Astrophysics Group

Very Large Array Radio Telescope

People

Research Activities

1.  Theoretical Astrophysics

The major research areas are related to neutron stars and pulsars, which are rapidly spinning and magnetized neutron stars, including X-ray and gamma-ray emission mechanisms, stellar structure, stellar cooling and heating mechanisms and the internal activities, e.g. sudden unpinning of superfluid vortices. In addition to topics related to pulsars and neutron stars, we also study topics related to gamma-ray bursts, in particular the central engine problem, and high energy phenomena resulting from the stellar capture processes by supermassive black holes in the galactic center.

2.  Observational Astrophysics

(1) Prof. Kwok's research is mainly on the interstellar chemistry and stellar evolution. He is widely recognized for his theory on the origin of planetary nebulae, which has transformed our understanding of the death of Sun-like stars. His more recent accomplishments include the discovery of proto-planetary nebulae, the missing link in our understanding of the late stages of stellar evolution, and the discovery of the unidentified emission feature at 21 microns which is believed to be an unusual carbonaceous compound. Using space-based infrared telescopes, he has found that organic compounds with aromatic and aliphatic structures can be synthesized rapidly in the late stages of stellar evolution. These star-manufactured compounds are now known to have spread widely throughout the Galaxy, and are believed to have played a role in the chemical enrichment of the early solar system.

Prof. Kwok has been guest observer on most of the leading space and ground-based telescopes, including the Hubble Space Telescope, Infrared Space Observatory, the Gemini Telescopes, Canada-France-Hawaii Telescope, United Kingdom Infrared Telescope, the Very Large Array etc. Since 1994, he has served as the Canadian principal investigator of the Odin submillimeter satellite.

More details of current research programs can be found in http://www.scifac.hku.hk/kwok.

Prof. Kwok has published two recent books “Physics and Chemistry of the Interstellar Medium” (University Science Books, 2007) and “Organic Matter in the Universe” (Wiley: 2011). His previous books include “The Origin and Evolution of Planetary Nebulae” (Cambridge 2000) and “Cosmic Butterflies” (Cambridge 2001).

(2) Dr. Lim's research encompasses star formation, stellar magnetic activity and winds, late stellar evolution, as well as both nearby and distant galaxies. His primary focus in the field of star formation is to elucidate how binary and multiple stars systems form (as this constitutes the primary mode of star formation at solar masses), and his work has provided the first direct evidence for their formation through fragmentation of their parent molecular cores (the currently favored hypothesis). He made the first radio image of a star (Betelgeuse) other than our Sun, and is currently focused on elucidating how the extended atmospheres of evolved red supergiant stars are driven and how this is connected with their winds. His work on nearby galaxies with accreting supermassive black holes has shown for the first time that galaxy-galaxy interactions is the dominant mechanism for triggering active galactic nuclei in spiral galaxies. His latest research provides the most direct evidence yet that the cool molecular gas in the central cD galaxy of a galaxy cluster is deposited by an X-ray cooling flow, and he is currently focused on understanding the nature of the other gas components.

(3) Dr. Pun's research efforts focus on the observational studies of supernovae and supernova remnants. Supernovae are important objects in the astronomical world: they create the chemical history of the universe, energize the interstellar gas, and provide the only direct evidence for an accelerating universe. We obtain images and spectra of young and old supernovae with ground-based telescopes and satellites, including the Hubble Space Telescope, to study the properties of these spectacular astronomical explosions. In addition, we also studied the high energy emission from close compact binary systems with data taken by the satellite missions such as Chandra X-Ray Observatories and XMM-Newton. Finally, we have been conducting the first comprehensive survey of the light pollution condition in Hong Kong by monitoring the night sky brightness across the city.

Some Representative Publications

Prof. K.S. Cheng

1. "Origin of the Fermi Bubble", K.S. Cheng, D. Chernyshov, V. Dogel, C.M. Ko and W.H. Ip, The Astrophysical Journal Letters, 731, L17: 1-4 (2011). 
2. "Pulsar High Energy Emissions from Outer Gap Accelerator Closed by a Magnetic Pair-creation Process", J. Takata, Y. Wang and K.S. Cheng, Astrophysical Journal, 715, 1318-1326 (2010). 
3. "High-redshift Gamma-ray Bursts: Observational Signatures of Superconducting Cosmic Strings?", K.S. Cheng, Y. Yu and T. Harko, Physical Review Letters, 104, 241102: 1-4 (2010). 
4. "A Three-Dimensional Outer Magnetospheric Gap Model for Gamma-Ray Pulsars: Geometry, Pair Production, Emission Morphologies, and Phase-Resolved Spectra", K.S. Cheng, M. Ruderman and L. Zhang, Astrophysical Journal, 537, 964-976 (2000). 
5. "High-energy Radiation from Rapidly Spinning Pulsars with Think Outer Gaps", L. Zhang and K.S. Cheng, The Astrophysical Journal, 487, 370-379 (1997).
    

Prof. S. Kwok

1. "Physics and Chemistry of the Interstellar Medium", Kwok, S., University Science Books (ISBN: 1-891389-46-7) (2006). 
2. "Nebula", Kwok, S. in McGraw-Hill Encyclopedia of Science and Science and Technology (2006). 
3. "The Synthesis of Organic and Inorganic Compounds in Evolved Stars", Kwok, S. Nature, 430, 985 (2004). 
4. "On the Origin of Infrared Plateau Features in Proto-Planetary Nebulae", Kwok, S., Volk, K., and Bernath, P. Astrophys. J., 554, L87 (2001). 
5. "Proto-Planetary Nebulae", Kwok, S. in Encyclopedia of Astronomy and Astrophysics, IOP publishing, p. 2168 (2001). 
6. "Proto-Planetary Nebulae", Kwok, S. Ann. Rev. Astron. Astrophys., 31, 63 (1993). 
    

Dr. J.J.L. Lim

1. Lim, Jeremy, Ao, YiPing, & Dinh-V-Trung 2008, Astrophysical Journal, 67, 252. “Radially Inflowing Molecular Gas in NGC 1275 Deposited by an X-Ray Cooling Flow in the Perseus Cluster”
2. Kuo, Cheng-Yu, Lim, Jeremy, Tang, Ya-Wen, & Ho, Paul T. P. 2008, Astrophysical Journal, 679, 1094. “Prevalence of Tidal Interactions among Local Seyfert Galaxies”
3. Tang, Ya-Wen, Kuo, Cheng-Yu, Lim, Jeremy, Ho, Paul T. P. 2008, Astrophysical Journal, 679, 1352. “Prevalence of Tidal Interactions among Local Seyfert Galaxies: The Control Experiment”
4. Lim, Jeremy & Takakuwa, Shigehisa 2006, Astrophysical Journal, 653, 425. “Properties and Formation of the Multiple Protostellar System L1551 IRS 5”
5. Lim, Jeremy, Leon, Stephane, Combes, Françoise, & Dinh-V-Trung 2000, Astrophysical Journal, 545, L93. “Molecular Gas in the Powerful Radio Galaxies 3C 31 and 3C 264: Major or Minor Mergers?”
6. Lim, Jeremy & Ho, Paul T. P. 1999, Astrophysical Journal, 510, L7. “Violent Tidal Disruptions of Atomic Hydrogen Gas in Quasar Host Galaxies”
7. Lim, Jeremy, Carilli, Chris L., White, Stephen M., Beasley, Anthony J., & Marson, Ralph G. 1999, Nature, 392, 575. “Large convection cells as the source of Betelgeuse's extended atmosphere”
8. Lim, Jeremy; White, Stephen M. 1996, Astrophysical Journal, 462, L91. “Limits to Mass Outflows from Late-Type Dwarf Stars”
    

Dr. J.C.S. Pun

1. "High resolution X-ray imaging of the center of IC342," D.S.Y. Mak, C.S.J. Pun, A.K.H. Kong, Astrophysical Journal, 686, 995 (2008). 
2. "Thin accretion disks onto brane world black holes," C.S.J. Pun, Z. Kovács, T. Harko, Physical Review D, 78, 084015 (2008). 
3. "Modeling the Hubble Space Telescope Ultraviolet and Optical Spectrum of Spot 1 on the Circumstellar Ring of SN 1987A," C.S.J. Pun, E. Michael, S.A. Zhekov, R. McCray, et al., Astrophysical Journal, 572, 906 (2002). 
4. "Physical Conditions in Circumstellar Gas Surrounding SN 1987A 12 Years After Outburst", S.P. Maran, G. Sonneborn, C.S.J. Pun, P. Lundqvist, R.C. Iping, and T.R. Gull, Astrophysical Journal, 545, 390 (2000). 
5. "Ultraviolet Observations of SN 1987A with the IUE Satellite", C.S.J. Pun, R.P. Kirshner, G. Sonneborn, et al., Astrophysical Journal Supplement, 99, 223 (1995).  

For details, please refer to Astrophysics Group Homepage.