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Chromospheres, transition regions, and coronas
Science (New York, N.Y.)
|February 24, 1984
Summary
Stellar temperature increases with altitude due to energy imbalances in the low-density chromosphere and corona. Magnetic fields significantly impact coronal heating and X-ray emissions, while shock waves heat chromospheres.
Area of Science:
- Astronomy and Astrophysics
- Stellar Physics
- Plasma Physics
Background:
- The temperature of a star increases with altitude from the photosphere outwards.
- Stellar photospheres are high-density regions effectively cooled by radiative energy loss.
- Low-density stellar chromospheres and coronas experience significant temperature increases when energy input exceeds radiative energy loss.
Purpose of the Study:
- To explain the temperature increase outward from a stellar photosphere.
- To investigate the energy balance in stellar chromospheres and coronas.
- To understand the influence of magnetic fields and shock waves on stellar atmospheric heating.
Main Methods:
- Analysis of local energy balance in stellar outer layers.
- Investigating radiative energy loss mechanisms.
- Examining the role of magnetic fields and shock-wave dissipation.
Main Results:
- Coronal heating and X-ray emission are strongly influenced by magnetic fields, causing significant variations between stars.
- Chromospheric emission shows relatively small variations.
- Temperature rises steeply in the low-density chromosphere and corona if energy input is not balanced by radiative losses, potentially reaching over 1 million degrees.
- Chromospheres are primarily heated by shock-wave energy dissipation, modulated by magnetic fields.
Conclusions:
- The temperature gradient in stellar outer atmospheres is governed by energy balance between input and radiative losses.
- Magnetic fields play a crucial role in coronal heating and emission characteristics.
- Shock waves are the likely primary heating mechanism for stellar chromospheres, with magnetic fields acting as a modifying factor.
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