Doppler-Zeeman mapping of the rapidly rotating magnetic CP star HD 37776

Khokhlova, V. L.; Vasilchenko, D. V.; Stepanov, V. V.; Romanyuk, I. I.

doi:10.1134/1.20380

Cited by 39 publications

(72 citation statements)

References 8 publications

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“…This object is often considered to be an example of the star with a quadrupolar magnetic field structure in the literature. Indeed, Bohlender (1994) and Khokhlova et al (2000) derived quadrupolar magnetic geometry models for HD 37776 based on fitting the longitudinal field curve and Stokes V profile variation, respectively. However, using a more extensive set of phase-resolved spectropolarimetric observations, Kochukhov et al (2011) showed that the circular polarisation spectra of HD 37776 cannot be fitted with an axisymmetric quadrupolar field structure.…”

Section: He-strong Bp Star Hd 37776mentioning

confidence: 99%

Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles

Kochukhov

2015

A&A

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Information about stellar magnetic field topologies is obtained primarily from high-resolution circular polarisation (Stokes V) observations. Because of their generally complex morphologies, the stellar Stokes V profiles are usually interpreted with elaborate inversion techniques such as Zeeman Doppler imaging (ZDI). Here we further develop a new method for interpreting circular polarisation signatures in spectral lines using cumulative Stokes V profiles (anti-derivative of Stokes V). This method is complimentary to ZDI and can be applied to validate the inversion results or when the available observational data are insufficient for an inversion. Based on the rigorous treatment of polarised line formation in the weak-field regime, we show that, for rapidly rotating stars, the cumulative Stokes V profiles contain information about the spatially resolved longitudinal magnetic field density. Rotational modulation of these profiles can be employed for a simple, qualitative characterisation of the stellar magnetic field topologies. We apply this diagnostic method to the archival observations of the weak-line T Tauri star V410 Tau and Bp He-strong star HD 37776. We show that the magnetic field in V410 Tau is dominated by an azimuthal component, in agreement with the ZDI map that we recover from the same data set. For HD 37776 the cumulative Stokes V profile variation indicates the presence of multiple regions of positive and negative field polarity. This behaviour agrees with the ZDI results, but contradicts the popular hypothesis that the magnetic field of this star is dominated by an axisymmetric quadrupolar component.

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Section: He-strong Bp Star Hd 37776mentioning

confidence: 99%

Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles

Kochukhov

2015

A&A

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“…The successful comparison of the predicted and observed light curves would not be possible without using the calculations of radiative ionization cross-section done by the Opacity Project team (Seaton et al 1992). Khokhlova et al 2000) and the observed one (Adelman & Pyper 1985, Adelman 1997b) in different colours. Right: Comparison of the predicted light variations of HR 7224 (calculated using the iron and silicon surface distribution according to Lehmann et al 2000) and the observed one (Adelman 1997a) in different colours.…”

Section: Discussionmentioning

confidence: 99%

“…We do not use any free parameter to fit the observed light curves. Khokhlova et al (2000). Silicon is overabundant on the visible disc around the phase φ = 0.…”

Section: Light Curve Calculationmentioning

confidence: 99%

The mechanism of the light variability of chemically peculiar stars

et al. 2009

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Abstract. Until recently, the mechanism of the light variability of chemically peculiar (CP) stars was unclear. To improve this situation, we started a theoretical and observational campaign aimed at the nature of the light variability of these stars. We use the TLUSTY model atmospheres calculated for the appropriate surface chemical composition to obtain the emergent flux and to predict the rotationally modulated light curves. We show on example of several wellstudied CP stars that their light variations can be explained as a result of i) the uneven surface distribution of the elements (creating overabundant regions), ii) the flux redistribution from the ultraviolet to the visible part of the spectrum (in the overabundant regions), and iii) rotation of the star. We show that the silicon and helium bound-free transitions and iron bound-bound transitions provide the main contribution to the flux redistribution. This result is also a very precise test of modern stellar model atmospheres. We conclude that the mentioned mechanism is a very promising explanation for the light variations in CP stars of earlier spectral types.

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“…The surface distribution of some other chemical elements, like silicon or carbon, also displays a spotted structure, which is, as a rule, disjunct from the helium distribution (see e.g. the well-studied He-rich star HD 37776; Khokhlova et al 2000). The enhanced redistribution of radiative flux from the ultraviolet to the visible region of hot CP stars causes the presence of large bright photometric spots, usually with overabundant silicon, which is the most efficient, having plenty of bound-free transition continua in the ultraviolet (Krtička et al 2007;Krtička et al 2015).…”

Section: Spectropolarimetrymentioning

confidence: 99%

Rotationally modulated variability and pulsations of the He-rich star CPD −62°2124 with an extraordinarily strong magnetic field

Hubrig

Mikulášek

Kholtygin

et al. 2017

Monthly Notices of the Royal Astronomical Society

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A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD −62 • 2124, which has a fractional main-sequence lifetime of about 60%. Strongly magnetic early-B type chemically peculiar stars in an advanced evolutionary state are of special interest to understand the evolution of the angular momentum and spin-down timescales in the presence of a global magnetic field. We exploited 17 FORS 2 low-resolution spectropolarimetric observations and 844 ASAS3 photometric measurements for the determination of the rotation period, pulsations, and the magnetic field geometry of the star. We calculated periodograms and applied phenomenological models of photometric, spectral and spectropolarimetric variability. We found that all quantities studied, specifically equivalent widths, the mean longitudinal magnetic field B z , and the flux in the V filter, vary with the same period P = 2.628 d, which was identified as the rotation period. The observed variations can be fully explained by a rigidly rotating main-sequence star with an uneven distribution of chemical elements, photometric spots, and a stable, nearly dipolar magnetic field with a polar field strength of about 21 kG, frozen into the body of the star. The magnetic field of CPD −62 • 2124 is tilted to the rotation axis by β = 28 • ± 7 • , while the inclination of the rotation axis towards the line of sight is only i = 20 • ± 5 • . In the acquired FORS 2 spectra, we detect short-term line profile variations indicating the presence of β Cephei type pulsations. As of today, no other pulsating star of this type is known to possess such a strong magnetic field.

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Doppler-Zeeman mapping of the rapidly rotating magnetic CP star HD 37776

Cited by 39 publications

References 8 publications

Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles

Diagnostic of stellar magnetic fields with cumulative circular polarisation profiles

The mechanism of the light variability of chemically peculiar stars

Rotationally modulated variability and pulsations of the He-rich star CPD −62°2124 with an extraordinarily strong magnetic field

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