Sgr A* Flare
The center of the Milky Way with the
supermassive black hole, Sgr A* at the
center of the image.
(UCLA GC Group)

The Galactic Center

The center of the Galaxy is a complex environment dominated by the gravitational effects of the supermassive black hole (Sgr A*). This black hole can be studied indirectly by observing the stars closest the black hole. As part of the UCLA Galactic Center Group, I am studying the dynamics and stellar populations of these stars through imaging and spectroscopy. We are also studying infrared emission from Sgr A*.

Evolved Stars

For my masters project I worked with Mark Morris on the study of the mass loss histories of pre-planetary nebulae (PPN). PPNs are interesting to study because they represent the final stage of stellar evolution for low to intermediate mass stars. During this and the earlier asymptotic giant branch (AGB) phase of their evolutions, these stars must lose most of their mass to become white dwarfs. We are trying to study mass loss by imaging PPNs in the far infrared, which can trace the dust ejected from these stars during their earlier evolutionary stage. By looking far from the star, we can also look back in time by seeing dust that was lost by stellar winds during the AGB. To do this, we are using the Spitzer Space Telescope with the MIPS array at 70 and 160 microns to image a sample of PPNs out very far from the star (> 800 arcseconds) in order to trace as long a mass loss history as we can. The paper I wrote on AFGL 2688 (the Egg Nebula), IRAS 16342-3814, and OH 231.8 +4.2 to be published in AJ is here:

A Spitzer Study of the Mass Loss Histories of Three Pre-Planetary Nebulae, Do, T., Morris, M, Sahai, R., and Stapelfeldt, K., ArXiv e-prints, 0707.0468

Galactic Center Structures

The Double Helix Nebula
A false color image of the
Double Helix Nebula (DHN).
Recent Spitzer Space Telescope images of the galactic center have shown some very interesting structures, such as the "Double Helix Nebula". This feature shows up at 24 microns as a double helix of dust, with its emission mostly likely due to tiny dust grains and PAHs (Polycyclic Aromatic Hydrocarbons). The reason for this familiar DNA-like structure is not completely clear at this time, but it may be due to the rotation of the circum-nuclear disk (CND) at the center of the Milky Way. The double helix has about the same width as the CND, and may be tracing an magnetic Alfven wave propagating out of this disk as it rotates around the galactic center. The paper on this structure was reported by Morris et al. in the March 16th, 2006 issue of Nature. For those without access to Nature, the astro/ph pre-print can be found here:

The Double Helix Nebula: a magnetic torsional wave propagating out of the Galactic centre, M. Morris, K. Uchida and T. Do, astro-ph/0512452.