ISSN 1783-3426

THE MASSIVE STAR NEWSLETTER

formely known as the hot star newsletter

*

No. 124

2011 July-August

Editors: Philippe Eenens (University of Guanajuato)

eenens@gmail.com

Raphael Hirschi (Keele University)

http://www.astroscu.unam.mx/massive_stars





CONTENTS OF THIS NEWSLETTER:

Abstracts of 12 accepted papers

The two components of the evolved massive binary LZ Cep. Testing the effects of binarity on stellar evolution
Variability in the CoRoT photometry of three hot O-type stars. HD 46223, HD 46150 and HD 46966.
Confirmation of the magnetic oblique rotator model for the Of?p star HD 191612
The Eddington factor as the key to understand the winds of the most massive stars. Evidence for a Gamma-dependence of Wolf-Rayet type mass loss
The bi-stability jump as the origin for multiple P-Cygni absorption components in Luminous Blue Variables
The strong magnetic field of the large-amplitude $beta$,Cephei pulsator V1449,Aql
N II 5668-5712, a New Class of Spectral Features in Eta Carinae
Critical Differences and Clues in Eta Car's 2009 Event
On the Origin of the Salpeter Slope for the Initial Mass Function
Jet formation from massive young stars: Magnetohydrodynamics versus radiation pressure
L-band spectroscopy of Galactic OB-stars
Further Results from the Galactic O-Star Spectroscopic Survey: Rapidly Rotating Late ON Giants

Meetings

Circumstellar Dynamics at High Resolution











PAPERS

Abstracts of 12 accepted papers

The two components of the evolved massive binary LZ Cep. Testing the effects of binarity on stellar evolution


L. Mahy (1), F. Martins (2), C. Machado (2), J.-F. Donati (3), J.-C. Bouret (4,5)

1: Institut d’Astrophysique et de Géophysique, Université de Liège, Belgium

2: LUPM–UMR 5299, CNRS & Université Montpellier II, France

3: IRAP–UMR 5277, CNRS & Université. de Toulouse, France

4: LAM–UMR 6110, CNRS & Université de Provence, France

5: NASA/GSFC, USA

Aims. We present an in-depth study of the two components of the binary system LZCep in order to constrain the effects of binarity on the evolution of massive stars.
Methods. We use a set of high-resolution, high signal–to-noise ratio optical spectra obtained over the orbital period of the system to perform a spectroscopic disentangling and derive an orbital solution. We subsequently determine the stellar properties of each component through an analysis with the CMFGEN atmosphere code. Finally, with the derived stellar parameters, we model the Hipparcos photometric light curve using the program NIGHTFALL to obtain the inclination and the real stellar masses.
Results. LZCep is a O9III+ON9.7V binary. It is as a semi-detached system in which either the primary or the secondary star almost fills up its Roche lobe. The dynamical masses are about 16.0 M⊙ (primary) and 6.5 M⊙ (secondary). The latter is lower than the typical mass of late–type O stars. The secondary component is chemically more evolved than the primary (which barely shows any sign of CNO processing), with strong helium and nitrogen enhancements as well as carbon and oxygen depletions. These properties (surface abundances and mass) are typical of Wolf-Rayet stars, although the spectral type is ON9.7V. The luminosity of the secondary is consistent with that of core He–burning objects. The preferred, tentative evolutionary scenario to explain the observed properties involves mass transfer from the secondary – which was initially more massive– towards the primary. The secondary is now almost a core He–burning object, probably with only a thin envelope of H–rich and CNO processed material. A very inefficient mass transfer is necessary to explain the chemical appearance of the primary. Alternative scenarios are discussed but they suffer from more uncertainties.

Reference: A&A, in press
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1106.6162

Comments: 11 pages, 10 figures, 3 tables

Email: mahy@astro.ulg.ac.be

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Variability in the CoRoT photometry of three hot O-type stars. HD 46223, HD 46150 and HD 46966.


R. Blomme (1), L. Mahy (2), C. Catala (3), J. Cuypers (1), E. Gosset (2), M. Godart (2), J. Montalban (2), P. Ventura (4), G. Rauw (2), T. Morel (2), P. Degroote (5), C. Aerts (5,6), A. Noels (2), E. Michel (3), F. Baudin (7), A. Baglin (3), M. Auvergne (3), R. Samadi (3)

(1) Royal Observatory of Belgium, Belgium
(2) Institut d'Astrophysique et de Geophysique, University of Liege, Belgium
(3) LESIA, Observatoire de Paris, France
(4) INAF, Osservatorio Astronomico di Roma, Italy
(5) Instituut voor Sterrenkunde, K.U. Leuven, Belgium
(6) Department of Astrophysics, University of Nijmegen, The Netherlands
(7) Institut d'Astrophysique Spatiale, Universite Paris-Sud, France

The detection of pulsational frequencies in stellar photometry is required as input for asteroseismological modelling. The second short run (SRa02) of the CoRoT mission has provided photometric data of unprecedented quality and time-coverage for a number of O-type stars.
We analyse the CoRoT data corresponding to three hot O-type stars, describing the properties of their light curves and we search for pulsational frequencies, which we then compare to theoretical model predictions.
We determine the amplitude spectrum of the data, using the Lomb-Scargle and a multifrequency HMM-like technique. Frequencies are extracted by prewhitening, and their significance is evaluated under the assumption that the light curve is dominated by red noise. We search for harmonics, linear combinations and regular spacings among these frequencies. We use simulations with the same time sampling as the data as a powerful tool to judge the significance of our results. From the theoretical point of view, we use the MAD non-adiabatic pulsation code to determine the expected frequencies of excited modes.
A substantial number of frequencies is listed, but none can be convincingly identified as being connected to pulsations. The amplitude spectrum is dominated by red noise. Theoretical modelling shows that all three O-type stars can have excited modes but the relation between the theoretical frequencies and the observed spectrum is not obvious.
The dominant red noise component in the hot O-type stars studied here clearly points to a different origin than the pulsations seen in cooler O stars. The physical cause of this red noise is unclear, but we speculate on the possibility of sub-surface convection, granulation, or stellar wind inhomogeneities being responsible.

Reference: A&A, in press
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1107.0267

Comments: 13 pages, 8 figures. Tables 2, 3 and 4 available on ftp://omaftp.oma.be/dist/astro/Blomme.R/CoRoT/

Email: Ronny.Blomme@oma.be

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Confirmation of the magnetic oblique rotator model for the Of?p star HD 191612


G.A. Wade, I.D. Howarth, R.H.D. Townsend, J.H. Grunhut, M. Shultz, J.-C. Bouret, A. Fullerton, W. Marcolino, F. Martins, Y. Naze, A. ud Doula, N.R. Walborn, J.-F. Donati, and the MiMeS Collaboration

Dept. of Physics, Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston, Ontario K7K 7B4, Canada
Dept. of Physics and Astronomy, UCL, Gower Place, London WC1E 6BT, United Kingdom
Dept. of Astronomy, University of Wisconsin-Madison, 475 N. Charter Street, Madison WI 53706-1582, USA
Dept. of Physics, Engineering Physics and Astronomy, Queen’s University, 99 University Avenue, Kingston, Ontario K7L 3N6, Canada
LAM-UMR 6110, CNRS & Universitd ́e Provence, rue Fre ́de ́ric Joliot-Curie, F-13388 Marseille Cedex 13, France
NASA/GSFC, Code 665, Greenbelt, MD 20771, USA
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
Observato ́rio do Valongo, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
LUPM-UMR5299, CNRS & Universite ́ Montpellier II, Place Euge`ne Bataillon, F-34095, Montpellier, France
FNRS-Institut d’Astrophysique et de Ge ́ophysique, Universite ́ de Lie`ge, Belgium
Penn State Worthington Scranton, 120 Ridge View Drive, Dunmore, PA, USA 18512
Observatoire Midi-Pyre ́n ́e ́es, 14 avenue E ́douard Belin, F-31400, Toulouse, France

This paper reports high-precision Stokes V spectra of HD 191612 acquired using the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, in the context of the Magnetism in Massive stars (MiMeS) Project. Using measurements of the equivalent width of the Hα line and radial velocities of various metallic lines, we have updated both the spectroscopic and orbital ephemerides of this star. We confirm the presence of a strong magnetic field in the photosphere of HD 191612, and detect its variability. We establish that the longitudinal field varies in a manner consistent with the spectroscopic period of 537.6 d, in an approximately sinusoidal fashion. The phases of minimum and maximum longitudinal field are respectively coincident with the phases of maximum and minimum Hα equivalent width and Hp magnitude. This demonstrates a firm connection between the magnetic field and the processes responsible for the line and continuum variability. Interpreting the variation of the longitudinal magnetic field within the context of the dipole oblique rotator model, and adopting an inclination i = 30◦ obtained assuming alignment of the orbital and rotational angular momenta, we obtain a best-fit surface magnetic field model with obliquity β = 67 ± 5◦ and polar strength Bd = 2450 ± 400 G . The inferred magnetic field strength implies an equatorial wind magnetic confinement parameter η∗ ≃ 50, supporting a picture in which the Hα emission and photometric variability have their origin in an oblique, rigidly rotating magnetospheric structure resulting from a magnetically channeled wind. This interpretation is supported by our successful Monte Carlo radiative transfer modeling of the photometric variation, which assumes the enhanced plasma densities in the magnetic equatorial plane above the star implied by such a picture, according to a geometry that is consistent with that derived from the magnetic field. Predictions of the continuum linear polarisation resulting from Thompson scattering from the magnetospheric material indicate that the Stokes Q and U variations are highly sensitive to the magnetospheric geometry, and that expected amplitudes are in the range of current instrumentation.

Reference: MNRAS, accepted and in press
Status: Manuscript has been accepted

Weblink: http://arxiv.org/pdf/1106.3008v1

Comments:

Email: wade-g@rmc.ca

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The Eddington factor as the key to understand the winds of the most massive stars. Evidence for a Gamma-dependence of Wolf-Rayet type mass loss


G. Gräfener^1, J.S. Vink^1, A. de Koter^2,4, N. Langer^3,4

(1) Armagh Observatory, College Hill, Armagh BT61 9DG, United Kingdom
(2) Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Science Park XH, Amsterdam, The Netherlands
(3) Argelander-Institut f¨ur Astronomie der Universit¨at Bonn, Auf dem H¨ugel 71, 53121 Bonn, Germany
(4) Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands

The most massive stars are thought to be hydrogen-rich Wolf-Rayet stars of late spectral subtype (WNh stars). In previous theoretical studies the enhanced mass loss of these stars has been attributed to their proximity to the Eddington limit. Here we investigate observed trends in the mass-loss properties of such young, very massive stars. We derive theoretical mass-luminosity relations for very massive stars, based on a large grid of stellar structure models. Using these relations, we estimate Eddington factors for a sample of stars, under different assumptions of their evolutionary status. We evaluate the resulting mass-loss relations, and compare them with theoretical predictions. We find observational evidence that the mass loss in the WR regime is dominated by the Eddington parameter Gamma_e, which has important consequences for the way we understand Wolf-Rayet stars and their mass loss. In addition, we derive wind masses that support the picture that the WNh stars in young stellar clusters are very massive, hydrogen-burning stars. Our findings suggest that the proximity to the Eddington limit is the physical reason for the onset of Wolf-Rayet type mass loss. This means that, e.g. in stellar evolution models, the Wolf-Rayet stage should be identified by large Eddington parameters, instead of a helium-enriched surface composition. The latter is most likely only a consequence of strong mass loss, in combination with internal mixing. For very massive stars, the enhanced Gamma-dependent mass loss is responsible for the formation of late WNh subtypes with high hydrogen surface abundances, partly close to solar. Because mass loss dominates the evolution of very massive stars, we expect a strong impact of this effect on their end products, in particular on the potential formation of black holes, and Gamma-Ray Bursts, as well as the observed upper mass limit of stars.

Reference: A&A
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1106.5361

Comments:

Email: ggr@arm.ac.uk

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The bi-stability jump as the origin for multiple P-Cygni absorption components in Luminous Blue Variables


Jose H. Groh (1) and Jorick S. Vink (2)

(1) Max-Planck-Institute for Radioastronomy, Germany; (2) Armagh Observatory, UK

Luminous Blue Variables (LBVs) oftentimes show double-troughed absorption in their strong Halpha lines, which are as yet not understood. Intriguingly, the feature has also been seen in the interacting supernova SN 2005gj, which was for this reason suggested to have an LBV progenitor. Our aims are to understand the double-troughed absorption feature in LBVs and investigate whether this phenomenon is related to wind variability. To this purpose, we perform time-dependent radiative transfer modeling using CMFGEN. We find that abrupt changes in the wind-terminal velocity - as expected from the bi-stability jump - are required to explain the double-troughed absorption profiles in LBVs. This strengthens scenarios that discuss the link between LBVs and SNe utilizing the progenitor's wind variability resulting from the bi-stability jump. We also discuss why the presence of double-troughed P-Cygni components may become an efficient tool to detect extra-galactic LBVs and how to analyze their mass-loss history on the basis of just one single epoch of spectral observations.

Reference: A&A 531, 10
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1106.3007

Comments:

Email: jgroh@mpifr.de

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The strong magnetic field of the large-amplitude $beta$,Cephei pulsator V1449,Aql


S.~Hubrig$^1$, I.~Ilyin$^1$, M.~Briquet$^{2,3}$, M.~Sch"oller$^4$, J.~F.~Gonz'alez$^5$, N.~Nu~nez$^5$, P. De Cat$^6$, T. Morel$^7$

$^1$ Leibniz-Institut f"ur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
$^2$ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, 3001~Leuven, Belgium
$^3$ LESIA, Observatoire de Paris, CNRS, UPMC, Universit'e Paris-Diderot, 92195 Meudon, France
$^4$ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei M"unchen, Germany
$^5$ Instituto de Ciencias Astronomicas, de la Tierra, y del Espacio (ICATE), 5400 San Juan, Argentina
$^6$ Koninklijke Sterrenwacht van Belgi"e, Ringlaan 3, 1180 Brussel, Belgium
$^7$ Institut d'Astrophysique et de G'eophysique, Universit'e de Li`ege, All'ee du 6 Ao^ut, B^at. B5c, 4000~Li`ege, Belgium

Only for very few $beta$~Cephei stars has the behaviour of the magnetic field
been studied over the rotation cycle. During the past two years we have obtained
multi-epoch polarimetric spectra of the $beta$~Cephei star V1449,Aql with
SOFIN at the Nordic Optical Telescope to search for a rotation period and to
constrain the geometry of the magnetic field.

The mean longitudinal magnetic field is measured at 13 different epochs. The new
measurements, together with the previous FORS,1 measurements, have been used
for the frequency analysis and the characterization of the magnetic field.

V1449,Aql so far possesses the strongest longitudinal magnetic field of up to
700,G among the $beta$,Cephei stars. The resulting periodogram displays three
dominant peaks with the highest peak at $f=0.0720$,d$^{-1}$ corresponding to a
period $P=13fd893$. The magnetic field geometry can likely be described by a
centred dipole with a polar magnetic field strength $B_{rm d}$ around 3,kG and
an inclination angle $beta$ of the magnetic axis to the rotation axis of
76$pm$4$^{circ}$. As of today, the strongest longitudinal magnetic fields are
detected in the $beta$,Cephei stars V1449,Aql and $xi^1$,CMa with large
radial velocity amplitudes. Their peak-to-peak amplitudes reach
$sim$90,km,s$^{-1}$ and $sim$33,km,s$^{-1}$, respectively. Concluding, we
briefly discuss the position of the currently known eight magnetic
$beta$,Cephei and candidate $beta$,Cephei stars in the Hertzsprung-Russell
(H-R) diagram.

Reference: A&A 531, L20 (2011)
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1107.0883

Comments:

Email: mschoell@eso.org

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N II 5668-5712, a New Class of Spectr