Search Publications
The spectrum of the planetary nebula NGC 6886
Hyung, Siek; Aller, Lawrence H.; Keyes, Charles D.
The relatively young, high-excitation planetary nebula (PN) NGC 6886 shows a remarkable variety of lines from both high- and low-excitation stages, i.e., from N^0 to N^4+, and as a result it provides unique opportunities for detailed studies of physical processes, using a theroetical model. By combining Hamilton echelle observations with UV data s…
Eclipse observations of an accretion disc wind
Knigge, C.; Horne, Keith; Mason, K. O. +5 more
The Goddard High Resolution Spectrometer on the Hubble Space Telescope has been used to monitor, through eclipse, the C iv 1550-A and He ii 1640-A lines in the spectrum of the nova-like cataclysmic variable UX UMa. Previous work has suggested that the Civ line arises in an accretion disc wind. The HST data confirm this, in that the line shows a br…
High-resolution IUE spectroscopy of fast winds from cataclysmic variables
Prinja, Raman K.; Rosen, R.
The winds from six dwarf novae and four nova-like cataclysmic variables are studied using 31 high-resolution IUE spectra. The data provide details on athe time- and phase-averaged nature of disc-driven outflows, which are diagnosed via the presence of P Cygni-like and extended absorption profiles due to the C IV, N V and Si IV resonance line doubl…
High-resolution radio images of the symbiotic star R Aquarii
Davis, R. J.; Bode, M. F.; Dougherty, S. M. +2 more
We present MERLIN radio observations of the nearby symbiotic star R Aquarii at 5 and 1.7 GHz with respective nominal resolutions of ~0.04 and 0.13 arcsec, comparable to the resolution of the optical and ultraviolet images obtained with the HST. Comparison with the HST images shows that the radio emission is associated with features observed at opt…
The luminosity-dependent broad-line region in active galactic nuclei
Gondhalekar, P. M.; O'Brien, P. T.; Goad, M. R.
We investigate the effect of non-linear line response on the observed variability characteristics of the broad emission lines in AGN. The line response is intrinsically non-linear due to the dependence of the thermal and ionization structure of the line-emitting gas on the incident continuum flux. The BLR models we use include the effect of emissi…
A model for the circumstellar nebula of SN 1987A
O'Brien, T. J.; Kahn, F. D.; Lloyd, H. M.
Supernova 1987A in the Large Magellanic Cloud is surrounded by an extended region of nebulosity likely to be composed of material ejected during the evolution of the progenitor star, and which has been subsequently illuminated by the supernova event itself. Recent Hubble Space Telescope (HST) images have revealed the presence of two large elliptic…
Monte Carlo simulations of the Rayleigh scattering effects in symbiotic stars
Schmid, H. M.
This paper investigates the Rayleigh scattering effects in symbiotic binaries using Monte Carlo simulations. The simulations calculate the scattering path of far-UV photons released from the hot component or from the emission nebula. A large fraction of these photons penetrate into the extended atmosphere and the wind of the cool giant, where Rayl…
Multifrequency monitoring of the Seyfert 1 galaxy NGC 4593 - II. A small, compact nucleus?
Glass, I. S.; Clavel, J.; Peterson, B. M. +4 more
We discuss the results of a campaign to monitor spectral variations in the low-luminosity Seyfert 1 galaxy NGC 4593, at X-ray, ultraviolet, optical and near-IR frequencies. The observations and data analysis have been described in a companion paper. The active nucleus in this galaxy is strongly and rapidly variable in all wavebands, implying that …
The evolution of QSO spectra
Koratkar, Anuradha; Francis, Paul J.
We study the rest-frame UV spectra of two samples of QSOs, a low-redshift (z~0.4) sample drawn from the IUE archives, and a high-redshift (z~2.2), optically selected sample, the Large Bright QSO Survey (LBQS). The samples overlap substantially in their range of absolute magnitudes and radio properties, allowing us to study directly the evolution o…
MERLIN observations of bipolar outflow from HM Sagittae
Davis, R. J.; Eyres, S. P. S.; Bode, M. F. +4 more
MERLIN maps of HM Sagittae at 6-cm and 18-cm wavelengths are presented. At 6 cm, the inner nebula has been mapped at a resolution of 60 milli-arcsec (mas), revealing two parallel ridge structures to the north and south of a deep central minimum. In addition, these central features are surrounded by a complex, weak structure. The ridges and many of…