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Nichols-Bohlin, Joy

Publications and source records attributed to Nichols-Bohlin, Joy.

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The violent interstellar environment around the Wolf-Rayet star HD 192163

IRAS Skyflux IR images, high-dispersion IUE UV spectra, optical spectra, and optical interference filter images are used to investigate the nature of the interstellar environment around the Wolf-Rayet star HD 192163. IRAS images show an apparent 1.5 x 1.8 deg IR emission shell very nearly centered on HD 192163, which is designated G75.5+2.4. It is suggested that this shell is a possible unrecognized SNR with an estimated age of not less than 100,000 yr if at the assumed 1.8-kpc distance of HD 192163. A well-defined 2 x 4.5 deg region of weak IR emission lying to the southeast of HD 192163 appears to be the IR signature of the Cyg OB1 superbubble. Analysis of IUE spectra shows that high-velocity components of UV interstellar absorption lines are present for both high and low ionization lines in 18 of 22 stars located in the Cyg OB1/OB3 direction with a velocity range of +/- 90 km/s. A possible evolutionary history for this region is outlined.

Nichols-Bohlin, Joy↗
NASA NTRS1992

An infrared supershell surrounding the Cygnus OB1 association

New studies are reported of a large, 2 x 5 deg peanut-shaped cavity in the far-infrared emission seen using IRAS data for the Cygnus X region. A more complete and better defined infrared supershell than reported by Lozinskaya and Repin (1990) is found and connected to the Cyg OB1 association. It is shown that the cavity represents the early stages of a superbubble produced by the winds and possible SNe from 10 to 20 massive stars. The locations and properties of these stars are used to estimate the energy deposition rate and to understand the manner in which supershells form and propagate. In Cyg OB1, spatially distributed subclustering appears to have played an important role in determining the nonspherical morphology of the superbubble.

Saken, Jon M.↗
NASA NTRS1992

Ultraviolet and optical spectral morphology of Melnick 42 and Radcliffe 136a in 30 Doradus

HST/GHRS ultraviolet spectrograms of the individual O3 If*/WN6-A object Mk 42 in 30 Dor and the adjacent, central multiple system R136a are compared with each other and with an appropriate sequence of O3 If* and WN6-A standards from the IUE archive. The analogous spectral montages covering the blue-violet regino, based on new, homogeneous, digital observations of the same stars with the CTIO 4 m telescope, are also presented. These comparisons show clearly the intermediate O3/WN nature of the Mk 42 spectrum, in terms of both emission-line strength (increasing with envelope density) and stellar-wind velocity (decreasing with envelope density). It is also shown that R136a possesses stronger WN spectral characteristics than Mk 42, in agreement with HST narrow-band imaging by the WF/PC Team.

Walborn, Nolan R.↗
NASA NTRS1990

High-velocity interstellar gas in the lines of sight to the Wolf-Rayet stars HD 97152 and HD 96548

The interstellar medium was studied in the direction to the WR stars HD 96548 and HD 97152, and the results are reported. New observational data on the UV spectra of several field stars near both these WR stars are presented. The high-velocity gas seen in the spectra of these stars suggests that the detected expanding interstellar gas structure consists of two OB cluster supershells. The presence of high-velocity absorption components in one of five field star spectra in the direction of the more isolated WR star HD 96548 suggests that this expanding gas does not originate from the optical ring nebula RCW 58 surrounding HD 96548, as previously believed, but instead indicates the detection of a previously unknown expanding interstellar shell in this line of sight.

Nichols-Bohlin, Joy↗
NASA NTRS1988

The recalibration of the IUE scientific instrument

The IUE instrument was recalibrated because of long time-scale changes in the scientific instrument, a better understanding of the performance of the instrument, improved sets of calibration data, and improved analysis techniques. Calibrations completed or planned include intensity transfer functions (ITF), low-dispersion absolute calibrations, high-dispersion ripple corrections and absolute calibrations, improved geometric mapping of the ITFs to spectral images, studies to improve the signal-to-noise, enhanced absolute calibrations employing corrections for time, temperature, and aperture dependence, and photometric and geometric calibrations for the FES.

Imhoff, Catherine L.↗
NASA NTRS1988

IUE's legacy for the future: The final archive and goals for its implementation

Requirements for the IUE archive, and how the signal/noise (S/N) ratio in photometrically corrected images can be enhanced considerably by cross-correlating the fixed pattern in a data image with that in a suitable flat-field image are described. From these cross-correlations it is feasible to derive an accurate geometrical correction to apply to the data image before applying the intensity transfer functions. The standard IUE processing software does not generate a sufficiently accurate geometric correction so that typical spatial errors of 1 to 2 pixels conspire with the large fixed pattern in raw images to produce significant misregistration noise. Tests on flat-field images demonstrate that an explicit geometric correction procedure can avoid most of the misregistration noise and can thereby improve the S/N ratio of IUE data by factors of 1.5 to 2.4.

Linsky, J. L.↗
NASA NTRS1987

Ultraviolet spectral morphology of the O stars. IV - The OB supergiant sequence

An atlas of 25 O3-B8 supergiant spectra in the wavelength ranges 1320-1580 A and 1620-1880 A is presented, based on high-resolution data from the IUE archives. The remarkably detailed relationship between the stellar-wind profiles and the optical spectral classifications throughout this sequence is emphasized. For instance, the (Si IV)/(C IV) ratio reverses between O4 and O6.5; and the B0, B0.5, and B0.7 Ia wind characteristics are each qualitatively unique and distinct from one another. The systematic behavior of nine stellar-wind features with ionization potentials ranging from 114 to 19 eV is summarized as a function of advancing spectral type.

Walborn, Nolan R.↗