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Spectral Diagnoses of Chromospheres and Winds in A-Type Stars

Published online by Cambridge University Press:  12 April 2016

Thierry Lanz*
Affiliation:
NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, USA
Ivan Hubeny
Affiliation:
Universities Space Research Association, NASA/GSFC, Code 681, Greenbelt, MD 20771, USA
*
NRC-NASA Research Associate

Abstract

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So far, neither chromospheres nor stellar winds have been directly detected in main-sequence A stars. While radiative diffusion requires extremely weak stellar winds to reproduce chemical anomalies (10−15 to 10−12Myr−1), two independent direct searches for mass loss set up upper limits to 10−10 Myr−1, which is still several orders of magnitude higher. We discuss some new recent possibilities to detect chromospheres which arise thanks to new NLTE model atmospheres. In the near future, some progress is also expected from new observations of Lyman α with HST and from the increased sensitivity of ROSAT in the X-ray domain.

Type
VI. Magneto-Hydrodynamical Phenomena in CP Stars
Copyright
Copyright © Astronomical Society of the Pacific 1993

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