Search

Future large, space-based observatories with starlight suppression technology, e.g., the Habitable Worlds Observatory (HWO), will directly image and characterize nearby Earth-like exoplanets. Prior limits on planet masses and system architectures from radial velocity (RV) measurements of potential exo-Earth hosts are critical to the success of HWO's science goals. Here, we present a uniform analysis of archival RVs from HIRES/Keck and HARPS/ESO of the most promising targets for the HWO exo-Earth survey. We analyze RVs and stellar activity indicators of 90 stars in the NASA ExEP Mission Star List and SPORES-HWO Catalog, finding 33 Keplerian signals associated with known planets and 12 signals associated with stellar activity. We also identify 5 new RV signals that we classify as either planet candidates or sources requiring confirmation, noting that the RV observations are biased toward cooler and less active stars. Assessing the sensitivity of the HIRES and HARPS data, we calculate RV limits ranging from $K_{\rm RV} = 0.6 \,{\rm m\,s}^{-1}$ (HD 10700) to $371 \,{\rm m\,s}^{-1}$ (HD 17925) in the middle of the conservative habitable zone (HZ), corresponding to projected planet masses of $5.4 \,{\rm M_\oplus}$ and $10.6 \,{\rm M_{Jup}}$ for those stars. The median HZ sensitivity limit of our sample is $M_{\rm p} \sin i \simeq 66 \,{\rm M_\oplus}$. This work demonstrates the need for future extreme precision radial velocity (EPRV) monitoring of high-priority targets for the next generation of DI missions that will search for habitable extrasolar systems. We advocate for the use of these results in developing future EPRV strategies., Comment: 55 pages, 12 figures, 9 tables, submitted to AAS Journals

Giant planets on long period orbits around the nearest stars are among the easiest to directly image. Unfortunately these planets are difficult to fully constrain by indirect methods, e.g., transit and radial velocity (RV). In this study, we present the discovery of a super-Jupiter, HD 222237 b, orbiting a star located $11.445\pm0.002$ pc away. By combining RV data, Hipparcos and multi-epoch Gaia astrometry, we estimate the planetary mass to be ${5.19}_{-0.58}^{+0.58}\,M_{\rm Jup}$, with an eccentricity of ${0.56}_{-0.03}^{+0.03}$ and a period of ${40.8}_{-4.5}^{+5.8}$ yr, making HD 222237 b a promising target for imaging using the Mid-Infrared Instrument (MIRI) of JWST. A comparative analysis suggests that our method can break the inclination degeneracy and thus differentiate between prograde and retrograde orbits of a companion. We further find that the inferred contrast ratio between the planet and the host star in the F1550C filter ($15.50\,\mu \rm m$) is approximately $1.9\times10^{-4}$, which is comparable with the measured limit of the MIRI coronagraphs. The relatively low metallicity of the host star ($\rm-0.32\,dex$) combined with the unique orbital architecture of this system presents an excellent opportunity to probe the planet-metallicity correlation and the formation scenarios of giant planets., Comment: 18 pages, 10 figures, 3 tables, accepted for publication in MNRAS

In this study, we introduce two new Krylov subspace methods for solving rectangular large-scale linear inverse problems. The first approach is a modification of the Hessenberg iterative algorithm that is based off an LU factorization and is therefore referred to as the least squares LU (LSLU) method. The second approach incorporates Tikhonov regularization in an efficient manner; we call this the Hybrid LSLU method. Both methods are inner-product free, making them advantageous for high performance computing and mixed precision arithmetic. Theoretical findings and numerical results show that Hybrid LSLU can be effective in solving large-scale inverse problems and has comparable performance with existing iterative projection methods.

We consider an $\ell_1$-regularized inverse problem where both the forward and regularization operators have a Kronecker product structure. By leveraging this structure, a joint decomposition can be obtained using generalized singular value decompositions. We show how this joint decomposition can be effectively integrated into the Split Bregman and Majorization-Minimization methods to solve the $\ell_1$-regularized inverse problem. Furthermore, for cases involving column-orthogonal regularization matrices, we prove that the joint decomposition can be derived directly from the singular value decomposition of the system matrix. As a result, we show that framelet and wavelet operators are efficient for these decomposition-based algorithms in the context of $\ell_1$-regularized image deblurring problems., Comment: 24 pages, 9 figures

While astronomers often assume that exoplanets are perfect spheres when analyzing observations, the subset of these distant worlds that are subject to strong tidal forces and/or rapid rotations are expected to be distinctly ellipsoidal or even triaxial. Since a planet's response to these forces is determined in part by its interior structure, measurements of an exoplanet's deviations from spherical symmetry can lead to powerful insights into its composition and surrounding environment. These shape deformations will imprint themselves on a planet's phase curve and transit lightcurve and cause small (1s-100s of parts per million) deviations from their spherical-planet counterparts. Until recently, these deviations were undetectable in typical real-world datasets due to limitations in photometric precision. Now, however, current and soon-to-come-online facilities such as JWST will routinely deliver observations that warrant the consideration of more complex models. To this end we present squishyplanet, a JAX-based Python package that implements an extension of the polynomial limb-darkened transit model presented in Agol et al. 2020 to non-spherical (triaxial) planets, as well as routines for modeling reflection and emission phase curves., Comment: 4 pages, accepted to JOSS

The stellar obliquity distribution of warm-Jupiter systems is crucial for constraining the dynamical history of Jovian exoplanets, as the warm Jupiters' tidal detachment likely preserves their primordial obliquity. However, the sample size of warm-Jupiter systems with measured stellar obliquities has historically been limited compared to that of hot Jupiters, particularly in hot-star systems. In this work, we present newly obtained sky-projected stellar obliquity measurements for warm-Jupiter systems, TOI-559, TOI-2025, TOI-2031, TOI-2485, TOI-2524, and TOI-3972, derived from the Rossiter-McLaughlin effect, and show that all six systems display alignment with a median measurement uncertainty of 13 degrees. Combining these new measurements with the set of previously reported stellar obliquity measurements, our analysis reveals that single-star warm-Jupiter systems tend to be aligned, even around hot stellar hosts. This alignment exhibits a 3.4-$\sigma$ deviation from the $T_{\rm eff}-\lambda$ dependency observed in hot-Jupiter systems, where planets around cool stars tend to be aligned, while those orbiting hot stars show considerable misalignment. The current distribution of spin-orbit measurements for Jovian exoplanets indicates that misalignments are neither universal nor primordial phenomena affecting all types of planets. The absence of misalignments in single-star warm-Jupiter systems further implies that many hot Jupiters, by contrast, have experienced a dynamically violent history., Comment: 18 pages, 2 figures, accepted for publication in ApJL

Brown dwarfs occupy a middle ground in mass space between gaseous giant planets and ultra-cool dwarf stars, and the characterisation of their orbital orientations may shed light on how these neighbouring objects form. We present an analysis of the Rossiter-McLaughlin (RM) effect across the transit of TOI-2533 $b$, a brown dwarf on a moderately eccentric ($e_b = 0.2476\pm0.0090$) and wide-separation ($a_b/R_\star = 13.34\pm0.30$) orbit around an F8-type star, using data from the NEID/WIYN spectrograph in combination with archival photometry and radial velocity observations. Spin-orbit analyses of brown dwarfs are relatively rare, and TOI-2533 stands out as the fifth brown dwarf system with a measured spin-orbit constraint. We derive a sky-projected stellar obliquity of $\lambda = -7\pm14^{\circ}$ for TOI-2533 $b$, finding that the brown dwarf is consistent with spin-orbit alignment. Our joint model also indicates that TOI-2533 $b$ falls near the lower bound of the hydrogen-burning minimum mass range (M$_b$ = $74.9\pm5.3$ M$_{\rm \tiny Jup}$). Ultimately, we find that TOI-2533 $b$ is consistent with formation from disc fragmentation in a primordially spin-orbit aligned orientation, although we cannot rule out the possibility that the system has been tidally realigned during its lifetime., Comment: 13 pages, 3 figures. Original submission 5/24/24; accepted 8/2/24

The degree of alignment between a star's spin axis and the orbital plane of its planets (the stellar obliquity) is related to interesting and poorly understood processes that occur during planet formation and evolution. Hot Jupiters orbiting hot stars ($\gtrsim$6250 K) display a wide range of obliquities, while similar planets orbiting cool stars are preferentially aligned. Tidal dissipation is expected to be more rapid in stars with thick convective envelopes, potentially explaining this trend. Evolved stars provide an opportunity to test the damping hypothesis, particularly stars that were hot on the main sequence and have since cooled and developed deep convective envelopes. We present the first systematic study of the obliquities of hot Jupiters orbiting subgiants that recently developed convective envelopes using Rossiter-McLaughlin observations. Our sample includes two newly discovered systems in the Giants Transiting Giants Survey (TOI-6029 b, TOI-4379 b). We find that the orbits of hot Jupiters orbiting subgiants that have cooled below $\sim$6250 K are aligned or nearly aligned with the spin-axis of their host stars, indicating rapid tidal realignment after the emergence of a stellar convective envelope. We place an upper limit for the timescale of realignment for hot Jupiters orbiting subgiants at $\sim$500 Myr. Comparison with a simplified tidal evolution model shows that obliquity damping needs to be $\sim$4 orders of magnitude more efficient than orbital period decay to damp the obliquity without destroying the planet, which is consistent with recent predictions for tidal dissipation from inertial waves excited by hot Jupiters on misaligned orbits., Comment: 22 pages, 14 figures, 3 tables

In 2010, Bakos and collaborators discovered a Neptune-sized planet transiting the K-dwarf HAT-P-11 every five days. Later in 2018, Yee and collaborators reported an additional Jovian-mass companion on a nine year orbit based on a decade of Doppler monitoring. The eccentric outer giant HAT-P-11c may be responsible for the peculiar polar orbit of the inner planet HAT-P-11b. However, Basilicata et al. (2024) recently suggested that the HAT-P-11c Doppler signal could be caused by stellar activity. In this research note, we extend the Yee et al. (2018) Doppler time series by six years. The combined dataset spanning 17 years covers nearly two orbits of the outer planet. Importantly, we observe two periastron passages of planet c and do not observe a coherent activity signature. Together with the previously reported astrometric acceleration of HAT-P-11 from Hipparcos and Gaia, we believe there is strong evidence for HAT-P-11c as a bona fide planet., Comment: 4 pages, 1 figure

Recent observations have demonstrated that some subset of even moderately wide-separation planet-hosting binaries are preferentially configured such that planetary and binary orbits appear to lie within the same plane. In this work, we explore dissipation during the protoplanetary disk phase, induced by disk warping as the system is forced into nodal recession by an inclined binary companion as a possible avenue of achieving orbit-orbit alignment. We analytically model the coupled evolution of the disk angular momentum vector and stellar spin vector under the influence of a distant binary companion. We find that a population of systems with random initial orientations can appear detectably more aligned after undergoing dissipative precession, and that this process can simultaneously produce an obliquity distribution that is consistent with observations. While dissipative precession proceeds efficiently in close binaries, favorable system properties (e.g., $r_{out} \gtrsim 100$ AU, $\alpha \gtrsim 0.05$, and/or $M_b/M_{*} \gtrsim 1$) are required to reproduce observed alignment trends at wider binary separations $a_\mathrm{b} \gtrsim450$ AU. Our framework further predicts that circum-primary planets in systems with high stellar mass ratios should be preferentially less aligned than planets in equal-mass stellar binary systems. We discover tentative evidence for this trend in \textit{Gaia} DR3 and TESS data. Our findings suggest that dissipative precession may play a significant role in sculpting orbital configurations in a sub-set of moderately-wide planet-hosting binaries, but is likely not solely responsible for their observed population-level alignment., Comment: 18 pages, 9 figures, accepted for publication in ApJ

We present optical spectroscopy of 710 solar neighborhood stars collected over twenty years to catalog chromospheric activity and search for stellar activity cycles. The California Legacy Survey stars are amenable to exoplanet detection using precise radial velocities, and we present their Ca II H and K time series as a proxy for stellar and chromospheric activity. Using the HIRES spectrometer at Keck Observatory, we measured stellar flux in the cores of the Ca II H and K lines to determine S-values on the Mt. Wilson scale and the log(R'HK) metric, which is comparable across a wide range of spectral types. From the 710 stars, with 52,372 observations, 285 stars are sufficiently sampled to search for stellar activity cycles with periods of 2-25 years, and 138 stars show stellar cycles of varying length and amplitude. S-values can be used to mitigate stellar activity in the detection and characterization of exoplanets. We use them to probe stellar dynamos and to place the Sun's magnetic activity into context among solar neighborhood stars. Using precise stellar parameters and time-averaged activity measurements, we find tightly constrained cycle periods as a function of stellar temperature between log(R'HK) of -4.7 and -4.9, a range of activity in which nearly every star has a periodic cycle. These observations present the largest sample of spectroscopically determined stellar activity cycles to date., Comment: 40 pages, 26 figures, submitted to ApJS

Multi-planet systems face significant challenges to detection. For example, further orbiting planets have reduced signal-to-noise ratio in radial velocity detection methods, and small mutual inclinations between planets can prevent them from all transiting. One mechanism to excite mutual inclination between planets is secular resonance, where the nodal precession frequencies of the planets align such as to greatly increase the efficiency of angular momentum transport between planets. These resonances can significantly misalign planets from one another, hindering detection, and typically can only occur when there are three or more planets in the system. Naively, systems can only be in resonance for particular combinations of planet semimajor axes and masses; however, effects that alter the nodal precession frequencies of the planets, such as the decay of stellar oblateness, can significantly expand the region of parameter space where resonances occur. In this work, we explore known three-planet systems, determine whether they are in (or were in) secular resonance due to evolving stellar oblateness, and demonstrate the implications of resonance on their detectability and stability. We show that about 20% of a sample of three planet transiting systems seem to undergo these resonances early in their lives., Comment: 24 pages, 11 figures, 5 tables

Image quality assessment (IQA) is not just indispensable in clinical practice to ensure high standards, but also in the development stage of novel algorithms that operate on medical images with reference data. This paper provides a structured and comprehensive collection of examples where the two most common full reference (FR) image quality measures prove to be unsuitable for the assessment of novel algorithms using different kinds of medical images, including real-world MRI, CT, OCT, X-Ray, digital pathology and photoacoustic imaging data. In particular, the FR-IQA measures PSNR and SSIM are known and tested for working successfully in many natural imaging tasks, but discrepancies in medical scenarios have been noted in the literature. Inconsistencies arising in medical images are not surprising, as they have very different properties than natural images which have not been targeted nor tested in the development of the mentioned measures, and therefore might imply wrong judgement of novel methods for medical images. Therefore, improvement is urgently needed in particular in this era of AI to increase explainability, reproducibility and generalizability in machine learning for medical imaging and beyond. On top of the pitfalls we will provide ideas for future research as well as suggesting guidelines for the usage of FR-IQA measures applied to medical images.

The Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new worlds, with TESS planet candidates now outnumbering the total number of confirmed planets from $\textit{Kepler}$. Owing to differences in survey design, TESS continues to provide planets that are better suited for subsequent follow-up studies, including mass measurement through radial velocity (RV) observations, compared to Kepler targets. In this work, we present the TESS-Keck Survey's (TKS) Mass Catalog: a uniform analysis of all TKS RV survey data which has resulted in mass constraints for 126 planets and candidate signals. This includes 58 mass measurements that have reached $\geq5\sigma$ precision. We confirm or validate 32 new planets from the TESS mission either by significant mass measurement (15) or statistical validation (17), and we find no evidence of likely false positives among our entire sample. This work also serves as a data release for all previously unpublished TKS survey data, including 9,204 RV measurements and associated activity indicators over our three year survey. We took the opportunity to assess the performance of our survey, and found that we achieved many of our goals including measuring the mass of 38 small ($<4R_{\oplus}$) planets, nearly achieving the TESS mission's basic science requirement. In addition, we evaluated the performance of the Automated Planet Finder (APF) as survey support and observed meaningful constraints on system parameters due to its more uniform phase coverage. Finally, we compared our measured masses to those predicted by commonly used mass-radius relations and investigated evidence of systematic bias., Comment: 51 pages (22 of text), 24 figures

Studying the relative orientations of the orbits of exoplanets and wide-orbiting binary companions (semimajor axis greater than 100 AU) can shed light on how planets form and evolve in binary systems. Previous observations by multiple groups discovered a possible alignment between the orbits of visual binaries and the exoplanets that reside in them. In this study, using data from \textit{Gaia} DR3 and TESS, we confirm the existence of an alignment between the orbits of small planets $(R<6 R_\oplus)$ and binary systems with semimajor axes below 700 AU ($p=10^{-6}$). However, we find no statistical evidence for alignment between planet and binary orbits for binary semimajor axes greater than 700 AU, and no evidence for alignment of large, closely-orbiting planets (mostly hot Jupiters) and binaries at any separation. The lack of orbital alignment between our large planet sample and their binary companions appears significantly different from our small planet sample, even taking into account selection effects. Therefore, we conclude that any alignment between wide-binaries and our sample of large planets (predominantly hot Jupiters) is probably not as strong as what we observe for small planets in binaries with semimajor axes less than 700 AU. The difference in the alignment distribution of hot Jupiters and smaller planets may be attributed to the unique evolutionary mechanisms occuring in systems that form hot Jupiters, including potentially destabilizing secular resonances that onset as the protoplanetary disk dissipates and high-eccentricity migration occurring after the disk is gone., Comment: 16 pages, 10 figures, submitted to AJ. Email corresponding author for data files

$\ell_1$ regularization is used to preserve edges or enforce sparsity in a solution to an inverse problem. We investigate the Split Bregman and the Majorization-Minimization iterative methods that turn this non-smooth minimization problem into a sequence of steps that include solving an $\ell_2$-regularized minimization problem. We consider selecting the regularization parameter in the inner generalized Tikhonov regularization problems that occur at each iteration in these $\ell_1$ iterative methods. The generalized cross validation and $\chi^2$ degrees of freedom methods are extended to these inner problems. In particular, for the $\chi^2$ method this includes extending the $\chi^2$ result for problems in which the regularization operator has more rows than columns, and showing how to use the $A-$weighted generalized inverse to estimate prior information at each inner iteration. Numerical experiments for image deblurring problems demonstrate that it is more effective to select the regularization parameter automatically within the iterative schemes than to keep it fixed for all iterations. Moreover, an appropriate regularization parameter can be estimated in the early iterations and used fixed to convergence., Comment: 23 pages, 12 figures

Despite decades of effort, the mechanisms by which the spin axis of a star and the orbital axes of its planets become misaligned remain elusive. Particularly, it is of great interest whether the large spin-orbit misalignments observed are driven primarily by high-eccentricity migration -- expected to have occurred for short-period, isolated planets -- or reflect a more universal process that operates across systems with a variety of present-day architectures. Compact multi-planet systems offer a unique opportunity to differentiate between these competing hypotheses, as their tightly-packed configurations preclude violent dynamical histories, including high-eccentricity migration, allowing them to trace the primordial disk plane. In this context, we report measurements of the sky-projected stellar obliquity ($\lambda$) via the Rossiter-McLaughlin effect for two sub-Saturns in multiple-transiting systems: TOI-5126 b ($\lambda=1\pm 48 ^\circ$) and TOI-5398 b ($\lambda=-8.1^{+5.3 \circ}_{-6.3}$). Both are spin-orbit aligned, joining a fast-growing group of just three other compact sub-Saturn systems, all of which exhibit spin-orbit alignment. In aggregate with archival data, our results strongly suggest that sub-Saturn systems are primordially aligned and become misaligned largely in the post-disk phase, as appears to be the case increasingly for other exoplanet populations., Comment: Accepted to AJ, 13 pages, 2 figures, 2 tables

In order to understand the relationship between planet multiplicity, mass, and composition, we present newly measured masses of five planets in two planetary systems: Kepler-323 and Kepler-104. We used the HIRES instrument at the W.M. Keck Observatory to collect 79 new radial velocity measurements (RVs) for Kepler-323, which we combined with 48 literature RVs from TNG/HARPS-N. We also conducted a reanalysis of the Kepler-104 system, using 44 previously published RV measurements. Kepler-323 b and c have masses of $2.0^{+1.2}_{-1.1}$ M$_\oplus$ and 6.5$\pm1.6$ M$_\oplus$, respectively, whereas the three Kepler-104 planets are more massive (10.0$\pm2.8$ M$_\oplus$, $7.1^{+3.8}_{-3.5}$ M$_\oplus$, and $5.5^{+4.6}_{-3.5}$ M$_\oplus$ for planets b, c, and d, respectively). The Kepler-104 planets have densities consistent with rocky cores overlaid with gaseous envelopes ($4.1^{+1.2}_{-1.1}$ g/cc, $2.9^{+1.7}_{-1.5}$ g/cc, and $1.6^{+1.5}_{-1.1}$ g/cc respectively), whereas the Kepler-323 planets are consistent with having rocky compositions ($4.5^{+2.8}_{-2.4}$ g/cc and $9.9^{+2.7}_{-2.5}$ g/cc). The Kepler-104 system has among the lowest values for gap complexity ($\mathcal{C}$ = 0.004) and mass partitioning ($\mathcal{Q}$ = 0.03); whereas, the Kepler-323 planets have a mass partitioning similar to that of the Inner Solar System ($\mathcal{Q}$ = 0.28 and $\mathcal{Q}$ = 0.24, respectively). For both exoplanet systems, the uncertainty in the mass partitioning is affected equally by (1) individual mass errors of the planets and (2) the possible existence of undetected low-mass planets, meaning that both improved mass characterization and improved sensitivity to low-mass planets in these systems would better elucidate the mass distribution among the planets., Comment: Accepted for publication in Astronomical Journal

Variable projection methods prove highly efficient in solving separable nonlinear least squares problems by transforming them into a reduced nonlinear least squares problem, typically solvable via the Gauss-Newton method. When solving large-scale separable nonlinear inverse problems with general-form Tikhonov regularization, the computational demand for computing Jacobians in the Gauss-Newton method becomes very challenging. To mitigate this, iterative methods, specifically LSQR, can be used as inner solvers to compute approximate Jacobians. This article analyzes the impact of these approximate Jacobians within the variable projection method and introduces stopping criteria to ensure convergence. We also present numerical experiments where we apply the proposed method to solve a blind deconvolution problem to illustrate and confirm our theoretical results., Comment: 18 pages, 5 figures

The extreme environments of ultra-short-period planets (USPs) make excellent laboratories to study how exoplanets obtain, lose, retain, and/or regain gaseous atmospheres. We present the confirmation and characterization of the USP TOI-1347 b, a $1.8 \pm 0.1$ R$_\oplus$ planet on a 0.85 day orbit that was detected with photometry from the TESS mission. We measured radial velocities of the TOI-1347 system using Keck/HIRES and HARPS-N and found the USP to be unusually massive at $11.1 \pm 1.2$ M$_\oplus$. The measured mass and radius of TOI-1347 b imply an Earth-like bulk composition. A thin H/He envelope (>0.01% by mass) can be ruled out at high confidence. The system is between 1 and 1.8 Gyr old; therefore, intensive photoevaporation should have concluded. We detected a tentative phase curve variation (3$\sigma$) and a secondary eclipse (2$\sigma$) in TESS photometry, which if confirmed could indicate the presence of a high-mean-molecular-weight atmosphere. We recommend additional optical and infrared observations to confirm the presence of an atmosphere and investigate its composition., Comment: 22 pages, 9 figures, accepted for publication in The Astronomical Journal

TOI-677 b is part of an emerging class of ``tidally-detached'' gas giants ($a/R_\star \gtrsim 11$) that exhibit large orbital eccentricities and yet low stellar obliquities. Such sources pose a challenge for models of giant planet formation, which must account for the excitation of high eccentricities without large changes in the orbital inclination. In this work, we present a new Rossiter-McLaughlin (RM) measurement for the tidally-detached warm Jupiter TOI-677 b, obtained using high-precision radial velocity observations from the PFS/Magellan spectrograph. Combined with previously published observations from the ESPRESSO/VLT spectrograph, we derive one of the most precisely constrained sky-projected spin-orbit angle measurements to date for an exoplanet. The combined fit offers a refined set of self-consistent parameters, including a low sky-projected stellar obliquity of $\lambda=3.2^{+1.6}_{-1.5}$ deg and a moderately high eccentricity of $e=0.460^{+0.019}_{-0.018}$, that further constrains the puzzling architecture of this system. We examine several potential scenarios that may have produced the current TOI-677 orbital configuration, ultimately concluding that TOI-677 b most likely had its eccentricity excited through disk-planet interactions. This system adds to a growing population of aligned warm Jupiters on eccentric orbits around hot ($T_{\rm eff}>6100$ K) stars., Comment: 16 pages, 4 figures, accepted for publication in the Astronomical Journal

We present and confirm TOI-1751 b, a transiting sub-Neptune orbiting a slightly evolved, solar-type, metal-poor star ($T_{eff} = 5996 \pm 110$ K, $log(g) = 4.2 \pm 0.1$, V = 9.3 mag, [Fe/H] = $-0.40 \pm 0.06$ dex) every 37.47 d. We use TESS photometry to measure a planet radius of $2.77_{-0.07}^{+0.15}~\rm{R_\oplus}$. We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of $14.5_{-3.14}^{+3.15} ~\rm{M_\oplus}$, and thus a planet density of $3.6 \pm 0.9 \, {\rm g}\,{\rm cm}^{-3}$. There is also a long-period ($\sim400~\rm{d}$) signal that is observed in only the Keck/HIRES data. We conclude that this long-period signal is not planetary in nature, and is likely due to the window function of the Keck/HIRES observations. This highlights the role of complementary observations from multiple observatories to identify and exclude aliases in RV data. Finally, we investigate potential compositions of this planet, including rocky and water-rich solutions, as well as theoretical irradiated ocean models. TOI-1751 b is a warm sub-Neptune, with an equilibrium temperature of $\sim 820$ K. As TOI-1751 is a metal-poor star, TOI-1751 b may have formed in a water-enriched formation environment. We thus favor a volatile-rich interior composition for this planet., Comment: 30 pages, 9 figures. Accepted for publication in AJ

As next-generation imaging instruments and interferometers search for planets closer to their stars, they must contend with increasing orbital motion and longer integration times. These compounding effects make it difficult to detect faint planets but also present an opportunity. Increased orbital motion makes it possible to move the search for planets into the orbital domain, where direct images can be freely combined with the radial velocity and proper motion anomaly, even without a confirmed detection in any single epoch. In this paper, we present a fast and differentiable multimethod orbit-modeling and planet detection code called Octofitter. This code is designed to be highly modular and allows users to easily adjust priors, change parameterizations, and specify arbitrary function relations between the parameters of one or more planets. Octofitter further supplies tools for examining model outputs including prior and posterior predictive checks and simulation-based calibration. We demonstrate the capabilities of Octofitter on real and simulated data from different instruments and methods, including HD 91312, simulated JWST/NIRISS aperture masking interferometry observations, radial velocity curves, and grids of images from the Gemini Planet Imager. We show that Octofitter can reliably recover faint planets in long sequences of images with arbitrary orbital motion. This publicly available tool will enable the broad application of multiepoch and multimethod exoplanet detection, which could improve how future targeted ground- and space-based surveys are performed. Finally, its rapid convergence makes it a useful addition to the existing ecosystem of tools for modeling the orbits of directly imaged planets., Comment: Published in AJ

Spatially-resolved images of debris disks are necessary to determine disk morphological properties and the scattering phase function (SPF) which quantifies the brightness of scattered light as a function of phase angle. Current high-contrast imaging instruments have successfully resolved several dozens of debris disks around other stars, but few studies have investigated trends in the scattered-light, resolved population of debris disks in a uniform and consistent manner. We have combined Karhunen-Loeve Image Projection (KLIP) with radiative-transfer disk forward modeling in order to obtain the highest quality image reductions and constrain disk morphological properties of eight debris disks imaged by the Gemini Planet Imager at H-band with a consistent and uniformly-applied approach. In describing the scattering properties of our models, we assume a common SPF informed from solar system dust scattering measurements and apply it to all systems. We identify a diverse range of dust density properties among the sample, including critical radius, radial width, and vertical width. We also identify radially narrow and vertically extended disks that may have resulted from substellar companion perturbations, along with a tentative positive trend in disk eccentricity with relative disk width. We also find that using a common SPF can achieve reasonable model fits for disks that are axisymmetric and asymmetric when fitting models to each side of the disk independently, suggesting that scattering behavior from debris disks may be similar to Solar System dust., Comment: 23+5 pages, 12+6 figures, 15 pages of Online Supplemental Material included; Accepted for publication in MNRAS

This study investigates the iterative regularization properties of two Krylov methods for solving large-scale ill-posed problems: the changing minimal residual Hessenberg method (CMRH) and a novel hybrid variant called the hybrid changing minimal residual Hessenberg method (H-CMRH). Both methods share the advantages of avoiding inner products, making them efficient and highly parallelizable, and particularly suited for implementations that exploit randomization and mixed precision arithmetic. Theoretical results and extensive numerical experiments suggest that H-CMRH exhibits comparable performance to the established hybrid GMRES method in terms of stabilizing semiconvergence, but H-CMRH has does not require any inner products, and requires less work and storage per iteration.

The current orbital geometries of exoplanet systems offer a fossilized record of the systems' dynamical histories. A particularly rich set of dynamical mechanisms is available to exoplanets residing in multi-star systems, which may have their evolution shaped by the gravitational influence of bound stellar companions. In this work, we examine the joint distribution of stellar obliquities and orbital orientations for transiting exoplanets residing within astrometrically resolved binary and triple-star systems. We leverage existing constraints on stellar obliquities in exoplanet systems, together with astrometric measurements from Gaia DR3, to uncover a set of fully-aligned, "orderly" exoplanet systems that exhibit evidence of both spin-orbit and orbit-orbit alignment. We also find evidence that the observed distribution of orbit-orbit orientations in our sample is more strongly peaked toward alignment than an isotropic distribution. Our results may be indicative of efficient viscous dissipation by nodally recessing protoplanetary disks, demonstrating a regime in which stellar companions produce and maintain order in planetary systems, rather than enhancing misalignments., Comment: 18 pages, 9 figures, accepted to AJ