Potential of a Sensitive Low Frequency Radio Telescope for Heliospheric Studies

Details Potential of a Sensitive Low Frequency Radio Telescope for Heliospheric Studies Potential of a Sensitive Low Frequency Radio Telescope for Heliospheric Studies

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmsm22a..06o&link_type=abstract

American Geophysical Union, Spring Meeting 2004, abstract #SM22A-06

Astronomy and Astrophysics

Astronomy

6924 Interferometry, 6954 Radio Astronomy, 6969 Remote Sensing, 6982 Tomography And Imaging, 6994 Instruments And Techniques

Scientific paper

A sensitive low frequency radio telescope array introduces a new generation digital aperture synthesis interferometer. A possible design could cover the 80-240 MHz frequency range and provide up to 32 MHz of observation bandwidth. Groups of orthogonal dipoles will serve as receptors and the collecting area will be distributed in a centrally condensed manner. The instrument will be optimised for high dynamic range snap shot imaging. The conversion of the receptor signal to the digital domain at the earliest available opportunity makes it possible to form multiple independent beams simultaneously. The current design allows up to 8 beams using the entire collecting area of the array and 256 beams per polarisation using only the part of the array lying within the central 2 km of the array (core). The instrument will also feature an All Sky Monitor, which will use the array core and will provide an image the entire field of view about every second. These unprecedented capabilities makes the instrument very effective for a variety of solar and heliospheric studies, in addition to its astronomical and astrophysical objectives. The high dynamic range imaging capability of the instrument makes it very useful for imaging the Sun. Due to steep spectral nature of the emission and the low frequencies of observation the instrument, it will be able to image the emission from the CMEs to distances beyond the fields of view of existing coronographs. When the CMEs become too faint to be imaged directly, interplanetary scintillation (IPS) techniques can be used to study them, allowing their evolution to be tracked till beyond 1 AU. The large multi- beaming capability of the array core makes it very attractive for IPS tomographic reconstruction of the velocity structure of the entire inner heliosphere. The full polarisation capability of the instrument allows us to exploit the effect of Faraday rotation (FR) to study the distribution of magnetic field and electron density along lines of sights to distant polarised sources. IPS and FR studies will yield information about both the quiescent and transient heliosphere. The use of IPS and FR data-sets from this instrument along with data from Thompson scattering imagers like SMEI and STEREO will provide much more complete information about the heliosphere. These data-sets when combined with good MHD solar wind propagation models will provide the opportunity for a tomographic reconstruction of the velocity, density, turbulence structure and magnetic field in the heliosphere. A very useful by-product of the calibration of this instrument will be exquisitely detailed information about the total electron content (TEC) of the ionosphere at the telescope site. The instrument will have about 5000 lines of sight piercing the ionosphere over a radius of 400 km, providing a very fine spatial sampling of the ionosphere. This information can be used to construct for the first time a 4D (3 spatial and 1 temporal) TEC model of the ionosphere at these spatial scales.

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