The eclipses of EX Hydrae

Two short runs of spectral data on EX Hya have been obtained. One of these provides a high time and wavelength resolution data set covering a cycle in the 67 min modulation and containing a deep eclipse. The other was acquired shortly preceding one of the relatively rare outbursts of this system. Examination of these data sets confirms features noted in other studies. In particular, a broadV/R eclipse effect' is seen in the Balmer lines, and a sharp peak in Balmer line equivalent width is detected at mid-eclipse. Also, the correlation with 67 min phase of the (O-C) residuals for optical eclipse time is examined in relation to the location of the eclipsed structure. The accretion curtain model of Rosenet al. (1988) is discussed and shown to be qualitatively consistent with the observational data in both the optical and X-ray bands.     

The nature of the eclipses of VZ Hydrae

Further study of the observedU, B, V light curves of VZ Hya reveals that the primary eclipse is an occultation.     

Formation of polar starspots through meridional circulation

To explain the observed intermingling of polarities in the magnetic field distributions of rapidly rotating stars, surface magnetic flux transport models demand the presence of fast meridional flows.We combine simulations of the pre-eruptive and post-eruptive magnetic flux transport in cool stars to investigate the influence of a fast meridional circulation on the latitudinal eruption pattern of magnetic flux tubes and on the polar magnetic field properties. Magnetic flux tubes rising through the convection zone experience an enhanced latitude-dependent poleward deflection through meridional flows, which renders the wings of stellar butterfly diagrams convex. The larger amount of magnetic flux emerging at higher latitudes supports the intermingling of opposite polarities of polar magnetic fields and yields magnetic flux densities in the polar regions about 20% higher than in the case disregarding the pre-eruptive deflection. Taking the pre-eruptive evolution of magnetic flux into account therefore eases the need for the fast meridional flows predicted by previous investigations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric modelling of starspots – II. The fortran code spotpic

A fortran code which computes synthetic light and colour curves of active, spotted stars has been developed. The main feature of this code is that it can simultaneously model the V light curve and the ( V − R )_c, ( V − I )_c, ( V − K ) colour data. It also uses new effective temperature–colour and Barnes–Evans-like calibrations, temperature and gravity-dependent limb darkening coefficients and different effective surface gravities for the spotted and unspotted photosphere. The code allows for two-component spots, i.e. spots with umbral and penumbral components. Various problematic spot configurations were investigated and we conclude that, in order to be able to differentiate spots with various thermal structures (umbrae, penumbrae, faculae) or polar spots from equatorial bands, the modelling of the infrared colours, especially ( V − I )_c and ( V − K ), is needed.     

Light deflection during solar eclipses

A simultaneity is observed between fluctuations in ellipticity of the solar corona and variation of the light deflection by the Sun, during the eclipses.

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Résumé On constate une simultanéité entre les fluctuations de l'ellipticité de la couronne solaire et les variations des déviations de la lumière, par le soleil, durant les éclipses.

     

Jovian satellite-satellite eclipses and occultations

Toward the end of 1973 and in the first part of 1974, when the planes of the orbits of the four large Galilean satellites cross the Sun and the Earth, satellite-satellite eclipses and occultations will occur. Calculations indicate that during this period 350 such events will occur, most of them potentially observable. From observation of a few of these events the ephemerides of the satellites can be improved, radii and limb darkening curves determined, and crude information about the degree and extent of albedo fluctuations deduced. If a concerted effort were made and a large fraction of these events carefully observed it would be possible to invert the light curves to obtain albedo maps of most of the surface area at a typical resolution of about 100km for JI and JII and somewhat poorer for JIII and JIV. In 1979—the next opportunity—there will be considerably fewer events, and only a relative few of them will be observable at night.     

Early eclipses of the Galilean satellites

A brief summary of the development of the theory of motion of the Galilean satellites is presented. Over 7700 eclipse observations have been collected and reduced using the Ephemeris E-2. They are of great potential in improving the ephemerides of the satellites and can yield important information on the evolution of the Galilean system.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980Presently a recipient of the Humboldt Award of the Alexander von Humboldt Foundation at the Astronomisches Rechen-Institut in Heidelberg and on leave from the Jet Propulsion Laboratory     

Scientific observations at total solar eclipses

The occasion of the longest totality of an eclipse in the 18 yr 111/3 d saros cycle leads to taking stock of the scientific value of ground-based eclipse observations in this space age. Though a number of space satellites from the U.S., Europe, Japan, and Russia study the Sun, scientists at eclipses can observe the solar chromosphere and corona at higher spatial resolution, at higher temporal resolution, and at higher spectral resolution than are possible aloft. Furthermore, eclipse expeditions can transport a wide variety of state-of-the-art equipment to the path of totality. Thus, for at least some years to come, solar eclipse observations will remain both scientifically valuable and cost-effective ways to study the outer solar atmosphere.     

Comet searches during four major eclipses

Photographic observations made during the solar eclipses of 1963, 1966, 1968, and 1970 indicate the presence of previously unidentified celestial objects in the near-angular vicinity of the Sun. Observational data and equipment are described. Possible origins of the objects are enumerated, as well as suggested future experiments to confirm the results.     

Scientific observations at total solar eclipses

The occasion of the longest totality of an eclipse in the 18 yr 11^1/3 d saros cycle leads to taking stock of the scientific value of ground-based eclipse observations in this space age. Though a number of space satellites from the U.S., Europe, Japan, and Russia study the Sun, scientists at eclipses can observe the solar chromosphere and corona at higher spatial resolution, at higher temporal resolution, and at higher spectral resolution than are possible aloft. Furthermore, eclipse expeditions can transport a wide variety of state-of-the-art equipment to the path of totality. Thus, for at least some years to come, solar eclipse observations will remain both scientifically valuable and cost-effective ways to study the outer solar atmosphere.     

Predictions for eclipses of Nereid by Neptune

Neptune will eclipse its satellite Nereid (Neptune II) on 2007 April 27 from 00 to 06 h UT and on 2008 April 21 from 12 to 17 h UT, with uncertainties of about 3 h; and a third eclipse may occur on 2009 April 17. These events offer unique opportunities for astrometric and geophysical measurement.     

Light variation of LX persei between eclipses

Two-colour photoelectric observations of LX Per carried out at Ege University Observatory in 1981 and 1982 observing seasons are presented. The light curve of the system has a wave-like distortion which migrates towards the decreasing orbital phase. The period of the retrograde migration of the wave-like distortion has been determined as 475 days. The amplitude of the wave appears to change with time periodically.     

Models for planetary eclipses of the uranian satellites

A model for computing the brightness of a satellite in the shadow of a planet is described, which takes into account the Sun–planet–satellite–sensor geometry, the satellite bi-directional reflectance function, and the refraction of sunlight in the planetary atmosphere. Synthetic light curves for eclipse ingress or egress of the five large satellites of Uranus are generated. The model luminosities can be fitted to photometric observations in order to calculate a precise distance between the centers of the satellite and the planet. Alternately, when the satellite ephemeris is accurately known the atmospheric state of the planet can be studied.     

Photometry of the lunar surface during lunar eclipses

The photometric observations of the lunar surface during lunar eclipses were carried out on four nights between 1972 to 1978, using the 91 cm reflector of the Dodaira Station of the Tokyo Astronomical Observatory. The photometry was performed in B-, V-, and R-colours, and arranged in accordance with the angular distance from the centre of the Earth's shadow. The results do not show any large systematic differences between the four nights, showing no support for Danjon's proposition.     

The disappearance of eclipses in the central star of the planetary nebula NGC 2346

This paper gives the result of photographic photography of the central star AGK3-0° 695 of the planetary nebula NGC 2346 made from 1981 through 1987. From it we see that after the large-amplitude eclipses which had started at the end of 1981 had continued for several years, the amplitude began to decrease rapidly in 1986 to ˜1.1 mag from ˜4 mag in 1984. In 1987, only irregular fluctuations with amplitudes ˜0.4 mag were present in the light curve and not longer any clear periodicity. A preliminary analysis of this phenomenon is carried out here.     

Ancient Chinese observations of physical phenomena attending solar eclipses

The realization that solar activity probably undergoes changes in qualitative character on time scales greater than the 11 or 22 year cycle but short compared to the duration of recorded history gives renewed importance to historical documents describing the state of solar activity. Modern eclipse observation reveal the presence of solar activity through the appearance of coronal structures and prominences. It has been widely remarked that eclipse records prior to the 18th century are uniformly silent on these conspicuous solar eclipse features, raising the possibility, however unlikely, that a change in solar activity has occurred which rendered them only recently noticeable. We present here material from ancient Chinese sources, primarily astrological, that describe phenomena attending solar eclipses that are almost certainly coronal structures and prominences. Thus, these aspects of the present character of solar activity have apparently occurred at other times in history, if not continuously.     

Coronal emission line profile observations at total solar eclipses

High resolution spectra of the coronal emission line Fe xiv at 530.3 nm obtained at the 30 May 1965 total solar eclipse are analyzed and interpreted. Deconvolution techniques that preserve the line intensity vs wavelength profile shape are developed to obtain further resolution improvement. The west limb coronal enhancement is determined to have temperatures less than 3 MK and turbulent velocities of ～25 km s^-1 decreasing with altitude. Temperature gradients provide evidence for marginal solar wind flow from this enhancement. Above the quiet photosphere in the southwest quadrant the comparison of line and continuum intensities and consideration of line width suggest to us the coronal region is filled with inhomogeneous plasma, dense enough in localized regions to maintain collisional excitation. Solar wind flow from this region obtains when turbulent velocities are assumed to contribute to the line broadening. We identify this region as a coronal hole and suggest that coronal material is heated by the quiet photosphere below.