Search Publications
Galaxy properties in low X-ray luminosity clusters at z=0.25
Smail, Ian; Bower, R. G.; Ziegler, B. L. +4 more
We present the first spectroscopic survey of intrinsically low X-ray luminosity clusters at z>> 0, with Hubble Space Telescope (HST) WFPC2 imaging and spectroscopy from Calar Alto and WHT-LDSS2. We study 172 confirmed cluster members in a sample of ten clusters at 0.23 < z < 0.3, with LX<~ 4 × 1043h-2
Resolved nuclear CO(1-0) emission in APM 08279+5255: gravitational lensing by a naked cusp?
Lewis, Geraint F.; Carilli, Chris; Papadopoulos, Padeli +1 more
The ultraluminous broad absorption line quasar APM 08279+5255 is one of the most luminous systems known. Here, we present an analysis of its nuclear emission. Its extended distribution suggests that the gravitational lens in this system is highly elliptical, probably a highly inclined disc. The quasar core, however, lies in the vicinity of a naked…
High-resolution observations and mass modelling of the CLASS gravitational lens B1152+199
Biggs, A. D.; Browne, I. W. A.; Wilkinson, P. N. +5 more
We present a series of high-resolution radio and optical observations of the CLASS gravitational lens system B1152+199 obtained with the Multi-Element Radio-Linked Interferometer Network, Very Long Baseline Array and Hubble Space Telescope . Based on the milliarcsecond-scale substructure of the lensed radio components and precise optical astrometr…
The status of Galactic field λ Bootis stars in the post-Hipparcos era
Kamp, I.; Paunzen, E.; Iliev, I. Kh. +1 more
The λ Bootis stars are Population I, late B- to early F-type stars, with moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O and S). To put constraints on the various existing theories that try to explain these peculiar stars, we investigate the observational p…
Timing analysis of the isolated neutron star RX J0720.4-3125
Cropper, Mark; Zavlin, Vyacheslav E.; Haberl, Frank +4 more
We present a combined analysis of XMM-Newton, Chandra and ROSAT observations of the isolated neutron star RX J0720.4-3125, spanning a total period of ~7yr. We develop a maximum likelihood periodogram for our analysis based on the ΔC statistic and the maximum likelihood method, which are appropriate for the treatment of sparse event lists. Our resu…
HST large-field weak lensing analysis of MS 2053-04: study of the mass distribution and mass-to-light ratio of X-ray luminous clusters at 0.22<z<0.83
van Dokkum, Pieter G.; Franx, Marijn; Hoekstra, Henk +1 more
We have detected the weak lensing signal induced by the cluster of galaxies MS 2053-04 (z=0.58) from a two-colour mosaic of six Hubble Space Telescope (HST) WFPC2 images. The best-fitting singular isothermal sphere model to the observed tangential distortion yields an Einstein radius rE=6.2+/-1.8arcsec, which corresponds to a velocity d…
Globular clusters and the Mira period-luminosity relation
Feast, Michael; Whitelock, Patricia; Menzies, John
A globular cluster distance scale based on Hipparcos parallaxes of subdwarfs has been used to derive estimates of MK for cluster Miras, including one in the Small Magellanic Cloud (SMC) globular cluster NGC 121. These lead to a zero-point of the Mira infrared period-luminosity (PL) relation, PL(K), in good agreement with that derived fr…
The optical counterpart of the ultraluminous X-ray source NGC 5204 X-1
Knigge, C.; Roberts, T. P.; Lira, P. +1 more
We use archival HST/WFPC2 V- and I-band images to show that the optical counterpart to the ultraluminous X-ray source NGC 5204 X-1, reported by Roberts et al., is composed of two sources separated by 0.5 arcsec. We have also identified a third source as a possible counterpart, which lies 0.8 arcsec from the nominal X-ray position. Point spread fun…
The dual dust chemistries of planetary nebulae with [WCL] central stars
Barlow, M. J.; Liu, X. -W.; Cohen, Martin +1 more
The rather rare class of central stars of planetary nebulae that show very low-excitation Wolf-Rayet spectra has been a subject of great interest, particularly in the infrared, since its discovery in the late 1960s. Further peculiarities have been found with the advent of infrared spectroscopy from ISO. Notably, these objects simultaneously betray…
Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars
Lambert, David L.; Lyubimkov, Leonid S.; Rostopchin, Sergey I. +1 more
Effective temperatures Teff, surface gravities logg and interstellar extinctions AV are found for 107 B stars. Distances d of the stars, which are based on the derived Teff, logg and AV values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the Teff and logg v…