2001A&A...372..208S


Query : 2001A&A...372..208S

2001A&A...372..208S - Astronomy and Astrophysics, volume 372, 208-226 (2001/6-2)

Wind circulation in selected rotating magnetic early-B stars.

SMITH M.A. and GROOTE D.

Abstract (from CDS):

The rotating magnetic B stars are a class of variables consisting of He-strong and some β Cep stars which have oblique dipolar magnetic fields. Such stars develop co-rotating, torus-shaped clouds by channeling wind particles from their magnetic poles to circumstellar regions centered around the plane of their magnetic equators. The rotation of the cloud-star complex permits the study of absorptions from the cloud as it occults the star. In this paper we describe a quantitative analysis of archival IUE data to map the properties of these clouds over four stars (HD 184927, σ Ori E, β Cep, and HR 6684). By computing spectral synthesis models for these stars, we find that only β Cep has a solar-like metallicity. Our analysis also shows that the metal composition across the surfaces of all these stars is at least approximately homogeneous. Using the Hubeny code CIRCUS, we demonstrate that the periodic variations of broad-band ultraviolet continuum fluxes can be explained fully by the absorptions of the co-rotating cloud. We show next that among selected lines, those arising from low-excitation states are selectively affected by cloud absorption and turbulence. Our analysis also quantifies the cloud temperatures and column densities required to match the absorptions of a number of weak to moderate strength resonance lines. These temperatures increase with the ionization potential of the parent ions of these various lines, a result which is consistent with radiative equilibrium models in which temperature increases with proximity to the star's surface. Although these attributes appear stable from one epoch to another, dynamic processes are nonetheless at work. Both the strengths and widths of resonance lines at occultation phases indicate the presence of a turbulence in the cloud which increases inwards. The spectroscopic hallmark of this stellar class is the presence of strong CIV and NV resonance line absorptions at occultation phases and of redshifted emissions of these lines at magnetic pole-on phases. The emissions have characteristics which seem most compatible with their generation by high-energy shocks at the wind-cloud interface, as predicted recently by Babel (1998, IAU Colloq. No. 169, 187).

Abstract Copyright:

Journal keyword(s): stars: individual: A|"CDS/simbad/smb.query.id "@251443" "Name=@251443" submit=submit null|β Cep">{β Cephei} - stars: individual: HR 6684 - stars: individual: σ Ori E - stars: individual: HD 184927 - stars: chemically peculiar - stars: magnetic fields

Simbad objects: 10

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Number of rows : 10
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 HD 36385 * 05 34 42.0500670480 +55 22 56.203914792   10.16 9.93     A 6 0
2 * tet01 Ori C SB* 05 35 16.4662967280 -05 23 22.921811880 4.20 5.15 5.13 4.91 4.73 O7Vp 1406 1
3 V* V1046 Ori SB* 05 35 21.8667428568 -04 29 39.024375324 5.66 6.43 6.56 6.61 6.74 B2/3V 303 0
4 * sig Ori E Y*O 05 38 47.2050040320 -02 35 40.521424812 5.66 6.38 6.46 6.84 7.08 B2IV-Vp_He 458 0
5 V* V901 Ori Ro* 05 40 56.3704617744 -01 30 25.856677224 5.96 6.82 6.96     B2V 334 2
6 HD 64740 * 07 53 03.6344819483 -49 36 46.956285817 3.48 4.40 4.63 4.76 4.97 B2V 211 0
7 HD 133518 * 15 06 55.9713564672 -52 01 47.204898312 5.57 6.29 6.39     B2IVpHe 94 0
8 V* V2052 Oph bC* 17 56 18.4001168880 +00 40 13.273317228 5.28 5.874 5.820     B3III 214 0
9 V* V1671 Cyg Ro* 19 35 32.0102348112 +31 16 35.933414736 6.44 7.29 7.44     B2V 128 0
10 * bet Cep bC* 21 28 39.5968513 +70 33 38.574681 2.05 3.01 3.23 3.33 3.55 B0.5IIIs 725 0

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