About

James P. Lloyd is a Professor in the Department of Astronomy at Cornell University, with a joint appointment in Mechanical and Aerospace Engineering. He holds a B.Sc. (Honours First Class) in Physics from the University of New South Wales and completed his graduate studies at the University of California, Berkeley, earning both an M.A. and a Ph.D. in Astrophysics. He was a Fulbright scholar at Berkeley and a Robert A. Millikan Prize Postdoctoral Scholar at the California Institute of Technology. His research broadly covers extrasolar planets and the development of astronomical instrumentation. He has expertise and experience in infrared detectors and instrumentation, adaptive optics, interferometry, coronagraphy, high contrast imaging, wavefront sensing, and precision radial velocity measurements. Professor Lloyd has participated in wintering over at the Amundsen-Scott South Pole Station twice, for which he was awarded the US Navy Antarctica Service Medal with Gold Winterover Bar. He has served on several panels including the National Academy of Sciences Astro 2010 Decadal Survey, the Evaluation of the Implementation of WFIRST/AFTA, and the NASA WFIRST Independent Evaluation and Technical Review panels. His current research activities at Cornell focus on the properties of extrasolar planets using data from the Kepler and GALEX missions, as well as the development of ground, balloon, and space-based instruments to detect and characterize these planets.

Research topics

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

Selected publications

• The James Webb Interferometer: Space-based Interferometric Detections of PDS 70 b and c at 4.8 <i>μ</i> m

  The Astronomical Journal · 2025-02-12 · 8 citations

  articleOpen access

  Abstract We observed the planet-hosting system PDS 70 with the James Webb Interferometer, JWST's aperture masking interferometric mode within NIRISS. Observing with the F480M filter centered at 4.8 μ m, we simultaneously fit geometrical models to the outer disk and the two known planetary companions. We redetect the protoplanets PDS 70 b and c at a signal-to-noise ratio (SNR) of 14.7 and 7.0, respectively. Our photometry of both PDS 70 b and c provides tentative evidence of mid-IR circumplanetary disk emission through fitting spectral energy distribution models to these new measurements and those found in the literature. We also newly detect emission within the disk gap at an SNR of ~4, a position angle of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>22</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>15</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> °, and an unconstrained separation within ~200 mas. Follow-up observations will be needed to determine the nature of this emission. We place a 5 σ upper limit of 208 ± 10 μ Jy on the flux of the candidate PDS 70 d at 4.8 μ m, which indicates that if the previously observed emission at shorter wavelengths is due to a planet, this putative planet has a different atmospheric composition than PDS 70 b or c. Finally, we place upper limits on emission from any additional planets in the disk gap. We find an azimuthally averaged 5 σ contrast upper limit &gt;7 mag at separations greater than 110 mas. These are the deepest limits to date within ~250 mas at 4.8 μ m and the first space-based interferometric observations of this system.

  PublisherDOI

• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. III. Aperture Masking Interferometric Observations of the Star HIP 65426 at 3.8 <i>μ</i>m

  The Astrophysical Journal Letters · 2025-04-09 · 3 citations

  articleOpen access

  Abstract We present aperture masking interferometry (AMI) observations of the star HIP 65426 at 3.8 μ m, as part of the JWST Direct Imaging Early Release Science program, obtained using the Near Infrared Imager and Slitless Spectrograph instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of 0.5 λ / D for an interferometer), which are inaccessible with the classical inner working angles of the JWST coronagraphs. When combined with JWST’s unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a 5 σ contrast of Δ m F380M ∼ 7.62 ± 0.13 mag relative to the host star at separations ​​​​​≳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> 07 , and the contrast deteriorates steeply at separations ≲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> 07. However, we detect no additional companions interior to the known companion HIP 65426b (at separation ∼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> 82 or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>8</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>31</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>108</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">au</mml:mi> </mml:math> ). Our observations thus rule out companions more massive than 10–12 M Jup at separations ∼10–20 au from HIP 65426, a region out of reach of ground- or space-based coronagraphic imaging. These observations confirm that the AMI mode on JWST is sensitive to planetary mass companions at close-in separations (≳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> 07), even for thousands of more distant stars at ∼100 pc, in addition to the stars in the nearby young moving groups and associations, as stated in previous works. This result will allow the planning and successful execution of future observations to probe the inner regions of nearby stellar systems, opening an essentially unexplored parameter space.

  PublisherDOI

• The James Webb Interferometer: Space-based interferometric detections of PDS 70 b and c at 4.8 $μ$m

  arXiv (Cornell University) · 2024-04-19 · 2 citations

  preprintOpen access

  We observed the planet-hosting system PDS 70 with the James Webb Interferometer, JWST's Aperture Masking Interferometric (AMI) mode within NIRISS. Observing with the F480M filter centered at 4.8 $μ$m, we simultaneously fit geometrical models to the outer disk and the two known planetary companions. We re-detect the protoplanets PDS 70 b and c at an SNR of 14.7 and 7.0, respectively. Our photometry of both PDS 70 b and c provides tentative evidence of mid-IR circumplanetary disk emission through fitting SED models to these new measurements and those found in the literature. We also newly detect emission within the disk gap at an SNR of $\sim$4, at a position angle of $220^{+10}_{-15}$ degrees, and an unconstrained separation within $\sim$200 mas. Follow-up observations will be needed to determine the nature of this emission. We place a 5$σ$ upper limit of 208 $\pm$ 10 $μ$Jy on the flux of the candidate PDS 70 d at 4.8 $μ$m, which indicates that if the previously observed emission at shorter wavelengths is due to a planet, this putative planet has a different atmospheric composition than PDS 70 b or c. Finally, we place upper limits on emission from any additional planets in the disk gap. We find an azimuthally averaged 5$σ$ contrast upper limit $&gt;$7 magnitudes at separations greater than 110 mas. These are the deepest limits to date within $\sim$250 mas at 4.8 $μ$m and the first space-based interferometric observations of this system.

  PublisherOA PDFDOI

• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. IV. NIRISS Aperture Masking Interferometry Performance and Lessons Learned

  The Astrophysical Journal Letters · 2024-02-19 · 9 citations

  articleOpen access

  Abstract We present a performance analysis for the aperture masking interferometry (AMI) mode on board the James Webb Space Telescope Near Infrared Imager and Slitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables, AMI accesses inner working angles down to and even within the classical diffraction limit. The scientific potential of this mode has recently been demonstrated by the Early Release Science (ERS) 1386 program with a deep search for close-in companions in the HIP 65426 exoplanetary system. As part of ERS 1386, we use the same data set to explore the random, static, and calibration errors of NIRISS AMI observables. We compare the observed noise properties and achievable contrast to theoretical predictions. We explore possible sources of calibration errors and show that differences in charge migration between the observations of HIP 65426 and point-spread function calibration stars can account for the achieved contrast curves. Lastly, we use self-calibration tests to demonstrate that with adequate calibration NIRISS F380M AMI can reach contrast levels of ∼9–10 mag at ≳ λ / D . These tests lead us to observation planning recommendations and strongly motivate future studies aimed at producing sophisticated calibration strategies taking these systematic effects into account. This will unlock the unprecedented capabilities of JWST/NIRISS AMI, with sensitivity to significantly colder, lower-mass exoplanets than lower-contrast ground-based AMI setups, at orbital separations inaccessible to JWST coronagraphy.

  PublisherDOI

• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. V. Do Self-consistent Atmospheric Models Represent JWST Spectra? A Showcase with VHS 1256–1257 b

  The Astrophysical Journal Letters · 2024-04-25 · 36 citations

  articleOpen access

  Abstract The unprecedented medium-resolution ( R λ ∼ 1500–3500) near- and mid-infrared (1–18 μ m) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 M Jup ) L–T transition (L7) companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling approach applying our Bayesian framework, ForMoSA . We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: T eff , log( g ), [M/H], C/O, γ , f sed , and R . Our findings reveal that each parameter’s estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS 1256 b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a T eff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log( g ). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST’s data for VHS 1256 b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.

  PublisherOA PDFDOI

• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems V: Do Self-Consistent Atmospheric Models Represent JWST Spectra? A Showcase With VHS 1256 b

  arXiv (Cornell University) · 2023-12-06 · 1 citations

  preprintOpen access

  The unprecedented medium-resolution (R~1500-3500) near- and mid-infrared (1-18um) spectrum provided by JWST for the young (140+/-20Myr) low-mass (12-20MJup) L-T transition (L7) companion VHS1256b gives access to a catalogue of molecular absorptions. In this study, we present a comprehensive analysis of this dataset utilizing a forward modelling approach, applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), [M/H], C/O, gamma, fsed, and R. Our findings reveal that each parameter's estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS1256b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST's data for VHS1256b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.

  PublisherOA PDFDOI

• The Near Infrared Imager and Slitless Spectrograph for JWST. V. Kernel Phase Imaging and Data Analysis

  Publications of the Astronomical Society of the Pacific · 2023-01-01 · 17 citations

  articleOpen access

  Abstract Kernel phase imaging (KPI) enables the direct detection of substellar companions and circumstellar dust close to and below the classical (Rayleigh) diffraction limit. The high-Strehl full pupil images provided by the James Webb Space Telescope (JWST) are ideal for application of the KPI technique. We present a kernel phase analysis of JWST NIRISS full pupil images taken during the instrument commissioning and compare the performance to closely related NIRISS aperture masking interferometry (AMI) observations. For this purpose, we develop and make publicly available the custom Kpi3Pipeline data reduction pipeline enabling the extraction of kernel phase observables from JWST images. The extracted observables are saved into a new and versatile kernel phase FITS file data exchange format. Furthermore, we present our new and publicly available fouriever toolkit which can be used to search for companions and derive detection limits from KPI, AMI, and long-baseline interferometry observations while accounting for correlated uncertainties in the model fitting process. Among the four KPI targets that were observed during NIRISS instrument commissioning, we discover a low-contrast (∼1:5) close-in (∼1 λ / D ) companion candidate around CPD-66 562 and a new high-contrast (∼1:170) detection separated by ∼1.5 λ / D from 2MASS J062802.01-663738.0. The 5 σ companion detection limits around the other two targets reach ∼6.5 mag at ∼200 mas and ∼7 mag at ∼400 mas. Comparing these limits to those obtained from the NIRISS AMI commissioning observations, we find that KPI and AMI perform similar in the same amount of observing time. Due to its 5.6 times higher throughput if compared to AMI, KPI is beneficial for observing faint targets and superior to AMI at separations ≳325 mas. At very small separations (≲100 mas) and between ∼250 and 325 mas, AMI slightly outperforms KPI which suffers from increased photon noise from the core and the first Airy ring of the point-spread function.

  PublisherOA PDFDOI

• The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope. IV. Aperture Masking Interferometry

  Publications of the Astronomical Society of the Pacific · 2023-01-01 · 22 citations

  articleOpen access

  Abstract The James Webb Space Telescope’s Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first such interferometer in space, operating at 3–5 μ m wavelengths, and a bright limit of ≃4 mag in W2. We describe the NIRISS Aperture Masking Interferometry (AMI) mode to help potential observers understand its underlying principles, present some sample science cases, explain its operational observing strategies, indicate how AMI proposals can be developed with data simulations, and how AMI data can be analyzed. We also present key results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI) technique benefits from AMI operational strategies, we also cover NIRISS KPI methods and analysis techniques, including a new user-friendly KPI pipeline. The NIRISS KPI bright limit is ≃8 W2 (4.6 μ m) magnitudes. AMI NRM and KPI achieve an inner working angle of ∼70 mas, which is well inside the ∼400 mas NIRCam inner working angle for its circular occulter coronagraphs at comparable wavelengths.

  PublisherOA PDFDOI

• SIZLE: Smallsat to Image Zodiacal Light Above Ecliptic

  2023-10-17

  article

  This paper presents the mission design of SIZLE (SmallSat to Image Zodiacal Light Above the Ecliptic), a pioneering endeavor tailored for NASA's Astrophysics Pioneers Program. SIZLE's main science mission will aim to address fundamental questions outlined in the Decadal Strategy for Planetary Science and Astrobiology 2023-2032. The primary objective of this mission is to enhance our understanding of interplanetary dust grains by capturing imagery of the zodiacal light. Furthermore, SIZLE aims to demonstrate the viability of solar sails as a propulsion system for reaching remote observation points above the ecliptic. The continuous thrust generated by solar winds equips spacecraft with the capability for extended missions requiring substantial changes in velocity. While practical realization of SIZLE's trajectory demands advancements in solar sail materials and technology, solar sails offer an enticing avenue for achieving SIZLE's mission objectives. This paper documents the mission and spacecraft design. The designed trajectory will put the spacecraft in a 30 degree inclined heliocentric orbit with a 1 AU semi-major axis. This final orbit maximises the science imaging capabilities of the mission. All scientific instruments and components on the spacecraft have been chosen as commercial off the shelf (COTS) components. This choice minimizes the time needed to manufacture the spacecraft since minimal integration and testing would be needed. The greatest technological development required for SIZLE would be advancements in solar sail technology.

  PublisherDOI

• The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems III: Aperture Masking Interferometric Observations of the star HIP 65426 at 3.8 um

  arXiv (Cornell University) · 2023-10-17

  preprintOpen access

  We present aperture masking interferometry (AMI) observations of the star HIP 65426 at $3.8\,\rm{μm}$ as a part of the JWST Direct Imaging Early Release Science (ERS) program obtained using the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument. This mode provides access to very small inner working angles (even separations slightly below the Michelson limit of $0.5λ/D$ for an interferometer), which are inaccessible with the classical inner working angles of the JWST coronagraphs. When combined with JWST's unprecedented infrared sensitivity, this mode has the potential to probe a new portion of parameter space across a wide array of astronomical observations. Using this mode, we are able to achieve a $5σ$ contrast of $Δm{\sim}7.62{\pm}0.13$ mag relative to the host star at separations ${\gtrsim}0.07{"}$, and the contrast deteriorates steeply at separations ${\lesssim}0.07{"}$. However, we detect no additional companions interior to the known companion HIP 65426 b (at separation ${\sim}0.82{"}$ or, $87^{+108}_{-31}\,\rm{au}$). Our observations thus rule out companions more massive than $10{-}12\,\rm{M_{Jup}}$ at separations ${\sim}10{-}20\,\rm{au}$ from HIP 65426, a region out of reach of ground or space-based coronagraphic imaging. These observations confirm that the AMI mode on JWST is sensitive to planetary mass companions at close-in separations (${\gtrsim}0.07{"}$), even for thousands of more distant stars at $\sim$100 pc, in addition to the stars in the nearby young moving groups as stated in previous works. This result will allow the planning and successful execution of future observations to probe the inner regions of nearby stellar systems, opening an essentially unexplored parameter space.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Infrared Doppler Planet Search with Externally Dispersed Interferometry

  NSF · $495k · 2005–2008

• Precision Adaptive Optics Imaging with Spatially Filtered Aperture Masking Interferometry

  NSF · $497k · 2007–2010

• Collaborative Research: Infrared RV Planet Search with Externally Dispersed Interferometry II: Optimization

  NSF · $244k · 2009–2012

Frequent coauthors

• Marshall D. Perrin

  Space Telescope Science Institute

  67 shared

• James R. Graham

  65 shared

• Paul Kalas

  61 shared

• Anand Sivaramakrishnan

  61 shared

• Bruce Macintosh

  39 shared

• C. E. Max

  University of California, Santa Cruz

  36 shared

• A. Boccaletti

  32 shared

• Donald T. Gavel

  University of California, Santa Cruz

  31 shared

Awards & honors

• US Navy Antarctica Service Medal with Gold Winterover Bar