Search Publications
Measurement of the ^12C/^13C ratio in planetary nebulae
Walsh, J. R.; Clegg, R. E. S.; Storey, P. J. +1 more
The ^12C/^13C isotopic ratio in the ionized gas in three planetary nebulae has been measured using a new method based on transitions caused by hyperfine effects. The C III] multiplet near 1908A has an F=1/2-1/2 transition at 1909.6A that is completely forbidden in ^12C, but allowed as a result of the non-zero nuclear spin of ^13C. The transition p…
The nature of the optical continuum in NGC5128 (CentaurusA)
Storchi-Bergmann, Thaisa; Kinney, Anne L.; Bica, Eduardo +1 more
We present long-slit observations of NGC5128 in the range lambdalambda3200-9800Angstroms, covering the nucleus and dust lane across the east-west direction, up to ~2.2kpc from the nucleus. The reddening-corrected continua and absorption features, when compared with those typical of a bulge stellar population, show that all locations within 1.8kpc …
Angular sizes of the faint blue galaxies
Im, M.; Griffiths, R. E.; Roche, N. +1 more
We investigate the angular sizes, morphologies and B-I colours of the 21≮I≮24 galaxies imaged on 10 Wide Field Planetary Camera fields. The number of galaxies with bluer colours (B-I<2.0) and moderately large angular sizes exceeds non-evolving predictions by a factor of ~2, but is consistent with pure L* evolution (PLE) models. There is also an…
Faint ultraviolet objects in the core of M13: optical counterparts of the low-luminosity X-ray source?
Ferraro, Francesco R.; Paltrinieri, Barbara; Fusi Pecci, Flavio +2 more
The core of the Galactic globular cluster M13 (NGC 6205) has been observed with WFPC2 on the Hubble Space Telescope through visual, blue, and mid- and far-UV filters in a programme devoted to studying the UV population in a sample of Galactic globular clusters. In the UV colour-magnitude diagrams derived from the HST images we have discovered thre…
The discovery of UV oscillations in WZ SGE
Sion, Edward M.; Wood, Janet H.; Cheng, F. H. +2 more
We report the discovery of ~28-s ultraviolet oscillations in the cataclysmic variable WZ Sge. The strength of the oscillations is strongly wavelength-dependent: the oscillation amplitude decreases rapidly from lambda~1500 to ~1250 A. We interpret this decrease as an indication that the spectrum of the oscillations contains a broad Lyalpha absorpti…
Models of optical/UV continuum in AGN: constraints from the NGC 5548 monitoring campaign
Czerny, B.; Loska, Z.
We analyse the data from the International Ultraviolet Explorer (IUE) observational campaign on the Seyfert galaxy NGC 5548 in the context of 10 phenomenological models. On the basis of the optical/UV data, as well as of constraints from the X-ray observations, we can favour one model of the nucleus: an accretion disc with an inner radius cut-off …
Hubble Space Telescope observations of M31 associations
Magnier, Eugene A.; Lewin, Walter H. G.; van Paradijs, Jan +2 more
We have used HST WFPC-2 observations of five fields along the eastern spiral arm regions of M31 to study the stellar populations. We use fits to stellar models to determine extinction individually for the stars in OB associations in these fields. The range of extinction within each cluster is the major constraint on our ability to determine accura…
On the interpretation of the extinction curves of R Coronae Borealis stars
Zubko, V. G.
The available extinction curves for some RCB stars (R CrB, RY Sgr, MV Sgr and V348 Sgr) have been analysed, making use of the method of regularization for solution of ill-posed problems. This approach allows an estimate of dust grain sizes responsible for fadings of RCB stars. A model involving graphite grains is shown to be preferable for the exp…
Timing the eclipse of HD185510
Simon, Theodore; Jeffery, C. Simon
HD185510 (=V1379 Aql) is an eclipsing double-lined RS CVn binary containing a K0 III/IV giant and a hot subluminous companion. An International Ultraviolet Explorer (IUE) ultraviolet light curve has been obtained through the eclipse of the companion with an average time resolution of one measurement every 19min. This was sufficient to resolve all …
3C 254: the alignment effect and unification schemes
Bremer, M. N.
3C 254 is a radio-loud quasar at z=0.734. Optical line and continuum emission from the underlying galaxy is clearly extended and aligned with the radio axis; the object shows the so-called `alignment effect' which is often seen in powerful radio galaxies. This is the clearest case yet of the continuum alignment effect in a radio-loud quasar. The o…