Engineering topics

Wills, B. J.

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

5 records

NASA NTRS1996

Optical Identification of Quasar 0917+7122 in the Direction of an Extreme-Ultraviolet Source

We report the optical identification of an R = 18.3 mag, z = 2.432 quasar at the position of a 6 cm radio source and a faint ROSAT PSPC X-ray source. The quasar lies within the error circles of unidentified extreme-UV (EUV) detections by the EUVE and ROSAT WFC all-sky surveys at approximately 400 A and approximately 150 A, respectively. A 21 cm H I emission measurement in the direction of the quasar with a 21'-diameter beam yields a total H I column density of N(sub H) = 3.3 x 10(exp 20) /sq cm, two orders of magnitude higher than the maximum allowed for transparency through the Galaxy in the EUV The source of the EUV flux is therefore probably nearby (approximately < 100 pc), and unrelated to the quasar.

Maoz, D.↗

NASA NTRS1985

The ultraviolet spectra of active galaxies with weak optical Fe II lines

Very weak optical Fe II lines are noted in the present simultaneous optical and IUE spectra of the two Seyfert galaxies Mrk 290 and Mrk 915. Strong and distinct UV features are also observed in the spectrum of Mrk 290. A synthetic spectrum fitting is conducted for all spectral features between 1900 and 5500 A, using the calculations of Netzer and Wills (1983). IUE archival spectra of the broad line radio galaxy 3C 390.3 is compared with optical data obtained during the same year, and evidence is found for strong UV Fe II lines. The present results demonstrate several new aspects of the spectra of active galactic nuclei, including the great amount of energy emitted by Fe II lines and the possible importance of dust and/or very high density clouds in such objects.

Netzer, H.↗

NASA NTRS1985

Broad emission features in QSOs and active galactic nuclei. II - New observations and theory of Fe II and H I emission

Seven QSOs of low to intermediate redshift are characterized on the basis of: 320-850-nm spectra obtained with the UVITS spectrograph and image-dissector scanner at the f/9 Cassegrain focus of the 2.7-m reflecting telescope at McDonald Observatory; improved model calculations for the Fe II, Mg II, and Balmer lines and the Balmer continuum; and the theoretical results of Netzer and Wills (1983). The data are presented in tables, spectra, and difference spectra and described in detail. Fe II is found to be the largest contributor to the emission line spectrum, with strong UV Fe II lines in all QSOs (regardless of the strength of the optical Fe II lines) and an abundance ratio suggesting a factor-of-three overabundance of Fe relative to Mg and probably H. A discrepancy between the observed Fe II strength and the predictions of dustless standard photoionization models is noted, and the addition of a high-density component to the models is suggested.

Wills, B. J.↗

NASA NTRS1984

Spectral characteristics of two types of low latitude aurorae

Attention is given to two types of aurorae whose low altitude emissions seem to be due to energy loss from trapped ring current ions or electrons whose energy is of the order of 1 eV. The spectral characteristics which predominate in the first type of aurora indicate direct precipitation of ring current particles as ions, and/or indirect precipitation as energetic neutrals, following charge transfer with exospheric H or O neutrals. The spectral characteristics of the second type indicate excitation by electrons and can yield brighter displays. The time variations of the emissions are found to be closely related to fluctuations of periods shorter than an hour in the magnetograms from nearby observatories.

Tinsley, B. A.↗

NASA NTRS1983

The QSO 1156+295 - A multifrequency study of recent activity

Photometric observations are presented for outbursts of the quasi-stellar object QSO 1156+295 in 1981 and 1982. High time resolution photometry is included showing variations on time scales of weeks to about half an hour. Data from early plate material show that the object may have been quite bright at the beginning of this century but was quite faint and probably inactive between about 1950 and the beginning of recent activity in 1977-1979. Some results of optical linear polarization are discussed. In examining spectrophotometric results, broadband spectra show very little change in spectral shape during changes in continuum brightness. High resolution spectra (0.1-A FWHM) show no evidence for the Mg II 2798-A absorption sometimes seen in optically violent variables and other QSOs. The radio flux density variations at several frequencies are documented and discussed and compared with the optical light curve. Models for 1156+295 are discussed including variability time scales, and the observed energy output is compared with a magnetic accretion disk model proposed by Shields and Wheeler (1976). Results are summarized and the different sizes of active and inactive regions of the object are compared.

Wills, B. J.↗