Engineering topics

Hrivnak, B. J.

Publications and source records attributed to Hrivnak, B. J..

5 records

NASA NTRS1992

Unusual 3 micron emission features in three proto-planetary nebulae

Medium-resolution 3-4 micron spectra have been obtained of three objects, IRAS 04296 + 3429, IRAS 22272 + 5435, and CRL 2688, which are in transition between the asymptotic red giant branch and the planetary nebula phase. All three show unusual 3-micron emission features. The two IRAS objects, already unusual in having 21 micron features, have remarkably strong 3.4-3.5 micron emission relative to the usually dominant 3.3-micron feature, with the spectrum of IRAS 04296 + 3429 being nearly identical to that of IRAS 05341 + 0852 (previously published). CRL 2688's spectrum bears some resemblance to those of the IRAS objects, but its 3.4-3.5 micron emission is not as strong. The relationships between the various emission features are discussed. CRL 2688 may be completing a transition between the '21-micron phase' and the 'normal phase', which is associated with dominant 3.3-micron emission, weak 3.4-3.6 micron features and plateau, and a lack of 21-micron emission.

Geballe, T. R.↗

NASA NTRS1989

Unidentified infrared features in proto-planetary nebulae

The discovery of an unidentified emission feature at 21 microns in the spectra of three protoplanetary nebulae is reported. These objects show large far infrared excess due to a circumstellar dust envelope surrounding a carbon rich central star. Optical, infrared and radio observations of three cool Infrared Astronomy Satellite sources suggest that they are carbon rich objects. Their low resolution spectra show a broad unidentified emission feature at 21 microns which could originate from the bending mode of a hydrocarbon molecule. The similarity of all three objects suggests that this feature is unlikely to be the result of instrumental effects.

Kwok, S.↗

NASA NTRS1986

HD 47755, a new eclipsing binary

The IUE spectra of the close binary star HD 47755 have been examined in order to determine its geometry, chemical composition, and light curve. UBV fluxes in the spectra, when dereddened for E(B-V) = 0.09 yield an effective temperature of 16,500 K. The ratio of the mean radii of the stars is found to agree well with an old blueband spectrophotometric value. Eclipses in the binary have been observed and a complex green light curve is derived. It is suggested that the wind from at least one of the components of HD 47755 is the source of the complexity in the light curve. The geometry of the HD 47755 is compared to that of V 641 Mon, A definite cluster member of NGC 2264. The interstellar line spectrum is found to be similar to that of V 641 Mon and the column densities for a few interstellar ions are given in a table. Evaluation of the nonastrometric evidence indicates that HD 47755 is also a member of NGC 2264.

Koch, R. H.↗

NASA NTRS1985

IUE spectroscopy, visible-band photometry, and polarimetry of HD 47732 (V641 Monocerotis)

Several high- and low-dispersion IUE spectra are described for the hot, massive close binary HD 47732. The stellar silicon lines do not show theoretically expected strength, the weakness being attributed to incipicent emission. A weak stellar wind is measurable with an expansion velocity of about 500 km/s. There is difficulty in fitting a model atmosphere to all of the IUE continuum and visible band and IR measures. These difficulties are resolved by appealing to a 22,500 K model atmosphere and a distinctive interstellar extinction law. Numerous V band measures show the polarization to be variable, but not strongly in a phased-locked way. This suggests sporadic outbursts of gas feeding the shell. Several seasonal V band light curves are discussed, and the seasonal variations among them are attributed to variable developments of a systemic shell which scatters the photospheric light and dilutes to a variable degree the light variation due to ellipticity of figure of the component stars.

Koch, R. H.↗

NASA NTRS1982

IUE spectroscopy, visible-band polarimetry, and radiometry of V641 Mon

This hot, double line, ellipsoidal variable member of NGC 2264 has been shown previously to be either a semi-detached or contact close binary. Low-resolution IUE spectra are best fitted to a Kurucz model atmosphere for very small (approximately 0.08 mag) E(B-V). The familiar interstellar absorption dip near lambda 2200 is apparently absent. A suitable model atmosphere can be fitted to the IUE fluxes, but flux excesses (compared to the model) appear for all the published U through L magnitudes. The spectrum of the B through L excess appears to follow a .0001 lambda dependence. It is shown that this cannot be interpreted as arising from another star fortuitously observed in the visible band or IR. Ground based polarization measures indicate V641 Mon to be a polarization variable. Previous and new V light curves show the amplitude of light variability itself to be variable by about a factor of 2. It is suggested that all these observed characteristics are best explained by postulating "third light" and identifying part of it with Rayleigh scattered starlight very near to the stars. From this same region there arise circumstellar absorptions which give rise to nontheoretical strengths for Si II and Si III lines.

Koch, R. H.↗