Nadine Manset

The MiMeS survey of magnetism in massive stars: introduction and overview

The Magnetism in Massive Stars (MiMeS) survey represents a highprecision systematic search for magnetic fields in hot, massive OB stars. To date, MiMeS Large Programs (ESPaDOnS@CFHT, Narval@TBL, HARPSpol@ESO3.6) and associated PI programs (FORS@VLT) have yielded nearly 1200 circular spectropolarimetric observations of over 350 OB stars. Within this sample, 20 stars are detected as magnetic. Follow-up observations of new detections reveals (i) a large diversity of magnetic properties, (ii) ubiquitous evidence for magnetic wind confinement in optical spectra of all magnetic O stars, and (iii) the presence of strong, organized magnetic fields in all known Galactic Of?p stars, and iv) a complete absence of magnetic fields in classical Be stars.

Detection of circular polarization in light scattered from photosynthetic microbes

The identification of a universal biosignature that could be sensed remotely is critical to the prospects for success in the search for life elsewhere in the universe. A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Because of the optical activity of chiral molecules, it has been hypothesized that this unique characteristic may provide a suitable remote sensing probe using circular polarization spectroscopy. Here, we report the detection of circular polarization in light scattered by photosynthetic microbes. We show that the circular polarization appears to arise from circular dichroism of the strong electronic transitions of photosynthetic absorption bands. We conclude that circular polarization spectroscopy could provide a powerful remote sensing technique for generic life searches.

The Polarizing Power of the Interstellar Medium in Taurus

We present a study of the polarizing power of dust in cold dense regions (dark clouds) compared with that of dust in the general interstellar medium (ISM). Our study uses new polarimetric, optical, and spectral classification data for 36 stars to carefully study the relation between polarization percentage (p) and extinction (AV) in the Taurus dark cloud complex. We find two trends in our p-AV study: (1) stars that are background to the warm ISM show an increase in p with AV, and (2) the percentage of polarization of stars that are background to cold dark clouds does not increase with extinction. We detect a break in the p-AV relation at an extinction of 1.3±0.2 mag, which we expect corresponds to a set of conditions where the polarizing power of the dust associated with the Taurus dark clouds drops precipitously. This break point places important restrictions on the use of polarimetry in studying interstellar magnetic fields.

ESPaDOnS: an echelle spectropolarimetric device for the observation of stars

ESPaDOnS is an ongoing project for a cross-dispersed echelle spectrograph/spectropolarimeter, for general community use at the Canada-France-Hawaii Telescope. This instrument will provide: (1) a complete optical spectrum from 370 to 1,000 nm in a single exposure, with a variable resolution between 50,000 and 75,000, (2) all polarization components of the stellar light, and (3) 20% peak total throughput. The wide spectral coverage will maximize the multiplex gain associated wtih multi-line techniques. The high resolution will give sufficient spatial resolution for Doppler and Zeeman-Doppler imaging of rapid rotators, increasing the sensitivity of the observations to small-scale structures. It will also allow accurate brightness, abundance and magnetic field mapping of moderate rotators, and help study stellar pulsations, abundances, and extrasolar planets. The possibility of recording two interleaved spectra will be very useful in polarimetric mode, and very convenient for faint object spectroscopy in non-polarimetric mode, where the spectrum of the adjacent sky will be recorded along with that of the target. The spectrographic is bench-mounted and fed by low-OH H-treated Ceram-Optec optical fibers from a Cassegran module containing all calibration and polarimetric facilities, making it possible to have extremely good wavelength stability and minimal instrumental polarization. The achromatic polarimeter includes one quarter-wave and two half-wave Fresnel rhombs coupled to a removable Wollaston prism. ESPaDOnS will be a unqiue instrument worldwide in polarimetric mode, competitive wiht similar instruments on 8-m class telescopes in non-polarimetric mode. Astronomers will be able to address with unprecedented details a broad range of important issues in stellar physics, circumstellar environments, and extrasolar planets.

PolarBase: A Database of High-Resolution Spectropolarimetric Stellar Observations

PolarBase is an evolving database that contains all stellar data collected with the ESPaDOnS and NARVAL high-resolution spectropolarimeters, in their reduced form, as soon as they become public. As of early 2014, observations of 2000 stellar objects throughout the Hertzsprung-Russell diagram are available. Intensity spectra are available for all targets, and the majority of the observations also include simultaneous spectra in circular or linear polarization, with the majority of the polarimetric measurements being performed only in circularly polarized light (Stokes V). Observations are associated with a cross-correlation pseudoline profile in all available Stokes parameters, greatly increasing the detectability of weak polarized signatures. Stokes V signatures are detected for more than 300 stars of all masses and evolutionary stages, and linear polarization is detected in 35 targets. The detection rate in Stokes V is found to be anticorrelated with the stellar effective temperature. This unique set of Zeeman detections offers the first opportunity to run homogeneous magnetometry studies throughout the H-R diagram. The Web interface of PolarBase is available at http://polarbase.irap.omp.eu.

Discovery of a strong magnetic field in the rapidly rotating B2 Vn star HR 7355

We report the detection of a strong, organized magnetic field in the He-variable early B-type star HR 7355 using spectropolarimetric data obtained with ESPaDOnS on the 3.6-m Canada– France–Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Program. HR 7355 is both the most rapidly rotating known main-sequence magnetic star and the most rapidly rotating He-strong star, with v sin i = 300 ± 15km s −1 and a rotational period of 0.521 4404 ± 0.000 0006 d. We have modelled our eight longitudinal magnetic field measurements assuming an oblique dipole magnetic field. Constraining the inclination of the rotation axis to be between 38 ◦ and 86 ◦ , we find the magnetic obliquity angle to be between 30 ◦ and 85 ◦ , and the polar strength of the magnetic field at the stellar surface to be between 13–17 kG. The photometric light curve constructed from HIPPARCOS archival data and new CTIO measurements shows two minima separated by 0.5 in rotational phase and occurring 0.25 cycles before/after the magnetic extrema. This photometric behaviour, coupled with previously reported variable emission of the Hα line (which we confirm), strongly supports the proposal that HR 7355 harbours a structured magnetosphere similar to that in the prototypical He-strong star, σ Ori E.

Spectroscopy of the growing circumstellar disk in the Delta Scorpii Be binary

We present the results of a spectroscopic monitoring program of the binary system Delta Scorpii, whose primary became a Be star after the last periastron encounter in the Summer of 2000. The observations cover a period of 2 years (March 2001–June 2003) and are a continuation of our previous campaign reported in Miroshnichenko et al. (2001). We found that the emission-line spectrum was gradually strengthening over the whole monitoring period.

HUNDRED THOUSAND DEGREE GAS IN THE VIRGO CLUSTER OF GALAXIES

The physical relationship between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of many galaxy clusters is not understood. It is unclear whether the ~104 K filaments have cooled and condensed from the ambient hot (~107 K) medium or have some other origin such as the infall of cold gas in a merger, or the disturbance of an internal cool reservoir of gas by nuclear activity. Observations of gas at intermediate temperatures (~105-106 K) can potentially reveal whether the central massive galaxies are gaining cool gas through condensation or losing it through conductive evaporation and hence identify plausible scenarios for transport processes in galaxy cluster gas. Here we present spectroscopic detection of ~105 K gas spatially associated with the Hα filaments in a central cluster galaxy, M87, in the Virgo Cluster. The measured emission-line fluxes from triply ionized carbon (C IV 1549 A) and singly ionized helium (He II 1640 A) are consistent with a model in which thermal conduction determines the interaction between hot and cold phases.

A new phase of activity of the Herbig Be star HD 200775 in 2001: Evidence for binarity

The results of high-resolution spectroscopy of the Herbig Be star HD 200775 obtained within the framework of a cooperative observing programme in 2000–2002 are presented. A new high-activity phase of the object’s Ha line occurred in the middle of 2001 in full agreement with a 3.68-year periodicity predicted by Miroshnichenko et al. (1998). A complicated picture of the Ha line profile variability near the activity maximum phase turned out to be very similar to that observed during the previous one in 1997. Variations of the radial velocity with the activity phase are detected in He I, Si II, and S II photospheric lines. The observed phenomena are interpreted in the framework of a model in which the star, together with its gaseous envelope, is a component of an eccentric binary system. A preliminary orbital solution is derived, and the system’s parameters are estimated from the radial velocity curves of the Ha emission line. We find that the orbital eccentricity is e ~ 0.3, the mean companion separation is ~1000 R?, and the secondary companion is most likely to be a ~3.5 M, pre-main sequence object. We emphasize the importance of coordinated spectroscopic and interferometric observations at different phases of the object’s activity for further understanding the properties of the system.

Toward Understanding the B[e] Phenomenon. II. New Galactic FS CMa Stars*

FS CMa stars form a group of objects with the B[e] phenomenon that were previously known as unclassified B[e] stars or B[e] stars with warm dust (B[e]WD) until recently. They exhibit strong emission-line spectra and strong IR excesses, most likely due to recently formed circumstellar dust. These properties have been suggested to be due to ongoing or recent rapid mass exchange in binary systems with hot primaries and various types of secondaries. The first paper of this series reported an analysis of the available information about previously known Galactic objects with the B[e] phenomenon, the initial selection of the FS CMa group objects, and a qualitative explanation of their properties. This paper reports the results of our new search for more FS CMa objects in the IRAS Point Source Catalog. We present new photometric criteria for identifying FS CMa stars as well as the first results of our observations of nine new FS CMa group members. With this addition, the FS CMa group has now 40 members, becoming