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27498 results in Astrophysics

Page 53 of 1375

  • 18 - Stellar Rotation

  • David F. Gray
  • Book:
    The Observation and Analysis of Stellar Photospheres
    Published online:
    05 January 2022
    Print publication:
    16 December 2021, pp 439-487

  • Summary

    Rotation of stars affects stellar spectra and stellar physics.Spectral lines are broadened and imprinted with the characteristic shape of the rotational velocity distribution, and there may be modulation from spots being carried across the visible hemisphere.Methods for extracting rotation rates from line profiles are discussed in detail.Results are summarized.Rotation circulates material inside stars, mixing chemicals and transporting angular momentum.And rotation couples with convection to generate magnetic fields.The magnetic fields produce many types of activity, including spots and flares and energy for coronae, and they hold on to escaping mass, acting as a magnetic brake on the rotation.We look into how rotation changes with time, with evolutionary stage, and for binaries with tidal interaction.

  • 1 - Introduction

  • Anvar Shukurov, University of Newcastle upon Tyne, Kandaswamy Subramanian, Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India
  • Book:
    Astrophysical Magnetic Fields
    Published online:
    23 December 2021
    Print publication:
    16 December 2021, pp 1-4
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  • 6 - The Black Body and Its Radiation

  • David F. Gray
  • Book:
    The Observation and Analysis of Stellar Photospheres
    Published online:
    05 January 2022
    Print publication:
    16 December 2021, pp 106-114

  • Summary

    The black body plays a central role in stellar atmospheres in describing the radiation field within the photosphere.The equation describing the photon distribution is Planck's law.Because the characteristics of black-body radiation are completely determined by the temperature of the black body, it forms a fundamental radiation standard, used to calibrate absolute radiant energy received from stars.

  • 3 - Spectroscopic Tools

  • David F. Gray
  • Book:
    The Observation and Analysis of Stellar Photospheres
    Published online:
    05 January 2022
    Print publication:
    16 December 2021, pp 50-80

  • Summary

    The main tool for studying stars is the spectrograph.Here we look at the astronomical aspects of spectrographs, how they work, and how to optimize them for stellar work.The characteristics of diffraction gratings are a central theme.The roles of the collimator and camera are then discussed, as is the resolving power of the final unit.Spectrographs using gratings in low orders are contrasted to echelle spectrographs used in high orders.Interferometers and Fourier spectroscopy isdiscussed briefly, as are some aspects of telescopes.

Page 53 of 1375