No description available.

The Bok globule B335 is a small molecular cloud in the solar neighbourhood near the galactic plane. The aim for this three-paper-study is to construct and analyze the extinction for this globule. The method we apply is to use the light from field stars behind the cloud in broadband filters ranging from UV to the mid-infrared. We have observations performed at the ESO telescopes at La Silla and Paranal as well as at the Nordic 2.5 m telescope at La Palma. Together with images and spectra from 2MASS-, ISO- and Spitzer-archives we are able to cover the wavelength range from 0.35 to 24 μm. An important tool to analyze these observations results in order to get the extinction is the grid of synthetic stellar atmospheric spectra provided by Hauschildt (2005). The extinction so received is a result in itself. From the analysis of the extinction wavelength dependence we derive properties of the dust, especially its composition and grain size distribution. By modeling the grain size distribution we are able to find the extinction from the reddening of the stars. We find that the extinction in the optical wavelength 0.35 to 2 μm range nicely follows the functional form described by Cardelli et al. (1989). Our result from the wavelength range redward of 2 μm show an extinction dependent on the part of the cloud examined. For the rim of the cloud we get an extinction similar to that reported earlier for the diffuse interstellar medium. From the central parts of the cloud, however, a higher extinction was found. Our grain size model contains a carbonaceous particle distribution and a silicate one. The result can be explained by depletion of carbon onto carbonaceous grains and also by carbon onto all grains including the silicates. Our modeling of the extinction and our classification of the background stars allow us to - determine the distance to the globule - estimate the gas column density ratio - estimate the mass of globule - get a handle on the dust conversion processes through the grain size distribution   From the water- and CO-ice spectra we are able to estimate the ice column densities. We find similar ice column densities for the two ices. The estimates differ, when calculated from band strengths or from Lorenz-Mie calculations of ice mantles on the grain size distribution, by a factor of two.

Herschel and JCMT surveys of nearby star-forming regions have provided excellent images of cold dust emission across several wavelengths with unprecedented dynamic range and resolutions. Here we present spectral emissivity index and temperature maps of dust in the star-forming clumps of the Perseus molecular cloud determined from fitting SEDs to the combined Herschel and JCMT observations in the 160 μm, 250 μm, 350 μm, 500 μm, and 850 μm bands, employing the technique developed by Sadavoy et al. (2013). In NGC1333, the most complex and active star-forming clump in Perseus, we demonstrate that CO line contamination in the JCMT SCUBA-2 850 μm band is typically insignificant. The derived spectral emissivity index, β, and dust temperature, T, ranges between 0.8 - 3.0 and 7 - 50 K, respectively. Throughout Perseus, we see indications of heating from B stars and embedded protostars, and smooth β variations on the smaller scales. The distribution of β values seen in each clump differs from one clump to another, and is in general different from the diffuse ISM values (i.e., ~2), suggesting that dust grain evolution is significant in star-forming clumps. We also found coincidences between low β regions and local temperature peaks as well as locations of outflows, which may provide hints to the origins of these low β value grains, and dust grain evolution in star-forming clumps in general. / Graduate / mcychen@uvic.ca

A unified theory of star formation remains one of the major unsolved issues in astrophysics. Presented here are the results of multi-molecular lines mapping of the entire giant molecular cloud G333, comprised sites of low- and high-mass star forming regions in various evolution stages of star formation. The result shows the spatial distribution of CS, HCO+, HCN and HNC are similar on large scales, while N2H+ seems to trace preferentially the very densest regions, possibly due to the chemical difference, that N2H+ is sensitive to temperature and readily destroyed by CO. Two analysis methods were used to characterise this large set of data cubes: GAUSSCLUMPS and principal component analysis (PCA). We found the clumps are heavily fragmented with a beam filling factor of ~0.2. We found no correlation between clump radius and line width, contradicts to Larson's Law. Possible explanation is the clumps are fragmented and unresolved with the resolution of Mopra beam, thus the decomposed clump radius is blended and no physical properties can be interpreted. PCA of the velocity dimension found no significant differences among CS, HCO+, HNC and C2H line emissions, suggesting these four molecules are `well-mixed' on large scale, possibly by turbulence. PCA of the integrated emission maps separates molecules into low (13CO and C18O) and high (the rest) density tracers, identifies anti-correlation between HCO+ and N2H+ (due to the depletion of CO). The possibility of removing the scanning patterns of the `on-the-fly' mapping with PCA was also explored. The detection of broad thermal SiO from the massive dense cold core G333.125-0.562, along with other collected transitions, suggesting the core will host massive star formation and the SiO emission arises from shocks associated with an outflow in the cold core. Result of the modelling infall with 3D radiative transfer code using the derived physical parameters have successfully reproduce the line profiles. Recent observation of the 3 and 7 mm continuum emission suggestive of warm dust emission rather than free-free emission from HII, further supports the core is in a very young stage of star formation.

La formation des planètes a lieu dans les disques protoplanétaires constitués de gaz et de poussières. Si ces dernières ne représentent que 1% de la masse totale du disque, elles jouent un rôle fondamental pour l’évolution chimique des disques en agissant comme catalyseurs pour la formation des molécules. Comprendre cette chimie est essentiel pour remonter aux conditions physiques initiales qui ont permis la naissance des planètes.Au cours de ma thèse, j’ai étudié la chimie à la surface des grains de poussières et son impact sur l’évolution chimique du nuage moléculaire, condition initale de la formation du disque, et du disque protoplanétaire. Grâce à des simulations numériques, à l’aide du code de chimie gaz-grain Nautilus, j’ai pu montrer l’importance des réactions de diffusion et des interactions gaz-grain pour les abondances des espèces en phase gazeuse. Les résultats du modèle couplés aux observations ont également mis en évidence les effets de la structure physique (température, densité, AV) sur la distribution des molécules dans les disques. / Planetary formation occurs in the protoplanetary disks of gas and dust. Although dust represents only 1% of the total disk mass, it plays a fundamental role in disk chemical evolution since it acts as a catalyst for the formation of molecules. Understanding this chemistry is therefore essential to determine the initial conditions from which planets form.During my thesis, I studied grain-surface chemistry and its impact on the chemical evolution of molecular cloud, initial condition for disk formation, and protoplanetary disk. Thanks to numerical simulations, using the gas-grain code Nautilus, I showed the importance of diffusion reactions and gas-grain interactions for the abundances of gas-phase species. Model results combined with observations also showed the effects of the physical structure (in temperature, density, AV) on the molecular distribution in disks.

Gasausströmungen, oft in der Form hoch kollimierter Jets, sind ein allgegenwärtiges Phänomen bei der Geburt neuer Sterne. Emission von stossangeregtem molekularem Wasserstoff bei Wellenlängen im nahen Infrarotbereich ist ein Merkmal ihrer Existenz und auch in eingebetteten, im Optischen obskurierten Ausströmungen generell gut zu beobachten. In dieser Arbeit werden die Resultate einer von Auswahleffekten freien, empfindlichen, grossflächigen Suche nach solchen Ausströmungen von Protosternen in der v=1-0 S(1) Linie molekularen Wasserstoffs bei einer Wellenlänge von 2.12 µm vorgestellt. Die Durchmusterung umfasst eine Fläche von etwa einem Quadratgrad in der Orion A Riesenmolekülwolke. Weitere Daten aus einem grossen Wellenlängenbereich werden benutzt, um die Quellen der Ausströmungen zu identifizieren. Das Ziel dieser Arbeit ist es, eine Stichprobe von Ausströmungen zu bekommen, die so weit wie möglich frei von Auswahleffekten ist, um die typischen Eigenschaften protostellarer Ausströmungen und deren Entwicklung festzustellen, sowie um die Rückwirkung der Ausströmungen auf die umgebende Wolke zu untersuchen.<br /> Das erste Ergebnis ist, dass Ausströmungen in Sternentstehungsgebieten tatsächlich sehr häufig sind: mehr als 70 Jet-Kandidaten werden identifiziert. Die meisten zeigen eine sehr irreguläre Morphologie anstelle regulärer oder symmetrischer Strukturen. Dies ist auf das turbulente, klumpige Medium zurückzuführen, in das sich die Jets hineinbewegen. Die Ausrichtung der Jets ist zufällig verteilt. Insbesondere gibt es keine bevorzugte Ausrichtung der Jets parallel zum grossräumigen Magnetfeld in der Wolke. Das legt nahe, dass die Rotations- und Symmetrieachse in einem protostellaren System durch zufällige, turbulente Bewegung in der Wolke bestimmt wird. <br /> <br /> Mögliche Ausströmungsquellen werden für 49 Jets identifiziert; für diese wird der Entwicklungsstand und die bolometrische Leuchtkraft abgeschätzt. Die Jetlänge und die H2 Leuchtkraft entwickeln sich gemeinsam mit der Ausströmungsquelle. Von null startend, dehnen sich die Jets schnell bis auf eine Länge von einigen Parsec aus und werden dann langsam wieder kürzer. Sie sind zuerst sehr leuchtkräftig, die H2 Helligkeit nimmt aber im Lauf der protostellaren Entwicklung ab. Die Längen- und H2 Leuchtkraftentwicklung lässt sich im Wesentlichen durch eine zuerst sehr hohe, dann niedriger werdende Massenausflussrate erklären, die auf eine zuerst sehr hohe, dann niedriger werdende Gasakkretionsrate auf den Protostern schliessen lässt (Akkretion und Ejektion sind eng verknüpft!). Die Längenabnahme der Jets erfordert eine ständig wirkende Abbremsung der Jets. Ein einfaches Modell einer simultanen Entwicklung eines Protosterns, seiner zirkumstellaren Umgebung und seiner Ausströmung (Smith 2000) kann die gemessenen H2- und bolometrischen Leuchtkräfte der Jets und ihrer Quellen reproduzieren, unter der Annahme, dass die starke Akkretionsaktivität zu Beginn der protostellaren Entwicklung mit einer überproportional hohen Massenausflussrate verbunden ist.<br /> <br /> Im Durchmusterungsgebiet sind 125 dichte Molekülwolkenkerne bekannt (Tatematsu et al. 1993). Jets (bzw. Sterne) entstehen in ruhigen Wolkenkernen, d.h. solchen mit einem niedrigen Verhältnis von interner kinetischer Energie zu gravitativer potentieller Energie; dies sind die Wolkenkerne höherer Masse. Die Wolkenkerne mit Jets haben im Mittel grössere Linienbreiten als die ohne Jets. Dies ist darauf zurückzuführen, dass sie bevorzugt in den massereicheren Wolkenkernen zu finden sind, welche generell eine grössere Linienbreite haben. Es gibt keinen Hinweis auf stärkere interne Bewegungen in Wolkenkernen mit Jets, die durch eine Wechselwirkung der Jets mit den Wolkenkernen erzeugt sein könnte. Es gibt, wie von der Theorie vorausgesagt, eine Beziehung zwischen der Linienbreite der Wolkenkerne und der H2 Leuchtkraft der Jets, wenn Jets von Klasse 0 und Klasse I Protosternen separat betrachtet werden; dabei sind Klasse 0 Jets leuchtkräftiger als Klasse I Jets, was ebenfalls auf eine zeitabhängige Akkretionsrate mit einer frühzeitigen Spitze und einem darauffolgenden Abklingen hinweist.<br /> <br /> Schliesslich wird die Rückwirkung der Jetpopulation auf eine Molekülwolke unter der Annahme strikter Vorwärtsimpulserhaltung betrachtet. Die Jets können auf der Skala einer ganzen Riesenmolekülwolke und auf den Skalen von Molekülwolkenkernen nicht genügend Impuls liefern, um die abklingende Turbulenz wieder anzuregen. Auf der mittleren Skala von molekularen Klumpen, mit einer Grösse von einigen parsec und Massen von einigen hundert Sonnenmassen liefern die Jets jedoch genügend Impuls in hinreichend kurzer Zeit, um die Turbulenz “am Leben zu erhalten” und können damit helfen, einen Klumpen gegen seinen Kollaps zu stabilisieren. / The presence of outflows, often in the form of well-collimated jets, is a phenomenon commonly associated with the birth of young stars. Emission from shock-excited molecular hydrogen at near-infrared wavelengths is one of the signposts of the presence of such an outflow, and generally can be observed even if the flow is obscured at optical wavelengths. In this thesis, I present the results of an unbiased, sensitive, wide-field search for flows from protostellar objects in the H2 v=1-0 S(1) line at a wavelength of 2.12 µm, covering a 1 square degree area of the Orion A giant molecular cloud. Further data covering a wide wavelength range are used to search for the driving sources of the flows. The aim of this work is to obtain a sample of outflows which is free from biases as far as possible, to derive the typical properties of the outflows, to search for evolutionary trends, and to examine the impact of outflows on the ambient cloud.<br /> The first result from this survey is that outflows are indeed common in star forming regions: more than 70 candidate jets are identified. Most of them have a fairly ill-defined morphology rather than a regular or symmetric structure, which is interpreted to be due to the turbulent, clumpy ambient medium into which the jets are propagating. The jets are randomly oriented. In particular, no alignment of the jets with the large scale ambient magnetic field is found, suggesting that the spin and symmetry axis in a protostellar object is determined by random, turbulent motions in the cloud. <br /> <br /> Candidate driving sources are identified for 49 jets, and their evolutionary stage and bolometric luminosity is estimated. The jet lengths and H2 luminosities evolve as a function of the age of the driving source: the jets grow quickly from zero length to a size of a few parsec and then slowly shorten again. The jets are very luminous early on and fade during the protostellar evolution. The evolution in length and H2 luminosity is attributed to an early phase of strong accretion, which subsequently decreases. The shortening of the jets with time requires the presence of a continuous deceleration of the jets. A simple model of the simultaneous evolution of a protostar, its circumstellar environment, and its outflow (Smith 2000) can reproduce the measured values of H2 luminosity and driving source luminosity under the assumption of a strong accretion plus high ejection efficiency phase early in the protostellar evolution.<br /> <br /> Tatematsu et al. (1993) found 125 dense cloud cores in the survey area. The jet driving sources are found to have formed predominantly in quiet cores with a low ratio of internal kinetic energy to gravitational potential energy; these are the cores with higher masses. The cores which are associated with jets have on average larger linewidths than cores without jets. This is due to the preferred presence of jets in more massive cores, which generally have larger linewidths. There is no evidence for additional internal motions excited by the interaction of the jets with the cores. The jet H2 luminosity and the core linewidth (as predicted by theory) are related, if Class 0 and Class I jets are considered separately; the relation lies at higher values of the H2 luminosity for the Class 0 jets than for Class I jets. This also suggests a time evolution of the accretion rate, with a strong peak early on and a subsequent decay.<br /> <br /> Finally, the impact of a protostellar jet population on a molecular cloud is considered. Under the conservative assumption of strict forward momentum conservation, the jets appear to fail to provide sufficient momentum to replenish decaying turbulence on the scales of a giant molecular cloud and on the scales of molecular cloud cores. At the intermediate scales of molecular clumps with sizes of a few parsec and masses of a few hundred solar masses, the jets provide enough momentum in a short enough time to potentially replenish turbulence and thus might help to stabilize the clump against further collapse.

This dissertation presents new Herschel observations at 70 micron, 160 micron, 250 micron, 350 micron, and 500 micron of the Perseus molecular cloud from the Herschel Gould Belt Survey. The Perseus molecular cloud is a nearby star-forming region consisting of seven main star-forming clumps. The Herschel observations are used to characterize and contrast the properties of these clumps, and to study their embedded core populations. First, we probed the exceptionally young clump, B1-E. Using complementary molecular line data, we demonstrate that B1-E is likely fragmenting into a first generation of dense cores in relative isolation. Such a core formation region has never been observed before. Second, we use complementary long wavelength observations at 850 micron to study the dust properties in the larger, more active B1 clump. We find that Herschel data alone cannot constrain well the dust properties of cold dust emission and that long wavelength observations are needed. Additionally, we find evidence of dust grain growth towards the dense cores in B1, where the dust emissivity index, beta, varies from the often assumed value of beta = 2. In the absence of long wavelength observations, however, assuming beta = 2 is preferable over measuring beta with the Herschel-only bands. Finally, we use the source extraction code, getsources, to identify the core populations within each clump from the Herschel data. In addition, we use complementary archival infrared observations to study their populations of young stellar objects (YSOs). We find that the more massive clumps have an excess of older stage YSOs, suggesting that these regions contracted first. Starless cores are typically associated with peaks in the column density, where those found towards regions of higher column density also have higher average densities and colder temperatures. Starless cores associated with a strong, local interstellar radiation field, however, have higher temperatures. We find that the clumps with the most prominent high column density tails also had the highest fractions of early-stage YSOs. This relation suggests that the quantity of high column density material corresponds to recent star formation activity. / Graduate / 0606

No description available.

Star formation is a complex hierarchical process that witnesses the transfer of mass among a range of scales from large diffuse molecular clouds to crowded clumps and finally down to prestellar cores. The final stage of this process has prestellar cores actively accreting matter while undergoing gravitational collapse on their way to becoming main sequence stars. This thesis presents multi wavelength submillimeter observations of the Perseus molecular cloud using 160 μm, 250 μm, 350 μm, and 500 μm maps of thermal dust emission from the Herschel space observatory. Additionally C18O J = 3 → 2 spectral line emission is observed in four star forming clumps within Perseus using the James Clerk Maxwell Telescope. Spectral line emission allows for the separation of material along the line of sight. Prestellar core mass is derived from observational maps using various source finding algorithms. The mass is overestimated when compared to prestellar core mass found from spectral line data. This overestimation can be mitigated with careful selection of source finding algorithm and background removal. Further, the prestellar core mass derived from spectral line data was the closest match to the initial stellar mass function over dust maps. However, both the spectral line masses and dust map masses do not agree with the IMF confirming a star forming efficiency factor in the evolutionary step between prestellar core and main sequence star. Lastly, a filamentary analysis finds that high mass stars preferentially form in crowded regions close to, or contained within, filament structure. / Thesis / Master of Science (MSc) / Star formation is a complex hierarchical process that witnesses the transfer of mass among a range of scales from large diffuse molecular clouds to crowded clumps and finally down to prestellar cores. The final stage of this process has prestellar cores actively accreting matter while undergoing gravitational collapse on their way to becoming main sequence stars. This thesis presents multi wavelength submillimeter observations of the Perseus molecular cloud using 160 μm, 250 μm, 350 μm, and 500 μm maps of thermal dust emission from the Herschel space observatory. Additionally carbon monoxide spectral line emission is observed in four star forming clumps within Perseus using the James Clerk Maxwell Telescope. Spectral line emission allows for the separation of material along the line of sight. Prestellar core mass is derived from observational maps using various source finding algorithms. The mass is overestimated when compared to prestellar core mass found from spectral line data. This overestimation can be mitigated with careful selection of source finding algorithm and background removal. Further, the prestellar core mass derived from spectral line data was the closest match to the initial stellar mass function over dust maps. However, both the spectral line masses and dust map masses do not agree with the IMF confirming a star forming efficiency factor in the evolutionary step between prestellar core and main sequence star. Lastly, a filamentary analysis finds that high mass stars preferentially form in crowded regions close to, or contained within, filament structure.

L'expérience H.E.S.S. est un réseau de télescope Tcherenkov, situé en Namibie, qui observe le rayonnement de sources astrophysiques de rayons gamma de très haute énergie. Depuis sa mise en service il y a plus de dix ans, H.E.S.S. a permis d'améliorer considérablement notre vision de l'univers à ces énergies. Depuis 2012, le démarrage de la deuxième phase de l'expérience avec la mise en service d'un cinquième télescope permet de baisser le seuil en énergie de l'expérience.L'optimisation d'une analyse multivariée au sein de l'expérience H.E.S.S. est présentée dans cette thèse. L'analyse Xeff a été amélioré en prenant en compte les conditions d'observations, et en introduisant de nouvelles variables dans l'estimateur. Un gain de sensibilité de l'analyse par rapport aux analyses standards est observé. Cette méthode a été ensuite utilisée pour diverses analyses de sources de rayons gamma.La prise en compte des effets de la focalisation de l'analyse de données de H.E.S.S. II est détaillée. L'ajustement de la distance entre la caméra et les miroir du cinquième télescope permet d'améliorer l'image dans le plan focal. L'amélioration de la reconstruction et le gain en sensibilité qui en découle est présenté.L'étude du rayonnement gamma de quatre candidats d'associations de vestiges de supernova et de nuages moléculaires est présentée : G349.7+0.2, W51, la nébuleuse de la Tornade, et HESS J1745-303. Une interprétation de ce rayonnement utilisant également les données de Fermi-LAT permet d'estimer l'origine dominante des mécanismes d'émission et d'appréhender l'efficacité d'accélération de particules par ces systèmes.Les travaux présentés dans cette thèse ont fait l'objet de deux notes internes à la collaboration H.E.S.S., de multiples présentations dans des conférences internationales et de publications scientifiques. / The H.E.S.S. experiment is an array of Cherenkov telescopes, located in Namibia, observing the very high energy gamma rays from astrophysical sources. H.E.S.S. greatly increased our understanding of the very high energy non thermal universe. Since 2012, a fifth telescope was installed at the center of the array. This improvement increase the energy range and the sensitivity of the detector.The optimization of a multivariate analysis method, within the H.E.S.S. framework, is presented in this thesis. The Xeff analysis is improved by taking into account the observation conditions and by increasing the number of discriminating variables. The sensitivity of this analysis compared to standard analyses is demonstrated. Xeff is then used to analyze several sources of gamma rays.The effects of the focus impacting the H.E.S.S. II data are described. They are taken into account in the analysis and an optimization of the distance between the mirrors and the camera is presented.The study of the gamma emission from four candidates of molecular clouds and supernova remnant associations is presented. The H.E.S.S. data from G349.7+0.2, W51, the Tornado nebula and HESS J1745-303 is performed. The interpretation of their emission, using also Fermi-LAT data, leads to the estimation of the particles acceleration efficiency in these objects.The work described in this thesis led to the production of two internal notes in the H.E.S.S. collaboration, to several presentations in international conferences, and scientific publications.