My current research focuses on the two closest circumnuclear regions, the Galactic Centre and the M31 nuclear bulge.
My main interest is massive stars, extinction law and star formation history.
The Galactic Center is the closet galactic nucleus. Because of the proximity, we can resolve individual stars. Thus, it is the best lab for us to study the interaction between the massive black hole and nearby environments.
Previously, most studies focused on three massive star clusters in the Galactic Center; Arches, Quintuplet and Central clusters. They are very young (< 10 Myr), massive (104 solar mass) and compact (< 2pc) star clusters.
However, massive stars outside these three clusters are unknown. In 2008, we obtained a large HST program to observe the central 39’ x 16’ with two narrow band filters, F187N and F190N.
The main purpose of this program is to find massive stars outsider of these three clusters (“Field” massive stars hereafter) through the enhanced Palpha emission line (1.87 micron) from the stellar atmosphere or the HII regions surrounding these massive stars. In total, we found 180 massive stars, 100 of which outsider of the three clusters.
Considering that massive stars likes to form in star clusters, these “Field” massive stars have three different origins. 1) ejected from the three star clusters by tidal forces or ‘three-body’ interaction. The tidal forces near the massive black hole is very strong. Therefore, the stars in the three clusters are expected to be stripped and fall into a tidal tail. Meanwhile, due to the mass segregation, the number density of massive stars in the cores of the clusters is high. Therefore, the three-body interaction between massive stars will form a close massive binary and ejected a massive star. 2) formed in-situ. The environment in the Galactic Center is hostile to new star formation, due to the high temperature, strong magnetic field and tidal forces. Massive star clusters could be preferred. If the “field” massive stars formed locally, the underlying star clusters should be much smaller than the three massive ones. This could challenge our understanding of star formation in this extreme environment.
The M31 Bulge
The M31 bulge is the second closest galactic nucleus. Compared to the Galactic Center, its advantage is that 1) it can be observed in the whole electromagnetic spectrum 2) we can ignore the differential difference of the radial distance of stars.
- Extinction Curves in the Bulge
- Stellar population
- Extinction Map