Overview of the ESPaDOnS LP
The hot survey component of BinaMIcS and the fossil field
One and half years after the start of the ESPaDOnS and Narval large programmes, about 200 snapshot observations of ~150 hot close SB2 systems have been obtained. I will review the first results of the survey, and their implication on the fossil field theory.
The weak magnetic field of Zeta Ori A
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 (Wade et al. 2013) 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. The O star ζ Ori A has been found to host a magnetic field by Bouret et al. (2008) and its field is the weakest ever reported in a massive star. However, the Zeeman signature in ζ Ori A is not clear. Besides if we use the measurement of the magnetic field provided by Bouret et al. to characterize the magnetosphere of ζ Ori A, we find that it is the only known magnetic star with a magnetic confinement parameter below 1 i.e without a magnetosphere. Later Hummel et al. (2013) found ζ Ori A to be a binary (Aa+Ab). As a consequence, the magnetic field measured by Bouret et al. has been underestimated. We present new spectropolarimetric Narval observations of ζ 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 check the presence of a magnetic field in ζ Ori A. We identify that it belongs to ζ Ori Aa and characterize it.
Tidally driven dynamos in a rotating sphere
Large-scale
fields may be controlled by tides, as suggested for the star tau-boo, Mars or the Early Moon. By simulating a small local patch of a rotating fluid, Barker&Lithwick (2014) have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested by the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use efficient spectral methods to solve the magnetohydrodynamic problem. Kinematic and self-consistent dynamos are simulated, showing that tides, via the elliptical instability, are capable of generating large-scale magnetic field.
Studying the radio emission from the magnetic massive stars.
We have carried out 1420 MHz and 610 MHz observations of 8 MiMeS targets with the Giant Metrewave Radio Telescope. We detect 5 stars in both 610 and 1420 MHz bands. The spectral index between 610 and 1420 MHz bands indicates towards a non-thermal origin of the radio emission. We also see a clear variability with phase in the radio emission for HD 133880, which is also seen in high frequency radio data with the ATCA. The result have important implications on the free free absorption by the surrounding medium, and hence the mass loss rate from the magnetic massive stars. Towards the end of the talk, I will also discuss the current status of the ongoing Very Large Array observations.
Collapse of turbulent, magnetised, and massive dense core: early fragmentation inhibition
History of the Magnetic Sun: The evolution of surface magnetic fields in young solar-type stars
The surface rotation rates of young solar-type stars decrease rapidly with age from the end of the pre-main sequence though the early main sequence. This suggests that there is also an important change in the dynamos operating in these stars, which should be observable in their surface magnetic fields. Here we present early results in a study aimed at observing the evolution of these magnetic fields through this critical time period. We are observing stars in open clusters and stellar associations to provide precise ages, and using Zeeman Doppler Imaging to characterize their complex magnetic fields.
While this project focuses on effectively single stars, it will provide an excellent control sample for comparison with the cool component of BinaMIcS. The faster rotating single solar-type stars are all young, in the age range studied by the HMS project. To understand the influence of tidal spin-up or other tidal effects on dynamo magnetic fields, it is essential to have a robust sample of fast rotating single stars for comparison.
Results for 11 stars, in four associations between 21 Myr and 257 Myr old, are presented. We find a trend towards weaker less dipolar magnetic fields with age, but have not yet identified clear trends with rotation period. Observations are in progress to extend the sample to a wider range of ages and rotation periods, including a 2 year LP at CFHT.
The curious case of Plaskett’s star: Are we unravelling the mystery?
Using physical models to interpret LSD profiles of magnetic stars
Follow-up interferometric observations
Decoupling of neutral matter and magnetic fields in low mass star formation
Spectroscopic analysis of hot binary systems
Overview of the Narval LP
Massive-Star Magnetospheres with Near-Infrared Glasses
Magnetospheres of massive stars are known to exhibit variable emission signatures in the Hydrogen recombination lines in spectroscopy in optical wavelengths (i.e. the Balmer series). These features have been used to study both the mass content and the structure of the magnetosphere. This work aims to broaden our knowledge of these circumstellar environments into the near-infrared (JHK bands). We explore the line profiles produced in the Brackett series, and search for variability. Infrared is fast becoming the next frontier, and this study represents a first step in utilizing the benefits of longer wavelengths over UV and optical.
Analytic Dynamical Magnetosphere (ADM)
Statistical Bayesian dipolar analysis of the MiMeS Survey Component sample, and application to the BinaMIcS Survey
Rotational, Magnetic, and Orbital Constraints From New ESPaDOnS Observations
The Magnetically Confined Wind of HD 35502
Current attempts to understand the formation and evolution of massive stars has been significantly hindered by a scarcity of observational data. Although it has been demonstrated that magnetic fields play an important role, the theoretical models predicting their effects on stellar evolution are relatively unconstrained. HD 35502 is a triple star system containing a primary magnetic B-type star which, given their rarity in the Milky Way, are important objects in terms of understanding stellar magnetism. The aim of this research is to determine key physical parameters of the triple system such as the orbital configuration and spectral types with a focus on the atmospheric and magnetic features of the massive B star. The current results along with the future goals of this research will be reviewed.
Spectroscopic analysis of the magnetic SB2 HD 5550