TY  - JOUR
A1  - Ignace, Rico
A1  - Gayley, Kenneth G.
A1  - Hamann, Wolf-Rainer
A1  - Huenemoerder, David P.
A1  - Oskinova, Lida
A1  - Pollock, Andy M. T.
A1  - McFall, Michael
T1  - THE XMM-NEWTON/EPIC X-RAY LIGHT CURVE ANALYSIS OF WR 6
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We obtained four pointings of over 100 ks each of the well-studied Wolf-Rayet star WR 6 with the XMM-Newton satellite. With a first paper emphasizing the results of spectral analysis, this follow-up highlights the X-ray variability clearly detected in all four pointings. However, phased light curves fail to confirm obvious cyclic behavior on the well-established 3.766 day period widely found at longer wavelengths. The data are of such quality that we were able to conduct a search for event clustering in the arrival times of X-ray photons. However, we fail to detect any such clustering. One possibility is that X-rays are generated in a stationary shock structure. In this context we favor a corotating interaction region (CIR) and present a phenomenological model for X-rays from a CIR structure. We show that a CIR has the potential to account simultaneously for the X-ray variability and constraints provided by the spectral analysis. Ultimately, the viability of the CIR model will require both intermittent long-term X-ray monitoring of WR 6 and better physical models of CIR X-ray production at large radii in stellar winds.
KW  - stars: individual (WR 6)
KW  - stars: winds, outflows
KW  - stars: Wolf-Rayet
KW  - X-rays: stars
Y1  - 2013
U6  - https://doi.org/10.1088/0004-637X/775/1/29
SN  - 0004-637X
VL  - 775
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Surlan, B.
A1  - Hamann, Wolf-Rainer
A1  - Aret, A.
A1  - Kubat, Jiří
A1  - Oskinova, Lida
A1  - Torres, A. F.
T1  - Macroclumping as solution of the discrepancy between Ha and P v mass
 loss diagnostics for O-type stars
JF  - ASTRONOMY & ASTROPHYSICS
N2  - Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Ha emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from 04 to 07) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Ha emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results. Our results show that with the mass-loss rates that fit Ha (and other Balmer and He II lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions. Macroclumping resolves the previously reported discrepancy between Ha and P v mass-loss diagnostics.
KW  - stars: winds, outflows
KW  - stars: mass-loss
KW  - stars: early-type
Y1  - 2013
U6  - https://doi.org/10.1051/0004-6361/201322390
SN  - 0004-6361
SN  - 1432-0746
VL  - 559
PB  - EDP SCIENCES S A
CY  - LES ULIS CEDEX A
ER  -