Search Publications
Missions
Journals
Publication Years
An Investigation of Gravitational Lensing in the Southern BL Lac PKS 0537-441
Lewis, Geraint F.; Ibata, Rodrigo A.
The BL Lac family of active galaxies possess almost featureless spectra and exhibit rapid variability over their entire spectral range. A number of models have been developed to explain these extreme properties, several of which have invoked the action of microlensing by substellar mass objects in a foreground galaxy; this not only introduces vari…
The space density of low-redshift active galactic nuclei
Boyle, B. J.; Londish, D.; Schade, D. J.
We present a new determination of the optical luminosity function (OLF) of active galactic nuclei (AGN) at low redshifts (z<0.15) based on Hubble Space Telescope (HST) observations of X-ray-selected AGN. The HST observations have allowed us to derive a true nuclear luminosity function for these AGN. The resulting OLF illustrates a two power-law…
ISO's Short Wavelength Spectrometer - Ultimate sensitivity. Reducing the effects of cosmic weather
Thi, W. F.; Valentijn, E. A.
Compared to the pre-launch measurements, the in-orbit noise levels of the Short Wavelength Spectrometer (SWS) detectors show a significant increase, considerably lowering the overall sensitivity. Cosmic ray impacts on the detectors and/or on the instrument electronics play an important role in the noise levels and consequently many observations of…
Angular diameter and effective temperature of a sample of 15M giants at 2.2µm from lunar occultation observations
Tej, Anandmayee; Chandrasekhar, T.
High angular resolution measurements of a sample of 15M giants at 2.2µm by the technique of lunar occultation are presented in this paper. We obtain angular diameters for 11 sources of which five are the first diameter measurements. For these resolved sources we have estimated the effective temperatures, which are consistent with previous ca…
High time-resolution spectroscopic imaging using intensified CCD detectors
Much, R.; Kawakami, H.; Fordham, J. L. A. +2 more
The micro-channel plate intensified CCD photon counting detector developed at University College London has been upgraded to allow time-resolved spectroscopic optical data to be acquired on periodical sources such as pulsars. First observing trials have been carried out, acquiring spectroscopic data on the Crab pulsar. The detector was phase locke…
Observed Associations between the Solar Interior, Corona, and Solar Wind
Habbal, Shadia Rifai; Woo, Richard; Armstrong, J. W.
Using polarized brightness (pB) measurements made by the High Altitude Observatory (HAO) Mauna Loa Mk III K-coronameter, we investigate the daily changes of path-integrated density at 1.15 Rsolar. During 1996, when simultaneous pB and helioseismology data were available, we find that the correlation of pB (at zero time lag and 20° latit…
Source of excitation of low-l solar p modes: characteristics and solar-cycle variations
Chaplin, W. J.; Elsworth, Y.; Appourchaux, T. +3 more
We investigate various properties of the excitation source that is responsible for driving the acoustic p-mode oscillations of the Sun. Current prejudice places this in the superadiabatic layer of the convection zone. We consider in detail how the precise nature of the resonant mode spectrum is modified: (i) as a result of the impact of different …
A spectroscopic study of the magnetic CP-star HR 1094
Wahlgren, G. M.; Nielsen, K.
The chemically peculiar star
The linear force-free field in a spherical shell using a new method to determine the coefficients of the eigenfunction expansion
Bromage, B. J. I.; Clegg, J. R.; Browning, P. K. +2 more
The linear force-free field of a plasma in between spherical shells is found allowing for inhomogeneous boundary conditions. A three-dimensional solution is found by analysis and used as a benchmark to test a solution in terms of an expansion of eigenfunctions where the coefficients are determined by a new method. Alternative methods are also appl…
Towards Understanding Solar Convection and Activity - (Invited Review)
Gough, Douglas
The dynamics of the large-scale eddies which advect angular momentum through the convection zone is controlled in a significant way by the boundary conditions, which, if they are not modelled adequately, do not lead to a distribution of angular velocity that is consistent with observation. The transition boundary layer separating the convection zo…