Search Publications
HSTUV measurements of wind structure and velocities in Local Group OB stars
Crowther, Paul A.; Prinja, Raman K.
Archival HST FOS and GHRS data sets have been used to collect ultraviolet evidence for large- and small-scale stellar wind structure in extragalactic Local Group OB stars (i.e. SMC, LMC including R136, M31, M33 and NGC 6822). By comparison with previous studies of Galactic OB stars, wind activity is principally diagnosed in individual spectrograms…
On the rotation-activity correlation for active binary stars
Doyle, J. G.; Mitrou, C. K.; Gunn, A. G.
We present an investigation of rotation-activity correlations using International Ultraviolet Explorer (IUE) SWP measurements of the Civ emission line at 1550Angstroms for 72 active binary systems. We use a standard stellar evolution code to derive non-empirical Rossby numbers, R_0, for each star in our sample and compare the resulting Civ rotatio…
Nuclear stellar discs in early-type galaxies - I. HST and WHT observations
van den Bosch, Frank C.; van der Marel, Roeland P.; Jaffe, Walter
We present multi-colour (U, V and I) photometry obtained with the second Wide Field and Planetary Camera (WFPC2) on the Hubble Space Telescope (HST), and spectra taken with the William Herschel Telescope (WHT) and the HST Faint Object Spectrograph (FOS), for the early-type galaxies NGC 4342 and 4570. These galaxies are intermediate between ellipti…
The Hubble Deep Field and the disappearing dwarf galaxies
Ferguson, Henry C.; Babul, Arif
Several independent lines of reasoning, both theoretical and observational, suggest that the very faint (B>~24) galaxies seen in deep images of the sky are small low-mass galaxies that have experienced a short epoch of star formation at redshifts 0.5<~z<~1 and have since faded into low-luminosity, low-surface-brightness objects. Such a sc…
Bar-driven evolution of S0s: the edge-on galaxy NGC 4570
van den Bosch, Frank C.; Emsellem, Eric
We present circumstantial evidence that the central region of the edge-on S0 galaxy NGC 4570, which harbours a 150-pc scale nuclear disc in addition to its main outer disc, has been shaped under the influence of a small (~500 pc) bar. This is based on the discovery of two edge-on rings, the locations of which are consistent with the inner Lindblad…
HST and ground-based eclipse observations of V2051 Ophiuchi: binary parameters
Horne, Keith; Baptista, Raymundo; Catalan, M. S. +1 more
We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B~=16.2 mag. In comparison with the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ~=4 and ~=5. Flickering activity is mostly suppressed and the light curve shows the eclip…
Cygnus A: stars, dust and cones
Sparks, William B.; Tadhunter, Clive; Jackson, Neal
We present new Hubble Space Telescope (HST) continuum and spectral line images of the radio galaxy Cygnus A. The images show much complex structure in the central kpc^2. Continuum images show the central dust lane in detail, allowing detailed maps of E(B-V) to be constructed; the dust appears to follow a roughly Galactic extinction law. The emissi…
Echoes from an irradiated disc in GRO J1655-40
Horne, Keith; O'Brien, K.; Chen, W. +2 more
We demonstrate correlated rapid variability between the optical/UV and X-ray emission for the first time in a soft X-ray transient, GRO J1655-40: Hubble Space Telescope (HST) light curves show similar features to those seen by the Rossi X-ray Timing Explorer (RXTE), but with mean delay of up to 10-20s. We interpret the correlations as the result o…
Long-term variability of the Be/X-ray binary A0535+26 - I. Optical and UV spectroscopy
Coe, M. J.; Steele, I. A.; Buckley, D. A. H. +11 more
The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A0535+26 are presented. It was found that throughout the period of the observations the line profile of Hα showed considerable variability. A correlation between the equivalent width of Hα and both V-band magnitude and (B-V) colour excess was observed, albeit wi…
Evidence for low-level AGN activity in the nucleus of the LINER galaxy NGC4594
Filippenko, A. V.; Ho, L. C.; Reichert, G. A. +4 more
We investigate the properties of the low-ionization nuclear emission-line region (LINER) galaxy, NGC4594, using data taken with the Faint Object Spectrograph on the Hubble Space Telescope (HST) and with the ASCA X-ray observatory. The ultraviolet spectrum shows only narrow-line emission (FWHM ~800-1000 km s^-1) with no evidence for broad emission-…