Zeitschriftenartikel: „Observation des jets“

1

Okita, Yuji, Katsutaka Nakamura, Yuuta Shiizaki und Daisuke Nobuta. „LASER OBSERVATION ON THE INNER FLOW STRUCTURE OF WATER JETS(Water Jet)“. Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2005 (2005): 337–42. http://dx.doi.org/10.1299/jsmeicjwsf.2005.337.

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2

Chen, Hao, und Gang Tao. „Research on Temperature Change and Microstructure Evolution of Bore in Steel Target Penetrated by Copper Jets“. Materials Science Forum 667-669 (Dezember 2010): 641–46. http://dx.doi.org/10.4028/www.scientific.net/msf.667-669.641.

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Copper fragments are found to adhere on penetration channel wall after copper jets penetrate steel target, and the research on it is helpful to know microstructure evolution of jets in the process of penetration and cooling time. This paper is based on the observation of bore in steel target penetrated by copper jets, and uses numerical simulation to study the process of copper jets penetration, then the change of temperature and grain size of jets adhered on penetration channel wall can be gotten, and the results agree with the observation of penetration channel wall taken by SEM. From the observations of copper and steel, we can get the conclusion that copper jets are not melted but have dynamic recrystallization in the process of penetration, then copper grain size increases obviously in cooling time, and twins are formed at the same time.

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Shen, Yuandeng. „Observation and modelling of solar jets“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, Nr. 2246 (Februar 2021): 20200217. http://dx.doi.org/10.1098/rspa.2020.0217.

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The solar atmosphere is full of complicated transients manifesting the reconfiguration of the solar magnetic field and plasma. Solar jets represent collimated, beam-like plasma ejections; they are ubiquitous in the solar atmosphere and important for our understanding of solar activities at different scales, the magnetic reconnection process, particle acceleration, coronal heating, solar wind acceleration, as well as other related phenomena. Recent high-spatio-temporal-resolution, wide-temperature coverage and spectroscopic and stereoscopic observations taken by ground-based and space-borne solar telescopes have revealed many valuable new clues to restrict the development of theoretical models. This review aims at providing the reader with the main observational characteristics of solar jets, physical interpretations and models, as well as unsolved outstanding questions in future studies.

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Guetta, Dafne, Roi Rahin, Imre Bartos und Massimo Della Valle. „Constraining the fraction of core-collapse supernovae harbouring choked jets with high-energy neutrinos“. Monthly Notices of the Royal Astronomical Society 492, Nr. 1 (06.01.2020): 843–47. http://dx.doi.org/10.1093/mnras/stz3245.

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ABSTRACT The joint observation of core-collapse supernovae with gamma-ray bursts shows that jets can be launched in the aftermath of stellar core collapse, likely by a newly formed black hole that accretes matter from the star. Such gamma-ray bursts have only been observed accompanying Type Ibc supernovae, indicating a stellar progenitor that lost its hydrogen envelope before collapse. According to recent hypothesis, it is possible that jets are launched in core-collapse events even when the progenitors still retain their hydrogen envelopes; however, such jets are not able to burrow through the star and will be stalled into the interior of the progenitor star before escaping. These jets are called choked jets. High-energy neutrinos produced by such choked jets could escape the stellar envelope and could be observed. Here, we examine how multimessenger searches for high-energy neutrinos and core-collapse supernovae can detect or limit the fraction of stellar collapses that produce jets. We find that a high fraction of jet production is already limited by previous observational campaigns. We explore possibilities with future observations using Large Synoptic Survey Telescope, IceCube, and Km3NET.

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Kayshap, P., K. Murawski, A. K. Srivastava und B. N. Dwivedi. „Rotating network jets in the quiet Sun as observed by IRIS“. Astronomy & Astrophysics 616 (August 2018): A99. http://dx.doi.org/10.1051/0004-6361/201730990.

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Aims. We perform a detailed observational analysis of network jets to understand their kinematics, rotational motion, and underlying triggering mechanism(s). We analyzed the quiet-Sun (QS) data. Methods. IRIS high-resolution imaging and spectral observations (slit-jaw images: Si IV 1400.0 Å; raster: Si IV 1393.75 Å) were used to analyze the omnipresent rotating network jets in the transition region (TR). In addition, we also used observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observation (SDO). Results. The statistical analysis of 51 network jets is performed to understand their various mean properties, e.g., apparent speed (140.16 ± 39.41 km s−1), length (3.16 ± 1.18 Mm), and lifetimes (105.49 ± 51.75 s). The Si IV 1393.75 Å line has a secondary component along with its main Gaussian, which is formed due to the high-speed plasma flows (i.e., network jets). The variation in Doppler velocity across these jets (i.e., blueshift on one edge and redshift on the other) signify the presence of inherited rotational motion. The statistical analysis predicts that the mean rotational velocity (i.e., ΔV) is 49.56 km s−1. The network jets have high-angular velocity in comparison to the other class of solar jets. Conclusions. The signature of network jets is inherited in TR spectral lines in terms of the secondary component of the Si IV 1393.75 Å line. The rotational motion of network jets is omnipresent, which is reported first for this class of jet-like features. The magnetic reconnection seems to be the most favorable mechanism for the formation of these network jets.

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Nagai, Hiroshi. „Inflow and Outflow (Jets) in NGC 1275“. Proceedings of the International Astronomical Union 14, S342 (Mai 2018): 69–72. http://dx.doi.org/10.1017/s1743921318005744.

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AbstractNGC 1275 is one of the best targets to study the high energy emission mechanism in radio galaxies and the accretion flow properties using a young re-started jet 3C 84 as a prober of subpc-to-pc scale environment. In this proceeding, we review the observation results from a series of our VLBI observations and discuss on the origin of gamma-ray emission and accretion flow properties. We also briefly present the preliminary results from our recent ALMA observations.

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Chen, Jiaxuan. „Formation mechanism of blazar jets“. Theoretical and Natural Science 19, Nr. 1 (08.12.2023): 169–75. http://dx.doi.org/10.54254/2753-8818/19/20230529.

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In research of astronomy, cosmology and the basic theoretical physics, the black hole is one of the most concerned celestial bodies. AGN is a kind of observation source with supermassive black hole as the central core, among which Blazar is the key observation subclass of the observer whose jet is facing the Earth. Therefore, the study of the jet has become an crucial subject of black hole research. In this paper, I start with the basic structure model of AGN, briefly describe the characteristics and mechanisms of each structure, especially the jet, and afterward introduce the observed spectral bimodal characteristics, focusing on the analysis of the existing jet formation mechanism from the radio band. Through the existing observations and data fitting, that is, the logarithmic linear fitting of the jet power to the luminosity of the accretion disc and the jet power to the mass and spin parameters of the black hole, corresponding to the Blandford&Payne and the Blandford&Znajek mechanism respectively. Finally, we analyze the conclusion of the two methods and draw the possibility of the two processes and the complementary relationship in theory. Incidentally, the model theory of mixed interpretation of the two mechanisms and processes is obtained.

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Hillier, A., und V. Polito. „Observation of bi-directional jets in a prominence“. Astronomy & Astrophysics 651 (Juli 2021): A60. http://dx.doi.org/10.1051/0004-6361/201935774.

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Quiescent prominences host a large range of flows, many driven by buoyancy, which lead to velocity shear. The presence of these shear flows could bend and stretch the magnetic field resulting in the formation of current sheets which can lead to magnetic reconnection. Though this has been hypothesised to occur in prominences, with some observations that are suggestive of this process, clear evidence has been lacking. In this paper we present observations performed on June 30, 2015 using the Interface Region Imaging Spectrograph Si IV and Mg II slit-jaw imagers of two bi-directional jets that occur inside the body of the prominence. Such jets are highly consistent with what would be expected from magnetic reconnection theory. Using this observation, we estimate that the prominence under study has an ambient field strength in the range of 4.5−9.2 G with ‘turbulent’ field strengths of 1 G. Our results highlight the ability of gravity-driven flows to stretch and fold the magnetic field of the prominence, implying that locally, the quiescent prominence field can be far from a static, force-free magnetic field.

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SHIMIZU, Seiji, Yukio HIRAOKA und Takanori NISHIYAMA. „Instantaneous Photographic Observation of Abrasive Water Suspension Jets“. JSME International Journal Series B 45, Nr. 4 (2002): 830–35. http://dx.doi.org/10.1299/jsmeb.45.830.

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10

Ishikawa, Tatsurou, und Seiji Shimizu. „208 High Speed Observation of Abrasive Water Jets“. Proceedings of Conference of Tohoku Branch 2008.43 (2008): 217–18. http://dx.doi.org/10.1299/jsmeth.2008.43.217.

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11

Panesar, Navdeep K., Viggo H. Hansteen, Sanjiv K. Tiwari, Mark C. M. Cheung, David Berghmans und Daniel Müller. „Solar Orbiter and SDO Observations, and a Bifrost Magnetohydrodynamic Simulation of Small-scale Coronal Jets“. Astrophysical Journal 943, Nr. 1 (01.01.2023): 24. http://dx.doi.org/10.3847/1538-4357/aca1c1.

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Abstract We report high-resolution, high-cadence observations of five small-scale coronal jets in an on-disk quiet Sun region observed with Solar Orbiter’s EUI/HRIEUV in 174 Å. We combine the HRIEUV images with the EUV images of SDO/AIA and investigate the magnetic setting of the jets using coaligned line-of-sight magnetograms from SDO/HMI. The HRIEUV jets are miniature versions of typical coronal jets as they show narrow collimated spires with a base brightening. Three out of five jets result from a detectable minifilament eruption following flux cancelation at the neutral line under the minifilament, analogous to coronal jets. To better understand the physics of jets, we also analyze five small-scale jets from a high-resolution Bifrost MHD simulation in synthetic Fe ix/Fe x emissions. The jets in the simulation reside above neutral lines and four out of five jets are triggered by magnetic flux cancelation. The temperature maps show evidence of cool gas in the same four jets. Our simulation also shows the signatures of opposite Doppler shifts (of the order of ±10 s of km s−1) in the jet spire, which is evidence of untwisting motion of the magnetic field in the jet spire. The average jet duration, spire length, base width, and speed in our observations (and in synthetic Fe ix/Fe x images) are 6.5 ± 4.0 min (9.0 ± 4.0 minutes), 6050 ± 2900 km (6500 ± 6500 km), 2200 ± 850 km, (3900 ± 2100 km), and 60 ± 8 km s−1 (42 ± 20 km s−1), respectively. Our observation and simulation results provide a unified picture of small-scale solar coronal jets driven by magnetic reconnection accompanying flux cancelation. This picture also aligns well with the most recent reports of the formation and eruption mechanisms of larger coronal jets.

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Erlandson, R. E., P. K. Swaminathan, C. I. Meng, B. J. Stoyanov, J. I. Zetzer, B. G. Gavrilov, Yu N. Kiselev und Yu A. Romanovsky. „observation of auroral emissions induced by artificial plasma jets“. Geophysical Research Letters 26, Nr. 11 (01.06.1999): 1553–56. http://dx.doi.org/10.1029/1999gl900282.

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Soyama, Hitoshi, Yoshiaki Yanauchi, Kazunori Sato, Toshiaki Ikohagi, Risaburo Oba und Ryoichiro Oshima. „High-speed observation of ultrahigh-speed submerged water jets“. Experimental Thermal and Fluid Science 12, Nr. 4 (Mai 1996): 411–16. http://dx.doi.org/10.1016/0894-1777(95)00124-7.

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14

KIRA, AKIO, KAZUYUKI HOKAMOTO, YASUHIRO UJIMOTO, SHOICHIRO KAI und MASAHIRO FUJITA. „OBSERVATION OF METAL JET IN EXTREMELY HIGH IMPULSIVE PRESSURE GENERATOR“. International Journal of Modern Physics B 22, Nr. 09n11 (30.04.2008): 1653–58. http://dx.doi.org/10.1142/s0217979208047213.

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A new technique has been developed to generate an extremely high impulsive pressure by using an explosive. A metal jet, typically observed in explosive welding is used in this technique. The behavior of metal jet is crucial to the design of pressure generator. The experimental observation was made by the collision of metal jet on a metal block surface. Many craters formed by the collision of metal jets on the surface of the metal block were observed. The craters were overlapped and distributed in a wide range. The diameter of the largest crater was 0.5 mm. The quantity of the discharged metal jets was found to be a function of the quantity of explosive. The total area of the craters is considered as proportional to the quantity of the discharged metal jets and the experimental conditions for the formation of large craters was investigated.

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Clarke, Cathie, Bo Reipurth und Eduardo Delgado-Donate. „Multiple Protostars, Jets, and the Origin of Brown Dwarfs“. International Astronomical Union Colloquium 191 (August 2004): 184–94. http://dx.doi.org/10.1017/s0252921100008733.

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AbstractThe observation that young stars are clustered in few body non-hierarchical multiple systems at very young ages has profound consequences for our understanding of the formation of stars, binaries and the disks and planets that may surround them. In this chapter we review theoretical progress made over the last decade in modeling the break up of these natal clusters and discuss a range of observational predictions that arise from these models, relating to the kinematics, binary statistics and possession of disks of both stars and brown dwarfs. We also argue that one of the most spectacular manifestations of dynamical interactions in young multiple systems should be the formation of giant Herbig-Haro flows, and present observational evidence that may be interpreted in this light.

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Venturi, Giacomo, Alessandro Marconi, Matilde Mingozzi, Giovanni Cresci, Stefano Carniani und Filippo Mannucci. „Turbulence/outflows perpendicular to low-power jets in Seyfert galaxies“. Proceedings of the International Astronomical Union 15, S359 (März 2020): 464–66. http://dx.doi.org/10.1017/s1743921320002197.

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AbstractWe present recent results from our MAGNUM survey of nearby active galactic nuclei (AGN), which exploits observations from the optical/near-IR integral field spectrograph MUSE at VLT. We detect strongly enhanced line widths in emission line maps of four galaxies perpendicularly to their low-power jets and AGN ionisation cones, indicative of turbulent/outflowing material. The observation of a similar phenomenon in other works suggests that it originates from an interaction mechanism between the jet and the galaxy disc through which it propagates.

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Wang, H., H. Lühr und A. J. Ridley. „Plasma convection jets near the poleward boundary of the nightside auroral oval and their relation to Pedersen conductivity gradients“. Annales Geophysicae 28, Nr. 4 (15.04.2010): 969–76. http://dx.doi.org/10.5194/angeo-28-969-2010.

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Abstract. In this work, we have shown that the ionospheric azimuthal plasma velocity jets near the open-closed field line boundary on the nightside can be associated with the peak in the ionospheric conductivity gradient. Both model and DMSP observations have been utilized to conduct this investigation. The model tests show that when the gradient of conductivity in the poleward boundary becomes sharper, convection peaks appear around the poleward edge of the aurora. The model results have been confirmed by DMSP observations. Hundreds of large ion flow events are identified from one year DMSP observations, with flow speed larger than 500 m/s that occurred poleward of the aurora. Among them, 280 (74%) events are found to be associated with conductivity gradient peaks. Most of the convection jets occur in winter when conductivity gradients are expected to be large. The convection jets tend to occur at later local times (21:00–22:00 MLT) at 70°–72° MLat. These events are preceded by increasing of the merging electric field suggesting that they occur after the expansion of the polar cap. Both observation and model results show that the conductivity gradient at the polar cap boundary are one of the important elements in establishing the convection jets.

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Nathanail, Antonios, Ramandeep Gill, Oliver Porth, Christian M. Fromm und Luciano Rezzolla. „On the opening angle of magnetized jets from neutron-star mergers: the case of GRB170817A“. Monthly Notices of the Royal Astronomical Society 495, Nr. 4 (25.05.2020): 3780–87. http://dx.doi.org/10.1093/mnras/staa1454.

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ABSTRACT The observations of GW170817/GRB170817A have confirmed that the coalescence of a neutron-star binary is the progenitor of a short gamma-ray burst (GRB). In the standard picture of a short GRB, a collimated highly relativistic outflow is launched after merger and it successfully breaks out from the surrounding ejected matter. Using initial conditions inspired from numerical-relativity binary neutron-star merger simulations, we have performed general-relativistic hydrodynamic (HD) and magnetohydrodynamic (MHD) simulations in which the jet is launched and propagates self-consistently. The complete set of simulations suggests that: (i) MHD jets have an intrinsic energy and velocity polar structure with a ‘hollow core’ subtending an angle θcore ≈ 4°–5° and an opening angle of θjet > ≳ 10°; (ii) MHD jets eject significant amounts of matter and two orders of magnitude more than HD jets; (iii) the energy stratification in MHD jets naturally yields the power-law energy scaling E(> Γβ) ∝ (Γβ)−4.5; (iv) MHD jets provide fits to the afterglow data from GRB170817A that are comparatively better than those of the HD jets and without free parameters; and (v) finally, both of the best-fitting HD/MHD models suggest an observation angle θobs ≃ 21° for GRB170817A.

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Xue, Xiao Chun, Yong Gang Yu und Qi Zhang. „Experimental Study on Expansion Process of High Pressure Twin Combustion-Gas Jets in Liquid“. Applied Mechanics and Materials 148-149 (Dezember 2011): 212–15. http://dx.doi.org/10.4028/www.scientific.net/amm.148-149.212.

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In order to investigate the multipoint ignition process and the combustion stability controlling mechanism of the bulk-loaded liquid propellant gun, the cylindrical stepped-wall observation chambers and cylindrical observation chambers are designed. The expansion process and interaction of high-speed twin combustion-gas jets in liquid are studied by high speed photographic system. The influence of chamber structure, nozzle diameter, dual-orifice interval, jet pressure on twin gas jets expansion process has been discussed.

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20

Soker, Noam. „Are jets rotating at the launching?“ Proceedings of the International Astronomical Union 5, H15 (November 2009): 249–50. http://dx.doi.org/10.1017/s1743921310009075.

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AbstractI argue that the Doppler shift asymmetries observed in some young stellar object (YSO) jets result from the interaction of the jets with the circumstellar gas, rather than from jets' rotation. The jets do rotate, but at a velocity much below claimed values. During the meeting I carefully examined new claims, and found problems with the claimed jets' rotation. I will challenge any future observation that will claim to detect jet rotation in YSOs that requires the jets (and not a wind) to be launched from radii much larger than the accreting stellar radius. I conclude that the most likely jets' launching mechanism involves a very efficient dynamo in the inner part of the accretion disk, with a jets' launching mechanism that is similar to solar flares (coronal mass ejection).

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Peters, Geraldine J. „Bipolar Jets, Hot Interaction Regions, and Colliding Winds in OB Interacting Binaries“. Proceedings of the International Astronomical Union 2, S240 (August 2006): 148–53. http://dx.doi.org/10.1017/s174392130700395x.

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AbstractContemporary information on the nature of the circumstellar environment in early-type interacting binaries derived from observation is discussed. Emphasis is placed on results from FUV spectroscopy. New spectra from the FUSE spacecraft and earlier FUV observations with IUE have revealed the presence of hot interaction regions, bipolar outflows, splash outflows, and accretion hot spots in Algol-type systems with B-type mass gainers. In addition, close O-type pairs and systems containing O + W stars show a shock-heated region generated from their colliding winds. Recent FUSE observations of an apparent hot accretion spot and associated splash plasma in the direct-impact system U Cephei are presented.

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Kuridze, D., T. V. Zaqarashvili, V. Henriques, M. Mathioudakis, F. P. Keenan und A. Hanslmeier. „KELVIN–HELMHOLTZ INSTABILITY IN SOLAR CHROMOSPHERIC JETS: THEORY AND OBSERVATION“. Astrophysical Journal 830, Nr. 2 (18.10.2016): 133. http://dx.doi.org/10.3847/0004-637x/830/2/133.

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23

Suzuki-Vidal, F., S. Patankar, S. V. Lebedev, S. N. Bland, H. Doyle, D. Bigourd, G. Burdiak et al. „Observation of energetic protons trapped in laboratory magnetic-tower jets“. New Journal of Physics 15, Nr. 12 (05.12.2013): 125008. http://dx.doi.org/10.1088/1367-2630/15/12/125008.

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24

Kornack, T. W., P. K. Sollins und M. R. Brown. „Experimental observation of correlated magnetic reconnection and Alfvénic ion jets“. Physical Review E 58, Nr. 1 (01.07.1998): R36—R39. http://dx.doi.org/10.1103/physreve.58.r36.

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25

Xing, Yi, Zhongxiang Wang, Xiao Zhang, Yang Chen und V. Jithesh. „Fermi Observation of the Jets of the Microquasar SS 433“. Astrophysical Journal 872, Nr. 1 (07.02.2019): 25. http://dx.doi.org/10.3847/1538-4357/aafc60.

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26

Liu, Jiajia, Fang Fang, Yuming Wang, Scott W. McIntosh, Yuhong Fan und Quanhao Zhang. „ON THE OBSERVATION AND SIMULATION OF SOLAR CORONAL TWIN JETS“. Astrophysical Journal 817, Nr. 2 (27.01.2016): 126. http://dx.doi.org/10.3847/0004-637x/817/2/126.

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27

KOBAYASHI, Ryota, Koichi NISHIBE, Kazuhiko YOKOTA und Kotaro SATO. „Observation of Behavior of Synthetic Jets in Asymmetric Flow Field“. Proceedings of Conference of Tokai Branch 2018.67 (2018): 326. http://dx.doi.org/10.1299/jsmetokai.2018.67.326.

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28

Hu, Zhitao, und Yonggang Yu. „Expansion characteristics of multiple wall jets in cylindrical observation chamber“. Applied Thermal Engineering 113 (Februar 2017): 1396–409. http://dx.doi.org/10.1016/j.applthermaleng.2016.11.140.

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29

Wilkinson, P. N., A. J. Kus, T. J. Pearson, A. C. S. Readhead und T. J. Cornwell. „The nuclear jets in 3C309.1 & 3C380“. Symposium - International Astronomical Union 119 (1986): 165–66. http://dx.doi.org/10.1017/s0074180900152556.

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8 station VLBI maps of the nuclear jets in 3C309.1 and 3C380 reveal complex, bent, structures which seem hard to reconcile with the concept of ballistic outflow. Together with the observation of “flaring” in the MERLIN/EVN map of the 3C309.1 jet the maps point strongly to the jets being confined fluid flows.

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30

Norman, Michael L. „Interpretation of Extragalactic Jets“. International Astronomical Union Colloquium 89 (1986): 425–37. http://dx.doi.org/10.1017/s0252921100086206.

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The subject of this paper is the interpretation of extragalactic radio jets. In this paper I will focus on what we have learned about the nature of extragalactic jets on the basis of model calculations. By model I mean any set of calculations, whether analytic, semi-analytic or numerical, which, when carried through from their respective assumptions to their internally self-consistent conclusions, help place constraints on the physical parameters and processes in the jets and their associated radio lobes. In this field, a visual inspection of a modern high-resolution radio interferometric observation (see review by PERLEY in these proceedings) often leads to statements like “that looks just like such and such in Landau and Lifschitz; I betcha that’s what’s going on!” This I call a speculation, or, at best, a hypothesis. I am addressing here the step beyond hypothesis, namely modeling, which is necessary to confront not only the object in question, but more importantly, the hypothesis itself. In the end, we will remember only the hypotheses.

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Qiu, Jiawei. „Misalignment of jet, orbital plane, and accretion disk observed in black hole binaries“. Theoretical and Natural Science 31, Nr. 1 (07.03.2024): 256–61. http://dx.doi.org/10.54254/2753-8818/31/20241148.

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Black holes are interesting objects and prove to be the leading edge of testing and verifying of our understandings in gravity. Among some of the most sought after quantities is the spin of the black hole: it is closely related to how the black hole system behaves. Various attempts have been made to derive the spin of black holes, in which the orientation in space could be deduced using the spectrum produced by the accretion disk, observation of the jets produced by black holes, and calculation of the orbit of black hole binaries using light and velocity curves. These observations, however, can sometimes lead to disagreeing results. In this paper, conflicts of the orientations of the spins of black holes measured using these different methods are presented. Sources including XTE J1550-564, V404 Cyg, and V4641 Sgr display misaligned accretion disk with orbital plane and/or jets. Explanations of how such misalignments could arise are also given, including warped accretion disks and precessing jets.

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Prior, Christopher, und Konstantinos N. Gourgouliatos. „Observational signatures of magnetic field structure in relativistic AGN jets“. Astronomy & Astrophysics 622 (Februar 2019): A122. http://dx.doi.org/10.1051/0004-6361/201834469.

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Context. Active galactic nuclei (AGN) launch highly energetic jets sometimes outshining their host galaxy. These jets are collimated outflows that have been accelerated near a supermassive black hole located at the centre of the galaxy. Their, virtually indispensable, energy reservoir is either due to gravitational energy released from accretion or due to the extraction of kinetic energy from the rotating supermassive black hole itself. In order to channel part of this energy to the jet, though, the presence of magnetic fields is necessary. The extent to which these magnetic fields survive in the jet further from the launching region is under debate. Nevertheless, observations of polarised emission and Faraday rotation measure confirm the existence of large scale magnetic fields in jets. Aims. Various models describing the origin of the magnetic fields in AGN jets lead to different predictions about the large scale structure of the magnetic field. In this paper we study the observational signatures of different magnetic field configurations that may exist in AGN jets in order to asses what kind of information regarding the field structure can be obtained from radio emission, and what would be missed. Methods. We explore three families of magnetic field configurations. First, a force-free helical magnetic field corresponding to a dynamically relaxed field in the rest frame of the jet. Second, a magnetic field with a co-axial cable structure arising from the Biermann-battery effect at the accretion disk. Third, a braided magnetic field that could be generated by turbulent motion at the accretion disk. We evaluate the intensity of synchrotron emission, the intrinsic polarization profile and the Faraday rotation measure arising from these fields. We assume that the jet consists of a relativistic spine where the radiation originates from and a sheath containing thermalised electrons responsible for the Faraday screening. We evaluate these values for a range of viewing angles and Lorentz factors. We account for Gaussian beaming that smooths the observed profile. Results. Radio emission distributions from the jets with dominant large-scale helical fields show asymmetry across their width. The Faraday rotation asymmetry is the same for fields with opposing chirality (handedness). For jets which are tilted towards the observer the synchrotron emission and fractional polarization can distinguish the field’s chirality. When viewed either side-on or at a Blazar type angle only the fractional polarization can make this distinction. Further this distinction can only be made if the direction of the jet propagation velocity is known, along with the location of the jet’s origin. The complex structure of the braided field is found not to be observable due to a combination of line of sight integration and limited resolution of observation. This raises the possibility that, even if asymmetric radio emission signatures are present, the true structure of the field may still be obscure.

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BADEN, ANDREW R. „JETS AND KINEMATICS IN HADRONIC COLLISIONS“. International Journal of Modern Physics A 13, Nr. 11 (30.04.1998): 1817–45. http://dx.doi.org/10.1142/s0217751x98000809.

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Analysis of colliding-beam hadron experiments [Formula: see text] often depend upon observation of "jets" — a highly collimated spray of particles such as π, K, e, μ and γ's forming clusters of energy deposition in calorimeters. In this paper we outline how to define jets from such clusters and discuss the meaning of jet quantities such as transverse energy and mass. Data from the DØ experiment are used to illustrate these concepts. In addition, we review the motivations for using certain optimal coordinates for describing energy–momentum four-vectors, and derive interesting relationships among the kinematic variables.

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Livio, Mario. „The Formation of Astrophysical Jets“. International Astronomical Union Colloquium 163 (1997): 845–66. http://dx.doi.org/10.1017/s0252921100044298.

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AbstractIt is assumed that the acceleration and collimation mechanisms of jets are the same in all the classes of astrophysical objects which are observed to produce jets. These classes now include: active galactic nuclei, young stellar objects, massive x-ray binaries, low mass x-ray binaries, black hole x-ray transients, symbiotic systems, planetary nebulae, and supersoft x-ray sources.On the basis of this assumption, an attempt is made, to identify the necessary ingredients for the acceleration and collimation mechanism. It is argued that: (i) jets are produced at the center of accretion disks which are threaded by a vertical magnetic field, (ii) the production of powerful jets requires, in addition, an energy/wind source associated with the central object. Tentative explanations for the presence of jets in some classes of objects and absence in others are given. Some critical observation that can test the ideas presented in this paper are suggested.

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Singha, Mainak, Christopher P. O’Dea und Stefi A. Baum. „What Drives the Ionized Gas Outflows in Radio-Quiet AGN?“ Galaxies 11, Nr. 4 (12.07.2023): 85. http://dx.doi.org/10.3390/galaxies11040085.

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We review the mechanisms driving the ionized gas outflows in radio-quiet (RQ) AGN. Although it constitutes ∼90% of the AGN population, what drives these outflows in these AGNs remains an open question. High-resolution imaging and integral field unit (IFU) observation is key to spatially resolving these outflows, whereas radio observations are important to comprehend the underlying radiative processes. Radio interferometric observations have detected linear, collimated structures on the hundreds of pc scale in RQ AGN, which may be very similar to the extended radio jets in powerful galaxies. Proper motions measured in some objects are sub-relativistic. Other processes, such as synchrotron radiation from shock-accelerated gas around the outflows could give rise to radio emissions as well. Near the launching region, these outflows may be driven by the thermal energy of the accretion disk and exhibit free–free emission. IFU observations on the other hand have detected evidence of both winds and jets and the outflows driven by them in radio-quiet AGN. Some examples include nearby AGN such as Mrk 1044 and HE 1353-1917. An IFU study of nearby (z <0.06) RQ AGN has found that these outflows may be related to their radio properties on <100 pc scale, rather than their accretion properties. Recent JWST observations of RQ AGN XID 2028 have revealed that radio jets and wind could inflate bubbles, create cavities, and trigger star formation. Future high-resolution multi-wavelength observations and numerical simulations taking account of both jets and winds are hence essential to understand the complex interaction between radio-quiet AGN and the host from sub-pc to kpc scales.

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Pavez, Cristian, José Pedreros, Ariel Tarifeño-Saldivia und Leopoldo Soto. „Observation of plasma jets in a table top plasma focus discharge“. Physics of Plasmas 22, Nr. 4 (April 2015): 040705. http://dx.doi.org/10.1063/1.4919260.

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37

Soyama, Hitoshi, Yoshiaki Yamauchi, Kazunori Sato, Toshiaki Ikohagi, Risaburo Oba und Ryoichiro Oshima. „High-Speed Observation of Ultra high-Speed Cavitating Submerged Water Jets.“ Transactions of the Japan Society of Mechanical Engineers Series B 59, Nr. 568 (1993): 3714–19. http://dx.doi.org/10.1299/kikaib.59.3714.

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38

Biermann, Peter L., und Peter A. Strittmatter. „Shockwaves in Extended Near-Relativistic Jets“. Symposium - International Astronomical Union 129 (1988): 85–86. http://dx.doi.org/10.1017/s0074180900134047.

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The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (active nuclei or knots in jets) is considered under the assumption that particle acceleration takes place in shockwaves. Energy losses due to synchrotron emission and Compton interactions set upper limits to both electron and proton energies. In this case the upstream disturbance of the flow is dominated by the most energetic protons which are postulated, by analogy with the solar wind, to excite a turbulent wave spectrum of Kolmogorov type in this region. We predict for near relativistic flows a spectral cutoff near 3 1014 Hz independent of magnetic field. The observation of a sharp spectral cutoff near 3 1014 Hz is thus independent evidence for near–relativistic flows in jets.

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Tassama, Abdissa, und Tolu Biressa. „Role of active galactic nuclei and flow of relativistic jets“. Proceedings of the International Astronomical Union 15, S356 (Oktober 2019): 252. http://dx.doi.org/10.1017/s1743921320003026.

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AbstractThe astrophysics of Active Galactic Nuclei (AGN) is one of the long outstanding issues in searches among the scientific communities raised with diverse perspectives like nebula, quasars, etc some decades ago. Currently, this exotic system is at least understood as the center of an active galaxy. Thus, the consensus of this recent theory has opened up a number of research issues for the progress of astrophysical science including how the hosting galaxy evolves with the AGN, how matter and energy flow towards and outwards, etc. Moreover, most of the AGNs possess Supermassive Black Holes (SMBHs) and accrete matter at a very high rate as current observations report. Consequently, both observations of electromagnetic (EM) spectrum and Gravity Waves (GWs) will considered to provide complementary information about the AGNs and the roles in their environments including black holes in their centers, outflow and inflow of matter-energy. Interested with this background rationale, we study the mechanisms of AGN interaction with its environment and flow of relativistic jets where General Relativistic (GR) Magneto-Hydrodynamic (MHD) equations are being considered. The solutions of the field equations are treated with a metric that involves charged systems for the possible relativistic jets including accretions. Then, numerical data is being generated using the latest version Mathematic software. Finally, the theoretical data is being compared with that of observation for validation of the model.

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Preston, R. A., S. J. Tingay, D. L. Jauncey, J. E. Reynolds, J. E. J. Lovell, P. M. Mcculloch, A. K. Tzioumis et al. „Monitoring the Jet in Centaurus A at 0.1 Parsec Resolution“. Symposium - International Astronomical Union 175 (1996): 21–22. http://dx.doi.org/10.1017/s0074180900079857.

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Centaurus A is the closest active extragalactic radio source, at a distance of approximately 3.5 Mpc, and is identified with the peculiar elliptical galaxy NGC 5128. As such it is a very important target for observations of the small-scale (sub-parsec) and large-scale (kpc) structures in extragalactic jets. Here we present Mk-II VLBI observations made at 8.4 GHz over a 4.3 year period from early 1991 until mid-1995, as well as a 4.8 GHz observation that was co-eval with one of the 8.4 GHz observations. All of the observations were made with the SHEVE array except for the last observation which was made with the VLBA. The dual-frequency observations identify the core of the radio source, while the multi-epoch observations show the complex structural evolution at a resolution of 0.1 pc. Subluminal motion of ≈ 0.15c is evident. Structural changes are observed on time scales shorter than four months.

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Baczko, A. K., R. Schulz, M. Kadler, E. Ros, M. Perucho, C. M. Fromm und J. Wilms. „Asymmetric jet production in the active galactic nucleus of NGC 1052“. Astronomy & Astrophysics 623 (26.02.2019): A27. http://dx.doi.org/10.1051/0004-6361/201833828.

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Context. Few active galactic nuclei (AGN) reveal double-sided jet systems. However, these systems are crucial to understand basic physical properties of extragalactic jets. Aims. We address the questions whether jets in AGN are symmetric in nature, how well they are collimated on small scales, and how they evolve with time. Methods. We monitored the sub-parsec scale morphology of NGC 1052 with the Very Long Baseline Array at 43 GHz from 2005 to 2009. Results. A detailed study of 29 epochs show a remarkable asymmetry between both jets. A kinematic analysis of the outflows reveals higher apparent velocities for the eastern (approaching) jet as compared to the western (receding) jet, i.e., βej = 0.529 ± 0.038 and βwj = 0.343 ± 0.037, respectively. Contradictory to previous studies, we find higher flux densities for the western jet as compared to the eastern. The distribution of brightness temperature and jet width features well-collimated jets up to 1 mas distance to the dynamic center and a nearly conical outflow further outward. By combining flux density ratios and velocities of the jet flows, we were unable to find a combination of intrinsic velocities and inclination angles of the jets that is consistent for all four years of observation; this contradicts findings for symmetrically evolving jets. Spectral index maps between quasi-simultaneous 22 GHz and 43 GHz observations support the existence of an optically thick absorber covering the innermost ≃1.6 mas around the 43 GHz central feature and an optically thin jet emission with a spectral index of ≤−1. Conclusions. Our results fit into a picture in which we expect larger internal energy and/or magnetic flux in the western jet and higher kinetic energy in the eastern jet. Previous observations at lower frequencies have found slower velocities of the moving jet features as compared to this work. Considering the different velocities in different areas, we suggest a spine-sheath structure with a faster inner layer and slower outer layer.

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Zhang, Yan-Jie, Qing-Min Zhang, Jun Dai, Zhe Xu und Hai-Sheng Ji. „Recurrent coronal jets observed by SDO/AIA“. Research in Astronomy and Astrophysics 21, Nr. 10 (01.11.2021): 262. http://dx.doi.org/10.1088/1674-4527/21/10/262.

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Abstract In this paper, we carried out multiwavelength observations of three recurring jets on 2014 November 7. The jets originated from the same region at the edge of AR 12205 and propagated along the same coronal loop. The eruptions were generated by magnetic reconnection, which is evidenced by continuous magnetic cancellation at the jet base. The projected initial velocity of jet2 is ∼402 km s−1. The accelerations in the ascending and descending phases of jet2 are not consistent, the former is considerably larger than the value of g ⊙ at the solar surface, while the latter is lower than g ⊙. There are two possible candidates of extra forces acting on jet2 during its propagation. One is the downward gas pressure from jet1 when it falls back and meets with jet2. The other is the viscous drag from the surrounding plasma during the fast propagation of jet2. As a contrast, the accelerations of jet3 in the rising and falling phases are constant, implying that the propagation of jet3 is not significantly influenced by extra forces.

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Bing, Qi, Huang Jian-Jun, Zhang Zhe-Huang und Wang De-Zhen. „Observation of Periodic Multiplication and Chaotic Phenomena in Atmospheric Cold Plasma Jets“. Chinese Physics Letters 25, Nr. 9 (September 2008): 3323–25. http://dx.doi.org/10.1088/0256-307x/25/9/061.

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44

Belloche, A. „Observation of rotation in star forming regions: clouds, cores, disks, and jets“. EAS Publications Series 62 (2013): 25–66. http://dx.doi.org/10.1051/eas/1362002.

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45

Zhao, L., und C. K. Ong. „Direct observation of photonic jets and corresponding backscattering enhancement at microwave frequencies“. Journal of Applied Physics 105, Nr. 12 (15.06.2009): 123512. http://dx.doi.org/10.1063/1.3151706.

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46

Punsly, Brian. „The Details of Limb Brightening Reveal the Structure of the Base of the Jet in M87 for the First Time“. Astrophysical Journal 936, Nr. 1 (01.09.2022): 79. http://dx.doi.org/10.3847/1538-4357/ac82f1.

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Abstract It has become commonplace in astronomy to describe the transverse coarse structure of jets in loosely defined terms such as “sheath” and “spine” based on discussions of parsec scale properties. But, the applicability, dimension, and prominence of these features on sub-light-year scales has previously been unconstrained by observation. The first direct evidence of jet structure near the source in M87 is extreme limb brightening (a double-rail morphology), 0.3–0.6 mas from the source, which is prominent in observations with high resolution and sensitivity. Intensity crosscuts of these images provide three strong, interdependent constraints on the geometry responsible for the double-rail morphology: the rail to rail separation, the peak to trough intensity ratio, and the rail widths. Analyzing these constraints indicates that half or more of the jet volume resides in a thick-walled, tubular, mildly relativistic, protonic jet only ∼0.25 lt-yr (or ∼300 M, where M is the central black hole mass in geometrized units) from the source. By contrast, the Event Horizon Telescope Collaboration interprets their observations with the aid of general relativistic magnetohydrodynamic simulations that produce an invisible (by construction) jet with a surrounding luminous, thin sheath. Yet, it is shown that synthetic images of simulated jets are center brightened 0.3–0.6 mas from the source. This serious disconnection with observation occurs in a region previously claimed in the literature to be well represented by the simulations. The limb brightening analysis motivates a discussion of possible simulation modifications to improve conformance with observations.

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Ighina, L., A. Moretti, F. Tavecchio, A. Caccianiga, S. Belladitta, D. Dallacasa, R. Della Ceca, T. Sbarrato und C. Spingola. „Direct observation of an extended X-ray jet at z = 6.1“. Astronomy & Astrophysics 659 (März 2022): A93. http://dx.doi.org/10.1051/0004-6361/202142676.

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We report on the direct observation of an extended X-ray jet in the z = 6.1 radio-loud active galactic nucleus PSO J030947.49+271757.31 from a deep Chandra X-ray observation (128 ksec). This detection represents the most distant kiloparsec-scale off-nuclear emission resolved in X-rays to date. The angular distance of the emission is ∼4″ (corresponding to ∼20 kpc at z = 6.1), along the same direction of the jet observed at parsec scales in previous VLBA high-resolution radio observations. Moreover, the 0.5–7.0 keV isophotes coincide with the extended radio emission as imaged by the VLA Sky Survey at 3 GHz. The rest-frame 2–10 keV luminosity of the extended component is L2 − 10 keV = 5.9 × 1044 erg s−1, about 8% of the core: this makes it one of the most luminous jets resolved in X-rays so far. Through spectral energy distribution modelling we find that this emission can be explained by the inverse Compton interaction with the photons of the cosmic microwave background, assuming that the jet’s physical parameters are similar to those in the local Universe. At the same time, we find that the radiation produced by a putative population of high-energy electrons through the synchrotron process observed at low redshift is quenched at high redshift, hence becoming negligible.

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Liu, C. M., A. Vaivads, Y. V. Khotyaintsev, H. S. Fu, D. B. Graham, K. Steinvall, Y. Y. Liu und J. L. Burch. „Cross-scale Dynamics Driven by Plasma Jet Braking in Space“. Astrophysical Journal 926, Nr. 2 (01.02.2022): 198. http://dx.doi.org/10.3847/1538-4357/ac4979.

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Abstract Plasma jets are ubiquitous in space. In geospace, jets can be generated by magnetic reconnection. These reconnection jets, typically at fluid scale, brake in the near-Earth region, dissipate their energies, and drive plasma dynamics at kinetic scales, generating field-aligned currents that are crucial to magnetospheric dynamics. Understanding of the cross-scale dynamics is fundamentally important, but observation of coupling among phenomena at various scales is highly challenging. Here we report, using unprecedentedly high-cadence data from NASA's Magnetospheric Multiscale Mission, the first observation of cross-scale dynamics driven by jet braking in geospace. We find that jet braking causes MHD-scale distortion of magnetic field lines and development of an ion-scale jet front that hosts strong Hall electric fields. Parallel electric fields arising from the ion-scale Hall potential generate intense electron-scale field-aligned currents, which drive strong Debye-scale turbulence. Debye-scale waves conversely limit intensity of the field-aligned currents, thereby coupling back to the large-scale dynamics. Our study can help in understanding how energy deposited in large-scale structures is transferred into small-scale structures in space.

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Xie, C., S. Y. Haffert, J. de Boer, M. A. Kenworthy, J. Brinchmann, J. Girard, I. A. G. Snellen und C. U. Keller. „A MUSE view of the asymmetric jet from HD 163296“. Astronomy & Astrophysics 650 (Juni 2021): L6. http://dx.doi.org/10.1051/0004-6361/202140602.

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Context. Jets and outflows are thought to play important roles in regulating star formation and disk evolution. An important question is how the jets are launched. HD 163296 is a well-studied Herbig Ae star that hosts proto-planet candidates, a protoplanetary disk, a protostellar jet, and a molecular outflow, which makes it an excellent laboratory for studying jets. Aims. We aim to characterize the jet at the inner regions and check if there are large differences with the features at large separations. A secondary objective is to demonstrate the performance of Multi Unit Spectroscopic Explorer (MUSE) in high-contrast imaging of extended line emission. Methods. MUSE in the narrow field mode (NFM) can provide observations at optical wavelengths with high spatial (∼75 mas) and medium spectral (R ∼ 2500) resolution. With the high-resolution spectral differential imaging technique, we can characterize the kinematic structures and physical conditions of jets down to 100 mas. Results. We detect multiple atomic lines in two new knots, B3 and A4, at distances of < 4″ from the host star with MUSE. The derived Ṁjet/Ṁacc is about 0.08 and 0.06 for knots B3 and A4, respectively. The observed [Ca II]/[S II] ratios indicate that there is no sign of dust grains at distances of < 4″. Assuming the A4 knot traced the streamline, we can estimate a jet radius at the origin by fitting the half width half maximum of the jet, which sets an upper limit of 2.2 au on the size of the launching region. Although MUSE has the ability to detect the velocity shifts caused by high- and low-velocity components, we found no significant evidence of velocity decrease transverse to the jet direction in our 500 s MUSE observation. Conclusions. Our work demonstrates the capability of using MUSE NFM observations for the detailed study of stellar jets in the optical down to 100 mas. The derived Ṁjet/Ṁacc, no dust grain, and jet radius at the star support the magneto-centrifugal models as a launching mechanism for the jet.

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Blackman, Eric G. „Pre-planetary nebulae: a context for principles, progress, and questions on how binaries and magnetic fields produce jets“. Proceedings of the International Astronomical Union 16, S366 (November 2020): 281–300. http://dx.doi.org/10.1017/s1743921322000278.

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AbstractAstrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of CE for close binaries (PPN-C). The physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.

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