Magnetic field measurements of ϵ Eridani from Zeeman broadening

Lehmann, L. T.; Künstler, A.; Carroll, T. A.; Strassmeier, K. G.

doi:10.1002/asna.201412162

Cited by 25 publications

(26 citation statements)

References 38 publications

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“…This quantity is consistent with our B f , as well as Valenti et al (1995) and Rueedi et al (1997), but is much smaller than our B f and that of Valenti et al (1995). While some discrepancies between studies are likely due to systematic errors or underestimated uncertainties, the results of Lehmann et al (2015) suggest that there is also important temporal variability to the Zeeman broadening of Eridani.…”

Section: Zeeman Broadeningsupporting

confidence: 93%

“…From our multi-component model we calculate i B i f i = 542 ± 219, although this quantity is dominated by the larger field bins with small, uncertain filling factors, thus we consider it effectively an upper limit. More recently, Lehmann et al (2015) investigated Zeeman broadening in Eridani spectra spanning 5 yr, using an approach based on principal component analysis. These authors report B f values varying between 124 ± 25 and 230 ± 21 G, possibly varying with a 3-yr cycle (e.g.…”

Section: Zeeman Broadeningmentioning

confidence: 99%

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Multi-instrumental view of magnetic fields and activity of ϵ Eridani with SPIRou, NARVAL, and TESS

Petit

Folsom

Donati

et al. 2021

A&A

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Aims. We report on observations of the active K2 dwarf ϵ Eridani based on contemporaneous SPIRou, NARVAL and TESS data obtained over two months in late 2018, when the activity of the star was reported to be in a non-cyclic phase. Methods. Near-infrared (NIR) spectropolarimetry was obtained using SPIRou over four nights in late September, while visible spectropolarimetry was collected with NARVAL over 20 nights, spread between 18 September and 07 November. We first recovered the fundamental parameters of the target from both visible and NIR spectral fitting. The large-scale magnetic field was investigated from polarimetric data. From unpolarized spectra, we estimated the total magnetic flux through Zeeman broadening of magnetically sensitive NIR lines and the chromospheric emission using the CaII H&K lines. The photometric monitoring, secured with TESS between 19 October and 15 November, is modelled with pseudo-periodic Gaussian process regression. Results. Fundamental parameters of ϵ Eridani derived from visible and NIR wavelengths provide us with consistent results, which also agree with published values. We report a progressive increase of macroturbulence towards larger NIR wavelengths. Zeeman broadening of individual lines highlights an unsigned surface magnetic field Bmono = 1.90 ± 0.13 kG, with a filling factor f = 12.5 ± 1.7% (unsigned magnetic flux Bf = 237 ± 36 G). The large-scale magnetic field geometry, chromospheric emission and broadband photometry display clear signs of non-rotational evolution over the course of data collection. Characteristic decay times deduced from the light curve and longitudinal field fall in the range 30–40 days, while the characteristic timescale of surface differential rotation, as derived through the evolution of the magnetic geometry, is equal to 57 ± 5 days. The large-scale magnetic field exhibits a combination of properties not observed previously for ϵ Eridani, with a surface field among the weakest previously reported, but this field is also mostly axisymmetric, and is dominated by a toroidal component.

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Section: Zeeman Broadeningsupporting

confidence: 93%

Section: Zeeman Broadeningmentioning

confidence: 99%

Multi-instrumental view of magnetic fields and activity of ϵ Eridani with SPIRou, NARVAL, and TESS

Petit

Folsom

Donati

et al. 2021

A&A

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“…We separated the short-time variation of the effective magnetic field, due to stellar rotation, from the long-term variation through the coefficient A 0 (defined in Eq. 12); we used a Fourier transform to discover that the best-fit period of the variation of A 0 (P 1 = 1099 ± 71 d) is close to the short cycle period in the S-index found by Metcalfe et al (2013) and to the period of the magnetic field found by the analysis of the Zeeman broadening (Lehmann et al 2015). Direct measurements of the effective magnetic field thus open up the possibility to determine the periods of the cycles of active cool stars.…”

Section: Resultsmentioning

confidence: 68%

The multi-line slope method for measuring the effective magnetic field of cool stars: an application to the solar-like cycle of ε Eri

Scalia

Leone

Gangi

et al. 2017

Monthly Notices of the Royal Astronomical Society

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A method for the determination of integrated longitudinal stellar fields from lowresolution spectra is the so-called slope method, which is based on the regression of the Stokes V signal against the first derivative of Stokes I. Here we investigate the possibility to extend this technique to measure the magnetic fields of cool stars from high resolution spectra. For this purpose we developed a multi-line modification to the slope method, called multi-line slope method. We tested this technique by analysing synthetic spectra computed with the Cossam code and real observations obtained with the high resolution spectropolarimeters Narval, HARPSpol and Catania Astrophysical Observatory Spectropolarimeter (CAOS). We show that the multi-line slope method is a fast alternative to the Least Squares Deconvolution (LSD) technique for the measurement of the effective magnetic fields of cool stars. Using a Fourier transform on the effective magnetic field variations of the star ε Eri, we find that the long term periodicity of the field corresponds to the 2.95 yr period of the stellar dynamo, revealed by the variation of the activity index.

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“…It is instructive to compare the results of the spectropolarimetric modeling with the measurements of total magnetic flux from Stokes I . Such measurements, based on principal component analysis of high and low Landé‐factor Stokes I line profiles, were presented for ϵ Eridani by Lehmann et al (). Clear short‐term variations of the surface‐averaged magnetic field of up to few tens of Gauss were detected together with evidence for a 3‐year cycle (see Figure ).…”

Section: Magnetic Cycles Of Solar‐type Starsmentioning

confidence: 99%

Surface magnetism of cool stars

et al. 2017

Self Cite

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Magnetic fields are essential ingredients of many physical processes in the interiors and envelopes of cool stars. Yet their direct detection and characterization is notoriously difficult, requiring high-quality observations and advanced analysis techniques. Significant progress has been recently achieved by several types of direct magnetic field studies on the surfaces of cool, active stars. In particular, complementary techniques of field topology mapping with polarization data and total magnetic flux measurements from intensity spectra have been systematically applied to different classes of active stars, leading to interesting and occasionally controversial results. In this paper, we summarize the current status of direct magnetic field studies of cool stars and investigations of surface inhomogeneities caused by the field, based on the material presented at the Cool Stars 19 splinter session.

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Magnetic field measurements of ϵ Eridani from Zeeman broadening

Cited by 25 publications

References 38 publications

Multi-instrumental view of magnetic fields and activity of ϵ Eridani with SPIRou, NARVAL, and TESS

Multi-instrumental view of magnetic fields and activity of ϵ Eridani with SPIRou, NARVAL, and TESS

The multi-line slope method for measuring the effective magnetic field of cool stars: an application to the solar-like cycle of ε Eri

Surface magnetism of cool stars

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