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
Solar System Physics Group
Solar Flare Radio Burst
EISCAT/MERLIN
observation of 0319+415
on 20050513:
Sudden intense
in signal power
simultaneously
EISCAT
and
sites.
variation
received
at
all
MERLIN
Seen before at EISCAT,
but this is first confirmation
from an independent radio
system.
Solar System Physics Group
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 Sunlike stars (& dwarf stars)
Solar System Physics Group
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 (“Rouillard blobs”)
Other uncatagorised “stuff” - but lots of it
Microstructure
IPS scale irregularities (10s-100s km)
Turbulence
Solar System Physics Group
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..)
Solar System Physics Group
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 40 minutes (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....
Solar System Physics Group
Long-Baseline IPS
• Cross-correlation used
to determine solar wind
velocity.
• Longer
antenna
baselines allow different
solar wind streams in
line of sight to be
determined accurately.
EISCAT IPS observation of CME on 14th May 2005; auto-correlation is top, remaining are
cross-correlations. Cross-correlation functions also show two adjacent fast streams. Baselines
projected onto sky plane: Bpar in radial direction, Bperp in meridional direction.
Solar System Physics Group
Some current IPS facilities – what they can do
Ootacamund: single antenna, 560m x 30m,
observes ~ >1000 sources/day at distances of
20-250 RSun
•
Can produce near-real time images of
Ne proxy, bulk flow speed
Ootacamund radio telescope (P.K. Manoharan)
•
Used as input to 3D tomographic
Fuji radio telescope (M. Tokumaru)
Nagoya
(STELab):
106m3D
x 41m
antenna,
reconstruction,
yields
Ne proxy
and 100m x
20
m antenna,
74m x 27
m antenna,
observes ~ 50
velocity
distributions
with
~10° angular
sources/day,
resolution inc. ~20-40 2-site observations at
distances of 30-200 RSun
•
Can produce daily maps of Ne proxy,
velocity 3 32m dishes, makes ~5 2-site observations
EISCAT:
•/day atGood
monthly
maps ofRNSun
distances
of ~15-100
e proxy, velocity
Used as input
to 3D tomography,
~20°
•
Accurate
measurements
of velocity
resolution
•angular
Can
detect other solar wind parameters e.g. field
rotation
Solar System Physics Group
•
Even small number of long-baseline
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
Solar System Physics Group
Combining Both IPS Methods:
CME, 13/14 May 2005
• Tomography image of CME
used to constrain EISCAT IPS
line of sight.
• More accurate speed of CME
in
interplanetary
space;
adjacent fast stream (or
associated magnetic field)
appears diverted ~15º from
radial:
– Better determination of
evolution of CMEs through
interplanetary space.
EISCAT IPS line of sight through tomography
image of CME. CME gave Earth glancing blow;
registered in ACE spacecraft data.
Solar System Physics Group
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,
~5°angular
resolution
in tomographic reconstructions looks achievable
exceed
100 2-site
observations/day
with LOFAR
data
(currently
being
verified!)
MWA will match (and probably exceed) number of sourceobservations/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
Solar System Physics Group
What’s needed
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
Need to safeguard non-core observing time for solar and heliospheric
experiments
IPS experiment for LOFAR needs building
Initial input – data stream produced by generic solar/heliosphere
Solar System Physics Group
nowledgements
CAT scientific association (EISCAT data)
Jackson, P. Hick and M.M. Bisi (CASS, UCSD), for tomographic reconstru
anoharan and M. Tokumaru for Ootacamund and Nagoya STELab informati
Solar System Physics Group