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Sample records for interstellar extinction band

  1. Interstellar Extinction

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

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

    SciTech Connect

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

    2011-06-01

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

  5. Neutral and ionized polycyclic aromatic hydrocarbons, diffuse interstellar bands and the ultraviolet extinction curve

    NASA Technical Reports Server (NTRS)

    Salama, Farid; Allamandola, Louis John

    1993-01-01

    Neutral naphthalene C10H8, phenanthrene C14H10 and pyrene C16H10 absorb strongly in the ultraviolet region and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these polycyclic aromatic hydrocarbons (PAHs) absorb in the visible C10H8(+) has 13 discrete absorption bands which fall between 6800 and 4500 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBs at 6520 and 6151 A, other strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in Ne, wavelengths which fall very close to the strongest DIB at 4430 A. If C16H10(+) or a closely related pyrene-like ion, is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. An intense, very broad UV-to-visible continuum is reported which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR radiation.

  6. Diffuse Interstellar Bands and the Ultraviolet Extinction Curves: The Missing Link Revisited

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    A large number of interstellar absorption features at ∼4000 Å–1.8 μm, known as the “diffuse interstellar bands” (DIBs), remains unidentified. Most recent works relate them to large polycyclic aromatic hydrocarbon (PAH) molecules or ultrasmall carbonaceous grains which are also thought to be responsible for the 2175 \\mathringA extinction bump and/or the far-ultraviolet (UV) extinction rise at {λ }-1> 5.9 μ {{{m}}}-1. Therefore, one might expect some relation between UV extinction and DIBs. Such a relationship, if established, could put important constraints on the carrier of DIBs. Over the past four decades, whether DIBs are related to the shape of the UV extinction curves has been extensively investigated. However, the results are often inconsistent, partly due to the inconsistencies in characterizing UV extinction. Here we re-examine the connection between the UV extinction curve and DIBs. We compile the extinction curves and the equivalent widths of 40 DIBs along 97 sightlines. We decompose the extinction curve into three Drude-like functions composed of the visible/near-infrared component, the 2175 \\mathringA bump, and the far-UV (FUV) extinction at {λ }-1> 5.9 μ {{{m}}}-1. We argue that the wavelength-integrated FUV extinction derived from this decomposition technique best measures the strength of the FUV extinction. No correlation is found between the FUV extinction and most (∼90%) of the DIBs. We have also shown that the color excess E(1300{--}1700), the extinction difference at 1300 and 1700 \\mathringA often used to measure the strength of the FUV extinction, does not correlate with DIBs. Finally, we confirm the earlier findings of no correlation between the 2175 \\mathringA bump and DIBs or between the 2175 \\mathringA bump and the FUV extinction. Dedicated to J. Mayo Greenberg (1922.1.14–2001.11.29) and Naomi Greenberg (1923.4.23–2015.8.19), who had always been a source of inspiration.

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

    SciTech Connect

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

    2010-11-15

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

  8. Interstellar extinction in the ultraviolet

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  9. Investigation of ultraviolet interstellar extinction

    NASA Technical Reports Server (NTRS)

    Payne, C.; Haramundanis, K. L.

    1973-01-01

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

  10. Interstellar grains: Effect of inclusions on extinction

    NASA Astrophysics Data System (ADS)

    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.

  11. Correlation properties of interstellar dust: Diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Somerville, W. B.

    1989-01-01

    Results are presented from a research program in which an attempt was made to establish the physical nature of the interstellar grains, and the carriers of the diffuse interstellar bands, by comparing relations between different observed properties; the properties used include the extinction in the optical and ultraviolet (including wavelength 2200 and the far-UV rise), cloud density, atomic depletions, and strengths of the diffuse bands. Observations and also data from literature were used, selecting particularly sight-lines where some observed property was found to have anomalous behavior.

  12. The Diffuse Interstellar Bands: Contributed papers

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  13. Interstellar fullerene compounds and diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Omont, Alain

    2016-05-01

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

  14. Correlation between molecular lines and diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Szczerba, Richard; Krelowski, J.; Walker, G. A. H.; Kennelly, E. T.; Sneden, C.; Volk, Kevin; Hill, G.

    1994-01-01

    Observations are presented of the Diffuse Interstellar Bands (DIB's) at 4726, 4763, and 4789 A and at 5780 and 5797 A together with the ultraviolet lines of CH and CN molecules for stars with different shapes of UV extinction curve. The new results concerning the relationship between different characteristics of the interstellar clouds; molecular lines, blue and yellow DIB's, and UV extinction curves are discussed.

  15. Investigation of ultraviolet interstellar extinction

    NASA Technical Reports Server (NTRS)

    Payne-Gaposchkin, C.; Haramundanis, K. L.

    1973-01-01

    The progress made during the past six months in utilizing Celescope OAO-2 data in a study of extinction is reported along with conclusions drawn from each inquiry. Areas recommended for further investigation are indicated.

  16. Diffuse Interstellar Bands in Emission

    NASA Astrophysics Data System (ADS)

    Williams, T. B.; Sarre, P.; Marshall, C. C. M.; Spekkens, K.; de Naray, R. Kuzio

    Recent Fabry-Pérot observations towards the galaxy NGC 1325 with the Southern African Large Telescope (SALT) led to the serendipitous discovery of an emission feature centered at 661.3 nm arising from material in the interstellar medium (ISM) of our Galaxy; this emission feature lies at the wavelength of one of the sharper and stronger diffuse bands normally seen in absorption. The flux of the feature is 4.2 +/- 0.5 × 10-18 es-1 cm-2 arcsec-2. It appears that this is the first observation of emission from a diffuse band carrier in the ISM, excited in this case by the interstellar radiation field. We present the discovery spectra and describe follow-up measurements proposed for SALT.

  17. VUV spectroscopy of carbon dust analogs: contribution to interstellar extinction

    NASA Astrophysics Data System (ADS)

    Gavilan, L.; Alata, I.; Le, K. C.; Pino, T.; Giuliani, A.; Dartois, E.

    2016-02-01

    Context. A full spectral characterization of carbonaceous dust analogs is necessary to understand their potential as carriers of observed astronomical spectral signatures such as the ubiquitous UV bump at 217.5 nm and the far-ultraviolet (FUV) rise common to interstellar extinction curves. Aims: Our goal is to study the spectral properties of carbonaceous dust analogs from the FUV to the mid-infrared (MIR) domain. We seek in particular to understand the spectra of these materials in the FUV range, for which laboratory studies are scarce. Methods: We produced analogs to carbonaceous interstellar dust encountered in various phases of the interstellar medium: amorphous hydrogenated carbons (a-C:H), for carbonaceous dust observed in the diffuse interstellar medium, and soot particles, for the polyaromatic component. Analogs to a-C:H dust were produced using a radio-frequency plasma reactor at low pressures, and soot nanoparticles films were produced in an ethylene (C2H4) flame. We measured transmission spectra of these thin films (thickness <100 nm) in the far-ultraviolet (190-250 nm) and in the vacuum-ultraviolet (VUV; 50-190 nm) regions using the APEX chamber at the DISCO beam line of the SOLEIL synchrotron radiation facility. These were also characterized through infrared microscopy at the SMIS beam line. Results: We successfully measured the transmission spectra of these analogs from λ = 1 μm to 50 nm. From these, we extracted the laboratory optical constants via Kramers-Kronig inversion. We used these constants for comparison to existing interstellar extinction curves. Conclusions: We extend the spectral measurements of these types of carbonaceous analogs into the VUV and link the spectral features in this range to the 3.4 μm band. We suggest that these two materials might contribute to different classes of interstellar extinction curves.

  18. Diffuse Interstellar Bands: Families and Correlations

    NASA Astrophysics Data System (ADS)

    Krełowski, J.

    2014-02-01

    The term ``families of diffuse bands'' (DIBs) appeared in 1986/87 when my collaborators: Gordon A.H. Walker, Bengt E. Westerlund and I found that the strength ratio of the major DIBs 5780 and 5797 is heavily variable. We proved that at the same E(B-V) the DIB intensities may vary by as much as a factor of three or more. A similar result was published by Karl Josafatsson and Ted Snow soon after. A decade later, we proved (with Chris Sneden) that certain DIB strength ratios seem to be related to intensities of the known features of simple molecular species; this led to the introduction of the so called σ and ζ type interstellar clouds. The former are characterized by very weak molecular features (but broad DIBs - very strong) while the latter by rather strong bands of simple radicals and weak broad DIBs. Currently we face a bunch of questions: are the DIB intensities related to those of certain molecular species, e.g. C2 as suggested by Lew Hobbs' and Ted Snow's group? Do the DIB profiles, found to be complex by Peter Sarre, depend on e.g. the rotational temperatures of simple, linear carbon species? Do the DIB profiles depend on the irradiation of interstellar clouds by nearby stars? The relative DIB strengths as well as those of the simple radicals seem to be related to the shapes of interstellar extinction curves. We thus face three players in the interstellar translucent clouds: dust particles, simple radicals and the DIB carriers. Apparently, their mutual relations depend on local physical parameters of intervening clouds; these relations are not clear yet.

  19. The Role of the Interstellar Extinction Law and Bandwidth Effects in Multicolor Photometry

    NASA Astrophysics Data System (ADS)

    Sudzius, J.; Bobinas, V.; Raudeliunas, S.

    The new mean interstellar extinction law covering the spectral range from 0.15 to 250 mu m is derived. This extinction law yields RBV={A_V/E_{B-V}}=3.17 for OB stars. The very broad band structure of the extinction law in the visible region of the spectrum is confirmed. It is shown that the new interstellar extinction law is suitable for the investigation of reddening parameters of photometric systems. The dependences of reddening parameters upon MK spectral types of stars in three photometric systems, Vilnius, UBV and uvby are discussed.

  20. Study of interstellar extinction by aggregate dust model

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, C.; Das, H. S.; Sen, A. K.

    Extinction generally occurs whenever electromagnetic radiation propagates through a medium containing small particles. The spectral dependence of extinction, or extinction curve, is a function of the composition, structure and size distribution of the particles. The study of interstellar extinction is important because they provide essential information for understanding the properties of the dust. In this work we have considered the aggregate dust model to interpret the extinction efficiency (Qext) of interstellar dust in the wavelength range 0.11-3.4 µm. Using Superposition T-matrix code with Ballistic Cluster-Cluster Aggregate (BCCA) aggregate having 64 number of monomers with graphite, astronomical silicates and amorphous carbon, the normalized extinction efficiency has been calculated for a well defined size distribution within a size range 0.001 to 0.077 micron of extinction near wavelength 2175 Å. The calculated normalized extinction efficiency curve is well matched with observed extinction efficiency.

  1. Fundamental absorption in solids and the wavelength dependence of interstellar extinction

    NASA Astrophysics Data System (ADS)

    Duley, W. W.; Whittet, D. C. B.

    1992-03-01

    It is found that the wavelength dependence of interstellar extinction between the 0.44-micron band an 8 microns follows a Tauc-Urbach law characteristic of amorphous semiconductors. This result implies that the majority of extinction in this wavelength range arises predominantly from an amorphous dust component. A comparison between laboratory and interstellar data suggests that this dust is likely to be amorphous carbon. The Tauc-Urbach dependence permits the ratio of total to selective extinction R(V) to be related to the optical properties of this dust component and provides a semiquantitative relation between R(V) and environmental conditions in the interstellar medium. It also supports an important connection between the physics of condensed matter and the optics of interstellar dust.

  2. Diffuse interstellar bands in reflection nebulae

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  3. Diffuse bands versus extinction parameters

    NASA Technical Reports Server (NTRS)

    Wegner, Walter; Snow, Theodore P.; Sneden, C.; Krelowski, Jacek

    1994-01-01

    All recent available, high quality measurements of the strong diffuse bands 5780 A and 5797 A have been collected. This includes those measurement derived from the authors's recent observations (February, May, and November 1993, taken with a echelle spectrograph) as well as those from a coude spectrograph and from literature. Equivalent widths of the diffuse interstellar bands (DIB's) at 5780 A and 5797 A have been measured on spectrograms. The measured signal-to-noise ratio (S/N) on their own spectrograms ranged from 250 to 500. The Johnson UBV data were used to estimate the color excesses of our targets.

  4. Diffuse Interstellar Bands in NGC 1448

    NASA Astrophysics Data System (ADS)

    Sollerman, J.; Cox, N.; Mattila, S.; Ehrenfreund, P.; Kaper, L.; Leibundgut, B.; Lundqvist, P.

    2005-01-01

    We present spectroscopic VLT/UVES observations of two emerging supernovae, the Type Ia SN 2001el and the Type II SN 2003hn, in the spiral galaxy NGC 1448. Our high resolution and high signal-to-noise spectra display atomic lines of Ca II, Na I, Ti II and K I in the host galaxy. In the line of sight towards SN 2001el, we also detect over a dozen diffuse interstellar bands (DIBs) within NGC 1448. These DIBs have strengths comparable to low reddening galactic lines of sight, albeit with some variations. In particular, a good match is found with the line of sight towards the σ type diffuse cloud (HD 144217). The DIBs towards SN 2003hn are significantly weaker, and this line of sight has also lower sodium column density. The DIB central velocities show that the DIBs towards SN 2001el are closely related to the strongest interstellar Ca II and Na I components, indicating that the DIBs are preferentially produced in the same cloud. The ratio of the λ 5797 and λ 5780 DIB strengths (r ˜ 0.14) suggests a rather strong UV field in the DIB environment towards SN 2001el. We also note that the extinction estimates obtained from the sodium lines using multiple line fitting agree with reddening estimates based on the colors of the Type Ia SN 2001el. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programmes 67.D-0227 and 71.D-0033). Table \\ref{tb:ISfit} and Figs. \\ref{fig:IS_MW} and \\ref{fig:6284} are only available in electronic form at http://www.edpsciences.org

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

    PubMed

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

    2014-08-15

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

  6. Ultraviolet photometry from the Orbiting Astronomical Observatory. II Interstellar extinction.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  7. Infrared diffuse interstellar bands in the Galactic Centre region.

    PubMed

    Geballe, T R; Najarro, F; Figer, D F; Schlegelmilch, B W; de la Fuente, D

    2011-11-02

    The spectrum of any star viewed through a sufficient quantity of diffuse interstellar material reveals a number of absorption features collectively called 'diffuse interstellar bands' (DIBs). The first DIBs were reported about 90  years ago, and currently well over 500 are known. None of them has been convincingly identified with any specific element or molecule, although recent studies suggest that the DIB carriers are polyatomic molecules containing carbon. Most of the DIBs currently known are at visible and very near-infrared wavelengths, with only two previously known at wavelengths beyond one micrometre (10,000 ångströms), the longer of which is at 1.318 micrometres (ref. 6). Here we report 13 diffuse interstellar bands in the 1.5-1.8 micrometre interval on high-extinction sightlines towards stars in the Galactic Centre. We argue that they originate almost entirely in the Galactic Centre region, a considerably warmer and harsher environment than where DIBs have been observed previously. The relative strengths of these DIBs towards the Galactic Centre and the Cygnus OB2 diffuse cloud are consistent with their strengths scaling mainly with the extinction by diffuse material.

  8. Probing the diffuse interstellar medium with diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  9. Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints

    NASA Technical Reports Server (NTRS)

    Zubko, Viktor; Dwek, Eli; Arendt, Richard G.

    2004-01-01

    We present new interstellar dust models which have been derived by simultaneously fitting the far ultraviolet to near infrared extinction, the diffuse infrared emission, and, unlike previous models, the elemental abundances in dust for the diffuse interstellar medium. We found that dust models consisting of a mixture of spherical graphite and silicate grains, polycyclic aromatic hydrocarbon (PAH) molecules, in addition to porous composite particles containing silicate, organic refractory, and water ice, provide an improved .t to the UV-to-infrared extinction and infrared emission measurements, while consuming the amounts of elements well within the uncertainties of adopted interstellar abundances, including B star abundances. These models are a signi.cant improvement over the recent Li & Draine (2001, ApJ, 554, 778) model which requires an excessive amount of silicon to be locked up in dust: 48 ppm (atoms per million of H atoms), considerably more than the solar abundance of 34 ppm or the B star abundance of 19 ppm.

  10. Polycyclic aromatic hydrocarbon ions and the diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Salama, F.; Allamandola, L. J.

    1995-01-01

    Neutral naphthalene (C10H8), phenanthrene (C14H10), and pyrene (C16H10) absorb strongly in the ultraviolet and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these Polycyclic Aromatic Hydrocarbons (PAHs) absorb in the visible. C10H8(+) has 12 discrete absorption bands which fall between 6800 and 5000 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBS at 6520, 6151, and 5965 A, other moderately strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in a Ne matrix, a position which falls very close to the strongest DIB, that at 4430 A. If C16H10(+), or a closely related pyrene-like ion is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. We also report an intense, very broad UV-to-visible continuum which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR.

  11. Unidentified infrared bands in the interstellar medium across the Galaxy

    NASA Astrophysics Data System (ADS)

    Kahanpää, J.; Mattila, K.; Lehtinen, K.; Leinert, C.; Lemke, D.

    2003-07-01

    We present a set of 6-12 mu m ISOPHOT-S spectra of the general interstellar medium of the Milky Way. This part of the spectrum is dominated by a series of strong, wide emission features commonly called the Unidentified Infrared Bands. The sampled area covers the inner Milky Way from l = -60 degr to +60 degr with a ten-degree step in longitude and nominal latitudes b = 0 degr, +/-1 degr. For each grid position the actual observed direction was selected from IRAS 100 mu m maps to minimize contamination by point sources and molecular clouds. All spectra were found to display the same spectral features. Band ratios are independent of band strength and Galactic coordinates. A comparison of total observed flux in band features and IRAS 100 mu m emission, a tracer for large interstellar dust grains, shows high correlation at large as well as small (1 arcmin) scales. This implies a strong connection between large dust grains and the elusive band carriers; the evolutionary history and heating energy source of these populations must be strongly linked. The average mid-infrared spectrum of the Milky Way is found to be similar to the average spectrum of spiral galaxy NGC 891 and the spectra of other spirals. The common spectrum can therefore be used as a template for the 6-12 mu m emission of late-type spiral galaxies. Finally, we show that interstellar extinction only weakly influences the observed features even at lambda  = 10 mu m, where the silicate absorption feature is strongest. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?I/A+A/405/999

  12. Interstellar extinction curve variations towards the inner Milky Way: a challenge to observational cosmology

    NASA Astrophysics Data System (ADS)

    Nataf, David M.; Gonzalez, Oscar A.; Casagrande, Luca; Zasowski, Gail; Wegg, Christopher; Wolf, Christian; Kunder, Andrea; Alonso-Garcia, Javier; Minniti, Dante; Rejkuba, Marina; Saito, Roberto K.; Valenti, Elena; Zoccali, Manuela; Poleski, Radosław; Pietrzyński, Grzegorz; Skowron, Jan; Soszyński, Igor; Szymański, Michał K.; Udalski, Andrzej; Ulaczyk, Krzysztof; Wyrzykowski, Łukasz

    2016-03-01

    We investigate interstellar extinction curve variations towards ˜4 deg2 of the inner Milky Way in VIJKs photometry from the OGLE-III (third phase of the Optical Gravitational Lensing Experiment) and VVV (VISTA Variables in the Via Lactea) surveys, with supporting evidence from diffuse interstellar bands and F435W, F625W photometry. We obtain independent measurements towards ˜2000 sightlines of AI, E(V - I), E(I - J) and E(J - Ks), with median precision and accuracy of 2 per cent. We find that the variations in the extinction ratios AI/E(V - I), E(I - J)/E(V - I) and E(J - Ks)/E(V - I) are large (exceeding 20 per cent), significant and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve have at least two degrees of freedom, and not one (e.g. RV), which we confirm with a principal component analysis. We derive a median value of = 13.44, which is ˜60 per cent higher than the `standard' value. We show that the Wesenheit magnitude WI = I - 1.61(I - J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of Type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ˜100 per cent and lack sensitivity to extinction curve variations.

  13. Interstellar Extinction and its Variation in the Galaxy

    NASA Astrophysics Data System (ADS)

    Ford Schlafly, Edward; Rix, Hans-Walter; Finkbeiner, Douglas P.; Green, Gregory; Lee, Albert; Meisner, Aaron M.

    2016-01-01

    Dust reddening is an important diagnostic of the interstellar medium and the dust grain size distribution, as well as a pervasive observational nuisance. Detailed studies of the dust extinction curve and its variation have hithertofore been largely limited to samples of hundreds of specially chosen stars. We use spectroscopy from APOGEE in combination with photometry from Pan-STARRS1, 2MASS, and WISE to characterize the dust extinction curve throughout much of the nearest few kiloparsecs of the Galactic plane using tens of thousands of stars. We make new measurements of the dust extinction curve and its variation, finding that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves, described, for instance, by R(V). Our data show little evidence of any need for further parameters. The local curvature of the extinction curve increases with decreasing R(V) throughout most of the optical and infrared: the extinction curve in the infrared is not more ``universal'' than in the optical, in contrast to several widely-used extinction curve parameterizations. We find that the shape of the dust extinction curve is rather uniform, with σ(R(V)) = 0.2, and with less than two percent of sight lines having R(V) > 4. However, significant spatially coherent variations in R(V) do exist. The primary variations are on scales much larger than individual molecular clouds, indicating that grain growth in dense molecular cloud environments is not the primary driver of R(V) variations in dust at large. Indeed, we find no correlation between R(V) and dust column density out to E(B-V) ≈ 2.

  14. Extragalactic interstellar extinction curves: Indicators of local physical conditions

    SciTech Connect

    Cecchi-Pestellini, Cesare; Viti, Serena; Williams, David A. E-mail: sv@star.ucl.ac.uk

    2014-06-20

    Normalized interstellar extinction curves (ISECs) in the Milky Way and other galaxies show a variety of shapes. This variety is attributed to differences along different sight lines in the abundances of the several dust and gas components contributing to extinction. In this paper we propose that these abundance differences are not arbitrary but are a specific consequence of the physical conditions on those sight lines. If this proposal is correct, then it implies that ISECs contain information about physical conditions in the regions generating extinction. This may be particularly important for high redshift galaxies where information on the conditions may be difficult to obtain. We adopt a model of extinction carriers in which the solid and gaseous components are not immutable but respond time-dependently to the local physics. We validate this model by fitting extinction curves measured on sight lines in the Magellanic Clouds and obtained for the gamma-ray burst afterglow GRB 080605. We present results for this model as follows: (1) we show that computed ISECs are controlled by a small number of physical parameters, (2) we demonstrate the sensitivity of computed ISECs to these parameters, (3) we compute as examples ISECs for particular galaxy types, and (4) we note that different galaxy types have different shapes of ISEC.

  15. Diffuse interstellar bands: a comprehensive laboratory study.

    PubMed

    Johnson, Fred M

    2006-12-01

    As a result of the search for the identity of the chromophores responsible for producing the diffuse interstellar bands, a comprehensive exposition of experimental data is presented, which implicates the following molecules: (1) The extremely stable organic molecules, magnesium tetrabenzoporphyrin (MgTBP) and H(2)TBP. (2) A paraffin matrix (referred to as "grains") containing TBPs. (3) A low concentration of pyridine (also within the grains), whose transmission window at 2175 A, accounts for the ubiquitous UV bump. The blue emission spectra associated with the central star, HD44179, of the Red Rectangle displays the fluorescence excitation spectra of bare MgTBP. This unique spectrum matches the low temperature lab data of MgTBP in the vapor phase. An effective grain temperature of 2.728 K (+/-0.008) was deduced, based on MgTBP's lowest measured vibrational state of 341 GHz.

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

    SciTech Connect

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

    2015-01-01

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

  17. New Interstellar Dust Models Consistent with Interstellar Extinction, Emission and Abundances Constraints

    NASA Technical Reports Server (NTRS)

    Zubko, V.; Dwek, E.; Arendt, R. G.; Oegerle, William (Technical Monitor)

    2001-01-01

    We present new interstellar dust models that are consistent with both, the FUV to near-IR extinction and infrared (IR) emission measurements from the diffuse interstellar medium. The models are characterized by different dust compositions and abundances. The problem we solve consists of determining the size distribution of the various dust components of the model. This problem is a typical ill-posed inversion problem which we solve using the regularization approach. We reproduce the Li Draine (2001, ApJ, 554, 778) results, however their model requires an excessive amount of interstellar silicon (48 ppM of hydrogen compared to the 36 ppM available for an ISM of solar composition) to be locked up in dust. We found that dust models consisting of PAHs, amorphous silicate, graphite, and composite grains made up from silicates, organic refractory, and water ice, provide an improved fit to the extinction and IR emission measurements, while still requiring a subsolar amount of silicon to be in the dust. This research was supported by NASA Astrophysical Theory Program NRA 99-OSS-01.

  18. TRES Survey of Variable Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Law, Charles; Milisavljevic, Dan; Crabtree, Kyle; Johansen, Sommer; Patnaude, Daniel

    2017-01-01

    Diffuse interstellar bands (DIBs) are absorption features commonly observed in optical/near-infrared spectra of stars and thought to be associated with polyatomic molecules that comprise a significant reservoir of organic material in the universe. However, because the central wavelengths of DIBs do not correspond with electronic transitions of known atomic or molecular species, the specific physical nature of their carriers remains inconclusive despite decades of observational, theoretical, and experimental research. It is well established that DIB carriers must be located in the interstellar medium, but the recent discovery of time-varying DIBs in the spectra of the extragalactic supernova SN 2012ap suggests that some may be created in massive star environments. We report evidence of short time-scale (˜1-60 days) variations in DIB absorption line substructure toward 3 of 17 massive stars observed as part of a pathfinder survey of variable DIBs. The detections are made in high-resolution optical spectra (R ˜ 44000) from the Tillinghast Reflection Echelle Spectrograph on the 1.5m Tillinghast telescope at the Smithsonian Astrophysical Observatory's Fred L. Whipple Observatory on Mt. Hopkins in Arizona. Our detections have signal-to-noise ratios of 5-15 around the features of interest, and are thus considered significant but requiring further investigation. We find that these changes are potentially consistent with interactions between stellar winds and DIB carriers in close proximity. Our findings motivate a larger survey to further characterize these variations and may establish a powerful new method for probing the poorly understood physical characteristics of DIB carriers.

  19. NEW ULTRAVIOLET EXTINCTION CURVES FOR INTERSTELLAR DUST IN M31

    SciTech Connect

    Clayton, Geoffrey C.; Gordon, Karl D.; Bohlin, R. C.; Bianchi, Luciana C.; Massa, Derck L.; Wolff, Michael J.; Fitzpatrick, Edward L. E-mail: bohlin@stsci.edu E-mail: bianchi@jhu.edu E-mail: edward.fitzpatrick@villanova.edu

    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.

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

    NASA Astrophysics Data System (ADS)

    Hoffman, John; Draine, B. T.

    2016-02-01

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

  1. ACCURATE MODELING OF X-RAY EXTINCTION BY INTERSTELLAR GRAINS

    SciTech Connect

    Hoffman, John; Draine, B. T. E-mail: draine@astro.princeton.edu

    2016-02-01

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

  2. INTERSTELLAR EXTINCTION LAW TOWARD THE GALACTIC CENTER III: J, H, K{sub S} BANDS IN THE 2MASS AND THE MKO SYSTEMS, AND 3.6, 4.5, 5.8, 8.0 {mu}m IN THE SPITZER/IRAC SYSTEM

    SciTech Connect

    Nishiyama, Shogo; Nagata, Tetsuya; Tamura, Motohide; Hatano, Hirofumi; Kato, Daisuke; Tanabe, Toshihiko; Sugitani, Koji

    2009-05-10

    We have determined interstellar extinction law toward the Galactic center (GC) at the wavelength from 1.2 to 8.0 {mu}m, using point sources detected in the IRSF/SIRIUS near-infrared (NIR) survey and those in the Two Micron All Sky Survey (2MASS) and Spitzer/IRAC/GLIMPSE II catalogs. The central region |l | {approx}<3.{sup 0}0 and |b | {approx}<1.{sup 0}0 has been surveyed in the J, H, and K{sub S} bands with the IRSF telescope and the SIRIUS camera whose filters are similar to the Mauna Kea Observatories (MKO) NIR photometric system. Combined with the GLIMPSE II point source catalog, we made K{sub S} versus K{sub S} - {lambda} color-magnitude diagrams (CMDs) where {lambda}=3.6, 4.5, 5.8, and 8.0 {mu}m. The K{sub S} magnitudes of bulge red clump stars and the K{sub S} - {lambda} colors of red giant branches are used as a tracer of the reddening vector in the CMDs. From these magnitudes and colors, we have obtained the ratios of total-to-selective extinction A{sub K{sub S}}/E{sub K{sub S}}{sub -{lambda}} for the four IRAC bands. Combined with A{sub {lambda}}/A{sub K{sub S}} for the J and H bands derived by Nishiyama et al., we obtain A{sub J} :A{sub H} :A{sub K{sub S}}:A {sub [3.6]}:A {sub [4.5]}:A {sub [5.8]}:A {sub [8.0]} = 3.02:1.73:1:0.50:0.39:0.36:0.43 for the line of sight toward the GC. This confirms the flattening of the extinction curve at {lambda} {approx}> 3 {mu}m from a simple extrapolation of the power-law extinction at shorter wavelengths, in accordance with recent studies. The extinction law in the 2MASS J, H, and K{sub S} bands has also been calculated, and good agreement with that in the MKO system is found. Thus, it is established that the extinction in the wavelength range of J, H, and K{sub S} is well fitted by a power law of steep decrease A {sub {lambda}} {proportional_to} {lambda}{sup -2.0} toward the GC. In nearby molecular clouds and diffuse interstellar medium, the lack of reliable measurements of the total-to-selective extinction ratios

  3. Centrosymmetric molecules as possible carriers of diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Kaźmierczak, M.; Schmidt, M. R.; Galazutdinov, G. A.; Musaev, F. A.; Betelesky, Y.; Krełowski, J.

    2010-11-01

    In this paper, we present new data with interstellar C2 (Phillips bands A 1 Πu-X1 Σ+g), from observations made with the Ultraviolet-Visual Echelle Spectrograph of the European Southern Observatory. We have determined the interstellar column densities and excitation temperatures of C2 for nine Galactic lines. For seven of these, C2 has never been observed before, so in this case the still small sample of interstellar clouds (26 lines of sight), where a detailed analysis of C2 excitation has been made, has increased significantly. This paper is a continuation of previous works where interstellar molecules (C2 and diffuse interstellar bands) have been analysed. Because the sample of interstellar clouds with C2 has increased, we can show that the width and shape of the profiles of some diffuse interstellar bands (6196 and 5797 Å) apparently depend on the gas kinetic and rotational temperatures of C2; the profiles are broader because of the higher values of the gas kinetic and rotational temperatures of C2. There are also diffuse interstellar bands (4964 and 5850 Å) for which this effect does not exist. Based on observations made with ESO telescopes at the Paranal Observatory under programme IDs 266.D-5655(A), 67.C-0281(A), 71.C-0513(C), 67.D-0439(A) and 082.C-0566(A) and at La Silla under programme IDs 078.C-0403(A), 076.C-0164(A) and 073.C-0337(A). Also based on observations made with the 1.8-m telescope in South Korea and the 2-m telescope at the International Centre for Astronomical and Medico-Ecological Research, Terskol, Russia. E-mail: kazmierczak@astri.uni.torun.pl (MK); schmidt@ncac.torun.pl (MRS); runizag@gmail.com (GAG); ybialets@eso.org (YB); jacek@astri.uni.torun.pl (JK)

  4. Extinction distances of Planetary Nebulae interacting with the interstellar medium

    NASA Astrophysics Data System (ADS)

    Pirzkal, N.; Kerber, F.; Roth, M.

    2000-12-01

    Distances to Planetary Nebulae (PNe) are notoriously unreliable. It is known that statistical methods such as the different versions of the Shklovsky--derived distance scales can not be applied to individual objects with any confidence. Various methods to estimate the distance of individual PN have been successfully applied in the past, e.g. using trigonometric parallaxes, radio and optical expansion rates, the central star's atmosphere, or the nature of companions in binary systems. However, these have the drawback of relying on some special properties of a PN, and require various combinations of very high S/N observations, of large time bases, and of extensive modeling. In the end, these methods can only be applied to a very small number of PNe. As a result, after more than 30 years of research, accurate and reliable distances are known for less than 5 2000 or so Galactic PNe. This is the largest single obstacle to a better understanding of the fundamental properties of PNe. One method which does not require us to make any assumptions about the PN and which can be applied to all PNe close to the Galactic plane is the extinction distance method. This method relies on the fact that most of the stars surrounding a target PN are either Main-Sequence stars or giants with known intrinsic colors. Using these, together with an a-priori dust extinction law, an extinction vs. distance relation can be determined for the field. We have applied this method to several PN fields which were observed in the B,V,Rc, and Ic bands. We report here on the first results and present extinction vs. distance relations in the direction of our target PNe. A discussion about the accuracy of the method and the derived distances is included.

  5. Fullerenes, Organics and the Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Foing, Bernard H.

    2016-07-01

    The status of DIB research has strongly advanced since 20 years [1], as well as the quest for fullerenes, PAHs and large organics in space. In 1994 we reported the discovery of two near IR diffuse bands coincident with C60+, confirmed in subsequent years [2-6] and now by latest laboratory experiments. A number of DIB observational studies have been published, dealing with: DIB surveys [1,7-10]; measurements of DIB families, correlations and environment dependences [11-14]; extragalactic DIBs [15, 16]. Resolved substructures were detected [17,18] and compared to predicted rotational contours by large molecules [19]. Polarisation studies provided upper limits constraints [20, 21]. DIBs carriers have been linked with organic molecules observed in the interstellar medium [22-25] such as IR bands (assigned to PAHs), Extended Red Emission or recently detected Anomalous Microwave Emission (AME, assigned to spinning dust) and with spectroscopic IR emission bands measured with ISO or Spitzer. Fullerenes and PAHs have been proposed to explain some DIBs and specific molecules were searched in DIB spectra [eg 2-6, 26-31]. These could be present in various dehydrogenation and ionisation conditions [32,33]. Experiments in the laboratory and in space [eg 34-36] allow to measure the survival and by-products of these molecules. We review DIB observational results and their interpretation, and discuss the presence of large organics, fullerenes, PAHs, graphenes in space. References [1] Herbig, G. 1995 ARA&A33, 19; [2] Foing, B. & Ehrenfreund, P. 1994 Natur 369, 296; [3] Foing, B. & Ehrenfreund, P. 1997 A&A317, L59; [4] Foing, B. & Ehrenfreund, P. 1995 ASSL202, 65; [5] Ehrenfreund, P., Foing, B. H. 1997 AdSpR19, 1033; [6] Galazutdinov, G. A. et al. 2000 MNRAS317, 750; [7] Jenniskens, P., Desert, F.-X. 1994 A&AS106, 39; [8] Ehrenfreund, P. et al. 1997 A&A318, L28; [9] Tuairisg, S. Ó. et al. 2000 A&AS142, 225; [10] Cox, N. et al. 2005 A&A438, 187; [11] Cami, J. et al. 1997A&A.326, 822

  6. A bibliography of papers on the diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Snow, Theodore P.; Barnes, Susan; Heitzmann, Maribeth

    1994-01-01

    Presented is a compilation of publications on the diffuse interstellar bands, found in the literature dating back to the first known mention of the bands. It has been attempted to make this list complete, but it must be recognized that some papers may be missing. Judgement was required in some cases where the diffuse bands are mentioned, but are not a central theme of a paper; in most instances we kept such papers in a list, rather than omitting them.

  7. Probing Milky Way Structure with Near-Infrared Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Zasowski, Gail; Ménard, Brice; Bizyaev, Dmitry; Garcia-Hernandez, D.; García Pérez, Ana; Hayden, Michael R.; Hearty, Fred; Holtzman, Jon A.; Johnson, Jennifer; Kinemuchi, Karen; Majewski, Steven R.; Nidever, David L.; Sellgren, Kristen; Shetrone, Matthew D.; Whelan, David G.; Wilson, John C.

    2015-01-01

    Astronomers have studied the set of interstellar absorption features known as the diffuse interstellar bands (DIBs) for nearly a century, characterizing them into families and using them as probes of local interstellar medium (ISM) conditions even while trying to understand their origin. Though most DIB studies have focused on the optical features, recent DIB identifications at infrared (IR) wavelengths -- where extinction by interstellar dust is significantly decreased -- provide us with tracers of ISM along heavily extincted, previously inaccessible sightlines. This talk will briefly summarize results from a project using the strongest of these IR DIBs (detected in more than 60,000 sightlines towards cool, distant giant stars observed as part of the SDSS-III/APOGEE survey) to characterize the large-scale distribution and properties of the Galactic ISM, including in the heavily reddened bulge and inner disk. The DIB absorption's tight correlation with foreground reddening makes it a powerful, independent probe of line-of-sight dust extinction. For the first time, we map the velocity field of a DIB on large scales and find that it displays the signature of the rotating Galactic disk. Three-dimensional modeling of the carrier distribution reveals not only large-scale gradients consistent with other ISM components, but also substructures that coincide with particular Galactic bulge and disk features. Finally, we find that features that are outliers in the distribution of DIB profile shapes may have an origin in circumstellar, rather than interstellar, environments along these particular sightlines, and the properties of these atypical features may contain clues towards identifying the currently-unknown carrier molecule of this DIB.

  8. Catalogue of diffuse interstellar band measurements

    NASA Technical Reports Server (NTRS)

    Snow, T. P., Jr.; York, D. G.; Welty, D. E.

    1976-01-01

    Diffuse-band data have been collected from the literature and reduced statistically to a common measurement system, enabling correlation analyses to be made with a larger quantity of data than previously possible. A full listing of the catalogued data is presented, along with some discussion of the correlations. One important application of such studies is the identification of cases of peculiar diffuse-band behavior, and a table is given showing all cases of band strengths deviating by more than twice the mean dispersion from the best-fit correlations. This table may be useful in planning further observations.

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Diffuse interstellar bands and PAHs in the Galaxy and beyond

    NASA Astrophysics Data System (ADS)

    Cox, Nick L. J.; Ehrenfreund, Pascale

    2006-09-01

    Diffuse interstellar bands (DIBs) are ubiquitously observed towards reddened stars throughout the Milky Way. In the past decade, DIBs have been observed in only a few extra-galactic lines of sight. The carriers of DIBs are likely large organic gas phase molecules that reside in the diffuse interstellar medium. However, ever since they were first observed in the 1920s their identity remains a mystery. Investigated candidate carriers include, but are not limited to, carbon chains, polycyclic aromatic hydrocarbons (PAHs), fullerenes and tubular PAHs. Recent advances and successes in laboratory and theoretical work have given a great boost to the study of large molecules under interstellar conditions, i.e. low temperature, gas phase. We present here a short overview of our recent (extra)-galactic DIBs observations and the related studies of PAH chemistry in these environments.

  11. A high-resolution study of near-infrared diffuse interstellar bands

    SciTech Connect

    Rawlings, M. G.; Adamson, A. J.; Kerr, T. H. E-mail: aadamson@gemini.edu

    2014-11-20

    We present high-resolution echelle spectroscopic observations of the two near-infrared (NIR) diffuse interstellar bands (DIBs) at 13175 Å and 11797.5 Å. The DIBs have been observed in a number of diffuse interstellar medium sightlines that exhibit a wide range of visual extinctions. Band profiles are similar to those seen in narrow DIBs, clearly asymmetric and can be closely fitted in most cases using two simple Gaussian components. Gaussian fits were generally found to be more successful than fits based on a multiple-cloud model using a template DIB profile. For a sample of nine objects in which both bands are observed, the strength of both NIR DIBs generally increases with A(V), and we report a correlation between the two observed bands over a large A(V) range and widely separated lines of sight. The strength of the two bands is also compared against those of two visual DIBs and the diffuse ISM aliphatic dust absorption feature at 3.4 μm previously detected in the same sightlines. We find that the NIR DIBs do not exhibit notable (anti)correlations with either. Implications of these observations on possible DIB carrier species are discussed.

  12. Interstellar Extinction in the Vicinity of the Galactic Center

    NASA Technical Reports Server (NTRS)

    Cotera, Angela S.; Simpson, Janet P.; Erickson, Edwin F.; Colgan, Sean W. J.; Burton, Michael G.; Allen, David A.

    2000-01-01

    We present J (1.2 microns), H (1-6 microns), K' (2.11 microns) and Br(gamma) (2.166 microns) images from four large regions within the central 40 pc of the Galaxy. Localized variations in the extinction, as determined by observations of the stellar population, are examined using the median H-K' color as a function of position within each region. As the value of the derived extinction from the stars is dependent upon the intrinsic magnitude of the assumed stellar type, the J-H vs. H-K' diagrams are first used to investigate the distribution of stellar types in the four regions. We find that there is a distinct OB population, contrary to earlier assumptions, with the ratio of K and M giants and supergiants to OB stars approximately twice that of the solar neighborhood. Although the on the scale of approx. l' fluctuations in the extinction are on the order of A(sub V) approx. 2, throughout the entire region the extinction varies from A(sub V) approx. greater than 25 to A(sub V) approx. less than 40. We also examine whether there is any variation in the extinction and stellar number density relative to the usual radio features in these regions and do not find a significant correlation. Spectral imaging in Br(gamma) 2.166 microns emission shows a strong morphological correspondence between the 6 cm radio images and the diffuse Br(gamma) emission. By comparing the theoretical Br(gamma) flux derived from the radio flux using recombination theory, with our measured Br(gamma) flux, we obtain a second, independent, estimate of the extinction. We compare the two data sets and find that the extinction as derived from the stars is consistently greater, sometimes by a factor of two, than the value of the extinction derived from the Br(gamma) images. The derived extinction in various regions, however, is insufficient for any of these regions-to be located behind the molecular clouds as previously observed in the Galactic Center, consistent with the theory that the observed radio

  13. Interstellar Extinction in the Vicinity of the Galactic Center

    NASA Technical Reports Server (NTRS)

    Cotera, Angela S.; Simpson, Janet P.; Erickson, Edwin F.; Colgan, Sean W. J.

    1998-01-01

    We present J (1.2 microns) H (1-6 microns) K' (2.11 microns) and Br(gamma) (2.166 microns) images from four large regions within the central 40 pc of the Galaxy. Localized variations in the extinction, as determined by observations of the stellar population, are examined using the median H-K' color as a function of position within each region. As the value of the derived extinction from the stars is dependent upon the intrinsic magnitude of the assumed stellar type, the J-H vs. H-K' diagrams are first used to investigate the distribution of stellar types in the four regions. We find that there is a distinct OB population, contrary to earlier assumptions, with the ratio of K and M giants and supergiants to OB stars approximately twice that of the solar neighborhood. Although the on the scale of approx. 1 min. fluctuations in the extinction are on the order of A(sub V) approx. greater than 2, throughout the entire region the extinction varies from A(sub V) approx. greater than 25 to A(sub V) approx. less than 40. We also examine whether there is any variation in the extinction and stellar number density relative to the unusual radio features in these regions and do not find a significant correlation. Spectral imaging in Br(gamma) 2.166 microns emission shows a strong morphological correspondence between the 6 cm radio images and the diffuse Br(gamma) emission. By comparing the theoretical Br(gamma) flux derived from the radio flux using recombination theory, with our measured Br(gamma) flux, we obtain a second, independent, estimate of the extinction. We compare the two data sets and find that the extinction as derived from the stars is consistently greater, sometimes by a factor of two, than the value of the extinction derived from the Br(gamma) images. The derived extinction in various regions, however, is insufficient for any of these regions to be located behind the molecular clouds as previously observed in the Galactic Center, consistent with the theory that

  14. Interstellar Extinction toward the Young Open Cluster NGC 1502

    NASA Astrophysics Data System (ADS)

    Topasna, Gregory A.; Kaltcheva, Nadia

    2017-01-01

    We present new multi-wavelength polarization measurements of 20 stars in the direction of the open cluster NGC 1502. Polarimetric results are combined with uvbyβ photometric data to obtain precise estimates of the total-to-selective extinction and distance for each star. NGC 1502 is located at the periphery of the Cam OB1 association and probably within the Orion Spur, with published distance estimates varying between 0.7 and 1.5 kpc. Our analysis suggests that the stars studied here form two concentrations along the line of sight. If a value of 3.2 for the total-to-selective extinction is assumed, the stars group at 0.8 ± 0.02 kpc and 1.1 ± 0.05 kpc. However, using the wavelength of maximum polarization to calculate the total-to-selective extinction for each star yields 0.9 ± 0.03 kpc and 1.3 ± 0.04 kpc, respectively. This approach indicates that combining polarimetric and uvbyβ data provides a more detailed stellar distribution of this region. Acknowledgments: Part of this work was supported by NSF grant AST-1516932.

  15. A measurement of interstellar polarization and an estimation of Galactic extinction for the direction of the X-ray black hole binary V404 Cygni

    NASA Astrophysics Data System (ADS)

    Itoh, Ryosuke; Tanaka, Yasuyuki T.; Kawabata, Koji S.; Uemura, Makoto; Watanabe, Makoto; Fukazawa, Yasushi; Kanda, Yuka; Akitaya, Hiroshi; Moritani, Yuki; Nakaoka, Tatsuya; Kawabata, Miho; Shiki, Kensei; Yoshida, Michitoshi; Oasa, Yumiko; Takahashi, Jun

    2017-02-01

    V404 Cygni is a well-known candidate for the black hole binary thought to have relativistic jets. It showed extreme outbursts in 2015 June, characterized by a large amplitude and short time variation of flux in the radio, optical, and X-ray bands. Not only disk emission but also synchrotron radiation from the relativistic jets was suggested by radio observations. However, it is difficult to measure the accurate spectral shape in the optical/near-infrared band because there are uncertainties of interstellar extinction. To estimate the extinction value for V404 Cygni, we performed photopolarimetric and spectroscopic observations of V404 Cygni and nearby field stars. Here, we estimate the Galactic extinction using interstellar polarization based on the observation that the origin of the optical polarization is the interstellar medium, and investigate the properties of interstellar polarization around V404 Cygni. We found a good correlation between the color excess and polarization degree in the field stars. We also confirmed that the wavelength dependence of the polarization degree in the highly polarized field stars was similar to that of V404 Cygni. Using the highly polarized field stars, we estimated the color excess for the (B - V) color and the extinction in the V band to be E(B - V) = 1.2 ± 0.2 and 3.0 < A(V) < 3.6, respectively. A tendency for a bluer peak of polarization (λmax < 5500 Å) was commonly seen in the highly polarized field stars, suggesting that the dust grains toward this region are generally smaller than the Galactic average. The corrected spectral energy distribution of V404 Cygni in the near-infrared and optical bands in our results indicated a spectral break between 2.5 × 1014 Hz and 3.7 × 1014 Hz, which might originate in the synchrotron self-absorption.

  16. STUDIES OF THE DIFFUSE INTERSTELLAR BANDS. III. HD 183143

    SciTech Connect

    Hobbs, L. M.; Thorburn, J. A.; York, D. G.; Bishof, M.; Oka, T.; Snow, T. P.; Friedman, S. D.; McCall, B. J.; Rachford, B.; Sonnentrucker, P.; Welty, D. E.

    2009-11-01

    Echelle spectra of HD 183143 [B7Iae, E(B - V) = 1.27] were obtained on three nights, at a resolving power R = 38,000 and with a signal-to-noise ratio approx 1000 at 6400 A in the final, combined spectrum. A catalog is presented of 414 diffuse interstellar bands (DIBs) measured between 3900 and 8100 A in this spectrum. The central wavelengths, the widths (FWHM), and the equivalent widths of nearly all of the bands are tabulated, along with the minimum uncertainties in the latter. Among the 414 bands, 135 (or 33%) were not reported in four previous, modern surveys of the DIBs in the spectra of various stars, including HD 183143. The principal result of this study is that the great majority of the bands in the catalog are very weak and fairly narrow. Typical equivalent widths amount to a few mA, and the bandwidths (FWHM) are most often near 0.7 A. No preferred wavenumber spacings among the 414 bands are identified which could provide clues to the identities of the large molecules thought to cause the DIBs. At generally comparable detection limits in both spectra, the population of DIBs observed toward HD 183143 is systematically redder, broader, and stronger than that seen toward HD 204827 (Paper II). In addition, interstellar lines of C{sub 2} molecules have not been detected toward HD 183143, while a very high value of N(C{sub 2})/E(B - V) is observed toward HD 204827. Therefore, either the abundances of the large molecules presumed to give rise to the DIBs, or the physical conditions in the absorbing clouds, or both, must differ significantly between the two cases.

  17. Dust in the small Magellanic cloud. 1: Interstellar polarization and extinction data

    NASA Technical Reports Server (NTRS)

    Magalhaes, A. M.; Rodrigues, C. V.; Coyne, C. V.; Piirola, V.

    1996-01-01

    The typical extinction curve for the Small Magellanic Cloud (SMC), in contrast to that for the Galaxy, has no bump at 2175 A and has a steeper rise into the far ultraviolet. For the Galaxy the interpretation of the extinction and, therefore, the dust content of the interstellar medium has been greatly assisted by measurements of the wavelength dependence of the polarization. For the SMC no such measurements existed. Therefore, to further elucidate the dust properties in the SMC we have for the first time measured linear polarization with five colors in the optical region of the spectrum for a sample of reddened stars. For two of these stars, for which there were no existing UV spectrophotometric measurements, but for which we measured a relatively large polarization, we have also obtained data from the International Ultraviolet Explorer (IUE) in order to study the extinction. We also attempt to correlate the SMC extinction and polarization data. The main results are: the wavelength of maximum polarization, lambda(sub max), in the SMC is typically smaller than that in the Galaxy; however, AZC 456, which shows the UV extinction bump, has a lambda(sub max) typical of that in the Galaxy, but its polarization curve is narrower and its bump is shifted to shorter wavelengths as compared to the Galaxy; and from an analysis of both the extinction and polarization data it appears that the SMC has typically smaller grains than those in the Galaxy. The absence of the extinction bump in the SMC has generally been thought to imply a lower carbon abundance in the SMC compared to the Galaxy. We interpret our results to mean that te size distribution of the interstellar grains, and not only the carbon abundance, is different in the SMC as compared to the Galaxy. In Paper 2 we present dust model fits to these observations.

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

    SciTech Connect

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

    2014-09-10

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

  19. Deviations of interstellar extinctions from the mean R-dependent extinction law

    NASA Technical Reports Server (NTRS)

    Mathis, John S.; Cardelli, Jason A.

    1992-01-01

    An analysis is conducted of the deviations from the mean extinction law A(lambda)/A(V) over UV wavelengths emphasizing sightlines through bright nebulosities vs dark clouds. The stellar sample is subdivided into sight lines with defined properties, and different behavior is noted for the deviations in the dark-cloud and bright-nebula sight lines. The deviations are correlated within the same wavenumber interval, but unique shapes for the FUV rise in the deviations are observed. Distributions of silicate grains are considered to account for the extinctions at certain wavenumbers that would explain the observations. The FUV rise in the extinctions is theorized to be related to the UV extinction of polycyclic aromatic hydrocarbons.

  20. DIBSyRCH: The Diffuse Interstellar Band Synchrotron Radiation Carrier Hunt: New Tools

    NASA Astrophysics Data System (ADS)

    Stockett, M. H.; Wood, M. P.; Lawler, J. E.

    2010-11-01

    The identity of the carrier molecules of the Diffuse Interstellar Bands (DIBs) is the most durable mystery of spectroscopic astronomy. The DIBs are persistent absorption features, >300 total, observed along many lines of sight through the Interstellar Medium (ISM). The DIBs are scattered throughout the visible and near infrared, with widths in the 2-100 cm-1 range. For nearly a century, laboratory spectroscopists have struggled to match astrophysical wavelengths to laboratory wavelengths of known molecules including a variety of stable molecules, radicals, cations, and anions. Many researchers have hypothesized that hydrocarbon molecules are responsible for the DIBs, due to the rich chemistry and high cosmic abundance of carbon and hydrogen. Though large Polycyclic Aromatic Hydrocarbons (PAHs) are now suspected to be the source of the DIBs, no definitive matches have yet been made to laboratory PAH spectra. Aromatic clusters are also thought to be an important constituent of the interstellar dust distribution and may contribute to the 2175 Å "bump" in the interstellar extinction curve. The Diffuse Interstellar Band Synchrotron Radiation Carrier Hunt (DIBSyRCH) experiment has been built at the Synchrotron Radiation Center (SRC) to test these hypotheses by conducting a spectroscopic survey of a broad range of cold, gas phase and clustered PAH molecules and ions. Using a custom echelle spectrograph and the innovative Cryogenic Circulating Advective Multi-Pass (CCAMP) absorption cell, we routinely achieve a detection sensitivity to molecular densities on the order of 107 cm-3 with a signal-to-noise ratio of 10,000 in 60 seconds of data collection in the visible. This instrument, coupled with the high spectral radiance of the synchrotron radiation continuum from the SRC's White Light Beamline, permits rapid acquisition of spectra covering broad wavelength regions with resolution appropriate for the DIBs. In order to obtain astrophysically relevant spectra of low

  1. AN ANALYSIS OF THE SHAPES OF INTERSTELLAR EXTINCTION CURVES. VI. THE NEAR-IR EXTINCTION LAW

    SciTech Connect

    Fitzpatrick, E. L.; Massa, D. E-mail: massa@derckmassa.net

    2009-07-10

    We combine new observations from the Hubble Space Telescope's Advanced Camera of Survey with existing data to investigate the wavelength dependence of near-IR (NIR) extinction. Previous studies suggest a power law form for NIR extinction, with a 'universal' value of the exponent, although some recent observations indicate that significant sight line-to-sight line variability may exist. We show that a power-law model for the NIR extinction provides an excellent fit to most extinction curves, but that the value of the power, {beta}, varies significantly from sight line to sight line. Therefore, it seems that a 'universal NIR extinction law' is not possible. Instead, we find that as {beta} decreases, R(V) {identical_to} A(V)/E(B - V) tends to increase, suggesting that NIR extinction curves which have been considered 'peculiar' may, in fact, be typical for different R(V) values. We show that the power-law parameters can depend on the wavelength interval used to derive them, with the {beta} increasing as longer wavelengths are included. This result implies that extrapolating power-law fits to determine R(V) is unreliable. To avoid this problem, we adopt a different functional form for NIR extinction. This new form mimics a power law whose exponent increases with wavelength, has only two free parameters, can fit all of our curves over a longer wavelength baseline and to higher precision, and produces R(V) values which are consistent with independent estimates and commonly used methods for estimating R(V). Furthermore, unlike the power-law model, it gives R(V)s that are independent of the wavelength interval used to derive them. It also suggests that the relation R(V) = -1.36 E(K-V)/(E(B-V)) - 0.79 can estimate R(V) to {+-}0.12. Finally, we use model extinction curves to show that our extinction curves are in accord with theoretical expectations, and demonstrate how large samples of observational quantities can provide useful constraints on the grain properties.

  2. VERY LARGE INTERSTELLAR GRAINS AS EVIDENCED BY THE MID-INFRARED EXTINCTION

    SciTech Connect

    Wang, Shu; Jiang, B. W.; Li, Aigen E-mail: bjiang@bnu.edu.cn E-mail: lia@missouri.edu

    2015-09-20

    The sizes of interstellar grains are widely distributed, ranging from a few angstroms to a few micrometers. The ultraviolet (UV) and optical extinction constrains the dust in the size range of a couple hundredths of micrometers to several submicrometers. The near and mid infrared (IR) emission constrains the nanometer-sized grains and angstrom-sized very large molecules. However, the quantity and size distribution of micrometer-sized grains remain unknown because they are gray in the UV/optical extinction and they are too cold and emit too little in the IR to be detected by IRAS, Spitzer, or Herschel. In this work, we employ the ∼3–8 μm mid-IR extinction, which is flat in both diffuse and dense regions to constrain the quantity, size, and composition of the μm-sized grain component. We find that, together with nano- and submicron-sized silicate and graphite (as well as polycyclic aromatic hydrocarbons), μm-sized graphite grains with C/H ≈ 137 ppm and a mean size of ∼1.2 μm closely fit the observed interstellar extinction of the Galactic diffuse interstellar medium from the far-UV to the mid-IR, as well as the near-IR to millimeter thermal emission obtained by COBE/DIRBE, COBE/FIRAS, and Planck up to λ ≲ 1000 μm. The μm-sized graphite component accounts for ∼14.6% of the total dust mass and ∼2.5% of the total IR emission.

  3. Interstellar extinction toward the Cas OB6 association: Where is the dust?

    NASA Technical Reports Server (NTRS)

    Hanson, Margaret Murray; Clayton, Geoffrey C.

    1993-01-01

    We have completed a multiband (ultraviolet, optical, and near-infrared) study of the interstellar extinction properties of nine massive stars in IC 1805 and IC 1848, which are both part of Cas OB6 in the Perseus spiral arm. Our analysis includes determination of absolute extinction over the wavelength range from 3 micrometers to 1250 A. We have attempted to distinguish between foreground dust and dust local to Cas OB6. This is done by quantitatively comparing extinction laws of the least reddened sightlines (sampling mostly foreground dust) versus the most reddened sightlines (sampling a larger fraction of the dust in the Cas OB6 region). We have combined previous investigations to better understand the evolution of the interstellar medium in this active star forming region. We found no variation of extinction curve behavior between moderately reddend and heavily reddened Cas OB6 stars. None of the curves show any significant deviation from the Cardelli-Clayton-Mathis (CCM) R(sub upsilon)-dependent extinction. They are all consistent with that seen from diffuse dust. Most or all of the dust along the line of sight may be foreground to Cas OB6. Massive star forming regions can show significant deviations from CCM behavior which have been attributed to processing of the dust grains. Any dust local to the association must exist far from the hot stars in IC 1805 and IC 1848. A previous episode of star formation may have already cleared out the region of most of the gas and dust. Evidence for this can be seen in H I and IRAS data of the region.

  4. The VLT-FLAMES Tarantula Survey. IX. The interstellar medium seen through diffuse interstellar bands and neutral sodium&

    NASA Astrophysics Data System (ADS)

    van Loon, J. Th.; Bailey, M.; Tatton, B. L.; Maíz Apellániz, J.; Crowther, P. A.; de Koter, A.; Evans, C. J.; Hénault-Brunet, V.; Howarth, I. D.; Richter, P.; Sana, H.; Simón-Díaz, S.; Taylor, W.; Walborn, N. R.

    2013-02-01

    Context. The Tarantula Nebula (a.k.a. 30 Dor) is a spectacular star-forming region in the Large Magellanic Cloud (LMC), seen through gas in the Galactic disc and halo. Diffuse interstellar bands (DIBs) offer a unique probe of the diffuse, cool-warm gas in these regions. Aims: The aim is to use DIBs as diagnostics of the local interstellar conditions, whilst at the same time deriving properties of the yet-unknown carriers of these enigmatic spectral features. Methods: Spectra of over 800 early-type stars from the Very Large Telescope Flames Tarantula Survey (VFTS) were analysed. Maps were created, separately, for the Galactic and LMC absorption in the DIBs at 4428 and 6614 Å and - in a smaller region near the central cluster R 136 - neutral sodium (the Na i D doublet); we also measured the DIBs at 5780 and 5797 Å. Results: The maps show strong 4428 and 6614 Å DIBs in the quiescent cloud complex to the south of 30 Dor but weak absorption in the harsher environments to the north (bubbles) and near the OB associations. The Na maps show at least five kinematic components in the LMC and a shell-like structure surrounding R 136, and small-scale structure in the Milky Way. The strengths of the 4428, 5780, 5797 and 6614 Å DIBs are correlated, also with Na absorption and visual extinction. The strong 4428 Å DIB is present already at low Na column density but the 6614, 5780 and 5797 Å DIBs start to be detectable at subsequently larger Na column densities. Conclusions: The carriers of the 4428, 6614, 5780 and 5797 Å DIBs are increasingly prone to removal from irradiated gas. The relative strength of the 5780 and 5797 Å DIBs clearly confirm the Tarantula Nebula as well as Galactic high-latitude gas to represent a harsh radiation environment. The resilience of the 4428 Å DIB suggests its carrier is large, compact and neutral. Structure is detected in the distribution of cool-warm gas on scales between one and >100 pc in the LMC and as little as 0.01 pc in the Sun

  5. Is a pyrene-like molecular ion the cause of the 4,430-A diffuse interstellar absorption band?

    NASA Technical Reports Server (NTRS)

    Salama, F.; Allamandola, L. J.

    1992-01-01

    The diffuse interstellar band (DIB) absorption features of astronomical spectra are suggested by recent results to be separable from the grains that cause visual extinction. Attention is presently given to laboratory measurements of the optical spectrum of the pyrene cation C16H10(+), which is one of the polycyclic aromatic hydrocarbon (PAH) molecular candidates proposed as carriers for DIBs. This ion exhibits an intense but strangely broad continuum similar to that of the naphthalene cation, so that this may be a common feature of all PAH cations and the basis of an explanation for PAHs' converting of an interstellar radiation fraction as large as that from the UV and visible range down to the IR.

  6. A Principal Component Analysis of the Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Ensor, T.; Cami, J.; Bhatt, N. H.; Soddu, A.

    2017-02-01

    We present a principal component (PC) analysis of 23 line-of-sight parameters (including the strengths of 16 diffuse interstellar bands, DIBs) for a well-chosen sample of single-cloud sightlines representing a broad range of environmental conditions. Our analysis indicates that the majority (∼93%) of the variations in the measurements can be captured by only four parameters The main driver (i.e., the first PC) is the amount of DIB-producing material in the line of sight, a quantity that is extremely well traced by the equivalent width of the λ5797 DIB. The second PC is the amount of UV radiation, which correlates well with the λ5797/λ5780 DIB strength ratio. The remaining two PCs are more difficult to interpret, but are likely related to the properties of dust in the line of sight (e.g., the gas-to-dust ratio). With our PCA results, the DIBs can then be used to estimate these line-of-sight parameters.

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

    NASA Astrophysics Data System (ADS)

    van Loon, Jacco Th.; Farhang, A.; Javadi, A.; Bailey, M.; Khosroshahi, H. G.

    The Sun lies in the middle of an enormous cavity of a million degree gas, known as the Local Bubble. The Local Bubble is surrounded by a wall of denser neutral and ionized gas. The Local Bubble extends around 100 pc in the plane of Galaxy and hundreds of parsecs vertically, but absorption-line surveys of neutral sodium and singly-ionized calcium have revealed a highly irregular structure and the presence of neutral clouds within an otherwise tenuous and hot gas. We have undertaken an all-sky, European-Iranian survey of the Local Bubble in the absorption of a number of diffuse interstellar bands (DIBs) to offer a novel view of our neighbourhood. Our dedicated campaigns with ESO's New Technology Telescope and the ING's Isaac Newton Telescope comprise high signal-to-noise, medium-resolution spectra, concentrating on the 5780 and 5797 Å bands which trace ionized/irradiated and neutral/shielded environments, respectively; their carriers are unknown but likely to be large carbonaceous molecules. With about 660 sightlines towards early-type stars distributed over distances up to about 200 pc, our data allow us to reconstruct the first ever 3D DIB map of the Local Bubble, which we present here. While we confirm our expectations that the 5780 Å DIB is relatively strong compared to the 5797 Å DIB in hot/irradiated regions such as which prevail within the Local Bubble and its walls, and the opposite is true for cooler/shielded regions beyond the confines of the Local Bubble, we unexpectedly also detect DIB cloudlets inside of the Local Bubble. These results reveal new insight into the structure of the Local Bubble, as well as helping constrain our understanding of the carriers of the DIBs.

  8. Analysis of interstellar extinction towards the hypergiant Cyg OB2 No. 12

    NASA Astrophysics Data System (ADS)

    Maryeva, O. V.; Chentsov, E. L.; Goranskij, V. P.; Karpov, S. V.

    The Cyg OB2 stellar association hosts an entire zoo of unique objects, and among them -- an enigmatic star Cyg OB2 No. 12 (Schulte 12, MT 304). MT 304 is enigmatic not only due to its highest luminosity (according to various estimates, it is one of the brightest stars in the Galaxy), but also because its reddening is anomalously large, greater than the mean reddening in the association. To explain the nature of anomalous reddening (AV≃ 10 mag) of MT 304, we carried out spectrophotometric observations of 25 stars located in its vicinity. We mapped interstellar extinction within the 2.5 arcmin radius and found it to increase towards MT 304. According to our results, the two most reddened stars in the association after MT 304 are J203240.35+411420.1 and J203239.90+411436.2, both located about 15 arcsec from it. Interstellar extinction AV towards these stars is about 9 mag. Our results favor the hypothesis of the circumstellar nature of reddening excess. In the second part of the paper we present the results of our modeling of MT 282 (B1 IV) and MT 343 (B1 V), which belong to the older population of the association and have ages greater than 10 Myr.

  9. Near Infrared Diffuse Interstellar Bands Toward the Cygnus OB2 Association

    NASA Astrophysics Data System (ADS)

    Hamano, Satoshi; Kobayashi, Naoto; Kondo, Sohei; Sameshima, Hiroaki; Nakanishi, Kenshi; Ikeda, Yuji; Yasui, Chikako; Mizumoto, Misaki; Matsunaga, Noriyuki; Fukue, Kei; Yamamoto, Ryo; Izumi, Natsuko; Mito, Hiroyuki; Nakaoka, Tetsuya; Kawanishi, Takafumi; Kitano, Ayaka; Otsubo, Shogo; Kinoshita, Masaomi; Kawakita, Hideyo

    2016-04-01

    We obtained the near-infrared (NIR) high-resolution (R ≡ λ/Δλ ∼ 20,000) spectra of the seven brightest early-type stars in the Cygnus OB2 association for investigating the environmental dependence of diffuse interstellar bands (DIBs). The WINERED spectrograph mounted on the Araki 1.3 m telescope in Japan was used to collect data. All 20 of the known DIBs within the wavelength coverage of WINERED (0.91 < λ < 1.36 μm) were clearly detected along all lines of sight because of their high flux density in the NIR wavelength range and the large extinction. The equivalent widths (EWs) of DIBs were not correlated with the column densities of C2 molecules, which trace the patchy dense component, suggesting that the NIR DIB carriers are distributed mainly in the diffuse component. On the basis of the correlations among the NIR DIBs both for stars in Cyg OB2 and stars observed previously, λλ10780, 10792, 11797, 12623, and 13175 are found to constitute a “family,” in which the DIBs are correlated well over the wide EW range. In contrast, the EW of λ10504 is found to remain almost constant over the stars in Cyg OB2. The extinction estimated from the average EW of λ10504 (AV ∼ 3.6 mag) roughly corresponds to the lower limit of the extinction distribution of OB stars in Cyg OB2. This suggests that λ10504 is absorbed only by the foreground clouds, implying that the carrier of λ10504 is completely destroyed in Cyg OB2, probably by the strong UV radiation field. The different behaviors of the DIBs may be caused by different properties of the DIB carriers.

  10. NEAR INFRARED DIFFUSE INTERSTELLAR BANDS TOWARD THE CYGNUS OB2 ASSOCIATION

    SciTech Connect

    Hamano, Satoshi; Kondo, Sohei; Sameshima, Hiroaki; Nakanishi, Kenshi; Kawakita, Hideyo; Kobayashi, Naoto; Ikeda, Yuji; Yasui, Chikako; Mizumoto, Misaki; Matsunaga, Noriyuki; Fukue, Kei; Yamamoto, Ryo; Izumi, Natsuko; Mito, Hiroyuki; Nakaoka, Tetsuya; Kawanishi, Takafumi; Kitano, Ayaka; Otsubo, Shogo; Kinoshita, Masaomi

    2016-04-10

    We obtained the near-infrared (NIR) high-resolution (R ≡ λ/Δλ ∼ 20,000) spectra of the seven brightest early-type stars in the Cygnus OB2 association for investigating the environmental dependence of diffuse interstellar bands (DIBs). The WINERED spectrograph mounted on the Araki 1.3 m telescope in Japan was used to collect data. All 20 of the known DIBs within the wavelength coverage of WINERED (0.91 < λ < 1.36 μm) were clearly detected along all lines of sight because of their high flux density in the NIR wavelength range and the large extinction. The equivalent widths (EWs) of DIBs were not correlated with the column densities of C{sub 2} molecules, which trace the patchy dense component, suggesting that the NIR DIB carriers are distributed mainly in the diffuse component. On the basis of the correlations among the NIR DIBs both for stars in Cyg OB2 and stars observed previously, λλ10780, 10792, 11797, 12623, and 13175 are found to constitute a “family,” in which the DIBs are correlated well over the wide EW range. In contrast, the EW of λ10504 is found to remain almost constant over the stars in Cyg OB2. The extinction estimated from the average EW of λ10504 (A{sub V} ∼ 3.6 mag) roughly corresponds to the lower limit of the extinction distribution of OB stars in Cyg OB2. This suggests that λ10504 is absorbed only by the foreground clouds, implying that the carrier of λ10504 is completely destroyed in Cyg OB2, probably by the strong UV radiation field. The different behaviors of the DIBs may be caused by different properties of the DIB carriers.

  11. Properties of interstellar dust responsible for extinction laws with unusually low total-to-selective extinction ratios of RV=1-2

    NASA Astrophysics Data System (ADS)

    Nozawa, Takaya

    2016-11-01

    It is well known that the extinction properties along lines of sight to Type Ia supernovae (SNe Ia) are described by steep extinction curves with unusually low total-to-selective extinction ratios of RV = 1.0 - 2.0 . In order to reveal the properties of interstellar dust that causes such peculiar extinction laws, we perform the fitting calculations to the measured extinction curves by applying a two-component dust model composed of graphite and silicate. As for the size distribution of grains, we consider two function forms of the power-law and lognormal distributions. We find that the steep extinction curves derived from the one-parameter formula by Cardelli et al. (1989) with RV=2.0, 1.5, and 1.0 can be reasonably explained even by the simple power-law dust model that has a fixed power index of - 3.5 with the maximum cut-off radii of amax ≃ 0.13 μm , 0.094 μm, and 0.057 μm , respectively. These maximum cut-off radii are smaller than amax ≃ 0.24 μm considered to be valid in the Milky Way, clearly demonstrating that the interstellar dust responsible for steep extinction curves is highly biased to smaller sizes. We show that the lognomal size distribution can also lead to good fits to the extinction curves with RV = 1.0 - 3.1 by taking the appropriate combinations of the relevant parameters. We discuss that the extinction data at ultraviolet wavelengths are essential for constraining the composition and size distribution of interstellar dust.

  12. Fullerenes and Buckyonions in the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Iglesias Groth, S.

    2004-09-01

    We have studied the contribution of single fullerenes and buckyonions to the interstellar extinction. The photoabsorption spectra of these molecules is predicted and compared with some of the most relevant features of interstellar extinction, the UV bump, far UV rise and the diffuse interstellar bands. We conclude that fullerenes and buckyonions may explain these features and make a preliminary estimate of the carbon fraction locked in these molecules.

  13. Laboratory investigation of the contribution of complex aromatic/aliphatic polycyclic hybrid molecular structures to interstellar ultraviolet extinction and infrared emission

    NASA Technical Reports Server (NTRS)

    Arnoult, K. M.; Wdowiak, T. J.; Beegle, L. W.

    2000-01-01

    We have demonstrated by experiment that, in an energetic environment, a simple polycyclic aromatic hydrocarbon (PAH) such as naphthalene will undergo chemical reactions that produce a wide array of more complex species (an aggregate). For a stellar wind of a highly evolved star (post-asymptotic giant branch [post-AGB]), this process would be in addition to what is expected from reactions occurring under thermodynamic equilibrium. A surprising result of that work was that produced in substantial abundance are hydrogenated forms that are hybrids of polycyclic aromatic and polycyclic alkanes. Infrared spectroscopy described here reveals a spectral character for these materials that has much in common with that observed for the constituents of circumstellar clouds of post-AGB stars. It can be demonstrated that a methylene (-CH2-) substructure, as in cycloalkanes, is the likely carrier of the 6.9 microns band emission of dust that has recently been formed around IRAS 22272+5433, NGC 7027, and CPD -56 8032. Ultraviolet spectroscopy previously done with a lower limit of 190 nm had revealed that this molecular aggregate can contribute to the interstellar extinction feature at 2175 angstroms. We have now extended our UV spectroscopy of these materials to 110 nm by a vacuum ultraviolet technique. That work, described here, reveals new spectral characteristics and describes how material newly formed during the late stages of stellar evolution could have produced an extinction feature claimed to exist at 1700 angstroms in the spectrum of HD 145502 and also how the newly formed hydrocarbon material would be transformed/aged in the general interstellar environment. The contribution of this molecular aggregate to the rise in interstellar extinction at wavelengths below 1500 angstroms is also examined. The panspectral measurements of the materials produced in the laboratory, using plasmas of H, He, N, and O to convert the simple PAH naphthalene to an aggregate of complex species

  14. Unusual relative strengths of the diffuse interstellar bands in some interstellar dust clouds

    NASA Technical Reports Server (NTRS)

    Krelowski, J.; Walker, G. A. H.

    1986-01-01

    Some of the diffuse interstellar features (DIBs) in the spectra of certain stars at high galactic latitudes (1 is greater than 15 degrees) are unusually weak or absent while others have the strength expected for their color excess. In some cases the stars are probably reddened by single interstellar clouds. There appear to be three families of DIBs. The effects of these families are examined. The existance of the three families implies that at least three agents cause the DIBs and that the proportions of the agents or the physical conditions giving rise to the DIBs can vary from cloud to cloud.

  15. VizieR Online Data Catalog: 3D interstellar extinct. map within nearest kpc (Gontcharov, 2012)

    NASA Astrophysics Data System (ADS)

    Gontcharov, G. A.

    2016-07-01

    The product of the previously constructed 3D maps of stellar reddening (2010AstL...36..584G) and Rv variations (2012AstL...38...12G) has allowed us to produce a 3D interstellar extinction map within the nearest kiloparsec from the Sun with a spatial resolution of 100pc and an accuracy of 0.2m. This map is compared with the 2D reddening map by Schlegel et al. (1998ApJ...500..525S), the 3D extinction map at high latitudes by Jones et al. (2011AJ....142...44J), and the analytical 3D extinction models by Arenou et al. (1992A&A...258..104A) and Gontcharov (2009AstL...35..780G). In all cases, we have found good agreement and show that there are no systematic errors in the new map everywhere except the direction toward the Galactic center. We have found that the map by Schlegel et al. (1998ApJ...500..525S) reaches saturation near the Galactic equator at E(B-V)>0.8m, has a zero-point error and systematic errors gradually increasing with reddening, and among the analytical models those that take into account the extinction in the Gould Belt are more accurate. Our extinction map shows that it is determined by reddening variations at low latitudes and Rv variations at high ones. This naturally explains the contradictory data on the correlation or anticorrelation between reddening and Rv available in the literature. There is a correlation in a thin layer near the Galactic equator, because both reddening and Rv here increase toward the Galactic center. There is an anticorrelation outside this layer, because higher values of Rv correspond to lower reddening at high and middle latitudes. Systematic differences in sizes and other properties of the dust grains in different parts of the Galaxy manifest themselves in this way. The largest structures within the nearest kiloparsec, including the Local Bubble, the Gould Belt, the Great Tunnel, the Scorpius, Perseus, Orion, and other complexes, have manifested themselves in the constructed map. (1 data file).

  16. SWIFT ULTRAVIOLET OBSERVATIONS OF SUPERNOVA 2014J IN M82: LARGE EXTINCTION FROM INTERSTELLAR DUST

    SciTech Connect

    Brown, Peter J.; Smitka, Michael T.; Wang, Lifan; Krisciunas, Kevin; Breeveld, Alice; Kuin, N. Paul; Page, Mat; De Pasquale, Massimiliano; Hartmann, Dieter H.; Milne, Peter A.; Siegel, Michael

    2015-05-20

    We present optical and ultraviolet (UV) photometry and spectra of the very nearby and highly reddened supernova (SN) 2014J in M82 obtained with the Swift Ultra-Violet/Optical Telescope (UVOT). Comparison of the UVOT grism spectra of SN 2014J with Hubble Space Telescope observations of SN2011fe or UVOT grism spectra of SN 2012fr are consistent with an extinction law with a low value of R{sub V} ∼1.4. The high reddening causes the detected photon distribution in the broadband UV filters to have a much longer effective wavelength than for an unreddened SN. The light curve evolution is consistent with this shift and does not show a flattening due to photons being scattered back into the line of sight (LOS). The light curve shapes and color evolution are inconsistent with a contribution scattered into the LOS by circumstellar dust. We conclude that most or all of the high reddening must come from interstellar dust. We show that even for a single dust composition, there is not a unique reddening law caused by circumstellar scattering. Rather, when considering scattering from a time-variable source, we confirm earlier studies that the reddening law is a function of the dust geometry, column density, and epoch. We also show how an assumed geometry of dust as a foreground sheet in mixed stellar/dust systems will lead to a higher inferred R{sub V}. Rather than assuming the dust around SNe is peculiar, SNe may be useful probes of the interstellar reddening laws in other galaxies.

  17. Is a pyrene-like molecular ion the cause of the 4,430-angstroms diffuse interstellar absorption band?

    NASA Technical Reports Server (NTRS)

    Salama, F.; Allamandola, L. J.

    1992-01-01

    The diffuse interstellar bands (DIBs), ubiquitous absorption features in astronomical spectra, have been known since early this century and now number more than a hundred. Ranging from 4,400 angstroms to the near infrared, they differ markedly in depth, width and shape, making the concept of a single carrier unlikely. Whether they are due to gas or grains is not settled, but recent results suggest that the DIB carriers are quite separate from the grains that cause visual extinction. Among molecular candidates the polycyclic aromatic hydrocarbons (PAHs) have been proposed as the possible carriers of some of the DIBs, and we present here laboratory measurements of the optical spectrum of the pyrene cation C16H10+ in neon and argon matrices. The strongest absorption feature falls at 4,435 +/- 5 angstroms in the argon matrix and 4,395 +/- 5 angstroms in the neon matrix, both close to the strong 4,430-angstroms DIB. If this or a related pyrene-like species is responsible for this particular band, it must account for 0.2% of all cosmic carbon. The ion also shows an intense but puzzling broad continuum, extending from the ultraviolet to the visible, similar to what is seen in the naphthalene cation and perhaps therefore a common feature of all PAH cations. This may provide an explanation of how PAHs convert a large fraction of interstellar radiation from ultraviolet and visible wavelengths down to the infrared.

  18. Update of the Catalogue of Diffuse Interstellar Bands by Snow et al. [1977

    NASA Astrophysics Data System (ADS)

    Guarinos, J.

    1988-05-01

    This bibliographic search has been undertaken in order to gather all data concerning four diffuse interstellar bands (4430 Å, 5780 Å, 5797 Å, 6284 Å) published since the Swow, York, and Welty (1977) catalogue (see Abstr. 19.131.102), and up to 1987.0.

  19. A weak diffuse interstellar band in the far-ultraviolet spectrum of zeta Ophiuchi?

    NASA Technical Reports Server (NTRS)

    Tripp, Todd M.; Cardelli, Jason A.; Savage, Blair D.

    1994-01-01

    Goddard High Resolution Spectrograph (GHRS) observations at 3.5 km/s resolution reveal several new weak unidentified interstellar absorption lines in the ultraviolet spectrum of zeta Ophiuchi. The unidentified line at 1369.13 A has the appearance and characteristics of a weak diffuse interstellar band (DIB). The line has a smooth profile similar to many optical diffuse interstellar bands (i.e., a shallow asymmetric profile), it is clearly broader than identified interstellar lines near it in wavelength, and its full width at half maximum in ergs is comparable to the widths of the weak optical DIBs. The asymmetric profile cannot be attributed to blended absorption from diffuse clouds at different velocities; at this resolution the two principal cloud complexes on the sight line at heliocentric velocities of -27 and -15 km/s are clearly separated. We compare this unidentified absorption feature to identified interstellar atomic and molecular absorption lines and optical DIBs observed on the zeta Oph and xi Per sight lines, and we conclude that it is reasonable to suggest that this absorption feature might be a DIB. This is not a unique interpretation however; the unidentified line could alternatively be due to gas in the zeta Oph H II region or a blend of unknown neutral atomic or molecular absorption lines.

  20. The dark cloud TGU H994 P1 (LDN 1399, LDN 1400, and LDN 1402): Interstellar extinction and distance

    NASA Astrophysics Data System (ADS)

    Straižys, V.; Čepas, V.; Boyle, R. P.; Munari, U.; Zdanavičius, J.; Maskoliūnas, M.; Kazlauskas, A.; Zdanavičius, K.

    2016-01-01

    The results of CCD photometry in the seven-colour Vilnius system, for about 1000 stars down to V = 20 mag and their two-dimensional spectral types, are used to investigate the interstellar extinction in a 1.5 square degree area in the direction of the dark cloud TGU H994 P1 (LDN 1399, LDN 1400 and LDN 1402) in Camelopardalis. Photometric classification of 18 brightest stars down to V = 12 mag was verified by the spectra obtained with the 1.22 m telescope of the Asiago Observatory. The interstellar extinction run with distance is investigated with the results of photometry in the Vilnius system, and 504 red clump giants, identified by combining the results of infrared photometry from the 2MASS and WISE surveys. A possible distance of 140 ± 11 pc to the TGU H994 P1 cloud seems to be acceptable. Alternative distances of the cloud are discussed. The complex of the Camelopardalis clouds probably has a considerable depth along the line of sight, similar to that observed in the Taurus-Auriga complex. The maximum extinction AV in the dark filaments is found to be about 6.5 mag. Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A31

  1. FUSE Measurements of Rydberg Bands of Interstellar CO between 925 and 1150 Å

    NASA Astrophysics Data System (ADS)

    Sheffer, Y.; Federman, S. R.; Andersson, B.-G.

    2003-11-01

    We report the detection of 11 Rydberg bands of CO in FUSE spectra of the sight line toward HD 203374A. Eight of these electronic bands are seen in the interstellar medium for the first time. Our simultaneous fit of five non-Rydberg A-X bands together with the strongest Rydberg band of CO, C-X (0-0), yields a four-component cloud structure toward the stellar target. With this model we synthesize the other Rydberg bands in order to derive their oscillator strengths. We find that the strength of some bands was underestimated in previously published results from laboratory measurements. The implication is important for theoretical calculations of the abundance of interstellar CO, because its dissociation and self-shielding depend on oscillator strengths for these bands. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE), which is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.

  2. Constant Intensities of Diffuse Interstellar Bands in the Spectrum of AE Aur

    NASA Astrophysics Data System (ADS)

    Krełowski, J.; Galazutdinov, G. A.; Bondar, A.; Byeong-Cheol, L.

    2017-03-01

    Using spectra of the star AE Aur (HD 34078), covering the period 1997-2016, we prove that all strong diffuse interstellar bands are of the same intensity during the whole period of observations (inside 3-5% of the intensity). This is in sharp contrast to the behavior of both CH and CH+ features which, during the last six years, declined sharply by 13% and 28% respectively. Diffuse bands seem to behave more or less as interstellar atomic lines. We checked also the behavior of CaII lines which should be of constant intensities as the carrier fills the space evenly. Our observations confirm this and allow us to re-estimate the distance to HD 34078.

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

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2016-01-01

    The Diffuse Interstellar Bands (DIBs) are a set of 500 absorption bands that are detected in the spectra of stars with interstellar clouds in the line of sight. DIBs are found from the NUV to the NIR in the spectra of reddened stars spanning different interstellar environments in our local, and in other galaxies. DIB carriers are a significant part of the interstellar chemical inventory. They are stable and ubiquitous in a broad variety of environments and play a unique role in interstellar physics/chemistry. It has long been realized that the solving of the DIB problem requires a strong synergy between astronomical observations, laboratory astrophysics, and astrophysical modeling of line-of-sights. PAHs are among the molecular species that have been proposed as DIB carriers. We will present an assessment of the PAH-DIB model in view of the progress and the advances that have been achieved over the past years through a series of studies involving astronomical observations of DIBs, laboratory simulation of interstellar analogs for neutrals and ionized PAHs, theoretical calculations of PAH spectra and the modelization of diffuse and translucent interstellar clouds. We will present a summary of what has been learned from these complementary studies, the constraints that can now be derived for the PAHs as DIB carriers in the context of the PAH-DIB model and how these constraints can be applied to the EDIBLES project. The spectra of several neutral and ionized PAHs isolated in the gas phase at low temperature have been measured in the laboratory under experimental conditions that mimic interstellar conditions and are compared with an extensive set of astronomical spectra of reddened, early type stars. The comparisons of astronomical and laboratory data provide upper limits for the abundances of specific neutral PAH molecules and ions along specific lines-of-sight. Something that is not attainable from infrared observations alone. We present the characteristics of the

  4. VizieR Online Data Catalog: Suppl. to Diffuse Interstellar Band Measurements (Guarinos 1988)

    NASA Astrophysics Data System (ADS)

    Guarinos, J.

    1997-02-01

    This bibliographic search has been undertaken in order to gather all data concerning four diffuse interstellar bands (DIB) published since the Snow, York, and Welty (1977) catalogue, and up to 1987.0. These four DIB are : 4430, 5780, 5797, and 6284 Angstrom. In the present set of data, no statistical reduction to a unique system has been made because most of the lists contain only few data. (1 data file).

  5. Further Studies of λ 5797.1 Diffuse Interstellar Band

    NASA Astrophysics Data System (ADS)

    Oka, Takeshi; Hobbs, L. M.; Welty, Daniel E.; York, Donald G.; Dahlstrom, Julie; Witt, Adolf N.

    2015-06-01

    The λ~5797.1 DIB is unique with its sharp central feature. We simulated the spectrum based on three premises: (1) Its carrier molecule is polar as concluded from the anomalous spectrum toward the star Herschel 36. (2) The central feature is Q-branch of a parallel band of a prolate top. (3) The radiative temperature of the environment is T_r = 2.73 K. A comparison with observed spectrum indicated that the carrier contains 5-7 heavy atoms. To further strengthen this hypothesis, we have looked for vibronic satellites of the λ~5797.1 DIB. Since its anomaly toward Her 36 was ascribed to the lengthening of bonds upon the electronic excitation, vibronic satellites involving stretch vibrations are expected. Among the 73 DIBs observed toward HD 183143 to the blue of 5797.1 Å, two DIBs, λ~5545.1 and λ~5494.2 stand out as highly correlated with λ~5797.1 DIB. Their correlation coefficients 0.941 and 0.943, respectively, are not sufficiently high to establish the vibronic relation by themselves but can be explained as due to high uncertainties due to their weakness and their stellar blends. They are above the λ~5797.1 DIB by 784.0 cm-1 and 951.2 cm-1, respectively, approximately expected for stretching vibrations. Another observations which may possibly be explained by our hypothesis is the emission at 5800 Å from the Red Rectangle Nebula called RR 5800. Our analysis suggests that λ~5797.1 DIB and RR 5800 are consistently explained as caused by the same molecule. T.H. Kerr, R.E. Hibbins, S.J. Fossey, J.R. Miles, P.J. Sarre, ApJ 495, 941 (1998) T. Oka, D.E. Welty, S. Johnson, D.G. York, J. Dahlstrom, L.M. Hobbs, ApJ 773, 42 (2013) J. Huang, T. Oka, Mol. Phys. J.P. Maier Special Issue in press. G.D. Schmidt, A.N. Witt, ApJ 383, 698 (1991)

  6. Electronic Spectroscopy of [FePAH](+) Complexes in the Region of the Diffuse Interstellar Bands: Multireference Wave Function Studies on [FeC6H6](+).

    PubMed

    Lanza, Mathieu; Simon, Aude; Ben Amor, Nadia

    2015-06-11

    The low-energy states and electronic spectrum in the near-infrared-visible region of [FeC6H6](+) are studied by theoretical approaches. An exhaustive exploration of the potential energy surface of [FeC6H6](+) is performed using the density functional theory method. The ground state is found to be a (4)A1 state. The structures of the lowest energy states ((4)A2 and (4)A1) are used to perform multireference wave function calculations by means of the multistate complete active space with perturbation at the second order method. Contrary to the density functional theory results ((4)A1 ground state), multireference perturbative calculations show that the (4)A2 state is the ground state. The vertical electronic spectrum is computed and compared with the astronomical diffuse interstellar bands, a set of near-infrared-visible bands detected on the extinction curve in our and other galaxies. Many transitions are found in this domain, corresponding to d → d, d → 4s, or d → π* excitations, but few are allowed and, if they are, their oscillation strengths are small. Even though some band positions could match some of the observed bands, the relative intensities do not fit, making the contribution of the [Fe-C6H6](+) complexes to the diffuse interstellar bands questionable. This work, however, lays the foundation for the studies of polycyclic aromatic hydrocarbons (PAHs) complexed to Fe cations that are more likely to possess d → π* and π → π* transitions in the diffuse interstellar bands domain. PAH ligands indeed possess a larger number of π and π* orbitals, respectively, higher and lower in energy than those of C6H6, which are expected to lead to lower energy d → π* and π → π* transitions in [FePAH](+) than in [FeC6H6](+) complexes.

  7. Probing the Local Bubble with Diffuse Interstellar Bands. III. The Northern Hemisphere Data and Catalog

    NASA Astrophysics Data System (ADS)

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; van Loon, Jacco Th.

    2015-02-01

    We present new high signal-to-noise ratio (S/N) observations of the diffuse interstellar bands (DIBs) in the Local Bubble and its surroundings. We observed 432 sightlines and obtain the equivalent widths of the λ5780 and λ5797 Å DIBs up to a distance of ~200 pc. All of the observations were carried out using the Intermediate Dispersion Spectrograph on the 2.5 m Isaac Newton Telescope, during three years, to reach a minimum S/N of ~2000. All of the λ5780 and λ5797 absorptions are presented in this paper and we tabulate the observed values of the interstellar parameters, λ5780, λ5797, Na ID1, and Na ID2, including the uncertainties.

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

    SciTech Connect

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; Van Loon, Jacco Th.

    2015-02-01

    We present new high signal-to-noise ratio (S/N) observations of the diffuse interstellar bands (DIBs) in the Local Bubble and its surroundings. We observed 432 sightlines and obtain the equivalent widths of the λ5780 and λ5797 Å DIBs up to a distance of ∼200 pc. All of the observations were carried out using the Intermediate Dispersion Spectrograph on the 2.5 m Isaac Newton Telescope, during three years, to reach a minimum S/N of ∼2000. All of the λ5780 and λ5797 absorptions are presented in this paper and we tabulate the observed values of the interstellar parameters, λ5780, λ5797, Na ID{sub 1}, and Na ID{sub 2}, including the uncertainties.

  9. A framework for resolving the origin, nature and evolution of the diffuse interstellar band carriers?

    NASA Astrophysics Data System (ADS)

    Jones, Anthony P.

    2014-10-01

    The carriers of the diffuse interstellar bands (DIBs) still remain an unknown commodity. Both dust and molecules have been suggested as carriers but none proposed have yet been able to explain the nature and the diversity of the DIBs. Hence, it is perhaps time to review the problem in terms of the intermediate-sized nano-particles. It is here proposed that the DIB carriers are the nm-sized and sub-nm-sized products of the UV photo-fragmentation of hydrogenated amorphous carbon grains, a-C(:H), and their heteroatom-doped variants, a-C:H:X (where X may be O, N, Mg, Si, Fe, S, Ni, P, …). An interstellar hydrogenated amorphous carbon dust evolutionary framework is described within which a solution to the age-old DIB problem could perhaps be found.

  10. Parsec-scale structures and diffuse bands in a translucent interstellar medium at z≃ 0.079

    NASA Astrophysics Data System (ADS)

    Srianand, R.; Gupta, N.; Rahmani, H.; Momjian, E.; Petitjean, P.; Noterdaeme, P.

    2013-01-01

    We present a detailed study of the QSO-galaxy pair [SDSS J163956.35+112758.7 (zq = 0.993) and SDSS J163956.38+112802.1 (zg = 0.079)] based on observations carried out using the Giant Metrewave Radio Telescope (GMRT), the Very Large Baseline Array (VLBA), the Sloan Digital Sky Survey and the ESO New Technology Telescope. We show that the interstellar medium of the galaxy probed by the QSO line of sight has near-solar metallicity [12+log(O/H) = 8.47 ± 0.25] and dust extinction [E(B - V) ˜ 0.83 ± 0.11] typical of what is usually seen in translucent clouds. We report the detection of absorption in the λ6284 diffuse interstellar band (DIB) with a rest equivalent width of 1.45 ± 0.20 Å. Our GMRT spectrum shows a strong 21-cm absorption at the redshift of the galaxy with an integrated optical depth of 15.70 ± 0.13 km s-1. Follow-up VLBA observations show that the background radio source is resolved into three components with a maximum projected separation of 89 pc at the redshift of the galaxy. One of these components is too weak to provide useful 21-cm H i information. The integrated H i optical depth towards the other two components are higher than that measured in our GMRT spectrum and differ by a factor 2. By comparing the GMRT and VLBA spectra we show the presence of structures in the 21-cm optical depth on parsec scales. We discuss the implications of such structures for the spin-temperature measurements in high-z damped Lyman α systems. The analysis presented here suggests that this QSO-galaxy pair is an ideal target for studying the DIBs and molecular species using future observations in optical and radio wavebands.

  11. Ion irradiation of carbonaceous interstellar analogues. Effects of cosmic rays on the 3.4 μm interstellar absorption band

    NASA Astrophysics Data System (ADS)

    Godard, M.; Féraud, G.; Chabot, M.; Carpentier, Y.; Pino, T.; Brunetto, R.; Duprat, J.; Engrand, C.; Bréchignac, P.; D'Hendecourt, L.; Dartois, E.

    2011-05-01

    Context. A 3.4 μm absorption band (around 2900 cm-1), assigned to aliphatic C-H stretching modes of hydrogenated amorphous carbons (a-C:H), is widely observed in the diffuse interstellar medium, but disappears or is modified in dense clouds. This spectral difference between different phases of the interstellar medium reflects the processing of dust in different environments. Cosmic ray bombardment is one of the interstellar processes that make carbonaceous dust evolve. Aims: We investigate the effects of cosmic rays on the interstellar 3.4 μm absorption band carriers. Methods: Samples of carbonaceous interstellar analogues (a-C:H and soot) were irradiated at room temperature by swift ions with energy in the MeV range (from 0.2 to 160 MeV). The dehydrogenation and chemical bonding modifications that occurred during irradiation were studied with IR spectroscopy. Results: For all samples and all ions/energies used, we observed a decrease of the aliphatic C-H absorption bands intensity with the ion fluence. This evolution agrees with a model that describes the hydrogen loss as caused by the molecular recombination of two free H atoms created by the breaking of C-H bonds by the impinging ions. The corresponding destruction cross section and asymptotic hydrogen content are obtained for each experiment and their behaviour over a large range of ion stopping powers are inferred. Using elemental abundances and energy distributions of galactic cosmic rays, we investigated the implications of these results in different astrophysical environments. The results are compared to the processing by UV photons and H atoms in different regions of the interstellar medium. Conclusions: The destruction of aliphatic C-H bonds by cosmic rays occurs in characteristic times of a few 108 years, and it appears that even at longer time scales, cosmic rays alone cannot explain the observed disappearance of this spectral signature in dense regions. In diffuse interstellar medium, the formation

  12. Assessment of the polycyclic aromatic hydrocarbon-diffuse interstellar band proposal

    NASA Technical Reports Server (NTRS)

    Salama, F.; Bakes, E. L.; Allamandola, L. J.; Tielens, A. G.

    1996-01-01

    The potential link between neutral and/or ionized polycyclic aromatic hydrocarbons (PAHs) and the diffuse interstellar band (DIB) carriers is examined. Based on the study of the general physical and chemical properties of PAHs, an assessment is made of their possible contribution to the DIB carriers. It is found that, under the conditions reigning in the diffuse interstellar medium, PAHs can be present in the form of neutral molecules as well as positive and/or negative ions. The charge distribution of small PAHs is dominated, however, by two charge states at one time with compact PAHs present only in the neutral and cationic forms. Each PAH has a distinct spectral signature depending on its charge state. Moreover, the spectra of ionized PAHs are always clearly dominated by a single band in the DIB spectral range. In the case of compact PAH ions, the strongest absorption band is of type A (i.e., the band is broad, falls in the high-energy range of the spectrum, and possesses a large oscillator strength), and seems to correlate with strong and broad DIBs. For noncompact PAH ions, the strongest absorption band is of type I (i.e., the band is narrow, falls in the low-energy range of the spectrum, and possesses a small oscillator strength), and seems to correlate with weak and narrow DIBs. Potential molecular size and structure constraints for interstellar PAHs are derived by comparing known DIB characteristics to the spectroscopic properties of PAHs. It is found that (i) only neutral PAHs larger than about 30 carbon atoms could, if present, contribute to the DIBs. (ii) For compact PAHs, only ions with less than about 250 carbon atoms could, if present, contribute to the DIBs. (iii) The observed distribution of the DIBs between strong/moderate and broad bands on the one hand and weak and narow bands on the other can easily be interpreted in the context of the PAH proposal by a distribution of compact and noncompact PAH ions, respectively. A plausible correlation

  13. Assessment of the Polycyclic Aromatic Hydrocarbon-Diffuse Interstellar Band Proposal

    NASA Technical Reports Server (NTRS)

    Salama, Farid; Bakes, F.; Allamandola, L.; Tielens, A. G. G. M.; Witteborn, Fred C. (Technical Monitor)

    1995-01-01

    The potential link between neutral and/or ionized polycyclic aromatic hydrocarbons (PAHs) and the diffuse interstellar band (DIB) carriers is examined. Based on the study of the general physical and chemical properties of PAHs, an assessment is made of their possible contribution to the DIB carriers. It is found that, under the conditions reigning in the diffuse interstellar medium, PAHs can be present in the form of neutral molecules as well as positive and/or negative ions. The charge distribution of small PAHs is dominated, however, by two charge states at one time with compact PAHs present only in the neutral and cationic forms. Each PAH has a distinct spectral signature depending on its charge state. Moreover, the spectra of ionized PAHs are always clearly dominated by a single band in the DIB spectral range. In the case of compact PAH ions, the strongest absorption band is of type A (i.e., the band is broad, falls in the high energy range of the spectrum, and possess a large oscillator strength), and seems to correlate with strong and broad DIBs. In the case of non-compact PAH ions, the strongest absorption band is of type I (i.e., the band is narrow, falls in the low energy range of the spectrum, and possess a small oscillator strength), and seems to correlate with weak and narrow DIBs. Potential molecular size and structure constraints for interstellar PAHs are derived by comparing known DIB characteristics to the spectroscopic properties of PAHs. It is found that: (i) Only neutral PAHs larger than about 30 carbon atoms could, if present, contribute to the DIBs. (ii) For compact PAHs, only ions with less than about 250 carbon atoms could, if present, contribute to the DIBs. (iii) The observed distribution of the DIBs between strong/moderate and broad bands on the one hand and weak and narrow bands on the other hand can easily be interpreted in the context of the PAH proposal by a distribution between compact and non-compact PAH ions, respectively. A

  14. Towards DIB mapping in galaxies beyond 100 Mpc. A radial profile of the λ5780.5 diffuse interstellar band in AM 1353-272 B

    NASA Astrophysics Data System (ADS)

    Monreal-Ibero, A.; Weilbacher, P. M.; Wendt, M.; Selman, F.; Lallement, R.; Brinchmann, J.; Kamann, S.; Sandin, C.

    2015-04-01

    Context. Diffuse interstellar bands (DIBs) are non-stellar weak absorption features of unknown origin found in the spectra of stars viewed through one or several clouds of the interstellar medium (ISM). Research of DIBs outside the Milky Way is currently very limited. In particular, spatially resolved investigations of DIBs outside of the Local Group are, to our knowledge, inexistent. Aims: In this contribution, we explore the capability of the high-sensitivity integral field spectrograph, MUSE, as a tool for mapping diffuse interstellar bands at distances larger than 100 Mpc. Methods: We used MUSE commissioning data for AM 1353-272 B, the member with the highest extinction of the Dentist's Chair, an interacting system of two spiral galaxies. High signal-to-noise spectra were created by co-adding the signal of many spatial elements distributed in a geometry of concentric elliptical half-rings. Results: We derived decreasing radial profiles for the equivalent width of the λ5780.5 DIB both in the receding and approaching side of the companion galaxy up to distances of ~4.6 kpc from the centre of the galaxy. The interstellar extinction as derived from the Hα/Hβ line ratio displays a similar trend, with decreasing values towards the external parts. This translates into an intrinsic correlation between the strength of the DIB and the extinction within AM 1353-272 B, consistent with the currently existing global trend between these quantities when using measurements for Galactic and extragalactic sightlines. Conclusions: It seems feasible to map the DIB strength in the Local Universe, which has up to now only been performed for the Milky Way. This offers a new approach to studying the relationship between DIBs and other characteristics and species of the ISM in addition to using galaxies in the Local Group or sightlines towards very bright targets outside the Local Group. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under program

  15. Dark clouds in the vicinity of the emission nebula Sh2-205: interstellar extinction and distances

    NASA Astrophysics Data System (ADS)

    Straižys, V.; Čepas, V.; Boyle, R. P.; Zdanavičius, J.; Maskoliūnas, M.; Kazlauskas, A.; Zdanavičius, K.; Černis, K.

    2016-05-01

    Results of CCD photometry in the seven-colour Vilnius system for 922 stars down to V = 16-17 mag and for 302 stars down to 19.5 mag are used to investigate the interstellar extinction in an area of 1.5 square degrees in the direction of the P7 and P8 clumps of the dark cloud TGU H942, which lies in the vicinity of the emission nebula Sh2-205. In addition, we used 662 red clump giants that were identified by combining the 2MASS and WISE infrared surveys. The resulting plots of extinction versus distance were compared with previous results of the distribution and radial velocities of CO clouds and with dust maps in different passbands of the IRAS and WISE orbiting observatories. A possible distance of the front edge of the nearest cloud layer at 130 ± 10 pc was found. This dust layer probably covers all the investigated area, which results in extinction of up to 1.8 mag in some directions. A second rise of the extinction seems to be present at 500-600 pc. Within this layer, the clumps P7 and P8 of the dust cloud TGU H942, the Sh2-205 emission nebula, and the infrared cluster FSR 655 are probably located. In the direction of these clouds, we identified 88 young stellar objects and a new infrared cluster. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A21

  16. Red spectra of the brightest stars in Cygnus OB2 - Possible detection of two new interstellar bands

    NASA Astrophysics Data System (ADS)

    Torres-Dodgen, Ana V.

    1990-12-01

    The stellar and interstellar spectra of the 12 brightest stars in the Cygnus OB2 association are described. The observations were made in the wavelength range 5800 A-8500 A, at about 7 A resolution. Two new lines, centered near 7430 A and 7932 A, may be previously undetected interstellar bands. The former may be formed in the interstellar medium as well as in the dust environment of Cyg OB2, while the latter may be formed only in the dust environment of Cyg OB2.

  17. Dust in the small Magellanic Cloud. 2: Dust models from interstellar polarization and extinction data

    NASA Technical Reports Server (NTRS)

    Rodrigues, C. V.; Magalhaes, A. M.; Coyne, G. V.

    1995-01-01

    We study the dust in the Small Magellanic Cloud using our polarization and extinction data (Paper 1) and existing dust models. The data suggest that the monotonic SMC extinction curve is related to values of lambda(sub max), the wavelength of maximum polarization, which are on the average smaller than the mean for the Galaxy. On the other hand, AZV 456, a star with an extinction similar to that for the Galaxy, shows a value of lambda(sub max) similar to the mean for the Galaxy. We discuss simultaneous dust model fits to extinction and polarization. Fits to the wavelength dependent polarization data are possible for stars with small lambda(sub max). In general, they imply dust size distributions which are narrower and have smaller mean sizes compared to typical size distributions for the Galaxy. However, stars with lambda(sub max) close to the Galactic norm, which also have a narrower polarization curve, cannot be fit adequately. This holds true for all of the dust models considered. The best fits to the extinction curves are obtained with a power law size distribution by assuming that the cylindrical and spherical silicate grains have a volume distribution which is continuous from the smaller spheres to the larger cylinders. The size distribution for the cylinders is taken from the fit to the polarization. The 'typical', monotonic SMC extinction curve can be fit well with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grain. However, amorphous carbon and silicate grains also fit the data well. AZV456, which has an extinction curve similar to that for the Galaxy, has a UV bump which is too blue to be fit by spherical graphite grains.

  18. Experimental indication of a naphthalene-base molecular aggregate for the carrier of the 2175 angstroms interstellar extinction feature

    NASA Technical Reports Server (NTRS)

    Beegle, L. W.; Wdowiak, T. J.; Robinson, M. S.; Cronin, J. R.; McGehee, M. D.; Clemett, S. J.; Gillette, S.

    1997-01-01

    Experiments where the simple polycyclic aromatic hydrocarbon (PAH) naphthalene (C10H8) is subjected to the energetic environment of a plasma have resulted in the synthesis of a molecular aggregate that has ultraviolet spectral characteristics that suggest it provides insight into the nature of the carrier of the 2175 angstroms interstellar extinction feature and may be a laboratory analog. Ultraviolet, visible, infrared, and mass spectroscopy, along with gas chromatography, indicate that it is a molecular aggregate in which an aromatic double ring ("naphthalene") structural base serves as the electron "box" chromophore that gives rise to the envelope of the 2175 angstroms feature. This chromophore can also provide the peak of the feature or function as a mantle in concert with another peak provider such as graphite. The molecular base/chromophore manifests itself both as a structural component of an alkyl-aromatic polymer and as a substructure of hydrogenated PAH species. Its spectral and molecular characteristics are consistent with what is generally expected for a complex molecular aggregate that has a role as an interstellar constituent.

  19. Laboratory evidence for highly unsaturated hydrocarbons as carriers of some of the diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Fulara, J.; Lessen, D.; Freivogel, P.; Maier, J. P.

    1993-12-01

    THERE are many absorption lines in the visible and near-infrared spectra of stars located on the far side of diffuse interstellar clouds. The origin of these 'diffuse interstellar bands' (DIBs) has remained an unanswered question since their discovery almost 70 years ago1,2. There are now over 100 known bands1,3-6 and it is clear from the range of line widths, depths and shapes that the lines are unlikely to come from a single 'carrier'. Many of the proposed carriers, such as gas-phase carbon chains7, fullerenes8 and dust grains9, fail in having ultraviolet absorption lines where none has yet been observed in the stellar spectra. Poly cyclic aromatic species such as Ci16H10+ (ref. 10) and C10H8 (ref. 11) were recently claimed to be good candidates for carriers of some of the DIBs. Here we present laboratory evidence that highly unsaturated hydrocarbons with carbon numbers 6-12 may be the carriers of some of the DIBs in the range 480-1,000 nm. We deposit mass-selected molecules in a neon matrix at 5 K and measure their near-infrared, visible and ultraviolet spectra. Not only do these species have visible and near-infrared lines corresponding to fifteen DIBs, but they also show no absorption lines in the ultraviolet, consistent with astronomical observations.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  1. A Catalog of 1.5273 um Diffuse Interstellar Bands Based on APOGEE Hot Telluric Calibrators

    NASA Astrophysics Data System (ADS)

    Elyajouri, M.; Monreal-Ibero, A.; Remy, Q.; Lallement, R.

    2016-08-01

    High resolution stellar spectroscopic surveys provide massive amounts of diffuse interstellar bands (DIBs) measurements. Data can be used to study the distribution of the DIB carriers and those environmental conditions that favor their formation. In parallel, recent studies have also proved that DIBs extracted from stellar spectra constitute new tools for building the 3D structure of the Galactic interstellar medium (ISM). The amount of details on the structure depends directly on the quantity of available lines of sight. Therefore there is a need to construct databases of high-quality DIB measurements as large as possible. We aim at providing the community with a catalog of high-quality measurements of the 1.5273 μm DIB toward a large fraction of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) hot stars observed to correct for the telluric absorption and not used for ISM studies so far. This catalog would complement the extensive database recently extracted from the APOGEE observations and used for 3D ISM mapping. We devised a method to fit the stellar continuum of the hot calibration stars and extracted the DIB from the normalized spectrum. Severe selection criteria based on the absorption characteristics are applied to the results. In particular limiting constraints on the DIB widths and Doppler shifts are deduced from the H i 21 cm measurements, following a new technique of decomposition of the emission spectra. From ˜16,000 available hot telluric spectra we have extracted ˜6700 DIB measurements and their associated uncertainties. The statistical properties of the extracted absorptions are examined and our selection criteria are shown to provide a robust dataset. The resulting catalog contains the DIB total equivalent widths, central wavelengths and widths. We briefly illustrate its potential use for the stellar and interstellar communities.

  2. Differences in concentration lengths computed using band-averaged mass extinction coefficients and band-averaged transmittance

    NASA Astrophysics Data System (ADS)

    Farmer, W. Michael

    1990-09-01

    An understanding of how broad-band transmittance is affected by the atmosphere is crucial to accurately predicting how broad-band sensors such as FLIRs will perform. This is particularly true for sensors required to function in an environment where countermeasures such as smokes/obscurants have been used to limit sensor performance. A common method of estimating the attenuation capabilities of smokes/obscurants released in the atmosphere to defeat broad-band sensors is to use a band averaged extinction coefficient with concentration length values in the Beer-Bouguer transmission law. This approach ignores the effects of source spectra, sensor response, and normal atmospheric attenuation, and can lead to results for band averages of the relative transmittance that are significantly different from those obtained using the source spectra, sensor response, and normal atmospheric transmission. In this paper we discuss the differences that occur in predicting relative transmittance as a function of concentration length using band-averaged mass extinction coefficients or computing the band-averaged transmittance as a function of source spectra. Two examples are provided to illustrate the differences in results. The first example is applicable to 8- to l4-um band transmission through natural fogs. The second example considers 3- to 5-um transmission through phosphorus smoke produced at 17% and 90% relative humidity. The results show major differences in the prediction of concentration length values by the two methods when the relative transmittance falls below about 20%.

  3. An investigation of the 661.3 nm diffuse interstellar band in Cepheid spectra

    NASA Astrophysics Data System (ADS)

    Kashuba, S. V.; Andrievsky, S. M.; Chekhonadskikh, F. A.; Luck, R. E.; Kovtyukh, V. V.; Korotin, S. A.; Krełowski, J.; Galazutdinov, G. A.

    2016-09-01

    We have investigated the diffuse interstellar band (DIB) at 661.3 nm seen in the spectra of Cepheid stars. After removal of the blending lines of ionized yttrium and neutral iron, we determined the equivalent widths (EWs) of the DIB and used these values to investigate the E(B - V)-DIB EW relation. The relation found from Cepheids matches that found in B stars. This relation can help to find the reddening for newly discovered Cepheids without extensive photometric data, and thus determine their distances. The relation between E(B - V) and the DIB EW does not yield precise reddening values. It is not a substitute for better photometric or spectroscopic methods. At best, it is indicative, but it provides some information that may not be otherwise available. Defining R* = E(B - V)/DIB EW, which we consider to be the analogue of R = E(B - V)/Av, we investigated the Galactic longitudinal dependence of R* assuming that the DIB EW value is representative of the interstellar absorption Av. We found that there is an apparent increase of the R* value that corresponds to the abnormal absorption seen towards Cygnus constellation. Finally, we constructed a 2D map of the DIB EW distribution in the Galactic disc basing on our rather limited sample of 253 spectra of 176 Cepheids.

  4. Identification of New Near-Infrared Diffuse Interstellar Bands in the Orion Nebula

    NASA Astrophysics Data System (ADS)

    Misawa, Toru; Gandhi, Poshak; Hida, Akira; Tamagawa, Toru; Yamaguchi, Tomohiro

    2009-08-01

    Large organic molecules and carbon clusters are basic building blocks of life, but their existence in the universe has not been confirmed beyond doubt. A number of unidentified absorption features (arising in the diffuse interstellar medium), usually called "Diffuse Interstellar Bands" (DIBs), are hypothesized to be produced by large molecules. Among these, buckminsterfullerene C60 has gained much attention as a candidate for DIB absorbers because of its high stability in space. Two DIBs at λ ~ 9577 Å and 9632 Å have been reported as possible features of C+ 60. However, it is still not clear how their existence depends on their environment. We obtained high-resolution spectra of three stars in/around the Orion Nebula, to search for any correlations of the DIB strength with carrier's physical conditions, such as dust abundance and UV radiation field. We find three DIBs at λ ~ 9017 Å, 9210 Å, and 9258 Å as additional C+ 60 feature candidates, which could support this identification. These DIBs have asymmetric profiles similar to the longer wavelength features. However, we also find that the relative strengths of DIBs are close to unity and differ from laboratory measurements, a similar trend as noticed for the 9577/9632 DIBs. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  5. Interstellar scattering effects on the detection of narrow-band signals

    SciTech Connect

    Cordes, J.M.; Lazio, T.J. )

    1991-07-01

    The detection and decoding of narrow-band radio signals are investigated after propagation through the turbulent, ionized interstellar medium. For most lines of sight through the Galaxy, spectral broadening due to scattering below about 0.1 Hz at 1 GHz occurs. Spectral broadening is therefore unimportant for the detection of hypothesized signals from extraterrestrial intelligence. Intensity scintillations, however, are of considerable importance. They both help and hinder detection: signals too weak to be detected without the scattering medium may be modulated above the detection threshold while, conversely, signals above threshold can be modulated below. In strong scattering (distances above about 100 pc at 1 GHz), multiple observations of a given target comprise a strategy that is superior to single observations even when the total time per target is held fixed. Decoding information carrying signals may encounter difficulties due to intensity scintillations. 49 refs.

  6. Excitation temperature of C2 and broadening of the 6196 Å diffuse interstellar band

    NASA Astrophysics Data System (ADS)

    Kaźmierczak, M.; Gnaciński, P.; Schmidt, M. R.; Galazutdinov, G.; Bondar, A.; Krełowski, J.

    2009-05-01

    This paper presents a finding of the correlation between the width of a strong diffuse interstellar band at 6196 Å and the excitation temperature of C2 based on high resolution and high signal-to-noise ratio spectra. The excitation temperature was determined from absorption lines of the Phillips A1Π_u-X1Σ+g and Mulliken D1Σ+_u-X1Σ+g systems. The width and shape of the narrow 6196 Å DIB profile apparently depend on the C2 temperature, being broader for higher values. Based on data collected at the ESO (8 m telescope at Paranal, 3.6 m and 2.2 m telescopes at La Silla) and observations made with the 1.8 m telescope in South Korea and the Cassegrain Fiber Environment in Hawaii.

  7. FIRST INFRARED BAND STRENGTHS FOR AMORPHOUS CO{sub 2}, AN OVERLOOKED COMPONENT OF INTERSTELLAR ICES

    SciTech Connect

    Gerakines, Perry A.; Hudson, Reggie L.

    2015-08-01

    Solid carbon dioxide (CO{sub 2}) has long been recognized as a component of both interstellar and solar system ices, but a recent literature search has revealed significant qualitative and quantitative discrepancies in the laboratory spectra on which the abundances of extraterrestrial CO{sub 2} are based. Here we report new infrared (IR) spectra of amorphous CO{sub 2}-ice along with band intensities (band strengths) of four mid-IR absorptions, the first such results in the literature. A possible thickness dependence for amorphous-CO{sub 2} IR band shapes and positions also is investigated, and the three discordant reports of amorphous CO{sub 2} spectra in the literature are addressed. Applications of our results are discussed with an emphasis on laboratory investigations and results from astronomical observations. A careful comparison with earlier work shows that the IR spectra calculated from several databases for CO{sub 2} ices, all ices being made near 10 K, are not for amorphous CO{sub 2}, but rather for crystalline CO{sub 2} or crystalline-amorphous mixtures.

  8. The 2140 cm-1 (4.673 microns) solid CO band: the case for interstellar O2 and N2 and the photochemistry of nonpolar interstellar ice analogs

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    The infrared spectra of CO frozen in nonpolar ices containing N2, CO2, O2, and H2O and the UV photochemistry of these interstellar/precometary ice analogs are reported. The spectra are used to test the hypothesis that the narrow 2140 cm-1 (4.673 microns) interstellar absorption feature attributed to solid CO might be produced by CO frozen in ices containing nonpolar species such as N2 and O2. It is shown that mixed molecular ices containing CO, N2, O2, and CO2 provide a good match to the interstellar band at all temperatures between 12 and 30 K both before and after photolysis. The optical constants (real and imaginary parts of the index of refraction) in the region of the solid CO feature are reported for several of these ices. The N2 and O2 absorptions at 2328 cm-1 (4.296 microns) and 1549 cm-1 (6.456 microns), respectively, are also shown. The best matches between the narrow interstellar band and the feature in the laboratory spectra of nonpolar ices are for samples which contain comparable amounts of N2, O2, CO2, and CO. Co-adding the CO band from an N2:O2:CO2:CO = 1:5:1/2:1 ice with that of an H2O:CO = 20:1 ice provides an excellent fit across the entire interstellar CO feature. The four-component, nonpolar ice accounts for the narrow 2140 cm-1 portion of the feature which is associated with quiescent regions of dense molecular clouds. Using this mixture, and applying the most recent cosmic abundance values, we derive that between 15% and 70% of the available interstellar N is in the form of frozen N2 along several lines of sight toward background stars. This is reduced to a range of 1%-30% for embedded objects with lines of sight more dominated by warmer grains. The cosmic abundance of O tied up in frozen O2 lies in the 10%-45% range toward background sources, and it is between 1% and 20% toward embedded objects. The amount of oxygen tied up in CO and CO2 frozen in nonpolar ices can be as much as 2%-10% toward background sources and on the order of 0

  9. Probing the Local Bubble with diffuse interstellar bands. I. Project overview and southern hemisphere survey

    NASA Astrophysics Data System (ADS)

    Bailey, Mandy; van Loon, Jacco Th.; Farhang, Amin; Javadi, Atefeh; Khosroshahi, Habib G.; Sarre, Peter J.; Smith, Keith T.

    2016-01-01

    Context. The Sun traverses a low-density, hot entity called the Local Bubble. Despite its relevance to life on Earth, the conditions in the Local Bubble and its exact configuration are not very well known. Besides that, there is some unknown interstellar substance that causes a host of absorption bands across the optical spectrum, called diffuse interstellar bands (DIBs). Aims: We have started a project to chart the Local Bubble in a novel way and learn more about the carriers of the DIBs, by using DIBs as tracers of diffuse gas and environmental conditions. Methods: We conducted a high signal-to-noise spectroscopic survey of 670 nearby early-type stars to map DIB absorption in and around the Local Bubble. The project started with a southern hemisphere survey conducted at the European Southern Observatory's New Technology Telescope and has since been extended to an all-sky survey using the Isaac Newton Telescope. Results: In this first paper in the series, we introduce the overall project and present the results from the southern hemisphere survey. We make available a catalogue of equivalent-width measurements of the DIBs at 5780, 5797, 5850, 6196, 6203, 6270, 6283, and 6614 Å, of the interstellar Na i D lines at 5890 and 5896 Å, and of the stellar He i line at 5876 Å. We find that the 5780 Å DIB is relatively strong throughout, as compared to the 5797 Å DIB, but especially within the Local Bubble and at the interface with a more neutral medium. The 6203 Å DIB shows similar behaviour with respect to the 6196 Å DIB. Some nearby stars show surprisingly strong DIBs, whereas some distant stars show very weak DIBs, indicating small-scale structure within, as well as outside, the Local Bubble. The sight lines with non-detections trace the extent of the Local Bubble especially clearly and show it opening out into the halo. Conclusions: The Local Bubble has a wall that is in contact with hot gas and/or a harsh interstellar radiation field. That wall is perforated

  10. ANOMALOUS DIFFUSE INTERSTELLAR BANDS IN THE SPECTRUM OF HERSCHEL 36. II. ANALYSIS OF RADIATIVELY EXCITED CH{sup +}, CH, AND DIFFUSE INTERSTELLAR BANDS

    SciTech Connect

    Oka, Takeshi; Welty, Daniel E.; Johnson, Sean; York, Donald G.; Hobbs, L. M.; Dahlstrom, Julie

    2013-08-10

    Absorption spectra toward Herschel 36 (Her 36) for the A-bar{sup 1}{Pi} Leftwards-Open-Headed-Arrow X-tilde{sup 1}{Sigma} transitions of CH{sup +} in the J = 1 excited rotational level and for the A-bar{sup 2}{Delta} Leftwards-Open-Headed-Arrow X-tilde{sup 2}{Pi} transitions of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and {approx}25.7 K and indicate high radiative temperatures of the environment of 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETRs) were observed. We interpret these ETRs as being due to a small decrease of the rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collisions and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, {beta} {identical_to} (B' - B)/B, is sufficiently high (3%-5%) and the radiative temperature is high (T{sub r} > 50 K). Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs {lambda}5780.5, {lambda}5797.1, and {lambda}6613.6 which show the pronounced ETRs are due to polar molecules that are sensitive to the radiative excitation. The requirement of high {beta} favors relatively small molecules with three to six heavy atoms. DIBs {lambda}5849.8, {lambda}6196.0, and {lambda}6379.3 that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small {beta}.

  11. Near-infrared Diffuse Interstellar Bands in 0.91-1.32 μm

    NASA Astrophysics Data System (ADS)

    Hamano, Satoshi; Kobayashi, Naoto; Kondo, Sohei; Ikeda, Yuji; Nakanishi, Kenshi; Yasui, Chikako; Mizumoto, Misaki; Matsunaga, Noriyuki; Fukue, Kei; Mito, Hiroyuki; Yamamoto, Ryo; Izumi, Natsuko; Nakaoka, Tetsuya; Kawanishi, Takafumi; Kitano, Ayaka; Otsubo, Shogo; Kinoshita, Masaomi; Kobayashi, Hitomi; Kawakita, Hideyo

    2015-02-01

    We present a comprehensive survey of diffuse interstellar bands (DIBs) in 0.91-1.32 μm with the newly developed near-infrared (NIR) spectrograph WINERED mounted on the Araki 1.3 m telescope in Japan. We obtained high-resolution (R = 28, 300) spectra of 25 early-type stars with color excesses of 0.07 < E(B - V) < 3.4. In addition to the 4 DIBs previously detected in this wavelength range, we identified 15 new DIBs, 7 of which were reported as DIB "candidates" by Cox. We analyze the correlations among NIR DIBs, strong optical DIBs, and the reddening of the stars. Consequently, we found that all NIR DIBs show weaker correlations with the reddening rather than the optical DIBs, suggesting that the equivalent widths of NIR DIBs depend on some physical conditions of the interstellar clouds, such as UV flux. Three NIR DIBs, λλ10780, 10792, and 11797, are found to be classifiable as a "family," in which the DIBs are well correlated with each other, suggesting that the carriers of these DIBs are connected with some chemical reactions and/or have similar physical properties such as ionization potential. We also found that the three strongest NIR DIBs, λλ10780, 11797, and 13175 are well correlated with the optical DIB λ5780.5, whose carrier is proposed to be a cation molecule with high ionization potential, indicating that the carriers of the NIR DIBs could be cation molecules. Based on data collected at the Araki 1.3m telescope, which is operated by the Koyama Astronomical Observatory, Kyoto Sangyo University.

  12. Exploring the diffuse interstellar bands with the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    We use star, galaxy and quasar spectra taken by the Sloan Digital Sky Survey to map out the distribution of diffuse interstellar bands (DIBs) induced by the Milky Way. After carefully removing the intrinsic spectral energy distribution of each source, we show that by stacking thousands of spectra, it is possible to measure statistical flux fluctuations at the 10-3 level, detect more than 20 DIBs and measure their strength as a function of position on the sky. We create a map of DIB absorption covering about 5000 deg2 and measure correlations with various tracers of the interstellar medium: atomic and molecular hydrogen, dust and polycyclic aromatic hydrocarbons (PAHs). After recovering known correlations, we show that each DIB has a different dependence on atomic and molecular hydrogen: while they are all positively correlated with N_{H I}, they exhibit a range of behaviours with N_{H_2} showing positive, negative or no correlation. We show that a simple parametrization involving only N_{H I} and N_{H_2} applied to all the DIBs is sufficient to reproduce a large collection of observational results reported in the literature: it allows us to naturally describe the relations between DIB strength and dust reddening (including the so-called skin effect), the related scatter, DIB pair-wise correlations and families, the affinity for σ/ζ-type environments and other correlations related to molecules. Our approach allows us to characterize DIB dependencies in a simple manner and provides us with a metric to characterize the similarity between different DIBs.

  13. Prediction of broadband attenuation computed using band-averaged mass extinction coefficients and band-averaged transmittance

    NASA Astrophysics Data System (ADS)

    Farmer, W. M.

    1991-09-01

    A common method of estimating the attenuation capabilities of military smokes/obscurants is to use a band-averaged mass-extinction coefficient with concentration-length values in the Beer-Bouguer transmission law. This approach ignores the effects of source spectra, sensor response, and normal atmospheric attenuation on broadband transmittance characteristics, which can significantly affect broadband transmittance. The differences that can occur in predicting relative transmittance as a function of concentration length by using band-averaged mass-extinction coefficients as opposed to more properly computing the band-averaged transmittance are discussed in this paper. Two examples are provided to illustrate the differences in results. The first example considers 3- to 5-micron and 8- to 14-micron band transmission through natural fogs. The second example considers 3- to 5-micron and 8- to 12-micron transmission through phosphorus-derived smoke (a common military obscurant) produced at 17 percent and at 90 percent relative humidity. Major differences are found in the values of concentration lengths predicted by the two methods when the transmittance relative to an unobscured atmosphere falls below about 20 percent. These results can affect conclusions concerning the detection of targets in smokes screens, smoke concentration lengths required to obscure a target, and radiative transport through polluted atmospheres.

  14. THE DIFFUSE INTERSTELLAR BANDS AND ANOMALOUS MICROWAVE EMISSION MAY ORIGINATE FROM THE SAME CARRIERS

    SciTech Connect

    Bernstein, L. S.; Cline, J. A.; Clark, F. O.; Lynch, D. K. E-mail: jcline@spectral.com E-mail: dave@thulescientific.com

    2015-11-10

    We argue that the observed spectroscopic and statistical properties of the diffuse interstellar band (DIB) carriers are those that are needed to produce the anomalous microwave emission (AME). We explore this idea using a carrier-impartial model for AME based on the observed DIB statistical properties. We show that an observed distribution of profile widths for narrow DIBs can be mapped into an AME spectrum. The mapping model is applied to width distributions observed for HD 204827 and HD 183143, selected because their spectroscopic and statistical properties bracket those for most other sight lines. The predicted AME spectra for these sight lines agree well with the range of spectral shapes, and peak frequencies, ∼23–31 GHz, typically observed for AME. We use the AME spectral profiles to derive a strong constraint between the average carrier size and its rotational temperature. The constraint is applied to a variety of postulated molecular carrier classes, including polycyclic aromatic hydrocarbons, fulleranes, hydrocarbon chains, and amorphous hydrocarbon clusters. The constraint favors small, cold carriers with average sizes of ∼8–15 carbon atoms, and average rotational temperatures of ∼3–10 K, depending on carrier type. We suggest new observations, analyses, and modeling efforts to help resolve the ambiguities with regard to carrier size and class, and to further clarify the DIB–AME relationship.

  15. PROBING THE LOCAL BUBBLE WITH DIFFUSE INTERSTELLAR BANDS. II. THE DIB PROPERTIES IN THE NORTHERN HEMISPHERE

    SciTech Connect

    Farhang, Amin; Khosroshahi, Habib G.; Javadi, Atefeh; Molaeinezhad, Alireza; Tavasoli, Saeed; Habibi, Farhang; Kourkchi, Ehsan; Rezaei, Sara; Saberi, Maryam; Van Loon, Jacco Th.; Bailey, Mandy; Hardy, Liam

    2015-02-10

    We present a new high signal-to-noise ratio spectroscopic survey of the Northern hemisphere to probe the Local Bubble and its surroundings using the λ5780 Å and λ5797 Å diffuse interstellar bands (DIBs). We observed 432 sightlines to a distance of 200 pc over a duration of three years. In this study, we establish the λ5780 and λ5797 correlations with Na I, Ca II and E {sub B-V}, for both inside and outside the Local Bubble. The correlations show that among all neutral and ionized atoms, the correlation between Ca II and λ5780 is stronger than its correlation with λ5797, suggesting that λ5780 is more associated with regions where Ca{sup +} is more abundant. We study the λ5780 correlation with λ5797, which shows a tight correlation within and outside the Local Bubble. In addition, we investigate the DIB properties in UV irradiated and UV shielded regions. We find that, within and beyond the Local Bubble, λ5797 is located in denser parts of clouds, protected from UV irradiation, while λ5780 is located in the low-density regions of clouds.

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

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2005-01-01

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

  17. Time Dependent Density Functional Theory Calculations of Large Compact PAH Cations: Implications for the Diffuse Interstellar Bands

    NASA Technical Reports Server (NTRS)

    Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)

    2002-01-01

    We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

  18. A SURVEY OF DIFFUSE INTERSTELLAR BANDS IN THE ANDROMEDA GALAXY: OPTICAL SPECTROSCOPY OF M31 OB STARS

    SciTech Connect

    Cordiner, Martin A.; Cox, Nick L. J.; Evans, Christopher J.; Trundle, Carrie; Smith, Keith T.; Sarre, Peter J.; Gordon, Karl D.

    2011-01-01

    We present the largest sample to date of intermediate-resolution blue-to-red optical spectra of B-type supergiants in M31 and undertake the first survey of diffuse interstellar bands (DIBs) in this galaxy. Spectral classifications, radial velocities, and interstellar reddenings are presented for 34 stars in three regions of M31. Based on a subset of these stars with foreground-corrected reddening E{sup M31}{sub B-V}{>=} 0.05, the strengths of the M31 DIBs are analyzed with respect to the amount of dust, ultraviolet radiation field strength, and polycyclic aromatic hydrocarbon emission flux. Radial velocities and equivalent widths are given for the {lambda}5780 and {lambda}6283 DIBs toward 11 stars. Equivalent widths are also presented for the following DIBs detected in three sightlines in M31: {lambda}{lambda}4428, 5705, 5780, 5797, 6203, 6269, 6283, 6379, 6613, 6660, and 6993. All of these M31 DIB carriers reside in clouds at radial velocities matching those of interstellar Na I and/or H I. The relationships between DIB equivalent widths and reddening (E{sup M31}{sub B-V}) are consistent with those observed in the local interstellar medium (ISM) of the Milky Way (MW). Many of the observed sightlines show DIB strengths (per unit reddening) which lie at the upper end of the range of Galactic values. DIB strengths per unit reddening are found (with 68% confidence) to correlate with the interstellar UV radiation field strength. The strongest DIBs are observed where the interstellar UV flux is lowest. The mean Spitzer 8/24 {mu}m emission ratio in our three fields is slightly lower than that measured in the MW, but we identify no correlation between this ratio and the DIB strengths in M31. Interstellar oxygen abundances derived from the spectra of three M31 H II regions in one of the fields indicate that the average metallicity of the ISM in that region is 12 + log [O/H] = 8.54 {+-} 0.18, which is approximately equal to the value in the solar neighborhood.

  19. Laboratory Determination of the Infrared Band Strengths of Pyrene Frozen in Water Ice: Implications for the Composition of Interstellar Ices

    NASA Technical Reports Server (NTRS)

    Hardegree-Ullman, E.E.; Gudipati, M.S.; Boogert, A.C.A.; Lignell, H.; Allamandola, L.J.; Stapelfeldt, K. R.; Werner, M.

    2014-01-01

    Broad infrared emission features (e.g., at 3.3, 6.2, 7.7, 8.6, and 11.3 micrometers) from the gas phase interstellar medium have long been attributed to polycyclic aromatic hydrocarbons (PAHs). A significant portion (10 to 20%) of the Milky Way's carbon reservoir is locked in PAH molecules, which makes their characterization integral to our understanding of astrochemistry. In molecular clouds and the dense envelopes and disks of young stellar objects (YSOs), PAHs are expected to be frozen in the icy mantles of dust grains where they should reveal themselves through infrared absorption. To facilitate the search for frozen interstellar PAHs, laboratory experiments were conducted to determine the positions and strengths of the bands of pyrene mixed with H2O and deuterium oxide ices. The deuterium oxide mixtures are used to measure pyrene bands that are masked by the strong bands of H2O, leading to the first laboratory determination of the band strength for the CH stretching mode of pyrene in water ice near 3.25 micrometers. Our infrared band strengths were normalized to experimentally determined ultraviolet (UV) band strengths, and we find that they are generally approximately 50% larger than those reported by Bouwman et al. (2011) based on theoretical strengths. These improved band strengths were used to reexamine YSO spectra published by Boogert et al. (2008) to estimate the contribution of frozen PAHs to absorption in the 5 to 8 micrometer spectral region, taking into account the strength of the 3.25 micrometer CH stretching mode. It is found that frozen neutral PAHs contain 5 to 9% of the cosmic carbon budget, and account for 2 to 9% of the unidentified absorption in the 5 to 8 micrometer region.

  20. Laboratory determination of the infrared band strengths of pyrene frozen in water ice: Implications for the composition of interstellar ices

    SciTech Connect

    Hardegree-Ullman, E. E.; Gudipati, M. S.; Werner, M.; Boogert, A. C. A.; Lignell, H.; Allamandola, L. J.; Stapelfeldt, K. R. E-mail: gudipati@jpl.nasa.gov

    2014-04-01

    Broad infrared emission features (e.g., at 3.3, 6.2, 7.7, 8.6, and 11.3 μm) from the gas phase interstellar medium have long been attributed to polycyclic aromatic hydrocarbons (PAHs). A significant portion (10%-20%) of the Milky Way's carbon reservoir is locked in PAH molecules, which makes their characterization integral to our understanding of astrochemistry. In molecular clouds and the dense envelopes and disks of young stellar objects (YSOs), PAHs are expected to be frozen in the icy mantles of dust grains where they should reveal themselves through infrared absorption. To facilitate the search for frozen interstellar PAHs, laboratory experiments were conducted to determine the positions and strengths of the bands of pyrene mixed with H{sub 2}O and D{sub 2}O ices. The D{sub 2}O mixtures are used to measure pyrene bands that are masked by the strong bands of H{sub 2}O, leading to the first laboratory determination of the band strength for the CH stretching mode of pyrene in water ice near 3.25 μm. Our infrared band strengths were normalized to experimentally determined ultraviolet band strengths, and we find that they are generally ∼50% larger than those reported by Bouwman et al. based on theoretical strengths. These improved band strengths were used to reexamine YSO spectra published by Boogert et al. to estimate the contribution of frozen PAHs to absorption in the 5-8 μm spectral region, taking into account the strength of the 3.25 μm CH stretching mode. It is found that frozen neutral PAHs contain 5%-9% of the cosmic carbon budget and account for 2%-9% of the unidentified absorption in the 5-8 μm region.

  1. Fulleranes and Carbon Nanostructures in the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Iglesias-Groth, Susana; Cataldo, Franco

    We review the potential contribution of single fullerenes and buckyonions to interstellar extinction. Photoabsorption spectra of these molecules are compared with some of the most relevant features of interstellar extinction, the UV bump, the far UV rise and the diffuse interstellar bands. According to semiempirical models, photoabsorption by fullerenes (single and multishell) could explain the shape, width and peak energy of the most prominent feature of the interstellar absorption, the UV bump at 2,175 Å. Other weaker transitions are predicted in the optical and near-infrared providing a potential explanation for diffuse interstellar bands. In particular, several fullerenes could contribute to the well known strong DIB at 4,430 Å comparing cross sections and available data for this DIB and the UV bump we estimate a density of fullerenes in the diffuse interstellar medium of 0.1-0.2 ppm. These molecules could then be a major reservoir for interstellar carbon. We give an estimation of the carbon fraction locked in these molecules. We discuss the rotation rates and electric dipole emission of hydrogenated icosahedral fullerenes in various phases of the interstellar medium. These molecules could be the carriers of the anomalous microwave emission detected by Watson et al. (Astrophys. J. 624:L89, 2005) in the Perseus molecular complex and Cassasus et al. (2006) in the dark cloud LDN 1622. Hydrogenated forms of fullerenes may account for the dust-correlated microwave emission detected in our Galaxy by Cosmic Microwave Background experiments.

  2. Observations and Analysis of Extended Tail Toward Red in the Diffuse Interstellar Bands of Herschel 36

    NASA Astrophysics Data System (ADS)

    Oka, Takeshi; Welty, Daniel E.; Johnson, Sean; York, Donald G.; Hobbs, Lew M.; Dahlstrom, Julie

    2013-06-01

    In the studies of the Diffuse Interstellar Bands (DIBs), the sightline toward Herschel 36 near the center of the HII region Messier 8 is unique. It shows spectra of CH^+ and CH in the first excited level indicating the presence of a cloud with high radiative temperature. The heating is most likely due to far infrared emission from the adjacent intense infrared source Her 36 SE at a distance of 0.25" from Her 36. The effect of the high radiative temperature on some DIBs is spectacular. It produces on a normally symmetric bell-shape line a very prominent Extended Tail toward Red (ETR) on prototypical DIBs λ 5780.5, λ 5797.1, and λ 6613 while other DIBs λ 5849.8, λ 6196.0, and λ 6379.3 are little affected. We interpret this as indicating that the carriers of the former 3 DIBs that are seriously affected by the radiation are polar molecules and the pronounced ETRs are the result of the decrease of rotational constant B (3 - 5 %) upon electronic excitation. High J rotational levels are pumped radiatively and with the negative (B' - B) produces the ETR. We have developed a model calculation of rotational distribution taking into account of both radiative and collisional processes. In view of the complexity of the problem linear molecules are considered. 7 parameters enter into the calculation but we find the fractional variation of B and the radiative temperature T_r are the most decisive. Although molecules with a general shape is beyond the scope of this work, we conclude that the 3 DIBs which show the pronounced ETRs are due to polar molecules and the requirement of high variation of B indicates that the molecules are not that large perhaps composed of 3-6 heavy atoms. The 3 DIBs that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small fractional variation of B. Goto, M., Stecklum, B., Linz, H., Feldt, M., Henning, Th., Pascucci, I., and Usuda, T. 2006, ApJ, 649 299. Oka, T., Welty, D. E., Johnson, S., York

  3. Redshift--Independent Distances of Spiral Galaxies: II. Internal Extinction at I Band

    NASA Astrophysics Data System (ADS)

    Giovanelli, R.; Haynes, M. P.; Salzer, J. J.; Wegner, G.; Dacosta, L. N.; Freudling, W.; Chamaraux, P.

    1993-12-01

    We analyze the photometric properties of a sample of 1450 Sbc--Sc galaxies with known redshifts, single--dish HI profiles and CCD I band images to derive laws that relate the measured isophotal radius at mu_I =23.5, magnitude, scale length and HI flux to the face--on aspect. Our results show that the central regions of spiral galaxies are substantially less transparent than most previous determinations suggest, but not as opaque as claimed by Valentijn (1990). Regions in the disk farther than two or three scale lengths from the center are close to completely transparent. In addition to statistically derived relations for the inclination dependence of photometric parameters, we present the results of a modelling exercise that utilizes the ``triplex'' model of Disney et al. (1989). Within the framework of that model, late spiral disks at I band have central optical depths on the order of tau_I ~ 5 and dust absorbing layers with scale heights on the order of half that of the stellar component. We discuss our results in light of previous determinations of internal extinction relations and point out the substantial impact of internal extinction on the scatter of the Tully--Fisher relation. We also find that the visual diameters by which large catalogs are constructed (UGC, ESO--Uppsala) are nearly proportional to face--on isophotal diameters.

  4. On the Nature of Interstellar Grains

    NASA Astrophysics Data System (ADS)

    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 < λ-1 < 1.94 μ-1 and 2.5 μ-1 < λ-1 < 3.0 μ-1. Over the more restricted waveband 4000-5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton 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.

  5. Measuring diffuse interstellar bands with cool stars. Improved line lists to model background stellar spectra

    NASA Astrophysics Data System (ADS)

    Monreal-Ibero, A.; Lallement, R.

    2017-03-01

    Context. Diffuse stellar bands (DIBs) are ubiquitous in stellar spectra. Traditionally, they have been studied through their extraction from hot (early-type) stars because of their smooth continuum. In an era in which there are several ongoing or planned massive Galactic surveys using multi-object spectrographs, cool (late-type) stars constitute an appealing set of targets. However, from the technical point of view, the extraction of DIBs in their spectra is more challenging because of the complexity of the continuum. Aims: In this contribution we provide the community with an improved set of stellar lines in the spectral regions associated with the strong DIBs at λ6196.0, λ6269.8, λ6283.8, and λ6379.3. These lines allow for the creation of better stellar synthetic spectra, reproducing the background emission and a more accurate extraction of the magnitudes associated with a given DIB (e.g., equivalent width, radial velocity). Methods: The Sun and Arcturus were used as representative examples of dwarf and giant stars, respectively. A high quality spectrum for each of them was modeled using TURBOSPECTRUM and the Vienna Atomic Line Database (VALD) stellar line list. The oscillator strength log (gf) and wavelength of specific lines were modified to create synthetic spectra in which the residuals in both the Sun and Arcturus were minimized. Results: The TURBOSPECTRUM synthetic spectra, based on improved line lists, reproduce the observed spectra for the Sun and Arcturus in the mentioned spectral ranges with greater accuracy. Residuals between the synthetic and observed spectra are always ≲10%, which is much better than residuals with previously existing options. We tested the new line lists with some characteristic spectra from a variety of stars, including both giant and dwarf stars, and under different degrees of extinction. As occurred with the Sun and Arcturus, residuals in the fits used to extract the DIB information are smaller when using synthetic spectra

  6. Interaction Between the Broad-Lined Type Ic Supernova 2012ap and Carriers of Diffuse Interstellar Bands

    NASA Technical Reports Server (NTRS)

    Milisavljevic, Dan; Margutti, Raffaella; Crabtree, Kyle N.; Foster, Jonathan B.; Soderberg, Alicia M.; Fesen, Robert A.; Parrent, Jerod T.; Sanders, Nathan E.; Drout, Maria R.; Kamble, Atish; Cenko, S. Bradley

    2014-01-01

    The diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond with electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad- lined Type Ic supernova SN2012ap that exhibit changes in equivalent width over short (. 30 days) timescales. The 4428 A and 6283 A DIB features get weaker with time, whereas the 5780 A feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of the DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.

  7. INTERACTION BETWEEN THE BROAD-LINED TYPE Ic SUPERNOVA 2012ap AND CARRIERS OF DIFFUSE INTERSTELLAR BANDS

    SciTech Connect

    Milisavljevic, Dan; Margutti, Raffaella; Crabtree, Kyle N.; Soderberg, Alicia M.; Sanders, Nathan E.; Drout, Maria R.; Kamble, Atish; Chakraborti, Sayan; Kirshner, Robert P.; Foster, Jonathan B.; Fesen, Robert A.; Parrent, Jerod T.; Pickering, Timothy E.; Cenko, S. Bradley; Silverman, Jeffrey M.; Marion, G. H. Howie; Vinko, Jozsef; Filippenko, Alexei V.; Mazzali, Paolo; Maeda, Keiichi; and others

    2014-02-10

    Diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond to electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova SN 2012ap that exhibit changes in equivalent width over short (≲ 30 days) timescales. The 4428 Å and 6283 Å DIB features get weaker with time, whereas the 5780 Å feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers.

  8. Radio Search for H2CCC toward HD 183143 as a Candidate for a Diffuse Interstellar Band Carrier

    NASA Astrophysics Data System (ADS)

    Araki, Mitsunori; Takano, Shuro; Yamabe, Hiromichi; Tsukiyama, Koichi; Kuze, Nobuhiko

    2012-07-01

    To clarify the authenticity of a recently proposed identification of H2CCC (linear-C3H2) as a diffuse interstellar band (DIB) carrier, we searched for the rotational transition of H2CCC at a frequency of 103 GHz toward HD 183143 using the 45 m telescope at the Nobeyama Radio Observatory. Although rms noise levels of 32 mK in the antenna temperature were achieved, detection of H2CCC was unsuccessful, producing a 3σ upper limit corresponding to a column density of 2.0 × 1013 cm-2. The upper limit indicates that the contribution of H2CCC to the DIB at 5450 Å is less than 1/25; thus, it is unlikely that the laboratory bands of the B 1 B 1-X 1 A 1 transition of H2CCC and the DIBs at 5450 Å (and also 4881 Å) toward HD 183143 are related.

  9. Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Reddy, Samala Nagaprasad; Mahapatra, S.

    2012-07-01

    Observation of broad and diffuse interstellar bands (DIBs) at 4881 Å and 5440 Å assigned to the optical absorption spectrum of Y-shaped propadienylidene (H2Cdbnd Cdbnd C:) molecule is theoretically examined in this paper. This molecule apparently absorbs in the same wavelength region as the observed DIBs and was suggested to be a potential carrier of these DIBs. This assignment mostly relied on the experimental data from radioastronomy and laboratory measurements. Motivated by these available experimental data we attempt here a theoretical study and investigate the detailed electronic structure and nuclear dynamics underlying the electronic absorption bands of propadienylidene molecule. Our results show that this molecule indeed absorbs in the wavelength region of the recorded DIBs. Strong nonadiabatic coupling between its energetically low-lying electronic states plays major role, initiates ultrafast internal conversion and contributes to the spectral broadening. Theoretical findings are finally compared with the available experimental and theoretical data and discussed in connection with the recorded DIBs.

  10. Interstellar Dust: Contributed Papers

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

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

  12. The interstellar C-H stretching band near 3.4 microns - Constraints on the composition of organic material in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Sandford, S. A.; Allamandola, L. J.; Tielens, A. G. G. M.; Pendleton, Y.; Sellgren, K.

    1991-01-01

    The composition and history of dust in the diffuse ISM was studied using 3600-2700/cm absorption spectra of objects which have widely varying amounts of visual extinctions along different lines of sight. The 3300/cm and 2950/cm features are attributed to O-H and C-H stretching vibrations, respectively. The O-H feature in OH 32.8-0.3 is suggestive of circumstellar water ice and is probably not due to material in the diffuse ISM. The features in the 3100-2700/cm region are attributed either to C-H vibrations or to M stars. The spectra of the latter show a series of narrow features in this region that are identified with photospheric OH. Objects in which these bands are seen include OH 01-477, T629-5, and the Galactic center source IRS 7. The C-H stretch feature of diffuse ISM dust has subpeaks which fall within 5/cm of C-H stretching vibrations in the -CH2- and -CH3 groups of saturated aliphatic hydrocarbons.

  13. HIGH-RESOLUTION OPTICAL SPECTROSCOPY OF DY Cen: DIFFUSE INTERSTELLAR BANDS IN A PROTO-FULLERENE CIRCUMSTELLAR ENVIRONMENT?

    SciTech Connect

    Garcia-Hernandez, D. A.; Lambert, David L. E-mail: nkrao@iiap.res.in

    2012-11-01

    We search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis star DY Cen for electronic transitions of the C{sub 60} molecule and diffuse interstellar bands (DIBs). We report the non-detection of the strongest C{sub 60} electronic transitions (e.g., those at {approx}3760, 3980, and 4024 A). The absence of C{sub 60} absorption bands may support recent laboratory results, which show that the {approx}7.0, 8.5, 17.4, and 18.8 {mu}m emission features seen in DY Cen-and other similar objects with polycyclic-aromatic-hydrocarbon-like dominated IR spectra-are attributable to proto-fullerenes or fullerene precursors rather than to C{sub 60}. DIBs toward DY Cen are normal for its reddening; the only exception is the DIB at 6284 A (possibly also the 7223 A DIB) which is found to be unusually strong. We also report the detection of a new broad (FWHM {approx} 2 A) and unidentified feature centered at {approx}4000 A. We suggest that this new band may be related to the circumstellar proto-fullerenes seen at infrared wavelengths.

  14. Dust evolution, a global view: II. Top-down branching, nanoparticle fragmentation and the mystery of the diffuse interstellar band carriers

    NASA Astrophysics Data System (ADS)

    Jones, A. P.

    2016-12-01

    The origin of the diffuse interstellar bands (DIBs), one of the longest-standing mysteries of the interstellar medium (ISM), is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS). The likely nature of the DIB carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the ISM. Based on the natural aromatic-rich moieties (asphaltenes) recovered from coal and oil, the likely structure of their interstellar analogues is investigated within the context of the diffuse band problem. It is here proposed that the top-down evolution of interstellar carbonaceous grains, and, in particular, a-C(:H) nanoparticles, is at the heart of the formation and evolution of the DIB carriers and their associations with small molecules and radicals, such as C2, C3, CH and CN. It is most probable that the DIBs are carried by dehydrogenated, ionized, hetero-cyclic, olefinic and aromatic-rich moieties that form an integral part of the contiguous structure of hetero-atom-doped hydrogenated amorphous carbon nanoparticles and their daughter fragmentation products. Within this framework, it is proposed that polyene structures in all their variants could be viable DIB carrier candidates.

  15. Dust evolution, a global view: II. Top-down branching, nanoparticle fragmentation and the mystery of the diffuse interstellar band carriers.

    PubMed

    Jones, A P

    2016-12-01

    The origin of the diffuse interstellar bands (DIBs), one of the longest-standing mysteries of the interstellar medium (ISM), is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS). The likely nature of the DIB carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the ISM. Based on the natural aromatic-rich moieties (asphaltenes) recovered from coal and oil, the likely structure of their interstellar analogues is investigated within the context of the diffuse band problem. It is here proposed that the top-down evolution of interstellar carbonaceous grains, and, in particular, a-C(:H) nanoparticles, is at the heart of the formation and evolution of the DIB carriers and their associations with small molecules and radicals, such as C2, C3, CH and CN. It is most probable that the DIBs are carried by dehydrogenated, ionized, hetero-cyclic, olefinic and aromatic-rich moieties that form an integral part of the contiguous structure of hetero-atom-doped hydrogenated amorphous carbon nanoparticles and their daughter fragmentation products. Within this framework, it is proposed that polyene structures in all their variants could be viable DIB carrier candidates.

  16. Dust evolution, a global view: II. Top-down branching, nanoparticle fragmentation and the mystery of the diffuse interstellar band carriers

    PubMed Central

    2016-01-01

    The origin of the diffuse interstellar bands (DIBs), one of the longest-standing mysteries of the interstellar medium (ISM), is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS). The likely nature of the DIB carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the ISM. Based on the natural aromatic-rich moieties (asphaltenes) recovered from coal and oil, the likely structure of their interstellar analogues is investigated within the context of the diffuse band problem. It is here proposed that the top-down evolution of interstellar carbonaceous grains, and, in particular, a-C(:H) nanoparticles, is at the heart of the formation and evolution of the DIB carriers and their associations with small molecules and radicals, such as C2, C3, CH and CN. It is most probable that the DIBs are carried by dehydrogenated, ionized, hetero-cyclic, olefinic and aromatic-rich moieties that form an integral part of the contiguous structure of hetero-atom-doped hydrogenated amorphous carbon nanoparticles and their daughter fragmentation products. Within this framework, it is proposed that polyene structures in all their variants could be viable DIB carrier candidates. PMID:28083089

  17. Modeling Linear Molecules as Carriers of the λ5797 Å and λ6613 Å Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Huang, Jane; Oka, Takeshi

    2014-06-01

    Electronic transitions of polar linear molecules have been modeled and compared to archival high resolution spectra of the diffuse interstellar bands (DIBs) at 5797 and 6613 Å. These two bands are notable for fine structure that has most commonly been attributed to the rotational structure of electronic transitions of gas-phase molecules. Most strikingly, the 5797 DIB has a sharp, narrow center peak that is characteristic of the Q branch of parallel transitions with non-zero Λ. This work is also motivated by Oka et al.'s analysis of the anomalously extended redward tails seen in certain DIBs toward Herschel 36, which are reminiscent of electronic transitions of polar linear molecules at high radiative temperatures. The determination of rotational distributions, which includes radiative and collisional effects, is based on the model presented in the earlier work. Thus far, the most promising models are a ^2Π ← ^2Π transition for the 5797 DIB and a ^2Δ ← ^2Π transition for the 6613 DIB, with the effects of spin-orbit coupling examined in each case. The degree of consistency of these transitions with respect to the anomalous DIBs toward Herschel 36 is also discussed. Sarre, P. J., Miles, J. R., Kerr, T. H. et al. 1995, MNRAS, 177L 41 Oka, T., Welty, D. E., Johnson, S. et al. 2013, ApJ, 773 42

  18. H2 Molecular Clusters with Embedded Molecules and Atoms as the Source of the Diffuse Interstellar Bands

    NASA Astrophysics Data System (ADS)

    Bernstein, L. S.; Clark, F. O.; Lynch, D. K.

    2013-05-01

    We suggest that the diffuse interstellar bands (DIBs) arise from absorption lines of electronic transitions in molecular clusters primarily composed of a single molecule, atom, or ion ("seed"), embedded in a single-layer shell of H2 molecules. Less abundant variants of the cluster, including two seed molecules and/or a two-layer shell of H2 molecules, may also occur. The lines are broadened, blended, and wavelength-shifted by interactions between the seed and surrounding H2 shell. We refer to these clusters as contaminated H2 clusters (CHCs). We show that CHC spectroscopy matches the diversity of observed DIB spectral profiles and provides good fits to several DIB profiles based on a rotational temperature of 10 K. CHCs arise from ~centimeter-sized, dirty H2 ice balls, called contaminated H2 ice macro-particles (CHIMPs), formed in cold, dense, giant molecular clouds (GMCs), and later released into the interstellar medium (ISM) upon GMC disruption. Attractive interactions, arising from Van der Waals and ion-induced dipole potentials, between the seeds and H2 molecules enable CHIMPs to attain centimeter-sized dimensions. When an ultraviolet (UV) photon is absorbed in the outer layer of a CHIMP, it heats the icy matrix and expels CHCs into the ISM. While CHCs are quickly destroyed by absorbing UV photons, they are replenished by the slowly eroding CHIMPs. Since CHCs require UV photons for their release, they are most abundant at, but not limited to, the edges of UV-opaque molecular clouds, consistent with the observed, preferred location of DIBs. An inherent property of CHCs, which can be characterized as nanometer size, spinning, dipolar dust grains, is that they emit in the radio-frequency region. We also show that the CHCs offer a natural explanation for the anomalous microwave emission feature in the ~10-100 GHz spectral region.

  19. Evidence for biodegradation products in the interstellar medium

    NASA Astrophysics Data System (ADS)

    Rauf, Kani; Wickramasinghe, Chandra

    2010-01-01

    The interstellar absorption band centred on 2175 Å that is conventionally attributed to monodisperse graphite spheres of radii 0.02 μm is more plausibly explained as arising from biologically derived aromatic molecules. On the basis of panspermia models, interstellar dust includes a substantial fraction of biomaterial in various stages of degradation. We have modeled such an ensemble of degraded biomaterial with laboratory spectroscopy of algae, grass pigments, bituminous coal and anthracite. The average ulrtraviolet absorption profile for these materials is centred at 2175 Å with a full width at half maximum of 250 Å, in precise agreement with the interstellar extinction observations. Mid-infrared spectra also display general concordance with the unidentified interstellar absorption features found in a wide variety of astronomoical sources.

  20. Extinction in young massive clusters

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino

    2016-01-01

    Up to ages of ~100 Myr, massive clusters are still swamped in large amounts of gas and dust, causing considerable and uneven levels of extinction. At the same time, large grains (ices?) produced by type II supernovae profoundly alter the interstellar medium (ISM), thus resulting in extinction properties very different from those of the diffuse ISM. To obtain physically meaningful parameters of stars (luminosities, effective temperatures, masses, ages, etc.) we must understand and measure the local extinction law. We have developed a powerful method to unambiguously determine the extinction law everywhere across a cluster field, using multi-band photometry of red giant stars belonging to the red clump (RC) and are applying it to young massive clusters in the Local Group. In the Large Magellanic Cloud, with about 20 RC stars per arcmin2, for each field we can easily derive an accurate extinction curve over the entire wavelength range of the photometry. As an example, we present the extinction law of the Tarantula nebula (30 Dor) based on thousands of stars observed as part of the Hubble Tarantula Treasury Project. We discuss how the incautious adoption of the Milky Way extinction law in the analysis of massive star forming regions may lead to serious underestimates of the fluxes and of the star formation rates by factors of 2 or more.

  1. Infrared extinction in the inner Milky Way through red clump giants

    SciTech Connect

    González-Fernández, C.; Asensio Ramos, A.; Garzón, F.; Cabrera-Lavers, A.; Hammersley, P. L.

    2014-02-20

    While the shape of the extinction curve in the infrared is considered to be set and the extinction ratios between infrared bands are usually taken to be approximately constant, a number of recent studies point to either a spatially variable behavior of the exponent of the power law or a different extinction law altogether. In this paper, we propose a method to analyze the overall behavior of the interstellar extinction by means of the red-clump population, and we apply it to those areas of the Milky Way where the presence of interstellar matter is heavily felt: areas located in 5° < l < 30° and b = 0°. We show that the extinction ratios traditionally used for the near infrared could be inappropriate for the inner Galaxy and we analyze the behavior of the extinction law from 1 μm to 8 μm.

  2. Infrared Spectra and Band Strengths of CH3SH, an Interstellar Molecule

    NASA Technical Reports Server (NTRS)

    Hudson, R. L.

    2016-01-01

    Three solid phases of CH3SH (methanethiol or methyl mercaptan) have been prepared and their mid-infrared spectra recorded at 10-110 degrees Kelvin, with an emphasis on the 17-100 degrees Kelvin region. Refractive indices have been measured at two temperatures and used to estimate ice densities and infrared band strengths. Vapor pressures for the two crystalline phases of CH3SH at 110 degrees Kelvin are estimated. The behavior of amorphous CH3SH on warming is presented and discussed in terms of Ostwald's step rule. Comparisons to CH3OH under similar conditions are made, and some inconsistencies and ambiguities in the CH3SH literature are examined and corrected.

  3. Interstellar and Cometary Dust

    NASA Technical Reports Server (NTRS)

    Mathis, John S.

    1997-01-01

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

  4. Cholinergic neuronal lesions in the medial septum and vertical limb of the diagonal bands of Broca induce contextual fear memory generalization and impair acquisition of fear extinction.

    PubMed

    Knox, Dayan; Keller, Samantha M

    2016-06-01

    Previous research has shown that the ventral medial prefrontal cortex (vmPFC) and hippocampus (Hipp) are critical for extinction memory. Basal forebrain (BF) cholinergic input to the vmPFC and Hipp is critical for neural function in these substrates, which suggests BF cholinergic neurons may be critical for extinction memory. In order to test this hypothesis, we applied cholinergic lesions to different regions of the BF and observed the effects these lesions had on extinction memory. Complete BF cholinergic lesions induced contextual fear memory generalization, and this generalized fear was resistant to extinction. Animals with complete BF cholinergic lesions could not acquire cued fear extinction. Restricted cholinergic lesions in the medial septum and vertical diagonal bands of Broca (MS/vDBB) mimicked the effects that BF cholinergic lesions had on contextual fear memory generalization and acquisition of fear extinction. Cholinergic lesions in the horizontal diagonal band of Broca and nucleus basalis (hDBB/NBM) induced a small deficit in extinction of generalized contextual fear memory with no accompanying deficits in cued fear extinction. The results of this study reveal that MS/vDBB cholinergic neurons are critical for inhibition and extinction of generalized contextual fear memory, and via this process, may be critical for acquisition of cued fear extinction. Further studies delineating neural circuits and mechanisms through which MS/vDBB cholinergic neurons facilitate these emotional memory processes are needed. © 2015 Wiley Periodicals, Inc.

  5. Interstellar magnesium abundances

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  6. OBSERVATIONS OF THE NEAR- TO MID-INFRARED UNIDENTIFIED EMISSION BANDS IN THE INTERSTELLAR MEDIUM OF THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Mori, Tamami I.; Sakon, Itsuki; Onaka, Takashi; Ohsawa, Ryou; Kaneda, Hidehiro; Umehata, Hideki E-mail: isakon@astron.s.u-tokyo.ac.jp

    2012-01-01

    We present the results of near- to mid-infrared slit spectroscopic observations (2.55-13.4 {mu}m) of the diffuse emission toward nine positions in the Large Magellanic Cloud with the infrared camera on board AKARI. The target positions are selected to cover a wide range of the intensity of the incident radiation field. The unidentified infrared bands at 3.3, 6.2, 7.7, 8.6, and 11.3 {mu}m are detected toward all the targets and ionized gas signatures; hydrogen recombination lines and ionic forbidden lines are detected toward three of them. We classify the targets into two groups: those without the ionized gas signatures (Group A) and those with the ionized signatures (Group B). Group A includes molecular clouds and photodissociation regions, whereas Group B consists of H II regions. In Group A, the band ratios of I{sub 3.3{mu}m}/I{sub 11.3{mu}m}, I{sub 6.2{mu}m}/I{sub 11.3{mu}m}, I{sub 7.7{mu}m}/I{sub 11.3{mu}m}, and I{sub 8.6{mu}m}/I{sub 11.3{mu}m} show positive correlation with the IRAS and AKARI colors, but those of Group B do not follow the correlation. We discuss the results in terms of the polycyclic aromatic hydrocarbon (PAH) model and attribute the difference to the destruction of small PAHs and an increase in the recombination due to the high electron density in Group B. In the present study, the 3.3 {mu}m band provides crucial information on the size distribution and/or the excitation conditions of PAHs and plays a key role in the distinction of Group A from B. The results suggest the possibility of the diagram of I{sub 3.3{mu}m}/I{sub 11.3{mu}m} versus I{sub 7.7{mu}m}/I{sub 11.3{mu}m} as an efficient diagnostic tool to infer the physical conditions of the interstellar medium.

  7. Retrieval of aerosol refractive index from extinction spectra with a damped harmonic-oscillator band model.

    PubMed

    Thomas, Gareth E; Bass, Stephen F; Grainger, Roy G; Lambert, Alyn

    2005-03-01

    A new method for the retrieval of the spectral refractive indices of micrometer-sized particles from infrared aerosol extinction spectra has been developed. With this method we use a classical damped harmonic-oscillator model of molecular absorption in conjunction with Mie scattering to model extinction spectra, which we then fit to the measurements using a numerical optimal estimation algorithm. The main advantage of this method over the more traditional Kramers-Kronig approach is that it allows the full complex refractive-index spectra, along with the parameters of the particle size distribution, to be retrieved from a single extinction spectrum. The retrieval scheme has been extensively characterized and has been found to provide refractive indices with a maximum uncertainty of approximately 10% (with a minimum of approximately 0.1%). Comparison of refractive indices calculated from measurements of a ternary solution of HNO3, H2SO4, and H2O with those published in J. Phys. Chem. A 104, 783 (2000) show similar differences as found by other authors.

  8. Near-Infrared Band Strengths of Molecules Diluted in N2 and H2O Ice Mixtures Relevant to Interstellar and Planetary Ices

    NASA Technical Reports Server (NTRS)

    Richey, Christina Rae; Gerakines, P.A.

    2012-01-01

    The relative abundances of ices in astrophysical environments rely on accurate laboratory measurements of physical parameters, such as band strengths (or absorption intensities), determined for the molecules of interest in relevant mixtures. In an extension of our previous study on pure-ice samples, here we focus on the near-infrared absorption features of molecules in mixtures with the dominant components of interstellar and planetary ices, H2O and N2. We present experimentally measured near-infrared spectral information (peak positions, widths, and band strengths) for both H2O- and N2-dominated mixtures of CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), and NH3 (ammonia). Band strengths were determined during sample deposition by correlating the growth of near-infrared features (10,000-4000 per centimeter, 1-2.5 micrometers) with better-known mid-infrared features (4000-400 per centimeter, 2.5-25 micrometers) at longer wavelengths.

  9. Extinction coefficients of CC and CC bands in ethyne and ethene molecules interacting with Cu+ and Ag+ in zeolites--IR studies and quantumchemical DFT calculations.

    PubMed

    Kozyra, Paweł; Góra-Marek, Kinga; Datka, Jerzy

    2015-02-05

    The values of extinction coefficients of CC and CC IR bands of ethyne and ethene interacting with Cu+ and Ag+ in zeolites were determined in quantitative IR experiments and also by quantumchemical DFT calculations with QM/MM method. Both experimental and calculated values were in very good agreement validating the reliability of calculations. The values of extinction coefficients of ethyne and ethene interacting with bare cations and cations embedded in zeolite-like clusters were calculated. The interaction of organic molecules with Cu+ and Ag+ in zeolites ZSM-5 and especially charge transfers between molecule, cation and zeolite framework was also discussed in relation to the values of extinction coefficients.

  10. High energy electron irradiation of interstellar carbonaceous dust analogs: Cosmic ray effects on the carriers of the 3.4 µm absorption band.

    PubMed

    Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Víctor J

    2016-11-01

    The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium (ISM), but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity vs electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H2 molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic ray destruction times for the 3.4 μm band carriers lie in the 10(8) yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 10(7) yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.

  11. High energy electron irradiation of interstellar carbonaceous dust analogs: Cosmic ray effects on the carriers of the 3.4 µm absorption band

    PubMed Central

    Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Víctor J.

    2017-01-01

    The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium (ISM), but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity vs electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H2 molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic ray destruction times for the 3.4 μm band carriers lie in the 108 yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 107 yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds. PMID:28133388

  12. High-energy Electron Irradiation of Interstellar Carbonaceous Dust Analogs: Cosmic-ray Effects on the Carriers of the 3.4 μm Absorption Band

    NASA Astrophysics Data System (ADS)

    Maté, Belén; Molpeceres, Germán; Jiménez-Redondo, Miguel; Tanarro, Isabel; Herrero, Víctor J.

    2016-11-01

    The effects of cosmic rays on the carriers of the interstellar 3.4 μm absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH3 and CH2 in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH3 and CH2 by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity versus electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H2 molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher-energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic-ray destruction times for the 3.4 μm band carriers lie in the 108 yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 107 yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.

  13. Observational Evidence for Radiative Interstellar Grain Alignment

    NASA Astrophysics Data System (ADS)

    Andersson, B.; Potter, S. B.; Andersson, B.; Potter, S.

    2011-11-01

    The alignment mechanisms of interstellar dust grains is a long standing astrophysical problem. Interstellar polarization was first discovered in 1949 and soon thereafter attributed to dichroic extinction caused by asymmetric dust grains aligned with the magnetic field. For a long time the alignment mechanism was thought to involve paramagnetic relaxation in rapidly spinning dust grains. Modern theory indicates that the classical alignment mechanisms are likely not efficient, but rather favor alignment through direct radiative torques. We have used multi-band polarimetry towards stars probing six nearby clouds to show that the wavelength of maximum polarization is linearly correlated with the visual extinction (Andersson & Potter 2007; AP07; where further details can be found). We find a universal relation with a common positive slope between the clouds and a DC offset correlated with the average of the total-to-selective extinction < RV > . These results provide strong observational support for radiatively driven grain alignment. Recent observations of an additional set of ≍60 sightlines in the Taurus cloud confirm and strengthen these results.

  14. MID-INFRARED EXTINCTION AND ITS VARIATION WITH GALACTIC LONGITUDE

    SciTech Connect

    Gao Jian; Jiang, B. W.; Li Aigen E-mail: bjiang@bnu.edu.c

    2009-12-10

    Based on the data obtained from the Spitzer/Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIPMSE) Legacy Program and the Two Micron All Sky Survey (2MASS) project, we derive the extinction in the four IRAC bands, [3.6], [4.5], [5.8], and [8.0] mum, relative to the 2MASS K{sub s} band (at 2.16 mum) for 131 GLIPMSE fields along the Galactic plane within |l| <= 65 deg., using red giants and red clump giants as tracers. As a whole, the mean extinction in the IRAC bands (normalized to the 2MASS K{sub s} band), A{sub [3.6]}/A{sub K{sub s}}approx0.63+-0.01, A{sub [4.5]}/A{sub K{sub s}}approx0.57+-0.03, A{sub [5.8]}/A{sub K{sub s}}approx0.49+-0.03, A{sub [8.0]}/A{sub K{sub s}}approx0.55+-0.03, exhibits little variation with wavelength (i.e., the extinction is somewhat flat or gray). This is consistent with previous studies and agrees with that predicted from the standard interstellar grain model for R{sub V} = 5.5 by Weingartner and Draine. As far as individual sightline is concerned, however, the wavelength dependence of the mid-infrared interstellar extinction A{sub l}ambda/A{sub K{sub s}} varies from one sightline to another, suggesting that there may not exist a 'universal' IR extinction law. We, for the first time, demonstrate the existence of systematic variations of extinction with Galactic longitude which appears to correlate with the locations of spiral arms as well as with the variation of the far-infrared luminosity of interstellar dust.

  15. Hubble Tarantula Treasury Project - IV. The extinction law

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino; Sabbi, Elena; Lennon, Daniel; Anderson, Jay; van der Marel, Roeland; Cignoni, Michele; Grebel, Eva K.; Larsen, Søren; Zaritsky, Dennis; Zeidler, Peter; Gouliermis, Dimitrios; Aloisi, Alessandra

    2016-02-01

    We report on the study of interstellar extinction across the Tarantula Nebula (30 Doradus), in the Large Magellanic Cloud, using observations from the Hubble Tarantula Treasury Project in the 0.3-1.6 μm range. The considerable and patchy extinction inside the nebula causes about 3500 red clump stars to be scattered along the reddening vector in the colour-magnitude diagrams, thereby allowing an accurate determination of the reddening slope in all bands. The measured slope of the reddening vector is remarkably steeper in all bands than in the the Galactic diffuse interstellar medium. At optical wavelengths, the larger ratio of total-to-selective extinction, namely RV = 4.5 ± 0.2, implies the presence of a grey component in the extinction law, due to a larger fraction of large grains. The extra large grains are most likely ices from supernova ejecta and will significantly alter the extinction properties of the region until they sublimate in 50-100 Myr. We discuss the implications of this extinction law for the Tarantula Nebula and in general for regions of massive star formation in galaxies. Our results suggest that fluxes of strongly star-forming regions are likely to be underestimated by a factor of about 2 in the optical.

  16. Towards a comprehensive electronic database of polycyclic aromatic hydrocarbons and its application in constraining the identities of possible carriers of the diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Tan, Xiaofeng

    2009-01-01

    A theoretical approach is developed to pre-select individual polycyclic aromatic hydrocarbons (PAHs) as possible carriers of the diffuse interstellar bands (DIBs). In this approach, a computer program is used to enumerate all PAH molecules with up to a specific number of fused benzene rings. Fast quantum chemical calculations are then employed to calculate the electronic transition energies, oscillator strengths, and rotational constants of these molecules. An electronic database of all PAHs with up to any specific number of benzene rings can be constructed this way. Comparison of the electronic transition energies, oscillator strengths, and rotational band contours of all PAHs in the database with astronomical spectra allows one to constrain the identities of individual PAHs as possible carriers of some of the intense narrow DIBs. Using the current database containing up to 10 benzene rings we have pre-selected 8 closed-shell PAHs as possible carriers of the famous λ6614 DIB.

  17. Galactic Extinction and Reddening from the South Galactic Cap u-band Sky Survey: u-band Galaxy Number Counts and u ‑ r  Color Distribution

    NASA Astrophysics Data System (ADS)

    Li, Linlin; Shen, Shiyin; Hou, Jinliang; Yuan, Fangting; Zhong, Jing; Zou, Hu; Zhou, Xu; Jiang, Zhaoji; Peng, Xiyan; Fan, Dongwei; Fan, Xiaohui; Fan, Zhou; He, Boliang; Jing, Yipeng; Lesser, Michael; Li, Cheng; Ma, Jun; Nie, Jundan; Wang, Jiali; Wu, Zhenyu; Zhang, Tianmeng; Zhou, Zhimin

    2017-02-01

    We study the integral Galactic extinction and reddening based on the galaxy catalog of the South Galactic Cap u-band Sky Survey (SCUSS), where u-band galaxy number counts and u ‑ r color distribution are used to derive the Galactic extinction and reddening respectively. We compare these independent statistical measurements with the reddening map of Schlegel et al. (SFD) and find that both the extinction and reddening from the number counts and color distribution are in good agreement with the SFD results at low extinction regions (E{(B-V)}{SFD}< 0.12 mag). However, for high extinction regions (E{(B-V)}{SFD}> 0.12 mag), the SFD map overestimates the Galactic reddening systematically, which can be approximated by a linear relation {{Δ }}E{(B-V)=0.43[E(B-V)}{SFD}-0.12]. By combining the results from galaxy number counts and color distribution, we find that the shape of the Galactic extinction curve is in good agreement with the standard RV = 3.1 extinction law of O’Donnell.

  18. On the source of the dust extinction in type Ia supernovae and the discovery of anomalously strong Na I absorption

    SciTech Connect

    Phillips, M. M.; Morrell, Nidia; Hsiao, E. Y.; Campillay, Abdo; Contreras, Carlos; Simon, Joshua D.; Burns, Christopher R.; Persson, Sven E.; Thompson, I. B.; Freedman, Wendy L.; Cox, Nick L. J.; Foley, Ryan J.; Karakas, Amanda I.; Patat, F.; Sternberg, A.; Williams, R. E.; Gal-Yam, A.; Leonard, D. C.; Stritzinger, Maximilian; Folatelli, Gastón; and others

    2013-12-10

    High-dispersion observations of the Na I D λλ5890, 5896 and K I λλ7665, 7699 interstellar lines, and the diffuse interstellar band at 5780 Å in the spectra of 32 Type Ia supernovae are used as an independent means of probing dust extinction. We show that the dust extinction of the objects where the diffuse interstellar band at 5780 Å is detected is consistent with the visual extinction derived from the supernova colors. This strongly suggests that the dust producing the extinction is predominantly located in the interstellar medium of the host galaxies and not in circumstellar material associated with the progenitor system. One quarter of the supernovae display anomalously large Na I column densities in comparison to the amount of dust extinction derived from their colors. Remarkably, all of the cases of unusually strong Na I D absorption correspond to 'Blueshifted' profiles in the classification scheme of Sternberg et al. This coincidence suggests that outflowing circumstellar gas is responsible for at least some of the cases of anomalously large Na I column densities. Two supernovae with unusually strong Na I D absorption showed essentially normal K I column densities for the dust extinction implied by their colors, but this does not appear to be a universal characteristic. Overall, we find the most accurate predictor of individual supernova extinction to be the equivalent width of the diffuse interstellar band at 5780 Å, and provide an empirical relation for its use. Finally, we identify ways of producing significant enhancements of the Na abundance of circumstellar material in both the single-degenerate and double-degenerate scenarios for the progenitor system.

  19. THE SEARCH FOR THE DIFFUSE INTERSTELLAR BANDS AND OTHER MOLECULES IN COMETS 17P (HOLMES) AND C/2007 W1 (BOATTINI)

    SciTech Connect

    O'Malia, K. K. J.; Snow, T. P.; Thorburn, J. A.; Hammergren, M.; Dembicky, J.; Hobbs, L. M.; York, D. G.

    2010-01-01

    We present the search for both diffuse interstellar bands (DIBs) and molecules in Comet 17P (Holmes) and Comet C/2007 W1 (Boattini) occultation observations. Absorption spectra were taken during stellar occultations by Comet Holmes of 31 and beta Persei, and the occultation of BD+22 216 by Comet Boattini. While no signature of the comets was detected, we present upper limits for some common cometary molecules such as C{sub 2}, C{sub 3}, CH, CN and for the most common DIBs. We did not detect either comet in absorption, most likely because of the large distance between the line of sight to the star and the nucleus of the comet. Interstellar sight lines with comparable reddening to what was measured in Comet Holmes have DIB equivalent widths between 5 and 50 mA. However, future observations with closer approaches to a background star have great potential for spatially mapping molecule distributions in comets, and in discovering DIBs, if they are present, in comets. Future observations could detect DIBs and molecules if they are done: (1) less than approx10{sup 4}-10{sup 3} km from the nucleus (2) with a signal to noise in the background star of approx300 and (3) with a resolving power of at least 38,000.

  20. Broad Balmer Wings in BA Hyper/Supergiants Distorted by Diffuse Interstellar Bands: Five Examples in the 30 Doradus Region from the VLT-FLAMES Tarantula Survey

    NASA Astrophysics Data System (ADS)

    Walborn, Nolan R.; Sana, Hugues; Evans, Christopher J.; Taylor, William D.; Sabbi, Elena; Barbá, Rodolfo H.; Morrell, Nidia I.; Maíz Apellániz, Jesús; Sota, Alfredo; Dufton, Philip L.; McEvoy, Catherine M.; Clark, J. Simon; Markova, Nevena; Ulaczyk, Krzysztof

    2015-08-01

    Extremely broad emission wings at Hβ and Hα have been found in VLT-FLAMES Tarantula Survey data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of Hβ and the shortward wing of Hα. These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, although we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables (LBVs). No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminous supergiants are approaching the LBV stage for the first time. Their locations in the HRD and presumed evolutionary tracks are consistent with that possibility. The available evidence for spectroscopic variations of these objects is reviewed, while recent photometric monitoring does not reveal variability. A search for circumstellar nebulae has been conducted, with an indeterminate result for one of them.

  1. BROAD BALMER WINGS IN BA HYPER/SUPERGIANTS DISTORTED BY DIFFUSE INTERSTELLAR BANDS: FIVE EXAMPLES IN THE 30 DORADUS REGION FROM THE VLT-FLAMES TARANTULA SURVEY

    SciTech Connect

    Walborn, Nolan R.; Sana, Hugues; Sabbi, Elena E-mail: hsana@stsci.edu; and others

    2015-08-10

    Extremely broad emission wings at Hβ and Hα have been found in VLT-FLAMES Tarantula Survey data for five very luminous BA supergiants in or near 30 Doradus in the Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical, which we have found to be caused by very broad diffuse interstellar bands (DIBs) in the longward wing of Hβ and the shortward wing of Hα. These DIBs are well known to interstellar but not to many stellar specialists, so that the asymmetries may be mistaken for intrinsic features. The broad emission wings are generally ascribed to electron scattering, although we note difficulties for that interpretation in some objects. Such profiles are known in some Galactic hyper/supergiants and are also seen in both active and quiescent Luminous Blue Variables (LBVs). No prior or current LBV activity is known in these 30 Dor stars, although a generic relationship to LBVs is not excluded; subject to further observational and theoretical investigation, it is possible that these very luminous supergiants are approaching the LBV stage for the first time. Their locations in the HRD and presumed evolutionary tracks are consistent with that possibility. The available evidence for spectroscopic variations of these objects is reviewed, while recent photometric monitoring does not reveal variability. A search for circumstellar nebulae has been conducted, with an indeterminate result for one of them.

  2. Determination of the extinction law of dust in SNRs

    NASA Astrophysics Data System (ADS)

    Yu, Bin; Jiang, Biwei

    2016-06-01

    Dust plays an important role in astrophysics, and the demand to characterize and understand dust is increasingly appreciated. In addition to asymptotic giant branch stars evolved from low- and intermediate-mass star, supernovae (SNe) are an important contributor to interstellar dust. On the other hand, SNe destroy interstellar dust due to its violent shock waves. How much SNe contribute to and affect interstellar dust is very unclear. The estimation of amount of dust from per SN has an uncertainty of three orders. Rather than from the dust emission, we study the dust property of SNR through its extinction, which has the advantage of avoiding the very uncertain dust temperature. The SNR S147 is chosen as the first target. Based on the LAMOST spectroscopic survey and the UCAC4 photometric catalog, the intrinsic color index is derived with its relation to the effective temperature given the spectral luminosity and metallicity in a way similar to Wang & Jiang (2014). Based on the color excess in various bands, the extinction curve is derived. Finally, we present a dust model to fit the extinction curve, which explores the properties of the dust in S147 including the dust size distribution, dust composition and shape etc. The properties are compared with that of the normal interstellar dust.

  3. Carriers of the mid-IR emission bands in PNe reanalysed. Evidence of a link between circumstellar and interstellar aromatic dust

    NASA Astrophysics Data System (ADS)

    Joblin, C.; Szczerba, R.; Berné, O.; Szyszka, C.

    2008-10-01

    Context: It has been shown that the diversity of the aromatic emission features can be rationalized into different classes of objects, in which differences between circumstellar and interstellar matter are emphasised. Aims: We probe the links between the mid-IR emitters observed in planetary nebulae (PNe) and their counterparts in the interstellar medium in order to probe a scenario in which the latter have been formed in the circumstellar environment of evolved stars. Methods: The mid-IR (6-14 μm) emission spectra of PNe and compact H II regions were analysed on the basis of previous work on photodissociation regions (PDRs). Galactic, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) objects were considered in our sample. Results: We show that the mid-IR emission of PNe can be decomposed as the sum of six components. Some components made of polycyclic aromatic hydrocarbon (PAH) and very small grain (VSG) populations are similar to those observed in PDRs. Others are fitted in an evolutionary scenario involving the destruction of the aliphatic component observed in the post-AGB stage, as well as strong processing of PAHs in the extreme conditions of PNe that leads to a population of very large ionized PAHs. This species called PAHx are proposed as the carriers of a characteristic band at 7.90 μm. This band can be used as part of diagnostics that identify PNe in nearby galaxies and is also observed in galactic compact H II regions. Conclusions: These results support the formation of the aromatic very small dust particles in the envelopes of evolved stars, in the Milky Way, as well as in the LMC and SMC, and their subsequent survival in the interstellar medium. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the

  4. Interstellar PAHs

    NASA Technical Reports Server (NTRS)

    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.

  5. Near-infrared absorption spectroscopy of interstellar hydrocarbon grains

    NASA Technical Reports Server (NTRS)

    Pendleton, Y. J.; Sandford, S. A.; Allamandola, L. J.; Tielens, A. G. G. M.; Sellgren, K.

    1994-01-01

    We present new 3600 - 2700/cm (2.8 - 3.7 micrometer) spectra of objects whose extinction is dominated by dust in the diffuse interstellar medium. The observations presented here augment an ongoing study of the organic component of the diffuse interstellar medium. These spectra contain a broad feature centered near 3300/cm (3.0 micrometers) and/or a feature with a more complex profile near 2950/cm (3.4 micrometers), the latter of which is attributed to saturated aliphatic hydrocarbons in interstellar grains and is the primary interest of this paper. As in our earlier work, the similarity of the absorption bands near 2950/cm (3.4 micrometers) along different lines of sight and the correlation of these features with interstellar extinction reveal that the carrier of this band lies in the dust in the diffuse interstellar medium (DISM). At least 2.5% of the cosmic carbon in the local interstellar medium and 4% toward the Galactic center is tied up in the carrier of the 2950/cm (3.4 micrometer) band. The spectral structure of the diffuse dust hydrocarbon C-H stretch absorption features is reasonably similar to UV photolyzed laboratory ice residues and is quite similar to the carbonaceous component of the Murchison meteorite. The similarity between the DISM and the meteoritic spectrum suggests that some of the interstellar material originally incorporated into the solar nebula may have survived relatively untouched in primitive solar system bodies. Comparisons of the DISM spectrum to hydrogenated amorphous carbon and quenched carbonaceous composite are also presented. The A(sub V)/tau ratio for the 2950/cm (3.4 micrometer) feature is lower toward the Galactic center than toward sources in the local solar neighborhood (approximately 150 for the Galactic center sources vs. approximately 250 for the local ISM sources). A similar trend has been observed previously for silicates in the diffuse medium by Roche & Aitken, suggesting that (1) the silicate and carbonaceous

  6. Laboratory Astrochemistry: Interstellar PAHs

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  7. Detection of organic matter in interstellar grains.

    PubMed

    Pendleton, Y J

    1997-06-01

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

  8. Laboratory optical spectroscopy of the thiophenoxy radical and its profile simulation as a diffuse interstellar band based on rotational distribution by radiation and collisions

    SciTech Connect

    Araki, Mitsunori; Niwayama, Kei; Tsukiyama, Koichi

    2014-11-01

    The gas-phase optical absorption spectrum of the thiophenoxy radical (C{sub 6}H{sub 5}S), a diffuse interstellar band (DIB) candidate molecule, was observed in the discharge of thiophenol using a cavity ringdown spectrometer. The ground-state rotational constants of the thiophenoxy radical were theoretically calculated, and the excited-state rotational constants were determined from the observed rotational profile. The rotational profile of a near prolate molecule having C {sub 2v} symmetry was simulated on the basis of a rotational distribution model by radiation and collisions. Although the simulated profile did not agree with the observed DIBs, the upper limit of the column density for the thiophenoxy radical in the diffuse clouds toward HD 204827 was evaluated to be 2 × 10{sup 13} cm{sup –2}. The profile simulation indicates that rotational distribution by radiation and collisions is important to reproduce a rotational profile for a DIB candidate and that the near prolate C {sub 2v} molecule is a possible candidate for DIB with a band width variation dependent on the line of sight.

  9. A new model for the interpretation of the unidentified infrared bands (UIBS) of the diffuse interstellar medium and of the protoplanetary nebulae

    NASA Astrophysics Data System (ADS)

    Cataldo, Franco; Keheyan, Yeghis; Heymann, Dieter

    2002-04-01

    In this work we started from the basic idea that the pure polycyclic aromatic hydrocarbons (PAHs) cannot be the real carriers of the unidentified infrared bands (UIBs), the emission spectra coming from a large variety of astronomical objects. Instead we propose a new model taken from petroleum chemistry which, we can show, is able to match both the UIBs and even the protoplanetary nebulae (PPNe) spectra. PAHs such as phenanthrene, benzoperylene, coronene and pentacene, are too pure and too specific to really exist in the interstellar medium. Instead our model proposes that the carrier of UIBs and PPNe are complex molecular mixtures like those obtained as fractions during the petroleum refining processes. These molecular mixtures are so complex that practically the investigators did not try to identify each individual component but characterized the mixture with an average molecular structure that takes into account both the average molecular weight and the average content of aromatic, naphtenic (cycloaliphatic) and aliphatic (paraffinic) fraction. We show by infrared spectroscopy that petroleum fractions obtained at certain steps of the refining process are able to match the UIBs and the PPNe infrared bands with the advantage of not being so specific as PAHs are. Namely we have used as samples a distillate aromatic extract (DAE) a treated residual aromatic extract (T-RAE) and finally a naphtenic oil. Among the three samples examined, the DAE sample was the best in matching the UIBs and PPNe spectra.

  10. Are Silicon Nanoparticles an Interstellar Dust Component?

    NASA Astrophysics Data System (ADS)

    Li, Aigen; Draine, B. T.

    2002-01-01

    Silicon nanoparticles (SNPs) with oxide coatings have been proposed as the source of the observed ``extended red emission'' (ERE) from interstellar dust. We calculate the thermal emission expected from such particles, both in a reflection nebula such as NGC 2023 and in the diffuse interstellar medium (ISM). It is shown that Si/SiO2 SNPs (both neutral and charged) would produce a strong emission feature at 20 μm. The observational upper limit on the 20 μm feature in NGC 2023 imposes an upper limit of less than 0.2 parts per million in Si/SiO2 SNPs. The observed ERE intensity from NGC 2023 then gives a lower bound on the product ηPLf0, where ηPL<1 is the photoluminescence efficiency for a neutral SNP and f0<=1 is the fraction of SNPs that are uncharged. For foreground extinction A0.68μm=1.2mag, we find ηPLf0>0.24 for Si/SiO2 SNPs in NGC 2023. Measurement of the R-band extinction toward the ERE-emitting region could strengthen this lower limit. The ERE emissivity of the diffuse interstellar medium appears to require >~42% of solar Si abundance in Si/SiO2 SNPs even with ηPLf0=1. We predict IR emission spectra and show that DIRBE photometry appears to rule out such high abundances of free-flying SNPs in the diffuse ISM. We conclude that if the ERE is due to SNPs, they must be either in clusters or attached to larger grains.

  11. THE MID-INFRARED EXTINCTION LAW AND ITS VARIATION IN THE COALSACK NEBULA

    SciTech Connect

    Wang Shu; Gao Jian; Jiang, B. W.; Chen Yang; Li Aigen E-mail: jiangao@bnu.edu.cn E-mail: cheny@bnu.edu.cn

    2013-08-10

    In recent years, the wavelength dependence of interstellar extinction from the ultraviolet (UV) to the near- and mid-infrared (IR) has been studied extensively. Although it is well established that the UV/optical extinction law varies significantly among the different lines of sight, it is not clear how IR extinction varies among various environments. In this work, using the color-excess method and taking red giants as the extinction tracer, we determine interstellar extinction A{sub {lambda}} in the four Spitzer/IRAC bands in [3.6], [4.5], [5.8], [8.0] {mu}m (relative to A{sub K{sub s}}, extinction in the Two Micron All Sky Survey (2MASS) K{sub s} band at 2.16 {mu}m) of the Coalsack nebula, a nearby starless dark cloud, based on the data obtained from the 2MASS and Spitzer/GLIMPSE surveys. We select five individual regions across the nebula that span a wide variety of physical conditions ranging from diffuse and translucent to dense environments, as traced by the visual extinction, the Spitzer/MIPS 24 {mu}m emission, and CO emission. We find that A{sub {lambda}}/A{sub K{sub s}}, mid-IR extinction relative to A{sub K{sub s}}, decreases from diffuse to dense environments, which may be explained in terms of ineffective dust growth in dense regions. The mean extinction (relative to A{sub K{sub s}}) is calculated for the four IRAC bands as well and exhibits a flat mid-IR extinction law consistent with previous determinations for other regions. Extinction in the IRAC 4.5 {mu}m band is anomalously high, much higher than that of the other three IRAC bands, and cannot be explained in terms of CO and CO{sub 2} ice. Mid-IR extinction in the four IRAC bands has also been derived for four representative regions in the Coalsack Globule 2, which respectively exhibit strong ice absorption, moderate or weak ice absorption, and very weak or no ice absorption. The derived mid-IR extinction curves are all flat, with A{sub {lambda}}/A{sub K{sub s}} increasing with the decrease of the

  12. The Origin and Evolution of Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Dwek, Eli; Houches, Les

    2006-01-01

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

  13. Heteroatom-doped hydrogenated amorphous carbons, a-C:H:X. "Volatile" silicon, sulphur and nitrogen depletion, blue photoluminescence, diffuse interstellar bands and ferro-magnetic carbon grain connections

    NASA Astrophysics Data System (ADS)

    Jones, A. P.

    2013-07-01

    Context. Hydrogenated amorphous carbons, a-C:H, can incorporate a variety of heteroatoms, which can lead to interesting effects. Aims: We investigate the doping of interstellar a-C:H grains with, principally, Si, O, N and S atoms within the astrophysical context. Methods: A search of the literature on doped a-C:H reveals a number of interesting phenomena of relevance to astrophysics. Results: X dopants in a-C:H:X materials can affect the sp3/sp2 ratio (X = Si, O and N), lead to blue photoluminescence (undoped or X = N), induce ferromagnetic-like behaviour (X = N and S) or simply be incorporated (depleted) into the structure (X = Si, O, N and S). Si and N atoms could also incorporate into fullerenes, possibly forming colour-centres that could mimic diffuse interstellar bands. Conclusions: Doped a-C:H grains could explain several dust-related conundrums, such as: "volatile" Si in photo-dissociation regions, S and N depletion in molecular clouds, blue luminescence, some diffuse interstellar bands and ferromagnetism in carbonaceous grains.

  14. Physical Properties of White Dwarfs from Multi-Band Photometry

    NASA Astrophysics Data System (ADS)

    Raddi, R.

    2017-03-01

    We describe a hierarchical Bayesian model to measure the physical parameters (mass, cooling age, distance, interstellar extinction) of single white dwarfs using only multi-band UV to IR photometry. We test our model on a set of known white dwarfs with well-assessed atmospheric parameters, determined via optical spectroscopy. Looking forward to the results of the ESA Gaia mission, we derive the posterior distributions of white dwarf parameters in two different scenarios with known or unknown parallaxes.

  15. Interstellar Grain Mantles

    NASA Technical Reports Server (NTRS)

    Witteborn, F.; Goebel, J.; Bregman, J.; Allamandola, Louis J.; Dhendecourt, L. B.; Tielens, Alexander G. G. M.

    1984-01-01

    Techniques for determining the composition of small dust grains in interstellar matter are discussed. The best way to study the composition of interstellar grain mantles is by infrared spectroscopy. The absorption features in a complete infrared spectrum from 2 to 15 microns can be used as fingerprints to identify the absorbing molecule. Ground-based observations around 3 microns confirmed the presence of H2O ice in interstellar grain mantles, through the detection of the 3.08 micron OH stretching vibration. The detection of other molecules, in particular the carbon bearing molecules, is however hampered by atmospheric absorption in the 5-8 micron region and the presence of the strong ice and silicate bands, which dominate the 3 and 10 micron region respectively. Kuiper Airborne Observatory observations of the 5-8 micron region of the spectrum are therefore extremely important to determine the composition of interstellar grain mantles. The 5 to 8 micron spectra of molecular cloud sources was obtained using a 24 detector grating spectrometer. An important characteristic of this spectrometer is that the whole spectrum is obtained simultaneously. It is therefore relatively easy to correct for atmospheric transmission.

  16. The structure and evolution of hydrogenated amorphous carbon grains and mantles in the interstellar medium

    NASA Astrophysics Data System (ADS)

    Jones, A. P.; Duley, W. W.; Williams, D. A.

    1990-12-01

    Hydrogenated amorphous carbons (HACs) have been proposed as the major constituent of interstellar dust. The HAC model can account successfully for observed properties of interstellar dust, and has great predictive power. A review is presented of relevant laboratory data on amorphous carbon, known to exist in three major phases: graphitic, diamondlike, and polymeric. These data indicate the probable nature of HAC in the interstellar medium. The properties of the HAC dust model, the deposition of HAC in the interstellar medium, and its evolution as interstellar conditions change are summarized. The properties of laboratory HAC in its various forms account successfully for observed interstellar extinction and for variations in extinction, for infrared emission features, and for extended red emission seen in reflection nebulae. A full evolutionary sequence that links the various HAC modifications found in different interstellar environments is proposed. It is concluded that the interstellar dust is an active component of the interstellar medium, responsive to its environment.

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

    SciTech Connect

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

    2013-08-10

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

  18. Laboratory Astrochemistry: Interstellar PAH Analogs

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  19. A Search for Interstellar Carbon-60

    NASA Astrophysics Data System (ADS)

    Nuccitelli, Dana; Richter, Matthew J.; McCall, Benjamin J.

    Carbon-60 has been proposed as a potentially important interstellar molecule. While there is a mounting body of indirect evidence suggesting that interstellar C60 exists, no direct spectroscopic detection toward an astronomical object has been made.We present here the results of our search for interstellar C60 in five sources using TEXES (the Texas Echelon Cross Echelle Spectrograph; Lacy et al. 2002). 1. Introduction The discovery of Buckminsterfullerene, C60, by Kroto et al. (1985) launched a new branch of chemical research. It is sometimes forgotten that the impetus for the experimental discovery of "buckyballs" was an attempt to understand the formation of long-chain carbon molecules in interstellar and circumstellar material. The stability of the molecule was recognized immediately and led to the suggestion that C60 may be widely distributed in the interstellar medium. Currently, only indirect evidence exists for interstellar C60. Because the ionization potential of C60 is relatively low the majority of C60 along optical/UV lines-of-sight will be ionized. Two electronic transitions of C60+, observed in rare gas matrices, lie near two diffuse interstellar bands (DIBs) near 9600Å (Foing & Ehrenfreund 1997). Detecting neutral C60 may be easier toward an embedded source using infrared vibrational bands, such as the one near 1184 cm-1 (&lambda=8.45 μm). The exact location and width of the band depends on the gas temperature. Assuming the average temperature is fairly low (T<100 K), the band structure should be be fairly narrow, which argues for high spectral resolution. 2. Observations We searched for the C60 1184 cm-1 vibrational band in three high- extinction molecular cloud sources (AFGL 2136, AFGL 2591, NGC 7538 IRS 1), the mass-loss star NML Cygni, and R Corona Borealis.We used TEXES, the Texas Echelon-cross-Echelle Spectrograph, a high resolution, mid-IR spectrograph (Lacy et al. 2002) on the 3m NASA IRTF. In highresolution mode, TEXES provides resolving

  20. Extinction properties of infinitely long graphite cylinders

    NASA Astrophysics Data System (ADS)

    Jazbi, B.; Hoyle, F.; Wickramasinghe, N. C.

    1991-12-01

    The extinction efficiencies of randomly oriented infinite graphite cylinders, including hollow cylinders are calculated, using the rigorous Kerker-Matijevic formulas. The peak in the mid-UV extinction varies in wavelength with particle radius and cavity size in a way that makes such particles of limited interest as models of interstellar grains.

  1. Interstellar grains within interstellar grains

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  2. Variations in the Peak Position of the 6.2 micron Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population

    NASA Technical Reports Server (NTRS)

    Hudgins, Douglas M.; Bauschlicher, Charles W.; Allamandola, L. J.

    2005-01-01

    more nitrogen atoms within the interior of the carbon skeleton of a PAH cation induces a significant blueshift in the position of the dominant CC stretching feature of these compounds that is suf6cient to account for the position of the interstellar bands. Subsequent studies of the effects of substitution by other heteroatoms (O and Si), metal ion complexation (Fe(+), Mg(+), and Mg(2+)), and molecular symmetry variation-all of which fail to reproduce the blueshift observed in the PANH cations-indicate that N appears to be unique in its ability to accommodate the position of the interstellar 6.2 micron bands while simultaneously satisfying the other constraints of the astrophysical problem. This result implies that the peak position of the interstellar feature near 6.2 micron traces the degree of nitrogen substitution in the population, that most of the PAHs responsible for the interstellar IR emission features incorporate nitrogen within their aromatic networks, and that a lower limit of 1%-2% of the cosmic nitrogen is sequestered within the interstellar PAH population. Finally, in view of the ubiquity and abundance of interstellar PAHs and the permanent dipoles and distinctive electronic structures of these nitrogen-substituted variants, this work impacts a wide range of observational phenomena outside of the infrared region of the spectrum including the forest of unidentified molecular rotational features and the anomalous Galactic foreground emission in the microwave, and the diffuse interstellar bands (DIBs) and other structure in the interstellar extinction curve in the ulhviolet/visible. These astrophysical ramifications are discussed, and the dipole moments and rotational constants are tabulated to facilitate further investigations of the astrophysical role of nitrogen-substituted aromatic compounds.

  3. The peculiar extinction of Herschel 36

    NASA Technical Reports Server (NTRS)

    Donn, B.; Hecht, J. H.; Helfer, H. L.; Wolf, J.; Pipher, J. L.

    1982-01-01

    The extinction of Herschel 36 was measured and found to be peculiar in the same sense as that observed in Orion. Following the treatment of Mathis and Wallenhorst, this can be explained by the presence of large silicate and graphite grains than are normally found in the interstellar medium. Correcting the stellar flux for foreground extinction results in a residual extinction curve for the associated dust cloud, with an unusually small normalized extinction (less than 1.0) at 1500 A. This low UV extinction may be due to the effects of scattering by the dust cloud material.

  4. A study of the fundamental characteristics of 2175A extinction

    NASA Technical Reports Server (NTRS)

    Cardelli, Jason A.; Savage, Blair D.

    1987-01-01

    The characteristics of interstellar extinction were studied in the region of the 2175 A feature for lines of sight which appear to exhibit unusually weak ultraviolet extinction. The analysis was based upon a parameterization of the observed extinction via fitting specific mathematical functions in order to determine the position and width of the 2175 A feature. The data are currently being analyzed.

  5. THE MID-INFRARED EXTINCTION LAW IN THE OPHIUCHUS, PERSEUS, AND SERPENS MOLECULAR CLOUDS

    SciTech Connect

    Chapman, Nicholas L.; Mundy, Lee G.; Lai, Shih-Ping; Evans, Neal J. II

    2009-01-01

    We compute the mid-IR extinction law from 3.6 to 24 {mu}m in three molecular clouds-Ophiuchus, Perseus, and Serpens-by combining data from the 'Cores to Disks' Spitzer Legacy Science program with deep JHK{sub s} imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the {chi}{sup 2} deviation of the data from two extinction law models. Because our {chi}{sup 2} maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6-8 {mu}m, we see evidence for grain growth. Below A{sub K{sub s}}= 0.5, our extinction law is well fitted by the Weingartner and Draine R{sub V} = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for A{sub K{sub s}}{>=}1, the data are more consistent with the Weingartner and Draine R{sub V} = 5.5 model that uses larger maximum dust grain sizes. At 24 {mu}m, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our {chi}{sup 2} maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.

  6. Infrared emission from interstellar PAHs

    NASA Technical Reports Server (NTRS)

    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.

  7. Absorbing ice model of interstellar grains.

    NASA Technical Reports Server (NTRS)

    Swamy, K. S. K.; Jackson, W. M.; Donn, B. D.

    1971-01-01

    Extinction curves have been calculated for Mie scattering by grains with a refractive index m equals to n - ik, where n was between 1.3 and 2.0 and k varied from 0 to 0.5. A good fit for the observed interstellar extinction in the wavelength region of 0.1 to 2.0 microns was obtained for particles with a radius of 0.1 micron and m equal to 1.3 - 0.2i. Inclusion of the changes in the refractive index in the vacuum ultraviolet region due to the strong absorptions of methane, ammonia and water does not appreciably alter these results. Theoretical extinction curves for the composite medium of H2O, NH3, CH4, and graphite show a general agreement with the observed interstellar reddening curve over the whole spectral range, in addition to producing kinks in the far-ultraviolet region.

  8. Search for diffuse band profile variations in the rho Ophiuchi cloud

    SciTech Connect

    Snow, T.P.; Timothy, J.G.; Sear, S.

    1982-01-01

    High signal-to-noise profiles of the broad diffuse interstellar band at 4430 A were obtained on the 2.2-m telescope at the Mauna Kea Observatory, using the newly-developed pulse-counting multi-anode microchannel array detector system in an effort to determine whether the band profile varies with mean grain size as expected if the band is produced by absorbers embedded in grain lattices. The lack of profile variability over several lines of sight where independent evidence indicates that the mean grain size varies shows that lambda 4430 is probably not formed by the same grains that are responsible for interstellar extinction at visible wavelengths. The possibility that this band is created by a population of very small ( approximately 100 A) grains is still viable, as is the hypothesis that it has a molecular origin.

  9. Interstellar Alcohols

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  10. Dust models post-Planck: constraining the far-infrared opacity of dust in the diffuse interstellar medium

    NASA Astrophysics Data System (ADS)

    Fanciullo, L.; Guillet, V.; Aniano, G.; Jones, A. P.; Ysard, N.; Miville-Deschênes, M.-A.; Boulanger, F.; Köhler, M.

    2015-08-01

    Aims: We compare the performance of several dust models in reproducing the dust spectral energy distribution (SED) per unit extinction in the diffuse interstellar medium (ISM). We use our results to constrain the variability of the optical properties of big grains in the diffuse ISM, as published by the Planck collaboration. Methods: We use two different techniques to compare the predictions of dust models to data from the Planck HFI, IRAS, and SDSS surveys. First, we fit the far-infrared emission spectrum to recover the dust extinction and the intensity of the interstellar radiation field (ISRF). Second, we infer the ISRF intensity from the total power emitted by dust per unit extinction, and then predict the emission spectrum. In both cases, we test the ability of the models to reproduce dust emission and extinction at the same time. Results: We identify two issues. Not all models can reproduce the average dust emission per unit extinction: there are differences of up to a factor ~2 between models, and the best accord between model and observation is obtained with the more emissive grains derived from recent laboratory data on silicates and amorphous carbons. All models fail to reproduce the variations in the emission per unit extinction if the only variable parameter is the ISRF intensity: this confirms that the optical properties of dust are indeed variable in the diffuse ISM. Conclusions: Diffuse ISM observations are consistent with a scenario where both ISRF intensity and dust optical properties vary. The ratio of the far-infrared opacity to the V band extinction cross-section presents variations of the order of ~20% (40-50% in extreme cases), while ISRF intensity varies by ~30% (~60% in extreme cases). This must be accounted for in future modelling. Appendices are available in electronic form at http://www.aanda.org

  11. Near-Infrared Band Strengths of Molecules Diluted in N2 and H20 Ice Mixtures Relevant to Interstellar and Planetary Ices

    NASA Technical Reports Server (NTRS)

    Richey, C. R.; Richey, Christina R.

    2012-01-01

    In order to determine the column density of a component of an ice from its infrared absorption features, the strengths of these features must be known. The peak positions, widths, profiles, and strengths of a certain ice component's infrared absorption features are affected be the overall composition of the ice. Many satellites within the solar system have surfaces that are dominated by H2O or N2 and ices in the interstellar medium (ISM) are primarily composed of H2O. The experiments presented here focus on the near-infrared absorption features of CO, CO2, CH4, and NH3 (nu=10,000-4,000/cm, lambda=1-2.5 microns) and the effects of diluting these molecules in N2 or H2O ice (mixture ratio of 5:1). This is a continuation of previous results published by our research group.

  12. Interstellar isomers

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  13. Interstellar nomads

    NASA Astrophysics Data System (ADS)

    Finney, B. R.; Jones, E. M.

    The possibility that free-wandering comets, those not tied to the gravitational influence of any star, can support a significant human population is considered. The energy sources of such a population would be deuterium from the comets and starlight gathered by gigantic mirrors. The energy budgets of such communities and their possible social structures are addressed from an anthropological perspective. A typical grouping or tribe might comprise 500 people and be divided into bands of about 25 individuals living in spacious habitats built of cometary materials and tending a 'farm' of starlight mirrors about 30,000 km across. The bands would exchange marriageable youths and gather at intervals for community rituals.

  14. Enigmatic extinction: An investigation of the 2175 A extinction bump in M101, the Pinwheel Galaxy

    NASA Astrophysics Data System (ADS)

    Danowski, Meredith Elaine

    Dust is a critical component of the universe, affecting energy flow and the dynamics of star and planetary disk evolution. The light we measure when observing the universe is absorbed and scattered (extinguished) by dust. Studies indicate that active formation of high mass stars modifies the ultraviolet (UV) dust extinction curve, removing the characteristic bump at 2175 A. For a half century, the source of this bump has not been positively identified. Dust grain models suggest that a leading contender is polycyclic aromatic hydrocarbons. The spiral galaxy M101 is an ideal laboratory, with many HII regions, plus steep metallicity and ionization gradients. The role of environment in this enigmatic "bump-less'' extinction was investigated in M101 with observations from both a sounding rocket mission and the Hubble Space Telescope (HST).. The Interstellar Absorption Gradient Experiment Rocket (IMAGER) mission was designed to probe the correlations between dust extinction and environment through photometric observations of the apparent strengths of the 2175 A bump and UV continuum in M101. IMAGER flew and collected data on November 21, 2012. Although in-flight anomalies caused significant cross-talk, the mission demonstrated the feasibility of simultaneous imaging in three medium-width UV bands. With angular resolution poorer than one arcminute in all bands, and inadequate signal in the field-of-view, these data proved unsuitable for aperture photometry. This analysis method cannot be used with these data to draw conclusions about the correlations between environment and ultraviolet extinction. Spectroscopic observations were performed with the Space Telescope Imaging Spectrograph (STIS) instrument aboard the HST. With additional data from the Spitzer Space Telescope, and radiative transfer and stellar evolution models, the correlation between the bump and the aromatic features was probed across HII regions spanning wide ranges of metallicity and radiation field

  15. Extinction maps toward the Milky Way bulge: Two-dimensional and three-dimensional tests with apogee

    SciTech Connect

    Schultheis, M.; Zasowski, G.; Allende Prieto, C.; Beaton, R. L.; García Pérez, A. E.; Majewski, S. R.; Beers, T. C.; Bizyaev, D.; Frinchaboy, P. M.; Ge, J.; Hearty, F.; Schneider, D. P.; Holtzman, J.; Muna, D.; Nidever, D.; Shetrone, M. E-mail: gail.zasowski@gmail.com

    2014-07-01

    Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.

  16. Interstellar Predation

    NASA Astrophysics Data System (ADS)

    Cockell, C. S.; Lee, M.

    Although chemosynthesis and photosynthesis can theoretically supply enough energy for intelligence, for reasons elucidated here, heterotrophy and specifically phagotrophy (ingestion of prey) are likely to make predation a characteristic of life and extraterrestrial intelligence (ETI). Here, the Earth's biota is used to consider the nature of interstellar predation. The ability of the ETI to directly ingest a biota will be determined by the chiral preference of the ETI, the compatibility of the biochemistry used in life on Earth with the molecules required by the ETI and the potential toxicity of the macromolecules. If chirality is determined by astrophysical factors and not by the specificities of terrestrial origins of life and if molecules found in terrestrial organisms are also represented in ETIs (which could plausibly include hydrated carbohydrides and many amino acids that are similar or identical to amino acids found in meteoritic or cometary material) then the Earth might represent a universally appreciated resource. The Earth's biota could be used as an energy supply or, if other forms of technology have advanced to the point where bioreactors can be exclusively used to supply a civilization with food, as a culinary curiosity. Even in the absence of metabolic compatibility, technology can be used to extract useful products from an undigestible biota, similarly to the industrial biotransformation of cellulose. The value of the resource will also be determined by the availability of prey. Planets at stages in biological evolution where the surface is dominated by just one or several large (>5kg), abundant, easily captured organisms are particu- larly attractive to predators because harvesting techniques can be standardized. We discuss implications for exobiology and the `Fermi Paradox'.

  17. PAHs in Translucent Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    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.

  18. Interstellar Dust Models Towards Some IUE Stars

    NASA Astrophysics Data System (ADS)

    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.

  19. A search for interstellar anthracene towards the Perseus anomalous microwave emission region

    NASA Astrophysics Data System (ADS)

    Iglesias-Groth, S.; Manchado, A.; Rebolo, R.; González Hernández, J. I.; García-Hernández, D. A.; Lambert, D. L.

    2010-10-01

    We report the discovery of a new broad interstellar (or circumstellar) band at 7088.8 +/- 2.0 Å coincident to within the measurement uncertainties with the strongest band of the anthracene cation (C14H10+) as measured in gas-phase laboratory spectroscopy at low temperatures. The band is detected in the line of sight of star Cernis 52, a likely member of the very young star cluster IC 348, and is probably associated with cold absorbing material in an intervening molecular cloud of the Perseus star-forming region where various experiments have recently detected anomalous microwave emission. From the measured intensity and available oscillator strength we find a column density of implying that ~0.008 per cent of the carbon in the cloud could be in the form of C14H10+. A similar abundance has been recently claimed for the naphthalene cation in this cloud. This is the first location outside the Solar system where specific polycyclic aromatic hydrocarbons (PAHs) are identified. We report observations of interstellar lines of CH and CH+ that support a rather high column density for these species and for molecular hydrogen. The strength ratio of the two prominent diffuse interstellar bands at 5780 and 5797 Å suggests the presence of a `zeta'-type cloud in the line of sight (consistent with steep far-ultraviolet extinction and high molecular content). The presence of PAH cations and other related hydrogenated carbon molecules which are likely to occur in this type of clouds reinforces the suggestion that electric dipole radiation from fast-spinning PAHs is responsible of the anomalous microwave emission detected towards Perseus.

  20. EXTINCTION IN STAR-FORMING DISK GALAXIES FROM INCLINATION-DEPENDENT COMPOSITE SPECTRA

    SciTech Connect

    Yip, Ching-Wa; Szalay, Alex S.; Wyse, Rosemary F. G.; Budavari, Tamas; Dobos, Laszlo; Csabai, Istvan E-mail: szalay@pha.jhu.ed

    2010-02-01

    Extinction in galaxies affects their observed properties. In scenarios describing the distribution of dust and stars in individual disk galaxies, the amplitude of the extinction can be modulated by the inclination of the galaxies. In this work, we investigate the inclination dependency in composite spectra of star-forming disk galaxies from the Sloan Digital Sky Survey Data Release 5. In a volume-limited sample within a redshift range 0.065-0.075 and a r-band Petrosian absolute magnitude range -19.5 to -22 mag which exhibits a flat distribution of inclination, the inclined relative to face-on extinction in the stellar continuum is found empirically to increase with inclination in the g, r, and i bands. Within the central 0.5 intrinsic half-light radius of the galaxies, the g-band relative extinction in the stellar continuum for the highly inclined objects (axis ratio b/a = 0.1) is 1.2 mag, agreeing with previous studies. The extinction curve of the disk galaxies is given in the rest-frame wavelengths 3700-8000 A, identified with major optical emission and absorption lines in diagnostics. The Balmer decrement, Halpha/Hbeta, remains constant with inclination, suggesting a different kind of dust configuration and/or reddening mechanism in the H II region from that in the stellar continuum. One factor is shown to be the presence of spatially non-uniform interstellar extinction, presumably caused by clumped dust in the vicinity of the H II region.

  1. X-ray Haloes and Scattering by Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu

    2003-01-01

    The presence of dust in the general interstellar medium is inferred f r o m the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

  2. X-ray Haloes and Scattering by Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu

    2003-01-01

    The presence of dust in the general interstellar medium is inferred from the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

  3. Rethinking Extinction

    PubMed Central

    Dunsmoor, Joseph E.; Niv, Yael; Daw, Nathaniel; Phelps, Elizabeth A.

    2015-01-01

    Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior, and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories. PMID:26447572

  4. Rethinking Extinction.

    PubMed

    Dunsmoor, Joseph E; Niv, Yael; Daw, Nathaniel; Phelps, Elizabeth A

    2015-10-07

    Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories.

  5. The Optical-infrared Extinction Curve and Its Variation in the Milky Way

    NASA Astrophysics Data System (ADS)

    Schlafly, E. F.; Meisner, A. M.; Stutz, A. M.; Kainulainen, J.; Peek, J. E. G.; Tchernyshyov, K.; Rix, H.-W.; Finkbeiner, D. P.; Covey, K. R.; Green, G. M.; Bell, E. F.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Martin, N. F.; Metcalfe, N.; Wainscoat, R. J.; Waters, C.

    2016-04-01

    The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium. Here we present new measurements of the dust extinction curve and its variation toward tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies. We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, the Two Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We find that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves described by R(V). The extinction curve is more uniform than suggested in past works, with σ (R(V))=0.18, and with less than one percent of sight lines having R(V)\\gt 4. Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in R(V) throughout the Galactic plane. These variations are on scales much larger than individual molecular clouds, indicating that R(V) variations must trace much more than just grain growth in dense molecular environments. Indeed, we find no correlation between R(V) and dust column density up to E(B-V)≈ 2. Second, we discover a strong relationship between R(V) and the far-infrared dust emissivity.

  6. Organic molecules in translucent interstellar clouds.

    PubMed

    Krełowski, Jacek

    2014-09-01

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

  7. Molecular Spectroscopy in Astrophysics: Interstellar PAHs

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  8. Laboratory Studies of Interstellar PAH Analogs

    NASA Technical Reports Server (NTRS)

    Salama, Farid; DeVincenzi, Donald (Technical Monitor)

    2000-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  10. Observational evidence of dust evolution in galactic extinction curves

    SciTech Connect

    Cecchi-Pestellini, Cesare; Casu, Silvia; Mulas, Giacomo; Zonca, Alberto E-mail: silvia@oa-cagliari.inaf.it E-mail: azonca@oa-cagliari.inaf.it

    2014-04-10

    Although structural and optical properties of hydrogenated amorphous carbons are known to respond to varying physical conditions, most conventional extinction models are basically curve fits with modest predictive power. We compare an evolutionary model of the physical properties of carbonaceous grain mantles with their determination by homogeneously fitting observationally derived Galactic extinction curves with the same physically well-defined dust model. We find that a large sample of observed Galactic extinction curves are compatible with the evolutionary scenario underlying such a model, requiring physical conditions fully consistent with standard density, temperature, radiation field intensity, and average age of diffuse interstellar clouds. Hence, through the study of interstellar extinction we may, in principle, understand the evolutionary history of the diffuse interstellar clouds.

  11. Do you know the extinction in your young massive cluster?

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino; Sabbi, Elena; HTTP Team

    2015-08-01

    Up to ages of a few 100 Myr, massive clusters are still swamped in large amounts of gas and dust from their primordial cocoons. This causes considerable and uneven levels of extinction across the cluster that we must understand and measure if we want to extract any physically meaningful parameters, from basic luminosities and effective temperatures to masses and ages. We have developed a powerful method to unambiguously determine the extinction law and the absolute value of the extinction in a uniform way across a cluster field, using multi-band photometry of red giant stars belonging to the red clump (RC). Since these stars share very similar physical properties, they allow us to derive the absolute extinction in a straightforward and reliable way. In the Magellanic Clouds, with about 20 RC stars arcmin-2 or ~150 objects in a typical HST pointing, we can easily derive a solid and self-consistent absolute extinction curve over the entire wavelength range of the photometry, with no need for spectroscopy.I will show an application of this method to the Hubble Tarantula Treasury Project's observations of the Tarantula nebula, containing the massive R136 cluster. We have measured the absolute extinction towards about 3600 objects and the extinction law in the range 0.3 - 1.6 μm. At optical wavelengths, the extinction curve is almost parallel to that of the diffuse Galactic interstellar medium (ISM), but the value of RV = AV/E(B-V) = 4.5 ± 0.2 that we measure indicates that in the optical there is an extra grey component due to a larger fraction of large grains. Using the RV = 3.1 value typical of the diffuse Galactic ISM would severely underestimate the luminosities and masses and overestimate the ages of the stars in the cluster. At wavelengths longer than ~ 1 μm, the contribution of this additional component tapers off as λ-1.5, like in the Milky Way, suggesting that the nature of the grains is otherwise similar to those in our Galaxy, but with a ~ 2 times higher

  12. Near-infrared extinction with discretised stellar colours

    NASA Astrophysics Data System (ADS)

    Juvela, M.; Montillaud, J.

    2016-01-01

    Context. Near-infrared (NIR) extinction remains one of the most reliable methods of measuring the column density of dense interstellar clouds. Extinction can be estimated using the reddening of the light of background stars. Several methods exist (e.g., NICE, NICER, NICEST, GNICER) to combine observations of several NIR bands into extinction maps. Aims: We present a new method of estimating extinction based on NIR multiband observations and examine its performance. Methods: Our basic method uses a discretised version of the distribution of intrinsic stellar colours directly. The extinction of individual stars and the average over a resolution element are estimated with Markov chain Monte Carlo (MCMC) methods. Several variations of the basic method are tested, and the results are compared to NICER calculations. Results: In idealised settings or when photometric errors are large, the results of the new method are very close to those of NICER. Clear advantages can be seen when the distribution of intrinsic colours cannot be described well with a single covariance matrix. The MCMC framework makes it easy to consider additional effects such as those of completeness limits and contamination by galaxies or foreground stars. A priori information about relative column density variations at sub-beam scales can result in a significant increase in accuracy. For observations of high photometric precision, the results could be further improved by considering the magnitude dependence of the intrinsic colours. Conclusions: The MCMC computations are time-consuming, but the calculation of large extinction maps is already practical. The same methods can be used with direct optimisation, with significantly less computational work. Faster methods, like NICER, perform very well in many cases even when the basic assumptions no longer hold. The new methods are useful mostly when photometric errors are small, the distribution of intrinsic colours is well known, or one has prior knowledge

  13. Interstellar grain chemistry and organic molecules

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  14. Science with the Galactic O-Star Spectroscopic Survey (GOSSS): the relationship between DIBs, the ISM, and extinction

    NASA Astrophysics Data System (ADS)

    Penades Ordaz, M.; Maíz Apellániz, J.; Sota, A.; Alfaro, E. J.; Walborn, N. R.; Barbá, R. H.; Morrell, N. I.; Arias, J. I.; Gamen, R. C.

    2011-11-01

    In this poster we show our preliminary analysis of DIBs (Diffuse Interstellar Bands) and other interstellar absorption lines with the purpose of understanding their origin and their relationship with extinction. We use the biggest Galactic O-star blue-violet spectroscopic sample ever (GOSSS, see Maíz Apellániz, these proceedings). This sample allows a new insight on this topic because of the adequacy of O-star spectra, the sample number (700 by early 2010 and increasing; 400 are used here), and their distribution in the Milky Way disk. We confirm the high correlation coefficients between different DIBs and E(B-V), though the detailed behavior of each case shows small differences. We also detect a moderately low correlation coefficient between CaII lambda 3934 (Ca K) and E(B-V) with a peculiar spatial distribution that we ascribe to the relationship between line saturation and velocity profiles for CaII lambda 3934.

  15. Observations of interstellar zinc

    NASA Technical Reports Server (NTRS)

    Jura, M.; York, D.

    1981-01-01

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

  16. NASA's IBEX Observes Interstellar Matter

    NASA Video Gallery

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

  17. The Extinction Properties of and Distance to the Highly Reddened Type IA Supernova 2012CU

    NASA Astrophysics Data System (ADS)

    Huang, X.; Raha, Z.; Aldering, G.; Antilogus, P.; Bailey, S.; Baltay, C.; Barbary, K.; Baugh, D.; Boone, K.; Bongard, S.; Buton, C.; Chen, J.; Chotard, N.; Copin, Y.; Fagrelius, P.; Fakhouri, H. K.; Feindt, U.; Fouchez, D.; Gangler, E.; Hayden, B.; Hillebrandt, W.; Kim, A. G.; Kowalski, M.; Leget, P.-F.; Lombardo, S.; Nordin, J.; Pain, R.; Pecontal, E.; Pereira, R.; Perlmutter, S.; Rabinowitz, D.; Rigault, M.; Rubin, D.; Runge, K.; Saunders, C.; Smadja, G.; Sofiatti, C.; Stocker, A.; Suzuki, N.; Taubenberger, S.; Tao, C.; Thomas, R. C.; Nearby Supernova Factory, (The

    2017-02-01

    Correcting Type Ia Supernova brightnesses for extinction by dust has proven to be a vexing problem. Here we study the dust foreground to the highly reddened SN 2012cu, which is projected onto a dust lane in the galaxy NGC 4772. The analysis is based on multi-epoch, spectrophotometric observations spanning from 3300–9200 Å, obtained by the Nearby Supernova Factory. Phase-matched comparison of the spectroscopically twinned SN 2012cu and SN 2011fe across 10 epochs results in the best-fit color excess of (E(B-V), RMS) = (1.00, 0.03) and total-to-selective extinction ratio of (R V , RMS) = (2.95, 0.08) toward SN 2012cu within its host galaxy. We further identify several diffuse interstellar bands and compare the 5780 Å band with the dust-to-band ratio for the Milky Way (MW). Overall, we find the foreground dust-extinction properties for SN 2012cu to be consistent with those of the MW. Furthermore, we find no evidence for significant time variation in any of these extinction tracers. We also compare the dust extinction curve models of Cardelli et al., O’Donnell, and Fitzpatrick, and find the predictions of Fitzpatrick fit SN 2012cu the best. Finally, the distance to NGC4772, the host of SN 2012cu, at a redshift of z = 0.0035, often assigned to the Virgo Southern Extension, is determined to be 16.6 ± 1.1 Mpc. We compare this result with distance measurements in the literature.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  19. CaFe interstellar clouds

    NASA Astrophysics Data System (ADS)

    Bondar, A.; Kozak, M.; Gnaciński, P.; Galazutdinov, G. A.; Beletsky, Y.; Krełowski, J.

    2007-07-01

    A new kind of interstellar cloud is proposed. These are rare (just a few examples among ~300 lines of sight) objects with the CaI 4227-Å, FeI 3720-Å and 3860-Å lines stronger than those of KI (near 7699 Å) and NaI (near 3302 Å). We propose the name `CaFe' for these clouds. Apparently they occupy different volumes from the well-known interstellar HI clouds where the KI and ultraviolet NaI lines are dominant features. In the CaFe clouds we have not found either detectable molecular features (CH, CN) or diffuse interstellar bands which, as commonly believed, are carried by some complex, organic molecules. We have found the CaFe clouds only along sightlines toward hot, luminous (and thus distant) objects with high rates of mass loss. In principle, the observed gas-phase interstellar abundances reflect the combined effects of the nucleosynthetic history of the material, the depletion of heavy elements into dust grains and the ionization state of these elements which may depend on irradiation by neighbouring stars. Based on data collected using the Maestro spectrograph at the Terskol 2-m telescope, Russia; and on data collected using the ESO Feros spectrograph; and on data obtained from the ESO Science Archive Facility acquired with the UVES spectrograph, Chile. E-mail: `arctur'@rambler.ru (AB); marizak@astri.uni.torun.pl (MK); pg@iftia.univ.gda.pl (PG); gala@boao.re.kr (GAG); ybialets@eso.org (YB); jacek@astri.uni.torun.pl (JK)

  20. Polarimetry of the Interstellar Medium

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  1. Boussard Interstellar Ramjet Engine

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The Boussard Interstellar Ramjet engine concept uses interstellar hydrogen scooped up from its environment as the spacecraft passes by to provide propellant mass. The hydrogen is then ionized and then collected by an electromagentic field. In this image, an onboard laser is uded to heat the plasma, and the laser or electron beam is used to trigger fusion pulses thereby creating propulsion.

  2. Infrared Emission From Interstellar PAHs, New Probes of the Interstellar Medium

    NASA Technical Reports Server (NTRS)

    Hudgins, D. M.; Allamandola, L. J.

    2002-01-01

    Tremendous strides have been made in the understanding of interstellar material over the past twenty years thanks to significant, parallel developments in two closely related areas: observational IR astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely unknown 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, impossibly large molecules by early interstellar chemistry standards, is very strong. PAH spectral features are now being used as new probes of the ISM. PAH ionization states reflect the ionization balance of the medium while PAH size and structure reflect the energetic and chemical history of the medium. Aromatic carbon-rich materials ranging in size from PAHs and PAH nanoclusters, to sub-micron and micron-sized dust grains represent an important component of the ISM. These species: (1) dominate the heating and cooling of interstellar clouds via energetic photoelectron ejection and infrared (IR) emission; (2) moderate the ionization balance in photodissociation regions and molecular clouds; (3) moderate the composition of the gas phase and play an important role in determining the chemistry of the ISM; (4) contribute to the interstellar extinction in the near IR, visible, and UV spectral regions; and (5) convert UV, visible, and near-IR radiation to mid- and far-IR radiation in the ISM and, as such, are responsible for the well known, widespread family of mid-IR emission features with major components near 3.3, 6.2, 7.7, 8.6, and 11.3 microns.

  3. PAH in the laboratory and interstellar space

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  4. The Organic Component of Interstellar Dust

    NASA Technical Reports Server (NTRS)

    Pendleton, Yvonne

    2003-01-01

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

  5. Mass extinctions and missing matter

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.

    1984-01-01

    The possible influence of 'invisible matter' on the solar system's comet halo, and therefore on quasi-periodic cometary bombardment of the earth and consequent mass extinctions, is briefly addressed. Invisible matter consisting of small or cold interstellar molecular clouds could significantly modulate the comet background flux, while invisible matter consisting of a large population of old, dead stars with a relatively small galactic concentration probably could not. It is also shown that the downward force exerted by the Galaxy will perturb the halo, but will not produce any periodicity.

  6. Laboratory evidence for ionized polycyclic aromatic hydrocarbons in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Szczepanski, Jan; Vala, Martin

    1993-01-01

    The infrared absorption from neutrals and cations of four PAHs - naphthalene, anthracene, pyrene, and perylene - integrated over the spectral regions corresponding to the interstellar bands are compared with astronomical observations. It is found that the interstellar bands cannot be explained solely on the basis of neutral PAH species, but that cations must be a significant, and in some cases dominant, component.

  7. Presolar/Interstellar Materials

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  8. Extinctions of life

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1988-01-01

    This meeting presentation examines mass extinctions through earth's history. Extinctions are charted for marine families and marine genera. Timing of marine genera extinctions is discussed. Periodicity in extinctions during the Mesozoic and Cenozoic eras is plotted and compared with Paleozoic extinction peaks. The role of extinction in evolution and mankind's role in present extinctions are examined.

  9. The galactic distribution of aliphatic hydrocarbons in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.; Pendleton, Yvonne J.; Allamandola, Louis J.

    1995-01-01

    The infrared absorption feature near 2950(exp -1) (3.4 micron), characteristic of dust in the diffuse interstellar medium (ISM), is attributed to C-H stretching vibrations of aliphatic hydrocarbons. We show here that the strength of the band does not scale linearly with visual extinction everywhere, but instead increases more rapidly for objects near the center of the Galaxy, a behavior that parallels that of the Si-O stretching band due to silicate materials in the diffuse ISM. This implies that the grains responsible for the diffuse medium aliphatic C-H and silicate Si-O stretching bands are different from those responsible for much of the observed visual extinction. It also suggests that the distribution of the carbonaceous component of the diffuse ISM is not uniform throughout the Galaxy, but instead may increase in density toward the center of the Galaxy. 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 silicate-core, organic-mantle grains. Several possible models of the distribution of this material are presented and it is demonstrated that the inner parts of the Galaxy has a carrier density that is 5 to 35 times higher than in the local ISM. Depending on the model used, the density of aliphatic material in the local ISM is found to be about 1 to 2 -CH3 groups m(exp -3) and about 2 to 5 -CH2- groups m(exp -3). These densities are consistent with the strengths of the 2955 and 2925 cm(exp -1) (3.4 micron) band being described by the relations A(sub nu)/tau(sub 2955 cm(exp -1)) = 270 +/- 40 and A(sub nu)/tau(sub 2925 cm(exp -1)) = 250 +/- 40 in the local diffuse ISM.

  10. Influence of the nature of the absorption band on the potential performance of high molar extinction coefficient ruthenium(II) polypyridinic complexes as dyes for sensitized solar cells.

    PubMed

    Gajardo, Francisco; Barrera, Mauricio; Vargas, Ricardo; Crivelli, Irma; Loeb, Barbara

    2011-07-04

    When tested in solar cells, ruthenium polypyridinic dyes with extended π systems show an enhanced light-harvesting capacity that is not necessarily reflected by a high (collected electrons)/(absorbed photons) ratio. Provided that metal-to-ligand charge transfer bands, MLCT, are more effective, due to their directionality, than intraligand (IL) π-π* bands for the electron injection process in the solar cell, it seems important to explore and clarify the nature of the absorption bands present in these types of dyes. This article aims to elucidate if all the absorbed photons of these dyes are potentially useful in the generation of electric current. In other words, their potentiality as dyes must also be analyzed from the point of view of their contribution to the generation of excited states potentially useful for direct injection. Focusing on the assignment of the absorption bands and the nature of the emitting state, a systematic study for a series of ruthenium complexes with 4,4'-distyryl-2,2'-dipyridine (LH) and 4,4'-bis[p-(dimethylamino)-α-styryl]-2,2'-bipyridine (LNMe(2)) "chromophoric" ligands was undertaken. The observed experimental results were complemented with TDDFT calculations to elucidate the nature of the absorption bands, and a theoretical model was proposed to predict the available energy that could be injected from a singlet or a triplet excited state. For the series studied, the results indicate that the percentage of MLCT character to the anchored ligand for the lower energy absorption band follows the order [Ru(deebpy)(2)(LNMe(2))](PF(6))(2) > [Ru(deebpy)(2)(LH)](PF(6))(2) > [Ru(deebpy)(LH)(2)](PF(6))(2), where deebpy is 4,4'-bis(ethoxycarbonyl)-2,2'-bipyridine, predicting that, at least from this point of view, their efficiency as dyes should follow the same trend.

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

    PubMed

    Maier, John P; Campbell, Ewen K

    2016-09-13

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

  12. Interstellar Dust - A Review

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2012-01-01

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

  13. Extinction in SC galaxies

    NASA Astrophysics Data System (ADS)

    Giovanelli, Riccardo; Haynes, Martha P.; Salzer, John J.; Wegner, Gary; da Costa, Luiz N.; Freudling, Wolfram

    1994-06-01

    We analyze the photometric properties of a sample of Sbc-Sc galaxies with known redshifts, single-dish H I profiles, and Charge Coupled Device (CCD) I band images. We derive laws that relate the measured isophotal radius at muI = 23.5, magnitude, scale length, and H I flux to the face-on aspect. We find spiral galaxies to be substantially less transparent than suggested in most previous determinations, but not as opaque as claimed by Valentijn (1990). Regions in the disk farther than two or three scale lengths from the center are close to completely transparent. In addition to statistically derived relations for the inclination dependence of photometric parameters, we present the results of a modeling exercise that utilizes the 'triplex' model of Disney et al. (1989) to obtain upper limits of the disk opacity. Within the framework of that model, and with qualitative consideration of the effects of scattering on extinction, we estimate late spiral disks at I band to have central optical depths tauI(0) less than 5 and dust absorbing layers with scale heights on the order of half that of the stellar component or less. We discuss our results in light of previous determinations of internal extinction relations and point out the substantial impact of internal extinction on the scatter of the Tully-Fisher relation. We also find that the visual diameters by which large catalogs are constructed (UGC, ESO-Uppsala) are nearly proportional to face-on isophotal diameters.

  14. Australian Extinctions

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    Massive extinctions of animals and the arrival of the first humans in ancient Australia--which occurred 45,000 to 55,000 years ago--may be linked. Researchers at the Carnegie Institution, University of Colorado, Australian National University, and Bates College believe that massive fires set by the first humans may have altered the ecosystem of…

  15. Interstellar chemistry - Polycyanoacetylene formation

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  16. Observations of interstellar zinc

    NASA Technical Reports Server (NTRS)

    York, D. G.; Jura, M.

    1982-01-01

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

  17. Discovery of interstellar rubidium

    NASA Technical Reports Server (NTRS)

    Jura, M.; Smith, W. H.

    1981-01-01

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

  18. Interstellar organic chemistry.

    NASA Technical Reports Server (NTRS)

    Sagan, C.

    1972-01-01

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

  19. Carriers of the astronomical 2175 ? extinction feature

    SciTech Connect

    Bradley, J; Dai, Z; Ernie, R; Browning, N; Graham, G; Weber, P; Smith, J; Hutcheon, I; Ishii, H; Bajt, S; Floss, C; Stadermann, F

    2004-07-20

    The 2175 {angstrom} extinction feature is by far the strongest spectral signature of interstellar dust observed by astronomers. Forty years after its discovery the origin of the feature and the nature of the carrier remain controversial. The feature is enigmatic because although its central wavelength is almost invariant its bandwidth varies strongly from one sightline to another, suggesting multiple carriers or a single carrier with variable properties. Using a monochromated transmission electron microscope and valence electron energy-loss spectroscopy we have detected a 5.7 eV (2175 {angstrom}) feature in submicrometer-sized interstellar grains within interplanetary dust particles (IDPs) collected in the stratosphere. The carriers are organic carbon and amorphous silicates that are abundant and closely associated with one another both in IDPs and in the interstellar medium. Multiple carriers rather than a single carrier may explain the invariant central wavelength and variable bandwidth of the astronomical 2175 {angstrom} feature.

  20. SEARCHING FOR NAPHTHALENE CATION ABSORPTION IN THE INTERSTELLAR MEDIUM

    SciTech Connect

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

    2011-05-01

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

  1. Enabling interstellar probe

    NASA Astrophysics Data System (ADS)

    McNutt, Ralph L.; Wimmer-Schweingruber, Robert F.; International Interstellar Probe Team

    2011-04-01

    The scientific community has advocated a scientific probe to the interstellar medium for over 30 years. While the Voyager spacecraft have passed through the termination shock of the solar wind, they have limited lifetimes as their radioisotope power supplies decay. It remains unclear whether they can reach the heliopause, the boundary between shocked solar wind and interstellar plasmas, and, in any case, they will not reach the undisturbed interstellar medium. As with most exploratory space missions, their ongoing observations continue to raise even more questions about the nature of the interaction of our heliosphere and the interstellar medium. Scientific questions including: What is the nature of the nearby interstellar medium? How do the Sun and galaxy affect the dynamics of the heliosphere? What is the structure of the heliosphere? How did matter in the solar system and interstellar medium originate and evolve? can only be answered by an "interstellar precursor" probe. Such a mission is required to make in situ measurements in the interaction region and interstellar medium itself at distances far from the Sun, but in a finite mission lifetime. By launching a probe toward the incoming "interstellar wind," whose direction is known, the distance to be traveled can be minimized but is still large. The current consensus is that a scientifically compelling mission must function to at least a distance of 200 astronomical units (AU) from the Sun and return a reasonable stream of data during the voyage. The central problem is that of providing a means of propulsion to accelerate a probe from the Solar System. Even with a low-mass payload and spacecraft, achieving the high speeds needed, even with gravity assists, have remained problematic. Voyager 1, the fastest object ever to leave the system is now traveling ˜3.6 AU/yr, and a credible probe must reach at least 2-3 times this speed. The use of an Ares V is an approach for enabling a fast interstellar precursor

  2. The Extinction properties of and distance to the highly reddened Type~Ia supernova SN 2012cu

    NASA Astrophysics Data System (ADS)

    Huang, Xiaosheng; Raha, Zachary; Aldering, Greg Scott; Antilogus, Pierre; Bailey, Stephen J.; Charles, Baltay; Barbary, Kyle H.; Baugh, Derek; Boone, Kyle; Bongard, Sebastien; Buton, Clement; Chen, Juncheng; Chotard, Nicolas; Copin, Yannick; Fagrelius, Parker; Fakhouri, Hannah; Feindt, Ulrich; Fouchez, Dominique; Gangler, Emmanuel; Hayden, Brian; Hillebrandt, Wolfgang; Kim, Alex G.; Kowalski, Marek; Leget, Pierre-Francois; Lombardo, Simona; Nordin, Jakob; Pain, Reynald; Pecontal, Emmanuel; Pereira, Rui; Perlmutter, Saul; Rabinowitz, David L.; Rigault, Mickael; Rubin, David; Runge, Karl; Saunders, Clare; Smadja, Gerard; Sofiatti, Caroline; Stocker, Andrew; Suzuki, Nao; Taubenberger, Stefan; Tao, Charling; Thomas, Rollin

    2017-01-01

    Correction of Type Ia SN brightnesses for extinction by dust has proven to be a vexing problem. Here we study the dust foreground to the highly reddened SN 2012cu, which is projected onto a dust lane in the galaxy NGC 4772. The analysis is based on multi-epoch, spectrophotometric observations spanning 3,300 - 9,200 A, obtained by the Nearby Supernova Factory. Phase-matched comparison of the spectroscopically twinned SN 2012cu and SN 2011fe across 10 epochs results in the best-fit color excess of (E(B - V ), RMS) = (1.00, 0.03) and total-to-selective extinction ratio of (RV , RMS) = (2.95, 0.09) toward SN 2012cu within its host galaxy. We further identify several diffuse interstellar bands, and compare the 5780 A band with the dust-to-band ratio for the Milky Way. Overall, we find the foreground dust-extinction properties for SN 2012cu to be consistent with those of the Milky Way. Furthermore we find no evidence for significant time variation in any of these extinction tracers. We also compare the dust extinction curves of Cardelli et al. (1989), O’Donnell (1994), and Fitzpatrick (1999), and find the predictions of Fitzpatrick (1999) fit SN 2012cu the best. Finally, the distance to NGC4772, the host of SN 2012cu, at a redshift of z = 0.0035, often assigned to the Virgo Southern Extension, is determined to be 16.6±1.1 Mpc. We compare this result with distance measurements in the literature.

  3. Interstellar Antifreeze: Ethylene Glycol

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  4. Photodissociation of interstellar N2

    NASA Astrophysics Data System (ADS)

    Li, X.; Heays, A. N.; Visser, R.; Ubachs, W.; Lewis, B. R.; Gibson, S. T.; van Dishoeck, E. F.

    2013-07-01

    Context. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been properly studied. The partitioning of nitrogen between N and N2 controls the formation of more complex prebiotic nitrogen-containing species. Aims: 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. Methods: We used an approach similar to that adopted for CO in which we simulated the full high-resolution line-by-line absorption + dissociation spectrum of N2 over the relevant 912-1000 Å wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schrödinger 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 protoplanetary disk. Results: The unattenuated photodissociation rate in the Draine (1978, ApJS, 36, 595) radiation field assuming an N2 excitation temperature of 50 K is 1.65 × 10-10 s-1, with an uncertainty of only 10%. Most of the photodissociation occurs through bands in the 957-980 Å range. The N2 rate depends slightly on the temperature through the variation of predissociation probabilities with rotational quantum number for some bands. Shielding functions are provided for a range of H2 and H column densities, with H2 being much more effective than H in reducing the N2 rate inside a cloud. Shielding by CO is not effective. The new rates are 28% lower than the previously recommended values. Nevertheless, diffuse cloud models still fail to reproduce the possible detection of interstellar N2

  5. Interstellar H(3)(+).

    PubMed

    Oka, Takeshi

    2006-08-15

    Protonated molecular hydrogen, H(3)(+), is the simplest polyatomic molecule. It is the most abundantly produced interstellar molecule, next only to H(2), although its steady state concentration is low because of its extremely high chemical reactivity. H(3)(+) is a strong acid (proton donor) and initiates chains of ion-molecule reactions in interstellar space thus leading to formation of complex molecules. Here, I summarize the understandings on this fundamental species in interstellar space obtained from our infrared observations since its discovery in 1996 and discuss the recent observations and analyses of H(3)(+) in the Central Molecular Zone near the Galatic center that led to a revelation of a vast amount of warm and diffuse gas existing in the region.

  6. Interstellar H3+

    PubMed Central

    Oka, Takeshi

    2006-01-01

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

  7. Stardust Interstellar Preliminary Examination (ISPE)

    NASA Astrophysics Data System (ADS)

    Westphal, A. J.; Allen, C.; Bajt, S.; Basset, R.; 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.; Ferroir, T.; Floss, C.; Flynn, G. J.; Frank, D.; Gainsforth, Z.; Grün, E.; Hoppe, P.; Kearsley, A.; Lemelle, L.; Leroux, H.; Lettieri, R.; Marchant, W.; Mendez, B.; Nittler, L. R.; Ogliore, R.; Postberg, F.; Sandford, S. A.; Schmitz, S.; Silversmit, G.; Simionovici, A.; Srama, R.; Stadermann, F. J.; Stephan, T.; Stroud, R. M.; Susini, J.; Sutton, S.; Trieloff, M.; Tsou, P.; Tsuchiyama, A.; Tyliczszak, T.; Vekemans, B.; Vincze, L.; Warren, J.; Zolensky, M. E.

    2009-03-01

    The Stardust Interstellar Preliminary Examination (ISPE) is a three-year effort to characterize the Stardust interstellar dust collection and collector using non-destructive techniques. We summarize the status of the ISPE.

  8. TIME VARIATION OF AV AND RV FOR TYPE Ia SUPERNOVAE BEHIND INTERSTELLAR DUST

    NASA Astrophysics Data System (ADS)

    Huang, Xiaosheng; Biederman, M.; Herger, B.; Aldering, G. S.

    2014-01-01

    TIME VARIATION OF AV AND RV FOR TYPE Ia SUPERNOVAE BEHIND NON-UNIFORM INTERSTELLAR DUST ABSTRACT We investigate the time variation of the visual extinction, AV, and the total-to-selective extinction ratio, RV, resulting from interstellar dust in front of an expanding photospheric disk of a type Ia supernova (SN Ia). We simulate interstellar dust clouds according to a power law power spectrum and produce extinction maps that either follow a pseudo-Gaussian distribution or a lognormal distribution. The RV maps are produced through a correlation between AV and RV. With maps of AV and RV generated in each case (pseudo-Gaussian and lognormal), we then compute the effective AV and RV for a SN as its photospheric disk expands behind the dust screen. We find for a small percentage of SNe the AV and RV values can vary by a large factor from day to day in the first 40 days after explosion.

  9. Voyager Interstellar Mission (VIM)

    NASA Technical Reports Server (NTRS)

    Rudd, R.; Textor, G.

    1991-01-01

    The DSN (Deep Space Network) mission support requirements for the Voyager Interstellar Mission (VIM) are summarized. The general objectives of the VIM are to investigate the interplanetary and interstellar media and to continue the Voyager program of ultraviolet astronomy. The VIM will utilize both Voyager spacecraft for the period from January 1990 through December 2019. The mission objectives are outlined and the DSN support requirements are defined through the presentation of tables and narratives describing the spacecraft flight profile; DSN support coverage; frequency assignments; support parameters for telemetry, control and support systems; and tracking support responsibility.

  10. A Rigorous Attempt to Verify Interstellar Glycine

    NASA Technical Reports Server (NTRS)

    Snyder, L. E.; Lovas, F. J.; Hollis, J. M.; Friedel, D. N.; Jewell, P. R.; Remijan, A.; Ilyushin, V. V.; Alekseev, E. A.; Dyubko, S. F.

    2004-01-01

    In 2003, Kuan, Charnley, and co-workers reported the detection of interstellar glycine (NH2CH2COOH) based on observations of 27 lines in 19 different spectral bands in one or more of the sources Sgr BP(N-LMH), Orion KL, and W51 e1/e2. They supported their detection report with rotational temperature diagrams for all three sources. In this paper, we present essential criteria which can be used in a straightforward analysis technique to confirm the identity of an interstellar asymmetric rotor such as glycine. We use new laboratory measurements of glycine as a basis for applying this analysis technique, both to our previously unpublished 12 m telescope data and to the previously published SEST data of Nummelin and colleagues. We conclude that key lines necessary for an interstellar glycine identification have not yet been found. We identify several common molecular candidates that should be examined further as more likely carriers of the lines reported as glycine. Finally, we illustrate that rotational temperature diagrams used without the support of correct spectroscopic assignments are not a reliable tool for the identification of interstellar molecules. Subject headings: ISM: abundances - ISM: clouds - ISM: individual (Sagittarius B2[N-

  11. Impossible Extinction

    NASA Astrophysics Data System (ADS)

    Cockell, Charles S.

    2003-03-01

    Every 225 million years the Earth, and all the life on it, completes one revolution around the Milky Way Galaxy. During this remarkable journey, life is influenced by calamitous changes. Comets and asteroids strike the surface of the Earth, stars explode, enormous volcanoes erupt, and, more recently, humans litter the planet with waste. Many animals and plants become extinct during the voyage, but humble microbes, simple creatures made of a single cell, survive this journey. This book takes a tour of the microbial world, from the coldest and deepest places on Earth to the hottest and highest, and witnesses some of the most catastrophic events that life can face. Impossible Extinction tells this remarkable story to the general reader by explaining how microbes have survived on Earth for over three billion years. Charles Cockell received his doctorate from the University of Oxford, and is currently a microbiologist with rhe Search for Extraterrestrial Intelligence Institute (SETI), based at the British Antarctic Survey in Cambridge, UK. His research focusses on astrobiology, life in the extremes and the human exploration of Mars. Cockell has been on expeditions to the Arctic, Antarctic, Mongolia, and in 1993 he piloted a modified insect-collecting ultra-light aircraft over the Indonesian rainforests. He is Chair of the Twenty-one Eleven Foundation for Exploration, a charity that supports expeditions that forge links between space exploration and environmentalism.

  12. The Voyager Interstellar Mission.

    PubMed

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

    1997-01-01

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

  13. Interstellar molecular clouds.

    PubMed

    Bally, J

    1986-04-11

    The interstellar medium in our galaxy contains matter in a variety of states ranging from hot plasma to cold and dusty molecular gas. The molecular phase consists of giant clouds, which are the largest gravitationally bound objects in the galaxy, the primary reservoir of material for the ongoing birth of new stars, and the medium regulating the evolution of galactic disks.

  14. Evolution of Interstellar Grains

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  15. Interstellar dust at our doorstep

    NASA Astrophysics Data System (ADS)

    Sterken, V. J.

    2013-12-01

    Interstellar dust has long been researched by astronomical methods to learn about its size distribution, grain properties and composition. However, interstellar dust grains also move through the solar system. They were detected for the first time in-situ with the Ulysses dust detector in 1993. In addition, in 2006, the Stardust mission returned three interstellar dust grain candidates back to Earth after a collection period of 195 days. In this talk we elaborate on how the current in-situ ISD measurement methods are a valuable addition to the knowledge about interstellar dust inferred from classical astronomy. We also discuss the role of interstellar dust dynamics and simulations herein.

  16. Airborne and laboratory studies of interstellar PAHs

    NASA Technical Reports Server (NTRS)

    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.

  17. Search for interstellar adenine

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  18. Do you know the extinction in your young massive cluster?

    NASA Astrophysics Data System (ADS)

    de Marchi, Guido; Panagia, Nino; Sabbi, Elena

    2017-03-01

    Up to ages of ~ 100 Myr, massive clusters are still swamped in large amounts of gas and dust, with considerable and uneven levels of extinction. At the same time, large grains (ices?) produced by type II supernovae profoundly alter the interstellar medium (ISM), thus resulting in extinction properties very different from those of the diffuse ISM. To obtain physically meaningful parameters of stars, from basic luminosities and effective temperatures to masses and ages, we must understand and measure the local extinction law. This problem affects all the massive young clusters discussed in his volume.

  19. CHIPS: The Cosmic Hot Interstellar Plasma Spectrometer

    NASA Astrophysics Data System (ADS)

    Dixon, W. V.; Hurwitz, M.; Jelinsky, P.; Welsh, B. Y.; Edelstein, J. E.; Siegmund, O. H. W.; McKee, C. F.; Malina, R. F.; Hawkins, I.; Vallerga, J. V.; Breitschwerdt, D.; Slavin, J.

    1998-12-01

    The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS), a University-Class Explorer (UNEX) mission, will carry out all-sky spectroscopy of the diffuse background at wavelengths from 90 to 260 Angstroms with a peak resolution of lambda / 150 (about 0.5 eV). CHIPS data will help determine the electron temperature, ionization conditions, and cooling mechanisms of the million-degree plasma believed to fill the local interstellar bubble. The majority of the luminosity from diffuse million-degree plasma is expected to emerge in the poorly-explored CHIPS band, making CHIPS data of relevance in a wide variety of Galactic and extragalactic astrophysical environments. The compact CHIPS instrument will be accommodated aboard a commercial FAISAT communications spacecraft currently scheduled for launch in mid to late 2001.

  20. Confirmation of interstellar methylene

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    Four spectral emission features of the N(sub KK) = 4(sub 04) -3(sub 13) rotational transition of methylene (CH2) have been detected at signal levels 5-7 sigma above noise toward the hot core of the Orion-KL nebula and the molecular cloud in proximity to the continuum source W51 M. Specifically, in both sources we have resolved the F = 6-5, 5-4, and 4-3 hyperfine transitions of the J = 5-4 fine-structure levels and detected the blended hyperfine structure of the J = 4-3 fine structure levels. At the J = 3-2 fine-structure levels, we have observed new transitions of NS, a known interstellar molecule, which severely contaminates the search for CH2 hyperfine transitions. These new sensitive observations finally confirm the existence of interstellar CH2 which was tentatively reported by us some years ago.

  1. Detecting interstellar migrations

    NASA Astrophysics Data System (ADS)

    Matloff, Gregory L.; Pazmino, John

    1997-01-01

    Interstellar migrations may occur when a civilization's star enters the red giant phase, thereby dooming the life-bearing planet. Ecologically self-contained 'world ships', massing billions of kilograms and propelled by hyperthin, space manufactured solar sails thousands of kilometers in diameter unfurled near the home star are possible vehicles to transfer a threatened civilization to a neighboring star. Consideration of the nearest red giants reveals that Pollux is the nearest formerly solar-type red giant. Known stellar neighbors of Pollux are surveyed to determine likely directions for an interstellar migration departing Pollux. Such migrations might consist of many world ships launched over millennia on voyages of about 1000 terrestrial-year duration; discovery of such events will be serendipitous. The difficulties of observing solar-sail star ships near Pollux are considered. A facility dedicated to imaging extrasolar planets within 10 parsecs might be capable of detecting these large spacecraft.

  2. Extinction and dust properties in a clumpy medium

    NASA Astrophysics Data System (ADS)

    Scicluna, P.; Siebenmorgen, R.

    2015-12-01

    The dust content of the universe is primarily explored via its interaction with stellar photons, which are absorbed or scattered by the dust, producing the effect known as interstellar extinction. However, owing to the physical extension of the observing beam, real observations may detect a significant number of dust-scattered photons. This may result in a change in the observed (or effective) extinction with a dependence on the spatial distribution of the dust and the spatial resolution of the instrument. We investigate the influence of clumpy dust distributions on the effective extinction toward both embedded sources and those seen through the diffuse interstellar medium (ISM). We use a Monte Carlo radiative transfer code to examine the effective extinction for various geometries. By varying the number, optical depth and volume-filling factor of clumps inside the model for spherical shells and the diffuse interstellar medium (ISM), we explore the evolution of the extinction curve and effective optical depth. Depending on the number of scattering events in the beam, the extinction curve is observed to steepen in homogeneous media and flatten in clumpy media. As a result, clumpy dust distributions are able to reproduce extinction curves with arbitrary RV,eff, the effective ratio of total-to-selective extinction. The flattening is also able to "wash out" the 2175 Å bump and results in a shift of the peak to shorter wavelengths. The mean RV,eff of a shell is shown to correlate with the optical depth of an individual clump and the wavelength at which a clump becomes optically thick. Similar behaviour is seen for edge-on discs or tori. However, at grazing inclinations the combination of extinction and strong forward scattering results in chaotic behaviour. Caution is therefore advised when attempting to measure extinction in AGN tori for example or toward SNIa or GRB afterglows. In face-on discs, the shape of the scattered continuum is observed to change significantly

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

    NASA Technical Reports Server (NTRS)

    Pei, Yichuan C.

    1992-01-01

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

  4. Search for fullerenes and PAHs in the diffuse interstellar medium

    NASA Astrophysics Data System (ADS)

    Ehrenfreund, P.; Foing, B. H.

    1995-02-01

    Recent studies suggest carbon-containing molecules as the best candidates for carriers of the unidentified diffuse interstellar bands (DIBs). considering their abundance and ability to form stable bonds in interstellar space. We have searched for new DIBs in the near-IR and have detected two new diffuse bands that are consistent with laboratory measurements of C 60+ in a neon matrix. Criteria for this possible identification are discussed. From these observations and the DIB treasured absorption. we estimate that up to 0.9% of interstellar carbon could be in the form of C 60+ We also searched for poly cyclic aromatic hydrocarbon (PAH) canons and have derived corresponding limits for the presence of the coronene C 24H 12 and ovalene C 32H 14 cations in space. We have studied the ionization properties of these PAH cations, which could explain their selective destruction. From these results we discuss the role of fullerenes and PAHs as possible DIB carriers.

  5. Interstellar hydrogen sulfide.

    NASA Technical Reports Server (NTRS)

    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.

  6. Interstellar Grain Surface Chemistry

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  7. Infrared emission spectra of candidate interstellar aromatic molecules

    NASA Technical Reports Server (NTRS)

    Schlemmer, S.; Balucani, N.; Wagner, D. R.; Steiner, B.; Saykally, R. J.

    1996-01-01

    Interstellar dust is responsible, through surface reactions, for the creation of molecular hydrogen, the main component of the interstellar clouds in which new stars form. Intermediate between small, gas-phase molecules and dust are the polycyclic aromatic hydrocarbons (PAHs). Such molecules could account for 2-30% of the carbon in the Galaxy, and may provide nucleation sites for the formation of carbonaceous dust. Although PAHs have been proposed as the sources of the unidentified infrared emission bands that are observed in the spectra of a variety of interstellar sources, the emission characteristics of such molecules are still poorly understood. Here we report laboratory emission spectra of several representative PAHs, obtained in conditions approximating those of the interstellar medium, and measured over the entire spectral region spanned by the unidentified infrared bands. We find that neutral PAHs of small and moderate size can at best make only a minor contribution to these emission bands. Cations of these molecules, as well as much larger PAHs and their cations, remain viable candidates for the sources of these bands.

  8. Stardust Interstellar Preliminary Examination

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  9. Innovative interstellar explorer

    NASA Astrophysics Data System (ADS)

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

    2006-09-01

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

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

    NASA Technical Reports Server (NTRS)

    Salama, Farid

    2005-01-01

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

  11. Filling the gap --near UV, optical and near IR extinction

    NASA Astrophysics Data System (ADS)

    Massa, Derck

    2014-10-01

    We propose a SNAP program to obtain STIS low resolution near-UV, optical and near-IR (G430L and G750L) spectra for a set of O7-B7 class III-V stars in the Galaxy and Magellanic Clouds with available IUE or HST/STIS UV spectropotometry, optical photometry and 2MASS IR photometry. Together with the existing data, the new observations will provide complete photometric and spectrophotometric coverage from 1150 to 10000 A and enable us to produce complete extinction curves from the far-UV to the near-IR, with well-determined values of R(V). The proposed set of 150 program sight lines includes the full range of interstellar extinction curve types from both the Galaxy and the Magellanic Clouds. The new data will allow us to examine variability in the near-UV through near-IR spectral regions, including the UV-optical "knee", and the "Very Broad Structure" and to verify the applicability of the near IR extinction law recently derived by Fitzpatrick and Massa (2009). We will examine the response of these features to different interstellar environments and their relationship to other curve features. These are largely unexplored aspects of the extinction curves which will provide additional constraints on the properties of interstellar grains. The curves will be derived using model atmospheres for the program stars, eliminating the need for standard stars.

  12. Charting the Interstellar Magnetic Field causing the Interstellar Boundary Explorer (IBEX) Ribbon of Energetic Neutral Atoms

    NASA Astrophysics Data System (ADS)

    Frisch, P. C.; Berdyugin, A.; Piirola, V.; Magalhaes, A. M.; Seriacopi, D. B.; Wiktorowicz, S. J.; Andersson, B.-G.; Funsten, H. O.; McComas, D. J.; Schwadron, N. A.; Slavin, J. D.; Hanson, A. J.; Fu, C.-W.

    2015-12-01

    .8}-27.6+23.5 between {B}{POL} and the bulk LSR velocity the local interstellar material indicates a geometry that is consistent with an expanding superbubble. The efficiency of grain alignment in the local interstellar medium has been assessed using stars where both polarization data and hydrogen column density data are available. Nearby stars appear to have larger polarizations than expected based on reddened sightlines, which is consistent with previous results, but uncertainties are large. Optical polarization and color excess E(B - V) data indicate the presence of nearby interstellar dust in the BICEP2 field. Color excess E(B - V) indicates an optical extinction of AV > 0.6 in the BICEP2 field, while the polarization data indicate that AV > 0.09 mag. The IBEX Ribbon ISMF extends to the boundaries of the BICEP2 region.

  13. Molecular diagnostics of interstellar shocks

    NASA Astrophysics Data System (ADS)

    Hartquist, T. W.; Dalgarno, A.; Oppenheimer, M.

    1980-02-01

    The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

  14. Molecular diagnostics of interstellar shocks

    NASA Technical Reports Server (NTRS)

    Hartquist, T. W.; Dalgarno, A.; Oppenheimer, M.

    1980-01-01

    The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

  15. Visualizing Interstellar's Wormhole

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  16. The nature of extinction.

    PubMed

    Delord, Julien

    2007-09-01

    The phenomenon of species extinction raises more and more concern among ecologists facing the actual crisis of biodiversity. Scientific investigations of the causes and effects of extinction must be completed by a philosophical analysis of the concept of extinction that aims to clarify the meanings of the term 'extinction' and to analyse modalities, criteria and degrees of extinction. We will focus our attention on the apparent paradox of the possible 'resurrection' of species in the near future with the help of genetic biotechnology and cloning techniques. The ontological background of the extinction concept is analysed in relation to the idea of species as classes. We will also show that there is no simple analogy between death and species extinction, and develop a conceptualist and dualistic system of supra-individual entities (species vs. population), supported by an instrumentalist approach to genetic manipulations which transform species into interactive kinds, which can go extinct and be recreated.

  17. Grey Milky Way extinction from SDSS stellar photometry

    NASA Astrophysics Data System (ADS)

    Gorbikov, Evgeny; Brosch, Noah

    2010-01-01

    We report results concerning the distribution and properties of galactic extinction at high galactic latitudes derived from stellar statistics using the Sloan Digital Sky Survey (SDSS). We use the classical Wolf diagram method to identify regions with extinction, and derive the extinction and the extinction law of the dust using all five SDSS spectral bands. We estimate the distance to the extinguishing medium using simple assumptions about the stellar populations in the line of sight. We report the identification of three extinguishing clouds, each a few tens of pc wide, producing 0.2-0.4 mag of g'-band extinction, located 1-2 kpc away or 0.5-1 kpc above the Galactic plane. All clouds exhibit grey extinction, i.e. almost wavelength independent in the limited spectral range of the SDSS. We discuss the implication of this finding on general astrophysical questions.

  18. Interstellar carbon in meteorites

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  19. An interstellar precursor mission

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  20. ULTRAVIOLET EXTINCTION AT HIGH GALACTIC LATITUDES

    SciTech Connect

    Peek, J. E. G.; Schiminovich, David

    2013-07-01

    In order to study the properties and effects of high Galactic latitude dust, we present an analysis of 373,303 galaxies selected from the Galaxy Evolution Explorer All-Sky Survey and Wide-field Infrared Explorer All-Sky Data Release. By examining the variation in aggregate ultraviolet colors and number density of these galaxies, we measure the extinction curve at high latitude. We additionally consider a population of spectroscopically selected galaxies from the Sloan Digital Sky Survey to measure extinction in the optical. We find that dust at high latitude is neither quantitatively nor qualitatively consistent with standard reddening laws. Extinction in the FUV and NUV is {approx}10% and {approx}35% higher than expected, with significant variation across the sky. We find that no single R{sub V} parameter fits both the optical and ultraviolet extinction at high latitude, and that while both show detectable variation across the sky, these variations are not related. We propose that the overall trends we detect likely stem from an increase in very small silicate grains in the interstellar medium.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  2. Interstellar scattering and resolution limitations

    NASA Astrophysics Data System (ADS)

    Dennison, Brian

    Density irregularities in both the interplanetary medium and the ionized component of the interstellar medium scatter radio waves, resulting in limitations on the achievable resolution. Interplanetary scattering (IPS) is weak for most observational situations, and in principle the resulting phase corruption can be corrected for when observing with sufficiently many array elements. Interstellar scattering (ISS), on the other hand, is usually strong at frequencies below about 8 GHz, in which case intrinsic structure information over a range of angular scales is irretrievably lost. With the earth-space baselines now planned, it will be possible to search directly for interstellar refraction, which is suspected of modulating the fluxes of background sources.

  3. Infrared absorption and emission characteristics of interstellar PAHs

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    The mid-infrared interstellar emission spectrum with features at 3.28, 6.2, 7.7, 8.7 and 11.3 microns is discussed in terms of the Polycyclic Aromatic Hydrocarbon (PAH) hypothesis, which is based on the suggestive, but inconclusive comparison between the interstellar emission spectrum with the infrared absorption and Raman spectra of a few PAHs. The fundamental vibrations of PAHs and PAH-like species which determine the IR and Raman properties are discussed. Interstellar IR band emission is due to relaxation from highly vibrationally excited PAHs excited by ultraviolet photons. The excitation/emission process is described and the IR fluorescence from one PAH, chrysene, is traced. Generally, there is sufficient energy to populate several vibrational levels in each mode. Molecular vibrational potentials are anharmonic and emission from these higher levels will fall at lower frequencies and produce weak features to the red of the stronger fundamentals. This process is also described and can account for some spectroscopic details of the interstellar emission spectra previously unexplained. Analysis of the interstellar spectrum shows that PAHs contain between 20 and 30 carbon atoms are responsible for the emission.

  4. Optical spectroscopy of IRAS sources with infrared emission bands. II. IRAS 04324+5106, 06114+1745, 20319+3958, and 22539+5758

    SciTech Connect

    Cohen, M.; Jones, B.F.; Walker, H.J.; Lick Observatory, Santa Cruz, CA; Search for Extraterrestrial Intelligence Institute, Los Altos, CA )

    1989-06-01

    The paper presents long-slit optical spectra and microwave CO spectra of four nebulous counterparts to IRAS sources showing PAH emission features: 04324+5106, 06114+1745, 20319+3958, and 22539+5758. IRAS 22539+5758 is associated with a bipolar nebula. All are allied with B-type stars that suffer appreciable circumstellar extinction, and whose environs show atomic emission lines; three represent mixed reflection/emission nebulosities. Three show spectroscopic evidence for outflows at about 100 km/s. One, 06114+1745, exhibits indications of enhanced diffuse interstellar bands. It is concluded that extinction alone is insufficient to yield enhanced DIBs and that peculiar circumstellar abundances and/or physical conditions must play a role. 20 refs.

  5. Optical spectroscopy of IRAS sources with infrared emission bands. II - IRAS 04324+5106, 06114+1745, 20319+3958, and 22539+5758

    NASA Technical Reports Server (NTRS)

    Cohen, Martin; Jones, B. F.; Walker, H. J.

    1989-01-01

    The paper presents long-slit optical spectra and microwave CO spectra of four nebulous counterparts to IRAS sources showing PAH emission features: 04324+5106, 06114+1745, 20319+3958, and 22539+5758. IRAS 22539+5758 is associated with a bipolar nebula. All are allied with B-type stars that suffer appreciable circumstellar extinction, and whose environs show atomic emission lines; three represent mixed reflection/emission nebulosities. Three show spectroscopic evidence for outflows at about 100 km/s. One, 06114+1745, exhibits indications of enhanced diffuse interstellar bands. It is concluded that extinction alone is insufficient to yield enhanced DIBs and that peculiar circumstellar abundances and/or physical conditions must play a role.

  6. The Interstellar Medium in the Small Magellanic Cloud: Results from MCELS

    NASA Astrophysics Data System (ADS)

    Winkler, P. F.; Smith, R. C.; Points, S. D.; MCELS Team

    2015-05-01

    The interstellar medium (ISM) provides the playing field where gas and dust are cycled into and out of stars through dynamic and complex interactions, including H II regions, planetary nebulae, supernovae and their remnants, superbubbles, and gigantic supershells. The relative proximity and low extinction make the Large and Small Magellanic Clouds ideal venues for studying the ISM: its constituents, energetics, and interaction with the underlying stellar populations. The Magellanic Cloud Emission Line Survey (MCELS) surveyed both the LMC and SMC over six years using the Curtis Schmidt Telescope at CTIO to produce deep images in Hα, [S II] and [O III] lines, plus matched red and green continuum bands for star subtraction. The survey covers the central 8×8 degrees of the LMC and 4.5× 3.5 degrees of the SMC—most of the gaseous extent of both galaxies—at a resolution of 5″ or better. This enables us to identify and study structures on scales ranging from 1 pc to global. In this paper we highlight some of the results from MCELS, concentrating on the SMC. These include deep inventories of PNe and SNRs, analysis of H II regions and their optical depth, and extended structures on the scale of the entire galaxy. We also include some brief historical anecdotes.

  7. Theoretical Modeling of Interstellar Chemistry

    NASA Technical Reports Server (NTRS)

    Charnley, Steven

    2009-01-01

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

  8. PAH Clusters as Sources of Interstellar Infrared Emission

    NASA Astrophysics Data System (ADS)

    Roser, J. E.; Ricca, A.

    2015-03-01

    Polycyclic aromatic hydrocarbons (or PAHs) have been the subject of astrochemical research for several decades as principal sources of the interstellar aromatic infrared emission bands. PAH clusters could possibly contribute to these emission bands, but a lack of data on their infrared properties has made this hypothesis difficult to evaluate. Here we investigate homogeneous neutral PAH clusters by measuring the mid-infrared absorption spectra of the five nonlinear PAH molecules phenanthrene, chrysene, pyrene, perylene, and benzo[ghi]perylene within solid argon ice at a fixed temperature of 5 K. We attribute observed spectral shifts in their principal absorption bands as a function of argon/PAH ratio to clustering of the PAH molecules within the argon matrix. These shifts are related to the cluster structures forming in the matrix and the topology of the monomer PAH molecule. We predict that interstellar PAH molecules that are relatively large (no fewer than 50 carbon atoms per molecule) and compact will have clusters that contribute to the asymmetrically red-shaded profile of the interstellar 11.2 μm emission band.

  9. POLYCYCLIC AROMATIC HYDROCARBON CLUSTERS AS SOURCES OF INTERSTELLAR INFRARED EMISSION

    SciTech Connect

    Roser, J. E.; Ricca, A.

    2015-03-10

    Polycyclic aromatic hydrocarbons (or PAHs) have been the subject of astrochemical research for several decades as principal sources of the interstellar aromatic infrared emission bands. PAH clusters could possibly contribute to these emission bands, but a lack of data on their infrared properties has made this hypothesis difficult to evaluate. Here we investigate homogeneous neutral PAH clusters by measuring the mid-infrared absorption spectra of the five nonlinear PAH molecules phenanthrene, chrysene, pyrene, perylene, and benzo[ghi]perylene within solid argon ice at a fixed temperature of 5 K. We attribute observed spectral shifts in their principal absorption bands as a function of argon/PAH ratio to clustering of the PAH molecules within the argon matrix. These shifts are related to the cluster structures forming in the matrix and the topology of the monomer PAH molecule. We predict that interstellar PAH molecules that are relatively large (no fewer than 50 carbon atoms per molecule) and compact will have clusters that contribute to the asymmetrically red-shaded profile of the interstellar 11.2 μm emission band.

  10. Is extinction forever?

    PubMed Central

    Bridge, Eli S.; Crawford, Priscilla H. C.; Hough, Daniel J.; Kelly, Jeffrey F.; Patten, Michael A.

    2015-01-01

    Mistrust of science has seeped into public perception of the most fundamental aspect of conservation—extinction. The term ought to be straightforward, and yet, there is a disconnect between scientific discussion and public views. This is not a mere semantic issue, rather one of communication. Within a population dynamics context, we say that a species went locally extinct, later to document its return. Conveying our findings matters, for when we use local extinction, an essentially nonsensical phrase, rather than extirpation, which is what is meant, then we contribute to, if not create outright, a problem for public understanding of conservation, particularly as local extinction is often shortened to extinction in media sources. The public that receives the message of our research void of context and modifiers comes away with the idea that extinction is not forever or, worse for conservation as a whole, that an extinction crisis has been invented. PMID:25711479

  11. The Interstellar Conspiracy

    NASA Technical Reports Server (NTRS)

    Johnson, Les; Matloff, Gregory L.

    2005-01-01

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

  12. Interstellar Glycolaldehyde: The First Sugar

    NASA Astrophysics Data System (ADS)

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

    2000-09-01

    Interstellar glycolaldehyde (CH2OHCHO) has been detected in emission toward the Galactic center source Sagittarius B2(N) by means of millimeter-wave rotational transitions. Glycolaldehyde is an important biomarker since it is structurally the simplest member of the monosaccharide sugars that heretofore have gone undetected in interstellar clouds. There is no consensus as to how any such large complex molecules are formed in the interstellar clouds. It may be that the typical environment of dense interstellar clouds is favorable to glycolaldehyde synthesis by means of the polymerization of formaldehyde (H2CO) molecules either on grain surfaces or in the gas phase. Alternatively, we speculate that glycolaldehyde and other complex molecules may undergo assembly from functional molecular groups on grain surfaces. Utilizing common chemical precursors, a chance process could account for the high degree of isomerism observed in complex interstellar molecules (e.g., methyl formate, acetic acid, and glycolaldehyde). This work suggests that the phenomenon of isomerism be investigated further as a means of potentially constraining interstellar chemistry routes for those individual sources where the condition of good source-beam coupling can be achieved.

  13. Modelling interstellar organics: relevance for the identification of unidentified interstellar features

    NASA Astrophysics Data System (ADS)

    Malloci, Giuliano

    2003-02-01

    This thesis is part of the research activity of the Astrochemistry Group of the Cagliari Astronomical Observatory and the Physics Department at the University of Cagliari. The subjects of this work are two specific astrophysical problems concerning the Interstellar Medium (ISM) analysis: 1) the identification of Diffuse Interstellar Bands (DIBs) - Unidentified Infrared Bands (UIBs); 2) the identification of the Extended Red Emission (ERE). A new theoretical approach to the spectroscopic identification of these specific Unidentified Interstellar Features is presented.Concerning the DIBs-UIBs, this work is an extension of a computational Monte-Carlo model developed in the past few years by our group (Mulas G. A&A 1998,338,243) with the aim to integrate quantum-chemical ab initio tecnhiques in it and thus produce a self-contained molecular simulator. Concerning ERE, a general recipe is developed in order to extrapolate the expected photoluminescence of small particles starting from available laboratory results obtained on bulk samples. All the numerical results were obtained for interstellar carbonaceous compounds, hence the title ``Modelling interstellar organics'' given to the thesis. In particular, a specific molecule belonging to the class of polycyclic aromatic hydrocarbons (PAHs) is chosen as a test case to discuss the PAHs-DIBs-UIBs proposal, while the optical properties of laboratory samples of hydrogenated amorphous carbon (HAC) are used to obtain numerical results to be compared with luminescence phenomena such as ERE originating from some solid component of the ISM. The introductive chapter is intended to introduce the unfamiliar reader to the specific topic under study, and a short overview of the scientific scenario involved is given. Then, Part I and II discuss separately the two models above and represent the body of the work; each chapter follows a standard article format: introduction, theoretical method, numerical results, discussion and

  14. ON GALACTIC DENSITY MODELING IN THE PRESENCE OF DUST EXTINCTION

    SciTech Connect

    Bovy, Jo; Rix, Hans-Walter; Schlafly, Edward F.; Green, Gregory M.; Finkbeiner, Douglas P.

    2016-02-20

    Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic midplane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of small-scale structure in the extinction. This formalism demonstrates that the spatially complex effect of extinction on the selection function of a pencil-beam or contiguous sky survey is equivalent to a low-pass filtering of the extinction-affected selection function with the smooth density field. We find that the angular resolution of current 3D extinction maps is sufficient for analyzing Gaia sub-samples of millions of stars. However, the current distance resolution is inadequate and needs to be improved by an order of magnitude, especially in the inner Galaxy. We also present a practical and efficient method for properly taking the effect of extinction into account in analyses of Galactic structure through an effective selection function. We illustrate its use with the selection function of red-clump stars in APOGEE using and comparing a variety of current 3D extinction maps.

  15. MODELING GALACTIC EXTINCTION WITH DUST AND 'REAL' POLYCYCLIC AROMATIC HYDROCARBONS

    SciTech Connect

    Mulas, Giacomo; Casu, Silvia; Cecchi-Pestellini, Cesare; Zonca, Alberto E-mail: silvia@oa-cagliari.inaf.it E-mail: azonca@oa-cagliari.inaf.it

    2013-07-01

    We investigate the remarkable apparent variety of galactic extinction curves by modeling extinction profiles with core-mantle grains and a collection of single polycyclic aromatic hydrocarbons. Our aim is to translate a synthetic description of dust into physically well-grounded building blocks through the analysis of a statistically relevant sample of different extinction curves. All different flavors of observed extinction curves, ranging from the average galactic extinction curve to virtually 'bumpless' profiles, can be described by the present model. We prove that a mixture of a relatively small number (54 species in 4 charge states each) of polycyclic aromatic hydrocarbons can reproduce the features of the extinction curve in the ultraviolet, dismissing an old objection to the contribution of polycyclic aromatic hydrocarbons to the interstellar extinction curve. Despite the large number of free parameters (at most the 54 Multiplication-Sign 4 column densities of each species in each ionization state included in the molecular ensemble plus the 9 parameters defining the physical properties of classical particles), we can strongly constrain some physically relevant properties such as the total number of C atoms in all species and the mean charge of the mixture. Such properties are found to be largely independent of the adopted dust model whose variation provides effects that are orthogonal to those brought about by the molecular component. Finally, the fitting procedure, together with some physical sense, suggests (but does not require) the presence of an additional component of chemically different very small carbonaceous grains.

  16. A Science-enhanced Database of GALEX UV spectra to Characterize Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Bianchi, Luciana

    The Galaxy Evolution Explorer (GALEX) has performed the first surveys of the sky in the Ultraviolet (UV). Its unprecedented database, including almost 300 million photometric source measurements in far-UV (FUV) and near-UV (NUV), offers unique sensitivity for studying selected classes of astrophysical objects, such as hot stars, star-forming galaxies, and z<2 QSOs. GALEX imaging data have been amply mined; science-enhanced source catalogs enable comprehensive investigations long after the mission is concluded. GALEX has also collected 125,564 UV spectra (range 1344-2831Ang; resolution about 200(FUV) - 120(NUV)): a homogeneous template tenfold larger and at fainter fluxes than the IUE target sample. Yet, this unique resource has hardly been exploited, due to poor calibration and lack of standard quality assessment of the complex grism spectral extraction. The homogeneous set of >120,000 UV spectra distributed all over the sky will enable - among other investigations - derivation of UV extinction curves for thousands of sightlines throughout the Milky Way (MW), yielding information on properties of interstellar dust that cannot be obtained otherwise, and, furthermore, validating extinction maps derived from vastly larger photometric samples. Our proposed map of MW dust properties will be 3D, since Gaia will provide accurate distances for all stellar sources. The first step to make this study possible will be to classify all sources in the [grism, hence serendipitous] GALEX spectroscopic sample, and to assess quality and flux calibration. We will combine multi-band photometry of the spectral sources (GALEX, SDSS, Pan-STARRs, ...), any existing information (e.g., from SIMBAD), available IUE spectra (about 100) and SDSS spectra (8,000), besides examining the UV spectral features. Hot stellar sources constitute over half of the GALEX spectroscopic sample. For those with spectra of sufficient quality (about 9,000 in NUV, >1,000 in FUV+NUV) we will derive UV extinction

  17. Interstellar molecular clouds

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Technical Reports Server (NTRS)

    Glownia, James H.; Sorokin, Peter P.

    1994-01-01

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

  19. Current status of the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) university-class explorer mission

    NASA Astrophysics Data System (ADS)

    Hurwitz, Mark

    2003-12-01

    We present a status report on CHIPS, the Cosmic Hot Interstellar Plasma Spectrometer. CHIPS is the first NASA University-Class Explorer (UNEX) project, and was launched on January 13, 2003. The grazing incidence CHIPS spectrograph is surveying selected regions of the sky for diffuse emission in the comparatively unexplored wavelength band between 90 and 260 Å. These data are providing important new constraints on the temperature, ionization state, and emission measure of hot plasma in the "local bubble" of the interstellar medium.

  20. Stardust interstellar preliminary examination (ISPE).

    SciTech Connect

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

    2009-03-23

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

  1. Extinction law in the range 0.4-4.8 μm and the 8620 Å DIB towards the stellar cluster Westerlund 1

    NASA Astrophysics Data System (ADS)

    Damineli, A.; Almeida, L. A.; Blum, R. D.; Damineli, D. S. C.; Navarete, F.; Rubinho, M. S.; Teodoro, M.

    2016-12-01

    The young stellar cluster Westerlund 1 (Wd 1: l = 339.6°, b = -0.4°) is one of the most massive in the local Universe, but accurate parameters are pending on better determination of its extinction and distance. Based on our photometry and data collected from other sources, we have derived a reddening law for the cluster line-of-sight representative of the Galactic plane (-5° < b <+5°) in the window 0.4-4.8 μm: The power-law exponent α = 2.13 ± 0.08 is much steeper than those published a decade ago (1.6-1.8) and our index RV = 2.50 ± 0.04 also differs from them, but in very good agreement with recent works based on deep surveys in the inner Galaxy. As a consequence, the total extinction AKs = 0.74 ± 0.08 (AV = 11.40 ± 2.40) is substantially smaller than previous results (0.91-1.13), part of which (AKs = 0.63 or AV = 9.66) is from the interstellar medium. The extinction in front of the cluster spans a range of ΔAV ˜8.7 with a gradient increasing from SW to NE across the cluster face, following the same general trend of warm dust distribution. The map of the J - Ks colour index also shows a trend of reddening in this direction. We measured the equivalent width of the diffuse interstellar band at 8620 Å (the `GAIA DIB') for Wd 1 cluster members and derived the relation AKs = 0.612 EW - 0.191 EW2. This extends the Munari et al. relation, valid for EB-V < 1, to the non-linear regime (AV > 4).

  2. Probing the Grains Responsible for Extinction Using Small Magellanic Cloud Sightlines

    NASA Astrophysics Data System (ADS)

    Gordon, Karl

    2002-07-01

    Small Magellanic Cloud sightlines have the greatest potential to relate specific interstellar extinction features to distinct grain properties. The reasons for this are 1} prominent extinction features such as the 2175 Angstrom bump and the far-ultraviolet rise vary among SMC targets and 2} grain types may be very different from those in the Galaxy. Specifically, Welty et al. {2001} recently identified an SMC sightline that contains dust, but no silicate grains. Silicates are a dominant source of extinction in all dust models; the SMC may be the only location where the importance of silicates can be verified or disproven. We propose to explore the relationship between grain types and extinction toward 2 SMC stars with very different extinction curves; AzV 18 lacks a 2175 Angstrom bump and has a strong far-UV rise while the extinction curve towards the SMC star AzV 456 has a prominent 2175 Angstrom bump and a much weaker far-UV rise. We will compare the interstellar abundances of atoms that are prevalent in silicates {Si, Mg, Fe} toward these 2 stars and use the results to constrain dust extinction models. These SMC observations, which can only be obtained with STIS, are the only direct way to probe the connection between grain types/environments and extinction. The results from this study will be useful for modeling and understanding all regions that contain dust {AGN, circumstellar disks, star formation regions, etc.}.

  3. Secondary extinctions of biodiversity.

    PubMed

    Brodie, Jedediah F; Aslan, Clare E; Rogers, Haldre S; Redford, Kent H; Maron, John L; Bronstein, Judith L; Groves, Craig R

    2014-12-01

    Extinctions beget further extinctions when species lose obligate mutualists, predators, prey, or hosts. Here, we develop a conceptual model of species and community attributes affecting secondary extinction likelihood, incorporating mechanisms that buffer organisms against partner loss. Specialized interactors, including 'cryptic specialists' with diverse but nonredundant partner assemblages, incur elevated risk. Risk is also higher for species that cannot either evolve new traits following partner loss or obtain novel partners in communities reorganizing under changing environmental conditions. Partner loss occurs alongside other anthropogenic impacts; multiple stressors can circumvent ecological buffers, enhancing secondary extinction risk. Stressors can also offset each other, reducing secondary extinction risk, a hitherto unappreciated phenomenon. This synthesis suggests improved conservation planning tactics and critical directions for research on secondary extinctions.

  4. Interstellar Sweat Equity

    NASA Astrophysics Data System (ADS)

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

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

  5. Gradual extinction reduces reinstatement

    PubMed Central

    Shiban, Youssef; Wittmann, Jasmin; Weißinger, Mara; Mühlberger, Andreas

    2015-01-01

    The current study investigated whether gradually reducing the frequency of aversive stimuli during extinction can prevent the return of fear. Thirty-one participants of a three-stage procedure (acquisition, extinction and a reinstatement test on day 2) were randomly assigned to a standard extinction (SE) and gradual extinction (GE) procedure. The two groups differed only in the extinction procedure. While the SE group ran through a regular extinction process without any negative events, the frequency of the aversive stimuli during the extinction phase was gradually reduced for the GE group. The unconditioned stimulus (US) was an air blast (5 bar, 10 ms). A spider and a scorpion were used as conditioned stimuli (CS). The outcome variables were contingency ratings and physiological measures (skin conductance response, SCR and startle response). There were no differences found between the two groups for the acquisition and extinction phases concerning contingency ratings, SCR, or startle response. GE compared to SE significantly reduced the return of fear in the reinstatement test for the startle response but not for SCR or contingency ratings. This study was successful in translating the findings in rodent to humans. The results suggest that the GE process is suitable for increasing the efficacy of fear extinction. PMID:26441581

  6. Mass extinction: a commentary.

    PubMed

    Raup, D M

    1987-01-01

    Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions. Although strongly interconnected the four claims are independent in the sense that none depends on the others. Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies. An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales. If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated. This is line of reasoning can only be considered an hypothesis for testing. In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth. The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.

  7. Mass extinction: a commentary

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1987-01-01

    Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions. Although strongly interconnected the four claims are independent in the sense that none depends on the others. Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies. An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales. If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated. This is line of reasoning can only be considered an hypothesis for testing. In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth. The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.

  8. Interstellar Propulsion Research Within NASA

    NASA Technical Reports Server (NTRS)

    Johnson, Les; Cook, Stephen (Technical Monitor)

    2001-01-01

    NASA is actively conducting advanced propulsion research and technology development in various in-space transportation technologies with potential application to interstellar missions and precursors. Within the last few years, interest in the scientific community in interstellar missions as well as outer heliospheric missions, which could function as interstellar precursor missions, has increased. A mission definition team was charted by NASA to define such a precursor, The Interstellar Probe, which resulted in a prioritization of relatively near-term transportation technologies to support its potential implementation. In addition, the goal of finding and ultimately imaging extra solar planets has raised the issue of our complete inability to mount an expedition to such as planet, should one be found. Even contemplating such a mission with today's technology is a stretch of the imagination. However, there are several propulsion concepts, based on known physics, that have promise to enable interstellar exploration in the future. NASA is making small, incremental investments in some key advanced propulsion technologies in an effort to advance their state-of-the-art in support potential future mission needs. These technologies, and their relative maturity, are described.

  9. Interstellar neutrals in interplanetary space

    SciTech Connect

    Hovestadt, D.; Moebius, E. )

    1989-03-01

    The solar system is moving through the interstellar medium with a velocity of about 20 km/s. The neutral interstellar gas, which thereby penetrates the heliosphere, is subject to ionization by solar UV radiation, charge exchange with the solar wind, and electron collisions. The newly created ions are then picked by the solar wind through interaction of interstellar neutrals with the interplanetary magnetic field. The pick-up ions with their peculiar elemental composition probably also constitute the source particles of the Anomalous Cosmic Ray Component (ACR). In this report descriptions of the interaction with the solar wind are reviewed. While most of the constituents are already ionized far beyond the orbit of the Earth, neutral helium (because of its high ionization potential) approaches the Sun to {lt}1 AU. The pick-up of interstellar He{sup +} ions has recently been directly observed for the first time. The observed velocity distribution of He{sup +} extending up to twice the solar wind velocity can be explained in terms of pitch angle scattering of the ions probably by interplanetary Alven waves and subsequent adiabatic cooling in the expanding solar wind. Thermal coupling of the He{sup +} to the solar wind is negligible in the inner heliosphere. Detailed studies of the pick-up distribution provide a method to investigate the interplanetary propagation parameters and the state of the local interstellar medium.

  10. Radical formation, chemical processing, and explosion of interstellar grains

    NASA Technical Reports Server (NTRS)

    Greenberg, J. M.

    1976-01-01

    The ultraviolet radiation in interstellar space is shown to create a sufficient steady-state density of free radicals in the grain mantle material consisting of oxygen, carbon, nitrogen, and hydrogen to satisfy the critical condition for initiation of chain reactions. The criterion for minimum critical particle size for maintaining the chain reaction is of the order of the larger grain sizes in a distribution satisfying the average extinction and polarization measures. The triggering of the explosion of interstellar grains leading to the ejection of complex interstellar molecules is shown to be most probable where the grains are largest and where radiation is suddenly introduced; i.e., in regions of new star formation. Similar conditions prevail at the boundaries between very dark clouds and H II regions. When the energy released by the chemical activity of the free radicals is inadequate to explode the grain, the resulting mantle material must consist of extremely large organic molecules which are much more resistant to the hostile environment of H II regions than the classical dirty-ice mantles made up of water, methane, and ammonia.

  11. Laboratory Formation and Analysis of the Materials Comprising Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Scott, Alan Douglas

    The optical properties of interstellar dust analogs are investigated. Thin, solid, amorphous films are deposited on a substrate through excimer laser ablation. This process is analogous to the vapour deposition of atoms and ions which is thought to occur in stellar outflows and the interstellar medium (ISM). Refractive indices are calculated for typical polymeric hydrogenated amorphous carbon (HAC) films. Thickness dependent void structure is shown to influence the resultant density of the substance. Refractive indices are also determined for amorphous magnesium silicates in both the pyroxene (MgSiO3) and olivine (Mg2SiO4) composites. A plausible dust grain model is constructed which successfully reproduces the major features of the diffuse interstellar extinction. The effects of thermal annealing and dehydrogenation of HAC are investigated. The resulting graphitized HAC is shown to exhibit a spectral signature which is commonly associated with gas phase polycyclic aromatic hydrocarbons (PAHs). Thermal emission from HAC is observed for the first time and is shown to be an excellent match to various anomalous unidentified infrared (UIR) emitters. The emission from HAC closely resembles those rare sources labelled Type B UIR emitters in recent works by Geballe (1996) and Tokunaga (1996). Near threshold laser ionization mass spectroscopy (LIMS) of HAC is shown to produce large ionized molecular clusters including fullerenes. The astrophysical implications of these results are discussed.

  12. Interstellar Isotopes: Prospects with ALMA

    NASA Technical Reports Server (NTRS)

    Charnley Steven B.

    2010-01-01

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

  13. The relationship between infrared, optical, and ultraviolet extinction

    NASA Astrophysics Data System (ADS)

    Cardelli, Jason A.; Clayton, Geoffrey C.; Mathis, John S.

    1989-10-01

    The parameterized extinction data of Fitzpatrick and Massa (1986, 1988) for the ultraviolet and various sources for the optical and near-infrared are used to derive a meaningful average extinction law over the 3.5 micron to 0.125 wavelength range which is applicable to both diffuse and dense regions of the interstellar medium. The law depends on only one parameter R(V) = A(V)/E(B-V). An analytic formula is given for the mean extinction law which can be used to calculate color excesses or to deredden observations. The validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature and very efficient.

  14. Measuring Interstellar Inheritance and Its Consequences

    NASA Astrophysics Data System (ADS)

    Alexander, C. M. O'D.; Nittler, L. R.; Davidson, J.; Ciesla, F. J.

    2016-08-01

    CIs, chondrite matrices and IDP accreted ~10 % of pristine interstellar material (ices, silicates, organics). The non-solar O isotopic compositions of most solar materials reflect early heating of interstellar dust and ices in FU Orionis outbursts.

  15. The formation of interstellar jets

    NASA Technical Reports Server (NTRS)

    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.

  16. Interstellar helium in interplanetary space

    NASA Technical Reports Server (NTRS)

    Feldman, W. C.; Lange, J. J.; Scherb, F.

    1972-01-01

    The velocity distribution function of He(+) in the solar wind at 1 AU is calculated with the assumption that the source is photoionization of a cold (T = 100 K), neutral interstellar wind. If the spiral magnetic field is noise free, the velocity distribution is diffuse and would not produce a peak at 4(E over Q) sub H in an E over Q particle spectrum. If the velocity of the interstellar wind with respect to the sun lies in the ecliptic, a large variation of the He(+) number density with respect to ecliptic longitude is expected.

  17. Interstellar Initiative Web Page Design

    NASA Technical Reports Server (NTRS)

    Mehta, Alkesh

    1999-01-01

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

  18. Interstellar Grains: 50 Years On

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, N. Chandra

    2011-12-01

    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-reviewedpublicationsbytheauthorand/orFredHoyle. Theprevailingreluctancetoaccepttheseclear-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.

  19. Electric propulsion and interstellar flight

    SciTech Connect

    Matloff, G.L.

    1987-01-01

    Two general classes of interstellar space-flights are defined: endothermic and exothermic. Endothermic methods utilize power sources external to the vehicle and associated technology. Faster exothermic methods utilize on-board propulsive power sources or energy-beam technology. Various proposed endothermic electric propulsion methods are described. These include solar electric rockets, mass drivers, and ramjets. A review of previously suggested exothermic electric propulsion methods is presented. Following this review is a detailed discussion of possible near future application of the beamed-laser ramjet, mainly for ultimate relativistic travel. Electric/magnetic techniques offer an excellent possibility for decelerating an interstellar vehicle, regardless of the acceleration technique. 20 references.

  20. Diffuse interstellar clouds as a chemical laboratory - The chemistry of diatomic carbon species

    NASA Technical Reports Server (NTRS)

    Federman, S. R.; Huntress, W. T., Jr.

    1989-01-01

    The chemistry of C2, CH, and CO in diffuse interstellar clouds is analyzed and compared to absorption line measurements toward background stars. Analytical expressions in terms of column densities are derived for the rate equations. The results indicate that in clouds with 4 mag of visual extinction, the abundance of C+ has to decrease by a factor of about 15 from the value traditionally used for clouds with 1 mag of extinction. The rate coefficients for the reactions C+ + CH - C2+ + H and C+ + H2 - CH2+ + h-nu need to be reduced from previous estimates. Chemical arguments are presented for the revised rate coefficients.

  1. Beliefs about Human Extinction

    SciTech Connect

    Tonn, Bruce Edward

    2009-11-01

    This paper presents the results of a web-based survey about futures issues. Among many questions, respondents were asked whether they believe humans will become extinct. Forty-five percent of the almost 600 respondents believe that humans will become extinct. Many of those holding this believe felt that humans could become extinct within 500-1000 years. Others estimated extinction 5000 or more years into the future. A logistic regression model was estimated to explore the bases for this belief. It was found that people who describe themselves a secular are more likely to hold this belief than people who describe themselves as being Protestant. Older respondents and those who believe that humans have little control over their future also hold this belief. In addition, people who are more apt to think about the future and are better able to imagine potential futures tend to also believe that humans will become extinct.

  2. On the question of interstellar travel

    NASA Technical Reports Server (NTRS)

    Wolfe, J. H.

    1985-01-01

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

  3. Experimental interstellar organic chemistry - Preliminary findings

    NASA Technical Reports Server (NTRS)

    Khare, B. N.; Sagan, C.

    1973-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  5. Extinction and the fossil record

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, ,. J. r. (Principal Investigator)

    1994-01-01

    The author examines evidence of mass extinctions in the fossil record and searches for reasons for such large extinctions. Five major mass extinctions eliminated at least 40 percent of animal genera in the oceans and from 65 to 95 percent of ocean species. Questions include the occurrence of gradual or catastrophic extinctions, causes, environment, the capacity of a perturbation to cause extinctions each time it happens, and the possibility and identification of complex events leading to a mass extinction.

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

    NASA Astrophysics Data System (ADS)

    Corrales, Lia

    2016-06-01

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

  7. Stardust Interstellar Preliminary Examination (ISPE)

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  8. Term Projects on Interstellar Comets

    ERIC Educational Resources Information Center

    Mack, John E.

    1975-01-01

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

  9. Isotopic Fractionation in Interstellar Chemistry

    NASA Technical Reports Server (NTRS)

    Charnley, Steven

    2009-01-01

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

  10. THE IMPACT OF ACCURATE EXTINCTION MEASUREMENTS FOR X-RAY SPECTRAL MODELS

    SciTech Connect

    Smith, Randall K.; Valencic, Lynne A.; Corrales, Lia

    2016-02-20

    Interstellar extinction includes both absorption and scattering of photons from interstellar gas and dust grains, and it has the effect of altering a source's spectrum and its total observed intensity. However, while multiple absorption models exist, there are no useful scattering models in standard X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created by scattering from dust grains, are detected around even moderately absorbed sources, and the impact on an observed source spectrum can be significant, if modest, compared to direct absorption. By convolving the scattering cross section with dust models, we have created a spectral model as a function of energy, type of dust, and extraction region that can be used with models of direct absorption. This will ensure that the extinction model is consistent and enable direct connections to be made between a source's X-ray spectral fits and its UV/optical extinction.

  11. Is extinction age dependent?

    USGS Publications Warehouse

    Doran, N.A.; Arnold, A.J.; Parker, W.C.; Huffer, F.W.

    2006-01-01

    Age-dependent extinction is an observation with important biological implications. Van Valen's Red Queen hypothesis triggered three decades of research testing its primary implication: that age is independent of extinction. In contrast to this, later studies with species-level data have indicated the possible presence of age dependence. Since the formulation of the Red Queen hypothesis, more powerful tests of survivorship models have been developed. This is the first report of the application of the Cox Proportional Hazards model to paleontological data. Planktonic foraminiferal morphospecies allow the taxonomic and precise stratigraphic resolution necessary for the Cox model. As a whole, planktonic foraminiferal morphospecies clearly show age-dependent extinction. In particular, the effect is attributable to the presence of shorter-ranged species (range < 4 myr) following extinction events. These shorter-ranged species also possess tests with unique morphological architecture. The morphological differences are probably epiphenomena of underlying developmental and heterochronic processes of shorter-ranged species that survived various extinction events. Extinction survivors carry developmental and morphological characteristics into postextinction recovery times, and this sets them apart from species populations established independently of extinction events. Copyright ?? 2006, SEPM (Society for Sedimentary Geology).

  12. The Sun's dusty interstellar environment

    NASA Astrophysics Data System (ADS)

    Sterken, Veerle

    2016-07-01

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

  13. Diamonds in dense molecular clouds - A challenge to the standard interstellar medium paradigm

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Sandford, S. A.; Tielens, A. G. G. M.; Herbst, T. M.

    1993-01-01

    Observations of a newly discovered infrared C-H stretching band indicate that interstellar diamond-like material appears to be characteristic of dense clouds. In sharp contrast, the spectral signature of dust in the diffuse interstellar medium is dominated by -CH2- and -CH3 groups. This dichotomy in the aliphatic organic component between the dense and diffuse media challenges standard assumptions about the processes occurring in, and interactions between, these two media. The ubiquity of this interstellar diamond-like material rules out models for meteoritic diamond formation in unusual circumstellar environments and implies that the formation of the diamond-like material is associated with common interstellar processes or stellar types.

  14. Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

    NASA Astrophysics Data System (ADS)

    Hudson, R. L.; Loeffler, M. J.; Yocum, K. M.

    2017-02-01

    Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

  15. Protection from extinction.

    PubMed

    Rescorla, Robert A

    2003-05-01

    The effect of the presence of a conditioned inhibitor on extinction of excitatory conditioning was studied in one magazine approach and three autoshaping experiments using rats and pigeons. In each case, the presence of an inhibitor reduced responding to an exciter during extinction but allowed substantial recovery of responding to that exciter when subsequently tested separately. Control stimuli with a history of being irrelevant to reinforcement or being nonreinforced had less of a protective effect. This constitutes a clear demonstration of protection from extinction, a phenomenon of substantial theoretical and applied importance.

  16. Temporal Dynamics of Recovery from Extinction Shortly after Extinction Acquisition

    ERIC Educational Resources Information Center

    Archbold, Georgina E.; Dobbek, Nick; Nader, Karim

    2013-01-01

    Evidence suggests that extinction is new learning. Memory acquisition involves both short-term memory (STM) and long-term memory (LTM) components; however, few studies have examined early phases of extinction retention. Retention of auditory fear extinction was examined at various time points. Shortly (1-4 h) after extinction acquisition…

  17. Modelling the extinction of Steller's sea cow

    PubMed Central

    Turvey, S.T; Risley, C.L

    2005-01-01

    Steller's sea cow, a giant sirenian discovered in 1741 and extinct by 1768, is one of the few megafaunal mammal species to have died out during the historical period. The species is traditionally considered to have been exterminated by ‘blitzkrieg’-style direct overharvesting for food, but it has also been proposed that its extinction resulted from a sea urchin population explosion triggered by extirpation of local sea otter populations that eliminated the shallow-water kelps on which sea cows fed. Hunting records from eighteenth century Russian expeditions to the Commander Islands, in conjunction with life-history data extrapolated from dugongs, permit modelling of sea cow extinction dynamics. Sea cows were massively and wastefully overexploited, being hunted at over seven times the sustainable limit, and suggesting that the initial Bering Island sea cow population must have been higher than suggested by previous researchers to allow the species to survive even until 1768. Environmental changes caused by sea otter declines are unlikely to have contributed to this extinction event. This indicates that megafaunal extinctions can be effected by small bands of hunters using pre-industrial technologies, and highlights the catastrophic impact of wastefulness when overexploiting resources mistakenly perceived as ‘infinite’. PMID:17148336

  18. Modelling the extinction of Steller's sea cow.

    PubMed

    Turvey, S T; Risley, C L

    2006-03-22

    Steller's sea cow, a giant sirenian discovered in 1741 and extinct by 1768, is one of the few megafaunal mammal species to have died out during the historical period. The species is traditionally considered to have been exterminated by 'blitzkrieg'-style direct overharvesting for food, but it has also been proposed that its extinction resulted from a sea urchin population explosion triggered by extirpation of local sea otter populations that eliminated the shallow-water kelps on which sea cows fed. Hunting records from eighteenth century Russian expeditions to the Commander Islands, in conjunction with life-history data extrapolated from dugongs, permit modelling of sea cow extinction dynamics. Sea cows were massively and wastefully overexploited, being hunted at over seven times the sustainable limit, and suggesting that the initial Bering Island sea cow population must have been higher than suggested by previous researchers to allow the species to survive even until 1768. Environmental changes caused by sea otter declines are unlikely to have contributed to this extinction event. This indicates that megafaunal extinctions can be effected by small bands of hunters using pre-industrial technologies, and highlights the catastrophic impact of wastefulness when overexploiting resources mistakenly perceived as 'infinite'.

  19. Thermalization of Interstellar CO

    NASA Astrophysics Data System (ADS)

    Oka, Takeshi; Xiao, Han; Lynch, Phillip

    2009-06-01

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

  20. Extinction of oscillating populations

    NASA Astrophysics Data System (ADS)

    Smith, Naftali R.; Meerson, Baruch

    2016-03-01

    Established populations often exhibit oscillations in their sizes that, in the deterministic theory, correspond to a limit cycle in the space of population sizes. If a population is isolated, the intrinsic stochasticity of elemental processes can ultimately bring it to extinction. Here we study extinction of oscillating populations in a stochastic version of the Rosenzweig-MacArthur predator-prey model. To this end we develop a WKB (Wentzel, Kramers and Brillouin) approximation to the master equation, employing the characteristic population size as the large parameter. Similar WKB theories have been developed previously in the context of population extinction from an attracting multipopulation fixed point. We evaluate the extinction rates and find the most probable paths to extinction from the limit cycle by applying Floquet theory to the dynamics of an effective four-dimensional WKB Hamiltonian. We show that the entropic barriers to extinction change in a nonanalytic way as the system passes through the Hopf bifurcation. We also study the subleading pre-exponential factors of the WKB approximation.

  1. Extinction with multiple excitors.

    PubMed

    McConnell, Bridget L; Miguez, Gonzalo; Miller, Ralph R

    2013-06-01

    Four conditioned suppression experiments with rats, using an ABC renewal design, investigated the effects of compounding the target conditioned excitor with additional, nontarget conditioned excitors during extinction. Experiment 1 showed stronger extinction, as evidenced by less renewal, when the target excitor was extinguished in compound with a second excitor, relative to when it was extinguished with associatively neutral stimuli. Critically, this deepened extinction effect was attenuated (i.e., more renewal occurred) when a third excitor was added during extinction training. This novel demonstration contradicts the predictions of associative learning models based on total error reduction, but it is explicable in terms of a counteraction effect within the framework of the extended comparator hypothesis. The attenuated deepened extinction effect was replicated in Experiments 2a and 3, which also showed that pretraining consisting of weakening the association between the two additional excitors (Experiments 2a and 2b) or weakening the association between one of the additional excitors and the unconditioned stimulus (Experiment 3) attenuated the counteraction effect, thereby resulting in a decrease in responding to the target excitor. These results suggest that more than simple total error reduction determines responding after extinction.

  2. Ionization in nearby interstellar gas

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  3. Interstellar Grains: 50 Years on

    NASA Astrophysics Data System (ADS)

    Wickramasinghe, N. C.

    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.

  4. Representing culture in interstellar messages

    NASA Astrophysics Data System (ADS)

    Vakoch, Douglas A.

    2008-09-01

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

  5. Silicon chemistry in interstellar clouds

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  6. RUBIDIUM IN THE INTERSTELLAR MEDIUM

    SciTech Connect

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

    2009-11-20

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

  7. Endangered and Extinct Radioactivity

    NASA Astrophysics Data System (ADS)

    Leising, M. D.

    1993-07-01

    Gamma ray spectroscopy holds great promise for probing nucleosynthesis in individual nucleosynthesis events, via observations of short-lived radioactivity, and for measuring global galactic nucleosynthesis today with detections of longer-lived radioactivity. Many of the astrophysical issues addressed by these observations are precisely those that must be understood in order to interpret observations of extinct radioactivity in meteorites. It was somewhat surprising that the former case was realized first for a Type II supernova, when both 56Co [1] and 57Co [2] were detected in SN 1987A. These provide unprecedented constraints on models of Type II explosions. Live 26Al in the galaxy might come from Type II supernovae and their progenitors, and if this is eventually shown to be the case, can constrain massive star evolution, supernova nucleosynthesis, the galactic Type II supernova rate, and even models of the chemical evolution of the galaxy [3]. Titanium-44 is produced primarily in the alpha-rich freezeout from nuclear statistical equilibrium, possibly in Type Ia [4] and almost certainly in Type II supernovae [5]. The galactic recurrence time of these events is comparable to the 44Ti lifetime, so we expect to be able to see at most a few otherwise unseen 44Ti remnants at any given time. No such remnants have been detected yet [6]. Very simple arguments lead to the expectation that about 4 x 10^-4 M(sub)solar mass of 44Ca are produced per century. The product of the supernova frequency times the 44Ti yield per event must equal this number. Even assuming that only the latest event would be seen, rates in excess of 2 century^-1 are ruled out at >=99% confidence by the gamma ray limits. Only rates less than 0.3 century^-1 are acceptable at >5% confidence, and this means that the yield per event must be >10^-3 M(sub)solar mass to produce the requisite 44Ca. Rates this low are incompatible with current estimates for Type II supernovae and yields this high are also very

  8. Interstellar-medium Mapping in M82 through Light Echoes around Supernova 2014J

    NASA Astrophysics Data System (ADS)

    Yang, Yi; Wang, Lifan; Baade, Dietrich; Brown, Peter. J.; Cracraft, Misty; Höflich, Peter A.; Maund, Justyn; Patat, Ferdinando; Sparks, William B.; Spyromilio, Jason; Stevance, Heloise F.; Wang, Xiaofeng; Wheeler, J. Craig

    2017-01-01

    We present multiple-epoch measurements of the size and surface brightness of the light echoes from supernova (SN) 2014J in the nearby starburst galaxy M82. Hubble Space Telescope (HST) ACS/WFC images were taken ∼277 and ∼416 days after B-band maximum in the filters F475W, F606W, and F775W. Observations with HST WFC3/UVIS images at epochs ∼216 and ∼365 days are included for a more complete analysis. The images reveal the temporal evolution of at least two major light-echo components. The first one exhibits a filled ring structure with position-angle-dependent intensity. This radially extended, diffuse echo indicates the presence of an inhomogeneous interstellar dust cloud ranging from ∼100 to ∼500 pc in the foreground of the SN. The second echo component appears as an unresolved luminous quarter-circle arc centered on the SN. The wavelength dependence of scattering measured in different dust components suggests that the dust producing the luminous arc favors smaller grain sizes, while that causing the diffuse light echo may have sizes similar to those of the Milky Way dust. Smaller grains can produce an optical depth consistent with that along the supernova-Earth line of sight measured by previous studies around maximum light. Therefore, it is possible that the dust slab from which the luminous arc arises is also responsible for most of the extinction toward SN 2014J. The optical depths determined from the Milky Way-like dust in the scattering matters are lower than the optical depth produced by the dust slab.

  9. Stress and Fear Extinction

    PubMed Central

    Maren, Stephen; Holmes, Andrew

    2016-01-01

    Stress has a critical role in the development and expression of many psychiatric disorders, and is a defining feature of posttraumatic stress disorder (PTSD). Stress also limits the efficacy of behavioral therapies aimed at limiting pathological fear, such as exposure therapy. Here we examine emerging evidence that stress impairs recovery from trauma by impairing fear extinction, a form of learning thought to underlie the suppression of trauma-related fear memories. We describe the major structural and functional abnormalities in brain regions that are particularly vulnerable to stress, including the amygdala, prefrontal cortex, and hippocampus, which may underlie stress-induced impairments in extinction. We also discuss some of the stress-induced neurochemical and molecular alterations in these brain regions that are associated with extinction deficits, and the potential for targeting these changes to prevent or reverse impaired extinction. A better understanding of the neurobiological basis of stress effects on extinction promises to yield novel approaches to improving therapeutic outcomes for PTSD and other anxiety and trauma-related disorders. PMID:26105142

  10. Dust evolution processes constrained by extinction curves in nearby galaxies

    NASA Astrophysics Data System (ADS)

    Hou, Kuan-Chou; Hirashita, Hiroyuki; Michałowski, Michał J.

    2016-12-01

    Extinction curves, especially those in the Milky Way (MW), the Large Magellanic Cloud (LMC), and the Small Magellanic Cloud (SMC), have provided us with a clue to the dust properties in the nearby Universe. We examine whether or not these extinction curves can be explained by well-known dust evolution processes. We treat the dust production in stellar ejecta, destruction in supernova shocks, dust growth by accretion and coagulation, and dust disruption by shattering. To make a survey of the large parameter space possible, we simplify the treatment of the grain size distribution evolution by adopting the "two-size approximation," in which we divide the grain population into small (≲0.03 μm) and large (≳0.03 μm) grains. It is confirmed that the MW extinction curve can be reproduced in reasonable ranges for the time-scale of the above processes with a silicate-graphite mixture. This indicates that the MW extinction curve is a natural consequence of the dust evolution through the above processes. We also find that the same models fail to reproduce the SMC/LMC extinction curves. Nevertheless, this failure can be remedied by giving higher supernova destruction rates for small dust particles dust and considering amorphous carbon for carbonaceous dust; these modifications in fact fall in line with previous studies. Therefore, we conclude that the current dust evolution scenario composed of the aforementioned processes is successful in explaining the extinction curves. All the extinction curves favor efficient interstellar processing of dust, especially strong grain growth by accretion and coagulation.

  11. Biological extinction in earth history

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1986-01-01

    Virtually all plant and animal species that have ever lived on the earth are extinct. For this reason alone, extinction must play an important role in the evolution of life. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses.

  12. Structure and Dynamics of the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    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. Interstellar and interplanetary solids in the laboratory

    NASA Astrophysics Data System (ADS)

    Dartois, Emmanuel; Alata, Ivan; Engrand, Cécile; Brunetto, Rosario; Duprat, Jean; Pino, Thomas; Quirico, Eric; Remusat, Laurent; Bardin, Noémie; Mostefaoui, Smail; Morinaud, Gilles; Crane, Bruno; Szwec, Nicolas; Delauche, Lucie; Jamme, Frédéric; Sandt, Christophe; Dumas, Paul

    The composition of interstellar matter is driven by environmental parameters and results from extreme interstellar medium physico-chemical conditions. Astrochemists must rely on remote observations to monitor and analyze the interstellar solids composition. They bring additional information from the study of analogues produced in the laboratory, placed in simulated space environments. Planetologists and cosmochemists access and spectroscopically examine collected extraterrestrial material in the laboratory. Diffuse interstellar medium and molecular clouds observations set constraints on the composition of organic solids that can then be compared with collected extraterrestrial materials analyses, to shed light on their possible links.

  14. DETERMINING INTERSTELLAR CARBON ABUNDANCES FROM STRONG-LINE TRANSITIONS

    SciTech Connect

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

    2011-01-15

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

  15. Species extinction mires ecosystem

    SciTech Connect

    Holzman, D.

    1990-03-26

    Extinction is normal in the evolution of life, but amphibians, insects, birds and mammals are vanishing at an alarming pace. While habitat destruction, overexploitation and pollution are among the main causes, some disappearances cannot be explained. The extinction problem among amphibians mirrors the general, worldwide phenomenon. A synergism of insults may be responsible. Chance events such as a dry year might occasionally clean out a pond. But a larger lake nearby would replenish it. Now acid pollution adds to the ponds' burden while stocking of amphibian-eating sport fish in the lake - which happens even in natural parks - would destroy the source of replenishment. Some fear that extinctions ultimately could destroy nature's fabric.

  16. Interstellar grains in primitive meteorites - Diamond, silicon carbide, and graphite

    NASA Technical Reports Server (NTRS)

    Anders, Edward; Zinner, Ernst

    1993-01-01

    Primitive meteorites contain a few parts per million (ppm) of pristine interstellar grains that provide information on nuclear and chemical processes in stars. Their interstellar origin is proven by highly anomalous isotopic ratios, varying more than 1000-fold for elements such as C and N. Most grains isolated thus far are stable only under highly reducing conditions (C/O greater than 1), and apparently are 'stardust' formed in stellar atmospheres. Microdiamonds, of median size about 10 A, are most abundant (about 400-1800 ppm) but least understood. They contain anomalous noble gases including Xe-HL, which shows the signature of the r- and p-processes. Silicon carbide, of grain size 0.2-10 microns and abundance about 6 ppm, shows the signature of the s-process and apparently comes mainly from red giant carbon (AGB) stars of 1-3 solar masses. Some grains appear to be not less than 10 exp 9 a older than the solar system. Graphite spherules of grain size 0.8-7 microns and abundance less than 2 ppm contain highly anomalous C and noble gases, as well as large amounts of fossil Mg-26 from the decay of extinct Al-26. They seem to come from at least three sources, probably AGB stars, novae, and Wolf-Rayet stars.

  17. Supernovae and mass extinctions

    NASA Technical Reports Server (NTRS)

    Vandenbergh, S.

    1994-01-01

    Shklovsky and others have suggested that some of the major extinctions in the geological record might have been triggered by explosions of nearby supernovae. The frequency of such extinction events will depend on the galactic supernova frequency and on the distance up to which a supernova explosion will produce lethal effects upon terrestrial life. In the present note it will be assumed that a killer supernova has to occur so close to Earth that it will be embedded in a young, active, supernova remnant. Such young remnants typically have radii approximately less than 3 pc (1 x 10(exp 19) cm). Larger (more pessimistic?) killer radii have been adopted by Ruderman, Romig, and by Ellis and Schramm. From observations of historical supernovae, van den Bergh finds that core-collapse (types Ib and II) supernovae occur within 4 kpc of the Sun at a rate of 0.2 plus or minus 0.1 per century. Adopting a layer thickness of 0.3 kpc for the galacitc disk, this corresponds to a rate of approximately 1.3 x 10(exp -4) supernovae pc(exp -3) g.y.(exp -1). Including supernovae of type Ia will increase the total supernovae rate to approximately 1.5 x 10(exp -4) supernovae pc(exp -3) g.y.(exp -1). For a lethal radius of R pc the rate of killer events will therefore be 1.7 (R/3)(exp 3) x 10(exp -2) supernovae per g.y. However, a frequency of a few extinctions per g.y. is required to account for the extinctions observed during the phanerozoic. With R (extinction) approximately 3 pc, the galactic supernova frequency is therefore too low by 2 orders of magnitude to account for the major extinctions in the geological record.

  18. Intersystem transitions of interstellar carbon monoxide toward zeta Ophiuchi

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  19. Single nanowire extinction spectroscopy.

    PubMed

    Giblin, Jay; Vietmeyer, Felix; McDonald, Matthew P; Kuno, Masaru

    2011-08-10

    Here we show the first direct extinction spectra of single one-dimensional (1D) semiconductor nanostructures obtained at room temperature utilizing a spatial modulation approach. (1) For these materials, ensemble averaging in conventional extinction spectroscopy has limited our understanding of the interplay between carrier confinement and their electrostatic interactions. (2-4) By probing individual CdSe nanowires (NWs), we have identified and assigned size-dependent exciton transitions occurring across the visible. In turn, we have revealed the existence of room temperature 1D excitons in the narrowest NWs.

  20. Extinction from a paleontological perspective

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1993-01-01

    Extinction of widespread species is common in evolutionary time (millions of years) but rare in ecological time (hundreds or thousands of years). In the fossil record, there appears to be a smooth continuum between background and mass extinction; and the clustering of extinctions at mass extinctions cannot be explained by the chance coincidence of independent events. Although some extinction is selective, much is apparently random in that survivors have no recognizable superiority over victims. Extinction certainly plays an important role in evolution, but whether it is constructive or destructive has not yet been determined.

  1. POROSITY AND BAND-STRENGTH MEASUREMENTS OF MULTI-PHASE COMPOSITE ICES

    SciTech Connect

    Bossa, Jean-Baptiste; Fransen, Coen; Cazaux, Stéphanie; Linnartz, Harold; Maté, Belén; Ortigoso, Juan; Pilling, Sergio; Rocha, Will Robson Monteiro

    2015-11-20

    We use experimental mid-infrared optical constants and extended effective medium approximations to determine the porosity and the band strengths of multi-phase composite ices grown at 30 K. A set of porous H{sub 2}O:CH{sub 4} ices are taken as a prototypical example. As a benchmark and proof of concept, the stoichiometry of the ice constituents is retreived with good accuracy from the refractive indices and the extinction coefficients of the reference binary ice mixtures with known compositions. Accurate band strengths are then calculated from experimental mid-infrared spectra of complex ices. We notice that the presence of pores has only a small effect on the overall band strengths, whereas a water dilution can considerably alter them. Different levels of porosity are observed depending on the abundance of methane used as a gas contaminant premixed with water prior to background deposition. The absorption profiles are also found to vary with deposition rate. To explain this, we use Monte Carlo simulations and we observe that the deposition rate strongly affects the pore size distribution as well as the ice morphology through reorganization processes. Extrapolated to genuine interstellar ices, the methodology presented in this paper can be used to evaluate the porosity and to quantify the relative abundances from observational data.

  2. IUE spectroscopy, visible-band photometry, and polarimetry of HD 47732 (V641 Monocerotis)

    NASA Technical Reports Server (NTRS)

    Koch, R. H.; Bradstreet, D. H.; Blitzstein, W.; Hrivnak, B. J.; Pfeifer, R. J.; Perry, P. M.

    1985-01-01

    Several high- and low-dispersion IUE spectra are described for the hot, massive close binary HD 47732. The stellar silicon lines do not show theoretically expected strength, the weakness being attributed to incipicent emission. A weak stellar wind is measurable with an expansion velocity of about 500 km/s. There is difficulty in fitting a model atmosphere to all of the IUE continuum and visible band and IR measures. These difficulties are resolved by appealing to a 22,500 K model atmosphere and a distinctive interstellar extinction law. Numerous V band measures show the polarization to be variable, but not strongly in a phased-locked way. This suggests sporadic outbursts of gas feeding the shell. Several seasonal V band light curves are discussed, and the seasonal variations among them are attributed to variable developments of a systemic shell which scatters the photospheric light and dilutes to a variable degree the light variation due to ellipticity of figure of the component stars.

  3. Hydrogenation of polycyclic aromatic hydrocarbons as a factor affecting the cosmic 6.2 micron emission band

    NASA Technical Reports Server (NTRS)

    Beegle, L. W.; Wdowiak, T. J.; Harrison, J. G.

    2001-01-01

    While many of the characteristics of the cosmic unidentified infrared (UIR) emission bands observed for interstellar and circumstellar sources within the Milky Way and other galaxies, can be best attributed to vibrational modes of the variants of the molecular family known as polycyclic aromatic hydrocarbons (PAH), there are open questions that need to be resolved. Among them is the observed strength of the 6.2 micron (1600 cm(-1)) band relative to other strong bands, and the generally low strength for measurements in the laboratory of the 1600 cm(-1) skeletal vibration band of many specific neutral PAH molecules. Also, experiments involving laser excitation of some gas phase neutral PAH species while producing long lifetime state emission in the 3.3 micron (3000 cm(-1)) spectral region, do not result in significant 6.2 micron (1600 cm(-1)) emission. A potentially important variant of the neutral PAH species, namely hydrogenated-PAH (H(N)-PAH) which exhibit intriguing spectral correlation with interstellar and circumstellar infrared emission and the 2175 A extinction feature, may be a factor affecting the strength of 6.2 micron emission. These species are hybrids of aromatic and cycloalkane structures. Laboratory infrared absorption spectroscopy augmented by density function theory (DFT) computations of selected partially hydrogenated-PAH molecules, demonstrates enhanced 6.2 micron (1600 cm(-1)) region skeletal vibration mode strength for these molecules relative to the normal PAH form. This along with other factors such as ionization or the incorporation of nitrogen or oxygen atoms could be a reason for the strength of the cosmic 6.2 micron (1600 cm(-1)) feature.

  4. Herschel Observations of Interstellar Chloronium

    NASA Astrophysics Data System (ADS)

    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, Zsófia; Phillips, Thomas G.; Sandqvist, Aage; Sonnentrucker, Paule; van der Tak, Floris; Wolfire, Mark G.

    2012-03-01

    Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, 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-1 cloud) and W31C. Both the para-H35 2Cl+ and para-H37 2Cl+ isotopologues were detected, through observations of their 111-000 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 ~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 ~2 × 1013 cm-2 and ~1.2 × 1013 cm-2, respectively, for chloronium in these two sources. We obtained upper limits on the para-H35 2Cl+ line strengths toward H2 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 ~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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  5. Deuterium enrichment of interstellar dusts

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  6. Narrow-band Imagery of the ISM using the RCT

    NASA Astrophysics Data System (ADS)

    Walter, D. K.; Gelderman, R.; Guinan, E.; Howell, S.; Mattox, J. R.; McGruder, C. H., III; Davis, D.; Everett, M.

    2003-05-01

    We present the first results of imaging the Interstellar Medium (ISM) using narrow-band filters with the Robotically Controlled Telescope (RCT). The RCT is the recently refurbished 1.3-meter telescope at the Kitt Peak National Observatory. Details regarding the RCT can be found elsewhere at this meeting (Gelderman, R. et al.). Our filters are centered on diagnostic, nebular emission lines of the ions H+, He+, S+, N+ and O++. Objects of interest in the galactic and extragalactic ISM were observed including the starburst galaxy NGC 4449. Ionization ratio maps include [OIII]/Hβ, [NII]/Hα and the C(Hβ) extinction map from the ratio of Hα/Hβ. Electron densities are derived from the ratio of images taken through filters centered on the sulfur lines at 671.7 and 673.1 nm. Refurbishment of the RCT has been made possible by NASA NAG 58-762. Funding for filters and additional equipment has been made possible by NASA OSS NAG 5-10145 and NASA MU-SPIN NCC 5-534.

  7. Biogeography and extinction

    SciTech Connect

    Jablonski, D.

    1985-01-01

    The geographic ranges of species and clades, and the deployment of those clades among biogeographic provinces, are important determinants of rates and patterns of extinction. Studies of Late Cretaceous mollusks of the Gulf and Atlantic Coastal Plain confirm that species duration is closely correlated with geographic range during times of normal, background extinction. When species that originate in the last 2 myr of the Cretaceous, the correlation increases significantly. The fact that even these truncated species frequently attained broad geographic ranges indicates that during background times duration is a function of geographic range and not vice versa. However, during the end-Cretaceous mass extinction, it is clade geographic range and not the within-province ranges of its constituent species that determines survivorship: about 55% of the widespread genera but only 12% of the endemic genera survive, regardless of the ranges of their individual species. Thus, clade geographic range is an irreducible property, with effects decoupled from species-level or organismic traits that determine species' geographic ranges. Clades with tropical distributions suffer disproportionately, again independent of species' geographic range magnitudes. Survivorship of taxa or morphologies during mass extinctions may have little to do with adaptation at the organismic or even species level, but depends at least in part on clade-level traits that are less important during background times.

  8. Context, Learning, and Extinction

    ERIC Educational Resources Information Center

    Gershman, Samuel J.; Blei, David M.; Niv, Yael

    2010-01-01

    A. Redish et al. (2007) proposed a reinforcement learning model of context-dependent learning and extinction in conditioning experiments, using the idea of "state classification" to categorize new observations into states. In the current article, the authors propose an interpretation of this idea in terms of normative statistical inference. They…

  9. The mechanisms causing extinction debts.

    PubMed

    Hylander, Kristoffer; Ehrlén, Johan

    2013-06-01

    Extinction debts can result from many types of habitat changes involving mechanisms other than metapopulation processes. This is a fact that most recent literature on extinction debts pays little attention to. We argue that extinction debts can arise because (i) individuals survive in resistant life-cycle stages long after habitat quality change, (ii) stochastic extinctions of populations that have become small are not immediate, and (iii) metapopulations survive long after that connectivity has decreased if colonization-extinction dynamics is slow. A failure to distinguish between these different mechanisms and to simultaneously consider both the size of the extinction debt and the relaxation time hampers our understanding of how extinction debts arise and our ability to prevent ultimate extinctions.

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

    NASA Technical Reports Server (NTRS)

    Stone, Bradley M.

    1998-01-01

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

  11. Status of the cosmic hot interstellar plasma spectrometer (CHIPS) university-class explorer mission

    NASA Astrophysics Data System (ADS)

    Hurwitz, Mark; Davis, Robert; Dawson, Simon; Dobson, Patricia; Donakowski, William; Friedman, Assi; Gaines, Geoffrey A.; Edelstein, Jerry; Hemphill, Richelieu; Hoberman, Jane; Janicik, Jeffrey; Jelinsky, Patrick N.; Lampton, Michael L.; Marchant, Wiliam; Marckwordt, Mario; Mirczak, Jareb; Sasseen, Timothy P.; Sholl, Michael; Siegmund, Oswald H. W.; Sirk, Martin; Stone, David; Sulack, Steven; Riddle Taylor, Ellen; Veno, Michael; Wolff, Jonathan

    2003-02-01

    We present a status report on CHIPS, the Cosmic Hot Interstellar Plasma Spectrometer. CHIPS is the first NASA University-Class Explorer (UNEX) project. CHIPS was selected in 1998 and is now scheduled for launch in December of 2002. The grazing incidence CHIPS spectrograph will survey the sky and record spectra of diffuse emission in the comparatively unexplored wavelength band between 90 and 260 Å. These data will provide important new constraints on the temperature, ionization state, and emission measure of hot plasma in the "local bubble" of the interstellar medium.

  12. Simulation of optical interstellar scintillation

    NASA Astrophysics Data System (ADS)

    Habibi, F.; Moniez, M.; Ansari, R.; Rahvar, S.

    2013-04-01

    Aims: Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected on a longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. The aim of the study described in this paper is to fully simulate the scintillation process, starting from the molecular cloud description as a fractal object, ending with the simulations of fluctuating stellar light curves. Methods: Fast Fourier transforms are first used to simulate fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated from a Fresnel integral that also uses fast Fourier transform techniques. Regularisation procedure and computing limitations are discussed, along with the effect of spatial and temporal coherency (source size and wavelength passband). Results: We quantify the expected modulation index of stellar light curves as a function of the turbulence strength - characterised by the diffraction radius Rdiff - and the projected source size, introduce the timing aspects, and establish connections between the light curve observables and the refractive cloud. We extend our discussion to clouds with different structure functions from Kolmogorov-type turbulence. Conclusions: Our study confirms that current telescopes of ~4 m with fast-readout, wide-field detectors have the capability of discovering the first interstellar optical scintillation effects. We also show that this effect should be unambiguously distinguished from any other type of variability through the observation of desynchronised light curves, simultaneously measured by two distant telescopes.

  13. Components in interstellar molecular hydrogen

    NASA Technical Reports Server (NTRS)

    Spitzer, L., Jr.; Morton, W. A.

    1976-01-01

    Results are reported for precise spectrophotometric measurements of the profiles of selected Lyman absorption lines produced by hydrogen molecules in various rotational levels along the line of sight to 13 stars which have shown some evidence for an increase in line width with increasing rotational quantum number (J). The line profiles were measured by multiple scans with the Copernicus satellite telescope. Based on analysis of the radial velocities, derivations of the column densities, and line-profile fitting, the following conclusions are made: (1) the increase in interstellar H2 line width with increasing J results from the presence of the most shortward component, which is relatively weak at low J but becomes more important at higher J; (2) the relative column densities found for the different J levels in each component may be fitted by a theoretical model in which rotational excitation is due to absorption of UV photons followed by radiative quadrupole spontaneous transitions or collisionally induced downward transitions between different J levels; (3) the atomic hydrogen density is between 300 and 1000 per cu cm in the most shortward component for each of three stars; (4) the approaching gas which produces each shortward component must be in the form of thin sheets; and (5) the sheets are the compressed gas behind a shock front moving through the interstellar medium.

  14. Interstellar Material towards eta UMa

    NASA Astrophysics Data System (ADS)

    Frisch, P. C.; Jenkins, E. B.; Welty, D. E.; Johns-Krull, C.

    1999-05-01

    The star eta UMa (B3 V, vsini=205 km s(-1) , d=31 pc, l=101(o) , b=+65(o) ) samples nearby interstellar gas in a high latitude direction relatively devoid of material. IMAPS, Hubble GHRS Echelle, and ground based optical data are combined to present a comprehensive picture of the interstellar material (ISM) in this direction. Two main components dominate: the blue-shifted component which appears to be ionized, and the dominant, red-shifted, component which exhibits a low electron density ( ~ 0.2 cm(-3) ). However, the Mg(o/Mg^+) ratio and C(+) fine-structure lines yield different ionizations, depending on the adopted temperature, similar to differences found in the diffuse material towards 23 Ori (Welty et al. 1999). The IMAPS and GHRS data give C, N, O, and Fe column densities, which form the basis for calculating the gas-to-dust mass ratio for the main component using a ``missing mass'' calculation combined with an assumed reference abundance (Frisch et al. 1999). Comparing the eta UMa value with other diffuse cloud values then further constrains uncertainties in N(H(o) ) values for this sightline.

  15. Thermodynamics and Charging of Interstellar Iron Nanoparticles

    NASA Astrophysics Data System (ADS)

    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.

  16. Mass Extinctions Past and Present.

    ERIC Educational Resources Information Center

    Allmon, Warren Douglas

    1987-01-01

    Discusses some parallels that seem to exist between mass extinction recognizable in the geologic record and the impending extinction of a significant proportion of the earth's species due largely to tropical deforestation. Describes some recent theories of causal factors and periodicities in mass extinction. (Author/TW)

  17. The quantitative assessment of UV extinction derived from IUE data of giants and supergiants

    NASA Technical Reports Server (NTRS)

    Cardelli, Jason A.; Sembach, Kenneth R.; Mathis, John S.

    1992-01-01

    It is shown here that the UV interstellar extinction towards hot luminous stars can be determined as accurately as for hot main-sequence stars. An atlas of IUE dereddened fluxes is presented for 13 lightly reddened stars within the 1160-3125 A range. The fluxes of these stars how absorption line strengths that allow a rather accurate determination of relative temperatures and luminosities which is more suitable for the determination of UV extinction via the pair method than choosing a comparison star based on quoted optical MK classifications.

  18. Interstellar Neutral Gas Flow Measurements with the Interstellar Boundary Explorer (IBEX) - Implications on Interstellar Medium and Heliosphere Diagnostics

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    The Interstellar Boundary Explorer (IBEX) observes the interstellar neutral gas flow tra-jectories at their perihelion in Earth's orbit every year from December through late March, when the Earth moves into the oncoming flow. Surprisingly, the initial quantita-tive analysis resulted in a somewhat different interstellar flow vector with noticeably lower speed than obtained previously. In comparison with astronomical observations of the flow vectors of neighboring interstellar clouds, this result locates the solar system within the Local Interstellar Cloud (LIC), contrary to the previous determination, which indicated values between the LIC and the G-Cloud. This year, the fifth season is being accumulated, providing a database over increasing solar activity and with varying view-ing strategies. These recurring observations of the interstellar flow pattern and its spatial distribution allow us to consolidate the derived physical conditions of the surrounding interstellar medium. We can also track variations in the flow at 1 AU that may arise from solar cycle related changes in ionization and radiation pressure for H and explore any other variations of the neutral gas flow. Based on the angular distributions in latitude and longitude, the neutral flow observations also indicate the presence of a secondary compo-nent for most of the species, which most probably stems from charge exchange with ions in the outer heliosheath. We will review our observations and discuss implications for the LIC and its interaction with the heliosphere in the light of a growing data set and improv-ing analysis techniques.

  19. Anthracene Clusters and the Interstellar Infrared Emission Features

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  20. Anthracene clusters and the interstellar infrared emission features

    SciTech Connect

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

    2014-03-10

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

  1. BRILLIANT PEBBLES: A METHOD FOR DETECTION OF VERY LARGE INTERSTELLAR GRAINS

    SciTech Connect

    Socrates, Aristotle; Draine, Bruce T. E-mail: draine@astro.princeton.edu

    2009-09-01

    A photon of wavelength {lambda} {approx} 1 {mu}m interacting with a dust grain of radius a{sub p} {approx} 1 mm (a 'pebble') undergoes scattering in the forward direction, largely within a small characteristic diffraction angle {theta}{sub s} {approx} {lambda}/a{sub p} {approx} 100''. Though millimeter-size dust grains contribute negligibly to the interstellar medium's visual extinction, the signal they produce in scattered light may be detectable, especially for variable sources. Observations of light scattered at small angles allow for the direct measurement of the large grain population; variable sources can also yield tomographic information of the interstellar medium's mass distribution. The ability to detect brilliant pebble halos requires a careful understanding of the instrument point-spread function.

  2. Neuronal circuits of fear extinction.

    PubMed

    Herry, Cyril; Ferraguti, Francesco; Singewald, Nicolas; Letzkus, Johannes J; Ehrlich, Ingrid; Lüthi, Andreas

    2010-02-01

    Fear extinction is a form of inhibitory learning that allows for the adaptive control of conditioned fear responses. Although fear extinction is an active learning process that eventually leads to the formation of a consolidated extinction memory, it is a fragile behavioural state. Fear responses can recover spontaneously or subsequent to environmental influences, such as context changes or stress. Understanding the neuronal substrates of fear extinction is of tremendous clinical relevance, as extinction is the cornerstone of psychological therapy of several anxiety disorders and because the relapse of maladaptative fear and anxiety is a major clinical problem. Recent research has begun to shed light on the molecular and cellular processes underlying fear extinction. In particular, the acquisition, consolidation and expression of extinction memories are thought to be mediated by highly specific neuronal circuits embedded in a large-scale brain network including the amygdala, prefrontal cortex, hippocampus and brain stem. Moreover, recent findings indicate that the neuronal circuitry of extinction is developmentally regulated. Here, we review emerging concepts of the neuronal circuitry of fear extinction, and highlight novel findings suggesting that the fragile phenomenon of extinction can be converted into a permanent erasure of fear memories. Finally, we discuss how research on genetic animal models of impaired extinction can further our understanding of the molecular and genetic bases of human anxiety disorders.

  3. Interstellar and circumstellar medium in the direction to IR source IRAS 01005+7910

    NASA Astrophysics Data System (ADS)

    Sendzikas, E. G.

    2016-01-01

    Using the high-resolution spectra obtained at the 6-meter telescope of the SAO RAS over 2002-2013, we studied the spectral features of the lines of interstellar medium. The radial velocities of the Na I 5890 Å, Na I 5896 Å, Ca II 3934 Å and Ca II 3968 Å absorption lines were analyzed. Seven diffuse interstellar bands 4964, 5780, 5797, 6196, 6203, 6379 Å were identified in the optical spectrum of IRAS01005+7910. Radial velocities V r and equivalent widths W λ of these DIBs were measured, for which the values of the interstellar reddening E B-V and column density of neutral hydrogen log [N(H)] were calculated.

  4. Pulsar extinction. [astrophysics

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Baker, K.; Turk, J. S.

    1975-01-01

    Radio emission from pulsars, attributed to an instability associated with the creation of electron-positron pairs from gamma rays was investigated. The condition for pair creation therefore lead to an extinction condition. The relevant physical processes were analyzed in the context of a mathematical model, according to which radiation originated at the polar caps and magnetic field lines changed from a closed configuration to an open configuration at the force balance or corotation radius.

  5. Discovery of Interstellar Hydrogen Fluoride

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  6. Discovery of Interstellar Hydrogen Fluoride

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  7. Abundance fluctuations in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1982-01-01

    The determination of abundances within the interstellar medium is reviewed. It appears that interstellar abundances within 1 kpc of the Sun are uniform to within a factor of two or three, but it is not yet possible to determine whether there are real fluctuations at this level except for deuterium for which the factor of two variations appear to be real. Establishing the level of local fluctuations in the abundances is of considerable importance for understanding the history of nucleosynthesis in the solar neighborhood, the evolution of the interstellar medium and the formation of stars.

  8. Local interstellar medium and modeling the heliosphere

    NASA Astrophysics Data System (ADS)

    Ratkiewicz, R.; Barnes, A.; Spreiter, J. R.

    2000-11-01

    We use the best currently available estimates for interstellar parameters to update and expand the earlier study of Ratkiewicz et al. [1998]. We report (1) a more complete survey of the morphology of the heliosphere and the ways it may be modified by variation of external interstellar parameters, (2) a detailed classification of the several asymmetries and distortions associated with exterior field-flow obliquity, including cross sections of the three-dimensional structure in all three principal planes, (3) an analysis of the transition from supermagnetosonic to nearly transmagnetosonic flow, and (4) specific results for the heliosphere for the best current understanding of conditions in the local interstellar medium.

  9. The interstellar connection to solar system bodies

    NASA Technical Reports Server (NTRS)

    Greenberg, J. Mayo; Hage, Joniek

    1991-01-01

    Solar system bodies such as comets and meteorites are examined for interstellar signatures which may ultimately indicate what the protoplanetary nebula conditions were at the time the bodies formed. This involves retracing the sequence starting with a dense interstellar cloud, through the accretion disk phase of the protoplanetary nebula to the various steps in the aggregation process and finally to the physical and chemical metamorphic processes in the final body during the subsequent 4.55 billion years. Models of interstellar dust and comets which aid in such analysis are presented.

  10. Speckles in interstellar radio-wave scattering

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  11. Infrared absorption and emission characteristics of interstellar PAHs (Polycyclic Aromatic Hydrocarbon)

    SciTech Connect

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

    1986-01-01

    The mid-infrared interstellar emission spectrum with features at 3050, 1610, 1300, 1150, and 885 cm/sup -1/ (3.28, 6.2, 7.7, 8.7 and 11.3 microns) is discussed in terms of the Polycyclic Aromatic Hydrocarbon (PAH) hypothesis. This hypothesis is based on the suggestive, but inconclusive comparison between the interstellar emission spectrum with the infrared absorption and Raman spectra of a few PAHs. The fundamental vibrations of PAHs and PAH-like species which determine the ir and Raman properties are discussed. Interstellar ir band emission is due to relaxation from highly vibrationally excited PAHs which have been excited by ultraviolet photons. The excitation/emission process is described in general and the ir fluorescence from one PAH, chrysene, is traced in detail. Generally, there is sufficient energy to populate several vibrational levels in each mode. Molecular vibrational potentials are anharmonic and emission from these higher levels will fall at lower frequencies and produce weak features to the red of the stronger fundamentals. This process is also described and can account for some spectroscopic details of the interstellar emission spectra previously unexplained. Analysis of the interstellar spectrum shows that PAHs containing between 20 and 30 carbon atoms are responsible for the emission. 43 refs., 11 figs.

  12. Niagara Falls Cascade Model for Interstellar Energetic Ions in the Heliosheath

    NASA Astrophysics Data System (ADS)

    Cooper, John F.

    The origin of anomalous cosmic ray ions has long been assumed to be heliospheric pickup ion production from interstellar neutrals and acceleration at the solar wind termination shock. The Voyager-1 shock crossing showed a well-defined boundary for sharply increased keV ion fluxes in the heliosheath but no sign of local acceleration. Ion flux spectra at keV to MeV energies are instead unfolding with outward passage to approximate the E(-1.5) power-law expected for compressional magnetic tubulence. This spectrum provides excellent connection over many energy decades of a maxwellian distribution for local interstellar plasma ions to well-known flux spectra of high energy galactic ions at GeV energies. The Niagara Falls cascade model is proposed that the heliosheath is a transitional region for direct entry of ions from the local interstellar ‘river’ through a permeable heliopause into the supersonic outer heliosphere. As Voyager-1 moves outwards in the heliosheath to the heliopause, energy-dependent transport features can appear in the transitional 0.01 - 1 GeV/n energy band but otherwise a general unfolding to the interstellar limiting spectrum should continue by this model. Spectral regions then become dominated by bulk plasma flow at low energy, cascade transport at intermediate energies, and interstellar shock acceleration at higher energies.

  13. Infrared absorption and emission characteristics of interstellar PAHs. [Polycyclic Aromatic Hydrocarbon

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    The mid-infrared interstellar emission spectrum with features at 3.28, 6.2, 7.7, 8.7 and 11.3 microns is discussed in terms of the Polycyclic Aromatic Hydrocarbon (PAH) hypothesis, which is based on the suggestive, but inconclusive comparison between the interstellar emission spectrum with the infrared absorption and Raman spectra of a few PAHs. The fundamental vibrations of PAHs and PAH-like species which determine the IR and Raman properties are discussed. Interstellar IR band emission is due to relaxation from highly vibrationally excited PAHs excited by ultraviolet photons. The excitation/emission process is described and the IR fluorescence from one PAH, chrysene, is traced. Generally, there is sufficient energy to populate several vibrational levels in each mode. Molecular vibrational potentials are anharmonic and emission from these higher levels will fall at lower frequencies and produce weak features to the red of the stronger fundamentals. This process is also described and can account for some spectroscopic details of the interstellar emission spectra previously unexplained. Analysis of the interstellar spectrum shows that PAHs contain between 20 and 30 carbon atoms and are responsible for the emission.

  14. Mid-infrared Extinction and Fresh Silicate Dust towards the Galactic Center

    NASA Astrophysics Data System (ADS)

    Voshchinnikov, Nikolai V.; Henning, Thomas; Il’in, Vladimir B.

    2017-03-01

    We interpret the interstellar extinction observed toward the Galactic center (GC) in the wavelength range λ = 1–20 μm. Its main feature is the flat extinction at 3–8 μm whose explanation is still a problem for cosmic dust models. We search for the structure and chemical composition of dust grains that could explain the observed extinction. In contrast to earlier works, we use laboratory measured optical constants and consider particles of different structures. We show that a mixture of compact grains of aromatic carbon and of some silicate is better suited for reproducing the flat extinction in comparison with essentially porous grains or aliphatic carbon particles. Metallic iron should be located inside the particle, i.e., it cannot form layers on silicate grains as the extinction curves then become very peculiar. We find a model including aromatic carbonaceous particles and three-layered particles with an olivine-type silicate core, a thin, very porous layer and a thin envelope of magnetite that provides a good (but still not perfect) fit to the observational data. We suggest that such silicate dust should be fresh, i.e., recently formed in the atmospheres of late-type stars in the central region of the Galaxy. We assume that this region has a radius of about 1 kpc and produces about half of the observed extinction. The remaining part of extinction is caused by a “foreground” material being practically transparent at λ =4{--}8 μ {{m}}.

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

    NASA Astrophysics Data System (ADS)

    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

  16. A Numerical Investigation of the Extinction of Low Strain Rate Diffusion Flames by an Agent in Microgravity

    NASA Technical Reports Server (NTRS)

    Puri, Ishwar K.

    2004-01-01

    Our goal has been to investigate the influence of both dilution and radiation on the extinction process of nonpremixed flames at low strain rates. Simulations have been performed by using a counterflow code and three radiation models have been included in it, namely, the optically thin, the narrowband, and discrete ordinate models. The counterflow flame code OPPDIFF was modified to account for heat transfer losses by radiation from the hot gases. The discrete ordinate method (DOM) approximation was first suggested by Chandrasekhar for solving problems in interstellar atmospheres. Carlson and Lathrop developed the method for solving multi-dimensional problem in neutron transport. Only recently has the method received attention in the field of heat transfer. Due to the applicability of the discrete ordinate method for thermal radiation problems involving flames, the narrowband code RADCAL was modified to calculate the radiative properties of the gases. A non-premixed counterflow flame was simulated with the discrete ordinate method for radiative emissions. In comparison with two other models, it was found that the heat losses were comparable with the optically thin and simple narrowband model. The optically thin model had the highest heat losses followed by the DOM model and the narrow-band model.

  17. Filtering of interstellar dust in the heliosphere

    NASA Astrophysics Data System (ADS)

    Sterken, V. J.

    2012-08-01

    The space between the stars is filled with gas and interstellar dust (ISD). The dust grains cause extinction of the starlight that we observe and they play an important role in the evolution of galaxies and in the formation of stellar and planetary systems. The ISD has been long observed by astronomical methods, the grains were measured by in-situ measurements of spacecraft in the solar system and even samples of interstellar material have been brought back to Earth by the Stardust mission in 2006. Many questions on the composition, morphology and size distribution of ISD still exist today which require more and improved measurements. Modeling and understanding the ISD flow through the solar system is needed to interpret these observations and to fully extract the information on ISD grains carried by these measurements. Also, the modelling is necessary for designing and optimizing future ISD missions. The modeling in this thesis follows this flow of ISD through the solar system taking into account three main forces: solar gravity, solar radiation pressure force and Lorentz forces resulting from the motion of the charged grains through the interplanetary magnetic field (IMF). Simulations of dust trajectories over a large range of grain parameters β and Q/m were performed. β is the ratio of solar radiation pressure force to gravity and depends on the grain size, morphology and material. Q/m is the charge to mass ratio. The influence of solar radiation pressure force and Lorentz forces on the trajectories, densities and fluxes were systematically studied. Radiation pressure reduces gravitational attraction and can become even dominant (β > 1) for particles of about 0.2 μm radius, leading to a void region downstream from the Sun: the β -cone. The ISD flow under the influence of solar radiation pressure and gravity only is axi-symmetric, stationary and can even be calculated analytically. Lorentz force becomes stronger for smaller grains having higher Q=m and

  18. Interstellar material in the solar system

    NASA Technical Reports Server (NTRS)

    Wood, J. A.

    1986-01-01

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

  19. Astrochemistry: Fullerene solves an interstellar puzzle

    NASA Astrophysics Data System (ADS)

    Ehrenfreund, Pascale; Foing, Bernard

    2015-07-01

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

  20. Interstellar Polycyclic Aromatic Compounds and Astrophysics

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  1. A Proposal for an Interstellar Rosetta Stone

    NASA Astrophysics Data System (ADS)

    Dumas, S.

    2010-04-01

    Interstellar radio messages is our only, and probably best, way to communicate with another alien civilisation. Since the delay of communication over long distance is considerable, the content of the broadcast is very important.

  2. Cosmocultural Evolution: Cosmic Motivation for Interstellar Travel?

    NASA Astrophysics Data System (ADS)

    Lupisella, M.

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

  3. Models for the water-ice librational band in cool dust: possible observational test

    NASA Astrophysics Data System (ADS)

    Robinson, G.

    2014-01-01

    Of all the water-ice (H2O-ice) bands the librational band, occurring at a wavelength of about 12 μm, has proved to be the most difficult to detect observationally and also to reproduce in radiative transfer models. In fact, the case for the positive identification of the feature is strong in only a few astronomical objects. A previously suggested explanation for this is that so-called radiative transfer effects may mask the feature. In this paper, radiative transfer models are produced which unambiguously reveal the presence of the librational band as a separate resolved feature provided that there is no dust present which radiates significantly in the 10-μm region, specifically silicate-type dust. This means that the maximum dust temperature must be ≲50 K. In this case, the models indicate that the librational band may clearly be observed as an absorption feature against the stellar continuum. This suggests that the feature may be best observed by obtaining the 10-μm spectrum of stars either with very cool circumstellar dust shells, with Tmax ≲ 50 K, or those without circumstellar dust shells at all but with interstellar extinction. The first option might, however, require unrealistically large amounts of dust in the circumstellar shell in order to produce measurable absorption. Thus, the best place to look for the water-ice librational band may not be protostars with the remnants of their dust cloud still present, or evolved objects with ejected dust shells, as one might first think, because of the warm dust (Tmax ≫ 50 K) usually present in the shells of these objects. If objects associated with very cool dust exclusively do show the 3.1-μm water-ice band in deep absorption, but the librational band still does not appear, this may imply that it is not radiative transfer effects which suppress the librational band, and that some other mechanism for its suppression is in play. One possibility is that a low water-ice to silicate abundance may mask the

  4. MEST- avoid next extinction

    NASA Astrophysics Data System (ADS)

    Cao, Dayong

    2012-11-01

    Asteroid 2011 AG5 will impact on Earth in 2040. (See Donald K. Yoemans, ``Asteroid 2011 AG5 - A Reality Check,'' NASA-JPL, 2012) In 2011, The author say: the dark hole will take the dark comet to impact our solar system in 20 years, and give a systemic model between the sun and its companion-dark hole to explain why were there periodicity mass extinction on earth. (see Dayong Cao, BAPS.2011.CAL.C1.7, BAPS.2011.DFD.LA.24, BAPS.2012.APR.K1.78 and BAPS.2011.APR.K1.17) The dark Asteroid 2011 AG5 (as a dark comet) is made of the dark matter which has a space-time (as frequence-amplitude square) center- a different systemic model from solar systemic model. It can asborb the space-time and wave. So it is ``dark.'' When many dark matters hit on our earth, they can break our atom structure and our genetic code to trigger the Mass Extinction. In our experiments, consciousness can change the systematic model and code by a life-informational technology. So it can change the output signals of the solar cell. (see Dayong Cao, BAPS.2011.MAR.C1.286 and BAPS.2012.MAR.P33.14) So we will develop the genetic code of lives to evolution and sublimation, will use the dark matter to change the systemic model between dark hole and sun and will avoid next extinction.

  5. Gas absorption and dust extinction towards the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Hasenberger, Birgit; Forbrich, Jan; Alves, João; Wolk, Scott J.; Meingast, Stefan; Getman, Konstantin V.; Pillitteri, Ignazio

    2016-08-01

    Aims: We characterise the relation between the gas and dust content of the interstellar medium towards young stellar objects in the Orion Nebula Cluster. Methods: X-ray observations provide estimates of the absorbing equivalent hydrogen column density NH based on spectral fits. Near-infrared extinction values are calculated from intrinsic and observed colour magnitudes (J - H) and (H - Ks) as given by the VISTA Orion A survey. A linear fit of the correlation between column density and extinction values AV yields an estimate of the NH/AV ratio. We investigate systematic uncertainties of the results by describing and (if possible) quantifying the influence of circumstellar material and the adopted extinction law, X-ray models, and elemental abundances on the NH/AV ratio. Results: Assuming a Galactic extinction law with RV = 3.1 and solar abundances by Anders & Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197), we deduce an NH/AV ratio of (1.39 ± 0.14) × 1021 cm-2 mag-1 for Class III sources in the Orion Nebula Cluster where the given error does not include systematic uncertainties. This ratio is consistent with similar studies in other star-forming regions and approximately 31% lower than the Galactic value. We find no obvious trends in the spatial distribution of NH/AV ratios. Changes in the assumed extinction law and elemental abundances are demonstrated to have a relevant impact on deduced AV and NH values, respectively. Large systematic uncertainties associated with metal abundances in the Orion Nebula Cluster represent the primary limitation for the deduction of a definitive NH/AV ratio and the physical interpretation of these results. The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/593/A7

  6. Observations of Interstellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Crutcher, R.; Heiles, C.; Troland, T.

    This article describes how interstellar magnetic fields are detected, measured, and mapped, the results of such observations, and the role played by interstellar magnetic fields in the physics of the interstellar medium. A goal of the observations is the measurement of the morphology and strengths of the uniform (Bu) and random (Br) components of magnetic fields. Observational techniques probe either the component of B parallel to the line of sight (B_parallel) or in the plane of the sky (B_⊥). Tracers of B_parallel are Faraday rotation of the position angle of linearly polarized radiation and Zeeman splitting of spectral lines. Tracers of B_⊥ are the strength of synchrotron radiation and linear polarization of syn chrotron radiation and of emission or absorption from dust and spectral lines. Starlight polarization shows that on large spatial scales the Galactic magnetic field is not heavily tangled (B_u/B_r ≈ 0.7 - 1.0), that the field is generally parallel to the Galactic plane near the plane, that the local field points approximately along the local spiral arm (pitch angle 9.4(°) , center of curvature 7.8 kpc distant towards ℓ ≈ -15.4(°) ), and that off the Galactic plane there is considerable small-scale structure to the field. Galactic synchrotron emission shows magnetic spiral arms with a total strength B_t ≈ 6 #55G and B_u ≈ 4 #55G. Pulsar data show evidence for reversals of the field direction with Galactic radius and yield B_r ≈ 5 #55G and B_u ≈ 1.5 #55G; the morphology of the large-scale mean field is consistent with dynamo generation. H I Zeeman detections for diffuse clouds yield B_parallel char 126 5 - 20 #55G with many limits B_parallel #55G. A recent survey of Galactic H I in absorption against extragalactic sources confirms the result that the fields in diffuse clouds are often quite weak. The critical parameter for evaluating the importance of magnetic fields in star formation is the ratio of the mass to the magnetic flux, M

  7. The Abundance of Interstellar Fluorine

    NASA Technical Reports Server (NTRS)

    Lauroesch, James T.

    2005-01-01

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

  8. The interstellar gas experiment: Analysis in progress

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  9. A Three-Dimensional Look at the High Galactic Latitude Interstellar Medium

    NASA Astrophysics Data System (ADS)

    McGehee, Peregrine M.

    2015-01-01

    The structure of and relationship between ISM structures seen at high Galactic latitude is explored with the aid of distances determined from optical reddening profiles obtained from analysis of the Sloan Digital Sky Survey DR9 photometric catalog. This three-dimensional map contains high latitude molecular clouds, dust associated with intermediate velocity (-100 km/s < vlsr < -30 km/s) HI gas, and the ubiquitous Galactic cirrus. The distances and errors in the distances for the extinction layers due to the presence of interstellar dust are computed via a Monte Carlo algorithm. The reliability of the distance determination method is characterized as a function of the far-IR based extinction values predicted by Schlegel, Finkbeiner, and Davis (1998). The limiting performance of this technique is found in the results for the "blank field" regions defined by A_r < 0.05, whose reddening profiles are dominated by measurement noise and astrophysical scatter.

  10. Experimental and Theoretical Studies of Interstellar Grains. Ph.D. Thesis - Maryland Univ., College Park, 1982

    NASA Technical Reports Server (NTRS)

    Nuth, J. A., III

    1981-01-01

    Steady state vibrational populations of SiO and CO in dilute black body radiation fields were calculated as a function of total pressure, kinetic temperature and chemical composition of the gas. Approximate calculations for polyatomic molecules are presented. Vibrational disequilibrium becomes increasingly significant as total pressure and radiation density decrease. Many regions of postulated grain formation are found to be far from thermal equilibrium before the onset of nucleation. Calculations based upon classical nucleation theory or equilibrium thermodynamics are expected to be of dubious value in such regions. Laboratory measurements of the extinction of small iron and magnetite grains were made from 195 nm to 830 nm and found to be consistent with predictions based upon published optical constants. This implies that small iron particles are not responsible for the 220 nm interstellar extinction features. Additional measurements are discussed.

  11. Interstellar O2. II - VUV oscillator strengths of Schumann-Runge lines and prospects for Space Telescope observations

    NASA Technical Reports Server (NTRS)

    Smith, P. L.; Griesinger, H. E.; Black, J. H.; Yoshino, K.; Freeman, D. E.

    1984-01-01

    Interstellar molecular oxygen should be detectable in interstellar clouds through observation of its absorption lines in the spectra of background stars. This paper describes and presents the results of measurements of oscillator strengths for some lines in the vacuum ultraviolet (VUV) spectrum of O2. Lines of the (13, 0) through (16, 0) bands of the B 3Sigma(-)u - X 3Sigma(-)g, Schumann-Runge system between 1760 A and 1790 A will be the most suitable for searches for absorption by interstellar O2 with the High Resolution Spectrograph on Space Telescope. The strongest lines in these bands have oscillator strengths of about 3 x 10 to the -5th.

  12. Amino Acid Formation on Interstellar Dust Particles

    NASA Astrophysics Data System (ADS)

    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.

  13. The hydrogen coverage of interstellar PAHs

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  14. The hydrogen coverage of interstellar PAHs

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  15. The Physical Character of Small-Scale Interstellar Structures

    NASA Technical Reports Server (NTRS)

    Lauroesch, James T.

    2005-01-01

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

  16. Periodicity in marine extinction events

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. John, Jr.; Raup, David M.

    1986-01-01

    The periodicity of extinction events is examined in detail. In particular, the temporal distribution of specific, identifiable extinction events is analyzed. The nature and limitations of the data base on the global fossil record is discussed in order to establish limits of resolution in statistical analyses. Peaks in extinction intensity which appear to differ significantly from background levels are considered, and new analyses of the temporal distribution of these peaks are presented. Finally, some possible causes of periodicity and of interdependence among extinction events over the last quarter billion years of earth history are examined.

  17. The impact of mass extinctions

    NASA Technical Reports Server (NTRS)

    Flessa, Karl W.

    1988-01-01

    In the years since Snowbird an explosive growth of research on the patterns, causes, and consequences of extinction was seen. The fossil record of extinction is better known, stratigraphic sections were scrutinized in great detail, and additional markers of environmental change were discovered in the rock record. However flawed, the fossil record is the only record that exists of natural extinction. Compilations from the primary literature contain a faint periodic signal: the extinctions of the past 250 my may be regulary spaced. The reality of the periodicity remains a subject for debate. The implications of periodicity are so profound that the debate is sure to continue. The greater precision from stratigraphic sections spanning extinction events has yet to resolve controversies concerning the rates at which extinctions occurred. Some sections seem to record sudden terminations, while others suggest gradual or steplike environmental deterioration. Unfortunately, the manner in which the strata record extinctions and compile stratigraphic ranges makes a strictly literal reading of the fossil record inadvisable. Much progress was made in the study of mass extinctions. The issues are more sharply defined but they are not fully resolved. Scenarios should look back to the phenomena they purport to explain - not just an iridium-rich layer, but the complex fabric of a mass extinction.

  18. Tracking interstellar space weather toward timing-array millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Bhat, N. D. R.; Ord, S. M.; Tremblay, S. E.; Shannon, R. M.; van Straten, W.; Kaplan, D. L.; Macquart, J.-P.; Kirsten, F.

    2016-07-01

    Recent LIGO detection of milli-Hertz gravitational wave (GW) signals from a black-hole merger event has further reinforced the important role of Pulsar timing array (PTA) experiments in the GW astronomy. PTAs exploit the clock-like stability of fast-spinning millisecond pulsars (MSPs) to make a direct detection of ultra-low frequency (nano-Hertz) gravitational waves. The science enabled by PTAs is thus highly complementary to that possible by LIGO-like detectors. PTAs are also a key science objective for the SKA. PTA efforts over the past few years suggest that interstellar propagation effects on pulsar signals may ultimately limit the detection sensitivity of PTAs unless they are accurately measured and corrected for in timing measurements. Interstellar medium (ISM) effects are much stronger at lower radio frequencies and therefore the MWA presents an exciting and unique opportunity to calibrate interstellar propagation delays. This will potentially lead to enhanced sensitivity and scientific impact of PTA projects. Since our first demonstration of ability to form a coherent (tied-array) beam by reprocessing the recorded VCS data (Bhat et al. 2016), we have successfully ported the full processing chain to the Galaxy cluster of Pawsey and demonstrated the value of high-sensitivity multi-band pulsar observations that are now possible with the MWA. Here we propose further observations of two most promising PTA pulsars that will be nightly objects in the 2016B period. Our main science driver is to characterise the nature of the turbulent ISM through high-quality scintillation and dispersion studies including the investigation of chromatic (frequency-dependent) DMs. Success of these efforts will define the breadth and scope of a more ambitious program in the future, bringing in a new science niche for the MWA and SKA-low.

  19. Probing the Diffuse Interstellar Medium at AU Scales

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

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

  20. AN OPTICAL SURVEY FOR MILLIMETER-SIZED INTERSTELLAR METEOROIDS

    SciTech Connect

    Musci, R.; Weryk, R. J.; Brown, P.; Campbell-Brown, M. D.; Wiegert, P. A.

    2012-02-01

    We report high-resolution multi-station observations of meteors by the Canadian Automated Meteor Observatory recorded from 2009 June to 2010 August. Our survey has a limiting detection magnitude of +5 mag in R band, equivalent to a limiting meteoroid mass of {approx}2 Multiplication-Sign 10{sup -7} kg. The high metric trajectory accuracy (of the order of 30 m perpendicular to the solution and 200 m along track) allows us to determine velocities with average uncertainty of <1.5% in speed and {approx}0.{sup 0}4 in the radiant direction. A total of 1739 meteors had measured orbits. The data have been searched for meteors in hyperbolic orbits, which are potentially of interstellar origin. We found 22 potential hyperbolic meteors among our sample, with only two of them having a speed at least 3{sigma} above the hyperbolic limit. For our one-year survey we find no clear evidence of interstellar meteoroids at millimeter sizes in a weighted time-area product of {approx}10{sup 4} km{sup 2} hr. Backward integrations performed for these 22 potentially hyperbolic meteors to check for close encounters with planets show no considerable changes in their orbits. Detailed examination leads us to conclude that our few identified events are most likely the result of measurement error. We find an upper limit of f{sub ISP} < 2 Multiplication-Sign 10{sup -4} km{sup -2} hr{sup -1} for the flux of interstellar meteoroids at Earth with a limiting mass of m > 2 Multiplication-Sign 10{sup -7} kg.

  1. Tracking Interstellar Space Weather Toward Timing-Array Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Bhat, N. D. R.; Ord, S. M.; Tremblay, S. E.; Shannon, R. M.; van Straten, W.; Kaplan, D. L.; Macquart, J.-P.; Kirsten, F.

    2017-01-01

    The recent LIGO detection of milli-Hertz gravitational wave (GW) signals from black-hole merger events has further reinforced the important role of Pulsar timing array (PTA) experiments in the GW astronomy. PTAs exploit the clock-like stability of fast-spinning millisecond pulsars (MSPs) to make a direct detection of ultra-low frequency (nano-Hertz) gravitational waves, and this is a key science objective for the SKA. The science enabled by PTAs is highly complementary to that possible with LIGO-like detectors. PTA efforts of the past few years clearly suggest that interstellar propagation effects on pulsar signals may ultimately limit the detection sensitivity of PTAs if they are not accurately measured and corrected for in timing measurements. Interstellar medium (ISM) effects are much stronger at lower radio frequencies and therefore the MWA presents an exciting and unique opportunity to calibrate interstellar propagation delays. This will potentially lead to enhanced sensitivity and scientific impact of PTA projects. Since our demonstration early this year of our ability to form a coherent (tied-array) beam by re-processing the recorded VCS data (Bhat et al. 2016), we have successfully ported the full processing pipeline on to the Galaxy cluster of Pawsey and also demonstrated the value of high-sensitivity multi-band pulsar observations that are now possible with the MWA. Here we propose further observations of three most promising PTA pulsars that will be nightly objects in the 2017A period. The main science driver is to characterise the nature of the turbulent ISM through high-quality scintillation and dispersion studies including the investigation of chromatic (frequency-dependent) DMs. Success of these efforts will define the breadth and scope of a more ambitious program in the future, bringing in a new science niche for MWA and SKA-low.

  2. Determining the extragalactic extinction law with SALT - II. Additional sample

    NASA Astrophysics Data System (ADS)

    Finkelman, Ido; Brosch, Noah; Kniazev, Alexei Y.; Väisänen, Petri; Buckley, David A. H.; O'Donoghue, Darragh; Gulbis, Amanda; Hashimoto, Yas; Loaring, Nicola; Romero-Colmenero, Encarni; Sefako, Ramotholo

    2010-12-01

    We present new results from an ongoing programme to study the dust extragalactic extinction law in E/S0 galaxies with dust lanes with the Southern African Large Telescope (SALT) during its performance verification phase. The wavelength dependence of the dust extinction for seven galaxies is derived in six spectral bands ranging from the near-ultraviolet atmospheric cut-off to the near-infrared. The derivation of an extinction law is performed by fitting model galaxies to the unextinguished parts of the image in each spectral band, and subtracting from these the actual images. We compare our results with the derived extinction law in the Galaxy and find them to run parallel to the Galactic extinction curve with a mean total-to-selective extinction value of RV = 2.71 +/- 0.43. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them to range from 104 to 107 Msolar. We study the case of the well-known dust-lane galaxy NGC2685 for which Hubble Space Telescope/Wide Field Planetary Camera 2 (HST/WFPC2) data are available to test the dust distribution on different scales. Our results imply a scale-free dust distribution across the dust lanes, at least within ~1arcsec (~60 pc) regions. Based on observations made with the Southern African Large Telescope (SALT). E-mail: ido@wise.tau.ac.il (IF); noah@wise.tau.ac.il (NB); akniazev@saao.ac.za (AYK); petri@saao.ac.za (PV); dibnob@saao.ac.za (DAHB); dod@saao.ac.za (DO); amanda@saao.ac.za (AG); hashimot@ntnu.edu.tw (YH); nsl@saao.ac.za (NL); erc@saao.ac.za (ER-C); rrs@saao.ac.za (RS)

  3. Interstellar Transfer of Planetary Microbiota

    NASA Astrophysics Data System (ADS)

    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.

  4. Characterization of Interstellar Organic Molecules

    NASA Astrophysics Data System (ADS)

    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.

  5. Characterization of Interstellar Organic Molecules

    SciTech Connect

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

    2008-11-06

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

  6. Modeling Extragalactic Extinction through Gamma-Ray Burst Afterglows

    NASA Astrophysics Data System (ADS)

    Zonca, Alberto; Cecchi-Pestellini, Cesare; Mulas, Giacomo; Casu, Silvia; Aresu, Giambattista

    2016-09-01

    We analyze extragalactic extinction profiles derived through gamma-ray burst afterglows, using a dust model specifically constructed on the assumption that dust grains are not immutable but respond, time-dependently, to the local physics. Such a model includes core-mantle spherical particles of mixed chemical composition (silicate core, sp2, and sp3 carbonaceous layers), and an additional molecular component in the form of free-flying polycyclic aromatic hydrocarbons. We fit most of the observed extinction profiles. Failures occur for lines of sight, presenting remarkable rises blueward of the bump. We find a tendency for the carbon chemical structure to become more aliphatic with the galactic activity, and to some extent with increasing redshifts. Moreover, the contribution of the molecular component to the total extinction is more important in younger objects. The results of the fitting procedure (either successes and failures) may be naturally interpreted through an evolutionary prescription based on the carbon cycle in the interstellar medium of galaxies.

  7. Complex Organics from Laboratory Simulated Interstellar Ices

    NASA Technical Reports Server (NTRS)

    Dworkin, J. P.

    2003-01-01

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

  8. HAC: Band Gap, Photoluminescence, and Optical/Near-Infrared Absorption

    NASA Technical Reports Server (NTRS)

    Witt, Adolf N.; Ryutov, Dimitri; Furton, Douglas G.

    1996-01-01

    We report results of laboratory measurements which illustrate the wide range of physical properties found among hydrogenated amorphous carbon (HAC) solids. Within this range, HAC can match quantitatively the astronomical phenomena ascribed to carbonaceous coatings on interstellar grains. We find the optical band gap of HAC to be well correlated with other physical properties of HAC of astronomical interest, and conclude that interstellar HAC must be fairly hydrogen-rich with a band gap of E(sub g) is approx. greater than 2.0 eV.

  9. A study of the dust distribution and extinction law in Mon R2

    NASA Technical Reports Server (NTRS)

    Natta, A.; Beckwith, S.; Beck, S. C.; Evans, N. J., II; Moorwood, A. F. M.

    1986-01-01

    Observations were obtained at wavelengths from 1.5 to 7.5 microns with beams varying in diameter from 4 to 28 arcsec of infrared hydrogen recombination lines toward the Mon R2 IRS1 H II region. It is found that the data cannot be fitted with the extinction law which characterizes the interstellar medium unless the obscuring matter is clumped on a small scale of not greater than 0.3 arcsec; in which case considerable fluctuations in the amount of extinction on scales smaller than 1 arcsec are expected. The data of Simon et al. (1983) suggest a dip in the extinction about 5 arcsec from the 2-micron and radio continuum peak, and rule out models with uniform dust and clump distributions.

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

    SciTech Connect

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

    2013-06-10

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

  11. The prebiotic molecules observed in the interstellar gas

    PubMed Central

    Thaddeus, P

    2006-01-01

    Over 130 molecules have been identified in the interstellar gas and circumstellar shells, the largest among them is a carbon chain with 13 atoms and molecular weight of 147 (twice that of the simplest amino acid glycine). The high reliability of astronomical identifications, as well as the fairly accurate quantitative analysis which can often be achieved, is emphasized. Glycine itself has been claimed, but a recent analysis indicates that few, if any, of the astronomical radio lines attributed to glycine are actually from that molecule. Polycyclic aromatic hydrocarbons (PAHs) have long been proposed as the source of the unidentified infrared bands between 3 and 16 μm, but no single PAH has been identified in space, partly because PAHs generally have weak or non-existent radio spectra. A remarkable exception is the non-planar corannulene molecule (C20H10) that has a strong radio spectrum; in the rich molecular cloud TMC-1, it is found that less than 10−5 of the carbon is contained in this molecule, suggesting that PAHs are not the dominant large molecules in the interstellar gas, as has been claimed. Owing to inherent spectroscopic limitations, determining the structures of the large molecules in space may require capture of the dust grains, which are continually entering the outer Solar System. PMID:17008209

  12. Plasmonic modes and extinction properties of a random nanocomposite cylinder

    SciTech Connect

    Moradi, Afshin

    2014-04-15

    We study the properties of surface plasmon-polariton waves of a random metal-dielectric nanocomposite cylinder, consisting of bulk metal embedded with dielectric nanoparticles. We use the Maxwell-Garnett formulation to model the effective dielectric function of the composite medium and show that there exist two surface mode bands. We investigate the extinction properties of the system, and obtain the dependence of the extinction spectrum on the nanoparticles’ shape and concentration as well as the cylinder radius and the incidence angle for both TE and TM polarization.

  13. The ratio of carbon monoxide to molecular hydrogen in interstellar dark clouds

    NASA Technical Reports Server (NTRS)

    Dickman, R. L.

    1978-01-01

    LTE (C-13)O column densities are compared with the corresponding values of beam-convolved visual extinction at more than 100 locations within 38 different interstellar dark clouds. A roughly linear correlation is found to exist between these two quantities for visual extinctions in the range from about 1.5 to 5 mag. It is argued that this correlation can be extended up to about 10 mag and that the standard gas-to-extinction ratio can be expected to remain valid in the sources studied. The correlation of LTE (C-13)O column density with visual extinction is used to obtain an equation for the H2 column density associated with a given (C-13)O column density. It is shown that if the clouds studied are assumed to be chemically homogeneous, the equation obtained implies that at least 12% of all gas-phase carbon is in the form of CO. Comparison of the observational data with various theories proposed for molecule formation in dark clouds indicates that Langer's (1977) ion-molecule scheme accounts well for the observations when the fractionation channel of Watson et al. (1976) is included.

  14. The mid-infrared extinction law in the darkest cores of the Pipe Nebula

    NASA Astrophysics Data System (ADS)

    Ascenso, J.; Lada, C. J.; Alves, J.; Román-Zúñiga, C. G.; Lombardi, M.

    2013-01-01

    Context. The properties of dust grains, in particular their size distribution, are expected to differ from the interstellar medium to the high-density regions within molecular clouds. Aims: We measure the mid-infrared extinction law produced by dense material in molecular cloud cores. Since the extinction at these wavelengths is caused by dust, the extinction law in cores should depart from what is found in low-density environments if the dust grains have different properties. Methods: We used the unbiased LINES method to measure the slope of the reddening vectors in color-color diagrams. We derived the mid-infrared extinction law toward the dense cores B59 and FeSt 1-457 in the Pipe Nebula over a range of visual extinction between 10 and 50 mag, using a combination of Spitzer/IRAC and ESO NTT/VLT data. Results: The mid-infrared extinction law in both cores departs significantly from a power law between 3.6 and 8 μm, suggesting that these cores contain dust with a considerable fraction of large dust grains. We find no evidence of any dependence in the extinction law with column density up to 50 mag of visual extinction in these cores, and no evidence of any variation between our result and those for other clouds at lower column densities reported elsewhere in the literature. This suggests either that large grains are present even in low column density regions or that the existing dust models need to be revised at mid-infrared wavelengths. We find a small but significant difference in the extinction law of the two cores, which we tentatively associate with the onset of star formation in B59. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 62.I-0866, 65.I-0083, 67.C-0514, and 069.C-0426.

  15. USING M DWARF SPECTRA TO MAP EXTINCTION IN THE LOCAL GALAXY

    SciTech Connect

    Jones, David O.; West, Andrew A.; Foster, Jonathan B.

    2011-08-15

    We use spectra of more than 56,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) to create a high-latitude extinction map of the local Galaxy. Our technique compares spectra from the stars in the SDSS Data Release 7 M dwarf sample in low-extinction lines of sight, as determined by Schlegel et al., to other SDSS M dwarf spectra in order to derive improved distance estimates and accurate line-of-sight extinctions. Unlike most previous studies, which have used a two-color method to determine extinction, we fit extinction curves to fluxes across the spectral range from 5700 to 9200 A for every star in our sample. Our result is an A{sub V} map that extends from a few tens of pc to approximately 2 kpc away from the Sun. We also use a similar technique to create a map of R{sub V} values within approximately 1 kpc of the Sun and find that they are consistent with the widely accepted diffuse interstellar medium value of 3.1. Using our extinction data, we derive a dust scale height for the local Galaxy of 119 {+-} 15 pc and find evidence for a local dust cavity.

  16. Originations and Extinctions

    NASA Astrophysics Data System (ADS)

    Ray, Tane; Moseley, Leo; Jan, Naeem

    We analyse the fossil data of Benton1 with and without interpolation schemes. By Fourier transform analysis, we find a frequency dependence of the amplitude of 1/f for the various interpolation schemes used in the past. We illustrate that shuffling the interpolated data changes the spectra only slightly. On the other hand, an identical analysis performed on the raw (uninterpolated) fossil data gives a flat frequency spectrum. We conclude that the 1/f behavior is an artifact of the interpolation schemes. We next introduce a simulation of extinctions driven only by interactions between two trophic levels. Fourier transform analysis of the simulation data shows a frequency dependence of 1/f. When the data are grouped into a form resembling the fossil record the frequency dependence vanishes, giving a flat spectrum. Our simulation produces a frequency spectrum that agrees with the observed fossil record.

  17. Acoustic integrated extinction

    PubMed Central

    Norris, Andrew N.

    2015-01-01

    The integrated extinction (IE) is defined as the integral of the scattering cross section as a function of wavelength. Sohl et al. (2007 J. Acoust. Soc. Am. 122, 3206–3210. (doi:10.1121/1.2801546)) derived an IE expression for acoustic scattering that is causal, i.e. the scattered wavefront in the forward direction arrives later than the incident plane wave in the background medium. The IE formula was based on electromagnetic results, for which scattering is causal by default. Here, we derive a formula for the acoustic IE that is valid for causal and non-causal scattering. The general result is expressed as an integral of the time-dependent forward scattering function. The IE reduces to a finite integral for scatterers with zero long-wavelength monopole and dipole amplitudes. Implications for acoustic cloaking are discussed and a new metric is proposed for broadband acoustic transparency. PMID:27547100

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  19. Organic chemistry and biology of the interstellar medium

    NASA Technical Reports Server (NTRS)

    Sagan, C.

    1973-01-01

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

  20. Aspects of the interstellar medium in starburst galaxies

    NASA Technical Reports Server (NTRS)

    Fanelli, Michael N.

    1990-01-01

    Researchers are engaged in a multifaceted program to investigate the stellar content and star formation history of actively star-forming galaxies. A large body of stellar spectra have been examined to identify spectral features characteristic of specific stellar types. These spectral diagnostics are then calibrated in terms of temperature (spectral type), gravity (luminosity class) and metallicity. The spectral data is compiled into a stellar library whose members represent specific locations in the HR diagram. Through the use of population synthesis techniques, both optimizing and evolutionary approaches, the stellar luminosity function in composite populations can be determined by analysis of their integrated light. Researchers have concentrated on the ultraviolet wavelength region (lambda lambda 1200 to 3200), utilizing the International Ultraviolet Explorer (IUE) archives supplemented by additional observations. In the optical, virtually all stars will contribute to the integrated light. In the ultraviolet however, cool stars will produce negligible flux due to their steep ultraviolet-to-visual continua, greatly simplifying the investigation of the hot component in a composite population. The researchers' initial stellar library has been applied to several blue compact galaxies, (BCGs), a class of starburst galaxy which is UV luminous. BCGs possess a complex interstellar medium which affects the emergent stellar continuum in several ways. This presents a challenge to the stellar analysis but affords insight into the properties of the gas and dust from which the massive OB stars have formed. The optimizing synthesis method solves for the stellar luminosity function and extinction simultaneously. This therefore provides an independent measure of the extinction affecting the hot population component. Despite the rise of the reddening law towards the ultraviolet, BCGs are found to be brighter in the ultraviolet than expected.

  1. Pinpointing and preventing imminent extinctions.

    PubMed

    Ricketts, Taylor H; Dinerstein, Eric; Boucher, Tim; Brooks, Thomas M; Butchart, Stuart H M; Hoffmann, Michael; Lamoreux, John F; Morrison, John; Parr, Mike; Pilgrim, John D; Rodrigues, Ana S L; Sechrest, Wes; Wallace, George E; Berlin, Ken; Bielby, Jon; Burgess, Neil D; Church, Don R; Cox, Neil; Knox, David; Loucks, Colby; Luck, Gary W; Master, Lawrence L; Moore, Robin; Naidoo, Robin; Ridgely, Robert; Schatz, George E; Shire, Gavin; Strand, Holly; Wettengel, Wes; Wikramanayake, Eric

    2005-12-20

    Slowing rates of global biodiversity loss requires preventing species extinctions. Here we pinpoint centers of imminent extinction, where highly threatened species are confined to single sites. Within five globally assessed taxa (i.e., mammals, birds, selected reptiles, amphibians, and conifers), we find 794 such species, three times the number recorded as having gone extinct since 1500. These species occur in 595 sites, concentrated in tropical forests, on islands, and in mountainous areas. Their taxonomic and geographical distribution differs significantly from that of historical extinctions, indicating an expansion of the current extinction episode beyond sensitive species and places toward the planet's most biodiverse mainland regions. Only one-third of the sites are legally protected, and most are surrounded by intense human development. These sites represent clear opportunities for urgent conservation action to prevent species loss.

  2. Extinction of Harrington's mountain goat

    PubMed Central

    Mead, Jim I.; Martin, Paul S.; Euler, Robert C.; Long, Austin; Jull, A. J. T.; Toolin, Laurence J.; Donahue, Douglas J.; Linick, T. W.

    1986-01-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters. Images PMID:16593655

  3. Extinction of Harrington's Mountain Goat

    NASA Astrophysics Data System (ADS)

    Mead, Jim I.; Martin, Paul S.; Euler, Robert C.; Long, Austin; Jull, A. J. T.; Toolin, Laurence J.; Donahue, Douglas J.; Linick, T. W.

    1986-02-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters.

  4. Extinction of Harrington's mountain goat

    SciTech Connect

    Mead, J.I.; Martin, P.S.; Euler, R.C.; Long, A.; Jull, A.J.T.; Toolin, L.J.; Donahue, D.J.; Linick, T.W.

    1986-02-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 +/- 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters.

  5. Measuring Extinction with ALE

    NASA Astrophysics Data System (ADS)

    Zimmer, Peter C.; McGraw, J. T.; Gimmestad, G. G.; Roberts, D.; Stewart, J.; Smith, J.; Fitch, J.

    2007-12-01

    ALE (Astronomical LIDAR for Extinction) is deployed at the University of New Mexico's (UNM) Campus Observatory in Albuquerque, NM. It has begun a year-long testing phase prior deployment at McDonald Observatory in support of the CCD/Transit Instrument II (CTI-II). ALE is designed to produce a high-precision measurement of atmospheric absorption and scattering above the observatory site every ten minutes of every moderately clear night. LIDAR (LIght Detection And Ranging) is the VIS/UV/IR analog of radar, using a laser, telescope and time-gated photodetector instead of a radio transmitter, dish and receiver. In the case of ALE -- an elastic backscatter LIDAR -- 20ns-long, eye-safe laser pulses are launched 2500 times per second from a 0.32m transmitting telescope co-mounted with a 50mm short-range receiver on an alt-az mounted 0.67m long-range receiver. Photons from the laser pulse are scattered and absorbed as the pulse propagates through the atmosphere, a portion of which are scattered into the field of view of the short- and long-range receiver telescopes and detected by a photomultiplier. The properties of a given volume of atmosphere along the LIDAR path are inferred from both the altitude-resolved backscatter signal as well as the attenuation of backscatter signal from altitudes above it. We present ALE profiles from the commissioning phase and demonstrate some of the astronomically interesting atmospheric information that can be gleaned from these data, including, but not limited to, total line-of-sight extinction. This project is funded by NSF Grant 0421087.

  6. Excitation of interstellar hydrogen chloride

    NASA Technical Reports Server (NTRS)

    Neufild, David A.; Green, Sheldon

    1994-01-01

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

  7. Spectral Observations of Diffuse FUV Emission from the Hot Phase of the Interstellar Medium with DUVE

    NASA Astrophysics Data System (ADS)

    Korpela, Eric John

    One of the keys to understanding the structure and distribution of interstellar matter in the galaxy is understanding the distribution of the low density hot (105 K-106 K) phase of the interstellar medium (ISM). Because of its low density and lack of easily observable tracers, this phase is much more difficult to observe than the cooler high density components of the ISM. Because gas of this temperature emits mainly in the far ultraviolet (912 A-1800 A), extreme ultraviolet (80 A-912 A), and (for gas hotter than 106 K) X-rays, observations in these bands can provide important constraints to the distribution of this gas. Because of interstellar opacity at EUV wavelengths, only FUV and X-ray observations can provide clues to the properties of hot gas outside the immediate solar neighborhood. I present results from a search for FUV emission from the diffuse ISM conducted with an orbital FUV spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer, which covers the band from 950 A to 1080 A with 3.2 A resolution, observed a region of low neutral hydrogen column density near the south galactic pole for a total effective integration time of 1583 seconds. The only emission line detected was a geocoronal hydrogen line at 1026 A. I am able to place upper limits to several emission features that provide constraints to interstellar plasma parameters. I am also able to place limits to continuum emission throughout the bandpass. I compare these limits and other diffuse observations with several models of the structure of the interstellar medium and discuss the ramifications of these models.

  8. Spectral observations of diffuse FUV emission from the hot phase of the interstellar medium with DUVE

    NASA Astrophysics Data System (ADS)

    Korpela, Eric John

    One of the keys to understanding the structure and distribution of interstellar matter in the galaxy is understanding the distribution of the low density hot (105 K-106 K) phase of the interstellar medium (ISM). Because of its low density and lack of easily observable tracers, this phase is much more difficult to observe than the cooler high density components of the ISM. Because gas of this temperature emits mainly in the far ultraviolet (912 A-1800 A), extreme ultraviolet (80 A-912 A), and (for gas hotter than 106 K) X-rays, observations in these bands can provide important constraints to the distribution of this gas. Because of interstellar opacity at EUV wavelengths, only FUV and X- ray observations can provide clues to the properties of hot gas outside the immediate solar neighborhood. I present results from a search for FUV emission from the diffuse ISM conducted with an orbital FUV spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer, which covers the band from 950 A to 1080 A with 3.2 A resolution, observed a region of low neutral hydrogen column density near the south galactic pole for a total effective integration time of 1583 seconds. The only emission line detected was a geocoronal hydrogen line at 1026 A. I am able to place upper limits to several emission features that provide constraints to interstellar plasma parameters. I am also able to place limits to continuum emission throughout the bandpass. I compare these limits and other diffuse observations with several models of the structure of the interstellar medium and discuss the ramifications of these models.

  9. The end-Permian mass extinction: A complex, multicausal extinction

    NASA Technical Reports Server (NTRS)

    Erwin, D. H.

    1994-01-01

    The end-Permian mass extinction was the most extensive in the history of life and remains one of the most complex. Understanding its causes is particularly important because it anchors the putative 26-m.y. pattern of periodic extinction. However, there is no good evidence for an impact and this extinction appears to be more complex than others, involving at least three phases. The first began with the onset of a marine regression during the Late Permian and resulting elimination of most marine basins, reduction in habitat area, and increased climatic instability; the first pulse of tetrapod extinctions occurred in South Africa at this time. The second phase involved increased regression in many areas (although apparently not in South China) and heightened climatic instability and environmental degradation. Release of gas hydrates, oxidation of marine carbon, and the eruption of the Siberian flood basalts occurred during this phase. The final phase of the extinction episode began with the earliest Triassic marine regression and destruction of nearshore continental habitats. Some evidence suggests oceanic anoxia may have developed during the final phase of the extinction, although it appears to have been insufficient to the sole cause of the extinction.

  10. The local complex of O and B stars. I - Distribution of stars and interstellar dust

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Frogel, J. A.

    1974-01-01

    The O-B5 stars, supergiants, young clusters, and associations within 1 kpc of the sun populate two flat systems inclined to each other by 19 to 22 deg. The historical background, statistical significance, composition, spatial arrangement of the contents, and interstellar extinction in the two belts are discussed. A more or less random distribution in space and in age characterizes the O-B5 stars of the 'galactic belt', which is aligned nearly along the Milky Way. The 'Gould belt' is inclined to the Milky Way (north in Sco-Oph and south in Orion), and exhibits a projected distribution of O-B5 stars in its mean plane that resembles a 'dragonfly', with five major features defining it. A crude 'diameter' of the system is 750 to 1000 pc, and the sun's position is eccentric, lying toward Ophiuchus. The nuclear age of the system, while not unique, may be characterized as 30 m.y. from the spectral type of the broad main-sequence turnup near B2-5. Most of the O-B2 stars and youngest stellar groups near the sun belong to the Gould belt, but both belts have approximately equal space densities of B3-B5 stars and similar average values of interstellar extinction.-

  11. Discovery of molecular hydrogen fluorescence in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Martin, Christopher; Hurwitz, Mark; Bowyer, Stuart

    1990-01-01

    The first detection of molecular hydrogen fluorescence in the diffuse interstellar medium is reported. Using the Berkeley UVX Shuttle Spectrometer, H2 Lyman band fluorescence has been observed in four directions, each with high significance. Molecular hydrogen fluorescence is detected in all directions that have previously been found to contain significant CO emission. A simple equilibrium model has been developed that includes attenuation of the incident UV radiation field by H2 line and dust continuum absorption. Evidence is found that the gas in the CO emission portions of the clouds may be clumpy, with a filling factor less than 0.2 and an average density greater than 30/cu cm in most cases.

  12. The heating of interstellar clouds by vibrationally excited molecular hydrogen

    NASA Technical Reports Server (NTRS)

    Stecher, T. P.; Williams, D. A.

    1972-01-01

    The possibility that vibrationally excited H2 may be collisionally de-excited, so providing a heating mechanism for interstellar clouds which operates by coupling the stellar radiation to the gas, is discussed. The majority of excitations in the Lyman and Werner bands of H2 return the molecules to the ground electronic state in a vibrationally excited level, the most favored level being 7. The heating rate obtained in this way is compared with other mechanisms which have been postulated, and the results of calculations of temperature as a function of depth into clouds of different densities are presented. It appears that this mechanism is a significant one, which should be taken into account in detailed models of dense clouds.

  13. Shielding of CO from dissociating radiation in interstellar clouds

    NASA Technical Reports Server (NTRS)

    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.

  14. A Laboratory Route to Interstellar Ice

    NASA Astrophysics Data System (ADS)

    van Broekhuizen, Fleur Antoinette

    2005-06-01

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

  15. Prospective of Photon Propulsion for Interstellar Flight

    NASA Astrophysics Data System (ADS)

    Bae, Young K.

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

  16. Composition, structure and chemistry of interstellar dust

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  17. Innovative Interstellar Explorer (I2E)

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  18. Hydrocarbons on Saturns Satellites: Relationship to Interstellar Dust and the Solar Nebula

    NASA Technical Reports Server (NTRS)

    Cruikshank, D. P.

    2012-01-01

    To understand the origin and evolution of our Solar System, and the basic components that led to life on Earth, we study interstellar and planetary spectroscopic signatures. The possible relationship of organic material detected in carbonaceous meteorites, interplanetary dust particles (IDPs), comets and the interstellar medium have been the source of speculation over the years as the composition and processes that governed the early solar nebula have been explored to understand the extent to which primitive material survived or became processed. The Cassini VIMS has provided new data relevant to this problem. Three of Saturn's satellites, Phoebe, Iapetus, and Hyperion, are found to have aromatic and aliphatic hydrocarbons on their surfaces. The aromatic hydrocarbon signature (C-H stretching mode at 3.28 micrometers) is proportionally significantly stronger (relative to the aliphatic bands) than that seen in other Solar System bodies (e.g., comets) and materials (Stardust samples, IDPs, meteorites) and the distinctive sub-features of the 3.4 micrometer aliphatic band (CH2 and CH3 groups) are reminiscent of those widely detected throughout the diffuse ISM. Phoebe may be a captured object that originated in the region beyond the present orbit of Neptune, where the solar nebula contained a large fraction of original interstellar ice and dust that was less processed than material closer to the Sun. Debris from Phoebe now resident on Iapetus and Hyperion, as well as o Phoebe itself, thus presents a unique blend of hydrocarbons, amenable to comparisons with interstellar hydrocarbons and other Solar System materials. The dust ring surrounding Saturn, in which Phoebe is embedded, probably originated from a collision with Phoebe. Dust ring particles are the likely source of the organic-bearing materials, and perhaps the recently identified small particles of Fe detected on Saturn's satellites. Lab measurements of the absolute band strengths of representative aliphatic and

  19. The Extinction Toward the Galactic Bulge from RR Lyrae Stars

    SciTech Connect

    Kunder, A; Popowski, P; Cook, K; Chaboyer, B

    2007-11-07

    The authors present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, they derive the selective extinction coefficient R{sub V,VR} = A{sub V}/E(V-R) = 4.2 {+-} 0.2. this value is what is expected for a standard extinction law with R{sub V,BV} = 3.1 {+-} 0.3

  20. Detection of a New Interstellar Molecule: Thiocyanic Acid HSCN

    NASA Astrophysics Data System (ADS)

    Halfen, D. T.; Ziurys, L. M.; Brünken, S.; Gottlieb, C. A.; McCarthy, M. C.; Thaddeus, P.

    2009-09-01

    A new interstellar molecule, HSCN (thiocyanic acid), an energetic isomer of the well-known species HNCS, has been detected toward Sgr B2(N) with the Arizona Radio Observatory 12 m telescope. Eight rotational transitions in the Ka = 0 ladder were observed in the 2 mm and 3 mm bands. Five consecutive transitions in the 3 mm band are unblended, but three in the 2 mm band are partially masked by lines of other molecules. The peak intensity of all eight transitions are well described by a rotational temperature that is in very good agreement with that of many other molecules in this source. The line width and radial velocity of HSCN match closely with those of the ground state isomer HNCS (isothiocyanic acid), HNCO (isocyanic acid), and HOCN (cyanic acid); preliminary maps indicate that all four molecules are similarly distributed in Sgr B2. Although HSCN is calculated to lie over 3000 K higher in energy than HNCS, its column density of 1.3 × 1013 cm-2 in Sgr B2(N) is only three times lower than that of HNCS. The fractional abundances of HSCN and HNCS relative to H2 are 4.5 × 10-12 and 1.1 × 10-11. By analogy with the isomeric pair HCN and HNC, these two sulfur-bearing isomers are plausibly formed from a common cation precursor.

  1. Interstellar Environments and Dust Properties toward Cygnus OB2 No. 12: A Reassessment

    NASA Astrophysics Data System (ADS)

    Whittet, D. C. B.

    2015-10-01

    The B-type hypergiant Cygnus OB2 no. 12 is a popular target for studies of interstellar phenomena at visible-infrared wavelengths because of its exceptional brightness for a star dimmed by some 10 mag of visual extinction. A lack of detectable ice absorption has led investigators to regard the line of sight as a standard for studies of the “diffuse” interstellar medium (ISM), an assumption challenged both by observations of molecular gas toward the star and by uncertainties concerning the degree to which such a luminous object may affect its local environment. This paper presents a reassessment of the nature of the material responsible for extinction toward Cyg OB2 no. 12. The excess relative to other cluster members appears to occur in translucent clumps within an extensive network of clouds in the region. Attenuation of the ambient radiation field is sufficient in the cores of the clumps to support the presence of gas-phase molecules, but not to sustain detectable ice formation. In general, the optical properties of dust in the clumps are closely similar to those observed in typical diffuse interstellar material, with the notable exception of an unusually low value for the wavelength of maximum polarization. The implied enhancement of polarization by small grains is attributed to increased alignment efficiency in an enhanced magnetic field. This caveat apart, the results of the current paper provide reassurance that Cyg OB2 no. 12 is, indeed, an appropriate choice for studies that target diffuse and translucent phases of the ISM.

  2. INTERSTELLAR ENVIRONMENTS AND DUST PROPERTIES TOWARD CYGNUS OB2 NO. 12: A REASSESSMENT

    SciTech Connect

    Whittet, D. C. B.

    2015-10-01

    The B-type hypergiant Cygnus OB2 no. 12 is a popular target for studies of interstellar phenomena at visible-infrared wavelengths because of its exceptional brightness for a star dimmed by some 10 mag of visual extinction. A lack of detectable ice absorption has led investigators to regard the line of sight as a standard for studies of the “diffuse” interstellar medium (ISM), an assumption challenged both by observations of molecular gas toward the star and by uncertainties concerning the degree to which such a luminous object may affect its local environment. This paper presents a reassessment of the nature of the material responsible for extinction toward Cyg OB2 no. 12. The excess relative to other cluster members appears to occur in translucent clumps within an extensive network of clouds in the region. Attenuation of the ambient radiation field is sufficient in the cores of the clumps to support the presence of gas-phase molecules, but not to sustain detectable ice formation. In general, the optical properties of dust in the clumps are closely similar to those observed in typical diffuse interstellar material, with the notable exception of an unusually low value for the wavelength of maximum polarization. The implied enhancement of polarization by small grains is attributed to increased alignment efficiency in an enhanced magnetic field. This caveat apart, the results of the current paper provide reassurance that Cyg OB2 no. 12 is, indeed, an appropriate choice for studies that target diffuse and translucent phases of the ISM.

  3. Positron annihilation in the interstellar medium

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  4. Long-Term Perspectives on Interstellar Flight

    NASA Astrophysics Data System (ADS)

    Michaud, M. A. G.

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

  5. Synthesis of prebiotic glycerol in interstellar ices.

    PubMed

    Kaiser, Ralf I; Maity, Surajit; Jones, Brant M

    2015-01-02

    Contemporary mechanisms for the spontaneous formation of glycerol have not been able to explain its existence on early Earth. The exogenous origin and delivery of organic molecules to early Earth presents an alternative route to their terrestrial in situ formation since biorelevant molecules like amino acids, carboxylic acids, and alkylphosphonic acids have been recovered from carbonaceous chondrites. Reported herein is the first in situ identification of glycerol, the key building block of all cellular membranes, formed by exposure of methanol-based - interstellar model ices to ionizing radiation in the form of energetic electrons. These results provide compelling evidence that the radiation-induced formation of glycerol in low-temperature interstellar model ices is facile. Synthesized on interstellar grains and eventually incorporated into the "building material" of solar systems, biorelevant molecules such as glycerol could have been dispensed to habitable planets such as early Earth by comets and meteorites.

  6. Observations of interstellar chlorine and phosphorus

    NASA Technical Reports Server (NTRS)

    Jura, M.; York, D. G.

    1978-01-01

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

  7. Investigating nearby exoplanets via interstellar radar

    NASA Astrophysics Data System (ADS)

    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. On Al-26 and other short-lived interstellar radioactivity

    NASA Technical Reports Server (NTRS)

    Clayton, Donald D.; Hartmann, Dieter H.; Leising, Mark D.

    1993-01-01

    Several authors have shown that massive stars exploding at a rate of about three per century can account for a large portion, if not all, of the observed interstellar Al-26. In a separate argument using models of Galactic chemical evolution, Clayton (1984) showed that the Al-26/Al-27 production ratio was not large enough to maintain enough Al-26 in the Galactic disk gas of about 10 exp 10 solar masses having solar composition. We present a resolution of those conflicting arguments. A past history of Galactic infall growing the Galactic disk so dilutes the stable Al-27 concentration that the two approaches can be brought into near agreement. If massive stars dominate the production of Al-26, we suggest that the apparent shortfall of their Al-26/Al-27 yield ratio is to be interpreted as evidence for significant growth of the Galactic disk. We also discuss the implications of these arguments for other extinct radioactivities in meteorites, using I-129 and Sm-146 as examples.

  9. COMET SHOWERS ARE NOT INDUCED BY INTERSTELLAR CLOUDS

    SciTech Connect

    Morris, D.E.

    1985-11-01

    Encounters with interstellar clouds (IC) have been proposed by Rampino and Stothers as a cause of quasi-periodic intense comet showers leading to earth impacts, in order to explain the periodicity in marine mass extinctions found by Raup and Sepkoski. The model was described further, criticized and defended. The debate has centered on the question of whether the scale height of the clouds is small enough (in comparison to the amplitude of the oscillation of the solar system about the plane of the Galaxy) to produce a modulation in the rate of encounters. We wish to point out another serious, we believe fatal, defect in this model - the tidal fields of ICs are not strong enough to produce intense comet showers leading to earth impacts by bringing comets of the postulated inner Oort cloud into earth crossing orbits, except possibly during very rare encounters with very dense clouds. We will show that encounters with abundant clouds of low density cannot produce comet showers; cloud density N > 10{sup 3} atoms cm{sup -3} is needed to produce an intense comet shower leading to earth impacts. Furthermore, the tidal field of a dense cloud during a distant encounter is too weak to produce such showers. As a consequence, comet showers induced by ICs will be far less frequent than showers caused by passing stars. This conclusion is independent of assumptions about the radial distribution of comets in the inner Oort cloud.

  10. Plant invasions and extinction debts.

    PubMed

    Gilbert, Benjamin; Levine, Jonathan M

    2013-01-29

    Whether introduced species invasions pose a major threat to biodiversity is hotly debated. Much of this debate is fueled by recent findings that competition from introduced organisms has driven remarkably few plant species to extinction. Instead, native plant species in invaded ecosystems are often found in refugia: patchy, marginal habitats unsuitable to their nonnative competitors. However, whether the colonization and extinction dynamics of these refugia allow long-term native persistence is uncertain. Of particular concern is the possibility that invasive plants may induce an extinction debt in the native flora, where persistence over the short term masks deterministic extinction trajectories. We examined how invader impacts on landscape structure influence native plant persistence by combining recently developed quantitative techniques for evaluating metapopulation persistence with field measurements of an invaded plant community. We found that European grass invasion of an edaphically heterogeneous California landscape has greatly decreased the likelihood of the persistence of native metapopulations. It does so via two main pathways: (i) decreasing the size of native refugia, which reduces seed production and increases local extinction, and (ii) eroding the dispersal permeability of the matrix between refugia, which reduces their connectivity. Even when native plant extinction is the deterministic outcome of invasion, the time to extinction can be on the order of hundreds of years. We conclude that the relatively short time since invasion in many parts of the world is insufficient to observe the full impact of plant invasions on native biodiversity.

  11. Mass Extinctions in Earth's History

    NASA Astrophysics Data System (ADS)

    Ward, P. D.

    2002-12-01

    Mass extinctions are short intervals of elevated species death. Possible causes of Earth's mass extinctions are both external (astronomical) and internal (tectonic and biotic changes from planetary mechanisms). Paleontologists have identified five "major" mass extinctions (>50 die-off in less than a million years) and more than 20 other minor events over the past 550 million years. Earlier major extinction events undoubtedly also occurred, but we have no fossil record; these were probably associated with, for example, the early heavy bombardment that cleared out the solar system, the advent of oxygen in the atmosphere, and various "snowball Earth" events. Mass extinctions are viewed as both destructive (species death ) and constructive, in that they allow evolutionary innovation in the wake of species disappearances. From an astrobiological perspective, mass extinctions must be considered as able both to reduce biodiversity and even potentially end life on any planet. Of the five major mass extinctions identified on Earth, only one (the Cretaceous/Tertiary event 65 million years ago that famously killed off the dinosaurs ) is unambiguously related to the impact of an asteroid or comet ( 10-km diameter). The Permian/Triassic (250 Myr ago) and Triassic/Jurassic (202 Myr ago) events are now the center of debate between those favoring impact and those suggesting large volume flooding by basaltic lavas. The final two events, Ordovician (440 Myr ago) and Devonian (370 Myr ago) have no accepted causal mechanisms.

  12. The learning of fear extinction.

    PubMed

    Furini, Cristiane; Myskiw, Jociane; Izquierdo, Ivan

    2014-11-01

    Recent work on the extinction of fear-motivated learning places emphasis on its putative circuitry and on its modulation. Extinction is the learned inhibition of retrieval of previously acquired responses. Fear extinction is used as a major component of exposure therapy in the treatment of fear memories such as those of the posttraumatic stress disorder (PTSD). It is initiated and maintained by interactions between the hippocampus, basolateral amygdala and ventromedial prefrontal cortex, which involve feedback regulation of the latter by the other two areas. Fear extinction depends on NMDA receptor activation. It is positively modulated by d-serine acting on the glycine site of NMDA receptors and blocked by AP5 (2-amino-5-phosphono propionate) in the three structures. In addition, histamine acting on H2 receptors and endocannabinoids acting on CB1 receptors in the three brain areas mentioned, and muscarinic cholinergic fibers from the medial septum to hippocampal CA1 positively modulate fear extinction. Importantly, fear extinction can be made state-dependent on circulating epinephrine, which may play a role in situations of stress. Exposure to a novel experience can strongly enhance the consolidation of fear extinction through a synaptic tagging and capture mechanism; this may be useful in the therapy of states caused by fear memory like PTSD.

  13. The Link Between UV Extinction and Infrared Cirrus

    NASA Technical Reports Server (NTRS)

    Hackwell, John A.; Hecht, James; Canterna, Ronald

    1997-01-01

    Low resolution spectra from the International Ultraviolet Explorer satellite were used to derive ultraviolet extinction curves for stars in four clusters away from the galactic plane. The extinction in three of the clusters is very similar to the general interstellar curve defined by Seaton. Stars in the fourth region, near the Rho Ophiuci dark cloud, have extinction curves that are characterized by a small "linear" term component. The star BD +36 deg 781 is unique amongst the 20 stars observed in that it shows evidence for extinction by diamond grains near 1700 angstroms. We used data from the final release of the IRAS Sky Survey Atlas (ISSA) to determine the 60 micron to 100 micron intensity ratio for the infrared cirrus. The ISSA data, which have been corrected for zodiacal light, gave intensity ratios that are more robust and self-consistent than for other data sets that we used. When the infrared and ultraviolet data are combined, we see a general trend for low values of the ultraviolet "linear term" (al) to correlate with high values of 60 micron/100 micron ratio. This implies that, in regions where the average dust temperature is hotter (high 60 micron/100 micron ratio), there is a relative absence of the small silicate grains that are responsible for the ultraviolet linear term. However, the new data do not bear out our earlier contention that the 60 micron and 100 micron emissions are poorly correlated spatially in regions where the 60 micron/100 micron ratio is low. Only NGC 1647 shows this result. It may be that the different dust types are particularly poorly mixed in this area.

  14. Spatial Distributions and Interstellar Reaction Processes

    NASA Astrophysics Data System (ADS)

    Neill, Justin L.; Steber, Amanda L.; Muckle, Matt T.; Zaleski, Daniel P.; Lattanzi, Valerio; Spezzano, Silvia; McCarthy, Michael C.; Remijan, Anthony J.; Friedel, Douglas N.; Widicus Weaver, Susanna L.; Pate, Brooks H.

    2011-05-01

    Methyl formate presents a challenge for the conventional chemical mechanisms assumed to guide interstellar organic chemistry. Previous studies of potential formation pathways for methyl formate in interstellar clouds ruled out gas-phase chemistry as a major production route, and more recent chemical kinetics models indicate that it may form efficiently from radical-radical chemistry on ice surfaces. Yet, recent chemical imaging studies of methyl formate and molecules potentially related to its formation suggest that it may form through previously unexplored gas-phase chemistry. Motivated by these findings, two new gas-phase ion-molecule formation routes are proposed and characterized using electronic structure theory with conformational specificity. The proposed reactions, acid-catalyzed Fisher esterification and methyl cation transfer, both produce the less stable trans-conformational isomer of protonated methyl formate in relatively high abundance under the kinetically controlled conditions relevant to interstellar chemistry. Gas-phase neutral methyl formate can be produced from its protonated counterpart through either a dissociative electron recombination reaction or a proton transfer reaction to a molecule with larger proton affinity. Retention (or partial retention) of the conformation in these neutralization reactions would yield trans-methyl formate in an abundance that exceeds predictions under thermodynamic equilibrium at typical interstellar temperatures of interstellar clouds. Motivated by new theoretical predictions, the rotational spectrum of trans-methyl formate has been measured for the first time in the laboratory, and seven lines have now been detected in the interstellar medium using the publicly available PRIMOS survey from the NRAO Green Bank Telescope.

  15. HST STIS Observations of Interstellar Chlorine

    NASA Astrophysics Data System (ADS)

    Becker, Valerie Rose; Dirks, Cody; Meyer, David M.; Cartledge, Stefan I. B.

    2017-01-01

    Among the dominant ions of abundant elements in the diffuse interstellar medium, only chlorine (Cl II) has a rapid exothermic reaction with molecular hydrogen (H2) that should lead to the dominance of its atomic form (Cl I) in clouds where most of the hydrogen is in H2. We present the results of an archival study of the interstellar Cl I λ1347.24 absorption observed at high spectral resolution toward 41 stars with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST). Our key goals in this survey are to explore the relationship between interstellar N(Cl I) and N(H2) with a larger sample and a larger N(H2) range (16.44 < log N(H2) < 20.87) than the Copernicus interstellar survey of Moomey et al. (2012). We additionally contrast it with the high-z QSO damped Lyman-alpha system (DLA) findings of Balashev et al. (2015). We find that for log N(H2) > 19.0, the HST STIS sample is consistent with the Copernicus data and high-z DLA samples in indicating a linear trend of increasing N(Cl I) with increasing N(H2). Furthermore, all of the interstellar sightlines with log f(H2) > -0.5 have log N(Cl I) > 13.5, and those with log f(H2) < -1.5 have log N(Cl I) < 13.5, where f(H2)=2N(H2)/[2N(H2)+N(H I)] is the fractional amount of H2 in H. Consequently, observations of interstellar Cl I can potentially trace the H2 fraction of the “CO-dark” gas marking the transition between diffuse atomic and dense CO molecular clouds.

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

    NASA Technical Reports Server (NTRS)

    1996-01-01

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

  17. Preliminary Examination of the Interstellar Collector of Stardust

    NASA Astrophysics Data System (ADS)

    Westphal, A. J.; Allen, C. C.; Bastien, R.; Borg, J.; Brenker, F.; Bridges, J. C.; Brownlee, D. E.; Butterworth, A. L.; Floss, C.; Flynn, G. J.; Frank, D.; Gainsforth, Z.; Gruen, E.; Hoppe, P.; Kearsley, A. T.; Leroux, H.; Nittler, L. R.; Sandford, S. A.

    2008-03-01

    We describe the Stardust Interstellar Preliminary Examination (ISPE), which will use non-destructive, non-invasive techniques to identify and characterize candidate interstellar impacts in the Stardust aerogel and foil collectors.

  18. Extinction, ejecta masses, and radial velocities of novae

    NASA Technical Reports Server (NTRS)

    Williams, Robert E.

    1994-01-01

    Interstellar reddening is determined for a number of recent novae based upon emission-line ratios which are generally observable using CCDs. Large values of extinction are found for most systems, possibly indicative of an intrinsic component of reddening in postoutburst novae. The unusual characteristics of the (O I) lines in novae, which are strong and optically thick, require a large population of very dense globules which are the likely sites of dust formation. These pyroclasts must be ejected from the white dwarf. The total mass of the neutral gas in the globules in some of the objects is substantially larger than the masses normally derived for the ionized ejecta of novae. The distribution of radial velocities of Galactic novae in the Tololo sample, although uncertain, shows an asymmetry in having predominantly negative values. Either high internal absorption in the expanding ejecta skews the emission lines to bluer wavelengths, or most of the novae are moving out from the center of the Galaxy.

  19. An Analysis of Dust Halo and Extinction Toward X Persei

    NASA Technical Reports Server (NTRS)

    Valencic, Lynne A.; Smith, Randall K.

    2007-01-01

    Interstellar dust grain models are not sufficiently constrained by UV extinction curves to be able to distinguish between them. By testing grain models in the X-ray regime and applying elemental abundance constraints, we show to what extent the models can reproduce the observables in these regimes, and if they are capable of doing so while respecting the abundance limits. We tested the MRN and WD grain models. The fits to the X-ray data do not allow us to distinguish between MRN and WD; both models provide reasonable fits, but cannot do so while respecting the elemental abundance constraints. The situation in the UV regime is similar. Both MRN and WD underestimate the hydrogen column density NH. The model of ZDA provides promising results, as it finds NH much closer to the UV-measured value; further testing of this model is called for.

  20. New theories about ancient extinctions

    USGS Publications Warehouse

    Spall, H.

    1986-01-01

    But all this may be changing. Mass extinctions have been very much in the news in the last few years, triggered in large part by the proposal that the extinction of the dinosaurs and marine animals was caused by a catastrophic collision between the Earth and an extra-terrestrial body (bolide). Recently an equally contentious suggestion has been made that mass extinctions have swept the Earth every 26 to 31 million years for at least the last 250 million years-caused by encounters with some kind of extra-terrestrial object such as one of the asteroids or the comets. 

  1. Interstellar gas in the Gum Nebula

    NASA Technical Reports Server (NTRS)

    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.

  2. Interstellar magnetic field effects on the heliosphere

    NASA Astrophysics Data System (ADS)

    Ratkiewicz, Romana; Ben-Jaffel, Lotfi; McKenzie, James F.; Webb, Gary M.

    2003-09-01

    This paper summarizes the numerical results obtained by three-dimensional MHD simulations of the interaction between the solar wind and interstellar medium in Ratkiewicz and Ben-Jaffel [2002], Ratkiewicz and McKenzie [2002], and Ratkiewicz and Webb [2002]. We analyze the configuration in which Maxwell stresses lead to squeezing and/or pushing the heliospheric boundary. In particular, we explain the mechanism giving rise to a suction effect of the heliopause. Numerical results for the case of aligned interstellar MHD flow are compared with previous studies.

  3. Indirect observation of unobservable interstellar molecules

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  4. Electron energy loss spectrometry of interstellar diamonds

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  5. Problems of Interplanetary and Interstellar Trade

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2006-01-01

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

  7. Deflection of the Interstellar Neutral Hydrogen Flow Across the Heliospheric Interface: an Interstellar Magnetic Compass

    NASA Astrophysics Data System (ADS)

    Lallement, R.; Eric, Q.; Jean-Loup, B.; Dimitra, K.; Risto, P.

    2005-05-01

    Analyses of SOHO-SWAN observations show that the interstellar neutral H flow direction differs by about 4 degrees from the neutral He flow direction recently derived with an unprecedented accuracy using combined data sets (Mobius et al, 2004). The most likely explanation is a distortion of the heliospheric interface under the action of an inclined interstellar magnetic field, with imprints of the distorsion on the neutral H flow due to charge-transfer reactions between H atoms and ions. The direction of the ambient interstellar magnetic field and the heliospheric shape can be derived from the observed deviation. Implications for Voyager trajectories are discussed.