Michael Gully-Santiago, PhD

astronomer and technologist

hello, most folks just call me gully

I am a scientist and technologist living in Austin, Texas. I characterize stars and exoplanets using high resolution spectroscopy and probabilistic inference. I recently joined the Exoplanet Atmospheres research group with UT Austin Professor Caroline Morley. We want to measure the atmospheres of exoplanets, with a long view of finding out which exoplanets are habitable. I specialize in quantifying astrophysical uncertainty in the atmospheric measurement process. Previously I worked for the K2 mission, which continues to revolutionize our understanding of exoplanets and stellar activity among other topics. I contribute to the scientific Python ecosystem including the lightkurve toolkit for time series data anlysis and the spectral inference framework Starfish. For my PhD I led metrology with the UT Austin Silicon Diffractive Optics Group, where I lithographically patterned immersion gratings. During a NASA GSRP fellowship at the JPL Microdevices Lab I improved the precision of these devices even further. Recently I’ve become excited about GPUs, autodiff, and other modern numerical innovations that stand to catalyze astronomical discovery.


igully [at] utexas [dot] edu

The University of Texas at Austin
Department of Astronomy
2515 Speedway, Stop C1400
Austin, Texas 78712-1205



Placing the spotted T Tauri star LkCa 4 on an HR diagram 2017
Michael Gully-Santiago, Gregory J. Herczeg, Ian Czekala, Garrett Somers, Konstantin Grankin, Kevin Covey, J.F Donati, Silvia Alencar, Gaitee Hussain, Benjamin Shappee, Greg Mace, Jae-Joon Lee, T. Holoien, Jessy Jose, Chun-Fan Liu
Astrophysical Journal, 836, 2, 26 pages

Optical characterization of gaps in directly bonded Si compound optics using infrared spectroscopy 2015
Michael Gully-Santiago, Daniel T. Jaffe, Victor White
Applied Optics, 54, 34, 16 pages

High performance Si immersion gratings patterned with electron beam lithography 2014
Gully-Santiago, M.A; Jaffe, D.T.; Brooks, C.B.; Wilson, D.W.; and Muller, R.E.
Proc. SPIE

Near-infrared metrology of high-performance silicon immersion gratings 2012
Gully-Santiago, M.; Wang, W.; Deen, C.; and Jaffe, D.
Proc. SPIE

Confirmation and Characterization of Young Disk-Bearing Brown Dwarfs and sub-Brown Dwarfs 2011
Gully-Santiago, M. A., K. N. Allers, and D. T. Jaffe
Cool Stars 16

High-performance silicon grisms for 1.2-8.0 micron- detailed results from the JWST-NIRCam devices 2010
Gully-Santiago, M.; Wang, W.; Deen, C.; Kelly, D.; Greene, T. P.; Bacon, J.; Jaffe, D. T.
Proc. SPIE

The First SPIE software Hack Day 2014
S. Kendrew, C. Deen, N. Radziwill, S. Crawford, J. Gilbert, Gully-Santiago, M., and P. Kubanek
Proc. SPIE

New metrology techniques improve the production of silicon diffractive optics 2014
C. B. Brooks, Gully-Santiago, M., M. Grigas, and D. T. Jaffe
Proc. SPIE

Manufacturing of silicon immersion gratings for infrared spectrometers 2010
W. Wang, Gully-Santiago, M., C. Deen, D. J. Mar, and D. T. Jaffe
Proc. SPIE


Quantifying starspots and their implications for stellar ages

Starspots have occupied a major avenue of my recent research focus, leading in part to my work at Kepler/K2. Kepler researchers take for granted the mere existence of starspots as the dominant method of assigning rotation periods to stars. My major breakthrough on starspots came when I realized that starspots possess both the familiar “AC” signal, but also a less familiar “DC” signal, a part of starspot geometry that is always visible from the perspective of the observer.

Spectral inference of IGRINS data

IGRINS is a high resolution (R~45,000) spectrograph covering the entire H- and K- near-IR spectral windows in a single exposure. This immense spectral grasp presents both a new scientific competitive advantage, and an analysis challenge. For the last three years I have developed computational approaches to overcome those challenges. The technique emulates synthetic spectra from pre-computed stellar model grid to compare with IGRINS data. The implementation of this approach, Starfish by Ian Czekala, is openly developed on GitHub, parallelized, and permissively licensed. The code provides an extensible modular framework for deriving intrinsic and extrinsic stellar properties. My work is centered around extending the code to model starspots, protostars, brown dwarfs, and sub-giants.

Discovery and characterization of young brown dwarfs

The dearth of brown dwarfs is a manifestation of the stellar Initial Mass Function (IMF). Their rarity and the observational challenges of detecting them have conspired to yield small samples of brown dwarfs. Despite these limitations, brown dwarfs offer a unique astrophysical laboratory, to which we can ask the question “how do circumstellar disks change as a function of central object mass”. The agregate properties of young brown dwarfs serve as a bellwether for how astrophysical processes govern star formation. We are learning about circumstellar disk dispersal timescales as a function of central object mass. These ideas ultimately inform our understanding of planetary habitability, and the diversity of stellar and planetary systems.

Silicon Immersion gratings

The Jaffe Silicon Diffractive Optics Group has been making diffraction gratings out of monocrystalline silicon for over 3 decades. Silicon is an excellent optical material in the infrared because of its high (n = 3.4) refractive index, which shrinks Si immersed wavelength, and reduces the overall size (and cost) of an infrared spectrograph design by a factor of about 3 to 10. Weisong Wang and I custom-made the Si immersion grating for IGRINS.


I have started recording audio interviews at the Kepler/K2 Guest Observer Office at NASA Ames. I aspire to collect audio interviews with many more professional astronomers with a focus on frontiers in modern astrophysics. I am an avid listener of podcasts. You can follow me on the new Breaker podcast app to see which ones are my favorites. As a graduate student at UT Austin I produced and co-hosted 30 original science podcast for the KVRX science radio show They Blinded Me With Science.


Measuring fundamental properties of young stars November 18, 2016
Columbia University Stellar and Planetary lunch talk, NYC, USA

Forward Modeling IGRINS Spectra with Starfish November 12, 2015
High Resolution Spectroscopy with IGRINS Workshop, Seoul, South Korea

Data Science in Astronomy with Git and GitHub January 31, 2014
Grad Student Postdoc Seminar UT Austin Astronomy, Austin, TX

Ideas for Metrology of Silicon Diffractive Optics November 1, 2013
UT Austin Astronomy, Si Optics Group, Austin, TX

Zygo Interferometry of Echelle Gratings November 10, 2013
UT Austin Astronomy, Si Optics Group, Austin, TX

Direct bonded Silicon Optics November 11, 2013
UT Austin Astronomy, Si Optics Group, Austin, TX

SPIE 2012 Invited talk about Silicon Immersion Gratings July 6, 2012
SPIE Astronomical Telescopes and Instrumentation, Amsterdam, Netherlands

McDonald Observatory Board of Visitors Invited Public Talk February 11, 2011
UT Austin BOV meeting, ACES, Austin, TX