Search Publications
X-ray absorption in Seyfert 2 galaxies
Perola, G. C.; Fiore, F.; Guainazzi, M. +1 more
We have studied the correlation among X-ray absorption, optical reddening and nuclear dust morphology in Seyfert 2 galaxies. Two main conclusions emerge: (i) the Balmer decrement and the amount of X-ray absorption are anticorrelated over a wide range of column density, 1021<~NH<~1024cm- 2 - the cor…
Cyclic and secular variation in the temperatures and radii of extreme helium stars
Pollacco, Don; Jeffery, C. Simon; Starling, Rhaana L. C. +1 more
The ultraviolet properties of 17 extreme helium stars have been examined using 150 IUE spectra. Combining short-wave and long-wave image pairs and using a grid of hydrogen-deficient model atmospheres and a χ2 minimization procedure, 70 measurements of effective temperature (Teff), angular diameters (θ) and interstellar extinc…
Structural evolution in elliptical galaxies: the age-shape relation
Forbes, Duncan A.; Ryden, Barbara S.; Terlevich, A. I.
We test the hypothesis that the apparent axial ratio of an elliptical galaxy is correlated with the age of its stellar population. We find that old ellipticals (with estimated ages t>7.5Gyr) are rounder on average than younger ellipticals. The statistical significance of this shape difference is greatest at small radii; a Kolmogorov-Smirnov tes…
Modelling the first probable two-plane lens system B2114+022: reproducing two compact radio cores A and D
Mao, Shude; Chae, Kyu-Hyun; Augusto, Pedro
We test possible lensing scenarios of the JVAS system B2114+022, in which two galaxies at different redshifts (`G1' at z1=0.3157 and `G2' at z2=0.5883) are found within 2arcsec of quadruple radio sources. For our investigation, we use possible lensing constraints derived from a wealth of data on the radio sources obtained wit…
Deep colour-magnitude diagrams of LMC field stars imaged with HST
Santiago, B. X.; Gilmore, G. F.; Johnson, R. A. +2 more
We present deep photometry (V<~26) in V and I bands obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope for 7 fields ~5° away from the Large Magellanic Cloud centre. The fields contain, typically, 2000 stars each. Isochrones were fitted to the colour-magnitude diagrams in order to identify different star popu…
The anomalous intensities of helium lines in a coronal hole
Jordan, C.; Macpherson, K. P.; Smith, G. R.
Observations made at the quiet Sun-centre with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instruments on the Solar and Heliospheric Observatory (SOHO) have shown that the intensities of the resonance lines of HeI and HeII are significantly larger than predicted by emission measure dist…
Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
Koen, Chris
A selection criterion based on the relative strength of the largest peaks in the amplitude spectra, and an information criterion are used in combination to search for multiperiodicities in Hipparcos epoch photometry. The method is applied to all stars which have been classified as variable in the Hipparcos catalogue: periodic, unsolved and microva…
The stellar composition of the star formation region CMa R1 - II. Spectroscopic and photometric observations of nine young stars
de Winter, D.; van den Ancker, M. E.; Tjin A Djie, H. R. E. +4 more
We present new high- and low-resolution spectroscopic and photometric data of nine members of the young association CMa R1. All the stars have circumstellar dust at some distance, as could be expected from their association with reflection nebulosity. Four stars (HD52721, HD53367, LkHα220 and LkHα218) show Hα emission and we argue that they are He…
HST/STIS observations of the high-velocity interstellar cloud HVC 291.2-41.2+80: a warm, mainly ionized high-velocity cloud
Sembach, K. R.; Keenan, F. P.; Lehner, N.
We present intermediate-resolution HST/STIS spectra of a high-velocity interstellar cloud (vLSR=+80kms-1) towards DI1388, a young star in the Magellanic Bridge located between the Small and Large Magellanic Clouds. The STIS data have a signal-to-noise ratio (S/N) of 20-45 and a spectral resolution of about 6.5kms-1…
Photometric properties of the Arp 220 super star clusters
Taniguchi, Yoshiaki; Shioya, Yasuhiro; Trentham, Neil
We investigate the photometric properties of six super stellar clusters (SSCs) seen in both the optical and near-infrared Hubble Space Telescope images of the local ultraluminous starburst galaxy Arp 220. Three of the SSCs are located in the central 0.5-kpc region. The remaining three are in the circumnuclear region between 0.5 and 2.5kpc from the…