Letteratura scientifica selezionata sul tema "Protostellar jets"

By using ASCA, Koyama et al. (1994, 1996) carried out a systematic survey of hard X-ray sources in molecular clouds and revealed that protostars are strong hard X-ray emitting sources. Some of them show flare-like activities. Protostellar flares differ from solar flares in their total energy(1035-36 erg), size(several times the radius of protostar), and higher temperature(8keV). Protostellar flares are also observed in lower energy band by ROSAT in YLW15 (Grosso et al. 1997). By extending the model of solar flares associated with footpoint shearing motion, we proposed a model of protostellar flares in which the magnetic field connecting the protostar and the disk disrupt by twist injection from the rotating disk(Hayashi et al. 1996).

Aims. We aim to study the causal link between the knotty jet structure in CARMA 7, a young Class 0 protostar in the Serpens South cluster, and episodic accretion in young protostellar disks. Methods. We used numerical hydrodynamics simulations to derive the protostellar accretion history in gravitationally unstable disks around solar-mass protostars. We compared the time spacing between luminosity bursts Δτmod, caused by dense clumps spiralling on the protostar, with the differences of dynamical timescales between the knots Δτobs in CARMA 7. Results. We found that the time spacing between the bursts have a bi-modal distribution caused by isolated and clustered luminosity bursts. The former are characterized by long quiescent periods between the bursts with Δτmod = a few × (103–104) yr, whereas the latter occur in small groups with time spacing between the bursts Δτmod = a few × (10–102) yr. For the clustered bursts, the distribution of Δτmod in our models can be fit reasonably well to the distribution of Δτobs in the protostellar jet of CARMA 7, if a certain correction for the (yet unknown) inclination angle with respect to the line of sight is applied. The Kolmogorov–Smirnov test on the model and observational data sets suggests the best-fit values for the inclination angles of 55–80°, which become narrower (75–80°) if only strong luminosity bursts are considered. The dynamical timescales of the knots in the jet of CARMA 7 are too short for a meaningful comparison with the long time spacings between isolated bursts in our models. Moreover, the exact sequences of time spacings between the luminosity bursts in our models and knots in the jet of CARMA 7 were found difficult to match. Conclusions. Given the short time that has passed since the presumed luminosity bursts (tens to hundreds years), a possible overabundance of the gas-phase CO in the envelope of CARMA 7 compared to what could be expected from the current luminosity may be used to confirm the burst nature of this object. More sophisticated numerical models and observational data on jets with longer dynamical timescales are needed to further explore the possible causal link between luminosity bursts and knotty jets.

AbstractWe describe the appearance and significance of HH212, the most symmetric two-sided molecular hydrogen jet/counterjet system yet discovered. This prototype embedded protostellar H2 jet emanates from a low-luminosity isolated protostar in Orion. It exhibits matched pairs of knots and bow-shocks interpreted as arising from a time-variable source, which we take to indicate that protostellar accretion through the encircling disk is non-steady and pulsed.

Some topics in the theory of jets are reviewed. These include jet precession, unconfined jets, the origin of knots, the internal shock model as a unifying theme from protostellar jets to gamma-ray bursts, relations between the Blandford-Znajek and MHD disk-wind models, and jet collimation in magnetic acceleration models.

Recent development on the theory and numerical modeling of solar flares and jets is reviewed with emphasis on the magnetic reconnection model. Application to protostellar flares and jets is also discussed.

In the context of the CALYPSO IRAM-PdBI Lai•ge Program we performed the first statistical survey of protostellar jets by analysing molecular emission in a sample of 21 protostars covering a broad range of internal luminosities (Lint from 0.035 L⊙ to 47 L⊙). We find that the outflow phenomenon is ubiquitous in our sample of protostars, with wide-angle outflows detected in CO (2 - 1) in all sources, and high-velocity collimated jets detected in SiO (5-4) in 80% of the sources with Lint > 1 L⊙. The protostellar flows have an onion-like structure, with the SiO jet (opening angle, α ~ 10°) nested into a wider angle SO (α ~ 15°) and CO (α ~ 25°) outflows. Interestingly, protostellar jets show several properties in common with the atomic jets associated with more evolved sources (106 yr), e.g. one third of the jets show velocity asymmetry of ~ 1.3-2 between the two lobes, and the mass-loss rates are ~ 1% - 50% of the mass accretion rates. This suggests that the same launching mechanism is at work and that the correlation between mass ejection and mass accretion holds along the star-formation process from 104 yr up to a few Myr.

Astrophysikalische Jets sind ausgedehnte, kollimierte Massenausflüsse von verschiedenen astronomischen Objekten. Zeitabhängige magnetohydrodynamische (MHD) Simulationen der Jet-Entwicklung müssen den Akrretionsprozess in der Scheibe berücksichtigen, da der Jet aus der Scheibenmaterie gespeist wird. Allerdings ist die simultane Berechnung der Entwicklung von Scheibe und Jet schwierig, da die charakteristischen Zeitskalen unterschiedlich sind. Selbstähnliche Modelle zeigten, daß eine Beschreibung der Jetentstehung aus einer Akkretionsscheibe durch rein magnetische Prozesse möglich ist.
In this thesis the magnetohydrodynamic jet formation and the effects of magnetic diffusion on the formation of axisymmetric protostellar jets have been investigated in three different simulation sets. The time-dependent numerical simulations have been performed, using the magnetohydrodynamic ZEUS-3D code.

Using telescopes such as the Hubble Space Telescope, astronomers observe parsec-scale plasma jets emerging from Young Stellar Objects and colliding with the interstellar medium, generating shock structures. A set of mathematically rigorous scaling transformations exists allowing dynamic scaled models of radiative, yet otherwise ideal, hydrodynamic flows to be created in the laboratory. In this thesis two experiments are presented in which plasma jets were produced using high-intensity lasers. In the first of these, the effects on jet collimation of radiative emission and the presence of a gaseous ambient medium were studied, with a view to learning about the effects of these factors on YSO jets by studying their scaled laboratory counterparts. The second experiment was designed to be similar to the first in order to investigate applying the scaling relations to scaling between laboratory experiments. Previous work in this area has shown that jets made in vacuo from materials with a higher mean atomic number form narrower, better-collimated jets (e.g. Shigemori 2000). Also, for jets propagating into a gas, shock structures similar to those seen in simulations of the interaction of a YSO jet with the interstellar medium have been observed (e.g. Nicolai 2008). In this thesis, both of these results are replicated, and the collimation work extended with a study of the collimation of jets in 50 mb He gas. The energies of the laser pulses used in the first experiment were over an order of magnitude lower than those used in previous studies of cylindrically-symmetric jets. This gives the replication and development of previous work added significance, showing that the same physics can be used to describe the behaviour of a plasma on a smaller energy scale and demonstrating that jet modelling experiments can potentially be done using university-scale laser facilities.

L’efficacité observée dans la formation des étoiles jusqu’au parsec ne dépasse pas quelques pourcents, sans oublier le décalage de la fonction initiale de masse (IMF) à seulement ∼30% de la masse du cœur pré-stellaire initial. Comprendre en détail le processus derrière d’aussi faibles efficacités reste encore à ce jour une question ouverte. En outre, les simulations numériques les plus récentes ont démontré que la turbulence et les champs magnétiques à eux seuls ne peuvent suffire à reproduire de telles valeurs. Elles montrent que la rétroaction des flots protostellaires joue un rôle crucial en perturbant les écoulements d’accrétion, en évacuant la matière des cœurs, et/ou en maintenant la turbulence. Malheureusement, que ce soit en termes de volume de nuage affecté, d’impulsion injectée, de masse entraînée, ou d’impact sur le disque et l’enveloppe en effondrement : l’importance de cette rétroaction dépend fortement de la géométrie sous-jacente du vent protostellaire. Cette dernière reste encore débattue : "vent X grand angle" rapide, vent de disque MHD plus lent, ou jet collimaté ? De toute évidence, afin d’évaluer fiablement l’impact de la rétroaction des flots sur la formation stellaire, il est d’une importance cruciale de déterminer la géométrie de vent la plus réaliste (et/ou les géométries que nous pouvons exclure). Pour apporter une nouvelle contribution quant à cette question, nous présentons des simulations numériques de flots poussés par un jet pulsé collimaté, lancé à travers un cœur pré-stellaire stratifié. Nous comparons nos simulations avec les observations ALMA récentes, ainsi qu’avec les prédictions analogues pour un vent X grand angle. Nos simulations sont les premières à combiner sur une échelle de 0.1 pc la variabilité du jet, la stratification en densité de l’enveloppe et des échelles de temps de 10 000 ans comparables aux flots jeunes observés. Les prédictions de nos simulations en termes de largeur de flot, de diagrammes position-vitesse, et de distribution masse-vitesse, montrent une ressemblance frappante avec les observations ALMA de flots CO tels que HH46/47 et CARMA-7. L'accord est même plus prometteur qu'avec les modèles de flots poussés par un "vent X grand angle". Ces résultats pourraient avoir une implication majeure sur le rôle des flots dans la régulation de la formation stellaire
A long-standing open question in star formation is the process responsible for its low efficiency on parsec scales (a few %), and for shifting down the Initial Mass Function (IMF) to only ∼30% of the prestellar core mass distribution. The most recent numerical simulations show that neither turbulence nor magnetic fields can, alone, reproduce these low efficiencies, and that feedback by protostellar outflows must play a crucial role by disrupting accretion streams, expelling material from cores, and/or sustaining turbulence. Unfortunately, the magnitude of outflow feedback (affected cloud volume, injected momentum, entrained mass, impact on the disk and infalling envelope) depends strongly on the underlying protostellar wind geometry, which remains uncertain and heavily debated: a fast wide-angle "X-wind”, a slower MHD disk wind, a narrow jet ? Clearly, if we want to reliably assess the role of outflow feedback in star formation, it is of utmost importance to determine which wind geometry is the most realistic (and/or which one can be excluded). As a new contribution towards this goal, we present, for the first time, numerical predictions for outflows driven by a narrow pulsed jet in a stratified prestellar core. We compare our simulations against recent ALMA observations and analogous predictions for a wide-angle X-wind. Our simulations are the first to combine jet variability, ambient density-stratification, and long timescales up to 10 000 yrs (typical of young outflows) on scales up to 0.1 pc. We find that the predicted widths, position-velocity diagrams, and mass-velocity distribution, show striking resemblance with ALMA observations of CO outflows such as HH46/47 and CARMA-7, and in closer agreement than models based on a wide-angle "X-wind". The results obtained in this work could have major implications for the feedback of protostellar outflows on star formation

In questa tesi viene presentata una analisi detagliata delle propieta' di accrescimento ed eiezione da stelle giovanni estinte di basa massa attraverso osservazioni ad alta risoluzione angolare nel vicino infrarosso effettuate con la camera infrarossa ISAAC. In questo modo, sono state analizzate la fisica, cinematica e dinamica di 5 getti di Classe 0/I (HH1, HH111, HH212 / HH34, HH46-47) al fine di ricavare informazioni circa l'origine dei getti e la dipendenza delle loro propieta' fisiche rispetto allo stadio evolutivo della sorgente. Inoltre, le propieta' di accrescimento di un campione di dieci sorgenti di Classe I sono state misurate con lo scopo di acertare loro stadio evolutivo. Tutti i getti studiati sono stati osservati per mezzo di emisione atomica e molecolare, traciate da righe di [FeII] e H2. Applicando tecniche di diagnostica nel vicino infrarosso, sono stati ricavati importanti parametri fisici. In particolare, un punto fondamentale di questa tesi e' stato derivare come varianno le propieta' fisiche di questi oggetti in funzione della velocita' radiale dello getto. Ad essempio, ne risulta che la densita' elettronica decresce al diminuire della velocita' a grande distanza dalla sorgente, con valori medi intorno 2600-6200 cm3. Inoltre, e' stata ricavata la masa trasportata da i getti che risulta maggiore di quella trovata in oggetti piu' evoluti di tipo TTauri, mentre il rapporto tra eiezione e accrescimento rimane approssimativamente costante indipendentemente dallo stato evolutivo dalla sorgente. E' stata altresi' studiata in detaglio la regione interna dei getti di Classe I con il preciso fine di determinarne il mechanismo di lancio. Come per i getti da stelle di tipo TTauri, la cinematica delle regioni interne e' caratterizzata da due componenti ad alta e bassa velocita' (HVC and LVC) in entrambe le emissioni atomiche e molecolare. La componente a bassa velocita' nei getti di Class I ragiunge distanze maggiori dalla sorgente (fino a 1000 AU) che nei getti di tipo TTauri. Inoltre, contrariamente a quanto trovato lontano dalla sorgente, nelle vicinanze della stella la densita' elettronica aumenta al diminuire della velocita', mentre la componente ad alta velocita' trasporta sempre la maggiore quantita' di masa. I risultati qui mostrati sono stati inoltre confrontati con le predizione trovate dai modelli di lancio di getti. Mentre le propieta' cinematiche sono, al meno qualitativamente, riprodotte da questi modelli, nessuno di loro riesce ad spiegare l'andamento osservato dalla densita' elettronica in funzione della velocita'. D'altraparte, non e' possibile stabilire alcuna correlazione tra la presenza di indicatori di acrescimento ed egezione entro il campione di sorgenti di Classe I. Inoltre, diversamente da cio' che previsto per le stelle giovanni, soltanto quatro delle dieci sorgenti hanno una luminosita' dominata da accrescimento. Questo risultato sembra suggerire che la maggioranza di stelle giovanni clasificate come Classe I sono in realta' sorgenti molto piu' evolute che hanno gia' acquisito la maggior parte della loro massa. Nonostante cio', i valori di tasa di accrescimento ottenuti sono in media piu' alti di quelli trovati in stelle di tipo TTauri della stessa masa.
In this thesis a study of the accretion and ejection properties of low mass embedded protostar (the so-called Class 0/I sources) through ISAAC NIR high angular observations is presented. The physics, kinematics and dynamics of five Class 0/I jets (HH1, HH111,HH212 / HH34, HH46-47) have been analysed in order to give some insights about the jet generation and the dependence of the jet properties on the evolutionary stage of the source. In addition, the accretion properties of a sample of ten Class I sources have been measured in order to revise their evolutionary status. All the studied jets have been observed through atomic and molecular emission, traced by [FeII] and H2 transitions. Applying near-IR diagnostic techniques important physical parameters have been inferred. In particular, one milestone of this thesis was to derive the physical properties of embedded protostellar jets as a function of the jet radial velocity. For instance, at large distances from the source, the electron density (ne) has been found to decrease with lower velocities. Average values over the brightest knots of 2600-6200 cm3 have been found. The amount of mass transported along the flows has been also inferred. The results show that Class 0/I jets transport more mass than the more evolved jets from CTTS, while the accretion to ejection ratio remains roughly constant independently of the evolutionary stage of the source. The inner region of Class I jets has been studied in detail in order to constrain the jet launching mechanism. Similarly to what found in CTTS jets, Class I jets present two velocity components at high and low velocity (the HVC and LVC) in both the atomic and molecular gas. The LVC in Class I jets reaches, however, larger distances (up to 1000 AU from the source) with respect to jets from CTTS. At variance with what found at large distances from the source, in the inner jet region, ne increases with decreasing velocity, while the mass flux along the jet is always higher in the HVC. When comparing these results with the predictions of MHD jet launching models, the kinematical characteristics of the line emission are found to be, at least qualitatively, reproduced by the studied models. None of them can explain, however, the extent of the LVC and the velocity dependence of electron density that is observed. On the other hand, the study of the set of Class I sources reveals no clear correlation between accretion and ejection features. In addition, in spite of what is expected by embedded protostars, only four of the ten sources show accretion dominated luminosities. This result suggests that most of the objects considered as Class I sources are, instead, more evolved sources that have already acquired most of their mass. Despite this fact, the inferred mass accretion rates are larger that those found in CTTS of the same mass.

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.
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.

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.

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.

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.
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.

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.

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.

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.

Le milieu interstellaire, berceau des étoiles, constitue un terrain de jeu fantastique pour un physicien par sa richesse et la complexité des phénomènes mis en jeu. Comprendre les détails de la formation stellaire est un des grands défis de l’astrophysique moderne. La complexité des problèmes étudiés dans cette thèse fait des simulations numériques un outil précieux qui m’a permis d’étudier deux aspects fondamentaux de la formation stellaire. La première partie de mon travail est consacrée à comprendre l’origine de la rotation des disques de gaz et de poussière entourant les jeunes étoiles, dans lesquels se forment les planètes. La seconde est l’étude de la formation des amas d’étoiles. S’il est reconnu que les étoiles se forment en groupe, les processus influant sur la formation de ces amas et sur leur structure sont mal connus. L’étude sera particulièrement focalisée sur l’influence des jets de matière émis par les jeunes étoiles sur ces amas
The interstellar medium is the cradle of stars. It is a fantastic playground for physicists due to its richness and the complexity of the phenomena involved. Understanding the details of star formation is one of the great challenges of modern astrophysics.The complexity of the problems studied in this thesis makes numerical simulations a valuable tool. It has allowed me to study two fundamental aspects of star formation. The first part of my work is devoted to understanding the origin of the rotation of the disks made of gas and dust that surround young stars and in which planets form. The second is the study of the formation of star clusters. While it is known that stars form in clusters, the processes that influence the formation of these clusters and their structure are poorly understood. The study will focus particularly on the influence of jets of matter emitted by young stars on these clusters

Protostellar jets are a vital part of the star formation process. They are responsible for the removal of excess angular momentum critical to the growth of protostars, while feeding that angular momentum back into molecular clouds to regulate the formation of stellar cores and gravitational collapse. To better understand the origin and impact of protostellar jets, this thesis investigates the launching of protostellar disc winds and the driving of non-isothermal turbulence in the interstellar medium. In the first part of this thesis, we explore how the structure of protostellar discs relates to the properties of the wind-launching region, which directly effects the large-scale properties of the jet. In order to study the launching of disc winds, we first design a 1+1.5D magnetohydrodynamic (MHD) model of the launching region in the [r,z] plane. We take into account the three diffusion mechanisms of non-ideal MHD (Ohm, Hall, and ambipolar) by calculating their contributions at the disc midplane and using a simplified, vertically-scaled approach for higher z. We observe that most of the mass launched by the wind is concentrated within a radially localized region a fraction of an astronomical unit (au) in width, in agreement with current observations. We find that the footprint radius and the wind efficiency, measured by the ratio of the wind mass-loss rate to the rate of material accreted onto the star, are a strong function of the model parameters, namely the mass accretion rate, magnetic field strength, and surface density profile of the disc. Understanding the structure of the wind-launching region has important We subsequently improve the 1+1.5D models by removing the vertical scaling approximation to the non-ideal MHD terms and calculate the magnetic diffusivities self-consistently at all heights above the disc midplane. This results in increased field-matter coupling surrounding the midplane, increasing the poloidal magnetic field bending and compressing the disc via enhanced magnetic pressure gradients. It also shifts the wind-launching region to smaller radii, decreases the overall wind mass-loss rate by an order of magnitude, and generates a radially symmetric wind mass-loss profile. In the second part of this thesis, we investigate the properties of driven, turbulent, adiabatic gas. The density variance--Mach number relation of the turbulent interstellar medium is a key ingredient for analytical models of star formation. We examine the robustness of the standard, isothermal form of this relation in the non-isothermal regime, specifically testing ideal gases with diatomic molecular and monatomic adiabatic indices. Stirring the gas with purely solenoidal forcing at low wavenumbers, we find that as the gas heats in adiabatic compressions, it evolves along a curve in the density variance-Mach number plane, but deviates significantly from the standard isothermal relation. We provide new empirical and theoretical relations that take the adiabatic index into account and provide good fits for a range of Mach numbers.