Pulsation in the atmosphere of the roAp star HD 24712

Ryabchikova, T. A.; Sachkov, Mikhail; Weiß, W. W.; Kallinger, T.; Kochukhov, O.; Bagnulo, S.; Ilyin, I.; Landstreet, J. D.; Leone, F.; Curto, G. Lo; Lüftinger, T.; Lyashko, D.; Magazzù, A.

doi:10.1051/0004-6361:20066365

Cited by 57 publications

(90 citation statements)

References 29 publications

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“…These measurements agree closely with the results obtained for the same stars at other telescopes (e.g. Ryabchikova et al 2007;Ilyin 2012). Repeated observations of a very slowly rotating Ap star γ Equ reveals no systematic differences in the Stokes V profiles during the entire period of our observations of II Peg.…”

Section: Spectropolarimetric Observationssupporting

confidence: 91%

Magnetic field topology of the RS CVn star II Pegasi

Kochukhov

Mantere

Hackman

et al. 2013

A&A

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Context. The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of cool stars magnetic field topologies were reconstructed from the time series of spectropolarimetric observations using the Zeeman Doppler imaging (ZDI) method, often yielding surprising and controversial results. Aims. In this study we follow a long-term evolution of the magnetic field topology of the RS CVn binary star II Peg using a more self-consistent and physically more meaningful modelling approach compared to previous ZDI studies. Methods. We collected high-resolution circular polarisation observations of II Peg using the SOFIN spectropolarimeter at the Nordic Optical Telescope. These data cover 12 epochs spread over 7 years, comprising one of the most comprehensive spectropolarimetric data sets acquired for a cool active star. A multi-line diagnostic technique in combination with a new ZDI code is applied to interpret these observations. Results. We have succeeded in detecting clear magnetic field signatures in average Stokes V profiles for all 12 data sets. These profiles typically have complex shapes and amplitudes of ∼10 −3 of the unpolarised continuum, corresponding to mean longitudinal fields of 50-100 G. Magnetic inversions using these data reveals evolving magnetic fields with typical local strengths of 0.5-1.0 kG and complex topologies. Despite using a self-consistent magnetic and temperature mapping technique, we do not find a clear correlation between magnetic and temperature features in the ZDI maps. Neither do we confirm the presence of persistent azimuthal field rings found in other RS CVn stars. Reconstruction of the magnetic field topology of II Peg reveals significant evolution of both the surface magnetic field structure and the extended magnetospheric field geometry on the time scale covered by our observations. From 2004 to 2010 the total field energy drastically declined and the field became less axisymmetric. This also coincided with the transition from predominantly poloidal to mainly toroidal field topology. Conclusions. A qualitative comparison of the ZDI maps of II Peg with the prediction of dynamo theory suggests that the magnetic field in this star is produced mainly by the turbulent α 2 dynamo rather than the solar αΩ dynamo. Our results do not show a clear active longitude system, nor is there evidence of the presence of an azimuthal dynamo wave.

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Section: Spectropolarimetric Observationssupporting

confidence: 91%

Magnetic field topology of the RS CVn star II Pegasi

Kochukhov

Mantere

Hackman

et al. 2013

A&A

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“…The variability period found by Preston (1972) was confirmed by photometric observations by Wolff & Morrison (1973). Many studies of the magnetic field of HD 24712 have been carried out (Preston 1972;Brown & Landstreet 1981;Mathys 1991Mathys , 1994Mathys & Hubrig 1997;Ryabchikova et al 1997;Leone et al 2000;Wade et al 2000a;Leone & Catanzaro 2004;Ryabchikova et al 2005Ryabchikova et al , 2007. Below we will use some of these measurements for improving the rotational period of the star.…”

Section: Hd 24712mentioning

confidence: 63%

“…Spectroscopic and photometric techniques are able to provide information about the different pulsation modes and hence about the atmospheric layers at different optical depths in the stellar atmosphere. Some investigators (e.g., Ryabchikova et al 2007) have used radial velocity amplitudes of different spectral lines, which are measured from spectroscopic data, as a function of optical depth to describe the properties of pulsational waves in the atmospheric layers where these spectral lines are formed. Although this type of analysis is only possible for a few bright roAp stars, such investigations have demonstrated that for understanding the phenomenon of roAp stars a good knowledge of the vertical structure of their surface layers is essential.…”

Section: Introductionmentioning

confidence: 99%

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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“…The observations and data reduction were described by Ryabchikova et al (2007b). The spectrum was observed close to magnetic maximum, which coincides roughly with the REE spectral line intensity maximum.…”

Section: Praseodymium In the Roap Star Hd 24 712mentioning

confidence: 67%

“…HD 24 712 possesses a magnetic field with a mean magneticfield modulus B that increases from 2.5 kG at magnetic minimum to ∼3.1-3.3 kG at magnetic maximum (Ryabchikova et al 2007b). We ignore the influence of the magnetic field on atmospheric structure, based on the results of Kochukhov et al (2005) who demonstrated that the difference in temperature and gas pressure distributions between magnetic and non-magnetic model atmospheres with T eff = 8000 K does not exceed 30 K and 6%, respectively, for field strengths smaller than 5 kG.…”

Section: Programs and Model Atmospheresmentioning

confidence: 99%

Non-LTE line formation for Pr ii and Pr iii in A and Ap stars

Mashonkina¹,

Ryabchikova

Ryabtsev

et al. 2008

A&A

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Aims. Non-local thermodynamical equilibrium (non-LTE) line formation for singly-ionized and doubly-ionized praseodymium is considered for a range of effective temperatures between 7250 K and 9500 K. We evaluate the influence of departures from LTE on Pr abundance determinations and determine a distribution of the Pr abundance in the atmosphere of the roAp star HD 24 712 from a non-LTE analysis of the Pr ii and Pr iii lines. Methods. A comprehensive model atom for Pr ii/iii is presented based on the measured and the predicted energy levels, in total, 6708 levels of Pr ii and Pr iii and the ground state of Pr iv. Calculations of the Pr ii energy levels and oscillator strengths for the transitions in Pr ii and Pr iii are described.Results. The dependence of non-LTE effects on the atmospheric parameters is discussed. At T eff ≥ 8000 K, departures from LTE lead to the overionization of Pr ii and, therefore, to systematically depleted total absorption in the line and positive abundance corrections. At the lower temperatures, different lines of Pr ii may be either weakened or amplified depending on the line strength. The non-LTE effects strengthen the Pr iii lines and lead to negative abundance corrections. Non-LTE corrections grow with effective temperature for the Pr ii lines, and, in contrast, they decline for the Pr iii lines. The Pr ii/iii model atom is applied to determine the Pr abundance in the atmosphere of the roAp star HD 24 712 from the lines of two ionization stages. In the chemically uniform atmosphere with [Pr/H] = 3, the departures from LTE may explain only a small part (approximately 0.3 dex) of the difference between the LTE abundances derived from the Pr ii and Pr iii lines ( 2 dex). We find that the lines of both ionization stages are fitted for the vertical distribution of praseodymium, where the Pr enriched layer with [Pr/H] ≥ 4 exists in the outer atmosphere at log τ 5000 < −4. The departures from LTE for Pr ii/iii are strong in the stratified atmosphere and have the opposite sign for the Pr ii and Pr iii lines. The praseodymium stratification analysis of roAp stars has to be performed based on non-LTE line formation. Using the revised partition function of Pr ii and experimental transition probabilities, we determine the solar non-LTE abundance to be log (Pr/H) = −11.15 ± 0.08.

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Pulsation in the atmosphere of the roAp star HD 24712

Cited by 57 publications

References 29 publications

Magnetic field topology of the RS CVn star II Pegasi

Magnetic field topology of the RS CVn star II Pegasi

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

Non-LTE line formation for Pr ii and Pr iii in A and Ap stars

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