Magnetic Field Observations of the Ap Star γ Equ

Further investigations of the Ap star γ Equ (SCHOLZ , 1975) showed that a very slow variation of the longitudinal magnetic field exists, with a change of sign in the years 1970/1971. In three spectrograms obtained near of the crossover points of the longitudinal magnetic field hints are given at the presence of a transversal magnetic field of about 3500 Gauß. The radial velocity measurements show no definitive variations.     

The binary nature of the Ap star 53 Cam

The radial velocities of the Ap star 53 Cam = HD 65339 show a longtime variation corresponding to a binary motion. For the elements of the binary system the following values were derived: K = 8km/s, γ = -2.2 km/s, P = 2380 days. e = 0.56, ω = 10°, and a · sin i = 22 · 10⁷ km. A second period of about 1850 days is indicated but this value seems to be a spurious period. Investigations of ZEEMAN spectrograms made by several authors gave a magnetic period of a bout 8 days. This period, interpreted as rotational period of the star, obviously differs a little for various observational times depending on the position in the binary orbit; so that the period is smaller at the time of the apastron passage. At present it is not possible to decide wheter this behaviour – if real – preponderantly reflects changes of the velocity of rotation or of the magnetic field. Furthermore the radial velocities show a dependence on the state of ionization of the elements in such a way that evidently lines from neutral elements have larger radial velocities (absolute values) than those of the ionized elements. These differences also depend on the position in the binary orbit as mentioned for the magnetic periods.     

Spektrographische Untersuchungen des magnetischen Sterns α2CVn

The main purpose of this paper was the examination of the Cassegrain-spectrograph of the 2-m-universaltelescope at Tautenburg for investigations of magnetic stars. Therefore from 26 spectrograms of the well known magnetically variable star α²CVn taken with a reciprocal linear dispersion of 10 Å/mm variations of radial velocity and magnetic field strength for some lines of Eu II, Cr II, Si II, Mg II were determined. The results agree well with those of Babcock [5] and Struve and Swings [2], derived from spectrograms of higher dispersion. The large variation in the radial velocity of Eu II and Cr II is confirmed. In the oblique rotator model this requires a very strong concentration of Eu II at the poles and of Cr II at the equator.     

Radial velocity and magnetic field measurements of the a-type supergiant ν cep (HD 207260)

On the basis of 55 Zeeman spectrograms obtained at Tautenburg in the years 1975–1979 the effective magnetic fields and the radial velocities of the supergiant ν Cep (HD 207260) were determined. For the effective magnetic field a slow variation occurring on a time scale of years was found. The spectrograms taken at the first time show only moderate effective magnetic field strengths of a few hundred Gauß, but in the year 1978 values of +2000 Gauß were detected. The measured radial velocities show a longtime variability similar to that of the magnetic field as well as more rapid changes. A periodical variation of the radial velocity with a period of ∼ 39.9 days, perhaps produced by the rotation of the star, is indicated. The Balmer absorption lines H_β, H_β, and H_δ have different radial velocities refering to the presence of an expanding envelope. Moreover, there exist significant differences between the velocities of various elements respectively ions of 1–4 km/s.     

Self-excitation of motions in near-convection zones and the generation of solar magnetic field

In view of the recently discovered time variations in rotation velocity within the solar differentially rotating tachocline (Howe et al. 2000), we study conditions for the equilibrium and excitation of motions in nonrigidly rotating magnetized layers of the radiative zones located near the boundaries of the convection zone. The emphasis is on the possible relationship between quasi-periodic tachocline pulsations and the generation of a nonaxisymmetric magnetic field in the convection zone. This field generation is studied under the assumption that it results from a reduction in the expenditure of energy on convective heat transport. The (antisymmetric about the equator) field is shown to increase in strength if there are both a radial gradient in angular velocity and steady-state axisymmetric meridional circulation of matter. The sense of circulation is assumed to change (causing the sign of the generated field to change) after the maximum permissible field strength is reached. This is apparently attributable to the excitation of the corresponding turbulent viscosity of the medium. It is also important that the cyclic field variations under discussion are accompanied by variations in solar-type dipole magnetic field.     

Spectroscopic investigations of the magnetic Ap star HD 9996

Spectroscopic measurements of the Ap star HD 9996 yielded the radial velocity and the strength of the effective magnetic field. From the reversal of the magnetic field periods smaller than 4.92 years can be excluded. We cannot state an exact period, but a value of 20.60 years seems to be the most probable one. Further we find hints at a short period of about 1.8 days for the variations in the radial velocities as well as in the magnetic field strengths. The elements of the binary motion were derived.     

The magnetic field variation of the Ap star HR 465

The magnetic field of HR 465 varies with a period of 23.3 yr. The number and intensity of the absorption lines show their extrema at the times of the cross-over points of the magnetic field in contrast to the phase relation of these quantities known for most short-time magnetic Ap stars. Apart from the variations produced by the binary motion no further general velocity changes were found. The radial velocity determined by lines of the neutral elements differ somewhat significantly from those of the ionized elements. The interpretation causes difficulties in all discussed models; a precession model seems to be a little more favourable than a rigid-rotator or alternating dynamo model.     

The proton temperature and the total hourly variance of the magnetic field components in different solar wind speed regions

A comparison has been made between the predictions of the theory for radial variations of both Alfvénic fluctuations and solar wind proton temperatures proposed by Tu (1987, 1988) and the statistical results of hourly averaged plasma and magnetic field data observed by Helios 1 and 2 from launch through 1980 for different solar wind speed regimes. The comparison shows that for speed ranges between 500–800 km s^-1, the radial variation of the proton temperature between 0.3 and 1 AU can be explained by heating from the cascade energy determined by the radial variation of the total variance of magnetic field vector. The explanation of the radial variations of both temperature and the total variance of magnetic fields for speed ranges less than 400 km s ^-1 is less clear.This project was supported by National Natural Science Foundation of China for Tu's part of the work.     

Multiparameter Computations of Solar Wind Characteristics in the Near-Earth Space from the Data on the Solar Magnetic Field

The solar wind parameters were analyzed using the concept which is being developed by the authors and assumes the existence of several systems of magnetic fields of different scales on the Sun. It was demonstrated that the simplest model with one source surface and a radial expansion does not describe the characteristics of the quiet solar wind adequately. Different magnetic field subsystems on the Sun affect the characteristics of the solar wind plasma in a different way, even changing the sign of correlation. New multiparameter schemes were developed to compute the velocity and the magnetic field components of the solar wind. The radial component of the magnetic field in the solar corona and the tilt of the heliospheric current sheet, which determines the degree of divergence of field lines in the heliosphere, were taken into account when calculating the magnetic field in the solar wind. Both the divergence of field lines in the corona and the strength of the solar magnetic field are allowed for in calculating the solar wind speed. The suggested schemes provide a considerably higher computation accuracy than that given by commonly used one-parameter models.     

High Effective Magnetic Field Strengths of the Magnetic Star 53 Camelopardalis

New measurements of the effective magnetic field strengths of 53 Cam yield essentially higher values than formerly published measurements. Three ZEEMAN -spectrograms yielded for the magnetic field +6800, – 11400 and – 7500 Gauß at the phases 0.17, 0.75 and 0.87 cycles after the positive crossover.     

A Spectrographic Study of the Shell Star EW Lac (217050)

Investigation of 38 Zeeman spectrograms of the Be star EW Lac obtained in three successive years, 1978, 1979, and 1980, yield no hints at the occurrence of a global magnetic field larger than 150 Gauß. The temporal variations of the radial velocities of the Balmer and metallic absorption lines indicate a disturbance travelling through the envelope of EW Lac from the inner to the outer parts. The observed variations of the line widths and equivalent widths of the metallic lines suggest that the physical parameters remarkable change. These results together with the measured variations of the radial velocity and intensity of the emission features of H_β can be explained by a thick elliptical ring surrounding EW Lac.     

The magnetic field and rotational period of 53 Camelopardalis

The magnetic Ap star 53 Cam has been described as the best object for testing theories of elemental diffusion in the presence of a stellar magnetic field. It is thus vital to determine the rotational period of this very important star as accurately as possible. An improved period (8.026 81±0.000 04 d) is derived here by combining new measurements of the effective magnetic field with previously published values.     

Dynamics of an ensemble of clumps embedded in a magnetized ADAF

We investigate the effects of a global magnetic field on the dynamics of an ensemble of clumps within a magnetized advection-dominated accretion flow by ignoring interactions between the clumps and then solving the collisionless Boltzman equation.In the strong-coupling limit,in which the averaged radial and rotational velocities of the clumps follow dynamics described by an Advection-Dominated Accretion Flow(ADAF),the root mean square radial velocity of the clumps is calculated analytically for different magnetic field configurations.The value of the root mean square radial velocity of the clumps increases by increasing the strength of the radial or vertical components of the magnetic field,but a purely toroidal magnetic field geometry leads to a reduction in the value of the root mean square radial velocity of the clumps in the inner parts by increasing the strength of this component.Moreover,dynamics of the clumps strongly depend on the amount of advected energy so that the value of the root mean square radial velocity of the clumps increases in the presence of a global magnetic field as the flow becomes more advective.     

Line variability in the spectrum of supergiant α Cam

CCD spectra taken with the PFES and CEGS echelle spectrographs attached to the 6-m Special Astrophysical Observatory (Russian Academy of Sciences) telescope and the 2-m Shamakha Astrophysical Observatory (National Academy of Sciences of Azerbaijan) telescope, respectively, were used to study the line-profile variations in the spectrum of the hot supergiant α Cam. No fast (≤1.5 h) line-profile and radial-velocity variations were found. Some of the systematic effects that cause spurious variability are considered. The Hα-profile variability appears symmetric relative to the radial velocity of the star’s center of mass and is attributable to variable blueshifted and redshifted emission and/or absorption components superimposed on a variable photospheric profile. The Hα line shows evidence of a large-scale mass ejection from the stellar surface, which is also traceable in other spectral lines. The He II 4686 line exhibits an inverse P Cyg profile, while the red wing of the He I 5876 line shows weak and variable emission. The fast (on characteristic time scales of shorter than an hour) variability of the He II 4686 profile that was previously revealed by our observations (Kholtygin et al. 2000) is called into question. A comparison of the observational data on the variability of ultraviolet and optical line profiles for the supergiant αCam suggests that nonradial motions are mainly responsible for the radial-velocity and line-profile variability.     

MHD simulations of rayleigh-taylor instability in young supernova remnants

Radio observations shows that young supernova remnants such as Tycho and Cas A generally exhibit a circular clumpy shell. This shell shows a radial magnetic field whose equipartition strength is 2 to 3 orders of magnitude higher than the interstellar field. A simple compression of the ambient field by the shock can explain neither of these observations. We show that the Rayleigh-Taylor instability which occurs at the ejecta/ISM interface can explain these observations. We have done MHD simulations of the instability in the shell of Type-I supernova remnants for the first time by utilizing moving grid technique. Our simulation shows that Rayleigh-Taylor and Kelvin-Helmholtz instabilities amplify ambient magnetic fields locally and produce the clumpy radio shell. Strong magnetic field lines draped around the Rayleigh-Taylor fingers produce the radial B-vector polarization, whereas thermal bremsstrahlung from the dense fingers themselves produce the clumpy X-ray emission.     

The radial velocity variations of certainOii,Siiii, andNii lines — A confirmation of the shell ejection in the P cygni stellar wind

The radial velocity variations of the components of someOii, Siiii, andNii lines in P Cyg spectrum are investigated during the period 1981–1983. All data are analyzed in terms of a model which implies a multiple ejection of shells in the stellar wind. It is shown that the observed phenomenon is not periodic, but it occurs on a time-scale between 110 and 160 days with the most frequently observed length of the cycle of about 110 days. The shells move away from the star with an acceleration that is greater at low velocities than at high ones. The radial velocity variations ofOii, Siiii, andNii lines agree with these of hydrogen lines if we assume velocity and excitation condition differences inside the shell.     

Production of pulses and interpulses in pulsars

Pulsars accelerate the charged particles moving along their magnetic field lines due to their rapidly spinning motion. Particles gain maximum energy from pulsars within the light cylinder when they are moving along the field lines perpendicular to the rotation velocity. In pulsars with non-aligned rotation and magnetic axes, the production of two intense and sharp pulses (main pulse and interpulse) separated by 180° longitude occur at the two regions near the light cylinder where the rotation velocity is perpendicular to the magnetic field. Since the radiating particles move radially along the relativistically compressed magnetic field lines, the observer in the stationary frame receives beamed and transversely compressed radiation pulse. Near the light cylinder position angle varies smoothly during pulsar rotation in a way as Radhakrishnan and Cook (1969) expect its variation near the magnetic pole, as the field lines experience relativistic compression in the direction of rotation. The motion of two charge species along the field lines produce orthogonal modes at each pulse longitude.     

The binary system 53 Cam

The orbital elements of the spectroscopic binary 53 Cam were revised using 136 radial velocity measurements. The positions in the vicinity of the periastron predicted for the secondary under the assumption of the spectroscopic orbital elements do not agree with those found by speckle interferometric observations. Nevertheless, we try to estimate the mass of the secondary and the dimensions of the binary system.     

Radial velocity measurements of the spectra of Zeta Aurigae outside eclipses

Radial velocities of both components of Zeta Aurigae have been measured on 39 grating spectra obtained in the interval February 1970-November 1981.The evaluation of the orbital elements of the primary component confirmed, the elements observed so far. The velocity variation of the secondary component has been determined according to the method described by Popper (1961) yieldingK _B=30.57±5.97 (m.e.) km s^–1. The masses of the components were found to beM _K sin³ i=6.4±1.7 andM _B sin³ i=4.5±0.9 solar masses. With the elements obtained a radial velocity curve of the B-star has been calculated. Comparison of the radial velocities derived from the hydrogen lines of the B-star with the calculated radial velocity curve shows systematic deviations which indicate that these lines originate partly in an expanding circumstellar envelope of the system. The main constituent of the envelope must be neutral hydrogen of high density. Variations of the radial velocities indicate density variations due to condensations inside this envelope.     

Vertical Chromium Distribution in the Atmospheres of CP Stars. II. Modeling

Vertical chromium distributions in the atmospheres of several Ap and Am stars are fitted using detailed modeling of the profiles of CrII lines. The vertical distributions obtained for Ap stars are consistent with Babel's results of an investigation of Cr lines in the spectrum of the Ap star 53 Cam. It is shown that the observational data cannot be interpreted in terms of the hypothesis that microturbulent velocity varies with depth.