Magnetic field measurements of CP stars from hydrogen line cores

Kudryavtsev, D. O.; Romanyuk, I. I.

doi:10.1002/asna.201111588

Cited by 20 publications

(18 citation statements)

References 17 publications

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“…As a matter of fact, the quadratic field of HD 125248 varies between ∼ 8 and ∼ 11 kG (see Table B.1). The longitudinal field of HD 184471 is only marginally weaker, with extrema of −0.1 and +0.9 kG (Kudryavtsev & Romanyuk 2012). We obtained one AURELIE spectrum of this star in May 1993, where the line Fe ii λ 6149.2 shows incipient resolution.…”

Section: Referencesmentioning

confidence: 92%

Ap stars with resolved magnetically split lines: Magnetic field determinations from StokesIandVspectra

Mathys

2017

A&A

111

232

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Aims. We present the results of a systematic study of the magnetic fields and other properties of the Ap stars with resolved magnetically split lines. Methods. This study is based on new measurements of the mean magnetic field modulus, the mean longitudinal magnetic field, the crossover, the mean quadratic magnetic field, and the radial velocity of 43 stars, complemented by magnetic data from the literature for 41 additional stars. Results. Stars with resolved magnetically split lines represent a significant fraction, of the order of several percent, of the whole population of Ap stars. Most of them are genuine slow rotators, whose consideration provides new insight into the long-period tail of the distribution of the periods of the Ap stars. Emerging correlations between rotation periods and magnetic properties provide important clues for the understanding of the braking mechanisms that have been at play in the early stages of stellar evolution. The geometrical structures of the magnetic fields of Ap stars with magnetically resolved lines appear in general to depart slightly, but not extremely, from centred dipoles. However, there are a few remarkable exceptions, which deserve further consideration. We suggest that pulsational crossover can be observed in some stars; if confirmed, this would open the door to the study of non-radial pulsation modes of degree ℓ too high for photometric or spectroscopic observations. How the lack of short orbital periods among binaries containing an Ap component with magnetically resolved lines is related with their (extremely) slow rotation remains to be fully understood, but the very existence of a correlation between the two periods lends support to the merger scenario for the origin of Ap stars.

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Section: Referencesmentioning

confidence: 92%

Ap stars with resolved magnetically split lines: Magnetic field determinations from StokesIandVspectra

Mathys

2017

A&A

111

232

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“…The atmospheric structure of roAp stars is very complex, showing horizontal and vertical variations of chemical elements and possible gradients of the magnetic field intensity. These properties have been studied in a number of works (Nesvacil et al 2004;Shulyak et al 2009;Kochukhov et al 2009;Shulyak et al 2010;Kudryavtsev & Romanyuk 2012;Nesvacil et al 2013). In general, these studies showed that, although the atmospheric structure deviates systematically from that of normal stars, it is not particularly anomalous in the sense that it can still be approximated by a steep temperature decline followed by roughly isothermal upper layers.…”

Section: Massmentioning

confidence: 99%

A theoretical tool for the study of radial velocities in the atmospheres of roAp stars

Quitral-Manosalva

Cunha

Kochukhov

2018

Monthly Notices of the Royal Astronomical Society

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Over the last decade significant amounts of high-spectral and time-resolution spectroscopic data have been acquired for a number of rapidly oscillating Ap stars. Progress in the understanding of the information held by these data requires the development of theoretical models that can be directly compared with them. In this work we present a theoretical model for the radial velocities of roAp stars that takes full account of the coupling between the pulsations and the magnetic field. We explore the impact on the radial velocities of changing the position of the observer, the mode frequency and angular degree, as well as of changing the region of the disk where the elements are concentrated. We find that for integrations over the full disc, in the outermost layers the radial velocity is generally dominated by the acoustic waves, showing a rapid increase in amplitude. The most significant depth-variations in the radial velocity phase are seen for observers directed towards the equator and for even degree modes with frequencies close to, or above the acoustic cutoff. Comparison between the radial velocities obtained for spots of elements located around the magnetic poles and around the magnetic equator, shows that these present distinct amplitude-phase relations, resembling some of the differences seen in the observations. Finally, we discuss the conditions under which one may expect to find false nodes in the pulsation radial velocity of roAp stars.

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“…Although this method of deriving B z from the hydrogen lines relies on the same basic assumptions as the widely used photopolarimetric technique of Angel & Landstreet (1970), it is not equivalent to the latter method because it is applied to narrow cores of the hydrogen lines instead of the Stark-broadened wings. At the same time, our differential technique is more similar to the hydrogen line measurement approach used by Kudryavtsev & Romanyuk (2012) and Monin et al (2012).…”

Section: Longitudinal Field From the Hydrogen Line Coresmentioning

confidence: 99%

“…These features are formed significantly higher in comparison to metal lines; they are sufficiently wide and show easily measurable Stokes V signatures. Kudryavtsev & Romanyuk (2012) derived magnetic field from the Hβ core for a sample of Ap stars. Their measurements showed that for the majority of stars the mean longitudinal magnetic field determined from Hβ is significantly lower than B z obtained from the metal lines in the same spectra.…”

Section: Vertical Magnetic Field Gradientmentioning

confidence: 99%

“…Their measurements showed that for the majority of stars the mean longitudinal magnetic field determined from Hβ is significantly lower than B z obtained from the metal lines in the same spectra. Kudryavtsev & Romanyuk (2012) attributed this to the existence of a radial gradient of the magnetic field. This implies that magnetic field strength in the atmospheres of Ap stars decreases in the radial direction significantly faster than expected for a simple dipolar field topology.…”

Section: Vertical Magnetic Field Gradientmentioning

confidence: 99%

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Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712

Rusomarov

Kochukhov

Piskunov

et al. 2013

A&A

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Context. High-resolution spectropolarimetric observations provide simultaneous information about stellar magnetic field topologies and three-dimensional distributions of chemical elements. High-quality spectra in the Stokes IQUV parameters are currently available for very few early-type magnetic chemically peculiar stars. Here we present analysis of a unique full Stokes vector spectropolarimetric data set, acquired for the cool magnetic Ap star HD 24712 with a recently commissioned spectropolarimeter. Aims. The goal of our work is to examine the circular and linear polarization signatures inside spectral lines and to study variation of the stellar spectrum and magnetic observables as a function of rotational phase. Methods. HD 24712 was observed with the HARPSpol instrument at the 3.6-m ESO telescope over a period of 2010-2011. We achieved full rotational phase coverage with 43 individual Stokes parameter observations. The resulting spectra have a signal-to-noise ratio of 300-600 and resolving power exceeding 10 5 . The multiline technique of least-squares deconvolution (LSD) was applied to combine information from the spectral lines of Fe-peak and rare earth elements. Results. We used the HARPSPol spectra of HD 24712 to study the morphology of the Stokes profile shapes in individual spectral lines and in LSD Stokes profiles corresponding to different line masks. From the LSD Stokes V profiles we measured the longitudinal component of the magnetic field, B z , with an accuracy of 5-10 G. We also determined the net linear polarization from the LSD Stokes Q and U profiles. Combining previous B z measurements with our data allowed us to determine an improved rotational period of the star, P rot = 12.45812 ± 0.00019 d. We also measured the longitudinal magnetic field from the cores of Hα and Hβ lines. The analysis of B z measurements showed no evidence for a significant radial magnetic field gradient in the atmosphere of HD 24712. We used our B z and net linear polarization measurements to determine parameters of the dipolar magnetic field topology. We found that magnetic observables can be reasonably well reproduced by the dipolar model, although significant discrepancies remain at certain rotational phases. We discovered rotational modulation of the Hα core and related it to a non-uniform surface distribution of rare earth elements.

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Magnetic field measurements of CP stars from hydrogen line cores

Cited by 20 publications

References 17 publications

Ap stars with resolved magnetically split lines: Magnetic field determinations from StokesIandVspectra

Ap stars with resolved magnetically split lines: Magnetic field determinations from StokesIandVspectra

A theoretical tool for the study of radial velocities in the atmospheres of roAp stars

Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712

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