Academia Sinica Institute of Astronomy & Astrophysics
中央研究院天文及天文物理研究所
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Research > Interstellar and Circumstellar Medium

Interstellar and Circumstellar Medium

Using astrochemistry to probe jet structure and energetics in black hole X-ray binaries
Evidence of a Binary-Induced Spiral from an Incomplete Ring Pattern of CIT 6
The Dust Input from Evolved Stars to The Magellanic Clouds
Map of the abundance of the CS molecule
Artist impression of fullerenes in front of a planetary nebulae.
Artist impression of fullerenes in front of a planetary nebulae.
The location of the C60 containing Planetary Nebulae (blue symbols) in the Milky Way
The location of the C60 containing Planetary Nebulae (blue symbols) in the Milky Way
Crystallization of circumstellar silicates
lattice structure of crystalline silicate
lattice structure of amorphous silicate
crystalline silicates (1)
crystalline silicates (2)
The evolution of dust abundance
Spectral energy distribution of pulsed emission from a middle-aged pulsar B1951+32
CO(6-5) line at 690 GHz of the proto-planetary nebula CRL 618
Spectrum centered around 143 GHz of carbon star CW Leo
CO(2-1) emission from carbon star R Scl
Evolution of dust abundance
The crystalline fraction of interstellar silicates in starburst galaxies

The space between the stars is not empty, but instead it is filled with gas and dust, and is referred to as the interstellar medium (ISM). Most of the ISM is occupied by low density gas, which makes up about 90% of the volume, but only 1% of the mass in the ISM, but intermediate and high density regions exist too.

Schematic chemical structure of the circumstellar shell of an AGB star
The life cycle of dust in the interstellar medium of a galaxy
Stars form the molecular cloud (center) and develop either as a high-mass (right) or a low-mass star (left). Upon a supernova explosion in case of high-mass stars, or a process of more gradual mass loss (AGB/Planetary Nebula phase), material enriched by the products of nucleosynthesis is ejected from the stars, and added to the ISM. Dust formation takes place in the stellar ejecta.

The densest regions, molecular clouds, are the areas where star formation occurs, and where the interstellar gas gets compacted into stars. These young stars are often surrounded by the remnants of the molecular clouds from which they formed, or, at a later stage, by a circumstellar disk from which planets are forming. Post-main-sequence stars, but also massive main-sequence stars, lose stellar mass, often enriched with the products of nucleosynthesis, which forms a chemically interesting circumstellar environment. The stellar ejecta eventually get deposited into to the ISM, and drive the chemical evolution of galaxies.

The interstellar and circumstellar (ICSM) group studies the physical and chemical properties of the ISM and circumstellar environments. The group is very diverse, consisting of observers (mostly infrared/submm) and modellers, studying various (non-stellar) aspects of the life cycle of matter in galaxies. Research topics include: the gas and dust mass loss history of Asymptotic Giant Branch (AGB) stars; the chemical composition of AGB envelopes; the effect of binarity on the physical structure of the circumstellar envelope; chemical composition of molecular and translucent clouds; astrochemistry; the circumstellar environment of young stars; proto-brown dwarfs; planetary nebulae; dust production by supernovae; the life cycle of gas and dust in galaxies, particularly the Magellanic Clouds; astromineralogy; dust in the early universe, and in active galaxies.

Schematic chemical structure of the circumstellar shell of an AGB star
Schematic chemical structure of the circumstellar shell of an AGB star
The top half of the plot represents the chemistry in an oxygen-rich environment (C/O < 1), and the bottom half of the figure shows the carbon-rich counterpart. The logarithmic scale at the bottom shows the distance and temperature to the center of the star. Several distinct zones can be identified, namely the molecular formation region and the dust formation region, where conditions are governed by the density and the stellar radiation field, and the outermost region where the chemistry is dominated by the impinging interstellar radiation.
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