VI Emission Lines Research Articles

Simulations of the Raman-scattered O vI emission lines in symbiotic stars

Simulations of the Raman-scattered O vI emission lines in symbiotic stars

ORFEUS Observations of AM Herculis

The Orbiting and Retrievable Far and Extreme UV Spectrometer (ORFEUS) telescope has observed AM Her in its high optical state at high spectral resolution in the 912-1176 A band. Spectra at two phases show O VI emission lines with a broad and narrow component structure similar to that of the optical emission lines. We find that the O VI lines are optically thick, and that the densities in the broad- and narrow-component regions differ by a factor of 100. The most puzzling aspect of the observations is the continuum, which is softer than expected, but does not show definite Lyman absorption lines. We discuss the implications for the 'soft X-ray excess' of AM Her stars.

Morphology & Kinematics of the ‘Born–Again’ Planetary Abell 78

Abell 78 is one of a group of planetaries having an old, H–rich nebula surrounding a hot star which has more recently ejected highly–processed, H–deficient material. The A78 central star has O VI emission lines and a 3700 km s−1 hot wind, and is surrounded by knots of very dusty, H-deficient material. These objects are thought to have suffered a late helium shell flash which resulted in the central star (then a white dwarf) returning to the AGB and ejecting highly-processed material.

Global O VI line emission from the Cygnus Loop supernova remnant and direct kinematic measurement of the associated shock

A far-ultraviolet spectrophotometric emission-line mapping of the Cygnus Loop supernova remnant is presented. These are results from the first flight of the rocket-borne, High Resolution Emission Line Spectrometer. The spatial distribution of the emission is that of a limb-brightened shell, and similar to soft X-ray maps. The emission-line profiles, which are broader than the instrument resolution, were consistent with uniformly expanding shell models. Best-fit values give a radial expansion velocity to the emissive region of 185(+/-19) km/s and a reddening-corrected average surface brightness of 8.8(+/-3.6) x 10 exp -6 ergs/sq cm s sr in the doublet. Comparison of the observed brightness with predictions of both radiative and nonradiative shock models provides constraints for the global blast wave ram pressure as well as a "covering factor" of the intermediate velocity shock.

Detection of highly ionized silicon in the planetary nebulae NGC 6302 and NGC 6537

Observations of two high-excitation helium-rich PNs are reported, showing Si VI and Si VII near-IR forbidden line emission from NGC 6302 and forbidden Si VI line emission from NGC 6537. The fluxes observed from NGC 6302 are 3.8 X 10 to the -11 ergs/sq cm sec for the forbidden Si VI line at 1.96 microns and 4.3 X 10 to the -11 ergs/ sq cm sec for the forbidden Si VII line at 2.48 microns. Abundances for Si (5+) and Si (6+) are derived and the central star temperatures are estimated using the abundance ratio. It is found that NGC 6302 probably has the hottest central star of any planetary that has been observed. 39 references.

Contamination induced changes in photon emission from Nb and Nb/V alloys

Changes in NbI and VI line emission and continuum emission with contamination by O 2 and CO background pressures have been studied from ion bombarded Nb and Nb/V alloys. Broad band continua and discrete broad features (possibly molecular) are noted. Importantly, the NbI and VI line emission intensities are found to peak at the same oxygen exposure for a particular alloy and that the exposure for the intensity peak increases with the Nb concentration of the alloy. Intensity enhancements for the atomic lines also change with the alloy concentration and are greater for the VI 411.1 nm line from the bombarded alloys than the pure V, but less for the NbI 405.9 nm line from the bombarded alloys than the pure Nb. An explanation of these changes would include the Nb, V and O atoms all influencing the excitation process, which may involve the quasimolecular formation model. These matrix effects are reported here for proton emission for the first time, and may have an important influence on SIPS chemical analysis when oxygen is present. Unlike the atomic lines, continuum emission does not reflect the changes in the alloy concentrations. The continuum emission is shown to be particularly sensitive to surface cleanliness. Significant differences in the continuum emission are found for bombardment of Nb under O 2 and Co background pressure contamination.