Upon the Separation of the Spectral Lines of Thorium in the Magnetic Field

AbstractBroadband linear polarization in the spectra of Ap stars is believed to be due to differential saturation between σ and π Zeeman components in spectral lines. This mechanism has been known for a long time to be the main agent of a similar phenomenon observed in sunspots. Since this phenomenon has been carefully calibrated in the solar case, it can be confidently used to deduce the magnetic field of Ap stars.Given the magnetic configuration of a rotating star, it is possible to deduce the broadband polarization at any phase. Calculations performed for the oblique dipole model show that the resulting polarization diagrams are very sensitive to the values of i (the angle between the rotation axis and the line of sight) and β (the angle between the rotation and magnetic axes). The dependence on i and β is such that the four-fold ambiguity typical of the circular polarization observations ((i,β), (β,i), (π-i,π-β), (π-β,π-i)) can be removed.

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The magnetic field of β Cep and the Be phenomenon

International Astronomical Union Colloquium ◽

10.1017/s0252921100056074 ◽

2000 ◽

Vol 175 ◽

pp. 324-329 ◽

Cited By ~ 10

Author(s):

H.F. Henrichs ◽

J.A. de Jong ◽

J.-F. Donati ◽

C. Catala ◽

G.A. Wade ◽

...

Keyword(s):

Magnetic Field ◽

Longitudinal Magnetic Field ◽

Rotation Period ◽

Spectral Lines ◽

Be Stars ◽

Full Paper ◽

Rapid Rotation ◽

Rotator Model ◽

Maximum Field ◽

The Magnetic Field

AbstractNew circular spectropolarimetric observations of the B1 IIIe star β Cep (υsini = 25 km s−1) show a sinusoidally varying weak longitudinal magnetic field (~ 200 G peak-to-peak). The period corresponds to the 12 day period in the stellar wind variations observed in ultraviolet spectral lines. Maximum field occurs at maximum emission in the UV wind lines. This gives compelling evidence for a magnetic-rotator model for this star, with an unambiguous rotation period of 12 days.The similarity between the Hα emission phases in β Cep and in Be stars suggests that the origin of the Be phenomenon does not have to be rapid rotation: we propose that in β Cep the velocity to bring material in (Keplerian) orbit is provided by the high corotation velocity at the Alfvén radius (~10 R*), whereas in Be stars this is done by the rapid rotation of the surface. In both cases the cause of the emission phases has still to be found. Weak temporary magnetic fields remain the strongest candidate.A full paper, with results including additional measurements in June and July 1999, will appear in A & A.

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Magnetic fields of rapidly oscillating Ap stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100117099 ◽

1993 ◽

Vol 139 ◽

pp. 132-132

Author(s):

G. Mathys

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Magnetic Fields ◽

Zeeman Effect ◽

Rotation Frequency ◽

Spectral Lines ◽

Driving Mechanism ◽

Line Splitting ◽

Ap Stars ◽

The Magnetic Field

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.

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Some Properties of Magnetic Variables

International Astronomical Union Colloquium ◽

10.1017/s0252921100032693 ◽

1971 ◽

Vol 15 ◽

pp. 59-62 ◽

Cited By ~ 1

Author(s):

Karl D. Rakoš

Keyword(s):

Magnetic Field ◽

Light Curve ◽

Spectral Lines ◽

Light Curves ◽

Magnetic Pole ◽

Yellow Light ◽

The Past ◽

Oblique Rotator ◽

Ap Stars ◽

The Magnetic Field

It is certain, that the mechanism causing variations of the magnetic field and spectral lines in Ap stars must also cause variations in their luminosities. The light curves are synchronous with the magnetic variations and usually the maximum of the positive magnetic field strength coincides with the minimum of the light curve. In the past the oblique rotator theory was not able to explain easily such brightness change. There is no simple reason to suppose, that the brightness of the surface of a star would increase or decrease at one magnetic pole only. Since that time a few stars were found with some indications for secondary minima and maxima in the light curves, but the first established double wave in a light curve was recently found by H. M. MAITZEN and K. D. RAKOš in HD 125 248 (1970), see Figure 1. It is a very exciting result, only the light curve in yellow light shows two maxima and two minima. The light curves in blue and ultraviolet are very smooth and show no evidence for secondary waves.

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Measurements of local magnetic fields in a solar flare by splitting of emissive peaks in cores of spectral lines

Bulletin of Taras Shevchenko National University of Kyiv Astronomy ◽

10.17721/btsnua.2018.57.47-52 ◽

2018 ◽

pp. 47-52 ◽

Cited By ~ 1

Author(s):

V. Lozitsky

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Solar Flare ◽

Filling Factor ◽

Spectral Lines ◽

Local Fields ◽

Strong Component ◽

Component Structure ◽

Local Magnetic Fields ◽

The Magnetic Field

We present study of solar flare of 19 July 2000 which arose in active region NOAA 9087 and had M 5.6 / 3N importance. Observational material was obtained with the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. The local magnetic fields in this flare were measured by the splitting of emissive peaks of the FeI 5269.54, FeII 4923.93, Нα, Нβ, Нγand D3 HeI lines. The basic idea of the method is based on the fact that the flare emission in some spectral lines is clearly divided into two components: (1) wider and unpolarized, and (2) more narrow and polarized, with significant Zeeman splitting. This is indication to the two-component structure of the magnetic field, with substantially different magnetic fields and thermodynamical conditions in these two components. Due to the fact that the polarized emission is quite confidently separated from the unpolarized, it is possible to measure the local magnetic fields directly in the second (strong) component regardless of the filling factor. It was found that in the bright place of this flare, which was projected on the sunspot penumbra, the effective magnetic field Beff in the FeI 6301.5 i 6302.5 lines measured by splitting of the Fraunhofer profiles, was 900 G. However, the splitting of emissive peaks in Нα, Нβ, Нγ and D3 lines corresponds to 1000 G, 1400 G, 1450 G and about zero, respectively, with errors of 30-50 G for abovenamed FeI lines and about 100–150 G for other lines. This difference in the results is probably due to the fact that in the case of FeI 6301.5 i 6302.5 lines, the Beff value represents several parameters, including the value of the background field, the filling factor, and the intensity of the local fields in the strong component. In contrast, data on the Нα, Нβ, Нγ, and D3 lines mainly reflect local fields in the strong component and indicate the nonmonotonous distribution of the magnetic field with height in solar atmosphere, with its maximum at the chromospheric level. Earlier in this flare, when constructing its semi-empirical model, local amplification of the magnetic field at the photospheric level was discovered, and its value reached 1500 G. These data are confirmed by direct measurements of splitting of emissive peaks in FeI 5269.54 and FeII 4923.93 lines, according to which the magnetic field in the flare was 1250 ± 100 G. Thus, in this flare there were at least two regions (possibly two flat layers) of local amplification of the magnetic field.

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Investigations of space magnetism at the Crimean Astrophysical Observatory. II. Direct spectropolarimetric measurements of stellar magnetic fields

Acta Astrophysica Taurica ◽

10.31059/aat.vol1.iss2.pp26-36 ◽

2020 ◽

Vol 1 (2) ◽

pp. 26-36

Author(s):

Sergei Plachinda ◽

Varvara Butkovskaya

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Spectral Lines ◽

Crimean Astrophysical Observatory ◽

Scientific School ◽

Pulsation Period ◽

Echelle Spectrograph ◽

Direct Measurements ◽

Stellar Magnetic Fields ◽

The Magnetic Field

A research on stellar magnetism in Crimea was initiated by pioneer works of A.B. Severny, V.E. Stepanov, and D.N. Rachkovsky. Today, the study of stellar magnetic fields is a key field of research at the Crimean Astrophysical Observatory (CrAO). The 2.6 m Shajn telescope equipped with the echelle spectrograph ESPL, CCD, and Stokesmeter (a circular polarization analyzer) allows us to study the magnetic field of bright stars up to 5m–6m. The Single Line (SL) technique is developed for measuring magnetic fields at CrAO. This technique is based on the calculation of the Zeeman effect in individual spectral lines. A key advantage of the SL technique is its ability to detect local magnetic fields on the surface of stars. Many results in the field of direct measurements of stellar magnetic fields were obtained at CrAO for the first time. In particular, the magnetic field on supergiants (ǫ Gem), as well as on a number of subgiants, giants, and bright giants was first detected. This, and investigations of other authors, confirmed the hypothesis that a magnetic field is generated at all the stages of evolution of late-type stars, including the stage of star formation. The emergence of large magnetic flux tubes at the surface of stars of V-IV-III luminosity classes (61 Cyg A, β Gem, β Aql) was first registered. In subgiants, the magnetic field behavior with the activity cycle was first established for β Aql. Using the long-term Crimean spectroscopic and spectropolarimetric observations of α Lyr, the 22-year variability cycle of the star, supposedly associated with meridional flows, is confirmed. Magnetic field variability with the pulsation period was first detected for different types of pulsating variables: the classical Cepheid β Aql, the low-amplitude β Cep-type variable γ Peg, and others. In this review we cover more than a half-century history of the formation of the Crimean scientific school for high-precision direct measurements of stellar magnetic fields.

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Solar image denoising with convolutional neural networks

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936069 ◽

2019 ◽

Vol 629 ◽

pp. A99 ◽

Cited By ~ 3

Author(s):

C. J. Díaz Baso ◽

J. de la Cruz Rodríguez ◽

S. Danilovic

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Spatial Coherence ◽

Principal Component ◽

Real Data ◽

Spectral Lines ◽

Solar Chromosphere ◽

Weak Signals ◽

Statistical Characterization ◽

The Magnetic Field

The topology and dynamics of the solar chromosphere are greatly affected by the presence of magnetic fields. The magnetic field can be inferred by analyzing polarimetric observations of spectral lines. Polarimetric signals induced by chromospheric magnetic fields are, however, particularly weak, and in most cases very close to the detection limit of current instrumentation. Because of this, there are only few observational studies that have successfully reconstructed the three components of the magnetic field vector in the chromosphere. Traditionally, the signal-to-noise ratio of observations has been improved by performing time-averages or spatial averages, but in both cases, some information is lost. More advanced techniques, like principal-component analysis, have also been employed to take advantage of the sparsity of the observations in the spectral direction. In the present study, we use the spatial coherence of the observations to reduce the noise using deep-learning techniques. We designed a neural network that is capable of recovering weak signals under a complex noise corruption (including instrumental artifacts and non-linear post-processing). The training of the network is carried out without a priori knowledge of the clean signals, or an explicit statistical characterization of the noise or other corruption. We only use the same observations as our generative model. The performance of this method is demonstrated on both synthetic experiments and real data. We show examples of the improvement in typical signals obtained in current telescopes such as the Swedish 1 m Solar Telescope. The presented method can recover weak signals equally well no matter what spectral line or spectral sampling is used. It is especially suitable for cases when the wavelength sampling is scarce.

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Spectropolarimetric analysis of an active region filament

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834790 ◽

2019 ◽

Vol 625 ◽

pp. A128 ◽

Cited By ~ 6

Author(s):

C. J. Díaz Baso ◽

M. J. Martínez González ◽

A. Asensio Ramos

Keyword(s):

Magnetic Field ◽

Magnetic Properties ◽

Active Region ◽

Spectral Lines ◽

Component Model ◽

Vector Magnetic Field ◽

Solar Filaments ◽

Magnetic Filed ◽

The Magnetic Field

Aims. The determination of the magnetic filed vector in solar filaments is made possible by interpreting the Hanle and Zeeman effects in suitable chromospheric spectral lines like those of the He I multiplet at 10 830 Å. We study the vector magnetic field of an active region filament (NOAA 12087). Methods. Spectropolarimetric data of this active region was acquired with the GRIS instrument at the GREGOR telescope and studied simultaneously in the chromosphere with the He I 10 830 Å multiplet and in the photosphere Si I 10 827 Å line. As has been done in previous studies, only a single-component model was used to infer the magnetic properties of the filament. The results are put into a solar context with the help of the Solar Dynamic Observatory images. Results. Some results clearly point out that a more complex inversion had to be performed. First, the Stokes V map of He I does not show a clear signature of the presence of the filament. Second, the local azimuth map follows the same pattern as Stokes V; it appears that polarity of Stokes V is conditioning the inference to very different magnetic fields even with similar linear polarization signals. This indication suggests that the Stokes V could be dominated from below by the magnetic field coming from the active region, and not from the filament itself. This evidence, and others, will be analyzed in depth and a more complex inversion will be attempted in the second part of this series.

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Magnetosphere of Hot Jupiter HD209458b and transit absorption in lines related to the upper atmosphere

10.5194/epsc2021-88 ◽

2021 ◽

Author(s):

Ildar Shaikhislamov ◽

Maxim Khodachenko ◽

Ilya Miroshnichenko ◽

Marina Rumenskikh ◽

Artem Berezutsky

Keyword(s):

Magnetic Field ◽

Magnetic Dipole ◽

Stellar Wind ◽

Mass Loss Rate ◽

Spectral Lines ◽

Upper Atmosphere ◽

Russian Science ◽

Mhd Simulations ◽

The Magnetic Field ◽

Hot Jupiter

Using the global 3D multi-fluid HD and its extension to MHD we simulated the measured HD209458b transit absorption depths at the FUV lines, and at the NIR line (10830 &#197;) of metastable helium HeI(23S) triplet, paying attention to possible change of the absorption profiles due to the presence of planetary intrinsic magnetic field. As continuation of our previous studies of HD209458b (Shaikhislamov et al. 2018, 2020), the inclusion of the HeI(23S) line into consideration and the comparison with corresponding measurements allows to constrain the helium abundance by He/H ~ 0.02, and stellar XUV flux at 1 a.u. by FXUV ~10 erg cm2 s-1 at 1 a.u. For the first time, we studied the influence of the planetary dipole magnetic field with a model which self-consistently describes the generation of the escaping upper atmospheric flow of a magnetized hot Jupiter, formation of magnetosphere and its interaction with the stellar wind. We simulated the absorption in the most of spectral lines for which measurements have been made. MHD simulations have shown that the planetary magnetic dipole moment &#181;P = 0.61 of the Jovian value, which produces the magnetic field equatorial surface value of 1 G, profoundly changes the character of the escaping planetary upper atmosphere. The total mass loss rate in this case is reduced by 2 times, as compared to the non-magnetized planet. In particular, we see the formation of the dead- and the wind- zones around the planet with the different character of plasma motion there. The 3D MHD modelling also confirmed the previous 2D MHD simulations result of Khodachenko et al (2015) that the escaping PW forms a thin magnetodisk in the equatorial region around the planet. The significantly reduced velocity of PW at the low altitudes around the planet, and especially at the night side, results in the stronger photo-ionization of species and significantly lower densities of the corresponding absorbing elements. Altogether, the reduced velocities and lower densities result in significant decrease of the absorption at Ly&#945; (HI), OI, and CII lines, though the absorption at HeI(23S) line remains nearly the same. As it was shown in our previous papers, the dense and fast stellar wind, interacting with the escaping upper atmosphere of HD209458b, generates sufficient amount of Energetic Neutral Atoms (ENAs) to produce significant absorption in the high-velocity blue wing of the Ly&#945; line. However, according to the performed 3D MHD modelling reported here, the planetary magnetic dipole field with the equatorial surface value of Bp=1 G prevents the formation of ENAs, especially in the trailing tail. This effect opens a possibility to constrain the range of planetary magnetic field values for the evaporating hot Jupiters and warm Neptunes in the stellar-planetary systems where sufficiently strong SW is expected. The presented results fitted to the available measurements indicate that the magnetic field of HD209458b should be at least an order of magnitude less than that of the Jupiter. This conclusion agrees with the previous estimates, based on more simplified models (e.g., Kislyakova et al. 2014) and much less observational data, when only Ly&#945; absorption was considered. We believe that the application of 3D MHD models simulating the escape of upper atmospheres of hot exoplanets and the related transits at the available for measurement spectral lines, sensitive to the dynamics of planetary plasma affected by the MF, opens a way for probing and quantifying of exoplanetary magnetic fields and sheds more light on their nature. This work was supported by grant &#8470; 18-12-00080 of the Russian Science Foundation and grant &#8470; 075-15-2020-780 of the Russian Ministry of Education and Science. &#160; Khodachenko, M.L., Shaikhislamov, I.F., Lammer, H., et al., 2015, ApJ, 813, 50. Shaikhislamov, I. F., Khodachenko, M. L., Lammer, H., et al., 2018, ApJ,&#160;866(1), 47. Shaikhislamov, I. F., Khodachenko, M. L., Lammer, et al., 2020, MNRAS,&#160;491(3), 3435-3447

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