The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections

We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s^-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s^-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702     

Comet P/Shoemaker-Levy 9 Collision with Jupiter: A Model of G-Site Dust Composition

Scattering models of aerosol particles at the G-impact site (18 July1994) are presented for a number of likely compositional candidates. Two differing dust particle population distribution functions are taken, along with varying aerosol cloud densities, leading to differing optical depths. A number of models including graphite, amorphous carbon, astrophysical silicate, water ice and a number of organic compounds are discussed, but no single material provides a fully satisfactory fit to the published observations. A porous silicate/graphite composite is found to provide a good fit to the spectral data. This revised version was published online in July 2006 with corrections to the Cover Date.     

A survey of nova remnants

Exnovae and nova shells are generally faint and difficult to observe. Only a few have been studied, and even less of them in sufficient detail. We give a progress report on our survey of exnovae and nova shells, especially on the results of a spectral survey of novae in the southern Milky Way. The three-dimensional structure in the light of H derived for the nebula of GK Per is displayed.Based on observations obtained at the European Southern Observatory, La Silla, Chile, and at the Centro Astronomico Hispano-Aleman Calar Alto, Spain, operated by the Max-Planck-Institut für Astronomie, Heidelberg.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Age distribution of open clusters as a function of their linear diameter and age-dependence of cluster masses

From the well-observed data of star clusters, the age distribution of galactic clusters is obtianed as a function of their linear diameter and it is concluded that the observed age distribution of clusters for different linear diameter intervals within 1500 pc, is not seriously affected by the selection effects. If we assume that the rate of formation of clusters is constant, the lifetimes _1/2 of the clusters for different linear diameter intervals have been obtained and it is found that the clusters with a linear diameter in the range 0–1.9 pc have longer lifetimes than the clusters having linear diameters larger than 2.0 pc.Total masses of 57 clusters have been obtained using the catalogues of Piskunov (1983) and Myakutinet al. (1984). A study of age-dependence of cluster masses, based on the total masses of the clusters obtained in the present study and the cluster masses given by Bruch and Sanders (1983) and Lynga (1983b), shows that there is a decreasing trend in the total mass with the age, however, there is an increasing trend after the age of about 10⁸ yr. It is also concluded that the initial rate of formation of rich clusters was relatively higher than the present rate of formation.     

Kinetic Alfvén waves in extended radio sources

We study a model of extended radio sources (ERS), in particular, extragalactic jets and radio lobes, which are inhomogeneous and where noncompressive Alfvén and surface Alfvén waves (and not shocks and magnetosonic waves) are primarily excited. We assume that a negligible thermal population exists (i.e., the ion density at the low-energy cut-off of the power law distribution is greater than the ion density of the thermal population, if present). Due to internal instabilities and/or the interaction of the ERS with the ambient medium, surface Alfvén waves (SAW) are created. We show that even very small amplitude SAW are mode converted to kinetic Alfvén waves (KAW) which produce large moving accelerating potentials , parallel to the magnetic field. Neglecting nonlinear perturbations, and for typical physical parameters of ERS, we obtaine1 MeV. Wesuggest that these potentials are important in acceleration (e.g., injection energy) and reacceleration of electrons in ERS. We show that energy losses by synchrotron radiation can be compensated by reacceleration by KAW. The relation between KAW acceleration, and previously studied cyclotron-resonance acceleration by Alfvén waves, is discussed.     

Some comments on the asymptotic limit of antiproton-proton flux ratio at the top of the atmosphere

Using the leaky-box model the upper limit of the antiproton-proton flux ratio at the top of the atmosphere has been estimated from the latest primary nucleon spectrum and accelerator data on inclusive reactions. The estimated value of flux ratio comes out to be (3.6±0.3)×10^–4 is in accord with the previous results but still far from the measurements.     

X-ray and ultraviolet observations of AG Draconis during quiescence and outburst

We describe the first X-ray monitoring of a symbiotic star during phases of enhanced activity. AG Dra is a Pop II object with a composite spectrum, characterized by a cool K-type component, prominent high ionization emission lines and a strong UV continuum which is attributed to a hot dwarf companion. Periodic variability of the UV radiation during minimum could be attributed to the orbital motion of the system. In April 1980 HEAO-2 detected an intense, soft X-ray flux from AG Dra, stronger than in other symbiotic stars. After one major outburst of November 1980, which continued until 1983, two more outbursts occurred in February 1985 and January 1986, and coordinated X-ray (EXOSAT) and ultraviolet (IUE) observations were organized to study the behaviour of AG Dra during different activity phases. EXOSAT observations made during decline after the 1985 outburst, revealed a weak X-ray flux in the Thin Lexan filter of the Low Energy dedtector. Observations made during minimum, in June and November 1985, at phases 0.22 and 0.50 of the UV light curve, disclosed the presence of an intense X-ray flux, which was not occulted in November. AG Dra was again observed with EXOSAT in February 1986 when the stellar luminosity was still at maximum. No X-ray flux was detected, in spite of the prominent, high ionization UV spectrum observed with IUE.A detailed discussion of the X-ray and ultraviolet results on AG Dra in the light of possible models is in progress.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

On ‘bimodality of the solar cycle’ and the duration of cycle 21

The period-growth dichotomy of the solar cycle predicts that cycle 21, the present solar cycle, will be of long duration (>133 mo), ending after July 1987. Bimodality of the solar cycle (i.e., cycles being distributed into two groups according to cycle length, based on a comparison to the mean cycle period) is clearly seen in a scatter diagram of descent versus ascent durations. Based on the well-observed cycles 8–20, a linear fit for long-period cycles (being a relatively strong inverse relationship that is significant at the 5% level and having a coefficient of determination r ² 0.66) suggests that cycle 21, having an ascent of 42 mo, will have a descent near 99 mo; thus, cycle duration of about 141 mo is expected. Like cycle 11, cycle 21 occurs on the downward envelope of the sunspot number curve, yet is associated with an upward first difference in amplitude. A comparison of individual cycle, smoothed sunspot number curves for cycles 21 and 11 reveals striking similarity, which suggests that if, indeed, cycle 21 is a long-period cycle, then it too may have an extended tail of sustained, low, smoothed sunspot number, with cycle 22 minimum occurring either in late 1987 or early 1988.     

Ultraviolet solar irradiance measurement from 200 to 358 nm during spacelab 1 mission

The paper presents the results obtained from the UV-spectrometer of the Solar Spectrum Experiment during the Spacelab 1 mission in December 1983. The irradiance data concern 492 passbands, which are located between 200 and 358 nm at almost equidistant wavelengths separated by about 0.3 nm. The passbands have a well-defined, bell-shaped profile with a full width at half maximum of about 1.3 nm. The data, which have an error budget between 4 and 5%, agree closely with the spectral distributions observed by Heath (1980) and Mentall et al. (1981) and confirm that the solar irradiance and the fluxes of Sun-like stars show about the same spectral distribution down to at least 240 nm.     

Group Doppler effect in anisotropic plasmas

In anisotropic plasmas, the radiative power emitted and the power observed per unit solid angle should be calculated along the direction of the group velocityv _g . The two power functions referred differ by a product of two factors: one is the group Doppler factor and the other is the squeezing effect of the radiative energy due to the dependence ofv _g on direction. In this paper, the group Doppler factor is derived using two different methods, and the relevant physical concepts are analyzed in details. A number of numerical examples pertaining to astrophysical situations are presented, to illustrate the significance of the group Doppler effect with respect to the wave Doppler effect which is valid in isotropic media.