arXiv subjects

Stuart Bowyer

Publications and source records attributed to Stuart Bowyer.

21 records · Page 2Linked to original sources

arXiv1998

EUVE Observations of Neutron Stars

We present the results of searches for EUV emission from neutron stars conducted with the EUVE Deep Survey and Scanner Telescopes. To date, 21 fields containing known neutron stars have been observed in the Lexan/Boron (40--190 angstrom) band. Of these, 11 fields were simultaneously observed in the Aluminum/Carbon (160-385 angstrom) band. Five neutron stars which have been detected in the EUV have been reported previously; no new detections have been made in the studies reported here. For those sources not detected, we have used the observations to obtain limits on the spectral flux from the neutron stars in these bands. We provide means to convert these fluxes into intrinsic source fluxes for black-body and power law spectra for varying levels of absorption by the interstellar medium.

astro-ph↗

arXiv1998

Spectral Observations of Diffuse Far-Ultraviolet Emission from the Hot Phase of the Interstellar Medium with the Diffuse Ultraviolet Experiment

One of the keys to interpreting the character and evolution of interstellar matter in the galaxy is understanding the distribution of the low density hot (10^5 K -10^6 K) phase of the interstellar medium (ISM). This phase is much more difficult to observe than the cooler high density components of the ISM because of its low density and lack of easily observable tracers. Because gas of this temperature emits mainly in the far ultraviolet (912 angstrom - 1800 angstroms) and extreme ultraviolet (80 angstrom - 912 angstrom), and (for gas hotter than 10^6 K) X-rays, observations in these bands can provide important constraints to the distribution of this gas. Because of interstellar opacity at EUV wavelengths, only FUV and X-ray observations can provide clues to the properties of hot gas from distant regions. We present results from a search for FUV emission from the diffuse ISM conducted with an orbital FUV spectrometer, DUVE, which was launched in July, 1992. The DUVE spectrometer, which covers the band from 950 angstrom to 1080 angstrom with 3.2 angstrom resolution, observed a region of low neutral hydrogen column density near the south galactic pole for a total effective integration time of 1583 seconds. The only emission line detected was a geocoronal hydrogen line at 1025 angstrom. We are able to place upper limits to several expected emission features that provide constraints on interstellar plasma parameters. We are also able to place limits on the continuum emission throughout the bandpass. We compare these limits and other diffuse observations with several models of the structure of the interstellar medium and discuss the ramifications.

astro-ph↗

arXiv1997

ORFEUS-I Observations of Molecular Hydrogen in the Galactic Disk

We present measurements of interstellar H_2 absorption lines in the continuum spectra of seven early-type stars in the Galactic disk at distances between 1 and 4 kpc. Five of these stars provide lines of sight through the Sagittarius spiral arm. The spectra, obtained with the Berkeley EUV/FUV spectrometer on the ORFEUS telescope in 1993 September, have a resolution of 3000 and statistical signal-to-noise ratios between 20 and 80. We determine column densities for each observed rotational level and derive excitation temperatures and densities for the H_2 clouds along each line of sight. Our data continue the relationships among H_2 column density, fractional molecular abundance, and reddening apparent in Copernicus observations of nearby stars, indicating a common mechanism for H_2 production. Estimates of cloud temperatures and densities are consistent with those derived from Copernicus data. We find that the molecular fraction of hydrogen is nearly constant over a wide range of distances and mean reddenings, consistent with a model in which a significant fraction of the neutral ISM is associated with H_2-bearing molecular clouds, even along low-density lines of sight.

astro-ph↗