DOCSLIB.ORG

Progress on Coronal, Interplanetary, Foreshock, and Outer Heliospheric Radio Emissions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Progress on Coronal, Interplanetary, Foreshock, and Outer Heliospheric Radio Emissions Publ. Astron. Soc. Aust., 2000, 17, 22–34. Progress on Coronal, Interplanetary, Foreshock, and Outer Heliospheric Radio Emissions Iver H. Cairns1, P. A. Robinson1 and G. P. Zank2 1School of Physics, University of Sydney, Sydney, NSW 2006, Australia [email protected], [email protected] 2Bartol Research Institute, University of Delaware, Newark, DE 19176, USA [email protected] Received 1999 November 8, accepted 2000 January 14 Abstract: Type II and III solar radio bursts are associated with shock waves and streams of energetic electrons, respectively, which drive plasma waves and radio emission at multiples of the electron plasma frequency as they move out from the corona into the interplanetary medium. Analogous plasma waves and radiation are observed from the foreshock region upstream of Earth’s bow shock. In situ spacecraft observations in the solar wind have enabled major progress to be made in developing quantitative theories for these phenomena that are consistent with available data. Similar processes are believed responsible for radio emissions at 2–3 kHz that originate in the distant heliosphere, from where the solar wind interacts with the local interstellar medium. The primary goal of this paper is to review the observations and theories for these four classes of emissions, focusing on recent progress in developing detailed theories for the plasma waves and radiation in the source regions. The secondary goal is to introduce and review stochastic growth theory, a recent theory which appears quantitatively able to explain the wave observations in type III bursts and Earth’s foreshock and is a natural theory to apply to type II bursts, the outer heliospheric emissions, and perhaps astrophysical emissions. Keywords: radiation mechanisms: non-thermal—waves—instabilities—Sun: radio radiation—interplanetary medium—shock waves 1 Introduction and Overview (e.g. Melrose 1976, 1986; Wu & Lee 1979; Zarka 1998), as well as for solar ‘spike’ bursts in the Intense radio emissions are generated in numerous microwave and decimetric bands (e.g. Melrose 1986; regions of our solar system, including the solar Benz 1993). In each of these source regions, and corona and solar wind, regions near shock waves, in general for the mechanism to be eective for the magnetospheres and auroral regions of Earth, direct emission into escaping radiation, the electron Jupiter, and the gaseous outer planets, and the gyrofrequency exceeds the electron plasma frequency regions of the outer heliosphere where the solar fp (i.e. fce fp) and the electrons have excess wind interacts with the local interstellar medium energy in their motions perpendicular to the magnetic (see e.g. Melrose 1980, 1986; McLean & Labrum eld. The second mechanism is often called called 1985; Benz 1993; Kurth et al. 1984; Gurnett ‘plasma emission’ or ‘radiation at multiples of the et al. 1993; Zarka 1998). Two basic generation plasma frequency’ (Ginzburg & Zheleznyakov 1959; mechanisms are currently believed to be responsible Melrose 1980, 1986; Benz 1993) since it involves the for these emissions, both of them involving collective generation of free-space radiation near fp and near plasma eects and not the single-particle process 2fp; this mechanism involves a sequence of steps in of synchrotron emission currently favoured in most which excess electron energy is rst converted by a theories for astrophysical radio sources. The rst plasma instability into electrostatic Langmuir waves mechanism, cyclotron maser emission (Wu & Lee with frequencies near fp, after which Langmuir wave 1979; Melrose 1986; Benz 1993; Zarka 1998), involves energy is converted into fp and 2fp radiation by the direct generation of x- and o-mode radiation various linear or nonlinear plasma processes. near the electron gyrofrequency fce or its harmonics The primary aim of this paper is to summarise the by a plasma instability driven by semi-relativistic progress made in the last ve years in understanding electrons. This mechanism is believed responsible the generation and properties of type II and III for radio emissions from the auroral regions of solar radio bursts in the corona and solar wind, Earth (AKR), Jupiter and the gaseous outer planets radiation from the foreshock region upstream of q Astronomical Society of Australia 2000 10.1071/AS00011 1323-3580/00/010022$05.00 Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.126, on 26 Sep 2021 at 17:16:43, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1071/AS00022 Heliospheric Radio Emissions 23 Figure 1—Schematic illustration of the source regions and phenomena involved in type II and III solar radio bursts in the corona and solar wind and those observed in Earth’s foreshock. Figure 2—Schematic dynamic spectra for type II and III bursts and the fp and 2fp radiation from Earth’s foreshock. Earth’s bow shock, and low-frequency radiation of Earth’s bow shock but downstream from the observed by the Voyager spacecraft in the outer tangent solar wind eld line has been observed to heliosphere. These emissions are all either observed contain energetic electrons which stream away from or believed to be radiation produced at multiples the bow shock, driving Langmuir waves and fp and of fp. The properties and source environments of 2fp radio emissions. Type II radio bursts have these emissions are briey introduced next; they long been interpreted in terms of electron beams are described in more detail in Sections 3–6 below. accelerated by shock waves (Wild 1950), which then For close to 50 years type III bursts have been drive Langmuir waves and fp and 2fp radiation, but associated (Figure 1) with electron beams released observational evidence has been elusive (Nelson & during solar ares that stream from the corona Melrose 1985). Very recently, however, Bale et al. into the solar wind and drive Langmuir waves and (1999) and Reiner et al. (1997, 1998) have reported radiation at fp and 2fp (Wild 1950; Ginzburg & convincing evidence that the radiation is produced Zheleznyakov 1959), as reviewed by Melrose (1980), in an upstream foreshock region, strongly analogous Goldman (1983) and Suzuki & Dulk (1985). The to Earth’s foreshock, as suggested previously on electron beams, Langmuir waves and radio emissions theoretical grounds (Cairns 1986a). Figure 2 shows have now all been observed in situ (e.g. Gurnett & schematic dynamic spectra for these three classes Anderson 1976; Lin et al. 1981, 1986). Similarly, of emissions. Since the type III electrons move for over 20 years, the foreshock region upstream at speeds (01–03)c that are much faster than Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.126, on 26 Sep 2021 at 17:16:43, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1071/AS00022 24 I. H. Cairns et al. the Type II shock (500–1000 km s1), and since of 26 km s1 along the axis of symmetry in the solar wind plasma frequency varies inversely Figure 3, leading to the minimum distances between with heliocentric distance R (in steady-state), the the Sun and the termination shock, heliopause, etc. type III radiation drifts much more rapidly to low lying along this axis. The outer heliospheric radio frequencies than the type II radiation. Note that the emissions occur in sporadic, transient outbursts type III radiation tends to be relatively continuous (Kurth et al. 1984, 1987; Gurnett et al. 1993) and broadband, type II bursts tend to be very which have been associated with global shock waves intermittent but to show distinct fp and 2fp bands, reaching the vicinity of the heliopause and then while the foreshock 2fp radiation is present relatively producing radio emissions (Gurnett et al. 1993); continuously. Figure 3 illustrates schematically such a moving shock. Figure 4 shows schematic dynamic spectra for the radio emissions, which are widely interpreted in terms of two components (Cairns, Kurth & Gurnett 1992): the ‘transient component’ which drifts upwards in frequency with time and the ‘2 kHz component’ which remains approximately xed in frequency and lasts longer. Current estimates for fp in the VLISM lie in the range 16–35 kHz (Zank 1999a). Figure 3—The plasma boundaries associated with the solar wind’s interaction with the VLISM: the termination shock, the heliopause, the (possible) outer bow shock, and the inner and outer heliosheath regions inside and outside, respectively, the heliopause. The dashed circle represents a Figure 4—Schematic dynamic spectra of the radio emissions global, transient shock wave, moving away from the Sun into observed by the Voyager spacecraft in the outer heliosphere, the outer heliosphere, which may drive the outer heliospheric showing the transient emissions and the 2 kHz component. radio emissions. These four classes of emission are naturally grouped Figure 3 is a schematic of the large-scale structures together for several reasons, despite their widely predicted to result in the outer heliosphere from the dierent locations and plasma environments. First, interaction of the super-Alfvenic, supersonic solar type II and III bursts and the foreshock radiation wind and the plasma of the very local interstellar are all observed to be generated near fp and 2fp in medium (VLISM): the solar wind undergoes a the source region, as is also believed (but not yet shock transition to a sub-Alfvenic ow at the demonstrated) for the outer heliospheric emissions. termination shock and is then deected around the Second, recent observations (Reiner et al. 1998, 1999; heliopause, a contact discontinuity which separates Bale et al. 1999) show that interplanetary type II the (shocked) solar wind and (possibly shocked) bursts are produced in foreshock regions upstream VLISM plasmas (e.g. Zank 1999a). An outer bow of certain travelling interplanetary shocks, directly shock will exist if the VLISM plasma ows super- analogous to the radiation from Earth’s foreshock, as Alfvenically relative to our solar system.
Load more

Recommended publications
  • And Type Ii Solar Outbursts
    X-641-65-68 / , RADIO EMISSION FROM SHOCK WAVES - AND TYPE II SOLAR OUTBURSTS FEBRUARY 1965 \ -1 , GREENBELT, MARYLAND , X-641-65- 68 RADIO EMISSION FROM SHOCK WAVES AND TYPE II SOLAR OUTBURSTS bY Derek A. Tidman February 1965 NASA-Goddard Space Flight Center Greenbelt, Maryland * RADIO EMISSION FROM SHOCK WAVES AND TYPE 11 SOLAR OUTBURSTS Derek A. Tidman* NASA-Goddard Space Flight Center Greenbelt, Maryland ABSTRACT A model for Type 11 solar radio outbursts is discussed. The radiation is hypothesized to originate in the process of collective bremsstrahlung emitted by non-thermal electron and ion density fluctuations in a plasma containing a flux of energetic electrons. The source of radiation is assumed to be a collisionless plasma shock wave rising through the solar corona. It is also suggested that the collisionless bow shocks of the earth and planets in the solar wind might be similar but weaker sources of low frequency emission with a similar two- harmonic structure to Type 11 emission. * Permanent address: Institute for Fluid Dynamics and Applied Mathematics, University of Maryland, College Park, Maryland. iii RADIO EMISSION FROM SHOCK WAVES AND TYPE II SOLAR OUTBURSTS by Derek A. Tidman NASA-Goddard Space Flight Center Greenbelt, Maryland INTRODUCTION In a previous paper' we calculated the bremsstrahlung emitted from thermal plasmas which co-exist with a flux of energetic (suprathermal) electrons. It was found that under some circumstances the radiation emitted from such plasmas can be greatly increased compared to the emission from a Maxwellian plasma with no energetic particles present. The enhanced emission occurs at the funda- mental and second harmonic of the electron plasma frequency.
    [Show full text]
  • Arxiv:1712.09051V1 [Astro-Ph.SR] 25 Dec 2017
    Solar Physics DOI: 10.1007/•••••-•••-•••-••••-• Origin of a CME-related shock within the LASCO C3 field-of-view V.G.Fainshtein1 · Ya.I.Egorov1 c Springer •••• Abstract We study the origin of a CME-related shock within the LASCO C3 field-of-view (FOV). A shock originates, when a CME body velocity on its axis surpasses the total velocity VA + VSW , where VA is the Alfv´envelocity, VSW is the slow solar wind velocity. The formed shock appears collisionless, because its front width is manifold less, than the free path of coronal plasma charged particles. The Alfv´envelocity dependence on the distance was found by using characteristic values of the magnetic induction radial component and of the proton concentration in the Earth orbit, and by using the known regularities of the variations in these solar wind characteristics with distance. A peculiarity of the analyzed CME is its formation at a relatively large height, and the CME body slow acceleration with distance. We arrived at a conclusion that the formed shock is a bow one relative to the CME body moving at a super Alfv´envelocity. At the same time, the shock formation involves a steeping of the front edge of the coronal plasma disturbed region ahead of the CME body, which is characteristic of a piston shock. Keywords: Sun, Coronal Mass Ejection, Shock 1. Introduction The assumption that, ahead of solar material bunches that were earlier thought to be emitted during solar flares, a shock may emerge in the interplanetary space was already stated in 1950s (Gold, 1962). Based on observations of coronal mass ejections (CMEs) in 1973-1974 (Skylab era), Gosling et al., 1976 supposed that a bow shock should emerge ahead of sufficiently fast CEs.
    [Show full text]
  • On One Effect of Coronal Mass Ejections Influence on The
    On one effect of coronal mass ejections influence on the envelopes of hot Jupiters Zhilkin A.G.,∗ Bisikalo D.V., Kaigorodov P.V. Institute of astronomy of the RAS, Moscow, Russia Abstract It is now established that the hot Jupiters have extensive gaseous (ionospheric) envelopes, which expanding far beyond the Roche lobe. The envelopes are weakly bound to the planet and affected by strong influence of stellar wind fluctuations. Also, the hot Jupiters are lo- cated close to the parent star and therefore the magnetic field of stellar wind is an important factor, determining the structure their magne- tosphere. At the same time, for a typical hot Jupiter, the velocity of stellar wind plasma, flowing around the atmosphere, is close to the Alfv´envelocity. This should result in stellar wind parameters fluctua- tions (density, velocity, magnetic field), that can affect the conditions of formation of bow shock waves around a hot Jupiter, i. e. to switch flow from sub-Alfv´ento super-Alfv´enmode and back. In this paper, based on the results of three-dimensional numerical MHD modeling, it is confirmed that in the envelope of hot Jupiter, which is in Alfv´en point vicinity of the stellar wind, both disappearance and appearance of the bow shock wave occures under the action of coronal mass ejec- tion. The paper also shows that this effect can influence the observa- tional manifestations of hot Jupiter, including luminosity in energetic part of the spectrum. arXiv:1911.02880v1 [astro-ph.EP] 7 Nov 2019 1 Introduction One of the most important tasks of modern astrophysics is to study the mechanisms of mass loss by hot Jupiters.
    [Show full text]
  • SHOCKS and ENERGETIC PARTICLES Sun – Wind – Planets
    SHOCKS, TURBULENCE & ENERGETIC PARTICLES STFC Summer School, St Andrews 2016 David Burgess Astronomy Unit Queen Mary University of London With thanks to Manfred Scholer OUTLINE • Why shocks? • Shocks in the solar system • Turbulence in the solar wind • Some shock physics • MHD conservation relations & discontinuities • Shock parameters • Structure of collisionless shocks • Observations of energetic particles • Particle acceleration at shocks • Shock drift acceleration • Diffusive shock acceleration • Modelling interplanetary energetic particles Object in supersonic flow – Why a shock is needed If flow sub-sonic information about If flow super-sonic signals get swept object can transmitted via sound downstream and cannot inform upstream waves against flow flow about presence of object Flow can respond to the information A shock is launched which stands in and is deflected around obstacle in a upstream flow and effects a super- to sub- laminar fashion sonic transition The sub-sonic flow behind the shock can now be deflected around the object Fluid moves with velocity v; a disturbance occurs at 0 and propagates with velocity of sound c relative to the fluid The velocity of the disturbance relative to 0 is v + c n, where n is unit vector in any direction (a) v<c : a disturbance from any point in a sub-sonic flow eventually reaches any point (b) v>c: a disturbance from position 0 can reach only the area within a cone given by opening angle 2α, where sin α =c / v Surface a disturbance can reach is called the Mach surface Ernst Mach Examples
    [Show full text]
  • Some Key Concepts in Solar Terrestrial Physics • What Is The
    Some Key Concepts in Solar Terrestrial Physics • What is the solar power source? : fusion (pp CNO cycles) • How do we know this? : neutrinos and fit to Standard Solar Model • Summarize the Standard Solar Model : Hydrostatic equilibrium and other assumptions gives 4 ordinary differential equations and 4 unknowns • Why does energy transport by convection dominate in the Convection Zone? :plasma becomes opaque to photons because atoms begin to form as T drops. • Describe the Solar Spectrum : black body spectrum at 6000 oK dominates • What physical phenomenon allows us to study Solar Seismology? : from Doppler shift can study photosphere motions result in Sound waves and Buoyancy oscillations: Standing Waves • What are some of the main features of the Photosphere? : sunspots, granules and supergranules. T ~ 6,000 oK, • What is the Frozen in Condition for magnetic fields and plasma? :plasma moves with magnetic field • What is a plasma? :ionized gas • Discuss the concepts of temperature, density and basic response time of plasma : describe plasma frequency and Debye Length (plasmas shield E-fields from net charged regions) • What is the real length of the sunspot cycle? : about 22 years • Is the 'solar constant' really constant? : no the Luminosity is NOT constant • Since the Corona is above the photosphere, it must be cooler, right? : no it is HOT: T ~ 106 K. CME (coronal Mass Ejections) • What is the source for the Solar Wind? : main source: coronal holes. Supersonic (super Alfvenic) • What is the so called Garden hose angle for Interplanetary magnetic field : about 45o at Earth, depends on speed of solar wind and rotation rate of sun • What is the Heliosphere? :extent of the solar wind, which extends to the Interstellar medium.
    [Show full text]
  • White Paper for Heliophysics 2050 Kinetic Effects of Solar Driving On
    Heliophysics 2050 White Papers (2021) 4083.pdf White Paper for Heliophysics 2050 Kinetic effects of solar driving on magnetospheres Li-Jen Chen, Michael Collier, John Dorelli, Shing Fung, Daniel Gershman, Judith Karpen, Robert Michell, Jonathan Ng, Douglas Rowland, Marilia Samara, David Sibeck, Shan Wang Heliophysics Science Division NASA Goddard Space Flight Center (Contact email: [email protected]) September 2020 In this white paper, we discuss kinetic effects of solar driving on magnetospheres and interconnected science topics envisioned for future major research directions in heliophysics. We recommend (1) promotion of global particle simulations to address how these kinetic effects impact the evolution of magnetized planets and bodies in the heliosphere, past and present; and (2) advancing NASA’s high end computing to exascale to provide the critical ground for (1). An underlying connection between collisionless shocks, turbulence, and magnetic reconnection leads to complex interactions in the geospace environment, as revealed by global kinetic simulations in 2D [Karimabadi et al., 2014] and 3D (Figure 1). Ions reflected off the segment of the bow shock where the surface normal is quasi-parallel to the interplanetary magnetic field lead to generation of intense turbulence. This turbulence takes the forms of nonlinear waves that penetrate into the inner magnetosphere [Takahashi et al., 2016], and steepened magnetic structures [e.g., Schwartz et al., 1992; Chen et al., 2020] resulting in plasma heating, particle acceleration, and reconnection. At the shock, the turbulence causes the formation of high speed jets that penetrate the bow shock and bombard the magnetopause a few times per hour leading to dayside reconnection [Hietala et al., 2018].
    [Show full text]
  • Interstellar Probe to Explore the Sun's Influences Propagating Beyond The
    Interstellar Probe to Explore the Sun’s Influences Propagating Beyond the Heliosphere Parisa Mostafavi�, G. P. Zank�, D. J. McComas�, L. Burgala4, J. Richardson5, G. Webb2, E. Provornikova1, P. Brandt1 1. Johns Hopkins University Applied Physics Lab, 2. University of Alabama in Huntsville, 3. Princeton University, 4. NASA Goddard Space Flight Center, 5. Massachusetts Institute of Technology Introduction The heliosphere is controlled by the motion of the Sun through the interstellar space. Although humankind has explored the region of space about the Earth quite extensively, the distant heliosphere beyond the planets remains almost entirely unexplored with only the two Voyager spacecraft, New Horizons, and the early Pioneer 10 and 11 spacecraft returning the in-situ observations of this most distant region. Moreover, remote observations of energetic neutral atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) at 1 au and Cassini/INCA at 10 au revealed interesting structure related to the interstellar medium. Voyager 1 and 2 crossed the heliopause in 2012 and 2018, respectively, and are both continue to make in-situ measurements of the very local interstellar medium (VLISM; the nearby region of the LISM affected by physical processes associated with the heliosphere) for the first time. Voyager 1 and 2 have identified and partially answered many interesting questions about the outer heliosphere and the VLISM while raising numerous new questions, many of which have profound implications for the detailed structure and properties of the heliosphere and our place in the galaxy. One particularly interesting topic is the influence of the large-scale disturbances and small-scale turbulences generated by the dynamical Sun on the VLISM.
    [Show full text]
  • Interstellar Heliospheric Probe/Heliospheric Boundary Explorer Mission—A Mission to the Outermost Boundaries of the Solar System
    Exp Astron (2009) 24:9–46 DOI 10.1007/s10686-008-9134-5 ORIGINAL ARTICLE Interstellar heliospheric probe/heliospheric boundary explorer mission—a mission to the outermost boundaries of the solar system Robert F. Wimmer-Schweingruber · Ralph McNutt · Nathan A. Schwadron · Priscilla C. Frisch · Mike Gruntman · Peter Wurz · Eino Valtonen · The IHP/HEX Team Received: 29 November 2007 / Accepted: 11 December 2008 / Published online: 10 March 2009 © Springer Science + Business Media B.V. 2009 Abstract The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current under- standing of the Suns immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of The IHP/HEX Team. See list at end of paper. R. F. Wimmer-Schweingruber (B) Institute for Experimental and Applied Physics, Christian-Albrechts-Universität zu Kiel, Leibnizstr. 11, 24098 Kiel, Germany e-mail: [email protected] R. McNutt Applied Physics Laboratory, John’s Hopkins University, Laurel, MD, USA N. A. Schwadron Department of Astronomy, Boston University, Boston, MA, USA P. C. Frisch University of Chicago, Chicago, USA M. Gruntman University of Southern California, Los Angeles, USA P. Wurz Physikalisches Institut, University of Bern, Bern, Switzerland E. Valtonen University of Turku, Turku, Finland 10 Exp Astron (2009) 24:9–46 interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region.
    [Show full text]
  • Radio Emission from the Heliopause Triggered by an Interplanetary Shock Author(S): D
    Radio Emission from the Heliopause Triggered by an Interplanetary Shock Author(s): D. A. Gurnett, W. S. Kurth, S. C. Allendorf, R. L. Poynter Source: Science, New Series, Vol. 262, No. 5131 (Oct. 8, 1993), pp. 199-203 Published by: American Association for the Advancement of Science Stable URL: http://www.jstor.org/stable/2882326 Accessed: 16/06/2010 15:06 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=aaas. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Association for the Advancement of Science is collaborating with JSTOR to digitize, preserve and extend access to Science.
    [Show full text]
  • Observing Stellar Bow Shocks
    Observing stellar bow shocks A.C. Sparavigna a and R. Marazzato b a Department of Physics, Politecnico di Torino, Torino, Italy b Department of Control and Computer Engineering, Politecnico di Torino, Torino, Italy Abstract For stars, the bow shock is typically the boundary between their stellar wind and the interstellar medium. Named for the wave made by a ship as it moves through water, the bow shock wave can be created in the space when two streams of gas collide. The space is actually filled with the interstellar medium consisting of tenuous gas and dust. Stars are emitting a flow called stellar wind. Stellar wind eventually bumps into the interstellar medium, creating an interface where the physical conditions such as density and pressure change dramatically, possibly giving rise to a shock wave. Here we discuss some literature on stellar bow shocks and show observations of some of them, enhanced by image processing techniques, in particular by the recently proposed AstroFracTool software. Keywords : Shock Waves, Astronomy, Image Processing 1. Introduction Due to the presence of space telescopes and large surface telescopes, equipped with adaptive optics devices, a continuously increasing amount of high quality images is published on the web and can be freely seen by scientists as well as by astrophiles. Among the many latest successes of telescope investigations, let us just remember the discovery with near-infrared imaging of many extra-solar planets, such as those named HR 8799b,c,d [1-3]. However, the detection of faint structures remains a challenge for large instruments. After high resolution images have been obtained, further image processing are often necessary, to remove for instance the point-spread function of the instrument.
    [Show full text]
  • The Infant Bow Shock: a New Frontier at a Weak Activity Comet
    A&A 619, L2 (2018) Astronomy https://doi.org/10.1051/0004-6361/201834225 & c ESO 2018 Astrophysics LETTER TO THE EDITOR The infant bow shock: a new frontier at a weak activity comet Herbert Gunell1,2?, Charlotte Goetz3;?, Cyril Simon Wedlund4, Jesper Lindkvist2, Maria Hamrin2, Hans Nilsson5, Kristie Llera6, Anders Eriksson7, and Mats Holmström5 1 Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, 1180 Brussels, Belgium e-mail: [email protected] 2 Department of Physics, Umeå University, 901 87 Umeå, Sweden 3 Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany e-mail: [email protected] 4 Department of Physics, University of Oslo, Box 1048 Blindern, 0316 Oslo, Norway 5 Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden 6 Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238, USA 7 Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, 751 21 Uppsala, Sweden Received 12 September 2018 / Accepted 15 October 2018 ABSTRACT The bow shock is the first boundary the solar wind encounters as it approaches planets or comets. The Rosetta spacecraft was able to observe the formation of a bow shock by following comet 67P/Churyumov–Gerasimenko toward the Sun, through perihelion, and back outward again. The spacecraft crossed the newly formed bow shock several times during two periods a few months before and after perihelion; it observed an increase in magnetic field magnitude and oscillation amplitude, electron and proton heating at the shock, and the diminution of the solar wind further downstream. Rosetta observed a cometary bow shock in its infancy, a stage in its development not previously accessible to in situ measurements at comets and planets.
    [Show full text]
  • The Outer Heliospheric Radio Emission: Observations and Theory
    — 12 — The Outer Heliospheric Radio Emission: Observations and Theory Rudolf A. Treumann1 Geophysics Section, Ludwig-Maximilians-University, Munich, Germany Raymond Pottelette CETP/CNRS, St. Maur des Foss´es,France Abstract. This chapter provides a brief review of the observation and interpre- tation of radio emission from the outer heliosphere in the view of the new knowledge obtained about the outer heliosphere after the Voyager passage of the termination shock. It is discussed whether the termination shock and inner heliosheath could serve as the radiation sources. It is argued that the conditions at both places are not favourable for emitting observable radio waves. Moreover, the observation of electron plasma waves without radiation in the foreshock of the termination shock suggests that the plasma there is unable to excite radiation. It is too cold to excite ion-acoustic waves for scat- tering Langmuir waves or modulating the plasma, while the mere existence of plasma oscillations identifies the termination shock as a non-perpendicular or at least a non-stationary shock that is supercritical enough to reflect elec- tron beams – and probably also ions beams. In this case it must be a shock that is mediated by the hot pick-up ion component. We therefore confirm the proposal that the radiation can only be produced by interaction between the heliopause plasma and a strong global interplanetary shock wave. We present arguments that put the electron beam primed mechanism of stochastically growing lower-hybrid wave for the production of the observed radiation in question. A possible replacement for this mechanism is the combination of shock acceleration of electrons and reconnection between the spiral inter- planetary field and the interstellar field.
    [Show full text]