S. P. Tarafdar

X-ray observations of planetary nebulae with the Exosat satellite

Twelve planetary nebulae have been observed with X-ray detectors in the Exosat satellite. Eight planetary nebulae are found to emit detectable X-rays, out of which four are reported here for the first time. Six of these are extended nebulae, while two are nebulae of smaller size. The detection of the six older nebulae agrees with the earlier suggestion that the X-rays from the central star are visible when the nebula disperses or when the heavy elements in the central star atmosphere settle down. In the two nebulae NGC 4361 and NGC 1535, the X-ray luminosity is high enough to ionize carbon in the nebula and to allow the X-radiation emerge without absorption. 12 refs.

Elemental abundance enhancement in cosmic rays and their relation to interstellar depletion

We have shown that a correlation exists between the enhancement of abundance of heavy nuclei in cosmic rays and their depletion in interstellar space. A correlation also exists between the abundance enhancement and condensation temperature. We suggest that these correlations imply that much of the heavy nuclei content of cosmic rays may come from grains. A possible model is that grains in star-cloud complexes are accelerated to injection energies by radiation pressure in a supernova explosion and, subsequently, the grain debris is accelerated by shocks to cosmic ray energies.

On the variation of specific angular momentum among Main Sequence stars

The specific angular momentum is found to vary with mass for earlier and later-type Main Sequence stars. Of various plausible causes, the difference in the interior density distribution of earlier and later-type stars is not sufficient enough to explain the difference either in angular momentum or in its gradient between earlier and later-type stars. The non-rigid rotation, however, may account for this difference in specific angular momentum as well as its gradient, if faster angular velocity in the interior for later-type and/or slower angular velocity for earlier-type stars than the surface value is allowed. A few other possibilities have also been briefly considered to understand this difference.

Hα emission from late type be stars

We show here that the Hα flux from late type Be stars can be explained as emission from an HII region formed in the gas envelope around the Be star, by the UV flux emitted by a helium star binary companion. We also discuss the observability of the helium star companions.

The X-ray hardness ratio variation in low-mass X-ray binaries

AbstractThe behaviour of the hardness ratio in low-mass X-ray binaries (LMXRB) indicates that at some value of mass accretion raten

Line profile variations in Be stars

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The X-ray intensity-hardness ratio relation in LMXRB

n, the X-ray intensity decreases with increasingn