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Heliospheric physics with LOFAR Andy Breen, Richard Fallows Solar System Physics Group

Heliospheric physics with LOFAR Andy Breen, Richard Fallows Solar System Physics Group Aberystwyth University Mario Bisi Center for Astrophysics and Space Sciences University of California, San Diego. Heliospheres and stellarspheres.

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Heliospheric physics with LOFAR Andy Breen, Richard Fallows Solar System Physics Group

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  1. Heliospheric physics with LOFAR Andy Breen, Richard Fallows Solar System Physics Group Aberystwyth University Mario Bisi Center for Astrophysics and Space Sciences University of California, San Diego

  2. Heliospheres and stellarspheres Solar wind: supersonic outflow of plasma from Sun into space Carries solar magnetic field with it Carries solar disturbances out to planets Carves out cavity in interstellar medium – heliosphere Similar winds found around all Sun-like stars (& dwarf stars)‏

  3. Examples of heliospheric structures • Macrostructure • Background structure • basically bimodal (most clearly at solar minimum) • fast flow above open field regions, slow flow above streamers • origin of slow wind not well-understood • Stream interaction regions • Coronal mass ejections • “Mesostructure” • Smaller scale features than macrostructure • Very obvious in STEREO HI images • CME internal structure • Smaller transients (“Sheeley blobs”, “Rouillard blobs”)‏ • Other uncatagorised “stuff” - but lots of it • Microstructure • IPS scale irregularities (10s-100s km)‏ • Turbulence

  4. Examples of macro- and mesoscale structures in the solar wind, April 2007 (STEREO HI-1A)‏ How do these structures interact with each other and with the background wind? How is the structure of the background wind influenced by interaction with these structures? Interaction between structures and solar system objects (e.g. comets, planetary environments..)

  5. White-light imaging and radio observations or, why do we need radio observations now we've got STEREO? Temporal resolution STEREO HI cameras return images every 40minutes (inner field, HI-1) or 2 hours (outer field, HI-2). Radio scintillation (IPS) measurements can give density-proxy and bulk velocity estimates on < 10 minute cadences Different sensitivity to electron density: White light imagers observe photospheric light Thomson-scattered by solar wind electrons – linear sensitivity to Ne IPS observes interference pattern cast by refraction (by solar wind turbulence) of signals from deep-sky sources - ~ Ne2 sensitivity Multi-site IPS measurements can detect other solar wind properties e.g. magnetic field rotation in CMEs/transients....

  6. 3D velocity reconstruction from EISCAT IPS data (B.V. Jackson and M.M. Bisi) • To study: • Internal structure of CMEs • CME/solar wind interaction • CME/SIR interaction • Evolution of mesoscale structure • Interaction of mesoscale structure with CMEs and SIRs • Interaction of solar wind structures with comets and planetary environments • Cometary and planetary tails • Need at least as good spatial resolution (sources/day..) as Ootacamund, many more long-baseline 2-site observations/day than STELab or EISCAT

  7. LOFAR LOFAR should provide all these things! Ample collecting area Plenty of combinations of 2-site observations Should be able to match Ootacamund’s number of source-observations/day, exceed 100 2-site observations/day (currently being verified!) ~5°angular resolution in tomographic reconstructions looks achievable with LOFAR data MWA will match (and probably exceed) number of source-observations/day, but won’t offer 2-site measurements Won’t be able to study physical parameters (turbulence, flow direction) that LOFAR will be able to detect

  8. LOFAR – what's needed for IPS • IPS requires: • Rapid sampling rate (>50 Hz, ideally >100 Hz) • Wide receiver pass-band (> 10 MHz) • Only total received power measurements are required • Want to observe as many sources/day as possible, on as many days as possible • Want to make many 2-site measurements • Experiment should run on “remote” (non-core) sites, ideally in background mode • Want to observe > 1 source at a time – multiple beams • Need to automatically schedule, make, pipeline and 1st- stage process observations

  9. First results Time-series of received power from 3C273 on LOFAR LBA, Nov. 2010

  10. 3C273 on LBA, November 2010 – scintillation clearly present

  11. Scintillation spectrum from LOFAR LBA 3C273 Clear scintillation out to > 5 Hz Form consistent with IPS (scintillation from solar wind)

  12. What’s needed now • Need to safeguard non-core observing time for solar and heliospheric experiments • IPS experiment for LOFAR needs further development • 2-site measurements • Multi-beam capability • Automatic pipelining • Automated scheduling • 1st IPS LOFAR observations now carried out • More development run-time needed • 1st long-baseline 2-site observations (Netherlands-Chilbolton?) to be trialled this winter (aim!)

  13. Acknowledgements EISCAT scientific association (EISCAT data) B.V. Jackson, P. Hick (CASS, UCSD), for help - and code - for tomographic reconstructions LOFAR staff for invaluable help with IPS experiment development LOFAR Pulsars KSP busy group for help and co-operation with IPS experiment development

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