Projects for Students

Most of the research projects listed below requires Python Programming. In addition to the projects below, I am also looking for a student to help me set up an optical instrumentation lab at the Astronomy Building. If this is something you are interested in, please do not hesitate to contact me.

Globular clusters (GCs) might get tidally disrupted by the Milky Way's gravitational force and form tidal tails. Several GCs have reported possible tidal tails or extra-tidal features (e.g. references in this paper, this paper, and supplement table 1 in this paper, etc.). Southern Stellar Stream Spectroscopic Survey (S5) and DESI provides line-of-sight velocities and metallicities to help the search of tidal tails around these GCs. The student will develop a Bayesian based statistical model to search for tidal tails around these GCs using Gaia plus spectroscopic data from S5 and DESI. See this paper as a start. Also this project are similar to Project 8 on stream search.

Southern Stellar Stream Spectroscopic Survey (S5) has observed more than one dozens of stellar streams in our Milky Way, See this paper for the latest results from S5 as well and the observational properties of these stellar streams. It is crucial to compare these observational data with simulations to understand the properties of the streams as well as to test whether the models are consistent with the observations. See this paper as an example of some comparison we have made with FIRE simulations. The student will continue on this effort, creating some mock observations with simulations and compare with the S5 observations.

While over 60 satellites galaxies have been discovered in the Milky Way, only a handful of them appear to be on orbits whose pericenters are near enough to the Milky Way for them to have experienced significant tidal disturbance. The Southern Stellar Stream Spectroscopic Survey (S5) has collected extensive spectroscopic data on three of such systems. These three systems all show extremely large size and low surface brightness. The student will perform kinematic, metallicity and orbital analysis on these three galaxies using data from S5 and Gaia EDR3, to understand their formation and evolution.

Stellar systems such as galaxies and globular clusters can be disrupted to form stellar streams in our Milky Way, providing a snapshot of accretion that can be compared directly with theoretical models of the formation and evolution of galaxies. Thanks to various modern space-based and ground-based imaging and spectroscopic surveys, we now have both the kinematic and chemical information of over a dozen stellar streams. The student will develop a statistical model to assess the membership of each stream candidate star with full 6D phase space and metallicity information and assess how the model might affect the underlying kinematic and metallicity properties of the streams. This project will explore developing and applying new statistical and computational techniques which will be largely used in the next generation spectroscopic surveys.

Description: The distribution of dark matter in dwarf galaxies can have important implications on our understanding of the particle physics properties of dark matter. In particular, the stellar kinematic data could be used to constrain the cusp or core profile of the dark matter inner halo, the so-called "cusp/core problem". This project will result in a forecast on the capability to determine the cusp/core profile with all high probable member stars selected with Gaia proper motion. See this paper for details on methodology if you are interested in.

Description: Southern Stellar Stream Spectroscopic Survey (S5) has observed over 2000 BHB stars at 16 to 20 mag. This sample could be used to study the kinematics of the outer halo of the Milky Way, especially on the study of the LMC-induced sloshing of the Galactic halo (see example ) and the recent massive merger: Gaia-Enceladus-Sausage.

Blue horizontal branch (BHB) stars are great distant tracers as they are bright and can probe the Milky Way to a very far distance, and is a super useful tool for probing the Milky Way halo density profile as well as for searching for interesting structures (e.g. star clusters, dwarf galaxies) in the Milky Way. However, the color of BHB stars are similar to another type of star -- blue straggler stars (BSs), which are usually 10-50x closer at the same brightness. Therefore, it is scientifically important to separate these two different populations of stars in an efficient way. Luckily, the high-precision photometry data from Dark Energy Survey (DES, a wide-field imaging survey that contains 400 million astronomical objects) show separate sequences in multi-color space. The student will determine the probability of a star being a BHB or BS star using a statistical approach, given the brightness and color of the stars and their measurement uncertainties from DES. The student will also explore this project using various machine learning methods. This project will create one of the largest samples of BHB stars to probe the Milky Way down to a distance > 300 kpc (~1 million light year!).

Description: The high precision of the photometry from the Dark Energy Camera (DECam) enables photometric metallicity measurements. This project aims to develop a data-driven model via machine learning (see example ), to connect the DECam and the spectroscopic metallicity from the Southern Stellar Stream Spectroscopic Survey (S5) . The derived model will then be applied to all the globular clusters and dwarf galaxies observed by DEcam for further metallicity constraints. See Figure 12 in this paper if you are interested in.

Description: This project aim to perform consistent reductions and measurements for three ultra-faint dwarf galaxies using the public archival data from the GIRAFFE spectrograph on the Very Large Telescope (VLT). The first paper of this paper of this series has been accepted by ApJ (here) and was led by an undergraduate student (now a PhD student at MIT). Two more papers are expected from this series. This project has two branches, one is working on the catalog data directly, another is to start from the raw data and get familiar with data reduction in optical spectroscopic data.

Description: Large photometric surveys have discovered a large number of faint stellar systems in the outer halo of the Milky Way, including the ultra-faint dwarf galaxies and low-luminosity star clusters. It has become increasingly difficult to distinguish between these two populations, but the distinction is crucial to robustly measure the faint end of the galaxy luminosity function. This project aims to characterize Milky Way's outer halo star clusters. Read the original observing proposal if you are interested in this project. This project could also lead to additonal observing proposals led by the student.

Description: The orbital motion of close binary systems in ultra-faint dwarf galaxies (UFDs) may potentially inflate the velocity dispersions of the systems which are so far the only way to constrain the dynamical masses and therefore the dark matter content in these UFDs. This project aims to identify individual binaries in six UFDs with data collected from Magellan Telescope, and model the entire data set probabilistically to recover unbiased estimate of the velocity dispersions and the dynamical masses of the system. Read the original observing proposal if you are interested in this project. The student will learn how to reduce spectroscopic data as the first step for this project. Alternatively, the student will compile a list of binary stars in UFD with available velocity measurements and try to measure the orbital period with JOKER. This project could lead to a graduate student thesis project.