Opacity in the upper atmosphere of AU Mic

Francis Keenan; Shaun Bloomfield; Michail Mathioudakis; D.J. Christian; J.L. Linsky

Opacity in the upper atmosphere of AU Mic

Francis Keenan, Shaun Bloomfield, Michail Mathioudakis, D.J. Christian, J.L. Linsky

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Abstract

In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C III multiplet and O VI resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C III in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C III observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C III 1175.71 Angstrom component of the multiplet. Using a lower limit to the electron density (10(11) cm(-3))we derive an effective thickness of

Original language	English
Pages (from-to)	219-224
Number of pages	6
Journal	Astronomy and Astrophysics
Volume	390
Issue number	1
Publication status	Published - Jul 2002

ASJC Scopus subject areas

Space and Planetary Science

Cite this

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title = "Opacity in the upper atmosphere of AU Mic",

abstract = "In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C III multiplet and O VI resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C III in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C III observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C III 1175.71 Angstrom component of the multiplet. Using a lower limit to the electron density (10(11) cm(-3))we derive an effective thickness of",

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T1 - Opacity in the upper atmosphere of AU Mic

AU - Keenan, Francis

AU - Bloomfield, Shaun

AU - Mathioudakis, Michail

AU - Christian, D.J.

AU - Linsky, J.L.

PY - 2002/7

Y1 - 2002/7

N2 - In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C III multiplet and O VI resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C III in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C III observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C III 1175.71 Angstrom component of the multiplet. Using a lower limit to the electron density (10(11) cm(-3))we derive an effective thickness of

AB - In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C III multiplet and O VI resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C III in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C III observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C III 1175.71 Angstrom component of the multiplet. Using a lower limit to the electron density (10(11) cm(-3))we derive an effective thickness of

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M3 - Article

SN - 0004-6361

VL - 390

SP - 219

EP - 224

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 1

ER -

Opacity in the upper atmosphere of AU Mic

Abstract

ASJC Scopus subject areas

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