Detection of a weak surface magnetic field on Sirius A: are all tepid stars magnetic?

Petit, P.; Lignières, F.; Aurière, M.; Wade, G. A.; Alina, D.; Ballot, J.; Böhm, T.; Jouve, L.; Oza, A.; Paletou, F.; Théado, S.

doi:10.1051/0004-6361/201117573

Cited by 114 publications

(111 citation statements)

References 33 publications

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“…However, ultra-weak magnetic fields have recently been detected in some A stars (Lignières et al 2009;Petit et al 2011;Blazère et al 2014). These fields might possibly also exist in higher mass stars, although attempts to detect them in B stars have been unsuccessful so far (Neiner et al 2014;Wade et al 2014a).…”

Section: Discussionmentioning

confidence: 99%

Search for magnetic fields in particle-accelerating colliding-wind binaries

Neiner

Grunhut

Leroy

et al. 2015

A&A

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Context. Some colliding-wind massive binaries, called particle-accelerating colliding-wind binaries (PACWB), exhibit synchrotron radio emission, which is assumed to be generated by a stellar magnetic field. However, no measurement of magnetic fields in these stars has ever been performed. Aims. We aim at quantifying the possible stellar magnetic fields present in PACWB to provide constraints for models. Methods. We gathered 21 high-resolution spectropolarimetric observations of 9 PACWB available in the ESPaDOnS, Narval and HarpsPol archives. We analysed these observations with the least squares deconvolution method. We separated the binary spectral components when possible. Results. No magnetic signature is detected in any of the 9 PACWB stars and all longitudinal field measurements are compatible with 0 G. We derived the upper field strength of a possible field that could have remained hidden in the noise of the data. While the data are not very constraining for some stars, for several stars we could derive an upper limit of the polar field strength of the order of 200 G. Conclusions. We can therefore exclude the presence of strong or moderate stellar magnetic fields in PACWB, typical of the ones present in magnetic massive stars. Weak magnetic fields could however be present in these objects. These observational results provide the first quantitative constraints for future models of PACWB.

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Section: Discussionmentioning

confidence: 99%

Search for magnetic fields in particle-accelerating colliding-wind binaries

Neiner

Grunhut

Leroy

et al. 2015

A&A

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“…14, we expand the region between 10 −5 to 10 −4 . A few times 10 −5 is the region where many of the recently detected weak magnetic fields are reported (e.g., Aurière et al 2009Aurière et al , 2010Lignières et al 2009;Grunhut et al 2010;Konstantinova-Antova et al 2010;Petit et al 2011;Fossati et al 2013). Despite the low noise level, we see that the COG method interprets a nonnegligible amount of the noise as a magnetic field (between 2 and 10 G).…”

Section: Absolute Limits Of the Cog And Omp Methodsmentioning

confidence: 99%

“…This is the typical situation for stars with long rotation periods and/or in situations where the amount A&A 563, A56 (2014) of telescope time is limited. Such observations are responsible for a number of exciting magnetic field detection in recent times (e.g., Aurière et al 2007Aurière et al , 2009Lignières et al 2009;Aurière et al 2010;Grunhut et al 2010;Konstantinova-Antova et al 2010;Sennhauser & Berdyugina 2011;Petit et al 2011;Fossati et al 2013). Because many of the observed polarimetric line profiles are buried in noise, the investigations rely on a prior line profile reconstruction technique, such as the least-square-deconvolution (LSD; Donati et al 1997), principalcomponent-analysis (PCA;, or singularvalue-decomposition (SVD; Carroll et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Detecting and quantifying stellar magnetic fields

Carroll¹,

Strassmeier²

2014

A&A

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Context. In recent years, we have seen a rapidly growing number of stellar magnetic field detections for various types of stars. Many of these magnetic fields are estimated from spectropolarimetric observations (Stokes V) by using the so-called center-of-gravity (COG) method. Unfortunately, the accuracy of this method rapidly deteriorates with increasing noise and thus calls for a more robust procedure that combines signal detection and field estimation. Aims. We introduce an estimation method that provides not only the effective or mean longitudinal magnetic field from an observed Stokes V profile but also uses the net absolute polarization of the profile to obtain an estimate of the apparent (i.e., velocity resolved) absolute longitudinal magnetic field. Methods. By combining the COG method with an orthogonal-matching-pursuit (OMP) approach, we were able to decompose observed Stokes profiles with an overcomplete dictionary of wavelet-basis functions to reliably reconstruct the observed Stokes profiles in the presence of noise. The elementary wave functions of the sparse reconstruction process were utilized to estimate the effective longitudinal magnetic field and the apparent absolute longitudinal magnetic field. A multiresolution analysis complements the OMP algorithm to provide a robust detection and estimation method.Results. An extensive Monte-Carlo simulation confirms the reliability and accuracy of the magnetic OMP approach where a mean error of under 2% is found. Its full potential is obtained for heavily noise-corrupted Stokes profiles with signal-to-noise variance ratios down to unity. In this case a conventional COG method yields a mean error for the effective longitudinal magnetic field of up to 50%, whereas the OMP method gives a maximum error of 18%. It is, moreover, shown that even in the case of very small residual noise on a level between 10 −3 and 10 −5 , a regime reached by current multiline reconstruction techniques, the conventional COG method incorrectly interprets a large portion of the residual noise as a magnetic field, with values of up to 100 G. The magnetic OMP method, on the other hand, remains largely unaffected by the noise, regardless of the noise level the maximum error is no greater than 0.7 G.

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“…Large surveys such as MIMES 2 and others use ESPaDOnS and NARVAL fiber-fed spectropolarimeters at spectral resolutions greater than 60 000 are examples (Wade et al 2010Grunhut et al 2012). These programs combine many individual spectral lines over many spectral orders to derive a single representative pseudo line profile (Donati et al 1997;Kochukhov et al 2010;Sennhauser et al 2009;Kochukhov & Sudnik 2013;Petit et al 2011).…”

Section: Spectropolarimetric Instruments Errors and Suppression Tecmentioning

confidence: 99%

Calibrating and stabilizing spectropolarimeters with charge shuffling and daytime sky measurements

Harrington

Kuhn

Nevin

2015

A&A

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Well-calibrated spectropolarimetry studies at resolutions of R > 10 000 with signal-to-noise ratios (S/Ns) better than 0.01% across individual line profiles, are becoming common with larger aperture telescopes. Spectropolarimetric studies require high S/N observations and are often limited by instrument systematic errors. As an example, fiber-fed spectropolarimeters combined with advanced line-combination algorithms can reach statistical error limits of 0.001% in measurements of spectral line profiles referenced to the continuum. Calibration of such observations is often required both for cross-talk and for continuum polarization. This is not straightforward since telescope cross-talk errors are rarely less than ∼1%. In solar instruments like the Daniel K. Inouye Solar Telescope (DKIST), much more stringent calibration is required and the telescope optical design contains substantial intrinsic polarization artifacts. This paper describes some generally useful techniques we have applied to the HiVIS spectropolarimeter at the 3.7 m AEOS Telescope on Haleakala. HiVIS now yields accurate polarized spectral line profiles that are shot-noise limited to 0.01% S/N levels at our full spectral resolution of 10 000 at spectral sampling of ∼100 000. We show line profiles with absolute spectropolarimetric calibration for cross-talk and continuum polarization in a system with polarization cross-talk levels of essentially 100%. In these data the continuum polarization can be recovered to one percent accuracy because of synchronized charge-shuffling model now working with our CCD detector. These techniques can be applied to other spectropolarimeters on other telescopes for both night and daytime applications such as DKIST, TMT, and ELT which have folded non-axially symmetric foci.

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Detection of a weak surface magnetic field on Sirius A: are all tepid stars magnetic?

Cited by 114 publications

References 33 publications

Search for magnetic fields in particle-accelerating colliding-wind binaries

Search for magnetic fields in particle-accelerating colliding-wind binaries

Detecting and quantifying stellar magnetic fields

Calibrating and stabilizing spectropolarimeters with charge shuffling and daytime sky measurements

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