Some further measurements of Uranian ring condensations

The results of photometric observations of the occultation of BD-19° 4222 by Uranus on April 26, 1981 from two stations in India conform with the model proposed by Elliotet al. (1981).     

Photometric study of BZ Eridani

The 1980–1981U, B, andV observations of the eclipsing binary BZ Eridani have been presented. A new period of BZ Eri comes out to be 0^d.6641703. The colour curves of the system show appreciable variations, and are indicative of intrinsic variability. The secondary minimum falls nearly at phase 0.5. Some interesting features are given. The features of BZ Eri are changing. Some light variations are visible around the phase of the secondary minimum. The discussion reveals that BZ Eri is a complicated system.     

Photoelectric study of the eclipsing system CD Eridani

Limiting photometric solutions for the system CD Eri inB andV filters have been obtained. The secondary minimum was found to be absent.     

An Algol type binary with a δ Scuti component: RZ Cassiopeiae revisited

We present new BV photometry and spectroscopic observations of RZ Cassiopeiae. The light and radial velocity curves were formed by the new observations which have been analyzed simultaneously by using theWilson‐Dewinney code. The non‐synchronous rotational velocity v ₁ sin i = 76 ± 6 km s^–1, deduced for the primary component from the new spectroscopic observations, was also incorporated in the analysis. A time‐series analysis of the residual light curves revealed the multi‐periodic pulsations of the primary component of RZ Cas. The main peak in the frequency spectrum was observed at about 64.197 c d^–1 in both B and V bands. The pulsational constant was calculated to be 0.0116 days. This value corresponds to high overtones (n ∼ 6) of non‐radial mode oscillations.We find significant changes in the pulsational amplitude of the primary component from year to year. The peak‐to‐peak pulsational amplitude of the main frequency displays a decrease from 0.^m013 in 2000 to 0.^m002 in 2001 and thereafter we have found an increase again in the amplitude to 0.^m01 in the year 2002. We propose the mass transfer from the cool secondary to the pulsating primary as a possible explanation for such remarkable changes in the pulsational behavior of the primary component. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The equatorial latitude of auroral activity during 1972–1977

The equatorial latitude of auroral activity has been derived from both electron and optical observations with the DMSP satellites. Virtually all of the observations that were obtained during the 5-year interval June 1972-September 1977 have been used to construct a nearly continuous plot of invariant geomagnetic latitude versus time.This plot has two main characteristics: (1) A diurnal variation of approximately ± 5° which is associated with the precession of the Earth's magnetic dipole axis about the Earth's rotation axis; (2) an irregular variation of roughly 5–10° for intervals of one to several days associated with the occurrence of solar flares and coronal holes.With the help of a condensed, Bartels-type display of these measurements, we conclude that: (a) Modest auroral expansions (to ~ 60°) occur during the main body of high-speed streams from coronal holes; (b) great expansions (to < 55°) occur only during intervals of intense interplanetary magnetic fields such as may occur at the leading edge of a high-speed stream or at a flare-produced interplanetary shock.     

Period variations in BZ Eridani

The O-C diagram of BZ Eri has been presented for the first time, and the period variations present in the system have been analysed. In all, eight period decreases and eight period increases are noticed. Of these, four period decreases and seven period increases are appreciable. The strongest period changes are noticed in the interval 1960 to 1962. The total period change in different portions of the O-C diagram ranges from 1.17×10^–3 d to 3.96×10^–6 d. The trend of the period variation appears to have reversed around the year 1980.     

Calculation of anisotropy ratio of hard X-rays from solar flares — evidence for continuous electron injections/accelerations

Variation of electron energy and angular distributions has been studied as a function of column density by combining small-angle analytical treatment with large-angle Monte Carlo calculations. The distributions have been calculated for initial electron energy 300 keV and various incidence directions. Using these distributions and Sauter bremsstrahlung cross-section differential in photon energy and emission angle, we have calculated the X-ray energy and angular distributions for photon energies 10, 20, 50, 100, 150 and 200 keV. By taking the ratio of X-ray flux at 90 and 180°, we have computed the anisotropy ratio A as function of column density. Calculated anisotropy ratio compares well with ISEE-3 and PVO observations.     

Interplanetary baseline observations of type III solar radio bursts

Simultaneous observations of type III radio bursts from spacecraft separated by 0.43 AU have been made using the solar orbiters HELIOS-A and HELIOS-B. The burst beginning at 19:22 UT on March 28, 1976 has been located from the intersection of the source directions measured at each spacecraft, and from burst arrival time differences. The source positions range from 0.03 AU from the Sun at 3000 kHz to 0.08 AU at 585 kHz. The electron density along the burst trajectory, and the exciter velocity (=0.13c) were determined directly, without the need to assume a density model as has been done with single-spacecraft observations. The separation of HELIOS-A and -B has also provided the first measurements of burst directivity at low frequencies. For the March 28 burst the intensity observed from near the source longitude (HELIOS-B) was 3–10 dB greater than that from 60° west of the source (HELIOS-A).     

Abundance analysis of the long period southern cepheid RZ Vel

The long period classical cepheid RZ Vel (HD 73502) is known to be a member of an OB association, Vel OB1 in Vela, and a high metallicity is ascribed to it by the photometric work of Eggen (1982). We have done an abundance analysis for this long period (P = 20.4 days) and hence young (age ≈ 1.80×10⁷ yr) classical cepheid using high resolution CCD spectra with good S/N ratio. We have used a detailed model atmosphere method to derive the abundances of the light elements C, O, A1, S and of many Fe-peak elements and a few s-process elements. Our present work indicates near solar abundance for most of the elements for RZ Vel and hence we do not confirm the high metallicity derived photometrically by Eggen (1982) for this star     

Simultaneous five color (UBVRI) polarimetry of EF Eri

We present the first observations of the AM Her type object EF Eri where both the polarization and the photometric data are recorded simultaneously in five color bands (UBVRI). The position angle rotates strongly (30°) vs. wavelength from U to I, probably due to Faraday rotation or due to fact that the polarized radiation seen in the different wavelength bands comes from different parts of the accretion region. The phase dependence of the position angle requires field and accretion geometry more complicated than a simple centered dipole and a second emitting region producing weaker intermediate pulses in the infrared seems to be present. We derive the value of the inclination of the system i=55°±5°, the colatitude of the active pole ₁,= 38° ±5° and the second emitting region = 115° ± 5°, both of which are nearly at the same longitude facing the main accretion stream.Based on observations made at the European Southern Observatory, La Silla, Chile.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Microvariability and fast variability of stars. I. standard stars

This is a study of observations of the photometric quantities Vt and Bt, reported in the Hipparcos catalog, for 15 standard stars in order to search for microvariability and rapid variability in their emission. The microvariability is found to be characterized mainly by smooth fluctuations in the brightness. Changes in the magnitudes of the stars HD 28355 and HD 130109 with a period of ~150 min and an amplitude <0^m.02 appear to be caused by vertical shifts in their photospheres. Changes in the magnitudes with an amplitude of ~0^m.01 and a period of 11.4^d in the star e Eri were related to the rotation of spots. A similar microvariability period and amplitude in the star 51 Peg most likely originates in the influence of a planet.     

Short-period noncontact binaries

Five short-period noncontact binaries (GR Tau, UU Lyn, BV Eri, RU Eri, and BW Eri) are studied. It is found from photometric and spectroscopic observations that (1) both components are noncontact to each other but are very close to the respective Roche lobes; (2) period change does not appear or it is very small; and (3) component stars of UU Lyn and RU Eri are normal main sequence stars while those of GR Tau and BV Eri are smaller and less massive components indicating in an advanced evolutionary state having experienced mass reversal.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Spectral investigation of some Be stars for NRP variability

Spectroscopic observations of the Be stars Eri, Oph, 66 Oph, and Ori for the period 1982–1988 are reported. The NRP hypothesis was verified on the ground of rapid line profile variability, radial velocities, and equivalent widths. The star Eri is pulsating in bothl=2 andl=8 with period 0 _. ^d 7. Pulsation in modesl=2 andl=4 are observed in Hei profiles of Oph for May 1982. For radial velocities has been obtained a period 0 _. ^d 913. The H and H lines of 66 Oph for April–August 1983 are in emission state with two clearly expressed components with intensity variations. All the parameters measured have the same period of variation — 0 _. ^d 025. For Ori variations in line profiles for component Ab have been observed and a period of 0 _. ^d 463 found for the radial velocities.     

Water vapor abundance in Venus' middle atmosphere from Pioneer Venus OIR and Venera 15 FTS measurements

The Pioneer Venus Orbiter Infrared Radiometer and Venera 15 Fourier Transform Spectrometer observations of thermal emission from Venus' middle atmosphere between 10° S and 50° N have been independently re-analyzed using a common method to determine global maps of temperature, cloud optical depth, and water vapor abundance. The spectral regions observed include the strong 15 μm carbon dioxide band and the 45 μm fundamental rotational water band. The different spatial and spectral resolutions of the two instruments have necessitated the development of flexible analysis tools. New radiative transfer and retrieval models have been developed for this purpose based on correlated-k absorption tables calculated with up-to-date spectral line data. The common analysis of these two sets of observations has hence been possible for the first time. From the PV OIR observations, the cloud-top unit optical depth pressure showed a minimum of ∼110±10 mbars in the evening equatorial region and a maximum of ∼160±12 mbars in the morning mid-latitude regions. From the Venera 15 FTS spectra, the cloud-top pressure was found to increase from morning values of ∼120±10 to 200±30 mbars in the late afternoon/early evening region. The cloud-top water vapor abundances observed by the PV OIR instrument were found to fluctuate from 10±5 ppm at night up to 90±15 ppm in the equatorial cloud-top region shortly after the sub-solar point. The mean Venera 15 FTS water vapor abundances were found to be 12±5 ppm with only a slight enhancement over the equatorial latitude bands and no clear day-night distinction. The common analysis of these two sets of observations broadly validates previously published individual findings. The differences in the retrieved atmospheric state can no longer be attributed to radiative transfer modeling bias and suggest significant temporal variability in the middle atmosphere of Venus.     

Analysis of light variations of the eclipsing binary system XY ceti with Am spectra

The photoelectric light curves of XY Cet of Srivastava and Padalia (1975) and of Morrison and Morrison (1968), from which considerably different sets of photometric elements have previously been deduced, were re-analyzed in detail. The elements derived in the present study from Srivastava and Padalia's (1975)UBV observations arer _g=0.157±0.006 (p.e.),r _s=0.142±0.007,i=88°.4±0°.5,L _g=0.600±0.017, 0.602±0.015 and 0.584±0.018 forU, B andV, respectively. It is also found from their light curves that the system has an eccentric orbit withe cos =0.0026±0.0005. The elements deduced from theV observations of Morrison and Morrison (1968) are found to be in satisfactory agreement with those presented above.The existence of theAm characteristics of both components, which was recognized by earlier spectroscopic observations, are supported by theB-V andU-B color indices and [m ₁] value of the system. Both components are also found to have appreciably evolved, as expected for metallicline stars.     

The early-type variables

We review the observational status of several different kinds of intrinsic variables among the early-type stars and attempt to interpret the variations in terms of our current understanding of stellar pulsation. Four distinct types of intrinsic variable can be defined: the Cep, 53 Per, Oph and Eri stars. A simple observational classification scheme, which is readily interpreted in terms of pulsation properties, is proposed. The limits of the instability strip and pulsation constants for the Cep and 53 Per stars is discussed. Problems with the interpretation of Eri stars in terms of pulsation are pointed out. The observations are consistent with rotational modulation. A problem with mode identification in Eri stars is discussed.     

A photometric study of the short-period eclipsing binary BW Eridani

UBV observations of the short-period eclipsing binary BW Eri are reported and analyzed. The photometric parameters are determined. BW Eri is a detached or semidetached system.     

UBV observations of R CrB-type variables and related objects

UBV observations obtained during the period 1972–73 are presented for the following five R CrB Stars: GU Sgr, SU Tau, XX Cam, DZ And, V973 Oph, and the hydrogen-poor, carbonrich stars BD +10°2179 and HD 137613. Observations of SU Tau were obtained when it was coming out of the 1972 light minimum.     

Intensity profiles of a sunspot near the solar limb

Photo-electric observations of the intensity profile of a sunspot at a heliocentric angle of 76° at four wavelengths are reported. An intensity peak at the centre-side penumbra-photosphere border predicted by Jensen et al. (1969) has been observed.