About

Michael Fitzgerald is associated with the Planetary Systems Imager (PSI) project, an advanced instrument designed for the Thirty Meter Telescope (TMT). The PSI aims to address fundamental questions about the composition, formation, and history of planets orbiting other stars. As a second-generation instrument for TMT, PSI is capable of making detailed measurements not only of exoplanets but also of various objects within our own solar system. The instrument's design includes a high-order common-path adaptive optics system that corrects incoming light before it is directed to multiple backend instruments operating across different wavelength ranges, including 10-micron, 2-5 micron, and visible light. This setup allows for high-resolution characterization of exoplanet atmospheres through fiber-fed spectroscopy across multiple wavelength regions. Additionally, the PSISIM simulation tool, developed to support the instrument's development and survey planning, can simulate planetary populations with diverse spectral characteristics and observing sequences, aiding in the design of PSI and other instruments. Michael Fitzgerald's contact information is provided as mpfitz@ucla.edu, indicating his active role in this research and development effort.

Research topics

• Physics
• Optics
• Astronomy
• Astrophysics
• Astrobiology
• Computer Science
• Remote sensing
• Geology

Selected publications

• Limits On the Posteclipse Emission Spectrum of HD 80606 b From High-resolution Spectroscopy

  The Astronomical Journal · 2026-03-10

  articleOpen accessSenior author

  Abstract We present Keck/NIRSPEC K -band observations of HD 80606 b, one of the most eccentric known exoplanets. HD 80606 b was observed after secondary eclipse, close to periastron, when the planet passes within 0.03 au of HD 80606 and the rapid heating of the atmosphere may lead to extreme chemical changes and a temporary thermal inversion. The rapid change in the planetary radial velocity near periastron is sufficient to enable high-resolution cross-correlation spectroscopy analysis, which produces a tentative detection (SNR ∼ 4) of HD 80606 b. Injection-recovery tests appear to reject strong thermal inversions near periastron, consistent with recent results from JWST. We also perform atmospheric retrievals with free parameters for the pressure–temperature profile and with a profile matched to the JWST results, which suggest the presence of absorption features from CH 4 and CO. While HD 80606 b is not definitively detected in these data, these results are consistent with JWST observations, which found that the posteclipse atmosphere of HD 80606 b shows weak absorption features from these species. Future observations with higher spectral resolution and/or wider wavelength coverage are needed for a confident atmospheric detection of HD 80606 b via high-resolution spectroscopy alone, but such observations are a challenge to schedule due to the 111 days orbital period.

  PublisherDOI

• Reduced data products and models from "Limits on the post-eclipse spectrum of HD 80606 b from high-resolution spectroscopy"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-12

  datasetOpen accessSenior author

  This repository contains reduced data products, planetary and stellar models, and posteriors from Finnerty et al. 2026a. The repository contains all of the planet models plotted in that paper and/or used to compute Kp-vsys maps in conjunction with the included reduced data products. HD80606_jan21_NIRSPEC.h5 contains the reduced data products. The archive keys are "baryrv" (barycentric radial velocity for each frame in km/s), "time" (midpoint time of each frame, in JD), "flux" (extracted fluxes, shape nframes x norders x npixels, in counts), and "wave" (wavelength, shape norders x npixels, in microns). Raw data products are available via the Keck Observatory Archive. The files ending in "post_equal_weights.dat" are the equally weighted posterior samples produced by the MultiNest runs. Each row is a sample. Columns are the parameters, in the order listed in Table 2 of the paper. The final column is the computed log-likelihood of the sample. The files ending in "_emission_petit.dat" are planet models produced with petitRADTRANs. The first column is the wavenumber, in cm^-1, and the second column is the flux, in erg/s/cm^3. HD80606_T5500_logg4.5_Z0.5_vsini1.8_orders.npy is the stellar model used, which is based on the PHOENIX spectral library. This file must be opened with allow_pickel=True option in numpy.load. The 9 entries correspond to the nine spectral orders. For each order, there is an array with the full-resolution stellar model, with rotational broadening applied. The first column of the array is the wavelength (in micron), and the second is the flux in erg/s/cm^3.

  PublisherDOI

• Dynamical Architectures of S-type Transiting Planets in Binaries. II. A Dichotomy in Orbital Alignment of Small Planets in Close Binary Systems

  The Astronomical Journal · 2026-01-09

  articleOpen access

  Abstract Stellar multiplicity plays a crucial role in shaping planet formation and dynamical evolution. We present a survey of 54 TESS objects of interest (TOIs) within 300 pc that exhibit significant Hipparcos−Gaia astrometric accelerations. We identified 35 TOIs with stellar companions at projected separations between 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 1 and 2″ (or 10–200 au). We also identified 12 TOIs that could host planetary-mass or brown dwarf companions, including six that are newly discovered. Furthermore, we perform 3D orbital characterization for 12 binaries hosting confirmed planets or planet candidates, allowing us to constrain the line-of-sight mutual inclination, Δ I los , between the planetary and binary orbits. Combining our sample with previous measurements, we apply Bayesian hierarchical analysis to a total of 26 binary systems with S-type transiting planets ( r p &lt; 5 R ⊕ ). Specifically, we fit the Δ I los distribution with both single (Rayleigh) and mixture models (two-component Rayleigh and Rayleigh-isotropic mixture). We find the mixture models are strongly favored ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>Z</mml:mi> <mml:mo>≳</mml:mo> <mml:mn>13.9</mml:mn> </mml:math> , or ≈5 σ ), indicating the observed planet-binary Δ I los values likely originate from two underlying populations: one nearly aligned ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) and one with more scattered mutual inclinations ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>23</mml:mn> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> <mml:msubsup> <mml:mrow> <mml:mn>6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>7.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>8.8</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ). Alternatively, the misaligned systems can be equally well described by an isotropic distribution of inclinations. This observed dichotomy likely reflects different dynamical histories. Notably, the misaligned population only emerges in systems with stellar periastron distances &gt;40 au, while systems with close-in or eccentric stellar companions (periastron distances &lt;40 au) preserve planet−binary alignment.

  PublisherDOI

• Reduced data products and models from "Limits on the post-eclipse spectrum of HD 80606 b from high-resolution spectroscopy"

  Open MIND · 2026-02-12

  datasetSenior author

  This repository contains reduced data products, planetary and stellar models, and posteriors from Finnerty et al. 2026a. The repository contains all of the planet models plotted in that paper and/or used to compute Kp-vsys maps in conjunction with the included reduced data products. HD80606_jan21_NIRSPEC.h5 contains the reduced data products. The archive keys are "baryrv" (barycentric radial velocity for each frame in km/s), "time" (midpoint time of each frame, in JD), "flux" (extracted fluxes, shape nframes x norders x npixels, in counts), and "wave" (wavelength, shape norders x npixels, in microns). Raw data products are available via the Keck Observatory Archive. The files ending in "post_equal_weights.dat" are the equally weighted posterior samples produced by the MultiNest runs. Each row is a sample. Columns are the parameters, in the order listed in Table 2 of the paper. The final column is the computed log-likelihood of the sample. The files ending in "_emission_petit.dat" are planet models produced with petitRADTRANs. The first column is the wavenumber, in cm^-1, and the second column is the flux, in erg/s/cm^3. HD80606_T5500_logg4.5_Z0.5_vsini1.8_orders.npy is the stellar model used, which is based on the PHOENIX spectral library. This file must be opened with allow_pickel=True option in numpy.load. The 9 entries correspond to the nine spectral orders. For each order, there is an array with the full-resolution stellar model, with rotational broadening applied. The first column of the array is the wavelength (in micron), and the second is the flux in erg/s/cm^3.

  DOI

• On-sky Demonstration of Subdiffraction-limited Astronomical Measurement Using a Photonic Lantern

  The Astrophysical Journal Letters · 2025-10-22 · 1 citations

  articleOpen accessCorresponding

  Abstract Resolving fine details of astronomical objects provides critical insights into their underlying physical processes. This drives in part the desire to construct ever-larger telescopes and interferometer arrays and to observe at shorter wavelengths to lower the diffraction limit of angular resolution. Alternatively, one can aim to overcome the diffraction limit by extracting more information from a single telescope’s aperture. A promising way to do this is spatial-mode-based imaging, which projects a focal-plane field onto a set of spatial modes before detection, retaining focal-plane phase information that is crucial at small angular scales but typically lost in intensity imaging. However, the practical implementation of mode-based imaging in astronomy from the ground has been challenged by atmospheric turbulence. Here, we present the first on-sky demonstration of a subdiffraction-limited mode-based measurement, using a photonic-lantern-fed spectrometer installed on the Subaru Coronagraphic Extreme Adaptive Optics instrument at the Subaru Telescope. We introduce a novel calibration strategy that mitigates time-varying wave-front error and misalignment effects, leveraging simultaneously recorded focal-plane images and using a spectral-differential technique that self-calibrates the data. Observing the classical Be star β CMi, we detect spectral-differential spatial signals and reconstruct images of its H α -emitting disk. We achieve an unprecedented H α photocenter precision of ∼50 μ as in about 10 minutes of observation with a single telescope, measuring the disk’s nearside–farside asymmetry for the first time. This work demonstrates the high precision, efficiency, and practicality of photonic mode-based imaging techniques in recovering subdiffraction-limited information, opening new avenues for high-angular-resolution spectroscopic studies in astronomy.

  PublisherDOI

• Characterization of the Host Binary of the Directly Imaged Exoplanet HD 143811 AB b

  The Astrophysical Journal Letters · 2025-12-11 · 1 citations

  articleOpen accessCorresponding

  Abstract HD 143811 AB is the host star to the directly imaged planet HD 143811 AB b, which was recently discovered using data from the Gemini Planet Imager and Keck NIRC2. A member of the Sco-Cen star-forming region with an age of 13 ± 4 Myr, HD 143811 AB is somewhat rare among hosts of directly imaged planets, as it is a close stellar binary, with an ∼18-day period. Accurate values for the orbital and stellar parameters of this binary are needed to understand the formation and evolutionary history of the planet in orbit. We utilize archival high-resolution spectroscopy from FEROS on the MPG/ESO 2.2 m telescope to fit the orbit of the binary, and we combine with unresolved photometry to derive the basic stellar properties of the system. From the orbit, we derive precise values of orbital period of 18.59090 ± 0.00007 days and mass ratio of 0.886 ± 0.003. When combined with stellar evolutionary models, we find masses of both components of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>M</mml:mi> <mml:mi mathvariant="normal">A</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.3</mml:mn> <mml:msubsup> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> M ⊙ and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>M</mml:mi> <mml:mi mathvariant="normal">B</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.1</mml:mn> <mml:msubsup> <mml:mn>5</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.04</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> M ⊙ . While the current data are consistent with the planet and stellar orbits being coplanar, the 3D orientations of both systems are currently poorly constrained, with additional observations required to more rigorously test for coplanarity.

  PublisherDOI

• Characterization of the Host Binary of the Directly Imaged Exoplanet HD 143811 AB b

  ArXiv.org · 2025-09-08

  preprintOpen access

  HD~143811~AB is the host star to the directly imaged planet HD~143811~AB~b, which was recently discovered using data from the Gemini Planet Imager and Keck NIRC2. A member of the Sco-Cen star-forming region with an age of $13 \pm 4$ Myr, HD~143811~AB is somewhat rare among hosts of directly imaged planets as it is a close stellar binary, with an $\sim$18 day period. Accurate values for the orbital and stellar parameters of this binary are needed to understand the formation and evolutionary history of the planet in orbit. We utilize archival high-resolution spectroscopy from FEROS on the MPG/ESO 2.2-meter telescope to fit the orbit of the binary, and combine with unresolved photometry to derive the basic stellar properties of the system. From the orbit, we derive precise values of orbital period of $18.59098 \pm 0.00007$ days, and mass ratio of $0.885 \pm 0.003$. When combined with stellar evolutionary models, we find masses of both components of $M_A = 1.30^{+0.03}_{-0.05}$ M$_\odot$ and $M_B = 1.15^{+0.03}_{-0.04}$ M$_\odot$. While the current data are consistent with the planet and stellar orbits being coplanar, the 3D orientations of both systems are currently poorly constrained, with additional observations required to more rigorously test for coplanarity.

  PublisherOA PDFDOI

• Fringing analysis and forward modeling of Keck Planet Imager and Characterizer (KPIC) spectra

  Journal of Astronomical Telescopes Instruments and Systems · 2025-08-13 · 1 citations

  article
  PublisherDOI

• Calibration techniques for high angular resolution measurement with photonic lanterns on Subaru/SCExAO

  2025-09-18

  article

  Achieving high angular resolution in the visible and near-infrared is crucial for many subfields of astronomy. However, imaging resolution is typically limited to lambda/D for a single telescope. Recently, the use of photonic lanterns (PLs) for high angular resolution applications has gained interest due to their potential for super-resolution (sub-diffraction limit) capabilities. A PL can be used as a high-throughput compact integral field unit (IFU) when its single-mode outputs are fed into a diffraction-limited spectrograph. However, the sensitivity of the PLs to small angular scales makes them susceptible not only to the astronomical scene but also to static and time-varying wavefront errors, necessitating dedicated observation strategies and post-processing techniques for calibration. We present lessons learned with on-sky tests with a three-port infrared PL and a 19-port visible PL installed on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) testbed at the Subaru Telescope, isolating spatially resolved astronomical signals from wavefront errors using spectral-differential techniques and reconstructing spectral-differential images.

  PublisherDOI

• High Resolution ALMA Data of the Fomalhaut Debris Disk Confirms Apsidal Width Variation

  The Astrophysical Journal Letters · 2025-09-04 · 4 citations

  articleOpen access

  Abstract We present long-baseline observations of the Fomalhaut outer debris disk at 223 GHz (1.3 mm) from Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 5, which we use along with archival short-baseline observations to produce a 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> </mml:math> 57 resolution mosaic of the disk at a sensitivity of 7 μ Jy bm −1 . We use radial profiles to measure the disk at the ansae and find that the southeast (SE) side of the disk is 4 au wider than the northwest (NW) side as observed by ALMA. We also find that the peak brightness of the NW ansa is 21% ± 1% brighter than the SE ansa. We perform Markov Chain Monte Carlo fits of the ALMA visibilities using two analytical, eccentric disk models. Our results suggest that the model including a dispersion parameter for the proper eccentricity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> ), which accounts for additional scatter in the eccentricity of individual orbits, is preferred over the model without one. Such a model implies that self-gravitation, particle collisions, and close-packing could play a role in shaping the overall structure of the Fomalhaut disk, as is seen in eccentric planetary rings. Crucially, neither model can reproduce the brightness or width asymmetry near the NW ansa. No emission from the intermediate belt is detected, allowing us to place a 3 σ upper limit of 396 μ Jy at 1.3 mm. We also discover a spectral line in archival Cycle 3 data centered at ν obs ≈ 230.25 GHz at the location of the “Great Dust Cloud,” whose redshift from the expected CO line for Fomalhaut confirms the source is a background galaxy.

  PublisherDOI

Recent grants

• Collaborative Research: Mastering the photonic lantern: The key to transformative diffraction-limited spectroscopy

  NSF · $212k · 2021–2024

• First-Light Debris Disk Science with the Gemini Planet Imager

  NSF · $300k · 2014–2017

• Collaborative Research: Developing optimally customized-mode-selective photonic lanterns to enable the characterization of hundreds of exoplanets on solar system.

  NSF · $226k · 2023–2025

Frequent coauthors

• Paul Kalas

  253 shared

• Gaspard Duchêne

  University of California, Berkeley

  229 shared

• James R. Graham

  181 shared

• Dimitri Mawet

  163 shared

• Maxwell A. Millar‐Blanchaer

  160 shared

• Jason Wang

  159 shared

• Christian Marois

  154 shared

• Bruce Macintosh

  154 shared

Education

• Ph.D.

  University of California Berkeley

  2007

• M.A.

  University of California Berkeley

  2002

• B.S.

  California Institute of Technology

  2000