ScienceProblem: GalacticMaserFaradayRotation

PrimaryActor

Astronomer

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ScienceGoal

To see if foreground material causes rotation of maser polarisation vectors.

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DataSets

Galactic electron density information

Pulsar properties

(Extra)-galactic rotation measure mapping

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ProblemDescription:

OH (and other) maser emission can show Zeeman splitting due to the magnetic field of the sources (late-type star or star-forming region). In some directions, especially towards the Galactic centre, foreground material could rotate the apparent polarisation angle and thus the apparent source magnetic field direction.

We need to measure the rotation measure at the appropriate place and distance (which may be poorly known!). The electron density in the Galaxy is very inhomogenous.

A combination of all available data from PSR measurements, SNR, star-forming regions and other Milky Way sources of emission which can be used to find the 3-D electron density, as well as background sources, may help to solve this problem.

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CurrentSolution:

Search PSR SNR and other catalogues, attempt to relate to other informtion about the distribution of ionised gas in the Galaxy. Very difficult to establish distances, distinguish internal and line of sight rotation etc.

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VOSolution:

The VO could automatically provide the most accurate available distance estimates for each object (e.g. an old data set gives polarisation information, newer total-inensity data gives better distances - or at worst VO can use Galactic rotation curve information if velocities are available).

It may be necessary to search publications on individual objects to find the necessary information in the right volume of sky. That would then involve making the data compatible.

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KeyReferences:

Reid, M. J., Menten, K. M., & Argon, A. L. 2000, The Origins of Galactic Magnetic Fields, 24th meeting of the IAU, Joint Discussion 14, August 2000, Manchester, England. The Magnetic Field of the Milky Way

Pynzar', A. V. 1995, Astronomicheskij Zhurnal, vol. 72, p. 462 Correlation between the scattering parameters for pulsars and the emission measure of the galactic background

Taylor, J. H. & Cordes, J. M. 1993, Astrophysical Journal - Part 1 (ISSN 0004-637X), vol. 411, no. 2, p. 674-684. Pulsar distances and the galactic distribution of free electrons

Pynzar', A. V. 1993, Astronomicheskij Zhurnal (ISSN 0004-6299), vol. 70, no. 3, p. 480-491. The relationship between the emission measure and the dispersion measure of the Galactic background

Frail, D. A., Cordes, J. M., Hankins, T. H., & Weisberg, J. M. 1991, Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 382, Nov. 20, 1991, p. 168-181. Research supported by University of Toronto and National Astronomy and Ionosphere Center. H I absorption measurements toward 15 pulsars and the radial distribution of diffuse ionized gas in the Galaxy

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GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Science Problems Forum. For other ScienceProblems, refer to the ScienceProblemList.
Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.

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The problem needs to be more closely specified, including which datasets are required. Looks difficult to address in the near term.

-- NicholasWalton - 17 Apr 2002

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-- AnitaRichards - 01 Feb 2002