Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On magnetic inhibition of photospheric macro-turbulence generated in the
  iron-bump opacity zone of O-stars   Massive, hot OB-stars show clear evidence of strong macroscopic broadening
(in addition to rotation) in their photospheric spectral lines. This paper
examines the occurrence of such "macro-turbulence" in slowly rotating O-stars
with strong, organised surface magnetic fields. Focusing on the CIV 5811A line,
we find evidence for significant macro-turbulent broadening in all stars except
NGC1624-2, which also has (by far) the strongest magnetic field. Instead, the
very sharp CIV lines in NGC1624-2 are dominated by magnetic Zeeman broadening,
from which we estimate a dipolar field of approximately 20 kG. By contrast,
magnetic broadening is negligible in the other stars (due to their weaker field
strengths, on order 1 kG), and their CIV profiles are typically very broad and
similar to corresponding lines observed in non-magnetic O-stars. Quantifying
this by an isotropic, Gaussian macro-turbulence, we derive vmac = 2.2 (+-
0.9/2.2) km/s for NGC1624-2, and vmac = 20-65 km/s for the rest of the magnetic
sample. We use these observational results to test the hypothesis that the
field can stabilise the atmosphere and suppress the generation of
macro-turbulence down to stellar layers where the magnetic pressure PB and the
gas pressure Pg are comparable. Using a simple grey atmosphere to estimate the
temperature T0 at which PB = Pg, we find that T0 > Teff for all investigated
magnetic stars, but that T0 reaches the ~160000 K layers associated with the
iron opacity-bump in hot stars only for NGC1624-2. This is consistent with the
view that the responsible physical mechanism for photospheric O-star
macro-turbulence may be stellar gravity-mode oscillations excited by
sub-surface convection zones, and suggests that a sufficiently strong magnetic
field can suppress such iron-bump generated convection and associated
pulsational excitation.

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The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
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The categories of this paper are: stat
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The categories of this paper are: q-bio
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: cs
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ph
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The categories of this paper are: nucl-th