Numerical simulations of protostellar jetson the origin of the high-energy emission

  1. Ustamujic, Sabina
unter der Leitung von:
  1. Salvatore Orlando Doktorvater/Doktormutter
  2. Ana Inés Gómez de Castro Doktormutter

Universität der Verteidigung: Universidad Complutense de Madrid

Fecha de defensa: 21 von September von 2018

Gericht:
  1. Elisa de Castro Rubio Präsidentin
  2. Juan Carlos Vallejo Chavarino Sekretär
  3. Jorge Sanz Forcada Vocal
  4. Christophe Sauty Vocal
  5. Rafael Bachiller García Vocal
Fachbereiche:
  1. Física de la Tierra y Astrofísica

Art: Dissertation

Teseo: 148363 DIALNET

Zusammenfassung

The exploration of the physics of accretion and outflows in young stars is one of the main objectives of the World Space Observatory ¿ Ultraviolet (WSO-UV) project. Jets are a fundamental part of the formation and evolution processes of young stars, participating in the loss of mass and angular momentum from the whole system. They are detected in different wavelength bands and are ubiquitous at the earliest stages of star formation. However, many questions about the origin and feedback of protostellar jets remain unanswered. In this context, the study of high-energetic phenomena emitting in the extreme ultraviolet (EUV) and X-rays is fundamental as they could have a relevant role in ionizing large parts of the circumstellar environment. In particular, observations showed evidence of X-ray emitting sources characterized by different luminosities and locations within jets. In some cases, the X-ray emitting region is located at the base of the jet close to the star from which the jet originates while, in other cases, the X-ray source is located further away from the star. OBJECTIVES AND METHODOLOGY In this thesis we aim at investigating the origin of high-energy X-ray emission detected in several jets. We studied in detail the cases of HH 154 and DG Tau, where the emission is situated at the base of the jet, and the case of HH 248, where the emission is located further away from the driving source. For the study of X-ray emission arising from the base of the jet, we investigated the scenario of a protostellar jet collimated by the stellar magnetic field forming a quasi-stationary X-ray emitting shock in proximity of the jet base. We carried out a set of 2.5D magnetohydrodynamic numerical simulations that modelled supersonic jets ramming into a magnetized medium, performing a wide exploration of the parameter space characterizing the model. We synthesized the emission measure, X-ray luminosity and count rate from the simulations and compared these data with available observations (in particular, Chandra observations of HH 154 and DG Tau). For the X-ray emission originating from a X-ray source located further away from the star, we explored the scenario of a stellar jet that impacts a dense molecular cloud forming a X-ray emitting extended source. In this case, we modelled the impact of a jet against a dense cloud by 2D axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Also in this case, we synthesized the emission measure and X-ray luminosity from the simulations and compared our results with XMM-Newton observations of HH 248. RESULTS AND CONCLUSIONS Our model explains the origin of X-ray emission from protostellar jets in a natural way, being able to reproduce the observed jet properties at different evolutionary phases. Close to the driving source, the jet is collimated by the magnetic field forming a quasi-stationary shock at the base which emits in X-rays even when perturbations are present. Our hydrodynamic simulations showed that a jet that impacts a dense cloud can produce plasma with temperatures up to 107 K, leading to X-ray emission as a result. From these models, we derived the physical parameters that can give rise to X-ray emission consistent with observations of HH 154, DG Tau and HH 248. Thus, we suggest that the X-ray emitting source observed at the base of the jet in HH 154 and DG Tau is related to the quasi-stationary shock formed when the plasma is collimated by the magnetic field close to the driving source, while the extended X-ray source close to HH 248 corresponds to the jet impacting on a dense molecular cloud. Finally, the wide exploration of the parameter space characterizing the models performed, could be a useful tool to study and diagnose the physical properties of YSO jets over a broad range of physical conditions, from embedded to disk-bearing sources.