Tures in the Chromosphere, Whereas at Meter Wavelengths It Is of the Order of 1.5 X 106 Degrees, the Temperature of the Corona
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High-Frequency Waves in Solar and Stellar Coronae
A&A 463, 1165–1170 (2007) Astronomy DOI: 10.1051/0004-6361:20065956 & c ESO 2007 Astrophysics High-frequency waves in solar and stellar coronae V. G. Ledenev1,V.V.Tirsky2,andV.M.Tomozov1 1 Institute of Solar-Terrestrial Physics, Russian Academy of Sciences, PO Box 4026, Irkutsk, Russia e-mail: [email protected] 2 Institute of Laser Physics, Russian Academy of Sciences, Irkutsk Branch, Russia Received 3 July 2006 / Accepted 15 November 2006 ABSTRACT On the basis of a numerical solution of dispersion equation we analyze characteristics of low-damping high-frequency waves in hot magnetized solar and stellar coronal plasmas in conditions when the electron gyrofrequency is equal or higher than the electron plasma frequency. It is shown that branches that correspond to Z-mode and ordinary waves approach each other when the magnetic field increases and become practically indistinguishable in a broad region of frequencies at all angles between the wave vector and the magnetic field. At angles between the wave vector and the magnetic field close to 90◦, a wave branch with an anomalous dispersion may occur. On the basis of the obtained results we suggest a new interpretation of such events in solar and stellar radio emission as broadband pulsations and spikes. Key words. plasmas – turbulence – radiation mechanisms: non-thermal – Sun: flares – Sun: radio radiation – stars: flare 1. Introduction in the magnetic field and, consequently, for determining solar coronal parameters in the flare region. Magnetic field estima- It has been widely accepted that numerous flare processes with tions give values of the ratio ωHe/ωpe < 1 (Ledenev et al. -
Arxiv:1110.1805V1 [Astro-Ph.SR] 9 Oct 2011 Htte Olpet Ukaclrt H Lcrn,Rapid Emissions
Noname manuscript No. (will be inserted by the editor) Energy Release and Particle Acceleration in Flares: Summary and Future Prospects R. P. Lin1,2 the date of receipt and acceptance should be inserted later Abstract RHESSI measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized. RHESSI's precise measurements of hard X-ray continuum spectra enable model-independent deconvolution to obtain the parent elec- tron spectrum. Taking into account the effects of albedo, these show that the low energy cut- < off to the electron power-law spectrum is typically ∼tens of keV, confirming that the accel- erated electrons contain a large fraction of the energy released in flares. RHESSI has detected a high coronal hard X-ray source that is filled with accelerated electrons whose energy den- sity is comparable to the magnetic-field energy density. This suggests an efficient conversion of energy, previously stored in the magnetic field, into the bulk acceleration of electrons. A new, collisionless (Hall) magnetic reconnection process has been identified through theory and simulations, and directly observed in space and in the laboratory; it should occur in the solar corona as well, with a reconnection rate fast enough for the energy release in flares. The reconnection process could result in the formation of multiple elongated magnetic islands, that then collapse to bulk-accelerate the electrons, rapidly enough to produce the observed hard X-ray emissions. RHESSI's pioneering γ-ray line imaging of energetic ions, revealing footpoints straddling a flare loop arcade, has provided strong evidence that ion acceleration is also related to magnetic reconnection. -
Chapter 11 SOLAR RADIO EMISSION W
Chapter 11 SOLAR RADIO EMISSION W. R. Barron E. W. Cliver J. P. Cronin D. A. Guidice Since the first detection of solar radio noise in 1942, If the frequency f is in cycles per second, the wavelength radio observations of the sun have contributed significantly X in meters, the temperature T in degrees Kelvin, the ve- to our evolving understanding of solar structure and pro- locity of light c in meters per second, and Boltzmann's cesses. The now classic texts of Zheleznyakov [1964] and constant k in joules per degree Kelvin, then Bf is in W Kundu [1965] summarized the first two decades of solar m 2Hz 1sr1. Values of temperatures Tb calculated from radio observations. Recent monographs have been presented Equation (1 1. 1)are referred to as equivalent blackbody tem- by Kruger [1979] and Kundu and Gergely [1980]. perature or as brightness temperature defined as the tem- In Chapter I the basic phenomenological aspects of the perature of a blackbody that would produce the observed sun, its active regions, and solar flares are presented. This radiance at the specified frequency. chapter will focus on the three components of solar radio The radiant power received per unit area in a given emission: the basic (or minimum) component, the slowly frequency band is called the power flux density (irradiance varying component from active regions, and the transient per bandwidth) and is strictly defined as the integral of Bf,d component from flare bursts. between the limits f and f + Af, where Qs is the solid angle Different regions of the sun are observed at different subtended by the source. -
Structure of the Solar Chromosphere
Multi-Wavelength Investigations of Solar Activity Proceedings IAU Symposium No. 223, 2004 c 2004 International Astronomical Union A.V. Stepanov, E.E. Benevolenskaya & A.G. Kosovichev, eds. DOI: 10.1017/S1743921304005587 Structure of the solar chromosphere Sami K. Solanki Max-Planck-Institut f¨ur Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany, email: [email protected] Abstract. The chromosphere is an intriguing part of the Sun that has stubbornly resisted all attempts at a comprehensive description. Thus, observations carried out in different wavelength bands reveal very different, seemingly incompatible properties. Not surprisingly, a debate is raging between supporters of the classical picture of the chromosphere as a nearly plane parallel layer exhibiting a gentle temperature rise from the photosphere to the transition region and proponents of a highly dynamical atmosphere that includes extremely cool gas. New data are required in order settle this issue. Here a brief overview of the structure and dynamics of the solar chromosphere is given, with particular emphasis on the chromospheric structure of the quiet Sun. The structure of the magnetic field is also briefly discussed, although filaments and prominences are not considered. Besides the observations, contrasting models are also critically discussed. 1. Introduction: Chromospheric structure The solar chromosphere is traditionally defined as the layer, lying between the pho- tosphere and the transition region, where the temperature first starts to rise outwards. The lower boundary in this definition is formed by the temperature minimum layer. The upper boundary is less clearly marked, however, with a temperature around 1−2×104 K generally being prescribed. -
The Sun's Dynamic Atmosphere
Lecture 16 The Sun’s Dynamic Atmosphere Jiong Qiu, MSU Physics Department Guiding Questions 1. What is the temperature and density structure of the Sun’s atmosphere? Does the atmosphere cool off farther away from the Sun’s center? 2. What intrinsic properties of the Sun are reflected in the photospheric observations of limb darkening and granulation? 3. What are major observational signatures in the dynamic chromosphere? 4. What might cause the heating of the upper atmosphere? Can Sound waves heat the upper atmosphere of the Sun? 5. Where does the solar wind come from? 15.1 Introduction The Sun’s atmosphere is composed of three major layers, the photosphere, chromosphere, and corona. The different layers have different temperatures, densities, and distinctive features, and are observed at different wavelengths. Structure of the Sun 15.2 Photosphere The photosphere is the thin (~500 km) bottom layer in the Sun’s atmosphere, where the atmosphere is optically thin, so that photons make their way out and travel unimpeded. Ex.1: the mean free path of photons in the photosphere and the radiative zone. The photosphere is seen in visible light continuum (so- called white light). Observable features on the photosphere include: • Limb darkening: from the disk center to the limb, the brightness fades. • Sun spots: dark areas of magnetic field concentration in low-mid latitudes. • Granulation: convection cells appearing as light patches divided by dark boundaries. Q: does the full moon exhibit limb darkening? Limb Darkening: limb darkening phenomenon indicates that temperature decreases with altitude in the photosphere. Modeling the limb darkening profile tells us the structure of the stellar atmosphere. -
Radio Stars: from Khz to Thz Lynn D
Publications of the Astronomical Society of the Pacific, 131:016001 (32pp), 2019 January https://doi.org/10.1088/1538-3873/aae856 © 2018. The Astronomical Society of the Pacific. All rights reserved. Printed in the U.S.A. Radio Stars: From kHz to THz Lynn D. Matthews MIT Haystack Observatory, 99 Millstone Road, Westford, MA 01886 USA; [email protected] Received 2018 July 20; accepted 2018 October 11; published 2018 December 10 Abstract Advances in technology and instrumentation have now opened up virtually the entire radio spectrum to the study of stars. An international workshop, “Radio Stars: From kHz to THz”, was held at the Massachusetts Institute of Technology Haystack Observatory on 2017 November 1–3 to discuss the progress in solar and stellar astrophysics enabled by radio wavelength observations. Topics covered included the Sun as a radio star; radio emission from hot and cool stars (from the pre- to post-main-sequence); ultracool dwarfs; stellar activity; stellar winds and mass loss; planetary nebulae; cataclysmic variables; classical novae; and the role of radio stars in understanding the Milky Way. This article summarizes meeting highlights along with some contextual background information. Key words: Sun: general – stars: general – stars: winds – outflows – stars: activity – radio continuum: stars – radio lines: stars – (stars:) circumstellar matter – stars: mass-loss Online material: color figures 1. Background and Motivation for the Workshop Recent technological advances have led to dramatic improvements in sensitivity and achievable angular, temporal, Detectable radio emission1 is ubiquitous among stars and spectral resolution for observing stellar radio emission. As spanning virtually every temperature, mass, and evolutionary a result, stars are now being routinely observed over essentially stage. -
STELLAR RADIO ASTRONOMY: Probing Stellar Atmospheres from Protostars to Giants
30 Jul 2002 9:10 AR AR166-AA40-07.tex AR166-AA40-07.SGM LaTeX2e(2002/01/18) P1: IKH 10.1146/annurev.astro.40.060401.093806 Annu. Rev. Astron. Astrophys. 2002. 40:217–61 doi: 10.1146/annurev.astro.40.060401.093806 Copyright c 2002 by Annual Reviews. All rights reserved STELLAR RADIO ASTRONOMY: Probing Stellar Atmospheres from Protostars to Giants Manuel Gudel¨ Paul Scherrer Institut, Wurenlingen¨ & Villigen, CH-5232 Villigen PSI, Switzerland; email: [email protected] Key Words radio stars, coronae, stellar winds, high-energy particles, nonthermal radiation, magnetic fields ■ Abstract Radio astronomy has provided evidence for the presence of ionized atmospheres around almost all classes of nondegenerate stars. Magnetically confined coronae dominate in the cool half of the Hertzsprung-Russell diagram. Their radio emission is predominantly of nonthermal origin and has been identified as gyrosyn- chrotron radiation from mildly relativistic electrons, apart from some coherent emission mechanisms. Ionized winds are found in hot stars and in red giants. They are detected through their thermal, optically thick radiation, but synchrotron emission has been found in many systems as well. The latter is emitted presumably by shock-accelerated electrons in weak magnetic fields in the outer wind regions. Radio emission is also frequently detected in pre–main sequence stars and protostars and has recently been discovered in brown dwarfs. This review summarizes the radio view of the atmospheres of nondegenerate stars, focusing on energy release physics in cool coronal stars, wind phenomenology in hot stars and cool giants, and emission observed from young and forming stars. Eines habe ich in einem langen Leben gelernt, namlich,¨ dass unsere ganze Wissenschaft, an den Dingen gemessen, von kindlicher Primitivitat¨ ist—und doch ist es das Kostlichste,¨ was wir haben. -
What Do We See on the Face of the Sun? Lecture 3: the Solar Atmosphere the Sun’S Atmosphere
What do we see on the face of the Sun? Lecture 3: The solar atmosphere The Sun’s atmosphere Solar atmosphere is generally subdivided into multiple layers. From bottom to top: photosphere, chromosphere, transition region, corona, heliosphere In its simplest form it is modelled as a single component, plane-parallel atmosphere Density drops exponentially: (for isothermal atmosphere). T=6000K Hρ≈ 100km Density of Sun’s atmosphere is rather low – Mass of the solar atmosphere ≈ mass of the Indian ocean (≈ mass of the photosphere) – Mass of the chromosphere ≈ mass of the Earth’s atmosphere Stratification of average quiet solar atmosphere: 1-D model Typical values of physical parameters Temperature Number Pressure K Density dyne/cm2 cm-3 Photosphere 4000 - 6000 1015 – 1017 103 – 105 Chromosphere 6000 – 50000 1011 – 1015 10-1 – 103 Transition 50000-106 109 – 1011 0.1 region Corona 106 – 5 106 107 – 109 <0.1 How good is the 1-D approximation? 1-D models reproduce extremely well large parts of the spectrum obtained at low spatial resolution However, high resolution images of the Sun at basically all wavelengths show that its atmosphere has a complex structure Therefore: 1-D models may well describe averaged quantities relatively well, although they probably do not describe any particular part of the real Sun The following images illustrate inhomogeneity of the Sun and how the structures change with the wavelength and source of radiation Photosphere Lower chromosphere Upper chromosphere Corona Cartoon of quiet Sun atmosphere Photosphere The photosphere Photosphere extends between solar surface and temperature minimum (400-600 km) It is the source of most of the solar radiation. -
Bremsstrahlung (Free-Free Emission)
High energy solar/stellar atmospheres Eduard Kontar School of Physics and Astronomy University of Glasgow, UK STFC Summer School, Northumbria University, Sept 11 2017 Lecture outline I) Observations, motivations II) X-ray and emission mechanisms/properties III) Energetic particles from the Sun to the Earth IV) Particle acceleration mechanisms Solar flares and accelerated particles X-ray and radio impact Most GPS receivers in the sunlit hemisphere failed for ~10 minutes. (P. Kintner) at Dec 6th, 2006 (tracking less than 4 s/c) See Gary et al, 2008 Ionising radiation and impact on ionosphere Solar flares: basics rays Solar flares are rapid localised - brightening in the lower X atmosphere. More prominent in X-rays, UV/EUV and radio…. but can be seen from radio to 100 MeV waves radio Particles 1AU Particles Figure from Krucker et al, 2007 Solar Flares: Basics Solar flares are rapid localised brightening in the lower atmosphere. More prominent in X-rays, UV/EUV and radio…. but can be seen from radio to 100 MeV From Battaglia & Kontar, 2011 Energy ~2 1032 ergs From Emslie et al, 2004, 2005 “Standard” model of a solar flare/CME Energy release/acceleration Solar corona T ~ 106 K => 0.1 keV per particle Flaring region T ~ 4x107 K => 3 keV per particle Flare volume 1027 cm3 => (104 km)3 Plasma density 1010 cm-3 Photons up to > 100 MeV Number of energetic electrons 1036 per second Electron energies >10 MeV Proton energies >100 MeV Large solar flare releases about 1032 ergs (about half energy in energetic electrons) 1 megaton of TNT is equal to about 4 x 1022 ergs. -
Space Weather Study Through Analysis of Solar Radio Bursts Detected by a Single Station CALLSTO Spectrometer
https://doi.org/10.5194/angeo-2021-26 Preprint. Discussion started: 7 May 2021 c Author(s) 2021. CC BY 4.0 License. Space Weather Study through Analysis of Solar Radio Bursts detected by a Single Station CALLSTO Spectrometer Theogene Ndacyayisenga1, Ange Cyanthia Umuhire1, Jean Uwamahoro2, and Christian Monstein3 1University of Rwanda, College of Science and Technology, Kigali, Rwanda. 2University of Rwanda, College of Education, P.O. BOX 55, Rwamagana – Rwanda. 3Istituto Ricerche Solari (IRSOL), Università della Svizzera italiana (USI), CH-6605 Locarno-Monti, Switzerland. Correspondence: Theogene Ndacyayisenga ([email protected]) Abstract. This article summarizes the results of an analysis of solar radio bursts detected by the e-Compound Astronomical Low cost Low-frequency Instrument for spectroscopy and Transportable Observatory (e-CALLISTO) spectrometer hosted by the University of Rwanda, College of Education. The data analysed were detected during the first year (2014–2015) of the instrument operation. The Atmospheric Imaging Assembly (AIA) images on board the Solar Dynamics Observatory (SDO) 5 were used to check the location of propagating waves associated with type III radio bursts detected without solar flares. Using quick plots provided by the e-CALLISTO website, we found a total of 202 solar radio bursts detected by the CALLISTO station located in Rwanda. Among them, 5 are type IIs, 175 are type IIIs, and 22 type IVs radio bursts. It is found that all analysed type IIs and 37% of type III bursts are associated with impulsive solar flares while Type IV radio bursts are poorly ∼ associated with flares. Furthermore, all of the analysed type II bursts are associated with CMEs which is consistent with the 10 previous studies, and 44% of type IIIs show association with CMEs. -
Resolving the Radio Photospheres of Main Sequence Stars
Astro2020 Science White Paper Resolving the Radio Photospheres of Main Sequence Stars Thematic Areas: Resolved Stellar Populations and their Environments Principal Author: Name: Chris Carilli Institution: NRAO, Socorro, NM, 87801 Email: [email protected] Phone: 1-575-835-7306 Co-authors: B. Butler, K. Golap (NRAO), M.T. Carilli (U. Colorado), S.M. White (AFRL) Abstract We discuss the need for spatially resolved observations of the radio photospheres of main sequence stars. Such studies are fundamental to determining the structure of stars in the key transition region from the cooler optical photosphere to the hot chromosphere – the regions powering exo-space weather phenomena. Future large area radio facilities operating in the tens to 100 GHz range will be able to image directly the larger main sequence stars within 10 pc or so, possibly resolving the large surface structures, as might occur on eg. active M-dwarf stars. For more distant main sequence stars, measurements of sizes and brightnesses can be made using disk model fitting to the uv data down to stellar diameters of ∼ 0:4 mas. This size would include M0 V stars to a distance of 15 pc, A0 V stars to 60 pc, and Red Giants to 2.4 kpc. Based on the Hipparcos catalog, we estimate that there are at least 10,000 stars that will be resolved by the ngVLA. While the vast majority of these (95%) are giants or supergiants, there are still over 500 main sequence stars that can be resolved, with ∼ 50 to 150 in each spectral type (besides O stars). 1 Main Sequence Stars: Radio Photospheres The field of stellar atmospheres, and atmospheric activity, has taken on new relevance in the context of the search for habitable planets, due to the realization of the dramatic effect ’space weather’ can have on the development of life (Osten et al. -
Index to JRASC Volumes 61-90 (PDF)
THE ROYAL ASTRONOMICAL SOCIETY OF CANADA GENERAL INDEX to the JOURNAL 1967–1996 Volumes 61 to 90 inclusive (including the NATIONAL NEWSLETTER, NATIONAL NEWSLETTER/BULLETIN, and BULLETIN) Compiled by Beverly Miskolczi and David Turner* * Editor of the Journal 1994–2000 Layout and Production by David Lane Published by and Copyright 2002 by The Royal Astronomical Society of Canada 136 Dupont Street Toronto, Ontario, M5R 1V2 Canada www.rasc.ca — [email protected] Table of Contents Preface ....................................................................................2 Volume Number Reference ...................................................3 Subject Index Reference ........................................................4 Subject Index ..........................................................................7 Author Index ..................................................................... 121 Abstracts of Papers Presented at Annual Meetings of the National Committee for Canada of the I.A.U. (1967–1970) and Canadian Astronomical Society (1971–1996) .......................................................................168 Abstracts of Papers Presented at the Annual General Assembly of the Royal Astronomical Society of Canada (1969–1996) ...........................................................207 JRASC Index (1967-1996) Page 1 PREFACE The last cumulative Index to the Journal, published in 1971, was compiled by Ruth J. Northcott and assembled for publication by Helen Sawyer Hogg. It included all articles published in the Journal during the interval 1932–1966, Volumes 26–60. In the intervening years the Journal has undergone a variety of changes. In 1970 the National Newsletter was published along with the Journal, being bound with the regular pages of the Journal. In 1978 the National Newsletter was physically separated but still included with the Journal, and in 1989 it became simply the Newsletter/Bulletin and in 1991 the Bulletin. That continued until the eventual merger of the two publications into the new Journal in 1997.