Institute of Astronomy and Astrophysics, Preparatory Office

The Institute of Astronomy was among the first to be established when Academia Sinica was founded in 1928. The Institute built the famous Purple Mountain Observatory near the city of Nanking. The further growth of the Institute was discontinued because of the Second Sino-Japanese war and the civil war. In 1990, Dr. C. C. Lin, a member of Academia Sinica, proposed to re-establish the Institute of Astronomy and Astrophysics (ASIAA). In 1991, Academia Sinica's President Ta-You Wu set up a planning committee to draft a ten-year plan to develop astronomy in the R.O.C. Following the recommendation of the committee, Academia Sinica's Council approved the establishment of ASIAA in 1992. In 1993, a Preparatory Office was inaugurated with Dr. Typhoon Lee as the first director and an Advisory Committee chaired by Prof. Frank H. Shu was appointed. Dr. Chi Yuan was the director between 1994 and 1996. Dr. Fred Kwok Yung Lo has been designated to become the director in 1997. In July 1994, ASIAA signed a three-year collaboration agreement with the University of California-Berkeley, University of Illinois, and University of Maryland to have access to the world-class BIMA (Berkeley-Illinois-Maryland Association) millimeter interferometric array; this agreement will be extended for one more year until the summer of 1998. In June 1996, Acadamia Sinica signed an agreement with the Smithsonian Institution to build the world's first submillimeter interferometric array. ASIAA is located temporarily on the 4th floor of the Institute of Biochemistry Building.

RESEARCH

Finite element model of the reflector for the 6-meter antennas of the SAO/IAA submillimeter array to be installed atop mauna kea, Hawaii. The picture shows the backup structure CFRP struts, the chopping secondary mirror support, the composite hub and the steel reflector support weldment.

The Institute aims to conduct observational and theoretical research in order to understand the origin, structure, and evolution of the universe and its constituents. The initial emphasis on the observational front is radio astronomy, particularly in millimeter and submillimeter inter-ferometry. ASIAA also intends to build up its own in-strumentation research and development capability using modern technology from applied physics, electronics, and microwave engineering.

THE SMART Sub-Millimeter ARray of Taiwan PROJECT

• Following the recommendation of the ten-year plan of astronomy development in R.O.C., ASIAA will develop and build two sub-millimeter antennas based on the design of the Smithsonian Astrophysical Observatory (SAO). The two completed antennas will join the 6-antenna Sub-Millimeter Array (SMA; currently under construction) of SAO in Mauna Kea, Hawaii. ASIAA signed a contract with Aeronautic Industry Development Center (AIDC) to construct two antennas. ASIAA is collaborating with Tsing Hua University, Central University, and Taiwan University to fabricate key components for sub-mm receivers. ASIAA's receiver laboratory will integrate and test these receivers.

  The Sub-Millimeter Array (SMA) of the Smithsonian Astrophysical Observatory on the summit of Mauna Kea in Hawaii (artist\'s conception). SMA will be the first sub-millimeter interfermetric array in the world.

• Design and trade-off studies, assembly and testing of radio telescope antennas.
• To use low temperature superconductor SIS Josephson junction to fabricate millimeter and submillimeter wave mixers and other related devices.
• To study applied superconductivity, superconducting devices, microwave physics, and thin films deposition.

THEORETICAL ASTROPHYSICS

• To understand the structure, the motion and the evo-lution of astronomical disk systems, including galactic disks, protostellar disks, and planetary rings. The emphasis is placed on a physical mechanism called resonance excitation, through which spiral waves in the disk are created by a rotating bar, a giant proto-planet, or a satellite.
• To study interstellar magnetic field, cosmic ray accel-eration mechanism, and spiral structure of Milky Way.

  Thermal dust emission from the northern component of the giant molecular cloud Sagittarius B2. This subarcsecond resolution continuum image was observed using the 9-antenna BIMA millimeter array.(Courtesy of Y.-J. Kuan)

• To study differentially rotating self-gravitating disk galaxies.
• To study the dynamics of Saturn's rings.

OBSERVATIONAL ASTRONOMY

• To study the dust emission from protostellar disks.
• To understand the star formation process by studying protostellar collapse and molecular outflows.
• To study the structure of high density molecular cloud cores around star forming regions.
• To investigate the nature of the newly discovered bipolar outflow object in the open cluster M36.
• Nuclear astrophysics and cosmochemistry: to investi-gate the abundance of nuclei in the solar system, stars, and interstellar media in order to study their sources, production processes, and evolution in galaxies and the universe.

  Bar-driven spiral density waves, computed with a 2-D hydro-code to simulate molecular gas flows in the central regions of disc galaxies.(Courtesy of C. Yuan & C.L. Kuo)

• Astrochemistry: to test grain-surface chemistry and gas-grain chemistry in the interstellar medium.
• Search for large, organic interstellar molecules.
• Radio stars, including the massive star £b Carinae, magnetic Bp stars, Sun-like stars in young open clusters, and precataclysmic binaries.
• Chemical evolution and stellar nucleosynthesis in our Galaxy.
• Sulfur isotope ratios in the Milky Way.
• Radio study of the Galactic center.
• Molecular and isotopic abundances in the Magellanic Clouds.
• Dynamical and molecular studies of the starburst galaxy NGC4945.
• Search for radio recombination lines from external ga-laxies.
• To study the molecular medium from redshifted gala-xies.

PERSONNEL AND FACILITIES

PERSONNEL

The 9-antenna (soon to be 10) BIMA (Berkeley-illinois-Maryland Association) interferometric array at Hat Creek, California, U.S.A. The BIMA array operates at the millimeter wavelength and can achieve an angular resolution as high as 0.4 arcsecond.

The Institute currently has 1 distinguished research fellow, 3 research fellows, 1 visiting associate research fellows, 1 antenna specialist, 4 assistant research fellows, 7 postdoctoral research fellows, 5 research assistants, and 4 administrative staff. The Institute is still in the process of expanding and recruiting. More staff memebers are being added at the time of writing.

FACILITIES

Through a collaboration agreement ASIAA has access to the BIMA (Berkeley-Illinois-Maryland Association) in-terferometric array located in northern California. The BIMA array consists of ten 6-meter antennas designed to operate in the 1 to 3 millimeter wavelength region.

A scene from the regular colloquium held at the conference room every Saturday morning.

The BIMA array can achieve sub-arcsecond angular resolution which is the highest among the only four such facilities in the world. ASIAA has a dedicated internet link to Berkeley for remote observing with the BIMA array as well as for transferring data from various astronomical observatories and archives. A network of workstations is available for image processing, model calculations, numerical simulations, and remote observations. A sub-millimeter/millimeter receiver laboratory is being set up. A library is also being set up, presently having appro-ximately 300 books and catalogs of celestial objects, and subscribing to 17 journals.

MAJOR RESULTS OF RESEARCH

THE SMART (Sub-Millimeter ARray of Taiwan) PROJECT

• The deposition system to grow a high quality Nb and Al thin film has been set up. The processes of mixer fabrication are being established.

THEORETICAL ASTROPHYSICS

• A comprehensive non-linear theory has been developed to explain various dynamical features associated with the spiral structures, revealed by the recent high reso-lution radio and optical observations. Observational tests of the theory are also sought by using the millimeter and submillimeter radio interferometry. The theory has been successfully applied in explaining the observations of the central bar-spiral structures of Seyfert galaxy NGC1068 and the spiral-ring structure so often observed in barred galaxies.
• Found self-similar analytic solution of ambipolar diffusion equation.
• Theoretically determined the spiral structure of the Milky Way galaxy.
• Employed the linear kinetic theory to determine the stability of a differentially rotating self-gravitating disk against small amplitude gravity perturbations.
• It is shown that small-scale density waves are effec-tively excited at the corotation resonance. This resonant self-excitation of density waves may be the cause of the irregular, small-scale structure observed in regions of low optical depth in Saturn's rings.

L1641N system, located in Orion A molecular cloud at a distance 1,500 light years, is a newly discovered protobinary. The image reveals two dust components separated by 1 second of arc (500 time the Sun-Earth distance), suggesting the existence of circumstellar disks.(Courtesy of J.-H Zhao)

OBSERVATIONAL ASTRONOMY

• Extremely high velocity outflows from several star forming regions were observed. It is not clear whether these outflows are swept-up ambient molecular material or the stellar wind/jet itself.
• A radiative transfer simulation code which can handle arbitrary velocity fields in a one-dimensional spherical molecular cloud was developed. This code can be used to explain the observations of protostellar collapse.
• A bipolar-outflow object was discovered in an old open cluster M36. If the object is an asymptotic giant branch (AGB) star, then it is a massive super-AGB; if it is a young stellar object, then it is unusual because old clusters rarely, if ever, contain on-going star formation.
• A protobinary system, L1641N, was discovered.
• h Carinae has been discovered which is currently undergoing a giant radio outburst. This outburst is seen as a brightening of gas clouds around the star.
• The first definitive confirmation of rotational modulation in the radio emission of a magnetic Bp star has been made, predicted by the present model for the radio emission of these stars.
• Intense radio emission from active solar-type stars in the Pleiades open cluster has been detected. Because open clusters have well determined ages, such studies provide accurate chronologies of the activity level of Sun-like stars at different ages.
• We have recently shown that the radio emission of the precataclysmic eclipsing binary V471 Tau suffers an eclipse once each orbital period, and from the properties of the radio lightcurve inferred that the radio emission arises from the region where extended magnetic loops on the Sun-like star interact with the dipolar mag-netosphere of the white dwarf.
• Our model of Galactic chemical evolution can fit the observed very well and therefore explain the isotopic ratios of C, N, and O.
• A systematic study of sulfur isotopes was carried out for the first time. The following results were found: a) a galactocentric dependence of ³²S/³⁴S ratios was observed; b) both ³²S/³⁴S and ³⁴S/³³S ratios are close to the solar ratios; c) for the first time ³⁶S was detected.
• A systematic study of molecular and isotopic abun-dances in the Magellanic Clouds was established for the first time, and the molecular and isotopic abun-dances are found to be very different from our Milky Way, which can be explained by the low metallicity and high UV radiation in the Magellanic Clouds.

  The 1995 Star Formation Workshop "Star and Planet Formation at High Angular Resolution" was held at Academia Sinica in July, 1995. This meeting was sponsored by the Institute of Astronomy & astrophysics (Academia Sinica), the Center for Astrophysics (Harvard-Smithsonian), and the Center for Star Formation Studies (UC-Berkeley, UC-Santa Cruz,and NASA-Ames). Nearly one hundred participants from 12 countries worldwide, such as the United States, Germany, France, Japan, the United Kingdom, and Canada, attended this meeting.

• Deuterium was detected in the Large Magellanic Cloud. This is the first definite detection of deuterium outside our Galaxy. The result is consistent with the D/H ratio obtained in the Galaxy and supports that the universe cannot be closed by baryons alone.
• A high precision and high sensitivity analytical technique was developed to search for the record of particle irradiation in the early solar system.
• An astrophysical model for star formation was applied to the processing of the earliest planetary solid material in the solar system.
• An unusually high grain-emissivity exponent near 3 mm, which implies the existence of ice-coated dust grains, was found in the dense cloud core of the giant molecular cloud Sagittarius B2.
• Various complex molecules were detected in the Heimat source Sgr B2(N). Together with other observational evidence for the existence of warm core-mantle grains, this is believed to be due to abundant variations as a result of enhanced grain-surface chemistry.
• Detected a number of radio recombination lines from external galaxies and modeled the line emission region in starburst galaxies.
• Discovery of Galactic center transient.
• Observed and modeled the high velocity cloud, re-vealing that this cloud moves towards the Galactic center and interacts with the central gravitational field.

RESEARCH STAFF

MEMBER OF THE ADVISORY COMMITTEE