Modeling the Distribution of Interstellar Scattering at Low Latitudes
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**Session 12 -- Interstellar medium**
*Display presentation, Monday, 9, 1995, 9:20am - 6:30pm*

## [12.11] Modeling the Distribution of Interstellar Scattering at Low Latitudes

*D.R. Iyengar (Carleton College), T. Ghosh, C.J. Salter (NAIC)*
The distribution of the ionized component of the interstellar medium
in our
Galaxy may be investigated through observations of compact
extragalactic
sources. Density fluctuations of the ionized material scatter the
radio waves
from these sources, resulting in the angular broadening of their
images. This

broadening is described by the following relation:
\begin{displaymath}
\theta_{arcsec} = 1.72 \times 10^{-2}
\lambda^{2.2}
\
\left(\int_{0}^{s}
C_{N}^{2}(s^{\prime}) ds^{\prime}
\right)^{0.6}
\end{displaymath}
where $C_{N}^{2}$ is a measure of the scattering strength, $\lambda$
is the
observing
wavelength in meters, and $s^{\prime}$ the line-of-sight distance to
the object in pc.
An estimate of the scattering strength along the line of sight to an
object may
thus be obtained by measuring the angular broadening of its image.
Observations of many objects allow the calculation of the scattering
strength
along a range of lines of sight, and a model of the large-scale
distribution of
the turbulence in the ionized component of the ISM may be obtained.

Earlier
studies have suggested a two-component distribution, with perhaps a
spiral
pattern at low latitudes.

In an attempt to verify this model, we have made VLBI observations at
0.61,
1.66, and 5 GHz of a sample of 26 flat-spectrum extragalactic sources
located
at $|b| < 1$ degree, and 9 deg. $< l < 109$ deg. Details of these
observations,
their data analysis, and the results are presented in this poster.

**Monday
program listing**