Photoelectric observation of AD Canis Minoris and the change in its period

I have carried out a large amount of photoelectric observation in the V-band on AD CMi. Small variations in maximum and minimum lights are found. A combined analysis of the 12 maximum times I determined and those by previous workers shows that the pulsation period of this star is continually increasing at a rate equal to (1.89 ± 0.09) × 10⁻⁸ d/yr. From its position in the “amplitude-period” diagram, it is inferred that this star has been pulsating for at least 8.6 million years.     

MHD oscillations in the solar spike radiation

In this paper the observed 1.4–1.6 s quasi-periodic oscillations in the spike radiation of the microwave outburst of 1981 May 16 are analysed in teras of MHD waves. We point out that the fast magnetoacoustic waves (“sausage” mode) propagating inside and outside a loop can modulate the magnetic field and the pitch angle distribution of the electron beams in the source region. The growth rate of electron-cyclotron-maser instability is then affected to give rise to the quasi-periodic oscillations. Quantitative estimates of relevant physical parameters are given.     

Tianjin photographic zenith tube observations

In this paper we analyse the observational data obtained by the Chinese-made PZT in the two periods 1979 Feb – 1980 May and 1981 Dec – 1983 March. The internal accuracy of single star is found to be m_u = ±13.0 ms, m_φ = ±0. “144 for the first period, and m_u = ±14.6 ms, m_φ = ±0.” 152 for the second. Correction of star position is found by the chain method. The systematic error caused by the sealed window of the evacuated chamber and the temperature effect of the plate scale are investigated. Monthly means of time and latitude are given.     

The effects of strong interaction on the observational discrimination between neutron and strange stars

Strange stars are compact objects similar to neutron stars composed of strange matter. This paper investigates the observational effects of the strong interaction between quarks. We believe: 1) that the conversion of a neutron star to a strange star is a large “period glitch” which is determined by the strong interaction; 2) that the strong interaction results in effective damping of oscillation of hot strange stars, which could be a new mechanism of driving supernova explosions; 3) that the strong interaction increases the difference in rotation between strange and neutron stars under high temperatures, making the minimum period for strange stars lower than that for neutron stars.     

NH3 observations of the molecular cloud NGC 2023

We observed the molecular cloud NGC 2023 in the NH₃ rotation-inversion lines NH₃(1.1) and NH₃(2.2). The hyperfine structures shown in these lines can be advantageously used to derive the physical parameters of the cloud. We re-confirm that the star HD 37903 is the unique exciting source of the cloud and heated dust is the exciting medium. Analysis leads to the conclusion that the star is located on the periphery of the cloud, as in Zuckerman's “blister” model. If HD 37003 originated in NGC 2023, then the star will have existed long enough to blow away the molecular cloud to a distance of 0.1 pc. There may exist clumps of relatively high density in the cloud.     

A “division” treatment of the sky background in CCD images

Considering the errors transmitted from all pre-treatments, I suggest a “division” method for removing the sky background including interference fringes in CCD images. Compared to the traditional method, which may be called a “subtraction” method, the “division” method is easier to carry out and gives more accurate brightness measurement especially for the fainter images.     

Structure in the EAS size spectrum: analysis of the CASA-MIA results

We present an analysis of the very recent data from the CASA-MIA extensive air shower array (M.A.K. Glasmacher, Ph.D. Thesis, University of Michigan (1998) in terms of a search for the structure in the shower size spectrum claimed by us from an analysis of “the world's data”. Our earlier claim is found to be supported to the extent that there is strong evidence for the existence of structure in the spectrum which cannot obviously be explained by the conventional Galactic Modulation Model. There is modest evidence for the structure being of “our” form and strong support for “our” mass composition when “corrected” to the interaction model advocated by us. None of the results are inconsistent with there having been a recent, nearby, single supernova.     

Rushing to equilibrium: a simple model for the collisional evolution of asteroids

A simple mathematical model for the evolution of a system of collisionally interacting bodies—such as the asteroid population—consists of two coupled, nonlinear, first-order differential equations for the abundances of “small” and “big” bodies. The model easily allows us to recover Dohnanyi's value for the exponent of the equilibrium mass distribution. Moreover, the model shows that any initial value for the ratio of “big” to “small” bodies rapidly relaxes to the equilibrium ratio, corresponding to the exponent, and that integrating the evolution equations backward in time—an attractive possibility to investigate the mass distribution of primordial planetesimals—leads to strong numerical instability.     

The huang-you star of the song dynasty-a chinese star list of the early medieval period

Records of observations of stars (including the determinatives of the 28 lunar mansions) have been collected and re-edited from five previous editions. After further consulting the star chart of XYXFY^* and the Suzhou planisphere, we obtain the definitive positions of 360 stars which we can convert into the right ascensions and declinations for 1052 A.D., and hence their identification. Of the traditional 282 asterisms comprising 1464 stars, this list has 282 asterisms comprising 1457 stars, lacking only the star Shaocheng on the left Wall of the Purple Enclosure and the 6 stars of the asterism Ligong. With positions based on actual observations, this list embodies the traditional Chinese star system. It is the second listing after the “Star List of Master Shi” of the Warring Period, and provides an important and reliable reference for historical researches.     

Solving the G-dwarf problem with a three-component model of the chemical evolution of the Galaxy

A three-component chemical evolution model of the Galaxy is presented, which we believe will cast a new light on the G-dwarf problem. The model is based on a scenario of the Galaxy consisting of three major evolutionary phases: halo, thick disk and thin disk, separated by two short interludes of rapid collapse. The evolution of different stellar populations are treated separately, the combination of which yields an overall metallicity distribution function for the solar neighbourhood. We tested three different models using the same set of basic equations: the “prompt initial enrichment” (PIE) model, the “proportional yield” (PPY) model and the “collapse” (CLP) model. Best-fit parameters are derived. The results show that the different populations have remarkably different IMFs, while mass exchange has only minimally affected the chemical evolution in the solar vicinity, so that the solar vicinity can be regarded as a closed system, at least in the late stage of the Galactic evolution.     

Observations of waves artificially stimulated by an electron beam inside a region with auroral precipitation

The POLAR 5 sounding rocket, launched from Andøya, Norway on 1 February, 1976 was of a “mother-daughter” configuration. An electron accelerator, mounted on the “daughter,” produced a pulsed electron beam with currents up to 130 mA and electron energies up to 10 keV. The waves, artificially stimulated by the injected electron beam, was studied using wave receivers, mounted on the “mother.” The receivers covered the frequency range from 0.1 kHz to 5 MHz.

In addition to the stimulated waves observed during beam injection, enhanced wave emissions were observed 10–20 ms after the end of beam injection. This emission seemed to be relatively independent of whether the electron beam is launched up or down along the geomagnetic field.

The high frequency emission observed after beam injection is found to be correlated with the passage through an auroral arc. In particular this emission is closely correlated with the flux of 4–5 keV auroral electrons.

The low frequency emissions observed after beam injection are concentrated in two bands below the lower hybrid frequency.

Different mechanisms for explaining the observed time delays between the beam injection and the observation of the emissions are discussed.     

Triple splitting with the F2-region of the ionosphere at high and mid-latitudes

The occurrence of the third (z-ray) component of the F2-trace on ionograms is investigated at high- and mid-latitudes. Diurnal variations show a systematic shift, with magnetic inclination, of the time of maximum occurrence. Seasonal variations show a winter maximum, and an inverse sunspot-cycle relationship exists. Maximum occurrence appears between a magnetic inclination of 70° and 80° with a fall-off either side.

Evidence is presented to suggest a z-ray association with “Spread-F” fronts, and a possible mechanism for the recording of the z-ray trace at the transmitter site is described. This involves longitudinal propagation of the o-mode at its normal reflection level, coupling at this point, and ultimate reflection for the z-ray mode as a result of sloping ionization contours belonging to “Spread-F” fronts extending in directions perpendicular to the magnetic meridian.

An association with V.L.F. emissions (“dawn-chorus”) is discussed.     

Response time of the high-latitude dayside ionosphere to sudden changes in the north-south component of the IMF

The time scale of the response of the high-latitude dayside ionospheric flow to changes in the North-South component of the interplanetary magnetic field (IMF) has been investigated by examining the time delays between corresponding sudden changes. Approximately 40 h of simultaneous IMF and ionospheric flow data have been examined, obtained by the AMPTE-UKS and -IRM spacecraft and the EISCAT “Polar” experiment, respectively, in which 20 corresponding sudden changes have been identified. Ten of these changes were associated with southward turnings of the IMF, and 10 with northward turnings. It has been found that the corresponding flow changes occurred simultaneously over the whole of the “Polar” field-of-view, extending more than 2° in invariant latitude, and that the ionospheric response delay following northward turnings is the same as that following southward turnings, though the form of the response is different in the two cases. The shortest response time, 5.5 ± 3.2 min, is found in the early- to mid-afternoon sector, increasing to 9.5 ± 3.0 min in the mid-morning sector, and to 9.5 ± 3.1 min near to dusk. These times represent the delays in the appearance of perturbed flows in the “Polar” field-of-view following the arrival of IMF changes at the subsolar magnetopause. Overall, the results agree very well with those derived by Etemadi et al. (1988, Planet. Space Sci. 36, 471) from a general cross-correlation analysis of the IMF B_z and “Polar” beam-swinging vector flow data.     

The HNCO ring in the Sgr B2 region

The large-scale structure associated with the 2′N HNCO peak in Sgr B2 [Minh, Y.C., Haikala, L., Hjalmarson, Å., Irvine, W.M., 1998. ApJ 498, 261 (Paper I)] has been investigated. A ring-like morphology of the HNCO emission has been found; this structure may be colliding with the Principal Cloud of Sgr B2. This “HNCO Ring” appears to be centered at (l,b) = (0.7°,−0.07°), with a radius of 5 pc and a total mass of 1.0 × 10⁵ to 1.6 × 10⁶ M. The expansion velocity of the Ring is estimated to be 30–40 km s⁻¹, which gives an expansion time scale of 1.5 × 10⁵ year. The morphology suggests that collision between the Ring and the Principal Cloud may be triggering the massive star formation in the Sgr B2 cloud sequentially, with the latest star formation taking place at the 2′N position. The chemistry related to HNCO is not certain yet, but if it forms mainly via reaction with the evaporated OCN⁻ from icy grain mantles, the observed enhancement of the HNCO abundance can be understood as resulting from shocks associated with the collision between the Principal Cloud and the expanding HNCO Ring.     

High time resolution observations of solar radio emission at four frequencies: evidence for energy release in microflares

As evidence for energy release in microflares, high time resolution observations of solar radio emission obtained with our “synchronous observation system of solar radio radiation with high time resolution at four frequencies (1.42, 2.13, 2.84 and 4.26 GHz)” from December 1989 to April 1993 are presented in this paper. The observed events include weak ms spikes, “spike-likes”, fast pulsations as well as two kinds of newly discovered fast fine structures, i.e., microwave type III bursts and microwave patch-like structures. A statistical study of the duration of fast fine structures has been made and on its basis the various types of phenomena are illustrated with actual examples.     

Influence of the pulsar parameters on γ-ray burst afterglows

By applying the fireball model of γ-ray burst with a central pulsar, the radiation fluxes of the afterglows of two γ-ray bursts, GRB970228 and GRB000301c, are calculated. The results of the calculation agree very well with the observations. The differing characters of the light curves with a “break” in the optical waveband R of the afterglows of two bursts are interpreted, in terms of differing pulsar parameter values.     

Evolutionary and structural properties of mirror star MACHOs

There can exist a hidden sector of the Universe in the form of parallel “mirror” world which has the same particle physics as the observable world and interacts with the latter only gravitationally. Big Bang nucleosynthesis bounds demand that the mirror sector should have a smaller temperature than the ordinary one. This implies that the mirror matter could play a role of dark matter, and in addition its chemical content should be dominated by helium. Here we study the evolutionary and structural properties of the mirror stars which essentially are similar to that of the ordinary stars but with higher helium contents. Being invisible in terms of photons, they could be observed only as MACHOs in the microlensing experiments. Using a numerical code, we compute evolution of stars with large helium abundances (Y = 0.30–0.80) and a wide range of masses, from 0.5 to 10 M. We found that helium dominated mirror star should have much faster evolutionary time (up to a factor 30) than the ordinary star with the same mass. In addition, we show the diagrams of luminosities, effective temperatures, central temperatures and densities, and compute the masses of the He-core at ignition and the minimum mass for carbon ignition, for different chemical compositions. The general conclusion is that mirror stars evolve faster as compared to ordinary ones, and explode earlier as type II supernovae, thus enriching the galactic halo of processed mirror gas with higher metallicity, with implications for MACHO observations and galaxy evolution.     

Solar radio events and geomagnetic storms

On the basis of a 24-hr patrol of solar radio noise established since the beginning of the International Geophysical Year, an identification is attempted of those solar flares which, on account of their associated radio responses, most probably were the cause of a geomagnetic storm. The cases for which we think the identification to be reliable are listed. It has appeared that great integrated intensity of the radio outburst at centimeter, decimeter and meter wavelengths is the primary criterion for identifying the solar flares responsible. Most of these giant radio outbursts, to which we assigned the “radio importance” figure 3 +, belong to the so-called type IV. Only a minor fraction of these events were accompanied by slow-drift bursts of type II. Of the importance 3 + radio outbursts about 60 per cent are clearly associated with the subsequent sudden commencement of a geomagnetic storm. Conversely, about 50 per cent of the sudden commencements of a storm can be related to an important radio event. Some reasons, why in a particular case the storm-outburst association may fail to exist, are mentioned.     

Optical positions of 3C 273

We have measured an optical position of 3C 273 in the AGK3 system using the 40cm astrograph of Shanghai Observatory. Combining with others' observations, we have derived a “proper motion”. A comparison with other results is made.     

Hill curves in the invariable plane of the general three-body problem

This paper discusses in detail the oscillation of the Hill curves in the invariable plane of the general three-body parameter with the “mean quadratic distance” .