Research Interest

"The reward of the young scientist is the emotional thrill of being the first person in the history of the world to see something or to understand something." - Cecilia Payne-Gaposchkin

I want to understand the astrophysical connections between stars and galaxies -- how galaxies can influence the elemental composition and formation of stars, and how stars can be used as tracers for galactic evolution. I am an ``end-to-end'' large survey-oriented scientist -- I develop novel methods to maximally harness information in the data through machine learning, build theoretical models, and confront them with observation via rigorous statistical inference.

I primarily work on the Milky Way, capitalizing on a wide range of on-going large-scale surveys and most key future surveys in the next decade, including spectroscopy (SDSS-V, DESI, PFS, JWST, APOGEE, GALAH, LAMOST), astrometry (Gaia), photometry (Gaia, HSC, LSST, WFIRST, DES, Euclid) and asteroseismology (TESS, Kepler).


Formation of the Milky Way


Galactic archaeology


Large survey sciences


Stellar spectra


Machine learning


Statistical inferences

I study the Milky Way

"We are part of this universe; we are in this universe, but perhaps more important than both of those facts, is that the universe is in us." - Neil deGrasse Tyson

Why do galaxies look the way they are today?

Understanding all physical processes responsible for the formation of galaxies is a fundamental, but unsolved problem in astrophysics. For example, we still do not have a detailed picture of when, where, and how stars in each component (disk, spiral arms, halo, bulge) of a galaxy formed, nor of the key processes responsible for its subsequent dynamical and chemical evolution after the stars formed.

The Milky Way as a sample organism

My research shines new light on this problem by studying how our own galaxy, the Milky Way evolves in the last 13 billion years. Since the Milky Way is the closest galaxy to us, it offers a unique opportunity to this problem; after all it is the only galaxy we can study individual stars in great detail. This research area which coined the term "Galactic archaeology" is going through a significant revolution in recent years as the observational landscape is rapidly changing.

Now is the best time to study the Milky Way

Surveys such as APOGEE, GALAH, and Gaia-ESO are collecting high-resolution spectra for 106 stars, 3 orders of magnitude more stars than what we had before, and are measuring >20 elemental abundances for each star. Importantly, this is complemented by other revolutionary astrometric and photometric surveys such as Gaia, TESS, LSST, and WFIRST which provide complementary yet crucial phase space (positions and velocities) information of stars and their stellar ages.

Astronomy, machine learning, and statistics

This revolutionary data however requires that we go beyond the classical astronomy and calls for better chemodynamics modeling of the Milky Way, sophisticated ways to harness the maximal spectral information from stellar spectra as well as advanced statistical tools to infer the Milky Way's evolution through the noisy data. To this end, my research operates at the cross-section between theoretical modeling, observational astronomy, machine learning and data science.

Research highlight 1 - ab initio spectral fitting

First, how well we can study the Milky Way depends critically on our ability to extract information from stellar spectra. However, no spectral analysis has attempted a self-consistent, simultaneous fitting of all parameters to the full spectral range. To this end, I developed a rigorous spectral fitting technique, The Payne which allows for such ab initio fitting, can measure multiple elemental abundances from low-resolution spectra, and facilitates the finding of unresolved stellar binaries.

Research highlight 2 - the Milky Way's global properties

And with millions of stars of which we can now extract precise properties, using them as tracers in the Milky Way, my research explores this unprecedented data to tell a complete story of the Milky Way. In particular, through careful statistical inference, we infer, quantitatively, global properties such as the star formation history of the Milky Way, the rate at which the Milky Way accumulates its metals, and what causes the Milky Way disk to "puff up" over time.

Research highlight 3 - how stars formed

Finally, my work also explores the possibility to go beyond just probing the global properties of the Milky Way. In particular, I have been leading the effort for "chemically tagging" the Milky Way. Like twins separated at birth, stars formed in clusters but were soon torn apart. I pioneered various work which use the chemical fingerprints of stars to shed light on how stars formed, in what sizes of aggregates, and at what rate metal produced in supernovae diffuses in the interstellar medium.

Most Recent Talk

02/2019 @ University of Florida (full screen)


Public Outreach

"All men have stars, but they are not the same things for different people. For some, who are travelers, the stars are guides. For others they are no more than little lights in the sky. For others, who are scholars, they are problems." - The Little Prince

TED: How do we study the stars (full screen)

TED: How to measure distances (full screen)

Interactive Modules: Interstellar Absorption and the Lyman Alpha Forest (full screen)


"The struggle itself towards the heights is enough to fill a man's heart. One must imagine Sisyphus happy." - Albert Camus

Download Resume

Professional Appointment


Hubble Postdoctoral Fellow

Funded by NASA for a fully independent postdoctoral research.


Joint Carnegie-Princeton-IAS Fellow

Joint postdoctoral fellowship from Princeton University, the Institute for Advanced Study in Princeton (where Albert Einstein worked!) and the Carnegie Observatories (where Erwin Hubble worked!).


Interim Postdoctoral Research Associate, Australian National University



Harvard University -- PhD Astrophysics

Advisor: Prof. Charlie Conroy


Ecole Polytechnique, France -- MSE, BSE Engineer's Degree

Diplome D'Ingenieur de l'Ecole Polytechnique
Equivalent to Master's and Bachelor's Degrees in Engineering
Concurrent double degrees from Singapore and France


National University of Singapore -- MSc, BSc Physics

Summa cum laude, best Physics major
Minor in Mathematics
Concurrent double degrees from Singapore and France


Hubble Fellowship - 2018-21

Prized postdoctoral fellowship from NASA

Carnegie-Princeton Fellowship - 2017-23

A joint prized postdoctoral fellowship from the Carnegie Observatories and Princeton University

Institute for Advanced Study School of Natural Sciences Fellowship - 2017-21

Awarded full funding for an independent research at the Institute for Advanced Study, Princeton

Dr. Pliny A. and Margaret H. Price Prize - 2016

Two finishing Ph.D.s awarded internationally

Selected to attend the Lindau Meeting of Nobel Laureates, Lindau, Germany

Prestigious meeting for young scientists below the age of 35

NASA Earth and Space Science Fellowship - 2015-16

Funded by NASA for a Ph.D. study

Malaysian Perdana Scholar Award - 2014

National merit award

Singapore National Academy of Science Award - 2012

Best Physics major

Institute of Physics Singapore Medal - 2011

Best Physics undergraduate

French Government Eiffel Scholarship - 2008-10

Full scholarship for a study in France

Jurong Book Prize, National University of Singapore - 2008

Best freshman/sophomore Physics major

Australian Mathematics Competition Gold Medal - 2005

Top 0.01% among entries from 8 countries

Research Milestones




1st/2nd/advisee authored publications






Departmental presentations


Conference presentations


Publications as lead authors (as 1st/2nd author or advisees' publications)

The vertical motion history of disk stars throughout the Galaxy
2018, ApJ, submitted.

Measuring radial orbit migration in the Galactic disk
2018, ApJ, submitted.

The Payne: self-consistent ab initio fitting of stellar spectra
2018, ApJ, submitted.

Measuring Oxygen abundances from stellar spectra without Oxygen lines
2018, ApJ, 860, 159.

A large and pristine sample of standard candles across the Milky Way
2018, ApJL, 858, L7.

Stellar ages and masses in the solar neighbourhood: Bayesian analysis using spectroscopy and Gaia DR1 parallaxes
2018, MNRAS, 477, 2606.

Discovery and characterization of 3000+ main-sequence binaries from APOGEE spectra
2018, MNRAS, 476, 528.

Metallicity fluctuation statistics in the interstellar medium and young stars. I. Variance and correlation
2018, MNRAS, 475, 2236.

Signatures of unresolved binaries in stellar spectra: implications for spectral fitting
2018, MNRAS, 473, 5043.

Photospheric diagnostics of core helium burning in giant stars
2018, ApJ, 853, 20

Measuring 14 elemental abundances with R=1,800 Lamost spectra
2017, ApJL 849, L9

Prospect for measuring abundances of >20 elements with low-resolution stellar spectra
2017, ApJ, 843, 32

Constructing polynomial spectral models for stars
2016, ApJL, 826, L25

Accelerated fitting of stellar spectra
2016, ApJ, 826, 83

APOGEE chemical tagging constraint on the maximum star cluster mass in the α-enhanced Galactic disk
2016, ApJ, 816, 10

Prospects for chemically tagging stars in the Galaxy
2015, ApJ, 807, 104

Constraining the Galactic potential via action-based distribution functions for mono-abundance stellar populations
2013, MNRAS, 434, 652

High resolution elemental abundance analysis of the open cluster IC 4756
2012, MNRAS, 427, 882

Galaxy Zoo: Dust lane early-type galaxies are tracers of recent, gas-rich minor mergers
2012, MNRAS, 423, 59

Galaxy Zoo: Dust and molecular gas in early-type galaxies with prominent dust lanes
2012, MNRAS, 423, 49

Principal component analysis on chemical abundance spaces
2012, MNRAS, 421, 1231


"We cannot work without hoping that others will advance further than we have. In principle, this progress goes on ad infinitum. " - Max Weber

Intermediate Algebra

Princeton Prison Teaching Innitiative
Teaching assistant

Stellar astrophysics

Harvard University
Teaching assistant

Classical Mechanics

National University of Singapore
Teaching assistant


National University of Singapore
Teaching assistant


National University of Singapore

Linear Algebra

National University of Singapore

Abstract algebra

National University of Singapore

Contact Me

Have a project you'd like to discuss?