Detectability of small-scale magnetic fields in early-type stars

Kochukhov, O.; Sudnik, N.

doi:10.1051/0004-6361/201321583

Cited by 33 publications

(40 citation statements)

References 47 publications

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“…It can also be applied to hotter B-type stars given that large enough wavelength coverage is provided. Though we did not test the method on these types of objects in this paper, there are quite a few examples where the LSD technique was successfully applied to hotter stars with the aim of looking for binary and/or spot signatures and of detecting magnetic fields (e.g., Petit 2011; Kochukhov et al 2011;Kochukhov & Sudnik 2013;Tkachenko et al 2012b;Aerts et al 2013).…”

Section: Discussionmentioning

confidence: 99%

Denoising spectroscopic data by means of the improved least-squares deconvolution method

Tkachenko

Reeth

Tsymbal

et al. 2013

A&A

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Context. The MOST, CoRoT, and Kepler space missions have led to the discovery of a large number of intriguing, and in some cases unique, objects among which are pulsating stars, stars hosting exoplanets, binaries, etc. Although the space missions have delivered photometric data of unprecedented quality, these data are lacking any spectral information and we are still in need of ground-based spectroscopic and/or multicolour photometric follow-up observations for a solid interpretation. Aims. The faintness of most of the observed stars and the required high signal-to-noise ratio (S/N) of spectroscopic data both imply the need to use large telescopes, access to which is limited. In this paper, we look for an alternative, and aim for the development of a technique that allows the denoising of the originally low S/N (typically, below 80) spectroscopic data, making observations of faint targets with small telescopes possible and effective. Methods. We present a generalization of the original least-squares deconvolution (LSD) method by implementing a multicomponent average profile and a line strengths correction algorithm. We tested the method on simulated and real spectra of single and binary stars, among which are two intrinsically variable objects. Results. The method was successfully tested on the high-resolution spectra of Vega and a Kepler star, KIC 04749989. Application to the two pulsating stars, 20 Cvn and HD 189631, showed that the technique is also applicable to intrinsically variable stars: the results of frequency analysis and mode identification from the LSD model spectra for both objects are in good agreement with the findings from literature. Depending on the S/N of the original data and spectral characteristics of a star, the gain in S/N in the LSD model spectrum typically ranges from 5 to 15 times. Conclusions. The technique introduced in this paper allows an effective denoising of the originally low S/N spectroscopic data. The high S/N spectra obtained this way can be used to determine fundamental parameters and chemical composition of the stars. The restored LSD model spectra contain all the information on line profile variations present in the original spectra of pulsating stars, for example. The method is applicable to both high-(>30 000) and low-(<30 000) resolution spectra, although the information that can be extracted from the latter is limited by the resolving power itself.

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Section: Discussionmentioning

confidence: 99%

Denoising spectroscopic data by means of the improved least-squares deconvolution method

Tkachenko

Reeth

Tsymbal

et al. 2013

A&A

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“…Piskunov & Kochukhov 2002;Kochukhov & Sudnik 2013). To check for spectral variability we have complemented our HARPS observations with highresolution (R ∼ 50 000) spectra from the IACOB (Simón-Díaz et al 2011aSimón-Díaz & Herrero 2014) and OWN (Barbá et al 2010) surveys.…”

Section: Radial Velocities and Line Profile Variationsmentioning

confidence: 99%

B fields in OB stars (BOB). Detection of a strong magnetic field in the non-peculiar O9.7V star HD 54879

Castro

Fossati

Hubrig

et al. 2015

A&A

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The number of magnetic stars detected among massive stars is small; nevertheless, the role played by the magnetic field in stellar evolution cannot be disregarded. Links between line profile variability, enhancements/depletions of surface chemical abundances, and magnetic fields have been identified for low-mass B-stars, but for the O-type domain this is almost unexplored. Based on FORS 2 and HARPS spectropolarimetric data, we present the first detection of a magnetic field in HD 54879, a single slowly rotating O9.7 V star. Using two independent and different techniques we obtained the firm detection of a surface average longitudinal magnetic field with a maximum amplitude of about 600 G, in modulus. A quantitative spectroscopic analysis of the star with the stellar atmosphere code  results in an effective temperature and a surface gravity of 33 000 ± 1000 K and 4.0 ± 0.1 dex. The abundances of carbon, nitrogen, oxygen, silicon, and magnesium are found to be slightly lower than solar, but compatible within the errors. We investigate line-profile variability in HD 54879 by complementing our spectra with spectroscopic data from other recent OB-star surveys. The photospheric lines remain constant in shape between 2009 and 2014, although Hα shows a variable emission. The Hα emission is too strong for a standard O9.7 V and is probably linked to the magnetic field and the presence of circumstellar material. Its normal chemical composition and the absence of photospheric line profile variations make HD 54879 the most strongly magnetic, non-variable single O-star detected to date.

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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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Detectability of small-scale magnetic fields in early-type stars

Cited by 33 publications

References 47 publications

Denoising spectroscopic data by means of the improved least-squares deconvolution method

Denoising spectroscopic data by means of the improved least-squares deconvolution method

B fields in OB stars (BOB). Detection of a strong magnetic field in the non-peculiar O9.7V star HD 54879

Calibrating and stabilizing spectropolarimeters with charge shuffling and daytime sky measurements

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