R. POPESCU, C. DUMITRACHE, P. POPESCU

Astronomical Institute of the Romanian Academy
Str. Cu?itul de Argint 5, 75212 Bucharest, Romania
E-mail: pradu@roastro.astro.ro, crisd@roastro.astro.ro, petre@roastro.astro.ro

Abstract. A prominence was observed during the total solar eclipse from 11 August 1999, at Bucharest Observatory, using an astrometrical instrument – the Danjon astrolabe, a CCD camera and an interferential filter near H?. The estimated resolution of the instrument is 0.475 arcsec/px. The fine structure of the prominence could be seen in our images.  We present a preliminary report of the eclipse experiment.

Key words: eclipse – prominence – corona.

V. COPACIU

National Institute of Meteorology and Hydrology
?os. Bucure?ti-Ploie?ti 97, 71552 Bucharest, Romania
E-mail: relatii@meteo.inmh.ro

S. M. YOUSEF

Astronomy and Meteorology Dept., Faculty of Science
Cairo University, Cairo, Egypt
E-mail: Shahinaz@sci-astro.cairo.eun.eg

Abstract. Radiation and thermal responses were measured during the 11 August 1999 total solar eclipse at Afuma?i atmospheric laboratory near Bucharest and at C?ld?ru?ani experimental hydrological station in Romania. It was found that the surface temperature at the first station dropped by 16.6°C to 29.9°C. Temperatures at 10 m, 7 m, 3 m and –5 cm also dropped to nearly this temperature. Although the temperature at C?ld?ru?ani was 34.1°C at the start of eclipse, the minimum temperature reached was 29°C. An independent observer at C?l?ra?i also found the minimum temperature to be about 30°C. In other words, the minimum temperature reached following the totality was 29 ± 0.5°C irrespective of location and height (from –5 cm to 10 m). This may be explained if the temperature of the shadow is about 29.5°C. The response time of the minimum temperature at the surface was about 18 minutes, which is comparable to the time when net radiation was negative. Net radiation dropped between 468 W/m2 to –39 W/m2 at C?ld?ru?ani. Cooling of air in response to cutting off the solar radiation must have caused changes in wind patterns.

Key words: solar eclipse – atmospheric responses – temperature – UVB – global radiation – net radiation.

ECLIPSE-97 SIBERIAN EXPEDITION

A. N. ARSENTIEV, A. N. BORODIN

Institute of Solar-Terrestrial Physics, Siberian Division, Russian Academy of Sciences
POB 4026.,Irkutsk, 664033, Russia
E-mail: arsan@iszf.irk.ru.

Abstract. The observations of the total solar eclipse of March 9, 1997 by the expedition of the Institute of Solar-Terrestrial Physics are presented.

Key words: solar eclipse – white-light corona – photographic observations – telescope – radial filter.

LARGE-SCALE POLAR CORONAL MAGNETIC FIELD MODEL
AND THE EXPECTED AUGUST 11, 1999 ECLIPSE CORONA

I. S. VESELOVSKY, A. N. ZHUKOV, O. A. PANASSENKO

Institute of Nuclear Physics, Moscow State University, 119899 Moscow, Russia
e-mail: anz2@dec1.npi.msu.su

S. KOUTCHMY

Institut d'Astrophysique de Paris – CNRS
98 bis, Boulevard Arago, F 75014, Paris, France

Abstract. We compare available SOHO/LASCO C2 images with the model calculations of the large-scale coronal magnetic field near the magnetic poles of the Sun. The model field consists of the ones of the dipole and of the thin current sheet in the plane perpendicular to the dipole. The positions of the dipole and the current sheet (representing the heliospheric current sheet) are obtained via comparison of the SOHO/LASCO, SOHO/EIT observations and coronal magnetic field calculations (Wilcox Solar Observatory). The values of the solar dipole vector components are taken from the same calculations of the coronal magnetic field. The strength of the heliospheric current sheet is obtained via analyses of the interplanetary magnetic field preliminary data from the ACE spacecraft. This model is better applicable during the solar cycle minimum. However, the obtained model polar magnetic field is in agreement with the observations near the solar maximum, when the polar plumes could be visible over the magnetic (and not heliographic) poles of the Sun if the magnetic dipole is perpendicular to the line of sight. The configuration of the solar corona during the August 11, 1999 total solar eclipse expected from our analysis does not contain polar plumes and will be close to the maximal-shape corona dominated by coronal rays and streamers.

Key words: corona – magnetic fields – heliospheric current sheet – plumes – streamers.

S. M. YOUSEF

Astronomy & Meteorology Dept., Faculty of Science
Cairo University, Cairo 12613, Egypt
E-mail: shahinaz@sci-astro.cairo.eun.eg

Abstract. The Holy Quran describes a phenomenon seen by young Abraham that can only fit a solar eclipse. Two criteria were given for this particular eclipse; first only one planet was seen as soon as it got dark and second no corona was seen. In order to justify the first selection rule, examinations of solar and planetary longitudes for total solar eclipses passing over Babel were carried out. Only the eclipse of the 1st of April 2470 BC meets this condition, as it was only Venus that was seen at that eclipse. The second selection rule was also naturally fulfilled, as Babel happened to be on the border of the totality zone hence no corona was seen, however all the time the moon glistened as Baily’s beads. There is no doubt that the prophet Abraham witnessed the 1st of April total solar eclipse that passed over Babel. This will put him about 470 years backward than it was previously anticipated.

Key words: solar eclipse – Quran – Abraham or Ibraheem – Babel – Baily’s beads – border – totality zone

V. M. MISHIN, V. I. SIDOROV, S. S. ADELKHANOV

Institute of Solar-Terrestrial Physics SD RAS, Irkutsk, Russia
E-mail: mit2@iszf.irk.ru

S. A. YAZEV

Institute of Solar-Terrestrial Physics SD RAS
Astronomical Observatory of Irkutsk State University, Irkutsk, Russia
E-mail: uustar@star.isu.ru

Abstract. The CSHKP model assumes that a two-ribbon flare is produced by a reconnection of the previously open magnetic flux ?. Based on this fundamental proposition, and using some simplifying assumptions, in this paper we determine the values of ? from H? data for two large flares taken at steps of a few minutes. Further, the values deduced for ? are used to calculate the values of the Poynting flux ?? entering the flaring region from the outside, and of the flare power Q. In each of the flares under investigation, we distinguish the first and second active phases, respectively, without and with a reconnection of the previously open magnetic flux. By well-known terminology of S. Masuda, these two phases produce, respectively, a soft X-ray loop-top flare and a hard X-ray above-the-loop-top flare.

Key words: solar flare – open magnetic flux – magnetic reconnection – flare ribbons – flare power.

A. C. DONEA1, C. LINDSEY 2, D. BRAUN 2, 3

1 Astronomical Institute of the Romanian Academy
Str. Cu?itul de Argint 5 ,RO-75212 Bucharest, Romania
E-mail: adonea@roastro.astro.ro

2 Solar Physics Research Corporation
4720 Calle Desecada, Tucson, AZ 85718, USA

3 High Altitude Observatory, National Center for Atmospheric Research
PO Box 3000, Boulder, CO 80307-3000, USA

Abstract. The helioseismic holography is a technique which allows the analysis of the photosphere of the Sun from the point of view of the acoustics. In this paper we shall discuss mainly the seismic image of the flare of July 9, 1996 which produced the largest sunquake observed by MDI-SOHO instrument. We emphasize the fact that the kernel-like structure observed in the seismic signature at both 3.5 mHz and 6 mHz egression power maps are not side lobes effect. The seismic signature reveals the presence of an extended acoustic source, much larger than the Doppler redshift motion observed in the MDI-SOHO Dopplergrams.

Key words: Sun – helioseismic holography – solar flares – oscillations.

J. KAŠPAROVÁ

Astronomical Institute, Academy of Sciences of the Czech Republic
Ond?ejov, 251 65, Czech Republic
E-mail: kasparov@sunkl.asu.cas.cz

Abstract. Analysis of the September 23, 1998 flare H? spectra and filtergrams is presented. Spectra were obtained using multichannel flare spectrograph (MFS) at the Astronomical Institute in Ond?ejov, Czech Republic, having a temporal resolution of 25 frames/s and a spatial resolution of ?1? decreased by seeing to 3? - 5?. High temporal resolution was firstly used for detecting of the chromosphere response to the pulse beam heating.

Key words: flare – particle beams – high temporal resolution.

V. KOROKHIN, L. AKIMOV, S. BELETSKY, I. BELKINA,
Y. VELIKODSKY, G. MARCHENKO, E. SHAPARENKO

Astronomical Observatory of Kharkov State University, Kharkov, Ukraine

Abstract. A technical description of the contemporary solar telescope of the Kharkov Astronomical Observatory (http://khassm.virtualave.net) is given, and the plan to future development is sketched. A wide range monitoring of solar activity including observations near UV range in Balmer continuum and the IR line of He 1083 nm is presented.

Key words: Sun – telescope – helium – calcium – Balmer – database – eruption.

S. A. YAZEV

Institute of Solar-Terrestrial Physics SD RAS
Astronomical Observatory of Irkutsk State University, Irkutsk, Russia
E-mail: uustar@star.isu.ru

Abstract. Over a period of years Dr. Sc. (Phys. & Math.) Valery Gavrilovich Banin (Institute of Solar-Terrestrial Physics at the Siberian Division of the Russian Academy of Sciences, Irkutsk, Russia), in collaboration with the author, was engaged in developing a method for describing complexes of activity on the Sun using the technique of areas of long activity (ALAs). In the summer of 1998 Dr. Banin died suddenly after a painful illness. Inasmuch as most of Banin and Yazev's papers are in Russian, while those written in English appeared in Russian journals and were not easily accessible to the Western reader, my intent in this paper is to offer a brief summary of the main results derived from implementing the above approach.

Key words: Sun – solar activity – areas of long activity.

U. LEIKO

Astronomical Observatory of Kyiv, Taras Shevchenko University
3, Observatorna vul., Kyiv-53, 254053, Ukraine
e-mail: leiko@aoku.freenet.kiev.ua

Abstract. The power spectrum of the time series of Stanford measurements of the solar mean magnetic field, 1975-1998, has been investigated. The discreet frequencies in the range of rotation periods are caused by the North-South asymmetry of the large scale photospheric magnetic field placing on different hemispheres. The northern magnetic field had stable rotation period ~26d.9 during both 21 and 22 solar cycle. The southern magnetic field rotated slower having period ~28d.05 during cycle 21 and ~28d.64 during cycle 22. The longtime period peaks had different values and character during different cycles. The periods 1y.02 and 0y.935 were weak during both cycles. The ~11years period was weak during both cycles but ~22 years period was large during the whole interval 1976-1988.

Key words: Sun – photosphere – solar magnetic field

M. PISHKALO, V. IVANCHUK

Astronomical Observatory of Kyiv Taras Shevchenko University
3, Observatorna vul., Kyiv-53, 01053, Ukraine
E-mail: pish@aoku.freenet.kiev.ua

Abstract. We compare the properties of H?-microejections with those of other chromospheric and transition region features, and conclude that the H?-microejections seem to be considered as transition region plasmoids. Using the simplest approximation, in which the gravity force is balanced by the diamagnetic acceleration, we obtain an upper estimation of the ratio of magnetic field strength in the solar atmosphere for the range of 5000 km to 25000 km.

Key words: Sun – chromosphere ? transition region ? magnetic fields.

C. DUMITRACHE

Astronomical Institute of the Romanian Academy
Str. Cu?itul de Argint 5, 75212 Bucharest, Romania
E-mail: crisd@roastro.astro.ro

Abstract. The present work focuses on some 2-D MHD numerical experiments, where the initial state is a current sheet, embedded in the solar hot corona. The gravitational effects and a complete energy equation are taken into account. The computations were made on an SGI - Challenge M supercomputer with the same code Alfven (see Forbes & Priest, 1982), based on SHASTA method (see Weber, 1978). The computational grid covers a distance of one (or more) solar radius, placed in a meridional solar plane and the gravitation is directed along the Ox axis. Some numerical simulations were made for different scales (one or more solar radius) taking into account mass injections, continuous or temporary, into the current sheet. Different solar features were obtained: flares, prominences, coronal streamers.

Key words: current sheet – corona – MHD numerical simulations

L. ZANGRILLI, P. NICOLOSI

Dipartimento di Ingegneria Elettronica ed Informatica
Università degli Studi di Padova, I-35131 Padova, Italy
Istituto Nazionale per la Fisica della Materia, Unità di Padova, Italy

G. POLETTO

Osservatorio Astrofisico di Arcetri, I-50125 Firenze, Italy

G. NOCI

Università di Firenze, I-50125 Firenze, Italy

Abstract. In this paper we investigate the latitudinal dependence of the outflow speed of the solar wind from SOHO/UVCS observations. To this end, we measure the intensity of the O VI doublet lines at 1031.9 Å and 1037.6 Å, and consider the ratio R = I1032/I1037 as a diagnostic for wind speed. At distances larger than 1.6 R?, a local minimum in the ratio R at mid latitudes is observed, that might be attributed to a local increase of the wind speed. To check whether this interpretation is plausible, we derived the velocity field of the solar wind from mass flux conservation, after mapping electron densities from synoptic observations and adopting a simple magnetic field configuration. It turns out that the outflow plasma speed shows a local peak at mid latitudes between 1.5 and 2.5 R?, as inferred from UVCS observations.

Key words: Sun – corona – UV radiation – line profiles – solar wind.

S. IBADOV

Institute of Astrophysics, Dushanbe 734042, Tajikistan
E-mail: subhon@academy.td.silk.org

F.S. IBODOV

Sternberg Astronomical Institute, Moscow 119899, Russia
E-mail: mshtf@sai.msu.ru

S. S. GRIGORIAN

Institute of Mechanics, Moscow 117192, Russia
E-mail: grigor@inmech.msu.su

Abstract. The possibility of production of metal atoms and ions in the solar atmosphere due to passages of cometary nuclei near the solar surface is considered. It is found that within the solar chromosphere an intense aerodynamic fragmentation of cometary nuclei occurs. This process results in an anomalous abundances of metal atoms and ions. Corresponding spectral observations are important for adequate interpretation of data of coronagraphic observations of the SOLWIND, SMM and SOHO-like missions.

Key words: solar chromosphere – sungrazing comets – metals – anomalous abundances.

L. BIGOT 1, J. PROVOST 1, G. BERTHOMIEU 1, W. A. DZIEMBOWSKI 2, P. R. GOODE 3

1 Département Cassini, UMR CNRS 6529, Observatoire de la Côte d'Azur
BP 4229, 06304 Nice CEDEX 4, France
E-mail: lbigot@obs-nice.fr, provost@obs-nice.fr, bertho@obs-nice.fr

2 Warsaw University Observatory
Al Ujazdowskie 4, PL-00-478 Warszawa, Poland
E-mail: wd@astrouw.edu.pl

3 Big Bear Solar Observatory, New Jersey Institute of Technology
40386 North Shore Lane, Big Bear City, CA 92314, U.S.A.
E-mail: pgoode@tesla.njit.edu

Abstract. We calculate the effect of a strong dipole magnetic field (0.5-1.5 kG) on stellar oscillations. To do this, we adopt a boundary layer approach, by taking into account the dynamical effect of the magnetic field only in a very thin layer, at the star surface. The magnetic field leads to a damping of oscillations due to Alfvénic wave losses of energy. It appears then an imaginary part of the frequency (~1-15 ?Hz) and a shift of the real part (~1-15 ?Hz). The mode identification is complicated: since the Lorentz force depends on the colatitude, one must represent the oscillations by a linear combination of  . We tackled non-axisymmetric oscillations (m   0) and then generalized the result of Dziembowski and Goode (1996). These magnetic effects strongly depend on the geometric nature of the mode (degree   and azimuthal order m). We apply our calculations to roAp stars, whose oscillations appear essentially as dipole modes ( = 1, m = 0) aligned with the magnetic axis. This work does not explain this geometrical preference, since it does not minimize Alfvénic losses of energy. However, it shows that one must take into account the magnetic field to identify modes in roAp stars.

Key words: stars – oscillations – magnetic fields – roAp stars.

A. GALEEV, I. BIKMAEV

Department of Astronomy, Kazan State University, 420008 Kazan, Russia
E-mail: almaz@ksu.ru, Ilfan.Bikmaev@ksu.ru

F. MUSAEV, G. GALAZUTDINOV

Special Astrophysical Observatory of the Russian AS, 357147 Russia
E-mail: faig@sao.ru, gala@sao.ru

Abstract. We present some results of the spectroscopic observations of 13 photometrical solar analog stars. The investigation of the spectral region near Li I 6707.8 line shows that this line in such type stars has the equivalent widths from 2 to 60 mÅ and these stars can be divided into two groups.

Key words: stars – solar-analogs – fundamental parameters – equivalent widths

E. A. BARANOVSKY, A. V. SHOUMKO

Crimean Astrophysical Obsrervatory, P/o Nauchny, Crimea, 98409 Ukraine
E-mail: Edward@crao.crimea.ua, alla@crao.crimea.ua

Abstract. The flare of importance 2 is studied in the H?, H?, H?, H Ca II, the lines of He I, D3 and ? 4471 Å, and photospheric lines using the spectra obtained on the echelle spectrograph of the Crimean Astrophysical Observatory.

Key words: Sun – flare – model.

I. ROUSSEV 1, R. ERDÉLYI 2, J. G. DOYLE 1, K. GALSGAARD 3

1 Armagh Observatory, College Hill, Armagh, BT61 9DG, N. Ireland (UK)
e-mail: ilr@star.arm.ac.uk, jgd@star.arm.ac.uk

2 Space & Atmosphere Research Center, Dept. of Applied Mathematics, University of Sheffield
Hicks Building, Hounsfield Road, Sheffield, S3 7RH, England (UK)
email: Robertus@sheffield.ac.uk

3 University of St. Andrews, North Hough, St.Andrews, KY16 9SS, Scotland (UK)
email: klaus@dcs.st-and.ac.uk

Abstract. We present preliminary results of modelling 2D magnetic reconnection in the solar transition region environment. Compressible magnetohydrodynamic (MHD) simulations are performed by using a 2D MHD code based on staggered meshes. The present work is an attempt to numerically simulate magnetic reconnection that occurs between newly emerging magnetic flux and the pre-existing network field, which is widely believed to cause explosive events observed in the solar atmosphere. The formation of asymmetric reconnection jets is demonstrated in this study. Nonlinear anisotropic thermal conduction, radiative losses, and volumetric heating are included in the energy equation in order to investigate the formation of reconnection jets more precisely, as these processes are of fundamental importance at that region. The role of both nonlinear anisotropic thermal conduction and radiative losses is found to be significant in the solar transition region.

Key words: Sun - transition region - explosive events - numerical simulations

U. S. BAYAZITOV, A. K. GALIEV

Bashkir State University, Frunze Str. 32, Ufa, 450074, Russia
E-mail: BayazitovUS@ic.bashedu.ru

Abstract. The precise determination of iron abundance in stellar objects and Solar system is the actual problem of modern astrophysics. Two authoritative researchers groups from Kiel (Holveger et al., 1995) and Oxford (Blackwell et al., 1995) determined the different values of Fe solar abundance (respectively 7.51 and 7.63 in logarithmic scale). We have redetermined iron abundance using non-LTE calculations. For this purpose the computer code MULTI and solar atmosphere models of R. Kurucz and VAL-C have been used. The 40-levels FeI atom model has been constructed also. The recent values of oscillator strengths and excitation levels have been taken. We measured the equivalent widths of 62 FeI lines using Sun observed spectra for the whole solar disk and for the disk centre. From the comparison of observed and calculated equivalent widths we have derived the iron abundance. For the VAL-C model it is equal to 7.51 and 7.53 for the whole disk and disk centre, respectively. For the Kurucz’s atmosphere model the corresponding values are equal to 7.53 (flux) and 7.55 for the disk centre lines. The present discrepancies of the above mentioned values for the Fe abundance are not the subject of our discussion. From our calculations we have derived the mean value 7.53 ? 0.02 of iron abundance that is closer to the value of Holveger et al. (1995).

Key words: Non-LTE calculations – Sun – abundances

I. PÉREZ 1, T. ROCA CORTÉS 2 and the GOLF team

1 Departamento de Astrofísica, U. de La Laguna, La Laguna, Tenerife, Spain
Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
E-mail: iperez@ll.iac.es

2 Departamento de Astrofísica, U. de La Laguna, La Laguna, Tenerife, Spain
Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
E-mail: trc@astro.iac.es

Abstract. The excitation of p-modes seems to be produced by turbulence in the convection zone (see, e.g., Kumar, 1997 and the references therein). Low-degree p-mode allowed a study of the energy distribution of the p-mode oscillations, concluding that it is of Boltzmann type (Elsworth et al., 1995; Chaplin et al., 1997). Moreover, these authors suggest that the observed distribution has the property that the high energy events exceed the Boltzmann value, wondering whether this property could have a cause other than stochastic excitation by turbulence. Amongst these, there can be: (a) an artifact due to its very small frequency resolution (? 28 ?Hz ? 10 hours), or (b) some other occasional energy release due to high energy magnetic events. In this work, the energetic distribution of the observed p-mode peaks is studied, having the posibility of using a higher (several) frequency resolution on the basis of the data collected by GOLF, onboard SOHO.

Key words: helioseismology – p-modes – excitation

D. E. FAWZY 1, Z. E. MUSIELAK 2, P. ULMSCHNEIDER 1

1 Institut für Theoretische Astrophysik, Universität Heidelberg, Heidelberg, Germany
E-mail: diaa@ita.uni-heidelberg.de, ulm@ita.uni-heidelberg.de

2 Physics Department, University of Texas, Arlington, USA

Abstract. The aim of the present work is to compute the generated nonlinear tube wave energy fluxes carried by longitudinal waves as a result of the interaction between a vertically directed thin magnetic flux tube and the turbulent medium in the stellar convection zone of late type stars. The computations are based on work by Ulmschneider and Musielak (1998). The current computations are for stars of gravities log g = 3,4,5 and temperature range from Teff = 3500 to 7000 K.

Key words: stars – chromosphere – convection zone – magnetic fields – MHD waves – numerical methods