Book contents
- Frontmatter
- Contents
- Participants
- Group Photograph
- Preface
- Foreword
- Acknowledgements
- The Physics of Polarization
- Polarized Radiation Diagnostics of Solar Magnetic Fields
- Polarized Radiation Diagnostics of Stellar Magnetic Fields
- Polarization Insights for Active Galactic Nuclei
- Compact Objects and Accretion Disks
- Astronomical Masers and their Polarization
- Interstellar magnetic fields and infrared-submillimeter spectropolarimetry
- Instrumentation for Astrophysical Spectropolarimetry
Astronomical Masers and their Polarization
Published online by Cambridge University Press: 21 May 2010
- Frontmatter
- Contents
- Participants
- Group Photograph
- Preface
- Foreword
- Acknowledgements
- The Physics of Polarization
- Polarized Radiation Diagnostics of Solar Magnetic Fields
- Polarized Radiation Diagnostics of Stellar Magnetic Fields
- Polarization Insights for Active Galactic Nuclei
- Compact Objects and Accretion Disks
- Astronomical Masers and their Polarization
- Interstellar magnetic fields and infrared-submillimeter spectropolarimetry
- Instrumentation for Astrophysical Spectropolarimetry
Summary
Maser radiation occurs naturally in interstellar space. Masers provide extremely bright beacons that trace small scale structure in the host environments, which range from comets all the way to external galaxies. The radiation is sometimes, though not always, polarized. When it is, the polarization can reach much higher levels than in thermal sources—the radiation from some masers is fully polarized. This chapter provides an overview of astronomical masers, discusses the differences between maser and non-maser radiation and covers the fundamental theory of maser radiation and its polarization.
In 1963, the first radio emission from an interstellar molecule, the hydroxyl radical OH, was discovered. The ground state of this molecule produces four radio lines at wavelengths of approximately 18 cm (figure 1). When an atomic or molecular system radiates in several lines, certain ratios are expected between the line intensities. However, almost from the start the emission patterns displayed by the four OH lines in most astronomical sources were peculiar, deviating considerably from expectations. In 1965 these peculiarities culminated with the discovery of radio line emission with such exceptional properties, the emitting substance was dubbed ‘mysterium’ for lack of an obvious explanation. The exceptional properties included extremely high brightness, line widths much narrower than in all previous cases and substantial polarization. It did not take too long, though, to realize that ‘mysterium’ radiation was simply maser emission from interstellar OH.
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- Chapter
- Information
- Astrophysical Spectropolarimetry , pp. 225 - 264Publisher: Cambridge University PressPrint publication year: 2001
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