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 materials in the DISM may be physically correlated and (2) there is either dust compositional variation in the galaxy or galactic variation in the grain population density distribution. We also note a possible absorption feature near 3050/cm (3.28 micrometers), a wavelength position that is characteristic of polycyclic aromatic hydrocarbons (PAHs).

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, provide insight into possible molecular structure details of newly formed hydrocarbon-rich interstellar dust and its transformation into aged material that becomes resident in the interstellar medium. Specifically the presence of naphthalene-like and butadiene-like conjugated structures as chromophores for the 2175 angstroms ultraviolet extinction feature is indicated.

The discovery of a new infrared emission feature at 1905 wavenumbers (5.25 microns) in the spectrum of BD + 30 deg 3639 and its relation to the polycyclic aromatic hydrocarbon model

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Bregman, J. D.; Sandford, S. A.; Tielens, A. G. G. M.; Witteborn, F. C.

1989-01-01

A new IR emission feature at 1905/cm (5.25 microns) has been discovered in the spectrum of BD + 30 deg 3639. This feature joins the family of well-known IR emission features at 3040, 2940, 1750, 1610, '1310', 1160, and 890/cm. The origin of this new feature is discussed and it is assigned to an overtone or combination band involving C-H bending modes of polycyclic aromatic hydrocarbons (PAHs). Laboratory work suggests that spectral studies of the 2000-1650/cm region may be very useful in elucidating the molecular structure of interstellar PAHs. The new feature, in conjunction with other recently discovered spectral structures, suggests that the narrow IR emission features originate in PAH molecules rather than large carbon grains.

Developing Automated Spectral Analysis Tools for Interstellar Features Extractionto Support Construction of the 3D ISM Map

NASA Astrophysics Data System (ADS)

Puspitarini, L.; Lallement, R.; Monreal-Ibero, A.; Chen, H.-C.; Malasan, H. L.; Aprilia; Arifyanto, M. I.; Irfan, M.

2018-04-01

One of the ways to obtain a detailed 3D ISM map is by gathering interstellar (IS) absorption data toward widely distributed background target stars at known distances (line-of-sight/LOS data). The radial and angular evolution of the LOS measurements allow the inference of the ISM spatial distribution. For a better spatial resolution, one needs a large number of the LOS data. It requires building fast tools to measure IS absorption. One of the tools is a global analysis that fit two different diffuse interstellar bands (DIBs) simultaneously. We derived the equivalent width (EW) ratio of the two DIBs recorded in each spectrum of target stars. The ratio variability can be used to study IS environmental conditions or to detect DIB family.

High-resolution spectra of the 3.29 micron interstellar emission feature - A summary

NASA Technical Reports Server (NTRS)

Tokunaga, A. T.; Sellgren, K.; Smith, R. G.; Nagata, T.; Sakata, A.; Nakada, Y.

1991-01-01

High spectral resolution observations of the 3.29-micron interstellar emission feature show two types of profiles. Type 1 has a central wavelength of 3.289-micron and is observed in extended objects such as planetary nebulae and H II regions. Type 2 has a central wavelength of 3.296 microns and is observed around a small number of stellar sources. Type 2 has a full width at half-maximum of 0.020 micron; Type 1 has a broader FWHM, perhaps as much as 0.042 micron, but this is uncertain because of contamination by Pf(delta) emission. These profiles are tabulated for comparison to laboratory data. It is found that no proposed identification for the 3.29-micron emission feature definitely matches the observational spectra, although amorphous aromatic materials and heated polycyclic aromatic hydrocarbons tend to fit the best.

"CHON" particles: The interstellar component of cometary dust

NASA Technical Reports Server (NTRS)

Lien, David J.

1998-01-01

Interstellar dust is characterized by strong absorption in the ultraviolet and the mid-IR. Current models of interstellar dust are based on three chemically distinct components: a form of carbon (usually graphite), a silicate, and a blend of polycyclic aromatic hydrocarbons or other carbonaceous material. Previous work using effective medium theories to understand the optical properties of cometary dust suggested that an amalgam of materials could reproduce the observed interstellar and cometary dust features. Recently, Lawler and Brownlee (1992) re-analyzed the PIA and PUMA-1 data sets from the Giotto flyby of P/Halley and discovered that the so-called "CHON" particles were actually composed of a blend of carbon-bearing and silicon-bearing materials. Based on effective medium theories, the absorption spectrum of such a material would display the spectral features of each of the components - strong UV absorption from the carbonaceous component and strong absorption in the IR from the silicate component. To test this idea, vapor-deposited samples were created using two different deposition techniques: sputtering with an argon RF magnetron and deposition from an argon plasma torch. Two different compositions were tested: a blend of graphite and silica in a 7:1 ratio and an amalgam of materials whose approximate composition matches the "CHON"-silicate abundances for the uncompressed PIA data set of Lawler and Brownlee: graphite, iron oxide, magnesium oxide, ammonium sulfate, calcium carbonate, and silica in mass ratios of 6:4.3:4:2.2:1:9. The samples were finely ground and pressed into 2" diameter disks using a 40 ton press. In all, four different experiments were performed: one with each of the compositions (C:SiO and "CHON") in both the RF magnetron and the plasma torch chambers. The RF magnetron created a uniform dark thin film on the substrate surface, and the plasma torch created a coating of small (<100 micron) diameter grey particles. The spectra of all four samples show a strong, broad absorption feature at around 220 nm as well as a strong but narrower absorption peak near 10 microns. The RF magnetron sputtered samples showed some sub-structure in the UV, and the peak of the absorption was shifted toward longer wavelengths. The UV absorption in the plasma torch deposited samples have no sub-structure, and the peak absorption is very near 220 nm. Strong absorption near 9 microns is seen in the spectra from both sample preparation techniques, and is consistent with the IR spectra of some terrestrial silicates. Other features, particularly at 6.2 and 8.6 microns, are seen in the interstellar medium. A strong feature near 2 microns is due to absorbed water in the sample. Based on the results of these experiments, there is evidence that a material with a composition similar to that detected in "CHON" particles in the coma of P/Halley have a spectral signature which reproduces the main absorption features of interstellar dust. This suggests that the "CHON" particles could be the interstellar component of cometary dust.

Polycyclic Aromatic Hydrocarbons and Infrared Astrophysics with Spitzer

NASA Technical Reports Server (NTRS)

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

2004-01-01

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. This paper will focus on recent applications of the NASA Ames PAH IR spectral Database to interpret astronomical observations made by the Spitzer Space telescope and other space based infrared instruments. Examples will be given showing how changes in the spectral characteristics of different objects reveal interstellar PAH characteristics such as structure, size and composition, as well as provide insight into the chemical history and physical nature of the emission zones.

Fröhlich resonance in carbon nanospiroids and the 2175 Å interstellar absorption feature

NASA Astrophysics Data System (ADS)

Yastrebov, Sergey; Chekulaev, Maxim; Siklitskaya, Alexandra; Majewski, Jacek A.; Smith, Roger

2017-02-01

This paper demonstrates that a free electron gas model accurately simulates the spectral dependence of optical extinction spectra for carbon spiroids under the assumption that free electrons are confined in an homogeneous spherical particle owing to the delocalisation of π electrons that occurs in the actual spectral range. This effect can occur in the spiroid, rather than a spheroid (onion) due to the variable radii of the spiral turns as a function of distance from the centre, which are smaller than typical values for the spheroid.

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.

Luminescence from Vacuum-Ultraviolet-Irradiated Cosmic Ice Analogs and Residue

NASA Technical Reports Server (NTRS)

Gudipati, Murthy S.; Dworkin, Jason P.; Chillier, Xavier D. F.; Allamandola, Louis J.

2003-01-01

Here we report a study of the optical luminescent properties for a variety of vacuum-ultraviolet (VUV)-irradiated cosmic ice analogs and the complex organic residues produced. Detailed results are presented for the irradiated, mixed molecular ice: H2O: CH3OH:NH3:CO(100:50:1:1), a realistic representation for an interstellar/precometary ice that reproduces all the salient infrared spectral features associated with interstellar ices. The irradiated ices and the room-temperature residues resulting from this energetic processing have remarkable photoluminescent properties in the visible (520-570 nm). The luminescence dependence on temperature, thermal cycling, and VUV exposure is described. It is suggested that this type of luminescent behavior might be applicable to solar system and interstellar observations and processes for various astronomical objects with an ice heritage. Some examples include grain temperature determination and vaporization rates, nebula radiation balance, albedo values, color analysis, and biomarker identification.

Luminescence from Vacuum-Ultraviolet-Irradiated Cosmic Ice Analogs and Residues

NASA Technical Reports Server (NTRS)

Gudipati, Murthy S.; Dworkin, Jason P.; Chillier, Xavier D. F.; Allamandola, Louis J.

2003-01-01

Here we report a study of the optical luminescent properties for a variety of vacuum-ultraviolet (VUV)- irradiated cosmic ice analogs and the complex organic residues produced. Detailed results are presented for the irradiated, mixed molecular ice: H2O:CH3OH:NH3:CO (100:50:1:1), a realistic representation for an interstellar/precometary ice that reproduces all the salient infrared spectral features associated with interstellar ices. The irradiated ices and the room-temperature residues resulting from this energetic processing have remarkable photoluminescent properties in the visible (520-570 nm). The luminescence dependence on temperature, thermal cycling, and VUV exposure is described. It is suggested that this type of luminescent behavior might be applicable to solar system and interstellar observations and processes for various astronomical objects with an ice heritage. Some examples include grain temperature determination and vaporization rates, nebula radiation balance, albedo values, color analysis, and biomarker identification.

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

NASA Technical Reports Server (NTRS)

Salama, Farid

2005-01-01

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-UV and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong VUV radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. 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. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20 cm(sup -1)) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10 cm(sup -1)). The laboratory data are discussed and compared with recent astronomical spectra of large and narrow DIBs and with the spectra of circumstellar environments of selected carbon stars and the implications for the interstellar PAH population are derived. Preliminary results also show that carbon nanoparticles are formed during the short residence time of the precursors in the plasma.

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 precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. 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. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20/cm) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10/cm).

UV-visible spectroscopy of PAHs and PAHNs in supersonic jet. Astrophysical Implications

NASA Astrophysics Data System (ADS)

Salma, Bejaoui; Salama, Farid

2017-06-01

Polycyclic Aromatic Hydrocarbon (PAHs) molecules are attracting much attention of the astrophysical and astrochemical communities since they are ubiquitous presence in space and could survive in the harsh interstellar medium (ISM). They are proposed as plausible carriers of the still unassigned diffuse interstellar bands (DIBs) for more than two decades now. The so-called PAH - DIB proposal has been based on the abundance of PAHs in the ISM and their stability against the photo and thermo dissociation. Nitrogen is one of the most abundant elements after hydrogen, helium, and carbon [1]. PANHs exhibit spectral features similar to PAHs and may also contribute to unidentified spectral bands.To prove PAHs-DIBs hypothesis, laboratory absorption spectra of aromatic under astrophysical relevant conditions are of crucial importance to compare with the observed DIBs spectra. The most challenging task is to reproduce as closely as technically possible, the physical and chemical conditions that are present in space. Interstellar PAHs are expected to be present as free, cold, neutral molecules and/or charged species [2]. In our laboratory, comparable conditions are achieved using an excellent platform developed in NASA Ames. Our cosmic simulation chamber (COSmIC) allow the measurements of gas phase spectra of neutral and ionized interstellar PAHs analogs by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion (˜ 100 K) [3]. Our approach to assign PAH as carriers of some DIBs is record the electronic spectra of cold PAHs in gas phase and systematic search for a possible correspondence in astronomical DIBs spectra. We report in this work UV-visible absorption spectra of neutral PAHs and PAHNs using the cavity ring down spectroscopy (CRDS) technique. We discuss the effect of the substitution of C-H bond(s) by a nitrogen atom(s) in spectroscopic features of PAHs and their astrophysical application.[1] L. Spitzer, 1978, Physical processes in the interstellar medium. New York Wiley-Interscience[2] F. Salama, E. Bakes, L.J. Allamandola, A.G.G.M. Tielens, Astrophys. J. 458 (1996) 621[3] L. Biennier, F. Salama, L. J. Allamandola, & J. J. Scherer, (2003) J. of Chemical Physics, 118(17), 7863-7872

Formation and Destruction Processes of Interstellar Dust: From Organic Molecules to carbonaceous Grains

NASA Technical Reports Server (NTRS)

Salama, F.; Biennier, L.

2004-01-01

The study of the formation and destruction processes of cosmic dust is essential to understand and to quantify the budget of extraterrestrial organic molecules. interstellar dust presents a continuous size distribution from large molecules, radicals and ions to nanometer-sized particles to micron-sized grains. The lower end of the dust size distribution is thought to be responsible for the ubiquitous spectral features that are seen in emission in the IR (UIBs) and in absorption in the visible (DIBs). The higher end of the dust-size distribution is thought to be responsible for the continuum emission plateau that is seen in the IR and for the strong absorption seen in the interstellar UV extinction curve. All these spectral signatures are characteristic of cosmic organic materials that are ubiquitous and present in various forms from gas-phase molecules to solid-state grains. Although dust with all its components plays an important role in the evolution of interstellar chemistry and in the formation of organic molecules, little is known on the formation and destruction processes of dust. Recent space observations in the UV (HST) and in the IR (ISO) help place size constraints on the molecular component of carbonaceous IS dust and indicate that small (ie., subnanometer) PAHs cannot contribute significantly to the IS features in the UV and in the IR. Studies of large molecular and nano-sized IS dust analogs formed from PAH precursors have been performed in our laboratory under conditions that simulate diffuse ISM environments (the particles are cold -100 K vibrational energy, isolated in the gas phase and exposed to a high-energy discharge environment in a cold plasma). The species (molecules, molecular fragments, ions, nanoparticles, etc) formed in the pulsed discharge nozzle (PDN) plasma source are detected with a high-sensitivity cavity ring-down spectrometer (CRDS). We will present new experimental results that indicate that nanoparticles are generated in the plasma. From these unique measurements, we derive information on the nature, the size and the structure of interstellar dust particles, the growth and the destruction processes of IS dust and the resulting budget of extraterrestrial organic molecules.

The discovery of a new infrared emission feature at 1905 wavenumbers (5.25 microns) in the spectrum of BD +30 degrees 3639 and its relation to the polycyclic aromatic hydrocarbon model

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Bregman, J. D.; Sandford, S. A.; Tielens, A. G.; Witteborn, F. C.; Wooden, D. H.; Rank, D.

1989-01-01

We have discovered a new IR emission feature at 1905 cm-1 (5.25 microns) in the spectrum of BD +30 degrees 3639. This feature joins the family of well-known IR emission features at 3040, 2940, 1750, 1610, "1310," 1160, and 890 cm-1 (3.3, 3.4, 5.7, 6.2, "7.7," 8.6, and 11.2 microns). The origin of this new feature is discussed and it is assigned to an overtone or combination band involving C-H bending modes of polycyclic aromatic hydrocarbons (PAHs). Laboratory work suggests that spectral studies of the 2000-1650 cm-1 (5.0-6.1 microns) region may be very useful in elucidating the molecular structure of interstellar PAHs. The new feature, in conjunction with other recently discovered spectral structure, suggests that the narrow IR emission features originate in PAH molecules rather than large carbon grains. Larger species are likely to be the source of the broad underlying "plateaus" seen in many of the spectra.

67P/Churyumov-Gerasimenko: a portrait of a primitive Solar System body

NASA Astrophysics Data System (ADS)

Capaccioni, Fabrizio; Arnold, Gabriele; Capria, Maria Teresa; Erard, Stéphane; Filacchione, Gianrico; De Sanctis, Maria Cristina; Bockelee-Morvan, Dominique; Raponi, Andrea; Ciarniello, Mauro; Leyrat, Cedric

2016-07-01

Comets harbour the most pristine material in our solar system in the form of ice, dust, silicates, and refractory organic material with interstellar heritage. The observations of the VIRTIS imaging spectrometer [1] onboard the Rosetta orbiter, have revealed a very complex surface showing varied morphologies related to active processes. Water ice at the surface of the nucleus have been identified in several areas as stable deposit [2] as well as diurnal frost [3] and implications for the evolution of the nucleus have been derived. The reflectance spectra collected across the surface display a low reflectance factor over the whole spectral range [4], two spectral slopes in the visible and near-infrared ranges and a broad absorption band centred at 3.2 μm. These spectral features describe a largely dehydrated surface, rich in organic compounds and opaque minerals [5]. The low albedo of comet 67P/CG is described by a dark refractory polyaromatic carbonaceous component mixed with opaque minerals. A semi-volatile component, consisting of a complex mix of low weight molecular species not volatilized at T~220 K, is likely a major carrier of the 3.2 μm band. COOH in carboxylic acids is the only chemical group that encompasses the broad width of this feature. It appears as a highly plausible candidate along with the NH4+ ion. Photolytic/thermal residues, produced in the laboratory from interstellar ice analogs, are potentially good spectral analogs [6]. [1] Coradini et al., SSRev, 128, 2007; [2] Filacchione et al, Nature, 529, 2016; [3] De Sanctis et al, Nature, 525, 2015; [4] Ciarniello et al, A&A, 583, 2015; [5] Capaccioni et al., Science, 347, 2015; [6] Quirico et al., Icarus, in press

The molecular inventory around protostars: water, organic molecules, and the missing oxygen problem

NASA Astrophysics Data System (ADS)

Neufeld, David A.

2018-06-01

Massive star formation is accompanied by significant chemical evolution in the surrounding interstellar gas. Here, grains are heated up and icy mantles evaporate, releasing a rich inventory of water and organic molecules into the gas-phase within “hot core” regions surrounding massive protostars. Because molecules on the grain surface present broad infrared features without rotational structure, only the most abundant molecules can be identified unambiguously in the solid phase; once released into the gas-phase, however, where they are free to rotate, the constituents of grain mantles can be identified easily by means of rotational spectroscopy at millimeter and submillimeter wavelengths or through rovibrational spectroscopy in the mid-infrared. While observations of pure-rotational emission lines provide a broad view of hot core chemistry, absorption line spectroscopy of rovibrational transitions can probe the very hottest material closest to the protostar. With access to the mid-infrared spectral region from above 99% of Earth’s water vapor, SOFIA provides a unique platform for high-resolution rovibrational spectroscopy of water and organic molecules, many of which have vibrational transitions in the 5 – 8 micron spectral region that is unobservable from the ground. High spectral resolution is essential for disentangling the rotational structure and providing reliable measurements of the molecular column densities and temperatures. Future SOFIA observations will help elucidate the inventory of water and organic molecules around young protostars, and can address a puzzle related to the “oxygen budget” in the interstellar medium: surprisingly, the main interstellar reservoirs of the third-most abundant element in the Universe have yet to be identified.

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 coverage in the 2-30 microns region, of lines of sight which sample dust in both dense and diffuse interstellar clouds, in order to uniquely specify the composition of interstellar organics. This paper reviews the information available from ground-based observations, although currently the Infrared Satellite Observatory is adding to our body of knowledge on this subject by providing more extensive wavelength coverage. The Murchison carbonaceous meteorite has also been used as an analog to the interstellar observations and has revealed a striking similarity between the light hydrocarbons in the meteorite and the ISM; therefore this review includes comparisons with the meteoritic analog as well as with relevant laboratory residues. Fundamental to the evolution of the biogenic molecules, to the process of planetary system formation, and perhaps to the origin of life, is the connection between the organic material found in the interstellar medium and that incorporated in the most primitive solar system bodies.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aller, Monique C.; Kulkarni, Varsha P.; Liger, Nicholas

2014-04-10

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

Infrared Spectroscopy of Carbonaceous-chondrite Inclusions in the Kapoeta Meteorite: Discovery of Nanodiamonds with New Spectral Features and Astrophysical Implications

NASA Astrophysics Data System (ADS)

Abdu, Yassir A.; Hawthorne, Frank C.; Varela, Maria E.

2018-03-01

We report the finding of nanodiamonds, coexisting with amorphous carbon, in carbonaceous-chondrite (CC) material from the Kapoeta achondritic meteorite by Fourier-transform infrared (FTIR) spectroscopy and micro-Raman spectroscopy. In the C–H stretching region (3100–2600 cm‑1), the FTIR spectrum of the Kapoeta CC material (KBr pellet) shows bands attributable to aliphatic CH2 and CH3 groups, and is very similar to IR spectra of organic matter in carbonaceous chondrites and the diffuse interstellar medium. Nanodiamonds, as evidenced by micro-Raman spectroscopy, were found in a dark region (∼400 μm in size) in the KBr pellet. Micro-FTIR spectra collected from this region are dramatically different from the KBr-pellet spectrum, and their C–H stretching region is dominated by a strong and broad absorption band centered at ∼2886 cm‑1 (3.47 μm), very similar to that observed in IR absorption spectra of hydrocarbon dust in dense interstellar clouds. Micro-FTIR spectroscopy also indicates the presence of an aldehyde and a nitrile, and both of the molecules are ubiquitous in dense interstellar clouds. In addition, IR peaks in the 1500–800 cm‑1 region are also observed, which may be attributed to different levels of nitrogen aggregation in diamonds. This is the first evidence for the presence of the 3.47 μm interstellar IR band in meteorites. Our results further support the assignment of this band to tertiary CH groups on the surfaces of nanodiamonds. The presence of the above interstellar bands and the absence of shock features in the Kapoeta nanodiamonds, as indicated by Raman spectroscopy, suggest formation by a nebular-condensation process similar to chemical-vapor deposition.

Modern Progress and Modern Problems in High Resolution X-ray Absorption from the Cold Interstellar Medium

NASA Astrophysics Data System (ADS)

Corrales, Lia; Li, Haochuan; Heinz, Sebastian

2018-01-01

With accurate cross-sections and higher signal-to-noise, X-ray spectroscopy can directly measure Milky Way gas and dust-phase metal abundances with few underlying assumptions. The X-ray energy band is sensitive to absorption by all abundant interstellar metals — carbon, oxygen, neon, silicon, magnesium, and iron — whether they are in gas or dust form. High resolution X-ray spectra from Galactic X-ray point sources can be used to directly measure metal abundances from all phases of the interstellar medium (ISM) along singular sight lines. We show our progress for measuring the depth of photoelectric absorption edges from neutral ISM metals, using all the observations of bright Galactic X-ray binaries available in the Chandra HETG archive. The cross-sections we use take into account both the absorption and scattering effects by interstellar dust grains on the iron and silicate spectral features. However, there are many open problems for reconciling X-ray absorption spectroscopy with ISM observations in other wavelengths. We will review the state of the field, lab measurements needed, and ways in which the next generation of X-ray telescopes will contribute.

Large Interstellar Polarisation Survey (LIPS). I. FORS2 spectropolarimetry in the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Bagnulo, Stefano; Cox, Nick L. J.; Cikota, Aleksandar; Siebenmorgen, Ralf; Voshchinnikov, Nikolai V.; Patat, Ferdinando; Smith, Keith T.; Smoker, Jonathan V.; Taubenberger, Stefan; Kaper, Lex; Cami, Jan; LIPS Collaboration

2017-12-01

Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope. Our spectra cover the wavelength range 380-950 nm at a spectral resolving power of about 880. We have produced a publicly available catalogue of 127 linear polarisation spectra of 101 targets. We also provide the Serkowski-curve parameters, as well as the wavelength gradient of the polarisation position angle for the interstellar polarisation along 76 different lines of sight. In agreement with previous literature, we found that the best-fit parameters of the Serkowski-curve are not independent of each other. However, the relationships that we obtained are not always consistent with what has been found in previous studies. Table 2 and reduced data are 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/608/A146

Near Infrared Emission of Highly Electronically Excited CO: A Sensitive Probe to Study the Interstellar Medium??

NASA Technical Reports Server (NTRS)

Gudipati, Murthy S.

2002-01-01

Among the various spectroscopic features of the second most abundant molecule in the space, CO, "the triplet - triplet transitions involving the lowest triplet state a(sup 3)II and the higher-lying a(sup 1)3 SIGMA (sup +), d(sup 3) (DELTA), e (sup 3) SIGMA (sup -) states spanning near-UV to mid-IR spectral range" have so far not been explored in astrophysical observations. The energies of these transitions are highly sensitive to the surroundings in which CO exists, i.e. gas-phase, polar or non-polar condensed phase. It is proposed here that these triplet-triplet emission/absorption bands can be used as a sensitive probe to investigate the local environments of CO, whether in the planetary atmosphere, stellar atmosphere or interstellar medium.

Fullerenes in Space.

PubMed

Maier, John P; Campbell, Ewen K

2017-04-24

In 1985 the football structure of C 60 , buckminsterfullerene was proposed and subsequently confirmed following its macroscopic synthesis in 1990. From the very beginning the role of C 60 and C 60 + in space was considered, particularly in the context of the enigmatic diffuse interstellar bands. These are absorption features found in the spectra of reddened star light. The first astronomical observations were made around one hundred years ago and despite significant efforts none of the interstellar molecules responsible have been identified. The absorption spectrum of C 60 + was measured in a 5 K neon matrix in 1993 and two prominent bands near 9583 Å and 9645 Å were observed. On the basis of this data the likely wavelength range in which the gas phase C 60 + absorptions should lie was predicted. In 1994 two diffuse interstellar bands were found in this spectral region and proposed to be due to C 60 + . It took over 20 years to measure the absorption spectrum of C 60 + under conditions similar to those prevailing in diffuse clouds. In 2015, sophisticated laboratory experiments led to the confirmation that these two interstellar bands are indeed caused by C 60 + , providing the first answer to this century old puzzle. Here, we describe the experiments, concepts and astronomical observations that led to the detection of C 60 + in interstellar space. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Spectral observations of the extreme ultraviolet background.

PubMed

Labov, S E; Bowyer, S

1991-04-20

A grazing incidence spectrometer was designed to measure the diffuse extreme ultraviolet background. It was flown on a sounding rocket, and data were obtained on the diffuse background between 80 and 650 angstroms. These are the first spectral measurements of this background below 520 angstroms. Several emission features were detected, including interplanetary He I 584 angstroms emission and geocoronal He II 304 angstroms emission. Other features observed may originate in a hot ionized interstellar gas, but if this interpretation is correct, gas at several different temperatures is present. The strongest of these features is consistent with O V emission at 630 angstroms. This emission, when combined with upper limits for other lines, restricts the temperature of this component to 5.5 < log T < 5.7, in agreement with temperatures derived from O VI absorption studies. A power-law distribution of temperatures is consistent with this feature only if the power-law coefficient is negative, as is predicted for saturated evaporation of clouds in a hot medium. In this case, the O VI absorption data confine the filling factor of the emission of f < or = 4% and the pressure to more than 3.7 x 10(4) cm-3 K, substantially above ambient interstellar pressure. Such a pressure enhancement has been predicted for clouds undergoing saturated evaporation. Alternatively, if the O V emission covers a considerable fraction of the sky, it would be a major source of ionization. A feature centered at about 99 angstroms is well fitted by a cluster of Fe XVIII and Fe XIX lines from gas at log T = 6.6-6.8. These results are consistent with previous soft X-ray observations with low-resolution detectors. A feature found near 178 angstroms is consistent with Fe X and Fe XI emission from gas at log T = 6; this result is consistent with results from experiments employing broad-band soft X-ray detectors.

The 3.4 micron emission in comets

NASA Technical Reports Server (NTRS)

Brooke, Tim Y.; Knacke, Roger F.; Owen, T. C.; Tokunaga, Alan T.

1989-01-01

Emission features near 3.4 microns were detected in comet Bradfield (1987s) on 17 Nov. 1987 UT, and, marginally, on two earlier dates, with the Cooled Grating Array Spectrometer at the NASA Infrared Radio Telescope Facility (IRTF) (Brooke et al., 1988b). The central wavelength (3.36 microns) and width (approx. 0.15 microns) of the strongest feature coincide with those observed in comet Halley. A weaker emission feature at 3.52 microns and a strong feature extending shortward of 2.9 microns were also detected. This brings the number of comets in which these three features have been seen to three, two new (Bradfield, Wilson) and one old (Halley). It seems almost certain that the 3.4 micron features are emissions by C-H groups in complex molecules. Based on the similarity of the 3.4 micron features in comets Halley and Wilson, the authors suggest that a particular set of organic compounds may be common to all comets (Brooke et al. 1988a). The absence of the feature in some comets could then be due to photodestruction or evaporation of the organics when the comet approaches the sun, in combination with a predominance of thermal emission from non C-H emitting grains. Detection of the 3.4 micron emission feature in comet Bradfield at 4 = 0.9 AU provides support for this argument. Complex organics in comets could have been formed by particle irradiation of parent ices in the nucleus or been incorporated as grains at the time the comets formed. Since the most heavily irradiated layers of Halley would have been lost in its hundreds of perihelion passages, the authors believe the more likely explanation is that the 3.4 micron emitting material was incorporated in comet nuclei at the time of formation. The 3.4 micron comet feature resembles, but is not identical to, the interstellar 3.29 micron (and longer wavelength) emission features and the broad 3.4 micron feature seen in absorption toward the Galactic center. Detailed comparisons of cometary and interstellar organics will require comet spectra with signal-to-noise and spectral resolution comparable to that available in spectra of the interstellar medium. Such observations are currently being planned.

(F)UV Spectral Analysis of Hot, Hydrogen-Rich Central Stars of Planetary Nebulae

NASA Astrophysics Data System (ADS)

Ziegler, M.; Rauch, T.; Werner, K.; Kruk, J. W.

2010-11-01

Metal abundances of CSPNe are not well known although they provide important constraints on AGB nucleosynthesis. We aim to determine metal abundances of two hot, hydrogen-rich CSPNe (namely of A35 and NGC3587, the latter also known as M97 or the Owl Nebula) and to derive Teff and log g precisely from high-resolution, high-S/N (far-) ultraviolet observations obtained with FUSE and HST/STIS. For this purpose, we utilize NLTE model atmospheres calculated with TMAP, the Tübingen Model Atmosphere Package. Due to strong line absorption of the ISM, simultaneous modeling of interstellar features has become a standard tool in our analyses. We present preliminary results, demonstrating the importance of combining stellar and interstellar models, in order to clearly identify and measure the strengths of strategic photospheric lines.

New Infrared Emission Features and Spectral Variations in Ngc 7023

NASA Technical Reports Server (NTRS)

Werner, M. W.; Uchida, K. I.; Sellgren, K.; Marengo, M.; Gordon, K. D.; Morris, P. W.; Houck, J. R.; Stansberry, J. A.

2004-01-01

We observed the reflection nebula NGC 7023, with the Short-High module and the long-slit Short-Low and Long-Low modules of the Infrared Spectrograph on the Spitzer Space Telescope. We also present Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) images of NGC 7023 at 3.6, 4.5, 8.0, and 24 m. We observe the aromatic emission features (AEFs) at 6.2, 7.7, 8.6, 11.3, and 12.7 m, plus a wealth of weaker features. We find new unidentified interstellar emission features at 6.7, 10.1, 15.8, 17.4, and 19.0 m. Possible identifications include aromatic hydrocarbons or nanoparticles of unknown mineralogy. We see variations in relative feature strengths, central wavelengths, and feature widths, in the AEFs and weaker emission features, depending on both distance from the star and nebular position (southeast vs. northwest).

INTERPRETATION OF THE STRUCTURE FUNCTION OF ROTATION MEASURE IN THE INTERSTELLAR MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Siyao; Zhang, Bing, E-mail: syxu@pku.edu.cn, E-mail: zhang@physics.unlv.edu

2016-06-20

The observed structure function (SF) of rotation measure (RM) varies as a broken power-law function of angular scales. The systematic shallowness of its spectral slope is inconsistent with the standard Kolmogorov scaling. This motivates us to examine the statistical analysis on RM fluctuations. The correlations of RM constructed by Lazarian and Pogosyan are demonstrated to be adequate in explaining the observed features of RM SFs through a direct comparison between the theoretically obtained and observationally measured SF results. By segregating the density and magnetic field fluctuations and adopting arbitrary indices for their respective power spectra, we find that when themore » SFs of RM and emission measure have a similar form over the same range of angular scales, the statistics of the RM fluctuations reflect the properties of density fluctuations. RM SFs can be used to evaluate the mean magnetic field along the line of sight, but cannot serve as an informative source on the properties of turbulent magnetic field in the interstellar medium. We identify the spectral break of RM SFs as the inner scale of a shallow spectrum of electron density fluctuations, which characterizes the typical size of discrete electron density structures in the observed region.« less

The Atacama Large Millimeter/submillimeter Array (alma): Early Results

NASA Astrophysics Data System (ADS)

Wootten, Alwyn

2012-06-01

New radioastronomical instruments, such as ALMA or the Jansky VLA, have increased spectral throughput by orders of magnitude over previously available capabilities. ALMA brings orders of magnitude increases in spectral sensitivity and spatial resolution over what has previously been available. These increased capabilities open new possibilities for studies of complex molecules in the interstellar medium. Complex interstellar molecules may form on the surfaces of interstellar grains, after which they may be liberated into the gas phase by shocks, radiation, or other external influences. Emission from complex molecules may be diluted owing to the large number of transitions large molecules may undergo, particularly in warm regions of interstellar clouds. High sensitivity and spatial resolution are necessary to explore the distributions and relationships of these molecules. Of particular interest are the distributions of large organic molecules. Observations which establish the relationships between various large molecules are now emerging from these new instruments and will be discussed.

Deep, Broadband Spectral Line Surveys of Molecule-rich Interstellar Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Widicus Weaver, Susanna L.; Laas, Jacob C.; Zou, Luyao

2017-09-01

Spectral line surveys are an indispensable tool for exploring the physical and chemical evolution of astrophysical environments due to the vast amount of data that can be obtained in a relatively short amount of time. We present deep, broadband spectral line surveys of 30 interstellar clouds using two broadband λ  = 1.3 mm receivers at the Caltech Submillimeter Observatory. This information can be used to probe the influence of physical environment on molecular complexity. We observed a wide variety of sources to examine the relative abundances of organic molecules as they relate to the physical properties of the source (i.e., temperature,more » density, dynamics, etc.). The spectra are highly sensitive, with noise levels ≤25 mK at a velocity resolution of ∼0.35 km s{sup −1}. In the initial analysis presented here, column densities and rotational temperatures have been determined for the molecular species that contribute significantly to the spectral line density in this wavelength regime. We present these results and discuss their implications for complex molecule formation in the interstellar medium.« less

Interstellar molecules and dense clouds.

NASA Technical Reports Server (NTRS)

Rank, D. M.; Townes, C. H.; Welch, W. J.

1971-01-01

Current knowledge of the interstellar medium is discussed on the basis of recent published studies. The subjects considered include optical identification of interstellar molecules, radio molecular lines, interstellar clouds, isotopic abundances, formation and disappearance of interstellar molecules, and interstellar probing techniques. Diagrams are plotted for the distribution of galactic sources exhibiting molecular lines, for hydrogen molecule, hydrogen atom and electron abundances due to ionization, for the densities, velocities and temperature of NH3 in the direction of Sagitarius B2, for the lower rotational energy levels of H2CO, and for temporal spectral variations in masing H2O clouds of the radio source W49. Future applications of the maser and of molecular microscopy in this field are visualized.

Peripherally hydrogenated neutral polycyclic aromatic hydrocarbons as carriers of the 3 micron interstellar infrared emission complex: results from single-photon infrared emission spectroscopy

NASA Technical Reports Server (NTRS)

Wagner, D. R.; Kim, H. S.; Saykally, R. J.

2000-01-01

Infrared emission spectra of five gas-phase UV laser-excited polycyclic aromatic hydrocarbons (PAHs) containing aliphatic hydrogens are compared with the main 3.3 microns and associated interstellar unidentified infrared emission bands (UIRs). We show that neutral PAHs can account for the majority of the 3 microns emission complex while making little contribution to the other UIR bands; peripherally hydrogenated PAHs produce a better match to astrophysical data than do those containing methyl side groups; 3.4 microns plateau emission is shown to be a general spectral feature of vibrationally excited PAHs containing aliphatic hydrogens, especially those containing methyl groups; and finally, hot-band and overtone emissions arising from aromatic C-H vibrations are not observed in laboratory emission spectra, and therefore, in contrast to current assignments, are not expected to be observed in the UIRs.

VizieR Online Data Catalog: DIB and NaD spectra of 3 nearby stars (Kohl+, 2016)

NASA Astrophysics Data System (ADS)

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

2016-05-01

The present data collection contains coadded spectra of tau Boo, HD 33608 and alpha CrB. This data was used to obtain the equivalent widths of interstellar features. The spectra show the wavelength regions around the Na D lines and around 5780Å. The latter location corresponds to a wavelength range where a strong diffuse interstellar band (DIB) is found in the spectrum of the early-type supergiant HD 183143. Each single spectrum has been corrected for telluric absorption and the wavelength axis has been shifted to the barycentric reference frame. However, the data has not been corrected for radial velocity of the star. The spectra have been acquired at the 1.2m Tigre telescope located in La Luz, Mexico. The spectral resolution of the HEROS spectrograph is 20000. A detailed description of the spectra is given in the aforementioned paper. (2 data files).

Spectral Deconvolution of the 6196 and 6614 Å Diffuse Interstellar Bands Supports a Common-carrier Origin

NASA Astrophysics Data System (ADS)

Bernstein, L. S.; Shroll, R. M.; Galazutdinov, G. A.; Beletsky, Y.

2018-06-01

We explore the common-carrier hypothesis for the 6196 and 6614 Å diffuse interstellar bands (DIBs). The observed DIB spectra are sharpened using a spectral deconvolution algorithm. This reveals finer spectral features that provide tighter constraints on candidate carriers. We analyze a deconvolved λ6614 DIB spectrum and derive spectroscopic constants that are then used to model the λ6196 spectra. The common-carrier spectroscopic constants enable quantitative fits to the contrasting λ6196 and λ6614 spectra from two sightlines. Highlights of our analysis include (1) sharp cutoffs for the maximum values of the rotational quantum numbers, J max = K max, (2) the λ6614 DIB consisting of a doublet and a red-tail component arising from different carriers, (3) the λ6614 doublet and λ6196 DIBs sharing a common carrier, (4) the contrasting shapes of the λ6614 doublet and λ6196 DIBs arising from different vibration–rotation Coriolis coupling constants that originate from transitions from a common ground state to different upper electronic state degenerate vibrational levels, and (5) the different widths of the two DIBs arising from different effective rotational temperatures associated with principal rotational axes that are parallel and perpendicular to the highest-order symmetry axis. The analysis results suggest a puckered oblate symmetric top carrier with a dipole moment aligned with the highest-order symmetry axis. An example candidate carrier consistent with these specifications is corannulene (C20H10), or one of its symmetric ionic or dehydrogenated forms, whose rotational constants are comparable to those obtained from spectral modeling of the DIB profiles.

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.

High Spectral Resolution Observation of the Soft Diffuse X-ray Background in the Direction of the Galactic Anti-Center

NASA Astrophysics Data System (ADS)

Wulf, Dallas; Eckart, Mega E.; Galeazzi, Massimiliano; Jaeckel, Felix; Kelley, Richard L.; Kilbourne, Caroline A.; McCammon, Dan; Morgan, Kelsey M.; Porter, Frederick S.; Szymkowiak, Andrew E.

2018-01-01

High spectral resolution observations in the soft x-rays are necessary for understanding and modelling the hot component of the interstellar medium and its contribution to the Soft X-ray Background (SXRB). This extended source emission cannot be resolved with most wavelength dispersive spectrometers, making energy dispersive microcalorimeters the ideal choice for these observations. We present here the analysis of the most recent sounding rocket flight of the University of Wisconsin-Madison/Goddard Space Flight Center X-ray Quantum Calorimeter (XQC), a large area silicon thermistor microcalorimeter. This 111 second observation integrates a nearly 1 steradian field of view in the direction of the galactic anti-center (l, b = 165°, -5°) and features ~5 eV spectral resolution below 1 keV. Direct comparison will also be made to the previous, high-latitude observations.

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.

UV photoabsorption cross sections of CO, N2, and SO2 for studies of the ISM and planetary atmospheres

NASA Technical Reports Server (NTRS)

Smith, Peter L.; Rufus, J.; Yoshino, K.; Parkinson, W. H.; Stark, Glenn; Pickering, Juliet C.; Thorne, A. P.

2002-01-01

We report high-resolution laboratory measurements of photoabsorption cross sections of CO, N2, and SO2 in the wavelength range 80 to 320 nm. The motivation is to provide the quantitative data that are needed to analyze observations of absorption by, and to model photochemical processes in, the interstellar medium and a number of planetary atmospheres. Because of the high resolution of the spectrometers used, we can minimize distortion of the spectrum that occurs when instrument widths are greater than the widths of spectral features being measured. In many cases, we can determine oscillator strengths of individual rotational lines - a unique feature of our work.

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

NASA Astrophysics Data System (ADS)

White, Douglas W.

2010-09-01

Solid CO2 has been detected in many lines of sight in the interstellar medium from infrared observatories. Spectral profiles from space-based observatories have suggested that CO2 on icy grain mantles is mixed with other common molecules such as H2O and CH 3OH in interstellar regions and that thermal annealing has occurred. The vibrational mode at 658 cm-1 (15.2 mum) is suspected to be a powerful diagnostic tool as to the composition of species on icy grain mantles as well as thermal histories. However, previous studies have not systematically investigated ice composition and temperature. Laboratory spectra of interstellar ice analogs have been created in this study order to better understand the physical properties of solid CO2 in these interstellar environments. Existing databases of ice composition studies and effects of ice thermal history were updated in this study to include a more systematic approach. The 658 cm-1 (15.2 mum) bending mode feature of CO2 is examined here and the subsequent astrophysical implications stated. In the first set of experiments, 47 mixtures of H2O,CH3OH, andCO2 were slowly warmed and mid-infrared absorption spectra were recorded at 5K intervals. The second set of experiments involved examining the CO2 bending mode feature of 10 different CO2-containing ice mixtures at different temperatures where ice segregation was suspected. In these experiments, the ice mixtures were slowly heated to the desired temperature for increasing time intervals before cooling down and recording mid-IR absorption spectra. These studies may be used to analyze IR data from space-based observatories such as the Spitzer Space Telescope Infrared Spectrograph as well other future IR observations of the interstellar medium. Finally, mass spectroscopy measurements were taken from temperature programmed desorption (TPD) experiments performed on several binary mixtures of H2O + CO2 and CH 3OH + CO2. Physical properties such as desorption energy of CO2 can be determined from the TPD traces of these experiments. The work provided here addresses the physical properties of solid CO 2 thermally processed in ice mixtures in interstellar environments by laboratory simulations spectroscopically analyzed by mid-infrared absorption profiles and TPD.

Detection of interstellar sodium hydroxide in self-absorption toward the galactic center

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Rhodes, P. J.

1982-01-01

A weak self-absorbed emission line, which is identified as the J = 4-3 transition of sodium hydroxide, has been detected in the direction of Sgr B2(OH). The correspondingly weak Sgr B2(QH) emission line U75406, previously reported as an unidentified spectral feature by other investigators, is consistent with the J = 3-2 transition of sodium hydroxide. This detection may represent the first evidence of a grain reaction formation mechanism for simple metal hydroxides. The detection of H62 Delta toward Orion A is also reported.

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.

Aliphatic Hydrocarbon Content of Interstellar Dust

NASA Astrophysics Data System (ADS)

Günay, B.; Schmidt, T. W.; Burton, M. G.; Afşar, M.; Krechkivska, O.; Nauta, K.; Kable, S. H.; Rawal, A.

2018-06-01

There is considerable uncertainty as to the amount of carbon incorporated in interstellar dust. The aliphatic component of the carbonaceous dust is of particular interest because it produces a significant 3.4 μm absorption feature when viewed against a background radiation source. The optical depth of the 3.4 μm absorption feature is related to the number of aliphatic carbon C-H bonds along the line of sight. It is possible to estimate the column density of carbon locked up in the aliphatic hydrocarbon component of interstellar dust from quantitative analysis of the 3.4 μm interstellar absorption feature providing that the absorption coefficient of aliphatic hydrocarbons incorporated in the interstellar dust is known. We report laboratory analogues of interstellar dust by experimentally mimicking interstellar/circumstellar conditions. The resultant spectra of these dust analogues closely match those from astronomical observations. Measurements of the absorption coefficient of aliphatic hydrocarbons incorporated in the analogues were carried out by a procedure combining FTIR and 13C NMR spectroscopies. The absorption coefficients obtained for both interstellar analogues were found to be in close agreement (4.76(8) × 10-18 cm group-1 and 4.69(14) × 10-18 cm group-1), less than half those obtained in studies using small aliphatic molecules. The results thus obtained permit direct calibration of the astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the interstellar medium.

HST/STIS Observations of the Local Interstellar Medium toward Very Nearby Stars: A Detailed Analysis of the a Centuari Sight Line

NASA Astrophysics Data System (ADS)

Dann, Julian; Redfield, Seth; Ayres, Thomas R.

2017-01-01

The Local Interstellar Medium (LISM), a region extending about 100 parsecs and in which the Sun is currently immersed, can only be studied using UV/optical absorption features against bright background stars. Perhaps in the future in-situ measurements will be possible (e.g., the Voyager spacecraft or Breakthrough Starshot-style missions). Using high-resolution observations with the Space Telescope Imaging Spectrograph (STIS) on-board the Hubble Space Telescope (HST), we have analyzed several very nearby sight lines to measure physical properties of the LISM. The data used in this study is a part of the Advanced Spectral Library (ASTRAL) Project, an HST Large Treasury Project, in which we have analyzed the spectra of fourteen nearby stars. LISM absorption features in these stellar spectra reveal key information about the abundances, temperature, and turbulence in the intervening gas. We have fit ion transitions in the near-UV for MgII, FeII, CII, DI, SiII, and OII. These absorption features provide direct measurements of the radial velocity, Doppler broadening parameter, and the column density along the line of sight. The presence of multiple local minima in the deep and narrow ISM profile is evidence of multiple clouds moving at different radial velocities.Included in our data set is the a Centauri sight line. We provide a detailed analysis of these new observations and a comparison with previous HST observations that were observed more than 20 years ago. A discussion of the physical properties along this line of sight is provided within the context of a Breakthrough Starshot mission. These high resolution and high signal-to-noise spectra will be important for making accurate estimations of the interstellar environment to help inform such an interstellar mission.We would like to acknowledge NASA HST Grant GO-12278 and GO-13346 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555, and a student fellowship from the Connecticut Space Grant Consortium for their support of this research.

Laboratory experiments on carbonaceous material as a source for the red rectangle visual emissions

NASA Technical Reports Server (NTRS)

Wdowiak, Thomas J.; Donn, Bertram; Nuth, Joseph A.; Chappelle, Emmett; Moore, Marla

1989-01-01

The authors subjected mixtures of CO, Ar, N2, H2O, and CH4 with 42 percent and 8 percent argon to an electrical discharge, froze out the reaction products at T about 20 K, and subsequently warmed the sample to room temperature. This resulted in a stable residue having broad-band fluorescence. It is suggested tht interstellar grains in the Red Rectangle/HD 44179 are coated with a residue of generally similar composition that is responsible for the broad emission feature in the 5400-7500 A spectral region.

Polycyclic aromatic hydrocarbons in stellar medium

NASA Astrophysics Data System (ADS)

Rastogi, Shantanu

2005-06-01

Polycyclic Aromatic Hydrocarbons (PAHs) are an important com- ponent of the Interstellar Medium (ISM). They are being used as probes for understanding of process and conditions of different astrophysical environments. The understanding of their IR spectra and its variations with PAH size and ionization state is useful in characterizing the ISM. Spectral features of model graphene sheets and also that of smaller PAH molecules are reported. The variation of intensity with charge state of the molecule shows that cations give a better correlation with observations. The relationship between changes in charge distribution with intensity changes upon ionization has been probed.

The Computational Science Education Reference Desk: A tool for increasing inquiry based learning in the science classroom

NASA Astrophysics Data System (ADS)

Joiner, D. A.; Stevenson, D. E.; Panoff, R. M.

2000-12-01

The Computational Science Reference Desk is an online tool designed to provide educators in math, physics, astronomy, biology, chemistry, and engineering with information on how to use computational science to enhance inquiry based learning in the undergraduate and pre college classroom. The Reference Desk features a showcase of original content exploration activities, including lesson plans and background materials; a catalog of websites which contain models, lesson plans, software, and instructional resources; and a forum to allow educators to communicate their ideas. Many of the recent advances in astronomy rely on the use of computer simulation, and tools are being developed by CSERD to allow students to experiment with some of the models that have guided scientific discovery. One of these models allows students to study how scientists use spectral information to determine the makeup of the interstellar medium by modeling the interstellar extinction curve using spherical grains of silicate, amorphous carbon, or graphite. Students can directly compare their model to the average interstellar extinction curve, and experiment with how small changes in their model alter the shape of the interstellar extinction curve. A simpler model allows students to visualize spatial relationships between the Earth, Moon, and Sun to understand the cause of the phases of the moon. A report on the usefulness of these models in two classes, the Computational Astrophysics workshop at The Shodor Education Foundation and the Conceptual Astronomy class at the University of North Carolina at Greensboro, will be presented.

Interstellar Deuterium, Nitrogen and Oxygen Abundances Toward BD+28(deg) 4211: Results from the Far Ultraviolet Spectroscopic Explorer

NASA Technical Reports Server (NTRS)

Sonneborn, George; Andre, Martial; Oliveira, Cristina; Hebrard, Guillaume; Howk, J. Christopher; Tripp, Todd M.; Chayer, Pierre; Friedman, Scott D.; Kruk, Jeffery W.; Jenkins, Edward B.;

A search for interstellar nitrous oxide

NASA Technical Reports Server (NTRS)

Wilson, W. J.; Snyder, L. E.

1981-01-01

An extensive search for interstellar nitrous oxide (N2O) has been made at two different frequencies, 75.4 and 100.5 GHz, in a number of molecular sources. No N2O signal was detected; however, a number of other spectral lines including two new transitions of methyl formate and several new unidentified lines were measured.

Focused Study of Thermonuclear Bursts on Neutron Stars

NASA Astrophysics Data System (ADS)

Chenevez, Jérôme

2009-05-01

X-ray bursters form a class of Low Mass X-Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric radius expansion bursts likely eject nuclear burning ashes into the interstellar medium, and may make possible the detection of photoionization edges. Indeed, theoretical models predict that absorption edges from 58Fe at 9.2 keV, 60Zn and 62Zn at 12.2 keV should be detectable by the future missions Simbol-X and NuSTAR. A positive detection would thus probe the nuclear burning as well as the gravitational redshift from the neutron star. Moreover, likely observations of atomic X-ray spectral components reflected from the inner accretion disk have been reported. The high spectral resolution capabilities of the focusing X-ray telescopes may therefore make possible to differentiate between the potential interpretations of the X-ray bursts spectral features.

Spectroscopy of prospective interstellar ions and radicals isolated in para-hydrogen matrices.

PubMed

Tsuge, Masashi; Tseng, Chih-Yu; Lee, Yuan-Pern

2018-02-21

para-Hydrogen (p-H 2 ) serves as a new host in matrix-isolation experiments for an investigation of species of astrochemical interest. Protonated and mono-hydrogenated species are produced upon electron bombardment during deposition of p-H 2 containing a precursor in a small proportion. The applications of this novel technique to generate protonated polycyclic aromatic hydrocarbons (H + PAH), protonated polycyclic nitrogen heterocycles (H + PANH), and their neutral counterparts, which are important in the identification of interstellar unidentified infrared emission bands, demonstrate its superiority over other methods. The clean production with little fragmentation, ease of distinction between protonated and neutral species, narrow lines and reliable relative infrared intensities of the lines, and broad coverage of the spectral range associated with this method enable us to assign the isomers unambiguously. The application of this method to the protonation of small molecules is more complicated partly because of the feasible fragmentation and reactions, and partly because of the possible proton sharing between the species of interest and H 2 , but, with isotopic experiments and secondary photolysis, definitive assignments are practicable. Furthermore, the true relative infrared intensities are critical to a comparison of experimental results with data from theoretical calculations. The spectra of a proton-shared species in solid p-H 2 might provide insight into a search for spectra of proton-bound species in interstellar media. Investigations of hydrogenated species involving the photolysis of Cl 2 or precursors of OH complement those using electron bombardment and provide an improved ratio of signal to noise. With careful grouping of observed lines after secondary photolysis and a comparison with theoretical predictions, various isomers of these species have been determined. This photolytic technique has been applied in an investigation of hydrogenated PAH and PANH, and the hydrogenation reactions of small molecules, which are important in interstellar ice and the evolution of life. The electronic transitions of molecules in solid p-H 2 have been little investigated. The matrix shift of the origins of transitions and the spectral width seem to be much smaller than those of noble-gas matrices; these features might facilitate a direct comparison of matrix spectra with diffuse interstellar bands, but further data are required to assess this possibility. The advantages and disadvantages of applying these techniques of p-H 2 matrix isolation to astrochemical research and their future perspectives are discussed.

Interstellar PAH Emission in the 11-14 micron Region: New Insights and a Tracer of Ionized PAHs

NASA Technical Reports Server (NTRS)

Hudgins, Douglas M.; Allamandola, Louis J.; Mead, Susan (Technical Monitor)

1999-01-01

The Ames infrared spectral database of isolated, neutral and ionized polycyclic aromatic hydrocarbons (PAHs) shows that aromatic CH out-of-plane bending frequencies are significantly shifted upon ionization. For non-adjacent and doubly-adjacent CH groups, the shift is pronounced and consistently toward higher frequencies. The non-adjacent modes are blueshifted by an average of 27 per cm and the doubly-adjacent modes by an average of 17 per cm. For triply- and quadruply-adjacent CH out-of-plane modes the ionization shifts are more erratic and typically more modest. As a result of these ionization shifts, both the non-adjacent and doubly-adjacent CH out-of-plane modes move out of the regions classically associated with their respective vibrations in neutral PAHs. The doubly-adjacent modes of ionized PAHs tend to fall into the frequency range traditionally associated with the non-adjacent modes, while the non-adjacent modes are shifted to frequencies above those normally attributed to out-of-plane bending vibrations. Consequently, the origin of the interstellar infrared emission feature near 11.2 microns, traditionally attributed to the out-of-plane bending of non-adjacent CH groups on PAHs is rendered ambiguous. Instead, this feature likely reflects contributions from both non-adjacent CH units in neutral PAHs and doubly-adjacent CH units in PAH cations, the dominant charge state in the most energetic emission regions. This greatly relieves the structural constraints placed on the interstellar PAH population by the dominance of the 11.2 micron band in this region and eliminates the necessity to invoke extensive dehydrogenation of the emitting species. Furthermore, these results indicate that the emission between 926 and 904 per cm (10.8 and 11.1 microns) observed in many sources can be unambiguously attributed to the non-adjacent CH out-of-plane bending modes of moderately-sized (fewer than 50 carbon atom) PAH cations making this emission an unequivocal tracer of ionized interstellar PAHs.

Characterizing the Interstellar and Circumgalactic Medium in Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Du, Xinnan; Shapley, Alice; Crystal Martin, Alison Coil, Charles Steidel, Tucker Jones, Daniel Stark, Allison Strom

2018-01-01

Rest-frame UV and optical spectroscopy provide valuable information on the physical properties of the neutral and ionized interstellar medium (ISM) in star-forming galaxies, including both the systemic interstellar component originating from HII regions, and the multi-phase outflowing component associated with star-formation feedback. My thesis focuses on both the systemic and outflowing ISM in star-forming galaxies at redshift z ~ 1-4. With an unprecedented sample at z~1 with the rest-frame near-UV coverage, we examined how the kinematics of the warm and cool phrases of gas, probed by the interstellar CIV and low-ionization features, respectively, relate to each other. The spectral properties of CIV strongly correlate with the current star-formation rate, indicating a distinct nature of highly-ionized outflowing gas being driven by massive star formation. Additionally, we used the same set of z~1 galaxies to study the properties of the systemic ISM in HII regions by analyzing the nebular CIII] emission. CIII] emission tends to be stronger in lower-mass, bluer, and fainter galaxies with lower metallicity, suggesting that the strong CIII] emitters at lower redshifts can be ideal analogs of young, bursty galaxies at z > 6, which are possibly responsible for reionizing the universe. We are currently investigating the redshift evolution of the neutral, circumgalactic gas in a sample of ~1100 Lyman Break Galaxies at z ~ 2-4. The negative correlation between Lya emission and low-ionization interstellar absorption line strengths appears to be universal across different redshifts, but the fine-structure line emitting regions are found to be more compact for higher-redshift galaxies. With the detailed observational constraints provided by the rest-UV and rest-optical spectroscopy, our study sheds light on how the interstellar and circumgalactic gas components and different phases of gas connect to each other, and therefore provides a comprehensive picture of the overall physical environment in typical star-forming galaxies.

The XMM-Newton View of Wolf-Rayet Bubbles

NASA Astrophysics Data System (ADS)

Guerrero, M.; Toala, J.

2017-10-01

The powerful stellar winds of Wolf-Rayet (WR) stars blow large bubble into the circumstellar material ejected in previous phases of stellar evolution. The shock of those stellar winds produces X-ray-emitting hot plasmas which tells us about the diffusion of processed material onto the interstellar medium, about processes of heat conduction and turbulent mixing at the interface, about the late stages of stellar evolution, and about the shaping of the circumstellar environment, just before supernova explosions. The unique sensitivity of XMM-Newton has been key for the detection, mapping and spectral analysis of the X-ray emission from the hot bubbles around WR stars. These observations underscore the importance of the structure of the interstellar medium around massive stars, but they have also unveiled unknown phenomena, such as blowouts of hot gas into the interstellar medium or spatially-resolved spectral properties of the hot gas, which disclose inhomogeneous chemical abundances and physical properties across these bubbles.

Laboratory absorption spectra of molecules at interstellar cloud temperatures - First measurements on CO at about 97 nm

NASA Technical Reports Server (NTRS)

Smith, P. L.; Yoshino, K.; Stark, G.; Ito, K.; Stevens, M. H.

1991-01-01

In the 91-100 nm spectral region, where absorption of photons by interstellar CO usually leads to dissociation, laboratory spectra obtained at 295 K show that most CO bands are both overlapped and perturbed. Reliable band oscillator strengths cannot be extracted from such spectra. As a consequence, synthetic extreme-ultraviolet absorption spectra for CO at the low temperatures that prevail in interstellar clouds are uncertain. A supersonic expansion technique has been used to cool CO to 30 K and three bands in the 97-nm region have been studied with high spectral resolution. The measured spectrum at 30 K is in reasonable agreement with some published modeled spectra, but the ratios of integrated cross sections are somewhat different from those determined from low resolution spectra obtained at 295 K, in which the bands are blended.

The Laboratory Production of Complex Organic Molecules in Simulated Interstellar Ices

NASA Technical Reports Server (NTRS)

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

2002-01-01

Much of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. Their low temperatures preclude most chemical reactions, but ionizing radiation can drive reactions that produce a suite of new species, many of which are complex organics. The Astrochemistry Lab at NASA Ames studies the UV radiation processing of interstellar ice analogs to better identify the resulting products and establish links between interstellar chemistry, the organics in meteorites, and the origin of life on Earth. Once identified, the spectral properties of the products can be quantified to assist with the search for these species in space. Of particular interest are findings that UV irradiation of interstellar ice analogs produces molecules of importance in current living organisms, including quinones, amphiphiles, and amino acids.

The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES)

NASA Astrophysics Data System (ADS)

Cami, J.; Cox, N. L.; Farhang, A.; Smoker, J.; Elyajouri, M.; Lallement, R.; Bacalla, X.; Bhatt, N. H.; Bron, E.; Cordiner, M. A.; de Koter, A..; Ehrenfreund, P.; Evans, C.; Foing, B. H.; Javadi, A.; Joblin, C.; Kaper, L.; Khosroshahi, H. G.; Laverick, M.; Le Petit, F..; Linnartz, H.; Marshall, C. C.; Monreal-Ibero, A.; Mulas, G.; Roueff, E.; Royer, P.; Salama, F.; Sarre, P. J.; Smith, K. T.; Spaans, M.; van Loon, J. T..; Wade, G.

2018-03-01

The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES) is a Large Programme that is collecting high-signal-to-noise (S/N) spectra with UVES of a large sample of O and B-type stars covering a large spectral range. The goal of the programme is to extract a unique sample of high-quality interstellar spectra from these data, representing different physical and chemical environments, and to characterise these environments in great detail. An important component of interstellar spectra is the diffuse interstellar bands (DIBs), a set of hundreds of unidentified interstellar absorption lines. With the detailed line-of-sight information and the high-quality spectra, EDIBLES will derive strong constraints on the potential DIB carrier molecules. EDIBLES will thus guide the laboratory experiments necessary to identify these interstellar “mystery molecules”, and turn DIBs into powerful diagnostics of their environments in our Milky Way Galaxy and beyond. We present some preliminary results showing the unique capabilities of the EDIBLES programme.

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.

An Essay on Interactive Investigations of the Zeeman Effect in the Interstellar Medium

ERIC Educational Resources Information Center

Woolsey, Lauren

2015-01-01

The paper presents an interactive module created through the Wolfram Demonstrations Project that visualizes the Zeeman effect for the small magnetic field strengths present in the interstellar medium. The paper provides an overview of spectral lines and a few examples of strong and weak Zeeman splitting before discussing the module in depth.…

A near infrared spectroscopic study of the interstellar gas in the starburst core of M82

NASA Technical Reports Server (NTRS)

Lester, Dan F.; Carr, John; Joy, Marshall; Gaffney, Niall

1990-01-01

Researchers used the McDonald Observatory Infrared Grating Spectrometer, to complete a program of spatially resolved spectroscopy of M82. The inner 300 pc of the starburst was observed with 4 inch (50 pc) resolution. Complete J, H and K band spectra with resolution 0.0035 micron (lambda/delta lambda=620 at K) were measured at the near-infrared nucleus of the galaxy. Measurements of selected spectral features including lines of FeII, HII and H2 were observed along the starburst ridge-line, so the relative distribution of the diagnostic features could be understood. This information was used to better define the extinction towards the starburst region, the excitation conditions in the gas, and to characterize the stellar populations there.

Featured Image: Diamonds in a Meteorite

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-04-01

This unique image which measures only 60 x 80 micrometers across reveals details in the Kapoeta meteorite, an 11-kg stone that fell in South Sudan in 1942. The sparkle in the image? A cluster of nanodiamonds discovered embedded in the stone in a recent study led by Yassir Abdu (University of Sharjah, United Arab Emirates). Abdu and collaborators showed that these nanodiamonds have similar spectral features to the interiors of dense interstellar clouds and they dont show any signs of shock features. This may suggest that the nanodiamonds were formed by condensation of nebular gases early in the history of the solar system. The diamonds were trapped in the surface material of the Kapoeta meteorites parent body, thought to be the asteroid Vesta. To read more about the authors study, check out the original article below.CitationYassir A. Abdu et al 2018 ApJL 856 L9. doi:10.3847/2041-8213/aab433

Spacelab

NASA Image and Video Library

1990-12-01

In this photograph, the instruments of the Astro-1 Observatory are erected in the cargo bay of the Columbia orbiter. Astro-1 was launched aboard the the Space Shuttle Orbiter Columbia (STS-35) mission on December 2, 1990. The Astro Observatory was designed to explore the universe by observing and measuring the ultraviolet radiation from celestial objects. Astronomical targets of observation selected for Astro missions included planets, stars, star clusters, galaxies, clusters of galaxies, quasars, remnants of exploded stars (supernovae), clouds of gas and dust (nebulae), and the interstellar medium. Astro-1 used a Spacelab pallet system with an instrument pointing system and a cruciform structure for bearing the three ultraviolet instruments mounted in a parallel configuration. The three instruments were:The Hopkins Ultraviolet Telescope (HUT), the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE), and the Ultraviolet Imaging Telescope (UIT). Also in the payload bay was the Broad Band X-Ray Telescope (BBXRT). Scientific return included approximately 1,000 photographs of the ultraviolet sky in the most extensive ultraviolet imagery ever attempted, the longest ultraviolet spectral observation of a comet ever made, and data never before seen on types of active galaxies called Seyfert galaxies. The mission also provided data on a massive supergiant star captured in outburst and confirmed that a spectral feature observed in the interstellar medium was due to graphite. In addition, Astro-1 acquired superb observations of the Jupiter magnetic interaction with one of its satellites.

Investigating the interstellar dust through the Fe K-edge

NASA Astrophysics Data System (ADS)

Rogantini, D.; Costantini, E.; Zeegers, S. T.; de Vries, C. P.; Bras, W.; de Groot, F.; Mutschke, H.; Waters, L. B. F. M.

2018-01-01

Context. The chemical and physical properties of interstellar dust in the densest regions of the Galaxy are still not well understood. X-rays provide a powerful probe since they can penetrate gas and dust over a wide range of column densities (up to 1024 cm-2). The interaction (scattering and absorption) with the medium imprints spectral signatures that reflect the individual atoms which constitute the gas, molecule, or solid. Aims: In this work we investigate the ability of high resolution X-ray spectroscopy to probe the properties of cosmic grains containing iron. Although iron is heavily depleted into interstellar dust, the nature of the Fe-bearing grains is still largely uncertain. Methods: In our analysis we use iron K-edge synchrotron data of minerals likely present in the ISM dust taken at the European Synchrotron Radiation Facility. We explore the prospects of determining the chemical composition and the size of astrophysical dust in the Galactic centre and in molecular clouds with future X-ray missions. The energy resolution and the effective area of the present X-ray telescopes are not sufficient to detect and study the Fe K-edge, even for bright X-ray sources. Results: From the analysis of the extinction cross sections of our dust models implemented in the spectral fitting program SPEX, the Fe K-edge is promising for investigating both the chemistry and the size distribution of the interstellar dust. We find that the chemical composition regulates the X-ray absorption fine structures in the post edge region, whereas the scattering feature in the pre-edge is sensitive to the mean grain size. Finally, we note that the Fe K-edge is insensitive to other dust properties, such as the porosity and the geometry of the dust. The absorption, scattering, and extinction cross sections of the compounds 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/609/A22

On the Detectability of CO Molecules in the Interstellar Medium via X-Ray Spectroscopy

NASA Technical Reports Server (NTRS)

Joachimi, Katerine; Gatuzz, Efrain; Garcia, Javier; Kallman, Timothy R.

2016-01-01

We present a study of the detectability of CO molecules in the Galactic interstellar medium using high-resolution X-ray spectra obtained with the XMM-Newton Reflection Grating Spectrometer. We analysed 10 bright low mass X-ray binaries (LMXBs) to study the CO contribution in their line of sights. A total of 25 observations were fitted with the ISMabs X-ray absorption model which includes photoabsorption cross-sections for Oi, Oii, Oiii and CO. We performed a Monte Carlo (MC) simulation analysis of the goodness of fit in order to estimate the significance of the CO detection. We determine that the statistical analysis prevents a significant detection of CO molecular X-ray absorption features, except for the lines of sight towards XTE J1718-330 and 4U 1636-53. In the case of XTE J1817-330, this is the first report of the presence of CO along its line of sight. Our results reinforce the conclusion that molecules have a minor contribution to the absorption features in the O K-edge spectral region. We estimate a CO column density lower limit to perform a significant detection with XMM-Newton of N(CO) greater than 6 x 10(exp 16) per sq cm for typical exposure times.

The Mysterious 6565 Å Absorption Feature of the Galactic Halo

NASA Astrophysics Data System (ADS)

Sethi, Shiv K.; Shchekinov, Yuri; Nath, Biman B.

2017-12-01

We consider various possible scenarios to explain the recent observation of what has been called a broad Hα absorption in our Galactic halo, with peak optical depth τ ≃ 0.01 and equivalent width W≃ 0.17 \\mathringA . We show that the absorbed feature cannot arise from the circumgalactic and ISM Hα absorption. As the observed absorption feature is quite broad ({{Δ }}λ ≃ 30 \\mathringA ), we also consider CNO lines that lie close to Hα as possible alternatives to explain the feature. We show that such lines could also not account for the observed feature. Instead, we suggest that it could arise from diffuse interstellar bands (DIBs) carriers or polyaromatic hydrocarbons (PAHs) absorption. While we identify several such lines close to the Hα transition, we are unable to determine the molecule responsible for the observed feature, partly because of selection effects that prevent us from identifying DIBs/PAHs features close to Hα using local observations. Deep integration of a few extragalactic sources with high spectral resolution might allow us to distinguish between different possible explanations.

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.

Evolution of magnetic field turbulence as observed by the Voyagers in the heliosheath and in the local interstellar medium.

NASA Astrophysics Data System (ADS)

Fraternale, F.; Iovieno, M.; Pogorelov, N.; Richardson, J. D.; Tordella, D.

2017-12-01

Voyager 1 (V1) left the heliosheath (HS) and entered the Local Interstellar Medium (LISM) in August 2012. At the same time, Voyager 2 (V2) was inside the HS and it is currently approaching the heliopause. The nature of the mainly compressive and "turbulent" fluctuations observed in the HS and in the LISM is still unclear. The presented study aims at describing the spatial and temporal evolution of turbulence in the HS and in the LISM. It shows a collection of power spectra of magnetic field fluctuations computed from consecutive periods since 2009. Unlike previous analysis, the highest resolution data (48 s) available are used to observe up to five frequency decades. Proper spectral recovery techniques applied in a previous work [Gallana et al, JGR 2016] are exploited to overcome the problem of missing data. Inside the HS, the achieved results are consistent with an anisotropic, mainly inertial, energy cascade in the frequency range [10-5,5·10-4] Hz, with spectral index ranging from -1.65 (V2) to -2 (V1) and energy spectral transfer around 10-19 erg/(cm3s). Anisotropy is significantly higher at V1 than at V2. In 2009 and 2010, tangential magnetic field fluctuations at V1 contain half of the fluctuating magnetic energy, which is not observed at V2. Large scales prior to the spectral break (f<10-5 Hz) are featured by a mild spectral decay with index between -0.95 and -1.5. Observations of small scales (5·10-4-2 Hz) are limited by the onboard magnetometer's accuracy, though some kinetic effects are still visible. LISM spectra in 2013.36 - 2014.65 are in agreement with previous observations [Burlaga, Florinski & Ness ApJ Lett, 2015]. A slightly flatter spectral trend than the Kolmogorov's is observed for the radial fluctuations at [10-7, 10-6] Hz. However, the tangential and normal components show nearly a f-1 decay. The evolution of turbulent spectra in the LISM is investigated.

Millimeter Wave Spectrum and Astronomical Search for Vinyl Formate

NASA Astrophysics Data System (ADS)

Alonso, E. R.; Kolesniková, L.; Tercero, B.; Cabezas, C.; Alonso, J. L.; Cernicharo, J.; Guillemin, J.-C.

2016-11-01

Previous detections of methyl and ethyl formate make other small substituted formates potential candidates for observation in the interstellar medium. Among them, vinyl formate is one of the simplest unsaturated carboxylic ester. The aim of this work is to provide direct experimental frequencies of the ground vibrational state of vinyl formate in a large spectral range for astrophysical use. The room-temperature rotational spectrum of vinyl formate has been measured from 80 to 360 GHz and analyzed in terms of Watson’s semirigid rotor Hamiltonian. Two thousand six hundred transitions within J = 3-88 and K a = 0-28 were assigned to the most stable conformer of vinyl formate and a new set of spectroscopic constants was accurately determined. Spectral features of vinyl formate were then searched for in Orion KL, Sgr B2(N), B1-b, and TMC-1 molecular clouds. Upper limits to the column density of vinyl formate are provided.

Infrared Spectroscopy of Anhydrous Interplanetary Dust Particles

NASA Technical Reports Server (NTRS)

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

2003-01-01

Infrared (IR) spectroscopy is the primary means of mineralogical analysis of materials outside our solar system. The identity and properties of circumstellar grains are inferred from spectral comparisons between astronomical observations and laboratory data from natural and synthetic materials. These comparisons have been facilitated by the Infrared Space Observatory (ISO), which obtained IR spectra from numerous astrophysical objects over a wide spectral range (out to 50/cm) where crystalline silicates and other phases have distinct features. The anhydrous interplanetary dust particles (IDPs) are particularly important comparison materials because some IDPs contain carbonaceous material with non-solar D/H and N-15/N-14 ratios and amorphous and crystalline silicates with non-solar 0- isotopic ratios, demonstrating that these IDPs contain preserved interstellar material. Here, we report on micro- Fourier transform (FT) IR spectrometry of IDPs, focusing on the inorganic components of primitive IDPs (FTIR spectra from the organic/carbonacecous materials in IDPs are described elsewhere).

Thermal and energetic processing of astrophysical ice analogues rich in SO2

NASA Astrophysics Data System (ADS)

Kaňuchová, Z.; Boduch, Ph.; Domaracka, A.; Palumbo, M. E.; Rothard, H.; Strazzulla, G.

2017-08-01

Context. Sulfur is an abundant element in the cosmos and it is thus an important contributor to astrochemistry in the interstellar medium and in the solar system. Astronomical observations of the gas and of the solid phases in the dense interstellar/circumstellar regions have evidenced that sulfur is underabundant. The hypothesis to explain such a circumstance is that it is incorporated in some species in the solid phase (I.e. as frozen gases and/or refractory solids) and/or in the gas phase, which for different reasons have not been observed so far. Aims: Here we wish to give a contribution to the field by studying the chemistry induced by thermal and energetic processing of frozen mixtures of sulfur dioxide (one of the most abundant sulfur-bearing molecules observed so far) and water. Methods: We present the results of a series of laboratory experiments concerning thermal processing of different H2O:SO2 mixtures and ion bombardment (30 keV He+) of the same mixtures. We used in situ Fourier transform infrared (FTIR) spectroscopy to investigate the induced effects. Results: The results indicate that ionic species such as HSO, HSO, and S2O are easily produced. Energetic processing also produces SO3 polymers and a sulfurous refractory residue. Conclusions: The produced ionic species exhibit spectral features in a region that, in astronomical spectra of dense molecular clouds, is dominated by strong silicate absorption. However, such a dominant feature is associated with some spectral features, some of which have not yet been identified. We suggest adding the sulfur-bearing ionic species to the list of candidates to help explain some of those features. In addition, we suggest that once expelled in the gas phase by sublimation, due to the temperature increase, and/or by non-thermal erosion those species would constitute a class of molecular ions not detected so far. We also suggest that molecular sulfur-bearing ions could be present on the surfaces and/or in the atmospheres of several objects in the solar system, for example icy satellites of the giant planets and comets.

Stardust Interstellar Preliminary Examination VII: Synchrotron X-Ray Fluorescence Analysis of Six Stardust Interstellar Candidates Measured with the Advanced Photon Source 2-ID-D Microprobe

NASA Technical Reports Server (NTRS)

Allen, Carlton C.; Anderson, David; Bastien, Ron K.; Brenker, Frank E.; Flynn, George J.; Frank, David; Gainsforth, Zack; Sandford, Scott A.; Simionovici, Alexandre S.; Zolensky, Michael E.

2014-01-01

The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 < or = Z < or = 30, on six "interstellar candidates," potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.

Stardust Interstellar Preliminary Examination VII: Synchrotron X-ray fluorescence analysis of six Stardust interstellar candidates measured with the Advanced Photon Source 2-ID-D microprobe

NASA Astrophysics Data System (ADS)

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

2014-09-01

The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 ≤ Z ≤ 30, on six "interstellar candidates," potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.

Sub-Millimeter Heterodyne Focal-Plane Arrays for High-Resolution Astronomical Spectroscopy

NASA Astrophysics Data System (ADS)

Goldsmith, Paul F.

2017-09-01

Spectral lines are vital tools for astronomy, particularly for studying the interstellar medium, which is widely distributed throughout the volume of our Milky Way and of other galaxies. Broadband emissions, including synchrotron, free-free, and thermal dust emissions give astronomers important information. However, they do not give information about the motions of, for example, interstellar clouds, the filamentary structures found within them, star-forming dense cores, and photon-dominated regions energized by massive young stars. For study of the interstellar medium, spectral lines at sub-millimeter wavelengths are particularly important, for two reasons. First, they offer the unique ability to observe a variety of important molecules, atoms, and ions, which are the most important gas coolants (fine-structure lines of ionized and neutral carbon, neutral oxygen), probes of physical conditions (high-J transitions of CO, HF, fine-structure lines of ionized nitrogen), and of obvious biogenic importance (H2O). In addition, high-resolution observations of spectral lines offer the unique ability to disentangle the complex motions within these regions and, in some cases, to determine their arrangement along the line of sight. To accomplish this, spectral resolution high enough to resolve the spectral lines of interest is required. We can measure the resolution of the spectrometer in terms of its resolution, R = f/δf, where f is the rest frequency of the line, and δJ is the frequency resolution of the spectrometer. More-active sources can be advantageously studied with R = 3 × 10^5, while more quiescent sources require R as high as 10^7.

Analysis of ultraviolet spectrophotometric data from Copernicus

NASA Technical Reports Server (NTRS)

Snow, T. P., Jr.

1979-01-01

Ultraviolet spectral data from the OAO 3 satellite are being used to study interstellar absorption lines and stellar and circumstellar lines in hot stars. The interstellar data are beneficial in analyzing the depletions of heavy elements from the gas phase and in elucidating how these depletions depend on physical conditions. Abundances in separate velocity components were determined from line profiles. Observations were carried out for interstellar abundances, both atomic and molecular, towards a number of stars. The better quality data are being analyzed for profile information and the lesser data are being used in curve-of-growth analyses. Molecular observations were carried out as well, N2 was sought; interstellar C2 was detected and its rotational excitation utilized to establish limits in interstellar cloud temperatures. An extensive search for H2O resulted in a tentative identification which will produce new information on chemical reaction rates. Interstellar depletions and grain properties in the rho Ophiuchi cloud, stellar wind variability, and circumstellar lines are also under study.

Unbiased Large Spectroscopic Surveys of Galaxies Selected by SPICA Using Dust Bands

NASA Astrophysics Data System (ADS)

Kaneda, H.; Ishihara, D.; Oyabu, S.; Yamagishi, M.; Wada, T.; Armus, L.; Baes, M.; Charmandaris, V.; Czerny, B.; Efstathiou, A.; Fernández-Ontiveros, J. A.; Ferrara, A.; González-Alfonso, E.; Griffin, M.; Gruppioni, C.; Hatziminaoglou, E.; Imanishi, M.; Kohno, K.; Kwon, J.; Nakagawa, T.; Onaka, T.; Pozzi, F.; Scott, D.; Smith, J.-D. T.; Spinoglio, L.; Suzuki, T.; van der Tak, F.; Vaccari, M.; Vignali, C.; Wang, L.

2017-11-01

The mid-infrared range contains many spectral features associated with large molecules and dust grains such as polycyclic aromatic hydrocarbons and silicates. These are usually very strong compared to fine-structure gas lines, and thus valuable in studying the spectral properties of faint distant galaxies. In this paper, we evaluate the capability of low-resolution mid-infrared spectroscopic surveys of galaxies that could be performed by SPICA. The surveys are designed to address the question how star formation and black hole accretion activities evolved over cosmic time through spectral diagnostics of the physical conditions of the interstellar/circumnuclear media in galaxies. On the basis of results obtained with Herschel far-infrared photometric surveys of distant galaxies and Spitzer and AKARI near- to mid-infrared spectroscopic observations of nearby galaxies, we estimate the numbers of the galaxies at redshift z > 0.5, which are expected to be detected in the polycyclic aromatic hydrocarbon features or dust continuum by a wide (10 deg2) or deep (1 deg2) blind survey, both for a given observation time of 600 h. As by-products of the wide blind survey, we also expect to detect debris disks, through the mid-infrared excess above the photospheric emission of nearby main-sequence stars, and we estimate their number. We demonstrate that the SPICA mid-infrared surveys will efficiently provide us with unprecedentedly large spectral samples, which can be studied further in the far-infrared with SPICA.

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

NASA Technical Reports Server (NTRS)

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

1982-01-01

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

Comprehensive Analysis of Interstellar Iso-PROPYL Cyanide up to 480 GHZ

NASA Astrophysics Data System (ADS)

Kolesniková, Lucie; Alonso, E. R.; Cabezas, Carlos; Mata, Santiago; Alonso, José L.

2016-06-01

Iso-propyl cyanide, also known as iso-butyronitrile, is a branched alkyl molecule recently detected in the interstellar medium. A combination of Stark-modulated microwave spectroscopy and frequency-modulated millimeter and submillimeter wave spectroscopy was used to analyze its rotational spectrum from 26 to 480 GHz. Spectral assignments and analysis include transitions from the ground state, eight excited vibrational states and 13C isotopologues. Results of this work should facilitate astronomers further observations of iso-propyl cyanide in the interstellar medium. A. Belloche, R. T. Garrod, H. S. P. Müller, K. M. Menten, Science, 2014, 345, 1584

Neutral gas and diffuse interstellar bands in the LMC

NASA Technical Reports Server (NTRS)

Danks, Anthony C.; Penprase, Brian

1994-01-01

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

Atomic gas in debris discs

NASA Astrophysics Data System (ADS)

Hales, Antonio S.; Barlow, M. J.; Crawford, I. A.; Casassus, S.

2017-04-01

We have conducted a search for optical circumstellar absorption lines in the spectra of 16 debris disc host stars. None of the stars in our sample showed signs of emission line activity in either Hα, Ca II or Na I, confirming their more evolved nature. Four stars were found to exhibit narrow absorption features near the cores of the photospheric Ca II and Na I D lines (when Na I D data were available). We analyse the characteristics of these spectral features to determine whether they are of circumstellar or interstellar origins. The strongest evidence for circumstellar gas is seen in the spectrum of HD 110058, which is known to host a debris disc observed close to edge-on. This is consistent with a recent ALMA detection of molecular gas in this debris disc, which shows many similarities to the β Pictoris system.

Boundary Conditions for the Paleoenvironment: Chemical and Physical Processes in the Pre-Solar Nebula

NASA Technical Reports Server (NTRS)

Irvine, William M.; Schloerb, F. Peter

1997-01-01

The basic theme of this program is the study of molecular complexity and evolution in interstellar clouds and in primitive solar system objects. Research has included the detection and study of a number of new interstellar molecules and investigation of reaction pathways for astrochemistry from a comparison of theory and observed molecular abundances. The latter includes studies of cold, dark clouds in which ion-molecule chemistry should predominate, searches for the effects of interchange of material between the gas and solid phases in interstellar clouds, unbiased spectral surveys of particular sources, and systematic investigation of the interlinked chemistry and physics of dense interstellar clouds. In addition, the study of comets has allowed a comparison between the chemistry of such minimally thermally processed objects and that of interstellar clouds, shedding light on the evolution of the biogenic elements during the process of solar system formation.

THE DETECTION OF INTERSTELLAR ETHANIMINE (CH{sub 3}CHNH) FROM OBSERVATIONS TAKEN DURING THE GBT PRIMOS SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loomis, Ryan A.; Zaleski, Daniel P.; Steber, Amanda L.

2013-03-01

We have performed reaction product screening measurements using broadband rotational spectroscopy to identify rotational transition matches between laboratory spectra and the Green Bank Telescope PRIMOS radio astronomy survey spectra in Sagittarius B2 North (Sgr B2(N)). The broadband rotational spectrum of molecules created in an electrical discharge of CH{sub 3}CN and H{sub 2}S contained several frequency matches to unidentified features in the PRIMOS survey that did not have molecular assignments based on standard radio astronomy spectral catalogs. Several of these transitions are assigned to the E- and Z-isomers of ethanimine. Global fits of the rotational spectra of these isomers in themore » range of 8-130 GHz have been performed for both isomers using previously published mm-wave spectroscopy measurements and the microwave measurements of the current study. Possible interstellar chemistry formation routes for E-ethanimine and Z-ethanimine are discussed. The detection of ethanimine is significant because of its possible role in the formation of alanine-one of the twenty amino acids in the genetic code.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Randall K.; Valencic, Lynne A.; Corrales, Lia, E-mail: lynne.a.valencic@nasa.gov

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 asmore » 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.« less

Infrared spectroscopy of dense clouds in the C-H stretch region - Methanol and 'diamonds'

NASA Technical Reports Server (NTRS)

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

1992-01-01

The paper presents high spectral resolution studies in the 3100-2600/cm range of the protostars NGC 7538 IRS9, W33A, W3 IRS 5, and S140 IRS 1. Well-resolved absorption bands at about 2825/cm and 2880/cm were found superposed on the LF wing of the strong O-H stretch feature. The 2880/cm band, previously detected toward W33A, is also in the spectrum of NGC 7538 IRS 9. The relative strength of these two bands varies, showing that they are associated with two different carriers. The new band at about 2880/cm falls near the position of C-H stretching vibrations in tertiary carbon atoms. The strength of this feature, in combination with the lack of strong features associated with primary and secondary carbon atoms, suggests that the carrier of the new feature has a diamondlike structure. This new feature is tentatively attributed to interstellar 'diamonds'. The detection of this band in the spectra of all four dense molecular clouds suggests that the carrier is ubiquitous in dense clouds.

THz Time-Domain Spectroscopy of Interstellar Ice Analogs

NASA Astrophysics Data System (ADS)

Ioppolo, Sergio; McGuire, Brett A.; de Vries, Xander; Carroll, Brandon; Allodi, Marco; Blake, Geoffrey

2015-08-01

The unambiguous identification of nearly 200 molecular species in different astronomical environments proves that our cosmos is a ‘Molecular Universe’. The cumulative outcome of recent observations, laboratory studies, and astrochemical models indicates that there is a strong interplay between the gas and the solid phase throughout the process of forming molecules in space. Observations of interstellar ices are generally limited to lines-of-sight along which infrared absorption spectroscopy is possible. Therefore, the identification of more complex prebiotic molecules in the mid-IR is difficult because of their low expected interstellar abundances and the overlap of their absorption features with those from the more abundant species. In the THz region, telescopes can detect Interstellar ices in emission or absorption against dust continuum. Thus, THz searches do not require a background point source. Moreover, since THz spectra are the fingerprint of inter- and intramolecular forces, complex species can present unique modes that do not overlap with those from simpler, more abundant molecules. THz modes are also sensitive to temperature and phase changes in the ice. Therefore, spectroscopy at THz frequencies has the potential to better characterize the physics and chemistry of the ISM. Currently, the Herschel Space Telescope, SOFIA, and ALMA databases contain a vast amount of new THz spectral data that require THz laboratory spectra for interpretation. The latter, however, are largely lacking. We have recently constructed a new THz time-domain spectroscopy system operating in the range between 0.3 - 7.5 THz. This work focuses on the laboratory investigation of the composition and structure of the most abundant interstellar ice analogs compared to some more complex species. Different temperatures, mixing ratios, and matrix isolation experiments will be shown. The ultimate goal of this research is to provide the scientific community with an extensive THz ice-database, which will allow quantitative studies of the ISM, and guide future astronomical observations of species in the solid phase.

Absorption and scattering by interstellar dust in the silicon K-edge of GX 5-1

NASA Astrophysics Data System (ADS)

Zeegers, S. T.; Costantini, E.; de Vries, C. P.; Tielens, A. G. G. M.; Chihara, H.; de Groot, F.; Mutschke, H.; Waters, L. B. F. M.; Zeidler, S.

2017-03-01

Context. We study the absorption and scattering of X-ray radiation by interstellar dust particles, which allows us to access the physical and chemical properties of dust. The interstellar dust composition is not well understood, especially on the densest sight lines of the Galactic plane. X-rays provide a powerful tool in this study. Aims: We present newly acquired laboratory measurements of silicate compounds taken at the Soleil synchrotron facility in Paris using the Lucia beamline. The dust absorption profiles resulting from this campaign were used in this pilot study to model the absorption by interstellar dust along the line of sight of the low-mass X-ray binary GX 5-1. Methods: The measured laboratory cross-sections were adapted for astrophysical data analysis and the resulting extinction profiles of the Si K-edge were implemented in the SPEX spectral fitting program. We derive the properties of the interstellar dust along the line of sight by fitting the Si K-edge seen in absorption in the spectrum of GX 5-1. Results: We measured the hydrogen column density towards GX 5-1 to be 3.40 ± 0.1 × 1022 cm-2. The best fit of the silicon edge in the spectrum of GX 5-1 is obtained by a mixture of olivine and pyroxene. In this study, our modeling is limited to Si absorption by silicates with different Mg:Fe ratios. We obtained an abundance of silicon in dust of 4.0 ± 0.3 × 10-5 per H atom and a lower limit for total abundance, considering both gas and dust of >4.4 × 10-5 per H atom, which leads to a gas to dust ratio of >0.22. Furthermore, an enhanced scattering feature in the Si K-edge may suggest the presence of large particles along the line of sight.

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.

Spectroscopic and photometric observations of M supergiants in Carina.

NASA Technical Reports Server (NTRS)

Humphreys, R. M.; Strecker, D. W.; Ney, E. P.

1972-01-01

Spectroscopic study of 30 Southern-Hemisphere M supergiants mostly in Carina in the blue and near-infrared, and photometrical study of these stars from 0.4 to 18 microns. The uncertainties in the determinations of interstellar extinction are discussed, and the spatial distribution of the M supergiants in the Carina arm is shown. The presence of the 11-micron excess attributed to silicate dust is a common feature. Stars of the same spectral type and luminosity class are remarkably homogeneous in their long-wave behavior. The silicate feature becomes more prominent in the more luminous stars and in stars of later spectral type. Four composite systems show little long-wave excess. The two VV Cephei objects have excesses probably produced by gas emission, and the other two have little or no excess - supporting the suggestion that the presence of the early star prohibits the formation of a dust envelope. Three stars - VY CMa, VX Sgr, and HD 9767 - appear to be extreme examples of stars with large excesses over the entire long-wave region. It is suggested that these objects are surrounded by large amounts of particulate material over a great range of distances from the stars.

A sounding rocket program in extreme and far ultraviolet interferometry

NASA Technical Reports Server (NTRS)

Chakrabarti, S.

1994-01-01

A self-compensating, all reflection interferometric (SCARI) spectrometer was developed that can provide high resolution measurements of spectral features at any wavelength. Several mechanical components were developed that aid the instrument's performance at the short wavelength range. Examples include an optical bench and modular removable precision mechanisms for alignment. Upon alignment and lock down of the interferometer with the latter, the device is removed to minimize weight. A ray-trace code was developed to simulate the instrument's performance. Interference patterns were obtained at the shortest wavelength: the hydrogen Lyman alpha (1216 A). A laboratory instrument was developed that will be flown aboard a Black Brant sounding rocket to study the very local interstellar medium.

A DETAILED FAR-ULTRAVIOLET SPECTRAL ATLAS OF MAIN-SEQUENCE B STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Myron A.

2010-02-01

We have constructed a detailed spectral atlas covering the wavelength region 930-1225 A for 10 sharp-lined B0-B9 stars near the main sequence. Most of the spectra we assembled are from the archives of the Far Ultraviolet Spectroscopic Explorer satellite, but for nine stars, wavelength coverage above 1188 A was taken from high-resolution International Ultraviolet Explorer or echelle Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra. To represent the tenth star at type B0.2 V, we used the Copernicus atlas of {tau} Sco. We made extensive line identifications in the region 949-1225 A of all atomic features having published oscillator strengths atmore » types B0, B2, and B8. These are provided as a supplementary data product-hence the term detailed atlas. Our list of found features totals 2288, 1612, and 2469 lines, respectively. We were able to identify 92%, 98%, and 98% of these features with known atomic transitions with varying degrees of certainty in these spectra. The remaining lines do not have published oscillator strengths. Photospheric lines account for 94%, 87%, and 91%, respectively, of all our identifications, with the remainder being due to interstellar (usually molecular H{sub 2}) lines. We also discuss the numbers of lines with respect to the distributions of various ions for these three most studied spectral subtypes. A table is also given of 162 least blended lines that can be used as possible diagnostics of physical conditions in B star atmospheres.« less

Analysis of ultraviolet spectrophotometric data from Copernicus. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snow, T.P. Jr

1979-04-17

Ultraviolet spectral data from the OAO 3 satellite are being used to study interstellar absorption lines and stellar and circumstellar lines in hot stars. The interstellar data are beneficial in analyzing the depletions of heavy elements from the gas phase and in elucidating how these depletions depend on physical conditions. Abundances in separate velocity components were determined from line profiles. Observations were carried out for interstellar abundances, both atomic and molecular, towards a number of stars. The better quality data are being analyzed for profile information and the lesser data are being used in curve-of-growth analyses. Molecular observations were carriedmore » out as well; N/sup 2/ was sought, interstellar C/sup 2/ was detected and its rotational excitation utilized to establish limits in interstellar cloud temperatures. An extensive search for H/sup 2/O resulted in a tentative identification which will produce new information on chemical reaction rates. Interstellar depletions and grain properties in the rho Ophiuchi cloud, stellar wind variability, and circumstellar lines are also under study.« less

Optical observations of nearby interstellar gas

NASA Astrophysics Data System (ADS)

Frisch, P. C.; York, D. G.

1984-11-01

Observations indicated that a cloud with a heliocentric velocity of approximately -28 km/s and a hydrogen column density that possibly could be on the order of, or greater than, 5 x 10 to the 19 power/square cm is located within the nearest 50 to 80 parsecs in the direction of Ophiuchus. This is a surprisingly large column density of material for this distance range. The patchy nature of the absorption from the cloud indicates that it may not be a feature with uniform properties, but rather one with small scale structure which includes local enhancements in the column density. This cloud is probably associated with the interstellar cloud at about the same velocity in front of the 20 parsec distant star alpha Oph (Frisch 1981, Crutcher 1982), and the weak interstellar polarization found in stars as near as 35 parsecs in this general region (Tinbergen 1982). These data also indicate that some portion of the -14 km/s cloud also must lie within the 100 parsec region. Similar observations of both Na1 and Ca2 interstellar absorption features were performed in other lines of sight. Similar interstellar absorption features were found in a dozen stars between 20 and 100 parsecs of the Sun.

Optical Observations of Nearby Interstellar Gas

NASA Technical Reports Server (NTRS)

Frisch, P. C.; York, D. G.

1984-01-01

Observations indicated that a cloud with a heliocentric velocity of approximately -28 km/s and a hydrogen column density that possibly could be on the order of, or greater than, 5 x 10 to the 19 power/square cm is located within the nearest 50 to 80 parsecs in the direction of Ophiuchus. This is a surprisingly large column density of material for this distance range. The patchy nature of the absorption from the cloud indicates that it may not be a feature with uniform properties, but rather one with small scale structure which includes local enhancements in the column density. This cloud is probably associated with the interstellar cloud at about the same velocity in front of the 20 parsec distant star alpha Oph (Frisch 1981, Crutcher 1982), and the weak interstellar polarization found in stars as near as 35 parsecs in this general region (Tinbergen 1982). These data also indicate that some portion of the -14 km/s cloud also must lie within the 100 parsec region. Similar observations of both Na1 and Ca2 interstellar absorption features were performed in other lines of sight. Similar interstellar absorption features were found in a dozen stars between 20 and 100 parsecs of the Sun.

Detection of Extraterrestrial Civilizations via the Spectral Signature of Advanced Interstellar Spacecraft

NASA Astrophysics Data System (ADS)

Zubrin, Robert

1994-07-01

This paper examines the possibility of detecting extraterrestrial civilizations by means of searching for the spectral signature of their interstellar transportation systems. The advantage of such an approach is that the characteristic power levels associated with interstellar transportation systems are many orders of magnitude greater than those required for communication, and so the signal strength may be much greater. Furthermore, unlike communication which is governed by a fairly arbitrary selection of technology and mutually agreed upon conventions, interstellar transportation systems are governed much more stringently by the laws of physics. For purposes of the present analysis we consider 4 methods of interstellar propulsion, the principles of which are fairly well understood. These are anti-matter rockets, fusion rockets, fission rockets, all of which can be used to either accelerate or decelerate a spacecraft, and magnetic sails, which can be used to decelerate a spacecraft by creating drag against the interstellar medium. The types of radiation emitted by each of these propulsion systems is described, and the signal strength for starships of a characteristic mass of 1 million tonnes traveling at speeds and acceleration levels characteristic of the various propulsion systems is estimated. It is shown that for the power level of ships considered, the high energy gamma radiation emitted by the anti-matter, fusion and fission propulsion systems would be undetectable at interstellar distances. Better opportunities for detection would be the bremsstrahlung radiation from the plasma confinement systems of fusion devices, which might be detectable at distances of about 1 light year, and visible light emitted from the radiators of anti-matter driven photon rocket, which might be detectable by the Hubble Space Telescope at a distance of several hundred light years provided the rocket nozzle is oriented towards the Earth. The most detectable form of starship radiation, however, was found to be the low frequency radio emissions of cyclotron radiation caused by interaction of the interstellar medium with a magnetic sail. The frequency of such radiation is given approximately by f=120(v/c)kHz, where v is the starship's velocity. Because the frequency of this radiation is lower than the Earth's ionospheric cut-off, an antenna for its reception would have to be space-based. However such a space-based antenna with a 6 km effective diameter could detect the magsail emission of a characteristic starship at distances of up to several thousand light years. Both photon rockets and magnetic sails would emit a signal that could easily be distinguished from natural sources. We conclude that the detection of extraterrestrial civilizations via the spectral signature of their spacecraft is possible in principle and recommend that the approach be studied further.

A New Probe of Line-of-sight Magnetic Field Tangling

NASA Astrophysics Data System (ADS)

Clark, S. E.

2018-04-01

The Galactic neutral hydrogen (H I ) sky at high Galactic latitudes is suffused with linear structure. Particularly prominent in narrow spectral intervals, these linear H I features are well aligned with the plane-of-sky magnetic field orientation as measured with optical starlight polarization and polarized thermal dust emission. We analyze the coherence of the orientation of these features with respect to line-of-sight velocity, and propose a new metric to quantify this H I coherence. We show that H I coherence is linearly correlated with the polarization fraction of 353 GHz dust emission. H I coherence constitutes a novel method for measuring the degree of magnetic field tangling along the line of sight in the diffuse interstellar medium. We propose applications of this property for H I -based models of the polarized dust emission in diffuse regions, and for studies of frequency decorrelation in the polarized dust foreground to the cosmic microwave background (CMB).

Recalescence during crystallization of stardust: Resolution of the amorphous interstellar medium paradox

NASA Astrophysics Data System (ADS)

Whittington, A. G.; Sehlke, A.; Speck, A. K.

2017-12-01

Dust that coalesces to form planetary systems originates around dying stars, before passing into the interstellar medium (ISM). Historically, observations of broad smooth features in the 10-µm region suggested that dust in circumstellar regions, and in the ISM, was mostly amorphous rather than crystalline. With improved space telescope capabilities, crystalline silicates were discovered in the circumstellar regions around both young and old stars, although they remain undetected in the ISM. Despite intensive study the precise conditions that lead to the formation of crystalline silicates are still unknown, and their absence in the ISM remains problematic. Here we show that recalescence (spontaneous reheating) of rapidly crystallizing dust can explain the formation and apparent disappearance of crystalline silicates in space. We have documented recalescence in rapidly crystallizing Mg-rich silicate melts, with local heating at the crystallization front exceeding 160˚C in some cases. In circumstellar dust shells, amorphous grains with similar compositions condense at temperatures near their glass transition, and if they crystallize, they will recalesce. The higher temperature (T) of newly crystallized dust allows crystalline spectral features to be seen, because flux emitted depends on T4. After cooling to ambient temperature, crystalline spectral features in the ISM are concealed by volumetrically dominant amorphous dust. Our results explain the existence of crystalline silicate pre-solar grains, which are older than the solar system, and have implications for radiative transfer modeling and hydrodynamics of dusty environments, which are sensitive to small variations in optical properties. Our observations of mm-scale temperature differences up to 100˚C in cooling lava suggest that thermal imaging of basaltic lava flows needs to be conducted with mm-scale spatial resolution (see figure; crucible is 5mm diameter). Temperatures recorded with low spatial resolution, which average cooler melt and hotter crystals in a single pixel, will systematically overestimate the temperature of the liquid phase. Only the surface of a lava flow is likely to cool quickly enough for recalescence to occur, but this is precisely the part of the lava that is monitored by thermal imaging.

Grain Spectroscopy

NASA Technical Reports Server (NTRS)

Allamandola, L. J.

1992-01-01

Our fundamental knowledge of interstellar grain composition has grown substantially during the past two decades thanks to significant advances in two areas: astronomical infrared spectroscopy and laboratory astrophysics. The opening of the mid-infrared, the spectral range from 4000-400 cm(sup -1) (2.5-25 microns), to spectroscopic study has been critical to this progress because spectroscopy in this region reveals more about a materials molecular composition and structure than any other physical property. Infrared spectra which are diagnostic of interstellar grain composition fall into two categories: absorption spectra of the dense and diffuse interstellar media, and emission spectra from UV-Vis rich dusty regions. The former will be presented in some detail, with the latter only very briefly mentioned. This paper summarized what we have learned from these spectra and presents 'doorway' references into the literature. Detailed reviews of many aspects of interstellar dust are given.

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.

The spectral energy distribution of Zeta Puppis and HD 50896

NASA Technical Reports Server (NTRS)

Holm, A. V.; Cassinelli, J. P.

1977-01-01

The ultraviolet spectral energy distribution of the O5f star Zeta Pup and the WN5 star HD 50896 are derived from OAO-2 observations with the calibration of Bless, Code, and Fairchild (1976). An estimate of the interstellar reddening (0.12 magnitude) of the Wolf-Rayet star is determined from the size of the characteristic interstellar extinction bump at 4.6 inverse microns. After correction for extinction, both stars show a flat energy distribution in the ultraviolet. The distribution of HD 50896 from 1100 A to 2 microns is in good agreement with results of extended model atmospheres, but some uncertainty remains because of the interstellar-extinction correction. The absolute energy distribution of Zeta Pup is fitted by a 42,000-K plane-parallel model if the model's flux is adjusted for the effects of electron scattering in the stellar wind and for UV line blanketing that was determined empirically from high-resolution Copernicus satellite observations. To achieve this fit, it is necessary to push both the spectroscopically determined temperature and the ultraviolet calibration to the limits of their probable errors.

Infrared spectroscopy of Jupiter and Saturn

NASA Technical Reports Server (NTRS)

Knacke, Roger F.

1993-01-01

Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter, Saturn, and Titan. In 1991 we obtained data at J, H, K, and M and made repeated observations of Titan's albedo as the satellite orbited Saturn. The J albedo is 12% +/- 3% greater than the albedo measured in 1979; the H and K albedos are the same. There was no evidence for variations at any wavelength over the eastern half of Titan's orbit. We also obtained low resolution (R=50) spectra of Titan between 3.1 and 5.1 microns. The spectra contain evidence for CO and CH3D absorptions. Spectra of Callisto and Ganymede in the 4.5 micron spectral region are featureless and give albedos of 0.08 and 0.04 respectively. If Titan's atmosphere is transparent near 5 microns, its surface albedo there is similar to Callisto's. In 1992 and 1993 we obtained further spectroscopic data of Titan with the UKIRT CGS4 spectrometer. We discovered two unexpected and unexplained spectral features in the 3-4 micron spectrum of Titan. An apparent emission feature near the 3 micron (nu sub 3) band of methane indicated temperatures higher than known to be present in Titan's upper stratosphere and may be caused by unexpected non-LTE emission. An absorption feature near 3.47 microns may be caused by absorption in solid grains or aerosols in Titan's clouds. The feature is similar but not identical to organics in the interstellar matter and in comets.

MILLIMETER WAVE SPECTRUM AND ASTRONOMICAL SEARCH FOR VINYL FORMATE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alonso, E. R.; Kolesniková, L.; Cabezas, C.

2016-11-20

Previous detections of methyl and ethyl formate make other small substituted formates potential candidates for observation in the interstellar medium. Among them, vinyl formate is one of the simplest unsaturated carboxylic ester. The aim of this work is to provide direct experimental frequencies of the ground vibrational state of vinyl formate in a large spectral range for astrophysical use. The room-temperature rotational spectrum of vinyl formate has been measured from 80 to 360 GHz and analyzed in terms of Watson’s semirigid rotor Hamiltonian. Two thousand six hundred transitions within J = 3–88 and K {sub a} = 0–28 were assignedmore » to the most stable conformer of vinyl formate and a new set of spectroscopic constants was accurately determined. Spectral features of vinyl formate were then searched for in Orion KL, Sgr B2(N), B1-b, and TMC-1 molecular clouds. Upper limits to the column density of vinyl formate are provided.« less

Spectrophotometry of Wolf-Rayet stars. I - Continuum energy distributions

NASA Technical Reports Server (NTRS)

Morris, Patrick W.; Brownsberger, Kenneth R.; Conti, Peter S.; Massey, Philip; Vacca, William D.

1993-01-01

All available low-resolution IUE spectra are assembled for Galactic, LMC, and SMC W-R stars and are merged with ground-based optical and NIR spectra in order to collate in a systematic fashion the shapes of these energy distributions over the wavelength range 0.1-1 micron. They can be consistently fitted by a power law of the form F(lambda) is approximately equal to lambda exp -alpha over the range 1500-9000 A to derive color excesses E(B-V) and spectral indices by removing the 2175-A interstellar absorption feature. The WN star color excesses derived are found to be in good agreement with those of Schmutz and Vacca (1991) and Koesterke et al. (1991). Significant heterogeneity in spectral index values was generally seen with any given subtype, but the groups consisting of the combined set of Galactic and LMC W-R stars, the separate WN and WC sequences, and the Galactic and LMC W-R stars all showed a striking and consistent Gaussian-like frequency distribution of values.

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.

SILICATE COMPOSITION OF THE INTERSTELLAR MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fogerty, S.; Forrest, W.; Watson, D. M.

2016-10-20

The composition of silicate dust in the diffuse interstellar medium and in protoplanetary disks around young stars informs our understanding of the processing and evolution of the dust grains leading up to planet formation. An analysis of the well-known 9.7 μ m feature indicates that small amorphous silicate grains represent a significant fraction of interstellar dust and are also major components of protoplanetary disks. However, this feature is typically modeled assuming amorphous silicate dust of olivine and pyroxene stoichiometries. Here, we analyze interstellar dust with models of silicate dust that include non-stoichiometric amorphous silicate grains. Modeling the optical depth alongmore » lines of sight toward the extinguished objects Cyg OB2 No. 12 and ζ Ophiuchi, we find evidence for interstellar amorphous silicate dust with stoichiometry intermediate between olivine and pyroxene, which we simply refer to as “polivene.” Finally, we compare these results to models of silicate emission from the Trapezium and protoplanetary disks in Taurus.« less

Direct spectroscopic evidence for ionized polycyclic aromatic hydrocarbons in the interstellar medium.

PubMed

Sloan, G C; Hayward, T L; Allamandola, L J; Bregman, J D; DeVito, B; Hudgins, D M

1999-03-01

Long-slit 8-13 micrometers spectroscopy of the nebula around NGC 1333 SVS 3 reveals spatial variations in the strength and shape of emission features that are probably produced by polycyclic aromatic hydrocarbons (PAHs). Close to SVS 3, the 11.2 micrometers feature develops an excess at approximately 10.8-11.0 micrometers and a feature appears at approximately 10 micrometers. These features disappear with increasing distance from the central source, and they show striking similarities to recent laboratory data of PAH cations, providing the first identification of emission features arising specifically from ionized PAHs in the interstellar medium.

Spectral Properties of Gas-phase Condensed Fullerene-like Carbon Nanoparticles from Far-ultraviolet to Infrared Wavelengths

NASA Astrophysics Data System (ADS)

Jäger, C.; Mutschke, H.; Henning, Th.; Huisken, F.

2008-12-01

Carbon solids are ubiquitous material in interstellar space. However, the formation pathway of carbonaceous matter in astrophysical environments, as well as in terrestrial gas-phase condensation reactions, is not yet understood. Laser ablation of graphite in different quenching gas atmospheres, such as pure He, He/H2, and He/H2O at varying pressures, is used to synthesize very small, fullerene-like carbon nanoparticles. The particles are characterized by very small diameters between 1 and 4 nm and a disturbed onion-like structure. The soot particles extracted from the condensation zone obviously represent a very early stage of particle condensation. The spectral properties have been measured from the far-ultraviolet (FUV; λ = 120 nm) to the mid-infrared (MIR; λ = 15 μm). The seedlike soot particles show strong absorption bands in the 3.4 μm range. The profile and the intensity pattern of the 3.4 μm band of the diffuse interstellar medium can be well reproduced by the measured 3.4 μm profile of the condensed particles; however, all the carbon which is left to form solids is needed to fit the intensity of the interstellar bands. In contrast to the assumption that onion-like soot particles could be the carriers of the interstellar ultraviolet (UV) bump, our very small onion-like carbon nanoparticles do not show distinct UV bands due to (π-π*) transitions.

Vibrational Spectroscopy after OSU - From C2- to Interstellar Polycyclic Aromatic Hydrocarbons

NASA Technical Reports Server (NTRS)

Allamandola, Louis J.

2006-01-01

The composition of interstellar ice and dust provides insight into the chemical history of the interstellar medium and early solar system. It is now possible to probe this unique and unusual chemistry and determine the composition of these microscopic interstellar particles which are hundreds to many thousands of light years away thanks to substantial progress in two areas: astronomical spectroscopic techniques in the middle-infrared, the spectral region most diagnostic of chemical composition, and laboratory simulations which realistically reproduce the critical conditions in various interstellar environments. High quality infrared spectra of many different astronomical sources, some associated with giant, dark molecular clouds -the birthplace of stars and planets- and others in more tenuous, UV radiation rich regions are now available. The fundamentals of IR spectroscopy and what comparisons of astronomical IR spectra with laboratory spectra of materials prepared under realistic simulated interstellar conditions tell us about the components of these materials is the subject of this talk. These observations have shown that mixed molecular ices comprised of H2O, CH3OH, CO, NH3 and H2CO contain most of the molecular material in molecular clouds and that gas phase, ionized polycyclic aromatic hydrocarbons (PAHs) are widespread and surprisingly abundant throughout most of the interstellar medium.

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.

Absolute Infrared Intensities and Interstellar Ice Abundances- From Neutrals to Ions

NASA Astrophysics Data System (ADS)

Gerakines, Perry

Infrared (IR) telescopes, such as Spitzer and SOFIA, have revealed a rich variety of chemical species trapped in interstellar ices. However, quantifying the abundances of these species has been difficult because some molecules, such as formaldehyde (H2CO), and some ions, such as ammonium (NH4+), have poorly-known IR optical parameters, such as band strengths and optical constants. In the case of NH4+, the most widely used band-intensity values are from a mere two measurements published over a decade ago. Those two experiments cannot be repeated or checked as the original publication provided no information on reaction temperature, heating rate, spectral resolution, and so forth, and the two authors are no longer active in the field. Moreover, neither kinetic data nor statistics on the two measurements were provided, clearly an unsatisfactory situation. Exacerbating the problem is that NH4+ is sometimes used as a check on the IR spectral intensities of other ions, such as OCN- (cyanate), which has its own checkered past. We propose to correct these problems associated with abundance determinations of selected interstellar ices. We will combine two recent successful efforts from our laboratory and measure band intensities for NH4+ and OCN-, as well as HCOO- (formate). To unravel the interstellar formate band requires that we also properly determine its spectral baseline to distinguish from co-absorbing species, primarily formaldehyde (H2CO). Since the latter also has, at best, poorly-determined IR absolute intensities, we will measure them at multiple temperatures and ice phases for this project. This work will build on our recent success in deriving optical constants from IR spectra for interstellar hydrocarbon and nitrile ices (Hudson et al., 2014a, 2014b), and in generating NH4+ in situ for a study of Jupiter's atmosphere (Loeffler and Hudson, 2015). As a bonus, the proposed measurements also will enable the determination of band-strengths for such ions as CN-, NO3-, HS-, and ClO4-. High-quality IR intensities of neutral covalently-bonded ice molecules have been measured and published by our team. We now propose to make the transition to ions.

AIRES: an Airborne Infra-Red Echelle Spectrometer for SOFIA

NASA Astrophysics Data System (ADS)

Erickson, E. F.; Haas, M. R.; Colgan, S. W. J.; Roellig, T.; Simpson, J. P.; Telesco, C. M.; Pina, R. K.; Young, E. T.; Wolf, J.

1997-12-01

The Stratospheric Observatory for Infrared Astronomy, SOFIA, is a 2.7 meter telescope which is scheduled to begin observations in a Boeing 747 in October 2001. Among other SOFIA science instruments recently selected for development is the facility spectrometer AIRES. AIRES is designed for studies of a broad range of phenomena occuring in the interstellar medium (ISM) which are uniquely enabled by SOFIA. Examples include accretion and outflow in protostars and young stellar objects, the morphology, dynamics, and excitation of neutral and ionized gas at the Galactic center, and the recycling of material to the ISM from evolved stars. Astronomers using AIRES will be able to select any wavelength from 17 to 210 mu m., with corresponding spectral resolving powers ranging from 60,000 to 4000 in less than a minute. This entire wavelength range is important because it contains spectral features, often widely separated in wavelength, which characterize fundamental ISM processes. AIRES will utilize two-dimensional detector arrays and a large echelle grating to achieve spectral imaging with excellent sensitivity and unparalleled angular resolution at these wavelengths. As a facility science instrument, AIRES will provide guest investigators frequent opportunities for far infrared spectroscopic observations when SOFIA begins operations.

News and Views: Gemini hits 1000 papers; Comet Elenin? Forget it! Sellers launches course; Merry Christmas from 18th-century Lapland; ET: where are they all hiding? SETI in the city; Complex organic molecules may not mean life

NASA Astrophysics Data System (ADS)

2011-12-01

No-one has yet found artefacts from an alien civilization, but have we looked hard enough? Astronomers seeking signs of extraterrestrial intelligence have suggested a novel approach: look for alien cities. The search for signs of life in the universe has included the detection of complex organic molecules, seen as a step on the way to living things. But now analysis of spectral signatures known as Unidentified Infrared Emission features found in stars, interstellar space and galaxies suggest that complex organic molecules can be made in stars in a matter of weeks without the presence of life.

Interstellar PAH emission in the 11-14 micron region: new insights from laboratory data and a tracer of ionized PAHs

NASA Technical Reports Server (NTRS)

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

1999-01-01

The Ames infrared spectral database of isolated, neutral and ionized polycyclic aromatic hydrocarbons (PAHS) shows that aromatic CH out-of-plane bending frequencies are significantly shifted upon ionization. For solo- and duet-CH groups, the shift is pronounced and consistently toward higher frequencies. The solo-CH modes are blueshifted by an average of 27 cm-1 and the duet-CH modes by an average of 17 cm-1. For trio- and quartet-CH groups, the ionization shifts of the out-of-plane modes are more erratic and typically more modest. As a result of these ionization shifts, the solo-CH out-of-plane modes move out of the region classically associated with these vibrations in neutral PAHS, falling instead at frequencies well above those normally attributed to out-of-plane bending, vibrations of any type. In addition, for the compact PAHs studied, the duet-CH out-of-plane modes are shifted into the frequency range traditionally associated with the solo-CH modes. These results refine our understanding of the origin of the dominant interstellar infrared emission feature near 11.2 microns, whose envelope has traditionally been attributed only to the out-of-plane bending of solo-CH groups on PAHS, and provide a natural explanation for the puzzling emission feature near 11.0 microns within the framework of the PAH model. Specifically, the prevalent but variable long-wavelength wing or shoulder that is often observed near 11.4 microns likely reflects the contributions of duet-CH units in PAH cations. Also, these results indicate that the emission between 926 and 904 cm-1 (10.8 and 11.1 microns) observed in many sources can be unambiguously attributed to the out-of-plane wagging, of solo-CH units in moderately sized (fewer than 50 carbon atom) PAH cations, making this emission an unequivocal tracer of ionized interstellar PAHS.

Theoretical microwave spectral constants for C2N, C2N/+/, and C3H

NASA Technical Reports Server (NTRS)

Green, S.

1980-01-01

Theoretical microwave spectral constants have been computed for C2N, C3H, and C2N(+). For C2N these are compared with values obtained from optical data. Calculated hyperfine constants are also presented for HNC, DNC, and HCNH(+). The possibility of observing these species in dense interstellar clouds is discussed.

PUMA: the first results of a nebular spectrograph for the study of the kinematics of interstellar medium

NASA Astrophysics Data System (ADS)

Langarica, Rosalia; Bernal, Abel; Rosado, Margarita; Cobos Duenas, Francisco J.; Garfias, Fernando; Gutierrez, Leonel; Le Coarer, Etienne; Tejada, Carlos; Tinoco, Silvio J.

1998-07-01

The kinematics of the interstellar medium may be studied by means of a scanning Fabry-Perot interferometer (SFPI). This allows the coverage of a wider field of view with higher spatial and spectral resolution than when a high-dispersion classical spectrograph is used. The system called PUMA consists of a focal reducer and a SFPI installed in the 2.1 m telescope of the San Pedro Martir National Astronomical Observatory (SPM), Mexico, in its f/7.5 configuration. It covers a field of view of 10 arcmin providing direct images as well as interferograms which are focused on a 1024 X 1024 Tektronix CCD, covering a wide spectral range. It is considered the integration of other optical elements for further developments. The optomechanical system and the developed software allow exact, remote positioning of all movable parts and control the FPI scanning and data acquisition. The parallelism of the interferometer plates is automatically achieved by a custom method. The PUMA provides spectral resolutions of 0.414 Angstrom and a free spectral range of 19.8 Angstrom. Results of high quality that compete with those obtained by similar systems in bigger telescopes, are presented.

EUV spectroscopy in astrophysics: The role of compact objects

NASA Astrophysics Data System (ADS)

Wood, K. S.; Kowalski, M. P.; Cruddace, R. G.; Barstow, M. A.

2006-01-01

The bulk of radiation from million-degree plasmas is emitted at EUV wavelengths. Such plasmas are ubiquitous in astrophysics, and examples include the atmospheres of white dwarfs, accretion phenomena in cataclysmic variables (CVs) and some active galactic nuclei (AGN), the coronae of active stars, and the interstellar medium (ISM) of our own galaxy as well as of others. Internally, white dwarfs are formally analogous to neutron stars, being stellar configurations where the thermal contribution to support is secondary. Both stellar types have various intrinsic and environmental parameters. Comparison of such analogous systems using scaled parameters can be fruitful. Source class characterization is mature enough that such analogies can be used to compare theoretical ideas across a wide dynamic range in parameters, one example being theories of quasiperiodic oscillations. However, the white dwarf side of this program is limited by the available photometry and spectroscopy at EUV wavelengths, where there exist critical spectral features that contain diagnostic information often not available at other wavelengths. Moreover, interstellar absorption makes EUV observations challenging. Results from an observation of the hot white dwarf G191-B2B are presented to demonstrate the promise of high-resolution EUV spectroscopy. Two types of CVs, exemplified by AM Her and EX Hya, are used to illustrate blending of spectroscopy and timing measurements. Dynamical timescales and envisioned performance parameters of next-generation EUV satellites (effective area >20 cm 2, spectral resolution >10,000) make possible a new level of source modeling. The importance of the EUV cannot be overlooked given that observations are continually being pushed to cosmological distances, where the spectral energy distributions of X-ray bright AGNs, for example, will have their maxima redshifted into the EUV. Sometimes wrongly dismissed for limitations of small bandwidth or local view from optical depth limitations, the EUV is instead a gold mine of information bearing upon key issues in compact objects, but it is information that must be won through the triple combination of high-spectral resolution, large area, and application of advanced theory.

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium.

PubMed

Chiar, J E; Pendleton, Y J; Geballe, T R; Tielens, A G

1998-11-01

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium

NASA Technical Reports Server (NTRS)

Chiar, J. E.; Pendleton, Y. J.; Geballe, T. R.; Tielens, A. G.

1998-01-01

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

Interstellar and Ejecta Dust in the Cas A Supernova Remnant

NASA Technical Reports Server (NTRS)

Arendt, Richard G.; Dwek, Eli; Kober, Gladys; Rho, Jonghee; Hwang, Una

2013-01-01

The ejecta of the Cas A supernova remnant has a complex morphology, consisting of dense fast-moving line emitting knots and diffuse X-ray emitting regions that have encountered the reverse shock, as well as more slowly expanding, unshocked regions of the ejecta. Using the Spitzer 5-35 micron IRS data cube, and Herschel 70, 100, and 160 micron PACS data, we decompose the infrared emission from the remnant into distinct spectral components associated with the different regions of the ejecta. Such decomposition allows the association of different dust species with ejecta layers that underwent distinct nuclear burning histories, and determination of the dust heating mechanisms. Our decomposition identified three characteristic dust spectra. The first, most luminous one, exhibits strong emission features at approx. 9 and 21 micron, and a weaker 12 micron feature, and is closely associated with the ejecta knots that have strong [Ar II] 6.99 micron and [Ar III] 8.99 micron emission lines. The dust features can be reproduced by magnesium silicate grains with relatively low MgO-to-SiO2 ratios. A second, very different dust spectrum that has no indication of any silicate features, is best fit by Al2O3 dust and is found in association with ejecta having strong [Ne II] 12.8 micron and [Ne III] 15.6 micron emission lines. A third characteristic dust spectrum shows features that best matched by magnesium silicates with relatively high MgO-to-SiO2 ratio. This dust is primarily associated with the X-ray emitting shocked ejecta and the shocked interstellar/circumstellar material. All three spectral components include an additional featureless cold dust component of unknown composition. Colder dust of indeterminate composition is associated with [Si II] 34.8 micron emission from the interior of the SNR, where the reverse shock has not yet swept up and heated the ejecta. The dust mass giving rise to the warm dust component is about approx. 0.1solar M. However, most of the dust mass is associated with the unidentified cold dust component. Its mass could be anywhere between 0.1 and 1 solar M, and is primarily limited by the mass of refractory elements in the ejecta. Given the large uncertainty in the dust mass, the question of whether supernovae can produce enough dust to account for ISM dust masses in the local and high-z universe remains largely unresolved.

The Frequency Evolution of Interstellar Pulse Broadening from Radio Pulsars

NASA Astrophysics Data System (ADS)

Löhmer, O.; Mitra, D.; Gupta, Y.; Kramer, M.; Ahuja, A.

2004-10-01

Using radio pulsars as probes of the interstellar medium (ISM) we study the frequency evolution of interstellar scattering. The frequency dependence of scatter broadening times, τsc, for most of the pulsars with low and intermediate dispersion measures (DM ≲ 400 pc cm-3) is consistent with the Kolmogorov spectrum of electron density fluctuations in a turbulent medium. In contrast, the measured τsc's for highly dispersed pulsars in the central region of the Galaxy are larger than expected and show a spectrum which is flatter than the Kolmogorov law. We analyse the first measurements of spectral indices of scatter broadening over the full known DM range and discuss possible explanations for the anomalous scattering behaviour along peculiar lines of sight (LOS).

UV spectroscopy including ISM line absorption: of the exciting star of Abell 35

NASA Astrophysics Data System (ADS)

Ziegler, M.; Rauch, T.; Werner, K.; Kruk, J. W.

Reliable spectral analysis that is based on high-resolution UV observations requires an adequate, simultaneous modeling of the interstellar line absorption and reddening. In the case of the central star of the planetary nebula Abell 35, BD-22 3467, we demonstrate our current standard spectral-analysis method that is based on the Tübingen NLTE Model-Atmosphere Package (TMAP). We present an on- going spectral analysis of FUSE and HST/STIS observations of BD-22 3467.

Dust silicate emission in FIR/submm

NASA Astrophysics Data System (ADS)

Coupeaud, A.; Demyk, K.; Mény, C.; Nayral, C.

2010-12-01

The far-infrared to millimeter wavelength (FIR-mm) range in astronomical observations is dominated by the thermal emission from large (10-100 nm) and cold (10-20 K) dust grains, which are in thermal equilibrium with the interstellar radiation field. However, the physics of the FIR-mm emission from such cold matter is not well understood as shown by the observed dependence with the temperature of the spectral index of the dust emissivity β and by the observed far infrared excess. Interestingly, a similar behaviour is observed in experiments of characterization of the spectral properties of dust analogues. We present a study of the optical properties of analogues of interstellar silicate grains at low temperature in the FIR/submm range aiming to understand their peculiar behaviour. Such studies are essential for the interpretation of the Herschel and Planck data.

Investigating the high-frequency spectral features of SNRs Tycho, W44 and IC443 with the Sardinia Radio Telescope

NASA Astrophysics Data System (ADS)

Loru, S.; Pellizzoni, A.; Egron, E.; Righini, S.; Iacolina, M. N.; Mulas, S.; Cardillo, M.; Marongiu, M.; Ricci, R.; Bachetti, M.; Pilia, M.; Trois, A.; Ingallinera, A.; Petruk, O.; Murtas, G.; Serra, G.; Concu, F. Buffa R.; Gaudiomonte, F.; Melis, A.; Navarrini, A.; Perrodin, D.; Valente, G.

2018-05-01

The main characteristics in the radio continuum spectra of Supernova Remnants (SNRs) result from simple synchrotron emission. In addition, electron acceleration mechanisms can shape the spectra in specific ways, especially at high radio frequencies. These features are connected to the age and the peculiar conditions of the local interstellar medium interacting with the SNR. Whereas the bulk radio emission is expected at up to 20 - 50 GHz, sensitive high-resolution images of SNRs above 10 GHz are lacking and are not easily achievable, especially in the confused regions of the Galactic Plane. In the framework of the early science observations with the Sardinia Radio Telescope in February-March 2016, we obtained high-resolution images of SNRs Tycho, W44 and IC443 that provided accurate integrated flux density measurements at 21.4 GHz: 8.8 ± 0.9 Jy for Tycho, 25 ± 3 Jy for W44 and 66 ± 7 Jy for IC443. We coupled the SRT measurements with radio data available in the literature in order to characterise the integrated and spatially-resolved spectra of these SNRs, and to find significant frequency- and region-dependent spectral slope variations. For the first time, we provide direct evidence of a spectral break in the radio spectral energy distribution of W44 at an exponential cutoff frequency of 15 ± 2 GHz. This result constrains the maximum energy of the accelerated electrons in the range 6 - 13 GeV, in agreement with predictions indirectly derived from AGILE and Fermi-LAT gamma-ray observations. With regard to IC443, our results confirm the noticeable presence of a bump in the integrated spectrum around 20 - 70 GHz that could result from a spinning dust emission mechanism.

On the nature of absorption features toward nearby stars

NASA Astrophysics Data System (ADS)

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

2016-06-01

Context. Diffuse interstellar absorption bands (DIBs) of largely unknown chemical origin are regularly observed primarily in distant early-type stars. More recently, detections in nearby late-type stars have also been claimed. These stars' spectra are dominated by stellar absorption lines. Specifically, strong interstellar atomic and DIB absorption has been reported in τ Boo. Aims: We test these claims by studying the strength of interstellar absorption in high-resolution TIGRE spectra of the nearby stars τ Boo, HD 33608, and α CrB. Methods: We focus our analysis on a strong DIB located at 5780.61 Å and on the absorption of interstellar Na. First, we carry out a differential analysis by comparing the spectra of the highly similar F-stars, τ Boo and HD 33608, whose light, however, samples different lines of sight. To obtain absolute values for the DIB absorption, we compare the observed spectra of τ Boo, HD 33608, and α CrB to PHOENIX models and carry out basic spectral modeling based on Voigt line profiles. Results: The intercomparison between τ Boo and HD 33608 reveals that the difference in the line depth is 6.85 ± 1.48 mÅ at the DIB location which is, however, unlikely to be caused by DIB absorption. The comparison between PHOENIX models and observed spectra yields an upper limit of 34.0 ± 0.3 mÅ for any additional interstellar absorption in τ Boo; similar results are obtained for HD 33608 and α CrB. For all objects we derive unrealistically large values for the radial velocity of any presumed interstellar clouds. In τ Boo we find Na D absorption with an equivalent width of 0.65 ± 0.07 mÅ and 2.3 ± 0.1 mÅ in the D2 and D1 lines. For the other Na, absorption of the same magnitude could only be detected in the D2 line. Our comparisons between model and data show that the interstellar absorption toward τ Boo is not abnormally high. Conclusions: We find no significant DIB absorption in any of our target stars. Any differences between modeled and observed spectra are instead attributable to inaccuracies in the stellar atmospheric modeling than to DIB absorption. The spectra are 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/591/A20

The interstellar N2 abundance towards HD 124314 from far-ultraviolet observations.

PubMed

Knauth, David C; Andersson, B-G; McCandliss, Stephan R; Moos, H Warren

2004-06-10

The abundance of interstellar molecular nitrogen (N2) is of considerable importance: models of steady-state gas-phase interstellar chemistry, together with millimetre-wavelength observations of interstellar N2H+ in dense molecular clouds predict that N2 should be the most abundant nitrogen-bearing molecule in the interstellar medium. Previous attempts to detect N2 absorption in the far-ultraviolet or infrared (ice features) have hitherto been unsuccessful. Here we report the detection of interstellar N2 at far-ultraviolet wavelengths towards the moderately reddened star HD 124314 in the constellation of Centaurus. The N2 column density is larger than expected from models of diffuse clouds and significantly smaller than expected for dense molecular clouds. Moreover, the N2 abundance does not explain the observed variations in the abundance of atomic nitrogen (N I) towards high-column-density sightlines, implying that the models of nitrogen chemistry in the interstellar medium are incomplete.

Copernicus observations of interstellar matter in the direction of HR 1099

NASA Technical Reports Server (NTRS)

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

1978-01-01

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

BD-22deg3467, a DAO-type Star Exciting the Nebula Abell 35

NASA Technical Reports Server (NTRS)

Ziegler, M.; Rauch, T.; Werner, K.; Koppen, J.; Kruk, J. W.

2013-01-01

Spectral analyses of hot, compact stars with non-local thermodynamical equilibrium (NLTE) model-atmosphere techniques allow the precise determination of photospheric parameters such as the effective temperature (T(sub eff)), the surface gravity (log g), and the chemical composition. The derived photospheric metal abundances are crucial constraints for stellar evolutionary theory. Aims. Previous spectral analyses of the exciting star of the nebula A35, BD-22deg3467, were based on He+C+N+O+Si+Fe models only. For our analysis, we use state-of-the-art fully metal-line blanketed NLTE model atmospheres that consider opacities of 23 elements from hydrogen to nickel. We aim to identify all observed lines in the ultraviolet (UV) spectrum of BD-22deg3467 and to determine the abundances of the respective species precisely. Methods. For the analysis of high-resolution and high signal-to-noise ratio (S/N) far-ultraviolet (FUSE) and UV (HST/STIS) observations, we combined stellar-atmosphere models and interstellar line-absorption models to fully reproduce the entire observed UV spectrum. Results. The best agreement with the UV observation of BD-22deg3467 is achieved at T(sub eff) = 80 +/- 10 kK and log g = 7.2 +/- 0.3. While T(sub eff) of previous analyses is verified, log g is significantly lower. We re-analyzed lines of silicon and iron (1/100 and about solar abundances, respectively) and for the first time in this star identified argon, chromium, manganese, cobalt, and nickel and determined abundances of 12, 70, 35, 150, and 5 times solar, respectively. Our results partially agree with predictions of diffusion models for DA-type white dwarfs. A combination of photospheric and interstellar line-absorption models reproduces more than 90% of the observed absorption features. The stellar mass is M approx. 0.48 Solar Mass. Conclusions. BD.22.3467 may not have been massive enough to ascend the asymptotic giant branch and may have evolved directly from the extended horizontal branch to the white dwarf state. This would explain why it is not surrounded by a planetary nebula. However, the star, ionizes the ambient interstellar matter, mimicking a planetary nebula.

MORE EVIDENCE THAT VOYAGER 1 IS STILL IN THE HELIOSPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gloeckler, G.; Fisk, L. A., E-mail: gglo@umich.edu

The investigators of the Voyager mission currently exploring the heliosheath have concluded and announced that Voyager 1 (V1) has crossed the heliopause and is now in the interstellar medium. This conclusion is based primarily on the plasma wave observations of Gurnett et al., which reveal a plasma electron density that resembles the density expected in the local interstellar medium. Fisk and Gloeckler have disputed the conclusion that V1 has crossed the heliopause, pointing out that to account for all the V1 observations, particularly the magnetic field direction together with the density, it is necessary to conclude that the higher densitiesmore » observed by Gurnett et al. are due to compressed solar wind. In this Letter it is shown that the model of Fisk and Gloeckler for the nose region of the heliosheath can account in detail for the intensity and spectral shape of Energetic Neutral Hydrogen observed by the Interstellar Boundary Explorer (IBEX) in the directions of V1 and Voyager 2 (V2). A key feature of the Fisk and Gloeckler model is the existence of a region in the heliosheath where the solar wind is compressed and heated, followed by a region where the solar wind is compressed but cold. The region of cold compressed solar wind provides a unique explanation for the low-energy IBEX observations, and since this is the region where V1 must now reside, the low-energy IBEX observations provide strong evidence that V1 is still in the heliosphere.« less

Analysis of Spectral-type A/B Stars in Five Open Clusters

NASA Astrophysics Data System (ADS)

Wilhelm, Ronald J.; Rafuil Islam, M.

2014-01-01

We have obtained low resolution (R = 1000) spectroscopy of N=68, spectral-type A/B stars in five nearby open star clusters using the McDonald Observatory, 2.1m telescope. The sample of blue stars in various clusters were selected to test our new technique for determining interstellar reddening and distances in areas where interstellar reddening is high. We use a Bayesian approach to find the posterior distribution for Teff, Logg and [Fe/H] from a combination of reddened, photometric colors and spectroscopic line strengths. We will present calibration results for this technique using open cluster star data with known reddening and distances. Preliminary results suggest our technique can produce both reddening and distance determinations to within 10% of cluster values. Our technique opens the possibility of determining distances for blue stars at low Galactic latitudes where extinction can be large and differential. We will also compare our stellar parameter determinations to previously reported MK spectral classifications and discuss the probability that some of our stars are not members of their reported clusters.

The pre- and post-accretion irradiation history of cometary ices

NASA Technical Reports Server (NTRS)

Chyba, Christopher; Sagan, Carl

1989-01-01

Comets Halley and Wilson exhibited similar 3.4 micron emission features at approx. 1 AU from the Sun. A simple model of thermal emission from organic grains fits the feature, provides optical depths in good agreement with spacecraft measurements, and explains the absence of longer-wavelength organic features as due to spectral heliocentric evolution (Chyba and Sagan, 1987). The model utilizes transmission spectra of organics synthesized in the laboratory by irradiation of candidate cometary ices; the authors have long noted that related gas-phase syntheses yield polycyclic aromatic hydrocarbons, among other organic residues (Sagan et al., 1967). The authors previously concluded (Chyba and Sagan, 1987) that Halley's loss of several meters' depth with each perihelion passage, combined with the good fit of the Halley 3.4 micron feature to that of comet Wilson (Allen and Wickramasinghe, 1987), argues for the primordial - but not necessarily interstellar - origin of cometary organics. The authors examine the relative importance to the formation of organics of the variety of radiation environments experienced by comets. They conclude that there is at present no compelling reason to choose any of three contributing mechanisms (pre-accretion UV, pre-accretion cosmic ray, and post-accretion radionuclide processing) as the most important.

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

NASA Technical Reports Server (NTRS)

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

1972-01-01

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

X-ray spectroscopic observations and modeling of supernova remnants

NASA Technical Reports Server (NTRS)

Shull, J. M.

1981-01-01

The X-ray observations of young remnants and their theoretical interpretation are described. A number of questions concerning the nature of the blast wave interaction with the interstellar gas and grains and of atomic processes in these hot plasmas are considered. It is concluded that future X-ray spectrometers with high collecting area, moderate spectral resolution and good spatial resolution can make important contributions to the understanding of supernova remnants in the Milky Way and neighboring galaxies and of their role in the global chemical and dynamical evolution of the interstellar medium.

Interstellar lines in the spectra of four stars

NASA Technical Reports Server (NTRS)

Hobbs, L. M.

1979-01-01

Observations of optical interstellar absorption lines arising from Na I, K I, and/or Ca II are reported in the spectra of HD 72127, Iota(1) Sco, 102 Her, and 6 Cas. Line components showing strikingly large Ca II/Na I ratios are found toward HD 72127 and are verified for 102 Her. The absorption toward Iota(1) Sco and 6 Cas illustrates features of the local galactic distribution of interstellar gas.

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

This paper presents the results of an investigation of the molecular characteristics that underlie the observed peak position and profile of the nominal 6.2 micron interstellar emission band generally attributed to the CC stretching vibrations of polycyclic aromatic hydrocarbons (PAHs). It begins with a summary of recent experimental and theoretical studies ofthe spectroscopic properties of large (>30 carbon atoms) PAH cations as they relate to this aspect of the astrophysical problem. It then continues with an examination of the spectroscopic properties of a number of PAH variants within the context of the interstellar 6.2 micron emission, beginning with a class of compounds known as polycyclic aromatic nitrogen heterocycles (PANHs; PAHs with one or more nitrogen atoms substituted into their carbon skeleton). In this regard, we summarize the results of recent relevant experimental studies involving a limited set of small PANHs and their cations and then report the results of a comprehensive computational study that extends that work to larger PANH cations including many nitrogen-substituted variants of coronene(+) (C24H12(+)), ovalene(+) (C32H14(+)), circumcoronene(+) (C54H18(+)), and circum-circumcoronene(+) (C96H24(+)). Finally, we report the results of more focused computational studies of selected representatives from a number of other classes of PAH variants that share one or more of the key attributes of the PANH species studied. These alternative classes of PAH variants include (1) oxygen- and silicon-substituted PAH cations; (2) PAH-metal ion complexes (metallocenes) involving the cosmically abundant elements magnesium and iron; and (3) large, asymmetric PAH cations. Overall, the studies reported here demonstrate that increasing PAH size alone is insuEcient to account for the position of the shortest wavelength interstellar 6.2 micron emission bands, as had been suggested by earlier studies. On the other hand, this work reveals that substitution of one or 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.

Lunar and Planetary Science XXXVI, Part 10

NASA Technical Reports Server (NTRS)

2005-01-01

The Problem of Incomplete Mixing of Interstellar Components in the Solar Nebula: Very High Precision Isotopic Measurements with Isoprobes P and T. Finally: Presolar Graphite Grains Identified in Orgueil. Basaltic Ring Structures as an Analog for Ring Features in Athabasca Valles, Mars. Experimental Studies of the Water Sorption Properties of Mars-Relevant Porous Minerals and Sulfates. Silicon Isotope Ratio Variations in CAI Evaporation Residues Measured by Laser Ablation Multicollector ICPMS. Crater Count Chronology and Timing of Ridged Plains Emplacement at Schiaparelli Basin, Mars. Martian Valley Networks and Associated Fluvial Features as Seen by the Mars Express High Resolution Stereo Camera (HRSC). Fast-Turnoff Transient Electromagnetic (TEM) Field Study at the Mars Analog Site of Rio Tinto, Spain. Time Domain Electromagnetics for Mapping Mineralized and Deep Groundwater in Mars Analog Environments. Mineralogical and Seismological Models of the Lunar Mantle. Photometric Observations of Soils and Rocks at the Mars Exploration Rover Landing Sites. Thermal Infrared Spectral Deconvolution of Experimentally Shocked Basaltic Rocks Using Experimentally Shocked Plagioclase Endmembers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lees, R. M.; Xu, Li-Hong; Appadoo, D. R. T.

New astronomical facilities such as HIFI on the Herschel Space Observatory, the SOFIA airborne IR telescope and the ALMA sub-mm telescope array will yield spectra from interstellar and protostellar sources with vastly increased sensitivity and frequency coverage. This creates the need for major enhancements to laboratory databases for the more prominent interstellar 'weed' species in order to model and account for their lines in observed spectra in the search for new and more exotic interstellar molecular 'flowers'. With its large-amplitude internal torsional motion, methanol has particularly rich spectra throughout the FIR and IR regions and, being very widely distributed throughoutmore » the galaxy, is perhaps the most notorious interstellar weed. Thus, we have recorded new spectra for a variety of methanol isotopic species on the high-resolution FTIR spectrometer on the CLS FIR beamline. The aim is to extend quantum number coverage of the data, improve our understanding of the energy level structure, and provide the astronomical community with better databases and models of the spectral patterns with greater predictive power for a range of astrophysical conditions.« less

Missing Fe: hydrogenated iron nanoparticles

NASA Astrophysics Data System (ADS)

Bilalbegović, G.; Maksimović, A.; Mohaček-Grošev, V.

2017-03-01

Although it was found that the FeH lines exist in the spectra of some stars, none of the spectral features in the interstellar medium (ISM) have been assigned to this molecule. We suggest that iron atoms interact with hydrogen and produce Fe-H nanoparticles which sometimes contain many H atoms. We calculate infrared spectra of hydrogenated iron nanoparticles using density functional theory methods and find broad, overlapping bands. Desorption of H2 could induce spinning of these small Fe-H dust grains. Some of hydrogenated iron nanoparticles possess magnetic and electric moments and should interact with electromagnetic fields in the ISM. FenHm nanoparticles could contribute to the polarization of the ISM and the anomalous microwave emission. We discuss the conditions required to form FeH and FenHm in the ISM.

The Nature and Evolution of Interstellar Ices: Studies of Methanol and Carbon Monoxide

NASA Astrophysics Data System (ADS)

Chiar, Jean Elizabeth

The evolution of icy grain mantles is governed by the environment in which they exist. Infrared spectroscopy provides the observational means for detecting absorption features of molecules in the dust. The 3.3-4.0 μm spectral region contains the fundamental C-H stretching vibrations of alcohols and aliphatic hydrocarbons and provides a powerful method of characterizing the organic component of interstellar ices. I discuss hydrocarbon and methanol absorption in several lines of sight in Taurus. My results are consistent with a location for the 3.47 μm absorber in the grain mantle material rather than the core. The 3.54 μm methanol (CH3OH) feature is not detected in any of the sources and the possibility that methanol production requires warm conditions is discussed. The CO profile is observed in lines of sight toward embedded and background objects. Modeling of the CO features is accomplished by fitting laboratory data to the astronomical spectra. This is done for sources in several dark clouds. In general, CO spectra of field stars are best-fitted with pure (or mostly pure) CO along with a minor contribution from the polar component. In contrast, some embedded stars show distinctly different CO profiles. Their spectra are broader than those of field stars and some are best-fitted with laboratory mixtures which imply the presence of CO2. In other cases, where the CO-containing mantles exist in the foreground dust far away from the embedded object, the CO is in pure form. Observations of the 4.27 μm CO2 feature confirm the presence of processed dust along these same lines of sight. Thus, it is likely that the CO and CO2 exist in separate grain populations along the line of sight. In the final chapter of this thesis, I discuss the relevance of this work to origin of life studies.

Complex Organic Materials on Planetary Satellites and Other Small Bodies of the Solar System

NASA Technical Reports Server (NTRS)

Cruikshank, Dale P.

2006-01-01

The search for organic materials on small bodies of the Solar System is conducted spectroscopically from Earth-based telescopes and from spacecraft. Although the carbonaceous meteorites carry a significant inventory of complex organic solids, the sources of these meteorites have not been identified. Infrared spectra of a sample of the suspected sources, the C- and D-class asteroids, including new data from the Spitzer Space Telescope, show signatures of silicates, but none diagnostic of organic compounds. In the absence of discrete spectral features, the low albedos and colors in the visible and near-IR spectral regions are the principal links between the organic-bearing meteorites and the asteroids. While Pluto and a few trans-neptunian objects show spectral signatures of frozen CH4. Solid CH3OH has been identified on two Centaur objects in the outer Solar System. In some cases the red colors of those objects suggest the presence of tholins. The VIMS instrument aboard the Cassini spacecraft in orbit around Saturn has detected near-IR spectral features on at least three of Saturn's satellites that are indicative or suggestive of organic molecules. One entire hemisphere of the satellite Iapetus is covered with low-albedo material that shows a spectral signature of aromatic hydrocarbons (3.3 microns) and the -CH2 stretching mode bands of an aliphatic component. Organics absorbing at 3.44 microns are suspected in the region of the south pole of Enceladus, and also on the surface of Phoebe. Organic material may originate on icy bodies in the current epoch by various processes of energy deposition into native material, or they may fall to the surface from an external (probably cometary) source. Some organic material may be pre-solar, having originated in the interstellar medium before the formation of the Solar System. Using the techniques of remote sensing, its detection and analysis are slow and difficult.

Probing gas and dust in the tidal tail of NGC 5221 with the type Ia supernova iPTF16abc

NASA Astrophysics Data System (ADS)

Ferretti, R.; Amanullah, R.; Goobar, A.; Petrushevska, T.; Borthakur, S.; Bulla, M.; Fox, O.; Freeland, E.; Fremling, C.; Hangard, L.; Hayes, M.

2017-10-01

Context. Type Ia supernovae (SNe Ia) can be used to address numerous questions in astrophysics and cosmology. Due to their well known spectral and photometric properties, SNe Ia are well suited to study gas and dust along the lines-of-sight to the explosions. For example, narrow Na I D and Ca II H&K absorption lines can be studied easily, because of the well-defined spectral continuum of SNe Ia around these features. Aims: We aim to study the gas and dust along the line-of-sight to iPTF16abc, which occurred in an unusual location, in a tidal arm, 80 kpc from centre of the galaxy NGC 5221. Methods: Using a time-series of high-resolution spectra, we have examined narrow Na I D and Ca II H&K absorption features for variations in time, which would be indicative for circumstellar (CS) matter. Furthermore, we have taken advantage of the well known photometric properties of SNe Ia to determine reddening due to dust along the line-of-sight. Results: From the lack of variations in Na I D and Ca II H&K, we determine that none of the detected absorption features originate from the CS medium of iPTF16abc. While the Na I D and Ca II H&K absorption is found to be optically thick, a negligible amount of reddening points to a small column of interstellar dust. Conclusions: We find that the gas along the line-of-sight to iPTF16abc is typical of what might be found in the interstellar medium (ISM) within a galaxy. It suggests that we are observing gas that has been tidally stripped during an interaction of NGC 5221 with one of its neighbouring galaxies in the past 109 yr. In the future, the gas clouds could become the locations of star formation. On a longer time scale, the clouds might diffuse, enriching the circum-galactic medium (CGM) with metals. The gas profile along the line-of-sight should be useful for future studies of the dynamics of the galaxy group containing NGC 5221. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO DDT programme 297.D-5005(A), P. I. Ferretti.

Molecular Spectroscopy in Astrophysics: The Case of Polycyclic Aromatic Hydrocarbons

NASA Technical Reports Server (NTRS)

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

2000-01-01

The role of molecular spectroscopy in astrophysics and astrochemistry is discussed in the context of the study of large, complex, carbon-bearing molecules, namely, Polycyclic Aromatic Hydrocarbons or PAHs. These molecular species are now thought to be widespread in the interstellar medium in their neutral and ionized forms. Identifying the carriers responsible for unidentified interstellar spectral bands will allow to derive important information on cosmic elemental abundances as well as information on the physical conditions (density, temperature) reigning in specific interstellar environments. These, in turn, are key elements for a correct understanding of the energetic mechanisms that govern the origin and the evolution of the interstellar medium. A multidisciplinary approach - combining astronomical observations with laboratory simulations and theoretical modeling - is required to address these complex issues. Laboratory spectra of several PAHs, isolated at low temperature in inert gas matrices or seeded in a supersonic jet expansion, are discussed here and compared to the astronomical spectra of reddened, early type, stars. The electronic spectroscopy of PAHs in the ultraviolet, visible, and near-infrared domains is reviewed and an assessment of the potential contribution of PAHs to the interstellar extinction in the ultraviolet and in the visible is discussed.

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-

The interstellar abundances of tin and four other heavy elements

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Laboratory Needs for Interstellar Ice Studies

NASA Astrophysics Data System (ADS)

Boogert, Abraham C. A.

2012-05-01

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

Simulation of Infrared Spectra of Carbonaceous Grains

NASA Astrophysics Data System (ADS)

Dadswell, G.; Duley, W. W.

1997-02-01

Random covalent network (RCN) theory is applied to describe the infrared spectroscopic properties of carbonaceous solids with compositions containing a mixture of aromatic, aliphatic, and diamond-like hydrocarbons. Application of this technique to carbonaceous dust is equivalent to the synthesis of solids whose structure and bonding satisfy stoicheometry while minimizing strain energy. The result involves a range of compositions compatible with carbon bonding and the hydrogen concentration incorporated in the network. In general, only a limited range of compositions is available rather than the infinite number of possible compositions expected without the inclusion of these constraints. When compositions have been defined in this way, infrared spectra may be synthesized for comparison with astronomical spectra of interstellar carbonaceous solids. Such spectra contain components corresponding to absorption by CHn groups in which n = 1-3. We find, however, that additional spectral features, not included in our simple chemical model, must be present also in dust. We give plots of such spectra in the 3100-2800 cm-1 (3.2-3.6 μm) region for comparison with infrared spectra of interstellar dust. We have also developed an RCN formalism that incorporates oxygen into the carbon network as OH groups, and we show that this inclusion introduces a strong additional absorption band in the 3300 cm-1 (3.0 μm) region.

Rotational spectrum of methoxyamine up to 480 GHz: a laboratory study and astronomical search

NASA Astrophysics Data System (ADS)

Kolesniková, L.; Tercero, B.; Alonso, E. R.; Guillemin, J.-C.; Cernicharo, J.; Alonso, J. L.

2018-01-01

Aims: Methoxyamine is a potential interstellar amine that has been predicted by gas-grain chemical models for the formation of complex molecules. The aim of this work is to provide direct experimental frequencies of its ground-vibrational state in the millimeter- and submillimeter-wave regions to achieve its detection in the interstellar medium. Methods: Methoxyamine was chemically liberated from its hydrochloride salt, and its rotational spectrum was recorded at room temperature from 75 to 480 GHz using the millimeter-wave spectrometer in Valladolid. Many observed transitions revealed A-E splitting caused by the internal rotation of the methyl group, which had to be treated with specific internal rotation codes. Results: Over 400 lines were newly assigned for the most stable conformer of methoxyamine, and a precise set of spectroscopic constants was obtained. Spectral features of methoxyamine were then searched for in the Orion KL, Sgr B2, B1-b, and TMC-1 molecular clouds. Upper limits to the column density of methoxyamine were derived. Table 3 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/609/A24

Imaging of the PAH Emission Bands in the Orion Bar

NASA Technical Reports Server (NTRS)

Bregman, Jesse; Harker, David; Rank, David; Temi, Pasqiale; Morrison, David (Technical Monitor)

1994-01-01

The infrared spectrum of many planetary nebulae, HII regions, galactic nuclei, reflection nebulae, and WC stars are dominated by a set of narrow and broad features which for many years were called the "unidentified infrared bands". These bands have been attributed to several carbon-rich molecular species which all contain only carbon and hydrogen atoms, and fall into the class of PAH molecules or are conglomerates of PAH skeletons. If these bands are from PAHs, then PAHs contain 1-10% of the interstellar carbon, making them the most abundant molecular species in the interstellar medium after CO. From ground based telescopes, we have studied the emission bands assigned to C-H bond vibrations in PAHs (3.3, 11.3 microns) in the Orion Bar region, and showed that their distribution and intensities are consistent with a quantitative PAH model. We have recently obtained spectral images of the Orion Bar from the KAO at 6.2 and 7.7 microns using a 128 x 128 Si:Ga array camera in order to study the C-C modes of the PAH molecules. We will show these new data along with our existing C-H mode data set, and make a quantitative comparison of the data with the existing PAH model.

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) Mission Concept

NASA Technical Reports Server (NTRS)

Ennico, K. A.; Sandford, S. A.; Allamandola, L.; Bregman, J.; Cohen, M.; Cruikshank, D.; Dumas, C.; Greene, T.; Hudgins, D.; Kwok, S.

2004-01-01

The AstroBiology Explorer (ABE) mission concept consists of a dedicated space observatory having a 60 cm class primary mirror cooled to T < 50 K equipped with medium resolution cross-dispersed spectrometers having cooled large format near- and mid-infrared detector arrays. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The mission s observational program would make fundamental scientific progress in establishing the nature, distribution, formation and evolution of organic and other molecular materials in the following extra-terrestrial environments: 1) The Outflow of Dying Stars, 2) The Diffuse Interstellar Medium, 3) Dense Molecular Clouds, Star Formation Regions, and Young StellarPlanetary Systems, 4) Planets, Satellites, and Small Bodies within the Solar System, and 5 ) The Interstellar Media of Other Galaxies. ABE could make fundamental progress in all of these areas by conducting a 1 to 2 year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5-20 micron spectral range at a spectral resolution of R > 2000 of about 1500 objects including galaxies, stars, planetary nebulae, young stellar objects, and solar system objects. Keywords: Astrobiology, infrared, Explorers, interstellar organics, telescope, spectrometer, space, infrared detectors

The ESO Diffuse Interstellar Bands Large Exploration Survey: EDIBLES I. Project description, survey sample and quality assessment.

PubMed

Cox, Nick L J; Cami, Jan; Farhang, Amin; Smoker, Jonathan; Monreal-Ibero, Ana; Lallement, Rosine; Sarre, Peter J; Marshall, Charlotte C M; Smith, Keith T; Evans, Christopher J; Royer, Pierre; Linnartz, Harold; Cordiner, Martin A; Joblin, Christine; van Loon, Jacco Th; Foing, Bernard H; Bhatt, Neil H; Bron, Emeric; Elyajouri, Meriem; de Koter, Alex; Ehrenfreund, Pascale; Javadi, Atefeh; Kaper, Lex; Khosroshadi, Habib G; Laverick, Mike; Le Petit, Franck; Mulas, Giacomo; Roueff, Evelyne; Salama, Farid; Spaans, Marco

2017-10-01

The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the [Formula: see text] fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort to systematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES). The main objective is to build on and extend existing DIB surveys to make a major step forward in characterising the physical and chemical conditions for a statistically significant sample of interstellar lines-of-sight, with the goal to reverse-engineer key molecular properties of the DIB carriers. EDIBLES is a filler Large Programme using the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope at Paranal, Chile. It is designed to provide an observationally unbiased view of the presence and behaviour of the DIBs towards early-spectral type stars whose lines-of-sight probe the diffuse-to-translucent ISM. Such a complete dataset will provide a deep census of the atomic and molecular content, physical conditions, chemical abundances and elemental depletion levels for each sightline. Achieving these goals requires a homogeneous set of high-quality data in terms of resolution ( R ~ 70 000 - 100 000), sensitivity (S/N up to 1000 per resolution element), and spectral coverage (305-1042 nm), as well as a large sample size (100+ sightlines). In this first paper the goals, objectives and methodology of the EDIBLES programme are described and an initial assessment of the data is provided.

The ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES) . I. Project description, survey sample, and quality assessment

NASA Astrophysics Data System (ADS)

Cox, Nick L. J.; Cami, Jan; Farhang, Amin; Smoker, Jonathan; Monreal-Ibero, Ana; Lallement, Rosine; Sarre, Peter J.; Marshall, Charlotte C. M.; Smith, Keith T.; Evans, Christopher J.; Royer, Pierre; Linnartz, Harold; Cordiner, Martin A.; Joblin, Christine; van Loon, Jacco Th.; Foing, Bernard H.; Bhatt, Neil H.; Bron, Emeric; Elyajouri, Meriem; de Koter, Alex; Ehrenfreund, Pascale; Javadi, Atefeh; Kaper, Lex; Khosroshadi, Habib G.; Laverick, Mike; Le Petit, Franck; Mulas, Giacomo; Roueff, Evelyne; Salama, Farid; Spaans, Marco

2017-10-01

The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the C60^+ fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort tosystematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES). The main objective is to build on and extend existing DIB surveys to make a major step forward in characterising the physical and chemical conditions for a statistically significant sample of interstellar lines-of-sight, with the goal to reverse-engineer key molecular properties of the DIB carriers. EDIBLES is a filler Large Programme using the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope at Paranal, Chile. It is designed to provide an observationally unbiased view of the presence and behaviour of the DIBs towards early-spectral-type stars whose lines-of-sight probe the diffuse-to-translucent ISM. Such a complete dataset will provide a deep census of the atomic and molecular content, physical conditions, chemical abundances and elemental depletion levels for each sightline. Achieving these goals requires a homogeneous set of high-quality data in terms of resolution (R 70 000-100 000), sensitivity (S/N up to 1000 per resolution element), and spectral coverage (305-1042 nm), as well as a large sample size (100+ sightlines). In this first paper the goals, objectives and methodology of the EDIBLES programme are described and an initial assessment of the data is provided.

The ESO Diffuse Interstellar Bands Large Exploration Survey: EDIBLES I. Project description, survey sample and quality assessment

PubMed Central

Cox, Nick L. J.; Cami, Jan; Farhang, Amin; Smoker, Jonathan; Monreal-Ibero, Ana; Lallement, Rosine; Sarre, Peter J.; Marshall, Charlotte C. M.; Smith, Keith T.; Evans, Christopher J.; Royer, Pierre; Linnartz, Harold; Cordiner, Martin A.; Joblin, Christine; van Loon, Jacco Th.; Foing, Bernard H.; Bhatt, Neil H.; Bron, Emeric; Elyajouri, Meriem; de Koter, Alex; Ehrenfreund, Pascale; Javadi, Atefeh; Kaper, Lex; Khosroshadi, Habib G.; Laverick, Mike; Le Petit, Franck; Mulas, Giacomo; Roueff, Evelyne; Salama, Farid; Spaans, Marco

2017-01-01

The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the C60+ fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort to systematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES). The main objective is to build on and extend existing DIB surveys to make a major step forward in characterising the physical and chemical conditions for a statistically significant sample of interstellar lines-of-sight, with the goal to reverse-engineer key molecular properties of the DIB carriers. EDIBLES is a filler Large Programme using the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope at Paranal, Chile. It is designed to provide an observationally unbiased view of the presence and behaviour of the DIBs towards early-spectral type stars whose lines-of-sight probe the diffuse-to-translucent ISM. Such a complete dataset will provide a deep census of the atomic and molecular content, physical conditions, chemical abundances and elemental depletion levels for each sightline. Achieving these goals requires a homogeneous set of high-quality data in terms of resolution (R ~ 70 000 – 100 000), sensitivity (S/N up to 1000 per resolution element), and spectral coverage (305–1042 nm), as well as a large sample size (100+ sightlines). In this first paper the goals, objectives and methodology of the EDIBLES programme are described and an initial assessment of the data is provided. PMID:29151608

Boundary Conditions for the Paleoenvironment: Chemical and Physical Processes in Dense Interstellar Clouds: Summary of Research

NASA Technical Reports Server (NTRS)

Irvine, William M.

1999-01-01

The basic theme of this program was the study of molecular complexity and evolution for the biogenic elements and compounds in interstellar clouds and in primitive solar system objects. Research included the detection and study of new interstellar and cometary molecules and investigation of reaction pathways for astrochemistry from a comparison of theory and observed molecular abundances. The latter includes studies of cold, dark clouds in which ion-molecule chemistry should predominate, searches for the effects of interchange of material between the gas and solid phases in interstellar clouds, unbiased spectral surveys of particular sources, and systematic investigation of the interlinked chemistry and physics of dense interstellar clouds. In addition, the study of comets has allowed a comparison between the chemistry of such minimally thermally processed objects and that of interstellar clouds, shedding light on the evolution of the biogenic elements during the process of solar system formation. One PhD dissertation on this research was completed by a graduate student at the University of Massachusetts. An additional 4 graduate students at the University of Massachusetts and 5 graduate students from other institutions participated in research supported by this grant, with 6 of these thus far receiving PhD degrees from the University of Massachusetts or their home institutions. Four postdoctoral research associates at the University of Massachusetts also participated in research supported by this grant, receiving valuable training.

A Close Look At The Relationship Between WMAP (ILC) Small-Scale Features And Galactic HI Structure

NASA Astrophysics Data System (ADS)

Verschuur, Gerrit L.

2012-05-01

Galactic HI emission profiles surrounding two pairs of features located where large-scale filaments at very different velocities overlap were decomposed into Gaussian components. Families of components defined by similarity of center velocities and line widths were identified and found to be spatially related. Each of the two pairs of HI peaks straddle a high-frequency continuum source revealed in the WMAP survey data. It is suggested that where filamentary HI features are directly interacting high-frequency continuum radiation is being produced. The previously hypothesized mechanism for producing high-frequency continuum radiation involving free-free emission from electrons in the interstellar medium, in this case created where HI filaments interact to produce fractional ionizations of order 5 to 15%, fit the data very closely. The results confirm that WMAP data on small-scale structures believed to be cosmological in origin are in fact compromised by the presence of intervening galactic sources of interstellar electrons clumped on scales typical of interstellar HI structure.

Ab initio calculations for the spectral analysis of dimethyl ether (CH_3OCH_3) and their isotopologues

NASA Astrophysics Data System (ADS)

Senent, M. L.; Villa, M.; Dominguez-Gomez, R.; Alvarez-Bajo, O.; Carvajal, M.

2011-05-01

Dimethyl ether is a complex interstellar molecule with two internal rotors, which has a high abundance in the star-forming regions. This point, jointed with the recent development of the last-generation observatories operating at the sub-mm and mm wavelengths, has motivated a new laboratory spectral recording in this frequency range. In spite of that, the rotational spectra was only analysed in depth within its vibrational ground state and a new spectral analysis within the fundamental torsional states is in progress. These analysis were carried out with ERHAM, a global model that takes into account the large amplitude motions owing to the two equivalent internal CH3 tops. Nevertheless, their torsional modes in principle interact with the bending COC mode and an appropiate torsional-bending description would be needed in order to analyse the rotational spectra within higher excited states. In this work, a new analysis of the COC bending and the CH3 torsional degrees of freedom has been carried out by means of ab initio calculations. A new and more accurate three-dimensional Potential Energy Surface (PES), is obtained using the CCSD(T) level of theory. This approach has also been applied to other isotopologues of interest, as 13C-dimethyl ether and the monodeuterated species. The purpose of this study is to help in the assignment of new spectral lines of these species and hence to contribute in the spectral cleaning of the astronomical observations to the interstellar medium.

The ratio of neutral hydrogen to neutral helium in the local interstellar medium

NASA Astrophysics Data System (ADS)

Green, James Carswell

The results are described from a sounding rocket borne EUV spectrometer that was designed and built. This instrument operated from 400 to 1150A with a spectral resolution of approx. 15A. The instrument effective area was about 1 sq cm. The instrument was successfully launched, and observed the nearby DA white dwarf G191-B2B. From this observation, it was determined that the stellar effective temperature is 61,000 + or -4000 to 6000K, and the ratio of helium to hydrogen in the stellar photosphere is 1.0 + or -0.68 to 2.2 x 10-4. Additionally, the neutral column densities of helium and hydrogen were measured to the star. The neutral helium column density was determined from the first observation of the interstellar absorption edge at 504A. The ratio of neutral helium to neutral hydrogen constrains the mean ionization of the warm gas along the line of sight to G191-B2B. The fractional ionization of hydrogen (H II/H) is approx. less than 20 percent, unless significant helium ionization is present as well. The scenario where the fractional ionization of hydrogen is high (H II/H) approx. less than 40 percent and the helium is neutral is ruled out with 99 percent certainty. This result is consistent with some recent theoretical calculations. Using these results, a self-consistent model of the local interstellar medium along the line of sight to G191-B2B is developed. In addition, an unexpected emission feature at 584A was detected in this observation with a high level of significance. Possible sources of this emission are examined, including the companion K dwarf G191-B2A, and an emission nebula near or around G191-B2B.

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.

Distribution of CO2 in Saturn's Atmosphere from Cassini/cirs Infrared Observations

NASA Astrophysics Data System (ADS)

Abbas, M. M.; LeClair, A.; Woodard, E.; Young, M.; Stanbro, M.; Flasar, F. M.; Kunde, V. G.; Achterberg, R. K.; Bjoraker, G.; Brasunas, J.; Jennings, D. E.; the Cassini/CIRS Team

2013-10-01

This paper focuses on the CO2 distribution in Saturn's atmosphere based on analysis of infrared spectral observations of Saturn made by the Composite Infrared Spectrometer aboard the Cassini spacecraft. The Cassini spacecraft was launched in 1997 October, inserted in Saturn's orbit in 2004 July, and has been successfully making infrared observations of Saturn, its rings, Titan, and other icy satellites during well-planned orbital tours. The infrared observations, made with a dual Fourier transform spectrometer in both nadir- and limb-viewing modes, cover spectral regions of 10-1400 cm-1, with the option of variable apodized spectral resolutions from 0.53 to 15 cm-1. An analysis of the observed spectra with well-developed radiative transfer models and spectral inversion techniques has the potential to provide knowledge of Saturn's thermal structure and composition with global distributions of a series of gases. In this paper, we present an analysis of a large observational data set for retrieval of Saturn's CO2 distribution utilizing spectral features of CO2 in the Q-branch of the ν2 band, and discuss its possible relationship to the influx of interstellar dust grains. With limited spectral regions available for analysis, due to low densities of CO2 and interference from other gases, the retrieved CO2 profile is obtained as a function of a model photochemical profile, with the retrieved values at atmospheric pressures in the region of ~1-10 mbar levels. The retrieved CO2 profile is found to be in good agreement with the model profile based on Infrared Space Observatory measurements with mixing ratios of ~4.9 × 10-10 at atmospheric pressures of ~1 mbar.

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).

Implications of high-velocity interstellar H I absorption features

NASA Technical Reports Server (NTRS)

Cowie, L.; York, D. G.; Laurent, C.; Vidal-Madjar, A.

1979-01-01

Contributions to the interstellar H I column density at high velocities from immediate postshock gas and from the cooling gas behind a shock are compared. The detection of high-velocity H I in L-epsilon and L-delta for Iota Ori is reported and interpreted as cooling gas behind a shock of 100 km/s velocity. The immediate postshock gas should be observable for shock velocities greater than 200 km/s and permits direct determination of the velocities of adiabatic shocks in the interstellar medium. It is pointed out that interstellar L-alpha and L-beta lines may not have purely Lorentzian profiles if high-velocity H I is a widespread phenomenon.

Dust Spectroscopy and the Nature of Grains

NASA Technical Reports Server (NTRS)

Tielens, A. G. G. M.

2006-01-01

Ground-based, air-borne and space-based, infrared spectra of a wide variety of objects have revealed prominent absorption and emission features due to large molecules and small dust grains. Analysis of this data reveals a highly diverse interstellar and circumstellar grain inventory, including both amorphous materials and highly crystalline compounds (silicates and carbon). This diversity points towards a wide range of physical and chemical birthsites as well as a complex processing of these grains in the interstellar medium. In this talk, I will review the dust inventory contrasting and comparing both the interstellar and circumstellar reservoirs. The focus will be on the processes that play a role in the lifecycle of dust in the interstellar medium.

Simultaneous infrared and UV-visible absorption spectra of matrix-isolated carbon vapor

NASA Technical Reports Server (NTRS)

Kurtz, Joe; Huffman, Donald R.

1989-01-01

Carbon molecules were suggested as possible carriers of the diffuse interstellar bands. In particular, it was proposed that the 443 nm diffuse interstellar band is due to the same molecule which gives rise to the 447 nm absorption feature in argon matrix-isolated carbon vapor. If so, then an associated C-C stretching mode should be seen in the IR. By doing spectroscopy in both the IR and UV-visible regions on the same sample, the present work provides evidence for correlating UV-visible absorption features with those found in the IR. Early data indicates no correlation between the strongest IR feature (1997/cm) and the 447 nm band. Correlation with weaker IR features is being investigated.

Interstellar Polycyclic Aromatic Compounds and Astrophysics

NASA Technical Reports Server (NTRS)

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

1999-01-01

Polycyclic aromatic compounds (PACs), a class of organic molecules whose structures are characterized by the presence of two or more fused aromatic rings, have been the subject of astrophysical interest for nearly two decades. Large by interstellar standards (from as few as 20 to perhaps as many as several hundred atoms), it has been suggested that these species are among the most abundant interstellar molecules impacting a wide range of astrophysical phenomena including: the ubiquitous family of infrared emission bands observed in an ever-increasing assortment of astronomical objects; the subtle but rich array of discrete visible/near-infrared interstellar molecular absorption features known as the diffuse interstellar bands (DIBs); the broad near-infrared quasi-continuum observed in a number of nebulae known as excess red emission (ERE); the interstellar ultraviolet extinction curve and broad '2200 Angstrom bump'; the heating/cooling mechanisms of interstellar clouds. Nevertheless, until recently a lack of good-quality laboratory spectroscopic data on PACs under astrophysically relevant conditions (i.e. isolated, ionized molecules; ionized molecular clusters, etc.) has hindered critical evaluation and extension of this model

The Infrared Spectrum of Matrix Isolated Aminoacetonitrile: A Precursor to the Amino Acid Glycine

NASA Technical Reports Server (NTRS)

Bernstein, Max P.; Bauschlicher, Charles W., Jr.; Sandford, Scott A.

2003-01-01

We present infrared (IR) spectral data from matrix isolation experiments and density functional theory calculations on the pre-biologically interesting molecule aminoacetonitrile, a precursor to glycine. We find that this nitrile has an unusually weak nitrile (C=N) stretch in the infrared, in contrast to expectations based on measurements and models of other nitriles under astrophysical conditions. The absence of an observable nitrile absorption feature in the infrared will make the IR search for this molecule considerably more difficult, and will raise estimates of upper limits on nitriles in interstellar and outer Solar System ices. This is also of relevance to assessing the formation routes of the amino acid glycine, since aminoacetonitrile is the putative precursor to glycine via the Strecker synthesis, the mechanism postulated to have produced the amino acids in meteorites.

Laboratory and observational study of the interrelation of the carbonaceous component of interstellar dust and solar system materials

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Sanford, S. A.; Schutte, W. A.; Tielens, A. G. G. M.

1991-01-01

By studying the chemical and isotopic composition of interstellar ice and dust, one gains insight into the composition and chemical evolution of the solid bodies in the solar nebula and the nature of the material subsequently brought into the inner part of the solar system by comets and meteorites. It is now possible to spectroscopically probe the composition of interstellar ice and dust in the mid-infrared, the spectral range which is most diagnostic of fundamental molecular vibrations. We can compare these spectra of various astronomical objects (including the diffuse and dense interstellar medium, comets, and the icy outer planets and their satellites) with the spectra of analogs we produce in the laboratory under conditions which mimic those in these different objects. In this way one can determine the composition and abundances of the major constituents of the various ices and place general constraints on the types of organics coating the grains in the diffuse interstellar medium. In particular we have shown the ices in the dense clouds contain H2O, CH3OH, CO, perhaps some NH3 and H2CO, we well as nitriles and ketones or esters. Furthermore, by studying the photochemistry of these ice analogs in the laboratory, one gains insight into the chemistry which takes place in interstellar/precometary ices. Chemical and spectroscopic studies of photolyzed analogs (including deuterated species) are now underway. The results of some of these studies will be presented and implications for the evolution of the biogenic elements in interstellar dust and comets will be discussed.

Spectral Confusion for Cosmological Surveys of Redshifted C II Emission

NASA Technical Reports Server (NTRS)

Kogut, A.; Dwek, E.; Moseley, S. H.

2015-01-01

Far-infrared cooling lines are ubiquitous features in the spectra of star-forming galaxies. Surveys of redshifted fine-structure lines provide a promising new tool to study structure formation and galactic evolution at redshifts including the epoch of reionization as well as the peak of star formation. Unlike neutral hydrogen surveys, where the 21 cm line is the only bright line, surveys of redshifted fine-structure lines suffer from confusion generated by line broadening, spectral overlap of different lines, and the crowding of sources with redshift. We use simulations to investigate the resulting spectral confusion and derive observing parameters to minimize these effects in pencilbeam surveys of redshifted far-IR line emission. We generate simulated spectra of the 17 brightest far-IR lines in galaxies, covering the 150-1300 µm wavelength region corresponding to redshifts 0 < z < 7, and develop a simple iterative algorithm that successfully identifies the 158 µm [C II] line and other lines. Although the [C II] line is a principal coolant for the interstellar medium, the assumption that the brightest observed lines in a given line of sight are always [C II] lines is a poor approximation to the simulated spectra once other lines are included. Blind line identification requires detection of fainter companion lines from the same host galaxies, driving survey sensitivity requirements. The observations require moderate spectral resolution 700 < R < 4000 with angular resolution between 20? and 10', sufficiently narrow to minimize confusion yet sufficiently large to include a statistically meaningful number of sources.

High Resolution FIR and IR Spectroscopy of Methanol Isotopologues

NASA Astrophysics Data System (ADS)

Lees, R. M.; Xu, Li-Hong; Appadoo, D. R. T.; Billinghurst, B.

2010-02-01

New astronomical facilities such as HIFI on the Herschel Space Observatory, the SOFIA airborne IR telescope and the ALMA sub-mm telescope array will yield spectra from interstellar and protostellar sources with vastly increased sensitivity and frequency coverage. This creates the need for major enhancements to laboratory databases for the more prominent interstellar "weed" species in order to model and account for their lines in observed spectra in the search for new and more exotic interstellar molecular "flowers." With its large-amplitude internal torsional motion, methanol has particularly rich spectra throughout the FIR and IR regions and, being very widely distributed throughout the galaxy, is perhaps the most notorious interstellar weed. Thus, we have recorded new spectra for a variety of methanol isotopic species on the high-resolution FTIR spectrometer on the CLS FIR beamline. The aim is to extend quantum number coverage of the data, improve our understanding of the energy level structure, and provide the astronomical community with better databases and models of the spectral patterns with greater predictive power for a range of astrophysical conditions.

Observational analysis of the well-correlated diffuse bands: 6196 and 6614 Å

NASA Astrophysics Data System (ADS)

Krełowski, J.; Galazutdinov, G. A.; Bondar, A.; Beletsky, Y.

2016-08-01

We confirm, using spectra from seven observatories, that the diffuse bands 6196 and 6614 are very tightly correlated. However, their strength ratio is not constant as well as profile shapes. Apparently, the two interstellar features do not react in unison to the varying physical conditions of different interstellar clouds.

The interstellar medium and the highly ionized species observed in the spectrum of the nearby white dwarf G191-B2B

NASA Technical Reports Server (NTRS)

Bruhweiler, F. C.; Kondo, Y.

1981-01-01

High-resolution spectra of the nearby (48 pc) white dwarf G191-B2B, obtained with the International Ultraviolet Explorer, reveal sharp resonance lines of N V, C IV, and Si IV. The origin of these features is most likely linked to the white dwarf, possibly being formed in an expanding halo around the star. Interstellar lines of C II, N I, Mg II, Si II, and Fe II are also seen in the spectrum. Analysis of these features indicates an average neutral hydrogen number density of 0.064 for this line of sight. In combination with the recent EUV and soft X-ray results, this is interpreted to mean that the interstellar medium in the most immediate solar vicinity is of the normal density n approximately equal to 0.1/cu cm of lower ionization, while just beyond it, at least in some directions, is a hot lower density plasma. These results are apparently in conflict with the model of the interstellar medium by McKee and Ostriker (1977) in its present form.

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.

Cosmic rays, gamma rays and synchrotron radiation from the Galaxy

DOE PAGES

Orlando, Elena

2012-07-30

Galactic cosmic rays (CR), interstellar gamma-ray emission and synchrotron radiation are related topics. CR electrons propagate in the Galaxy and interact with the interstellar medium, producing inverse-Compton emission measured in gamma rays and synchrotron emission measured in radio. I present an overview of the latest results with Fermi/LAT on the gamma-ray diffuse emission induced by CR nuclei and electrons. Then I focus on the recent complementary studies of the synchrotron emission in the light of the latest gamma-ray results. Relevant observables include spectral indices and their variations, using surveys over a wide range of radio frequencies. As a result, thismore » paper emphasizes the importance of using the parallel study of gamma rays and synchrotron radiation in order to constrain the low-energy interstellar CR electron spectrum, models of propagation of CRs, and magnetic fields.« less

Processing Mechanisms for Interstellar Ices: Connections to the Solar System

NASA Technical Reports Server (NTRS)

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

1995-01-01

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

Free radical OH, a molecule of astrophysical and aeronomic interest. [radio sources (astronomy) - spectroscopic analysis

NASA Technical Reports Server (NTRS)

Mohan, H.; SHARDANAND

1975-01-01

The chemistry and physics of the gaseous OH free radical as it applies to interstellar space, planetary atmospheres, and the sun is presented. Topics considered are: (1) rotational-vibrational transitions; (2) dissociation and ionization processes; (3) spectral characteristics.

Spectral Study of A 1Π–X 1Σ+ Transitions of CO Relevant to Interstellar Clouds

NASA Astrophysics Data System (ADS)

Cheng, Junxia; Zhang, Hong; Cheng, Xinlu

2018-05-01

Highly correlated ab initio calculations were performed for an accurate determination of the A 1Π–X 1Σ+ system of the CO molecule. A highly accurate multi-reference configuration interaction approach was used to investigate the potential energy curves (PECs) and the transition dipole moment curve (TDMC). The resultant PECs and TDMC found by using the aug-cc-pV5Z (aV5Z) basis set and 5330 active spaces are in good agreement with the experimental data. Moreover, the Einstein A coefficients, lifetimes, ro-vibrational intensities, absorption oscillator strengths, and integrated cross sections are calculated so that the vibrational bands include v″ = 0–39 \\to v‧ = 0–23. For applications in the atmosphere and interstellar clouds, we studied the transition lineshapes to Gaussian and Lorentzian profiles at different temperatures and pressures. The intensities were calculated at high temperature that was used to satisfy some astrophysical applications, such as in planetary atmospheres. The results are potentially useful for important SAO/NASA Astrophysics Data System and databases such as HITRAN, HITEMP, and the National Institute of Standards and Technology. Because the results from many laboratory techniques and our calculations now agree, analyses of interstellar CO based on absorption from A 1Π–X 1Σ+ are no longer hindered by present spectral parameters.

Stellar ultraviolet colors and interstellar extinction

NASA Technical Reports Server (NTRS)

Peytremann, E.; Davis, R. J.

1972-01-01

A sample of celescope results is studied. Most of the sample stars belong to the Orion and Vela regions. Stars with visual excess E(B-V) less than 0.05 are selected in order to derive relationships of intrinsic color index versus spectral type. The resulting intrinsic color-color relations are compared with existing blanketed and unblanketed model calculations. Finally, the preceding intrinsic relations are utilized to derive some results on interstellar extinction. Owing to the rather large scatter in the celescope data, the Vela stars give the more significant results because their visible excess E(B-V) is, in general, larger than that for the Orion stars.

A rare gas optics-free absolute photon flux and energy analyzer to provide absolute photoionization rates of inflowing interstellar neutrals

NASA Technical Reports Server (NTRS)

Judge, Darrell L.

1994-01-01

A prototype spectrometer has been developed for space applications requiring long term absolute EUV photon flux measurements. The energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer, followed by an electron multiplier detector, pulses due to individual electrons are counted. The overall efficiency of this process can be made essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided. A very important feature of this approach is its freedom from the problem of overlapping spectral orders that plagues grating EUV spectrometers. An instrument with these features has not been flown before, but is essential to further advances in our understanding of solar EUV flux dynamics, and the coupled dynamics of terrestrial and planetary atmospheres. The detailed characteristics of this optics-free spectrometer are presented in the publications section.

High-energy Gamma Rays from the Milky Way: Three-dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porter, T. A.; Moskalenko, I. V.; Jóhannesson, G., E-mail: tporter@stanford.edu

High-energy γ -rays of interstellar origin are produced by the interaction of cosmic-ray (CR) particles with the diffuse gas and radiation fields in the Galaxy. The main features of this emission are well understood and are reproduced by existing CR propagation models employing 2D galactocentric cylindrically symmetrical geometry. However, the high-quality data from instruments like the Fermi Large Area Telescope reveal significant deviations from the model predictions on few to tens of degrees scales, indicating the need to include the details of the Galactic spiral structure and thus requiring 3D spatial modeling. In this paper, the high-energy interstellar emissions frommore » the Galaxy are calculated using the new release of the GALPROP code employing 3D spatial models for the CR source and interstellar radiation field (ISRF) densities. Three models for the spatial distribution of CR sources are used that are differentiated by their relative proportion of input luminosity attributed to the smooth disk or spiral arms. Two ISRF models are developed based on stellar and dust spatial density distributions taken from the literature that reproduce local near- to far-infrared observations. The interstellar emission models that include arms and bulges for the CR source and ISRF densities provide plausible physical interpretations for features found in the residual maps from high-energy γ -ray data analysis. The 3D models for CR and ISRF densities provide a more realistic basis that can be used for the interpretation of the nonthermal interstellar emissions from the Galaxy.« less

Absolute, Extreme-Ultraviolet Solar Spectral Irradiance Monitor (AESSIM)

DTIC Science & Technology

1994-04-01

molecular constituents [Meier 1991]. This radiation is the principal source of energy for producing and maintaining the complex, time-dependent, thermal...158.4 nm emisions for interstellar wind studies. After -2005, there is unlikely to be sufficient power to provide the requisite heating of the scan

VEGAS: VErsatile GBT Astronomical Spectrometer

NASA Astrophysics Data System (ADS)

Bussa, Srikanth; VEGAS Development Team

2012-01-01

The National Science Foundation Advanced Technologies and Instrumentation (NSF-ATI) program is funding a new spectrometer backend for the Green Bank Telescope (GBT). This spectrometer is being built by the CICADA collaboration - collaboration between the National Radio Astronomy Observatory (NRAO) and the Center for Astronomy Signal Processing and Electronics Research (CASPER) at the University of California Berkeley.The backend is named as VErsatile GBT Astronomical Spectrometer (VEGAS) and will replace the capabilities of the existing spectrometers. This backend supports data processing from focal plane array systems. The spectrometer will be capable of processing up to 1.25 GHz bandwidth from 8 dual polarized beams or a bandwidth up to 10 GHz from a dual polarized beam.The spectrometer will be using 8-bit analog to digital converters (ADC), which gives a better dynamic range than existing GBT spectrometers. There will be 8 tunable digital sub-bands within the 1.25 GHz bandwidth, which will enhance the capability of simultaneous observation of multiple spectral transitions. The maximum spectral dump rate to disk will be about 0.5 msec. The vastly enhanced backend capabilities will support several science projects with the GBT. The projects include mapping temperature and density structure of molecular clouds; searches for organic molecules in the interstellar medium; determination of the fundamental constants of our evolving Universe; red-shifted spectral features from galaxies across cosmic time and survey for pulsars in the extreme gravitational environment of the Galactic Center.

The Dissipation Range of Interstellar Turbulence

NASA Astrophysics Data System (ADS)

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

2013-06-01

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

The detection of interstellar C I in the immediate vicinity of the sun

NASA Technical Reports Server (NTRS)

Bruhweiler, F. C.; Kondo, Y.

1982-01-01

Multiple stacked IUE spectra reveal the presence of interstellar C I 1657 in the trough of a corresponding photospheric feature in the nearby star, Alpha PsA (d = 7 pc). This represents the first detection of this neutral atom in the interstellar medium within the immediate vicinity of the sun. It is suggested that C I may be a much better diagnostic tool in studying the local interstellar medium than the neutral species K I and Na I, which are observable at visual wavelengths. Variations in C I column density, coupled with b-values deduced from the Mg II doublet ratio, may prove to be an important means to unravel density and temperature fluctuations in the very local interstellar medium. Comparison of the line of sight toward Alpha PsA with previous Copernicus interstellar Mg II results for that of Alpha Leo tentatively indicates that the distribution of Mg II in the local cloud is not homogeneous about the sun. Rough constraints on the ionization fraction of hydrogen toward Alpha PsA do not conflict with previous data, implying that the very local interstellar medium is significantly ionized.

Large Scale Spectral Line Mapping of Galactic Regions with CCAT-Prime

NASA Astrophysics Data System (ADS)

Simon, Robert

2018-01-01

CCAT-prime is a 6-m submillimeter telescope that is being built on the top of Cerro Chajnantor (5600 m altitude) overlooking the ALMA plateau in the Atacama Desert. Its novel Crossed-Dragone design enables a large field of view without blockage and is thus particularly well suited for large scale surveys in the continuum and spectral lines targeting important questions ranging from star formation in the Milky Way to cosmology. On this poster, we focus on the large scale mapping opportunities in important spectral cooling lines of the interstellar medium opened up by CCAT-prime and the Cologne heterodyne instrument CHAI.

Interstellar proteins and the discovery of a new absorption feature at lambda = 2800 A

NASA Astrophysics Data System (ADS)

Karim, L. M.; Hoyle, F.; Wickramasinghe, N. C.

1983-07-01

In order to check the presence of biogenic materials in interstellar grains, the spectra of three early-type, heavily reddened stars recorded by the IUE were examined. These stars showed comparatively weak absorption at 2200 A, minimizing the effect of graphite grains. A broad absorption feature centered on 2800 A is discovered in HD 14250 and interpreted to be due to the amino acid tryptophan. Comparison of the spectrum with that of the calculated extinction behavior of graphite spheres of radii 0.02 microns suggests that the latter are not responsible for the observed spectrum.

VizieR Online Data Catalog: Far-UV spectral atlas of O-type stars (Smith, 2012)

NASA Astrophysics Data System (ADS)

Smith, M. A.

2012-10-01

In this paper, we present a spectral atlas covering the wavelength interval 930-1188Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. (4 data files).

Infrared diffuse interstellar bands

NASA Astrophysics Data System (ADS)

Galazutdinov, G. A.; Lee, Jae-Joon; Han, Inwoo; Lee, Byeong-Cheol; Valyavin, G.; Krełowski, J.

2017-05-01

We present high-resolution (R ˜ 45 000) profiles of 14 diffuse interstellar bands in the ˜1.45 to ˜2.45 μm range based on spectra obtained with the Immersion Grating INfrared Spectrograph at the McDonald Observatory. The revised list of diffuse bands with accurately estimated rest wavelengths includes six new features. The diffuse band at 15 268.2 Å demonstrates a very symmetric profile shape and thus can serve as a reference for finding the 'interstellar correction' to the rest wavelength frame in the H range, which suffers from a lack of known atomic/molecular lines.

Microanalysis of Hypervelocity Impact Residues of Possible Interstellar Origin

NASA Technical Reports Server (NTRS)

Stroud, Rhonda M.; Achilles, Cheri; Allen, Carlton; Anasari, Asna; Bajt, Sasa; Bassim, Nabil; Bastien, Ron S.; Bechtel, H. A.; Borg, Janet; Brenker, Frank E.;

Mineralogical Characterization of Fe-Bearing AGB and Supernova Silicate Grains From the Queen Alexandra Range 99177 Meteorite

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Keller, L. P.; Messenger, S.; Rahman, Z.

2017-01-01

Spectroscopic observations of the circumstellar envelopes of evolved O-rich stars indicate the dust is mostly amorphous silicate with olivine-like compositions. Spectral modeling suggests these grains are Fe-rich [Mg/(Mg+Fe) 0.5], but it is not known whether the Fe is distributed within the silicate matrix or exists as metal inclusions. In contrast, the crystalline silicates are inferred to be extremely Mg-rich [Mg/(Mg+Fe) > 0.95]. The mineralogies and chemical compositions of dust in supernova (SN) remnants are not as well constrained, but abundant silicates of olivine-like and enstatite-like compositions have been fit to the infrared emission features. Silicates in the interstellar medium (ISM) are >99% amor-phous and Fe-bearing. The dearth of crystalline silicates in the ISM requires that some amorphization or destruction mechanisms process these grains.

Decorrelation dynamics and spectra in drift-Alfven turbulence

NASA Astrophysics Data System (ADS)

Fernandez Garcia, Eduardo

Motivated by the inability of one-fluid magnetohydrodynamics (MHD) to explain key turbulence characteristics in systems ranging from the solar wind and interstellar medium to fusion devices like the reversed field pinch, this thesis studies magnetic turbulence using a drift-Alfven model that extends MHD by including electron density dynamics. Electron effects play a significant role in the dynamics by changing the structure of turbulent decorrelation in the Alfvenic regime (where fast Alfvenic propagation provides the fastest decorrelation of the system): besides the familiar counter-propagating Alfvenic branches of MHD, an additional branch tied to the diamagnetic and eddy-turn- over rates enters in the turbulent response. This kinematic branch gives hydrodynamic features to turbulence that is otherwise strongly magnetic. Magnetic features are observed in the RMS frequency, energy partitions, cross-field energy transfer and in the turbulent response, whereas hydrodynamic features appear in the average frequency, self-field transfer, turbulent response and finally the wavenumber spectrum. These features are studied via renormalized closure theory and numerical simulation. The closure calculation naturally incorporates the eigenmode structure of the turbulent response in specifying spectral energy balance equations for the magnetic, kinetic and internal (density) energies. Alfvenic terms proportional to cross correlations and involved in cross field transfer compete with eddy-turn-over, self transfer, auto-correlation terms. In the steady state, the kinematic terms dominate the energy balances and yield a 5/3 Kolmogorov spectrum (as observed in the interstellar medium) for the three field energies in the strong turbulence, long wavelength limit. Alfvenic terms establish equipartition of kinetic and magnetic energies. In the limit where wavelengths are short compared to the gyroradius, the Alfvenic terms equipartition the internal and magnetic energies resulting in a steep (-2) spectrum fall-off for those energies while the largely uncoupled kinetic modes still obey a 5/3 law. From the numerical simulations, the response function of drift-Alfven turbulence is measured. Here, a statistical ensemble is constructed from small perturbations of the turbulent amplitudes at fixed wavenumber. The decorrelation structure born out of the eigenmode calculation is verified in the numerical measurement.

Spectral softening in the X-RAY afterglow of GRB 130925A as predicted by the dust scattering model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Yi-Nan; Shao, Lang, E-mail: lshao@hebtu.edu.cn

2014-07-01

Gamma-ray bursts (GRBs) usually occur in a dense star-forming region with a massive circumburst medium. The small-angle scattering of intense prompt X-ray emission off the surrounding dust grains will have observable consequences and sometimes can dominate the X-ray afterglow. In most of the previous studies, only the Rayleigh-Gans (RG) approximation is employed for describing the scattering process, which works accurately for the typical size of grains (with radius of a ≤ 0.1 μm) in the diffuse interstellar medium. When the size of the grains may significantly increase, as in a more dense region where GRBs would occur, the RG approximationmore » may not be valid enough for modeling detailed observational data. In order to study the temporal and spectral properties of the scattered X-ray emission more accurately with potentially larger dust grains, we provide a practical approach using the series expansions of anomalous diffraction (AD) approximation based on the complicated Mie theory. We apply our calculations to understand the puzzling X-ray afterglow of recently observed GRB 130925A that showed a significant spectral softening. We find that the X-ray scattering scenarios with either AD or RG approximation adopted could well reproduce both the temporal and spectral profile simultaneously. Given the plateau present in the early X-ray light curve, a typical distribution of smaller grains as in the interstellar medium would be suggested for GRB 130925A.« less

Spectral Softening in the X-Ray Afterglow of GRB 130925A as Predicted by the Dust Scattering Model

NASA Astrophysics Data System (ADS)

Zhao, Yi-Nan; Shao, Lang

2014-07-01

Gamma-ray bursts (GRBs) usually occur in a dense star-forming region with a massive circumburst medium. The small-angle scattering of intense prompt X-ray emission off the surrounding dust grains will have observable consequences and sometimes can dominate the X-ray afterglow. In most of the previous studies, only the Rayleigh-Gans (RG) approximation is employed for describing the scattering process, which works accurately for the typical size of grains (with radius of a <= 0.1 μm) in the diffuse interstellar medium. When the size of the grains may significantly increase, as in a more dense region where GRBs would occur, the RG approximation may not be valid enough for modeling detailed observational data. In order to study the temporal and spectral properties of the scattered X-ray emission more accurately with potentially larger dust grains, we provide a practical approach using the series expansions of anomalous diffraction (AD) approximation based on the complicated Mie theory. We apply our calculations to understand the puzzling X-ray afterglow of recently observed GRB 130925A that showed a significant spectral softening. We find that the X-ray scattering scenarios with either AD or RG approximation adopted could well reproduce both the temporal and spectral profile simultaneously. Given the plateau present in the early X-ray light curve, a typical distribution of smaller grains as in the interstellar medium would be suggested for GRB 130925A.

Interstellar dust and related topics; Proceedings of the Symposium, State University of New York, Albany, N.Y., May 29-June 2, 1972

NASA Technical Reports Server (NTRS)

Greenberg, J. M. (Editor); Van De Hulst, H. C.

1973-01-01

Theoretical studies and observations of interstellar dust are described in papers dealing with the passive properties of dust grains, their physical and chemical activities in the interstellar medium, and their interactions in association with stars. The papers are grouped according to the principal topics of (1) extinction and polarization, (2) diffuse interstellar features, (3) dust around and in close association with stars, (4) reflection nebulae and other aspects of dust scattering properties, (5) alignment mechanisms, (6) distribution of molecules and processes of molecule formation, (7) radiation effects on dust, (8) physical and chemical interactions of dust with the ambient medium, and (9) gas and dust in H II regions. Individual items are announced in this issue.

Interstellar Scattering Towards the Galactic Center as Probed by OH/IR Stars

NASA Technical Reports Server (NTRS)

Vanlangevelde, Huib Jan; Frail, Dale A.; Cordes, James M.; Diamond, Philip J.

1992-01-01

Angular broadening measurements are reported of 20 OH/IR stars near the galactic center. This class of sources is known to have bright, intrinsically compact (less than or equal to 20 mas) maser components within their circumstellar shells. VLBA antennas and the VLA were used to perform a MKII spectral line VLBI experiment. The rapid drop in correlated flux with increasing baseline, especially for sources closest to the galactic center, is attributed to interstellar scattering. Angular diameters were measured for 13 of our sources. Lower limits were obtained for the remaining seven. With the data, together with additional data taken from the literature, the distribution was determined of interstellar scattering toward the galactic center. A region was found of pronounced scattering nearly centered on SgrA*. Two interpretations are considered for the enhanced scattering. One hypothesis is that the scattering is due to a clump of enhanced turbulence, such as those that lie along lines of sight to other known objects, that has no physical relationship to the galactic center. The other model considers the location of the enhanced scattering to arise in the galactic center itself. The physical implications of the models yield information on the nature of interstellar scattering.

Ultraviolet observations of the gas phase abundances in the diffuse clouds toward Zeta Ophiuchi at 3.5 kilometers per second resolution

NASA Technical Reports Server (NTRS)

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

1992-01-01

Goddard High Resolution Spectrograph echelle mode measurements at 3.5 km/s resolution are presented for interstellar absorption produced by C II, O I, Mg I, Mg II, Al III, P II, Cr II, Mn II, Fe II, Ni II, Cu II, Zn II, Ga II, Ge II, and Kr I. The absorption line measurements are converted into representations of apparent column density per unit velocity in order to study the multicomponent nature of the absorption. The high spectral resolution of the measurements allows a comparative study of gas phase abundances for many species in the absorbing clouds near -27 and -15 km/s with a typical precision of about 0.05 dex. The matter absorbing near -27 km/s is situated in the local interstellar medium and has log N(H I) of about 19.74. This absorption provides information about the modest 'base' depletion associated with the lower density interstellar medium. The depletion results suggest that accretion processes are operating interstellar clouds that exhibit similar depletion efficiencies for some elements but much higher depletion efficiencies for others.

The Bending Vibrations of the C_3-ISOTOPOLOGUES in the 1.9 Terahertz Region

NASA Astrophysics Data System (ADS)

Breier, A.; Büchling, Thomas; Lutter, Volker; Schnierer, Rico; Fuchs, Guido W.; Giesen, Thomas

2016-06-01

Short carbon chains are fundamental for the chemistry of stellar and interstellar ambiences. The linear carbon chain molecule C_3 has been found in various interstellar and circumstellar environments, encompassing diffuse interstellar clouds, star forming regions, shells of late type stars, as well as cometary tails. Due to the lack of a permanent dipole moment C_3 can only be detected by electronic transitions in the visible spectral range or by vibrational bands in the mid-and far-infrared region. We performed experiments where C_3 was produced via laser-ablation of a graphite rod with a 3 bar He purge and a subsequent adiabatic expansion into a vaccum resulting in a supersonic jet. We report laboratory measurements of the lowest bending mode transitions of six 13C-isotopologues of the linear C_3 molecule. Fifty-eight transitions have been measured between 1.8-1.9 THz with an accuracy of better than 1 MHz. Molecular parameters have been derived to give accurate line frequency positions of all 13C isotopologues to ease their future interstellar detection. A dedicated observation for singly substituted 13CCC is projected within the SOFIA airborne observatory mission.

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-enriched provides evidence for a connection between intact organic material in the interstellar medium and in meteorites. Thus, some of the oxidized aromatics, amphiphiles, amino acids, hydroxy acids, and other compounds found in meteorites may have had an interstellar ancestry and not solely a product of parent body aqueous alteration. Such compounds should also be targeted for searches of organics in cometary dust.

Comment on "The shape and composition of interstellar silicate grains"

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, J P; Ishii, H

2007-09-27

In the paper entitled 'The shape and composition of interstellar silicate grains' (A & A, 462, 667-676 (2007)), Min et al. explore non-spherical grain shape and composition in modeling the interstellar 10 and 20 {micro}m extinction features. This progression towards more realistic models is vitally important to enabling valid comparisons between dust observations and laboratory measurements. Min et al. proceed to compare their model results with GEMS (glass with embedded metals and sulfides) from IDPs (interplanetary dust particles) and to discuss the nature and origin of GEMS. Specifically, they evaluate the hypothesis of Bradley (1994) that GEMS are interstellar (IS)more » amorphous silicates. From a comparison of the mineralogy, chemical compositions, and infrared (IR) spectral properties of GEMS with their modeling results, Min et al. conclude: 'GEMS are, in general, not unprocessed leftovers from the diffuse ISM'. This conclusion is based, however, on erroneous and incomplete GEMS data. It is important to clarify first that Bradley (1994) never proposed that GEMS are unprocessed leftovers from the diffuse ISM, nor did he suggest that individual subnanogram mass GEMS are a representative sampling of the enormous mass of silicates in the diffuse ISM. Bradley (1994) simply showed that GEMS properties are consistent with those of IS amorphous silicates. It is widely accepted that circumstellar outflows are important sources of IS silicates, and whether GEMS are processed or not, the circumstellar heritage of some has been rigorously confirmed through measurements of non-solar oxygen (O) isotope abundances (Messenger et al., 2003; Floss et al., 2006). Keller et al. (2000) assert that even GEMS without detectable O isotope anomalies are probably also extrasolar IS silicates because they are embedded in carbonaceous material with non-solar D/H isotopic composition. (Much of the silicate dust in the ISM may be isotopically homogenized (Zhukovska et al., 2007)). Recent measurements show that the elemental compositions of GEMS with non-solar isotopic compositions are 'remarkably similar' to those with solar isotopic compositions (Keller & Messenger, 2007). About 80% of all isotopically anomalous IS silicates identified to date are GEMS with detectable and variable O isotopic memories of a circumstellar ancestry (Messenger, 2007). Bradley (1999) proposed that GEMS are IS silicates from 'a presolar interstellar molecular cloud, presumably the local molecular cloud from which the solar system formed'. Although based on incorrect data (detailed below), Min et al. propose that most GEMS actually formed in the presolar molecular cloud, and they further propose that none of them are IS silicates. IS silicate sources include molecular clouds, circumstellar outflows, supernovae, and even recently discovered black hole winds (Molster & Waters; 2003; Jones, 2005; Zhukovska et al. 2007; Markwick-Kemper et al. 2007). The average IS 10 {micro}m extinction feature observed along lines of sight towards the galactic center (modeled by Min et al.) presumably provides a good average for IS silicates, but it cannot distinguish amorphous silicates originating in the presolar molecular cloud from amorphous silicates originating in other interstellar molecular clouds or indeed other sources of amorphous IS silicates. Even if most GEMS accreted in the presolar molecular cloud, then they must also be representatives of some portion of the IS amorphous silicate population. Laboratory heating experiments indicate it is highly unlikely that GEMS were modified in a protoplanetary accretion disk environment (Brownlee et al. 2005). In summary, Min et al. conclude from their modeling of the shape and composition of IS silicates that the properties of GEMS are generally inconsistent with those of IS silicates. First, it has been rigorously confirmed via ion microprobe measurements that some GEMS are indeed presolar IS silicates. Second, regardless of whether GEMS, or components of GEMS, originated in presolar circumstellar outflows or a presolar molecular cloud they are all IS silicates. Third, key GEMS data reported in Min et al. are inaccurate. Had complete isotopic, chemical, mineralogical and infrared (IR) spectral properties of GEMS been considered, Min et al. may have concluded that the properties of GEMS, although not an exact match, are generally consistent with those of amorphous silicates in the ISM.« less

Stardust Interstellar Preliminary Examination V: XRF Analyses of Interstellar Dust Candidates at ESRF ID13

NASA Technical Reports Server (NTRS)

Brenker, Frank E.; Westphal, Andrew J.; Simionovici, Alexandre S.; Flynn, George J.; Gainsforth, Zack; Allen, Carlton C.; Sanford, Scott; Zolensky, Michael E.; Bastien, Ron K.; Frank, David R.

2014-01-01

Here, we report analyses by synchrotron X-ray fluorescence microscopy of the elemental composition of eight candidate impact features extracted from the Stardust Interstellar Dust Collector (SIDC). Six of the features were unambiguous tracks, and two were crater-like features. Five of the tracks are so-called midnight tracks that is, they had trajectories consistent with an origin either in the interstellar dust stream or as secondaries from impacts on the Sample Return Capsule (SRC). In a companion paper reporting synchrotron X-ray diffraction analyses of ISPE candidates, we show that two of these particles contain natural crystalline materials: the terminal particle of track 30contains olivine and spinel, and the terminal particle of track 34 contains olivine. Here, we show that the terminal particle of track 30, Orion, shows elemental abundances, normalized to Fe, that are close to CI values, and a complex, fine-grained structure. The terminal particle of track 34, Hylabrook, shows abundances that deviate strongly from CI, but shows little fine structure and is nearly homogenous. The terminal particles of other midnight tracks, 29 and 37, had heavy element abundances below detection threshold. A third, track28, showed a composition inconsistent with an extraterrestrial origin, but also inconsistent with known spacecraft materials. A sixth track, with a trajectory consistent with secondary ejecta from an impact on one of the spacecraft solar panels, contains abundant Ce and Zn. This is consistent with the known composition of the glass covering the solar panel. Neither crater-like feature is likely to be associated with extraterrestrial materials. We also analyzed blank aerogel samples to characterize background and variability between aerogel tiles. We found significant differences in contamination levels and compositions, emphasizing the need for local background subtraction for accurate quantification.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Ramanpreet; Kaper, Lex; Ellerbroek, Lucas E.

We present the optical to near-infrared spectrum of MAXI J1659-152 during the onset of its 2010 X-ray outburst. The spectrum was obtained with X-shooter on the ESO Very Large Telescope early in the outburst simultaneous with high-quality observations at both shorter and longer wavelengths. At the time of the observations, the source was in the low-hard state. The X-shooter spectrum includes many broad ({approx}2000 km s{sup -1}), double-peaked emission profiles of H, He I, and He II, characteristic signatures of a low-mass X-ray binary during outburst. We detect no spectral signatures of the low-mass companion star. The strength of themore » diffuse interstellar bands results in a lower limit to the total interstellar extinction of A{sub V} {approx_equal} 0.4 mag. Using the neutral hydrogen column density obtained from the X-ray spectrum we estimate A{sub V} {approx_equal} 1 mag. The radial velocity structure of the interstellar Na I D and Ca II H and K lines results in a lower limit to the distance of {approx}4 {+-} 1 kpc, consistent with previous estimates. With this distance and A{sub V} , the dereddened spectral energy distribution represents a flat disk spectrum. The two 10 minute X-shooter spectra show significant variability in the red wing of the emission-line profiles, indicating a global change in the density structure of the disk, though on a timescale much shorter than the typical viscous timescale of the disk.« less

VizieR Online Data Catalog: The ESO DIBs Large Exploration Survey (Cox+, 2017)

NASA Astrophysics Data System (ADS)

Cox, N. L. J.; Cami, J.; Farhang, A.; Smoker, J.; Monreal-Ibero, A.; Lallement, R.; Sarre, P. J.; Marshall, C. C. M.; Smith, K. T.; Evans, C. J.; Royer, P.; Linnartz, H.; Cordiner, M. A.; Joblin, C.; van Loon, J. T.; Foing, B. H.; Bhatt, N. H.; Bron, E.; Elyajouri, M.; de Koter, A.; Ehrenfreund, P.; Javadi, A.; Kaper, L.; Khosroshadi, H. G.; Laverick, M.; Le Petit, F.; Mulas, G.; Roueff, E.; Salama, F.; Spaans, M.

2018-01-01

We constructed a statistically representative survey sample that probes a wide range of interstellar environment parameters including reddening E(B-V), visual extinction AV, total-to-selective extinction ratio RV, and molecular hydrogen fraction fH2. EDIBLES provides the community with optical (~305-1042nm) spectra at high spectral resolution (R~70000 in the blue arm and 100000 in the red arm) and high signal-to-noise (S/N; median value ~500-1000), for a statistically significant sample of interstellar sightlines. Many of the >100 sightlines included in the survey already have auxiliary available ultraviolet, infrared and/or polarisation data on the dust and gas components. (2 data files).

Submillimeter heterodyne detection of interstellar carbon monoxide at 434 micrometers

NASA Technical Reports Server (NTRS)

Fetterman, H. R.; Clifton, B. J.; Peck, D. D.; Tannenwald, P. E.; Koepf, G. A.; Goldsmith, P. F.; Erickson, N. R.; Buhl, D.; Mcavoy, N.

1981-01-01

Laser heterodyne observations of submillimeter emissions from carbon monoxide in the Orion molecular cloud are reported. High frequency and spatial resolution observations were made at the NASA Infrared Telescope Facility on Mauna Kea by the use of an optically pumped laser local oscillator and quasi-optical Schottky diode mixer for heterodyne detection of the J = 6 - 5 rotational transition of CO at 434 microns. Spectral analysis of the 434-micron emission indicates that the emitting gas is optically thin and is at a temperature above 180 K. Results thus demonstrate the potential contributions of ground-based high-resolution submillimeter astronomy to the study of active regions in interstellar molecular clouds.

Radio emission from supernova remnants in a cloudy interstellar medium

NASA Technical Reports Server (NTRS)

Blandford, R. D.; Cowie, L. L.

1982-01-01

The van der Laan (1962) theory of SNR radio emission is modified in light of the inhomogeneity of the interstellar medium, and in order to allow for particle acceleration in shock fronts. It is proposed that most of the radio emission in 10-20 pc radius SNRs originates in cold interstellar clouds that have been crushed by the high pressure hot gas within the expanding remnant. Under these circumstances, simple reacceleration of ambient interstellar cosmic ray electrons can account for the surface brightness-diameter distribution of observed remnants, with the additional, relativistic particle energy compensating for the decreased filling factor of the radio-emitting regions. Warm interstellar gas, at about 8000 K, may also be compressed within very large SNRs (of radius of 30-100 pc) and account for both the giant radio loops, when these SNRs are seen individually, and the anomalously bright galactic nonthermal radio background, which may be the superposition of a number of such features.

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)

Latittudinal and energy dependence of energetic neutral atom spectral indices measured by the Interstellar Boundary Explorer

DOE PAGES

Desai, M. I.; Allegrini, F.; Dayeh, M. A.; ...

2015-03-30

Here, we investigate the latitudinal and energy dependence of the globally distributed 0.5-6 keV energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) during the first 3 yrs of the mission. Our results are: (1) the ENA spectral indices at the two lowest energies (0.89 and 1.47 keV) exhibit no clear trend with ecliptic latitude θ, while those at ~2.29 and ~3.41 keV exhibit a clear latitudinal pattern; flatter spectra occur above 60° latitude and steeper spectra occur ±30° of the equator. (2) The latitudinal dependence of the spectral indices at different energies can be represented bymore » the cosine function γ =a 0 + a 1 cos (a 2θ) with unique offsets, amplitudes, and phase angles; the higher energy ENA indices transition to successively larger amplitudes within ±45° of the equator. The results confirm the previously reported latitudinal organization of the ENA spectra and their remarkable similarity to that of the solar wind (SW) speed observed by Ulysses in the inner heliosphere. And while earlier studies showed that the ~0.5-6 keV globally distributed ENA spectral indices could be represented as single power laws over much of the sky, our new results indicate that this is an over-simplification because the spectral indices have an energy and latitude dependence. Furthermore, this dependence is an important factor that must be taken into consideration by models and simulations that seek to map the IBEX ENA observations back to the latitudinal profile of the SW speed structure observed in the inner heliosphere.« less

Latitudinal and Energy Dependence of Energetic Neutral Atom Spectral Indices Measured by the Interstellar Boundary Explorer

NASA Astrophysics Data System (ADS)

Desai, M. I.; Allegrini, F.; Dayeh, M. A.; Funsten, H.; Heerikhuisen, J.; McComas, D. J.; Fuselier, S. A.; Pogorelov, N.; Schwadron, N. A.; Zank, G. P.; Zirnstein, E. J.

2015-04-01

We investigate the latitudinal and energy dependence of the globally distributed 0.5-6 keV energetic neutral atom (ENA) spectra measured by the Interstellar Boundary Explorer (IBEX) during the first 3 yrs of the mission. Our results are: (1) the ENA spectral indices at the two lowest energies (0.89 and 1.47 keV) exhibit no clear trend with ecliptic latitude θ, while those at ˜2.29 and ˜3.41 keV exhibit a clear latitudinal pattern; flatter spectra occur above 60° latitude and steeper spectra occur ±30° of the equator. (2) The latitudinal dependence of the spectral indices at different energies can be represented by the cosine function γ ={{a}0}+{{a}1}cos ({{a}2}θ ) with unique offsets, amplitudes, and phase angles; the higher energy ENA indices transition to successively larger amplitudes within ±45° of the equator. Our results confirm the previously reported latitudinal organization of the ENA spectra and their remarkable similarity to that of the solar wind (SW) speed observed by Ulysses in the inner heliosphere. While earlier studies showed that the ˜0.5-6 keV globally distributed ENA spectral indices could be represented as single power laws over much of the sky, our new results indicate that this is an over-simplification because the spectral indices have an energy and latitude dependence. This dependence is an important factor that must be taken into consideration by models and simulations that seek to map the IBEX ENA observations back to the latitudinal profile of the SW speed structure observed in the inner heliosphere.

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.

Optical spectrum of proflavine and its ions

NASA Astrophysics Data System (ADS)

Bonaca, A.; Bilalbegović, G.

2010-06-01

Motivated by possible astrophysical and biological applications we calculate visible and near UV spectral lines of proflavine (C13H11N3, 3,6-diaminoacridine) in vacuum, as well as its anion, cation, and dication. The pseudopotential density functional and time-dependent density functional methods are used. We find a good agreement in spectral line positions calculated by two real-time propagation methods and the Lanczos chain method. Spectra of proflavine and its ions show characteristic UV lines which are good candidates for a detection of these molecules in interstellar space and various biological processes.

An atlas of optical spectrophotometry of Wolf-Rayet carbon and oxygen stars

NASA Technical Reports Server (NTRS)

Torres, Ana V.; Massey, Philip

1987-01-01

The atlas contains a homogeneous set of optical spectrophotometric observations (3300-7300 A) at moderate resolution (about 10 A) of almost all WC and WO stars in the Galaxy, the LMC, and the SMC. The data are presented in the form of spectral tracings (in magnitude units) arranged by subtype, with no correction for interstellar reddening. A montage of prototype stars of each spectral class is also shown. Comprehensive line identifications are given for the optical lines of WC and WO spectra, with major contributions tabulated and unidentified lines noted.

Theoretical study of deuteronated PAHs as carriers for IR emission features in the ISM

NASA Astrophysics Data System (ADS)

Buragohain, Mridusmita; Pathak, Amit; Sarre, Peter; Onaka, Takashi; Sakon, Itsuki

2015-11-01

This work proposes deuteronated PAH (DPAH+) molecules as a potential carrier of the 4.4 and 4.65 μm mid-infrared emission bands that have been observationally detected towards the Orion and M17 regions. Density Functional Theory calculations have been carried out on DPAH+ molecules to see the variations in the spectral behaviour from that of a pure polycyclic aromatic hydrocarbon (PAH). DPAH+ molecules show features that arise due to the stretching of the aliphatic C-D bond. Deuterated PAHs have been previously reported as carriers for such features. However, preferred conditions of ionization of PAHs in the interstellar medium (ISM) indicates the possibility of the formation of DPAH+ molecules. Comparison of band positions of DPAH+s shows reasonable agreement with the observations. We report the effect of size of the DPAH+ molecules on band positions and intensities. This study also reports a D/H ratio ([D/H]_{sc}; the ratio of C-D stretch and C-H stretch bands per [D/H]_{num}) that is decreasing with the increasing size of DPAH+s. It is noted that large DPAH+ molecules (no. of C atoms ˜50) match the D/H ratio that has been estimated from observations. This ratio offers prospects to study the deuterium abundance and depletion in the ISM.

Telescopic and meteor observation of `Oumuamua, the first known interstellar asteroid

NASA Astrophysics Data System (ADS)

Ye, Quan-Zhi

2018-04-01

1I/2017 U1 ('Oumuamua), a recently discovered asteroid in a hyperbolic orbit, is the first macroscopic object of extrasolar origin identified in the solar system. I will present imaging and spectroscopic observations of 'Oumuamua as well as a search of meteor activity potentially linked to this object using the Canadian Meteor Orbit Radar. We find that 'Oumuamua exhibits a moderate spectral gradient of 10%+-6% per 100 nm, a value lower than that of outer solar system bodies, indicative of a formation and/or previous residence in a warmer environment. Imaging observation and spectral line analysis show no evidence that 'Oumuamua is presently active. Negative meteor observation is as expected, since ejection driven by sublimation of commonly known cometary species such as CO requires an extreme ejection speed of ~40 m/s at ~100 au in order to reach the Earth. No obvious candidate stars are proposed as the point of origin for 'Oumuamua. Given a mean free path of ~109 ly in the solar neighborhood, 'Oumuamua has likely spent a very long time in interstellar space before encountering the solar system.

Carbon atom clusters in random covalent networks: PAHs as an integral component of interstellar HAC

NASA Astrophysics Data System (ADS)

Jones, A. P.

1990-11-01

Using a random covalent network (RCN) model for the structure of hydrogenated amorphorous carbon (HAC) and the available laboratory data, it is shown that aromatic species are a natural consequence of the structure of amorphous carbons formed in the laboratory. Amorphous carbons in the interstellar medium are therefore likely to contain a significant fraction of Polycyclic aromatic hydrocarbons (PAH) species within the 'amorphous' matrix making up these materials. This aromatic component can be produced in situ during the accretion of gas phase carbon species on to grains in the interstellar medium under hydrogen-poor conditions, or subsequent to deposition as a result of photolysis (photodarkening). The fraction of interstellar carbon present in HAC in the form of PAHs, based upon a RCN model, is consistent with the observed Unidentified infrared (UIR) emission features.

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;

VizieR Online Data Catalog: methoxy radical (CH3O) rotational spectrum (Laas+,

NASA Astrophysics Data System (ADS)

Laas, J. C.; Widicus Weaver, S. L.

2017-08-01

The methoxy radical (CH3O) has recently been detected interstellar medium and may be an important tracer of methanol-related chemistry in cold sources. Despite its importance, the spectral information needed to guide further astronomical searches is limited. We have therefore studied the low-temperature rotational spectrum in the laboratory within the spectral range of 246-303GHz. We have combined these new measurements with results from a number of literature reports to refine the molecular parameters and provide an updated and improved spectral line catalog. We present here the results of the laboratory studies and the refined analysis for the millimeter and submillimeter spectrum of methoxy. (1 data file).

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.

A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. I. The observational data

NASA Astrophysics Data System (ADS)

Olofsson, A. O. H.; Persson, C. M.; Koning, N.; Bergman, P.; Bernath, P. F.; Black, J. H.; Frisk, U.; Geppert, W.; Hasegawa, T. I.; Hjalmarson, Å.; Kwok, S.; Larsson, B.; Lecacheux, A.; Nummelin, A.; Olberg, M.; Sandqvist, Aa.; Wirström, E. S.

2007-12-01

Aims:Spectral line surveys are useful since they allow identification of new molecules and new lines in uniformly calibrated data sets. The subsequent multi-transition analysis will provide improved knowledge of molecular abundances, cloud temperatures and densities, and may also reveal previously unsuspected blends of molecular lines, which otherwise may lead to erroneous conclusions. Nonetheless, large portions of the sub-millimetre spectral regime remain unexplored due to severe absorptions by H{2}O and O{2} in the terrestrial atmosphere. The purpose of the measurements presented here is to cover wavelength regions at and around 0.55 mm - regions largely unobservable from the ground. Methods: Using the Odin astronomy/aeronomy satellite, we performed the first spectral survey of the Orion KL molecular cloud core in the bands 486-492 and 541-576 GHz with rather uniform sensitivity (22-25 mK baseline noise). Odin's 1.1 m size telescope, equipped with four cryo-cooled tuneable mixers connected to broad band spectrometers, was used in a satellite position-switching mode. Two mixers simultaneously observed different 1.1 GHz bands using frequency steps of 0.5 GHz (25 h each). An on-source integration time of 20 h was achieved for most bands. The entire campaign consumed 1100 orbits, each containing one hour of serviceable astro-observation. Results: We identified 280 spectral lines from 38 known interstellar molecules (including isotopologues) having intensities in the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart from the ground state rotational 1{1,0}-1{0,1} transitions of ortho-H{2}O, H{2}18O and H{2}17O, the high energy 6{2,4}-7{1,7} line of para-H{2}O (Eu=867 K) and the HDO(2{0,2}-1{1,1}) line have been observed, as well as the 1{0}-0{1} lines from NH{3} and its rare isotopologue 15NH{3}. We suggest assignments for some unidentified features, notably the new interstellar molecules ND and SH-. Severe blends have been detected in the line wings of the H{2}18O, H{2}17O and 13CO lines changing the true linewidths of the outflow emission. Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the Centre National d'Études Spatiales (CNES, France). The Swedish Space Corporation (SSC) was the industrial prime contractor and is also responsible for the satellite operation. Appendix B is only available at electronic form at http://www.aanda.org

Interstellar dehydrogenated PAH anions: vibrational spectra

NASA Astrophysics Data System (ADS)

Buragohain, Mridusmita; Pathak, Amit; Sarre, Peter; Gour, Nand Kishor

2018-03-01

Interstellar polycyclic aromatic hydrocarbon (PAH) molecules exist in diverse forms depending on the local physical environment. Formation of ionized PAHs (anions and cations) is favourable in the extreme conditions of the interstellar medium (ISM). Besides in their pure form, PAHs are also likely to exist in substituted forms; for example, PAHs with functional groups, dehydrogenated PAHs etc. A dehydrogenated PAH molecule might subsequently form fullerenes in the ISM as a result of ongoing chemical processes. This work presents a density functional theory (DFT) calculation on dehydrogenated PAH anions to explore the infrared emission spectra of these molecules and discuss any possible contribution towards observed IR features in the ISM. The results suggest that dehydrogenated PAH anions might be significantly contributing to the 3.3 μm region. Spectroscopic features unique to dehydrogenated PAH anions are highlighted that may be used for their possible identification in the ISM. A comparison has also been made to see the size effect on spectra of these PAHs.

A Spatial Study of X-ray Properties in Superbubble 30 Dor C with XMM-Newton

NASA Astrophysics Data System (ADS)

Babazaki, Yasunori; Mitsuishi, Ikuyuki; SANO, Hidetoshi; Yoshiike, Satoshi; Fukuda, Tatsuya; Maruyama, Shohei; Fujii, Kosuke; Fukui, Yasuo; Tawara, Yuzuru; Matsumoto, Hironori

2015-08-01

Supernova remnants (SNRs) in the Galaxy are believed to be most likely accelerators of cosmic-rays (CRs) in an energy range less than 3×10^15 eV. Thus SNRs emit synchrotron X-rays by high-energy electrons. Sano et al. (2014) investigated spatially-resolved X-ray spectral properties of a shell-type SNR RX1713.77-3946 which shows strong non-thermal X-ray emissions. A large variation in the photon index is found and the photon index tends to be hard with increasing an interstellar gas density, suggesting that CR electrons are efficiently accelerated in denser interstellar gas environments. Few studies have focused on a photon index variation in superbubbles which possess 100-1000 pc diameter shells of swept-up interstellar materials containing hot (~10^6 K) shock-heated gas. The superbubble 30 Dor C in the Large Magellanic Cloud is one of the best targets for examining the photon index variation, because 30 Dor C is by far strong non-thermal X-ray emissions, and thus provides an ideal laboratory for probing non-thermal emission mechanisms in the supperbubble. We investigated X-ray spectral properties of the superbubble with a high spatial resolution of on the order of 10 pc. Consequently, the spectra in the west region of 30 Dor C can be described with a combination of absorbed thermal and non-thermal models while the spectra in the east region can be fitted with an absorbed non-thermal model. The photon index and intensity in 2-10 keV show variations of 2.0-3.5 and (0.6-8.0) × 10^-7 erg/s/cm^2, respectively. The temperature of the thermal component ranges from ~0.1 to ~0.3 keV. We will discuss an interaction between the hot gas and an interstellar gas using mutiwavelength data.

Atypical dust species in the ejecta of classical novae

NASA Astrophysics Data System (ADS)

Helton, L. A.; Evans, A.; Woodward, C. E.; Gehrz, R. D.

2011-03-01

A classical nova outburst arises from a thermonuclear runaway in the hydrogen-rich material accreted onto the surface of a white dwarf in a binary system. These explosions can produce copious amounts of heavy element enriched material that are ejected violently into the surrounding interstellar medium. In some novae, conditions in the ejecta are suitable for the formation of dust of various compositions, including silicates, amorphous carbon, silicon carbide, and hydrocarbons. Multiple dust grain types are sometimes produced in the same system. CO formation in novae may not reach saturation, thus invalidating the usual paradigm in which the C:O ratio determines the dust species. A few novae, such as V705 Cas and DZ Cru, have exhibited emission features near 6, 8, and 11 μmthat are similar to "Unidentified Infrared" (UIR) features, but with significant differences in position and band structure. Here, we present Spitzer IRS spectra of two recent dusty novae, V2361 Cyg and V2362 Cyg, that harbor similar peculiar emission structures superimposed on features arising from carbonaceous grains. In other astronomical objects, such as star forming regions and young stellar objects, emission peaks at 6.2, 7.7, and 11.3 μmhave been associated with polycyclic aromatic hydrocarbon (PAH) complexes. We suggest that hydrogenated amorphous carbon (HAC) may be the source of these features in novae based upon the spectral behavior of the emission features and the conditions under which the dust formed.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardegree-Ullman, E. E.; Gudipati, M. S.; Werner, M.

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 conductedmore » 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.« less

H{sub 2} MOLECULAR CLUSTERS WITH EMBEDDED MOLECULES AND ATOMS AS THE SOURCE OF THE DIFFUSE INTERSTELLAR BANDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 ({sup s}eed{sup )}, embedded in a single-layer shell of H{sub 2} molecules. Less abundant variants of the cluster, including two seed molecules and/or a two-layer shell of H{sub 2} molecules, may also occur. The lines are broadened, blended, and wavelength-shifted by interactions between the seed and surrounding H{sub 2} shell. We refer to these clusters as contaminated H{sub 2} clusters (CHCs). We show that CHC spectroscopy matches the diversity of observed DIB spectralmore » profiles and provides good fits to several DIB profiles based on a rotational temperature of 10 K. CHCs arise from {approx}centimeter-sized, dirty H{sub 2} ice balls, called contaminated H{sub 2} 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 H{sub 2} 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 {approx}10-100 GHz spectral region.« less

OT2_pgolds01_6: Herschel [NII] Observations to Define the Source of [CII] Emission

NASA Astrophysics Data System (ADS)

Goldsmith, P.

2011-09-01

The 158 micron line of ionized carbon is the strongest single long-wavelength emission feature from the interstellar medium and is the most important coolant of gas in which hydrogen is in atomic form. It is a key determinant of the evolution of these largely atomic regions into denser, cooler molecular clouds in which new stars are formed, and is widely used as a tracer of star formation in the Milky Way and other galaxies. There is, however, an ongoing, serious controversy about the origin of the [CII] emission, which has been asserted to come from the extended low-density warm interstellar medium, but has more generally been associated with the primarily molecular photon dominated regions (PDRs) intimately associated with massive, young stars. We propose a combined HIFI and PACS study of the two far-infrared [NII] fine structure lines in order to resolve the important question of the fraction of CII emission that arises in ionized gas. Specifically, we will (1) utilize the fact that due to its ionization potential NII is found only in HII regions, and with PACS 122 and 205 micron observations, determine electron densities in a sample of such regions in the Galactic plane; (2) utilize available data on radio free-free and H-alpha emission to determine the NII column densities and from this the CII column densities in the HII regions; (3) use the electron densities to determine the fraction of CII emission arising in the ionized interstellar medium. These observations will be carried out at 150 of the positions in the Galactic plane observed in [CII] by the GOT-C+ project. We will also carry out HIFI observations of 10 selected positions in the 205 micron line to determine spectral characteristics of the NII emission line, which with CII, CI, and CO profiles already in hand will serve as a further discriminant among the proposed sources of CII emission.

The GBT PRIMOS Project - A Broadband Spectral Line Survey of SgrB2N from 300 MHz to 46 GHz

NASA Astrophysics Data System (ADS)

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

2013-01-01

Broadband, very sensitive, high spectral resolution spectral line surveys in recent years have made profound impacts into the understanding of interstellar reaction processes and in the identification of new molecular material in astronomical environments. Molecular line surveys are studies of the spectra of astronomical sources over a wide and usually continuous range of frequencies in order to determine the chemical composition (i.e., "molecular inventory"), physical properties (temperature, density), and kinematics of such regions. The National Radio Astronomy Observatory's (NRAO) 100-m Robert C. Byrd Green Bank Telescope (GBT) PRebiotic Interstellar MOlecule Survey (PRIMOS) Legacy Project started in Jan 2008 and concluded in July 2011. The PRIMOS project recorded a nearly frequency-continuous astronomical spectrum from 300 MHz to 46 GHz towards the Sgr B2(N) molecular cloud, with the pointing position centered on the Large Molecule Heimat (LMH). The PRIMOS data have resulted in numerous new detections and discoveries in astrochemistry. The data have also been widely used to demonstrate advances in molecular astrophysics in a variety of venues and have been instrumental in training the next generation of astronomers and chemists. The GBT is the only telescope in the world capable of making these groundbreaking discoveries. This presentation will highlight the recent successes from the survey and how to access these publically-available observations.

Update on IBEX and the outer boundary of the space radiation environment

NASA Astrophysics Data System (ADS)

McComas, D. J.; IBEX Science Team

2012-11-01

The Interstellar Boundary Explorer (IBEX) mission has been remotely observing the global interaction of our heliosphere with the local interstellar medium for over three years. Initially, IBEX generated the first all-sky maps of Energetic Neutral Atoms (ENAs) emanating in from the boundaries of our heliosphere over the energy range from ˜0.1-6 keV. Using these observations, the IBEX team discovered a smoothly varying, globally distributed ENA flux overlaid by a narrow "ribbon" of significantly enhanced ENA emissions. Since the initial publication of these results in a special issue of Science magazine (November 2009), IBEX has completed five more energy-resolved sets of sky maps and discovered small but important time variations in the interaction, separated the ribbon from globally distributed ENA fluxes, measured the energy spectral shape and inferred ion source temperatures, and carried out many other observational and theoretical studies of the outer heliosphere. In a second major area of observations - direct measurements of Interstellar Neutral (ISN) atoms - just published, IBEX observations of ISN He atoms show that the speed and direction (the motion of the heliosphere with respect to the interstellar medium) is slower and from a somewhat different direction than that thought from prior Ulysses observations. These observations also show evidence for a previously unknown and unanticipated secondary population of Helium. In addition, IBEX is providing the first direct quantitative measurements of the ISN H parameters and the first direct measurements of interstellar Ne and the interstellar Neon/Oxygen abundance ratio; this ratio is significantly different than the solar abundance ratio. Finally, IBEX was recently maneuvered into a unique, long-term stable orbit, which has a very low radiation environment and requires no orbit maintenance. Thus, IBEX will likely continue to provide revolutionary observations of the outer heliosphere and local interstellar medium for many years to come.

The distribution of interstellar dust in the solar neighborhood

NASA Technical Reports Server (NTRS)

Gaustad, John E.; Van Buren, Dave

1993-01-01

We surveyed the IRAS data base at the positions of the 1808 O6-B9.5 stars in The Bright Star Catalog for extended objects with excess emission at 60 microns, indicating the presence of interstellar dust at the location of the star. Within 400 pc the filling factor of the interstellar medium, for dust clouds with a density greater than 0.5/cu cm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the density distribution function appears to follow a power law index - 1.25. When the dust clouds are mapped onto the galactic plane, the sun appears to be located in a low-density region of the interstellar medium of width about 60 pc extending at least 500 pc in the direction of longitudes 80 deg - 260 deg, a feature we call the 'local trough'.

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.

A new method to determine the interstellar reddening towards WN stars

NASA Technical Reports Server (NTRS)

Conti, Peter S.; Morris, Patrick W.

1990-01-01

An empirical approach to determine the redding in WN stars is presented, in which the measured strengths of the emission lines of He II at 1640 and 4686 A are used to estimate the extinction. The He II emission lines at these wavelengths are compared for a number of WN stars in the Galaxy and the LMC. It is shown that the equivalent width ratios are single valued and are independent of the spectral subtypes. The reddening for stars in the Galaxy is derived using a Galactic extinction law and observed line flux ratios, showing good agreement with previous determinations of reddening. The possible application of the method to study the absorption properties of the interstellar medium in more distant galaxies is discussed.

A young solar twin in the Rosette cluster NGC 2244 line of sight

NASA Astrophysics Data System (ADS)

Huber, Jeremy M.; Kielkopf, John F.; Mengel, Matthew; Carter, Bradley D.; Ferland, Gary J.; Clark, Frank O.

2018-05-01

Based on prior precision photometry and cluster age analysis, the bright star GSC 00154-01819 is a possible young pre-main sequence member of the Rosette cluster, NGC 2244. As part of a comprehensive study of the large-scale structure of the Rosette and its excitation by the cluster stars, we noted this star as a potential backlight for a probe of the interstellar medium and extinction along the sight line towards a distinctive nebular feature projected on to the cluster centre. New high-resolution spectra of the star were taken with the University College London Echelle Spectrograph of the AAT. They reveal that rather than being a reddened spectral type B or A star within the Mon OB2 association, it is a nearby, largely unreddened, solar twin of spectral type G2V less than 180 Myr old. It is about 219 pc from the Sun with a barycentric radial velocity of +14.35 ± 1.99 km s-1. The spectrum of the Rosette behind it and along this line of sight shows a barycentric radial velocity of +26.0 ± 2.4 km s-1 in H α, and a full width at half-maximum velocity dispersion of 61.94 ± 1.38 km s-1.

No evidence for interstellar proteins

NASA Astrophysics Data System (ADS)

Koch, R. H.; Davies, R. E.

1984-03-01

The claim by Karim et al. (1983) that the broad interstellar feature near 280 nm suggests the existence of proteinaceous matter in the interstellar medium is addressed. From astronomical and biochemical arguments it is shown that no quantitative measures of optical depth can be derived from the published data and that there is a great wealth of organic molecules which have absorptions at or near this wavelength interval. The amino acid tryptophan is one such molecule but the deduced spectrum does not satisfy two other properties of its spectrum. In particular, the 280 nm absorption for tryptophan refers to an aqueous solution of the molecule, and no liquid water is expected to exist in the ISM.

Galactic civilizations: Population dynamics and interstellar diffusion

NASA Technical Reports Server (NTRS)

Newman, W. I.; Sagan, C.

1978-01-01

The interstellar diffusion of galactic civilizations is reexamined by potential theory; both numerical and analytical solutions are derived for the nonlinear partial differential equations which specify a range of relevant models, drawn from blast wave physics, soil science, and, especially, population biology. An essential feature of these models is that, for all civilizations, population growth must be limited by the carrying capacity of the environment. Dispersal is fundamentally a diffusion process; a density-dependent diffusivity describes interstellar emigration. Two models are considered: the first describing zero population growth (ZPG), and the second which also includes local growth and saturation of a planetary population, and for which an asymptotic traveling wave solution is found.

Laboratory study of methyl isocyanate ices under astrophysical conditions

NASA Astrophysics Data System (ADS)

Maté, B.; Molpeceres, G.; Timón, V.; Tanarro, I.; Escribano, R.; Guillemin, J. C.; Cernicharo, J.; Herrero, V. J.

2017-10-01

Methyl isocyanate has been recently detected in comet 67P/Churyumov-Gerasimenko (67P/CG) and in the interstellar medium. New physicochemical studies on this species are now necessary as tools for subsequent studies in astrophysics. In this work, infrared spectra of solid CH3NCO have been obtained at temperatures of relevance for astronomical environments. The spectra are dominated by a strong, characteristic multiplet feature at 2350-2250 cm-1, which can be attributed to the asymmetric stretching of the NCO group. A phase transition from amorphous to crystalline methyl isocyanate is observed at ˜90 K. The band strengths for the absorptions of CH3NCO in ice at 20 K have been measured. Deuterated methyl isocyanate is used to help with the spectral assignment. No X-ray structure has been reported for crystalline CH3NCO. Here we advance a tentative theoretical structure, based on density functional theory (DFT) calculations, derived taking the crystal of isocyanic acid as a starting point. A harmonic theoretical spectrum is then calculated for the proposed structure and compared with the experimental data. A mixed ice of H2O and CH3NCO was formed by simultaneous deposition of water and methyl isocyanate at 20 K. The absence of new spectral features indicates that methyl isocyanate and water do not react appreciably at 20 K, but form a stable mixture. The high CH3NCO/H2O ratio reported for comet 67P/CG, and the characteristic structure of the 2350-2250 cm-1 band, makes it a very good candidate for future astronomical searches.

The origin and evolution of dust in interstellar and circumstellar environments

NASA Technical Reports Server (NTRS)

Whittet, Douglas C. B.; Leung, Chun M.

1993-01-01

This status report covers the period from the commencement of the research program on 1 Jul. 1992 through 30 Apr. 1993. Progress is reported for research in the following areas: (1) grain formation in circumstellar envelopes; (2) photochemistry in circumstellar envelopes; (3) modeling ice features in circumstellar envelopes; (4) episodic dust formation in circumstellar envelopes; (5) grain evolution in the diffuse interstellar medium; and (6) grain evolution in dense molecular clouds.

Correlation between diffuse interstellar bands (DIBs) and interstellar extinction using data from Bosscha Compact Spectrograph

NASA Astrophysics Data System (ADS)

Puspitarini, L.; Malasan, H. L.; Aprilia; Arifyanto, M. I.; Lallement, R.; Irfan, M.; Puspitaningrum, E.

2018-04-01

A longstanding challenge in astronomical spectroscopy is to uncover the carriers of diffuse interstellar bands (DIBs). They are broad absorption features due to the interstellar matter (ISM). They are seen in stellar spectra of background stars or other astronomical objects. Although we do not know utterly the carriers of the DIBs, they can be a promising tracer of the ISM. One of the interesting properties is their correlations with the interstellar (IS) extinction. For each band, the correlation has considerable dispersion and differences that possibly due to the IS physical conditions. Some DIBs are sensitive to the stellar radiation field, and some are not. To study the effect, we measured the DIB observed in Be/B stars spectra. The stars were observed by using Bosscha Compact Spectrograph at the Bosscha Observatory, Lembang, Indonesia. We performed an automated fitting of a combination of a smooth stellar continuum, the DIB profile, and a synthetic telluric transmission to the spectrum. The DIB measurements were compared to the general DIBs-extinction relationship. The correlation is found to be in good agreement with previous determinations.

H2 as a Possible Carrier of the DIBs?

NASA Astrophysics Data System (ADS)

Ubachs, W.

2014-02-01

In the 1990s the hydrogen molecule, by far the most abundant molecular species in the interstellar medium, has been proposed as a possible carrier of the diffuse interstellar bands. While some remarkable coincidences were found in the rich spectrum of inter-Rydberg transitions of this molecule with DIB-features, both in frequency position as in linewidth, some open issues remained on a required non-linear optical pumping scheme that should explain the population of certain intermediate levels and act as a selection mechanism. Recently a similar scheme has been proposed relating the occurrence of the UV-bump (the ubiquitous 2170 Å extinction feature) to the spectrum of H2, therewith reviving the H2 hypothesis.

A Broad 22 Micron Emission Feature in the Carina Nebula H ii Region.

PubMed

Chan; Onaka

2000-04-10

We report the detection of a broad 22 µm emission feature in the Carina Nebula H ii region by the Infrared Space Observatory (ISO) short-wavelength spectrometer. The feature shape is similar to that of the 22 µm emission feature of newly synthesized dust observed in the Cassiopeia A supernova remnant. This finding suggests that both of the features are arising from the same carrier and that supernovae are probably the dominant production sources of this new interstellar grain. A similar broad emission dust feature is also found in the spectra of two starburst galaxies from the ISO archival data. This new dust grain could be an abundant component of interstellar grains and can be used to trace the supernova rate or star formation rate in external galaxies. The existence of the broad 22 µm emission feature complicates the dust model for starburst galaxies and must be taken into account correctly in the derivation of dust color temperature. Mg protosilicate has been suggested as the carrier of the 22 µm emission dust feature observed in Cassiopeia A. The present results provide useful information in studies on the chemical composition and emission mechanism of the carrier.

Photochemistry of polycyclic aromatic hydrocarbons in cosmic water ice. II. Near UV/VIS spectroscopy and ionization rates

NASA Astrophysics Data System (ADS)

Bouwman, J.; Cuppen, H. M.; Steglich, M.; Allamandola, L. J.; Linnartz, H.

2011-05-01

Context. Mid-infrared emission features originating from polycyclic aromatic hydrocarbons (PAHs) are observed towards photon dominated regions in space. Towards dense clouds, however, these emission features are quenched. Observations of dense clouds show that many simple volatile molecules are frozen out on interstellar grains, forming thin layers of ice. Recently, observations have shown that more complex non-volatile species, presumably including PAHs, also freeze out and contribute to the ongoing solid-state chemistry. Aims: The study presented here aims at obtaining reaction rate data that characterize PAH photochemistry upon vacuum ultraviolet (VUV) irradiation in an interstellar H2O ice analogue to explore the potential impact of PAH:H2O ice reactions on overall interstellar ice chemistry. To this end, the experimental results are implemented in a chemical model under simple interstellar cloud conditions. Methods: Time-dependent near-UV/VIS spectroscopy on the VUV photochemistry of anthracene, pyrene, benzo[ghi]perylene and coronene containing interstellar H2O ice analogs is performed at 25 and 125 K, using an optical absorption setup. Results: Near-UV/VIS absorption spectra are presented for these four PAHs and their photoproducts including cationic species trapped in H2O ice. Oscillator strengths of the cation absorption bands are derived relative to the oscillator strength of the neutral parent PAH. The loss of the parent and growth of PAH photoproducts are measured as a function of VUV dose, yielding solid state reaction constants. The rate constants are used in an exploratory astrochemical model, to assess the importance of PAH:H2O ice photoprocessing in UV exposed interstellar environments, compared with the timescales in which PAH molecules are incorporated in interstellar ices. Conclusions: All four PAHs studied here are found to be readily ionized upon VUV photolysis when trapped in H2O ice and exhibit similar rates for ionization at astronomically relevant temperatures. Depending on the relative efficiency of H2O photodesorption and PAH photoionization in H2O ice, the latter may trigger a charge induced aromatic solid state chemistry, in which PAH cations play a central role.

Probing the Origin and Evolution of Interstellar and Protoplanetary Biogenic Molecules:A Comprehensive Survey of Interstellar Ices with SPHEREx

NASA Astrophysics Data System (ADS)

Melnick, Gary J.; SPHEREx Science Team

2016-01-01

Many of the most important building blocks of life are locked in interstellar and protoplanetary ices. Examples include H2O, CO, CO2, and CH3OH, among others. There is growing evidence that in some environments, such as within the cores of dense molecular clouds and the mid-plane of protoplanetary disks, the amounts of these species in ices far exceeds that in the gas phase. As a result, collisions between ice-bearing bodies and newly forming planets are thought to be a major means of delivering these key species to young planets. There currently exist fewer than 250 ice absorption spectra toward Galactic molecular clouds, which is insufficient to reliably trace the ice content of clouds through the various stages of collapse to star and planet formation, or assess the effects of their environments and physical conditions, such as cloud density, internal temperature, presence or absence of embedded sources, external UV and X-ray radiation, gas-phase composition, or cosmic-ray ionization rate, on the ice composition for clouds at similar evolutionary stages. Ultimately, our goal is to understand how these findings connect to our own Solar System.SPHEREx, which is a mission in NASA's Small Explorer (SMEX) program that was selected for a Phase A study in July 2015, will be a game changer for the study of interstellar, circumstellar, and protoplanetary disk ices. SPHEREx will obtain spectra over the entire sky in the optical and near-IR, including the 2.5 to 4.8 micron region, which contains the above biogenic ice features. SPHEREx will detect millions of potential background continuum point sources already catalogued by NASA's Wide-field Infrared Survey Explorer (WISE) at 3.4 and 4.6 microns for which there is evidence for intervening gas and dust based on the 2MASS+WISE colors with sufficient sensitivity to yield ice absorption spectra with SNR ≥ 100 per spectral resolution element. The resulting > 100-fold increase in the number of high-quality ice absorption spectra toward a wide variety of regions distributed throughout the Galaxy will reveal correlations between ice content and environment not possible with current spectra. Finally, SPHEREx will provide JWST with an ice source catalog for follow-up.

Blue Luminescence and Extended Red Emission: Possible Connections to the Diffuse Interstellar Bands

NASA Astrophysics Data System (ADS)

Witt, A. N.

2014-02-01

Blue luminescence (BL) and extended red emission (ERE) are observed as diffuse, optical-wavelength emissions in interstellar space, resulting from photoluminescence by ultraviolet(UV)-illuminated interstellar grains. Faintness and the challenge of separating the BL and ERE from the frequently much brighter dust-scattered continuum present major observational hurdles, which have permitted only slow progress in testing the numerous models that have been advanced to explain these two phenomena. Both the ERE, peaking near 680 nm (FWHM ~ 60 - 120 nm) and the BL, asymmetrically peaking at ~ 378 nm (FWHM ~ 45 nm), were first discovered in the Red Rectangle nebula. Subsequently, ERE and BL have been observed in other reflection nebulae, and in the case of the ERE, in carbon-rich planetary nebulae, H II regions, high-latitude cirrus clouds, the galactic diffuse ISM, and in external galaxies. BL exhibits a close spatial and intensity correlation with emission in the aromatic emission feature at 3.3 micron, most likely arising from small, neutral polycyclic aromatic hydrocarbon (PAH) molecules. The spectral characteristics of the BL also agree with those of fluorescence by PAH molecules with 13 to 19 carbon atoms. The BL phenomenon is thus most readily understood as the optical fluorescence of small, UV-excited aromatic molecules. The ERE, by contrast, though co-existent with mid-IR PAH emissions, does not correlate with emissions from either neutral or ionized PAHs. Instead, the spatial ERE morphology appears to be strictly governed by the density of far-UV (E >= 10.5 eV) photons, which are required for the ERE excitation. The most restrictive observational constraint for the ERE process is its exceptionally high quantum efficiency. If the ERE results from photo-excitation of a nano-particle carrier by photons with E >= 10.5 eV in a single-step process, the quantum efficiency exceeds 100%. Such a process, in which one to three low-energy optical photons may be emitted following a single far-UV excitation, is possible in highly isolated small clusters, e.g. small, dehydrogenated carbon clusters with about 20 to 28 carbon atoms. A possible connection between the ERE carriers and the carriers of DIBs may exist in that both are ubiquitous throughout the diffuse interstellar medium and both have an abundance of low-lying electronic levels with E <= 2.3 eV above the ground state.

Harnessing the Efficiency of 0(1D) Insertion Reactions for Prebiotic Astrochemistry

NASA Astrophysics Data System (ADS)

Widicus Weaver, Susanna

We propose a THz spectroscopic study of the small prebiotic molecules aminomethanol, methanediol, and methoxymethanol. These target molecules are predicted as the dominant products of photo-driven grain surface chemistry in interstellar environments, and are precursors to important prebiotic molecules like sugars and amino acids. These molecules are also expected to be major contributors to the spectral line density in the submillimeter spectral surveys from the Herschel and SOFIA observatories. We will use our custom mixing source to produce these molecules through O(1D) insertion reactions with the precursor molecules methyl amine, methanol, and dimethyl ether, respectively. We will then record their rotational spectra across the THz frequency range using our existing submillimeter spectrometer. This research will increase the science return from NASA missions because the target molecules serve as tracers of the simplest organic chemistry that can occur in starforming regions. This chemistry begins with methanol, which is the predominant organic molecule observed in interstellar ices. Methanol photodissociation leads to small organic radicals such as CH3O, CH2OH, and CH3. These radicals can undergo combination reactions on interstellar ices to form many of the complex organic molecules that are routinely observed in star-forming regions. Our target molecules aminomethanol, methanediol, and methoxymethanol are some of the simplest molecules that can form from this type of chemistry, and serve as tracers of ice mantle liberation in star-forming regions. These molecules also participate in gas-phase reactions that lead to amino acids and sugars, and as such are fundamentally important prebiotic molecules in interstellar environments. These types of small organic molecules also have high spectral line density, and are major contributors to line confusion in observational spectral surveys such as those conducted by Herschel and SOFIA. Therefore, the proposed research will aid in full data interpretation from Herschel and SOFIA observations. Currently there is no spectral information available for these molecules to guide observational studies, despite their importance in astrochemistry. This is because these molecules are difficult to study in laboratory settings due to their instability and reactivity. We are using highly exothermic O(1D) insertion reactions to produce these molecules in a supersonic expansion, and investigating the products using THz spectroscopy. This work builds on the work involved in our previous APRA award (Grant NNX11AI07G) "New THz Tools to Support Herschel Observations: Integrative Studies in Laboratory Spectroscopy, Observational Astronomy, and Chemical Modeling". In this previous award, we laid the groundwork for these experiments by constructing and benchmarking the spectrometer, designing and testing the molecular source used for the O(1D) reactions, and studying the proposed formation reactions for the laboratory work through computational studies. We have confirmed production of methanol from O(1D) insertion into methane, and then applied this chemistry to produce vinyl alcohol from ethylene. We have now also obtained preliminary spectra of aminomethanol. Here we propose to extend this work by finishing the aminomethanol characterization as well as examining methanediol and methoxymethanol during the next proposal period.

Preliminary Examination of the Interstellar Collector of Stardust

NASA Technical Reports Server (NTRS)

Westphal, A. J.; Allen, C.; Bastien, R.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Butterworth, A. L.; Floss, C.; Flynn, G.;

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

NASA Technical Reports Server (NTRS)

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

ACCURATE MODELING OF X-RAY EXTINCTION BY INTERSTELLAR GRAINS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, John; Draine, B. T., E-mail: jah5@astro.princeton.edu, E-mail: draine@astro.princeton.edu

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 bemore » 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.« less

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

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

Galactic interstellar abundance surveys with IUE and IRAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Steenberg, M.E.

1987-01-01

This thesis is a survey of interstellar densities, abundances, and cloud structure in the Galaxy, using two NASA satellites: the International Ultraviolet Explorer (IUE) and Infrared Astronomical Satellite (IRAS). From IUE high-resolution spectra, the author measured equivalent widths of 18 ultraviolet resonance transitions and derived column densities for Si/sup +/, Mn/sup +/, Fe/sup +/, S/sup +/, and Zn/sup +/ toward 261 early-type stars. From the IRAS all-sky survey he also measured the infrared cirrus flux. He examined the variations of the measured parameters with spectral type, E(B-V), galactic longitude and latitude, distance from the Sun, and mean density. The hydrogen-columnmore » densities, metal-column densities, and gas-to-dust ratio are in good agreement with Copernicus surveys. The derived interstellar abundances yield mean logarithmic depletions. These depletions correlate with mean density but not with the physical density derived from Copernicus H/sub 2/ rotational states. Abundance ratios indicate a larger Fe halo abundance compared to Si, Mn, S, or Zn, which may result from selective grain processing in shocks or from Type I supernovae.« less

Spitzer Observations of Dust Destruction in the Puppis A Supernova Remnant

NASA Technical Reports Server (NTRS)

Arendt, Richard G.; Dweek, Eli; Blair, William P.; Ghavamian, Parviz; Hwang, Una; Long, Knox X.; Petre, Robert; Rho, Jeonghee; Winkler, P. Frank

2010-01-01

The interaction of the Puppis A supernova remnant (SNR) with a neighboring molecular cloud provides a unique opportunity to measure the amount of grain destruction in an SNR shock. Spitzer Space Telescope MIPS imaging of the entire SNR at 24, 70, and 160 micrometers shows an extremely good correlation with X-ray emission, indicating that the SNR's IR radiation is dominated by the thermal emission of swept-up interstellar dust, collisionally heated by the hot shocked gas. Spitzer IRS spectral observations targeted both the Bright Eastern Knot (BEK) of the SNR where a small cloud has been engulfed by the supernova blast wave and outlying portions of the associated molecular cloud that are yet to be hit by the shock front. Modeling the spectra from both regions reveals the composition and the grain size distribution of the interstellar dust, both in front of and behind the SNR shock front. The comparison shows that the ubiquitous polycyclic aromatic hydrocarbons of the interstellar medium are destroyed within the BEK, along with nearly 25% of the mass of graphite and silicate dust grains.

The Properties of Single Interstellar Clouds: Cycle 1, SIDE-2 Observations

NASA Astrophysics Data System (ADS)

Hobbs, Lewis

1990-12-01

WE PROPOSE TO USE THE ECHELLE GRATING OF THE HIGH RESOLUTION SPECTROGRAPH OVER A TWO-YEAR PERIOD TO OBSERVE THE PROFILES OF INTERSTELLAR ABSORPTION LINES. THE COLUMN DENSITES OF 18 NEUTRAL OR IONIZED FORMS OF THE ELEMENTS C,N,O,Mg,Si,P,S,Fe, AND Zn WILL BE MEASURED IN THE APPROXIMATELY 100 INDIVIDUAL INTERSTELLAR CLOUDS ALONG THE LIGHT PATHS TO 18 BRIGHT, BROAD-LINED STARS OF EARLY SPECTRAL TYPE WITHIN 1 KPC OF THE SUN. THE PRIMARY PURPOSE OF THE OBSERVATIONS IS TO DETERMINE MORE ACCURATELY THAN WAS HITHERTO POSSIBLE THE FUNDAMENTAL PHYSICAL PROPERTIES OF THE RESOLVED CLOUDS, INCLUDING LINEAR SIZE, TEMPERATURE, TOTAL DENSITY, FRACTIONAL IONIZATION AND THE RELATIVE ABUNDANCES OF THE 9 SELECTED ELEMENTS. THE REST OF THIS OBSERVING PROGRAM IS CONTAINED IN APPROVED PROPOSAL ID = 2251; THE PROGRAM EUNUMERATED HERE CONSISTS OF THAT PART OF OUR ORIGINAL PROGRAM WHICH CAN BE CARRIED OUT USING ONLY SIDE 2 OF THE GHRS. THIS PROGRAM THEREFORE CONSISTS OF ECH-B OBSERVATIONS OF EACH OF 4 STARS AT 7 WAVELENGTHS. PROGRAM 2251 SHOULD BE CONSULTED FOR ADDITIONAL DETAILS.

The Properties of Single Interstellar Clouds: Hopr Repeat Cycle 1, SIDE-2 Observations

NASA Astrophysics Data System (ADS)

Hobbs, Lewis

1990-12-01

WE PROPOSE TO USE THE ECHELLE GRATING OF THE HIGH RESOLUTION SPECTROGRAPH OVER A TWO-YEAR PERIOD TO OBSERVE THE PROFILES OF INTERSTELLAR ABSORPTION LINES. THE COLUMN DENSITES OF 18 NEUTRAL OR IONIZED FORMS OF THE ELEMENTS C,N,O,Mg,Si,P,S,Fe, AND Zn WILL BE MEASURED IN THE APPROXIMATELY 100 INDIVIDUAL INTERSTELLAR CLOUDS ALONG THE LIGHT PATHS TO 18 BRIGHT, BROAD-LINED STARS OF EARLY SPECTRAL TYPE WITHIN 1 KPC OF THE SUN. THE PRIMARY PURPOSE OF THE OBSERVATIONS IS TO DETERMINE MORE ACCURATELY THAN WAS HITHERTO POSSIBLE THE FUNDAMENTAL PHYSICAL PROPERTIES OF THE RESOLVED CLOUDS, INCLUDING LINEAR SIZE, TEMPERATURE, TOTAL DENSITY, FRACTIONAL IONIZATION AND THE RELATIVE ABUNDANCES OF THE 9 SELECTED ELEMENTS. THE REST OF THIS OBSERVING PROGRAM IS CONTAINED IN APPROVED PROPOSAL ID = 2251; THE PROGRAM EUNUMERATED HERE CONSISTS OF THAT PART OF OUR ORIGINAL PROGRAM WHICH CAN BE CARRIED OUT USING ONLY SIDE 2 OF THE GHRS. THIS PROGRAM THEREFORE CONSISTS OF ECH-B OBSERVATIONS OF EACH OF 4 STARS AT 7 WAVELENGTHS. PROGRAM 2251 SHOULD BE CONSULTED FOR ADDITIONAL DETAILS.

The Properties of Single Interstellar Clouds Cycle 2

NASA Astrophysics Data System (ADS)

Hobbs, Lewis

1991-07-01

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

IRAS 08572+3915: constraining the aromatic versus aliphatic content of interstellar HACs

NASA Astrophysics Data System (ADS)

Dartois, E.; Geballe, T. R.; Pino, T.; Cao, A.-T.; Jones, A.; Deboffle, D.; Guerrini, V.; Bréchignac, Ph.; D'Hendecourt, L.

2007-02-01

We analyze dust features present in the mid-infrared (Spitzer) and recently published L-band (UKIRT) spectra of the infrared galaxy IRAS 08572+3915. The line of sight toward the AGN nucleus crosses a high column density of carbonaceous dust whose characteristic absorption features appear clearly. They provide a real insight into the chemical environment of the diffuse interstellar medium. Thanks to the moderate redshift of IRAS 08572+3915, the wavelength of the aromatic CH stretching mode is free of major telluric lines, and a strong observational constraint of Hsp2 /Hsp3 ≤ 0.08 has been determined. This limit clearly shows that the bonding of hydrogen atoms in interstellar hydrogenated amorphous carbon is highly aliphatic. The presence of a broad absorption feature centered at 6.2 μm, probably arising from olefinic/aromatic structures, corresponds to the backbone of this carbonaceous material, which is the major carbon-containing component of the interstellar medium along this line of sight. Based on observations made with the Spitzer Space Telescope (GO-3336 program), which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Based on data obtained at the United Kingdom Infrared Telescope, which is operated by the Joint Astronomy Center on behalf of the UK Particle Physics and Astronomy Research Council. Part of this work has been financed by the french CNRS program "Physique et Chimie du Milieu Interstellaire" (PCMI-CNRS). TRG's esearch is supported by the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Australia, Brazil, Canada, Chile, the United Kingdom, and the United States of America.

The Starship Philosophy: Its Heritage and Competitors

NASA Astrophysics Data System (ADS)

Ashworth, S.

The distinctive features of the astronautical philosophy characteristic of the current surge of interest in interstellar spaceflight are examined and contrasted with the conflicting features of more Earthbound philosophies in order to elucidate the presentday place and past heritage of the astronautical philosophy in human thought.

Constraining the Origin of Impact Craters on Al Foils from the Stardust Interstellar Dust Collector

NASA Technical Reports Server (NTRS)

Stroud, Rhonda M.; Achilles, Cheri; Allen, Carlton; Ansari, Asna; Bajt, Sasa; Bassim, Nabil; Bastien, Ron S.; Bechtel, H. A.; Borg, Janet; Brenker, Frank E.;

Controlling the emission profile of an H2 discharge lamp to simulate interstellar radiation fields

NASA Astrophysics Data System (ADS)

Ligterink, N. F. W.; Paardekooper, D. M.; Chuang, K.-J.; Both, M. L.; Cruz-Diaz, G. A.; van Helden, J. H.; Linnartz, H.

2015-12-01

Context. Microwave discharge hydrogen-flow lamps have been used for more than half a century to simulate interstellar ultraviolet radiation fields in the laboratory. Recent discrepancies between identical measurements in different laboratories, as well as clear wavelength dependent results obtained in monochromatic (synchrotron) experiments, hint at a more elaborate dependence on the exact discharge settings than assumed so far. Aims: We have investigated systematically two lamp geometries in full dependence of a large number of different running conditions and the spectral emission patterns are characterized for the first time with fully calibrated absolute flux numbers. Methods: A sophisticated plasma lamp calibration set-up has been used to record the vacuum-ultraviolet emission spectra with a spectral resolution of 0.5 nm and bandwidth of 1.6 nm in the 116-220 nm region. Spectra are compared with the output of a calibrated D2-lamp which allows a derivation of absolute radiance values. Results: The general findings of over 200 individual measurements are presented, illustrating how the lamp emission pattern depends on i) microwave power; ii) gas and gas mixing ratios; iii) discharge lamp geometry; iv) cavity positioning; and v) gas pressure.

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) Mission Concept

NASA Technical Reports Server (NTRS)

Ennico, Kimberly; Sandford, S.; Allamandola, L.; Bregman, J.; Cohen, M.; Cruikshank, D.; Dumas, C.; Greene, T.; Hudgins, D.; Kwok, S.

2004-01-01

The AstroBiology Explorer (ABE) mission concept consists of a modest dedicated space observatory having a 60 cm class primary mirror cooled to T less than 50 K equipped with medium resolution cross-dispersed spectrometers having cooled large format near- and mid-infrared detector arrays. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The mission's observaticxiai program woiild make fundamental scieztific: prngress in establishing the nature, distribution, formation and evolution of organic and other molecular materials in the following extra-terrestrial environments: 1) The Outflow of Dying Stars; 2) The Diffuse Interstellar Medium (DISM); 3) Dense Molecular Clouds, Star Formation Regions, and Young Stellar/Planetary Systems; 4) Planets, Satellites, and Small Bodies within the Solar System; and 5) The Interstellar Media of Other Galaxies ABE could make fundamental progress in all of these area by conducting a 1 to 2 year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5 - 20 micron spectral range at a spectral resolution of R greater than 2500 of about 1500 galaxies, stars, planetary nebulae, young stellar objects, and solar system objects.

The millimeter wave spectrum of methyl cyanate: a laboratory study and astronomical search in space^.

PubMed

Kolesniková, L; Alonso, J L; Bermúdez, C; Alonso, E R; Tercero, B; Cernicharo, J; Guillemin, J-C

2016-07-01

The recent discovery of methyl isocyanate (CH 3 NCO) in Sgr B2(N) and Orion KL makes methyl cyanate (CH 3 OCN) a potential molecule in the interstellar medium. The aim of this work is to fulfill the first requirement for its unequivocal identification in space, i.e. the availability of transition frequencies with high accuracy. The room-temperature rotational spectrum of methyl cyanate was recorded in the millimeter wave domain from 130 to 350 GHz. All rotational transitions revealed A - E splitting owing to methyl internal rotation and were globally analyzed using the ERHAM program. The data set for the ground torsional state of methyl cyanate exceeds 700 transitions within J″ = 10 - 35 and [Formula: see text] and newly derived spectroscopic constants reproduce the spectrum close to the experimental uncertainty. Spectral features of methyl cyanate were then searched for in Orion KL, Sgr B2(N), B1-b, and TMC-1 molecular clouds. Upper limits to the column density of methyl cyanate are provided.

Stardust Interstellar Preliminary Examination IV: Scanning Transmission X-Ray Microscopy Analyses of Impact Features in the Stardust Interstellar Dust Collector

NASA Technical Reports Server (NTRS)

Butterworth, Anna L.; Westphal, Andrew J.; Frank, David R.; Allen, Carlton C.; Bechtel, Hans A.; Sandford, Scott A.; Tsou, Peter; Zolensky, Michael E.

2014-01-01

We report the quantitative characterization by synchrotron soft X-ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector. Samples were analyzed in aerogel by acquiring high spatial resolution maps and high energy-resolution spectra of major rock-forming elements Mg, Al, Si, Fe, and others. We developed diagnostic screening tests to reject spacecraft secondary ejecta and terrestrial contaminants from further consideration as interstellar dust candidates. The results support an extraterrestrial origin for three interstellar candidates: I1043,1,30 (Orion) is a 3 pg particle with Mg-spinel, forsterite, and an iron-bearing phase. I1047,1,34 (Hylabrook) is a 4 pg particle comprising an olivine core surrounded by low-density, amorphous Mg-silicate and amorphous Fe, Cr, and Mn phases. I1003,1,40 (Sorok) has the track morphology of a high-speed impact, but contains no detectable residue that is convincingly distinguishable from the background aerogel. Twenty-two samples with an anthropogenic origin were rejected, including four secondary ejecta from impacts on the Stardust spacecraft aft solar panels, nine ejecta from secondary impacts on the Stardust Sample Return Capsule, and nine contaminants lacking evidence of an impact. Other samples in the collection included I1029,1,6, which contained surviving solar system impactor material. Four samples remained ambiguous: I1006,2,18, I1044,2,32, and I1092,2,38 were too dense for analysis, and we did not detect an intact projectile in I1044,3,33. We detected no radiation effects from the synchrotron soft X-ray analyses; however, we recorded the effects of synchrotron hard X-ray radiation on I1043,1,30 and I1047,1,34.

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.

SNR radio spectral index distribution and its correlation with polarization. a case study: the Lupus Loop

NASA Astrophysics Data System (ADS)

Borka Jovanović, V.; Jovanović, P.; Borka, D.

2017-04-01

We use radio-continuum all-sky surveys at 1420 and 408 MHz with the aim to investigate properties of the Galactic radio source Lupus Loop. The survey data at 1435 MHz, with the linear polarization of the southern sky, are also used. We calculate properties of this supernova remnant: the brightness temperature, surface brightness and radio spectral index. To determine its borders and to calculate its properties, we use the method we have developed. The non-thermal nature of its radiation is confirmed. The distribution of spectral index over its area is also given. A significant correlation between the radio spectral index distribution and the corresponding polarized intensity distribution inside the loop borders is found, indicating that the polarization maps could provide us information about the distribution of the interstellar medium, and thus could represent one additional way to search for new Galactic loops.

Comet Halley as an aggregate of interstellar dust and further evidence for the photochemical formation of organics in the interstellar medium

NASA Technical Reports Server (NTRS)

Briggs, R.; Ertem, G.; Ferris, J. P.; Greenberg, J. M.; Mccain, P. J.; Mendoza-Gomez, C. X.; Schutte, W.

1992-01-01

Photolysis of mixtures of CO:NH3:H2O at 12 K results in the formation of an organic residue which is not volatile in high vacuum at room temperature. Analysis of this fraction by GC-MS resulted in the detection of C2-C3 hydroxy acids and hydroxy amides, glycerol, urea, glycine, hexamethylene tetramine, formamidine and ethanolamine. Use of isotopically labeled gases made it possible to establish that the observed products were not contaminants. The reaction pathways for the formation of these products were determined from the position of the isotopic labels in the mass spectral fragments. The significance of these findings to the composition of comets and the origins of life is discussed.

X-Ray Background Survey Spectrometer (XBSS)

NASA Technical Reports Server (NTRS)

Sanders, W. T. (Principal Investigator); Paulos, R. J.

1996-01-01

The objective of this investigation was to perform a spectral survey of the low energy diffuse X-ray background using the X-ray Background Survey Spectrometer (XBSS) on board the Space Station Freedom (SSF). XBSS obtains spectra of the X-ray diffuse background in the 11-24 A and 44-84 A wavelength intervals over the entire sky with 15 deg spatial resolution. These X-rays are almost certainly from a very hot (10(exp 6) K) component of the interstellar medium that is contained in regions occupying a large fraction of the interstellar volume near the Sun. Astrophysical plasmas near 10(exp 6) K are rich in emission lines, and the relative strengths of these lines, besides providing information about the physical conditions of the emitting gas, also provide information about its history and heating mechanisms.

Stellar Evolutionary Effects on the Abundance of PAHS and SN-Condensed Dust in Galaxies

NASA Technical Reports Server (NTRS)

Dwek, Eli

2007-01-01

Spectral aid photometric observations of nearby galaxies show a correlation between the strength of their mid-IR aromatic features and their metal abundance, and a deficiency of these features in low-metallicity galaxies. The aromatic features are most commonly attributed to emission from PAH molecules. In this paper, we suggest that the observed correlation represents a trend of PAH abundance with galactic age, reflecting the delayed injection of PAHs and carbon dust into the ISM, by AGB stars in their final, post-AGB phase of their evolution. These AGB stars are the primary sources of PAHs and carbon dust in galaxies, and recycle their ejecta back to the interstellar medium only after a few hundred million years of evolution on the main sequence. In contrast, more massive stars that explode as Type II supernovae inject their metals and dust almost instantaneously after their formation. After determining the PAH abundances in 35 nearby galaxies, we use a chemical evolution model to show that the delayed injection of carbon dust by AGB stars provides a natural explanation to the dependence of the PAH content, in galaxies with metallicity. We also show that larger dust particles giving rise to the far-IR emission follow a distinct evolutionary trend closely related to the injection of dust by massive stars into the ISM.

Stars and their Environments at High-Resolution with IGRINS

NASA Astrophysics Data System (ADS)

Mace, Gregory; Jaffe, Daniel; Kaplan, Kyle; Kidder, Benjamin; Oh, Heeyoung; Sneden, Christopher; Afşar, Melike

2016-06-01

TheImmersion Grating Infrared Spectrometer (IGRINS) is a revolutionary instrument that exploits broad spectral coverage at high-resolution in the near-infrared. There are no moving parts in IGRINS and its high-throughput white-pupil design maximizes sensitivity. IGRINS on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory is nearly as sensitive as CRIRES at the 8 meter Very Large Telescope. However, IGRINS at R=45,000 has more than 30 times the spectral grasp of CRIRES. The use of an immersion grating facilitates a compact cryostat while providing simultaneous H and K band observations with complete wavelength coverage from 1.45 - 2.45 microns. Here we discuss details of instrument performance and summarize the application of IGRINS to stellar characterization, star formation in regions like Taurus and Ophiuchus, the interstellar medium, and photodissociation regions. IGRINS has the largest spectral grasp of any high-resolution, near-infrared spectrograph, allowing us to study star formation and evolution in unprecedented detail. With its fixed format and high sensitivity, IGRINS is a great survey instrument for star clusters, high signal-to-noise (SNR>300) studies of field stars, and for mapping the interstellar medium. As a prototype for GMTNIRS on the Giant Magellan Telescope, IGRINS represents the future of high-resolution spectroscopy. In the future IGRINS will be deployed to numerous facilities and will remain a versatile instrument for the community while producing a rich archive of uniform spectra.

SYMMETRY OF THE IBEX RIBBON OF ENHANCED ENERGETIC NEUTRAL ATOM (ENA) FLUX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Funsten, H. O.; Cai, D. M.; Higdon, D. M.

2015-01-20

The circular ribbon of enhanced energetic neutral atom (ENA) emission observed by the Interstellar Boundary Explorer (IBEX) mission remains a critical signature for understanding the interaction between the heliosphere and the interstellar medium. We study the symmetry of the ribbon flux and find strong, spectrally dependent reflection symmetry throughout the energy range 0.7-4.3 keV. The distribution of ENA flux around the ribbon is predominantly unimodal at 0.7 and 1.1 keV, distinctly bimodal at 2.7 and 4.3 keV, and a mixture of both at 1.7 keV. The bimodal flux distribution consists of partially opposing bilateral flux lobes, located at highest and lowest heliographic latitude extentsmore » of the ribbon. The vector between the ribbon center and heliospheric nose (which defines the so-called BV plane) appears to play an organizing role in the spectral dependence of the symmetry axis locations as well as asymmetric contributions to the ribbon flux. The symmetry planes at 2.7 and 4.3 keV, derived by projecting the symmetry axes to a great circle in the sky, are equivalent to tilting the heliographic equatorial plane to the ribbon center, suggesting a global heliospheric ordering. The presence and energy dependence of symmetric unilateral and bilateral flux distributions suggest strong spectral filtration from processes encountered by an ion along its journey from the source plasma to its eventual detection at IBEX.« less

Perspective: C60+ and laboratory spectroscopy related to diffuse interstellar bands

NASA Astrophysics Data System (ADS)

Campbell, E. K.; Maier, J. P.

2017-04-01

In the last 30 years, our research has focused on laboratory measurements of the electronic spectra of organic radicals and ions. Many of the species investigated were selected based on their potential astrophysical relevance, particularly in connection with the identification of appealing candidate molecules for the diffuse interstellar absorptions. Notably, carbon chains and derivatives containing hydrogen and nitrogen atoms in their neutral and ionic forms were studied. These data could be obtained after developing appropriate techniques to record spectra at low temperatures relevant to the interstellar medium. The measurement of gas phase laboratory spectra has enabled direct comparisons with astronomical data to be made and though many species were found to have electronic transitions in the visible where the majority of diffuse bands are observed, none of the absorptions matched the prominent interstellar features. In 2015, however, the first carrier molecule was identified: C60 + . This was achieved after the measurement of the electronic spectrum of C60 + -He at 6K in a radiofrequency ion trap.

Characterization of Type Ia Supernova Light Curves Using Principal Component Analysis of Sparse Functional Data

NASA Astrophysics Data System (ADS)

He, Shiyuan; Wang, Lifan; Huang, Jianhua Z.

2018-04-01

With growing data from ongoing and future supernova surveys, it is possible to empirically quantify the shapes of SNIa light curves in more detail, and to quantitatively relate the shape parameters with the intrinsic properties of SNIa. Building such relationships is critical in controlling systematic errors associated with supernova cosmology. Based on a collection of well-observed SNIa samples accumulated in the past years, we construct an empirical SNIa light curve model using a statistical method called the functional principal component analysis (FPCA) for sparse and irregularly sampled functional data. Using this method, the entire light curve of an SNIa is represented by a linear combination of principal component functions, and the SNIa is represented by a few numbers called “principal component scores.” These scores are used to establish relations between light curve shapes and physical quantities such as intrinsic color, interstellar dust reddening, spectral line strength, and spectral classes. These relations allow for descriptions of some critical physical quantities based purely on light curve shape parameters. Our study shows that some important spectral feature information is being encoded in the broad band light curves; for instance, we find that the light curve shapes are correlated with the velocity and velocity gradient of the Si II λ6355 line. This is important for supernova surveys (e.g., LSST and WFIRST). Moreover, the FPCA light curve model is used to construct the entire light curve shape, which in turn is used in a functional linear form to adjust intrinsic luminosity when fitting distance models.

THE MUSCLES TREASURY SURVEY. II. INTRINSIC LY α AND EXTREME ULTRAVIOLET SPECTRA OF K AND M DWARFS WITH EXOPLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Youngblood, Allison; France, Kevin; Loyd, R. O. Parke

2016-06-20

The ultraviolet (UV) spectral energy distributions (SEDs) of low-mass (K- and M-type) stars play a critical role in the heating and chemistry of exoplanet atmospheres, but are not observationally well-constrained. Direct observations of the intrinsic flux of the Ly α line (the dominant source of UV photons from low-mass stars) are challenging, as interstellar H i absorbs the entire line core for even the closest stars. To address the existing gap in empirical constraints on the UV flux of K and M dwarfs, the MUSCLES Hubble Space Telescope Treasury Survey has obtained UV observations of 11 nearby M and Kmore » dwarfs hosting exoplanets. This paper presents the Ly α and extreme-UV spectral reconstructions for the MUSCLES targets. Most targets are optically inactive, but all exhibit significant UV activity. We use a Markov Chain Monte Carlo technique to correct the observed Ly α profiles for interstellar absorption, and we employ empirical relations to compute the extreme-UV SED from the intrinsic Ly α flux in ∼100 Å bins from 100–1170 Å. The reconstructed Ly α profiles have 300 km s{sup −1} broad cores, while >1% of the total intrinsic Ly α flux is measured in extended wings between 300 and 1200 km s{sup −1}. The Ly α surface flux positively correlates with the Mg ii surface flux and negatively correlates with the stellar rotation period. Stars with larger Ly α surface flux also tend to have larger surface flux in ions formed at higher temperatures, but these correlations remain statistically insignificant in our sample of 11 stars. We also present H i column density measurements for 10 new sightlines through the local interstellar medium.« less

Magnetic Fields in the Galaxy

NASA Astrophysics Data System (ADS)

Mayo, Elizabeth A.

2009-01-01

Interstellar magnetic fields are believed to play a crucial role in the star-formation process, therefore a comprehensive study of magnetic fields is necessary in understanding the origins of stars. These projects use observational data obtained from the Very Large Array (VLA) in Socorro, NM. The data reveal interstellar magnetic field strengths via the Zeeman effect in radio frequency spectral lines. This information provides an estimate of the magnetic energy in star-forming interstellar clouds in the Galaxy, and comparisons can be made with these energies and the energies of self-gravitation and internal motions. From these comparisons, a better understanding of the role of magnetic fields in the origins of stars will emerge. NGC 6334 A is a compact HII region at the center of what is believed to be a large, rotating molecular torus (Kramer et al. (1997)). This is a continuing study based on initial measurements of the HI and OH Zeeman effect (Sarma et al. (2000)). The current study includes OH observations performed by the VLA at a higher spatial resolution than previously published data, and allows for a better analysis of the spatial variations of the magnetic field. A new model of the region is also developed based on OH opacity studies, dust continuum maps, radio spectral lines, and infrared (IR) maps. The VLA has been used to study the Zeeman effect in the 21cm HI line seen in absorption against radio sources in the Cygnus-X region. These sources are mostly galactic nebulae or HII regions, and are bright and compact in this region of the spectrum. HI absorption lines are strong against these regions and the VLA is capable of detecting the weak Zeeman effect within them. Support for this work was provided by the NSF PAARE program to South Carolina State University under award AST-0750814.

Infrared Photometric Properties of 709 Candidate Stellar Bowshock Nebulae

NASA Astrophysics Data System (ADS)

Kobulnicky, Henry A.; Schurhammer, Danielle P.; Baldwin, Daniel J.; Chick, William T.; Dixon, Don M.; Lee, Daniel; Povich, Matthew S.

2017-11-01

Arcuate infrared nebulae are ubiquitous throughout the Galactic Plane and are candidates for partial shells, bubbles, or bowshocks produced by massive runaway stars. We tabulate infrared photometry for 709 such objects using images from the Spitzer Space Telescope, the Wide-field Infrared Explorer, and the Herschel Space Observatory (HSO). Of the 709 objects identified at 24 or 22 μm, 422 are detected at the HSO 70 μm bandpass. Of these, only 39 are detected at HSO 160 μm. The 70 μm peak surface brightnesses are 0.5-2.5 Jy arcmin-2. Color temperatures calculated from the 24 to 70 μm ratios range from 80 to 400 K. Color temperatures from 70 to 160 μm ratios are systematically lower, 40-200 K. Both of these temperature are, on average, 75% higher than the nominal temperatures derived by assuming that dust is in steady-state radiative equilibrium. This may be evidence of stellar wind bowshocks sweeping up and heating—possibly fragmenting but not destroying—interstellar dust. Infrared luminosity correlates with standoff distance, R 0, as predicted by published hydrodynamical models. Infrared spectral energy distributions are consistent with interstellar dust exposed to either single radiant energy density, U={10}3{--}{10}5 (in more than half of the objects) or a range of radiant energy densities U min = 25 to U max = 103-105 times the mean interstellar value for the remainder. Hence, the central OB stars dominate the energetics, making these enticing laboratories for testing dust models in constrained radiation environments. The spectral energy densities are consistent with polycyclic aromatic hydrocarbon fractions {q}{PAH}≲ 1 % in most objects.

Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives

NASA Technical Reports Server (NTRS)

Du, Ping

1993-01-01

As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.

Interstellar Ice and Dust: The Feedstock of the Solar System

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Morrison, David (Technical Monitor)

1994-01-01

Studying the chemical and isotopic composition of interstellar ice and dust provides insight into the composition and chemical history of the solid bodies in the solar nebula and the nature of the material subsequently brought into the inner part of the solar system by comets and meteorites. It is now possible to probe the composition of these microscopic interstellar particles (some hundreds of light years away), thanks to substantial progress in two areas: astronomical spectroscopic techniques in the middle-infrared, the spectral region most diagnostic of composition; and laboratory simulations which realistically reproduce the critical conditions in various interstellar environments. High quality infrared spectra of many different astronomical sources, some associated with dark molecular clouds, and others in the diffuse interstellar medium (DISM) are now available. What comparisons of these spectra with laboratory spectra tell us about the complex organic components of these materials is the subject of this talk. Most interstellar material is concentrated in large molecular clouds where simple molecules are formed by gas phase and dust grain surface reactions. Gaseous species (except H2) striking the cold (10K) dust will stick, forming an icy grain mantle. This accretion, coupled with energetic particle bombardment and UV photolysis, will produce a complex chemical mixture containing volatile, non-volatile, and isotopically fractionated species. One can compare spectra of the diffuse and dense interstellar medium with the spectra of analogs produced in the laboratory under conditions which mimic those in these different environments. In this way one can determine the composition and abundances of the major constituents present and place general constraints on the types and relative abundances of organics coating the grains. Ices in dense clouds contain H2O, CH3OH, CO, perhaps some NH3 and H2CO, as well as nitriles and ketones or esters. There is some evidence that the later, more complex species, are also present on the grains in the DISM. The evidence for these materials, in addition to carbon rich materials such as amorphous carbon, microdiamonds, and polycyclic aromatic hydrocarbons will be reviewed and the possible connection with meteoritic organics will be discussed.

The Origins of Polycyclic Aromatic Hydrocarbons: Are They Everywhere?

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Morrison, David (Technical Monitor)

1994-01-01

During the past 15 years considerable progress in observational techniques has been achieved in the middle-infrared region (5000-500 per centimeter, 2-20 micron), the region where most diagnostic molecular vibrations occur. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds and others at their edges, are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas and solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. The two lectures will focus on the evidence that polycyclic aromatic hydrocarbons (PAHs) are an important, ubiquitous and abundant interstellar species. PAHs are. extremely stable species which can range in size from a few angstroms across to several hundred angstroms (PAHs are also the building blocks of amorphous carbon particles). This identification rests on the suggestive agreement between the laboratory spectra of PAHs with a set of IR emission bands which emanate from many different sources where ultraviolet starlight impinges on a "dusty" region. The picture is that individual PAHs are first pumped into highly vibrationally excited states and relax by fluorescence at their fundamental vibrational frequencies. That PAHs are a ubiquitous interstellar component has serious ramifications in other spectral regions as well, including the strong extinction in the ultraviolet, and the classic visible diffuse interstellar bands discovered more than 50 years ago (but unexplained to this day) The first part of the course will focus on the interpretation of astronomical spectra. The second lecture will start by showing how recent laboratory data on PAHs taken under realistic interstellar conditions has con borated the PAH hypothesis and led to great insight into the conditions in the PAH containing regions. This lecture will end by reviewing the ever-increasing evidence for interstellar PAHs in meteorites and interplanetary dust particles. This in conjunction with the recent suggestion that PAHs are abundant in Jupiter's atmosphere will make the point that "PAHs are Everywhere".

IBEX Mission update: New discoveries and a new orbit

NASA Astrophysics Data System (ADS)

McComas, D. J.; IBEX Science Team

2011-12-01

The Interstellar Boundary Explorer (IBEX) mission has been remotely observing the global interaction of our heliosphere with the local interstellar medium for over two and a half years. Initially, IBEX generated the first all-sky maps of Energetic Neutral Atoms (ENAs) emanating in from the boundaries of our heliosphere over the energy range from ~0.1-6 keV. Using these observations, the IBEX team discovered a smoothly varying, globally distributed ENA flux overlaid by a narrow "ribbon" of significantly enhanced ENA emissions. Since the initial publications of these results in a special issue of Science magazine (November 2009), IBEX has completed four more energy-resolved sets of sky maps and discovered small but important time variations in the interaction, separated the ribbon from globally distributed ENA fluxes, measured the energy spectral shape and inferred ion source temperatures, and carried out many other observational and theoretical studies. In addition, IBEX made the first observations of ENAs produced by backscatter and neutralization of the solar wind from the lunar regolith and provided the first energy and angle resolved ENA images of the subsolar magnetosheath and magnetospheric cusps and plasma sheet. Most recently, direct IBEX observations of Interstellar Neutral (ISN) He show that the speed and direction (the motion of the heliosphere with respect to the interstellar medium) is different than that thought from prior Ulysses observations. These observations also show evidence for a previously unknown and unanticipated secondary population of Helium. In addition, IBEX is providing the first direct quantitative measurements of the ISN H parameters and the first direct measurements of interstellar Ne and the interstellar Neon/Oxygen abundance ratio; this ratio is significantly different than the solar abundance ratio. IBEX was recently maneuvered into a unique, long-term stable orbit and has several decades worth of fuel for routine operations. Thus, IBEX will likely continue to provide revolutionary observations of numerous heliospheric, magnetospheric, and planetary phenomena for many years to come!

IBEX-Lo Observations of Secondary Interstellar Helium and Oxygen Distributions

NASA Astrophysics Data System (ADS)

Park, J.; Kucharek, H.; Moebius, E.; Kubiak, M. A.; Bzowski, M.; Galli, A.; McComas, D. J.

2015-12-01

Observations of the Interstellar Boundary EXplorer (IBEX) show, among other features, the pristine interstellar neutral gas flow and additional populations associated with neutral helium and oxygen. Kubiak et al. (2014, ApJS, 213, 29) discovered the "Warm Breeze", or additional He component, which is slower and warmer than the primary interstellar He population and its flow direction differs by about 19° from the interstellar neutral (ISN) flow. Park et al. (2015, ApJS, In Press) studied the combined count rate maps of heavy neutral atoms with three statistical analysis methods and found an extended tail of the ISN O flow, centered around 190° in ecliptic longitude and +15° in ecliptic latitude, or approximately 38° from the ISN O and Ne flow peak. The most likely sources for the Warm Breeze and the extended O tail may be secondary populations of interstellar He and O, created by charge exchange between ISN atoms and interstellar ions in the outer heliosheath. The charge exchange between interstellar He atoms and He+ ions is the most important reaction to generate the secondary neutral He in the outer heliosheath, with a reaction rate of 1.7×10-10 s-1 and a mean free path of ~950 AU. For O+, the charge exchange with interstellar H atoms with a rate ~1.0×10-9 s-1 and a mean free path of ~100 AU is most important. Because the differences in the reaction rates and atomic masses for He and O result in different velocity distributions in the outer heliosheath, the directional distributions of these populations at Earth orbit are not identical. In this study, we use the IBEX flux maps of the observed helium and oxygen atoms to compare their directional distributions. These observed distributions may provide constraints and information to improve our current understanding of the interactions in the outer heliosheath.

Abundances and Reactions of Sulfur Contianing Molecules in Interstellar Ices- Spectroscopic and Radiation-Chemical Investigations

NASA Astrophysics Data System (ADS)

Hudson, Reggie

Infrared (IR) telescopes, such as ISO, Spitzer, KAO, Keck, VLT, and IRTF, have revealed a rich variety of molecules trapped in interstellar ices. However, quantifying the abundances of these molecules has been difficult because reference IR data, such as band strengths and optical constants, often are poorly known. This scarcity of data has severe implications for the study of sulfur-containing molecules, such as OCS and SO2, since accurate molecular abundances are needed to address the missing-sulfur problem in interstellar space. The expected abundances of sulfur-containing species in dense molecular clouds are much higher than reported from telescopic observations, although the latter are based on laboratory data of questionable relevance, such as with liquids at room temperature compared to the 10 K ices of some interstellar regions. Exacerbating the problem is that few sulfur-containing molecules of any type have been examined in the laboratory under the necessary, relevant icy conditions. We propose to address and correct the problems associated with abundance determinations of interstellar sulfur-containing ices. We will combine several recent successful efforts from our laboratory and measure near- and mid-IR spectral intensities for ices containing SO2, OCS, H2S, CS2, CH3SH, and C2H5SH both in the presence and absence of H2O-ice. This work will be done at multiple temperatures and ice phases to generate reference IR spectra and band strengths, accompanied by refractive indices, and optical constants. Moreover, we will study the radiation chemistry of these molecules to determine their radiolytic half-lives (stabilities) and uncover product molecules that can become candidates for future searches and perhaps help better understand the missingsulfur problem. This proposal is a convergence of three lines of work in our laboratory: recent successes in deriving IR optical constants of interstellar molecular ices (Hudson et al. 2014a, 2014b), measurements of radiolytic stabilities of interstellar and planetary molecules (Gerakines & Hudson 2013, 2015), and our long history of working with sulfur-containing molecules and ions (Moore et al. 1988; Loeffler & Hudson 2010, 2012). Our collaborators were selected specifically for their interest in this proposal's focus and for their expertise in interstellar chemistry.

Copernicus observations of neutral hydrogen and deuterium in the direction of HR 1099

NASA Technical Reports Server (NTRS)

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

1979-01-01

High-resolution Copernicus U1 scans were obtained of the bright RS CVn binary HR 1099 (d = 33 pc, galactic longitude = 185 deg, galactic latitude = -41 deg) in October 1977. Strong emission at L-alpha was detected. The interstellar L-alpha absorption features of H I and D I were also observed. Analyses of these interstellar lines are reported in this paper. The average density of neutral H in the direction of this system is found to be 0.006-0.012 per cu cm, which, because the local density is higher, requires a marked inhomogeneity along this line of sight. This result, when combined with other recent studies of the local interstellar medium, suggests the sun is located within a moderate-density H I region.

Icarus Institute for Interstellar Sciences (IIS)

NASA Astrophysics Data System (ADS)

Cress, B.

2012-09-01

In this paper, a vision for a proposed interstellar research center, to be developed in the United States, will be presented. The major focus will be on an innovative approach to the planning and achieving a new sustainable world class facility devoted to the technologies and various science missions of multi-disciplined teams reaching for the stars. The project will provide the personnel, feature sets, facilities and equipment needed to initiate and support an aggressive program of advanced interstellar vehicle and propulsion design and implementation. Also shared will be personal insights and economic considerations gained during prior planning for a private research institute in Nevada, home to more than 300 international scientists. The views expressed in this discussion paper are the personal views of the author and not necessarily representing the entire Icarus team.

More on the lambda 2800 A 'interstellar extinction' feature

NASA Astrophysics Data System (ADS)

McLachlan, A.; Nandy, K.

1985-02-01

In a response made to a recent letter by Karim et al. (1984), it is shown that the examples of interstellar absorption at 2800 A that they attribute to proteinaceous material can all be attributed to overexposure of IUE detectors. It is pointed out that stars in the Large Magellanic Cloud show pronounced absorption at 2800 A which cannot be due to interstellar protein since there is no associated absorption at 2200 A; this lack of absorption cannot be due to presence of graphite, whose absorption is weak in the Cloud. The claim by Karim et al. that the spectra of eight stars show 2800 A absorption and that these spectra are saturation-free is considered, and it is shown that data processing problems at IUE ground stations make these spectra unreliable.

Signs of Asymmetry in Exploding Stars

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-03-01

Supernova explosions enrich the interstellar medium and can even briefly outshine their host galaxies. However, the mechanism behind these massive explosions still isnt fully understood. Could probing the asymmetry of supernova remnants help us better understand what drives these explosions?Hubble image of the remnant of supernova 1987A, one of the first remnants discovered to be asymmetrical. [ESA/Hubble, NASA]Stellar Send-OffsHigh-mass stars end their lives spectacularly. Each supernova explosion churns the interstellar medium and unleashes high-energy radiation and swarms of neutrinos. Supernovae also suffuse the surrounding interstellar medium with heavy elements that are incorporated into later generations of stars and the planets that form around them.The bubbles of expanding gas these explosions leave behind often appear roughly spherical, but mounting evidence suggests that many supernova remnants are asymmetrical. While asymmetry in supernova remnants can arise when the expanding material plows into the non-uniform interstellar medium, it can also be an intrinsic feature of the explosion itself.Simulation results clockwise from top left: Mass density, calcium mass fraction, oxygen mass fraction, nickel-56 mass fraction. Click to enlarge. [Adapted from Wollaeger et al. 2017]Coding ExplosionsThe presence or absence of asymmetry in a supernova remnant can hold clues as to what drove the explosion. But how can we best observe asymmetry in a supernova remnant? Modeling lets us explore different observational approaches.A team of scientists led by Ryan T. Wollaeger (Los Alamos National Laboratory) used radiative transfer and radiative hydrodynamics simulations to model the explosion of a core-collapse supernova. Wollaeger and collaborators introduced asymmetry into the explosion by creating a single-lobed, fast-moving outflow along one axis.Their simulations showed that while some chemical elements lingered near the origin of the explosion or were distributed evenly throughout the remnant, calcium was isolated to the asymmetrical region, hinting that spectral lines of calcium may be good tracersof asymmetry.Bolometric (top) and gamma-ray (bottom) synthetic light curves for the authors model for a range of simulated viewing angles. [Adapted from Wollaeger et al. 2017]Synthesizing SpectraWollaeger and collaborators then generated synthetic light curves and spectra from their models to determine which spectral features or characteristics indicated the presence of the asymmetric outflow lobe. They found that when an asymmetric outflow lobe is present, the peak luminosity of the explosion depends on the angle at which you view it; the highest luminosity occurs when the lobe is viewed from the side, while the lowest luminosity nearly40%dimmer is seen when the explosion is viewed down the barrel of the lobe. The dense outflow shades the central radioactive source from view, lowering the luminosity.This effect also plays out in the gamma-ray light curves; when viewed down the barrel, the shading of the central source by ahigh-density lobe slows the rise of the gamma-ray luminosity and changes the shape of the light curve compared to views from other vantage points.Another promising avenue for exploring asymmetry is a near-infrared band encompassing an emission line of singly-ionized calcium near 815 nm. Since calcium is confined within the outflow lobe in the simulation, its emission lines are blueshifted when the lobe points toward the observer.The authors point out that there is much more to be done in their models, such as including the effects of shock heating of circumstellar material, which can contribute strongly to the light curve, but these simulations bring us a step closer to understanding the nature of asymmetrical supernova remnants and the explosions that create them.CitationRyan T. Wollaeger et al 2017ApJ845168. doi:10.3847/1538-4357/aa82bd

Potential Line Structure Variability in DIB Features Observed in Pathfinder tres Survey

NASA Astrophysics Data System (ADS)

Law, Charles; Milisavljevic, Dan; Crabtree, Kyle N.; Johansen, Sommer Lynn

2017-06-01

The Diffuse Interstellar Bands (DIBs) are hundreds of spectral lines observed in sightlines towards many stars in the optical and near-infrared. Although most of these transitions remain unassigned, four of them have recently been assigned to C_{60}^{+} and C_{70}^{+}. In earlier observations of the visible spectrum of the extragalactic supernova SN 2012ap, we observed changes in the equivalent widths of DIBs on the timescale of its light curve, which indicated that some DIB carriers might exist closer to massive stars then previously believed. Motivated by these findings, we undertook a pathfinder survey of 17 massive stars with the Tillinghast Reflector Echelle Spectrograph at Fred L. Whipple Observatory in search of temporal variability in DIBs. In 3 of the 17 stars, we found possible evidence for variation in line substructure of DIBs λ5797 and λ6614. In this talk, we will discuss our efforts to model λ5797 toward MT-59 using contour simulations based on previously published spectral models from higher resolution observations. Although the SNR of this spectrum was only 5-15, our preliminary results suggest that the variations in molecular spectra over time might arise from changes in carrier temperature. These early results demonstrate the need for higher SNR spectra taken at multiple epochs to further explore potential temporal variability. If successful, time-variation could provide additional evidence to assist in identifying DIB carriers.

SCINTILLATION ARCS IN LOW-FREQUENCY OBSERVATIONS OF THE TIMING-ARRAY MILLISECOND PULSAR PSR J0437–4715

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, N. D. R.; Ord, S. M.; Tremblay, S. E.

2016-02-10

Low-frequency observations of pulsars provide a powerful means for probing the microstructure in the turbulent interstellar medium (ISM). Here we report on high-resolution dynamic spectral analysis of our observations of the timing-array millisecond pulsar PSR J0437–4715 with the Murchison Widefield Array (MWA), enabled by our recently commissioned tied-array beam processing pipeline for voltage data recorded from the high time resolution mode of the MWA. A secondary spectral analysis reveals faint parabolic arcs akin to those seen in high-frequency observations of pulsars with the Green Bank and Arecibo telescopes. Data from Parkes observations at a higher frequency of 732 MHz revealmore » a similar parabolic feature with a curvature that scales approximately as the square of the observing wavelength (λ{sup 2}) to the MWA's frequency of 192 MHz. Our analysis suggests that scattering toward PSR J0437–4715 predominantly arises from a compact region about 115 pc from the Earth, which matches well with the expected location of the edge of the Local Bubble that envelopes the local Solar neighborhood. As well as demonstrating new and improved pulsar science capabilities of the MWA, our analysis underscores the potential of low-frequency pulsar observations for gaining valuable insights into the local ISM and for characterizing the ISM toward timing-array pulsars.« less

Photodissociation Regions in the Interstellar Medium of Galaxies

NASA Technical Reports Server (NTRS)

Hollenbach, David J.; Tielens, A. G. G. M.; DeVincenzi, Donald L. (Technical Monitor)

1999-01-01

The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eV less than h(nu) less than 13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed Photo-Dissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C+, and O; rovibrational lines of H2, rotational lines of CO; broad middle features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H2 and C+ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 microns with the COJ = 1-0 emission, the COJ = 1-0 luminosity with the interstellar molecular mass, and the [CII] 158 microns plus [OI] 63 microns luminosity with the IR continuum luminosity. On a more global scale, MR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds.

Hubble Space Telescope observations of cool white dwarf stars: Detection of new species of heavy elements

NASA Technical Reports Server (NTRS)

Shipman, Harry; Barnhill, Maurice; Provencal, Judi; Roby, Scott; Bues, Irmela; Cordova, France; Hammond, Gordon; Hintzen, Paul; Koester, Detlev; Liebert, James

1995-01-01

Observations of cool white dwarf stars with the Hubble Space Telescope (HST) has uncovered a number of spectral features from previouslly unobserved species. In this paper we present the data on four cool white dwarfs. We present identifications, equivalent width measurements, and brief summaries of the significance of our findings. The four stars observed are GD 40 (DBZ3, G 74-7 (DAZ), L 745-46A (DZ), and LDS 749B (DBA). Many additional species of heavey elements were detected in GD 40 and G 74-7. In L 745-46A, while the detections are limited to Fe 1, Fe II, and Mg II, the quality of the Mg II h and K line profiles should permit a test of the line broadening theories, which are so crucial to abundance determinations. The clear detection of Mg II h and k in LDS 749 B should, once an abundance determination is made, provide a clear test of the hypothesis that the DBA stars are the result of accretion from the interstellar medium. This star contains no other clear features other than a tantalizing hint of C II 1335 with a P Cygni profile, and some expected He 1 lines.

Unveiling Vela: time variability of interstellar lines in the direction of the Vela supernova remnant - II. Na D and Ca II

NASA Astrophysics Data System (ADS)

Kameswara Rao, N.; Lambert, David L.; Reddy, Arumalla B. S.; Gupta, Ranjan; Muneer, S.; Singh, Harinder P.

2017-05-01

In a survey conducted between 2011 and 2012 of interstellar Na I D line profiles in the direction of the Vela supernova remnant (SNR), a few lines of sight showed dramatic changes in low-velocity absorption components with respect to profiles from 1993 to 1994 reported by Cha & Sembach. Three stars - HD 63578, HD 68217 and HD 76161 - showed large decrease in strength over the 1993-2012 interval. HD 68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is associated with γ2 Velorum wind bubble. Here, we present high spectral resolution observations of Ca II K lines obtained with the Southern African Large Telescope towards these three stars along with simultaneous observations of Na I D lines. These new spectra confirm that the Na D interstellar absorption weakened drastically between 1993-1994 and 2011-2012 but show for the first time that the Ca II K line is unchanged between 1993-1994 and 2015. This remarkable contrast between the behaviour of Na D and Ca II K absorption lines is a puzzle concerning gas presumably affected by the outflow from the SNR and the wind from γ2 Velorum.

The influence of atomic alignment on absorption and emission spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Heshou; Yan, Huirong; Richter, Philipp

2018-06-01

Spectroscopic observations play essential roles in astrophysics. They are crucial for determining physical parameters in the universe, providing information about the chemistry of various astronomical environments. The proper execution of the spectroscopic analysis requires accounting for all the physical effects that are compatible to the signal-to-noise ratio. We find in this paper the influence on spectroscopy from the atomic/ground state alignment owing to anisotropic radiation and modulated by interstellar magnetic field, has significant impact on the study of interstellar gas. In different observational scenarios, we comprehensively demonstrate how atomic alignment influences the spectral analysis and provide the expressions for correcting the effect. The variations are even more pronounced for multiplets and line ratios. We show the variation of the deduced physical parameters caused by the atomic alignment effect, including alpha-to-iron ratio ([X/Fe]) and ionisation fraction. Synthetic observations are performed to illustrate the visibility of such effect with current facilities. A study of PDRs in ρ Ophiuchi cloud is presented to demonstrate how to account for atomic alignment in practice. Our work has shown that due to its potential impact, atomic alignment has to be included in an accurate spectroscopic analysis of the interstellar gas with current observational capability.

UV observations of local interstellar medium.

NASA Astrophysics Data System (ADS)

Kurt, V.; Mironova, E.; Fadeev, E.

2008-12-01

The methods of the interstellar matter study are described. The brief information of space missions aimed at observations in the unreachable for ground based telescopes UV spectral range (IUE, As- tron, HST and GALEX.) is presented. The history of discovery of H and He atoms entering the Solar System from the local interstellar medium (LISM) is given in brief. The results of observations performed by the group from Stern- berg Astronomical Institute (SAI MSU) and Space Research Institute (IKI RAS) performed with the help of the missions Prognoz-5, Prognoz-6 and the stations Zond-1, Venera and Mars and aimed at estimation of all basic LISM parameters (the velocity of the Sun in relation to LISM, directions of movement, densities of H and He atoms, LISM temperature) are presented. We also describe the present-day investigations of LISM performed with SOHO and ULYSSES mis- sions including the direct registration of He atoms entering the Solar System. The problem of interaction between the incoming flow of the ISM atoms ("in- terstellar wind") and the area of two shocks at the heliopause border (100-200 AU) is discussed. The LISM parameters obtained using the available data are presented in two tables.

The Properties of Single Interstellar Clouds: Modified Cycle 1 Observations

NASA Astrophysics Data System (ADS)

Hobbs, Lewis

1990-12-01

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

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

NASA Technical Reports Server (NTRS)

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

2005-01-01

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

High-power terahertz lasers with excellent beam quality for local oscillator sources

NASA Astrophysics Data System (ADS)

Williams, Benjamin

Many molecular species that compose the interstellar medium have strong spectral features in the 2-5 THz range, and heterodyne spectroscopy is required to obtain ~km/s velocity resolution to resolve their complicated lineshapes and disentangle them from the background. Understanding the kinetics and energetics within the gas clouds of the interstellar medium is critical to understanding star formation processes and validating theories of galactic evolution. Herschel Observatory's heterodyne HIFI instrument provided several years of high-spectral-resolution measurements of the interstellar medium, although only up to 1.9 THz. The next frontier for heterodyne spectroscopy is the 2-6 THz region. However, development of heterodyne receivers above 2 THz has been severely hindered by a lack of convenient coherent sources of sufficient power to serve as local oscillators (LOs). The recently developed quantum-cascade (QC) lasers are emerging as candidates for LOs in the 1.5-5 THz range. The current generation of single-mode THz QC-lasers can provide a few milliwatts of power in a directive beam, and will be sufficient to pump single pixels and small-format heterodyne arrays (~10 elements). This proposal looks beyond the state-of-the-art, to the development of large format heterodyne arrays which contain on the order of 100-1000 elements. LO powers on the order of 10-100 mW delivered in a high-quality Gaussian beam will be needed to pump the mixer array - not only because of the microwatt mixer power requirement, but to account for large anticipated losses in LO coupling and distribution. Large format heterodyne array instruments are attractive for a dramatic speedup of mapping of the interstellar medium, particularly on airborne platforms such as the Stratospheric Observatory for Infrared Astronomy (SOFIA), and on long duration balloon platforms such as the Stratospheric Terahertz Observatory (STO), where observation time is limited. The research goal of this proposal is to demonstrate a new concept for terahertz quantum-cascade (QC) lasers designed to deliver scalable continuous-wave output power in the range of 10 to 100 mW or more in a near-diffraction limited output beam: a chip-scale THz quantum-cascade vertical-external-cavity-surface-emitting-laser (QC-VECSEL). We focus here on the development of a chip-scale version of size < 1 cm3 that oscillates in a single mode and can readily fit on a cold stage. The enabling technology for this proposed laser is an active metasurface reflector, which is comprised of a sparse array of antenna-coupled THz QC-laser sub-cavities. The metasurface reflector is part of the laser cavity such that multiple THz QC-laser sub-cavities are locked to a high-quality-factor cavity mode, which allows for scalable power combining with a favorable geometry for thermal dissipation and continuous-wave operation. We propose an integrated design, modeling, and experimental approach to design, fabricate, and characterize amplifying reflective QC metasurfaces and QC-VECSEL lasers. Demonstration laser devices will be developed at 2.7 THz and 4.7 THz, near the important frequencies for HD at 2.675 THz (for measurements of the hydrogen deuterium ratio and probing past star formation), and OI at 4.745 THz (a major coolant for photo-dissociation regions in giant molecular clouds). High resolution frequency measurements will be performed on a demonstration device at 2.7 THz will using downconversion with a Schottky diode sub-harmonic mixer to characterize the spectral purity, linewidth, and fine frequency tuning of this new type of QC-laser. This proposed laser is supporting technology for next-generation terahertz detectors.

Parameterized spectral distributions for meson production in proton-proton collisions

NASA Technical Reports Server (NTRS)

Schneider, John P.; Norbury, John W.; Cucinotta, Francis A.

1995-01-01

Accurate semiempirical parameterizations of the energy-differential cross sections for charged pion and kaon production from proton-proton collisions are presented at energies relevant to cosmic rays. The parameterizations, which depend on both the outgoing meson parallel momentum and the incident proton kinetic energy, are able to be reduced to very simple analytical formulas suitable for cosmic ray transport through spacecraft walls, interstellar space, the atmosphere, and meteorites.

Millimeter and Submillimeter Studies of O(^1D) Insertion Reactions to Form Molecules of Astrophysical Interest

NASA Astrophysics Data System (ADS)

Hays, Brian; Wehres, Nadine; Deprince, Bridget Alligood; Roy, Althea A. M.; Laas, Jacob; Widicus Weaver, Susanna L.

2015-06-01

While both the number of detected interstellar molecules and their chemical complexity continue to increase, understanding of the processes leading to their formation is lacking. Our research group combines laboratory spectroscopy, observational astronomy, and astrochemical modeling for an interdisciplinary examination of the chemistry of star and planet formation. This talk will focus on our laboratory studies of O(^1D) insertion reactions with organic molecules to produce molecules of astrophysical interest. By employing these reactions in a supersonic expansion, we are able to produce interstellar organic reaction intermediates that are unstable under terrestrial conditions; we then probe the products using millimeter and submillimeter spectroscopy. We benchmarked this setup using the well-studied O(^1D) + methane reaction to form methanol. After optimizing methanol production, we moved on to study the O(^1D) + ethylene reaction to form vinyl alcohol (CH_2CHOH), and the O(^1D) + methyl amine reaction to form aminomethanol (NH_2CH_2OH). Vinyl alcohol measurements have now been extended up to 450 GHz, and the associated spectral analysis is complete. A possible detection of aminomethanol has also been made, and continued spectral studies and analysis are underway. We will present the results from these experiments and discuss future applications of these molecular and spectroscopic techniques.

Voyager in-situ and Cassini Remote Measurements Suggest a Bubble-like Shape for the Global Heliosphere

NASA Astrophysics Data System (ADS)

Dialynas, K.; Krimigis, S. M.; Mitchell, D. G.; Decker, R. B.; Roelof, E. C.

2017-12-01

The Low Energy Charged Particle (LECP) in situ measurements from Voyager 1 and Voyager 2 (V1, V2) have revealed the reservoir of ions and electrons that constitute the heliosheath after crossing the termination shock 35 deg north and 32 deg south of the ecliptic plane at 94 and 84 astronomical units (1 AU=1.5x108 km), respectively. In August 2012, at 121.6 AU, V1 crossed the heliopause to enter the interstellar space, while V2 remains in the heliosheath since 2007. The advent of Energetic Neutral Atom (ENA, produced through charge exchange between ions and neutral particles flowing through the heliosphere) imaging, has revealed the global nature of the heliosheath at both high (5.2-55 keV, Cassini/Ion and Neutral Camera-INCA, from 10 AU) and low (<6 keV, Interstellar Boundary Explorer-IBEX, from 1 AU) energies. The presence of the two Voyagers measuring ions locally in the heliosheath contemporaneously with INCA global imaging through ENA in overlapping energy bands provides a powerful tool for examining the spatial, temporal, and spectral evolution of the source hot plasma ions. Here we report 5.2-55 keV ENA global images of the heliosphere from Cassini/INCA and compare them with V1,2/LECP 28-53 keV ions measured within the heliosheath over a 13-year period (2003-2016). The similarity between the time profiles of ENA and ions establish that the heliosheath ions are the source of ENA. These measurements also demonstrate that the heliosphere responds promptly, within 2-3 years, to outward propagating solar wind changes (manifested in solar sunspot numbers and solar wind energy input) in both the upstream (nose) and downstream (tail) hemispheres. These results, taken together with the V1 measurement of a 0.5 nT interstellar magnetic field and the enhanced ratio between particle pressure and magnetic pressure in the heliosheath, constrain the shape of the global heliosphere: by contrast to the magnetosphere-like heliotail (that past modeling broadly assumed for more than 55 years), a more symmetric, diamagnetic bubble-like heliosphere, with few substantial tail-like features is revealed.

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's vicinity. Stellar winds from the central cluster R 136 have created an expanding shell; some infalling gas is also detected, reminiscent of a galactic "fountain". Full Tables A.2-A.4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/550/A108

PAHs in the Ices of Saturn's Satellites: Connections to the Solar Nebula and the Interstellar Medium

NASA Technical Reports Server (NTRS)

Cruikshank, Dale P.; Pendleton, Yvonne J.

2015-01-01

Aliphatic hydrocarbons and PAHs have been observed in the interstellar medium (e.g., Allamandola et al. 1985, Pendleton et al. 1994, Pendleton & Allamandola 2002, Tielens 2013, Kwok 2008, Chiar & Pendleton 2008) The inventory of organic material in the ISM was likely incorporated into the molecular cloud in which the solar nebula condensed, contributing to the feedstock for the formation of the Sun, major planets, and the smaller icy bodies in the region outside Neptune's orbit (transneptunian objects, or TNOs). Additional organic synthesis occurred in the solar nebula (Ciesla & Sandford 2012). Saturn's satellites Phoebe, Iapetus, and Hyperion open a window to the composition of one class of TNO as revealed by the near-infrared mapping spectrometer (VIMS) on the Cassini spacecraft at Saturn. Phoebe (mean diameter 213 km) is a former TNO now orbiting Saturn (Johnson & Lunine 2005). VIMS spectral maps of Phoebe's surface reveal a complex organic spectral signature consisting of prominent aromatic (CH) and aliphatic hydrocarbon (=CH2, -CH3) absorption bands (3.2-3.6 micrometers). Phoebe is the source of a huge debris ring encircling Saturn, and from which particles ((is) approximately 5-20 micrometers size) spiral inward toward Saturn (Verbiscer et al. 2009). They encounter Iapetus and Hyperion where they mix with and blanket the native H2O ice of those two bodies. Quantitative analysis of the hydrocarbon bands on Iapetus demonstrates that aromatic CH is approximately 10 times as abundant as aliphatic CH2+CH3, significantly exceeding the strength of the aromatic signature in interplanetary dust particles, comet particles, and in carbonaceous meteorites (Cruikshank et al. 2014). A similar excess of aromatics over aliphatics is seen in the qualitative analysis of Hyperion and Phoebe itself (Dalle Ore et al. 2012). The Iapetus aliphatic hydrocarbons show CH2/CH3 (is) approximately 4, which is larger than the value found in the diffuse ISM ((is) approximately 2-2.5). Insofar as Phoebe is a primitive body that formed in the outer regions of the solar nebula and has preserved some of the original nebula inventory, it can be key in understanding the content and degree of processing of that nebular material. A dynamical subset of TNOs define the Kuiper Belt, from which the short-period comets originate. Particles collected from comet 81P/Wild contain PAHs with an interstellar signature of deuterium. By inference, the PAHs contained in Phoebe and now dusted on the surfaces of two other Saturn satellites share that interstellar origin. There are other Phoebe-like TNOs that are presently beyond our ability to study in the organic spectral region, but JWST will open that possibility for a number of objects.

Bulk and integrated acousto-optic spectrometers for radio astronomy

NASA Technical Reports Server (NTRS)

Chin, G.; Buhl, D.; Florez, J. M.

1981-01-01

The development of sensitive heterodyne receivers (front end) in the centimeter and millimeter range, and the construction of sensitive RF spectrometers (back end) enable the spectral lines of interstellar molecules to be detected and identified. A technique was developed which combines acoustic bending of a collimated coherent light beam by a Bragg cell followed by detection by a sensitive array of photodetectors (thus forming an RF acousto-optic spectrometer (AOS). An AOS has wide bandwidth, large number of channels, and high resolution, and is compact, lightweight, and energy efficient. The thrust of receiver development is towards high frequency heterodyne systems, particularly in the millimeter, submillimeter, far infrared, and 10 micron spectral ranges.

Spectral Analysis of PG 1034+001, the Exciting Star of Hewett 1

NASA Technical Reports Server (NTRS)

Kruk, J. W.; Mahsereci, M.; Ringat, E.; Rauch, T.; Werner, K.

2011-01-01

PG 1034+001 is an extremely hot, helium-rich DO-type star that excites the planetary nebula Hewett 1 and large parts of the surrounding interstellar medium. We present preliminary results of an ongoing spectral analysis by means of non-LTE model atmospheres that consider most elements from hydrogen to nickel. This analysis is based on high-resolution ultraviolet (FUSE, IUE) and optical (VLT/UVES, KECK) data. The results are compared with those of PG 1034+001's spectroscopic twin, the DO star PG 0038+ 199. Keywords. stars: abundances, stars: AGB and post-AGB, stars: atmospheres, stars: evolution, stars: individual (PG 1034+001, PG 0038+ 199), planetary nebulae: individual (Hewett 1)

Pulsar-Wind Nebulae and Magnetar Outflows: Observations at Radio, X-Ray, and Gamma-Ray Wavelengths

NASA Astrophysics Data System (ADS)

Reynolds, Stephen P.; Pavlov, George G.; Kargaltsev, Oleg; Klingler, Noel; Renaud, Matthieu; Mereghetti, Sandro

2017-07-01

We review observations of several classes of neutron-star-powered outflows: pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe interacting directly with interstellar medium (ISM), and magnetar-powered outflows. We describe radio, X-ray, and gamma-ray observations of PWNe, focusing first on integrated spectral-energy distributions (SEDs) and global spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering array of morphologies, with jets, trails, and other structures. Several of the 23 so far identified magnetars show evidence for continuous or sporadic emission of material, sometimes associated with giant flares, and a few "magnetar-wind nebula" have been recently identified.

A determination of the mass of Sagittarius A* from its radio spectral and source size measurements

NASA Technical Reports Server (NTRS)

Melia, Fulvio; Jokipii, J. R.; Narayanan, Ajay

1992-01-01

There is growing evidence that Sgr A* may be a million solar mass black hole accreting from the Galactic center wind. A consideration of the spectral and source size characteristics associated with this process can offer at least two distinct means of inferring the mass M, complementing the more traditional dynamical arguments. We show that M is unmistakably correlated with both the radio spectral index and the critical wavelength below which the intrinsic source size dominates over the angular broadening due to scattering in the interstellar medium. Current observations can already rule out a mass much in excess of 2 x 10 exp 6 solar masses and suggest a likely value close to 1 x 10 exp 6 solar masses, in agreement with an earlier study matching the radio and high-energy spectral components. We anticipate that such a mass may be confirmed with the next generation of source-size observations using milliarcsecond angular resolution at 0.5 - 1 cm wavelengths.

The first linear polarization spectra of Wolf-Rayet stars in the ultraviolet - EZ Canis Majoris and Theta Muscae

NASA Technical Reports Server (NTRS)

Schulte-Ladbeck, R. E.; Nordsieck, K. H.; Code, A. D.; Anderson, C. M.; Babler, B. L.; Bjorkman, K. S.; Clayton, G. C.; Magalhaes, A. M.; Meade, M. R.; Shepherd, D.

1992-01-01

During the 1990 December Astro-1 Space Shuttle mission, spectropolarimetry was conducted in the wavelength region from 1400 to 3200 A of the Wolf-Rayet stars EZ CMa (WN5) and Theta Mus (WC6 + O9.5I) with the Wisconsin Ultraviolet Photo-Polarimeter Experiment. The UV polarization of EZ CMa displays features which correspond to emission lines. This indicates a large, about 0.8 percent, intrinsic UV-continuum polarization, and provides further evidence that the wind of EZ CMa is highly distorted. The polarization of Theta Mus does not change across emission lines, or the strong interstellar 2200 A feature. The polarization decreases smoothly to shorter wavelengths, at constant position angle. The combined UV-optical polarization spectrum of Theta Mus can be described well with interstellar polarization following a Serkowski law.

The outer atmospheres of cool M giants: High-dispersion ultraviolet spectra of Rho Per, 2 Cen, and g Her

NASA Technical Reports Server (NTRS)

Eaton, Joel A.; Johnson, Hollis R.

1986-01-01

Long duration IUE spectra were obtained to extend coverage of cool giants studied in the ultraviolet at high dispersion to M6. The chromospheric spectra of the three stars, which consist of a profusion of Fe II lines and a few lines of Mg II, Mg I, Al II, C II, C I, Cr II, and Fe I, are remarkably similar, both among themselves and with respect to stars of earlier spectral type. These lines present a picture of a warm chromosphere that is static in the average but may be far from uniform in density and ionization. The Mg II emission lines of 2 Cen show 2 unresolved absorption components, the shorter at the velocity of the local interstellar medium. The longer is blueshifted from the star by 12 to 18 km/sec and must be one of very few observed shell lines uncontaminated by interstellar absorption.

Shape and evolution of wind-blown bubbles of massive stars: on the effect of the interstellar magnetic field

NASA Astrophysics Data System (ADS)

van Marle, A. J.; Meliani, Z.; Marcowith, A.

2015-12-01

Context. The winds of massive stars create large (>10 pc) bubbles around their progenitors. As these bubbles expand they encounter the interstellar coherent magnetic field which, depending on its strength, can influence the shape of the bubble. Aims: We wish to investigate if, and how much, the interstellar magnetic field can contribute to the shape of an expanding circumstellar bubble around a massive star. Methods: We use the MPI-AMRVAC code to make magneto-hydrodynamical simulations of bubbles, using a single star model, combined with several different field strengths: B = 5, 10, and 20 μG for the interstellar magnetic field. This covers the typical field strengths of the interstellar magnetic fields found in the galactic disk and bulge. Furthermore, we present two simulations that include both a 5 μG interstellar magnetic field and a warm (10 000 K) interstellar medium (ISM) and two different ISM densities to demonstrate how the magnetic field can combine with other external factors to influence the morphology of the circumstellar bubbles. Results: Our results show that low magnetic fields, as found in the galactic disk, inhibit the growth of the circumstellar bubbles in the direction perpendicular to the field. As a result, the bubbles become ovoid, rather than spherical. Strong interstellar fields, such as observed for the galactic bulge, can completely stop the expansion of the bubble in the direction perpendicular to the field, leading to the formation of a tube-like bubble. When combined with an ISM that is both warm and high density the bubble is greatly reduced in size, causing a dramatic change in the evolution of temporary features inside the bubble such as Wolf-Rayet ring nebulae. Conclusions: The magnetic field of the interstellar medium can affect the shape of circumstellar bubbles. This effect may have consequences for the shape and evolution of circumstellar nebulae and supernova remnants, which are formed within the main wind-blown bubble. Appendices and movies associated to Figs. A.1-A.12 are available in electronic form at http://www.aanda.org

DustEM: Dust extinction and emission modelling

NASA Astrophysics Data System (ADS)

Compiègne, M.; Verstraete, L.; Jones, A.; Bernard, J.-P.; Boulanger, F.; Flagey, N.; Le Bourlot, J.; Paradis, D.; Ysard, N.

2013-07-01

DustEM computes the extinction and the emission of interstellar dust grains heated by photons. It is written in Fortran 95 and is jointly developed by IAS and CESR. The dust emission is calculated in the optically thin limit (no radiative transfer) and the default spectral range is 40 to 108 nm. The code is designed so dust properties can easily be changed and mixed and to allow for the inclusion of new grain physics.

The Exobiological Role of Interstellar Polycyclic Aromatic Hydrocarbons and Ices

NASA Technical Reports Server (NTRS)

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

2002-01-01

Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Before this time, the composition of interstellar dust was largely guessed-at, the presence of ices in interstellar clouds ignored, and the notion that large, gas phase, carbon rich molecules might be abundant and widespread throughout the interstellar medium (ISM) considered impossible. Today, the composition of dust in the ISM is reasonably well constrained to micron-sized cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. Shrouded within the protective confines of cold, opaque molecular clouds--the birthplace of stars and planets--these cold dust particles secrete mantles of mixed molecular ices whose compositions are also well constrained. Finally, amidst the molecular inventory of these ice mantles are likely to be found polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by the standards of interstellar chemistry, the telltale infrared spectral signature of which is now recognized throughout the Universe. In the first part of this talk, we will review the spectroscopic evidence that forms the basis for the currently accepted abundance and ubiquity of PANs in the ISM. We will then look at a few specific examples which illustrate how experimental and theoretical data can be applied to interpret the interstellar spectra and track how the PAN population evolves as it passes from its formation site in the circumstellar outflows of dying stars, through the various phases of the ISM, and into forniing planetary systems. Nevertheless, despite the fact that PANs likely represent the single largest molecular reservoir of organic carbon in evolving planetary systems, they are not what would be considered "biogenic" molecules. Although interesting from a chemical and astrophysical standpoint, in the absence of a mechanism by which this population can be dislodged from the precipitous thermodynamic well afforded by their extensive aromatic networks, they are of little Astrobiological significance. Consequently, for the remainder of the talk, we will consider the photochemical evolution of PANS under conditions similar to those found in the ISM and in proto-planetary systems with an eye toward means by which this rich repository of pre-biotic organic "ore" might be converted into materials of greater importance to Astrobiology.

The millimeter wave spectrum of methyl cyanate: a laboratory study and astronomical search in space ⋆,⋆⋆

PubMed Central

Kolesniková, L.; Alonso, J. L.; Bermúdez, C.; Alonso, E. R.; Tercero, B.; Cernicharo, J.; Guillemin, J.-C.

2016-01-01

Aims The recent discovery of methyl isocyanate (CH3NCO) in Sgr B2(N) and Orion KL makes methyl cyanate (CH3OCN) a potential molecule in the interstellar medium. The aim of this work is to fulfill the first requirement for its unequivocal identification in space, i.e. the availability of transition frequencies with high accuracy. Methods The room-temperature rotational spectrum of methyl cyanate was recorded in the millimeter wave domain from 130 to 350 GHz. All rotational transitions revealed A-E splitting owing to methyl internal rotation and were globally analyzed using the ERHAM program. Results The data set for the ground torsional state of methyl cyanate exceeds 700 transitions within J″ = 10 – 35 and Ka″=0−13 and newly derived spectroscopic constants reproduce the spectrum close to the experimental uncertainty. Spectral features of methyl cyanate were then searched for in Orion KL, Sgr B2(N), B1-b, and TMC-1 molecular clouds. Upper limits to the column density of methyl cyanate are provided. PMID:27721514

Interstellar chemistry

PubMed Central

Klemperer, William

2006-01-01

In the past half century, radioastronomy has changed our perception and understanding of the universe. In this issue of PNAS, the molecular chemistry directly observed within the galaxy is discussed. For the most part, the description of the molecular transformations requires specific kinetic schemes rather than chemical thermodynamics. Ionization of the very abundant molecular hydrogen and atomic helium followed by their secondary reactions is discussed. The rich variety of organic species observed is a challenge for complete understanding. The role and nature of reactions involving grain surfaces as well as new spectroscopic observations of interstellar and circumstellar regions are topics presented in this special feature. PMID:16894148

Interstellar chemistry.

PubMed

Klemperer, William

2006-08-15

In the past half century, radioastronomy has changed our perception and understanding of the universe. In this issue of PNAS, the molecular chemistry directly observed within the galaxy is discussed. For the most part, the description of the molecular transformations requires specific kinetic schemes rather than chemical thermodynamics. Ionization of the very abundant molecular hydrogen and atomic helium followed by their secondary reactions is discussed. The rich variety of organic species observed is a challenge for complete understanding. The role and nature of reactions involving grain surfaces as well as new spectroscopic observations of interstellar and circumstellar regions are topics presented in this special feature.

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

NASA Astrophysics Data System (ADS)

Maier, John P.

2016-06-01

After the discovery of C60, the question of its relevance to the diffuse interstellar bands was raised. In 1987 H. W. Kroto wrote: ``The present observations indicate that C60 might survive in the general interstellar medium (probably as the ion C60/^+)''. In 1994 two diffuse interstellar bands (DIBs) at 9632 and 9577 Å/ were detected and proposed to be the absorption features of C60/^+. This was based on the proximity of these wavelengths to the two prominent absorption bands of C60/^+ measured by us in a neon matrix in 1993. Confirmation of the assignment required the gas phase spectrum of C60/^+ and has taken 20 years. The approach which succeeded confines C60/^+ ions in a radiofrequency trap, cools them by collisions with high density helium allowing formation of the weakly bound C60/^+--He complexes below 10 K. The photofragmentation spectrum of this mass-selected complex is then recorded using a cw laser. In order to infer the position of the absorption features of the bare C60/^+ ion, measurements on C60/^+--He_2 were also made. The spectra show that the presence of a helium atom shifts the absorptions by less than 0.2 Å, much less than the accuracy of the astronomical measurements. The two absorption features in the laboratory have band maxima at 9632.7(1) and 9577.5(1) Å, exactly the DIB wavelengths, and the widths and relative intensities agree. This leads to the first definite identification of now five bands among the five hundred or so DIBs known and proves the presence of gaseous C60/^+ in the interstellar medium. The absorption of cold C70/^+ has also been obtained by this approach. In addition the electronic spectra of a number of cations of astrophysical interest ranging from those of carbon chains including oxygen to larger polycyclic aromatic hydrocarbon could be measured in the gas phase at around 10 K in the ion trap but using an excitation-dissociation approach. The implications of these laboratory spectra in relation to the diffuse interstellar band absorptions can be discussed. H. W. Kroto, J. R. Heath, S. C. O'Brian, R. E. Curl & R. E. Smalley, Nature, 318, 162, 1985 H. W. Kroto in ``Polycyclic aromatic hydrocarbons and astrophysics'', eds. A. Leger, L. B. d'Hendecourt & N. Boccara, Reidel, Dordrecht, 1987, p.197 B. H. Foing & P. Ehrenfreund, Nature, 369, L296, 1994 J. Fulara, M. Jakobi & J. P. Maier, Chem. Phys. Lett., 211, 227, 1993 E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier, Nature, 523, 323, 2015 G. A. H. Walker, D. A. Bohlender, J. P. Maier & E. Campbell, Astrophys. J. Lett., 812, L8, 2015

On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular Clouds

NASA Technical Reports Server (NTRS)

Smith, R. G.; Charnely, S. B.; Pendleton, Y. J.; Wright, C. M.; Maldoni, M. M.; Robinson, G.

2011-01-01

Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H2O2), for the production of water (H2O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H2O2 ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H2O2 should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H2O2/H2O ice films between 2.5 and 200 micron, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 micron. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 micron found on the long-wavelength wing of the 3 micron H2O ice band. This gives an average upper limit for H2O2, as a percentage of H2O, of 9% +/- 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

AN INFRARED DIFFUSE CIRCUMSTELLAR BAND? THE UNUSUAL 1.5272 μm DIB IN THE RED SQUARE NEBULA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zasowski, G.; Chojnowski, S. Drew; Whelan, D. G.

The molecular carriers of the ubiquitous absorption features called the diffuse interstellar bands (DIBs) have eluded identification for many decades, in part because of the enormous parameter space spanned by the candidates and the limited set of empirical constraints afforded by observations in the diffuse interstellar medium. Detection of these features in circumstellar regions, where the environmental properties are more easily measured, is thus a promising approach to understanding the chemical nature of the carriers themselves. Here, using high-resolution spectra from the Apache Point Observatory Galactic Evolution Experiment survey, we present an analysis of the unusually asymmetric 1.5272 μm DIBmore » feature along the sightline to the Red Square Nebula (RSN) and demonstrate the likely circumstellar origin of about half of the DIB absorption in this line of sight. This interpretation is supported both by the velocities of the feature components and by the ratio of foreground to total reddening along the line of sight. The RSN sightline offers the unique opportunity to study the behavior of DIB carriers in a constrained environment and thus to shed new light on the carriers themselves.« less

Hot interstellar gas and ionization of embedded clouds

NASA Technical Reports Server (NTRS)

Cheng, K.-P.; Bruhweiler, F.

1990-01-01

Researchers present detailed photoionization calculations for the instellar cloud in which the Sun is embedded. They consider the EUV radiation field with contribution from discrete stellar sources and from a thermal bremsstrahlung-radiative recombination spectrum emitted from the surrounding 10 to the 6th power k coronal substrate. They establish lower limits to the fractional ionization of hydrogen and helium of 0.17 and 0.29 respectively. The high He ionization fraction results primarily from very strong line emission below 500 A originating in the surrounding coronal substrate while the H ionization is dominated by the EUV radiation from the discrete stellar sources. The dual effects of thermal conduction and the EUV spectrum of the 10 to the 6th k plasma on ionization in the cloud skin are explored. The EUV radiation field and Auger ionization have insignificant effects on the resulting ionic column densities of Si IV, C IV, N V and O VI through the cloud skin. Calculations show that the abundances of these species are dominated by collisional ionization in the thermal conduction front. Because of a low charge exchange rate with hydrogen, the ionic column density ratios of N (CIII)/N (CII) and N (NII)/N (NI) are dominated by the EUV radiation field in the local interstellar medium. These ratios should be important diagnostics for the EUV radiation field and serve as surrogate indicators of the interstellar He and H ionization fraction respectively. Spacecraft such as Lyman which is designed to obtain high resolution spectral data down to the Lyman limit at 912 A could sample interstellar lines of these ions.

Mid-infrared spectra of cometary dust: the evasion of its silicate mineralogy

NASA Astrophysics Data System (ADS)

Kimura, H.; Chigai, T.; Yamamoto, T.

2008-04-01

Infrared spectra of dust in cometary comae provide a way to identify its silicate constituents, and this is crucial for correctly understanding the condition under which our planetary system is formed. Recent studies assign a newly detected peak at a wavelength of 9.3 μm to pyroxenes and regard them as the most abundant silicate minerals in comets. Here we dispense with this pyroxene hypothesis to numerically reproduce the infrared features of cometary dust in the framework of our interstellar dust models. Presolar interstellar dust in a comet is modeled as fluffy aggregates consisting of submicrometer-sized organic grains with an amorphous-silicate core that undergoes nonthermal crystallization in a coma. We assert that forsterite (Mg2SiO4) is the carrier of all the observed features, including the 9.3 μm peak and that the major phase of iron is sulfides rather than iron-rich silicates.

Spectral-Spatial Scale Invariant Feature Transform for Hyperspectral Images.

PubMed

Al-Khafaji, Suhad Lateef; Jun Zhou; Zia, Ali; Liew, Alan Wee-Chung

2018-02-01

Spectral-spatial feature extraction is an important task in hyperspectral image processing. In this paper we propose a novel method to extract distinctive invariant features from hyperspectral images for registration of hyperspectral images with different spectral conditions. Spectral condition means images are captured with different incident lights, viewing angles, or using different hyperspectral cameras. In addition, spectral condition includes images of objects with the same shape but different materials. This method, which is named spectral-spatial scale invariant feature transform (SS-SIFT), explores both spectral and spatial dimensions simultaneously to extract spectral and geometric transformation invariant features. Similar to the classic SIFT algorithm, SS-SIFT consists of keypoint detection and descriptor construction steps. Keypoints are extracted from spectral-spatial scale space and are detected from extrema after 3D difference of Gaussian is applied to the data cube. Two descriptors are proposed for each keypoint by exploring the distribution of spectral-spatial gradient magnitude in its local 3D neighborhood. The effectiveness of the SS-SIFT approach is validated on images collected in different light conditions, different geometric projections, and using two hyperspectral cameras with different spectral wavelength ranges and resolutions. The experimental results show that our method generates robust invariant features for spectral-spatial image matching.

A Detailed Far-ultraviolet Spectral Atlas of O-type Stars

NASA Astrophysics Data System (ADS)

Smith, Myron A.

2012-10-01

In this paper, we present a spectral atlas covering the wavelength interval 930-1188 Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188 Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas, to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. We discuss the statistics of line populations among the various elemental ionization states. Also, as an aid to users we list those isolated lines that can be used to determine stellar temperatures and the presence of possible chemical anomalies. Finally, we have prepared FITS files that give pairs of merged spectra for stars in our population sequences, for access via MAST.

The Andromeda Optical and Infrared Disk Survey

NASA Astrophysics Data System (ADS)

Sick, Jonathan

The spectral energy distributions of galaxies inform us about a galaxy's stellar populations and interstellar medium, revealing stories of galaxy formation and evolution. How we interpret this light depends in part on our proximity to the galaxy. For nearby galaxies, detailed star formation histories can be extracted from the resolved stellar populations, while more distant galaxies feature the contributions of entire stellar populations within their integrated spectral energy distribution (SED). This thesis aims to resolve whether the techniques used to investigate stellar populations in distant galaxies are consistent with those available for nearby galaxies. As the nearest spiral galaxy, the Andromeda Galaxy (M31) is the ideal testbed for the joint study of resolved stellar populations and panchromatic SEDs. We present the Andromeda Optical and Infrared Disk Survey (ANDROIDS), which adds new near-UV to near-IR (u*g'r'i'JKs) imaging using the MegaCam and WIRCam cameras at the Canada-France-Hawaii telescope to the available M31 panchromatic dataset. To accurately subtract photometric background from our extremely wide-field (14 square degree) mosaics, we present observing and data reduction techniques with sky-target nodding, optimization of image-to-image surface brightness, and a novel hierarchical Bayesian model to trace the background signal while modelling the astrophysical SED. We model the spectral energy distributions of M31 pixels with MAGPHYS (da Cunha et al. 2008) and compare those results to resolved stellar population models of the same pixels from the Panchromatic Hubble Andromeda Treasury (PHAT) survey (Williams et al. 2017). We find substantial (0.3 dex) differences in stellar mass estimates despite a common use of the Chabrier (2003) initial mass function. Stellar mass estimated from the resolved stellar population is larger than any mass estimate from SED models or colour-M/L relations (CMLRs). There is also considerable diversity among CMLR estimators, largely driven by differences in the star formation history prior distribution. We find broad consistency between the star formation history estimated by integrated spectral energy distributions and resolved stars. Generally, spectral energy distribution models yield a stronger inside-out radial metallicity gradient and bias towards younger mean ages than resolved stellar population models.

Diamond, aromatic, aliphatic components of interstellar dust grains: Random covalent networks in carbonaceous grains

NASA Astrophysics Data System (ADS)

Duley, W. W.

1995-05-01

A formalism based on the theory of random covalent networks (RCNs) in amorphous solids is developed for carbonaceous dust grains. RCN solutions provide optimized structures and relative compositions for amorphous materials. By inclusion of aliphatic, aromatic, and diamond clusters, solutions specific to interstellar materials can be obtained and compared with infrared spectral data. It is found that distinct RCN solutions corresponding to diffuse cloud and molecular cloud materials are possible. Specific solutions are derived for three representative objects: VI Cyg No. 12, NGC 7538 (IRS 9), and GC IRS 7. While diffuse cloud conditions with a preponderance of sp2 and sp3 bonded aliphatic CH species can be reproduced under a variety of RCN conditions, the presence of an abundant tertiary CH or diamond component is highly constrained. These solutions are related quantitatively to carbon depletions and can be used to provide a quantitative estimate of carbon in these various dust components. Despite the abundance of C6 aromatic rings in many RCN solutions, the infrared absorption due to the aromatic stretch at approximately 3.3 micrometers is weak under all conditions. The RCN formalism is shown to provide a useful method for tracing the evolutionary properties of interstellar carbonaceous grains.

DirtyGrid I: 3D Dust Radiative Transfer Modeling of Spectral Energy Distributions of Dusty Stellar Populations

NASA Astrophysics Data System (ADS)

Law, Ka-Hei; Gordon, Karl D.; Misselt, Karl A.

2018-06-01

Understanding the properties of stellar populations and interstellar dust has important implications for galaxy evolution. In normal star-forming galaxies, stars and the interstellar medium dominate the radiation from ultraviolet (UV) to infrared (IR). In particular, interstellar dust absorbs and scatters UV and optical light, re-emitting the absorbed energy in the IR. This is a strongly nonlinear process that makes independent studies of the UV-optical and IR susceptible to large uncertainties and degeneracies. Over the years, UV to IR spectral energy distribution (SED) fitting utilizing varying approximations has revealed important results on the stellar and dust properties of galaxies. Yet the approximations limit the fidelity of the derived properties. There is sufficient computer power now available that it is now possible to remove these approximations and map out of landscape of galaxy SEDs using full dust radiative transfer. This improves upon previous work by directly connecting the UV, optical, and IR through dust grain physics. We present the DIRTYGrid, a grid of radiative transfer models of SEDs of dusty stellar populations in galactic environments designed to span the full range of physical parameters of galaxies. Using the stellar and gas radiation input from the stellar population synthesis model PEGASE, our radiative transfer model DIRTY self-consistently computes the UV to far-IR/sub-mm SEDs for each set of parameters in our grid. DIRTY computes the dust absorption, scattering, and emission from the local radiation field and a dust grain model, thereby physically connecting the UV-optical to the IR. We describe the computational method and explain the choices of parameters in DIRTYGrid. The computation took millions of CPU hours on supercomputers, and the SEDs produced are an invaluable tool for fitting multi-wavelength data sets. We provide the complete set of SEDs in an online table.

The MUSCLES Treasury Survey. II. Intrinsic LYα and Extreme Ultraviolet Spectra of K and M Dwarfs with Exoplanets*

NASA Astrophysics Data System (ADS)

Youngblood, Allison; France, Kevin; Loyd, R. O. Parke; Linsky, Jeffrey L.; Redfield, Seth; Schneider, P. Christian; Wood, Brian E.; Brown, Alexander; Froning, Cynthia; Miguel, Yamila; Rugheimer, Sarah; Walkowicz, Lucianne

2016-06-01

The ultraviolet (UV) spectral energy distributions (SEDs) of low-mass (K- and M-type) stars play a critical role in the heating and chemistry of exoplanet atmospheres, but are not observationally well-constrained. Direct observations of the intrinsic flux of the Lyα line (the dominant source of UV photons from low-mass stars) are challenging, as interstellar H I absorbs the entire line core for even the closest stars. To address the existing gap in empirical constraints on the UV flux of K and M dwarfs, the MUSCLES Hubble Space Telescope Treasury Survey has obtained UV observations of 11 nearby M and K dwarfs hosting exoplanets. This paper presents the Lyα and extreme-UV spectral reconstructions for the MUSCLES targets. Most targets are optically inactive, but all exhibit significant UV activity. We use a Markov Chain Monte Carlo technique to correct the observed Lyα profiles for interstellar absorption, and we employ empirical relations to compute the extreme-UV SED from the intrinsic Lyα flux in ˜100 Å bins from 100-1170 Å. The reconstructed Lyα profiles have 300 km s-1 broad cores, while >1% of the total intrinsic Lyα flux is measured in extended wings between 300 and 1200 km s-1. The Lyα surface flux positively correlates with the Mg II surface flux and negatively correlates with the stellar rotation period. Stars with larger Lyα surface flux also tend to have larger surface flux in ions formed at higher temperatures, but these correlations remain statistically insignificant in our sample of 11 stars. We also present H I column density measurements for 10 new sightlines through the local interstellar medium. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Particles

NASA Technical Reports Server (NTRS)

Abbas, Mian M.; Craven, Paul D.; Spann, James F.; Tankosic, Dragana; Six, N. Frank (Technical Monitor)

2002-01-01

A laboratory facility for levitating single isolated dust particles in an electrodynamics balance has been developing at NASA/Marshall Space Flight Center for conducting a variety of experimental, of astrophysical interest. The objective of this research is to employ this innovative experimental technique for studies of the physical and optical properties of the analogs of cosmic grains of 0.2-10 micron size in a chamber with controlled pressure/temperatures simulating astrophysical environments. In particular, we will carry out three classes of experiments to investigate the microphysics of the analogs of interstellar and interplanetary dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. These measurements will provide the much-needed photoelectric emission data relating to individual particles as opposed to that for the bulk materials available so far. (2) Infrared optical properties of dust particles obtained by irradiating the particles with radiation from tunable infrared diode lasers and measuring the scattered radiation. Specifically, the complex refractive indices, the extinction coefficients, the scattering phase functions, and the polarization properties of single dust grains of interest in interstellar environments, in the 1-25 micron spectral region will be determined. (3) Condensation experiments to investigate the deposition of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The increase in the mass or m/q ratio due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data wild permit determination of the sticking efficiencies of volatile gases of astrophysical interest. Preliminary results based on photoelectric emission experiments on 0.2-6.6 micron size silica particles exposed to UV radiation in the 120-200 nm spectral region will be presented.

Rotational Spectrum, Conformational Composition, and Quantum Chemical Calculations of Cyanomethyl Formate (HC(O)OCH2C≡N), a Compound of Potential Astrochemical Interest.

PubMed

Samdal, Svein; Møllendal, Harald; Carles, Sophie

2015-08-27

The rotational spectrum of cyanomethyl formate (HC(O)OCH2C≡N) has been recorded in the 12–123 GHz spectral range. The spectra of two conformers were assigned. The rotamer denoted I has a symmetry plane and two out-of plane hydrogen atoms belonging to the cyanomethyl (CH2CN) moiety. In the conformer called II, the cyanomethyl group is rotated 80.3° out of this plane. Conformer I has an energy that is 1.4(6) kJ/mol lower than the energy of II according to relative intensity measurements. A large number of rotational transitions have been assigned for the ground and vibrationally excited states of the two conformers and accurate spectroscopic constants have been obtained. These constants should predict frequencies of transitions outside the investigated spectral range with a very high degree of precision. It is suggested that cyanomethyl formate is a potential interstellar compound. This suggestion is based on the fact that its congener methyl formate (HC(O)OCH3) exists across a large variety of interstellar environments and the fact that cyanides are very prevalent in the Universe. The experimental work has been augmented by high-level quantum chemical calculations. The CCSD/cc-pVQZ calculations are found to predict structures of the two forms that are very close to the Born–Oppenheimer equilibrium structures. MP2/cc-pVTZ predictions of several vibration–rotation interaction constants were generally found to be rather inaccurate. A gas-phase reaction between methyl formate and the cyanomethyl radical CH2CN to produce a hydrogen atom and cyanomethyl formate was mimicked using MP2/cc-pVTZ calculations. It was found that this reaction is not favored thermodynamically. It is also conjectured that the possible formation of cyanomethyl formate might be catalyzed and take place on interstellar particles.

HI emission from the red giant Y CVn with the VLA and FAST

NASA Astrophysics Data System (ADS)

Hoai, Do T.; Nhung, Pham T.; Matthews, Lynn D.; Gérard, Eric; Le Bertre, Thibaut

2017-07-01

Imaging studies with the Very Large Array (VLA) have revealed HI emission associated with the extended circumstellar shells of red giants. We analyze the spectral map obtained on Y CVn, a J-type carbon star on the Asymptotic Giant Branch. The HI line profiles can be interpreted with a model of a detached shell resulting from the interaction of a stellar outflow with the local interstellar medium. We reproduce the spectral map by introducing a distortion along a direction corresponding to the star’s motion in space. We then use this fitting to simulate observations expected from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and discuss its potential for improving our description of the outer regions of circumstellar shells.

Theoretical modeling of the infrared fluorescence from interstellar polycyclic aromatic hydrocarbons

NASA Technical Reports Server (NTRS)

Schutte, W. A.; Tielens, A. G. G. M.; Allamandola, L. J.

1993-01-01

We have modeled the family of interstellar IR emission bands at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 microns by calculating the fluorescence from a size distribution of interstellar polycyclic aromatic hydrocarbons (PAHs) embedded in the radiation field of a hot star. It is found that the various emission bands are dominated by distinctly different PAHs, from molecules with much less than about 80 C atoms for the 3.3 micron feature, to molecules with 10 exp 2-10 exp 5 C atoms for the emission in the IRAS 12 and 25 micron bands. We quantitatively describe the influence on the emergent spectrum of various PAH properties such as the molecular structure, the amount of dehydrogenation, the intrinsic strength of the IR active modes, and the size distribution. Comparing our model results to the emission spectrum from the Orion Bar region, we conclude that interstellar PAHs are likely fully, or almost fully, hydrogenated. Moreover, it is found that the intrinsic strengths of the 6.2 and 7.7 micron C-C stretching modes, and the 8.6 micron C-H in-plane bending mode are 2-6 times larger than measured for neutral PAHs in the laboratory.

On the Organisation of World Ships and Other Gigascale Interstellar Space Exploration Projects

NASA Astrophysics Data System (ADS)

Ceyssens, F.; Driesen, M.; Wouters, K.

The development and deployment of world ships or other feats of interstellar exploration will without doubt require orders of magnitude more resources than needed for current or past megaprojects (Apollo, Iter, LHC,...). Question is how enough resources for such gigaprojects can be found in a scenario assuming limited, moderate economic growth throughout the next centuries, i.e. without human population and productivity continuing to grow exponentially, and without extreme events such as economic collapse or singularity.Three defining features of gigascale space projects are identified, which should be recognized to the fullest: their almost absolute nonprofit character, their massive cost in terms of time and resources and their non-urgency leading to procrastina- tion. It will be argued that the best chance of getting a world ship or another interstellar project started in this generation is to establish an international network of non governmental organizations (NGOs) focused on private and public fundraising for interstellar exploration and supporting a bottom-up societal movement, similar to e.g. the WWF. It will be shown that this path can reduce the massive barriers to entry as well as the level of governmental support needed.

The Arizona Radio Observatory 1 mm Spectral Survey of IRC +10216 and VY Canis Majoris (215-285 GHz)

NASA Astrophysics Data System (ADS)

Tenenbaum, E. D.; Dodd, J. L.; Milam, S. N.; Woolf, N. J.; Ziurys, L. M.

2010-10-01

A low noise (1σ rms ~ 3 mK) 1 mm spectral survey (214.5-285.5 GHz) of the oxygen-rich supergiant VY Canis Majoris and the carbon-rich asymptotic giant branch star IRC +10216 has been conducted using the Arizona Radio Observatory's 10 m Submillimeter Telescope. Here the complete data set is presented. This study, carried out with a new ALMA-type receiver, marks the first continuous band scan of an O-rich circumstellar envelope, and the most sensitive survey to date of IRC +10216. In VY CMa, 130 distinct molecular lines were detected, 14 of which cannot be identified; in IRC +10216, 717 lines were observed, with 126 features remaining unidentified. In the 1 mm bands of VY CMa and IRC +10216, emission is present from 18 and 32 different chemical compounds, respectively, with 10 species common to both sources. Many narrow emission lines were observed in both circumstellar shells, arising from vibrationally excited molecules and from refractory-containing species. Line profiles in VY CMa also exhibit a variety of different shapes, caused by the complex, asymmetric outflow of this object. The survey highlights the fact that C-rich and O-rich circumstellar envelopes are chemically interesting, and both are sources of new interstellar molecules. The high number of unidentified lines and the unreliable rest frequencies for known species such as NaCN indicate the need for additional laboratory spectroscopy studies.

Integrated spectral properties of 7 galactic open clusters

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Clariá, J. J.; Bica, E.; Piatti, A. E.

2000-01-01

This paper presents flux-calibrated integrated spectra in the range 3600-9000 Ä for 7 concentrated, relatively populous Galactic open clusters. We perform simultaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template cluster spectra with known parameters. For five clusters these two parameters have been determined for the first time (Ruprecht 144, BH 132, Pismis 21, Lyng\\aa 11 and BH 217), while the results here derived for the remaining two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270o and l = 0o, respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

The Arizona Radio Observatory 1 mm Spectral Survey of IRC (plus)10216 and VY Canis Majoris (215-285 GHz)

NASA Technical Reports Server (NTRS)

Tenenbaum, E. D.; Dodd, J. L.; Milam, S. N.; Woolf, N. J.; Ziurys, L. M.

2010-01-01

A low noise (1(sigma) rms approx. 3 mK) 1. nun spectral survey (214.5-285.5 GHz) of the oxygen-rich supergiant VY Canis Majoris and the carbon-rich asymptotic giant branch star IRC +10216 has been conducted using the Arizona Radio Observatory's 10 m Submillimeter Telescope. Here the complete data set is presented. This study, carried out with a new ALMA-type receiver, marks the first continuous band scan of an O-rich circumstellar envelope, and the most sensitive survey to date of IRC +10216. In VY CMa, 130 distinct molecular lines were detected, 14 of which cannot be identified; in IRC +10216, 717 lines were observed, with 126 features remaining unidentified. In the 1 mm bands of VY CMa and IRC +10216, emission is present from 18 and 32 different chemical compounds, respectively, with 10 species common to both sources. Many narrow emission lines were observed in both circumstellar shells, arising from vibrationally excited molecules and from refractory-containing species. Line profiles in VY CMa also exhibit a variety of different shapes, caused by the complex, asymmetric outflow of this object. The survey highlights the fact that C-rich and O-rich circumstellar envelopes are chemically interesting, and both are sources of new interstellar molecules. The high number of unidentified lines and the unreliable, rest frequencies for known species such as NaCN indicate the need for additional laboratory spectroscopy studies.

Diffuse Interstellar Bands. A Survey of Observational Facts

NASA Astrophysics Data System (ADS)

Krełowski, J.

2018-07-01

The paper presents and documents the most important observational results concerning the enigmatic diffuse interstellar bands (DIBs) that have remained unidentified since 1922. It demonstrates why the bands are commonly considered as having originated in many still unknown carriers. The mutual correlations of different DIBs, aiming at finding “families” of common origin, are briefly discussed. It was found that the strength ratio of the major DIBs, 5780 and 5797, is heavily variable; at the same E(B‑V), the DIB intensities may vary by as much as a factor of three or more. 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. In the former (prototype HD147165), broad DIBs are very strong, while the narrow ones and molecular features are weak. In the latter (prototype HD149757), narrow DIBs, as well as bands of simple radicals, are strong while the broad DIBs are weak (in relation to E(B‑V)). Details of the profiles of narrow DIBs, documenting their molecular origin, are presented. The relative DIB strengths as well as those of the simple radicals seem to be related to the shapes of interstellar extinction curves. Possible carriers of DIBs are only mentioned, as all of the proposed ones remain uncertain. The survey is biased in the sense that it presents the author’s point of view. It was prepared for the thirtieth anniversary of the first DIB survey, published in PASP (Krełowski 1988), and demonstrates how far our knowledge has evolved since then.

Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies

NASA Astrophysics Data System (ADS)

Vidal-García, A.; Charlot, S.; Bruzual, G.; Hubeny, I.

2017-09-01

We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (∼10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.

GOT C+: Galactic Plane Survey of the 1.9 THz [CII] Line

NASA Astrophysics Data System (ADS)

Langer, William

2012-01-01

The ionized carbon [CII] 1.9 THz fine structure line is a major gas coolant in the interstellar medium (ISM) and controls the thermal conditions in diffuse gas clouds and Photodissociation Regions (PDRs). The [CII] line is also an important tracer of the atomic gas and atomic to molecular transition in diffuse clouds throughout the Galaxy. I will review some of the results from the recently completed Galactic Observations of Terahertz C+ (GOT C+) survey. This Herschel Open Time Key Project is a sparse, but uniform volume sample survey of [CII] line emission throughout the Galactic disk using the HIFI heterodyne receiver. HIFI observations, with their high spectral resolution, isolate and locate individual clouds in the Galaxy and provide excitation information on the gas. I will present [CII] position-velocity maps that reveal the distribution and motion of the clouds in the inner Galaxy and discuss results on the physical properties of the gas using spectral observations of [CII] and ancillary HI and 12CO, 13CO, and C18O J=1-0 data. The [CII] emission is also a useful tracer of the "Dark H2 Gas", and I will discuss its distribution in a sample of interstellar clouds. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration.

A brief visit from a red and extremely elongated interstellar asteroid.

PubMed

Meech, Karen J; Weryk, Robert; Micheli, Marco; Kleyna, Jan T; Hainaut, Olivier R; Jedicke, Robert; Wainscoat, Richard J; Chambers, Kenneth C; Keane, Jacqueline V; Petric, Andreea; Denneau, Larry; Magnier, Eugene; Berger, Travis; Huber, Mark E; Flewelling, Heather; Waters, Chris; Schunova-Lilly, Eva; Chastel, Serge

2017-12-21

None of the approximately 750,000 known asteroids and comets in the Solar System is thought to have originated outside it, despite models of the formation of planetary systems suggesting that orbital migration of giant planets ejects a large fraction of the original planetesimals into interstellar space. The high predicted number density of icy interstellar objects (2.4 × 10 -4 per cubic astronomical unit) suggests that some should have been detected, yet hitherto none has been seen. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of the Solar System today, but there has been no way of telling whether the Solar System is typical of planetary systems. Here we report observations and analysis of the object 1I/2017 U1 ('Oumuamua) that demonstrate its extrasolar trajectory, and that thus enable comparisons to be made between material from another planetary system and from our own. Our observations during the brief visit by the object to the inner Solar System reveal it to be asteroidal, with no hint of cometary activity despite an approach within 0.25 astronomical units of the Sun. Spectroscopic measurements show that the surface of the object is spectrally red, consistent with comets or organic-rich asteroids that reside within the Solar System. Light-curve observations indicate that the object has an extremely oblong shape, with a length about ten times its width, and a mean radius of about 102 metres assuming an albedo of 0.04. No known objects in the Solar System have such extreme dimensions. The presence of 'Oumuamua in the Solar System suggests that previous estimates of the number density of interstellar objects, based on the assumption that all such objects were cometary, were pessimistically low. Planned upgrades to contemporary asteroid survey instruments and improved data processing techniques are likely to result in the detection of more interstellar objects in the coming years.

Multiwavelength study of accretion-powered pulsars

NASA Astrophysics Data System (ADS)

Nespoli, Elisa

2010-11-01

This thesis consists in a multi-frequency approach to High Mass X-ray Binaries (HMXBs), using infrared and X-ray data. On one side, the project aimed at the identification and characterization of IR counterparts to obscured HMXBs in the Scutum and Norma inner galactic arms. The identification of optical/IR counterparts to HMXBs is a necessary step to undertake detailed studies of these systems. With data limited to the high-energy range, the understanding of their complex structure and dynamics cannot be complete. In the last years, INTEGRAL has revealed the presence of an important population of heavily absorbed HMXBs in the Scutum and Norma regions, virtually unobservable below 4 keV. Optical counterparts to these obscured sources are hardly observable, due to the high interstellar extinction. Candidate counterparts to HMXBs were selected by means of a photometric search for emission-line stars in the error boxes of the X-ray sources detected by INTEGRAL. With this objective, I built up (Brγ-K)-(H-K) and (HeI-K)-(H-K) IR color-color diagrams, in which emission-line stars are expected to show up below the absorption-line stars sequence. I applied this technique to search for counterparts to Be/XRBs, whose transient nature prevents the counterpart identification with follow-up X-ray observations with high spatial resolution. For each field, one to four candidate counterparts were identified. I also took spectra of proposed counterparts. The confirmation and spectral classifications of the systems led to unveil the nature of nine INTEGRAL objects. On the other hand, this work intended to provide for the first time a systematic study of four Be/XRBs during giant (type II) outbursts. I employed RXTE data, applying the three techniques of color-color/hardness-intensity diagrams (CD/HID), spectral fitting and Fourier power-spectral analysis, simultaneously, and using the retrieved results and correlations to try to define and characterize spectral states for this class of systems. In this way I followed both a model-independent (CD/HID) and model-dependent approach (spectral fits) to investigate the rapid aperiodic variability as a function of spectral sates in HMXBs. I obtained lightcurves, energy and power spectra for a total number of 320 observations. From X-ray colors, spectral and timing fitting, I clearly identified in all the four systems two different spectral states, i.e. the Diagonal Branch (DB) and Horizontal Branch (HB). The HB corresponds to a lower-flux state, with larger rms than the DB. Also, the power-law photon index decreases with flux in the HB, while stays constant or increases in the DB. The HB shows lower characteristic frequencies of the noise components than in the DB. The cyclotron resonant scattering features are generally associated with the DB, while absent or weaker during the DB. We showed how the transition between the two states may correspond to the transition from the standing shock emission to the thermal mound emission due to the turning point from super-Eddington luminosity regime (DB) to sub-Eddington luminosity regime (HB). From color, spectral and timing point of view, differences among systems easily distinguishes two subgroups, with the slower pulsars, KS 1947+300 and EXO2030+375, on one side, and the faster ones, 4U 0115+63 and V 0332+53, on the other. The first group is characterized by softer spectra in the HB compared with the other systems. Hysteresis is not observed in the slower pulsars, while it is evident in V 0332+53 and 4U 0115+63. Cyclotron resonant scattering features are crucial in the spectral shape of V 0332+53 and 4U 0115+63, where also a harmonic is observed in the 3-30 keV energy range. They are instead absent or very weak in the first group. According to timing features, a strong difference between the two groups is the presence of QPOs in the faster pulsars.

Simultaneous Spectral-Spatial Feature Selection and Extraction for Hyperspectral Images.

PubMed

Zhang, Lefei; Zhang, Qian; Du, Bo; Huang, Xin; Tang, Yuan Yan; Tao, Dacheng

2018-01-01

In hyperspectral remote sensing data mining, it is important to take into account of both spectral and spatial information, such as the spectral signature, texture feature, and morphological property, to improve the performances, e.g., the image classification accuracy. In a feature representation point of view, a nature approach to handle this situation is to concatenate the spectral and spatial features into a single but high dimensional vector and then apply a certain dimension reduction technique directly on that concatenated vector before feed it into the subsequent classifier. However, multiple features from various domains definitely have different physical meanings and statistical properties, and thus such concatenation has not efficiently explore the complementary properties among different features, which should benefit for boost the feature discriminability. Furthermore, it is also difficult to interpret the transformed results of the concatenated vector. Consequently, finding a physically meaningful consensus low dimensional feature representation of original multiple features is still a challenging task. In order to address these issues, we propose a novel feature learning framework, i.e., the simultaneous spectral-spatial feature selection and extraction algorithm, for hyperspectral images spectral-spatial feature representation and classification. Specifically, the proposed method learns a latent low dimensional subspace by projecting the spectral-spatial feature into a common feature space, where the complementary information has been effectively exploited, and simultaneously, only the most significant original features have been transformed. Encouraging experimental results on three public available hyperspectral remote sensing datasets confirm that our proposed method is effective and efficient.

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.

HIghZ: A search for HI absorption in high-redshift radio galaxies

NASA Astrophysics Data System (ADS)

Allison, J.; Callingham, J.; Sadler, E.; Wayth, R.; Curran, S.; Mahoney, E.

2017-01-01

We will use the unique low-frequency spectral capability of the MWA to carry out a pilot survey for neutral gas in the interstellar medium of the most distant (z>5) radio galaxies in the Universe. Through detection of the HI 21-cm line in absorption we aim to place stringent lower limits on the source redshift, confirming its location in the early Universe. Our sample makes use of the excellent wide-band spectral information available from the recently completed MWA GLEAM survey, from which we have selected a sample of ultra-steep peaked-spectrum radio sources that have a spectral turnover below 300 MHz. These sources should be ideal candidates for high-redshift compact radio galaxies since they have (a) spectral peaks that turnover below 1GHz and (b) very steep (alpha < -1.0) spectral indices that are consistent with the high density environments expected for radio galaxies in the early Universe. Using the MWA, we aim to verify this hypothesis through the detection of significant column densities of cold HI. This pathfinder project will provide important technical information that will inform future absorption surveys both with the MWA and, ultimately, the SKA-LOW telescope.

Stochastic and Deterministic Approaches to Gas-grain Modeling of Interstellar Sources

NASA Astrophysics Data System (ADS)

Vasyunin, Anton; Herbst, Eric; Caselli, Paola

During the last decade, our understanding of the chemistry on surfaces of interstellar grains has been significantly enchanced. Extensive laboratory studies have revealed complex structure and dynamics in interstellar ice analogues, thus making our knowledge much more detailed. In addition, the first qualitative investigations of new processes were made, such as non-thermal chemical desorption of species from dust grains into the gas. Not surprisingly, the rapid growth of knowledge about the physics and chemistry of interstellar ices led to the development of a new generation of astrochemical models. The models are typically characterized by more detailed treatments of the ice physics and chemistry than previously. The utilized numerical approaches vary greatly from microscopic models, in which every single molecule is traced, to ``mean field'' macroscopic models, which simulate the evolution of averaged characteristics of interstellar ices, such as overall bulk composition. While microscopic models based on a stochastic Monte Carlo approach are potentially able to simulate the evolution of interstellar ices with an account of most subtle effects found in a laboratory, their use is often impractical due to limited knowledge about star-forming regions and huge computational demands. On the other hand, deterministic macroscopic models that often utilize kinetic rate equations are computationally efficient but experience difficulties in incorporation of such potentially important effects as ice segregation or discreteness of surface chemical reactions. In my talk, I will review the state of the art in the development of gas-grain astrochemical models. I will discuss how to incorporate key features of ice chemistry and dynamics in the gas-grain astrochemical models, and how the incorporation of recent laboratory findings into gas-grain models helps to better match observations.

Spectral dependence of texture features integrated with hyperspectral data for area target classification improvement

NASA Astrophysics Data System (ADS)

Bangs, Corey F.; Kruse, Fred A.; Olsen, Chris R.

2013-05-01

Hyperspectral data were assessed to determine the effect of integrating spectral data and extracted texture feature data on classification accuracy. Four separate spectral ranges (hundreds of spectral bands total) were used from the Visible and Near Infrared (VNIR) and Shortwave Infrared (SWIR) portions of the electromagnetic spectrum. Haralick texture features (contrast, entropy, and correlation) were extracted from the average gray-level image for each of the four spectral ranges studied. A maximum likelihood classifier was trained using a set of ground truth regions of interest (ROIs) and applied separately to the spectral data, texture data, and a fused dataset containing both. Classification accuracy was measured by comparison of results to a separate verification set of test ROIs. Analysis indicates that the spectral range (source of the gray-level image) used to extract the texture feature data has a significant effect on the classification accuracy. This result applies to texture-only classifications as well as the classification of integrated spectral data and texture feature data sets. Overall classification improvement for the integrated data sets was near 1%. Individual improvement for integrated spectral and texture classification of the "Urban" class showed approximately 9% accuracy increase over spectral-only classification. Texture-only classification accuracy was highest for the "Dirt Path" class at approximately 92% for the spectral range from 947 to 1343nm. This research demonstrates the effectiveness of texture feature data for more accurate analysis of hyperspectral data and the importance of selecting the correct spectral range to be used for the gray-level image source to extract these features.

A new automated spectral feature extraction method and its application in spectral classification and defective spectra recovery

NASA Astrophysics Data System (ADS)

Wang, Ke; Guo, Ping; Luo, A.-Li

2017-03-01

Spectral feature extraction is a crucial procedure in automated spectral analysis. This procedure starts from the spectral data and produces informative and non-redundant features, facilitating the subsequent automated processing and analysis with machine-learning and data-mining techniques. In this paper, we present a new automated feature extraction method for astronomical spectra, with application in spectral classification and defective spectra recovery. The basic idea of our approach is to train a deep neural network to extract features of spectra with different levels of abstraction in different layers. The deep neural network is trained with a fast layer-wise learning algorithm in an analytical way without any iterative optimization procedure. We evaluate the performance of the proposed scheme on real-world spectral data. The results demonstrate that our method is superior regarding its comprehensive performance, and the computational cost is significantly lower than that for other methods. The proposed method can be regarded as a new valid alternative general-purpose feature extraction method for various tasks in spectral data analysis.

SPECTRAL INTENSITIES OF ANTIPROTONS AND THE NESTED LEAKY-BOX MODEL FOR COSMIC RAYS IN THE GALAXY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cowsik, R.; Madziwa-Nussinov, T., E-mail: cowsik@physics.wustl.edu

2016-08-20

In this paper we note that the spectral intensities of antiprotons observed in Galactic cosmic rays in the energy range ∼1–300 GeV by BESS, PAMELA, and AMS instruments display nearly the same spectral shape as that generated by primary cosmic rays through their interaction with matter in the interstellar medium, without any significant modifications. More importantly, a constant residence time of ∼2.3 ± 0.7 million years in the Galactic volume, independent of the energy of cosmic rays, matches the observed intensities. A small additional component of secondary antiprotons in the energy range below 10 GeV, generated in cocoon-like regions surroundingmore » the cosmic-ray sources, seems to be present. We discuss this result in the context of observations of other secondary components such as positrons and boron, and the bounds on anisotropy of cosmic rays. In the nested leaky-box model the spectral intensities of antiprotons and positrons can be interpreted as secondary products of cosmic-ray interactions.« less

The Effect of Molecular Contamination on the Emissivity Spectral Index in Orion A

NASA Astrophysics Data System (ADS)

Coudé, Simon; Bastien, Pierre; Drabek, Emily; Johnstone, Doug; Hatchell, Jennifer

2013-07-01

The emissivity spectral index is a critical component in the study of the physical properties of dust grains in cold and optically thin interstellar star forming regions. Since submillimeter astronomy is an ideal tool to measure the thermal emission of those dust grains, it can be used to characterize this important parameter. We present the SCUBA-2 shared risks observations at 450 μm and 850 μm of the Orion A molecular cloud obtained at the James-Clerk-Maxwell telescope. Previous studies showed that molecular emission lines can also contribute significantly to the measured fluxes in those continuum bands. We use HARP 12CO 3-2 maps to evaluate the total molecular line contamination in the SCUBA-2 maps and its effect on the determination of the spectral index in highly contaminated areas. With the corrected fluxes, we have obtained new spectral index maps for different regions of the well-known integral-shaped filament. This work is part of an ongoing effort to characterize the properties of star forming regions in the Gould belt with the new instruments available at the JCMT.

Laser Induced Fluorescence Spectroscopy of Neutral and Ionized Polycyclic Aromatic Hydrocarbons in the Cosmic Simulation Chamber

NASA Technical Reports Server (NTRS)

Bejaoui, Salma; Salama, Farid; Contreras, Cesar; Sciamma O'Brien, Ella; Foing, Bernard; Pascale, Ehrenfreund

2015-01-01

Polycyclic aromatic hydrocarbon (PAH) molecules are considered the best carriers to account for the ubiquitous infrared emission bands. PAHs have also been proposed as candidates to explain the diffuse interstellar bands (DIBs), a series of absorption features seen on the interstellar extinction curve and are plausible carriers for the extended red emission (ERE), a photoluminescent process associated with a wide variety of interstellar environments. Extensive efforts have been devoted over the past two decades to characterize the physical and chemical properties of PAH molecules and ions in space. Absorption spectra of PAH molecules and ions trapped in solid matrices have been compared to the DIBs. Absorption spectra of several cold, isolated gas-phase PAHs have also been measured under experimental conditions that mimic the interstellar conditions. The purpose of this study is to provide a new dimension to the existing spectroscopic database of neutral and single ionized PAHs that is largely based on absorption spectra by adding emission spectroscopy data. The measurements are based on the laser induced fluorescence (LIF) technique and are performed with the Pulsed Discharge Nozzle (PDN) of the COSmIC laboratory facility at NASA Ames laboratory. The PDN generates a plasma in a free supersonic jet expansion to simulate the physical and the chemical conditions in interstellar environments. We focus, here, on the fluorescence spectra of large neutral PAHs and their cations where there is a lack of fluorescence spectroscopy data. The astronomical implications of the data (e.g., ERE) are examined.

Submillimeter Measurements of Photolysis Products in Interstellar Ice Analogs: A New Experimental Technique

NASA Technical Reports Server (NTRS)

Milam, Stefanie N.; Weaver, Susanna Widicus

2012-01-01

Over 150 molecular species have been confirmed in space, primarily by their rotational spectra at millimeter/submillimeter wavelengths, which yield an unambiguous identification. Many of the known interstellar organic molecules cannot be explained by gas-phase chemistry. It is now presumed that they are produced by surface reactions of the simple ices and/or grains observed and released into the gas phase by sublimation, sputtering, etc. Additionally, the chemical complexity found in meteorites and samples returned from comets far surpasses that of the remote detections for the interstellar medium (ISM), comets, and planetary atmospheres. Laboratory simulations of interstellar/cometary ices have found, from the analysis of the remnant residue of the warmed laboratory sample, that such molecules are readily formed; however, it has yet to be determined if they are formed during the warm phase or within the ice during processing. Most analysis of the ice during processing reveals molecular changes, though the exact quantities and species formed are highly uncertain with current techniques due to overwhelming features of simple ices. Remote sensing with high resolution spectroscopy is currently the only method to detect trace species in the ISM and the primary method for comets and icy bodies in the Solar System due to limitations of sample return. We have recently designed an experiment to simulate interstellar/cometary/planetary ices and detect trace species employing the same techniques used for remote observations. Preliminary results will be presented.

Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Hydrocarbon Cations. 3; The Polyacenes Anthracene, Tetracence, and Pentacene

NASA Technical Reports Server (NTRS)

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

1995-01-01

Gaseous, ionized polycyclic aromatic hydrocarbons (PAHS) are thought to be responsible for a very common family of interstellar infrared emission bands. Unfortunately, very little infrared spectroscopic data are available on ionized PAHS. Here we present the near- and mid-infrared spectra of the polyacene cations anthracene, tetracene, and pentacene. We also report the vibrational frequencies and relative intensities of the pentacene anion. The cation bands corresponding to the CC modes are typically about 10-20 times more intense than those of the CH out-of-plane bending vibrations. For the cations the CC stretching and CH in-plane bending modes give rise to bands which are an order of magnitude stronger than for the neutral species, and the CH out-of-plane bends produce bands which are 3-20 times weaker than in the neutral species. This behavior is similar to that found for most other PAH cations. The most intense PAH cation bands fall within the envelopes of the most intense interstellar features. The strongest absorptions in the polyacenes anthracene, tetracene, and pentacene tend to group around 1400/cm (between about 1340 and 1500/cm) and near 1180/cm, regions of only moderate interstellar emission. These very strong polyacene bands tend to fall in gaps in the spectra of the other PAH cations studied to date suggesting that while PAHs with polyacene structures may contribute to specific regions of the interstellar emission spectra, they are not dominant members of the interstellar PAH family.

Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Hydrocarbon Cations. 3. The Polyacenes Anthracene, Tetracene, and Pentacene

NASA Technical Reports Server (NTRS)

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

1995-01-01

Gaseous, ionized Polycyclic Aromatic Hydrocarbons (PAH's) are thought to be responsible for a very common family of interstellar infrared emission bands. Unfortunately, very little infrared spectroscopic data are available on ionized PAH's. Here we present the near- and mid-infrared spectra of the polyacene cations anthracene, tetracene, and pentacene. We also report the vibrational frequencies and relative intensities of the pentacene anion. The cation bands corresponding to the CC modes are typically about 10-20 times more intense than those of the CH out-of-plane bending vibrations. For the cations the CC stretching and CH in-plane bending modes give rise to bands which are an order of magnitude stronger than for the neutral species, and the CH out-of-plane bends produce bands which are 3-20 times weaker than in the neutral species. This behavior is similar to that found for most other PAH cations. The most intense PAH cation bands fall within the envelopes of the most intense interstellar features. The strongest absorptions in the polyacenes anthracene, tetracene, and pentacene tend to group around 1400 / cm (between about 1340 and 1500 / cm) and near 1180 /cm, regions of only moderate interstellar emission. These very strong polyacene bands tend to fall in gaps in the spectra of the other PAH cations studied to date suggesting that while PAHs with polyacene structures may contribute to specific regions of the interstellar emission spectra, they are not dominant members of the interstellar PAH family.

The Nature of Carbon Dioxide Bearing Ices in Quiescent Molecular Clouds

NASA Astrophysics Data System (ADS)

Whittet, D. C. B.; Cook, A. M.; Chiar, J. E.; Pendleton, Y. J.; Shenoy, S. S.; Gerakines, P. A.

2009-04-01

The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO2 near 15 μm has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC 5146). We show the profile of the feature to be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20 K. The polar component accounts for ~85% of the CO2 in the line of sight. We compare for the first time 15 μm profiles in three widely separated dark clouds (Taurus, Serpens, and IC 5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO2/H2O ratio in the three clouds have little or no effect on the 15 μm profile. The abundance of elemental oxygen in the ices appears to be a unifying factor, displaying consistent behavior in the three clouds. We conclude that the ice formation process is robust and uniformly efficient, notwithstanding compositional variations arising from differences in how the O is distributed between the primary species (H2O, CO2, and CO) in the ices.

ISM DUST GRAINS AND N-BAND SPECTRAL VARIABILITY IN THE SPATIALLY RESOLVED SUBARCSECOND BINARY UY Aur

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skemer, Andrew J.; Close, Laird M.; Hinz, Philip M.

2010-03-10

The 10 {mu}m silicate feature is an essential diagnostic of dust-grain growth and planet formation in young circumstellar disks. The Spitzer Space Telescope has revolutionized the study of this feature, but due to its small (85 cm) aperture, it cannot spatially resolve small/medium-separation binaries ({approx}<3''; {approx}< 420 AU) at the distances of the nearest star-forming regions ({approx}140 pc). Large, 6-10 m ground-based telescopes with mid-infrared instruments can resolve these systems. In this paper, we spatially resolve the 0.''88 binary, UY Aur, with MMTAO/BLINC-MIRAC4 mid-infrared spectroscopy. We then compare our spectra to Spitzer/IRS (unresolved) spectroscopy, and resolved images from IRTF/MIRAC2, Keck/OSCIR,more » and Gemini/Michelle, which were taken over the past decade. We find that UY Aur A has extremely pristine, interstellar medium (ISM)-like grains and that UY Aur B has an unusually shaped silicate feature, which is probably the result of blended emission and absorption from foreground extinction in its disk. We also find evidence for variability in both UY Aur A and UY Aur B by comparing synthetic photometry from our spectra with resolved imaging from previous epochs. The photometric variability of UY Aur A could be an indication that the silicate emission itself is variable, as was recently found in EX Lupi. Otherwise, the thermal continuum is variable, and either the ISM-like dust has never evolved, or it is being replenished, perhaps by UY Aur's circumbinary disk.« less

The Origin of Dust in the Early Universe

NASA Technical Reports Server (NTRS)

Dwek, Eli

2011-01-01

In this talk I will describe the origin of dust in the early universe. I will be presenting observations of the spectral energy distribution of the galaxy J1148+5251, and present estimates of the dust mass in this high redshift (z=6.4) object. I will then discuss the origin of this dust, and the role of SN and AGB stars as dust sources, and the effect of SNRs on the destruction of dust in the interstellar medium of this galaxy.

The Origin of Dust in the Early Universe

NASA Technical Reports Server (NTRS)

Dwek, Eliahu

2010-01-01

In this talk I will describe the origin of dust in the early universe. I will be presenting observations of the spectral energy distribution of the galaxy J1148+5251, and present estimates of the dust mass in this high redshift (z=6.4) object. I will then discuss the origin of this dust, and the role of SN and AGB stars as dust sources, and the effect of SNRs on the destruction of dust in the interstellar medium of this galaxy.

Terahertz source requirements for molecular spectroscopy

NASA Astrophysics Data System (ADS)

De Lucia, Frank C.; Goyette, Thomas M.

1994-06-01

Molecular spectroscopy was the earliest application in the terahertz spectral region and remains one of the most important. With the development of modern technology, spectroscopy has expanded beyond the laboratory and is the basis for a number of important remote sensing systems, especially in atmospheric science and studies of the interstellar medium. Concurrently, these spectroscopic applications have been one of the prime motivators for the development of terahertz technology. This paper will review these issues in the context of the requirements placed on future technology developments by spectroscopic applications.

Terahertz source requirements for molecular spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Lucia, F.C.; Goyette, T.M.

1994-12-31

Molecular spectroscopy was the earliest application in the terahertz spectral region and remains one of the most important. With the development of modern technology, spectroscopy has expanded beyond the laboratory and is the basis for a number of important remote sensing systems, especially in atmospheric science and studies of the interstellar medium. Concurrently, these spectroscopic applications have been one of the prime motivators for the development of terahertz technology. This paper will review these issues in the context of the requirements placed on future technology developments by spectroscopic applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, M. L.; McLaughlin, M. A.; Lam, M. T.

We analyze dispersion measure (DM) variations of 37 millisecond pulsars in the nine-year North American Nanohertz Observatory for Gravitational Waves (NANOGrav) data release and constrain the sources of these variations. DM variations can result from a changing distance between Earth and the pulsar, inhomogeneities in the interstellar medium, and solar effects. Variations are significant for nearly all pulsars, with characteristic timescales comparable to or even shorter than the average spacing between observations. Five pulsars have periodic annual variations, 14 pulsars have monotonically increasing or decreasing trends, and 14 pulsars show both effects. Of the four pulsars with linear trends thatmore » have line-of-sight velocity measurements, three are consistent with a changing distance and require an overdensity of free electrons local to the pulsar. Several pulsars show correlations between DM excesses and lines of sight that pass close to the Sun. Mapping of the DM variations as a function of the pulsar trajectory can identify localized interstellar medium features and, in one case, an upper limit to the size of the dispersing region of 4 au. Four pulsars show roughly Kolmogorov structure functions (SFs), and another four show SFs less steep than Kolmogorov. One pulsar has too large an uncertainty to allow comparisons. We discuss explanations for apparent departures from a Kolmogorov-like spectrum, and we show that the presence of other trends and localized features or gradients in the interstellar medium is the most likely cause.« less

UV absorption investigation of ferromagnetically filled ultra-thick carbon onions, carriers of the 217.5 nm Interstellar Absorption Feature

NASA Astrophysics Data System (ADS)

Boi, Filippo S.; Zhang, Xiaotian; Ivaturi, Sameera; Liu, Qianyang; Wen, Jiqiu; Wang, Shanling

2017-12-01

Carbon nano-onions (CNOs) are fullerene-like structures which consist of quasi-spherical closed carbon shells. These structures have become a subject of great interest thanks to their characteristic absorption feature of interstellar origin (at 217.5 nm, 4.6 μm-1). An additional extinction peak at 3.8 μm-1 has also been reported and attributed to absorption by graphitic residues between the as-grown CNOs. Here, we report the ultraviolet absorption properties of ultra-thick CNOs filled with FePt3 crystals, which also exhibit two main absorption peaks—features located at 4.58 μm-1 and 3.44 μm-1. The presence of this additional feature is surprising and is attributed to nonmagnetic graphite flakes produced as a by-product in the pyrolysis experiment (as confirmed by magnetic separation methods). Instead, the feature at 4.58 μm-1 is associated with the π-plasmonic resonance of the CNOs structures. The FePt3 filled CNOs were fabricated in situ by an advanced one-step fast process consisting in the direct sublimation and pyrolysis of two molecular precursors, namely, ferrocene and dichloro-cyclooctadiene-platinum in a chemical vapour deposition system. The morphological, structural, and magnetic properties of the as-grown filled CNOs were characterized by a means of scanning and transmission electron microscopy, X-ray diffraction, and magnetometry.

Photochemistry of PAHs in cosmic water ice. The effect of concentration on UV-VIS spectroscopy and ionization efficiency

NASA Astrophysics Data System (ADS)

Cuylle, Steven H.; Allamandola, Louis J.; Linnartz, Harold

2014-02-01

Context. Observations and models show that polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium. Like other molecules in dense clouds, PAHs accrete onto interstellar dust grains, where they are embedded in an ice matrix dominated by water. In the laboratory, mixed molecular ices (not containing PAHs) have been extensively studied using Fourier transform infrared absorption spectroscopy. Experiments including PAHs in ices have started, however, the concentrations used are typically much higher than the concentrations expected for interstellar ices. Optical spectroscopy offers a sensitive alternative. Aims: We report an experimental study of the effect PAH concentration has on the electronic spectra and the vacuum UV (VUV) driven processes of PAHs in water-rich ices. The goal is to apply the outcome to cosmic ices. Methods: Optical spectroscopic studies allow us to obtain in-situ and quasi real-time electronic solid state spectra of two prototypical PAHs (pyrene and coronene) embedded in water ice under VUV photoprocessing. The study is carried out on PAH:H2O concentrations in the range of 1:30 000 to pure PAH, covering the temperature range from 12 to 125 K. Results: PAH concentration strongly influences the efficiency of PAH cation formation. At low concentrations, ionization efficiencies are over 60% dropping to about 15% at 1:1000. Increasing the PAH concentration reveals spectral broadening in neutral and cation PAH spectra attributed to PAH clustering inside the ice. At the PAH concentrations expected for interstellar ices, some 10 to 20% may be present as cations. The presence of PAHs in neutral and ion form will add distinctive absorption bands to cosmic ice optical spectra and this may serve as a tool to determine PAH concentrations.

Cooked GEMS - Insights into the Hot Origins of Crystalline Silicates in Circumstellar Disks and the Cold Origins of GEMS

NASA Technical Reports Server (NTRS)

Brownlee, D. E.; Joswiak, D. J.; Bradley, J. P.; Matrajt, G.; Wooden, D. H.

2005-01-01

The comparison of interstellar, circumstellar and primitive solar nebula silicates has led to a significant conundrum in the understanding of the nature of solid materials that begin the planet forming processes. Crystalline silicates are found in circumstellar regions around young stars and also evolved stars ejecting particles into the interstellar medium (ISM) but they are not seen in the interstellar medium itself, the source material for star and planet formation. Crystalline silicates are minor to major components of all known early solar system materials that have been examined as meteorites or interplanetary dust samples. The strong presence of Mg-rich crystalline silicates in Oort cloud comets and their minor presence in some Kuiper belt comets is also indicated by 11.2 m peak in approx. 10 microns "silicate" infrared feature. This evidence strongly indicates that Mg-rich crystalline silicates were abundant components of the solar nebula disk out to at least 10 AU, and present out to 30 AU.

Primary gamma rays. [resulting from cosmic ray interaction with interstellar matter

NASA Technical Reports Server (NTRS)

Fichtel, C. E.

1974-01-01

Within this galaxy, cosmic rays reveal their presence in interstellar space and probably in source regions by their interactions with interstellar matter which lead to gamma rays with a very characteristic energy spectrum. From the study of the intensity of the high energy gamma radiation as a function of galactic longitude, it is already clear that cosmic rays are almost certainly not uniformly distributed in the galaxy and are not concentrated in the center of the galaxy. The galactic cosmic rays appear to be tied to galactic structural features, presumably by the galactic magnetic fields which are in turn held by the matter in the arm segments and the clouds. On the extragalactic scale, it is now possible to say that cosmic rays are not universal at the density seen near the earth. The diffuse celestial gamma ray spectrum that is observed presents the interesting possibility of cosmological studies and possible evidence for a residual universal cosmic ray density, which is much lower than the present galactic cosmic ray density.

Extended nebular emission in CALIFA early-type galaxies

NASA Astrophysics Data System (ADS)

Gomes, J. M.; Papaderos, P.; Kehrig, C.; Vílchez, J. M.; Lehnert, M. D.

2015-02-01

The morphological, spectroscopic and kinematical properties of the warm interstellar medium ( wim ) in early-type galaxies (ETGs) hold key observational constraints to nuclear activity and the buildup history of these massive quiescent systems. High-quality integral field spectroscopy (IFS) data with a wide spectral and spatial coverage, such as those from the CALIFA survey, offer a precious opportunity for advancing our understanding in this respect. We use deep IFS data from CALIFA (califa.caha.es) to study the wim over the entire extent and optical spectral range of 32 nearby ETGs. We find that all ETGs in our sample show faint (Hα equivalent width EW(Hα)~0.5 ... 2 Å) extranuclear nebular emission extending out to >=2 Petrosian50 radii. Confirming and strengthening our conclusions in Papaderos et al. (2013, hereafter P13) we argue that ETGs span a broad continuous sequence with regard to the properties of their wim , and they can be roughly subdivided into two characteristic classes. The first one (type i) comprises ETGs with a nearly constant EW(Hα)~1-3 Å in their extranuclear component, in quantitative agreement with (even though, no proof for) the hypothesis of photoionization by the post-AGB stellar component being the main driver of extended wim emission. The second class (type ii) consists of virtually wim -evacuated ETGs with a large Lyman continuum (Ly c) photon escape fraction and a very low (<=0.5 Å) EW(Hα) in their nuclear zone. These two ETG classes appear indistinguishable from one another by their LINER-specific emission-line ratios. Additionally, here we extend the classification by P13 by the class i+ which stands for a subset of type i ETGs with low-level star-forming activity in contiguous spiral-arm like features in their outermost periphery. These faint features, together with traces of localized star formation in several type i&i+ systems point to a non-negligible contribution from young massive stars to the global ionizing photon budget in ETGs.

High sensitivity, wide coverage, and high-resolution NIR non-cryogenic spectrograph, WINERED

NASA Astrophysics Data System (ADS)

Ikeda, Yuji; Kobayashi, Naoto; Kondo, Sohei; Otsubo, Shogo; Hamano, Satoshi; Sameshima, Hiroaki; Yoshikawa, Tomoshiro; Fukue, Kei; Nakanishi, Kenshi; Kawanishi, Takafumi; Nakaoka, Tetsuya; Kinoshita, Masaomi; Kitano, Ayaka; Asano, Akira; Takenaka, Keiichi; Watase, Ayaka; Mito, Hiroyuki; Yasui, Chikako; Minami, Atsushi; Izumu, Natsuko; Yamamoto, Ryo; Mizumoto, Misaki; Arasaki, Takayuki; Arai, Akira; Matsunaga, Noriyuki; Kawakita, Hideyo

2016-08-01

Near-infrared (NIR) high-resolution spectroscopy is a fundamental observational method in astronomy. It provides significant information on the kinematics, the magnetic fields, and the chemical abundances, of astronomical objects embedded in or behind the highly extinctive clouds or at the cosmological distances. Scientific requirements have accelerated the development of the technology required for NIR high resolution spectrographs using 10 m telescopes. WINERED is a near-infrared (NIR) high-resolution spectrograph that is currently mounted on the 1.3 m Araki telescope of the Koyama Astronomical Observatory in Kyoto-Sangyo University, Japan, and has been successfully operated for three years. It covers a wide wavelength range from 0.90 to 1.35 μm (the z-, Y-, and J-bands) with a spectral resolution of R = 28,000 (Wide-mode) and R = 80,000 (Hires-Y and Hires-J modes). WINERED has three distinctive features: (i) optics with no cold stop, (ii) wide spectral coverage, and (iii) high sensitivity. The first feature, originating from the Joyce proposal, was first achieved by WINERED, with a short cutoff infrared array, cold baffles, and custom-made thermal blocking filters, and resulted in reducing the time for development, alignment, and maintenance, as well as the total cost. The second feature is realized with the spectral coverage of Δλ/λ 1/6 in a single exposure. This wide coverage is realized by a combination of a decent optical design with a cross-dispersed echelle and a large format array (2k x 2k HAWAII- 2RG). The Third feature, high sensitivity, is achieved via the high-throughput optics (>60 %) and the very low noise of the system. The major factors affecting the high throughput are the echelle grating and the VPH cross-disperser with high diffraction efficiencies of 83 % and 86 %, respectively, and the high QE of HAWAII-2RG (83 % at 1.23 μm). The readout noise of the electronics and the ambient thermal background radiation at longer wavelengths could be major noise sources. The readout noise is 5.3 e- for NDR = 32, and the ambient thermal background is significantly reduced to 0.05 e- pix-1 sec-1 at 273 K. As a result, the limiting magnitudes of WINERED are estimated to be mJ = 13.8 mag for the 1.3 m telescope, mJ = 16.9 mag for the 3.6 m telescope, and mJ = 19.2 mag for 10 m telescope with adoptive optics, respectively. Finally, we introduce some scientific highlights provided by WINERED for both emission and absorption line objects in the fields of stars, the interstellar medium, and the solar system.

Probing the Origin and Evolution of Interstellar and Protoplanetary Biogenic Ices with SPHEREx

NASA Astrophysics Data System (ADS)

Melnick, Gary; SPHEREx Science Team

2018-01-01

Many of the most important building blocks of life are locked in interstellar and protoplanetary ices. Examples include H2O, CO, CO2, and CH3OH, among others. There is growing evidence that within the cores of dense molecular clouds and the mid-plane of protoplanetary disks the abundance of these species in ices far exceeds that in the gas phase. As a result, collisions between ice-bearing bodies and newly forming planets are thought to be a major means of delivering these key species to young planets. There currently exist fewer than 250 ice absorption spectra toward Galactic molecular clouds, which is insufficient to reliably trace the ice content of clouds through the various evolutionary stages of collapse to form stars and planets. Likewise, the current number of spectra is inadequate to assess the effects of environment, such as cloud density and temperature, presence or absence of embedded sources, external FUV and X-ray radiation, gas-phase composition, or cosmic-ray ionization rate, on the ice composition of clouds at similar stages of evolution. Ultimately, our goal is to understand how these findings connect to our own Solar System.SPHEREx will be a game changer for the study of interstellar, circumstellar, and protoplanetary disk ices. SPHEREx will obtain spectra over the entire sky in the optical and near-IR, including the 2.5 to 5.0 micron region, which contains the above biogenic ice features. SPHEREx will detect millions of potential background continuum point sources already catalogued by NASA’s Wide-field Infrared Survey Explorer (WISE) at 3.4 and 4.6 microns for which there is evidence for intervening gas and dust based on the 2MASS+WISE colors with sufficient sensitivity to yield ice absorption spectra with SNR ≥ 100 per spectral resolution element. The resulting > 100-fold increase in the number of high-quality ice absorption spectra toward a wide variety of regions distributed throughout the Galaxy will reveal correlations between ice content and environment not possible with current spectra or the limited number that will be obtained with JWST. Finally, because SPHEREx and JWST will overlap beyond 2022, SPHEREx will provide JWST with a complete ice source catalog for follow-up.

Observations of Sk-69 deg 203 and the interstellar extinction towards SN 1987A

NASA Technical Reports Server (NTRS)

Fitzpatrick, Edward L.; Walborn, Nolan R.

1990-01-01

Optical and UV spectroscopic observations of the Large Magellanic Cloud (LMC) star Sk-69 deg 203 are discussed. The optical data reveal Sk-69 deg 203 to be a BO.7 Ia supergiant with a moderate nitrogen enhancement, and its UV spectrum is consistent with this classification. UV interstellar extinction curves were constructed for the star using, as flux standards, two lightly reddened LMS supergiants, which bracket Sk-69 deg 203's spectral type. The resultant extinction curves are consistent with the extinction law derived previously for the 30 Doradus region, and the results for Sk-69 deg 203 suggest that the general 30 Doradus extinction law is appropriate for dereddening the observed fluxes of SN 1987A. Published H I 21 observations place SN 1987A in a region with a strong E-W gradient in the total hydrogen content. Comparison with the H I column density implied by the reddening indicates that the supernova is imbedded approximately in the middle of the main H I complex.

Measurement of cosmic ray positron and negatron spectra between 50 and 800 MeV. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Daugherty, J. K.

1974-01-01

A balloon-borne magnetic spectrometer was used to measure the spectra of cosmic ray positrons and negatrons at energies between 50 and 800 MeV. Comparisons of the separate positron and negatron spectra observed near the earth with their expected intensities in interstellar space can be used to investigate the complex (and variable) interaction of galactic cosmic rays with the expanding solar wind. The present measurements, which have established finite values or upper limits for the positron and negatron spectral between 50 and 800 MeV, have confirmed earlier evidence for the existence of a dominant component of negatrons from primary sources in the galaxy. The present results are shown to be consistent with the hypothesis that the positron component is in fact mainly attributable to collisions between cosmic ray nuclei and the interstellar gas. The estimate of the absolute intensities confirm the indications from neutron monitors that in 1972 the interplanetary cosmic ray intensities were already recovering toward their high levels observed in 1965.

The far-infrared spectrum of the OH radical

NASA Technical Reports Server (NTRS)

Brown, J. M.; Schubert, J. E.; Evenson, K. M.; Radford, H. E.

1982-01-01

It is thought likely that the study of spectral lines in the far-infrared might provide at least as much information about the physics and chemistry of the interstellar environment as radioastronomy. However, by comparison with the microwave region, the far-infrared is largely unexplored. There is a pressing need for good laboratory data to aid searches and assignments of spectra from the interstellar clouds and nebulae. Brown et al. (1981) have conducted a study of the laser magnetic resonance (LMR) spectrum of the OH radical in its ground state at far-infrared wavelengths. The present investigation is concerned with the computation of the frequencies of individual hyperfine transitions involving all rotational levels up to J = 4 1/2. The results of the calculation are presented in a table. The results are summarized in a diagram which shows the low-lying energy levels of OH. The frequencies of transitions between levels studied directly in the LMR spectrum are quite reliable.

Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

NASA Technical Reports Server (NTRS)

Cox, D. P.; Anderson, P. R.

1981-01-01

An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

On the Time Variation of Dust Extinction and Gas Absorption for Type Ia Supernovae Observed through a Nonuniform Interstellar Medium

NASA Astrophysics Data System (ADS)

Huang, X.; Aldering, G.; Biederman, M.; Herger, B.

2017-11-01

For Type Ia supernovae (SNe Ia) observed through a nonuniform interstellar medium (ISM) in its host galaxy, we investigate whether the nonuniformity can cause observable time variations in dust extinction and in gas absorption due to the expansion of the SN photosphere with time. We show that, owing to the steep spectral index of the ISM density power spectrum, sizable density fluctuation amplitudes at the length scale of typical ISM structures (≳ 10 {pc}) will translate to much smaller fluctuations on the scales of an SN photosphere. Therefore, the typical amplitude of time variation due to a nonuniform ISM, of absorption equivalent widths, and of extinction, would be small. As a result, we conclude that nonuniform ISM density should not impact cosmology measurements based on SNe Ia. We apply our predictions based on the ISM density power-law power spectrum to the observations of two highly reddened SNe Ia, SN 2012cu and SN 2014J.

On the Time Variation of Dust Extinction and Gas Absorption for Type Ia Supernovae Observed Through Non-uniform Interstellar Medium

NASA Astrophysics Data System (ADS)

Huang, Xiaosheng; Aldering, Gregory; Biederman, Moriah; Herger, Brendan

2018-01-01

For Type Ia supernovae (SNe Ia) observed through a non-uniform interstellar medium (ISM) in its host galaxy, we investigate whether the non-uniformity can cause observable time variations in dust extinction and in gas absorption due to the expansion of the SN photosphere with time. We show that, owing to the steep spectral index of the ISM density power spectrum, sizable density fluctuation amplitudes at the length scale of typical ISM structures (>~ 10 pc) will translate to much smaller fluctuations on the scales of a SN photosphere. Therefore the typical amplitude of time variation due to non-uniform ISM, of absorption equivalent widths and of extinction, would be small. As a result, we conclude that non-uniform ISM density should not impact cosmology measurements based on SNe Ia. We apply our predictions based on the ISM density power law power spectrum to the observations of two highly reddened SNe Ia, SN 2012cu and SN 2014J.

Ultraviolet photometry from the orbiting astronomical observatory. XVI - The stellar Lyman-alpha absorption line

NASA Technical Reports Server (NTRS)

Savage, B. D.; Panek, R. J.

1974-01-01

The stellar Lyman-alpha line at 1216 A was observed in 29 lightly reddened stars of spectral type B2.5 to B9 by a far-UV spectrophotometer on OAO-2. The equivalent widths obtained range from 15 A at type B2.5 to 65 A at type B8; in the late-B stars, the L-alpha line removes 2 to 3% of the total stellar flux. In this sampling, the strength of the L-alpha line correlates well with measures of the Balmer discontinuity and Balmer line strengths; luminosity classification does not seem to affect the line strength. The observed line widths also agree with the predictions of Mihala's grid of non-LTE model atmospheres. In some cases, the L-alpha line influences the interstellar column densities reported in the interstellar OAO-2 L-alpha survey. Hence, these data toward lightly reddened B2 and B1.5 stars should be regarded as upper limits only.

The Astrophysical Weeds: Rotational Transitions in Excited Vibrational States

NASA Astrophysics Data System (ADS)

Alonso, José L.; Kolesniková, Lucie; Alonso, Elena R.; Mata, Santiago

2017-06-01

The number of unidentified lines in the millimeter and submillimeter wave surveys of the interstellar medium has grown rapidly. The major contributions are due to rotational transitions in excited vibrational states of a relatively few molecules that are called the astrophysical weeds. necessary data to deal with spectral lines from astrophysical weeds species can be obtained from detailed laboratory rotational measurements in the microwave and millimeter wave region. A general procedure is being used at Valladolid combining different time and/or frequency domain spectroscopic tools of varying importance for providing the precise set of spectroscopic constants that could be used to search for this species in the ISM. This is illustrated in the present contribution through its application to several significant examples. Fortman, S. M., Medvedev, I. R., Neese, C.F., & De Lucia, F.C. 2010, ApJ,725, 1682 Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile, L. Kolesniková, E. R. Alonso, S. Mata, and J. L. Alonso, The Astrophysical Journal Supplement Series 2017, (in press).

The Evolution of the Interstellar Medium in the Mildly Disturbed Spiral Galaxy NGC 4647

NASA Astrophysics Data System (ADS)

Young, L. M.; Rosolowsky, E.; van Gorkom, J. H.; Lamb, S. A.

2006-10-01

We present matched-resolution maps of H I and CO emission in the Virgo Cluster spiral NGC 4647. The galaxy shows a mild kinematic disturbance in which one side of the rotation curve flattens but the other side continues to rise. This kinematic asymmetry is coupled with a dramatic asymmetry in the molecular gas distribution but not in the atomic gas. An analysis of the gas column densities and the interstellar pressure suggests that the H2/H I surface density ratio on the east side of the galaxy is 3 times higher than expected from the hydrostatic pressure contributed by the mass of the stellar disk. We discuss the probable effects of ram pressure, gravitational interactions, and asymmetric potentials on the interstellar medium and suggest it is likely that a m=1 perturbation in the gravitational potential could be responsible for all of the galaxy's features. Kinematic disturbances of the type seen here are common, but the curious thing about NGC 4647 is that the molecular distribution appears more disturbed than the H I distribution. Thus, it is the combination of the two gas phases that provides such interesting insight into the galaxy's history and into models of the interstellar medium.

The peculiar behaviour of the 5780 and 5797 DIBs in HD25137

NASA Technical Reports Server (NTRS)

Porceddu, Ignazio; Benvenuti, P.

1994-01-01

The interstellar environment close to the high latitude molecular cloud Lynds 1569 (L1569, Lynds 1962), also known as MBM 18 (Magnani, Blitz and Mundy, 1985), has been analyzed by Penrase et al. (1990) and Penrase (1993). Their observations of the CH, CH(sup+), and CN molecular features, are consistent with a region having a high molecular and reduced dust content. They also observed the background star HD 24263- located 8 degrees far from the center of L1569 - reporting a CH rich line of sight and the presence of two intervening clouds from a sodium lines spectra. The infrared excess which has been revealed by the IRAS survey at 12 microns might suggest the presence of PAH's molecules, the well know candidate for the Unidentified Infrared Bands and Diffuse Interstellar Bands. This interesting scenario led to the investigation of the behavior of the diffuse interstellar bands toward HD 25137, which is supposed to be a background object for L1569 (Penrase et al., 1990); as well as the field star HD 24263. As part of a wider observational program devoted to study the HLC's special environments, the observations of the diffuse interstellar bands (DIB's) at 5780 and 5797 lambda lambda in the direction of the two above mentioned stars, HD 24263 and HD 25137 are presented here.

GAME: GAlaxy Machine learning for Emission lines

NASA Astrophysics Data System (ADS)

Ucci, G.; Ferrara, A.; Pallottini, A.; Gallerani, S.

2018-06-01

We present an updated, optimized version of GAME (GAlaxy Machine learning for Emission lines), a code designed to infer key interstellar medium physical properties from emission line intensities of ultraviolet /optical/far-infrared galaxy spectra. The improvements concern (a) an enlarged spectral library including Pop III stars, (b) the inclusion of spectral noise in the training procedure, and (c) an accurate evaluation of uncertainties. We extensively validate the optimized code and compare its performance against empirical methods and other available emission line codes (PYQZ and HII-CHI-MISTRY) on a sample of 62 SDSS stacked galaxy spectra and 75 observed HII regions. Very good agreement is found for metallicity. However, ionization parameters derived by GAME tend to be higher. We show that this is due to the use of too limited libraries in the other codes. The main advantages of GAME are the simultaneous use of all the measured spectral lines and the extremely short computational times. We finally discuss the code potential and limitations.

Scattering characteristics of relativistically moving concentrically layered spheres

NASA Astrophysics Data System (ADS)

Garner, Timothy J.; Lakhtakia, Akhlesh; Breakall, James K.; Bohren, Craig F.

2018-02-01

The energy extinction cross section of a concentrically layered sphere varies with velocity as the Doppler shift moves the spectral content of the incident signal in the sphere's co-moving inertial reference frame toward or away from resonances of the sphere. Computations for hollow gold nanospheres show that the energy extinction cross section is high when the Doppler shift moves the incident signal's spectral content in the co-moving frame near the wavelength of the sphere's localized surface plasmon resonance. The energy extinction cross section of a three-layer sphere consisting of an olivine-silicate core surrounded by a porous and a magnetite layer, which is used to explain extinction caused by interstellar dust, also depends strongly on velocity. For this sphere, computations show that the energy extinction cross section is high when the Doppler shift moves the spectral content of the incident signal near either of olivine-silicate's two localized surface phonon resonances at 9.7 μm and 18 μm.

[The research on separating and extracting overlapping spectral feature lines in LIBS using damped least squares method].

PubMed

Wang, Yin; Zhao, Nan-jing; Liu, Wen-qing; Yu, Yang; Fang, Li; Meng, De-shuo; Hu, Li; Zhang, Da-hai; Ma, Min-jun; Xiao, Xue; Wang, Yu; Liu, Jian-guo

2015-02-01

In recent years, the technology of laser induced breakdown spectroscopy has been developed rapidly. As one kind of new material composition detection technology, laser induced breakdown spectroscopy can simultaneously detect multi elements fast and simply without any complex sample preparation and realize field, in-situ material composition detection of the sample to be tested. This kind of technology is very promising in many fields. It is very important to separate, fit and extract spectral feature lines in laser induced breakdown spectroscopy, which is the cornerstone of spectral feature recognition and subsequent elements concentrations inversion research. In order to realize effective separation, fitting and extraction of spectral feature lines in laser induced breakdown spectroscopy, the original parameters for spectral lines fitting before iteration were analyzed and determined. The spectral feature line of' chromium (Cr I : 427.480 nm) in fly ash gathered from a coal-fired power station, which was overlapped with another line(FeI: 427.176 nm), was separated from the other one and extracted by using damped least squares method. Based on Gauss-Newton iteration, damped least squares method adds damping factor to step and adjust step length dynamically according to the feedback information after each iteration, in order to prevent the iteration from diverging and make sure that the iteration could converge fast. Damped least squares method helps to obtain better results of separating, fitting and extracting spectral feature lines and give more accurate intensity values of these spectral feature lines: The spectral feature lines of chromium in samples which contain different concentrations of chromium were separated and extracted. And then, the intensity values of corresponding spectral lines were given by using damped least squares method and least squares method separately. The calibration curves were plotted, which showed the relationship between spectral line intensity values and chromium concentrations in different samples. And then their respective linear correlations were compared. The experimental results showed that the linear correlation of the intensity values of spectral feature lines and the concentrations of chromium in different samples, which was obtained by damped least squares method, was better than that one obtained by least squares method. And therefore, damped least squares method was stable, reliable and suitable for separating, fitting and extracting spectral feature lines in laser induced breakdown spectroscopy.

The cosmic-ray and gas content of the Cygnus region as measured in γ -rays by the Fermi Large Area Telescope

DOE PAGES

Ackermann, M.

2012-02-01

Context. The Cygnus region hosts a giant molecular-cloud complex that actively forms massive stars. Interactions of cosmic rays with interstellar gas and radiation fields make it shine at γ-ray energies. Several γ-ray pulsars and other energetic sources are seen in this direction. Aims. In this paper we analyze the γ-ray emission measured by the Fermi Large Area Telescope in the energy range from 100 MeV to 100 GeV in order to probe the gas and cosmic-ray content on the scale of the whole Cygnus complex. The γ-ray emission on the scale of the central massive stellar clusters and from individualmore » sources is addressed elsewhere. Methods. The signal from bright pulsars is greatly reduced by selecting photons in their off-pulse phase intervals. We compare the diffuse γ-ray emission with interstellar gas maps derived from radio/mm-wave lines and visual extinction data. A general model of the region, including other pulsars and γ-ray sources, is sought. Results. The integral Hi emissivity above 100 MeV averaged over the whole Cygnus complex amounts to [2.06 ± 0.11 (stat.) +0.15 -0.84 (syst.)] × 10 -26 photons s -1 sr -1 H-atom -1, where the systematic error is dominated by the uncertainty on the Hi opacity to calculate its column densities. The integral emissivity and its spectral energy distribution are both consistent within the systematics with LAT measurements in the interstellar space near the solar system. The average XCO = N(H2)/WCO ratio is found to be [1.68 ± 0.05 (stat.) +0.87 -0.10 (Hi opacity)] × 1020 molecules cm -2 (K km s -1) -1, consistent with other LAT measurements in the Local Arm. We detect significant γ-ray emission from dark neutral gas for a mass corresponding to ~ 40% of what is traced by CO. The total interstellar mass in the Cygnus complex inferred from its γ-ray emission amounts to 8 +5 -1 × 106M⊙ at a distance of 1.4 kpc. Conclusions. Despite the conspicuous star formation activity and high masses of the interstellar clouds, the cosmic-ray population in the Cygnus complex averaged over a few hundred parsecs is similar to that of the local interstellar space.« less

The Cosmic-Ray and Gas Content of the Cygnus Region as Measured in Gamma Rays by the Fermi Large Area Telescope

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Belfiore, A.; Bellazzini, R.; Berenji, B.;

High Resolution Spectroscopy in the Far UV: Observations of the Interstellar Medium by IMAPS on ORFEUS-SPAS

NASA Astrophysics Data System (ADS)

Jenkins, Edward B.; Reale, Michael A.; Zucchino, Paul M.; Sofia, Ulysses J.

1996-09-01

The Interstellar Medium Absorption Profile Spectrograph (IMAPS) is an objectivegrating, echelle spectrograph built to observe the spectra of bright, hot stars over the spectral region 950 1150Å, below the wavelength coverage of HST. This instrument has a high wavelength resolving power, making it especially well suited for studies of interstellar absorption lines. Following a series of sounding rocket flights in the 1980's, IMAPS flew on its first Shuttle-launched orbital mission in September 1993, as a partner in the ORFEUS-SPAS program sponsored by the US and German Space Agencies, NASA and DARA. On ORFEUS-SPAS, IMAPS spent one day of orbital time observing the spectra of 10 O- and early B-type stars. In addition to outlining how IMAPS works, we document some special problems that had an influence on the data, and we explain the specific steps in data reduction that were employed to overcome them. This discussion serves as a basic source of information for people who may use archival data from this flight, as well as those who are interested in some specific properties of the data that will be presented in forthcoming research papers. IMAPS is scheduled to fly once again on ORFEUS-SPAS in late 1996. On this flight, 50% of the observing time available for IMAPS and two other spectrographs on the mission will be available to guest observers.

Phase transition between atomic and molecular hydrogen in nearby spiral galaxies

NASA Astrophysics Data System (ADS)

Tanaka, Ayako; Nakanishi, Hiroyuki; Kuno, Nario; Hirota, Akihiko

2014-06-01

We compared theoretical and observational molecular mass fractions (fmol: ratio of molecular gas density to total gas density) using observational data of ten nearby spiral galaxies. For determination of fmol, the three parameters-interstellar pressure P, UV radiation U, and metallicity Z-were obtained from the spectral line data of 12CO(J = 1-0), H I, Hα, [O III], and [O II]. Interstellar pressure was calculated with the sum of the hydrogen gas densities and the stellar potential based on the Ks-band data. For most data other than metallicity, we used archived NRO CO Atlas, THINGS, SINGS, and 2MASS data. For comparison, we also investigated the dependence of the CO-to-H2 conversion factor XCO. It was found that the theoretical fmol agreed with the observational fmol only when the interstellar pressure is calculated with both the gas density and stellar disk potential. To fit observations more accurately, either the metallicity or the UV radiation needs to be adjusted. It was also found that, in UV radiation scaling, scaling factor γ has a correlation with the diffuse fraction of the Hα emission line data, fDIG. As for XCO, it was shown that the difference between both values of fmol becomes the least when XCO is 1.0 × 1020 cm-2 (K km s-1)-1.

Variations on a theme - the evolution of hydrocarbon solids. I. Compositional and spectral modelling - the eRCN and DG models

NASA Astrophysics Data System (ADS)

Jones, A. P.

2012-04-01

Context. The compositional properties of hydrogenated amorphous carbons are known to evolve in response to the local conditions. Aims: We present a model for low-temperature, amorphous hydrocarbon solids, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, that can be used to study and predict the evolution of their properties in the interstellar medium. Methods: We adopt an adaptable and prescriptive approach to model these materials, which is based on a random covalent network (RCN) model, extended here to a full compositional derivation (the eRCN model), and a defective graphite (DG) model for the hydrogen poorer materials where the eRCN model is no longer valid. Results: We provide simple expressions that enable the determination of the structural, infrared and spectral properties of amorphous hydrocarbon grains as a function of the hydrogen atomic fraction, XH. Structural annealing, resulting from hydrogen atom loss, results in a transition from H-rich, aliphatic-rich to H-poor, aromatic-rich materials. Conclusions: The model predicts changes in the optical properties of hydrogenated amorphous carbon dust in response to the likely UV photon-driven and/or thermal annealing processes resulting, principally, from the radiation field in the environment. We show how this dust component will evolve, compositionally and structurally in the interstellar medium in response to the local conditions. Appendices A and B are available in electronic form at http://www.aanda.org

The extinction and dust-to-gas structure of the planetary nebula NGC 7009 observed with MUSE

NASA Astrophysics Data System (ADS)

Walsh, J. R.; Monreal-Ibero, A.; Barlow, M. J.; Ueta, T.; Wesson, R.; Zijlstra, A. A.

2016-04-01

Context. Dust plays a significant role in planetary nebulae. Dust ejected with the gas in the asymptotic giant branch (AGB) phase is subject to the harsh environment of the planetary nebula (PN) while the star is evolving towards a white dwarf. Dust surviving the PN phase contributes to the dust content of the interstellar medium. Aims: The morphology of the internal dust extinction has been mapped for the first time in a PN, the bright nearby Galactic nebula NGC 7009. The morphologies of the gas, dust extinction and dust-to-gas ratio are compared to the structural features of the nebula. Methods: Emission line maps in H Balmer and Paschen lines were formed from analysis of MUSE cubes of NGC 7009 observed during science verification of the instrument. The measured electron temperature and density from the same cube were employed to predict the theoretical H line ratios and derive the extinction distribution across the nebula. After correction for the interstellar extinction to NGC 7009, the internal AV/NH has been mapped for the first time in a PN. Results: The extinction map of NGC 7009 has considerable structure, broadly corresponding to the morphological features of the nebula. The dust-to-gas ratio, AV/NH, increases from 0.7 times the interstellar value to >5 times from the centre towards the periphery of the ionized nebula. The integrated AV/NH is about 2× the mean ISM value. A large-scale feature in the extinction map is a wave, consisting of a crest and trough, at the rim of the inner shell. The nature of this feature is investigated and instrumental and physical causes considered; no convincing mechanisms were identified to produce this feature, other than AGB mass loss variations. Conclusions: Extinction mapping from H emission line imaging of PNe with MUSE provides a powerful tool for revealing the properties of internal dust and the dust-to-gas ratio. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 060.A-9347(A).

The 1.4-2.7 micron spectrum of the point source at the galactic center

NASA Technical Reports Server (NTRS)

Treffers, R. R.; Fink, U.; Larson, H. P.; Gautier, T. N., III

1976-01-01

The spectrum of the 2-micron point source at the galactic center is presented over the range from 1.4 to 2.7 microns. The two-level-transition CO band heads are seen near 2.3 microns, confirming that the radiation from this source is due to a cool supergiant star. The heliocentric radial velocity is found to be - 173 (+ or -90) km/s and is consistent with the star being in orbit about a dense galactic nucleus. No evidence is found for Brackett-gamma emission, and no interstellar absorption features are seen. Upper limits for the column densities of interstellar H2, CH4, CO, and NH3 are derived.

Pilot Search for 54-MHz Maser Emission from Interstellar Hydroxyl Using LOFAR

NASA Astrophysics Data System (ADS)

Hoffman, Ian M.; Heald, G.; Oonk, R.; McKean, J.; Mol, J.; Hessels, J.; Toribio, C.; LOFAR Collaboration

2014-01-01

We present the results of the most sensitive search to date for the two 54-MHz spectral lines of the hydroxyl (OH) molecule. These are the preliminary results of a larger, planned observational campaign. The splitting of the rotational ground state of the hydroxyl molecule gives rise to the four familiar 1.7-GHz transitions by which OH is known in the interstellar medium. There are also two magnetic-dipole transitions among these states at frequencies of 53.2 MHz and 55.1 MHz. These 54-MHz transitions have never been detected astronomically. Because of the relative weakness of the magnetic-dipole emission process, it is expected that only maser emission will generate a detectable 54-MHz signal. Two previous searches have been conducted by other authors with other instruments toward Galactic sources of known 1720-MHz OH maser emission: three sources were searched at 55.1 MHz and two other sources were searched at 53.2 MHz, resulting in upper limits of approximately 30 Jy for spectral channels of 2 km/s in width. In preparation for our future observational campaign that will apply the unprecedented sensitivity of LOFAR to the search for 54-MHz OH emission, we conducted a pilot project using six hours of Commissioning Time. These observations employed 21 48-element stations and produced a spectral resolution of approximately 0.5 km/s for both the 53.2- and 55.1-MHz lines. This spectral resolution is a considerable improvement over previous searches since it is suitable both for resolving the characteristically narrow width of maser lines and for identifying radiofrequency interference. In our pilot observations, no emission was detected at either frequency with an upper limit of approximately 3 Jy. We observed the Galactic sources W75N and W3(OH), neither of which have been searched previously at either frequency. We discuss the astrophysical implications of these sensitive non-detections. LOFAR, the Low Frequency Array designed and constructed by ASTRON, has facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the International LOFAR Telescope (ILT) foundation under a joint scientific policy.

Comparison of the 3.36 micrometer feature to the ISM

NASA Technical Reports Server (NTRS)

Tokunaga, Alan T.; Brooke, Timothy Y.

1988-01-01

It has been noted that the 3.36 micrometer emission feature is not the same as that of any ISM band at 3.4 micrometer. This is documented herein. There is no convincing analog to the cometary 3.36 micrometer emission feature seen in the Interstellar Matter band. This fact suggests that if the carbonaceous material in comets came from the ISM, it was either further processed in the solar nebula or has a different appearance because of the different excitation environment of the sun and ISM.

Data Field Modeling and Spectral-Spatial Feature Fusion for Hyperspectral Data Classification.

PubMed

Liu, Da; Li, Jianxun

2016-12-16

Classification is a significant subject in hyperspectral remote sensing image processing. This study proposes a spectral-spatial feature fusion algorithm for the classification of hyperspectral images (HSI). Unlike existing spectral-spatial classification methods, the influences and interactions of the surroundings on each measured pixel were taken into consideration in this paper. Data field theory was employed as the mathematical realization of the field theory concept in physics, and both the spectral and spatial domains of HSI were considered as data fields. Therefore, the inherent dependency of interacting pixels was modeled. Using data field modeling, spatial and spectral features were transformed into a unified radiation form and further fused into a new feature by using a linear model. In contrast to the current spectral-spatial classification methods, which usually simply stack spectral and spatial features together, the proposed method builds the inner connection between the spectral and spatial features, and explores the hidden information that contributed to classification. Therefore, new information is included for classification. The final classification result was obtained using a random forest (RF) classifier. The proposed method was tested with the University of Pavia and Indian Pines, two well-known standard hyperspectral datasets. The experimental results demonstrate that the proposed method has higher classification accuracies than those obtained by the traditional approaches.

Supernova Remnants As Laboratories For Determining The Properties Of Ejecta Dust And The Processing Of Dust Grains In Shocks

NASA Astrophysics Data System (ADS)

Dwek, Eli; Temim, Tea

Recent infrared satellites, such as the Spitzer, Herschel, and WISE, have obtained a wealth of spectral and broadband data on the infrared (IR) emission from dust in supernova remnants (SNRs). Supernovae (SNe) are important producers of newly condensed dust during the early free-expansion phase of their evolution, and the dominant destroyers of dust during the subsequent remnant phase of their evolution. The infrared observations hold the key for determining their role in the origin and evolution of dust in the universe. We propose to model the composition, abundance, and size distribution of the dust in select Galactic and Magellanic Cloud remnants. As explained in detail below, the remnants were selected for the availability of IR and X-ray observations. All selected remnants have Spitzer IRS spectral data in the 5-35 μm regions which allow us to determine the effect of grain processing in the shock. Some have spectral maps that allow the distinction between the IR emission from SN-condensed and swept up circumstellar and interstellar dust. All remnants have also been covered by Spitzer, Herschel, and WISE imaging, and have existing X-ray Chandra and/or XMM observations. The dust in some remnants is radiatively-heated by a pulsar wind nebula, and in others collisionally- heated by shocked X-ray or line emitting gas. We will use physical models to calculate the radiative and collisional heating of SNR dust, the equilibrium or fluctuating dust temperatures, and the resulting IR emission for various dust compositions and size distributions. Specific examples of Cas A, SN1987A, the Crab Nebula, and Puppis A, are discussed in detail to illustrate our modeling approach. Our study will be the first comprehensive and physical analysis of a large sample of SNRs in different evolutionary states and different astrophysical environments. They will cover a wide range of interactions between the dust grains and their surroundings, including the radioactively- powered and/or shocked SN ejecta, hard X-rays and EUV radiation fields, and shocked circumstel- lar/interstellar gas. Our study will shed light on the evolution of dust grains from their explosive formation sites, through their violent injection into the ISM, and ultimate demise or survival as they travel through a network of interstellar shock waves. It will constitute a major advance in our understanding of the origin and evolution of dust in the Milky Way, in galaxies in general, and especially in the early universe.

FOCUSR: Feature Oriented Correspondence using Spectral Regularization–A Method for Precise Surface Matching

PubMed Central

Lombaert, Herve; Grady, Leo; Polimeni, Jonathan R.; Cheriet, Farida

2013-01-01

Existing methods for surface matching are limited by the trade-off between precision and computational efficiency. Here we present an improved algorithm for dense vertex-to-vertex correspondence that uses direct matching of features defined on a surface and improves it by using spectral correspondence as a regularization. This algorithm has the speed of both feature matching and spectral matching while exhibiting greatly improved precision (distance errors of 1.4%). The method, FOCUSR, incorporates implicitly such additional features to calculate the correspondence and relies on the smoothness of the lowest-frequency harmonics of a graph Laplacian to spatially regularize the features. In its simplest form, FOCUSR is an improved spectral correspondence method that nonrigidly deforms spectral embeddings. We provide here a full realization of spectral correspondence where virtually any feature can be used as additional information using weights on graph edges, but also on graph nodes and as extra embedded coordinates. As an example, the full power of FOCUSR is demonstrated in a real case scenario with the challenging task of brain surface matching across several individuals. Our results show that combining features and regularizing them in a spectral embedding greatly improves the matching precision (to a sub-millimeter level) while performing at much greater speed than existing methods. PMID:23868776

Quantitative lithologic mapping in spectral ratio feature space - Volcanic, sedimentary and metamorphic terrains

NASA Technical Reports Server (NTRS)

Campos-Marquetti, Raul, Jr.; Rockwell, Barnaby

1990-01-01

The nature of spectral lithologic mapping is studied utilizing ratios centered around the wavelength means of TM imagery. Laboratory-derived spectra are analyzed to determine the two-dimensional relationships and distributions visible in spectral ratio feature space. The spectral distributions of various rocks and minerals in ratio feature space are found to be controlled by several spectrally dominant molecules. Three study areas were examined: Rawhide Mining District, Nevada; Manzano Mountains, New Mexico; and the Sevilleta Long Term Ecological Research site in New Mexico. It is shown that, in the comparison of two ratio plots of laboratory reflectance spectra, i.e., 0.66/0.485 micron versus 1.65/2.22 microns with those derived from TM data, several molecules spectrally dominate the reflectance characteristic of surface lithologic units. Utilizing the above ratio combination, two areas are successfully mapped based on their distribution in spectral ratio feature space.

Augmentation of the IUE Ultraviolet Spectral Atlas

NASA Astrophysics Data System (ADS)

Wu, Chi-Chao

Most likely IUE is the only and last satellite which will support a survey program to record the ultraviolet spectrum of a large number of bright normal stars. It is important to have a library of high quality Low dispersion spectra of sufficient number of stars that provide good coverage in spectral type and luminosity class. Such a library is invaluable for stellar population synthesis of galaxies, studying the nature of distant galaxies, establishing a UV spectral classification system, providing comparison stars for interstellar extinction studies and for peculiar objects or binary systems, studying the effects of temperature, gravity and metallicity on stellar UV spectra, and as a teaching aid. We propose to continue observations of normal stars in order to provide (1) a more complete coverage of the spectral type and luminosity class, and (2) more than one star per spectral typeluminosity class combination to guard against variability and peculiarity, and to allow a finite range of temperature, gravity, and metallicity in a given combination. Our primary goal is to collect the data and make them available to the community immediately (without claiming the 6-month proprietary right). The data will be published in the IUE Newsletter as soon as practical, and the data will be prepared for distribution by the IUE Observatory and the NSSDC.

Thermal Pressure in Diffuse H2 Gas Measured by Herschel [C II] Emission and FUSE UV H2 Absorption

NASA Astrophysics Data System (ADS)

Velusamy, T.; Langer, W. D.; Goldsmith, P. F.; Pineda, J. L.

2017-04-01

UV absorption studies with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite have made important observations of H2 molecular gas in Galactic interstellar translucent and diffuse clouds. Observations of the 158 μm [C II] fine-structure line with Herschel trace the same H2 molecular gas in emission. We present [C II] observations along 27 lines of sight (LOSs) toward target stars of which 25 have FUSE H2 UV absorption. Two stars have only HST STIS C II λ2325 absorption data. We detect [C II] 158 μm emission features in all but one target LOS. For three target LOSs that are close to the Galactic plane, | {\\text{}}b| < 1°, we also present position-velocity maps of [C II] emission observed by Herschel Heterodyne Instrument in the Far Infrared (HIFI) in on-the-fly spectral-line mapping. We use the velocity-resolved [C II] spectra observed by the HIFI instrument toward the target LOSs observed by FUSE to identify [C II] velocity components associated with the H2 clouds. We analyze the observed velocity integrated [C II] spectral-line intensities in terms of the densities and thermal pressures in the H2 gas using the H2 column densities and temperatures measured by the UV absorption data. We present the H2 gas densities and thermal pressures for 26 target LOSs and from the [C II] intensities derive a mean thermal pressure in the range of ˜6100-7700 K cm-3 in diffuse H2 clouds. We discuss the thermal pressures and densities toward 14 targets, comparing them to results obtained using the UV absorption data for two other tracers C I and CO. Our results demonstrate the richness of the far-IR [C II] spectral data which is a valuable complement to the UV H2 absorption data for studying diffuse H2 molecular clouds. While the UV absorption is restricted to the directions of the target star, far-IR [C II] line emission offers an opportunity to employ velocity-resolved spectral-line mapping capability to study in detail the clouds’ spatial and velocity structures.

Laboratory Spectroscopy of Large Carbon Molecules and Ions in Support of Space Missions. A New Generation of Laboratory & Space Studies

NASA Technical Reports Server (NTRS)

Salama, Farid; Tan, Xiaofeng; Cami, Jan; Biennier, Ludovic; Remy, Jerome

2006-01-01

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. A long-standing and major challenge for laboratory astrophysics has been to measure the spectra of large carbon molecules in laboratory environments that mimic (in a realistic way) the physical conditions that are associated with the interstellar emission and absorption regions [1]. This objective has been identified as one of the critical Laboratory Astrophysics objectives to optimize the data return from space missions [2]. An extensive laboratory program has been developed to assess the properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space. We present and discuss the gas-phase electronic absorption spectra of neutral and ionized PAHs measured in the UV-Visible-NIR range in astrophysically relevant environments and discuss the implications for astrophysics [1]. The harsh physical conditions of the interstellar medium characterized by a low temperature, an absence of collisions and strong VUV radiation fields - have been simulated in the laboratory by associating a pulsed cavity ringdown spectrometer (CRDS) with a supersonic slit jet seeded with PAHs and an ionizing, penning-type, electronic discharge. We have measured for the {\\it first time} the spectra of a series of neutral [3,4] and ionized [5,6] interstellar PAHs analogs in the laboratory. An effort has also been attempted to quantify the mechanisms of ion and carbon nanoparticles production in the free jet expansion and to model our simulation of the diffuse interstellar medium in the laboratory [7]. These experiments provide {\\it unique} information on the spectra of free, large carbon-containing molecules and ions in the gas phase. We are now, for the first time, in the position to directly compare laboratory spectral data on free, cold, PAH ions and carbon nano-sized carbon particles with astronomical observations in the UV-NIR range (interstellar UV extinction, DIBs in the NUV-NIR range). This new phase offers tremendous opportunities for the data analysis of current and upcoming space missions geared toward the detection of large aromatic systems Le., the "new frontier space missions" (Spitzer, HST, COS, JWST, SOFIA,...).

Mapping minerals, amorphous materials, environmental materials, vegetation, water, ice and snow, and other materials: The USGS tricorder algorithm

NASA Technical Reports Server (NTRS)

Clark, Roger N.; Swayze, Gregg A.

1995-01-01

One of the challenges of Imaging Spectroscopy is the identification, mapping and abundance determination of materials, whether mineral, vegetable, or liquid, given enough spectral range, spectral resolution, signal to noise, and spatial resolution. Many materials show diagnostic absorption features in the visual and near infrared region (0.4 to 2.5 micrometers) of the spectrum. This region is covered by the modern imaging spectrometers such as AVIRIS. The challenge is to identify the materials from absorption bands in their spectra, and determine what specific analyses must be done to derive particular parameters of interest, ranging from simply identifying its presence to deriving its abundance, or determining specific chemistry of the material. Recently, a new analysis algorithm was developed that uses a digital spectral library of known materials and a fast, modified-least-squares method of determining if a single spectral feature for a given material is present. Clark et al. made another advance in the mapping algorithm: simultaneously mapping multiple minerals using multiple spectral features. This was done by a modified-least-squares fit of spectral features, from data in a digital spectral library, to corresponding spectral features in the image data. This version has now been superseded by a more comprehensive spectral analysis system called Tricorder.

TRES survey of variable diffuse interstellar bands

NASA Astrophysics Data System (ADS)

Law, Charles J.; Milisavljevic, Dan; Crabtree, Kyle N.; Johansen, Sommer L.; Patnaude, Daniel J.; Margutti, Raffaella; Parrent, Jerod T.; Drout, Maria R.; Sanders, Nathan E.; Kirshner, Robert P.; Latham, David W.

2017-09-01

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, the central wavelengths of almost all DIBs do not correspond with electronic transitions of known atomic or molecular species and the specific physical nature of their carriers remains inconclusive despite decades of observational, theoretical and experimental research. It is well established that DIB carriers are 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. Here, we report evidence of short time-scale (∼10-60 d) changes in DIB absorption line substructure towards 3 of 17 massive stars observed as part of a pathfinder survey of variable DIBs conducted with the 1.5-m Tillinghast telescope and Tillinghast Reflector Echelle Spectrograph (TRES) at Fred L. Whipple Observatory. The detections are made in high-resolution optical spectra (R ∼ 44 000) having signal-to-noise ratios of 5-15 around the 5797 and 6614 Å features, and are 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.

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.

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.

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.

The Nanograv Nine-Year Data Set: Measurement and Analysis of Variations in Dispersion Measures

NASA Technical Reports Server (NTRS)

Jones, M. L.; McLaughlin, M. A.; Lam, M. T.; Cordes, J. M.; Levin, L.; Chatterjee, S.; Arzoumanian, Z.; Crowter, K.; Demorest, P. B.; Dolch, T.;

Hyperspectral remote sensing image retrieval system using spectral and texture features.

PubMed

Zhang, Jing; Geng, Wenhao; Liang, Xi; Li, Jiafeng; Zhuo, Li; Zhou, Qianlan

2017-06-01

Although many content-based image retrieval systems have been developed, few studies have focused on hyperspectral remote sensing images. In this paper, a hyperspectral remote sensing image retrieval system based on spectral and texture features is proposed. The main contributions are fourfold: (1) considering the "mixed pixel" in the hyperspectral image, endmembers as spectral features are extracted by an improved automatic pixel purity index algorithm, then the texture features are extracted with the gray level co-occurrence matrix; (2) similarity measurement is designed for the hyperspectral remote sensing image retrieval system, in which the similarity of spectral features is measured with the spectral information divergence and spectral angle match mixed measurement and in which the similarity of textural features is measured with Euclidean distance; (3) considering the limited ability of the human visual system, the retrieval results are returned after synthesizing true color images based on the hyperspectral image characteristics; (4) the retrieval results are optimized by adjusting the feature weights of similarity measurements according to the user's relevance feedback. The experimental results on NASA data sets can show that our system can achieve comparable superior retrieval performance to existing hyperspectral analysis schemes.

FAINT EXTENDED OH EMISSION FROM THE LOCAL INTERSTELLAR MEDIUM IN THE DIRECTION l Almost-Equal-To 108 Degree-Sign , b Almost-Equal-To 5 Degree-Sign

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Ronald J.; Rodriguez, Monica Ivette; Black, John H.

We have mapped faint 1667 OH line emission (T{sub A} Almost-Equal-To 20-40 mK in our Almost-Equal-To 30' beam) along many lines of sight in the Galaxy covering an area of Almost-Equal-To 4 Degree-Sign Multiplication-Sign 4 Degree-Sign in the general direction of l Almost-Equal-To 108 Degree-Sign , b Almost-Equal-To 5 Degree-Sign . The OH emission is widespread, similar in extent to the local H I (r {approx}< 2 kpc) both in space and in velocity. The OH profile amplitudes show a good general correlation with those of H I in spectral channels of Almost-Equal-To 1 km s{sup -1}; this relation ismore » described by T{sub A} (OH) Almost-Equal-To 1.50 Multiplication-Sign 10{sup -4} T{sub B} (H I) for values of T{sub B} (H I) {approx}< 60-70 K. Beyond this the H I line appears to 'saturate', and few values are recorded above Almost-Equal-To 90 K. However, the OH brightness continues to rise, by a further factor Almost-Equal-To 3. The OH velocity profiles show multiple features with widths typically 2-3 km s{sup -1}, but less than 10% of these features are associated with CO(1-0) emission in existing surveys of the area smoothed to comparable resolution.« less

Measurements of Lyman-Alpha Escape From HST Far-UV Spectral SNAP Survey of 33 Starforming Galaxies: Initial Results

NASA Astrophysics Data System (ADS)

Redwine, Keith

2018-01-01

This thesis will describe and analyze far-UV spectra from nearby starforming galaxies to investigate how line features like the hydrogen Lyman-alpha (Lyα) line at 1216 Å are related to the local properties of the host galaxy. It has been suggested that Lyα can be used as a proxy for the escape of Lyman continuum (LyC) radiation, the escape of of which from bright regions of galaxies is of particular interest. Most notably, the reionization epoch of neutral atomic hydrogen in the universe over a redshift range from z∼6 to z∼12, was highly dependent on the flux of ionizing LyC photons in the interstellar and intergalactic media. Expanding our understanding of the dynamics of the Lyα escape fraction (fLyα) from the local environment of its emission could be key to determining a total LyC escape fraction (fLyC) across all morphologies of galaxies. The wide range of Lyα emitters and absorbors (occasionally both) of this Cycle 22 SNAP survey observed by the Cosmic Origins Spectrograph (COS) onboard Hubble Space Telescope (HST) provides a unique look at far-UV spectra in candidate LyC emitters. Lyα profiles are easily observable in short exposures, and line features discernable in the low-resolution G140L mode can inform and guide future observations by COS or other FUV spectroscopy.

Hitomi observations of the LMC SNR N 132 D: Highly redshifted X-ray emission from iron ejecta

NASA Astrophysics Data System (ADS)

Hitomi Collaboration; Aharonian, Felix; Akamatsu, Hiroki; Akimoto, Fumie; Allen, Steven W.; Angelini, Lorella; Audard, Marc; Awaki, Hisamitsu; Axelsson, Magnus; Bamba, Aya; Bautz, Marshall W.; Blandford, Roger; Brenneman, Laura W.; Brown, Gregory V.; Bulbul, Esra; Cackett, Edward M.; Chernyakova, Maria; Chiao, Meng P.; Coppi, Paolo S.; Costantini, Elisa; de Plaa, Jelle; de Vries, Cor P.; den Herder, Jan-Willem; Done, Chris; Dotani, Tadayasu; Ebisawa, Ken; Eckart, Megan E.; Enoto, Teruaki; Ezoe, Yuichiro; Fabian, Andrew C.; Ferrigno, Carlo; Foster, Adam R.; Fujimoto, Ryuichi; Fukazawa, Yasushi; Furuzawa, Akihiro; Galeazzi, Massimiliano; Gallo, Luigi C.; Gandhi, Poshak; Giustini, Margherita; Goldwurm, Andrea; Gu, Liyi; Guainazzi, Matteo; Haba, Yoshito; Hagino, Kouichi; Hamaguchi, Kenji; Harrus, Ilana M.; Hatsukade, Isamu; Hayashi, Katsuhiro; Hayashi, Takayuki; Hayashida, Kiyoshi; Hiraga, Junko S.; Hornschemeier, Ann; Hoshino, Akio; Hughes, John P.; Ichinohe, Yuto; Iizuka, Ryo; Inoue, Hajime; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Ishisaki, Yoshitaka; Iwai, Masachika; Kaastra, Jelle; Kallman, Tim; Kamae, Tsuneyoshi; Kataoka, Jun; Katsuda, Satoru; Kawai, Nobuyuki; Kelley, Richard L.; Kilbourne, Caroline A.; Kitaguchi, Takao; Kitamoto, Shunji; Kitayama, Tetsu; Kohmura, Takayoshi; Kokubun, Motohide; Koyama, Katsuji; Koyama, Shu; Kretschmar, Peter; Krimm, Hans A.; Kubota, Aya; Kunieda, Hideyo; Laurent, Philippe; Lee, Shiu-Hang; Leutenegger, Maurice A.; Limousin, Olivier; Loewenstein, Michael; Long, Knox S.; Lumb, David; Madejski, Greg; Maeda, Yoshitomo; Maier, Daniel; Makishima, Kazuo; Markevitch, Maxim; Matsumoto, Hironori; Matsushita, Kyoko; McCammon, Dan; McNamara, Brian R.; Mehdipour, Missagh; Miller, Eric D.; Miller, Jon M.; Mineshige, Shin; Mitsuda, Kazuhisa; Mitsuishi, Ikuyuki; Miyazawa, Takuya; Mizuno, Tsunefumi; Mori, Hideyuki; Mori, Koji; Mukai, Koji; Murakami, Hiroshi; Mushotzky, Richard F.; Nakagawa, Takao; Nakajima, Hiroshi; Nakamori, Takeshi; Nakashima, Shinya; Nakazawa, Kazuhiro; Nobukawa, Kumiko K.; Nobukawa, Masayoshi; Noda, Hirofumi; Odaka, Hirokazu; Ohashi, Takaya; Ohno, Masanori; Okajima, Takashi; Ota, Naomi; Ozaki, Masanobu; Paerels, Frits; Paltani, Stéphane; Petre, Robert; Pinto, Ciro; Porter, Frederick S.; Pottschmidt, Katja; Reynolds, Christopher S.; Safi-Harb, Samar; Saito, Shinya; Sakai, Kazuhiro; Sasaki, Toru; Sato, Goro; Sato, Kosuke; Sato, Rie; Sato, Toshiki; Sawada, Makoto; Schartel, Norbert; Serlemtsos, Peter J.; Seta, Hiromi; Shidatsu, Megumi; Simionescu, Aurora; Smith, Randall K.; Soong, Yang; Stawarz, Łukasz; Sugawara, Yasuharu; Sugita, Satoshi; Szymkowiak, Andrew; Tajima, Hiroyasu; Takahashi, Hiromitsu; Takahashi, Tadayuki; Takeda, Shin'ichiro; Takei, Yoh; Tamagawa, Toru; Tamura, Takayuki; Tanaka, Takaaki; Tanaka, Yasuo; Tanaka, Yasuyuki T.; Tashiro, Makoto S.; Tawara, Yuzuru; Terada, Yukikatsu; Terashima, Yuichi; Tombesi, Francesco; Tomida, Hiroshi; Tsuboi, Yohko; Tsujimoto, Masahiro; Tsunemi, Hiroshi; Tsuru, Takeshi Go; Uchida, Hiroyuki; Uchiyama, Hideki; Uchiyama, Yasunobu; Ueda, Shutaro; Ueda, Yoshihiro; Uno, Shin'ichiro; Urry, C. Megan; Ursino, Eugenio; Watanabe, Shin; Werner, Norbert; Wilkins, Dan R.; Williams, Brian J.; Yamada, Shinya; Yamaguchi, Hiroya; Yamaoka, Kazutaka; Yamasaki, Noriko Y.; Yamauchi, Makoto; Yamauchi, Shigeo; Yaqoob, Tahir; Yatsu, Yoichi; Yonetoku, Daisuke; Zhuravleva, Irina; Zoghbi, Abderahmen

2018-03-01

We present Hitomi observations of N 132 D, a young, X-ray bright, O-rich core-collapse supernova remnant in the Large Magellanic Cloud (LMC). Despite a very short observation of only 3.7 ks, the Soft X-ray Spectrometer (SXS) easily detects the line complexes of highly ionized S K and Fe K with 16-17 counts in each. The Fe feature is measured for the first time at high spectral resolution. Based on the plausible assumption that the Fe K emission is dominated by He-like ions, we find that the material responsible for this Fe emission is highly redshifted at ˜ 800 km s-1 compared to the local LMC interstellar medium (ISM), with a 90% credible interval of 50-1500 km s-1 if a weakly informative prior is placed on possible line broadening. This indicates (1) that the Fe emission arises from the supernova ejecta, and (2) that these ejecta are highly asymmetric, since no blueshifted component is found. The S K velocity is consistent with the local LMC ISM, and is likely from swept-up ISM material. These results are consistent with spatial mapping that shows the He-like Fe concentrated in the interior of the remnant and the S tracing the outer shell. The results also show that even with a very small number of counts, direct velocity measurements from Doppler-shifted lines detected in extended objects like supernova remnants are now possible. Thanks to the very low SXS background of ˜ 1 event per spectral resolution element per 100 ks, such results are obtainable during short pointed or slew observations with similar instruments. This highlights the power of high-spectral-resolution imaging observations, and demonstrates the new window that has been opened with Hitomi and will be greatly widened with future missions such as the X-ray Astronomy Recovery Mission (XARM) and Athena.

Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics

NASA Astrophysics Data System (ADS)

Tielens, Alexander; "PDRs4ever" team

2018-06-01

Massive stars disrupt their natal molecular cloud material by dissociating molecules, ionizing atoms and molecules, and heating the gas and dust. These processes drive the evolution of interstellar matter in our Galaxy and throughout the Universe from the era of vigorous star formation at redshifts of 1-3, to the present day. Much of this interaction occurs in Photo-Dissociation Regions (PDRs) where far-ultraviolet photons of these stars create a largely neutral, but warm region of gas and dust. PDR emission dominates the IR spectra of star-forming galaxies and also provides a unique tool to study in detail the physical and chemical processes that are relevant for inter- and circumstellar media including diffuse clouds, molecular cloud and protoplanetary disk surfaces, globules, planetary nebulae, and starburst galaxies.We propose to provide template datasets designed to identify key PDR characteristics in the full 1-28 μm JWST spectra in order to guide the preparation of Cycle 2 proposals on star-forming regions in our Galaxy and beyond. We plan to obtain the first spatially resolved, high spectral resolution IR observations of a PDR using NIRCam, NIRSpec and MIRI. We will observe a nearby PDR with well-defined UV illumination in a typical massive star-forming region. JWST observations will, for the first time, spatially resolve and perform a tomography of the PDR, revealing the individual IR spectral signatures from the key zones and sub-regions within the ionized gas, the PDR and the molecular cloud. These data will test widely used theoretical models and extend them into the JWST era. We will assist the community interested in JWST observations of PDRs through several science-enabling products (maps of spectral features, template spectra, calibration of narrow/broad band filters in gas lines and PAH bands, data-interpretation tools e.g. to infer gas physical conditions or PAH and dust characteristics). This project is supported by a large international team of one hundred scientists collaborators.

Feature Transformation Detection Method with Best Spectral Band Selection Process for Hyper-spectral Imaging

NASA Astrophysics Data System (ADS)

Chen, Hai-Wen; McGurr, Mike; Brickhouse, Mark

2015-11-01

We present a newly developed feature transformation (FT) detection method for hyper-spectral imagery (HSI) sensors. In essence, the FT method, by transforming the original features (spectral bands) to a different feature domain, may considerably increase the statistical separation between the target and background probability density functions, and thus may significantly improve the target detection and identification performance, as evidenced by the test results in this paper. We show that by differentiating the original spectral, one can completely separate targets from the background using a single spectral band, leading to perfect detection results. In addition, we have proposed an automated best spectral band selection process with a double-threshold scheme that can rank the available spectral bands from the best to the worst for target detection. Finally, we have also proposed an automated cross-spectrum fusion process to further improve the detection performance in lower spectral range (<1000 nm) by selecting the best spectral band pair with multivariate analysis. Promising detection performance has been achieved using a small background material signature library for concept-proving, and has then been further evaluated and verified using a real background HSI scene collected by a HYDICE sensor.

Cosmic-ray electrons and galactic radio emission - A conflict

NASA Technical Reports Server (NTRS)

Badhwar, G. D.; Daniel, R. R.; Stephens, S. A.

1977-01-01

An analysis which takes into account the observed energy spectrum of cosmic-ray electrons above 5 GeV and calculated mean magnetic field data shows that the observed spectral index of the radio continuum in the Galaxy is in conflict with some of the cosmic-ray electron measurements. It is found that the absolute intensities of cosmic-ray electrons measured by some of the experimenters are so low that they cannot be reconciled either with the interstellar magnetic field limits or with the extent of the galactic disk toward the anticenter.

Influencia de diferentes ecuaciones de transformacion del sistema UBVal RGU en el estudio fotometrico de cumulos galacticos.

NASA Astrophysics Data System (ADS)

Huestamendia Aparicio, G.

Three-colour photometry of ten open clusters in the RGU system has been carried out. The calibration sequence has been defined using the Buser's transformation equations between the UBV and RGU systems, while in earlier works the Steinlin's formulae have been used. The results have been compared with those given in these works. Some differences have been found in G, G-R and U-G as a function of the spectral type and the interstellar absorption. They have a systematic character.

Detection of Interstellar Urea

NASA Astrophysics Data System (ADS)

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

2010-11-01

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

Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the Submillimeter Array

NASA Astrophysics Data System (ADS)

Zernickel, A.; Schilke, P.; Schmiedeke, A.; Lis, D. C.; Brogan, C. L.; Ceccarelli, C.; Comito, C.; Emprechtinger, M.; Hunter, T. R.; Möller, T.

2012-10-01

Aims: We aim at deriving the molecular abundances and temperatures of the hot molecular cores in the high-mass star-forming region NGC 6334I and consequently deriving their physical and astrochemical conditions. Methods: In the framework of the Herschel guaranteed time key program CHESS (Chemical HErschel Surveys of Star forming regions), NGC 6334I is investigated by using the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory. A spectral line survey is carried out in the frequency range 480-1907 GHz, and further auxiliary interferometric data from the Submillimeter Array (SMA) in the 230 GHz band provide spatial information for disentangling the different physical components contributing to the HIFI spectrum. The spectral lines in the processed Herschel data are identified with the aid of former surveys and spectral line catalogs. The observed spectrum is then compared to a simulated synthetic spectrum, assuming local thermal equilibrium, and best fit parameters are derived using a model optimization package. Results: A total of 46 molecules are identified, with 31 isotopologues, resulting in about 4300 emission and absorption lines. High-energy levels (Eu > 1000 K) of the dominant emitter methanol and vibrationally excited HCN (ν2 = 1) are detected. The number of unidentified lines remains low with 75, or <2% of the lines detected. The modeling suggests that several spectral features need two or more components to be fitted properly. Other components could be assigned to cold foreground clouds or to outflows, most visible in the SiO and H2O emission. A chemical variation between the two embedded hot cores is found, with more N-bearing molecules identified in SMA1 and O-bearing molecules in SMA2. Conclusions: Spectral line surveys give powerful insights into the study of the interstellar medium. Different molecules trace different physical conditions like the inner hot core, the envelope, the outflows or the cold foreground clouds. The derived molecular abundances provide further constraints for astrochemical models. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org

Computational Confirmation of the Carrier for the ``XCN'' Interstellar Ice Band: OCN- Charge Transfer Complexes

NASA Astrophysics Data System (ADS)

Park, Jin-Young; Woon, David E.

2004-01-01

Recent experimental studies provide evidence that the carrier for the so-called XCN feature at 2165 cm-1 (4.62 μm) in young stellar objects is an OCN-/NH+4 charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RNC isonitriles have been considered, Greenberg's conjecture that OCN- is associated with the XCN feature has persisted for over 15 years. In this work, we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN-/NH+4 CT complexes arising from HNCO and NH3 in a water ice environment. Density functional theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN-, shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN-/NH+4 CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for the HNCO and HOCN cases are 2181 and 2202 cm-1, respectively.

Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer Complexes

NASA Technical Reports Server (NTRS)

Park, J.-Y.; Woon, D. E.

2004-01-01

Recent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.

SPECTRAL PROPERTIES OF {approx}0.5-6 keV ENERGETIC NEUTRAL ATOMS MEASURED BY THE INTERSTELLAR BOUNDARY EXPLORER (IBEX) ALONG THE LINES OF SIGHT OF VOYAGER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desai, M. I.; Allegrini, F. A.; Dayeh, M. A.

2012-04-20

Energetic neutral atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) provide powerful diagnostics about the origin of the progenitor ion populations and the physical mechanisms responsible for their production. Here we survey the fluxes, energy spectra, and energy dependence of the spectral indices of {approx}0.5-6 keV ENAs measured by IBEX-Hi along the lines of sight of Voyager 1 and 2. We compare the ENA spectra observed at IBEX with predictions of Zank et al. who modeled the microphysics of the heliospheric termination shock to predict the shape and relative contributions of three distinct heliosheath ion populations. We show thatmore » (1) the ENA spectral indices exhibit similar energy dependence along V1 and V2 directions-the spectrum hardens to {gamma} {approx} 1 between {approx}1 and 2 keV and softens to {gamma} {approx} 2 below {approx}1 keV and above {approx}2 keV, (2) the observed ENA fluxes agree to within {approx}50% of the Zank et al. predictions and are unlikely to be produced by core solar wind (SW) ions, and (3) the ENA spectra do not exhibit sharp cutoffs at {approx}twice the SW speed as is typically observed for shell-like pickup ion (PUI) distributions in the heliosphere. We conclude that ENAs at IBEX are generated by at least two types of ion populations whose relative contributions depend on the ENA energy: transmitted PUIs in the {approx}0.5-5 keV energy range and reflected PUIs above {approx}5 keV energy. The {approx}0.5-5 keV PUI distribution is probably a superposition of Maxwellian or kappa distributions and partially filled shell distributions in velocity space.« less

Administrative Report on Training Awards

NASA Technical Reports Server (NTRS)

Woodward, Charles E.

1999-01-01

During the tenure of this award, the recipient (David Harker) conducted areas of research which resulted in the award of a doctorate degree (August 1999) from the University of Wyoming. The primary science activity was investigation of silicate dust mineralogy in comets, particularly comet C/1995 O1 (Hale-Bopp). Determination of the dust mineralogy permits us to address an important astrophysical question of relevance to the origins and evolution of solar systems, "Do comets contain relic interstellar dust grains? Since, comets represent the frozen reservoirs of primitive proto-solar dust and ice, we can gain insight into the problem of understanding the formation of protoplanetesimals in the. early solar nebula. Mid-infrared spectrophotometry (7 - 14 micron, R approx. = 180 - 360) of Hale-Bopp was obtained with the NASA/Ames HIFOGS at four distinct epochs pre- and post- perihelion ion from 1996 October through 1997 June. These observations were conducted at the Wyoming Infrared Observatory and the NASA Infrared Telescope Facility, and were supported by funds from this training grant. The emission at mid-IR wavelengths in cometary comae arises from carbon grains, and small silicate grains which produce resonance features. Hale-Bopp had the strongest silicate feature observed from any comet to date. Theoretical calculations utilizing Mie Scattering Theory were employed to construct Synthetic cometary spectra to fit with the observed HIFOGS 10 microns spectral feature of Hale-Bopp. Our analysis suggests that the observed spectra can be modeled with the Hanner grain size distribution peaked at alpha((sub p) = 0.2 microns of fractal porous grains with porosity parameter D = 2.5. This model spectrum also fits photometry points in the 3 - 5 microns region. Comparison with the ISO SWS spectrum of Hale-Bopp obtained 1996 October reveals that the crystalline olivine grains must be at it temperature hotter than computed from Mie theory.

Non-water-ice constituents in the surface material of the icy Galilean satellites from the Galileo near-infrared mapping spectrometer investigation

USGS Publications Warehouse

McCord, T.B.; Hansen, G.B.; Clark, R.N.; Martin, P.D.; Hibbitts, C.A.; Fanale, F.P.; Granahan, J.C.; Segura, M.; Matson, D.L.; Johnson, T.V.; Carlson, R.W.; Smythe, W.D.; Danielson, G.E.

1998-01-01

We present evidence for several non-ice constituents in the surface material of the icy Galilean satellites, using the reflectance spectra returned by the Galileo near infrared mapping spectrometer (NIMS) experiment. Five new absorption features are described at 3.4, 3.88, 4.05, 4.25, and 4.57 ??m for Callisto and Ganymede, and some seem to exist for Europa as well. The four absorption bands strong enough to be mapped on Callisto and Ganymede are each spatially distributed in different ways, indicating different materials are responsible for each absorption. The spatial distributions are correlated at the local level in complex ways with surface features and in some cases show global patterns. Suggested candidate spectrally active groups, perhaps within larger molecules, producing the five absorptions include C-H, S-H, SO2, CO2, and C???N. Organic material like tholins are candidates for the 4.57- and 3.4-??m features. We suggest, based on spectroscopic evidence, that CO2 is present as a form which does not allow rotational modes and that SO2 is present neither as a frost nor a free gas. The CO2, SO2, and perhaps cyanogen (4.57 ??m) may be present as very small collections of molecules within the crystal structure, perhaps following models for radiation damage and/or for comet and interstellar grain formation at low temperatures. Some of the dark material on these surfaces may be created by radiation damage of the CO2 and other carbon-bearing species and the formation of graphite. These spectra suggest a complex chemistry within the surface materials and an important role for non-ice materials in the evolution of the satellite surfaces. Copyright 1998 by the American Geophysical Union.

ISM Dust Grains and N-band Spectral Variability in the Spatially Resolved Subarcsecond Binary UY Aur

NASA Astrophysics Data System (ADS)

Skemer, Andrew J.; Close, Laird M.; Hinz, Philip M.; Hoffmann, William F.; Greene, Thomas P.; Males, Jared R.; Beck, Tracy L.

2010-03-01

The 10 μm silicate feature is an essential diagnostic of dust-grain growth and planet formation in young circumstellar disks. The Spitzer Space Telescope has revolutionized the study of this feature, but due to its small (85 cm) aperture, it cannot spatially resolve small/medium-separation binaries (lsim3''; <~ 420 AU) at the distances of the nearest star-forming regions (~140 pc). Large, 6-10 m ground-based telescopes with mid-infrared instruments can resolve these systems. In this paper, we spatially resolve the 0farcs88 binary, UY Aur, with MMTAO/BLINC-MIRAC4 mid-infrared spectroscopy. We then compare our spectra to Spitzer/IRS (unresolved) spectroscopy, and resolved images from IRTF/MIRAC2, Keck/OSCIR, and Gemini/Michelle, which were taken over the past decade. We find that UY Aur A has extremely pristine, interstellar medium (ISM)-like grains and that UY Aur B has an unusually shaped silicate feature, which is probably the result of blended emission and absorption from foreground extinction in its disk. We also find evidence for variability in both UY Aur A and UY Aur B by comparing synthetic photometry from our spectra with resolved imaging from previous epochs. The photometric variability of UY Aur A could be an indication that the silicate emission itself is variable, as was recently found in EX Lupi. Otherwise, the thermal continuum is variable, and either the ISM-like dust has never evolved, or it is being replenished, perhaps by UY Aur's circumbinary disk. The observations reported here were partially obtained at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement no. NCC 5-538 with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program.

Black Holes, Worm Holes, and Future Space Propulsion

NASA Technical Reports Server (NTRS)

Barret, Chris

2000-01-01

NASA has begun examining the technologies needed for an Interstellar Mission. In 1998, a NASA Interstellar Mission Workshop was held at the California Institute of Technology to examine the technologies required. Since then, a spectrum of research efforts to support such a mission has been underway, including many advanced and futuristic space propulsion concepts which are being explored. The study of black holes and wormholes may provide some of the breakthrough physics needed to travel to the stars. The first black hole, CYGXI, was discovered in 1972 in the constellation Cygnus X-1. In 1993, a black hole was found in the center of our Milky Way Galaxy. In 1994, the black hole GRO J1655-40 was discovered by the NASA Marshall Space Flight center using the Gamma Ray Observatory. Today, we believe we have found evidence to support the existence of 19 black holes, but our universe may contain several thousands. This paper discusses the dead star states - - both stable and unstable, white dwarfs, neutron stars, pulsars, quasars, the basic features and types of black holes: nonspinning, nonspinning with charge, spinning, and Hawking's mini black holes. The search for black holes, gravitational waves, and Laser Interferometer Gravitational Wave Observatory (LIGO) are reviewed. Finally, concepts of black hole powered space vehicles and wormhole concepts for rapid interstellar travel are discussed in relation to the NASA Interstellar Mission.

AKARI Near-infrared Spectroscopic Observations of Interstellar Ices in the Edge-on Starburst Galaxy NGC 253

NASA Astrophysics Data System (ADS)

Yamagishi, Mitsuyoshi; Kaneda, Hidehiro; Ishihara, Daisuke; Oyabu, Shinki; Onaka, Takashi; Shimonishi, Takashi; Suzuki, Toyoaki

2011-04-01

We present the spatially resolved near-infrared (2.5-5.0 μm) spectra of the edge-on starburst galaxy NGC 253 obtained with the Infrared Camera on board AKARI. Near the center of the galaxy, we clearly detect the absorption features of interstellar ices (H2O: 3.05 μm, CO2: 4.27 μm, and XCN: 4.62 μm) and the emission of polycyclic aromatic hydrocarbons (PAHs) at 3.29 μm and the hydrogen recombination line Brα at 4.05 μm. We find that the distributions of the ices differ from those of the PAH and gas. We calculate the column densities of the ices and derive the abundance ratios of N(CO2)/N(H2O) = 0.17 ± 0.05. They are similar to those obtained around the massive young stellar objects in our Galaxy (0.17 ± 0.03), although a much stronger interstellar radiation field and higher dust temperature are expected near the center of NGC 253.

High-resolution ultraviolet observations of interstellar lines toward Zeta Persei observed with the balloon-borne ultraviolet stellar spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snow, T.P.; Lamers, H.J.G.L.M.; Joseph, C.L.

1987-10-01

The balloon-borne ultraviolet stellar spectrometer payload has been used to obtain high-resolution data on interstellar absorption lines toward Zeta Per. The only lines clearly present in the 2150-2450 region were several Fe II features, which show double structure. The two velocity components were sufficiently well separated that it was possible to construct separate curves of growth to derive the Fe II column densities for the individual components. These column densities and the component velocity separation were then used to compute a realistic two-component curve of growth for the line of sight to Zeta Per, which was then used to reanalyzemore » existing ultraviolet data from Copernicus. The results were generally similar to an earlier two-component analysis of the Copernicus data, with the important exception that the silicon depletion increased from near zero to about 1 dex. This makes the Zeta Per depletion pattern quite similar to those derived for other reddened lines of sight, supporting the viewpoint that the general diffuse interstellar medium has a nearly constant pattern of depletions. 31 references.« less

The jet-ISM interactions in IC 5063

NASA Astrophysics Data System (ADS)

Mukherjee, Dipanjan; Wagner, Alexander Y.; Bicknell, Geoffrey V.; Morganti, Raffaella; Oosterloo, Tom; Nesvadba, Nicole; Sutherland, Ralph S.

2018-05-01

The interstellar medium of the radio galaxy IC 5063 is highly perturbed by an AGN jet expanding in the gaseous disc of the galaxy. We model this interaction with relativistic hydrodynamic simulations and multiphase initial conditions for the interstellar medium and compare the results with recent observations. As the jets flood through the intercloud channels of the disc, they ablate, accelerate, and disperse clouds to velocities exceeding 400 km s-1. Clouds are also destroyed or displaced in bulk from the central regions of the galaxy. Our models with jet powers of 1044 and 1045 erg s-1 are capable of reproducing many of the observed features in the position velocity diagram of IC 5063, and confirm the notion that the jet is responsible for the strongly perturbed gas dynamics seen in the ionized, neutral, and molecular gas phases. In our simulations, we also see strong venting of the jet plasma perpendicular to the disc, which entrains clumps and diffuse filaments into the halo of the galaxy. Our simulations are the first 3D hydrodynamic simulations of the jet and interstellar matter of IC 5063.

Fatigue crack detection by nonlinear spectral correlation with a wideband input

NASA Astrophysics Data System (ADS)

Liu, Peipei; Sohn, Hoon

2017-04-01

Due to crack-induced nonlinearity, ultrasonic wave can distort, create accompanying harmonics, multiply waves of different frequencies, and, under resonance conditions, change resonance frequencies as a function of driving amplitude. All these nonlinear ultrasonic features have been widely studied and proved capable of detecting fatigue crack at its very early stage. However, in noisy environment, the nonlinear features might be drown in the noise, therefore it is difficult to extract those features using a conventional spectral density function. In this study, nonlinear spectral correlation is defined as a new nonlinear feature, which considers not only nonlinear modulations in ultrasonic waves but also spectral correlation between the nonlinear modulations. The proposed nonlinear feature is associated with the following two advantages: (1) stationary noise in the ultrasonic waves has little effect on nonlinear spectral correlation; and (2) the contrast of nonlinear spectral correlation between damage and intact conditions can be enhanced simply by using a wideband input. To validate the proposed nonlinear feature, micro fatigue cracks are introduced to aluminum plates by repeated tensile loading, and the experiment is conducted using surface-mounted piezoelectric transducers for ultrasonic wave generation and measurement. The experimental results confirm that the nonlinear spectral correlation can successfully detect fatigue crack with a higher sensitivity than the classical nonlinear coefficient.

Diatoms in comets

NASA Technical Reports Server (NTRS)

Hoover, R.; Hoyle, F.; Wallis, M. K.; Wickramasinghe, N. C.

1986-01-01

The fossil record of the microscopic algae classified as diatoms suggests they were injected to earth at the Cretaceous boundary. Not only could diatoms remain viable in the cometary environment, but also many species might replicate in illuminated surface layers or early interior layers of cometary ice. Presumably they reached the solar system on an interstellar comet as an already-evolved assemblage of organisms. Diatoms might cause color changes to comet nuclei while their outgassing decays and revives around highly elliptical orbits. Just as for interstellar absorption, high-resolution IR observations are capable of distinguishing whether the 10-micron feature arises from siliceous diatom material or mineral silicates. The 10-30-micron band and the UV 220-nm region can also provide evidence of biological material.

Detection of the aromatic molecule benzonitrile (c-C6H5CN) in the interstellar medium

NASA Astrophysics Data System (ADS)

McGuire, Brett A.; Burkhardt, Andrew M.; Kalenskii, Sergei; Shingledecker, Christopher N.; Remijan, Anthony J.; Herbst, Eric; McCarthy, Michael C.

2018-01-01

Polycyclic aromatic hydrocarbons and polycyclic aromatic nitrogen heterocycles are thought to be widespread throughout the universe, because these classes of molecules are probably responsible for the unidentified infrared bands, a set of emission features seen in numerous Galactic and extragalactic sources. Despite their expected ubiquity, astronomical identification of specific aromatic molecules has proven elusive. We present the discovery of benzonitrile (c-C6H5CN), one of the simplest nitrogen-bearing aromatic molecules, in the interstellar medium. We observed hyperfine-resolved transitions of benzonitrile in emission from the molecular cloud TMC-1. Simple aromatic molecules such as benzonitrile may be precursors for polycyclic aromatic hydrocarbon formation, providing a chemical link to the carriers of the unidentified infrared bands.

Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359

NASA Technical Reports Server (NTRS)

Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin

1995-01-01

We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a signal-to-noise ratio of approximately 50:1. We detect interstellar lines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) = 15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greater than 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/- 0.02. Assuming solar reference abundances, the diffuse clouds containing Mg, S, and Ge along the sight line have average logarithmic depletions D(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2 +/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smaller than is typical of diffuse clouds in the solar vicinity. Galactic rotational modeling of the N v profiles indicates that the highly ionized gas traced by this ion has a scale height of approximately 1 kpc if gas at large z-distances corotates with the underlying disk gas. Rotational modeling of the Si iv and C iv profiles measured by the IUE satellite yields similar scale height estimates. The scale height results contrast with previous studies of highly ionized gas in the outer Milky Way that reveal a more extended gas distribtion with h approximately equals 3-4 kpc. We detect a high-velocity feature in N v and Si II v(sub LSR) approximately equals + 125 km/s) that is probably created in an interface between warm and hot gas.

The use of kerogen data in understanding the properties and evolution of interstellar carbonaceous dust

NASA Astrophysics Data System (ADS)

Papoular, R.

2001-11-01

A number of authors have, in the past decade, pointed to the similarity of the 3.4-mu m band of kerogen with that of the Galactic Centre (GC). Kerogen is a family of solid terrestrial sedimentary materials essentially made of C, H and O interlocked in a disordered, more or less aliphatic, structure. Here, the most recent results of the astronomical literature and the rich quantitative geochemical literature are tapped with two purposes in mind: extend the analogy to the mid-IR bands and, based on these new constraints, quantitatively assess the properties of the carrier dust. It is shown that the great diversity of IR astronomical IS (interstellar) dust is paralleled by the changes in kerogen spectra as the material spontaneously and continuously evolves (aromatizes) in the earth. Since the composition and structure of kerogen are known all along its evolution, it is possible, by spectral analogy, to estimate these properties for the corresponding astronomical carriers. The Galactic Centre 3.4 mu m feature is thus found to correspond to an early stage of evolution, for which the composition in C, H and O and the structure of the corresponding kerogen are known and reported here. The role of oxygen in the subsequent evolution and its contribution to different bands are stressed. The above provides new arguments in favour of the 3.4-mu m band, as well as the observed accompanying mid-IR bands, being carried by kerogen-like dust born in CS (circumstellar) envelopes, mostly of AGB (asymptotic giant branch) objects. Subsequent dust evolution in composition and structure (aromatization) is fast enough that the unidentified infrared bands can already show up in well-developed planetary nebulae (PNe), as observed. A fraction of incompletely evolved dust can escape into the diffuse IS medium and molecular clouds. As a consequence, aliphatic and aromatic features can both be detected in the sky, in emission (Proto-PNe, PNe and PDRs (photo-dissociation regions)) as well as in absorption (dense molecular clouds and diffuse ISM). Changes in wavelength and band width with line of sight are explained by changes in the nature and number of chemical functional groups composing the carrier material. Predictions of the kerogen model in the UV and far IR are proposed for testing.

Documentation of procedures for textural/spatial pattern recognition techniques

NASA Technical Reports Server (NTRS)

Haralick, R. M.; Bryant, W. F.

1976-01-01

A C-130 aircraft was flown over the Sam Houston National Forest on March 21, 1973 at 10,000 feet altitude to collect multispectral scanner (MSS) data. Existing textural and spatial automatic processing techniques were used to classify the MSS imagery into specified timber categories. Several classification experiments were performed on this data using features selected from the spectral bands and a textural transform band. The results indicate that (1) spatial post-processing a classified image can cut the classification error to 1/2 or 1/3 of its initial value, (2) spatial post-processing the classified image using combined spectral and textural features produces a resulting image with less error than post-processing a classified image using only spectral features and (3) classification without spatial post processing using the combined spectral textural features tends to produce about the same error rate as a classification without spatial post processing using only spectral features.

Spectroscopy of PAHs with carbon side chains

NASA Astrophysics Data System (ADS)

Rouille, G.; Steglich, M.; Carpentier, Y.; Huisken, F.; Henning, T.

2011-05-01

The presence of polycyclic aromatic hydrocarbons (PAHs) in space has been inferred ever since sp ecific infrared emission bands were interpreted as their collective fingerprint. In parallel, it has been admitted that the famous diffuse interstellar bands (DIBs), which are absorption features observed in the visible wavelength range, are bands belonging to the electronic spectra of free-flying interstellar molecules yet to be identified. As neutral PAHs of medium and large sizes exhibit absorption bands in the range where the DIBs are found, these molecules, which also fulfill other criteria, have been proposed as potential carriers. Studies of small PAHs in solutions have shown that adding an ethynyl side chain (--CCH) to their structure causes their electronic transitions to shift toward longer wavelengths. This fact, added to the observations of interstellar polyynyl radicals, motivated our current research project on PAHs carrying polyynyl side chains. In a first stage, we are measuring the electronic spectra of small PAHs and of their ethynyl and butadiynyl (--CCCCH) derivatives at cryogenic temperatures in rare gas matrices. Then, measurements will be carried out in supersonic jets, providing us with spectra obtained under conditions relevant to the study of free-flying interstellar molecules. The results of IR absorption measurements will be included in our set of new data. As a complement to our laboratory study on the substituted PAHs, quantum chemical calculations are carried out to interprete and simulate their IR and vibronic spectra. We use the density functional theory approach and its time-dependent extension for calculating the electronic ground states and the electronically excited states, respectively. Through the analysis of the new data, it will be determined whether PAHs carrying polyynyl side chains can play a role in interstellar phenomena. The latest results of this on-going project will be presented.

Three-dimensional Features of the Outer Heliosphere Due to Coupling between the Interstellar and Heliospheric Magnetic Field. V. The Bow Wave, Heliospheric Boundary Layer, Instabilities, and Magnetic Reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pogorelov, N. V.; Heerikhuisen, J.; Roytershteyn, V.

The heliosphere is formed due to interaction between the solar wind (SW) and local interstellar medium (LISM). The shape and position of the heliospheric boundary, the heliopause, in space depend on the parameters of interacting plasma flows. The interplay between the asymmetrizing effect of the interstellar magnetic field and charge exchange between ions and neutral atoms plays an important role in the SW–LISM interaction. By performing three-dimensional, MHD plasma/kinetic neutral atom simulations, we determine the width of the outer heliosheath—the LISM plasma region affected by the presence of the heliosphere—and analyze quantitatively the distributions in front of the heliopause. Itmore » is shown that charge exchange modifies the LISM plasma to such extent that the contribution of a shock transition to the total variation of plasma parameters becomes small even if the LISM velocity exceeds the fast magnetosonic speed in the unperturbed medium. By performing adaptive mesh refinement simulations, we show that a distinct boundary layer of decreased plasma density and enhanced magnetic field should be observed on the interstellar side of the heliopause. We show that this behavior is in agreement with the plasma oscillations of increasing frequency observed by the plasma wave instrument onboard Voyager 1. We also demonstrate that Voyager observations in the inner heliosheath between the heliospheric termination shock and the heliopause are consistent with dissipation of the heliospheric magnetic field. The choice of LISM parameters in this analysis is based on the simulations that fit observations of energetic neutral atoms performed by Interstellar Boundary Explorer .« less

Highlights of Astronomy, Vol. 16

NASA Astrophysics Data System (ADS)

Montmerle, Thierry

2015-04-01

Part I. Invited Discourses: 1. The Herschel view of star formation; 2. Past, present and future of Chinese astronomy; 3. The zoo of galaxies; 4. Supernovae, the accelerating cosmos, and dark energy; Part II. Joint Discussion: 5. Very massive stars in the local universe; 6. 3-D views of the cycling Sun in stellar context; 7. Ultraviolet emission in early-type galaxies; 8. From meteors and meteorites to their parent bodies: current status and future developments; 9. The connection between radio properties and high-energy emission in AGNs; 10. Space-time reference systems for future research; Part III. Special Sessions: 11. Origin and complexity of massive star clusters; 12. Cosmic evolution of groups and clusters of galaxies; 13. Galaxy evolution through secular processes; 14. New era for studying interstellar and intergalactic magnetic fields; 15. The IR view of massive stars: the main sequence and beyond; 16. Science with large solar telescopes; 17. The impact hazard: current activities and future plans; 18. Calibration of star-formation rate measurements across the electromagnetic spectrum; 19. Future large scale facilities; 20. Dynamics of the star-planet relations strategic plan and the Global Office of Astronomy for Development; 21. Strategic plan and the Global Office of Astronomy for Development; 22. Modern views of the interstellar medium; 23. High-precision tests of stellar physics from high-precision photometry; 24. Communicating astronomy with the public for scientists; 25. Data intensive astronomy; 26. Unexplained spectral phenomena in the interstellar medium; 27. Light pollution: protecting astronomical sites and increasing global awareness through education.

Energetic neutral atoms measured by the interstellar boundary explorer (IBEX): evidence for multiple heliosheath populations

DOE PAGES

Desai, M. I.; Allegrini, F. A.; Bzowski, M.; ...

2013-12-13

Energetic neutral atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) provide powerful diagnostics about the origin of the progenitor ion populations and the physical mechanisms responsible for their production. In this paper, we extend the work of Desai et al. and Fuselier et al. and combine and compare ENA spectra from the first 3 yr of observations by the IBEX-Hi and -Lo ENA imagers along the lines-of-sight (LOSs) from the inner heliosphere through to the locations of Voyager 1 and 2 with results from an updated physics-based model of the three-dimensional heliosphere and its constituent ion populations. Our resultsmore » show that (1) IBEX ENA fluxes and spectra above ~0.7 keV measured along the LOSs of the Voyagers are consistent with several models in which the parent pickup ion (PUI) populations originate in the inner heliosheath, and (2) a significant fraction of lower energy ENAs between ~0.1-0.5 keV may originate from interstellar neutral gas charge-exchanging with a non-thermalized (hot) population of PUIs in the outer heliosheath beyond the heliopause. Here we discuss the implications of ENAs observed by IBEX originating from distinct parent populations as well as from two distinct locations in the heliospheric interface. In conclusion, these results indicate that ENA spectral measurements at various energies can be used to remotely probe distinct physical processes operating in vastly different regions of the distant heliosphere.« less

Energetic Neutral Atoms Measured by the Interstellar Boundary Explorer (IBEX): Evidence for Multiple Heliosheath Ion Populations

NASA Astrophysics Data System (ADS)

Desai, M. I.; Allegrini, F.; Bzowski, M.; Dayeh, M. A.; Funsten, H. O.; Fuselier, S.; Kubiak, M. A.; McComas, D. J.; Pogorelov, N. V.; Schwadron, N.; Sokol, J. M.; Zank, G. P.; Zirnstein, E. J.

2013-12-01

Energetic Neutral Atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) provide powerful diagnostics about the origin of the progenitor ion populations and the physical mechanisms responsible for their production. In this paper, we extend the work of Desai et al. (2012) and Fuselier et al. (2012) and combine and compare ENA spectra from the first three years of observations by the IBEX-Hi and -Lo ENA imagers along the lines-of-sights (LOS) from the inner heliosphere through to the locations of Voyager 1 and 2 with results from an updated physics-based model of the 3D heliosphere and its constituent ion populations. Our results show that (1) IBEX ENA fluxes and spectra above ~0.7 keV measured along the LOS of the Voyagers are consistent with several models in which the parent pickup (PUI) populations originate in the inner heliosheath, and (2) a significant fraction of lower-energy ENAs between ~0.1-0.5 keV may originate from interstellar neutral gas charge-exchanging with a non-thermalized (hot) population of PUIs in the outer heliosheath beyond the heliopause. We discuss the implications of ENAs observed by IBEX originating from distinct parent populations as well as from two distinct locations in the heliospheric interface. These results indicate that ENA spectral measurements at various energies can be used to remotely probe distinct physical processes operating in vastly different regions of the distant heliosphere.

Energetic Neutral Atoms Measured by the Interstellar Boundary Explorer (IBEX): Evidence for Multiple Heliosheath Populations

NASA Astrophysics Data System (ADS)

Desai, M. I.; Allegrini, F. A.; Bzowski, M.; Dayeh, M. A.; Funsten, H.; Fuselier, S. A.; Heerikhuisen, J.; Kubiak, M. A.; McComas, D. J.; Pogorelov, N. V.; Schwadron, N. A.; Sokół, J. M.; Zank, G. P.; Zirnstein, E. J.

2014-01-01

Energetic neutral atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) provide powerful diagnostics about the origin of the progenitor ion populations and the physical mechanisms responsible for their production. In this paper, we extend the work of Desai et al. and Fuselier et al. and combine and compare ENA spectra from the first 3 yr of observations by the IBEX-Hi and -Lo ENA imagers along the lines-of-sight (LOSs) from the inner heliosphere through to the locations of Voyager 1 and 2 with results from an updated physics-based model of the three-dimensional heliosphere and its constituent ion populations. Our results show that (1) IBEX ENA fluxes and spectra above ~0.7 keV measured along the LOSs of the Voyagers are consistent with several models in which the parent pickup ion (PUI) populations originate in the inner heliosheath, and (2) a significant fraction of lower energy ENAs between ~0.1-0.5 keV may originate from interstellar neutral gas charge-exchanging with a non-thermalized (hot) population of PUIs in the outer heliosheath beyond the heliopause. We discuss the implications of ENAs observed by IBEX originating from distinct parent populations as well as from two distinct locations in the heliospheric interface. These results indicate that ENA spectral measurements at various energies can be used to remotely probe distinct physical processes operating in vastly different regions of the distant heliosphere.

Lifetimes and f-values of the D 2Σ- ← X 2Π system of OH and OD

NASA Astrophysics Data System (ADS)

Heays, Alan; de Oliveira, Nelson; Gans, Bérenger; Ito, Kenji; Boyé-Péronne, Séverine; Douin, Stéphane; Hickson, Kevin; Nahon, Laurent; Loison, Jean-Christophe

2017-10-01

The OH radical is abundant in the interstellar medium and cometary comae, where it plays a significant role in the photochemical cycle of water. Also, the oxidising potential of the Earth atmosphere is influenced by this molecule. The OH lifetime in the presence of ultraviolet radiation is of prime interest in all these locations. The vacuum-ultraviolet absorption of the D 2Σ- ← X 2Π system contributes to a reduction of this lifetime. It also provides an independent way to observe the OH molecule in the interstellar medium. But a reliable oscillator strength (f-value) is needed. Vacuum-ultraviolet absorption of the D 2Σ- ← X 2Π system of OH and OD was recorded with high spectral resolution in a plasma-discharge radical source and using synchrotron radiation coupled to the unique ultraviolet Fourier-transform spectrometer on the DESIRS beamline of synchrotron SOLEIL. Line oscillator strengths are absolutely calibrated with respect to the well-known A 2Σ+ ← X 2Π system. The new oscillator strength decreases the best-estimate lifetime of OH in an interstellar radiation field and reduces its uncertainty. We also measured line broadening of the excited D 2Σ- v=0 and 1 levels for the first time and find a lifetime for these states which is 5 times shorter than theoretically predicted.This new data will aid in the interpretation of astronomical observations and help improve photochemical models in many contexts.

THE COMPOSITION OF INTERSTELLAR GRAINS TOWARD ζ OPHIUCHI: CONSTRAINING THE ELEMENTAL BUDGET NEAR THE DIFFUSE-DENSE CLOUD TRANSITION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poteet, Charles A.; Whittet, Douglas C. B.; Draine, Bruce T., E-mail: charles.poteet@gmail.com

2015-03-10

We investigate the composition of interstellar grains along the line of sight toward ζ Ophiuchi, a well-studied environment near the diffuse-dense cloud transition. A spectral decomposition analysis of the solid-state absorbers is performed using archival spectroscopic observations from the Spitzer Space Telescope and Infrared Space Observatory. We find strong evidence for the presence of sub-micron-sized amorphous silicate grains, principally comprised of olivine-like composition, with no convincing evidence of H{sub 2}O ice mantles. However, tentative evidence for thick H{sub 2}O ice mantles on large (a ≈ 2.8 μm) grains is presented. Solid-state abundances of elemental Mg, Si, Fe, and O aremore » inferred from our analysis and compared to standard reference abundances. We find that nearly all of the Mg and Si atoms along the line of sight reside in amorphous silicate grains, while a substantial fraction of the elemental Fe resides in compounds other than silicates. Moreover, we find that the total abundance of elemental O is largely inconsistent with the adopted reference abundances, indicating that as much as ∼156 ppm of interstellar O is missing along the line of sight. After taking into account additional limits on the abundance of elemental O in other O-bearing solids, we conclude that any missing reservoir of elemental O must reside on large grains that are nearly opaque to infrared radiation.« less

VizieR Online Data Catalog: First Fermi-LAT Inner Galaxy point source catalog (Ajello+, 2016)

NASA Astrophysics Data System (ADS)

Ajello, M.; Albert, A.; Atwood, W. B.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caputo, R.; Caragiulo, M.; Caraveo, P. A.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Desiante, R.; di Venere, L.; Drell, P. S.; Favuzzi, C.; Ferrara, E. C.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Gomez-Vargas, G. A.; Grenier, I. A.; Guiriec, S.; Gustafsson, M.; Harding, A. K.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Jogler, T.; Johannesson, G.; Johnson, A. S.; Kamae, T.; Karwin, C.; Knodlseder, J.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Magill, J.; Maldera, S.; Malyshev, D.; Manfreda, A.; Mayer, M.; Mazziotta, M. N.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Raino, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Ritz, S.; Sanchez-Conde, M.; Parkinson, P. M. S.; Sgro, C.; Siskind, E. J.; Smith, D. A.; Spada, F.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tajima, H.; Takahashi, H.; Thayer, J. B.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vianello, G.; Winer, B. L.; Wood, K. S.; Zaharijas, G.; Zimmer, S.

2018-01-01

The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1-100GeV from a 15°x15° region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the γ-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ~1kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15°x15° region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM. (2 data files).

Fermi-Lat Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center

NASA Technical Reports Server (NTRS)

Ajello, M.; Albert, A.; Atwood, W.B.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Brandt, T. J.;

Spectral studies of cosmic X-ray sources

NASA Astrophysics Data System (ADS)

Blissett, R. J.

1980-01-01

The conventional "indirect" method of reduction and data analysis of spectral data from non-dispersive X-ray detectors, by the fitting of assumed spectral models, is examined. The limitations of this procedure are presented, and alternative schemes are considered in which the derived spectra are not biased to an astrophysical source model. A new method is developed in detail to directly restore incident photon spectra from the detected count histograms. This Spectral Restoration Technique allows an increase in resolution, to a degree dependent on the statistical precision of the data. This is illustrated by numerical simulations. Proportional counter data from Ariel 5 are analysed using this technique. The results obtained for the sources Cas A and the Crab Nebula are consistent with previous analyses and show that increases in resolution of up to a factor three are possible in practice. The source Cyg X-3 is closely examined. Complex spectral variability is found, with the continuum and iron-line emission modulated with the 4.8 hour period of the source. The data suggest multi-component emission in the source. Comparing separate Ariel 5 observations and published data from other experiments, a correlation between the spectral shape and source intensity is evident. The source behaviour is discussed with reference to proposed source models. Data acquired by the low-energy detectors on-board HEAO-1 are analysed using the Spectral Restoration Technique. This treatment explicitly demonstrates the existence of oxygen K-absorption edges in the soft X-ray spectra of the Crab Nebula and Sco X-1. These results are considered with reference to current theories of the interstellar medium. The thesis commences with a review of cosmic X-ray sources and the mechanisms responsible for their spectral signatures, and continues with a discussion of the instruments appropriate for spectral studies in X-ray astronomy.

An improved feature extraction algorithm based on KAZE for multi-spectral image

NASA Astrophysics Data System (ADS)

Yang, Jianping; Li, Jun

2018-02-01

Multi-spectral image contains abundant spectral information, which is widely used in all fields like resource exploration, meteorological observation and modern military. Image preprocessing, such as image feature extraction and matching, is indispensable while dealing with multi-spectral remote sensing image. Although the feature matching algorithm based on linear scale such as SIFT and SURF performs strong on robustness, the local accuracy cannot be guaranteed. Therefore, this paper proposes an improved KAZE algorithm, which is based on nonlinear scale, to raise the number of feature and to enhance the matching rate by using the adjusted-cosine vector. The experiment result shows that the number of feature and the matching rate of the improved KAZE are remarkably than the original KAZE algorithm.

Spectral and Temporal Properties of the Ultraluminous X-Ray Pulsar in M82 from 15 years of Chandra Observations and Analysis of the Pulsed Emission Using NuSTAR

NASA Astrophysics Data System (ADS)

Brightman, Murray; Harrison, Fiona; Walton, Dominic J.; Fuerst, Felix; Hornschemeier, Ann; Zezas, Andreas; Bachetti, Matteo; Grefenstette, Brian; Ptak, Andrew; Tendulkar, Shriharsh; Yukita, Mihoko

2016-01-01

The recent discovery by Bachetti et al. of a pulsar in M82 that can reach luminosities of up to 1040 erg s-1, a factor of ˜100 times the Eddington luminosity for a 1.4 M⊙ compact object, poses a challenge for accretion physics. In order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.5-8 keV X-ray emission from this source from 15 years of Chandra observations. We analyze 19 ACIS observations where the point-spread function (PSF) of the pulsar is not contaminated by nearby sources. We fit the Chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in M82. We carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of >10%, which we account for during spectral modeling with a convolution model. When fitted with a power-law model, the average photon index when the source is at high luminosity (LX > 1039 erg s-1) is Γ = 1.33 ± 0.15. For the disk blackbody model, the average temperature is Tin = 3.24 ± 0.65 keV, the spectral shape being consistent with other luminous X-ray pulsars. We also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous X-ray pulsars. In addition, we present spectral analysis from NuSTAR over the 3-50 keV range where we have isolated the pulsed component. We find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where Γ = 0.6 ± 0.3 and {E}{{C}}={14}-3+5 keV. While the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9/19 (47%) observations that we analyzed, the pulsar appears to be emitting at a luminosity in excess of 1039 erg s-1, greater than 10 times its Eddington limit.

Spectral and Temporal Properties of the Ultra-Luminous X-Ray Pulsar in M82 from 15 Years of Chandra Observations and Analysis of the Pulsed Emission Using NuSTAR

NASA Technical Reports Server (NTRS)

Brightman, Murray; Harrison, Fiona; Walton, Dominic J.; Fuerst, Felis; Zezas, Andreas; Bachetti, Matteo; Grefenstette, Brian; Ptak, Andrew; Tendulkar, Shriharsh; Yukita, Mihoko

2016-01-01

The recent discovery by Bachetti et al. of a pulsar in M82 that can reach luminosities of up to 10(exp 40) erg s(exp -1), a factor of approximately 100 times the Eddington luminosity for a 1.4 solar mass compact object, poses a challenge for accretion physics. In order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.58 keV X-ray emission from this source from 15 years of Chandra observations. We analyze 19 ACIS observations where the point-spread function (PSF) of the pulsar is not contaminated by nearby sources. We fit the Chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in M82. We carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of 10, which we account for during spectral modeling with a convolution model. When fitted with a power-law model, the average photon index when the source is at high luminosity (LX greater than 10(exp 39) erg s(exp -1) is equal to gamma 1.33 +/-.0.15. For the disk blackbody model, the average temperature is T(sub in) 3.24 +/- 0.65 keV, the spectral shape being consistent with other luminous X-ray pulsars. We also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous X-ray pulsars. In addition, we present spectral analysis from NuSTAR over the 3-50 keV range where we have isolated the pulsed component. We find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where gamma is equal to 0.6 +/- 0.3 and E(sub C) is equal to 14(exp +5) (sub -3)) keV. While the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9/19 (47%) observations that we analyzed, the pulsar appears to be emitting at a luminosity in excess of 10( exp (39) erg s (exp -1), greater than 10 times its Eddington limit.

On the Gas Content and Efficiency of AGN Feedback in Low-redshift Quasars

NASA Astrophysics Data System (ADS)

Shangguan, Jinyi; Ho, Luis C.; Xie, Yanxia

2018-02-01

The interstellar medium is crucial to understanding the physics of active galaxies and the coevolution between supermassive black holes and their host galaxies. However, direct gas measurements are limited by sensitivity and other uncertainties. Dust provides an efficient indirect probe of the total gas. We apply this technique to a large sample of quasars, whose total gas content would be prohibitively expensive to measure. We present a comprehensive study of the full (1 to 500 μm) infrared spectral energy distributions of 87 redshift <0.5 quasars selected from the Palomar-Green sample, using photometric measurements from 2MASS, WISE, and Herschel, combined with Spitzer mid-infrared (5–40 μm) spectra. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we decompose various overlapping contributions to the integrated spectral energy distribution, including starlight, warm dust from the torus, and cooler dust on galaxy scales. This procedure yields a robust dust mass, which we use to infer the gas mass, using a gas-to-dust ratio constrained by the host galaxy stellar mass. Most (90%) quasar hosts have gas fractions similar to those of massive, star-forming galaxies, although a minority (10%) seem genuinely gas-deficient, resembling present-day massive early-type galaxies. This result indicates that “quasar mode” feedback does not occur or is ineffective in the host galaxies of low-redshift quasars. We also find that quasars can boost the interstellar radiation field and heat dust on galactic scales. This cautions against the common practice of using the far-infrared luminosity to estimate the host galaxy star formation rate.

High-latitude dust clouds LDN 183 and LDN 169: distances and extinctions

NASA Astrophysics Data System (ADS)

Straižys, V.; Boyle, R. P.; Zdanavičius, J.; Janusz, R.; Corbally, C. J.; Munari, U.; Andersson, B.-G.; Zdanavičius, K.; Kazlauskas, A.; Maskoliūnas, M.; Černis, K.; Macijauskas, M.

2018-03-01

Interstellar extinction is investigated in a 2°× 2° area containing the dust and molecular clouds LDN 183 (MBM 37) and LDN 169, which are located at RA = 15h 54m, Dec = - 3°. The study is based on a photometric classification in spectral and luminosity classes of 782 stars selected from the catalogs of 1299 stars down to V = 20 mag observed in the Vilnius seven-color system. For control, the MK types for the 18 brightest stars with V between 8.5 and 12.8 mag were determined spectroscopically. For 14 stars, located closer than 200 pc, distances were calculated from trigonometric parallaxes taken from the Gaia Data Release 1. For about 70% of the observed stars, two-dimensional spectral types, interstellar extinctions AV, and distances were determined. Using 57 stars closer than 200 pc, we estimate that the front edge of the clouds begins at 105 ± 8 pc. The extinction layer in the vicinities of the clouds can be about 20 pc thick. In the outer parts of the clouds and between the clouds, the extinction is 0.5-2.0 mag. Behind the Serpens/Libra clouds, the extinction range does not increase; this means that the dust layer at 105 pc is a single extinction source. 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/611/A9

The search for extraterrestrial life: Recent developments; Proceedings of the Symposium, Boston University, MA, June 18-21, 1984

NASA Astrophysics Data System (ADS)

Papagiannis, M. D.

The conference presents papers on the history of the search for extraterrestrial life, the scientific rationale and methods used in the search for other planetary systems, the detection of distant planets with the Space Telescope, planetary searches using optical astrometric interferometers, and infrared spectral identification of complex organic molecules in interstellar grains. Also considered are universal protein ancestors from hydrogen cyanide and water, astronomical sources of polarized light and their role in determining molecular chirality on earth, the universal diagrams and life in the universe, the precambrian evolution of terrestrial life and a thermodynamic approach to the occurrance and appearance of galactic life forms. Papers are also presented on the Ohio Seti program, lunar reflections of terrestrial radio leakage, the multichannel spectrum analyzer, software implementation of detection algorithms for the MCSA, the Serendip II design, galactic colonization and competition in a young galactic disk, implications of ancient and future migrations, extraterrestrial intelligence, the inevitability and the possible structures of supercivilizations, planetary, interplanetary and interstellar organic matter, and universal aspects of biological evolution.

Infrared Spectra and Optical Constants of Elusive Amorphous Methane

NASA Technical Reports Server (NTRS)

Gerakines, Perry A.; Hudson, Reggie L.

2015-01-01

New and accurate laboratory results are reported for amorphous methane (CH4) ice near 10 K for the study of the interstellar medium (ISM) and the outer Solar System. Near- and mid-infrared (IR) data, including spectra, band strengths, absorption coefficients, and optical constants, are presented for the first time for this seldom-studied amorphous solid. The apparent IR band strength near 1300 cm(exp -1) (7.69 micrometer) for amorphous CH4 is found to be about 33% higher than the value long used by IR astronomers to convert spectral observations of interstellar CH4 into CH4 abundances. Although CH4 is most likely to be found in an amorphous phase in the ISM, a comparison of results from various laboratory groups shows that the earlier CH4 band strength at 1300 cm(exp -1) (7.69 micrometer) was derived from IR spectra of ices that were either partially or entirely crystalline CH4 Applications of the new amorphous-CH4 results are discussed, and all optical constants are made available in electronic form.

The search for extraterrestrial life: Recent developments; Proceedings of the Symposium, Boston University, MA, June 18-21, 1984

NASA Technical Reports Server (NTRS)

Papagiannis, M. D. (Editor)

1985-01-01

The conference presents papers on the history of the search for extraterrestrial life, the scientific rationale and methods used in the search for other planetary systems, the detection of distant planets with the Space Telescope, planetary searches using optical astrometric interferometers, and infrared spectral identification of complex organic molecules in interstellar grains. Also considered are universal protein ancestors from hydrogen cyanide and water, astronomical sources of polarized light and their role in determining molecular chirality on earth, the universal diagrams and life in the universe, the precambrian evolution of terrestrial life and a thermodynamic approach to the occurrance and appearance of galactic life forms. Papers are also presented on the Ohio Seti program, lunar reflections of terrestrial radio leakage, the multichannel spectrum analyzer, software implementation of detection algorithms for the MCSA, the Serendip II design, galactic colonization and competition in a young galactic disk, implications of ancient and future migrations, extraterrestrial intelligence, the ineviability and the possible structures of supercivilizations, planetary, interplanetary and interstellar organic matter, and universal aspects of biological evolution.

UV action spectroscopy of protonated PAH derivatives. Methyl substituted quinolines

NASA Astrophysics Data System (ADS)

Klærke, B.; Holm, A. I. S.; Andersen, L. H.

2011-08-01

Aims: We investigate the production of molecular photofragments upon UV excitation of PAH derivatives, relevant for the interstellar medium. Methods: The action absorption spectra of protonated gas-phase methyl-substituted quinolines (CH3 - C9H7NH+) have been recorded in the 215-338 nm spectral range using the electrostatic storage ring ELISA, an electrospray ion source and 3 ns UV laser pulses. Results: It is shown that the absorption profile is both redshifted and broadened when moving the methyl group from the heterocycle containing nitrogen to the homoatomic ring. The absorption profiles are explained by TD-DFT calculations. The dissociation time of the studied molecules is found to be of several milliseconds at 230 nm and it is shown that after redistribution of the absorbed energy the molecules dissociate in several channels. The dissociation time found is an order of magnitude faster than the estimated IR relaxation time. Photophysical properties of both nitrogen containing and methyl-substituted PAHs are interesting in an astrophysical context in connection with identifying the aromatic component of the interstellar medium.

Inference of a 7.75 eV lower limit in the ultraviolet pumping of interstellar polycyclic aromatic hydrocarbon cations with resulting unidentified infrared emissions

NASA Technical Reports Server (NTRS)

Robinson, M. S.; Beegle, L. W.; Wdowiak, T. J.

1997-01-01

The discrete infrared features known as the unidentified infrared (UIR) bands originating in starburst regions of other galaxies, and in H II regions and planetary nebulae within the Milky Way, are widely thought to be the result of ultraviolet pumped infrared fluorescence of polycyclic aromatic hydrocarbon (PAH) molecules and ions. These UIR emissions are estimated to account for 10%-30% of the total energy emitted by galaxies. Laboratory absorption spectra including the vacuum ultraviolet region, as described in this paper, show a weakening of the intensity of absorption features as the population of cations increases, suggesting that strong pi* <-- pi transitions are absent in the spectra of PAH cations. This implies a lower energy bound for ultraviolet photons that pump infrared emissions from such ions at 7.75 eV, an amount greater than previously thought. The implications include size and structure limitations on the PAH molecules and ions which are apparent constituents of the interstellar medium. Also, this might affect estimations of the population of early-type stars in regions of rapid star formation.

Classification of fresh and frozen-thawed pork muscles using visible and near infrared hyperspectral imaging and textural analysis.

PubMed

Pu, Hongbin; Sun, Da-Wen; Ma, Ji; Cheng, Jun-Hu

2015-01-01

The potential of visible and near infrared hyperspectral imaging was investigated as a rapid and nondestructive technique for classifying fresh and frozen-thawed meats by integrating critical spectral and image features extracted from hyperspectral images in the region of 400-1000 nm. Six feature wavelengths (400, 446, 477, 516, 592 and 686 nm) were identified using uninformative variable elimination and successive projections algorithm. Image textural features of the principal component images from hyperspectral images were obtained using histogram statistics (HS), gray level co-occurrence matrix (GLCM) and gray level-gradient co-occurrence matrix (GLGCM). By these spectral and textural features, probabilistic neural network (PNN) models for classification of fresh and frozen-thawed pork meats were established. Compared with the models using the optimum wavelengths only, optimum wavelengths with HS image features, and optimum wavelengths with GLCM image features, the model integrating optimum wavelengths with GLGCM gave the highest classification rate of 93.14% and 90.91% for calibration and validation sets, respectively. Results indicated that the classification accuracy can be improved by combining spectral features with textural features and the fusion of critical spectral and textural features had better potential than single spectral extraction in classifying fresh and frozen-thawed pork meat. Copyright © 2014 Elsevier Ltd. All rights reserved.

Simulations of Galactic polarized synchrotron emission for Epoch of Reionization observations

NASA Astrophysics Data System (ADS)

Spinelli, M.; Bernardi, G.; Santos, M. G.

2018-06-01

The detection of the redshifted cosmological 21 cm line signal requires the removal of the Galactic and extragalactic foreground emission, which is orders of magnitude brighter anywhere in the sky. Foreground cleaning methods currently used are efficient in removing spectrally smooth components. However, they struggle in the presence of not spectrally smooth contamination that is, therefore, potentially the most dangerous one. An example of this is the polarized synchrotron emission, which is Faraday rotated by the interstellar medium and leaks into total intensity due to instrumental imperfections. In this work we present new full-sky simulations of this polarized synchrotron emission in the 50 - 200 MHz range, obtained from the observed properties of diffuse polarized emission at low frequencies. The simulated polarized maps are made publicly available, aiming to provide more realistic templates to simulate the effect of instrumental leakage and the effectiveness of foreground separation techniques.

Laboratory investigations

NASA Technical Reports Server (NTRS)

Russell, Ray W.

1988-01-01

Laboratory studies related to cometary grains and the nuclei of comets can be broken down into three areas which relate to understanding the spectral properties, the formation mechanisms, and the evolution of grains and nuclei: (1) Spectral studies to be used in the interpretation of cometary spectra; (2) Sample preparation experiments which may shed light on the physical nature and history of cometary grains and nuclei by exploring the effects on grain emissivities resulting from the ways in which the samples are created; and (3) Grain processing experiments which should provide insight on the interaction of cometary grains with the environment in the immediate vicinity of the cometary nucleus as the comet travels from the Oort cloud through perihelion, and perhaps even suggestions regarding the relationship between interstellar grains and cometary matter. A summary is presented with a different view of lab experiments than is found in the literature, concentrating on measurement techniques and sample preparations especially relevant to cometary dust.

Airborne astronomy with a 150 micrometer - 500 micrometer heterodyne spectrometer

NASA Technical Reports Server (NTRS)

Betz, A. L.

1991-01-01

This report summarizes work done under NASA Grant NAG2-254 awarded to the University of California. The project goal was to build a far-infrared heterodyne spectrometer for NASA's Kuiper Airborne Observatory (KAO), and to use this instrument to observe atomic and molecular spectral lines from the interstellar medium. This goal was successfully achieved; the spectrometer is now in routine use aboard the KAO. Detections of particular note have been the 370 micrometers line of neutral atomic carbon, the 158 micrometers transition of ionized carbon, many of the high-J rotational lines of 12CO and 13CO between J=9-8 and J=22-21, the 119 micron ground-state rotational line of OH, and the 219 micron ground-state rotational line of H2D(+). All of these lines were observed at spectral resolutions exceeding 1 part in 10(exp 6), thereby allowing accurate line shapes and Doppler velocities to be measured.

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.

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.

Infrared spectra of interstellar deuteronated PAHs

NASA Astrophysics Data System (ADS)

Buragohain, Mridusmita; Pathak, Amit; Sarre, Peter

2015-08-01

Polycyclic Aromatic Hydrocarbon (PAH) molecules have emerged as a potential constituent of the ISM that emit strong features at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.7 μm with weaker and blended features in the 3-20μm region. These features are proposed to arise from the vibrational relaxation of PAH molecules on absorption of background UV photons (Tielens 2008). These IR features have been observed towards almost all types of astronomical objects; say H II regions, photodissociation regions, reflection nebulae, planetary nebulae, young star forming regions, external galaxies, etc. A recent observation has proposed that interstellar PAHs are major reservoir for interstellar deuterium (D) (Peeters et al. 2004). According to the `deuterium depletion model' as suggested by Draine (2006), some of the Ds formed in the big bang are depleted in PAHs, which can account for the present value of D/H in the ISM. Hence, study of deuterated PAHs (PADs) is essential in order to measure D/H in the ISM.In this work, we consider another probable category of the large PAH family, i.e. Deuteronated PAHs (DPAH+). Onaka et al. have proposed a D/H ratio which is an order of magnitude smaller than the proposed value of D/H by Draine suggesting that if Ds are depleted in PAHs, they might be accommodated in large PAHs (Onaka et al. 2014). This work reports a `Density Functional Theory' calculation of large deuteronated PAHs (coronene, ovalene, circumcoronene and circumcircumcoronene) to determine the expected region of emission features and to find a D/H ratio that is comparable to the observational results. We present a detailed analysis of the IR spectra of these molecules and discuss the possible astrophysical implications.ReferencesDraine B. T. 2006, in ASP Conf. Ser. 348, Proc. Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE, ed. G. Sonneborn, H. Moos, B-G Andersson (San Francisco, CA:ASP) 58Onaka T., Mori T. I., Sakon I., Ohsawa R., Kaneda H., Okada Y., Tanaka M., 2014, ApJ,780,114Peeters E., Allamandola L. J., Bauschlicher C. W., Jr., Hudgins D. M., Sandford S. A., Tielens A. G. G. M., 2004, ApJ, 604, 252Tielens A. G. G. M. 2008, ARA&A, 46, 289

Hyperspectral Features of Oil-Polluted Sea Ice and the Response to the Contamination Area Fraction

PubMed Central

Li, Ying; Liu, Chengyu; Xie, Feng

2018-01-01

Researchers have studied oil spills in open waters using remote sensors, but few have focused on extracting reflectance features of oil pollution on sea ice. An experiment was conducted on natural sea ice in Bohai Bay, China, to obtain the spectral reflectance of oil-contaminated sea ice. The spectral absorption index (SAI), spectral peak height (SPH), and wavelet detail coefficient (DWT d5) were calculated using stepwise multiple linear regression. The reflectances of some false targets were measured and analysed. The simulated false targets were sediment, iron ore fines, coal dust, and the melt pool. The measured reflectances were resampled using five common sensors (GF-2, Landsat8-OLI, Sentinel3-OLCI, MODIS, and AVIRIS). Some significant spectral features could discriminate between oil-polluted and clean sea ice. The indices correlated well with the oil area fractions. All of the adjusted R2 values exceeded 0.9. The SPH model1, based on spectral features at 507–670 and 1627–1746 nm, displayed the best fitting. The resampled data indicated that these multi-spectral and hyper-spectral sensors could be used to detect crude oil on the sea ice if the effect of noise and spatial resolution are neglected. The spectral features and their identified changes may provide reference on sensor design and band selection. PMID:29342945

A Real-Time Infrared Ultra-Spectral Signature Classification Method via Spatial Pyramid Matching

PubMed Central

Mei, Xiaoguang; Ma, Yong; Li, Chang; Fan, Fan; Huang, Jun; Ma, Jiayi

2015-01-01

The state-of-the-art ultra-spectral sensor technology brings new hope for high precision applications due to its high spectral resolution. However, it also comes with new challenges, such as the high data dimension and noise problems. In this paper, we propose a real-time method for infrared ultra-spectral signature classification via spatial pyramid matching (SPM), which includes two aspects. First, we introduce an infrared ultra-spectral signature similarity measure method via SPM, which is the foundation of the matching-based classification method. Second, we propose the classification method with reference spectral libraries, which utilizes the SPM-based similarity for the real-time infrared ultra-spectral signature classification with robustness performance. Specifically, instead of matching with each spectrum in the spectral library, our method is based on feature matching, which includes a feature library-generating phase. We calculate the SPM-based similarity between the feature of the spectrum and that of each spectrum of the reference feature library, then take the class index of the corresponding spectrum having the maximum similarity as the final result. Experimental comparisons on two publicly-available datasets demonstrate that the proposed method effectively improves the real-time classification performance and robustness to noise. PMID:26205263

Grain Growth and Silicates in Dense Clouds

NASA Technical Reports Server (NTRS)

Pendeleton, Yvonne J.; Chiar, J. E.; Ennico, K.; Boogert, A.; Greene, T.; Knez, C.; Lada, C.; Roellig, T.; Tielens, A.; Werner, M.;

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 plausible correlation between PAH charge states and DIB "families" is thus provided by the PAH-DIB proposal. Following this proposal, DIB families would provide tracers of conditions within a cloud which globally determine the relative importance of cations, anions, and neutral species, rather than tracers of a specific species. Observational predictions are given to establish the viability of the PAH hypothesis. It is concluded that small PAH ions are very promising candidates as DIB carriers provided their population is dominated by a finite number (100-200) of species. A key test for the PAH proposal, consisting of laboratory and astronomical investigations of the ultraviolet range, is called for.

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 between PAH charge states and DIB "families" is thus provided by the PAH-DIB proposal. Following this proposal, DIB families would reflect conditions within a cloud which locally determine the relative importance of cations, anions, and neutral species, rather than tracers of a specific species. Observational predictions are given to establish the viability of the PAH hypothesis. It is concluded that small PAH ions are very promising candidates as DIB carriers provided their population is dominated by a finite number (100-200) of species. A key test for the PAH proposal, consisting of laboratory and astronomical investigations in the ultraviolet range, is called for.

A Herschel [C ii] Galactic plane survey. II. CO-dark H2 in clouds

NASA Astrophysics Data System (ADS)

Langer, W. D.; Velusamy, T.; Pineda, J. L.; Willacy, K.; Goldsmith, P. F.

2014-01-01

Context. H i and CO large scale surveys of the Milky Way trace the diffuse atomic clouds and the dense shielded regions of molecular hydrogen clouds, respectively. However, until recently, we have not had spectrally resolved C+ surveys in sufficient lines of sight to characterize the ionized and photon dominated components of the interstellar medium, in particular, the H2 gas without CO, referred to as CO-dark H2, in a large sample of interstellar clouds. Aims: We use a sparse Galactic plane survey of the 1.9 THz (158 μm) [C ii] spectral line from the Herschel open time key programme, Galactic Observations of Terahertz C+ (GOT C+), to characterize the H2 gas without CO in a statistically significant sample of interstellar clouds. Methods: We identify individual clouds in the inner Galaxy by fitting the [C ii] and CO isotopologue spectra along each line of sight. We then combine these spectra with those of H i and use them along with excitation models and cloud models of C+ to determine the column densities and fractional mass of CO-dark H2 clouds. Results: We identify1804 narrow velocity [C ii] components corresponding to interstellar clouds in different categories and evolutionary states. About 840 are diffuse molecular clouds with no CO, ~510 are transition clouds containing [C ii] and 12CO, but no 13CO, and the remainder are dense molecular clouds containing 13CO emission. The CO-dark H2 clouds are concentrated between Galactic radii of ~3.5 to 7.5 kpc and the column density of the CO-dark H2 layer varies significantly from cloud to cloud with a global average of 9 × 1020 cm-2. These clouds contain a significant fraction by mass of CO-dark H2, that varies from ~75% for diffuse molecular clouds to ~20% for dense molecular clouds. Conclusions: We find a significant fraction of the warm molecular ISM gas is invisible in H i and CO, but is detected in [C ii]. The fraction of CO-dark H2 is greatest in the diffuse clouds and decreases with increasing total column density, and is lowest in the massive clouds. The column densities and mass fraction of CO-dark H2 are less than predicted by models of diffuse molecular clouds using solar metallicity, which is not surprising as most of our detections are in Galactic regions where the metallicity is larger and shielding more effective. There is an overall trend towards a higher fraction of CO-dark H2 in clouds with increasing Galactic radius, consistent with lower metallicity there. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)

NASA Astrophysics Data System (ADS)

Belloche, A.; Müller, H. S. P.; Menten, K. M.; Schilke, P.; Comito, C.

2013-11-01

Context. The discovery of amino acids in meteorites fallen to Earth and the detection of glycine, the simplest of them, in samples returned from a comet to Earth strongly suggest that the chemistry of the interstellar medium is capable of producing such complex organic molecules and that they may be widespread in our Galaxy. Aims: Our goal is to investigate the degree of chemical complexity that can be reached in the interstellar medium, in particular in dense star-forming regions. Methods: We performed an unbiased, spectral line survey toward Sgr B2(N) and (M), two regions where high-mass stars are formed, with the IRAM 30 m telescope in the 3 mm atmospheric transmission window. Partial surveys at 2 and 1.3 mm were performed in parallel. The spectra were analyzed with a simple radiative transfer model that assumes local thermodynamic equilibrium but takes optical depth effects into account. Results: About 3675 and 945 spectral lines with a peak signal-to-noise ratio higher than 4 are detected at 3 mm toward Sgr B2(N) and (M), i.e. about 102 and 26 lines per GHz, respectively. This represents an increase by about a factor of two over previous surveys of Sgr B2. About 70% and 47% of the lines detected toward Sgr B2(N) and (M) are identified and assigned to 56 and 46 distinct molecules as well as to 66 and 54 less abundant isotopologues of these molecules, respectively. In addition, we report the detection of transitions from 59 and 24 catalog entries corresponding to vibrationally or torsionally excited states of some of these molecules, respectively, up to a vibration energy of 1400 cm-1 (2000 K). Excitation temperatures and column densities were derived for each species but should be used with caution. The rotation temperatures of the detected complex molecules typically range from ~50 to 200 K. Among the detected molecules, aminoacetonitrile, n-propyl cyanide, and ethyl formate were reported for the first time in space based on this survey, as were five rare isotopologues of vinyl cyanide, cyanoacetylene, and hydrogen cyanide. We also report the detection of transitions from within twelve new vibrationally or torsionally excited states of known molecules. Absorption features produced by diffuse clouds along the line of sight are detected in transitions with low rotation quantum numbers of many simple molecules and are modeled with ~30-40 velocity components with typical linewidths of ~3-5 km s-1. Conclusions: Although the large number of unidentified lines may still allow future identification of new molecules, we expect most of these lines to belong to vibrationally or torsionally excited states or to rare isotopologues of known molecules for which spectroscopic predictions are currently missing. Significant progress in extending the inventory of complex organic molecules in Sgr B2(N) and deriving tighter constraints on their location, origin, and abundance is expected in the near future thanks to an ongoing spectral line survey at 3 mm with ALMA in its cycles 0 and 1. The present single-dish survey will serve as a solid basis for the line identification and analysis of such an interferometric survey. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Figures 2-7 and Tables 6-107 are available in electronic form at http://www.aanda.orgThe observed and synthetic 3 mm spectra of Sgr B2(N) and (M), as well as the lists of line identifications corresponding to the blue lab- els in Figs. 2-7, are 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/559/A47

Temporal evolution of ion spectral structures during a geomagnetic storm: Observations and modeling

NASA Astrophysics Data System (ADS)

Ferradas, C.; Zhang, J.; Spence, H. E.; Kistler, L. M.; Larsen, B.; Reeves, G. D.; Skoug, R. M.; Funsten, H. O.

2016-12-01

During the last decades several missions have recorded the presence of dynamic spectral features of energetic ions in the inner magnetosphere. We present a case study of the temporal evolution of H+, He+, and O+ spectral structures throughout the geomagnetic storm of 2 October 2013. We use data from the Helium, Oxygen, Proton, and Electron (HOPE) mass spectrometer onboard Van Allen Probe A to analyze the spectral structures in the energy range of 1- 50 keV. We find that the characteristics of the ion structures follow a cyclic pattern, the observed features changing dramatically as the storm starts and then returning to its initial pre-storm state. Quiet, pre-storm times are characterized by multiple and often complex flux structures at narrow energy bands. During the storm main phase, the observed features become simple, with no nose structures or only one nose structure present in the energy-time spectrograms. As the inner magnetosphere recovers from the storm, more complex structures appear once again. Additionally, the heavy ion spectral features are generally more complex than the H+ features, with multiple noses being observed more often in the heavy ion spectra. We use a model of ion drift and losses due to charge exchange to understand the formation of the spectral features and their species dependence.

Absorption by Spinning Dust: A Contaminant for High-redshift 21 cm Observations

NASA Astrophysics Data System (ADS)

Draine, B. T.; Miralda-Escudé, Jordi

2018-05-01

Spinning dust grains in front of the bright Galactic synchrotron background can produce a weak absorption signal that could affect measurements of high-redshift 21 cm absorption. At frequencies near 80 MHz where the Experiment to Detect the Global EoR Signature (EDGES) has reported 21 cm absorption at z≈ 17, absorption could be produced by interstellar nanoparticles with radii a≈ 50 \\mathringA in the cold interstellar medium (ISM), with rotational temperature T ≈ 50 K. Atmospheric aerosols could contribute additional absorption. The strength of the absorption depends on the abundance of such grains and on their dipole moments, which are uncertain. The breadth of the absorption spectrum of spinning dust limits its possible impact on measurement of a relatively narrow 21 cm absorption feature.

Hydrocarbons on Saturn's satellites Iapetus and Phoebe

USGS Publications Warehouse

Cruikshank, D.P.; Wegryn, E.; Dalle, Ore C.M.; Brown, R.H.; Bibring, J.-P.; Buratti, B.J.; Clark, R.N.; McCord, T.B.; Nicholson, P.D.; Pendleton, Y.J.; Owen, T.C.; Filacchione, G.; Coradini, A.; Cerroni, P.; Capaccioni, F.; Jaumann, R.; Nelson, R.M.; Baines, K.H.; Sotin, Christophe; Bellucci, G.; Combes, M.; Langevin, Y.; Sicardy, B.; Matson, D.L.; Formisano, V.; Drossart, P.; Mennella, V.

2008-01-01

Material of low geometric albedo (pV ??? 0.1) is found on many objects in the outer Solar System, but its distribution in the saturnian satellite system is of special interest because of its juxtaposition with high-albedo ice. In the absence of clear, diagnostic spectral features, the composition of this low-albedo (or "dark") material is generally inferred to be carbon-rich, but the form(s) of the carbon is unknown. Near-infrared spectra of the low-albedo hemisphere of Saturn's satellite Iapetus were obtained with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft at the fly-by of that satellite of 31 December 2004, yielding a maximum spatial resolution on the satellite's surface of ???65 km. The spectral region 3-3.6 ??m reveals a broad absorption band, centered at 3.29 ??m, and concentrated in a region comprising about 15% of the low-albedo surface area. This is identified as the C{single bond}H stretching mode vibration in polycyclic aromatic hydrocarbon (PAH) molecules. Two weaker bands attributed to {single bond}CH2{single bond} stretching modes in aliphatic hydrocarbons are found in association with the aromatic band. The bands most likely arise from aromatic and aliphatic units in complex macromolecular carbonaceous material with a kerogen- or coal-like structure, similar to that in carbonaceous meteorites. VIMS spectra of Phoebe, encountered by Cassini on 11 June 2004, also show the aromatic hydrocarbon band, although somewhat weaker than on Iapetus. The origin of the PAH molecular material on these two satellites is unknown, but PAHs are found in carbonaceous meteorites, cometary dust particles, circumstellar dust, and interstellar dust. ?? 2007 Elsevier Inc. All rights reserved.

The Galactic Centre Mini-Spiral in the MM-Regime

NASA Technical Reports Server (NTRS)

Kunneriath, D.; Eckart, A.; Vogel, S. N.; Teuben, P.; Muzic, I.; Schoedel, R.; Garcia-Marin, M.; Moultaka, J.; Staguhn, J.; Straubmeier, C.;

Establishing a Network of faint DA white dwarfs as Spectrophotometric Standards

NASA Astrophysics Data System (ADS)

Saha, Abhijit; Narayan, Gautham; Holberg, Jay; Matheson, Thomas; Olszewski, Edward; Stubbs, Christopher; Bohlin, Ralph; Sabbi, Elena; Deustua, Susana; Rest, Armin; Axelrod, Tim; MacKenty, John W.; Camarota, Larry; Gilliland, Ron

2015-08-01

Systematic uncertainties in photometric calibration are the dominant source of error in current type Ia supernova dark energy studies, as well as other forefront cosmology efforts, e.g. photo-redshift determinations for weak lensing mass tomography. Current and next-generation ground-based all-sky surveys require a network of calibration stars with 1) known SEDs (to properly and unambiguously take into account filter differences), and 2) that are on a common photometric zeropoint scale across the sky to sub-percent accuracy. We are using a combination of HST panchromatic photometry and ground based spectroscopy to establish such an essential network of faint primary photometric standards, exploiting the well-understood spectral energy distributions of DA white dwarf stars that are free from the complications of observing through the Earth's time-variable atmosphere. The Balmer features in the spectra are used to deduce the two parameters (temperature and log(g)) from which we model the spectral energy distribution (SED) from these stars which have pure hydrogen atmospheres. By comparing against panchromatic broadband HST photometry, and allowing for an achromatic zero-point adjustment and mild scaling of the interstellar reddening, we find that model prediction and observation agree to a few milli-mag. By combining the zero-point and reddening adjustments with the modeled SED, for each star we obtain the incident SED above the terrestrial atmosphere, thus establishing these objects as spectrophotometric standards. We are pursuing 23 objects between 16 and 19 mag spread over the sky uniformly around the equator and northern mid-latitudes, with plans to extend this to southern latitudes. This precision photometric heritage from HST will benefit essentially all existing and upcoming survey projects, and in prticular, directly addresses one of the current barriers to understanding the nature of dark energy.

Shedding light on the Type Ia supernova extinction puzzle: dust location found

NASA Astrophysics Data System (ADS)

Bulla, M.; Goobar, A.; Dhawan, S.

2018-06-01

The colour evolution of reddened Type Ia supernovae can place strong constraints on the location of dust and help address the question of whether the observed extinction stems from the interstellar medium or from circumstellar material surrounding the progenitor. Here we analyse BV photometry of 48 reddened Type Ia supernovae from the literature and estimate the dust location from their B - V colour evolution. We find a time-variable colour excess E(B - V) for 15 supernovae in our sample and constrain dust to distances between 0.013 and 45 pc (4 × 1016 - 1020 cm). For the remaining supernovae, we obtain a constant E(B - V) evolution and place lower limits on the dust distance from the explosion. In all the 48 supernovae, the inferred dust location is compatible with an interstellar origin for the extinction. This is corroborated by the observation that supernovae with relatively nearby dust (≲ 1 pc) are located close to the center of their host galaxy, in high-density dusty regions where interactions between the supernova radiation and interstellar clouds close by are likely to occur. For supernovae showing time-variable E(B - V), we identify a potential preference for low RV values, unusually strong sodium absorption and blue-shifted and time-variable absorption features. Within the interstellar framework, this brings evidence to a proposed scenario where cloud-cloud collisions induced by the supernova radiation pressure can shift the grain size distribution to smaller values and enhance the abundance of sodium in the gaseous phase.

HelMod in the Works: From Direct Observations to the Local Interstellar Spectrum of Cosmic-Ray Electrons

NASA Astrophysics Data System (ADS)

Boschini, M. J.; Della Torre, S.; Gervasi, M.; Grandi, D.; Jóhannesson, G.; La Vacca, G.; Masi, N.; Moskalenko, I. V.; Pensotti, S.; Porter, T. A.; Quadrani, L.; Rancoita, P. G.; Rozza, D.; Tacconi, M.

2018-02-01

The local interstellar spectrum (LIS) of cosmic-ray (CR) electrons for the energy range 1 MeV to 1 TeV is derived using the most recent experimental results combined with the state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. Two propagation packages, GALPROP and HELMOD, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HELMOD, which provides the modulated spectra for specific time periods of the selected experiments for model-data comparison. The optimized HelMod parameters are then used to adjust GALPROP parameters to predict a refined LIS with the procedure repeated subject to a convergence criterion. The parameter optimization uses an extensive data set of proton spectra from 1997 to 2015. The proposed CR electron LIS accommodates both the low-energy interstellar spectra measured by Voyager 1 as well as the high-energy observations by PAMELA and AMS-02 that are made deep in the heliosphere; it also accounts for Ulysses counting rate features measured out of the ecliptic plane. The interstellar and heliospheric propagation parameters derived in this study agree well with our earlier results for CR protons, helium nuclei, and anti-protons propagation and LIS obtained in the same framework.

Fisk-Gloeckler Suprathermal Proton Spectrum in the Heliosheath and the Local Interstellar Medium

NASA Technical Reports Server (NTRS)

Cooper, John F.; Kasprzak, W. T.; Mahaffy, P. R.; Niemann, H. B.; Hartle, R. E.; Paschalidis, N.; Chornay, D.; Coplan, M.; Johnson, R. E.

2010-01-01

Convergence of suprathermal keV-MeV proton and ion spectra approximately to the Fisk-Gloeckler (F-G) form j(E) = j(sub 0) E(sup -1.5) in Voyager land 2 heliosheath measurements is suggestive of distributed acceleration in Kolmogorov turbulence which may extend well beyond the heliopause into the local interstellar medium (LISM). Turbulence of this type is already indicated by interstellar radio scintillation measurements of electron density power spectra. Previously published extrapolations (Cooper et al., 2003, 2006) of the LISM proton spectrum from eV to GeV energies are highly consistent with the F-G power-law and further indicative of such turbulence and LISM effectiveness of the F-G cascade acceleration process. The LISM pressure computed from this spectrum well exceeds that from current estimates for the LISM magnetic field, so exchange of energy between the protons and the magnetic field would likely have a strong role in evolution of the turbulence as per the F-G theory and as long ago proposed for cosmic ray energies by Parker and others. Pressure-dependent estimates of the LISM field strength should not ignore this potentially strong and even dominant contribution from the plasma. Presence of high-beta suprathermal plasma on LISM field lines could significantly affect interactions with the heliospheric outer boundary region and might potentially account for distributed and more discrete features in ongoing measurements of energetic neutral emission from the Interstellar Boundary Explorer (IBEX) mission.

Magnetic Fields in the Interstellar Medium

NASA Astrophysics Data System (ADS)

Clark, Susan

2017-01-01

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

The nature and origin of interstellar diamond

NASA Technical Reports Server (NTRS)

Blake, David F.; Freund, Friedemann; Shipp, Ruth; Krishnan, Kannan F. M.; Echer, Charles J.

1988-01-01

The C-delta component of the Allende meteorite is a microscopic diamond some of whose properties seem in conflict with those expected of diamond. High spatial resolution analytical data are presented here which may help explain such results. Surface and interfacial carbon atoms in the component, which may comprise as much as 25 percent of the total, impart an 'amorphous' character to some spectral data. These data support the proposed high-pressure conversion of amorphous carbon and graphite into diamonds due to grain-grain collisions in the ISM, although a low-pressure mechanism of formation cannot be ruled out.

Picture gallery: A structured presentation of OAO-2 photometric data supported by UBV, ANS, and TD1 observations

NASA Technical Reports Server (NTRS)

Koornneed, J.; Meade, M. R.; Wesselius, P. R.; Code, A. D.; Vanduinen, R.

1981-01-01

Stellar fluxes for 531 stars in the wavelength range lambda 5500-1330A lambda are presented in the form of graphs. The stars are divided into 52 different categories on the basis of their spectral types and objects within one category are shown together. The agreement between the various ultraviolet photometric systems for early type stars is generally better than 0.10 mag. Stars with known and/or observed variability have been grouped separately. A list of stars with observed photometric properties which are indicative of stellar or interstellar anomalies is also provided.

Hot chemistry in the diffuse medium: spectral signature in the H2 rotational lines

NASA Astrophysics Data System (ADS)

Verstraete, L.; Falgarone, E.; Pineau des Forets, G.; Flower, D.; Puget, J. L.

1999-03-01

Most of the diffuse interstellar medium is cold, but it must harbor pockets of hot gas to explain the large observed abundances of molecules like CH+ and HCO+. Because they dissipate locally large amounts of kinetic energy, MHD shocks and coherent vortices in turbulence can drive endothermic chemical reactions or reactions with large activation barriers. We predict the spectroscopic signatures in the H2 rotational lines of MHD shocks and vortices and compare them to those observed with the ISO-SWS along a line of sight through the Galaxy which samples 20 magnitudes of mostly diffuse gas.

Spectroscopy of hot subdwarf binaries

NASA Astrophysics Data System (ADS)

Kreuzer, Simon; Irrgang, Andreas; Heber, Ulrich

2018-06-01

We present a status report of our spectroscopic analysis of subdwarf binaries consisting of a subdwarf and a F/G/K-type main-sequence companion. These systems selected from SDSS photometry show significant excess in the (infra-)red which can not be explained by interstellar reddening. Inspection of SDSS spectra revealed that most of them are composite spectrum sdB binaries. Once their spectra are disentangled, a detailed spectral analysis can be carried out. It reveals Teff, log g and the metal abundance of each individual star. The cool companion is of particular interest, because its spectrum reveals the original chemical composition of the binary.

Radio Emission from a Young Supernova Remnant Interacting with an Interstellar Cloud: Magnetohydrodynamic Simulation with Relativistic Electrons

NASA Astrophysics Data System (ADS)

Jun, Byung-Il; Jones, T. W.

1999-02-01

We present two-dimensional MHD simulations of the evolution of a young Type Ia supernova remnant (SNR) during its interaction with an interstellar cloud of comparable size at impact. We include for the first time in such simulations explicit relativistic electron transport. This was done using a simplified treatment of the diffusion-advection equation, thus allowing us to model injection and acceleration of cosmic-ray electrons at shocks and their subsequent transport. From this information we also model radio synchrotron emission, including spectral information. The simulations were carried out in spherical coordinates with azimuthal symmetry and compare three different situations, each incorporating an initially uniform interstellar magnetic field oriented in the polar direction on the grid. In particular, we modeled the SNR-cloud interactions for a spherical cloud on the polar axis, a toroidal cloud whose axis is aligned with the polar axis, and, for comparison, a uniform medium with no cloud. We find that the evolution of the overrun cloud qualitatively resembles that seen in simulations of simpler but analogous situations: that is, the cloud is crushed and begins to be disrupted by Rayleigh-Taylor and Kelvin-Helmholtz instabilities. However, we demonstrate here that, in addition, the internal structure of the SNR is severely distorted as such clouds are engulfed. This has important dynamical and observational implications. The principal new conclusions we draw from these experiments are the following. (1) Independent of the cloud interaction, the SNR reverse shock can be an efficient site for particle acceleration in a young SNR. (2) The internal flows of the SNR become highly turbulent once it encounters a large cloud. (3) An initially uniform magnetic field is preferentially amplified along the magnetic equator of the SNR, primarily because of biased amplification in that region by Rayleigh-Taylor instabilities. A similar bias produces much greater enhancement to the magnetic energy in the SNR during an encounter with a cloud when the interstellar magnetic field is partially transverse to the expansion of the SNR. The enhanced magnetic fields have a significant radial component, independent of the field orientation external to the SNR. This leads to a strong equatorial bias in synchrotron brightness that could easily mask any enhancements to electron-acceleration efficiency near the magnetic equator of the SNR. Thus, to establish the latter effect, it will be essential to establish that the magnetic field in the brightest regions are actually tangential to the blast wave. (4) The filamentary radio structures correlate well with ``turbulence-enhanced'' magnetic structures, while the diffuse radio emission more closely follows the gas-density distribution within the SNR. (5) At these early times, the synchrotron spectral index due to electrons accelerated at the primary shocks should be close to 0.5 unless those shocks are modified by cosmic-ray proton pressures. While that result is predictable, we find that this simple result can be significantly complicated in practice by SNR interactions with clouds. Those events can produce regions with significantly steeper spectra. Especially if there are multiple cloud encounters, this interaction can lead to nonuniform spatial spectral distributions or, through turbulent mixing, produce a spectrum that is difficult to relate to the actual strength of the blast wave. (6) Interaction with the cloud enhances the nonthermal electron population in the SNR in our simulations because of additional electron injection taking place in the shocks associated with the cloud. Together with point 3, this means that SNR-cloud encounters can significantly increase the radio emission from the SNR.

Laboratory Reflectance Spectra in the Middle-infrared: Effects of Grain Size on Spectral Features

NASA Astrophysics Data System (ADS)

Le Bras, A.; Erard, S.; Fulchignoni, M.

2000-10-01

Since spectral mineral features are sensitive to surface parameters, interpretation of remote-sensing asteroids spectra in terms of mineral composition is not easy nor unique, and laboratory spectra are needed in order to understand the influence of each parameter. We developped an experimental program at IAS, using the 2.5-120 microns interferometer spectrometer, to study the influence of surface parameters on mineral features. We present here the results obtained variing the grain size. We studied grain size effects with two types of terrestrial rocks: anorthosite (bright) and basalte (dark) in the 2-40 microns range. We observed variations of the spectral contrast with grain size, shifts in wavelengths and variations of the intensity of some characteristic spectral features, and appearence of transparency features at wavelengths longer than 8 microns.

Airborne spectroradiometry: The application of AIS data to detecting subtle mineral absorption features

NASA Technical Reports Server (NTRS)

Cocks, T. D.; Green, A. A.

1986-01-01

Analysis of Airborne Imaging Spectrometer (AIS) data acquired in Australia has revealed a number of operational problems. Horizontal striping in AIS imagery and spectral distortions due to order overlap were investigated. Horizontal striping, caused by grating position errors can be removed with little or no effect on spectral details. Order overlap remains a problem that seriously compromises identification of subtle mineral absorption features within AIS spectra. A spectrometric model of the AIS was developed to assist in identifying spurious spectral features, and will be used in efforts to restore the spectral integrity of the data.

Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center

DOE PAGES

Ajello, M.

2016-02-26

The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission towards the Galactic centre (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1 - 100 GeV from a 15° X15° region about the direction of the GC, and implications for the interstellar emissions produced by cosmic ray (CR) particles interacting with the gas and radiation fields in the inner Galaxy and for the point sources detected. Specialised interstellar emission models (IEMs) are constructed that enable separation ofmore » the γ-ray emission from the inner ~ 1 kpc about the GC from the fore- and background emission from the Galaxy. Based on these models, the interstellar emission from CR electrons interacting with the interstellar radiation field via the inverse Compton (IC) process and CR nuclei inelastically scattering off the gas producing γ-rays via π⁰ decays from the inner ~ 1 kpc is determined. The IC contribution is found to be dominant in the region and strongly enhanced compared to previous studies. A catalog of point sources for the 15 °X 15 °region is self-consistently constructed using these IEMs: the First Fermi–LAT Inner Galaxy point source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs, including the Third Fermi–LAT Source Catalog (3FGL). In general, the spatial density of 1FIG sources differs from those in the 3FGL, which is attributed to the different treatments of the interstellar emission and energy ranges used by the respective analyses. Three 1FIG sources are found to spatially overlap with supernova remnants (SNRs) listed in Green’s SNR catalog; these SNRs have not previously been associated with high-energy γ-ray sources. Most 3FGL sources with known multi-wavelength counterparts are also found. However, the majority of 1FIG point sources are unassociated. After subtracting the interstellar emission and point-source contributions from the data a residual is found that is a sub-dominant fraction of the total flux. But, it is brighter than the γ-ray emission associated with interstellar gas in the inner ~ 1 kpc derived for the IEMs used in this paper, and comparable to the integrated brightness of the point sources in the region for energies & 3 GeV. If spatial templates that peak toward the GC are used to model the positive residual and included in the total model for the 1515°X° region, the agreement with the data improves, but they do not account for all the residual structure. The spectrum of the positive residual modelled with these templates has a strong dependence on the choice of IEM.« less

Fermi-LAT observations of the diffuse γ-ray emission: Implications for cosmic rays and the interstellar medium

DOE PAGES

Ackermann, M.; Ajello, M.; Atwood, W. B.; ...

2012-04-09

The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Our observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. In ordermore » to assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. Here, we provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.« less

Fermi-LAT Observations of the Diffuse γ-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium

NASA Astrophysics Data System (ADS)

Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Digel, S. W.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gaggero, D.; Gargano, F.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grove, J. E.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Horan, D.; Hou, X.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Sadrozinski, H. F.-W.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Wood, M.; Yang, Z.; Ziegler, M.; Zimmer, S.

2012-05-01

The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.

FERMI-LAT OBSERVATIONS OF THE DIFFUSE {gamma}-RAY EMISSION: IMPLICATIONS FOR COSMIC RAYS AND THE INTERSTELLAR MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Ajello, M.; Bechtol, K.

The {gamma}-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse {gamma}-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. To assess uncertaintiesmore » associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X{sub CO} factor, the ratio between integrated CO-line intensity and H{sub 2} column density, the fluxes and spectra of the {gamma}-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as {gamma}-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. We also provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.« less

Fermi-LAT observations of the diffuse γ-ray emission: Implications for cosmic rays and the interstellar medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Ajello, M.; Atwood, W. B.

The γ-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Our observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi Large Area Telescope (Fermi-LAT) mission and compare with models of the diffuse γ-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas, and radiation fields. In ordermore » to assess uncertainties associated with the astrophysical input, a grid of models is created by varying within observational limits the distribution of cosmic-ray sources, the size of the cosmic-ray confinement volume (halo), and the distribution of interstellar gas. An all-sky maximum-likelihood fit is used to determine the X CO factor, the ratio between integrated CO-line intensity and H2 column density, the fluxes and spectra of the γ-ray point sources from the first Fermi-LAT catalog, and the intensity and spectrum of the isotropic background including residual cosmic rays that were misclassified as γ-rays, all of which have some dependency on the assumed diffuse emission model. The models are compared on the basis of their maximum-likelihood ratios as well as spectra, longitude, and latitude profiles. Here, we provide residual maps for the data following subtraction of the diffuse emission models. The models are consistent with the data at high and intermediate latitudes but underpredict the data in the inner Galaxy for energies above a few GeV. Possible explanations for this discrepancy are discussed, including the contribution by undetected point-source populations and spectral variations of cosmic rays throughout the Galaxy. In the outer Galaxy, we find that the data prefer models with a flatter distribution of cosmic-ray sources, a larger cosmic-ray halo, or greater gas density than is usually assumed. Our results in the outer Galaxy are consistent with other Fermi-LAT studies of this region that used different analysis methods than employed in this paper.« less

Unraveling the 10 micron "silicate" feature of protostars: the detection of frozen interstellar ammonia

NASA Technical Reports Server (NTRS)

Lacy, J. H.; Faraji, H.; Sandford, S. A.; Allamandola, L. J.

1998-01-01

We present infrared spectra of four embedded protostars in the 750-1230 cm-1 (13.3-8.1 microns) range. For NGC 7538 IRS 9, a new band is reported at 1110 cm-1 (9.01 microns, and several others may be present near 785, 820, 900, 1030, and 1075 cm-1 (12.7, 12.2, 11.1, 9.71, and 9.30 microns). The band 1110 cm-1 is attributed to frozen NH3. Its position and width imply that the NH3 is frozen in a polar, H2O-rich interstellar ice component. The NH3/H2O ice ratio inferred for NGC 7538 IRS 9 is 0.1, making NH3 as important a component as CH3OH and CO2 in the polar ices along this line of sight. At these concentrations, hydrogen bonding between the NH3 and H2O can account for much of the enigmatic low-frequency wing on the 3240 cm-1 (3.09 microns) H2O interstellar ice band. The strength of the implied NH3 deformation fundamental at 1624 cm-1 (6.158 microns) can also account for the absorption at this position reported by ISO.

Observational results of a multi-telescope campaign in search of interstellar urea [(NH{sub 2}){sub 2}CO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Remijan, Anthony J.; Snyder, Lewis E.; Kuo, Hsin-Lun

In this paper, we present the results of an observational search for gas phase urea [(NH{sub 2}){sub 2}CO] observed toward the Sgr B2(N-LMH) region. We show data covering urea transitions from ∼100 GHz to 250 GHz from five different observational facilities: the Berkeley-Illinois-Maryland-Association (BIMA) Array, the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the NRAO 12 m telescope, the IRAM 30 m telescope, and the Swedish-ESO Submillimeter Telescope (SEST). The results show that the features ascribed to urea can be reproduced across the entire observed bandwidth and all facilities by best-fit column density, temperature, and source size parameters whichmore » vary by less than a factor of two between observations merely by adjusting for telescope-specific parameters. Interferometric observations show that the emission arising from these transitions is cospatial and compact, consistent with the derived source sizes and emission from a single species. Despite this evidence, the spectral complexity of both (NH{sub 2}){sub 2}CO and of Sgr B2(N) makes the definitive identification of this molecule challenging. We present observational spectra, laboratory data, and models, and discuss our results in the context of a possible molecular detection of urea.« less

An atlas of Copernicus ultraviolet spectra of Wolf-Rayet stars

NASA Technical Reports Server (NTRS)

Johnson, H. M.

1978-01-01

An atlas of Copernicus UV scans is presented, and line identifications are tabulated, for the Wolf-Rayet stars Gamma-2 Vel (WC 8 + O7), HD 50896 (= EZ CMa; WN 5), and HD 92740 (WN 7). The atlas covers the wavelength ranges from 946.8 to 3182 A for Gamma-2 Vel, from 1012 to 1294 A for HD 50896, and from 1051 to 1243 A for HD 92740. The wavelengths include corrections for components of satellite velocity, earth velocity, and stellar heliocentric velocity; each spectral feature is classified as interstellar, photospheric, emission, UV-displaced P Cygni line absorption, or P Cygni line emission. UV-edge velocities of the P Cygni profiles are estimated, P Cygni profile types are discussed, and the results are compared with Copernicus scans of OB stars exhibiting UV P Cygni profiles. It is noted that: (1) the line-strength ratio of molecular hydrogen to atomic species appears to be substantially greater in the scans of the WN stars than in the Gamma-2 Vel scans; (2) some of the P Cygni profiles in Gamma-2 Vel differ significantly from the corresponding profiles in OB stars; and (3) there may be a slight inverse correlation between ejection velocities and excitation potentials in Gamma-2 Vel.

Centrally Concentrated X-Ray Radiation from an Extended Accreting Corona in Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Liu, B. F.; Taam, Ronald E.; Qiao, Erlin; Yuan, Weimin

2017-10-01

The X-ray emission from bright active galactic nuclei (AGNs) is believed to originate in a hot corona lying above a cold, geometrically thin accretion disk. A highly concentrated corona located within ˜10 gravitational radii above the black hole is inferred from observations. Based on the accretion of interstellar medium/wind, a disk corona model has been proposed in which the corona is well coupled to the disk by radiation, thermal conduction, as well as by mass exchange. Such a model avoids artificial energy input to the corona and has been used to interpret the spectral features observed in AGN. In this work, it is shown that the bulk emission size of the corona is very small for the extended accretion flow in our model. More than 80% of the hard X-ray power is emitted from a small region confined within 10 Schwarzschild radii around a non-spinning black hole, which is expected to be even smaller accordingly for a spinning black hole. Here, the corona emission is more extended at higher Eddington ratios. The compactness parameter of the corona, l=\\tfrac{L}{R}\\tfrac{{σ }{{T}}}{{m}{{e}}{c}3}, is shown to be in the range of 1-33 for Eddington ratios of 0.02-0.1. Combined with the electron temperature in the corona, this indicates that electron-positron pair production is not dominant in this regime. A positive relation between the compactness parameter and photon index is also predicted. By comparing the above model predictions with observational features, we find that the model is in agreement with observations.

Dust composition and mass-loss return from the luminous blue variable R71 in the LMC

NASA Astrophysics Data System (ADS)

Guha Niyogi, S.; Min, M.; Meixner, M.; Waters, L. B. F. M.; Seale, J.; Tielens, A. G. G. M.

2014-09-01

Context. We present an analysis of mid- and far-infrared (IR) spectrum and spectral energy distribution (SED) of the luminous blue variable (LBV) R71 in the Large Magellanic Cloud (LMC). Aims: This work aims to understand the overall contribution of high-mass LBVs to the total dust-mass budget of the interstellar medium (ISM) of the LMC and compare this with the contribution from low-mass asymptotic giant branch (AGB) stars. As a case study, we analyze the SED of R71. Methods: We compiled all the available photometric and spectroscopic observational fluxes from various telescopes for a wide wavelength range (0.36-250 μm). We determined the dust composition from the spectroscopic data, and derived the ejected dust mass, dust mass-loss rate, and other dust shell properties by modeling the SED of R71. We noted nine spectral features in the dust shell of R71 by analyzing Spitzer Space Telescope spectroscopic data. Among these, we identified three new crystalline silicate features. We computed our model spectrum by using 3D radiative transfer code MCMax. Results: Our model calculation shows that dust is dominated by amorphous silicates, with some crystalline silicates, metallic iron, and a very tiny amount of polycyclic aromatic hydrocarbon (PAH) molecules. The presence of both silicates and PAHs indicates that the dust has a mixed chemistry. We derived a dust mass of 0.01 M⊙, from which we arrive at a total ejected mass of ≈5 M⊙. This implies a time-averaged dust mass-loss rate of 2.5 × 10-6 M⊙ yr-1 with an explosion about 4000 years ago. We assume that the other five confirmed dusty LBVs in the LMC loose mass at a similar rate, and estimate the total contribution to the mass budget of the LMC to be ≈10-5 M⊙ yr-1, which is comparable to the contribution by all the AGB stars in the LMC. Conclusions: Based on our analysis on R71, we speculate that LBVs as a class may be an important dust source in the ISM of the LMC.

Forest tree species clssification based on airborne hyper-spectral imagery

NASA Astrophysics Data System (ADS)

Dian, Yuanyong; Li, Zengyuan; Pang, Yong

2013-10-01

Forest precision classification products were the basic data for surveying of forest resource, updating forest subplot information, logging and design of forest. However, due to the diversity of stand structure, complexity of the forest growth environment, it's difficult to discriminate forest tree species using multi-spectral image. The airborne hyperspectral images can achieve the high spatial and spectral resolution imagery of forest canopy, so it will good for tree species level classification. The aim of this paper was to test the effective of combining spatial and spectral features in airborne hyper-spectral image classification. The CASI hyper spectral image data were acquired from Liangshui natural reserves area. Firstly, we use the MNF (minimum noise fraction) transform method for to reduce the hyperspectral image dimensionality and highlighting variation. And secondly, we use the grey level co-occurrence matrix (GLCM) to extract the texture features of forest tree canopy from the hyper-spectral image, and thirdly we fused the texture and the spectral features of forest canopy to classify the trees species using support vector machine (SVM) with different kernel functions. The results showed that when using the SVM classifier, MNF and texture-based features combined with linear kernel function can achieve the best overall accuracy which was 85.92%. It was also confirm that combine the spatial and spectral information can improve the accuracy of tree species classification.

High-energy radiation from collisions of high-velocity clouds and the Galactic disc

NASA Astrophysics Data System (ADS)

del Valle, Maria V.; Müller, A. L.; Romero, G. E.

2018-04-01

High-velocity clouds (HVCs) are interstellar clouds of atomic hydrogen that do not follow normal Galactic rotation and have velocities of a several hundred kilometres per second. A considerable number of these clouds are falling down towards the Galactic disc. HVCs form large and massive complexes, so if they collide with the disc a great amount of energy would be released into the interstellar medium. The cloud-disc interaction produces two shocks: one propagates through the cloud and the other through the disc. The properties of these shocks depend mainly on the cloud velocity and the disc-cloud density ratio. In this work, we study the conditions necessary for these shocks to accelerate particles by diffusive shock acceleration and we study the non-thermal radiation that is produced. We analyse particle acceleration in both the cloud and disc shocks. Solving a time-dependent two-dimensional transport equation for both relativistic electrons and protons, we obtain particle distributions and non-thermal spectral energy distributions. In a shocked cloud, significant synchrotron radio emission is produced along with soft gamma rays. In the case of acceleration in the shocked disc, the non-thermal radiation is stronger; the gamma rays, of leptonic origin, might be detectable with current instruments. A large number of protons are injected into the Galactic interstellar medium, and locally exceed the cosmic ray background. We conclude that under adequate conditions the contribution from HVC-disc collisions to the galactic population of relativistic particles and the associated extended non-thermal radiation might be important.

Prebiotic chemical evolution in the astrophysical context.

PubMed

Ziurys, L M; Adande, G R; Edwards, J L; Schmidt, D R; Halfen, D T; Woolf, N J

2015-06-01

An ever increasing amount of molecular material is being discovered in the interstellar medium, associated with the birth and death of stars and planetary systems. Radio and millimeter-wave astronomical observations, made possible by high-resolution laboratory spectroscopy, uniquely trace the history of gas-phase molecules with biogenic elements. Using a combination of both disciplines, the full extent of the cycling of molecular matter, from circumstellar ejecta of dying stars - objects which expel large amounts of carbon - to nascent solar systems, has been investigated. Such stellar ejecta have been found to exhibit a rich and varied chemical content. Observations demonstrate that this molecular material is passed onto planetary nebulae, the final phase of stellar evolution. Here the star sheds almost its entire original mass, becoming an ultraviolet-emitting white dwarf. Molecules such as H2CO, HCN, HCO(+), and CCH are present in significant concentrations across the entire age span of such nebulae. These data suggest that gas-phase polyatomic, carbon-containing molecules survive the planetary nebula phase and subsequently are transported into the interstellar medium, seeding the chemistry of diffuse and then dense clouds. The extent of the chemical complexity in dense clouds is unknown, hindered by the high spectral line density. Organic species such as acetamide and methyl amine are present in such objects, and NH2CHO has a wide Galactic distribution. However, organophosphorus compounds have not yet been detected in dense clouds. Based on carbon and nitrogen isotope ratios, molecular material from the ISM appears to become incorporated into solar system planetesimals. It is therefore likely that interstellar synthesis influences prebiotic chemistry on planet surfaces.

Searching for Cost-Optimized Interstellar Beacons

NASA Astrophysics Data System (ADS)

Benford, Gregory; Benford, James; Benford, Dominic

2010-06-01

What would SETI beacon transmitters be like if built by civilizations that had a variety of motives but cared about cost? In a companion paper, we presented how, for fixed power density in the far field, a cost-optimum interstellar beacon system could be built. Here, we consider how we should search for a beacon if it were produced by a civilization similar to ours. High-power transmitters could be built for a wide variety of motives other than the need for two-way communication; this would include beacons built to be seen over thousands of light-years. Extraterrestrial beacon builders would likely have to contend with economic pressures just as their terrestrial counterparts do. Cost, spectral lines near 1 GHz, and interstellar scintillation favor radiating frequencies substantially above the classic "water hole." Therefore, the transmission strategy for a distant, cost-conscious beacon would be a rapid scan of the galactic plane with the intent to cover the angular space. Such pulses would be infrequent events for the receiver. Such beacons built by distant, advanced, wealthy societies would have very different characteristics from what SETI researchers seek. Future searches should pay special attention to areas along the galactic disk where SETI searches have seen coherent signals that have not recurred on the limited listening time intervals we have used. We will need to wait for recurring events that may arriarrive in intermittent bursts. Several new SETI search strategies have emerged from these ideas. We propose a new test for beacons that is based on the Life Plane hypotheses.

An IFU-view of Planetary Nebulae: Exploring NGC 6720 (Ring Nebula) with KCWI

NASA Astrophysics Data System (ADS)

Hoadley, Keri; Matuszewski, Matt; Hamden, Erika; Martin, Christopher; Neill, Don; Kyne, Gillian

2018-01-01

Studying the interaction between the ejected stellar material and interstellar clouds is important for understanding how stellar deaths influences the pollution of matter that will later form other stars. Planetary nebulae provide ideal laboratories to study such interactions. I will present on a case study of one close-by planetary nebula, the Ring Nebula (M 57, NGC 6720), to infer the abundances, temperatures, structures, and dynamics of important atomic and ionic species in two distinct regions of the nebula using a newly-commissioned integral field spectrograph (IFS) on Keck: the Keck Cosmic Web Imager (KCWI). The advantage of an IFS over traditional filter-imaging techniques is the ability to simultaneously observe the spectrum of any given pixel in the imaging area, which provides crucial information about the dynamics of the observed region. This technique is powerful for diffuse or extended astrophysical objects, and I will demonstrate the different imaging and spectral modes of KCWI used to observe the Ring Nebula.KCWI observations of the Ring Nebula focused mainly on the innermost region of the nebula, with a little coverage of the Inner Ring. We also observed the length of the Ring in one set of observations, for which we will estimate the elemental abundances, temperatures, and dynamics of the region. KCWI observations also capture an inner arc and blob that have distinctly difference characteristics than the Ring itself and may be a direct observation of either the planetary nebula ramming into an interstellar cloud projected onto the sightline or a dense interstellar cloud being illuminated by the stellar continuum from the hot central white dwarf.

Millimeter and submillimeter wave spectra of 13C-glycolaldehydes

NASA Astrophysics Data System (ADS)

Haykal, I.; Motiyenko, R. A.; Margulès, L.; Huet, T. R.

2013-01-01

Context. Glycolaldehyde (CH2OHCHO) is the simplest sugar and an important intermediate in the path toward forming more complex biologically relevant molecules. Astronomical surveys of interstellar molecules, such as those available with the very sensitive ALMA telescope, require preliminary laboratory investigations of the microwave and submillimeter-wave spectra of molecular species including new isotopologs - to identify these in the interstellar media. Aims: To achieve the detection of the 13C isotopologs of glycolaldehyde in the interstellar medium, their rotational spectra in the millimeter and submillimeter-wave regions were studied. Methods: The spectra of 13CH2OHCHO and CH2OH13CHO were recorded in the 150-945 GHz spectral range in the laboratory using a solid-state submillimeter-wave spectrometer in Lille. The observed line frequencies were measured with an accuracy of 30 kHz up to 700 GHz and of 50 kHz above 700 GHz. We analyzed the spectra with a standard Watson Hamiltonian. Results: About 10 000 new lines were identified for each isotopolog. The spectroscopic parameters were determined for the ground- and the three lowest vibrational states up to 945 and 630 GHz. Previous microwave assignments of 13CH2OHCHO were not confirmed. Conclusions: The provided line-lists and sets of molecular parameters meet the needs for a first astrophysical search of 13C-glycolaldehydes. Full Tables 3 and 4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A96

OT1_ebergin_5: A Systematic Survery of the Water D to H Ratio in Hot Molecular Cores

NASA Astrophysics Data System (ADS)

Bergin, E.

2010-07-01

The D/H ratio of water and the enrichment of HDO relative to H2O in comets, oceans, and interstellar water vapor, has been posited as one of the primary links between chemistry in the cold (T = 10-20 K) dense interstellar medium (ISM) and chemistry in the Solar Nebula. However, there are only ~10 measurements of HDO/H2O, even in hot (T > 100 K) molecular cores, which have the most favorable chemistry (due to fossil evaporation of D-enriched ices) and excitation. In addition the existing measurements have a wide range of uncertainty, making it impossible to discern the presence of source-to-source variations, which could hint at the origin of deuterium enrichments in the dense ISM. We propose here to change this statistic with a systematic survey of HDO and H2O in a sample of 20 hot molecular cores spanning a two order of magnitude range in mass and luminosity. This will increase the number of known water D/H ratios by ~200%. This program is unique in scope for Herschel and requires the uniformity in calibration and high spectral resolution offered by the HIFI instrument. With the stability of HIFI we will be able to derive D/H ratios with significantly less uncertainty. Our observations will be combined with theoretical chemical models to explore the statistics offered by this sample. By looking at a large number of objects with a range of conditions we aim to unlock the secrets of water deuteration in the interstellar space.