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Research School of Astronomy & Astrophysics
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THE ANU ASTROPHYSICAL THEORY CENTRE
1. STAFF
Head and Professor D. T. Wickramasinghe, B.A.(Cantab), M.A. (Cantab), Ph.D. (Cantab), F.R.A.S.
Senior Lecturer L. Ferrario, Laurea in Astronomia (Bologna), Ph.D. (ANU)
QEII Research Fellow S. Vennes, Ph.D. (Montreal)
Research Fellow M. de Kool, Ph.D. (University of Amsterdam)
Research Fellow/Lecturer J. Li , Ph.D. (Sussex) R. Sutherland, Ph.D.
ARC Research Associate J. Murray O. Dittman
Honorary Fellow Emeritus Professor D.W.N. Stibbs, M.Sc. (Syd), D.Phil. (Oxon), F.R.A.S., F.R.S.E.
Associate Members Professor M. Dopita, MSSSO Professor K.C. Freeman, MSSSO Dr. A. Kalnajs, MSSSO Dr. D. McClelland, Department of Physics Dr. P. Wood, MSSSO
Visiting Fellows Dr. N. Arav, Lawrence Livermore National Laboratory, USA Dr C. Pichon, Observatoire de Strasbourg, France Professor B. Warner, University of Cape Town Professor R. Webbink, Illinois, USA Professor R. Wehrse, Institute Theoretische Astrophysik, Heidelberg, Germany
Graduate Students M. Burgess M. Buxton W. El-Khoury R. Soria
Honours Students Rachel Moody James Blair
Graduate Diploma Student S. Tantisrisuk | ||
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Annual Report 1998 | |||
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2. OPERATION OF THE CENTRE
1998 was an exceptionally productive year for research, with over 30 scientific publications appearing in print and 25 more scientific articles in press or submitted for publication. The year began with Dr. Stephane Vennes taking up his QEII Fellowship at the Centre. The Centre also had two ARC research associates, Dr. James Murray and Dr. Olaf Dittman, and several externally funded visitors, which made for a lively scientific environment. The visitors to the Centre included Dr Pichon of the Observatoire de Strasbourg funded by a French government initiative to promote Franco-Australian scientific exchanges who worked with Dr. Murray, Professor Ron Webbink of the University of Illinois funded by the NSF, Dr. Arav funded by the MSSSO visitor program who worked with Dr. deKool, and visits by Professors Warner and Wehrse funded by ARC grants who continued their collaborative work with Ferrario, Wickramasinghe and Li.
One of the tasks undertaken during the year was the rewriting of the undergraduate entry on Astronomy and Astrophysics in the Faculty handbook which brought it in line with the requirements of the Departments of Mathematics, Physics and RSAA. Paul Francis played a major role in this endeavour. The staff at MSSSO continued to make valuable contributions to the teaching of the Honours program in astronomy and astrophysics operated under the auspices of the Astrophysical Theory Centre.
There was much discussion on the question of broadening the scope of the Centre to formally incorporate all activities in Astronomy in the Faculties, including first and second year undergraduate teaching. The funds which accrue from teaching of undergraduate Astronomy in the Faculties should go towards the further development of the discipline via the Centre, but the precise mechanism by which this could be achieved remained unresolved. This is an issue which needs to be revisited in 1999.
Finally, the Centre ran a very successful 2-day workshop (12-13 November) organised by Martijn deKool on "Magnetic Fields and Accretion". Participants included Professor Andrew King from the University of Leceister, UK, and astronomers from the Universities of Sydney, Melbourne and Tasmania.
3. RESEARCH ACTIVITIES
White Dwarfs
Vennes continued his studies of the properties of degenerate stars, the final stage of evolution for most stars. Fundamental properties (Age, mass) is derived using numerical modelling of the atmospheric properties. The project combines ground-based and space-borne observatories with advanced numerical techniques, and continues to yield new information on the fundamental properties of these stars.
One of the highlights of the research on magnetic white dwarfs was the work done by Ferrario, Vennes and Wickramasinghe on the stars 1RXS J0823.6-2525 (a single magnetic white dwarf) and EUVEJ1439+75.0 (a double degenerate with a magnetic component) which added weight to the growing evidence based on parallaxes, and space velocities, and surface gravity determinations that magnetic white dwarfs tended | |||
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on the average to be more massive than the non magnetic white dwarfs. Additionally, the double degenerate is a candidate Type IA Supernova precursor. These results have important implications for the origin of magnetic fields in stars, and for the role-played by magnetic fields in star formation.
Li, Ferrario and Wickramasinghe proposed an imaginative model for the peculiar white magnetic dwarf GD356 -the only white dwarf known to show the Balmer lines of hydrogen totally in emission. The model, which postulates that this star has a metallic Earth type planetary core orbiting a magnetic white dwarf, aroused much scientific and popular interest, and was featured in New Scientist, and Sky and Telescope.
Accretion Disc Structure
Accretion of matter onto compact objects like black holes, neutron stars and white dwarfs is the most efficient energy generation mechanism known, and provides the power for the most luminous astronomical objects. Because the accreting matter always has some angular momentum, matter can not fall directly towards the compact object but first forms a disc around it. Most of the accretion luminosity is expected to come from such discs.
Wickramasinghe in collaboration with Shaviv and Wehrse continued his research on various aspects of the structure and radiation properties of accretion discs. The research focussed on investigating the effects of inefficient radiative cooling on the vertical structure of accretion discs, and in particular on the question of the importance of the radial advection of energy. One of the important results which appears to be emerging from this research is that viscously heated optically thin accretion discs, which cannot radiate efficiently, are prone to the development of hydrodynamic coronal type outflows perpendicular to the disc. These outflows may develop in preference to advective flows in the radial direction.
De Kool has developed a new computer code to study the vertical structure of such accretion discs, with special emphasis on the thermal stability of the disc atmosphere. It was found that such disc atmospheres are thermally unstable under a wide range of conditions, implying that all cool accretion discs will lose some mass in the form of a wind. The conditions under which this wind could lead to the complete destruction of a cool disc were identified. This result has important consequences for the transition from cold discs to the low-luminosity, hot advection dominated discs that have been discussed vigorously in the recent literature, and seem to be required by some observations.
In some astronomical systems, such as pre-main sequence stars (Classic T Tauri stars), close binaries (either magnetic cataclysmic variables or accreting neutron stars), the accretion can be channelled by magnetic field lines. In collaboration with Greg Wilson (Department of Mathematics), Li investigated the standard magnetic-channelled flow, and found a solution to the Bernoulli integral. The solution reveals new physics: the funnel accretion is initiated by magnetic levitation. They find that the funnel should not be in corotation with the central star, opposite to common belief. Combining our earlier work, they now have a more consistent model for magnetic accretion. | ||
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Annual Report 1998 | |||
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Radiative Shock Theory
In 1998 major steps forward were made in the understanding of the 3D radiative hydrodynamic shock models carried out in 1997-1998 on the ANUSF Fujistu Supercomputer. In three dimensional shock models, coherence and thermal stratification seen in lower dimensional shock models is lost even in homogeneous models as the small but unavoidable numerical noise acts as a seed for instability. The much greater phase space of the three dimensional case allows coherent pulsations to degrade rapidly into a quasi steady-state with cooling, heating, expansion and collapse taking place on many scales and locations in the post shock material. In 1998 the extent of numerical imperfections in the ZEUS 3D code were examined by developing taking an independent PPM hydrocode (VH1) and incorporating the same cooling processes. The comparison of the two codes by Sutherland and Bicknell will now allow us to understand out earlier results better and provide the means of extending our simulations to more demanding simulations such as inhomogeneous models where our understanding of the intrinsic numerical instabilities will be essential.
Plasma Theory
New calculations of free-free transition matrix element integrals are performed by Sutherland using modern symbolic computing techniques to evaluate the hypergeometric functions with complex arguments. The results are presented in both graphical and tabular form including accurate extrapolation methods. The results are accurate to the level of ~10-4 beyond which relativistic corrections would be needed, which are not included. The results are also computed over a very wide range of scaled ionic temperature (g2) and wavelength, extending earlier results to new regimes encountered in highly photoionised and non-equilibrium ionisation plasmas. These results will be useful in the spectral range from sub-millimetre to hard X-ray wavelengths and temperatures from 10K to 109 K.
Planetary Nebulae
Sutherland and Dopita have constructed theoretical self-consistent models of Planetary Nebulae including detailed dust heating. Galactic, LMC and SMC abundance patterns are used in a comparison of dusty and dust free models. We show that dust has a strong effect on the thermal structure and emission line spectrum of highly ionised species in Planetary Nebulae. These models have implications for excitation and energy balance methods for determining central star temperatures. We present results for [OIII]l5007 and [NII]l6583 lines for galactic, LMC and SMC abundances.
Active Galaxies
Bicknell, Sutherland and Dopita constructed a jet-cloud interaction model to explain the major features revealed by the detailed radio, optical and spectroscopic data on the high-redshift radio galaxy 4C41.17 (z=3.8), in which there is evidence for star formation along the radio axis. The interaction of a high-powered (~1048 ergs s-1) jet with a dense cloud in the halo of 4C41.17 produces shock-excited emission-line nebulosity and induces star formation. The CIII] to CIV line ratio and the CIV luminosity (attributed to the shock rather than star formation) imply that the pre-shock density in the line-emitting cloud is high enough (hydrogen density ~300 cm-3) that shock initiated star formation could proceed on a timescale (~106 yrs) well within | |||
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the dynamical age (~3x107 yrs) of the radio source. Broad (s ~470-600 kms-1) emission lines are attributed to photoionised emission in filaments of gas entrained by the jet. Our interpretation of the data provides a physical basis for the alignment of the radio, emission-line and UV continuum images in some of the highest redshift radio galaxies.
Magnetically Confined Accretion Flows
Ferrario continued to develop her models of the thermal structure of accretion funnels heated externally by hard and soft X-rays and to relate them to observations of magnetic cataclysmic variables. The ultimate aim of these investigations is to provide self-consistent models for the continuum and line emission from these systems. An interesting new result was the demonstration that the observed line spectra of AM Herculis type systems required funnels, which had an additional source of heating close to its base. This heating appears to arise from the region where matter first interacts with the magnetic field and is probably due to either magnetic reconnection or weak shocks.
Ferrario has also investigated the signatures that are to be expected in the power spectra of Intermediate Polars, which accrete via a disc or an accretion stream. This work has shown that disc fed accretion is characterised by low radial velocity amplitudes and that the dominant power in the optical continuum and line fluxes is at the spin frequency of the white dwarf. In contrast, stream fed accretion is characterised by high velocity amplitudes and the line and continuum radiation exhibits significant optical power at the side band frequency. The characteristics of the power spectrum has been shown to change with increase in magnetic field as the polarised cyclotron emission from the shocks make a significant contribution to the optical radiation.
Accreting Pulsars
GX 1+4, is a binary system with a giant star, and a neutron star, which accretes via a slow stellar wind. The x-ray luminosity and the spin rate change are often anti-correlated, opposite to what is expected from the standard model. A retrograde accretion disc has been proposed to explain this unexpected feature. Murray, de Kool and Li performed simulations of retrograde discs using smooth Particle Hydrodynamics, and were available to show that this model requires that reversals in accretion torques are accompanied by a minimum in accretion luminosity. This is in good agreement with the observations of GX1+4.
Broad Absorption Line Quasars
About 10% of quasars (accreting supermassive black holes in centres of some galaxies) show extremely broad, blueshifted absorption lines of many ultraviolet resonance lines in their spectra. These lines indicate the presence of fast, wind-like outflows with speeds about one tenth of the speed of light. It is likely that all quasars contain such outflows, and the analysis and interpretation of these lines are currently the most promising avenues to a better understanding of many quasar phenomena. | ||
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Annual Report 1998 | |||
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De Kool has been continuing his collaboration with Dr Arav from Lawrence Livermore Laboratories (USA) on the analysis of BALQSO spectra.They obtained new, high resolution spectra taken with the Keck telescope that allowed us to resolve a long-standing problem in BALQSO research, namely to what extent the depth of the absorption lines is determined by partial covering of the continuum background source rather than pure optical depth of the absorber. They were able to show convincingly that at least in one BALQSO the absorption profile is determined almost exclusively by partial covering. This implies that many previous works claiming very high metal abundances in the BAL material are likely to be erroneous. In Dec. 1998 they were awarded 40 orbits of Space Telescope time for further BALQSO studies, so that this is expected to remain a very active area of research.
Distant Galaxy Cluster
Francis and Woodgate used the Hubble Space Telescope to study one of the most distant clusters of galaxies yet discovered. The study shows that the cluster is very massive and contains many seemingly old, well-established elliptical galaxies. This poses a challenge to many cosmological theories, which do not predict that either massive galaxy clusters or old elliptical galaxies should exist in the distant universe.
Solar Eclipses
Li and Ciyuan Liu, Shaanxi Astronomical Observatory, and Li have reinvestigated an ancient Chinese record 'during the first year of King Yi, the day dawned twice'. The 'double dawn' is interpreted as an eclipse occurring at dawn and has been used to date the first year of King Yi when the Chinese chronicle events began. Based on their investigations, they suggest that the Chinese chronicle be moved back by almost half a century. This work also confirms the earliest and also most complete solar eclipse record, which is invaluable to geophysical and astronomical studies.
4. STUDENT SUPERVISION
Graduate Students M. Burgess (Supervisors; Wickramasinghe and Wu) M. Buxton (Supervisors; Vennes, Ferrario and Wickramasinghe) W. El-Khoury (Supervisors; Wickramasinghe, Roberts and Bessell) R. Soria (Supervisors; Freeman, deKool and Li)
Honours Students Alex Ridgewell (ANU co-supervisor; Francis) Rachel Moody (Supervisor; Kalnajs) James Blair (Supervisor; Vennes)
5. GRANTS AND AWARDS
Small ARC (Ferrario) "An Observational Study of Isolated and Accreting Magnetic White Dwarfs'', $17,000 | |||
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Small ARC (Li, Ferrario, Wickramasinghe) "Magnetic Braking and Accretion in AM Hers", $13,000
Small ARC (Francis), $6,000
Large ARC (Wickramasinghe) "High field Magnetic White Dwarfs", $53,000
QEII Grant (Vennes), $76,760
6. CONFERENCES, OVERSEAS VISITS AND SEMINARS
Martijn de Kool gave a talk on "Magnetic Energy Dissipation and the Vertical Structure of Accretion Discs" at the ANUATC workshop " Magnetic Fields and Accretion" (12-13 October). He also presented a talk at the MSSSO workshop on "Active Galactic Nuclei" (7-9 Dec).
Jianke Li attended the workshop on "Magnetic Cataclysmic Variable Stars" held at Annapolis, Maryland, USA (12-18 July) and gave a talk on "Stream/Disc/Magnetosphere interaction". He also presented talks at the ANUATC workshop, "Magnetic Fields and Accretion", (12-13 October), ANU, and the MSO workshop "Active Galactic Nuclei", 3-4 December, ANU.
Lilia Ferrario attended the workshop on "Magnetic Cataclysmic Variable Stars" held at Annapolis, Maryland, USA (12-18 July). Presented an invited review paper entitled "Emission Line Formation in Accretion Funnels in AM Herculis Systems". She also presented papers entitled "Phase Resolved Spectroscopy of EUVE J2115-586" with Buxton, Vennes and Wickramasinghe, "The New Magnetic CV 1RXS J1016.94103: One More System in the Period Gap'' with Vennes and Wickramasinghe, "Power Spectra of Disced and Discless Accretors" with Wickramasinghe, and "Spiral waves and periodic accretion in intermediate polars" with Murray, Armitage and Wickramasinghe. She also attended a workshop on "Magnetic Fields and Accretion'' held at the ANU, and presented a paper entitled "Magnetised Accretion Flows In CVs".
Paul Francis attended and presented papers at the American Astronomical Society Meeting: 7-10th Jan 1998., Harley Wood Winter School on Galaxy Evolution (Invited speaker), 3-5th July 1998, Astronomical Society of Australia Annual Meeting: 6th-9th July 1998. (gave 2 talks), Australian Relativity Society meeting: 6th-10th July 1998 (Invited speaker), Third Stromlo Symposium "The Galactic Halo", 17th-21st August. Presented poster, Workshop on the Sydney University Molonglo Sky Survey, 23rd November 1998, Stromlo AGN workshop (member LOC and speaker) 3rd-4th December.
Stephane Vennes gave a talk on the "Properties of X-ray selected White Dwarfs" at the annual meeting of the ASA (Adelaide, July 98).
Dayal Wickramasinghe attended the workshop on "Magnetic Cataclysmic Variable Stars", held at Annapolis, Maryland, USA (12-18 July) and presented an invited paper on "Power Spectra of Disced and Discless Accretors".
7. COLLABORATIVE RESEARCH | ||
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Annual Report 1998 | |||
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De Kool collaborated with Dr. N. Arav, Lawrence Livermore National Laboratories.
Ferrario collaborated with S. Larsson (Stockholm University), K. Wu (Special Research Centre for Theoretical Astrophysics, University of Sydney), and with P. Barrett (NASA/Goddard Space Flight Centre) on "Quasi-periodic oscillations in accretion shocks", and with S. Vennes, M. McConnell (University of New Hampshire), Drake, S. (NASA/GSFC) and P. Barrett (NASA/GSFC) on "Simultaneous optical and radio observations of the gamma-ray emitting white dwarf RE J0317-853". She also collaborated with R. Wehrse (Institute for Theoretical Astrophysics, University of Heidelberg) on "3-D Radiation transfer in X-ray heated accretion columns, with D. Buckley (South African Astronomical Observatory) and D. T. Wickramasinghe on the Modelling of polarised emission from accretion shocks in magnetic binaries, and with R. Webbink (University of Illinois), D. T. Wickramasinghe and J. Li on Magnetic braking and evolution of magnetic binaries.
Francis collaborated with Dr Bruce Woodgate of NASA/GSFC (USA) on a Hubble Space Telescope study of a galaxy cluster at redshift 2.38. He also collaborated with Dr Rachel Webster of the University of Melbourne, and Dr Michael Drinkwater of the University of New South Wales, on a study of red quasars in the Parkes Half-Jansky survey; with Dr Michael Brotherton of Lawrence Livermore National Laboratory (USA), on the use of Principal Components Analysis to analyse QSO emission lines; and with Dr Gerry Williger and Dr Sally Heap of NASA Goddard Space-Flight Center in a study of highly ionised zones in the inter-galactic medium, as revealed by gaps in the Helium II Gunn-Peterson Effect- "Analysis and Interpretation of Broad Absorption Line QSO spectra".
Murray, Ferrario and Wickramasinghe collaborated with Phil Armitage (Canadian Institute for Theoretical Astrophysics) on 'spiral waves in accretion discs'.
Murray and Wickramasinghe collaborated with Brian Warner (University of Cape Town) on 'Dynamical instabilities in accretion discs in systems with intermediate mass ratio'.
Murray worked with Christophe Pichon (Observatoire de Strasbourg) on 'non-linear stability of galactic discs to spiral perturbations'.
Vennes collaborated with Jean Dupuis at University of California at Berkeley on NASA's Advanced Xray Astronomical Facility (AXAF) Guest Observer program.
Wickramasinghe collaborated with Drs Chris Tout and Eniko Regos of the University of Cambridge on a project on the "Evolution of Black Hole Binary Systems". He also collaborated with Professor Giora Shaviv of the Israel Institute of Technology, and Professor Rainer Wehrse of the University of Heidelberg on a project on the "Vertical Structure of Accretion Discs". | |||
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8. PROFESSIONAL SERVICE and ACTIVITIES
Lilia Ferrario is a representative of the Department of Mathematics on the Board of the Faculty of Science and a member of the Graduate Program in Astronomy and Astrophysics. She was also on the selection committee for 3 appointments (level A/B) in the School of Mathematical Sciences.
Paul Francis is a member of the following National Committees; Astronomical Society of Australia Education sub-committee, MSO Exploratory Board. He is also a member of the following MSSSO Committees: Astrophysics Teaching Committee, Scholarships Committee, Exploratory liaison committee, RSAA visitors committee, Graduate program committee, RSAA Director selection liaison committee.
Professor Wickramasinghe was on the selection committees for promotions to levels C, D and E in the Faculty of Science and in SMS.
9. PUBLICATIONS
Armitage, P. J. and Murray, J., 1998, "Simulations of spiral structure in the accretion disc of IP~Pegasi during outburst", MNRAS, 297, L81-L85.
Buckley, D. A. H., Cropper, M., Ramsay, G., and Wickramasinghe, D. T., 1998, "The new intermediate polar RX J1238-38: a system below the period gap?", MNRAS, 299, 83.
Buckley, D. A., Ferrario, L., Wickramasinghe, D. T., Bailey, J., 1998, "Polarimetry of the eclipsing polar RX J0929.1-2404", MNRAS, 295, 899,
Buxton, M., Vennes, S., Ferrario, L., and Wickramasinghe, D. T., 1998, IAU Circ. 6815; GS 1354-64
De Kool M., Li, H, and McCray, R., 1998, "Thermal Evolution of the Envelope of the SN 1987A", Ap. J., 508, 857.
Dupuis, J., Vennes, S., Chayer, P., Hurwitz, M., and Bowyer, S., 1998, "Properties of the Hot DA White Dwarf HZ 43 Based on Far-Ultraviolet ORFEUS-SPAS II Observation", The Astrophysical Journal Letters, 500, 45-49.
Ferrario, L., Vennes, S., and Wickramasinghe, D.T., 1998, "1RXS J0823.6-2525, a new ultramassive magnetic white dwarf", MNRAS, 299, L1-L4.
Ferrario, L., and Wehrse, R., 1998, "3-D Thermal Structure of Magnetically Confined Accretion Flows", A.S.P. Conference Series, Editors: Howell, S., Kuulkers, E., and Woodward, C., 137, 302-306.
Ferrario, L., Wickramasinghe, D. T., Liebert, J., Schmidt, G. D., Biegin, J. H., 1998, "Constraints on GD356 as a Magnetic Binary", ASP, 137, 479.
Francis, P. J. Woodgate, B. E. and Danks, A. C. 1998, in "The Young Universe", proceedings of Rome conference, Eds. S. D'Odorico, A. Fontana, E. Giallongo, p 496 - 503,"Galaxy Clusters and Large Scale Structure at High Redshifts".
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Francis, P. J. Woodgate B. E. and Danks. A. C. 1998, in "The Nature of Elliptical Galaxies", proceedings of the Second Stromlo Symposium, Eds M. Arnaboldi, G. S. Da Costa and P. Saha, p 551),"Discovery of a Cluster of Elliptical Galaxies".
Li, J., 1998, "On singularities of a cool relativistic pulsar wind", PASA, 15, 328.
Li, J., 1998, "Compact stars and accretion discs", PASA, 15.
Li, J., Ferrario, L., Wickramasinghe, D. T., 1998, "Planets around White Dwarfs", ApJ, 503, 151.
Li, J., Wickramasinghe, D. T., 1998, "On the spin-up spin-down torque torque reversals in disc accreting pulsars" MNRAS, 300, 1015.
Li, J. and Wickramasinghe D.T., 1998, " Torque reversals in disc accreting pulsars", PASP, 15, 250.
Li, J., Wickramasinghe, D. T., 1998, "Magnetic braking in magnetic binary stars" MNRAS, 300, 718.
Masci, F. J., Webster, R. J. and Francis,P. J. 1998, "Host Galaxy Contributions to the Colours of 'Red' Quasars", MNRAS, 301, 975.
Murray, J., 1998, "Simulations of superhumps and superoutbursts", MNRAS, 297, pp 323-333.
Murray, J. and Armitage,P. J., 1998, "Accretion discs in cataclysmic variables: Tidal instabilities and superhumps", MNRAS, 300, pp 561-567" Regos, E., Tout, C. A., Wickramasinghe, D.T., 1998, "The Unusual Evolutionary State of GRO J1655-40", ApJ, 509, 362.
Siebert, J. Brinkmann, W. Drinkwater, M. J. Yuan, W. Francis, P. J. Peterson, B. A., Webster, R. L., 1998, "X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?", MNRAS 301, 261.
Soria, R., Wickramasinghe, D. T., Hunstead, R. W., Wu, K., 1998, "Measuring the Motion of the Black Hole in GRO J1655-40", ApJ, 495L, 95S.
Vennes, S., Christian, D.J., and Thorstensen, J.R., 1998, "Hot White Dwarfs in the Extreme-Ultraviolet Explorer Survey. IV. DA White Dwarfs with Bright Companions", Ap. J., 502, 763-787.
Vennes, S., Dupuis, J., Chayer, P., Polomski, E.P., V.D.Dixon, W., and Hurwitz, M., 1998, "The Complete Spectral Energy Distribution and the Atmospheric Properties of the Helium-Rich White Dwarf MCT 0501-2858", Ap. J. Letts, 500,41-44.
Wickramasinghe, D. T. in Kleinmann, S. J. et al; 1998, ApJ, 495, 424; "Understanding the Cool DA White Dwarf Pulsator, G29-38".
Wickramasinghe, D. T., 1998, "Accretion Disc Instabilities of X-ray heated discs in Black Hole X-ray Transients", Proc. Calcutta Conf. on black holes. | |||
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Wickramasinghe D. T. and Li, J., 1998, "Period gap and the magnetic CVs", PASA, 15.
Wickramasinghe, D., Li, J., 1998, "New Results on Magnetic Braking in Magnetic CVs", ASP, 137, 198.
Wickramasinghe, D. T., 1998, "Accretion Disc Instabilities of X-ray heated discs in Black Hole X-ray Transients", ASP, 137, 43.
Williger, G. M., Francis, P. J., Malumuth, E., and Woodgate, B. E. 1998, in "The Next Generation Space Telescope: Science Drivers and Technological Challenges", 34th Liege Astrophysics colloquium, June 1998, p. 261,"On the Nature of Red Galaxies in the Early Universe ".
Papers (in press)
Arav, N., Korista, K.T., de Kool, M. Junkarinen V.T. and Begelman, M.C. "HST observations of the Broad Absorption Line Quasar PG 0946+301", ApJ.
El-Khoury, W., and Wickramasinghe, D.T., 1998, "S-curves of X-ray heated accretion discs and the black hole soft X-ray transients", MNRAS.
Buxton, M., Vennes, S., Wickramasinghe, D.T., and Ferrario, L., "Phase Resolved Spectroscopy of EUVE J2115-586", Proc. Annappolis Workshop of Magnetic Cataclysmic Variables .
Brotherton, M. S. and Francis., P. J., in "Quasars as Standard Candles for Astronomy", Proc. of CTIO conference. Ed. G. Ferland and J. Baldwin, "The Intermediate Line Region and the Baldwin Effect", PASP .
Buckley, D. Cropper, M., Ramsay, G., Wickramasinghe, D.T., Hellier, C. Beardmore, A., "On the nature of the new below-gap intermediate polar RX J1238-38'', 1999, Proc. Annapolis Workshop on Magnetic Cataclysmic Variables
Christian, D. J.&Vennes, S., "Detection of two strong flares from EUVE J1438-432, AJ.
El-Khoury, W. and Li J., "A magnetic field in AM CVn?", Proc. Anappolis Workshop of Magnetic Cataclysmic Variables.
Ferrario, L., and Wehrse, R., "Emission Line Formation in Accretion Funnels in AM Herculis Systems", A.S.P. Conference Series, Editors: Mukai, K., and Hellier, C.
Francis, P. J., Wilson, G. M., and Woodgate, B. E. in "The Galactic Halo", proceedings of the Third Stromlo Symposium. Ed. B. K. Gibson, T. S. Axelrod and M. E. Putman, (ASP, San Francisco), in press "QSO Absorption Lines and the Halos of Cluster Galaxies".
Francis, P. J., and Wills, B. J. 1998, to appear in "Quasars as Standard Candles for Astronomy", proceedings of CTIO conference. Ed. G. Ferland and J. Baldwin, PASP in press,"Introduction to Principal Components Analysis"
Francis,P. J. Woodgate B. E. and Danks. A. C. 1997, to appear in "Looking Deep in | ||
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the Southern Sky", proceedings of the ESO/ATNF workshop, Eds. R. Morganti and W. Couch, in press."On the Nature of Red Galaxies in the Early Universe"
Li, J., "Magnetic braking in the present Sun", MNRAS, 302, 203.
Li, J., "Stream/Magnetosphere/Disc interaction", Proc. Anappolis Workshop of Magnetic Cataclysmic Variables, Annapolis, Maryland, USA , in press.
Murray, J., Armitage, P., Ferrario, L., and Wickramasinghe, D.T., 1999, "The effects of tidally induced disc structure on white dwarf accretion in intermediate polars'', MNRAS.
Murray, J.,Armitage, P. J., Ferrario, L., Wickramasinghe, D. T., "Spiral waves and periodic accretion in intermediate polars", in Proc. Annapolis Workshop on Magnetic Cataclysmic Variables, eds K. Mukai, C. Hellier.
Murray, J., Armitage, P.J., Warner, B., and Wickramasinghe, D.T. 1998, 'Tidal Instability of Accretion Disks', in Proceedings of the Kyoto Disk Instability Workshop, eds S. Mineshige, C.Wheeler.
Murray, J., Armitage, P., Ferrario, L., and Wickramasinghe, D.T., "Spiral Waves and Periodic Accretion in Intermediate Polars'', A.S.P. Conference Series, Editors: Mukai, K., and Hellier, C.
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