Search Publications
Star formation history and dust content of galaxies drawn from ultraviolet surveys
Kong, X.; Brinchmann, J.; Charlot, S. +1 more
We compile a new sample of 115 nearby, non-Seyfert galaxies spanning a wide range of star formation activities, from starburst to nearly dormant, based on ultraviolet observations with various satellites. We combine these observations with infrared observations to study the relation between ratio of total far-infrared to ultraviolet luminosity and…
On the origin of the C IV Baldwin effect in active galactic nuclei
Laor, Ari; Baskin, Alexei
The origin of the luminosity dependence of the equivalent width (EW) of broad emission lines in active galactic nuclei (AGN) - the Baldwin effect - is not firmly established yet. We explore this question for the broad C IVλ1549 line using the Boroson & Green sample of the 87 z<= 0.5 Bright Quasar Survey (BQS) quasars. Useful UV spectra of t…
Chemical abundances of planetary nebulae from optical recombination lines - I. Observations and plasma diagnostics
Liu, Y.; Barlow, M. J.; Liu, X. -W. +1 more
We have obtained deep optical spectra of medium resolution for a sample of 12 Galactic planetary nebulae (PNe). Optical recombination lines (ORLs) from carbon, nitrogen and oxygen have been detected in 11 of them and neon ORLs in nine of them. All spectra were obtained by scanning a long slit across the nebular surface, yielding relative line inte…
Period and light variations for the cool, overcontact binary BX Pegasi
Han, Wonyong; Kim, Ho-Il; Lee, Jae Woo +2 more
New charge-coupled device photometric observations of the W UMa-type binary BX Pegasi (BX Peg) were collected on four nights from 1999 October to 2000 September. The light curve was covered completely in each season. Seven new times of minimum light were determined. It was found that the orbital period of the system has varied recently in a sinuso…
Physical conditions in the planetary nebula NGC 6543
Liu, X. -W.; Wesson, R.
We present analysis of spectra and Hubble Space Telescope (HST) images of NGC 6543, the Cat's Eye Nebula. Using HST WFPC2 images taken in narrow-band filters isolating Hα and Hβ, we have produced an extinction map towards the nebula, and find that c(Hβ) is low, at ~0.1, and exhibits only very small spatial variations across the surface of the nebu…
Observations and three-dimensional photoionization modelling of the Wolf-Rayet planetary nebula NGC 1501
Rauch, T.; Barlow, M. J.; Zhang, Y. +4 more
Deep optical spectra of the high-excitation planetary nebula NGC 1501 and its W04 central star are presented. A recombination line abundance analysis of the emission-line spectrum of the central star yields He:C:O mass fractions of 0.36:0.48:0.16, similar to those of PG 1159 stars. A detailed empirical analysis of the nebular collisionally excited…
The stellar composition of the star formation region CMa R1 - III. A new outburst of the Be star component in Z CMa
van den Ancker, M. E.; Acke, B.; Tjin A Djie, H. R. E. +5 more
We report on a recent event in which, after more than a decade of slow fading, the visual brightness of the massive young binary Z CMa suddenly started to rise by about 1 mag in 1999 December, followed by a rapid decline to its previous brightness over the next six months. This behaviour is similar to that exhibited by this system around its erupt…
Hydrogen in the atmosphere of the evolved WN3 Wolf-Rayet star WR 3: defying an evolutionary paradigm?
Crowther, P. A.; Morel, T.; Chené, A. -N. +6 more
WR 3 is the brightest very early-type WN star in the sky. Based on several years of time-resolved spectroscopy and precision photometry on various time-scales, we deduce that WR 3 is most likely a single, weak-lined star of type WN3ha (contrary to its current catalogue-type of WN3 + O4), with H lines occurring both in emission and absorption in it…
Modelling of dust scattering toward the Coalsack
Shalima, P.; Murthy, Jayant
Murthy, Henry & Holberg discovered intense far-ultraviolet (FUV) (λλ912-1600) emission from the direction of the Coalsack molecular cloud 10 years ago. We have used their results in conjunction with a Monte Carlo model for the scattering in the region to show that the scattering is from dust in the foreground of the Coalsack. The albedo of the…
Mid-infrared imaging and modelling of the dust shell around post-AGB star HD 187885 (IRAS 19500-1709)
Gledhill, T. M.; Clube, K. L.
We present 10- and 20-µm images of IRAS 19500-1709 taken with the mid-infrared camera, OSCIR, mounted on the Gemini North Telescope. An extended circumstellar envelope is detected, with the N-band image indicating an elongation in a north-east-south-west direction. We use a dust radiation transport code to fit the spectral energy distributio…