arXiv subjects

Judah Van Zandt

Publications and source records attributed to Judah Van Zandt.

At least 19 recordsLinked to original sources

arXiv2026

POSEIDON III: The Aligned Orbit of the Hot Neptune Around the Hot Star WASP-195

Stellar obliquities provide important clues as to the formation and migration histories of planetary systems, but measurements remain scarce for Neptune-mass planets, especially those orbiting hot stars (above the Kraft break). Here we present observations of the Rossiter-McLaughlin effect in the hot-star/hot-Neptune system WASP-195 ($T_{\rm eff}=6470\pm100$ K, $v\sin{i_\star}=10.5\pm1.1$ km s$^{-1}$) obtained with the Keck Planet Finder and NEID spectrographs. A joint analysis of these observations, archival photometry, and archival radial velocities yields a sky-projected stellar obliquity of $λ=-10\pm7^\circ$, consistent with spin-orbit alignment. This makes WASP-195 one of the few hot-star/hot-Neptune systems with a measured obliquity. Archival radial velocities from SOPHIE exclude Jupiter-mass planets within approximately 3 au at $5σ$ confidence. The aligned and nearly circular orbit is naturally consistent with a history of disk-driven migration, although coplanar high-eccentricity migration or Roche-lobe overflow cannot be ruled out. We also investigate why so few Neptunes around hot stars have measured obliquities. Their scarcity likely reflects a combination of the lower intrinsic occurrence of short-period Neptunes around hot stars and the difficulty of confirming planet candidates in this regime, where rapid stellar rotation broadens spectral lines and hampers conventional radial-velocity confirmation. Rapid rotation also increases the detectability of the Rossiter-McLaughlin effect, a feature that could help to widen the planet confirmation bottleneck while expanding the obliquity census of small planets around hot stars.

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arXiv2026

Evidence for an Extended Hydrogen Outflow on WASP-12 b

Recent observations of atmospheric escape from planets orbiting early-type stars indicate that planets with higher Roche filling factors have significantly higher mass loss rates. For three of these planets, full-orbit observations have revealed the presence of large leading and trailing tails of escaping planetary material. These 3D outflow geometries encode information about the underlying outflow physics, and can also be used to constrain their stellar wind properties and to predict their long-term orbital evolution. We present new evidence for extended H$α$ and H$β$ absorption from escaping hydrogen for a fourth planet, WASP-12 b. We observed WASP-12 b with the Keck Planet Finder on Keck I over a period of approximately eight hours centered on the transit. We find a H$α$ and H$β$ absorption signal in the stellar rest frame that is strongest during the transit (H$α$ amplitude: $2.66\pm0.25\%$, H$β$ amplitude: $2.88\pm0.43\%$), with evidence of both pre- and post-transit absorption. This measurement is consistent with outflow models where the escaping gas overflows the planet's Roche lobe and is advected into the stellar rest frame before being tidally sheared into extended tails. This outflow behavior is qualitatively similar to previous H$α$ observations of this planet as well as observations of extended outflows from other gas giants orbiting early-type stars.

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arXiv2026

The $γ$ Cephei System: Updated Orbits, Dynamical Architecture, and Limits on Additional Companions

The $γ$ Cephei system hosts one of the first exoplanets discovered and is orbited by one of the closest known stellar companions to a planet-hosting star. Here, we derive updated orbital fits for $γ$ Cep AB, the stellar binary, and Ab, the planet, by combining literature data with \textit{Hipparcos-Gaia} astrometry, new radial velocities (RVs), and adaptive optics imaging. We acquired 328 RVs of $γ$ Cep A with Keck/HIRES, AFP/Levy, McDonald/Tull, and Whipple/TRES, and eight adaptive optics imaging epochs with Keck/NIRC2, including the earliest spatially resolved image of $γ$ Cep B in 2003. These observations extend the precision RV baseline of $γ$ Cep to 45 years and the direct imaging baseline to 23 years, improving inferred orbital parameter precisions by a factor of 2--10 compared to previous work. For $γ$ Cep B, we derive a semi-major axis of $a_B=20.07 \pm 0.06$ AU, a mass of $M_B=415 \pm 2$ $M_{Jup}$ ($0.396 \pm 0.002$ $M_{\odot}$), an eccentricity of $e_B=0.422 \pm 0.002$, and an inclination of $i_B=119.8^{\circ}\pm0.1^{\circ}$. For $γ$ Cep Ab, we find a separation of $a_{Ab}=1.978 \pm 0.007$ AU, a minimum mass of $M_{Ab} \sin i = 1.62 \pm 0.04$ $M_{Jup}$, and an eccentricity of $e_{Ab}=0.07 \pm0.03$. Using the RV residuals and dynamical constraints, we rule out additional Jovians between 2.5--20 AU, and companions more massive than Neptune for $a<1$ AU, both at $>90\%$ confidence. The absence of additional giant planets over a broad range of orbital separations is consistent with a dynamically sculpted system in which the close stellar companion limited the formation or long-term survival of other distant companions.

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arXiv2026

Spin-Orbit Alignment of Two Neptune-size Planets Younger than 500 Myr: TOI-560 b and TOI-5082 b

Stellar obliquity measurements provide a direct probe of planetary system dynamics, but remain sparse for Neptune-size planets, particularly at young ages. We present Rossiter-McLaughlin measurements for two young Neptune-size planets, TOI-560 b and TOI-5082 b, using time-resolved Keck Planet Finder (KPF) spectroscopy and joint modeling with TESS transit photometry. We measure sky-projected obliquities of $λ_b = -25 \pm 16^\circ$ for TOI-560 b and $λ_b = 19^{+17}_{-13}{}^\circ$ for TOI-5082 b. Combining these constraints with stellar rotation periods and spectroscopic estimates of $v\sin i_\star$, we obtain 95% upper limits of $ψ< 69.7^\circ$ and $ψ< 50.5^\circ$, respectively. Both systems are therefore consistent with low-to-moderate true obliquities and show no evidence of strong spin-orbit misalignment. With ages of $480 \pm 190$ Myr for TOI-560 b and $180 \pm 9$ Myr for TOI-5082 b (a likely member of the CRIUS197 stellar association), the systems are in a key evolutionary phase when post-disk dynamical processes such as secular interactions may begin to manifest. Nevertheless, both systems remain consistent with low obliquity. In the broader context of young systems with existing measurements, these results support an emerging picture in which Neptune-size planets at $\lesssim 1$ Gyr are commonly found in low-obliquity configurations.

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arXiv2026

A Smooth Transition from Giant Planets to Brown Dwarfs from the Radial Occurrence Distribution

Measuring the occurrence rates of celestial objects is a valuable way to study their origins and evolution. Giant planets and brown dwarfs produce large Doppler signatures that are easily detectable by modern instrumentation, and legacy radial velocity (RV) surveys have now achieved full orbital coverage for periods $\lesssim$30 years. However, the Doppler method's sensitivity to companion minimum mass $M_c \sin i$ -- as opposed to true mass $M_c$ -- prevents unambiguous characterization using RVs alone, as purported giant planets may be brown dwarfs or stars on inclined orbits. Here we combined legacy RVs with absolute astrometry to re-fit the orbits of 195 companions from the California Legacy Survey. Nearly 50% (8/18) of the ``brown dwarfs" ($M_c \sin i$=13--80 $M_{Jup}$) we refit had true masses above 80 $M_{Jup}$. We incorporated our orbital posteriors and target sensitivity maps into a Poisson likelihood model to calculate occurrence as a function of true companion mass $M_c$ (0.8--80 $M_{Jup}$) and separation $a$ (0.3--30 AU). The semi-major axis distributions of objects in this range vary smoothly with mass, with Jupiter analogs favoring an abrupt increase in occurrence near 1 AU and brown dwarfs exhibiting a gradual enhancement at wider separations. Marginalized companion occurrence between 1--10 AU decreases smoothly with mass, with brown dwarfs having the lowest occurrence rate: $0.9^{+0.5}_{-0.4}$%. Jupiter analogs are 10 times as common as brown dwarfs per mass interval in this range, demonstrating that the brown dwarf desert extends to 10 AU. The smooth variation in these distributions disfavors a sharp transition mass between ``bottom-up" core accretion and ``top-down" gravitational instability formation mechanisms, and rather suggests that these processes may produce companions in overlapping mass ranges.

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arXiv2026

Gaia Exoplanet Orbits, Demographics, and Evolution Survey (GEODES): Characteristics of Three Long-Period Companions Accelerating their Host Stars

The upcoming release of $Gaia$ DR4 will yield thousands of giant planet candidates, eventually enabling studies of giant planet eccentricities, masses, and occurrence rates across a broad range of stellar host masses, metallicities, and ages. However, some of these planet candidates are expected to be false positives, and even genuine detections will require additional observations to precisely determine their orbits and masses. We present here the first results of the $Gaia$ Exoplanet Orbits, Demographics, and Evolution Survey (GEODES), an observational campaign to identify the most promising planet candidate hosts for pre-DR4 vetting and post-DR4 validation and characterization. In this paper we showcase three systems from our broader sample exhibiting both tangential and radial accelerations, each representing a distinct outcome of our survey strategy. We combine $Hipparcos$, $Hipparcos$-$Gaia$, $Gaia$ DR2, and $Gaia$ DR3 absolute astrometry with adaptive optics (AO) imaging and precision RVs to constrain companion masses and orbits. HIP 18512, a nearby (15.3 pc) K4V dwarf, hosts a low-mass stellar companion at 10.87" $\pm$ 0.07" (166 AU) which produces significant RV and astrometric accelerations on its host star. The RV trend and astrometric acceleration of the nearby (24.2 pc) K4V star HIP 45839, together with an AO imaging non-detection, constrain the companion to $a$ = 17.9^{+4.8}_{-2.7} AU ($P$ = 70--127 years) and $M$ = 45.2^{+10.5}_{-12.7} $M_{Jup}$. In the case of HIP 81991 (43.8 pc, G5V), the astrometric and RV data indicate that the companion has a separation of 6.4^{+0.6}_{-0.3} AU ($P$ = 14.4--17.7 years) and a mass of 9.5^{+5.4}_{-2.2} $M_{Jup}$, and is more likely a planet (65%) than a brown dwarf (35%).

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arXiv2026

An Outer Giant Planet or Brown Dwarf in the 51 Pegasi System?

51 Pegasi harbors the first confirmed extrasolar planet orbiting a Sun-like star. Decades of continued radial velocity (RV) observations have since uncovered signatures of an additional distant companion in the system from a shallow radial acceleration. We present new constraints on the mass and separation of a potential outer companion based on a synthesis of RVs, absolute astrometry, and new high-contrast imaging. Our analysis combines 31 years of new and previously published RV measurements from the OHP/ELODIE, Lick/Hamilton, Keck/HIRES, and APF/Levy spectrographs; a $\sim$25-year baseline of absolute astrometry from Hipparcos and Gaia; and deep imaging from Keck/NIRC2 and HST/WFPC2. We find evidence for curvature in the RVs, which when combined with non-detections from imaging and astrometry point to a super-Jupiter at $\simeq$15--100 AU or brown dwarf companion at $\approx$20--170 AU. However, the inferred radial acceleration of the host star is driven primarily by the Lick/Hamilton dataset and its slope is consistent with long-term instrument drift, calling into question the nature of the long-period signal. If an outer companion is present, it could explain the origin of the inner hot Jupiter if 51 Peg b arrived at its current location through high-eccentricity migration. On the other hand, if the signal is spurious, the exceptional baseline rules out Jovian planets within $\sim$10 AU and most brown dwarfs within several tens of AU, implying that the system is devoid of massive companions. Continued RV and astrometric monitoring together with high-contrast imaging can be used to distinguish these scenarios.

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arXiv2025

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

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 $0.1^{\prime\prime}$ to $2^{\prime\prime}$ (or $10-200$ AU). We also identified 12 TOIs that could host planetary-mass or brown dwarf companions, including 6 that are newly discovered. Furthermore, we perform three-dimensional orbital characterization for 12 binaries hosting confirmed planets or planet candidates, allowing us to constrain the line-of-sight mutual inclination, $ΔI_{\mathrm{los}}$, 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 ($r_p<5R_{\oplus}$). Specifically, we fit the $ΔI_{\mathrm{los}}$ distribution with both single (Rayleigh) and mixture models (two-component Rayleigh and Rayleigh-isotropic mixture). We find the mixture models are strongly favored ($\log Z\gtrsim13.9$, or $\approx$5$σ$), indicating the observed planet-binary $ΔI_{\mathrm{los}}$ values likely originate from two underlying populations: one nearly aligned ($σ_1 = 2^{\circ}.4^{+0.7}_{-0.9}$) and one with more scattered mutual inclinations ($σ_2 = 23^{\circ}.6^{+8.8}_{-7.1}$). 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 $>40$ AU while systems with close-in or eccentric stellar companions (periastron distances $<40$ AU) preserve planet-binary alignment.

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arXiv2025

The Transition from Giant Planets to Brown Dwarfs beyond 1 au from the Stellar Metallicity Distribution

Giant planets and brown dwarfs are thought to form via a combination of pathways, including bottom-up mechanisms in which gas is accreted onto a solid core and top-down mechanisms in which gas collapses directly into a gravitationally-bound object. One can distinguish the prevalence of these mechanisms using host star metallicities. Bottom-up formation thrives in metal-rich environments, whereas top-down formation is weakly dependent on ambient metal content. Using a hierarchical Bayesian model and the results of the California Legacy Survey (CLS), a low-bias and homogeneously analyzed radial velocity survey, we find evidence for a transition in the stellar metallicity distribution at a companion mass of $γ= 27_{-8}^{+12} \, M_{\rm Jup}$ for companions with orbital separations between $1-50$ au. Companions below and above this threshold tend to orbit stars with higher ($\rm{[Fe/H]} = 0.17 \pm 0.12$ dex) and lower ($\rm{[Fe/H]} = -0.03 \pm 0.10$ dex) metallicities, respectively. Previous studies of relatively close-in companions reported evidence of a lower transition mass of $\leq 10 \, {\rm M_{\rm Jup}}$. When applied to the CLS sample, our model predicts the probability of a transition in the stellar metallicity distribution at or below $10 \, { M_{\rm Jup}}$ to be $< 1 \%$. We compare our results to estimates of $γ$ gleaned from other observational metrics and discuss implications for planet formation theory.

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arXiv2025

Orbital Eccentricities Suggest a Gradual Transition from Giant Planets to Brown Dwarfs

To date, hundreds of sub-stellar objects with masses between $1-80\ M_{\rm Jup}$ have been detected orbiting main-sequence stars. The current convention uses the deuterium-burning limit, $M_c \approx 13 M_{\rm Jup}$ to divide this population between giant planets and brown dwarfs. However, this classification heuristic is largely divorced from any formation physics and may not accurately reflect the astrophysical nature of these objects. Previous work has suggested that a transition from ``planet-like'' to ``brown-dwarf-like'' characteristics occurs somewhere in the range $1-10 M_{\rm Jup}$, but precise the crossover mass and whether the transition is gradual or abrupt remains unknown. Here, we explore how the occurrence rate, host star metallicity, and orbital eccentricities vary as a function of mass in a sample of 70 Doppler-detected sub-stellar objects ($0.8 < M_c/M_{\rm Jup} < 80$) from the California Legacy Survey. Our population consists of objects near and beyond the water ice line ($1 < a / \text{AU} < 10$), providing valuable clues to the details of giant planet formation physics at a location in the proto-stellar disk where planet formation efficiency is thought to be enhanced. We find that occurrence rate, host star metallicity, and orbital eccentricity all change gradually across the mass range under consideration, suggesting that ``bottom-up'' core accretion mechanisms and ``top-down'' gravitational instability mechanisms produce objects that overlap in mass. The observed eccentricity distributions could arise either from different formation channels or from post-formation dynamical interactions between massive sub-stellar objects.

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arXiv2025

AstroQ: Automated Scheduling of Cadenced Astronomical Observations

Astronomy relies heavily on time domain observations. To maximize the scientific yield of such observations, astronomers must carefully match the observational cadence to the phenomena of interest. This presents significant scheduling challenges for observatories with multiple large programs, each with different cadence needs. To address this challenge, we developed AstroQ, an automated framework for scheduling cadenced observations. We tested this on a suite of Doppler exoplanet programs at Keck Observatory, where the algorithm powers the KPF-Community Cadence project. As a point of reference, AstroQ can determine the provably optimal ordering of 3680 observations of 200 targets -- each with its own cadence needs and accessibility constraints -- over a six month period to five minute time resolution. Schedules of this size may be constructed in ~120 seconds on modern workstation, enabling dynamic rescheduling due to weather changes, target-of-opportunity interrupts, and other needs. A key advantage of AstroQ over manual scheduling is realistic projections of program completion, savings in human effort, and elimination of human bias in balancing many programs. AstroQ is open source and may be applied to other scheduling needs, both in astronomy and beyond.

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arXiv2025

Stellar Obliquity of the Ultra-Short-Period Planet System HD 93963

We report an observation of the Rossiter-McLaughlin (RM) effect of the transiting planet HD 93963 Ac, a mini-Neptune planet orbiting a G0-type star with an orbital period of $P_{\rm{c}} = 3.65\,\mathrm{d}$, accompanied by an inner super-Earth planet with $P_{\rm{b}} = 1.04\,\mathrm{d}$. We observed a full transit of planet c on 2024 May 3rd UT with Keck/KPF. The observed RM effect has an amplitude of $\sim 1\,\mathrm{m\,s}^{-1}$ and implies a sky-projected obliquity of $λ= 14^{+17}_{-19}$ degrees for HD 93963 Ac. Our dynamical analysis suggests that the two inner planets are likely well aligned with the stellar spin, to within a few degrees, thus allowing both to transit. Along with WASP-47, 55 Cnc, and HD 3167, HD 93963 is the fourth planetary system with an ultra-short-period planet and obliquity measurement(s) of any planet(s) in the system. HD 93963, WASP-47, and 55 Cnc favor largely coplanar orbital architectures, whereas HD 3167 has been reported to have a large mutual inclination ($\sim$100$^\circ$) between its transiting planets b and c. In this configuration, the probability that both planets transit is low. Moreover, one planet would quickly evolve to be non-transiting due to nodal precession. Future missions such as ESO/PLATO should detect the resulting transit duration variations. We encourage additional obliquity measurements of the HD 3167 system to better constrain its orbital architecture.

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arXiv2025

TOI-6324b: An Earth-Mass Ultra-Short-Period Planet Transiting a Nearby M Dwarf

We report the confirmation of TOI-6324 b, an Earth-sized (1.059 $\pm$ 0.041 R$_\oplus$) ultra-short-period (USP) planet orbiting a nearby ($\sim$20 pc) M dwarf. Using the newly commissioned Keck Planet Finder (KPF) spectrograph, we have measured the mass of TOI-6324 b 1.17 $\pm$ 0.22 M$_\oplus$. Because of its extremely short orbit of just $\sim$6.7 hours, TOI-6324 b is intensely irradiated by its M dwarf host, and is expected to be stripped of any thick, H/He envelope. We were able to constrain its interior composition and found an iron core mass fraction (CMF = 27$\pm$37%) consistent with that of Earth ($\sim$33%) and other confirmed USPs. TOI-6324 b is the closest to Earth-sized USP confirmed to date. TOI-6324 b is a promising target for JWST phase curve and secondary eclipse observations (Emission Spectroscopy Metric = 25) which may reveal its surface mineralogy, day-night temperature contrast, and possible tidal deformation. From 7 sectors of TESS data, we report a tentative detection of the optical phase curve variation with an amplitude of 42$\pm$28 ppm.

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arXiv2025

Planet Masses, Radii, and Orbits from NASA's K2 Mission

We report the masses, sizes, and orbital properties of 86 planets orbiting 55 stars observed by NASA's K2 Mission with follow-up Doppler measurements by the HIRES spectrometer at the W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory. Eighty-one of the planets were discovered from their transits in the K2 photometry, while five were found based on subsequent Doppler measurements of transiting planet host stars. The sizes of the transiting planets range from Earth-size to larger than Jupiter (1-3 REarth is typical), while the orbital periods range from less than a day to a few months. For 32 of the planets, the Doppler signal was detected with significance greater than 5-sigma (51 were detected with >3-sigma significance). An important characteristic of this catalog is the use of uniform analysis procedures to determine stellar and planetary properties. This includes the transit search and fitting procedures applied to the K2 photometry, the Doppler fitting techniques applied to the radial velocities, and the spectral modeling to determine bulk stellar parameters. Such a uniform treatment will make the catalog useful for statistical studies of the masses, densities, and system architectures of exoplanetary systems. This work also serves as a data release for all previously unpublished RVs and associated stellar activity indicators obtained by our team for these systems, along with derived stellar and planet parameters.

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arXiv2025

The TESS-Keck Survey XXIV: Outer Giants may be More Prevalent in the Presence of Inner Small Planets

We present the results of the Distant Giants Survey, a three-year radial velocity (RV) campaign to search for wide-separation giant planets orbiting Sun-like stars known to host an inner transiting planet. We defined a distant giant to have $a$ = 1--10 AU and $M_{p} \sin i = 70-4000$ \mearth~ = 0.2-12.5 \mj, and required transiting planets to have $a<1$ AU and $R_{p} = 1-4$ \rearth. We assembled our sample of 47 stars using a single selection function, and observed each star at monthly intervals to obtain $\approx$30 RV observations per target. The final catalog includes a total of twelve distant companions: four giant planets detected during our survey, two previously known giant planets, and six objects of uncertain disposition identified through RV/astrometric accelerations. Statistically, half of the uncertain objects are planets and the remainder are stars/brown dwarfs. We calculated target-by-target completeness maps to account for missed planets. We found evidence for a moderate enhancement of distant giants (DG) in the presence of close-in small planets (CS), P(DG|CS) = $30^{+14}_{-12}\%$, over the field rate of P(DG) = $16^{+2}_{-2}\%$. No enhancement is disfavored ($p \sim$ 8%). In contrast to a previous study, we found no evidence that stellar metallicity enhances P(DG|CS). We found evidence that distant giant companions are preferentially found in systems with multiple transiting planets and have lower eccentricities than randomly selected giant planets. This points toward dynamically cool formation pathways for the giants that do not disturb the inner systems.

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arXiv2024

No evidence for a metallicity-dependent enhancement of distant giant companions to close-in small planets in the California Legacy Survey

Understanding the relationship between close-in small planets (CS) and distant giants (DG) is central to understanding the formation of planetary systems like our own. Most studies of this connection have found evidence for a positive correlation, though significant statistical and systematic uncertainties remain due to differences in sample size, target selection bias, and even the definitions of `close-in small' and `distant giant' planets. Recently, Bryan & Lee (2024) conducted a study of 184 stars hosting super-Earths ($M \sin i = 1-20 \, M_{E}$ or $R = 1-4 \, R_{E}$) to determine the effect of stellar metallicity on the prevalence of distant giant companions ($M \sin i = 0.5-20 \, M_{Jup}$, $a = 1-10$ AU). They found that such giants are twice as common in the presence of inner planets, but \textit{only} in metal-rich systems: P(DG|CS, [Fe/H]>0) = $28^{+4.9}_{-4.6}\%$ vs. P(DG|[Fe/H]>0) = $14.3 ^{+2.0}_{-1.8}\%$. Further, they found that this correlation disappears for metal-poor stars: P(DG|CS, [Fe/H]$\leq$0) = $4.5^{+2.6}_{-1.9}\%$ vs. P(DG|[Fe/H]$\leq$0) = $5.0^{+1.6}_{-1.3}\%$. We conducted an analogous study to test whether this effect was present in the California Legacy Survey sample. Using the same planet definitions, we did not find evidence for an enhancement in metal-rich systems: P(DG|CS, [Fe/H]>0) = $14^{+12}_{-8}\%$ vs. P(DG|[Fe/H]>0) = $16.4^{+2.5}_{-2.4}\%$. We also found a $2σ$ tension between our conditional rate and a 2x enhancement. The discrepancy between our findings and theirs may arise from a variety of sources, underscoring the need for large exoplanet surveys to overcome both small number statistics and sample inhomogeneities.

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arXiv2024

The Compositions of Rocky Planets in Close-in Orbits Tend to be Earth-Like

Hundreds of exoplanets between 1-1.8 times the size of the Earth have been discovered on close in orbits. However, these planets show such a diversity in densities that some appear to be made entirely of iron, while others appear to host gaseous envelopes. To test this diversity in composition, we update the masses of 5 rocky exoplanets (HD 93963 A b, Kepler-10 b, Kepler-100 b, Kepler-407 b, and TOI-1444 b) and present the confirmation of a new planet (TOI-1011) using 187 high precision RVs from Gemini/MAROON-X and Keck/KPF. Our updated planet masses suggest compositions closer to that of the Earth than previous literature values for all planets in our sample. In particular, we report that two previously identified ``super-Mercuries'' (Kepler-100 b and HD 93963 A b) have lower masses that suggest less iron-rich compositions. We then compare the ratio of iron to rock-building species to the abundance ratios of those elements in their host stars. These updated planet compositions do not suggest a steep relationship between planet and host star compositions, contradictory to previous results, and suggest that planets and host stars have similar abundance ratios.

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arXiv2024

The HD 191939 Exoplanet System is Well-Aligned and Flat

We report the sky-projected spin-orbit angle $λ$ for HD 191939 b, the innermost planet in a 6 planet system, using Keck/KPF to detect the Rossiter-McLaughlin (RM) effect. Planet b is a sub-Neptune with radius 3.4 $\pm$ 0.8 R$_{\oplus}$ and mass 10.0 $\pm$ 0.7 M$_{\oplus}$ with an RM amplitude $<$1 ms$^{-1}$. We find the planet is consistent with a well-aligned orbit, measuring $λ= \, $ 3.7 $\pm$ 5.0 degrees. Additionally, we place new constraints on the mass and period of the distant super-Jupiter, planet f, finding it to be 2.88 $\pm$ 0.26 $M_J$ on a 2898 $\pm$ 152 day orbit. With these new orbital parameters, we perform a dynamical analysis of the system and constrain the mutual inclination of the non-transiting planet e to be smaller than 12 degrees relative to the plane shared by the inner three transiting planets. Additionally, the further planet f is inclined off this shared plane, the greater the amplitude of precession for the entire inner system, making it increasingly unlikely to measure an aligned orbit for planet b. Through this analysis, we show that this system's wide variety of planets are all well-aligned with the star and nearly co-planar, suggesting that the system formed dynamically cold and flat out of a well-aligned proto-planetary disk, similar to our own solar system.

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