UBV photometry of RT Persei

Photoelectric and absolute elements of the system RT Per have been determined inU, B, andV filters. It is suggested that the primary star may be surrounded by a gaseous disk.     

Particle dynamics in reconnection field configurations

Trajectories of test particles are studied numerically in two types of reconnection magnetic field configurations, a single X-line magnetic field configuration and a tearing magnetic field configuration. Both adiabatic and nonadiabatic motions are examined, with special emphasis on net energy gain and time spent in the neutral line regions. They spend typically one characteristic gyroperiod in the X-line region and are ejected predominantly along field lines in the vicinity of the separatrix. Both adiabatic and nonadiabatic test particles in the tearing-type field configuration are channelled into and accelerated along the O-line region. It may be inferred from these test particle results that particle energizations are significant along the O-line region, but not along the X-line region. These results are in qualitative agreement with those obtained by a self-consistent particle simulation.     

Magnetospheric asymmetries associated with the y-component of the IMF

Observed magnetospheric asymmetries which occur in response to the y-component of the IMF are discussed in terms of the open model of the magnetosphere. The torque which the IMF exerts on the magnetosphere about the Earth-Sun axis results in asymmetric addition of open flux tubes to the tail lobes about the noon-midnight meridian. In response an IMF-associated B_y field appears across the tail lobes. The ratio between internal and external B_y fields will generally be same as the ratio between internal and external electric fields. If the tail flux asymmetry is related to an asymmetric distribution of the field normal to the tail magnetopause then an asymmetry in tail lobe electric field and plasma populations will immediately result, as observed. If the flux asymmetry is associated with a twist in the tail then the B_y field will appear but not necessary the electric field and plasma asymmetries. Generally both effects may occur together. Simple open tail lobe models are derived which demonstrate the asymmetry effects. These represent more physically satisfactory models of the tail and its plasma populations than available hitherto, but they remain somewhat unrealistic in a number of respects. Finally, it is shown that the observed asymmetry effects on closed (auroral zone) field lines may be at least qualitatively accounted for if the cross-magnetosphere IMF-associated B_y field pervades not only the open but also the closed field line regime, as may be generally expected.     

Accurate Determination of Electron Densities in Active and Quiescent Prominences: the Mid-Infrared Advantage

We have analyzed all lines in the MIR (8 to 20 micron) spectra of a quiescent and two time-frames of an active prominence. In the quiescent prominence, in addition to those lines found by Zirker (1985), we have identified a higher excitation hydrogen line and two helium recombination lines. Accounting for instrumental broadening, we can further separate out the Doppler and the Stark contributions to the line width. The former yields maximum temperatures of 6200 K, 34000 K and 12000 K and the latter electric field strengths of 7, 17, and 10 V cm^-1 for the above prominences, respectively. We show that these electric fields when divided by 2.2 are equal to the normal electric field in Holtsmark's quasi-static Stark broadening theory. Hence, we obtain electron densities of N₃=2.4(0.3), 9.1(1.2), and 5.5(0.6) in units of 10¹⁰ cm^-3 respectively. Using the same assumptions as made by Zirker, namely, (1) the strongest line (7-6) is optically thin, (2) the population of the lower level (n=6) is determined by direct radiative recombination and photo-ionization, (3) the equality of proton and electron densities, and (4) the thickness of the prominence is at least 10⁸ cm, we derive a new inequality, N_e 1.83 × 10⁸ T^0.75 e^-2195/T. Substituting our maximum temperatures into the right-hand side, we find upper bound N_e values of 9, 43, and 30 in the same units as above. These upper bound values are comfortably higher than our measurement, unlike those of Zirker's derived from the same set of assumptions. We have also observed the helium recombination spectrum which has been postulated by Tandberg-Hanssen as one of three possible ways of equilibrating the triplet/singlet ratio. Surprisingly, it is present in the quiescent as well as in the active prominence. We show that no meaningful values can be found for the turbulent velocities by combining the helium with the hydrogen line widths.     

Variability of Circumstellar Emission from Dust Envelopes Around Carbon Stars

The main constituents of the dust, produced around late-type carbon stars, are thought to be carbon and silicon carbide (SiC), although their exact nature is not yet well established. This subject has been addressed by several authors and good fits of a large number of IRAS sources (chosen among the carbon stars exhibiting the SiC feature at about 11.3 m) were obtained. In this work we use the same procedure on a limited number of objects, of the same type, taking into account the variability of such sources and the changes induced in their IR spectra. For this purpose, the chosen stars have been observed with a spectral resolution higher than that available for the IRAS data (/ 50), using the CGS3 instrument of the UKIRT telescope, both in the low ( / 160) and in the high ( / 500) resolution configuration. The results are discussed and some preliminary conclusions are drawn.     

Stellar polarization and the structure of the magnetic field of our galaxy

The stellar polarization data have been examined using a new catalogue containing accurate stellar distances. On the assumption of a magnetic alignment hypothesis, correlations on the larger distance scale indicate the existence of a dominant regular magnetic field, although its characteristics are difficult to determine. Within 500 pc its direction is towardsl45° and beyond this towardsl60°, though it is clear that such a longitudinal model is too simple. There is also some evidence for an inclination of this field to the galactic plane. The distribution of the polarization vectors away from the galactic plane has been examined and it is proposed that the two largest loop structures, previously identified as Supernova remnants, are linked by the regular field. Incremental polarization maps have been produced but they show little correlation with the spiral structure. The polarization appears to be saturated at about 1 kpc from the Sun, which is explained as the result of an observational selection effect. On the smaller distance scales an autocorrelation analysis in different directions has revealed no obvious coherence in the irregular component on scales greater than 50 pc.     

Silicon monoxide and the 10 μm interstellar feature

Laboratory spectra of SiO particles of 1 m radius show a broad structureless extinction peak at 9.6m. The wavelength dependence of extinction from SiO, an amorphous silicon oxide, provides a good match to that of interstellar dust.     

Generation of 1–30 Hz waves near the plasmapause by resonant electron-instability

A generation mechanism for 1–30 Hz waves of the second category, observed near the plasmapause by Taylor and Lyons (1976), is suggested in terms of a resonant electron instability. The instability arises because of the resonant interaction between the ring current electrons outside the plasmapause and the ordinary mode drift waves. The instability can generate waves in the frequency range from 0.45 to 35.0 Hz in the region between L = 4.5 and 5.5. The instability can also explain satisfactorily the other properties such as no changes in the proton distributions, the direction of the wave magnetic field and the localization of the region of wave activity, associated with these waves.