• Leonard Strachan

      Articles written in Journal of Astrophysics and Astronomy

    • Ultraviolet Spectroscopic Observations of Coronal Streamers in the SOHO Era

      Leonard Strachan

      More Details Abstract Fulltext PDF

      Measurements made with the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory can be used to determine physical parameters in the solar corona such as hydrogen and ion kinetic temperatures, electron densities, and absolute elemental abundances. Hydrogen and ion outflow velocities can be determined by combining the UV spectroscopic measurements with white light polarized brightness measurements. These combined measurements can be used to reveal physical characteristics of coronal streamers. To date we have studied plasma properties, such as the variation of plasma outflows in quiescent streamers, primarily in classic helmet streamers at solar minimum. Outflows have not been observed in the centers of coronal streamers suggesting that these are closed magnetic field regions.We propose to study all of the coronal streamers in the UVCS synoptic dataset in order to investigate different types of streamers and their long-term evolution.

    • Next Generation UV Coronagraph Instrumentation for Solar Cycle-24

      John L. Kohl Rajmal Jain Steven R. Cranmer Larry D. Gardner Anil K. Pradhan John C. Raymond Leonard Strachan

      More Details Abstract Fulltext PDF

      Ultraviolet coronagraph observations of the extended solar corona (defined here as 1.5 to 10 solar radii from Sun-center) have become a powerful tool for obtaining detailed empirical descriptions of coronal holes, streamers, and coronal mass ejections. The empirical models resulting from ultraviolet coronagraph observations provide the constraints needed to test and guide theoretical models aimed at determining the physical processes that control solar wind acceleration, CME heating and acceleration, and solar energetic particle (SEP) acceleration. Measurements to date from sounding rockets, the shuttle deployed Spartan 201 satellite and the Solar and Heliospheric Observatory (SOHO) have utilized high resolution spectroscopy over a very limited instantaneous field of view. New concepts for next generation instrumentation include imaging ultraviolet spectrocoronagraphs and large aperture ultraviolet coronagraph spectrometers. An imaging instrument would be the first to obtain absolute spectral line intensities of the extended corona over a wide field of view. Such images would provide the absolute intensities of spectral lines that can be used to determine densities and outflow velocities of specific coronal ions. Measurements from several charge states of a given element will allow electron temperatures to be determined. These measurements combined with observations of H I Ly𝛼 provide absolute chemical abundances (relative to hydrogen) for observed elements. Ultraviolet imaging would be highly complementary to a large-aperture ultraviolet coronagraph spectrometer designed for high spectral resolution observations over a small instantaneous field of view. The images would be used to select targets for more detailed spectroscopic studies with the large aperture UV coronagraph spectrometer and to provide time dependent empirical descriptions of the regions surrounding the narrow instantaneous field of view of the large aperture instrument. Descriptions of both the imaging ultraviolet spectrocoronagraph and the large aperture ultraviolet coronagraph spectrometer are provided. Recommended co-observing instruments are described.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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