Volume 10, Issue 1
March 1989, pages 1-138
pp 1-20 March 1989
During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H2 O+ emission was recorded in thecoma at ∼ 0h UT on 1986 March 13. Observations were carried out using a special IHW filter for H2 O+ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24‡39’N,72‡ 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ∼ 35km s−1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet
pp 21-34 March 1989
Starting from a set of general equations governing the dynamics of a magneto-fluid around a compact object on curved space time, a fairly simple analytical solution for a test disc having only azimuthal component of velocity has been obtained. The electromagnetic field associated has a modified dipole configuration which admits a reasonable pressure profile for the case of fully relativistic treatment of Keplerian type of velocity distribution
pp 35-45 March 1989
DifferentialBV photometry of UX Ari obtained on 58 nights during 1984-85, 1985-86, 1986-87, and 1987-88 observing season is presented. We find that (B-V) is phase dependent with the system being reddest at the light maximum and we interpret this as due to the variable fractional contribution by the G5 V component to the total light at shorter wavelengths. An analysis of the available data indicates that at larger amplitudes of the photometric wave the brightness at maximum increases and that at minimum decreases and both converge to δV ≃ −1.0 mag at very low amplitudes. It implies that the low wave amplitudes are essentially due to more homogeneity in the surface distribution of spots rather than due to low levels of spot activity. The variation in wave amplitude is found to be near-sinusoidal with a period around 13–14 years
pp 47-83 March 1989
We present here an extensive list of internally consistent oscillator strengths for Fe I lines. We have compiled and critically reviewed the oscillator strengths existing in literature. An attempt has been made to scale the oscillator strengths derived by different workers to that of Blackwell and his collaborators and prepare a single consistent set of oscillator strengths.
We have calibrated a loggf- log λ- E1- log I relationship that can be used for calculatinggf values for Fe I lines with nogf values available. We demonstrate that standard error of such a calibration can be considerably reduced by binning the data in 0.5 eV range in excitation potential.
We also tabulate systematic corrections to be applied to the oscillator strengths of Kurucz & Peytremann (1975) for lines belonging to different multiplets
pp 85-88 March 1989
Results of a search for occultations of stars in the SAO catalogue by Saturn’s outer magnetosphere during 1989-1990 are presented. A total of nine events are predicted to occur during this period. The most favourable event will be the occultation of 28 Sgr (SAO 187255) during July 2–3, 1989. Occultations of SAO 187036, SAO 188348 and SAO 188120 occur near opposition and therefore can be observed over a wide longitude range
pp 89-112 March 1989
A theory of sequential fragmentation is presented that describes a cascade of fragmentation and refragmentation,i.e., continued comminution. It is shown that the theory reproduces one of the two major empirical descriptors that have traditionally been used to describe the mass distributions from fragmentation experiments. Additional experimental evidence is presented to further validate the theory, and includes explosive aerosolization, grinding in a ball mill, and simulated volcanic action. Also presented are some astronomical applications of the theory including infalling extraterrestrial material, siderophile concentrations in black magnetic spherules of possible meteoritic origin, the asteroids, the distribution of galactic masses, and the initial mass function of stars
pp 113-118 March 1989
HR 8107, a reported new Be star, has been observed spectrophotometrically. The energy distribution curve of the star has been compared with those of other stars of similar spectral and luminosity types and model atmospheres. On the basis of comparison with model atmospheres an effective temperature has been assigned to the star
pp 119-138 March 1989
None of the tentative black-hole identifications has remained without serious difficulties. As a class, the black-hole candidates differ in no obvious property from neutron-star binaries other than in their estimated high mass. We favour an interpretation of the black-hole candidates as binary neutron stars surrounded by a more or less massive accretion disc
Volume 40 | Issue 5
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