GBT02A-012

Probing HI Structure On Sub-A.U. - A.U. Scales: Hydrodynamical or MHD Turbulence?

Abstract

It is known that the Galactic HI is turbulent on parsec scales (Green 1993, Crovisier and Dickey 1983). It has also been demonstrated that the Galactic HI has fluctuations on scales down to ~10 A.U. (c.f. Faison et.al 1998 and references therein). It is likely that the HI A.U. scale fluctuations are part of the same turbulence that is present on parsec scales (c.f. Desphande 2000). However this has not been conclusively demonstrated (i.e. no power spectrum of these fluctuations has been measured). There is also the question of whether the Galactic HI turbulence is hydrodynamical (HD) or magnetohydrodynamical (MHD). We propose observations of PSR B0329+54 which can answer these questions in a novel way. The GBT can measure the HI absorption against PSR B0329+54 to an opacity of 0.1 in less than the diffractive timescale. This allows a "dynamic spectrum" of HI absorption towards PSR B0329+54 to be made. This will allow for the possibility of observing HI fluctuations on scales << A.U. If observed this would indicate the presence of MHD turbulence in the HI. We also propose multi-epoch observations of PSR B0329+54 in order to determine the power spectrum of HI fluctuations vs. time (and distance due to the pulsars proper motion). This will allow us to determine if the A.U. scale HI fluctuations are part of the parsec scale HI turublence. If the HI turbulence is HD and the inner scale of the turbulence is measured, then we can directly estimate the kinematic viscosity of the Galactic HI.

Front Ends

Gregorian L(1.15 to 1.73 GHz)

Back Ends

Spectral Processor

Type of Observing

Monitor
Pulsar

Switching Type

Created: Fri May 31 15:39:28 Eastern Daylight Time 2002