- Laboratory for Space Research
The University of Hong Kong
405B 4/F Block A Cyberport 4
Hong Kong
Sun Kwok
The University of Hong Kong, Laboratory for Space Research, Faculty Member
- Prof. Kwok is a Chair Professor of Space Science and Director of the Laboratory for Space Research at the University ... moreProf. Kwok is a Chair Professor of Space Science and Director of the Laboratory for Space Research at the University of Hong Kong. Between 2006 and 2016, he served as Dean of Science at The University of Hong Kong, and before that as Faculty Professor of the University of Calgary in Calgary, Canada, and Director and Distinguished Research Fellow of the Institute of Astronomy and Astrophysics of Academia Sinica of Taiwan.
Prof. Kwok is the author of over 350 papers in professional journals. He has also written a number of books, including Origin and Evolution of Planetary Nebulae (Cambridge, 2000), Cosmic Butterflies (Cambridge, 2001), and Physics and Chemistry of the Interstellar Medium, (University Science Books, 2006), Organic Matter in the Universe (Wiley, 2011) and Stardust: the cosmic seeds of life (Springer, 2013).
Prof. Sun Kwok is the current President of Commission F3 Astrobiology of the International Astronomical Union (IAU). Previously, he has served as President of Commission 34 (interstellar Matter), as well as the chairman of IAU Planetary Nebulae Working Group between 1994 and 2001.edit
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Techniques of computational quantum chemistry (CQC) are used to explore the vibrational modes of complex organic molecules with mixed aromatic and aliphatic structures.
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During the late asymptotic giant branch (AGB) phase of stellar evolution, the element carbon is created through the triple-α nuclear reaction. This is followed by the synthesis of other heavy elements via neutron capture in the core and... more
During the late asymptotic giant branch (AGB) phase of stellar evolution, the element carbon is created through the triple-α nuclear reaction. This is followed by the synthesis of other heavy elements via neutron capture in the core and the dredge-up of these elements to the surface by convection. Simple molecules and solid-state minerals begin to form in the upper photosphere. These molecules and solids are ejected into the interstellar medium by a strong stellar wind. During the subsequent post-AGB evolution, complex organics with aromatic and aliphatic structures are synthesized in the circumstellar envelope. Planetary nebulae, formed by swept-up circumstellar material, are found to show strong spectral signatures of ions, atoms, molecules, and inorganic and organic solids. These ejected materials of planetary nebulae serve as primordial ingredients of formation of new stars and planetary systems. Stellar synthesized organic solids may survive their journeys through the interstel...
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A family of unidentified infrared emission (UIE) bands has been observed throughout the Universe. The current observed spectral properties of the UIE bands are summarized. These properties are discussed in the frameworks of different... more
A family of unidentified infrared emission (UIE) bands has been observed throughout the Universe. The current observed spectral properties of the UIE bands are summarized. These properties are discussed in the frameworks of different models of the chemical carriers of these bands. The UIE carriers represent a large reservoir of carbon in the Universe, and play a significant role in the physical and chemical processes in the interstellar medium and galactic environment. A correct identification of the carrier of the UIE bands is needed to use these bands as probes of galactic evolution.
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The discovery of rapid synthesis of complex organic solids in the late stages of stellar evolution has led to a new realization that carbonaceous compounds can be a major significant component of interstellar dust. Signatures of aromatic... more
The discovery of rapid synthesis of complex organic solids in the late stages of stellar evolution has led to a new realization that carbonaceous compounds can be a major significant component of interstellar dust. Signatures of aromatic and aliphatic solids are seen in interstellar clouds as well as the diffuse interstellar medium. Similar features are also seen in the integrated spectrum of galaxies. This has raised the possibilities that many of the unidentified astronomical phenomena such as the diffuse interstellar bands, the 217 nm feature, the extended red emission, the 21 and 30 µm emission features, could also arise from complex organics. In this paper, we discuss the possible chemical structures of these organic solids and the relationships between circumsmtellar and interstellar dust with the organics found in meteorites, asteroids, comets and planetary satellites. The possibility that all these organics share a common origin is discussed.
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Recent millimeter-wave and infrared spectroscopic observations have identified a large number of organic molecules through their rotational and vibrational transitions. In particular, the detections of the stretching and bending modes of... more
Recent millimeter-wave and infrared spectroscopic observations have identified a large number of organic molecules through their rotational and vibrational transitions. In particular, the detections of the stretching and bending modes of aliphatic and aromatic compounds have revealed a continuous synthesis of organic materials at the late stages of stellar evolution. High resolution imaging observations in the submillimeter (e.g., SMA) and in the mid-infrared (e.g., Gemini) have made possible the mapping of the distribution of these compounds, allowing us to infer the history of circumstellar chemistry. In this paper, we present some of the recent spectroscopic and imaging observations of the circumstellar envelopes of evolved stars and discuss a scenario of chemical evolution including the possible role of photochemistry in the late stages of stellar evolution. 2007 Published by Elsevier Ltd on behalf of COSPAR.
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HM Sagittae is one of the most unusual objects in the Galaxy for it displays activity in every spectral band from x-ray to radio. Its present variable-star designation was given after the discovery of its optical brightening from 16m to... more
HM Sagittae is one of the most unusual objects in the Galaxy for it displays activity in every spectral band from x-ray to radio. Its present variable-star designation was given after the discovery of its optical brightening from 16m to 12m between April and September 1975 (Dokuchaeva and Balazs 1976). It was soon found to have a rich emissionline spectrum similar to that of a planetary nebula (Stover and Sivertsen 1977). Post-brightening monitoring of the object by Ciatti, Mammano and Vittone (1977, 1978) found the B and V magnitudes to be variable with amplitudes of at least one magnitude. Evidence for increasing excitation was found by Ciatti, Mammano and Vittone (1979) with Hell 4686 emerging in October 1978. Wolf-Rayet features of velocities up to 2000 km s-1 have also been seen (Belyakina, Gershberg and Shakhovskaya 1978, 1979; Brown et al. 1978; Ciatti et al. 1978; Wallerstein 1978; Allen 1980; Andrillat and Swings 1982). Analysis of the forbidden line ratios gives an estimat...
Research Interests: Physics and COLLOQUIUM
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The progress in planetary nebulae (PN) research reported in this symposium is reviewed in the context of our current understanding of the PN phenomenon.
Water is the common ground between astronomy and planetary science as the presence of water on a planet is universally accepted as essential for its potential habitability. Water assists many biological chemical reactions leading to... more
Water is the common ground between astronomy and planetary science as the presence of water on a planet is universally accepted as essential for its potential habitability. Water assists many biological chemical reactions leading to complexity by acting as an effective solvent. It shapes the geology and climate on rocky planets, and is a major or primary constituent of the solid bodies of the outer solar system. Water ice seems universal in space and is by far the most abundant condensed-phase species in our universe. Water-rich icy layers cover dust particles within the cold regions of the interstellar medium and molecular ices are widespread in the solar system. The poles of terrestrial planets (e.g. Earth, Mars) and most of the outer-solar-system satellites are covered with ice. Smaller solar system bodies, such as comets and Kuiper Belt Objects (KBOs), contain a significant fraction of water ice and trace amounts of organics. Beneath the ice crust of several moons of Jupiter and...
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Abstract. We report the detection of the 30 µm emission feature from the C-rich post–Asymptotic Giant Branch (post– AGB) star IRAS 04296+3429 based on ISO SWS observations. ISO data show that there is a clear substructure in the 30 µm... more
Abstract. We report the detection of the 30 µm emission feature from the C-rich post–Asymptotic Giant Branch (post– AGB) star IRAS 04296+3429 based on ISO SWS observations. ISO data show that there is a clear substructure in the 30 µm feature in the form of a plateau which extends from 26 to 27 µm. This is confirmed by the ISO SWS data for another post-AGB object IRAS 22272+5435, which has the strongest known 30 µm band accounting for about 24 % of its total infrared (IR) emission or 12 % of the bolometric luminosity. In the case of IRAS 04296+3429 we estimate that about 85 % of the total energy is emitted in the infrared of which about 15–22% (depending on the estimated continuum level) is contributed by the 30 µm band. The total energy emitted in the band is at least comparable for both sources, while the energy emitted in the 21 µm band seems to be about 3 times larger in the case of IRAS 04296+3429, if they have the same bolometric luminosity. Grains of pure MgS could be respons...
We present the results of a molecular line survey of the extreme carbon star CRL 3068. The observations were carried out with the Arizona Radio Observatory (ARO) 12 m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at the λ... more
We present the results of a molecular line survey of the extreme carbon star CRL 3068. The observations were carried out with the Arizona Radio Observatory (ARO) 12 m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at the λ 2 mm and λ 1.3 mm atmospheric windows. The observations cover the frequency bands from 130 to 162 GHz and 219.5 to 267.5 GHz. The typical sensitivities achieved are TR < 15 mK and TR < 7 mK for the ARO 12 m and SMT, respectively. Seventy-two individual emission features belonging to 23 molecular species and isotopologues were detected. Only three faint lines remain unidentified. The species c-C3H, CH3CN, SiC2, and the isotopologues, C17O, C18O, HC15N, HN13C, C33S, C34S, 13CS, 29SiS, and 30SiS are detected in this object for the first time. Rotational-diagram analysis is carried out to determine the column densities and excitation temperatures. The isotopic ratios of the elements C, N, O, S, and Si have also been estimated. The results are con...
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Infrared spectroscopic observations have shown that complex organics with mixed aromatic-aliphatic structures are synthesized in large quantities during the late stages of stellar evolution. These organics are ejected into the... more
Infrared spectroscopic observations have shown that complex organics with mixed aromatic-aliphatic structures are synthesized in large quantities during the late stages of stellar evolution. These organics are ejected into the interstellar medium and spread across the Galaxy. Due to the sturdy structures of these organic particles, they can survive through long journeys across the Galaxy under strong UV background and shock conditions. The implications that stellar organics were embedded in the primordial solar nebula is discussed.
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Seven compact PNe with high radio surface brightness (and therefore presumably young) were observed with theHSTWFPC2 under cycle 8 program 8307 (PI: S. Kwok). Observations were made with three narrow-band filters, F656N (Hα), F658N... more
Seven compact PNe with high radio surface brightness (and therefore presumably young) were observed with theHSTWFPC2 under cycle 8 program 8307 (PI: S. Kwok). Observations were made with three narrow-band filters, F656N (Hα), F658N ([NII]) and F502N ([OIII]). The [NII] images of six of the nebulae are shown in Figure 1.
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The family of unidentified infrared emission features, consisting of discrete and plateau features in the mid-infrared, are now observed in distant galaxies. A significant fraction of the total energy output of some infrared galaxies is... more
The family of unidentified infrared emission features, consisting of discrete and plateau features in the mid-infrared, are now observed in distant galaxies. A significant fraction of the total energy output of some infrared galaxies is emitted in these features. Comparisons of these features with those observed in the circumstellar and interstellar media suggest that these organic species are synthesized and ejected by evolved stars. Models of possible chemical structures of the carrier of these features are discussed.
Research Interests: Physics and Astrophysics
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Current theories on the▶ origin of life are centered on the hypothesis that under suitable conditions (e.g., a primordial soup), simple molecules can be synthesized into complex organic compounds which later develop into self-replicating... more
Current theories on the▶ origin of life are centered on the hypothesis that under suitable conditions (e.g., a primordial soup), simple molecules can be synthesized into complex organic compounds which later develop into self-replicating living organisms. An initial laboratory basis for this hypothesis was the Miller-Urey experiment, in which a mixture of gaseous molecules (hydrogen, water, ammonia, methane) when subjected to electric discharge yielded complex organics such as amino acids. The discoveries of insoluble organic matter in carbonaceous meteorites (Cronin et al. 1987), organic contents in interplanetary dust particles (Flynn et al. 2003), and complex organic dust synthesized by stars (Kwok 2004) have raised the possibility that externally delivered organics may have allowed the origin of life on Earth to bypass some of the first steps of organic synthesis on the early Earth (Ehrenfreund et al. 2006; Kwok 2009).
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ABSTRACT
Research Interests: Engineering and Physics
Seven compact PNe with high radio surface brightness (and therefore presumably young) were observed with theHSTWFPC2 under cycle 8 program 8307 (PI: S. Kwok). Observations were made with three narrow-band filters, F656N (Hα), F658N... more
Seven compact PNe with high radio surface brightness (and therefore presumably young) were observed with theHSTWFPC2 under cycle 8 program 8307 (PI: S. Kwok). Observations were made with three narrow-band filters, F656N (Hα), F658N ([NII]) and F502N ([OIII]). The [NII] images of six of the nebulae are shown in Figure 1.
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Research Interests: Engineering and Physics
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The abundances of 16 well studied have been determined. New ISO measurements have been combined with optical and ultraviolet data from the literature, in an attempt to obtain accurate values. Only He, O, C, N, Ne, Ar, and S are... more
The abundances of 16 well studied have been determined. New ISO measurements have been combined with optical and ultraviolet data from the literature, in an attempt to obtain accurate values. Only He, O, C, N, Ne, Ar, and S are considered. High values of N/O are sometimes, but not always, found in bipolar nebulae. On the other hand, some bipolar nebulae show low values of N/O, and it is concluded that no simple relationship between morphology and composition exists.
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As part of a comprehensive study of the origins of aspherical structure in protoplanetary (PPN) and planetary nebulae (PN), we report here high-resolution H (F160W) and K (F222M) images of 3 bipolar PPN, Roberts 22, Hen 401, and the... more
As part of a comprehensive study of the origins of aspherical structure in protoplanetary (PPN) and planetary nebulae (PN), we report here high-resolution H (F160W) and K (F222M) images of 3 bipolar PPN, Roberts 22, Hen 401, and the Boomerang Nebula, obtained with NICMOS/HST. All 3 objects have substantial cold, dense molecular envelopes seen in mm-wave CO lines. Amongst these,
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High-resolution near-infrared HST NICMOS (F160W, F222M) images and polarization (2 μm) observations were made of four bipolar proto-planetary nebulae (PPNs): IRAS 17150−3224, IRAS 17441−2411, IRAS 17245−3951, and IRAS 16594−4656. The... more
High-resolution near-infrared HST NICMOS (F160W, F222M) images and polarization (2 μm) observations were made of four bipolar proto-planetary nebulae (PPNs): IRAS 17150−3224, IRAS 17441−2411, IRAS 17245−3951, and IRAS 16594−4656. The first three of these are viewed nearly edge-on, and for the first time the central stars in them are seen. Color maps reveal a reddened torus between the bipolar lobes in the edge-on cases, with bluer lobes. The polarization values are high, with maximum values ranging from 40 to 80%. The polarization patterns are basically centrosymmetric, with some deviations in the low polarization equatorial regions. For IRAS 17150−3224, circumstellar arcs are seen at 1.6 μm, along with a newly-discovered loop in the equatorial region. Bright caps are seen at the end of the lobes, indicating that they are not open-ended. A distinct point-symmetric pattern is seen in the strengths of the polarization vectors, especially in IRAS 17150−3224. HST NICMOS observations pro...
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It is now known that strong stellar winds develop in stars mostly at the red and blue sides of the HR diagram. However, although the mass loss rates observed in O and M stars are comparable, the corresponding wind velocities are vastly... more
It is now known that strong stellar winds develop in stars mostly at the red and blue sides of the HR diagram. However, although the mass loss rates observed in O and M stars are comparable, the corresponding wind velocities are vastly different. It would thus be of great interest to find a binary system, containing both a cool and a hot star each with its own wind, and observe the resultant interaction. For a long time, α Sco (M1.5 Iab + B2.5 V) was the only known example (Kudritzki and Reimers 1978, van der Hucht et al. 1980). The situation in this case is best illustrated by a VLA map made by Gibson (1979) who finds that a shock develops at the surface of interaction of the two winds. In this paper I shall describe another binary system in which two stellar winds are interacting with dramatic effects.
The idea that planetary nebulae (PN) originated from outer layers of red giants goes back to Shlovskii (1956). This hypothesis was supported by Abell and Goldreich (1966) who argued convincingly that red giants are the most likely... more
The idea that planetary nebulae (PN) originated from outer layers of red giants goes back to Shlovskii (1956). This hypothesis was supported by Abell and Goldreich (1966) who argued convincingly that red giants are the most likely progenitors of PN. Although this is generally accepted today, the details of the transition from red giants to PN remain in controversy. It was pointed out by Paczyński (1971 a) that PN progenitors must have similar luminosities to central stars of PN, and therefore are likely to be late-type supergiants undergoing double-shell burning. The advent of infrared astronomy led to the discovery that most, if not all, late-type giants and supergiants are losing mass at rates of 10-6 - 10-5 Mʘyr-1 (Gehrz and Woolf 1971). Such mass loss rates greatly exceed the nuclear burning rate (6 x 10-8 - 5 x 10-7 Mʘyr-1 for stars with core masses between 0.6 and 1.2 Mʘ) and must be the dominant factor in the late evolution of intermediate mass stars. The observation of white...
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As stars evolve up the asymptotic giant branch (AGB), they begin to lose mass at a high rate, and in the process they create extended circumstellar molecular envelopes. Since the transition from AGB to planetary nebula stages is of the... more
As stars evolve up the asymptotic giant branch (AGB), they begin to lose mass at a high rate, and in the process they create extended circumstellar molecular envelopes. Since the transition from AGB to planetary nebula stages is of the order of 1000 yr, the remnant of such molecular envelopes should still be observable in pro to-planetary nebulae (PPN) and planetary nebulae (PN). Recent ground-based survey of cool IRAS sources have discovered ~30 candidates of PPN (Kwok 1992). These sources show the characteristic “double-peak” energy distribution. The cool component is due to the remnant of the AGB dust envelope, and the hot component represents the reddened photosphere. The fact that the two components are clearly separated suggests that the dust envelope is well detached from the photosphere. Radiative transfer model fits to the spectral energy distributions of PPN suggest a typical separation of ~1 arc sec between the dust envelope and the photosphere, and such “hole-in-the-midd...
NGC 7027 has been observed in eleven molecular species (in seventeen transitions) in the 200 and 300 GHz bands with the James Clarke Maxwell Telescope (Hasegawa…