Laird Close
· Professor, Department of Astronomy, & Astronomer, Steward ObservatoryVerifiedUniversity of Arizona · Astronomy
Active 1990–2026
About
Laird Close is a Professor in the Department of Astronomy and an Astronomer at Steward Observatory at the University of Arizona. He earned his Ph.D. in 1995 from the University of Arizona. His areas of interest include Brown Dwarfs, Adaptive optics, Instrumentation, Infrared Astronomy, Extrasolar planets, Galactic Astronomy, Star Formation, and Astrobiology. He specializes in novel astronomical observations utilizing new adaptive optics instrumentation, which removes the blurring effects of the Earth's atmosphere to study at very high resolution. His research focuses on low-mass stars, brown dwarfs, and extrasolar planets, as well as massive old AGB stars, young stars in the process of forming, and solar system objects like Titan and binary asteroids. He has been involved in the development of several adaptive optics systems and high-contrast high-resolution infrared cameras. Laird Close is the head scientist (PI) of the Magellan Adaptive Secondary AO system in Chile. He is a member of the American Astronomical Society and has received awards including the CAREER Program Award from the National Science Foundation in 2004, the NSERC Canadian Graduate Fellowship Abroad Award from 1991-1995, and the UBC Arthur Crooker Physics Prize in 1989.
Research topics
- Astrophysics
- Physics
- Astronomy
Selected publications
A Multiband Study of the HR 4796A Disk in the Optical Using MagAO-X
The Astrophysical Journal · 2026-04-16
articleOpen accessAbstract We present total intensity images of the debris disk around HR 4796A from observations spanning 2023 to 2025 with the Magellan extreme adaptive optics instrument (MagAO-X). We detected the disk at high signal-to-noise ratios at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>g</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>527</mml:mn> </mml:math> nm), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>r</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>615</mml:mn> </mml:math> nm), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>i</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>762</mml:mn> </mml:math> nm), and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>z</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>909</mml:mn> </mml:math> nm). Additionally, we present images collected using the “star-hopping” technique that show the entirety of the disk, including the dramatic forward-scattering at the minor axis. We subjected our images to a battery of modeling techniques to constrain the geometry and photometry of the disk. Leveraging our clear detections of the disk’s minor axis, we modeled the scattering phase function (SPF) using a basis of the Legendre polynomials. To mitigate self-subtraction artifacts in our angular differential imaging, we implemented a forward-modeling pipeline that generates a pixel-based freeform disk forward model leading to a deconvolved image of the disk. Our best-fit disk models reveal (1) highly forward-scattering SPFs with a minimum at the ∼65 ∘ scattering angle, (2) a faint halo of dust just exterior to the spine of the disk that is not well-described by a broken power-law density profile, (3) a red spectral slope for the dust, and finally (4) a compact, clump-like feature in the freeform disk models. Our empirically measured SPFs suggest that the scattering is dominated by large, highly absorptive grains. However, we emphasize the need for testing advanced irregular grain models using our SPFs to learn more about the physical and chemical properties of this complex system.
Direct spectroscopic confirmation of the young embedded proto-planet WISPIT 2c
ArXiv.org · 2026-03-23
articleOpen accessWISPIT 2 is a nearby young star with a multi-ringed disk which was recently confirmed to host a ~4.9 MJup gas giant planet embedded in a large (60 au) gap at a radial separation of 57 au from the host star. We confirm and characterise a second, close-in planet in the WISPIT 2 system using a combination of new VLT/SPHERE H-band dual-polarisation imaging and VLTI/GRAVITY K-band interferometric observations of the WISPIT 2 system. The GRAVITY detection is consistent with a point-like source while its extracted K-band spectrum shows CO band-head absorption at 2.3 microns and a continuum shape consistent with a young giant planet. From the GRAVITY data we extract a medium resolution K-band spectrum of the companion and fit atmospheric model grids using the species tool with nested sampling to constrain its effective temperature, radius, and luminosity. We infer Teff of 1500-2600 K, a radius of 0.91-2.2 RJup, and a luminosity of (-3.47)-(-3.63). Comparison with evolutionary tracks implies a mass range of 8-12 MJup, approximately twice as massive as the previously confirmed WISPIT 2b. The astrometry rules out a background source and marginally detects orbital motion of WISPIT 2c, which needs further follow-up observations for confirmation. WISPIT 2 now becomes an analogue to PDS 70, offering a second laboratory for studying the formation and early evolution of a multi-planet system within its natal disk.
Concept, implementation, and on-sky commissioning of the AO polarimetric module on MagAO-X
2025-08-01
articleMagAO-X is the coronagraphic extreme adaptive optics system for the 6.5m Magellan Clay Telescope. In comparison with other AO instruments (e.g. Gemini Planet Imager and VLT/SPHERE-IRDIS-ZIMPOL) MagAO-X lacked polarimetric capabilities for high-contrast imaging. The most recent update on MagAO-X added a polarimetric module, allowing it to perform polarimetric differential imaging and, consequently, polarimetric characterization of circumstellar and circumplanetary disks in the ExAO regime and wavelength range 580-1050nm. Thus, increasing the MagAO-X range of capabilities, which includes several 520-1050nm ExAO coronagraphs. We report the conception, implementation and commissioning with on-sky results of the MagAO-X polarimetric module. An efficient concept of adding a rotating quarter-waveplate upstream of the outer instrument window and a polarized beam-splitter just before the twin science cameras is optimal to allow MagAO-X to perform polarimetric measurements. Mostly off-the-shelf components and a few custom parts were required for the hardware, where CAD and FEA modeling were employed to secure compatibility and structural integrity of the supports added on the instrument. A very short on-sky commissioning occurred during the MagAO-X 2025A run (April), using a well-known unpolarized calibration source, Lambda Vel, to first calibrate our polarizer on the 1.2% r’ (580-680nm) linear polarization from Magellan’s zecoat protected silver M3. The measured polarization (1.0%) from Lambda Vel was in-line with expectations for M3 polarization. This polarization module is a pathfinder for the polarimeter to be included on the GMagAO-X, the next generation instrument under development of the Giant Magellan Telescope.
The Astrophysical Journal Letters · 2025-08-26 · 11 citations
articleOpen access1st authorCorrespondingAbstract Excellent (<25 mas) H α images of the star TYC 5709-354-1 led to the discovery of a rare H α protoplanet. This star was discovered by the WISPIT survey to have a large multi-ring transitional disk, and is hereafter WISPIT 2. Our H α images of 2025 April 13 and 16 discovered an accreting (H α in emission) protoplanet: WISPIT 2b ( r = 309.43 ± 1.56 mas; (∼54 au deprojected), PA = 242 <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> 21 ± 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> 41) likely clearing a dust-free gap between the two brightest dust rings in the transitional disk. Our signal-to-noise ratio of 12.5 detection gave an H α ASDI contrast of (6.5 ± 0.5) × 10 −4 and an H α line flux of (1.29 ± 0.28) × 10 −15 erg s −1 cm −2 . We also present L ′ photometry from LBT/LMIRcam of the planet ( L ′ = 15.30 ± 0.05 mag), which, when coupled with an age of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>5</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> <mml:mo>.</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2</mml:mn> <mml:mo>.</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> Myr, yields a planet mass estimate of 5.3 ± 1.0 M jup from the DUSTY evolutionary models. WISPIT 2b is accreting at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>25</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:mn>17</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3</mml:mn> <mml:mo>.</mml:mo> <mml:mn>75</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> × 10 −12 M Sun yr −1 . WISPIT 2b is very similar to the other H α protoplanets in terms of mass, age, flux, and accretion rate. The inclination of the system ( i = 44°) is also, surprisingly, very similar to the other known H α protoplanet systems, which all cluster from 37° ≤ i ≤ 52°. We argue this clustering has only a ∼1.0% (2.6 σ ) probability of occurring randomly, and so we speculate that magnetospherical accretion might have a preferred inclination range (∼37°–52°) for the direct (cloud free, low extinction) line of sight to the H α line formation/shock region. We also find at 110 mas (∼15 au deprojected) a close companion candidate (CC1) that may be consistent with an inner dusty 9 ± 4 M jup planet.
Five New Sirius-like White Dwarf–Main-sequence Star Systems with MagAO-X
The Astronomical Journal · 2025-06-27
articleOpen accessAbstract Most known white dwarfs in multiple systems with main-sequence stars have been discovered with M-type companions, because the white dwarf causes detectable UV excess and bluer colors than expected from a single M star. Surveys have shown that the number of white dwarfs in Sirius-like systems within 100 pc of the Sun is lower than expected, suggesting that white dwarfs are being missed in the glare of their main-sequence companions. In this work we have leveraged the angular resolution and high-contrast capabilities, as well as optimization for visible wavelengths, of the extreme adaptive optics (ExAO) instrument MagAO-X to detect new white dwarf companions to AFGK stars. We present the first results of our survey with the ExAO instrument MagAO-X, called The ExAO Pup Search, of 18 targets with seven new candidate companions, five of which are confirmed to be white dwarfs. We discuss the new detections in the context of previous surveys and other detection metric sensitivities and show that we are sensitive to a region not probed by other surveys. Finally we discuss the future of the Pup Search in light of developing technologies.
The Astronomical Journal · 2025-04-11 · 9 citations
articleOpen accessAbstract Giant planets generate accretion luminosity as they form. Much of this energy is radiated in strong H α line emission, which has motivated direct imaging surveys at optical wavelengths to search for accreting protoplanets. However, compact disk structures can mimic accreting planets by scattering emission from the host star. This can complicate the interpretation of H α point sources, especially if the host star itself is accreting. We describe an approach to distinguish accreting protoplanets from scattered-light disk features using “accretion light echoes.” This method relies on variable H α emission from a stochastically accreting host star to search for a delayed brightness correlation with a candidate protoplanet. We apply this method to the candidate protoplanet AB Aur b with a dedicated Hubble Space Telescope Wide Field Camera 3 program designed to sequentially sample the host star and the candidate planet in H α while accounting for the light travel time delay and orbital geometry of the source within the protoplanetary disk. Across five epochs spanning 14 months, AB Aur b is over 20 times more variable than its host star; AB Aur’s H α emission changes by 15% while AB Aur b varies by 330%. These brightness changes are not correlated, which rules out unobstructed scattered starlight from the host star as the only source of AB Aur b’s H α emission and is consistent with tracing emission from an independently accreting protoplanet, inner disk shadowing effects, or a physically evolving compact disk structure. More broadly, accretion light echoes offer a novel tool to explore the nature of protoplanet candidates with well-timed observations of the host star prior to deep imaging in H α .
The Astrophysical Journal Letters · 2025-08-26 · 18 citations
articleOpen accessAbstract In the past decades, several thousand exoplanet systems have been discovered around evolved, main-sequence stars, revealing a wide diversity in their architectures. To understand how the planet formation process can lead to vastly different outcomes in system architecture, we have to study the starting conditions of planet formation within the disks around young stars. In this study, we are presenting high-resolution direct imaging observations with the Very Large Telescope/SPHERE of the young (∼5 Myr), nearby (∼133 pc), solar-analog designated as WISPIT 2 (= TYC 5709-354-1). These observations were taken as part of our survey program that explores the formation and orbital evolution of wide-separation gas giants. WISPIT 2 was observed in four independent epochs using polarized light and total intensity observations. They reveal for the first time an extended (380 au) disk in scattered light with a multi-ringed substructure. We directly detect a young protoplanet, WISPIT 2b, embedded in a disk gap and show that it is comoving with its host star. Multiple SPHERE epochs demonstrate that it shows orbital motion consistent with Keplerian motion in the observed disk gap. Our H - and K s -band photometric data are consistent with thermal emission from a young planet. By comparison with planet evolutionary models, we find a mass of the planet of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4.</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> M Jup . This mass is also consistent with the width of the observed disk gap, retrieved from hydrodynamic models. WISPIT 2b is the first unambiguous planet detection in a multi-ringed disk, making the WISPIT 2 system the ideal laboratory to study planet–disk interaction and subsequent evolution.
A dynamical dichotomy in large binary asteroids
Astronomy and Astrophysics · 2025-07-31
articleOpen accessContext . No less than 15% of large asteroids (with diameters greater than 140 km) have satellites. The commonly accepted mechanism for their formation is post-impact reaccumulation. However, the detailed physical and dynamical properties of these systems are not well understood, and many of them have not been studied in detail. Aims . We studied the population of large binary asteroid systems, in part through the characterization of (283) Emma and (762) Pulcova. To do so, we compared the gravitational fields predicted from the shape of the primary body with the non-Keplerian gravitational components identified in orbital models of the satellites of each system. We contextualize these systems in the greater population of large binary systems, thus providing clues to asteroid satellite formation. Methods . We reduced all historical high angular resolution adaptive optics (AO) images from ground-based telescopes to conduct astrometric and photometric measurements of each system’s components. We then determined orbital solutions for each system using the genoid algorithm. We modeled the shapes of the system primaries using light curve-inversion techniques scaled with stellar occultations and AO images, and we developed internal structure models using SHTOOLS. Finally, we compared the distribution of the physical and orbital properties of the known binary asteroid systems. Results . We find a very low residual orbital solution for Emma with a gravitational quadrupole J 2 value that is significantly lower than expected from the shape model, implying that Emma has a significantly nonhomogeneous internal structure, and an overall bulk density of 0.9 ± 0.3 g cm-3 −3 . The circular co-planar orbit of Pulcova’s satellite leaves substantial ambiguity in the orbital solution. We also find that the differences between these systems reflect an overall dichotomy within the population of large binary systems, with a strong correlation between primary elongation and satellite eccentricity observed in one group. Conclusions . We determine that there may be two distinct formation pathways influencing the end-state dichotomy in these binary systems, and that (762) Pulcova and (283) Emma belong to the two separate groups.
Orbits of very distant asteroid satellites
Astronomy and Astrophysics · 2025-04-26 · 1 citations
articleOpen accessContext . The very wide binary asteroid (VWBA) population is a small subset of the population of known binary and multiple asteroids made of systems with very widely orbiting satellites and long orbital periods, on the order of tens to hundreds of days. The origin of these systems is debatable, and most members of this population are poorly characterized. Aims . We aim to develop orbital solutions for some members of the VWBA population, allowing us to constrain possible formation pathways for this unusual population. Methods . We compiled all available high-angular-resolution imaging archival data of VWBA systems from large ground- and space-based telescopes. We measured the astrometric positions of the satellite relative to the primary at each epoch and analyzed the dynamics of the satellites using the Genoid genetic algorithm. Additionally, we used a NEATM thermal model to estimate the diameters of two systems, and we modeled the orbit of Litva’s inner satellite using photometric light curve observations. Results . We determine the effective diameters of binary systems (17246) Christophedumas and (22899) Alconrad to be 4.7 ± 0.4 km and 5.2 ± 0.3 km, respectively. We determine new orbital solutions for five systems, (379) Huenna, (2577) Litva, (3548) Eurybates, (4674) Pauling, and (22899) Alconrad. We find a significantly eccentric ( e = 0.30) best-fit orbital solution for the outer satellite of (2577) Litva, moderately eccentric ( e = 0.13) solutions for (22899) Alconrad, and a nearly circular solution for (4674) Pauling ( e = 0.04). We also confirm previously reported orbital solutions for (379) Huenna and (3548) Eurybates. Conclusions . It is unlikely that BYORP expansion could be solely responsible for the formation of VWBAs, as only (4674) Pauling matches the necessary requirements for active BYORP expansion. It is possible that the satellites of these systems were formed through YORP spin-up and then later scattered onto very wide orbits. Additionally, we find that some members of the population are unlikely to have formed satellites through YORP spin-up, and a collisional formation history is favored. In particular, this applies to VWBAs within large dynamical families, such as (22899) Alconrad and (2577) Litva, or large VWBA systems such as (379) Huenna and NASA’s Lucy mission target (3548) Eurybates.
ArXiv.org · 2025-02-20
preprintOpen accessGiant planets generate accretion luminosity as they form. Much of this energy is radiated in strong H$α$ line emission, which has motivated direct imaging surveys at optical wavelengths to search for accreting protoplanets. However, compact disk structures can mimic accreting planets by scattering emission from the host star. This can complicate the interpretation of H$α$ point sources, especially if the host star itself is accreting. We describe an approach to distinguish accreting protoplanets from scattered-light disk features using "accretion light echoes." This method relies on variable H$α$ emission from a stochastically accreting host star to search for a delayed brightness correlation with a candidate protoplanet. We apply this method to the candidate protoplanet AB Aur b with a dedicated Hubble Space Telescope Wide Field Camera 3 program designed to sequentially sample the host star and the candidate planet in H$α$ while accounting for the light travel time delay and orbital geometry of the source within the protoplanetary disk. Across five epochs spanning 14 months, AB Aur b is over 20 times more variable than its host star; AB Aur's H$α$ emission changes by 15% while AB Aur b varies by 330%. These brightness changes are not correlated, which rules out unobstructed scattered starlight from the host star as the only source of AB Aur b's H$α$ emission and is consistent with tracing emission from an independently accreting protoplanet, inner disk shadowing effects, or a physically evolving compact disk structure. More broadly, accretion light echoes offer a novel tool to explore the nature of protoplanet candidates with well-timed observations of the host star prior to deep imaging in H$α$.
Recent grants
The First Census of Accreting Proto-Planets inside the Gaps of Transitional Dust Disks
NSF · $294k · 2016–2019
CAREER: Direct Detection of Extrasolar Planets With Very High Contrast Adaptive Optics Imaging
NSF · $526k · 2004–2010
A Unified Distribution of Extrasolar Planets from 0.01 to 1000 AU
NSF · $325k · 2011–2014
NSF · $489k · 2012–2015
The Direct Detection of Giant Extrasolar Planets with the NICI Science Campaign
NSF · $206k · 2008–2011
Frequent coauthors
- 252 shared
Jared R. Males
University of Arizona
- 162 shared
Olivier Guyon
National Astronomical Observatory of Japan
- 139 shared
Katie M. Morzinski
- 127 shared
Beth Biller
- 123 shared
Philip M. Hinz
University of California, Santa Cruz
- 88 shared
Katherine B. Follette
Amherst College
- 76 shared
Andrew Skemer
University of California, Santa Cruz
- 75 shared
Maggie Kautz
University of Arizona
Labs
Awards & honors
- CAREER Program Award, National Science Foundation, 2004
- NSERC Canadian Graduate Fellowship Abroad Award 1991-1995
- Arthur Crooker Physics Prize, 1989
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