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Letteratura scientifica selezionata sul tema "Photodissociation Region"

Autore: Grafiati

Pubblicato: 2 novembre 2024

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Articoli di riviste sul tema "Photodissociation Region"

Tielens, A. G. G. M., e D. Hollenbach. "Photodissociation Regions - Part Two - a Model for the Orion Photodissociation Region". Astrophysical Journal 291 (aprile 1985): 747. http://dx.doi.org/10.1086/163112.

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Tielens, A. G. G. M., e D. Hollenbach. "Photodissociation regions. I - Basic model. II - A model for the Orion photodissociation region". Astrophysical Journal 291 (aprile 1985): 722. http://dx.doi.org/10.1086/163111.

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Klein, Randolf, Alexander Reedy, Christian Fischer, Leslie W. Looney, Sebastian Colditz, Dario Fadda, Alexander G. G. M. Tielens e Willam D. Vacca. "The Photodissociation and Ionization Fronts in M17-SW Localized with FIFI-LS on Board SOFIA". Astrophysical Journal 945, n. 1 (1 marzo 2023): 29. http://dx.doi.org/10.3847/1538-4357/acb823.

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Abstract To understand star formation rates, studying feedback mechanisms that regulate star formation is necessary. The radiation emitted by nascent massive stars play a significant role in feedback by photodissociating and ionizing their parental molecular clouds. To gain a detailed picture of the physical processes, we mapped the photodissociation region (PDR) M17-SW in several fine-structure and high-J CO lines with FIFI-LS, the far-infrared imaging spectrometer aboard SOFIA. An analysis of the CO and [O i]146 μm line intensities, combined with the far-infrared intensity, allows us to create a density and UV intensity map using a one-dimensional model. The density map reveals a sudden change in the gas density crossing the PDR. The strengths and limits of the model and the locations of the ionization and photodissociation front of the edge-on PDR are discussed.

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Escalante, V., e A. Góngora-T. "Photodissociation Regions in Planetary Nebulae". Symposium - International Astronomical Union 155 (1993): 220. http://dx.doi.org/10.1017/s0074180900170822.

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The photodissociation rate of H2 molecules by UV photons from PN central stars is generally several orders of magnitude larger than the rate produced by the average interstellar field (Sternberg 1988, Escalante et al. 1991). Thus, in neutral envelopes of PN's, H2 molecules are destroyed quickly, and a photodissociation region forms around ionization bounded nebulae. Observations of H2 in PN's reveal that not all the hydrogen is photodissociated, and it has been suggested that this is due to the existence of dense disks around the ionized region (Zuckerman and Gatley 1988).

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Bisbas, Thomas G., Jonathan C. Tan e Kei E. I. Tanaka. "Photodissociation region diagnostics across galactic environments". Monthly Notices of the Royal Astronomical Society 502, n. 2 (15 gennaio 2021): 2701–32. http://dx.doi.org/10.1093/mnras/stab121.

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ABSTRACT We present three-dimensional astrochemical simulations and synthetic observations of magnetized, turbulent, self-gravitating molecular clouds. We explore various galactic interstellar medium environments, including cosmic ray ionization rates in the range of ζCR = 10−17–$10^{-14}\, {\rm s}^{-1}$, far-UV intensities in the range of G0 = 1–103 and metallicities in the range of Z = 0.1–$2\, {\rm Z}_{\odot }$. The simulations also probe a range of densities and levels of turbulence, including cases where the gas has undergone recent compression due to cloud–cloud collisions. We examine: (i) the column densities of carbon species across the cycle of C ii, C i, and CO, along with O i, in relation to the H i-to-H2 transition; (ii) the velocity-integrated emission of [C ii] 158 μm, [13C ii] 158 μm, [C i] 609 μm and 370 μm, [O i] 63 μm and 146 μm, and of the first ten 12CO rotational transitions; (iii) the corresponding Spectral Line Energy Distributions; (iv) the usage of [C ii] and [O i] 63 μm to describe the dynamical state of the clouds; (v) the behaviour of the most commonly used ratios between transitions of CO and [C i]; and (vi) the conversion factors for using CO and C i as H2-gas tracers. We find that enhanced cosmic ray energy densities enhance all aforementioned line intensities. At low metallicities, the emission of [C ii] is well connected with the H2 column, making it a promising new H2 tracer in metal-poor environments. The conversion factors of XCO and XC i depend on metallicity and the cosmic ray ionization rate, but not on FUV intensity. In the era of ALMA, SOFIA, and the forthcoming CCAT-prime telescope, our results can be used to understand better the behaviour of systems in a wide range of galactic and extragalactic environments.

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Tielens, A. G. G. M. "Photodissociation Regions and Planetary Nebulae". Symposium - International Astronomical Union 155 (1993): 155–62. http://dx.doi.org/10.1017/s0074180900170330.

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FUV photons (<13.6eV) from the central star create a region of warm (≈1000K) atomic and molecular gas around Planetary Nebulae (PN). This paper reviews theoretical and observational characteristics of such regions, commonly called photodissociation regions or PDRs. PDRs around PN differ in some aspects from those in other galactic objects and this is briefly discussed with an emphasis on time dependent effects. It is concluded that, in evolved PN (texp>103 yr), molecules will only survive inside dense clumps (>106 cm−3). H2 emission from such dense gas will show a thermal spectrum in the low v states. Finally, the physical conditions in the PDR associated with NGC 7027 are compared to those in other galactic and extragalactic PDRs

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Hartquist, T. W., e A. Sternberg. "Photodissociation-region models of interstellar hydroxyl masers". Monthly Notices of the Royal Astronomical Society 248, n. 1 (gennaio 1991): 48–51. http://dx.doi.org/10.1093/mnras/248.1.48.

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Pellegrini, E. W., J. A. Baldwin, C. L. Brogan, M. M. Hanson, N. P. Abel, G. J. Ferland, H. B. Nemala, G. Shaw e T. H. Troland. "A Magnetically Supported Photodissociation Region in M17". Astrophysical Journal 658, n. 2 (aprile 2007): 1119–35. http://dx.doi.org/10.1086/511258.

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Guzmán, Viviana V., Jérôme Pety, Pierre Gratier, Javier R. Goicoechea, Maryvonne Gerin, Evelyne Roueff, Franck Le Petit e Jacques Le Bourlot. "Chemical complexity in the Horsehead photodissociation region". Faraday Discuss. 168 (2014): 103–27. http://dx.doi.org/10.1039/c3fd00114h.

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The interstellar medium is known to be chemically complex. Organic molecules with up to 11 atoms have been detected in the interstellar medium, and are believed to be formed on the ices around dust grains. The ices can be released into the gas-phase either through thermal desorption, when a newly formed star heats the medium around it and completely evaporates the ices; or through non-thermal desorption mechanisms, such as photodesorption, when a single far-UV photon releases only a few molecules from the ices. The first mechanism dominates in hot cores, hot corinos and strongly UV-illuminated PDRs, while the second dominates in colder regions, such as low UV-field PDRs. This is the case of the Horsehead were dust temperatures are ≃20–30 K, and therefore offers a clean environment to investigate the role of photodesorption. We have carried out an unbiased spectral line survey at 3, 2 and 1mm with the IRAM-30m telescope in the Horsehead nebula, with an unprecedented combination of bandwidth, high spectral resolution and sensitivity. Two positions were observed: the warm PDR and a cold condensation shielded from the UV field (dense core), located just behind the PDR edge. We summarize our recently published results from this survey and present the first detection of the complex organic molecules HCOOH, CH₂CO, CH₃CHO and CH₃CCH in a PDR. These species together with CH₃CN present enhanced abundances in the PDR compared to the dense core. This suggests that photodesorption is an efficient mechanism to release complex molecules into the gas-phase in far-UV illuminated regions.

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Federman, S. R., D. C. Knauth, David L. Lambert e B‐G Andersson. "Probing the Photodissociation Region toward HD 200775". Astrophysical Journal 489, n. 2 (10 novembre 1997): 758–65. http://dx.doi.org/10.1086/304804.

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Più fonti

Tesi sul tema "Photodissociation Region"

Guzman, Veloso Viviana. "Physical and Chemical Conditions in the Horsehead Photodissociation Region". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00950116.

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Les raies moléculaires tracent la structure du milieu interstellaire ainsi que les conditions physiques du gaz dans différents environnements allant des galaxies à haut redshift aux disques protoplanétaires. Pour bénéficier des diagnostics moléculaires les voies de formation et de destruction des molécules doivent être comprises quantitativement, tout comme les couplages entre la chimie en phase gazeuse et solide. Des jeux bien compris de données concernant des sources simples sont essentiels pour tester les prédictions des modèles théoriques. Cette thèse présente l'analyse d'un relevé spectral systématique à 1, 2 et 3mm avec le télescope IRAM-30m dans la Tête de Cheval, offrant une combinaison inédite de bande passante, haute résolution spectrale et sensibilité, en direction de deux positions: la région de photodissociation (PDR) et une cœure froid à proximité. Environ 30 espèces avec un maximum de 7 atomes sont détectées sans compter les isotopologues. Ces données sont complétées par des cartes interférométriques IRAM-PdBI à haute résolution d'espèces spécifiques. Les résultats de cette thèse incluent la detection de CF+, un nouveau diagnostic de gaz exposé à l'UV lointain; la détection d'une nouvelle molécule interstellaire, que nous attribuons au petit hydrocarbure C3H+; une étude approfondie des molécules organiques H2CO, CH3OH et CH3CN, qui indique que la photodésorption des glaces est un mécanisme efficace pour relâcher ces molécules en phase gazeuse; et la première détection de molécules organiques complexes, comme HCOOH, CH2CO, CH3CHO et CH3CCH dans une PDR, qui révèle la complexité chimique dans le gaz neutre éclairé en UV lointain.

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Guzman, Veloso Viviana. "Physical and chemical conditions in the horsehead photodissociation region". Paris 6, 2013. http://www.theses.fr/2013PA066526.

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Les raies moléculaires tracent la structure du milieu interstellaire ainsi que les conditions physiques du gaz dans différents environnements allant des galaxies à haut redshift aux disques protoplanétaires. Pour bénéficier des diagnostics moléculaires les voies de formation et de destruction des molécules doivent être comprises quantitativement, tout comme les couplages entre la chimie en phase gazeuse et solide. Des jeux bien compris de données concernant des sources simples sont essentiels pour tester les prédictions des modèles théoriques. Cette thèse présente l’analyse d’un relevé spectral systématique à 1, 2 et 3mm avec le télescope IRAM-30m dans la Tête de Cheval, offrant une combinaison inédite de bande passante, haute résolution spectrale et sensibilité, en direction de deux positions: la région de photodissociation (PDR) et une cœure froid à proximité. Environ 30 espèces avec un maximum de 7 atomes sont détectées sans compter les isotopologues. Ces données sont complétées par des cartes interférométriques IRAM-PdBI à haute résolution d’espèces spécifiques. Les résultats de cette thèse incluent la detection de CF+, un nouveau diagnostic de gaz exposé à l’UV lointain; la détection d’une nouvelle molécule interstellaire, que nous attribuons au petit hydrocarbure C3H+; une étude approfondie des molécules organiques H2CO, CH3OH et CH3CN, qui indique que la photodésorption des glaces est un mécanisme efficace pour relâcher ces molécules en phase gazeuse; et la première détection de molécules organiques complexes, comme HCOOH, CH2CO, CH3CHO et CH3CCH dans une PDR, qui révèle la complexité chimique dans le gaz neutre éclairé en UV lointain
Molecular lines are used to trace the structure of the interstellar medium and the physical conditions of the gas in different environments, from high-z galaxies to protoplanetary disks. To fully benefit from the diagnostic power of molecular lines, the formation and destruction paths of the molecules, including the interplay between gas-phase and grain surface chemistry, must be quantitatively understood. Well-defined sets of observations of simple template sources are key to benchmark the predictions of theoretical models. With that motivation, this thesis is focused on the observation and analysis of an unbiased spectral line survey at 3, 2 and 1mm with the IRAM-30m telescope in the Horsehead nebula, with an unprecedented combination of bandwidth, high spectral resolution and sensitivity. Two positions were observed: the warm photodissociation region (PDR) and a cold condensation shielded from the UV field. Approximately 30 species, with up to 7 atoms plus their isotopologues, are detected. These data are complemented by high-angular resolution IRAM-PdB interferometric maps of specific species. The results of this thesis include the detection of CF+, a new diagnostic of the UV illuminated gas; the detection of a new species in the ISM, tentatively attributed to C3H+; a deep study of the abundance, spatial distribution and excitation conditions of H2CO, CH3OH and CH3CN, which reveals that photo-desorption of ices is an efficient mechanism to re- lease molecules into the gas phase; and the first detection of the complex organic molecules, HCOOH, CH2CO, CH3CHO and CH3CCH in a PDR, which reveals the degree of chemical complexity reached in the UV illuminated neutral gas

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洪美思 e Mei-sze Hung. "Investigation of the Franck-Condon region photodissociation dynamics of linear and cyclic nitroalkanes using resonance Raman spectroscopy". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31215336.

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Hung, Mei-sze. "Investigation of the Franck-Condon region photodissociation dynamics of linear and cyclic nitroalkanes using resonance Raman spectroscopy /". Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19945863.

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Champion, Jason. "Photoevaporation des disques protoplanétaires par les photons UV d’étoiles massives proches : observation de proplyds et modélisation". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30392/document.

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Les disques protoplanétaires entourant les jeunes étoiles sont les embryons des systèmes planétaires. A différentes phases de leur évolution, ils peuvent subir d'importantes pertes de masse par photoévaporation : des photons énergétiques, issus de l'étoile centrale ou d'une étoile voisine, chauffe le disque qui perd en masse sous l'échappement des particules. Cependant, ce mécanisme et la physique sous-jacente n'ont que peu été contraints par les observations. Les objectifs de cette thèse sont d'étudier la photoévaporation dans le cas particulier où elle est due à des photons FUV, d'identifier les principaux paramètres physiques (densité, température) et processus (chauffage et refroidissement) impliqués, et d'estimer son impact sur l'évolution dynamique des disques. L'étude repose sur le couplage observations - modélisations des disques photoévaporés par les photons UV en provenance d'étoiles massives proches. Ces objets, appelés "proplyds", ont leur disque entouré d'une large enveloppe nourrie des flots de photoévaporation. A l'aide d'un modèle 1D d'une région de photodissociation, j'ai développé un modèle pour l'émission dans l'infrarouge lointain des proplyds. Ce modèle a été utilisé pour interpréter les observations, issues principalement de Herschel, pour quatre proplyds. Il apparait que les conditions physiques en surface de leur disque sont similaires: une densité de l'ordre de 10 6 par cm cube et une température d'environ 1000 K. Cette température est maintenue par un équilibre dynamique : si la surface se refroidit, la perte de masse diminue et l'enveloppe se réduit. L'atténuation UV produite par l'enveloppe diminue alors et le disque, recevant plus de photons UV, chauffe. La majorité du disque peut s'échapper sous forme de flots de photoévaporation avec des taux de perte de masse de quelques 10 -7 masse solaire par an ou plus, en accord avec les observations précédentes des traceurs du gaz ionisé. A la suite de ce travail, j'ai développé un modèle hydrodynamique 1D pour étudier l'évolution dynamique d'un disque en photoévaporation par un champ de rayonnement externe. [...]
Protoplanetary disks are found around young stars, and represent the embryonic stage of planetary systems. At different phases of their evolution, disks may undergo substantial mass-loss by photoevaporation: energetic photons from the central or a nearby star heat the disk, hence particles can escape the gravitational potential and the disk loses mass. However, this mechanism, and the underlying physics regulating photoevaporation, have not been well constrained by observations so far. The aims of this thesis are to study photoevaporation, in the specific case when it is driven by far-UV photons, to identify the main physical parameters (density, temperature) and processes (gas heating and cooling mechanisms) that are involved, and to estimate its impact on the disk dynamical evolution. The study relies on coupling observations and models of disks being photoevaporated by UV photons coming from neighbouring massive star(s). Those objects, also known as "proplyds", appear as disks surrounded by a large cometary shaped envelope fed by the photoevaporation flows. Using a 1D code of the photodissociation region, I developed a model for the far-IR emission of proplyds. This model was used to interpret observations, mainly obtained with the Herschel Space Observatory, of four proplyds. We found similar physical conditions at their disk surface: a density of the order of 10 6 cm and a temperature about 1000 K. We found that this temperature is maintained by a dynamical equilibrium: if the disk surface cools, its mass-loss rate declines and the surrounding envelope is reduced. Consequently, the attenuation of the UV radiation field by the envelope decreases and the disk surface, receiving more UV photons, heats up. Most of the disk is thus able to escape through photoevaporation flows leading to mass-loss rates of the order of 10 -7 solar mass per year or more, in good agreement with earlier spectroscopic observations of ionised gas tracers. Following this work, I developed a 1D hydrodynamical code to study the dynamical evolution of an externally illuminated protoplanetary disk. [...]

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Zannese, Marion. "Haute excitation de molécules dans les régions irradiées de formation stellaire et planétaire observées par le James Webb Space Telescope". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP082.

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La rétroaction radiative par les étoiles massives, qui chauffe et agite le gaz du nuage environnant, est un mécanisme dominant limitant la formation stellaire et planétaire. En effet, les observations montrent que seule 1-5 % de la masse des nuages moléculaires est convertie en étoiles. Au cours de cette thèse, je me suis intéressée aux régions neutres, chaudes et irradiées entre les milieux ionisés et moléculaires froids. Plus particulièrement, j'ai étudié comment l'excitation à la formation de certaines molécules (OH, CH+ et CH3+) permettaient d'établir des diagnostics simples et robustes pour contraindre les paramètres physiques et chimiques de ces régions. Pour ce faire, j'ai couplé un travail de modélisation détaillée du gaz, en utilisant des données de dynamique quantique, avec l'analyse des observations du James Webb Space Telescope. La couverture spectrale, la grande sensibilité et la résolution angulaire du JWST lui donne un accès inédit à la chimie et la microphysique des sous-structures à petites échelles des régions de photodissociation (PDR) et des régions chaudes des disques protoplanétaires (région interne ou vent photoévaporé). Ma thèse s'inscrit alors dans l'analyse des données du programme PDRs4All observant la Barre d'Orion et des disques protoplanétaires se trouvant dans la ligne de visée (en particulier d203-506).En préparation des observations, je me suis d'abord concentrée sur les prédictions de ce que pourrait détecter le JWST. J'ai alors étudié l'émission prompte de OH produit rotationnellement excité par la photodissociation de l'eau. Pour cela, j'ai utilisé le code PDR de Meudon, qui calcule de façon auto-cohérente le transfert de rayonnement, la chimie et le bilan thermique dans les PDRs. En implémentant l'émission prompte dans ce code, nous montrons alors que seuls les milieux suffisamment denses et chauds permettent d'exciter OH à la formation. La seconde partie de ma thèse présente l'analyse des spectres obtenus avec le JWST. Les signatures des molécules très excitées à la formation présentes dans ces données et analysées avec des modèles d'excitation à zone unique, basés sur des données de dynamique quantique, ont permis de révéler une chimie particulièrement active dans les régions chaudes et irradiées. Dans la Barre d'Orion et d203-506, nous révélons la détection de OH, CH+ et CH3+ ainsi que leur excitation à la formation, nous permettant de contraindre la chimie en action. En effet, l'émission rotationnelle de OH, modélisée auparavant et détectée dans l'infrarouge moyen, permet de révéler la photodissociation de l'eau. L'émission de OH et CH+, dans l'infrarouge proche trace la formation et l'excitation de ces espèces par pompage chimique via des réactions avec H2 : X + H2 → XH* + H. Ces raies d'émission nous permettent donc de révéler un cycle de formation et de destruction de l'eau très actif dans d203-506 (O <=> OH <=> H2O) ainsi que le début de la chaîne de la chimie du carbone (C+ → CH+ → CH2+ → CH3+) dans la PDR et le disque. Les modèles d'excitation nous ont permis d'identifier les processus d'excitation observés et de traduire l'intensité des raies mesurée en taux de formation et de destruction de ces espèces. Ils permettent également de contraindre les conditions physiques du milieu et peuvent être utilisées pour déterminer localement, à partir de l'intensité des raies observées, l'intensité du champ UV (pour la photodissociation de l'eau) ou la densité du gaz (pour l'émission prompte), ingrédients essentiels déterminant les conditions initiales de la formation stellaire et planétaire. Ces nouveaux diagnostics sont alors des clés d'analyse pour de nombreuses observations du JWST puisqu'il est attendu que ces processus soient détectés dans une multitude d'objets astrophysiques qui présentent des régions chaudes et irradiées (protoétoile, outflow, nébuleuse planétaire...)
Radiative feedback from massive stars, which heats and disperses the gas in the surrounding cloud, is a dominant mechanism limiting stellar and planetary formation. Indeed, observations show that only 1-5% of the mass of molecular clouds is converted into stars. In this thesis, I focused on the neutral, warm and irradiated regions between ionized and cold molecular media. In particular, I investigated how the excitation at the formation of certain molecules (OH, CH+ and CH3+) enabled simple and robust diagnostics to constrain the physical and chemical parameters of these regions. To do this, I coupled detailed gas modeling, using quantum dynamics data, with analysis of observations from the James Webb Space Telescope. The spectral coverage, high sensitivity and angular resolution of the JWST give unprecedented access to the chemistry and microphysics of the small-scale substructures of photodissociation regions (PDR) and the warm regions of protoplanetary disks (inner region or photoevaporated wind). My thesis is part of the analysis of data from the PDRs4All program observing the Orion Bar and protoplanetary disks in the line of sight (in particular d203-506).In preparation for the observations, I first concentrated on predicting what the JWST might detect. I studied the prompt emission of rotationally excited OH produced by the photodissociation of water. To this end, I used the Meudon PDR code, which self-consistently calculates the radiative transfer, the chemistry and the heat balance in PDRs. By implementing prompt emission in this code, we then show that only sufficiently dense and warm environments allow OH excitation at formation. The second part of my thesis presents the analysis of spectra obtained with the JWST. The signatures of highly excited molecules at formation observed in these data and analyzed with single-zone excitation models, based on quantum dynamics data, have revealed a particularly active chemistry in warm, irradiated regions. In the Orion Bar and d203-506, we reveal the detection of OH, CH+ and CH3+ as well as their excitation at formation, allowing us to constrain the chemistry in action. Indeed, OH rotational emission, previously modeled and detected in the mid-infrared, reveals the photodissociation of water. The near-infrared emission of OH and CH+ traces the formation and excitation of these species by chemical pumping via reactions with H2: X + H2 → XH* + H. These emission lines reveal a very active water formation and destruction cycle in d203-506 (O <=> OH <=> H2O), as well as the beginning of the carbon chemistry chain (C+ → CH+ → CH2+ → CH3+) in the PDR and disk. Excitation models have enabled us to identify the observed excitation processes and translate the measured line intensities into formation and destruction rates of these species. They also enable us to constrain the physical conditions of the medium, and can be used to determine locally, from the intensity of the observed lines, the intensity of the UV field (for the photodissociation of water) or the density of the gas (for prompt emission), which are essential ingredients determining the initial conditions of stellar and planetary formation. These new diagnostics will be key to the analysis of many JWST observations, since these processes are expected to be detected in a multitude of astrophysical objects with warm, irradiated regions (protostars, outflow, planetary nebulae, etc.)

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Parikka, Anna. "Properties and evolution of dense structures in the interstellar medium". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112221/document.

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Mon travail de thèse présente deux types de structures denses : des sources froides compactes détectées par Planck et des condensations denses dans une région de photodissociation (PDR), à savoir la Barre d’Orion. Les deux types de structures sont étroitement liées à la formation des étoiles. Les sources froides sont étudiées comme objets potentiellement gravitationnellement liés, c’est-à-dire comme objets préstellaires. La Barre d’Orion est intéressante en tant que PDR à fort champ UV (G0 ∼104) prototypique, avec plusieurs disques protoplanétaires connus, éclairés par les jeunes étoiles du Trapèze.D’abord, je présente un article publié dans A&A: The Physical state of selected cold clumps. Dans cet article, nous avons comparé les observations du continuum de la poussière par Herschel provenant de l’open time key program Galactic Cold Cores (Herschel) aux observations de raies moléculaires par le radiotélescope de 20-m de l’Onsala Space Observatory en Suède. Les objets ont été sélectionnés en fonction de leur luminosités et faibles températures de couleur des poussières (T∼10−15 K). Nous avons calculé les masses du viriel et de Bonnor-Ebert et les avons comparées aux masses déduites Ã partir des observations. Les résultats indiquent que la plupart des objets froids observés ne sont pas nécessairement préstellaires.Dans mon étude de la Barre d’Orion, j’utilise des observations de l’instrumentPACS d’Herschel du programme Unveiling the origin and excitation mechanisms of the warm CO, OH and CH+ . Je présente des cartes de 110” ×110” du cation méthylidyne (CH+ J=3-2), des doublets de OH à 84 μm, et des raies de CO á hauts J (J=19-18). C’est la première fois que ces traceurs des PDR ont présentés avec une telle résolution spatiale et un tel rapport signal-sur-bruit.La répartition spatiale de CH+ et OH montre la même structure de la Barre qui a été vue dans d’autres observations. La morphologie du CH+ et H2 confirme que la formation et l’excitation de CH+ est fortement dépendante du H2 excité vibrationnellement. Le maximum d’émission de OH84 μm correspond à un objet brillant jeune, identifié comme le disque protoplanetaire 244-440.Je présente également des transitions rotationnelles de CO de moyenne (∼20 K) et haute (∼1000 K) énergie. La morphologie de l’émission du CO rotationnellement excité est corrélée avec la présence des petites structures denses irradiées. Nous établissons le lien entre le coeur de ces structures, tracé en CS J=2-1 par Lee et al. (2013) et H 13 CN par Lis and Schilke (2003) et le bord de la PDR, tracé en CO J=19-18 et le H 2 vibrationnellement excitée. Nous montrons également que le CO est principalement excité par le chauffage UV
In this thesis I present a study of two kinds of dense ISM structures: compact cold sources detected by Planck and dense condensations in a photodissociation region (PDR), namely the Orion Bar detected by ground-based and Herschel telescopes. Both kinds of structures are closely related to star formation. The cold sources are investigated as potentially gravitationally bound, prestellar, objects. The Orion Bar is a highly FUV-illuminated (G0=104) prototypical PDR, with several known protoplanetary disks, illuminated by the young Trapezium stars.First I introduce a paper published in A&A: The Physical state of selected cold clumps. In this paper we compared the Herschel dust continuum observations from the open time key program Galactic Cold Cores to ground based molecular line observations from the 20-m radio telescope of the Onsala Space Observatory in Sweden. The clumps were selected based on their brightness and low dust color temperatures (T=10-15 K). We calculated the virial and Bonnor-Ebert masses and compared them to the masses calculated from the observations. The results indicate that most of the observed cold clumps are not necessarily prestellar.Then I move on to the warm and dense condensations of the ISM. In my study of the Orion Bar, I use observations from PACS instrument on board Herschel from the open time program Unveiling the origin and excitation mechanisms of the warm CO, OH and CH+. I present maps of 110”x110” of the methylidyne cation (CH+ J=3-2), OH doublets at 84 µm, and high-J CO (J=19-18). This is the first time that these PDR tracers are presented in such a high spatial resolution and high signal-to-noise ratio. The CH+ and OH have critical densities (1010 cm-3) and upper level energy temperatures (250 K). In addition the endothermicity of the CH+ + H2 reaction (4300 K) that forms CH+ is comparable to the activation barrier of the O + H2 reaction (4800 K) forming OH. Given these similarities it is interesting to compare their emission. The spatial distribution of CH+ and OH shows the same clumpy structure of the Bar that has been seen in other observations. The morphology of CH+ and H2 confirms that CH+ formation and excitation is strongly dependent on the vibrationally excited H2, while OH is not. The peak in the OH 84 µm emission corresponds to a bright young object, identified as the externally illuminated protoplanetary disk 244-440.Finally, I study the high-J CO in the Orion Bar. I also introduce low- and mid-J CO observations of the area. The high-J CO morphology shows a clumpy structure in the Bar and we establish a link between the dense core of the clumps, traced in CS J=2-1 by Lee et al. (2013) and in H13CN by Lis and Schilke (2003). We also show that the high-J CO is mainly excited by the UV heating

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Chrysostomou, Antonio. "Molecular hydrogen line emission from photodissociation regions". Thesis, University of Edinburgh, 1993. http://hdl.handle.net/1842/27794.

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The work presented in this thesis is dedicated to the study of the physical properties of photodissociation regions (PDRs), the surface layers of molecular clouds which are irradiated by ultraviolet radiation. The structure of PDRs is investigated with the development of an analytical model which incorporates the essential heating and cooling mechanisms in a PDR. The main parameters in the model are the density and the incident ultraviolet radiation field, above the ambient value in the solar neighbourhood, impinging on the surface (G₀) which dissociates the molecules in the PDR. It is demonstrated that when the ratio (n/G₀) is high (> 100 cm^-3) the attenuation of ultraviolet photons is dominated by H₂ self shielding which brings the HI/H₂ transition zone close to the surface of the cloud (A_{v <} 1). When the ratio is of order unity then the attenuation of ultraviolet photons is dominated by dust grains in the PDR. In this case, the HI/H₂ transition zone occurs at a depth of A_{v ~ 2 - 3. Images of the PDR in the northern bar of M17 show that there is a spatial coincidence, accurate to}~ 1 arcsec, of the H₂ and 3.28 μm emission regions (the 3.28 μm emission being a tracer of the hot edge of the PDR delineated by the HII/HI transition) placing a lower limit to the density in the clumps of 10⁵ cm^-3. This coincidence is also observed in other PDR sources (eg. NGC 2023) and can be readily explained if the sources are clumpy. It is not clear in the northern bar of M17, where G_{0 ~ 10}^4, whether shielding by dust or H_2 molecules is dominating the attenuation of ultraviolet photons. A uniform, high density PDR model is sufficient to reproduce the observed H_2 line intensity, however the images clearly reveal structures at the 2 arcsec level suggesting that a clumpy model is a realistic solution.

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Klumpe, Eric William. "Large-scale observations of H₂ emission in photodissociation regions /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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Hosokawa, Takashi. "Dynamical expansion of ionization and photodissociation regions and triggered star formation". 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/145081.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第11313号
理博第2871号
新制||理||1429(附属図書館)
22956
UT51-2005-D64
京都大学大学院理学研究科物理学･宇宙物理学専攻
(主査)教授嶺重慎, 教授中村卓史, 助教授鶴剛
学位規則第4条第1項該当

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Libri sul tema "Photodissociation Region"

Hollenbach, David. Time-dependent photodissociation regions. [Washington, DC: National Aeronautics and Space Administration, 1995.

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Antonella, Natta, e United States. National Aeronautics and Space Administration., a cura di. Time-dependent photodissociation regions. [Washington, DC: National Aeronautics and Space Administration, 1995.

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Hollenbach, David. Time-dependent photodissociation regions. [Washington, DC: National Aeronautics and Space Administration, 1995.

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Hollenbach, David. Time-dependent photodissociation regions. [Washington, DC: National Aeronautics and Space Administration, 1995.

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Capitoli di libri sul tema "Photodissociation Region"

Wolfire, Mark G., e Michael J. Kaufman. "Photodissociation Region". In Encyclopedia of Astrobiology, 1868–76. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-44185-5_1197.

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Wolfire, Mark G., e Michael J. Kaufman. "Photodissociation Region". In Encyclopedia of Astrobiology, 1–10. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-27833-4_1197-8.

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Wolfire, Mark G., e Michael J. Kaufman. "Photodissociation Region". In Encyclopedia of Astrobiology, 2294–301. Berlin, Heidelberg: Springer Berlin Heidelberg, 2023. http://dx.doi.org/10.1007/978-3-662-65093-6_1197.

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Rostas, F. "Photoabsorption and Photodissociation of CO in the 900–1200 Å Region". In Molecular Astrophysics, 704–5. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5432-8_46.

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Martín-Pintado, Jesús, e Asunción Fuente. "High-density filaments in the photodissociation region (PDR) associated with NGC 7023". In ESO Astrophysics Symposia, 214–17. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-540-69999-6_31.

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Wolfire, Mark G., e Michael J. Kaufman. "Photodissociation Regions". In Encyclopedia of Astrobiology, 1236–43. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-11274-4_1197.

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Sternberg, A. "Photodissociation Regions". In Springer Proceedings in Physics, 423–30. Berlin, Heidelberg: Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-642-18902-9_75.

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Tielens, A. G. G. M. "Photodissociation Regions and Planetary Nebulae". In Planetary Nebulae, 155–62. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-2088-3_43.

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Escalante, V., e A. Góngora-T. "Photodissociation Regions in Planetary Nebulae". In Planetary Nebulae, 220. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-2088-3_92.

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Graham, James R., T. M. Herbst, S. Beckwith, K. Matthews, G. Neugebauer, E. Serabyn e B. T. Soifer. "Photodissociation Regions in Young PN". In Infrared Astronomy with Arrays, 69–72. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1070-9_15.

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Atti di convegni sul tema "Photodissociation Region"

Johnson, Alan E., Anne B. Myers, Sanford Ruhman e Uri Banin. "Resonance Raman studies of I _{3 ^–} photodissociation in solution". In Modern Spectroscopy of Solids, Liquids, and Gases. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/msslg.1995.sfb4.

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The triiodide ion in solution has two strong, featureless electronic transitions spanning the blue to mid-uv spectral region which dissociate to I 2 – - and atomic iodine. Recent femtosecond pump-probe experiments have shown that the diiodide ion product is formed vibrating coherently. [1] Numerical simulations of the photodissociation event, both in the isolated molecule[2] and with solvent explicitly present, [3] are in qualitative agreement with the data, but rely on an empirical LEPS potential surface parameterized to reproduce the structureless absorption bands only. In order to explore the photodissociative potential surface more precisely, we have measured resonance Raman spectra, including absolute scattering cross sections, for I 3 – in ethanol, ethyl acetate, and acetonitrile at excitation wavelengths from 266 to 416 nm, as well as in the preresonant region at 488 nm.

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Johnston, M. V., P. L. Ross, S. E. Van Bramer e E. D. Leavitt. "Unimolecular Photochemistry Studied by Photodissociation-Photoionization Mass Spectrometry". In Laser Applications to Chemical Analysis. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/laca.1994.tub.8.

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Photochemical reactions are commonly studied in the condensed phase or in a high pressure gas. The primary photodissociation products are inferred from distributions of stable compounds produced by secondary reactions. As these investigations are extended to molecules of increasing size and complexity, identification of the primary products becomes difficult owing to the large number of possible secondary reactions. In photodissociation-photoionization mass spectrometry (PDPI-MS), molecular photodissociation is performed at low pressure in the source region of a mass spectrometer. After a short time delay, the neutral photodissociation products are softly ionized with coherent vacuum ultraviolet radiation and mass analyzed. Unlike photochemical experiments at high pressure, PDPI permits direct observation of the entire product distribution on the microsecond timescale.

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Kanda, Kazuhiro, Koichiro Mitsuke, Kaoru Suzuki e Toshio Ibuki. "Photodissociation of Butyl Cyanides and Butyl Isocyanides in the Vacuum UV Region". In SYNCHROTRON RADIATION INSTRUMENTATION: Ninth International Conference on Synchrotron Radiation Instrumentation. AIP, 2007. http://dx.doi.org/10.1063/1.2436423.

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Baranov, V. Yu, A. P. Dyadkin, Yu A. Kolesnikov, A. A. Kotov, V. P. Novikov, S. V. Pigulskii, A. S. Razumov e A. I. Starodubtsev. "Secondary Chemical Reaction Effects Upon Photodissociation of UF6". In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.cwf62.

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In this paper results of experimental research of UF6 dissociation using repetitively pulsed CF4 laser are presented. The pulse energy was in the range 45-130 mJ and the pressure of UF6 was 0.3-0.6 torr, the cell volume was 16 cm3. From pulse to pulse behavior of UF6 photodissociation relative yield, i.e. fraction of the dissociated molecules for every pulse related to the molecules number before pulse, is investigated. It is revealed that in the irradiated region of the cell where the radiation fluence is more than the threshold one, i.e., Φ ≥ Φ0 = 1 J·cm−2, from 35 to 50% of the UF6 molecules dissociate due to the first pulse and after some following pulses the relative yield sharply decreases. For a moment when the dissociated molecules fraction is a half of their quantity, the relative yield decreases by factors of 4 to 10, depending on initial UF6 pressure in the cell and on the pulse energy. To bring out causes of such effects, we consider here processes upon the photodissociation, i.e., diffusion of its products out off irradiated region, formation of UF5 polymers, recombination of UF5 and UF5 polymers with atomic fluorine, accumulation and losses of the atomic fluorine, ets. Estimations of the appropriate reaction roles and their possible effect upon relative photodissociation yield decreasing from pulse to pulse that was found in our experiments are presented.

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Mamilov, S. A., S. S. Esman, M. M. Asimov e A. I. Gisbrecht. "Quantum yields of the photodissociation of HbO2in the visible and near IR spectral region". In Eighteenth International School on Quantum Electronics: Laser Physics and Applications, a cura di Tanja Dreischuh, Sanka Gateva e Alexandros Serafetinides. SPIE, 2015. http://dx.doi.org/10.1117/12.2175629.

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Pomelnikov, I. A., D. S. Riashchikov e N. E. Molevich. "On the possible origin of substructures observed in the Orion Bar PDR". In 51-st All-Russian with international participation student scientific conference "Physics of Space", 157–60. Ural University Press, 2024. http://dx.doi.org/10.15826/b978-5-7996-3848-1.25.

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In this paper, the numerical simulation of shockwave pulse evolution, which propagates in the medium with the Orion Bar photodissociation region parameters, is performed. Modelled periodical structures fit with observed substructures by the characteristic size and frequency rate.

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Xie, Xiaoliang, Robert Dunn e John D. Simon. "Picosecond Polarization Studies of Protein Relaxation". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/up.1990.mc21.

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Picosecond polarization spectroscopies have been used to probe relaxation processes in heme proteins induced by ligand photodissociation. In particular, probing the N-band of myoglobin at 355 nm reveals a relaxation of several hundreds of picoseconds, over two orders of magnitude longer than the dynamics of photo-induced bond cleavage. Similar dynamics are also observed for studies in the Soret region. Time resolved linear dichroism studies confirm that the evolution of the CD signal does not arise from a change in the direction or degeneracies of the two degenerate, perpendicular transition moments of the heme. In addition, the time dependent spectral properties of the charge transfer absorption between the iron and the proximal histidine which results from photodissociation does not reveal any noticeable spectral shift on the time scale of the CD dynamics, strongly suggesting that the tilting of the proximal histidine is not causing the time dependent changes in the CD signal. These results suggest that the transient CD data is measuring a relaxation in the surrounding protein structure which is triggered by the photodissociation process.

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Baldwin, K. G. H., S. T. Gibson, B. R. Lewis, J. H. Carver e T. J. McIlrath. "Four Wave Difference Frequency Generation at 124nm for High Resolution Photoabsorption Studies of O2". In Short Wavelength Coherent Radiation: Generation and Applications. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/swcr.1991.tua7.

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Previous VUV generation techniques used to carry out high resolution absorption and photodissociation spectroscopy of molecular oxygen have relied on stimulated anti-Stokes Raman scattering to produce tunable VUV radiation(1,2). However, such studies are limited in practice by low conversion efficiencies to wavelengths >1500A in the Schumann-Runge band and continuum region.

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Kiseleva, M. B., G. Y. Zelikina, M. V. Buturlimova e K. G. Zolotarev. "Collision-induced absorption of mixture of oxygen with argon in the region of the Herzberg photodissociation continuum". In SPIE Proceedings, a cura di Leonid N. Sinitsa e Semen N. Mikhailenko. SPIE, 2004. http://dx.doi.org/10.1117/12.545662.

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Korn, G., O. Kittelmann, J. Ringling, A. Nazarkin e I. V. Hertel. "Generation of tunable femtosecond VUV pulses around 100nm by resonant and near resonant four-wave difference frequency mixing". In Applications of High Field and Short Wavelength Sources. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/hfsw.1997.sab5.

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Time resolved spectroscopic investigations of ultrafast processes at surfaces or in gaseous media, e. g. photodissociation and fragmentation of molecules and clusters1,2 require femtosecond pulses tunable in the vacuum ultraviolet (VUV) spectral range. Clusters show for instance a very strong dependence of the absorption peak on the their size. The region between 100nm-150nm is of special interest for small clusters. Single photon ionization will be possible for photons of this energy range.

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