References of "Bagnulo, Stefano"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailHow unique is Plaskett's star? A search for organized magnetic fields in short period, interacting or post-interaction massive binary systems★
Nazé, Yaël ULg; Neiner, Coralie; Grunhut, Jason et al

in Monthly Notices of the Royal Astronomical Society (2017), 467

Amongst O-type stars with detected magnetic fields, the fast rotator in the close binary called Plaskett's star shows a variety of unusual properties. Since strong binary interactions are believed to have ... [more ▼]

Amongst O-type stars with detected magnetic fields, the fast rotator in the close binary called Plaskett's star shows a variety of unusual properties. Since strong binary interactions are believed to have occurred in this system, one may wonder about their potential role in generating magnetic fields. Stokes V spectra collected with the low-resolution FORS2 and high-resolution ESPaDOnS and Narval spectropolarimeters were therefore used to search for magnetic fields in 15 interacting or post-interaction massive binaries. No magnetic field was detected in any of them, with 0 G always being within 2σ of the derived values. For 17 out of 25 stars in the systems observed at high resolution, the 90 per cent upper limit on the individual dipolar fields is below the dipolar field strength of Plaskett's secondary; a similar result is found for five out of six systems observed at low resolution. If our sample is considered to form a group of stars sharing similar magnetic properties, a global statistical analysis results in a stringent upper limit of ∼200 G on the dipolar field strength. Moreover, the magnetic incidence rate in the full sample of interacting or post-interaction systems (our targets + Plaskett's star) is compatible with that measured from large surveys, showing that they are not significantly different from the general O-star population. These results suggest that binary interactions play no systematic role in the magnetism of such massive systems. [less ▲]

Detailed reference viewed: 20 (2 ULg)
Full Text
Peer Reviewed
See detailThe puzzling properties of the magnetic O star Tr16-22
Nazé, Yaël ULg; Barbá, Rodolfo; Bagnulo, Stefano et al

in Astronomy and Astrophysics (2016), 596(A44), 1-7

Context. The detection of bright, hard, and variable X-ray emission in Tr16-22 prompted spectropolarimetric observations of this star, which in turn led to the discovery of a surface magnetic field. <BR ... [more ▼]

Context. The detection of bright, hard, and variable X-ray emission in Tr16-22 prompted spectropolarimetric observations of this star, which in turn led to the discovery of a surface magnetic field. <BR /> Aims: We want to further constrain the properties of this star, in particular to verify whether X-ray variations are correlated to changes in optical emission lines and magnetic field strength, as expected from the oblique rotator model that is widely accepted for magnetic O stars. <BR /> Methods: We have obtained new low-resolution spectropolarimetric and long-term high-resolution spectroscopic monitoring of Tr16-22, and we also analyse new, serendipitous X-ray data. <BR /> Results: The new X-ray observations are consistent with previous data, but their addition does not help to solve the ambiguity in the variation timescale because of numerous aliases. No obvious periodicity or any large variations are detected in the spectropolarimetric data of Tr16-22 obtained over three months. The derived field values appear to be in line with previous measurements, suggesting constancy of the field (though the possibility of small, short-term field variations cannot be excluded). Variations in the equivalent widths of Hα are very small, and they do not appear to be related to the X-ray timescale; the overall lack of large variations in optical emission lines is consistent with the magnetic field constancy. In addition, variations of the radial velocities indicate that Tr16-22 is probably a SB1 binary with a very long period. <BR /> Conclusions: Our new measurements of optical emission lines and magnetic field strength do not show an obvious correlation with X-ray variations. Our current data thus cannot be interpreted in terms of the common model, which assumes the electromagnetic emission associated with a wind confined by a dipolar field tilted with respect to the rotation axis. However, the sampling is imperfect and new data are needed to further constrain the actual periodicity of the various observed phenomena. If inconsistencies are confirmed, then we will need to consider alternative scenarios. Based on XMM-Newton observations (ObsIDs 0691970101, 0742850301, 0742850401, 0762910401) and ESO data (Prog. 386.D-0624A, 086.D-0997B, 089.D-0975A, 091.D-0090B, 095.D-0082).The reduced polarisation spectra (as ascii files) are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/596/A44">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/596/A44</A> [less ▲]

Detailed reference viewed: 23 (3 ULg)
Full Text
Peer Reviewed
See detailThe Calern Asteroid Polarimetric Survey using the Torino Polarimeter: assessment of instrument performances and first scientific results
Devogele, Maxime ULg; Cellino, Alberto; Bagnulo, Stefano et al

in Monthly Notices of the Royal Astronomical Society (2016)

A new polarimeter based on the Wedged double Wollaston concept has been built at the Torino Observatory and installed on a 1-meter telescope at the Calern observing station of the ``Observatoire de la C ... [more ▼]

A new polarimeter based on the Wedged double Wollaston concept has been built at the Torino Observatory and installed on a 1-meter telescope at the Calern observing station of the ``Observatoire de la C{\^o}te d'Azur''. Its main purpose is to carry out a polarimetric survey of Solar System objects. This survey is called CAPS (Calern Asteroid Polarimetric Survey). In this paper, the new Torino polarimeter (ToPo) and its preliminary validation campaign is described. The first results of the CAPS survey are also presented. A number of standard stars with known polarization states, as well as a number of asteroids for which the polarimetric properties are known, have been observed in order to assess the instrument accuracy. The instrument response over the field of view and also its stability over single nights and longer periods have also been tested. It has been found that the instrument polarization is stable within a few $10^{-4}$ units. The first polarimetric observations of a still limited number of asteroids show an excellent agreement with previously available data and make already some significant contributions by adding new data to a number of objects that had been poorly observed so far. [less ▲]

Detailed reference viewed: 51 (7 ULg)
Full Text
Peer Reviewed
See detailSpectral Variations of Of?p Oblique Magnetic Rotator Candidates in the Magellanic Clouds
Walborn, Nolan R.; Morrell, Nidia I.; Nazé, Yaël ULg et al

in Astronomical Journal (The) (2015), 150

Optical spectroscopic monitoring has been conducted of two O stars in the SMC and one in the LMC, the spectral characteristics of which place them in the Of?p category, which has been established in the ... [more ▼]

Optical spectroscopic monitoring has been conducted of two O stars in the SMC and one in the LMC, the spectral characteristics of which place them in the Of?p category, which has been established in the Galaxy to consist of oblique magnetic rotators. All of these Magellanic stars show systematic spectral variations typical of the Of?p class, further strengthening their magnetic candidacy to the point of virtual certainty. The spectral variations are related to photometric variations derived from Optical Gravitational Lensing Experiment data by Nazé et al. in a parallel study, which yields rotational periods for two of them. Now circular spectropolarimetry is required to measure their fields, and ultraviolet spectroscopy to further characterize their low-metallicity, magnetically confined winds, in support of hydrodynamical analyses. [less ▲]

Detailed reference viewed: 39 (3 ULg)
Full Text
Peer Reviewed
See detailMagnetometry of a sample of massive stars in Carina
Nazé, Yaël ULg; Bagnulo, Stefano; Petit, Véronique et al

in Monthly Notices of the Royal Astronomical Society (2012), 423

X-ray surveys of the Carina nebula have revealed a few hard and luminous sources associated with early-type stars. Such unusual characteristics for the high-energy emission may be related to magnetically ... [more ▼]

X-ray surveys of the Carina nebula have revealed a few hard and luminous sources associated with early-type stars. Such unusual characteristics for the high-energy emission may be related to magnetically confined winds. To search for the presence of magnetic fields in these objects, we performed a limited spectropolarimetric survey using the Focal reducer and low dispersion spectrograph (FORS) instrument. The multi-object mode was used, so that a total of 21 OB stars could be investigated during a one-night-long run. A magnetic field was detected in two objects of the sample, with a 6σ significance: Tr16-22 and 13. Such a detection was expected for Tr16-22, as its X-ray emission is too bright, variable and hard, compared to other late-type O or O+OB systems. It is more surprising for Tr16-13, a poorly known star which so far has never shown any peculiar characteristics. Subsequent monitoring is now needed to ascertain the physical properties of these objects and enable a full modelling of their magnetic atmospheres and winds. Based on data collected at ESO under Program ID 386.D-0624A. [less ▲]

Detailed reference viewed: 27 (1 ULg)
Full Text
See detailCircular Polarimetry Now Offered at EFOSC2
Saviane, Ivo; Piirola, Vilppu; Bagnulo, Stefano et al

in The Messenger (2007), 129

Starting from period P79, circular polarimetry measurements can be carried out with EFOSC2 at the ESO 3.6-m telescope. Here we describe the motivations behind the upgrade of the instrument, and a few ... [more ▼]

Starting from period P79, circular polarimetry measurements can be carried out with EFOSC2 at the ESO 3.6-m telescope. Here we describe the motivations behind the upgrade of the instrument, and a few results from the commissioning runs are used to show the excellent performance of the new polarimetry unit. [less ▲]

Detailed reference viewed: 21 (2 ULg)
Full Text
See detailDynamical modeling of the Deep Impact dust ejecta cloud
Bonev, Tanyu; Ageorges, Nancy; Bagnulo, Stefano et al

Report (2007)

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its ... [more ▼]

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its position and shape are governed by the physical properties of the dust grains. We use a Monte Carlo model to describe the evolution of the post-impact dust plume. The results of our dynamical simulations are compared to the data obtained with FORS2, the FOcal Reducer and low dispersion Spectrograph for the VLT of the European Southern Observatory (ESO), to derive the particle size distribution and the total amount of material contained in the dust ejecta cloud. [less ▲]

Detailed reference viewed: 30 (2 ULg)
Full Text
See detailDeep Impact at ESO Telescopes
Kaufl, Hans-Ullrich; Ageorges, Nancy; Bagnulo, Stefano et al

in The Messenger (2005), 121

This article is a first summary of the observations done with ESO telescopes and instrumentation in the context of NASA's Deep Impact (DI) space mission. The ESO observers were part of an extremely active ... [more ▼]

This article is a first summary of the observations done with ESO telescopes and instrumentation in the context of NASA's Deep Impact (DI) space mission. The ESO observers were part of an extremely active, communicative and thus successful worldwide network of observers. Through this network all information was freely exchanged and highlights are reported here as well. [less ▲]

Detailed reference viewed: 25 (2 ULg)