Peculiarity Parameters

1976 ◽  
Vol 32 ◽  
pp. 233-254
Author(s):  
H. M. Maitzen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Theoretical Work ◽  
Observational Evidence ◽  
Rotator Model ◽  
Peculiar Behaviour ◽  
Field Spectrum ◽  
Oblique Rotator ◽  
Ap Stars ◽  
The Way

Ap stars are peculiar in many aspects. During this century astronomers have been trying to collect data about these and have found a confusing variety of peculiar behaviour even from star to star that Struve stated in 1942 that at least we know that these phenomena are not supernatural. A real push to start deeper theoretical work on Ap stars was given by an additional observational evidence, namely the discovery of magnetic fields on these stars by Babcock (1947). This originated the concept that magnetic fields are the cause for spectroscopic and photometric peculiarities. Great leaps for the astronomical mankind were the Oblique Rotator model by Stibbs (1950) and Deutsch (1954), which by the way provided mathematical tools for the later handling pulsar geometries, anti the discovery of phase coincidence of the extrema of magnetic field, spectrum and photometric variations (e.g. Jarzebowski, 1960).

A Study of Line Profiles in The Oblique Rotator Model and a Comparison with the Ap Star B Coronae Borealis.

1976 ◽  
Vol 32 ◽  
pp. 611-612
Author(s):  
R. Freedman
Keyword(s):  
Magnetic Field ◽  
Polarized Light ◽  
Line Profiles ◽  
Circularly Polarized Light ◽  
Rotator Model ◽  
Oblique Rotator ◽  
Left And Right ◽  
Effects Of Rotation ◽  
Ap Stars ◽  
The Magnetic Field

A study was made of line profiles in left and right circularly polarized light for the Ap stars βCrB. The model adopted for the surface configuration of the magnetic field was that of Wolff and Wolff (1970) who used an oblique rotator offset along the axis of the dipole field. The line profiles were calculated in pure absorption using the method of Rachovsky (1969). Allowance was made for the depth dependence of all relevant physical variables, arbitrary angles of the magnetic field, and the effect of anomalous dispersion. The elements studied were Ce II, Gd II, Mn I and Fe I. In general, weak, unsaturated lines were chosen for analysis. The final profiles were corrected for the effects of rotation.

scholarly journals Magnetic Braking and the Oblique Rotator Model

1970 ◽  
Vol 4 ◽  
pp. 269-273
Author(s):  
L. Mestel ◽  
C. S. Selley
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Stellar Wind ◽  
Rotation Axis ◽  
Dynamical Evolution ◽  
Magnetic Star ◽  
Rotator Model ◽  
Oblique Rotator ◽  
Magnetic Braking

This work investigates the dynamical evolution of a rotating magnetic star which drives a stellar wind. The basic magnetic field of the star is supposed symmetric about an axis, which is inclined at an angle X to the rotation axis k (Figure 1). We adopt the familiar equations of an inviscid perfectly conducting gas. In a steady state, the velocity as seen in a frame rotating with the star is taken as

scholarly journals Doppler Images of Rapidly Rotating Ap Stars

1988 ◽  
Vol 132 ◽  
pp. 199-204
Author(s):  
Artie P. Hatzes
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Stellar Surface ◽  
Surface Distribution ◽  
Distribution Of Elements ◽  
Local Equivalent ◽  
Field Geometry ◽  
A New Technique ◽  
Ap Stars

The magnetic Ap stars are characterized by the presence of large magnetic fields which undergo periodic variations. These magnetic field variations are accompanied by spectral variations caused by the inhomogeneous distribution of elements on the stellar surface. It is believed that the magnetic field plays an important role in determining this distribution. Accurate maps of the surface distribution of elements would provide valuable probes as to the field geometry as well as provide clues to the role of the magnetic fields in the atmospheres of these stars. We have developed a new technique for mapping the local equivalent width on a stellar surface from the observed spectral line variations.

scholarly journals Magnetic fields of rapidly oscillating Ap stars

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.

scholarly journals Magnetic Field and Silicon diffusion in Bp-Si Stars

1988 ◽  
Vol 132 ◽  
pp. 329-332
Author(s):  
C. Mégessier ◽  
T. Lanz ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Zeeman Splitting ◽  
Open Clusters ◽  
Stellar Surface ◽  
Line Profiles ◽  
Abundance Distribution ◽  
Rotator Model ◽  
Oblique Rotator ◽  
Silicon Diffusion

SiII lines of magnetic Bp-Si stars in open clusters have been observed with the CAT (ESO) in order to get a mapping of the Silicon abundance distribution over the stellar surface, in the frame of the oblique rotator model. We point out the influence of the Zeeman splitting and of the abundance inhomogeneities on the line profiles.

scholarly journals Some Properties of Magnetic Variables

1971 ◽  
Vol 15 ◽  
pp. 59-62 ◽  
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.

scholarly journals The Heterogeneity of Surfaces of Magnetic AP Stars

1977 ◽  
Vol 4 (2) ◽  
pp. 389-394
Author(s):  
M. Hack
Keyword(s):  
Magnetic Field ◽  
Radial Velocity ◽  
Line Intensity ◽  
Velocity Variation ◽  
Field Variation ◽  
Crossover Effect ◽  
Oblique Rotator ◽  
Magnetic Stars ◽  
Ap Stars ◽  
Light Variability

AbstractThe observations of spectrum-variability and light-variability of Ap stars are reviewed. It is shown that these variations are interpretable as due to the changing aspect of the spotted surface as the star rotates. It is stressed that we understand fairly well the geometry of the phenomenon but the physics is very far from being understood.Magnetic Ap stars are probably those where the presence of a spotted surface is very evident. Their spectrum-variability (profiles, line-intensity and radial velocity), light-variability and magnetic field variability, all occurring with the same period, are explained in a simple way if we assume that these variations are due to the changing aspect of the spotted surface as the star rotates. The oblique rotator model was proposed by Babcock in 1949 and by Stibbs in 1950 and was worked out in great detail by Deutsch (1954). This model allows us to explain the magnetic field variation from some + 1000 to some - 1000 gauss in a few days; it explains the crossover effect, the line-width versus period relations, the line - intensity and radial velocity variation, and in part also the light curves. The main objection against the oblique rotator hypothesis was the supposed existence of many irregularly variable magnetic stars. However, the large number of observations accumulated in the last twenty years indicates that probably all magnetic Ap spectrum-variables are regular variables with periods which are generally of a few days, but includes a small group of long period variables (100 days up to 23 years for HD 9996). The light variability, which is the quantity measurable with the highest precision, has often remained undetected, because the amplitude is always small, in many cases few hundreths of magnitude.

scholarly journals Pulsation of Rotating Magnetic Stars

1993 ◽  
Vol 139 ◽  
pp. 134-134
Author(s):  
H. Shibahashi ◽  
M. Takata
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Magnetic Fields ◽  
Rotation Axis ◽  
Dipole Field ◽  
Dipole Mode ◽  
Magnetic Stars ◽  
Ap Stars ◽  
The Magnetic Field ◽  
Split Frequency

Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of obliquely rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We suppose that the star is rigidly rotating and that the magnetic field is a dipole field and its axis is oblique to the rotation axis. We treat the effects of the rotation and of the magnetic field as perturbations. In doing so, we suppose that the rotation of the star is slow enough so that the effect of the rotation on oscillations is smaller than that of the magnetic field.

The Ultraviolet Variations of ι Cas

1976 ◽  
Vol 32 ◽  
pp. 589-602
Author(s):  
M.R. Molnar ◽  
A.D. Mallama ◽  
D.G. Soskey ◽  
A.V. Holm
Keyword(s):  
Ultraviolet Light ◽  
Variable Star ◽  
Great Circle ◽  
Light Curves ◽  
Primary Minimum ◽  
Axis Of Rotation ◽  
Rotator Model ◽  
Oblique Rotator ◽  
Magnetic Dipole Field ◽  
Ap Stars

SummaryThe Ap variable star ι Cas was observed with the photometers on OAO-2 covering the spectral range λλ 1430-4250. The ultraviolet light curves show a double wave with primary minimum and maximum at ϕ = 0.00 and 0.35, respectively. Secondary minimum light is at ϕ = 0.65 with secondary maximum at ϕ = 0.85. The light curves longward of λ3150 vary in opposition to those shortward of this “null region”.Ground-based coude spectra show that the Fe II and Cr II line strengths have a double-wave variation such that maximum strength occurs at minimum ultraviolet light. We suggest that the strong ultraviolet opacities due to photoionization and line blanketing by these metals may cause the observed photometric variations.We have also constructed an oblique-rotator model which shows iron and chromium lying in a great circle band rather than in circular spots. These elements have been observed to lie in bands along the magnetic equator in several other Ap stars such as α2CVn, HD 173650, and 108 Aqr. Thus, we predict that the inclination of the magnetic dipole field with respect to the axis of rotation is about 84°.

The Influence of Light Variations on the Stellar Magnetic Fields Measurements

1976 ◽  
Vol 32 ◽  
pp. 441-448
Author(s):  
F.A. Catalano ◽  
G. Strazzulla
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radiation Field ◽  
Polarity Reversal ◽  
Effective Magnetic Field ◽  
Surface Field ◽  
Oblique Rotator ◽  
Inclination Angles ◽  
Stellar Magnetic Fields

SummaryIn the frame of the oblique rotator the radiation field is assumed to depend on the magnetic colatitude. Introducing this dependence in the effective magnetic field formula, a new expression for this has been derived.The calculations carried out in the case of a dipolar surface field having a polar intensity of 104gauss show that the amplitude of the variation and the polarity reversal both depend on the combination of the obliquity and inclination angles.

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