Issue |
A&A
Volume 408, Number 2, September III 2003
|
|
---|---|---|
Page(s) | 715 - 727 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20031007 | |
Published online | 17 November 2003 |
Radio and submillimetre observations of wind structure in ζ Puppis
1
Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
2
Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
Corresponding author: R. Blomme, Ronny.Blomme@oma.be
Received:
17
April
2003
Accepted:
24
June
2003
We present radio and submillimetre observations of the
O4I(n)f star ζ Pup, and discuss
structure in the outer region of its wind (~).
The properties of bremsstrahlung, the dominant emission process at these
wavelengths, make it sensitive to structure and allow us to
study how the amount of structure changes in the wind by comparing the fluxes
at different wavelengths.
Possible forms of structure at these distances include
Corotating Interaction Regions (CIRs), stochastic clumping, a disk or a polar
enhancement. As the CIRs are azimuthally asymmetric, they should result
in variability at submillimetre or radio wavelengths.
To look for this variability, we acquired 3.6 and 6 cm
observations with the Australia Telescope Compact
Array (ATCA), covering about two rotational
periods of the star. We supplemented these with archive observations
from the NRAO Very Large Array (VLA), which cover a much longer time scale.
We did not find variability at more than the ±20% level.
The long integration time does allow an accurate determination
of the fluxes at 3.6 and 6 cm.
Converting these fluxes into a mass loss rate, we find
.
This value confirms the significant discrepancy with the mass loss
rate derived from the Hα profile, making ζ Pup an
exception to the usually
good agreement between the Hα and radio mass loss rates.
To study the run of structure as a function of distance, we supplemented
the ATCA data by observing ζ Pup at 850 μm with the
James Clerk Maxwell Telescope (JCMT) and at 20 cm with the VLA.
A smooth wind model shows that the millimetre fluxes are too high compared to the
radio fluxes. While recombination of helium in the outer wind cannot be discounted
as an explanation, the wealth of evidence for structure strongly suggests
this as the explanation for the discrepancy. Model calculations show
that the structure needs to be present in the inner ~
of the wind, but that it decays significantly, or maybe even
disappears, beyond that radius.
Key words: stars: early-type / stars: individual: ζ Pup / stars: mass loss / stars: winds, outflows / radio continuum: stars
© ESO, 2003
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