| 1. |
- Wade, G. A., et al.
(författare)
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The MiMeS survey of magnetism in massive stars : introduction and overview
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:1, s. 2-22
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS (Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada-France-Hawaii Telescope, Narval at the Telescope Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6 m telescope, making MiMeS by far the largest systematic investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole fields above approximately 100 G, discuss the polarimetric performance, stability and uncertainty of the instrumentation, and summarize the previous and forthcoming publications.
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| 2. |
- Weigelt, G., et al.
(författare)
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VLTI-MATISSE chromatic aperture-synthesis imaging of eta Carinae's stellar wind across the Br alpha line Periastron passage observations in February 2020
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
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Tidskriftsartikel (refereegranskat)abstract
- Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis similar to 15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, eta Car A, is a luminous blue variable (LBV); the secondary, eta Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV eta Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of eta Car's WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Br alpha imaging of eta Car's distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of eta Car A's stellar windin several spectral channels distributed across the Br alpha 4.052 mu m line (spectral resolving power R similar to 960). Our observations were performed close to periastron passage in February 2020 (orbital phase similar to 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (similar to 14 au). The radius of the faintest outer wind regions is similar to 26 mas (similar to 60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 +/- 0.06 mas (6.54 +/- 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
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| 3. |
- Alecian, E., et al.
(författare)
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First HARPSpol discoveries of magnetic fields in massive stars
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 536, s. L6-
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Tidskriftsartikel (refereegranskat)abstract
- In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. We report on the first discoveries of magnetic fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and confirm the presence of a magnetic field at the surface of HD 105382 that was previously observed with a low spectral resolution device. The longitudinal magnetic field measurements strongly vary for HD 130807 from similar to-100 G to similar to 700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from similar to-40 to -80 G, and from similar to-300 to -600 G, respectively. The discovery and confirmation of three new magnetic massive stars, including at least two He-weak stars, is an important contribution to one of MiMeS objectives: the understanding of the origin of magnetic fields in massive stars and their impact on stellar structure and evolution.
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| 4. |
- Erba, C., et al.
(författare)
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Confirmation of ξ1 CMa’s ultra-slow rotation : magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 506:2, s. 2296-2308
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic beta Cep pulsator xi(1) CMa has the longest rotational period of any known magnetic B-type star. It is also the only magnetic B-type star with magnetospheric emission that is known to be modulated by both rotation and pulsation. We report here the first unambiguous detection of a negative longitudinal magnetic field in xi(1) CMa (< B-z > = -87 +/- 2 G in 2019 and < B-z > = -207 +/- 3 G in 2020), as well as the results of ongoing monitoring of the star's H alpha variability. We examine evidence for deviation from a purely dipolar topology. We also report a new HST UV spectrum of xi(1) CMa obtained near magnetic null that is consistent with an equatorial view of the magnetosphere, as evidenced by its similarity to the UV spectrum of beta Cep obtained near maximum emission. The new UV spectrum of xi(1) CMa provides additional evidence for the extremely long rotation period of this star via comparison to archival data.
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| 5. |
- Rivinius, T., et al.
(författare)
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Basic parameters and properties of the rapidly rotating magnetic helium-strong B star HR 7355
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 429:1, s. 177-188
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Tidskriftsartikel (refereegranskat)abstract
- The spectral and magnetic properties and variability of the B2Vnp emission-line magnetosphere star HR 7355 were analysed. The object rotates at almost 90 per cent of the critical value, meaning it is a magnetic star for which oblateness and gravity darkening effects cannot be ignored any longer. A detailed modelling of the photospheric parameters indicates that the star is significantly cooler than suggested by the B2 spectral type, with T-eff = 17 500 K atypically cool for a star with a helium-enriched surface. The spectroscopic variability of helium and metal lines due to the photospheric abundance pattern is far more complex than a largely dipolar, oblique magnetic field of about 11-12 kG may suggest. Doppler imaging shows that globally the most He-enriched areas coincide with the magnetic poles and metal-enriched areas with the magnetic equator. While most of the stellar surface is helium enriched with respect to the solar value, some isolated patches are depleted. The stellar wind in the circumstellar environment is governed by the magnetic field, i. e. the stellar magnetosphere is rigidly corotating with the star. The magnetosphere of HR 7355 is similar to the well known sigma Ori E: the gas trapped in the magnetospheric clouds is fairly dense, and at the limit to being optically thick in the hydrogen emission. Apart from a different magnetic obliquity, HR 7355 and the more recently identified HR 5907 have virtually identical stellar and magnetic parameters.
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