Search Publications
The nature of the cometary knots in the Helix planetary nebula (NGC7293)
Walsh, J. R.; Steffen, W.; Meaburn, J. +3 more
The system of cometary knots in the Helix planetary nebula (NGC7293) has been systematically observed using ground-based images and long-slit, high-resolution spectroscopy. CCD images in the [Nii] 6584-A line, taken with the ESO NTT, are used to determine the spatial distribution of the knots; images in the [Oiii] 5007-A line distinguish their pos…
HST Planetary Camera images of quasar host galaxies
Boksenberg, A.; Macchetto, F. D.; Crane, P. +6 more
We present Hubble Space Telescope (HST) images of seven low-redshift quasars (six taken with the Planetary Camera, one with the Wide Field Camera). These complete the sample of 14 quasars observed by the Faint Object Camera Investigation Definition Team (FOC IDT). Following subtraction of the quasar nuclear light, host galaxies can be seen in all …
The binary star population of the young cluster NGC 1818 in the Large Magellanic Cloud
Gilmore, Gerard; Elson, Rebecca A. W.; Sigurdsson, Steinn +2 more
We determine the binary star fraction as a function of radius in NGC 1818, a young rich cluster in the Large Magellanic Cloud, using Hubble Space Telescope images in bands F336W (~U) and F555W (~V). Our sample includes binaries with M_primary~2-5.5M_solar and M_secondary>~0.7M_primary. The binary fraction increases towards the cluster centre, f…
Galaxy surface brightness and size evolution to z~4
Im, M.; Griffiths, R. E.; Roche, N. +2 more
Using HST WFPC2 data, we estimate half-light radii, morphological classifications and rest-frame, blue-band absolute magnitudes for 270 galaxies with spectroscopic redshifts from z~0 to z=3.43, and 77 thought from their colours to be at 2.0<=z<=4.5. The mean blue-band surface brightness decreases by ~2 mag along the Hubble sequence from elli…
Mode switching in the nearby Mira-like variable R Doradus
Bedding, T. R.; Jones, A.; Zijlstra, Albert A. +1 more
We discuss visual observations spanning nearly 70 years of the nearby semiregular variable R Doradus. Using wavelet analysis, we show that the star switches back and forth between two pulsation modes having periods of 332d and about 175d, the latter with much smaller amplitude. Comparison with model calculations suggests that the two modes are the…
HST imaging of the globular clusters in the Fornax cluster: NGC1399 and NGC1404
Forbes, Duncan A.; Brodie, Jean P.; Grillmair, Carl J. +2 more
The Fornax cluster galaxies NGC1399 and NGC1404 are ideal for studying the effects of a cluster environment on globular cluster systems. Here we present new optical imaging of these two galaxies from both the Hubble Space Telescope's Wide Field and Planetary Camera 2 and the Cerro Tololo Inter-American Observatory 1.5-m telescope. The combination …
The edge-on spiral gravitational lens B1600+434
Koopmans, L. V. E.; Jackson, N.; de Bruyn, A. G.
We present new observations of the gravitational lens (GL) system B1600+434, strongly suggesting that the lens is an edge-on spiral galaxy. These observations are used to constrain the mass model of the system, in particular the oblateness and velocity dispersion of the dark matter halo around the lensing galaxy. From an analytical model we find a…
The absolute magnitude of field metal-poor horizontal branch stars
Gratton, Raffaele G.
Hipparcos satellite parallaxes for 22 metal-poor field horizontal branch stars with V_0<9 are used to derive their absolute magnitude. The weighted mean value is M_V=+0.69+/-0.10 for an average metallicity of [Fe/H]=-1.41 a somewhat brighter average magnitude of M_V=+0.60+/-0.12 for an average metallicity of [Fe/H]=-1.51 is obtained by eliminat…
HIPPARCOS and the age of the Galactic disc
Jimenez, Raul; Flynn, Chris; Kotoneva, Eira
We use the Hipparcos colour-magnitude diagram of field stars with Tycho colours to make a new minimum age estimate for the Galactic disc. The method is based on fits to the red envelope of subgiants in the Hipparcos colour-magnitude diagram with synthetic isochrones covering the range of disc metal abundance. The colours and luminosities of the is…
The Lutz-Kelker bias in trigonometric parallaxes
Groenewegen, Martin A. T.; Schrijver, Hans; Oudmaijer, Rene D.
The theoretical prediction that trigonometric parallaxes suffer from a statistical effect has become topical again now that the results of the Hipparcos satellite have become available. This statistical effect, the so-called Lutz-Kelker bias, causes observed parallaxes to be too large. This has the implication that inferred distances, and hence in…