Rr CrB and Algol – The First and Last Star in Zdeněk Kopal’s Life with Binaries

Several important turning points appeared in the personal life and scientific career of Zdeněk Kopal, every time, when he entered a new field of research. Four particular periods of his life will be commented in the present paper: the studies in Prague and early observations in the variable star programme of the Czech Astronomical Society; the first lectures on close binaries at Harvard; the intermezzo of lunar research; and the last period after 1989, when Zdeněk Kopal returned several times to Prague University.     

Hard X-ray images of possible reconnection in the flare of 21 May, 1980

An analysis of the growth of X-ray loops in the flare of 21 May, 1980, observed by HXIS on board SMM spacecraft, has been carried out with high time resolution in six energy channels from 3.5 to 30 keV. This analysis has revealed that the tops of the loops stay for minutes at a given altitude before, quite abruptly, other loop tops begin to appear above them. One of the jumps in altitude, from 27 000 to 45 000 km if the loops extended radially, which occurred quite late in the flare development, is studied in detail. The fact that the tops, of higher loops were first seen in the 22–30 keV energy channel, and only minutes later at lower energies, suggests a new release of energy in a very small volume high in the corona. An initial temperature of at least 50 × 10⁶ K is indicated by the data, inside a volume which may not exceed a few hundred km in diameter. A magnetic reconnection of previously distended field lines appears to be a likely candidate for the observed phenomenon.We also give some revised values of the characteristic parameters of the whole system of loops in this flare which has been the topic of several other studies.     

Real-time simulation of a potential magnetic field in a post-flare arch

We analyze the X-ray observations on 7–8 November of the last revival of a giant coronal arch first observed in the morning hours of 6 November, 1980. We compare these data with observations of earlier revivals of this arch, in order to determine whether the successive brightenings repeat without any apparent modification, or whether they show a varying behavior as they keep occurring. We also examine the magnetic structure of the revived arches in order to ascertain whether the subsequent phenomena involve the same magnetic configuration. The information about the magnetic structure of the last revival is the best we have, because the revival started close to the time of the Kitt Peak magnetogram which has been used for the magnetic modelling of the whole series of these giant arches.We conclude that while there seems to be some plasma depletion in the 7–8 November event, the real-time magnetic field modelling on this date seems to fit the observed footpoints better than the modelling on 6 November which had to use the same magnetogram for a situation occurring 24 to 36 hours earlier. The general topology does not show any significant change, apart perhaps in the field line inclination, but some flux tubes seem to have disappeared between 6 and 7 November. Nevertheless, both X-ray and H observations indicate that this magnetic structure basically kept its identity for more than 4 days.We also compare the two existing interpretations of the arch revivals: re-excitation of a permanent pre-existing structure (after Hick and vestka, 1987) and formation of each brightening through a separate reconnection (after Poletto and Kopp, 1988). Unfortunately, proximity to the limb does not allow one to decide between these two alternatives; it is suggested to look for other series of arch revivals utilizing our present knowledge about the behavior of the chromospheric footpoints of giant arches.     

Solar and interplanetary observations of the mass ejection on 7 May, 1979

We present observations of a mass ejection that was observed by five different instruments along its way from the solar surface to more than 100 solar radii. The instruments involved are the ground-based H coronagraph at Wrocaw, the white-light SOLWIND coronagraph on board the P78-1 satellite, zodiacal light photometers of the HELIOS B spacecraft, in situ plasma detectors and magnetometers on board the HELIOS B spacecraft, and interplanetary scintillation measurements on the ground. By using a CAT-scan analysis of the images obtained by the SOLWIND coronagraph near the Earth and HELIOS B photometers placed at 0.3 AU perpendicular to the Earth-Sun line, we have been able to get a three-dimensional density reconstruction of the mass ejection and fit the best velocity curve for its propagation. Although problems exist in smoothly joining the height-time curves (for instance, we had to reduce the brightness of the SOLWIND data by more than a factor of two to make the data sets agree photometrically), both this analysis and direct measurements by the other experiments clearly indicate higher speeds at greater distances from the Sun. The plasma acceleration in this case was obviously not limited only to distances within 3 R ₀ , as is usually the case, but continued beyond the outer limit of the coronagraph view at 8 R ₀ .The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Large-scale active coronal phenomena in Yohkoh SXT images

We discuss Yohkoh SXT observations of stationary giant post-flare arches which occurred on 3–6 May, 1992 and study in detail the last arch, associated with the flare at 19:02 UT on 5 May, which extended above the west limb. The arch was similar to the first giant arch discovered on board the SMM, on 21–22 May, 1980. We demonstrate that the long lifetimes of these structures necessarily imply additional energy input from the underlying active region: otherwise, conduction would cool these arches in less than one hour and even with the unlikely assumption of conduction inhibited, pure radiative cooling would not produce the temperature decrease observed. All arch tops, although varying in brightness, stayed for several days at a fairly constant altitude of 100 000 km, and the arch studied, on 5–6 May, was just a new brightening of the pre-existing decaying structure. The brightening was apparently due to inflow of hot plasma from the flare region. Yohkoh data confirm that these stationary arches are rare phenomena when compared with the rising arches studied in Paper I and with Uchida et al.'s expanding active regions.     

Climate Change in the Urals,Russia, Inferred from Borehole Temperature Data

Borehole temperatures in the central and south Urals were analysed for the past ground surface temperature (GST) signal. 31 highquality temperature logs were selected for this purpose and inverted with algorithms based on the generalised least squares theory. The signal to noise ratio was improved by averaging the results of individual borehole inversions. No distinct regional trends were found in the studied region except for some indications of more pronounced warming in the south. The mean GST history (GSTH) was characterised by cooling down to –0.6 °C in the 18th century and subsequent warming to 0.5 °C above the longterm mean at the beginning of this century, and to 1 – 1.5 °C by 1980. The stability of the mean GSTH was tested in dependence on the number of holes used for the averaging. It showed that any subset of 15 holes yielded a GSTH similar to that obtained from the whole set. A surface air temperature (SAT) time series comprising the period 1832 – 1989 was combined from 17 meteorological records. Its least squares warming rate of 1.1 °C per 100 years is somewhat higher than that of the GST (0.7 – 0.8°C/100 years) in the same period.     

Real-time raster projection for web maps

The virtual globe is the default visualization for Digital Earth applications, but it can only show one half of the Earth. This article introduces user-adjustable, on-the-fly projection of georeferenced raster images for web mapping and web GIS applications. This technique allows users to center a map on arbitrary locations, while still seeing the entire Earth surface. Modern web mapping libraries can apply map projection transformations to vector data in the browser, but they do not currently support the projection of raster images at interactive frame rates. We use the cross-platform WebGL (Web Graphics Library) graphics pipeline for hardware-accelerated projection of raster data in web browsers. Two algorithmic techniques – inverse per-fragment projection, and combined forward per-triangle and inverse per-fragment projection – for georeferenced raster imagery are documented. The resulting raster maps combine the ease of use and flexibility of interactive virtual globes with the ability to show the entire Earth. The adjustable projection of raster imagery allows users to observe global phenomena that are difficult to visualize on virtual globes or traditional maps with static projections.