Final Report Summary - TJ - COMPTON (Two-component jets - Comparing theory, observations and numerical simulations)
Summary and publications of project
Star formation is among the most actively research fields in astrophysics, not only because it deepens the understanding of the physical mechanisms involved, but also because it provides the answers concerning the origins of our own solar system. On the other hand, the exact same equations that describe the dynamics of magnetised plasmas during the birth of stars, describe also the laboratory plasmas on earth. Taming the latter is the key to fusion, a process that will give access to an almost infinite and cheap source of energy.
Young stellar objects (YSO) consist of two parts, a central object that will become a star and a surrounding disk, the remnants of which will form its planets (Matsakos et al 2010). Such systems are associated with two complex and interrelated phenomena, disk accretion and mass outflows.
In this project we have addressed some of the open questions related to jets, a critical phenomenon to understand how stars, like our sun, are formed. In particular, protostellar jets are supersonic and highly collimated mass outflows that propagate to large distances. Recent observational data as well as theoretical arguments support a two-component jet scenario, wherein a magneto-centrifugally accelerated disk wind, required to explain the high mass loss rates, surrounds and collimates a pressure driven stellar outflow. Adopting a theoretical approach, we have performed and analysed magneto-hydrodynamical (MHD) numerical simulations of YSO jets. Specifically, we have focussed on bridging the gap between the theoretical models of two-component YSO outflows with observations of protostellar jets. On the one hand, we have addressed some of the peculiar dynamical properties that some observed systems demonstrate, such as the velocity asymmetries between the red- and blue-shifted bipolar flows (Matsakos et al. 2012) and the counter-rotation of some jets (Sauty et al. 2012). On the other hand, we have studied the effects of radiation cooling effects in the time-dependent structure of the outflows (Matsakos et al. in preparation) and we have generated synthetic emission maps to directly compare with observations (Tesileanu et al. in preparation).
1. Matsakos, T., Vlahakis, N., Tsinganos, K., et al. 2010, ASPCS, Vol 424
2. Matsakos, T., Vlahakis, N., Tsinganos, K., Karampelas, K., Sauty, C., et al. 2012, A&A, 545, 53
3. Sauty, C., Cayatte, V., Lima, J. J. G., Matsakos, T. and Tsinganos, K. 2012, ApJ, 759, L1
4. Matsakos, T., Te ¸sileanu, O., Mignone, A., et al. in preparation 5. Tesileanu, O., Matsakos, T., Mignone, A., et al. in preparation 6. Tzeferacos, P., Mignone, A. and Matsakos, T., in preparation.
Career development of the researcher
The research activities as well as the expertise obtained on this scientific topic and the numerical methods, have further developed the skills and competences of the researcher, building a strong background for his career. In addition, the researcher was given the opportunity to co-edit the proceedings of the 9th International Conference of the Hellenic Astronomical Society: 'Advances in Hellenic astronomy during the IYA09' (Tsinganos, Hatzidimitriou and Matsakos 2010). In that volume 114 papers were presented, which not only did they familiarise him with a variety of astrophysical topics, but also developed his organisational and public outreach skills.
Development of lasting cooperation with the scientific and/or industrial environment of the country from which he/she has moved
The collaboration with O. Tesileanu (University of Bucharest) on the application of radiation cooling and emission map generation, as well as the rest of the Turin group on the two-component jet simulations and PLUTO related projects (S. Massaglia, E. Trussoni, A. Mignone, P. Tzeferacos) demonstrates the lasting collaboration that has been developed with the previous host country of the Marie Curie Fellowship. The collaboration is ongoing, with several new projects already in progress. In particular, the researcher has visited several times Turin and he has been invited to present the results of this work at a scientific meeting organised in March 2013.
Dissemination activities
The results of this work have been presented in a talk at the ninth international conference of the Hellenic Astronomical Society as well as in written form in the proceedings of the same conference (Matsakos, T., Vlahakis, N., Tsinganos, K., et al. 2010, ASPCS, Vol 424, edited by Tsinganos, K., Hatzidimitriou, D., Matsakos, T.). Moreover, the researcher has been invited to give seminars on the topic, e.g. at the National Observatory of Athens, Greece and the Service d' Astrophysique, IRFU/CEA, France.
The researcher has provided his previously acquired numerical expertise to help several PhD and post-graduate students at the Institute of Accelerating Systems and Applications (IASA) and the University of Athens. He introduced two post- graduate students to the numerical treatment of the MHD equations and guided them to perform YSO jet simulations as a part of their dissertations. In particular, the work done by one of those (Kostas Karampelas) has contributed to the results of a published paper (Matsakos et al. 2012). In addition, the researcher has helped with the discretisation and solution of differential equations on wind driven mass loss and magnetic braking problems, a contribution that has been acknowledged in the published paper of Nanouris et al. (2011).
Project management
The project was managed successfully in Athens by Prof. Kanaris Tsinganos and the staff of the IASA which is affiliated to the University of Athens. IASA provided the researcher with all requirements for a successful implementation of the present grant, i.e.: excellent office space, modern computers, full logistical support for the grant and all needed accommodation during the period of the grant.
Detailed scientific report for 'TJ-COMPTON', PERG05-GA-2009-249164
Summary
This project has addressed some of the open questions related to YSO jets, a critical phenomenon to understand of star formation. Protostellar jets are supersonic and highly collimated mass outflows that propagate to large distances. Recent observational data as well as theoretical arguments support a two-component jet scenario, wherein a magneto-centrifugally accelerated disk wind, required to explain the high mass loss rates, surrounds and collimates a pressure driven stellar outflow. Adopting a theoretical approach, we have performed and analysed MHD numerical simulations of YSO jets using the PLUTO code. In particular, this project has focussed on bridging the gap between the theoretical models of two-component YSO outflows with observations of protostellar jets. On the one hand, we have addressed some of the peculiar dynamical properties that some observed systems demonstrate, such as the velocity asymmetries between the red- and blue-shifted bipolar flows (Matsakos et al. 2012) and the counter-rotation of some jets (Sauty et al. 2012). On the other hand, we have studied the effects of radiation cooling effects in the time-dependent structure of the outflows (Matsakos et al. in preparation) and we have generated synthetic emission maps to directly compare with observations (Tesileanu et al. in preparation).
Project objectives for the period: Scientific objectives, work progress and achievements
Velocity asymmetries in YSO jets: Intrinsic and extrinsic mechanisms.
It is well established that some YSO jets (e.g. RW Aur) display different propagation speeds between their blue and red shifted parts, a feature possibly associated with the central engine or the environment in which the jet propagates. To understand the origin of asymmetric YSO jet velocities, we have investigated the efficiency of two candidate mechanisms, one based on the intrinsic properties of the system and the other on the role of the external medium. In particular, a parallel or anti-parallel configuration between the protostellar magnetosphere and the disk magnetic field has been considered and the resulting dynamics have been examined both in an ideal and in a resistive MHD regime. Moreover, we have explored the effects of a potential difference in the pressure of the environment, as a consequence of the nonuniform density distribution of molecular clouds. Ideal and resistive axisymmetric numerical simulations have been carried out for a variety of models, all of which were based on a combination of two analytical solutions, a disk wind and a stellar outflow. The initial two-component jet has been modified by either inverting the orientation of its inner magnetic field or imposing a constant surrounding pressure. The velocity profiles have been studied by assuming steady flows as well as a time variable ejection. Discrepancies between the speeds of the two outflows in opposite directions have been found to occur both due to unaligned magnetic fields and different outer pressures. In the former case, the asymmetry appeared only on the dependence of the velocity on the cylindrical distance, but the implied observed value was significantly altered when the density distribution was also taken into account. On the other hand, a nonuniform medium collimated the two jets unevenly, directly affecting their propagation speed. A further interesting feature of the pressure-confined outflow simulations has been the formation of static knots whose spacing seems to be associated with the ambient pressure. To sum up, jet velocity asymmetries are anticipated both when multipolar magnetic moments are present in the star-disk system and when nonuniform environments are considered. The latter is an external mechanism that can easily explain the large timescale of the phenomenon, whereas the former naturally relates it to the YSO intrinsic properties. These results have been published in conference proceedings (Matsakos et al. 2010), whereas a more detailed study is reported in Matsakos et al. (2012).
Counter-rotation in magneto-centrifugally driven jets and other winds.
Rotation measurements in jets from T Tauri stars are a rather difficult task. Some jets seem to be rotating in a direction opposite to that of the underlying disk, although it is not yet clear if this affects the totality or part of the outflows. On the other hand, Ulysses data also suggest that the solar wind may rotate in two opposite ways between the northern and southern hemispheres. We have shown that this result is not surprising as it may seem and that it emerges naturally from the ideal MHD equations. Specifically, counter-rotating jets do not contradict the magneto-centrifugal driving of the flow nor prevent extraction of angular momentum from the disk. The demonstration of this result has been shown by combining the ideal MHD equations for steady axisymmetric flows. In particular, provided that the jet is decelerated below some given threshold beyond the Alfven surface, the flow will change its direction of rotation locally or globally. Counter-rotation is also possible for only some layers of the outflow at specific altitudes along the jet axis. We have concluded that the counter rotation of winds or jets with respect to the source, star or disk, is not in contradiction with the magneto-centrifugal driving paradigm. This phenomenon may affect part of the outflow, either in one hemisphere, or only in some of the outflow layers. We have illustrated this effect with a time-dependent simulation and we have shown that it may not be permanent. This work has been presented in detail in Sauty et al. (2012).
Two-component YSO jet models: From theory to synthetic observations.
Astronomical observations, analytical solutions and numerical simulations have provided the building blocks to formulate the current theory of young stellar object jets. Although each approach has made great progress independently, it is only during the last decade that significant efforts are being made to bring the separate pieces together. Building on previous work that combined analytical solutions and numerical simulations, we apply a sophisticated cooling function to incorporate optically thin energy losses and create synthetic emission maps. Firstly, analytical disk and stellar outflow solutions are properly combined to initialise numerical two-component jet models inside the computational box. Secondly, magneto-hydrodynamical simulations are performed in two and a half dimensions (2.5D) self-consistently treating the ionisation and recombination of 29 ions. Finally, the outputs are post-processed to produce artificial observational data. The values for the density, temperature and velocity that the simulations provide along the axis are within the typical range of protostellar outflows. Moreover, the synthetic emission maps of the doublets [OI], [NII] and [SII] outline a well collimated and knot-structured jet, which is surrounded by a less dense and slower wind, not observable in these lines. The jet is found to have a small opening angle and a radius that is also comparable to observations. We conclude that the first two-component jet simulations, based on analytical models, that include ionisation and optically thin radiation losses demonstrate promising results for modelling specific young stellar object outflows. The generation of synthetic emission maps provides the link to observations, as well as the necessary feedback for the further improvement of the available models. The articles prepared for this work are going to be submitted shortly (Matsakos et al. in preparation, Tesileanu et al. in preparation).
Other projects.
As a member of the development team of PLUTO, a numerical code for computational astrophysics, the researcher has worked on the improvement of the thermal conduction module as well as the implementation of the implicit scheme of one-dimensional (1D) parabolic terms in HD/MHD. Moreover, a comparison of the efficiency of explicit, implicit and super time stepping techniques for the numerical integration of non-ideal MHD effects, such as resistivity, thermal conduction and viscosity, is underway. The tests that are being performed along with the results will be reported in Tzeferacos, Mignone and Matsakos (in preparation).
Bibliography:
1. Matsakos, T., Vlahakis, N., Tsinganos, K., et al. 2010, ASPCS, Vol 424
2. Matsakos, T., Vlahakis, N., Tsinganos, K., Karampelas, K., Sauty, C., et al. 2012, A&A, 545, 53
3. Matsakos, T., Tesileanu, O., Mignone, A., et al. in preparation
4. Nanouris, N., Kalimeris, A., Antonopoulou, E. and Rovithis-Livaniou, H. 2011, A&A, 535, 126
5. Sauty, C., Cayatte, V., Lima, J. J. G., Matsakos, T. and Tsinganos, K. 2012, ApJ, 759, L1
6. Tesileanu, O., Matsakos, T., Mignone, A., et al. in preparation
7. Tsinganos, K., Hatzidimitriou, D., Matsakos, T., 2010, Proceedings of the Ninth International Conference of the Hellenic Astronomical Society, ASPCS, Vol 424
8. Tzeferacos, P., Mignone, A. and Matsakos, T., in preparation
Star formation is among the most actively research fields in astrophysics, not only because it deepens the understanding of the physical mechanisms involved, but also because it provides the answers concerning the origins of our own solar system. On the other hand, the exact same equations that describe the dynamics of magnetised plasmas during the birth of stars, describe also the laboratory plasmas on earth. Taming the latter is the key to fusion, a process that will give access to an almost infinite and cheap source of energy.
Young stellar objects (YSO) consist of two parts, a central object that will become a star and a surrounding disk, the remnants of which will form its planets (Matsakos et al 2010). Such systems are associated with two complex and interrelated phenomena, disk accretion and mass outflows.
In this project we have addressed some of the open questions related to jets, a critical phenomenon to understand how stars, like our sun, are formed. In particular, protostellar jets are supersonic and highly collimated mass outflows that propagate to large distances. Recent observational data as well as theoretical arguments support a two-component jet scenario, wherein a magneto-centrifugally accelerated disk wind, required to explain the high mass loss rates, surrounds and collimates a pressure driven stellar outflow. Adopting a theoretical approach, we have performed and analysed magneto-hydrodynamical (MHD) numerical simulations of YSO jets. Specifically, we have focussed on bridging the gap between the theoretical models of two-component YSO outflows with observations of protostellar jets. On the one hand, we have addressed some of the peculiar dynamical properties that some observed systems demonstrate, such as the velocity asymmetries between the red- and blue-shifted bipolar flows (Matsakos et al. 2012) and the counter-rotation of some jets (Sauty et al. 2012). On the other hand, we have studied the effects of radiation cooling effects in the time-dependent structure of the outflows (Matsakos et al. in preparation) and we have generated synthetic emission maps to directly compare with observations (Tesileanu et al. in preparation).
1. Matsakos, T., Vlahakis, N., Tsinganos, K., et al. 2010, ASPCS, Vol 424
2. Matsakos, T., Vlahakis, N., Tsinganos, K., Karampelas, K., Sauty, C., et al. 2012, A&A, 545, 53
3. Sauty, C., Cayatte, V., Lima, J. J. G., Matsakos, T. and Tsinganos, K. 2012, ApJ, 759, L1
4. Matsakos, T., Te ¸sileanu, O., Mignone, A., et al. in preparation 5. Tesileanu, O., Matsakos, T., Mignone, A., et al. in preparation 6. Tzeferacos, P., Mignone, A. and Matsakos, T., in preparation.
Career development of the researcher
The research activities as well as the expertise obtained on this scientific topic and the numerical methods, have further developed the skills and competences of the researcher, building a strong background for his career. In addition, the researcher was given the opportunity to co-edit the proceedings of the 9th International Conference of the Hellenic Astronomical Society: 'Advances in Hellenic astronomy during the IYA09' (Tsinganos, Hatzidimitriou and Matsakos 2010). In that volume 114 papers were presented, which not only did they familiarise him with a variety of astrophysical topics, but also developed his organisational and public outreach skills.
Development of lasting cooperation with the scientific and/or industrial environment of the country from which he/she has moved
The collaboration with O. Tesileanu (University of Bucharest) on the application of radiation cooling and emission map generation, as well as the rest of the Turin group on the two-component jet simulations and PLUTO related projects (S. Massaglia, E. Trussoni, A. Mignone, P. Tzeferacos) demonstrates the lasting collaboration that has been developed with the previous host country of the Marie Curie Fellowship. The collaboration is ongoing, with several new projects already in progress. In particular, the researcher has visited several times Turin and he has been invited to present the results of this work at a scientific meeting organised in March 2013.
Dissemination activities
The results of this work have been presented in a talk at the ninth international conference of the Hellenic Astronomical Society as well as in written form in the proceedings of the same conference (Matsakos, T., Vlahakis, N., Tsinganos, K., et al. 2010, ASPCS, Vol 424, edited by Tsinganos, K., Hatzidimitriou, D., Matsakos, T.). Moreover, the researcher has been invited to give seminars on the topic, e.g. at the National Observatory of Athens, Greece and the Service d' Astrophysique, IRFU/CEA, France.
The researcher has provided his previously acquired numerical expertise to help several PhD and post-graduate students at the Institute of Accelerating Systems and Applications (IASA) and the University of Athens. He introduced two post- graduate students to the numerical treatment of the MHD equations and guided them to perform YSO jet simulations as a part of their dissertations. In particular, the work done by one of those (Kostas Karampelas) has contributed to the results of a published paper (Matsakos et al. 2012). In addition, the researcher has helped with the discretisation and solution of differential equations on wind driven mass loss and magnetic braking problems, a contribution that has been acknowledged in the published paper of Nanouris et al. (2011).
Project management
The project was managed successfully in Athens by Prof. Kanaris Tsinganos and the staff of the IASA which is affiliated to the University of Athens. IASA provided the researcher with all requirements for a successful implementation of the present grant, i.e.: excellent office space, modern computers, full logistical support for the grant and all needed accommodation during the period of the grant.
Detailed scientific report for 'TJ-COMPTON', PERG05-GA-2009-249164
Summary
This project has addressed some of the open questions related to YSO jets, a critical phenomenon to understand of star formation. Protostellar jets are supersonic and highly collimated mass outflows that propagate to large distances. Recent observational data as well as theoretical arguments support a two-component jet scenario, wherein a magneto-centrifugally accelerated disk wind, required to explain the high mass loss rates, surrounds and collimates a pressure driven stellar outflow. Adopting a theoretical approach, we have performed and analysed MHD numerical simulations of YSO jets using the PLUTO code. In particular, this project has focussed on bridging the gap between the theoretical models of two-component YSO outflows with observations of protostellar jets. On the one hand, we have addressed some of the peculiar dynamical properties that some observed systems demonstrate, such as the velocity asymmetries between the red- and blue-shifted bipolar flows (Matsakos et al. 2012) and the counter-rotation of some jets (Sauty et al. 2012). On the other hand, we have studied the effects of radiation cooling effects in the time-dependent structure of the outflows (Matsakos et al. in preparation) and we have generated synthetic emission maps to directly compare with observations (Tesileanu et al. in preparation).
Project objectives for the period: Scientific objectives, work progress and achievements
Velocity asymmetries in YSO jets: Intrinsic and extrinsic mechanisms.
It is well established that some YSO jets (e.g. RW Aur) display different propagation speeds between their blue and red shifted parts, a feature possibly associated with the central engine or the environment in which the jet propagates. To understand the origin of asymmetric YSO jet velocities, we have investigated the efficiency of two candidate mechanisms, one based on the intrinsic properties of the system and the other on the role of the external medium. In particular, a parallel or anti-parallel configuration between the protostellar magnetosphere and the disk magnetic field has been considered and the resulting dynamics have been examined both in an ideal and in a resistive MHD regime. Moreover, we have explored the effects of a potential difference in the pressure of the environment, as a consequence of the nonuniform density distribution of molecular clouds. Ideal and resistive axisymmetric numerical simulations have been carried out for a variety of models, all of which were based on a combination of two analytical solutions, a disk wind and a stellar outflow. The initial two-component jet has been modified by either inverting the orientation of its inner magnetic field or imposing a constant surrounding pressure. The velocity profiles have been studied by assuming steady flows as well as a time variable ejection. Discrepancies between the speeds of the two outflows in opposite directions have been found to occur both due to unaligned magnetic fields and different outer pressures. In the former case, the asymmetry appeared only on the dependence of the velocity on the cylindrical distance, but the implied observed value was significantly altered when the density distribution was also taken into account. On the other hand, a nonuniform medium collimated the two jets unevenly, directly affecting their propagation speed. A further interesting feature of the pressure-confined outflow simulations has been the formation of static knots whose spacing seems to be associated with the ambient pressure. To sum up, jet velocity asymmetries are anticipated both when multipolar magnetic moments are present in the star-disk system and when nonuniform environments are considered. The latter is an external mechanism that can easily explain the large timescale of the phenomenon, whereas the former naturally relates it to the YSO intrinsic properties. These results have been published in conference proceedings (Matsakos et al. 2010), whereas a more detailed study is reported in Matsakos et al. (2012).
Counter-rotation in magneto-centrifugally driven jets and other winds.
Rotation measurements in jets from T Tauri stars are a rather difficult task. Some jets seem to be rotating in a direction opposite to that of the underlying disk, although it is not yet clear if this affects the totality or part of the outflows. On the other hand, Ulysses data also suggest that the solar wind may rotate in two opposite ways between the northern and southern hemispheres. We have shown that this result is not surprising as it may seem and that it emerges naturally from the ideal MHD equations. Specifically, counter-rotating jets do not contradict the magneto-centrifugal driving of the flow nor prevent extraction of angular momentum from the disk. The demonstration of this result has been shown by combining the ideal MHD equations for steady axisymmetric flows. In particular, provided that the jet is decelerated below some given threshold beyond the Alfven surface, the flow will change its direction of rotation locally or globally. Counter-rotation is also possible for only some layers of the outflow at specific altitudes along the jet axis. We have concluded that the counter rotation of winds or jets with respect to the source, star or disk, is not in contradiction with the magneto-centrifugal driving paradigm. This phenomenon may affect part of the outflow, either in one hemisphere, or only in some of the outflow layers. We have illustrated this effect with a time-dependent simulation and we have shown that it may not be permanent. This work has been presented in detail in Sauty et al. (2012).
Two-component YSO jet models: From theory to synthetic observations.
Astronomical observations, analytical solutions and numerical simulations have provided the building blocks to formulate the current theory of young stellar object jets. Although each approach has made great progress independently, it is only during the last decade that significant efforts are being made to bring the separate pieces together. Building on previous work that combined analytical solutions and numerical simulations, we apply a sophisticated cooling function to incorporate optically thin energy losses and create synthetic emission maps. Firstly, analytical disk and stellar outflow solutions are properly combined to initialise numerical two-component jet models inside the computational box. Secondly, magneto-hydrodynamical simulations are performed in two and a half dimensions (2.5D) self-consistently treating the ionisation and recombination of 29 ions. Finally, the outputs are post-processed to produce artificial observational data. The values for the density, temperature and velocity that the simulations provide along the axis are within the typical range of protostellar outflows. Moreover, the synthetic emission maps of the doublets [OI], [NII] and [SII] outline a well collimated and knot-structured jet, which is surrounded by a less dense and slower wind, not observable in these lines. The jet is found to have a small opening angle and a radius that is also comparable to observations. We conclude that the first two-component jet simulations, based on analytical models, that include ionisation and optically thin radiation losses demonstrate promising results for modelling specific young stellar object outflows. The generation of synthetic emission maps provides the link to observations, as well as the necessary feedback for the further improvement of the available models. The articles prepared for this work are going to be submitted shortly (Matsakos et al. in preparation, Tesileanu et al. in preparation).
Other projects.
As a member of the development team of PLUTO, a numerical code for computational astrophysics, the researcher has worked on the improvement of the thermal conduction module as well as the implementation of the implicit scheme of one-dimensional (1D) parabolic terms in HD/MHD. Moreover, a comparison of the efficiency of explicit, implicit and super time stepping techniques for the numerical integration of non-ideal MHD effects, such as resistivity, thermal conduction and viscosity, is underway. The tests that are being performed along with the results will be reported in Tzeferacos, Mignone and Matsakos (in preparation).
Bibliography:
1. Matsakos, T., Vlahakis, N., Tsinganos, K., et al. 2010, ASPCS, Vol 424
2. Matsakos, T., Vlahakis, N., Tsinganos, K., Karampelas, K., Sauty, C., et al. 2012, A&A, 545, 53
3. Matsakos, T., Tesileanu, O., Mignone, A., et al. in preparation
4. Nanouris, N., Kalimeris, A., Antonopoulou, E. and Rovithis-Livaniou, H. 2011, A&A, 535, 126
5. Sauty, C., Cayatte, V., Lima, J. J. G., Matsakos, T. and Tsinganos, K. 2012, ApJ, 759, L1
6. Tesileanu, O., Matsakos, T., Mignone, A., et al. in preparation
7. Tsinganos, K., Hatzidimitriou, D., Matsakos, T., 2010, Proceedings of the Ninth International Conference of the Hellenic Astronomical Society, ASPCS, Vol 424
8. Tzeferacos, P., Mignone, A. and Matsakos, T., in preparation
