DOCSLIB.ORG

RADIO STARS and THEIR LIVES in the GALAXY Lynn D

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
RADIO STARS and THEIR LIVES in the GALAXY Lynn D Accepted to PASP A Preprint typeset using LTEX style emulateapj v. 12/16/11 RADIO STARS AND THEIR LIVES IN THE GALAXY Lynn D. Matthews1 Accepted to PASP ABSTRACT This paper summarizes the three-day international workshop Radio Stars and Their Lives in the Galaxy, held at the Massachusetts Institute of Technology Haystack Observatory on 2012 October 3-5. The workshop was organized to provide a forum for the presentation and discussion of advances in stellar and solar astrophysics recently (or soon to be) enabled by the latest generation of state-of-the- art observational facilities operating from meter to submillimeter wavelengths. The meeting brought together both observers and theorists to discuss how radio wavelength observations are providing new and unique insights into the workings of stars and their role in the Galactic ecosystem. Topics covered included radio emission from hot and cool stars (from the pre- to post-main-sequence), the Sun as a radio star, circumstellar chemistry, planetary nebulae, white dwarf binaries and novae, supernova progenitors, and radio stars as probes of the Galaxy. Subject headings: meeting summary, Stars — stars: AGB and post-AGB – stars: winds, outflows – circumstellar matter – radio lines: stars 1. BACKGROUND AND MOTIVATION FOR THE precision astrometry, and the routine study of sources at WORKSHOP a level of a few tens of µJy. We also heard how develop- Radio emission has now been detected from stars ments in theory, modeling, and laboratory astrophysics across the entire Hertzsprung-Russell (H-R) diagram, are improving our ability to interpret results. This paper spanning virtually every stage of stellar evolution. The attempts to summarize a sampling of the diverse array recent commissioning of a host of new and upgraded ob- topics presented and discussed at the Haystack work- servational facilities operating at wavelengths spanning shop. from the meter to the submillimeter has been leading 2. SCIENTIFIC SESSIONS to a rapid pace of discoveries in nearly every branch of stellar astrophysics. Motivated by these advances, a 3- The science program of the Haystack Radio Stars work- day workshop entitled “Radio Stars and Their Lives in shop comprised 33 oral presentations (13 invited reviews the Galaxy” was convened at the Massachusetts Institute and 20 contributed talks) and 7 posters. The com- of Technology (MIT) Haystack Observatory in Westford, plete program and presentation abstracts are available at Massachusetts on 2012 October 3-5. The workshop drew http://www.haystack.mit.edu/workshop/Radio-Stars/. a total of 50 participants from four continents and 13 The workshop was organized into seven scientific ses- countries and brought together both theorists and ob- sions: (I) An Overview of Stellar Radio Astronomy; (II) servers to participate in a program of oral presentations, Radio Emission from Pre-Main Sequence Stars; (III) Ra- posters, and discussions. The scientific program was de- dio Emission on the Main Sequence; (IV) Post-Main vised to bring together stellar astrophysicists from a va- Sequence Radio Stars; (V) Stellar Remnants; (VI) Ra- riety of sub-disciplines to stimulate cross-fertilization of dio Stars as Players in our Galaxy; (VII) Summary and ideas on unsolved problems common to the study of many Perspectives. This summary paper loosely follows this classes of stellar objects (e.g., mass loss, the driving of organization, but also attempts to synthesize recurrent bipolar outflows, and the generation of magnetic fields). themes and topics that spanned multiple sessions. In The first international workshop on Radio Stars took addition to summarizing new results presented by par- place in Ottawa, Canada in June 1979, at which time the ticipants, I strive to draw attention to topics where there discipline of stellar radio astronomy was approximately a was a consensus that our understanding is still limited, decade old (Feldman & Kwok 1979). The Very Large Ar- where controversies persist, and/or where future investi- ray (VLA) had not yet been commissioned, hence avail- gations are likely to prove fruitful. I close with a sum- able data were largely limited to single-dish flux den- mary of concerns and future challenges raised during the sity measurements at centimetric wavelengths without final discussion session. the advantages of imaging. Thirty-three years later, the 3. AN OVERVIEW OF STELLAR RADIO ASTRONOMY Haystack workshop made abundantly clear that stellar radio astronomy remains a vibrant field that is witnessing M. G¨udel (University of Vienna) opened the workshop a rapid pace of advances relevant to many of the most im- with a comprehensive overview of the versatility of the portant topics in stellar astrophysics. We witnessed how radio spectrum for understanding physical processes in new technologies are bringing dramatic advances in areas stars across the entire H-R diagram. He reviewed radio such as resolved imaging of radio photospheres, molec- emission mechanisms important for stellar sources and ular line imaging, dynamic imaging spectroscopy, high- emphasized that magnetic fields have now been shown to be important in nearly every type of stellar radio source. 1 MIT Haystack Observatory, Off Route 40, Westford, MA 01886 This point was underscored in many subsequent talks. USA; [email protected] G¨udel cited several “keywords” expected to define the 2 Matthews future of stellar radio astronomy, including µJy sensitiv- bremsstrahlung as the dominant jet emission mechanism. ity, time resolution, bandwidth, spectral resolution, and This work also established that dust emissivity is impor- frequency coverage. S. Kwok (The University of Hong tant even at centimeter wavelengths and that uncertain- Kong) reminded us of another during his closing talk: ties in the dust opacity index comprise the dominant un- dynamic range. Thanks to the truly impressive suite certainty in calculations of the luminosity of YSOs from of new and upgraded radio facilities that has come on- radio data (Ainsworth et al. 2012). line during the past few years, the workshop provided no shortage of illustrations of how recent gains in each 5. RADIO EMISSION FROM COOL MAIN SEQUENCE of these key areas are leading to breakthroughs in our STARS understanding of the workings of stars. 5.1. Emission from Ultracool Dwarfs 4. RADIO EMISSION FROM PRE-MAIN SEQUENCE STARS The interiors of stars later than ∼M3 are thought to be 4.1. The Radio-X-ray Connection in Young Stellar fully convective, predicting a breakdown in the αΩ dy- Objects namo mechanism for generating stellar magnetic fields. Furthermore, at the ultracool end of the H-R diagram It has been known for some time that young stellar ob- ( >M7), X-ray and Hα emission are seen to dramati- jects (YSOs) are producers of both X-ray and centimet- ∼ ric radio emission. However, as summarized by S. Wolk cally decline relative to the stellar bolometric luminos- (Harvard-Smithsonian Center for Astrophysics), to date ity, indicating sharp drops in chromospheric and coronal X-ray and radio observations of young clusters have re- heating. Consequently, perhaps one of the greatest sur- vealed a paltry number of simultaneous detections, with prises in stellar radio astronomy in the past decade has only a few percent of YSOs found to show both types of been the discovery of radio emission from ultracool (late emission (Forbrich et al. 2011; Forbrich & Wolk 2013). M, L, and T) dwarfs well in excess of what is predicted This comes as a surprise, since many of the YSOs are from the G¨udel-Benz relation, together with indications predicted to be bright enough for detection in the radio of very strong magnetic fields in some cases. based on the G¨udel-Benz relation2, yet fall short by two As described in the review by G. Hallinan (Califor- orders of magnitude or more. At the same time, several nia Institute of Technology), the emission from ultra- of the YSOs that are detected in the radio lie above the cool dwarfs has been found to comprise both broadband, G¨udel-Benz relation. Further, the radio detections are quiescent emission and periodic pulse-like flares. These not correlated with any identifiable X-ray properties of flares are nearly 100% circularly polarized and are rota- the sources. Together these results suggest that in YSOs tionally modulated, analogous to beamed radiation from the X-ray and radio emission are decoupled. pulsars. This points to an electron cyclotron maser as As described by Wolk, the Jansky Very Large Array the most likely emission mechanism—the same mecha- (JVLA) is soon expected to dramatically extend progress nism responsible for the radio emission from the planets in YSO studies, providing a jump by a factor of ∼20 in our solar system (e.g., Hallinan et al. 2007, 2008; Fig- in sensitivity over past VLA studies. This will greatly ure 1). Importantly, this means that the observed fre- improve radio detection statistics and allow polarization quency cutoff of the emission can be directly translated measurements for many more sources. In addition, the into a measure of the magnetic field strength, with values JVLA will provide the spectral coverage critical for ob- in the kilogauss range reported for the late M dwarfs and taining radio spectral indices and thus distinguishing be- brown dwarfs studied to date. tween thermal and non-thermal emission mechanisms. Rotation increases rapidly from the late M through Wolk described an ongoing campaign to simultaneously the T dwarfs, and the correlation between radio lumi- observe regions of Orion with Chandra and the JVLA, nosity and rotation rate was noted by several speakers. ∼ with first results expected in late 2012. M. G¨udel drew attention to a recent survey of 100 late- M and L dwarfs by McLean et al. (2012) that found that 4.2. Radio Emission from the Jets of Young Stellar for spectral types ∼>M7, the ratio of radio to bolomet- Objects ric luminosity increases with rotational velocity without In addition to their disks, winds, and coronae, the jets saturating.
Load more

Recommended publications
  • 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.
    [Show full text]
  • Quasistellar Objects: Overview ENCYCLOPEDIA of ASTRONOMY and ASTROPHYSICS
    eaa.iop.org DOI: 10.1888/0333750888/1585 Quasistellar Objects: Overview Patrick Osmer From Encyclopedia of Astronomy & Astrophysics P. Murdin © IOP Publishing Ltd 2006 ISBN: 0333750888 Institute of Physics Publishing Bristol and Philadelphia Downloaded on Thu Mar 02 22:43:08 GMT 2006 [131.215.103.76] Terms and Conditions Quasistellar Objects: Overview ENCYCLOPEDIA OF ASTRONOMY AND ASTROPHYSICS Quasistellar Objects: Overview Quasistellar objects, or quasars, were defined originally as star-like objects of large redshift. Quasars are believed to be powered by the accretion of matter onto massive black holes at the centers of galaxies, a process that emits more energy than thermonuclear reactions. Today, quasars are considered to be the most luminous members of the general class of objects called active galactic nuclei, or AGNs. Quasars are the most luminous objects in the universe. This article begins with a brief history of the discovery of quasars. Next it describes their main properties and the concepts that have been developed to explain them. It continues with a description of their nature and theoretical models. Then additional properties and topics are considered: absorption lines, host galaxies, Figure 1. Optical image of 3C273. The object looks stellar in and luminosity functions and evolution. this image except that it is accompanied by a jet of radiation extending to the lower right. (Credit National Optical Astronomy Observatories/National Science Foundation. History Copyright Association of Universities for Research in In 1960 Mathews and Sandage identified the radio source Astronomy Inc (AURA), all rights reserved.) 3C 48 (the 48th object in the 3rd Cambridge catalog of radio sources) with a star-like object of 16th magnitude.
    [Show full text]
  • 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.
    [Show full text]
  • Pos(Westerbork)006 S 4.0 International License (CC BY-NC-ND 4.0)
    Exploring the time-varying Universe PoS(Westerbork)006 Richard Strom ASTRON Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands E-mail: [email protected] Lodie Voûte ASTRON, Anton Pannekoek Inst. Of Astronomy, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands E-mail: [email protected] Benjamin Stappers School of Phys. & Astron., Alan Turing Bldg., University of Manchester, Oxford Road, Manchester M13 9PL, UK E-mail: [email protected] Gemma Janssen ASTRON Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands E-mail: [email protected] Jason Hessels ASTRON Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands E-mail: [email protected] 50 Years Westerbork Radio Observatory, A Continuing Journey to Discoveries and Innovations Richard Strom, Arnold van Ardenne, Steve Torchinsky (eds) Published with permission of the Netherlands Institute for Radio Astronomy (ASTRON) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Exploring the time-varying Universe Chapter 5.1 The earliest start Richard Strom* Introduction The WSRT interferometrically measures Fourier components of the sky bright- ness distribution from a region set by the primary beam of the telescope ele- ments, at a radio frequency determined by the receiver. This information is used to construct a two-dimensional image of radio emission from the piece of sky observed. Because it is an east-west interferometer array, the information obtained at any instant of time can only be used to construct a one-dimensional map (the telescope so synthesized has the response of a fan beam – narrow in one direction, but orthogonally very elongated).
    [Show full text]
  • Tures in the Chromosphere, Whereas at Meter Wavelengths It Is of the Order of 1.5 X 106 Degrees, the Temperature of the Corona
    1260 ASTRONOMY: MAXWELL PROC. N. A. S. obtained directly from the physical process, shows that the functions rt and d are nonnegative for x,y > 0. It follows from standard arguments that as A 0 these functions approach the solutions of (2). 4. Solution of Oriqinal Problem.-The solution of the problem posed in (2.1) can be carried out in two ways, once the functions r(y,x) and t(y,x) have been deter- mined. In the first place, since u(x) = r(y,x), a determination of r(y,x) reduces the problem in (2.1) to an initial value process. Secondly, as indicated in reference 1, the internal fluxes, u(z) and v(z) can be expressed in terms of the reflection and transmission functions. Computational results will be presented subsequently. I Bellman, R., R. Kalaba, and G. M. Wing, "Invariant imbedding and mathematical physics- I: Particle processes," J. Math. Physics, 1, 270-308 (1960). 2 Ibid., "Invariant imbedding and dissipation functions," these PROCEEDINGS, 46, 1145-1147 (1960). 3Courant, R., and P. Lax, "On nonlinear partial dyperential equations with two independent variables," Comm. Pure Appl. Math., 2, 255-273 (1949). RECENT DEVELOPMENTS IN SOLAR RADIO ASTRONOJIY* BY A. MAXWELL HARVARD UNIVERSITYt This paper deals briefly with present radio models of the solar atmosphere, and with three particular types of experimental programs in solar radio astronomy: radio heliographs, spectrum analyzers, and a sweep-frequency interferometer. The radio emissions from the sun, the only star from which radio waves have as yet been detected, consist of (i) a background thermal emission from the solar atmosphere, (ii) a slowly varying component, also believed to be thermal in origin, and (iii) nonthermal transient disturbances, sometimes of great intensity, which originate in localized active areas.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • Download This Article in PDF Format
    A&A 650, L20 (2021) Astronomy https://doi.org/10.1051/0004-6361/202140772 & c ESO 2021 Astrophysics LETTER TO THE EDITOR Large closed-field corona of WX Ursae Majoris evidenced from radio observations I. Davis1,2 , H. K. Vedantham1,3, J. R. Callingham1,4, T. W. Shimwell1,4, A. A. Vidotto5, P. Zarka6, T. P. Ray7, and A. Drabent8 1 ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, Dwingeloo 7991 PD, The Netherlands e-mail: [email protected] 2 Department of Physics and Astronomy, University of New Mexico, Albuquerque, USA 3 Kapteyn Astronomical Institute, University of Groningen, PO Box 72, 97200 AB Groningen, The Netherlands 4 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands 5 School of Physics, Trinity College Dublin, the University of Dublin, Dublin-2, Ireland 6 LESIA, CNRS – Observatoire de Paris, PSL 92190 Meudon, France 7 Dublin Institute for Advanced Studies, Dublin, Ireland 8 Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany Received 9 March 2021 / Accepted 29 April 2021 ABSTRACT The space-weather conditions that result from stellar winds significantly impact the habitability of exoplanets. The conditions can be calculated from first principles if the necessary boundary conditions are specified, namely the plasma density in the outer corona and the radial distance at which the plasma forces the closed magnetic field into an open geometry. Low frequency radio observations (ν . 200 MHz) of plasma and cyclotron emission from stars probe these magneto-ionic conditions. Here we report the detection of low-frequency (120–167 MHz) radio emission associated with the dMe6 star WX UMa.
    [Show full text]
  • Coherent Emission Mechanisms in Astrophysical Plasmas
    Reviews of Modern Plasma Physics manuscript No. (will be inserted by the editor) Coherent Emission Mechanisms in Astrophysical Plasmas D. B. Melrose Received: date / Accepted: date Abstract Three known examples of coherent emission in radio astronomical sources are reviewed: plasma emission, electron cyclotron maser emission (ECME) and pulsar radio emission. Plasma emission is a multi-stage mechanism with the first stage being gener- ation of Langmuir waves through a streaming instability, and subsequent stages involving partial conversion of the Langmuir turbulence into escaping radiation at the fundamental (F) and second harmonic (H) of the plasma frequency. The early development and subsequent refinements of the theory, motivated by application to solar radio bursts, are reviewed. The driver of the instability is faster electrons outpacing slower electrons, resulting in a positive gradient (df(vk)/dvk > 0) at the front of the beam. Despite many successes of the theory, there is no widely accepted explanation for type I bursts and various radio continua. The earliest models for ECME were purely theoretical, and the theory was later adapted and applied to Jupiter (DAM), the Earth (AKR), solar spike bursts and flare stars. ECME strongly favors the x mode, whereas plasma emission favors the o mode. Two drivers for ECME are a ring feature (implying df(v)/dv > 0) and a loss-cone feature. Loss-cone driven ECME was initially favored for all applications. The now favored driver for AKR is the ring-feature in a horseshoe distribution, which results from acceleration by a parallel electric on converging magnetic field lines. The driver in DAM and solar and stellar applications is uncertain.
    [Show full text]