Search Publications
A new model for the infrared emission of quasars
Rowan-Robinson, Michael
The optical-UV continua of 75 PG quasars are modelled to test two extreme hypotheses: (a) the range of continuum shapes observed is the result of different amounts of reddening of a single underlying continuum, and (b) the range of continuum slopes is entirely intrinsic, due to accretion discs being viewed at different inclinations. Although (a) i…
RE J0317-853: the hottest known highly magnetic DA white dwarf
Jordan, S.; Barstow, M. A.; O'Donoghue, D. +3 more
We report the discovery of a new highly magnetic DA white dwarf, RE J0317-853, through its detection as an EUV source by the ROSAT Wide Field Camera. A combination of far-UV and optical spectra indicates that the star has an effective temperature ~=50000K, making it the hottest known white dwarf with a measurable magnetic field. Furthermore, the m…
The high-temperature big blue bump in the Seyfert galaxy RE J1034+396
Siemiginowska, A.; Mason, K. O.; Pounds, K. A. +1 more
X-ray, UV and optical spectra are presented for a rare, EUV-bright Seyfert galaxy, RE J1034+396 (z=0.042). When combined, these data describe a very-high temperature big blue bump (BBB; kT_eff~100 eV) whose high energy turnover is observed in soft X-rays. The soft X-ray/UV flux ratio is extremely high, L_0.2keV/L_1200A~10, compared to AGN in gener…
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…
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…
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…