Abstract Digest IAUS307, 15.8.2014

Due to the deadline for proceeding contributions to IAUS 307, held in Geneva, and the large number of preprints from that conference, this edition consists only of publications submitted for the proceedings. Two more abstarct have already been publsihed in digest #2, future ones will be published in the normal digest again. IAUS307 proceedings abstracts:

  • IAUS 307: "The UVMag space project: UV and visible spectropolarimetry of massive stars" by Coralie Neiner and the UVMag consortium
  • IAUS 307: "Combining seismology and spectropolarimetry of hot stars" by Coralie Neiner et al.
  • IAUS 307: "Deep Photospheric Emission Lines as Probes for Pulsational Waves" by Th. Rivinius, M. Shultz, G.A. Wade
  • IAUS 307: "AMBER/VLTI Snapshot Survey on Circumstellar Environments" Th. Rivinius et al.
  • IAUS 307: "Plasma Leakage from the Centrifugal Magnetospheres of Magnetic B-Type Stars" by M. Shultz et al.
  • IAUS 307: "xi^1 CMa: An Extremely Slowly Rotating Magnetic B0.7 IV Star" by M. Shultz et al.
  • IAUS 307: "Beam me up, Spotty: Toward a new understanding of the physics of massive star photospheres" by A. David-Uraz, G. Wade, S. Owocki
  • IAUS 307: "The magnetic field of zeta Ori A" by A. Blazère et al.
  • IAUS 307: "3D and Some Other Things Missing from the Theory of Massive Star Evolution" by W.D. Arnett
  • IAUS 307: "Binarity of the LBV HR Car" by Th. Rivinius et al.
  • IAUS 307: "Unraveling the variability of sigma Ori E" by M.E. Oksala et al.
  • IAUS 307: "Magnetic fields and internal mixing of main sequence B stars" by G. Wade et al.
  • IAUS 307: "Probing high-mass stellar evolutionary models with binary stars" by A. Tkachenko

The UVMag space project: UV and visible spectropolarimetry of massive stars

Coralie Neiner and the UVMag consortium

UVMag is a medium-size space telescope equipped with a high-resolution spectropolarimeter working in the UV and visible domains. It will be proposed to ESA for a future M mission. It will allow scientists to study all types of stars as well as e.g. exoplanets and the interstellar medium. It will be particularly useful for massive stars, since their spectral energy distribution peaks in the UV. UVMag will allow us to study massive stars and their circumstellar environment (in particular the stellar wind) spectroscopically in great details. Moreover, with UVMag's polarimetric capabilities we will be able, for the first time, to measure the magnetic field of massive stars simultaneously at the stellar surface and in the wind lines, i.e. to completely map their magnetosphere.

Available at: arXiv:1407.8082


Combining seismology and spectropolarimetry of hot stars

Coralie Neiner et al.

Asteroseismology and spectropolarimetry have allowed us to progress significantly in our understanding of the physics of hot stars over the last decade. It is now possible to combine these two techniques to learn even more information about hot stars and constrain their models. While only a few magnetic pulsating hot stars are known as of today and have been studied with both seismology and spectropolarimetry, new opportunities - in particular Kepler2 and BRITE - are emerging and will allow us to rapidly obtain new combined results.

Available at: arXiv:1407.8087


Deep Photospheric Emission Lines as Probes for Pulsational Waves

Th. Rivinius, M. Shultz, G.A. Wade

Weak line emission originating in the photosphere is well known from O stars and widely used for luminosity classification. The physical origin of the line emission are NLTE effects, most often optical pumping by far-UV lines. Analogous lines in B stars of lower luminosity are identified in radially pulsating beta Cephei stars. Their diagnostic value is shown for radially pulsating stars, as these lines probe a much larger range of the photosphere than absorption lines, and can be traced to regions where the pulsation amplitude is much lower than seen in the absorption lines.

Available at: arXiv:1407.8133


AMBER/VLTI Snapshot Survey on Circumstellar Environments

Th. Rivinius et al.

OHANA is an interferometric snapshot survey of the gaseous circumstellar environments of hot stars, carried out by the VLTI group at the Paranal observatory. It aims to characterize the mass-loss dynamics (winds/disks) at unexplored spatial scales for many stars. The survey employs the unique combination of AMBER's high spectral resolution with the unmatched spatial resolution provided by the VLTI. Because of the spatially unresolved central OBA-type star, with roughly neutral colour terms, their gaseous environments are among the easiest objects to be observed with AMBER, yet the extent and kinematics of the line emission regions are of high astrophysical interest.

Available at: arXiv:1407.8135


Plasma Leakage from the Centrifugal Magnetospheres of Magnetic B-Type Stars

M. Shultz et al.

Magnetic B-type stars are often host to Centrifugal Magnetospheres (CMs). Here we describe the results of a population study encompassing the full sample of known magnetic early B-type stars, focusing on those with detectable CMs. We present revised rotational and magnetic parameters for some stars, clarifying their positions on the rotation-confinement diagram, and find that plasma densities within their CMs are much lower than those predicted by centrifugal breakout.

Available at: arXiv:1407.8503


xi^1 CMa: An Extremely Slowly Rotating Magnetic B0.7 IV Star

M. Shultz et al.

We present our analysis of 6 years of ESPaDOnS spectropolarimetry of the magnetic $\beta$ Cep star $\xi^1$ CMa (B0.7 IV). This high-precision magnetometry is consistent with a rotational period $P{\rm rot} >$ 40 yr. Absorption line profiles can be reproduced with a non-rotating model. We constrain $R_*$, $L_*$, and the stellar age via a Baade-Wesselink analysis. Spindown due to angular momentum loss via the magnetosphere predicts an extremely long rotational period if the magnetic dipole $B_{\rm d} > 6$ kG, a strength also inferred by the best-fit sinusoids to the longitudinal magnetic field measurements $B_{\rm Z}$ when phased with a 60-year $P_{\rm rot}$.

Available at: arXiv:1407.8505


Beam me up, Spotty: Toward a new understanding of the physics of massive star photospheres

Alexandre David-Uraz, Gregg Wade, Stan Owocki

For 30 years, cyclical wind variability in OB stars has puzzled the astronomical community. Phenomenological models involving co-rotating bright spots provide a potential explanation for the observed variations, but the underlying physics remains unknown. We present recent results from hydrodynamical simulations constraining bright spot properties and compare them to what can be inferred from space-based photometry. We also explore the possibility that these spots are caused by magnetic fields and discuss the detectability of such fields.

Available at: arXiv:1408.0029


The magnetic field of zeta Ori A

A. Blazère et al.

Magnetic fields play a significant role in the evolution of massive stars. About 7% of massive stars are found to be magnetic at a level detectable with current instrumentation and only a few magnetic O stars are known. Detecting magnetic field in O stars is particularly challenging because they only have few, often broad, lines to measure the field, which leads to a deficit in the knowledge of the basic magnetic properties of O stars. We present new spectropolarimetric Narval observations of zeta Ori A. We also provide a new analysis of both the new and older data taking binarity into account. The aim of this study was to confirm the presence of a magnetic field in zeta Ori A. We identify that it belongs to zeta Ori Aa and characterize it.

Available at: arXiv:1408.0178


3D and Some Other Things Missing from the Theory of Massive Star Evolution

W.D. Arnett

This is a sketch of a 321D approximation for stellar convection which is nonlocal, and thus has nonzero fluxes of KE (to be published in more detail elsewhere). Boundary conditions are discussed in a fluid dynamics context (i.e., predictions for overshoot, semiconvection and entrainment are analyzed). We plan to add this as an option to MESA. Inclusion of KE fluxes seems to help resolve the solar abundance problem (Asplund 2009). Smaller cores may ease the explosion problems with core collapse supernova simulations.

Available at: arXiv:1408.0326


Binarity of the LBV HR Car

Th. Rivinius et al.

VLTI/AMBER and VLTI/PIONIER observations of the LBV HR Car show an interferometric signature that could not possibly be explained by an extended wind, more or less symmetrically distributed around a single object. Instead, observations both in the Br$\gamma$ line and the H-band continuum are best explained by two point sources (or alternatively one point source and one slightly extended source) at about 2 mas separation and a contrast ratio of about 1:5. These observations establish that HR Car is a binary, but further interpretation will only be possible with future observations to constrain the orbit. Under the assumption that the current separation is close to the maximum one, the orbital period can be estimated to be of the order of 5 years, similar as in the $\eta$ Car system. This would make HR Car the second such LBV binary.

Available at: arXiv:1408.051


Unraveling the variability of sigma Ori E

M.E. Oksala et al.

Sigma Ori E (HD 37479) is the prototypical helium-strong star shown to harbor a strong magnetic field, as well as a magnetosphere consisting of two clouds of plasma. The observed optical (ubvy) light curve of sigma Ori E is dominated by eclipse features due to circumstellar material, however, there remain additional features unexplained by the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki. Using the technique of magnetic Doppler imaging (MDI), spectropolarimetric observations of sigma Ori E are used to produce maps of both the magnetic field topology and various elemental abundance distributions. We also present an analysis utilizing these computed MDI maps in conjunction with NLTE TLUSTY models to study the optical brightness variability of this star arising from surface inhomogeneities. It has been suggested that this physical phenomena may be responsible for the light curve inconsistencies between the model and observations.

Available at: arXiv:1408.0627


Magnetic fields and internal mixing of main sequence B stars"

G. Wade et al.

We have obtained high-quality magnetic field measurements of 19 sharp-lined B-type stars with precisely-measured N/C abundance ratios. Our primary goal is to test the idea that a magnetic field may explain extra drag (through the wind) on the surface rotation, thus producing more internal shear and mixing, and thus could provide an explanation for the appearance of slowly rotating N-rich main sequence B stars.

Available at: arXiv:1408.0383


Probing high-mass stellar evolutionary models with binary stars

A. Tkachenko

Mass discrepancy is one of the problems that is pending a solution in (massive) binary star research field. The problem is often solved by introducing an additional near core mixing into evolutionary models, which brings theoretical masses of individual stellar components into an agreement with the dynamical ones. In the present study, we perform a detailed analysis of two massive binary systems, V380 Cyg and Sigma Sco, to provide an independent, asteroseismic measurement of the overshoot parameter, and to test state-of-the-art stellar evolution models.

Available at: arXiv:1408.0949


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