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Abstract We present statistical results from the Epoch of Giant Planet Migration RV planet search program. This survey was designed to measure the occurrence rate of giant planets interior to the water ice line of young Sun-like stars, compare this to the prevalence of giant planets at older ages, and provide constraints on the timescale and dominant inward migration mechanism of giant planets. Our final sample amounts to 85 single young (20–200 Myr) G and K dwarfs that we target across a 4 yr time baseline with the near-infrared Habitable-zone Planet Finder spectrograph at McDonald Observatory’s Hobby-Eberly Telescope. As part of this survey, we discovered the young hot Jupiter HS Psc b. We characterize survey detection completeness with realistic injection-recovery tests and measure an occurrence rate of $1.9_{-1.4}^{+2.6}$% for intermediate-age giant planets ( $0.3M_{\mathrm{J}}<m\sin i<13M_{\mathrm{J}}$) within 2.5 au. This is lower than the field age occurrence rate for the same planet masses and separations and favors an increase in the prevalence of giant planets over time from ∼100 Myr to several Gyr, although our results cannot rule out a constant rate. A decaying planet occurrence rate is, however, strongly excluded. This suggests that giant planets located inside the water ice line originate from a combination of in situ formation or early migration coupled with longer-term inward scattering. The completeness-corrected prevalence of young hot Jupiters in our sample is $1.5_{-1.1}^{+2.2}$% —similar to the rate for field stars—and the 95% upper limit for young brown dwarfs within 5000 days is <3.6% . 

Abstract We report the discovery of a hot Jupiter candidate orbiting HS Psc, a K7 (≈0.7M_⊙) member of the ≈130 Myr AB Doradus moving group. Using radial velocities over 4 yr from the Habitable-zone Planet Finder spectrograph at the Hobby–Eberly Telescope, we find a periodic signal of $P_b={3.986}_{-0.003}^{+0.044}$days. A joint Keplerian and Gaussian process stellar activity model fit to the radial velocities yields a minimum mass of $m_p\sin i={1.5}_{-0.4}^{+0.6}$M_Jup. The stellar rotation period is well constrained by the Transiting Exoplanet Survey Satellite light curve (P_rot= 1.086 ± 0.003 days) and is not an integer harmonic nor alias of the orbital period, supporting the planetary nature of the observed periodicity. HS Psc b joins a small population of young, close-in giant planet candidates with robust age and mass constraints and demonstrates that giant planets can either migrate to their close-in orbital separations by 130 Myr or form in situ. Given its membership in a young moving group, HS Psc represents an excellent target for follow-up observations to characterize this young hot Jupiter further, refine its orbital properties, and search for additional planets in the system. 

The latest generation of high-resolution spectrographs on 10m-class telescopes are designed to pursue challenging science cases. Consequently, ever more precise calibration methods are necessary to enable trail-blazing science methodology. We present the High-Resolution Infrared SPectrograph for Exoplanet Characterization (HISPEC) Calibration Unit (CAL), designed to facilitate challenging science cases such as Doppler imaging of exoplanet atmospheres, precision radial velocity, and high-contrast, high-resolution spectroscopy of nearby exoplanets. CAL builds on the heritage of the pathfinder instrument, the Keck Planet Imager and Characterizer (KPIC)1–3 and utilizes four near-infrared (NIR) light sources encoded with wavelength information that are coupled into singlemode fibers. They can be used synchronously during science observations or asynchronously during daytime calibrations. A uranium hollow cathode lamp (HCL) and a series of gas cells provide absolute calibration from 0.98 μm to 2.46 μm. Two laser frequency combs (LFC) provide stable, time-independent wavelength information during observation, and CAL implements two low-finesse Fabry-Perot etalons as a complement to the LFCs. 

Abstract We revisit the long-studied radial velocity (RV) target HD 26965 using recent observations from the NASA-NSF “NEID” precision Doppler facility. Leveraging a suite of classical activity indicators, combined with line-by-line RV analyses, we demonstrate that the claimed 45-day signal previously identified as a planet candidate is most likely an activity-induced signal. Correlating the bulk (spectrally averaged) RV with canonical line activity indicators confirms a multiday “lag” between the observed activity indicator time series and the measured RV. When accounting for this lag, we show that much of the observed RV signal can be removed by a linear detrending of the data. Investigating activity at the line-by-line level, we find a depth-dependent correlation between individual line RVs and the bulk RVs, further indicative of periodic suppression of convective blueshift causing the observed RV variability, rather than an orbiting planet. We conclude that the combined evidence of the activity correlations and depth dependence is consistent with an RV signature dominated by a rotationally modulated activity signal at a period of ∼42 days. We hypothesize that this activity signature is due to a combination of spots and convective blueshift suppression. The tools applied in our analysis are broadly applicable to other stars and could help paint a more comprehensive picture of the manifestations of stellar activity in future Doppler RV surveys. 

Abstract Extreme precision radial velocity (EPRV) measurements contend with internal noise (instrumental systematics) and external noise (intrinsic stellar variability) on the road to 10 cm s⁻¹“exo-Earth” sensitivity. Both of these noise sources are well-probed using “Sun-as-a-star” RVs and cross-instrument comparisons. We built the Solar Calibrator (SoCal), an autonomous system that feeds stable, disk-integrated sunlight to the recently commissioned Keck Planet Finder (KPF) at the W. M. Keck Observatory. With SoCal, KPF acquires signal-to-noise ratio (S/N) ∼ 1200,R= 98,000 optical (445–870 nm) spectra of the Sun in 5 s exposures at unprecedented cadence for an EPRV facility using KPF’s fast readout mode (<16 s between exposures). Daily autonomous operation is achieved by defining an operations loop using state machine logic. Data affected by clouds are automatically flagged using a reliable quality control metric derived from simultaneous irradiance measurements. Comparing solar data across the growing global network of EPRV spectrographs with solar feeds will allow EPRV teams to disentangle internal and external noise sources and benchmark spectrograph performance. To facilitate this, all SoCal data products are immediately available to the public on the Keck Observatory Archive. We compared SoCal RVs to contemporaneous RVs from NEID, the only other immediately public EPRV solar data set. We find agreement at the 30–40 cm s⁻¹level on timescales of several hours, which is comparable to the combined photon-limited precision. Data from SoCal were also used to assess a detector problem and wavelength calibration inaccuracies associated with KPF during early operations. Long-term SoCal operations will collect upwards of 1000 solar spectra per six-hour day using KPF’s fast readout mode, enabling stellar activity studies at high S/N on our nearest solar-type star. 

Abstract The discovery and characterization of extrasolar planets using radial velocity (RV) measurements is limited by noise sources from the surfaces of host stars. Current techniques to suppress stellar magnetic activity rely on decorrelation using an activity indicator (e.g., strength of the Ca ii lines, width of the cross-correlation function, broadband photometry) or measurement of the RVs using only a subset of spectral lines that have been shown to be insensitive to activity. Here, we combine the above techniques by constructing a high-signal-to-noise activity indicator, the depth metric  ( t ) , from the most activity-sensitive spectral lines using the “line-by-line” method of Dumusque (2018). Analogous to photometric decorrelation of RVs or Gaussian progress regression modeling of activity indices, time series modeling of  ( t ) reduces the amplitude of magnetic activity in RV measurements; in an α CenB RV time series from HARPS, the RV rms was reduced from 2.67 to 1.02 m s −1 .  ( t ) modeling enabled us to characterize injected planetary signals as small as 1 m s −1 . In terms of noise reduction and injected signal recovery,  ( t ) modeling outperforms activity mitigation via the selection of activity-insensitive spectral lines. For Sun-like stars with activity signals on the m s −1 level, the depth metric independently tracks rotationally modulated and multiyear stellar activity with a level of quality similar to that of the FWHM of the CCF and log R HK ′ . The depth metric and its elaborations will be a powerful tool in the mitigation of stellar magnetic activity, particularly as a means of connecting stellar activity to physical processes within host stars. 

Abstract We introduce the OATMEAL survey, an effort to measure the obliquities of stars with transiting brown dwarf companions. We observed a transit of the close-in (P_orb= 1.74 days) brown dwarf GPX-1 b using the Keck Planet Finder spectrograph to measure the sky-projected angle between its orbital axis and the spin axis of its early F-type host star (λ). We measuredλ= 6.°9 ± 10.°0, suggesting an orbit that is prograde and well aligned with the stellar equator. Hot Jupiters around early F stars are frequently found to have highly misaligned orbits, with polar and retrograde orbits being commonplace. It has been theorized that these misalignments stem from dynamical interactions, such as von Zeipel–Kozai–Lidov cycles, and are retained over long timescales due to weak tidal dissipation in stars with radiative envelopes. By comparing GPX-1 to similar systems under the frameworks of different tidal evolution theories, we argued that the rate of tidal dissipation is too slow to have re-aligned the system. This suggests that GPX-1 may have arrived at its close-in orbit via coplanar high-eccentricity migration or migration through an aligned protoplanetary disk. Our result for GPX-1 is one of few measurements of the obliquity of a star with a transiting brown dwarf. By enlarging the number of such measurements and comparing them with hot-Jupiter systems, we will more clearly discern the differences between the mechanisms that dictate the formation and evolution of both classes of objects. 

Theories of planet formation predict that low-mass stars should rarely host exoplanets with masses exceeding that of Neptune. We used radial velocity observations to detect a Neptune-mass exoplanet orbiting LHS 3154, a star that is nine times less massive than the Sun. The exoplanet’s orbital period is 3.7 days, and its minimum mass is 13.2 Earth masses. We used simulations to show that the high planet-to-star mass ratio (>3.5 × 10⁻⁴) is not an expected outcome of either the core accretion or gravitational instability theories of planet formation. In the core-accretion simulations, we show that close-in Neptune-mass planets are only formed if the dust mass of the protoplanetary disk is an order of magnitude greater than typically observed around very low-mass stars. 

Abstract We report the discovery of a close-in (P_orb= 3.349 days) warm Neptune with clear transit timing variations (TTVs) orbiting the nearby (d= 47.3 pc) active M4 star, TOI-2015. We characterize the planet's properties using Transiting Exoplanet Survey Satellite (TESS) photometry, precise near-infrared radial velocities (RVs) with the Habitable-zone Planet Finder Spectrograph, ground-based photometry, and high-contrast imaging. A joint photometry and RV fit yields a radius $R_p={3.37}_{-0.20}^{+0.15}{R}_{\oplus }$, mass $m_p={16.4}_{-4.1}^{+4.1}{M}_{\oplus }$, and density ${\rho }_p={2.32}_{-0.37}^{+0.38}\mathrm{g}{\mathrm{cm}}^{-3}$for TOI-2015 b, suggesting a likely volatile-rich planet. The young, active host star has a rotation period ofP_rot= 8.7 ± 0.9 days and associated rotation-based age estimate of 1.1 ± 0.1 Gyr. Though no other transiting planets are seen in the TESS data, the system shows clear TTVs of super-period $P_{\sup }\approx 430\mathrm{days}$and amplitude ∼100 minutes. After considering multiple likely period-ratio models, we show an outer planet candidate near a 2:1 resonance can explain the observed TTVs while offering a dynamically stable solution. However, other possible two-planet solutions—including 3:2 and 4:3 resonances—cannot be conclusively excluded without further observations. Assuming a 2:1 resonance in the joint TTV-RV modeling suggests a mass of $m_b={13.3}_{-4.5}^{+4.7}{M}_{\oplus }$for TOI-2015 b and $m_c={6.8}_{-2.3}^{+3.5}{M}_{\oplus }$for the outer candidate. Additional transit and RV observations will be beneficial to explicitly identify the resonance and further characterize the properties of the system.