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The results of the analysis of the single-color (B) observations undertaken at the Stefanion Observatory for the red dwarf star AD Leo at any stage of the stellar activity (quiescence, weak flares, strong flares) indicate that (a) transient high-frequency oscillations occur during the flare event and during the quiet-star phase as well, and (b) the observed frequencies range between 0.0005 Hz (period 33 min) and 0.3 Hz (period 3 s) not rigorously bounded. However, the quiescence parts of the light curve that were analyzed belong to the preflare or after-flare state, that is, are connected with a major magnetic event (the observed flare). In this work, we find that transient oscillations appear far apart from the observed flares, during the quiet state of the star, as a result of the general magnetic activity of the star. The power spectrum of these oscillations resembles those of the solar-like oscillation spectra, that is, the sunquake spectra. Finally, a tentative estimation of the main physical parameters of the star, using asteroseismic analysis, is performed.

The knowledge and the perception of self-regulation mechanism of Earth’s surface temperature is studied through a questionnaire addressed to young students of Primary Education Department and Computer Science Department in the Aristotle University of Thessaloniki and the University of Thessaly respectively. Additionally we attempted to build a clear understanding of how the Earth’s self-regulation mechanism (ESRM) works through the carbon cycle, the greenhouse effect and the basic school physics. The evaluation of the results was based on the Pearson correlation coefficient, the corresponding significance level and the “Cronbach’s alpha” coefficient performed on the students’ sample. The vast majority of the students captured the global carbon cycle process, but signs of confusion and misunderstanding were detected concerning other factors affecting ESRM and the limits within it works.

In this paper we present the results of the analysis of the B -light curve for the flares of the red dwarf YZ CMin (dM4.5e), which were observed on February of 2002, with the help of the 30-inch Cassegrain telescope of the Stephanion Observatory, Greece. Discrete Fourier Transform analysis and the use of the Brownian Walk noise enable us to estimate the proper random noise and detect possible weak transient optical oscillations. Our results indicate that: (1) Transient high frequency oscillations occur during the flare event and during the quiet-star phase as well. (2) The observed frequencies range between 0.0083 Hz (period 2 min) and 0.3 Hz (period 3 s) is not rigorously bounded. The phenomenon is most pronounced during the flare state. (3) During the flare state: (a) Oscillations with period 2 to 1.5 min, 60 s, 11 s, 7.5 s, and 4 s appear around the maximum light state and persist during the whole flare state, (b) from the flare maximum phase on, a progressive increase of oscillations with periods 30 s, 20 s down to 4.0 s is markedly indicated, and (c) at the end of the flare only the oscillation of the pre-flare state do remain. Our observations are consistent with the phenomenology of impulsively exited oscillations on a coronal magnetic loop and subsequent chromospheric heating by electronic flux at the foot of the loop or/and by soft X-ray coronal emission. Our observation give evidence that more than one impulsive events may occur in the course of an observed flare (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This study explores the ideas of Greek prospective primary teachers about the anthropogenic greenhouse effect, particularly about its causes, consequences and cures. For this purpose, a survey was conducted: 265 prospective teachers completed a closed-form questionnaire. The results showed serious misconceptions in all areas (causes, consequences and cures). The most prominent misconception found by this survey is the conflation between the greenhouse effect and the ozone layer depletion, which is widely reported in the literature. There is also the notion that ‘good things’ (like clean beaches) can help ameliorate the greenhouse effect, whereas ‘bad things’ (like insecticides) can enhance it. One of the secondary results of the survey is that prospective teachers’ main source of information about the greenhouse effect is school. This calls for educational interventions to fight misconceptions at the source. Some suggestions are presented in this paper. The results of this study are compared with the results of two similar studies conducted in the UK and in Turkey.

Aims. We report results of a quantitative colorimetric UBVRI analysis of two flare events on the red dwarf EV Lac. The photometric data were obtained in September 2004, during the multi-site synchronous monitoring from the four observatories in Ukraine, Russia, Greece, and Bulgaria. These observations confirmed the presence of small-scale high-frequency oscillations (HFO) initially detected by Rodono (1974, A&A, 32, 337) and recently reconfirmed by the authors. Here we discuss the color characteristics of flares and HFO. Methods. Colorimetric analysis had been performed with the help of the time tracks in the UBVRI color-color diagrams from the earliest phase of flare development. Digital filtering technique was used to evaluate the time-dependent color indices. Results. As can be clearly seen in the diagrams, color indices oscillate on a time scale of seconds, far exceeding instrumental errors. Regarding the HFO, we conclude that the bulk of a flare oscillates during a major part of its lifetime between the states of hydrogen plasma opaque and transparent in the Balmer continuum. We find that at the peaks of oscillations the color tracks drift into the regions of color-color diagrams corresponding to a blackbody radiation, which provides an estimate of color temperatures from 17 000 to 22 000 K. We also find that flares cover ∼1% of the stellar disc.

V390 Aur is classified as a G8 spectral class active single giant by Fekel and Marshall (1991). Multi-site cooperative high-speed photoelectric monitoring was carried out for it in the period 1998-2003 as part of a program developed in Bulgaria recently to study chromospherically active evolved stars. Astronomers from Greece and Ukraine joined the flare activity study of V390 Aur in 2000. As a result, several flares with a duration from seconds to minutes were detected on this star at 3 observatories. Taking into account all the events detected, the flare rate of the star is estimated to 0.205 flares per hour. Comparison with the active dwarfs AD Leo and EV Lac indicates that the flare rate of V390 Aur is lower than that of AD Leo but comparable with the well-known flare star EV Lac. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A program of Many-sites Multi Channel simultaneous observations of flare stars by a network of telescops was initiated in 1998. The purpose of this program is to investigate the fine structure of the flares light-curve in UBVRI, depressing atmospheric and instrumental noises. In this paper we present the results of the observations on the Flare star EV Lac in the B color, which were carried out at the Stephanion observatory during the campaign of 1999. Discrete Fourier Transform analysis of the B-light curve of the largest flares reveal the presence of high frequency small amplitude oscillations with periods ranging between 6.9 sec and 20 sec in around the flare maximum phase. The oscillation amplitude ranges from 1.4 to 2.6 % of the star brightness in accordance with the results of the campaign of 1998 (Zhilyaev et al. 2000). In addition there is a tendency the higher frequencies to persist in the late phases of the flare evolution. The observations are consistent with the phenomenology of the evolution of a fast mode magneto-acoustic wave generated at the impulsive phase of the flare and traveling through the magnetic loop. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report results from a multiwavelength observing campaign conducted during 2000 March on the flare star AD Leo. Simultaneous data were obtained from several ground- and space-based observatories, including observations of eight sizable flares. We discuss the correlation of line and continuum emission in the optical and ultraviolet wavelength regimes, as well as the flare energy budget, and we find that the emission properties are remarkably similar even for flares of very different evolutionary morphology. This suggests a common heating mechanism and atmospheric structure that are independent of the detailed evolution of individual flares. We also discuss the Neupert effect, chromospheric line broadening, and velocity fields observed in several transition region emission lines. The latter show significant downflows during and shortly after the flare impulsive phase. Our observations are broadly consistent with the solar model of chromospheric evaporation and condensation following impulsive heating by a flux of nonthermal electrons. These data place strong constraints on the next generation of radiative hydrodynamic models of stellar flares.

We analyse the intensity oscillations observed in the gradual phase of a white-light flare on the RS CV n binary II Peg. Fast Fourier Transform power spectra and Wavelet analysis reveal a period of 220 s. The reliability of the oscillation is tested using several criteria. Oscillating coronal loop models are used to derive physical parameters such as temperature, electron density and magnetic field strength associated with the coronal loop. The derived parameters are consistent with the near-simultaneous X-ray observations of the flare. There is no evidence for oscillations in the quiescent state of the binary.

We describe multi-wavelength, simultaneous observations of the RS CVn star, II Pegasi, most of which were obtained during the first three weeks of September 1992. These observations were made using optical and infra-red broad-band photometry, ultraviolet and optical spectroscopy and microwave monitoring. We have detected photospheric spots and chromospheric flares, as well as deriving a description of mean conditions in the quiet chromosphere. One of the flares, observed in optical photometry and ultraviolet spectroscopy is one of the most energetic ever observed on this star. We demonstrate that in its "quiescent” state II Peg is continually variable in most of its chromospheric emissions, as well as in its coronal output.

The results of photometric, spectral and radio studies of the flare star EV Lac we obtained during the course of cooperative observations in 1994 and 1995 are presented. A quantitative analysis of the radiation emitted by two powerful flares using the colour-colour diagram confirms the previous conclusion on the essential heterogeneity of matter radiating in optical flares. From simultaneous observations of the star in UBVRI, K and H bands no significant brightness variations in IR were found in coincidence with observed small-amplitude optical flares, except a gradual decrease in the K-band following a 1.0 mag flare in the U-band. A differential spottedness of bright and dark hemispheres of EV Lac is estimated using observations in separate seasons and the total stellar spottedness is determined within the framework of the zonal spottedness model. Spectra of quiet and active states of the star in the blue-green region in 1994 and in the red region in 1995 are described: the characteristics of th...

Results of cooperative observations of the flare star EV Lac in September 1993 are presented. One of the about 30 optical flares detected was powerful enough to permit a quantitative analysis of its intrinsic radiation with the colour-colour technique. Sinusoidal brightness variations due to spottedness of the stellar surface was found to have an amplitude Δ V = 0.m0.24. Behaviour of the K band stellar brightness during strong and weak U band flares are considered. The upper limits of very fast optical brightness variations were estimated during both a moderate flare and quiet state of the star. No decametric bursts were observed during the campaign that could be certainly attributed to flare activity.

Results are presented for a large flare detected simultaneously on the RS CVn star, II Peg, by the X-ray satellite Ginga and from ground-based Johnson U-band measurements. The total U-band flare energy is determined. Using a smooth-burst model, the combined U-band plus X-ray radiative output is estimated.

Time resolved U-filter lightcurves of stellar flares on the dM4e star AD Leo have been measured to determine the flare frequency for individual observing seasons between 1972 and 1988. This report adds new data for 1984-1988. We use the number of flares with energy larger than 10∗∗30 erg, and the number of flare maxima with amplitudes larger than 0.3 as separate parameters to estimate flare frequencies. Chi-square tests do not reveal statistically significant variations of the flare frequency with time for 1972-1988.

We present seeing measurements from Mt. Holomon (Chalkidiki, Greece), a possible site for the establishment of a new University of Thessaloniki Observatory, using the Hartman — DIMM method. After two years of systematic observations we present the first robust results and give a first evaluation of the astronomical seeing characteristics, which are very promising. In order to check our system and method of analysis we have also taken similar seeing measurements at the Kryonerion Astronomical Station of the National Observatory of Athens. The Kryonerion measurements fully agree with previous, established, seeing results taken there. This agreement makes us feel comfortable of the credibility of our system.

In this paper we present the results of the analysis of the U‐light curve for a flare of magnitude 1.2, which was observed on September 2004, with the help of the 30‐inch Cassegrain telescope of the Stephanion Observatory. The results of both, DFT‐analysis and wavelet analysis, indicate that (a) Oscillations with period 1 to 1.5min, 11s, 7.5s and 5.5s appear during the pre‐flare state and persist during the whole flare state, (b) From the flare maximum phase on, a progressive increase of oscillations with periods 20s up to 4.0s is markedly indicated and (c) At the end of the flare only the oscillation of the pre‐flare state do remain. This result is in favour of (or does not contradict) the suggested explanation, i.e. the evolution of a fast mode magneto‐acoustic wave generated at the impulsive phase of the flare and traveling through the magnetic loop.

We present further evidence that the bright spot on the Moon observed on May 23, 1985, was a natural phenomenon that occurred slightly above the lunar surface. The interpretation that the spot could be attributed to an instantaneous reflection from a satellite's solar panel fails to explain several important characteristics of the observation.

During 57.4 hr of optical monitoring in the Johnson U- and B-bands of the RS CVn binary II Peg, 10 flares were detected. The absolute energies of these events are in the range 1-180×10 33 erg. This implies a flare activity in the U-band of 0.17 flares per hour, compared with 0.12 flares per hour from ultraviolet C IV data. A double power-law distribution is required to fit the cumulative flare-frequency distribution of the U-band flares

We present simultaneous starspot photometry and high resolution Hα spectroscopy of II Peg which gives evidence of differential motions in the chromosphere.

We present photographic evidence of a very short duration, strong flash from the surface of the Moon (near an irregularly shaped crater in Palus Somni). The flash covered a region roughly 22 by 18 km wide with a total energy of the order of 10 17 erg. The event is established to be slightly above the surface of the Moon. An explanation is proposed involving outgassing and a subsequent electrical discharge caused by a piezoelectric effect.

A study is made of the variation of the flare energy spectrum of the flare star EV Lac during the activity cycle of this star, based on the homogeneous series of observational data obtained at the Stephanion Observatory. The spectrum varies significantly during the 5 year activity cycle of this star. Analogous variation is also observed in the time-averaged rate of flare energy release of the star.