Joni Jayne Johnson

Ultraviolet Interstellar Polarization of Galactic Starlight.I.Observations by the Wisconsin Ultraviolet Photo Polarimeter Experiment

The Wisconsin Ultraviolet Photo Polarimeter Experiment (WUPPE) ew twice as part of NASAs Astro Spacelab missions in 1990 December and 1995 March. A systematic survey of the interstellar polarization in the ultraviolet was one of the main projects on both ights. The program was carefully crafted to 1) sample the galactic plane as uniformly as practicable, 2) explore sight lines of diverse chemical composition and morphology, and 3) measure the shape of the UV polarization through the full range of known wavelengths of peak polarization in the optical. We present here Astro-2 data for 20 previously unobserved sight lines and combine these with previously published UV data and with optical observations from the University of Wisconsins ground based facilities and elsewhere. We thus have spectropolarimetry from 1500 A to 10,000 A for 35 galactic objects in which the polarization appears to be dominated by the interstellar component. The extrapolation of the empirical Serkowski formula based only on visual data does not provide a reliable representation of the UV polarization. We nd that there are substantial diierences in the amount of UV polarization relative to that in the visual. This may indicate that the small and large aligned grain populations are somewhat independent and this may in turn provide a new diagnostic of varying conditions in the interstellar medium. Finally there are several cases in which the UV polarization is enhanced in the 2000 A to 3000 A range.

Photometry of variable AFGL sources

Results of infrared photometric observations of 63 AFGL sources over the past 9 years are presented. Using these data together with previous measurements of these stars, pulsation periods and mean photometric characteristics are determined. These stars are found to lie midway between optically identified Mira variables and the radio-luminous OH/IR stars in their period distribution and photometric properties. For the sample as a whole, there is no evidence for sudden or transient behavior such as a switch in pulsation mode. Rather, these stars suggest rapid, but continuous, evolution from shorter period Miras with weak mass loss to longer periods and larger mass-loss rates. The carbon-rich stars in the sample have the same period distribution as the oxygen-rich stars. None of the carbon stars have periods as long as those of the very long period radio-luminous OH/IR stars.

From red giant to planetary nebula : dust, asymmetry, and polarization

The polarization characteristics of stars in the stages of evolution from red giant to planetary nebula are investigated. Polarization is found to be a characteristic of the majority of these stars. The maximum observed polarization increases with age as the star evolves up the asymptotic giant branch (AGB) to the protoplanetary nebula phase, where the polarization reaches a maximum. The polarization then decreases as the star further evolves into a planetary nebula. These results indicate that aspherical mass loss is likely to be a continual feature of the late stages of stellar evolution, maintaining a clear continuity throughout the life of a star from the moment it first develops a measurable dust shell. The aspherical morphology seen in planetary nebulae has its origin in an intrinsic property of the star that is present at least as early as its arrival at the base of the AGB. 77 refs.

The First Ultraviolet and Optical Spectropolarimetry of the B[e] Star HD 50138

We report the first ultraviolet spectropolarimetry of the B[e] star HD 50138, obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment aboard the Astro-2 Space Shuttle mission in 1995 March. The data cover the spectral range 1500-3200 A. Spectropolarimetry obtained contemporaneously in the range of 3800-10,000 A in the visual-to-near-IR region are presented as well. The presence of intrinsic polarization is detected from the UV to the near-IR. Strong evidence of a thin gaseous disk around the star is found. An almost flat wavelength dependence of the intrinsic polarization in the optical spectral region indicates that electron scattering, rather than dust scattering, is the dominant polarizing mechanism, although a small contribution due to dust scattering cannot be completely ruled out. A small inclination of the disk away from edge-on with respect to the line of sight is suggested. Comparison with similar polarimetric observations obtained for different objects that have the same circumstellar geometry shows that the envelope of HD 50138 probably has a rather large density contrast between the equatorial and polar regions that does not produce a position angle flip like that observed in other objects, notably HD 45677.

Infrared observations of the recurrent novae V745 Sco and V3890 Sgr

Infrared photometric and spectral observations of the two newly identified recurrent novae V745 Sco and V3890 Sgr are presented. We find that these two objects have late-type giant stars in their systems, allowing us to group them in the RS Oph/T Crb subclass of recurrent novae. We reclassify the secondary of V745 Sco as an M4 III, and classify the secondary of V3890 Sgr as spectral type M5 III. The outburst luminosities of both V745 Sco and V3890 Sgr were similar to the Eddington luminosity for a 1.35 M ○ . white dwarf.

An infrared study of Orion Molecular Cloud-2 (OMC-2)

This paper reports 1.2-23 micron photometry for 11 discrete sources in Orion Molecular Cloud-2 (OMC-2). These data, combined with H and K photometric and K polarimetric images, are used to model the cluster sources. Most appear to be young stars of roughly solar mass. Some have circumstellar dust reradiation or reflection nebulosity. A model based on single scattering of light from an exciting star explains some features of the IRS 1 nebula, the largest reflection nebula in OMC-2. However, the red colors and high surface brightness of the IRS 1 nebula require a cool excitation source that is more luminous than far-infrared observations would indicate. 34 refs.