ritchey, Adam M

    2015-01-01

    We present moderately-high resolution echelle observations of the nucleus of NGC 5195, the line of sight to which samples intervening interstellar material associated with the outer spiral arm of M51. Our spectra reveal absorption from interstellar Na I, K I, Ca II, and CH+, and from a number of diffuse interstellar bands (DIBs), at a velocity close to that exhibited by H I 21 cm emission from M51 at the position of NGC 5195. The H I column density implied by the equivalent width of the 5780.5 DIB, based on the relationship between W(5780.5) and N(H I) derived for sight lines in the local Galactic interstellar medium, is consistent with the column density obtained from the integrated H I emission. The H2 column density predicted from the observed column density of K I, using the Galactic relationship between N(K I) and N(H2), is comparable to N(H I), suggesting a high molecular fraction (~0.65) for the M51 gas toward NGC 5195. The DIBs toward NGC 5195 are, on average, ~40% weaker than would be expected based ...

  3. TRIANGULATION OF THE INTERSTELLAR MAGNETIC FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Schwadron, N. A.; Moebius, E. [University of New Hampshire, Durham, NH 03824 (United States); Richardson, J. D. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Burlaga, L. F. [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); McComas, D. J. [Southwest Research Institute, San Antonio, TX 78228 (United States)

    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.

  4. Binaural Rendering in MPEG Surround

    Directory of Open Access Journals (Sweden)

    Kristofer Kjörling

    2008-04-01

    Full Text Available This paper describes novel methods for evoking a multichannel audio experience over stereo headphones. In contrast to the conventional convolution-based approach where, for example, five input channels are filtered using ten head-related transfer functions, the current approach is based on a parametric representation of the multichannel signal, along with either a parametric representation of the head-related transfer functions or a reduced set of head-related transfer functions. An audio scene with multiple virtual sound sources is represented by a mono or a stereo downmix signal of all sound source signals, accompanied by certain statistical (spatial properties. These statistical properties of the sound sources are either combined with statistical properties of head-related transfer functions to estimate “binaural parameters” that represent the perceptually relevant aspects of the auditory scene or used to create a limited set of combined head-related transfer functions that can be applied directly on the downmix signal. Subsequently, a binaural rendering stage reinstates the statistical properties of the sound sources by applying the estimated binaural parameters or the reduced set of combined head-related transfer functions directly on the downmix. If combined with parametric multichannel audio coders such as MPEG Surround, the proposed methods are advantageous over conventional methods in terms of perceived quality and computational complexity.

  5. Reduced surround inhibition in musicians.

    Science.gov (United States)

    Shin, Hae-Won; Kang, Suk Y; Hallett, Mark; Sohn, Young H

    2012-06-01

    To investigate whether surround inhibition (SI) in the motor system is altered in professional musicians, we performed a transcranial magnetic stimulation (TMS) study in 10 professional musicians and 15 age-matched healthy non-musicians. TMS was set to be triggered by self-initiated flexion of the index finger at different intervals ranging from 3 to 1,000 ms. Average motor evoked potential (MEP) amplitudes obtained from self-triggered TMS were normalized to average MEPs of the control TMS at rest and expressed as a percentage. Normalized MEP amplitudes of the abductor digiti minimi (ADM) muscles were compared between the musicians and non-musicians with the primary analysis being the intervals between 3 and 80 ms (during the movement). A mixed-design ANOVA revealed a significant difference in normalized ADM MEPs during the index finger flexion between groups, with less SI in the musicians. This study demonstrated that the functional operation of SI is less strong in musicians than non-musicians, perhaps due to practice of movement synergies involving both muscles. Reduced SI, however, could lead susceptible musicians to be prone to develop task-specific dystonia.

  6. Binaural Rendering in MPEG Surround

    Science.gov (United States)

    Breebaart, Jeroen; Villemoes, Lars; Kjörling, Kristofer

    2008-12-01

    This paper describes novel methods for evoking a multichannel audio experience over stereo headphones. In contrast to the conventional convolution-based approach where, for example, five input channels are filtered using ten head-related transfer functions, the current approach is based on a parametric representation of the multichannel signal, along with either a parametric representation of the head-related transfer functions or a reduced set of head-related transfer functions. An audio scene with multiple virtual sound sources is represented by a mono or a stereo downmix signal of all sound source signals, accompanied by certain statistical (spatial) properties. These statistical properties of the sound sources are either combined with statistical properties of head-related transfer functions to estimate "binaural parameters" that represent the perceptually relevant aspects of the auditory scene or used to create a limited set of combined head-related transfer functions that can be applied directly on the downmix signal. Subsequently, a binaural rendering stage reinstates the statistical properties of the sound sources by applying the estimated binaural parameters or the reduced set of combined head-related transfer functions directly on the downmix. If combined with parametric multichannel audio coders such as MPEG Surround, the proposed methods are advantageous over conventional methods in terms of perceived quality and computational complexity.

  7. The interstellar medium in Andromeda's dwarf spheroidal galaxies - I. Content and origin of the interstellar dust

    Science.gov (United States)

    De Looze, Ilse; Baes, Maarten; Bendo, George J.; Fritz, Jacopo; Boquien, Médéric; Cormier, Diane; Gentile, Gianfranco; Kennicutt, Robert C.; Madden, Suzanne C.; Smith, Matthew W. L.; Young, Lisa

    2016-07-01

    Dwarf spheroidal galaxies are among the most numerous galaxy population in the Universe, but their main formation and evolution channels are still not well understood. The three dwarf spheroidal satellites (NGC 147, NGC 185, and NGC 205) of the Andromeda galaxy are characterized by very different interstellar medium properties, which might suggest them being at different galaxy evolutionary stages. While the dust content of NGC 205 has been studied in detail in an earlier work, we present new Herschel dust continuum observations of NGC 147 and NGC 185. The non-detection of NGC 147 in Herschel SPIRE maps puts a strong constraint on its dust mass (≤128^{+124}_{-68} M⊙). For NGC 185, we derive a total dust mass Md = 5.1±1.0 × 103 M⊙, which is a factor of ˜2-3 higher than that derived from ISO and Spitzer observations and confirms the need for longer wavelength observations to trace more massive cold dust reservoirs. We, furthermore, estimate the dust production by asymptotic giant branch (AGB) stars and supernovae (SNe). For NGC 147, the upper limit on the dust mass is consistent with expectations of the material injected by the evolved stellar population. In NGC 185 and NGC 205, the observed dust content is one order of magnitude higher compared to the estimated dust production by AGBs and SNe. Efficient grain growth, and potentially longer dust survival times (3-6 Gyr) are required to account for their current dust content. Our study confirms the importance of grain growth in the gas phase to account for the current dust reservoir in galaxies.

  8. Black hole feedback in a multiphase interstellar medium

    Science.gov (United States)

    Bourne, Martin A.; Nayakshin, Sergei; Hobbs, Alexander

    2014-07-01

    Ultrafast outflows (UFOs) from supermassive black holes (SMBHs) are thought to regulate the growth of SMBHs and host galaxies, resulting in a number of observational correlations. We present high-resolution numerical simulations of the impact of a thermalized UFO on the ambient gas in the inner part of the host galaxy. Our results depend strongly on whether the gas is homogeneous or clumpy. In the former case all of the ambient gas is driven outward rapidly as expected based on commonly used energy budget arguments, while in the latter the flows of mass and energy de-couple. Carrying most of the energy, the shocked UFO escapes from the bulge via paths of least resistance, taking with it only the low-density phase of the host. Most of the mass is however in the high-density phase, and is affected by the UFO much less strongly, and may even continue to flow inwards. We suggest that the UFO energy leakage through the pores in the multiphase interstellar medium (ISM) may explain why observed SMBHs are so massive despite their overwhelmingly large energy production rates. The multiphase ISM effects reported here are probably under-resolved in cosmological simulations but may be included in prescriptions for active galactic nuclei feedback in future simulations and in semi-analytical models.

  9. Black hole feedback in a multiphase interstellar medium

    CERN Document Server

    Bourne, Martin A; Hobbs, Alexander

    2014-01-01

    Ultrafast outflows (UFOs) from supermassive black holes (SMBHs) are thought to regulate the growth of SMBHs and host galaxies, resulting in a number of observational correlations. We present high-resolution numerical simulations of the impact of a thermalized UFO on the ambient gas in the inner part of the host galaxy. Our results depend strongly on whether the gas is homogeneous or clumpy. In the former case all of the ambient gas is driven outward rapidly as expected based on commonly used energy budget arguments, while in the latter the flows of mass and energy decouple. Carrying most of the energy, the shocked UFO escapes from the bulge via paths of least resistance, taking with it only the low-density phase of the host. Most of the mass is however in the high-density phase, and is affected by the UFO much less strongly, and may even continue to flow inwards. We suggest that the UFO energy leakage through the pores in the multiphase interstellar medium (ISM) may explain why observed SMBHs are so massive d...

  10. Interstellar Probe: The Next Step To Flight

    Science.gov (United States)

    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

  11. Formation of star-forming clouds from the magnetised, diffuse interstellar medium

    CERN Document Server

    Banerjee, Robi

    2015-01-01

    Molecular clouds, the birthplaces of stars in galaxies, form dynamically from the diffuse atomic gas of the interstellar medium (ISM). The ISM is also threaded by magnetic fields which have a large impact on its dynamics. In particular, star forming regions must be magnetically supercrit- ical in order to accomodate gas clumps which can collapse under their own weight. Based on a parameter study of three dimensional magneto-hydrodyamical (MHD) simulations, we show that the long-standing problem of how such supercritical regions are generated is still an open issue.

  12. SOFT X-RAY IRRADIATION OF PURE CARBON MONOXIDE INTERSTELLAR ICE ANALOGUES

    Energy Technology Data Exchange (ETDEWEB)

    Ciaravella, A.; Candia, R.; Collura, A. [INAF-Osservatorio Astronomico di Palermo, P.za Parlamento 1, 90134 Palermo (Italy); Jimenez-Escobar, A.; Munoz Caro, G. M. [Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir, km 4, Torrejon de Ardoz, 28850 Madrid (Spain); Cecchi-Pestellini, C. [INAF-Osservatorio Astronomico di Cagliari, Strada n.54, Loc. Poggio dei Pini, I-09012 Capoterra (Italy); Giarrusso, S. [INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Via U. La Malfa 153, I-90146 Palermo (Italy); Barbera, M., E-mail: aciaravella@astropa.unipa.it [Dipartimento di Scienze Fisiche and Astronomiche, Universita di Palermo, Sezione di Astronomia, Piazza del Parlamento 1, I-90134 Palermo (Italy)

    2012-02-10

    There is an increasing evidence for the existence of large organic molecules in the interstellar and circumstellar medium. Very few among such species are readily formed in conventional gas-phase chemistry under typical conditions of interstellar clouds. Attention has therefore focused on interstellar ices as a potential source of these relatively complex species. Laboratory experiments show that irradiation of interstellar ice analogues by fast particles or ultraviolet radiation can induce significant chemical complexity. However, stars are sources of intense X-rays at almost every stage of their formation and evolution. Such radiation may thus provide chemical changes in regions where ultraviolet radiation is severely inhibited. After H{sub 2}O, CO is often the most abundant component of icy grain mantles in dense interstellar clouds and circumstellar disks. In this work we present irradiation of a pure carbon monoxide ice using a soft X-ray spectrum peaked at 0.3 keV. Analysis of irradiated samples shows formation of CO{sub 2}, C{sub 2}O, C{sub 3}O{sub 2}, C{sub 3}, C{sub 4}O, and CO{sub 3}/C{sub 5}. Comparison of X-rays and ultraviolet irradiation experiments, of the same energy dose, shows that X-rays are more efficient than ultraviolet radiation in producing new species. With the exception of CO{sub 2}, X-ray photolysis induces formation of a larger number of products with higher abundances, e.g., C{sub 3}O{sub 2} column density is about one order of magnitude higher in the X-ray experiment. To our knowledge this is the first report on X-ray photolysis of CO ices. The present results show that X-ray irradiation represents an efficient photo-chemical way to convert simple ices to more complex species.

  13. Human factors issues for interstellar spacecraft

    Science.gov (United States)

    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.

  14. Interstellar molecules - Formation in solar nebulae

    Science.gov (United States)

    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.

  15. Organic Synthesis in Simulated Interstellar Ice Analogs

    Science.gov (United States)

    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.

  16. Interstellar Turbulence II: Implications and Effects

    CERN Document Server

    Scalo, J

    2004-01-01

    Interstellar turbulence has implications for the dispersal and mixing of the elements, cloud chemistry, cosmic ray scattering, and radio wave propagation through the ionized medium. This review discusses the observations and theory of these effects. Metallicity fluctuations are summarized, and the theory of turbulent transport of passive tracers is reviewed. Modeling methods, turbulent concentration of dust grains, and the turbulent washout of radial abundance gradients are discussed. Interstellar chemistry is affected by turbulent transport of various species between environments with different physical properties and by turbulent heating in shocks, vortical dissipation regions, and local regions of enhanced ambipolar diffusion. Cosmic rays are scattered and accelerated in turbulent magnetic waves and shocks, and they generate turbulence on the scale of their gyroradii. Radio wave scintillation is an important diagnostic for small scale turbulence in the ionized medium, giving information about the power spe...

  17. Structural Evolution of Interstellar Polycyclic Aromatic Hydrocarbons

    Science.gov (United States)

    Hammonds, Mark; Candian, Alessandra; Mori, Tamami; Usui, Fumihiko; Onaka, Takashi

    2015-08-01

    Polycyclic Aromatic Hydrocarbons (PAHs) are an important reservoir for molecular carbon in the interstellar medium (ISM), and investigations into their chemistry and behaviour may be important to the understanding of how carbon is processed from simple forms into complex prebiotic molecules such as those detected in chondritic meteorites. In this study, infrared astronomical data from AKARI and other observatories are used together with laboratory and theoretical data to study variations in the structure of emitting PAHs in interstellar environments using spectroscopic decomposition techniques and bands arising from carbon-hydrogen bond vibrations at wavelengths from 3 - 14 microns. Results and inferences are discussed in terms of the processing of large carbonaceous molecules in astrophysical environments.

  18. Organic Synthesis in Simulated Interstellar Ice Analogs

    Science.gov (United States)

    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.

  19. Local Interstellar Magnetic Field Determined from the Interstellar Boundary Explorer Ribbon

    Science.gov (United States)

    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.

  20. Separation of the Interstellar Boundary Explorer Ribbon from Globally Distributed Energetic Neutral Atom Flux

    Science.gov (United States)

    Schwadron, N. A.; Allegrini, F.; Bzowski, M.; Christian, E. R.; Crew, G. B.; Dayeh, M.; DeMajistre, R.; Frisch, P.; Funsten, H. O.; Fuselier, S. A.; Goodrich, K.; Gruntman, M.; Janzen, P.; Kucharek, H.; Livadiotis, G.; McComas, D. J.; Moebius, E.; Prested, C.; Reisenfeld, D.; Reno, M.; Roelof, E.; Siegel, J.; Vanderspek, R.

    2011-04-01

    The Interstellar Boundary Explorer (IBEX) observes a remarkable feature, the IBEX ribbon, which has energetic neutral atom (ENA) flux over a narrow region ~20° wide, a factor of 2-3 higher than the more globally distributed ENA flux. Here, we separate ENA emissions in the ribbon from the distributed flux by applying a transparency mask over the ribbon and regions of high emissions, and then solve for the distributed flux using an interpolation scheme. Our analysis shows that the energy spectrum and spatial distribution of the ribbon are distinct from the surrounding globally distributed flux. The ribbon energy spectrum shows a knee between ~1 and 4 keV, and the angular distribution is approximately independent of energy. In contrast, the distributed flux does not show a clear knee and more closely conforms to a power law over much of the sky. Consistent with previous analyses, the slope of the power law steepens from the nose to tail, suggesting a weaker termination shock toward the tail as compared to the nose. The knee in the energy spectrum of the ribbon suggests that its source plasma population is generated via a distinct physical process. Both the slope in the energy distribution of the distributed flux and the knee in the energy distribution of the ribbon are ordered by latitude. The heliotail may be identified in maps of globally distributed flux as a broad region of low flux centered ~44°W of the interstellar downwind direction, suggesting heliotail deflection by the interstellar magnetic field.

  1. Kinetic chemistry of dense interstellar clouds

    Energy Technology Data Exchange (ETDEWEB)

    Graedel, T.E.; Langer, W.D.; Frerking, M.A.

    1982-03-01

    A detailed model of the time-dependent chemistry of dense interstellar clouds has been developed to study the dominant chemical processes in carbon and oxygen isotope fractionation, formation of nitrogen-containing molecules, evolution of product molecules as a function of cloud density and temperature, and other topics of interest. The full computation involves 328 individual reactions (expanded to 1067 to study carbon and oxygen isotope chemistry); photodegradation processes are unimportant in these dense clouds and are excluded.

  2. TAU as Tao. [interstellar spacecraft performance

    Science.gov (United States)

    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.

  3. Building Interstellar's black hole: the gravitational renderer

    OpenAIRE

    James, Oliver; Dieckmann, Sylvan; Pabst, Simon; Roberts, Paul-George H.; Thorne, Kip S.

    2015-01-01

    Interstellar is the first feature film to attempt depicting a black hole as it would actually be seen by somebody nearby. A close collaboration between the production's Scientific Advisor and the Visual Effects team led to the development of a new renderer, DNGR (Double Negative Gravitational Renderer) which uses novel techniques for rendering in curved space-time. Following the completion of the movie, the code was adapted for scientific research, leading to new insights into gravitational l...

  4. Local Interstellar Medium Kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds

    CERN Document Server

    Corradi, W J B; Knude, J

    2004-01-01

    The results of a spectroscopic programme aiming to investigate the kinematics of the local interstellar medium components towards the Southern Coalsack and Chamaeleon-Musca dark clouds are presented. The analysis is based upon high-resolution (R ~ 60,000) spectra of the insterstellar NaI D absorption lines towards 63 B-type stars (d l > 294 and -22 < b < 5. The radial velocities, column densities, velocity dispersions, colour excess and photometric distances to the stars are used to understand the kinematics and distribution of the interstellar cloud components. The analysis indicates that the interstellar gas is distributed in two extended sheet-like structures permeating the whole area, one at d < 60 pc and another around 120-150 pc from the Sun. The dust and gas feature around 120-150 pc seem to be part of an extended large scale feature of similar kinematic properties, supposedly identified with the interaction zone of the Local and Loop I bubbles.

  5. Iron: A Key Element for Understanding the Origin and Evolution of Interstellar Dust

    CERN Document Server

    Dwek, Eli

    2016-01-01

    The origin and depletion of iron differ from all other abundant refractory elements that make up the composition of the interstellar dust. Iron is primarily synthesized in Type Ia supernovae (SNe Ia) and in core collapse supernovae (CCSN), and is present in the outflows from AGB stars. Only the latter two are observed to be sources of interstellar dust, since searches for dust in SN~Ia have provided strong evidence for the absence of any significant mass of dust in their ejecta. Consequently, more than 65% of the iron is injected into the ISM in gaseous form. Yet, ultraviolet and X-ray observations along many lines of sight in the ISM show that iron is severely depleted in the gas phase compared to expected solar abundances. The missing iron, comprising about 90% of the total, is believed to be locked up in interstellar dust. This suggests that most of the missing iron must have precipitated from the ISM gas by cold accretion onto preexisting silicate, carbon, or composite grains. Iron is thus the only elemen...

  6. Ion-Neutral Collisions in the Interstellar Medium: Wave Damping and Elimination of Collisionless Processes

    CERN Document Server

    Spangler, Steven R; Redfield, Seth

    2010-01-01

    Most phases of the interstellar medium contain neutral atoms in addition to ions and electrons. This introduces differences in plasma physics processes in those media relative to the solar corona and the solar wind at a heliocentric distance of 1 astronomical unit. In this paper, we consider two well-diagnosed, partially-ionized interstellar plasmas. The first is the Diffuse Ionized Gas (DIG) which is probably the extensive phase in terms of volume. The second is the gas that makes up the Local Clouds of the Very Local Interstellar Medium (VLISM). Ion-neutral interactions seem to be important in both media. In the DIG, ion-neutral collisions are relatively rare, but sufficiently frequent to damp magnetohydrodynamic (MHD) waves (as well as propagating MHD eddies) within less than a parsec of the site of generation. This result raises interesting questions about the sources of turbulence in the DIG. In the case of the VLISM, the ion-neutral collision frequency is higher than that in the DIG, because the hydroge...

  7. The interstellar environment in the outer Galaxy as seen in gamma rays by Fermi

    CERN Document Server

    Tibaldo, Luigi; Mizuno, Tsunefumi

    2010-01-01

    Gamma-ray emission produced by interactions between cosmic rays (CRs) and interstellar gas traces the product of their densities throughout the Milky Way. The outer Galaxy is a privileged target of investigation to separate interstellar structures seen along the line of sight. Recent observations by the Fermi Large Area Telescope (LAT) shed light on open questions of the EGRET era about the distribution of CR densities and the census of the interstellar medium. The gradient of gamma-ray emissivities measured in the outer Galaxy is significantly flatter than predictions from widely used CR propagation models given the rapid decline of putative CR sources beyond the solar circle. Large propagation volumes, with halo heights up to 20 kpc, or a flat CR source distribution are required to match the data. Other viable possibilities include non-uniform CR diffusion properties or more gas than accounted for by the radio/mm-wave data. Gamma-ray data constrain the evolution of the Xco=N(H2)/W(CO) ratio within a few kpc...

  8. Enhanced Turbulence in M82 and M51 from Observations of Interstellar CH+

    Science.gov (United States)

    Ritchey, Adam M.; Welty, Daniel E.; Wallerstein, George

    2015-01-01

    Recent observations of diffuse molecular gas in M82 toward SN 2014J and in M51 toward its companion galaxy NGC 5195 have led to the discovery of high CH+ abundances in these extragalactic lines of sight. The column densities of CH+ are much higher in these directions (relative to the CH column densities) than would be expected based on other properties of the material. The equivalent widths of the λ5780.5 and λ5797.1 diffuse interstellar bands, for example, are suggestive of weak ambient radiation fields and/or significantly shielded environments, where the CH+ abundance would normally be expected to be rather low. We interpret these findings within the framework of recent models of turbulent dissipation regions, which find that the CH+ abundance is directly proportional to the average turbulent dissipation rate and inversely proportional to the square of the gas density. The high CH+ abundances toward SN 2014J and NGC 5195 then suggest that the average turbulent dissipation rates could be significantly enhanced in M82 and M51 (relative to typical values characterizing the local Galactic interstellar medium). As both M82 and M51 are interacting with neighboring galaxies, such enhanced interstellar turbulence could be due to those interactions, either directly (i.e., as a result of the gravitational encounter) or indirectly (e.g., through increased star formation and supernova rates).

  9. Chemistry of nitrile anions in the interstellar medium

    Energy Technology Data Exchange (ETDEWEB)

    Carles, S.; Le Garrec, J.-L.; Biennier, L. [Institut de Physique de Rennes, Département de Physique Moléculaire, Astrophysique de Laboratoire, UMR CNRS 6251, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex (France); Guillemin, J.-C. [Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837,35708 Rennes Cedex 7 (France)

    2015-12-31

    Despite the extreme conditions of temperature (down to 10K) and density (down to 100 molecules/cm{sup 3}), the giant molecular clouds and the circumstellar envelopes present a rich and complex chemistry. To date, more than 180 molecules have been detected in the InterStellar Medium (ISM) with a large abundance of nitriles (RC≡N). In addition, several anions have been recently observed in this medium: C{sub 4}H{sup ¯}, C{sub 6}H{sup ¯}, C{sub 8}H{sup ¯}, CN{sup ¯}, C{sub 3}N{sup ¯} and C{sub 5}N{sup ¯}. These last species should play a key role in the molecular growth towards complexity. To explore this hypothesis, their reactivity must be studied in the laboratory. The FALP-MS and the CRESU experimental apparatuses of the Rennes University are able to measure absolute rate coefficient of various chemical reactions, including the ion – molecule reactions, in gas phase at low temperature (from 300K for the FALP-MS down to 15K for the CRESU). Therefore, these experimental tools are particularly adapted to the kinetic studies of reactions potentially involved in the Interstellar Medium. One of the difficulties encountered in experiments with anions is their generation. We describe here the formation of the CN{sup ¯} and C{sub 3}N{sup ¯} anions by dissociative electron attachment on the molecular precursors BrCN and BrC{sub 3}N.

  10. Differential adsorption of CHON isomers at interstellar grain surfaces

    Science.gov (United States)

    Lattelais, M.; Pauzat, F.; Ellinger, Y.; Ceccarelli, C.

    2015-06-01

    Context. The CHON generic chemical formula covers different isomers such as isocyanic acid (HNCO), cyanic acid (HOCN), fulminic acid (HCNO), and isofulminic acid (HONC); the first three have been identified in a large variety of environments in the interstellar medium (ISM). Several phenomena could be at the origin of the observed abundances, such as different pathways of formation and destruction involving gas phase reactions with different possible activation barriers and/or surface processes depending on the local temperature and the nature of the support. Aims: The scope of this article is to shed some light on the interaction of the CHON isomers with interstellar grains as a function of the nature of the surface and to determine the corresponding adsorption energies in order to find whether this phenomenon could play a role in the abundances observed in the ISM. Methods: The question was addressed by means of numerical simulations using first principle periodic density functional theory (DFT) to represent the grain support as a solid of infinite dimension. Results: Regardless of the nature of the model surface (water ice, graphene, silica), two different classes of isomers were identified: weakly bound (HNCO and HCNO) and strongly bound (HOCN and HONC), with the adsorption energies of the latter group being about twice those of the former. The range of the adsorption energies is (from highest to lowest) HOCN > HONC > HNCO > HCNO. They are totally disconnected from the relative stabilities, which range from HNCO > HOCN > HCNO > HONC. Conclusions: The possibility of hydrogen bonding is the discriminating factor in the trapping of CHON species on grain surfaces. Whatever the environment, differential adsorption is effective and its contribution to the molecular abundances should not be ignored. The theoretical adsorption energies provided here could be profitably used for a more realistic modeling of molecule-surfaces interactions.

  11. Diffuse interstellar bands in M33

    CERN Document Server

    Smith, Keith T; Evans, Christopher J; Cox, Nick L J; Sarre, Peter J

    2013-01-01

    We present the first sample of diffuse interstellar bands (DIBs) in the nearby galaxy M33. Studying DIBs in other galaxies allows the behaviour of the carriers to be examined under interstellar conditions which can be quite different from those of the Milky Way, and to determine which DIB properties can be used as reliable probes of extragalactic interstellar media. Multi-object spectroscopy of 43 stars in M33 has been performed using Keck/DEIMOS. The stellar spectral types were determined and combined with literature photometry to determine the M33 reddenings E(B-V)_M33. Equivalent widths or upper limits have been measured for the {\\lambda}5780 DIB towards each star. DIBs were detected towards 20 stars, demonstrating that their carriers are abundant in M33. The relationship with reddening is found to be at the upper end of the range observed in the Milky Way. The line of sight towards one star has an unusually strong ratio of DIB equivalent width to E(B-V)_M33, and a total of seven DIBs were detected towards...

  12. Airborne and laboratory studies of interstellar PAHs

    Science.gov (United States)

    Allamandola, L. J.; Sandford, S. A.; Hudgins, D. M.; Witteborn, Fred C.

    1995-01-01

    A brief history of the observations which have led to the hypothesis that polycyclic aromatic hydrocarbons (PAH's) are the carriers of the widespread interstellar emission features near 3050, 1615, '1300' and 890 cm(exp -1) (3.29, 6.2, '7.7', and 11.2 mu m) is presented. The central role of airborne spectroscopy is stressed. The principal reason for the assignment to PAH's was the resemblance of the interstellar emission spectrum to the laboratory absorption spectra of PAH's and PAH-like materials. Since precious little information was available on the properties of PAH's in the forms that are thought to exist under interstellar conditions -isolated and ionized in the emission zones, with the smallest PAH's being dehydrogenated- there was a need for a spectral data base on PAH's taken in these states. Here, the relevant infrared spectroscopic properties of PAH's will be reviewed. These laboratory spectra show that relative band intensities are severely altered and that band frequencies shift. It is shown that these new data alleviate several of the spectroscopic criticisms previously leveled at the hypothesis.

  13. Cold gas and the disruptive effect of a young radio jet

    CERN Document Server

    Morganti, R; Maccagni, F M; Gereb, K; Oonk, J B R; Tadhunter, C N

    2015-01-01

    Newly born and young radio sources are in a delicate phase of their life. Their jets are fighting their way through the surrounding gaseous medium, strongly experiencing this interaction while, at the same time, impacting and affecting the interstellar medium (ISM). Here we present the results from two studies of HI (in absorption) and molecular gas illustrating what can be learned from these phases of the gas. We first describe a statistical study with the WSRT. The study shows that the young radio sources not only have an higher detection rate of HI, but also systematically broader and more asymmetric HI profiles, most of them blueshifted. This supports the idea that we are looking at young radio jets making their way through the surrounding ISM, which also appears to be, on average, richer in gas than in evolved radio sources. Signatures of the impact of the jet are seen in the kinematics of the gas. However, even among the young sources, we identify a population that remains undetected in HI even after st...

  14. Spatial and Temporal Variations in Interstellar Absorption toward HD 72127AB

    CERN Document Server

    Welty, Daniel E; Hobbs, L M

    2008-01-01

    New optical spectra of Ca II and Na I toward HD 72127AB provide additional evidence for both spatial and temporal variations in the complex interstellar absorption along the two sight lines; archival UV spectra yield information on the abundances, depletions, and physical conditions in the gas toward 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(H) ~ 2.5 x 10^{20} cm^{-2}] and the depletions and ionization in the main components at low LSR velocities also are similar. Toward HD 72127A, the main components are relatively cool (T 5000 K) may be largely responsible for the enhanced abundances of those trace neutral species toward HD 72127B. If the main components toward HD 72127AB are associated with material in the Vela SNR, the differences in abundances and physical conditions occur on scales of about 1100 AU.

  15. Molecular anions in circumstellar envelopes, interstellar clouds and planetary atmospheres: quantum dynamics of formation and evolution

    CERN Document Server

    Carelli, Fabio

    2012-01-01

    For decades astronomers and astrophysicists believed that only positively charged ions were worthy of relevance in drawing the networks for possible chemical reactions in the interstellar medium, as well as in modeling the physical conditions in most of astrophysical environments. Thus, molecular negative ions received minor attention until their possible existence was observationally confirmed (discovery of the first interstellar anion, C6H-), about thirty years after the first physically reasonable proposal on their actual detection was theoretically surmised by E.Herbst. In an astrophysical context, their role should be then found in their involvement in the charge balance as well as in the chemical evolution of the considered environment: depending on their amount and on the global gas density, in fact, the possible evolutive scenario could be susceptible of marked variations on the estimated time needed for reaching the steady state, their presence having thus also important repercussions on the final ch...

  16. Ubiquitous interstellar diamond and SiC in primitive chondrites - Abundances reflect metamorphism

    Science.gov (United States)

    Huss, Gary R.

    1990-01-01

    It is shown here that interstellar diamond and SiC were incorporated into all groups of chondrite meteorites. Abundances rapidly go to zero with increasing metamorphic grade, suggesting that metamorphic destruction is responsible for the apparent absence of these grains in most chondrites. In unmetamorphosed chondrites, abundances normalized to matrix content are similar for different classes. Diamond samples from chondrites of different classes have remarkably similar noble-gas constants and isotropic compositions, although constituent diamonds may have come from many sources. SiC seems to be more diverse, partly because grains are large enough to measure individually, but average characteristics seem to be similar from meteorite to meteorite. These observations suggest that various classes of chondritic meteorites sample the same solar system-wide reservoir of interstellar grains.

  17. Vacuum ultraviolet detection of the VLISM-heliosphere interaction. [very local interstellar medium

    Science.gov (United States)

    Judge, D. L.; Gangopadhyay, P.; Ogawa, H. S.; Blum, P.

    1992-01-01

    As the neutral components of the interstellar gas flow through the heliosphere their spatial distribution is modified by charge exchange with the solar plasma, photoionization, and radiation pressure. The deep space probes Pioneers 10/11 and Voyagers 1/2 have provided an opportunity to investigate this distribution through VUV observations of the heliospheric glow. Since the interactions of the inflowing neutrals with the heliosphere depend on both space and time it is particularly useful to have multiple spacecraft observations. Pioneer 10 is in the downstream region of the inflowing interstellar breeze at 50 AU while Pioneer 11 and Voyager 2 are upstream at about 30 AU. Voyager 1 is also upstream at about 40 AU but at a heliographic latitude of + 30 deg. Both temporal and spatial effects are expected to be quite different for the upstream and downstream regions. Some of the recent VUV data and its implications with respect to the heliospheric structure will be presented.

  18. MaNN: Multiple Artificial Neural Networks for modelling the Interstellar Medium

    CERN Document Server

    Grassi, T; Piovan, L; Buonomo, U; Chiosi, C

    2011-01-01

    Modelling the complex physics of the Interstellar Medium (ISM) in the context of large-scale numerical simulations is a challenging task. A number of methods have been proposed to embed a description of the ISM into different codes. We propose a new way to achieve this task: Artificial Neural Networks (ANNs). The ANN has been trained on a pre-compiled model database, and its predictions have been compared to the expected theoretical ones, finding good agreement both in static and in dynamical tests run using the Padova Tree-SPH code \\textsc{EvoL}. A neural network can reproduce the details of the interstellar gas evolution, requiring limited computational resources. We suggest that such an algorithm can replace a real-time calculation of mass elements chemical evolution in hydrodynamical codes.

  19. Molecular Dynamics Simulations of CO2 Formation in Interstellar Ices

    CERN Document Server

    Arasa, Carina; van Dishoeck, Ewine F; Kroes, Geert-Jan

    2013-01-01

    CO2 ice is one of the most abundant components in ice-coated interstellar ices besides H2O and CO, but the most favorable path to CO2 ice is still unclear. Molecular dynamics calculations on the ultraviolet photodissociation of different kinds of CO-H2O ice systems have been performed at 10 K in order to demonstrate that the reaction between CO and an OH molecule resulting from H2O photodissociation through the first excited state is a possible route to form CO2 ice. However, our calculations, which take into account different ice surface models, suggest that there is another product with a higher formation probability ((3.00+-0.07)x10-2), which is the HOCO complex, whereas the formation of CO2 has a probability of only (3.6+-0.7)x10-4. The initial location of the CO is key to obtain reaction and form CO2: the CO needs to be located deep into the ice. The HOCO complex becomes trapped in the cold ice surface in the trans-HOCO minimum because it quickly loses its internal energy to the surrounding ice, preventi...

  20. New Large Interstellar Molecules Detected with the GBT

    Science.gov (United States)

    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.

  1. The Ingenious Theory of Interstellar Trade

    Science.gov (United States)

    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

  2. NEW ULTRAVIOLET EXTINCTION CURVES FOR INTERSTELLAR DUST IN M31

    Energy Technology Data Exchange (ETDEWEB)

    Clayton, Geoffrey C. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Gordon, Karl D.; Bohlin, R. C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bianchi, Luciana C. [Department of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Massa, Derck L.; Wolff, Michael J. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Fitzpatrick, Edward L., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: bohlin@stsci.edu, E-mail: kgordon@stsci.edu, E-mail: bianchi@jhu.edu, E-mail: mjwolff@spacescience.org, E-mail: edward.fitzpatrick@villanova.edu [Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States)

    2015-12-10

    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.

  3. Chemical Simulations of Prebiotic Molecules: Interstellar Ethanimine Isomers

    Science.gov (United States)

    Quan, Donghui; Herbst, Eric; Corby, Joanna F.; Durr, Allison; Hassel, George

    2016-06-01

    The E- and Z-isomers of ethanimine (CH3CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s-1 in the foreground of continuum emission generated by H ii regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

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

    Science.gov (United States)

    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.

  5. New Ultraviolet Extinction Curves for Interstellar Dust in M31

    CERN Document Server

    Clayton, Geoffrey C; Bianchi, Luciana C; Massa, Derck L; Fitzpatrick, Edward L; Bohlin, R C; Wolff, Michael J

    2015-01-01

    New low-resolution UV spectra of a sample of reddened OB stars in M31 were obtained with HST/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 S/N than previous studies. Direct measurements of N(H I) were made using the Ly$\\alpha$ absorption lines enabling gas-to-dust ratios to be calculated. The sightlines have a range in galactocentric distance of 5 to 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 produc...

  6. The pathways of C: from AGB stars, to the Interstellar Medium, and finally into the protoplanetary disk

    Science.gov (United States)

    Trigo-Rodriguez, J. M.; Garcia-Hernandez, D. A.

    2011-05-01

    The origin, and role of C in the formation of first solar system aggregates is described. Stellar grains evidence demonstrates that Asymptotic Giant Branch (AGB) stars were nearby to the solar nebula at the time of solar system formation. Such stars continue to burn H and He in shells that surround the C-O core. During their evolution, flashes occur in the He shell and the C, and O produced are eventually dredged up into the star's envelop and then to the stellar surface, and finally masively ejected to the interstellar medium (IM). Once in a molecular cloud, the electrophilicity of C makes this element reactable with the surrounding gas to produce different molecular species. Primitive meteorites, particularly these known as chondrites, preserved primeval materials of the disk. The abundances of short-lived radionuclides (SLN), inferred to have been present in the early solar system (ESS), are a constraint on the birth and early evolution of the solar system as their relatively short half lives do not allow the observed abundances to be explained by galactic chemical evolution processes. We present a model of a 6.5 solar masses star of solar metallicity that simultaneously match the abundances of SLNs inferred to have been present in the ESS by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material, and taking into account a time interval between injection of SLNs and consolidation of chondrites equal to 0.53 Myr [2]. Such a polluting source does not overproduce 53Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements. The AGB stars released O- and C-rich gas with important oxidizing implications to first solar system materials as recently detected in circumstellar environments [3]. REF: [1] Lada C.J. and Lada E.A. 2003. Ann. Rev. A&A. 41: 57; [2] Trigo-Rodriguez J.M. et al. 2009. MAPS 44: 627; [3] Decin L. et al. 2010. Nature 467: 64.

  7. Widespread rotationally hot hydronium ion in the galactic interstellar medium

    Energy Technology Data Exchange (ETDEWEB)

    Lis, D. C.; Phillips, T. G. [Cahill Center for Astronomy and Astrophysics 301-17, California Institute of Technology, Pasadena, CA 91125 (United States); Schilke, P.; Comito, C.; Higgins, R., E-mail: dcl@caltech.edu, E-mail: tgp@submm.caltech.edu, E-mail: schilke@ph1.uni-koeln.de, E-mail: ccomito@ph1.uni-koeln.de, E-mail: higgins@ph1.uni-koeln.de [I. Physikalisches Institut, University of Cologne, Zülpicher Strasse 77, D-50937 Köln (Germany); and others

    2014-04-20

    We present new Herschel observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ∼500 K, rotational temperatures characterizing the population of the highly excited metastable H{sub 3}O{sup +} rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ∼380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic-ray fluxes, shocks, and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and the temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation of the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process not limited to the active environments associated with galactic nuclei.

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

    Energy Technology Data Exchange (ETDEWEB)

    De Luca, M.; Gerin, M.; Falgarone, E. [LERMA-LRA, UMR 8112 du CNRS, Observatoire de Paris, Ecole Normale Superieure, UPMC and UCP, 24 rue Lhomond, 75231 Paris Cedex 05 (France); Gupta, H.; Drouin, B. J.; Pearson, J. C. [Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109 (United States); Neufeld, D. [Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Teyssier, D. [European Space Astronomy Centre, ESA, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Lis, D. C.; Monje, R.; Phillips, T. G. [California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125 (United States); Goicoechea, J. R.; Godard, B.; Bell, T. A. [Centro de Astrobiologia (CSIC/INTA), Ctra. de Torrejon a Ajalvir, km 4, 28850 Torrejon de Ardoz, Madrid (Spain); Coutens, A. [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France)

    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.

  9. An economic analysis of US oil and gas laws:a case study of the legal issues surrounding shale gas in Pennsylvania%美国油气法特殊规则的经济实质分析--以宾夕法尼亚州页岩气司法实践为例

    Institute of Scientific and Technical Information of China (English)

    袁华江

    2014-01-01

    美国页岩气的发展与政府的财税支持和私营企业的技术突破紧密相关,页岩气革命的成功推动了美国经济的复苏,促进了美国财产法在社会发展中的适用创新。关于页岩气的司法实践是美国发展本国经济的制度要求,突出体现了判例法的灵活性、反映社会发展的及时性优点。美国页岩气产权的特殊确权规则可为我国矿产资源管理提供法制参考。%US shale gas development is closely related to government ifscal support and to the technological advances made by private enterprise. The success of the shale gas revolution has promoted the economic recovery of the US, and the application of American property law has been used to deal with various concerns regarding shale gas exploitation. The requirements of the American economy have led to legal action with regard to shale gas, and this has highlighted the advantages of the lfexibility of case law. While the particular laws afifrming US shale gas rights provide a legal reference for rationalizing shale gas rights and exploitation, coalbed methane property rights in China are not similarly rationalized.

  10. Condensation and Evaporation of Interstellar Clouds in Chemodynamical Models of Galaxies

    CERN Document Server

    Köppen, J; Hensler, G; Theis, Ch.

    1997-01-01

    The network of interactions between hot gas, cool clouds, massive stars, and stellar remnants used in the chemodynamical modeling of the interstellar medium is investigated for the types of its solutions. In a physically consistent formulation for the energy transfer during condensation, oscillations due to a cyclic switching between condensation and evaporation never occur. A closed-box system evolves in a hierarchy of equilibria: thermal balance in the cloud gas, star-formation self-regulated due to heating of the clouds by massive stars, and the balance of condensation and evaporation. Except for an initial transitory phase, the evolution of the metallicity follows that of the Simple Model quite closely. For galaxies with a high initial density, or if the condensation rate is low, the metals produced by the stars may remain stored in the hot gas phase even in evolved systems with low gas fractions.

  11. The effect of models of the interstellar media on the central mass distribution of galaxies

    Science.gov (United States)

    Christensen, C. R.; Governato, F.; Quinn, T.; Brooks, A. M.; Shen, S.; McCleary, J.; Fisher, D. B.; Wadsley, J.

    2014-05-01

    We compared the central mass distribution of dwarf and spiral galaxies simulated with three different models of the interstellar medium with increasing complexity: primordial (H+He) cooling, additional cooling via metal lines, and molecular hydrogen ( H2) with shielding of atomic and molecular hydrogen, in addition to metal-line cooling. We followed the evolution of four high-resolution, simulated galaxies with Vpeak gas was hotter and the feedback-heated gas cooled relatively slowly so less energy was required to expel it. When H2 was included, the accompanying shielding produced large amounts of clumpy, cold gas, and the supernova feedback was more highly concentrated. In contrast to the spiral galaxies, the dwarfs had similarly realistic concentrations and displayed similar behaviour across all models because their low metallicities resulted in smaller differences is the behaviour of the gas.

  12. Analysis of "Midnight" Tracks in the Stardust Interstellar Dust Collector: Possible Discovery of a Contemporary Interstellar Dust Grain

    Science.gov (United States)

    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.

  13. Stardust Interstellar Preliminary Examination IV: Scanning transmission X-ray microscopy analyses of impact features in the Stardust Interstellar Dust Collector

    Science.gov (United States)

    Butterworth, Anna L.; Westphal, Andrew J.; Tyliszczak, Tolek; Gainsforth, Zack; Stodolna, Julien; Frank, David R.; Allen, Carlton; Anderson, David; Ansari, Asna; Bajt, SašA.; Bastien, Ron K.; 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; Stadermann, Frank J.; Stephan, Thomas; Sterken, Veerle J.; Stroud, Rhonda M.; Sutton, Steven; Trieloff, Mario; Tsou, Peter; Tsuchiyama, Akira; Vekemans, Bart; Vincze, Laszlo; von Korff, Joshua; Wordsworth, Naomi; Zevin, Daniel; Zolensky, Michael E.

    2014-09-01

    We report the quantitative characterization by synchrotron soft X-ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector. Samples were analyzed in aerogel by acquiring high spatial resolution maps and high energy-resolution spectra of major rock-forming elements Mg, Al, Si, Fe, and others. We developed diagnostic screening tests to reject spacecraft secondary ejecta and terrestrial contaminants from further consideration as interstellar dust candidates. The results support an extraterrestrial origin for three interstellar candidates: I1043,1,30 (Orion) is a 3 pg particle with Mg-spinel, forsterite, and an iron-bearing phase. I1047,1,34 (Hylabrook) is a 4 pg particle comprising an olivine core surrounded by low-density, amorphous Mg-silicate and amorphous Fe, Cr, and Mn phases. I1003,1,40 (Sorok) has the track morphology of a high-speed impact, but contains no detectable residue that is convincingly distinguishable from the background aerogel. Twenty-two samples with an anthropogenic origin were rejected, including four secondary ejecta from impacts on the Stardust spacecraft aft solar panels, nine ejecta from secondary impacts on the Stardust Sample Return Capsule, and nine contaminants lacking evidence of an impact. Other samples in the collection included I1029,1,6, which contained surviving solar system impactor material. Four samples remained ambiguous: I1006,2,18, I1044,2,32, and I1092,2,38 were too dense for analysis, and we did not detect an intact projectile in I1044,3,33. We detected no radiation effects from the synchrotron soft X-ray analyses; however, we recorded the effects of synchrotron hard X-ray radiation on I1043,1,30 and I1047,1,34.

  14. Contour detection by surround suppression of texture

    NARCIS (Netherlands)

    Petkov, Nicolai; Tavares, JMRS; Jorge, RMN

    2007-01-01

    Based on a keynote lecture at Complmage 2006, Coimbra, Oct. 20-21, 2006, an overview is given of our activities in modelling and using surround inhibition for contour detection. The effect of suppression of a line or edge stimulus by similar surrounding stimuli is known from visual perception studie

  15. Multi-wavelength observations of a nearby multi-phase interstellar cloud

    CERN Document Server

    Nehme, C; Boulanger, F; Bourlot, J Le; Forets, G Pineau des; Falgarone, E

    2008-01-01

    High-resolution spectroscopic observations (UV HST/STIS and optical) are used to characterize the physical state and velocity structure of the multiphase interstellar medium seen towards the nearby (170 pc) star HD102065, located behind the tail of a cometary-shaped, infrared cirrus-cloud, in the area of interaction between the Sco-Cen OB association and the Local Bubble. We analyze interstellar components present along the line of sight by fitting multiple transitions from CO, CH, CH+, C I, S I, Fe I, Mg I, Mg II, Mn II, P II, Ni II, C II, N I, O I, Si III, C IV, and Si IV. The absorption spectra are complemented by H I, CO and C II emission-line spectra, H$_2$ column-densities derived from FUSE spectra, and IRAS images. Gas components of a wide range of temperatures and ionization states are detected along the line of sight. Most of the hydrogen column-density is in cold, diffuse, molecular gas at low LSR velocity. This gas is mixed with traces of warmer molecular gas traced by H2 in the J>2 levels, in whic...

  16. Observing Organic Molecules in Interstellar Gases: Non Equilibrium Excitation.

    Science.gov (United States)

    Wiesenfeld, Laurent; Faure, Alexandre; Remijan, Anthony; Szalewicz, Krzysztof

    2014-06-01

    In order to observe quantitatively organic molecules in interstellar gas, it is necessary to understand the relative importance of photonic and collisional excitations. In order to do so, collisional excitation transfer rates have to be computed. We undertook several such studies, in particular for H_2CO and HCOOCH_3. Both species are observed in many astrochemical environments, including star-forming regions. We found that those two molecules behave in their low-lying rotational levels in an opposite way. For cis methyl-formate, a non-equilibrium radiative transfer treatment of rotational lines is performed, using a new set of theoretical collisional rate coefficients. These coefficients have been computed in the temperature range 5 to 30 K by combining coupled-channel scattering calculations with a high accuracy potential energy surface for HCOOCH_3 -- He. The results are compared to observations toward the Sagittarius B2(N) molecular cloud. A total of 2080 low-lying transitions of methyl formate, with upper levels below 25 K, were treated. These lines are found to probe a cold (30 K), moderately dense (n ˜ 104 cm-3) interstellar gas. In addition, our calculations indicate that all detected emission lines with a frequency below 30 GHz are collisionally pumped weak masers amplifying the background of Sgr B2(N). This result demonstrates the generality of the inversion mechanism for the low-lying transitions of methyl formate. For formaldehyde, we performed a similar non-equilibrium treatment, with H_2 as the collisional partner, thanks to the accurate H_2CO - H_2 potential energy surface . We found very different energy transfer rates for collisions with para-H_2 (J=0) and ortho-H_2 (J=1). The well-known absorption against the cosmological background of the 111→ 101 line is shown to depend critically on the difference of behaviour between para and ortho-H_2, for a wide range of H_2 density. We thank the CNRS-PCMI French national program for continuous support

  17. Solar lens mission concept for interstellar exploration

    Science.gov (United States)

    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.

  18. Interstellar extinction by fractal polycrystalline graphite clusters?

    CERN Document Server

    Andersen, A C; Pustovit, V N; Niklasson, G A

    2001-01-01

    Certain dust particles in space are expected to appear as clusters of individual grains. The morphology of these clusters could be fractal or compact. To determine how these structural features would affect the interpretation of the observed interstellar extinction peak at $\\sim 4.6~\\mu$m, we have calculated the extinction by compact and fractal polycrystalline graphite clusters consisting of touching identical spheres. We compare three general methods for computing the extinction of the clusters, namely, a rigorous solution and two different discrete-dipole approximation methods.

  19. Diffuse Interstellar Bands and Their Families

    CERN Document Server

    Wszolek, B

    2006-01-01

    Diffuse interstellar bands (DIBs) still await an explanation. One expects that some progress in this field will be possible when all the known DIBs are divided into families in such a way that only one carrier is responsible for all bands belonging to the given family. Analysing high resolution optical spectra of reddened stars we try to find out spectroscopic families for two prominent DIBs, at 5780 and 5797 angstroms. Among the DIBs, observed in the spectral range from 5590 to 6830 angstroms, we have found 8 candidates to belong to 5780 spectroscopic family and the other 12 DIBs candidating to family of 5797 structure.

  20. Formation of Interstellar OH and CH

    Science.gov (United States)

    Kwak, Kyujin; Yoon, Jeongkwan; Hong, Seungyeong

    2017-01-01

    From the absorption spectra of bright UV-emitting stars, column densities of interstellar OH (3078 and 3082 Å) and CH (3886 and 3890 Å) have been measured simultaneously along about 20 sightlines. In order to understand the physical and chemical environments in which these two molecules exist, we perform numerical simulations by using Astrochem, a publically available astrochemical reaction code. We investigate the effect of cosmic ray, grain, environmental photon, and initial composition on the formation of these two molecules. We also compare our simulated results with observations of molecule-forming objects such as supernova remnants, molecular clouds, and evolved stars along the observed sightlines.

  1. Can spores survive in interstellar space?

    Science.gov (United States)

    Weber, P.; Greenberg, J. M.

    1985-01-01

    Experimental evidence is presented for the effects of very low temperature and UV radiation, characteristic of the interstellar medium, on the survival of bacteria. In the most general space environment, 10 percent survival times are only of the order of hundreds of years, too short for panspermia to work. In a substantial fraction of space within dark clouds, however, it is shown that, even with conservative figures, survival times as long as millions to tens of millions of years are attainable. In such conditions, clouds could transport organisms from one solar system to another in times significantly shorter than the mean survival time. This occurs with significant probability.

  2. Ambient Interstellar Pressure and Superbubble Evolution

    CERN Document Server

    Oey, M S

    2004-01-01

    High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous observed growth-rate discrepancy for supernova-driven superbubbles and stellar wind bubbles. Pressures of P/k ~ 1e5 cm-3 K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic ISM localizations. We demonstrate the sensitivity of shell growth to the ambient pressure, and suggest that superbubbles ultimately might serve as ISM barometers.

  3. Interstellar nomads: The problem of detecting comets

    Science.gov (United States)

    Jones, Eric M.; Newman, William I.; Campbell, Donald B.

    1993-01-01

    This paper shows that, using only a modest extrapolation of current phased-array radar and massively parallel processor computer technologies, radar transmitter in the outer solar system or in interstellar space could be used to detect comets passing within 1 or 2 AU of the transmitter. It discusses how this potential development could be instrumental to the colonisation of the outer solar system and beyond. This development is germane to contemporary investigations of the population of the Oort cloud as well as to the Search for Extraterrestrial Intelligence (SETI) question.

  4. A semi-analytic model of the turbulent multi-phase interstellar medium

    Science.gov (United States)

    Braun, H.; Schmidt, W.

    2012-04-01

    We present a semi-analytic model for the interstellar medium that considers local processes and structures of turbulent star-forming gas. A volume element of the interstellar medium is described as a multi-phase system, comprising a cold and a warm gas phase in effective (thermal plus turbulent) pressure equilibrium and a stellar component. The cooling instability of the warm gas feeds the cold phase, while various heating processes transfer cold gas to the warm phase. The cold phase consists of clumps embedded in diffuse warm gas, where only the molecular fraction of the cold gas may be converted into stars. The fraction of molecular gas is approximately calculated, using a Strömgren-like approach and the efficiency of star formation is determined by the state of the cold gas and the turbulent velocity dispersion on the clump length-scale. Gas can be heated by supernovae and ultraviolet emission of massive stars, according to the evolutionary stages of the stellar populations and the initial mass function. Since turbulence has a critical impact on the shape of the gaseous phases, on the production of molecular hydrogen and on the formation of stars, the consistent treatment of turbulent energy - the kinetic energy of unresolved motions - is an important new feature of our model. Besides turbulence production by supernovae and the cooling instability, we also take into account the forcing by large-scale motions. We formulate a set of ordinary differential equations, which statistically describes star formation and the exchange between the different budgets of mass and energy in a region of the interstellar medium with given mean density, size, metallicity and external turbulence forcing. By exploring the behaviour of the solutions, we find equilibrium states, in which the star formation efficiencies are consistent with observations. Kennicutt-Schmidt-like relations naturally arise from the equilibrium solutions, while conventional star formation models in

  5. LOCAL INTERSTELLAR MAGNETIC FIELD DETERMINED FROM THE INTERSTELLAR BOUNDARY EXPLORER RIBBON

    Energy Technology Data Exchange (ETDEWEB)

    Zirnstein, E. J.; Livadiotis, G.; McComas, D. J. [Southwest Research Institute, San Antonio, TX 78228 (United States); Heerikhuisen, J.; Pogorelov, N. V. [Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35899 (United States); Funsten, H. O., E-mail: ezirnstein@swri.edu [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2016-02-10

    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.

  6. The shape and composition of interstellar silicate grains

    NARCIS (Netherlands)

    Min, M.; Waters, L.B.F.M.; de Koter, A.; Hovenier, J.W.; Keller, L.P.; Markwick-Kemper, F.

    2007-01-01

    We investigate the composition and shape distribution of silicate dust grains in the interstellar medium. The effects of the amount of magnesium and iron in the silicate lattice are studied in detail. We fit the spectral shape of the interstellar 10 mu m extinction feature as observed towards the ga

  7. The shape and composition of interstellar silicate grains

    NARCIS (Netherlands)

    Min, M.; Waters, L.B.F.M.; de Koter, A.; Hovenier, J.W.; Keller, L.P.; Markwick-Kemper, F.

    2007-01-01

    We investigate the composition and shape distribution of silicate dust grains in the interstellar medium. The effects of the amount of magnesium and iron in the silicate lattice are studied in detail. We fit the spectral shape of the interstellar 10 mu m extinction feature as observed towards the

  8. The Interstellar Medium In Galaxies Seen A Billion Years After The Big Bang

    CERN Document Server

    Capak, P L; Jones, G; Casey, C M; Riechers, D; Sheth, K; Carollo, C M; Ilbert, O; Karim, A; LeFevre, O; Lilly, S; Scoville, N; Smolcic, V; Yan, L

    2015-01-01

    Evolution in the measured rest frame ultraviolet spectral slope and ultraviolet to optical flux ratios indicate a rapid evolution in the dust obscuration of galaxies during the first 3 billion years of cosmic time (z>4). This evolution implies a change in the average interstellar medium properties, but the measurements are systematically uncertain due to untested assumptions, and the inability to measure heavily obscured regions of the galaxies. Previous attempts to directly measure the interstellar medium in normal galaxies at these redshifts have failed for a number of reasons with one notable exception. Here we report measurements of the [CII] gas and dust emission in 9 typical (~1-4L*) star-forming galaxies ~1 billon years after the big bang (z~5-6). We find these galaxies have >12x less thermal emission compared with similar systems ~2 billion years later, and enhanced [CII] emission relative to the far-infrared continuum, confirming a strong evolution in the interstellar medium properties in the early u...

  9. Molecular evolution of contracting clouds - Basic methods and initial results. [interstellar processes

    Science.gov (United States)

    Gerola, H.; Glassgold, A. E.

    1978-01-01

    The relationship between the dynamics of the interstellar gas and the thermal and chemical effects associated with interstellar molecules and dust is investigated. The evolution of a rather massive isolated initially diffuse cloud under self-gravity is studied, using the equations of hydrodynamics; only radial motions are considered, and the heat, chemical, and radiative-transfer equations are solved simultaneously with the hydrodynamic equations. The relevant chemistry is described along with the thermal model, the radiative-transfer process, and the numerical methods employed. Results for a contracting cloud are discussed in terms of the problem of initial conditions, the dynamical evolution of the cloud, its chemical and thermal evolution, time scales, and column densities. It is shown that the chemical evolution of a massive contracting diffuse cloud is sensitive to such physical properties as temperature and ion abundances, that warm and cool versions of a typical cloud evolve differently, and that the physical origin of this effect is the level of heating due to H2 formation on interstellar dust grains.

  10. Laboratory Rotational Spectroscopy of the Interstellar Diatomic Hydride Ion SH+ (X 3Σ-)

    Science.gov (United States)

    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.

  11. Ion-Neutral Collisions in the Interstellar Medium: Wave Damping and Elimination of Collisionless Processes

    Science.gov (United States)

    Spangler, Steven R.; Savage, Allison H.; Redfield, Seth

    2011-09-01

    Most phases of the interstellar medium contain neutral atoms in addition to ions and electrons. This introduces differences in plasma physics processes in those media relative to the solar corona and the solar wind at a heliocentric distance of 1 astronomical unit. In this paper, we consider two well-diagnosed, partially-ionized interstellar plasmas. The first is the Warm Ionized Medium (WIM) which is probably the most extensive phase in terms of volume. The second is the gas of the Local Clouds of the Very Local Interstellar Medium (VLISM). Ion-neutral interactions seem to be important in both media. In the WIM, ion-neutral collisions are relatively rare, but sufficiently frequent to damp magnetohydrodynamic (MHD) waves (as well as propagating MHD eddies) within less than a parsec of the site of generation. This result raises interesting questions about the sources of turbulence in the WIM. In the case of the VLISM, the ion-neutral collision frequency is higher than that in the WIM, because the hydrogen is partially neutral rather than fully ionized. We present results showing that prominent features of coronal and solar wind turbulence seem to be absent in VLISM turbulence. For example, ion temperature does not depend on ion mass. This difference may be due to ion-neutral collisions, which distribute power from more effectively heated massive ions such as iron to other ion species and neutral atoms.

  12. High-resolution IUE observations of interstellar absorption lines in the Vela supernova remnant

    Science.gov (United States)

    Jenkins, E. B.; Wallerstein, G.; Silk, J.

    1984-01-01

    Ultraviolet spectra of 45 stars in the vicinity of the Vela supernova remnant were recorded by the short-wavelength echelle spectrograph aboard the International Ultraviolet Explorer (IUE). Over one-third of the stars show interstellar absorption lines at large radial velocities (greater than 60 km/s). The mapping of these high-velocity components in the sky suggests the motions are chaotic, rather than from a coherent expansion of the remnant material. In accord with earlier conclusions from Copernicus data, the gas at high velocity exhibits higher than normal ionization and shows substantially less depletion of nonvolatile elements than normal interstellar material at low velocities. Relatively strong lines from neutral carbon in the two excited fine-structure states indicate that the neutral clouds within the remnant have had their pressures enhanced by the passage of the blast wave from the supernova. Also, the remnant seems to show a significant enhancement in the abundances of low-velocity Si IV, C IV, and N V over those found in the general interstellar medium.

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

    CERN Document Server

    Aller, Monique C; York, Donald G; Welty, Daniel E; Vladilo, Giovanni; Som, Debopam

    2014-01-01

    Absorption lines in the spectra of distant quasars whose sightlines pass through foreground galaxies provide a valuable tool to probe the dust and gas compositions of the interstellar medium (ISM) in galaxies. The first evidence of silicate dust in a quasar absorption system (QAS) was provided through our detection of the 10 micron silicate feature in the z=0.52 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 QASs at 0.1interstellar silicate absorption features among the absorbers. This suggests that the silicate dust grain properties in these distant galaxies may differ relat...

  14. Following the Interstellar History of Carbon: From the Interiors of Stars to the Surfaces of Planets

    Science.gov (United States)

    Ziurys, L. M.; Halfen, D. T.; Geppert, W.; Aikawa, Y.

    2016-12-01

    The chemical history of carbon is traced from its origin in stellar nucleosynthesis to its delivery to planet surfaces. The molecular carriers of this element are examined at each stage in the cycling of interstellar organic material and their eventual incorporation into solar system bodies. The connection between the various interstellar carbon reservoirs is also examined. Carbon has two stellar sources: supernova explosions and mass loss from evolved stars. In the latter case, the carbon is dredged up from the interior and then ejected into a circumstellar envelope, where a rich and unusual C-based chemistry occurs. This molecular material is eventually released into the general interstellar medium through planetary nebulae. It is first incorporated into diffuse clouds, where carbon is found in polyatomic molecules such as H2CO, HCN, HNC, c-C3H2, and even C60+. These objects then collapse into dense clouds, the sites of star and planet formation. Such clouds foster an active organic chemistry, producing compounds with a wide range of functional groups with both gas-phase and surface mechanisms. As stars and planets form, the chemical composition is altered by increasing stellar radiation, as well as possibly by reactions in the presolar nebula. Some molecular, carbon-rich material remains pristine, however, encapsulated in comets, meteorites, and interplanetary dust particles, and is delivered to planet surfaces.

  15. Graphene Solar Photon Sails and Interstellar Arks

    Science.gov (United States)

    Matloff, G. L.

    2014-06-01

    A review of conceptual interstellar generation ships is followed by a presentation of optical and thermal properties of graphene and a discussion of kinematics/thermal-aspects of the solar-acceleration phase of a starship propelled by a graphene hollowbody solar-photon sail. The spacecraft departs from an initially parabolic solar orbit and the sail is oriented normal to the Sun during solar-acceleration. Perihelion is constrained to 0.1 AU because humans can tolerate ~3g for several hours without lasting effects. The 5 × 106 kg payload mass and 9.16 × 106 kg sail mass are applied as cosmic-ray shielding for the ship's 20-50 person population during the ~1,400-year cruise phase. Artificial gravity, the Coriolis Effect, closed-environment agriculture, illumination, on-board energy requirements, thermal dissipation, and hygiene/recreation are considered in a discussion of habitat design. Many concepts for mid-course trajectory correction are discussed including a new one that expels mass collected by a Cassenti toroidal ion scoop in a direction normal to the ship's trajectory. Although acceleration is affected by the unfurled sail, other options are discussed, as is the problem of protection from interstellar-dust erosion. As well as presenting the total mass budget, the conclusion reviews published variations and modifications on the generation-ship theme.

  16. Galactic civilizations - Population dynamics and interstellar diffusion

    Science.gov (United States)

    Newman, W. I.; Sagan, C.

    1981-01-01

    A model is developed of the interstellar diffusion of galactic civilizations which takes into account the population dynamics of such civilizations. The problem is formulated in terms of potential theory, with a family of nonlinear partial differential and difference equations specifying population growth and diffusion for an organism with advantageous genes that undergoes random dispersal while increasing in population locally, and a population at zero population growth. In the case of nonlinear diffusion with growth and saturation, it is found that the colonization wavefront from the nearest independently arisen galactic civilization can have reached the earth only if its lifetime exceeds 2.6 million years, or 20 million years if discretization can be neglected. For zero population growth, the corresponding lifetime is 13 billion years. It is concluded that the earth is uncolonized not because interstellar spacefaring civilizations are rare, but because there are too many worlds to be colonized in the plausible colonization lifetime of nearby civilizations, and that there exist no very old galactic civilizations with a consistent policy of the conquest of inhabited worlds.

  17. Temperature fluctuations of interstellar dust grains

    CERN Document Server

    Horn, Kobi; Biham, Ofer

    2007-01-01

    The temperatures of interstellar dust grains are analyzed using stochastic simulations, taking into account the grain composition and size and the discreteness of the photon flux. [...] The distribution of grain temperatures is calculated for a broad range of grain sizes and for different intensities of the interstellar radiation field, relevant to diffuse clouds and to PDRs. The dependence of the average grain temperature on its size is shown for different irradiation intensities. It is found that the average temperatures of grains with radii smaller than about 0.02 $\\mu$m are reduced due to the fluctuations. The average temperatures of grains of radii larger than about 0.35 $\\mu$m are also slightly reduced due to their more efficient emission of infrared radiation, particularly when exposed to high irradiation intensities. The average temperatures of silicate and carbonaceous grains are found to depend on the radiation field intensity X_MMP according to ~X_MMP^gamma, where the exponent gamma depends on the...

  18. Interstellar sulfur isotopes and stellar oxygen burning

    CERN Document Server

    Chin, Y N; Whiteoak, J B; Langer, N; Churchwell, E B; Chin, Y N

    1995-01-01

    A 12C32S, 13C32S, 12C34S, and 12C33S J = 2 - 1 line survey has been made to study interstellar 32S/34S and 34S/33S ratios from the galactic disk. The four CS isotopomers were detected in 20 star forming regions with galactocentric distances between 3 and 9 kpc. From a comparison of line velocities, the C33S J = 2 - 1 rest frequency is about 250 kHz below the value given in the Lovas (1992) catalog. Taking 12C/13C ratios from Wilson & Rood (1994) and assuming equal 12C32S and 13C32S excitation temperatures and beam filling factors, 12C32S opacities are in the range 3 to 15; average 32S/34S and 34S/33S isotope ratios are 24.4 +/- 5.0 and 6.27 +/- 1.01, respectively. While no systematic variation in the 34S/33S isotope ratio is found, the 32S/34S ratio increases with galactocentric distance when accounting for the 12C/13C gradient of the galactic disk. A fit to the unweighted data yields 32S/34S = 3.3 +/- 0.5 (dGC/kpc) + 4.1 +/- 3.1 with a correlation coefficient of 0.84. Since the interstellar sulfur (S) is...

  19. Prospects for the Detection of Interstellar Cyanovinylidene

    Science.gov (United States)

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

    2009-08-01

    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 HC3NH+ + e - dissociative recombination products, by rearrangements of the neutral chain radical HC3NH 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, NC2(H)O, and propynal, HC3(H)O, with structures qualitatively resembling cyanovinylidene, served to prove the adequacy of the calculational procedures employed.

  20. Facts and Artifacts in Interstellar Diamond Spectra

    Science.gov (United States)

    Mutschke, H.; Dorschner, J.; Henning, T.; Jager, C.; Ott, U.

    1995-12-01

    Absorption spectra of presolar diamonds extracted from the Murchison meteorite have been measured in the extended wavelength range 0.2--500 mu m in order to make available optical properties of this supposed component of interstellar carbon dust. In contrast to terrestrial natural and synthetic diamonds, spectra of the meteoritic diamonds show prominent bands in the middle-IR. In this Letter, experimental evidence is presented that the OH band at 3200 cm-1 and the CH bands in the 2800--3000 cm-1 range are not intrinsic features of the diamonds and that the band at 1100 cm-1 contains an artificial component due to the extraction procedure. In addition, in our spectra a conspicuous band at 120 cm-1 was found. If the intrinsic character of this band, which, up to now, is unidentified, is confirmed, it would offer a chance to observe interstellar diamonds, e.g., by the ISO satellite. We encourage laboratory astrophysicists and observers to study this promising possibility.