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We present Keck/KPIC Phase II K -band observations of the nontransiting hot Jupiter HD 143105 b. Using a cross-correlation approach, we make the first detection of the planetary atmosphere at ${K}_{{\rm{p}}}=18{5}_{-13}^{+11}$ km s ^−1 and an inferior conjunction time 2.5 hr before the previously published ephemeris. The retrieved K _p value, in combination with the orbital period, mass of the host star, and lack of transit detection, give an orbital inclination of $7{8}_{-12}^{\circ +2}$ and a true planet mass of 1.23 ± 0.10 M _J . While the equilibrium temperature of HD 143105 b is in the transition regime between noninverted and inverted atmospheres, our analysis strongly prefers a noninverted atmosphere. Retrieval analysis indicates the atmosphere of HD 143105 b is cloud free to approximately 1 bar and dominated by H _2 O absorption ( ${\mathrm{logH}}_{2}{{\rm{O}}}_{\mathrm{MMR}}=-3.{9}_{-0.5}^{+0.8}$ ), placing only an upper limit on the CO abundance ( ${\mathrm{logCO}}_{\mathrm{MMR}}\lt -3.7$ at 95% confidence). We place no constraints on the abundances of Fe, Mg, or ^13 CO. From these abundances, we place an upper limit on the carbon-to-oxygen ratio for HD 143105 b, C/O

The ~5 Myr PDS 70 is the only known system with protoplanets residing in the cavity of the circumstellar disk from which they formed, ideal for studying exoplanet formation and evolution within its natal environment. Here, we report the first spin constraint and C/O measurement of PDS 70b from Keck/KPIC high-resolution spectroscopy. We detected CO (3.8 σ ) and H _2 O (3.5 σ ) molecules in the PDS 70b atmosphere via cross correlation, with a combined CO and H _2 O template detection significance of 4.2 σ . Our forward-model fits, using BT-Settl model grids, provide an upper limit for the spin rate of PDS 70b (

Vortex fiber nulling (VFN) is a technique for detecting and characterizing faint companions at small separations from their host star. A near-infrared (∼2.3 μ m) VFN demonstrator mode was deployed on the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck Observatory and presented earlier. In this Letter, we present the first VFN companion detections. Three targets, HIP 21543 Ab, HIP 94666 Ab, and HIP 50319 B, were detected with host–companion flux ratios between 70 and 430 at and within one diffraction beamwidth ( λ / D ). We complement the spectra from KPIC VFN with flux ratio and position measurements from the CHARA Array to validate the VFN results and provide a more complete characterization of the targets. This Letter reports the first direct detection of these three M dwarf companions, yielding their first spectra and flux ratios. Our observations provide measurements of bulk properties such as effective temperatures, radial velocities, and $v\sin i$ , and verify the accuracy of the published orbits. These detections corroborate earlier predictions of the KPIC VFN performance, demonstrating that the instrument mode is ready for science observations.

We present high-resolution K -band emission spectra of the quintessential hot Jupiter HD 189733 b from the Keck Planet Imager and Characterizer. Using a Bayesian retrieval framework, we fit the dayside pressure–temperature profile, orbital kinematics, mass-mixing ratios of H _2 O, CO, CH _4 , NH _3 , HCN, and H _2 S, and the ^13 CO/ ^12 CO ratio. We measure mass fractions of ${\mathrm{logH}}_{2}{\rm{O}}=-{2.0}_{-0.4}^{+0.4}$ and $\mathrm{logCO}=-{2.2}_{-0.5}^{+0.5}$ , and place upper limits on the remaining species. Notably, we find logCH _4 < −4.5 at 99% confidence, despite its anticipated presence at the equilibrium temperature of HD 189733 b assuming local thermal equilibrium. We make a tentative (∼3 σ ) detection of ^13 CO, and the retrieved posteriors suggest a ^12 C/ ^13 C ratio similar to or substantially less than the local interstellar value. The possible ^13 C enrichment would be consistent with accretion of fractionated material in ices or in the protoplanetary disk midplane. The retrieved abundances correspond to a substantially substellar atmospheric C/O = 0.3 ± 0.1, while the carbon and oxygen abundances are stellar to slightly superstellar, consistent with core-accretion models which predict an inverse correlation between C/O and metallicity. The specific combination of low C/O and high metallicity suggests significant accretion of solid material may have occurred late in the formation process of HD 189733 b.

M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similar T _eff ∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution ( R ∼ 35,000) K -band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and find ${M}_{B}={88.0}_{-3.2}^{+3.4}\,{M}_{\mathrm{Jup}}$ , putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star with $a={38}_{-3}^{+4}$ au and e = 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect ^13 CO (7.8 σ significance) and tentatively detect ${{\rm{H}}}_{2}^{18}{\rm{O}}$ (3.7 σ significance) in the companion’s atmosphere and measure ${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}={98}_{-22}^{+28}$ and ${{\rm{H}}}_{2}^{16}{\rm{O}}/{{\rm{H}}}_{2}^{18}{\rm{O}}={240}_{-80}^{+145}$ after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure ${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}={79}_{-16}^{+21}$ and ${{\rm{C}}}^{16}{\rm{O}}/{{\rm{C}}}^{18}{\rm{O}}={288}_{-70}^{+125}$ for the primary star. These results demonstrate that HIP 55507 A and B have consistent ^12 C/ ^13 C and ^16 O/ ^18 O to the

Using Keck Planet Imager and Characterizer high-resolution ( R ∼ 35,000) spectroscopy from 2.29 to 2.49 μ m, we present uniform atmospheric retrievals for eight young substellar companions with masses of ∼10–30 M _Jup , orbital separations spanning ∼50–360 au, and T _eff between ∼1500 and 2600 K. We find that all companions have solar C/O ratios and metallicities to within the 1 σ –2 σ level, with the measurements clustered around solar composition. Stars in the same stellar associations as our systems have near-solar abundances, so these results indicate that this population of companions is consistent with formation via direct gravitational collapse. Alternatively, core accretion outside the CO snowline would be compatible with our measurements, though the high mass ratios of most systems would require rapid core assembly and gas accretion in massive disks. On a population level, our findings can be contrasted with abundance measurements for directly imaged planets with m < 10 M _Jup , which show tentative atmospheric metal enrichment compared to their host stars. In addition, the atmospheric compositions of our sample of companions are distinct from those of hot Jupiters, which most likely form via core accretion. For two companions with T _eff ∼ 1700–2000 K ( κ And b and GSC 6214–210 b), our best-fit models prefer a nongray cloud model with >3 σ significance. The cloudy models yield 2 σ −3 σ lower T _eff for these companions, though the C/O and [C/H] still agree between cloudy and clear models at the 1 σ level. Finally, we constrain ^12 CO/ ^13 CO for three companions with the highest signal-to-noise ratio data (GQ Lup b, HIP 79098b, and DH Tau b) and report $v\sin i$ and radial velocities for all companions.

The 1RXS J034231.8+121622 system consists of an M dwarf primary and a directly imaged low-mass stellar companion. We use high-resolution spectroscopic data from Keck/KPIC to estimate the objects' atmospheric parameters and radial velocities (RVs). Using PHOENIX stellar models, we find that the primary has a temperature of 3460 ± 50 K and a metallicity of 0.16 ± 0.04, while the secondary has a temperature of 2510 ± 50 K and a metallicity of ${0.13}_{-0.11}^{+0.12}$ . Recent work suggests this system is associated with the Hyades, giving it an older age than previous estimates. Both metallicities agree with current Hyades [Fe/H] measurements (0.11–0.21). Using stellar evolutionary models, we obtain significantly higher masses for the objects, 0.30 ± 0.15 M _⊙ and 0.08 ± 0.01 M _⊙ (84 ± 11 M _Jup ), respectively. Using the RVs and a new astrometry point from Keck/NIRC2, we find that the system is likely an edge-on, moderately eccentric ( ${0.41}_{-0.08}^{+0.27}$ ) configuration. We also estimate the C/O ratio of both objects using custom grid models, obtaining 0.42 ± 0.10 (primary) and 0.55 ± 0.10 (companion). From these results, we confirm that this system most likely went through a binary star formation process in the Hyades. The significant changes in this system's parameters since its discovery highlight the importance of high-resolution spectroscopy for both orbital and atmospheric characterization of directly imaged companions.

We present the projected rotational velocity and molecular abundances for HD 33632 Ab obtained via Keck Planet Imager and Characterizer (KPIC) high-resolution spectroscopy. HD 33632 Ab is a nearby benchmark brown dwarf companion at a separation of ∼20 au that straddles the L–T transition. Using a forward-modeling framework with on-axis host star spectra, which provides self-consistent substellar atmospheric and retrieval models for HD 33632 Ab, we derive a projected rotational velocity of 53 ± 3 km s ^−1 and carbon monoxide and water mass fractions of logCO = −2.3 ± 0.3 and logH _2 O = −2.7 ± 0.2, respectively. The inferred carbon-to-oxygen ratio (C/O = 0.58 ± 0.14), molecular abundances, and metallicity ([C/H] = 0.0 ± 0.2 dex) of HD 33632 Ab are consistent with its host star. Although detectable methane opacities are expected in L–T transition objects, we did not recover methane in our KPIC spectra, partly due to the high v sin i and to disequilibrium chemistry at the pressures to which we are sensitive. We parameterize the spin as the ratio of rotation to the breakup velocity, and compare HD 33632 Ab to a compilation of >200 very low-mass objects ( M ≲ 0.1 M _⊙ ) that have spin measurements in the literature. There appears to be no clear trend for the isolated low-mass field objects versus mass, but a tentative trend is identified for low-mass companions and directly imaged exoplanets, similar to previous findings. A larger sample of close-in gas giant exoplanets and brown dwarfs will critically examine our understanding of their formation and evolution through rotation and chemical abundance measurements.

Young, self-luminous super-Jovian companions discovered by direct imaging provide a challenging test for planet formation and evolution theories. By spectroscopically characterizing the atmospheric compositions of these super-Jupiters, we can constrain their formation histories. Here we present studies of the recently discovered HIP 99770 b, a 16 M _Jup high-contrast companion on a 17 au orbit, using the fiber-fed high-resolution spectrograph KPIC ( ${ \mathcal R }$ ∼ 35,000) on the Keck II telescope. Our K -band observations led to detections of H _2 O and CO in the atmosphere of HIP 99770 b. We carried out free retrieval analyses using petitRADTRANS to measure its chemical abundances, including the metallicity and C/O ratio, projected rotation velocity ( $v\sin i$ ), and radial velocity (RV). We found that the companion’s atmosphere has C/O $=\,{0.55}_{-0.04}^{+0.06}$ and [M/H] $=\,{0.26}_{-0.23}^{+0.24}$ (1 σ confidence intervals), values consistent with those of the Sun and with a companion formation via gravitational instability or core accretion. The projected rotation velocity $v\sin (i)\lt 7.8$ km s ^−1 is small relative to other directly imaged companions with similar masses and ages. This may imply a nearly pole-on orientation or effective magnetic braking by a circumplanetary disk. In addition, we added the companion-to-primary relative RV measurement to the orbital fitting and obtained updated constraints on orbital parameters. Detailed characterization of super-Jovian companions within 20 au like HIP 99770 b is critical for understanding the formation histories of this population.

We used the Keck Planet Imager and Characterizer to obtain high-resolution ( R ∼ 35,000) K -band spectra of κ Andromedae b, a planetary-mass companion orbiting the B9V star, κ Andromedae A. We characterized its spin, radial velocity, and bulk atmospheric parameters through use of a forward-modeling framework to jointly fit planetary spectra and residual starlight speckles, obtaining likelihood-based posterior probabilities. We also detected H _2 O and CO in its atmosphere via cross correlation. We measured a $v\sin (i)$ value for κ Andromedae b of 38.42 ± 0.05 km s ^−1 , allowing us to extend our understanding of the population of close-in bound companions at higher rotation rates. This rotation rate is one of the highest spins relative to breakup velocity measured to date, at close to 50% of breakup velocity. We identify a radial velocity $-{17.35}_{-0.09}^{+0.05}$ km s ^−1 , which we use with existing astrometry and radial velocity measurements to update the orbital fit. We also measure an effective temperature of 1700 ± 100 K and a $\mathrm{log}(g)$ of 4.7 ± 0.5 cgs dex.

GQ Lup B is one of the few substellar companions with a detected cicumplanetary disk (CPD). Observations of the CPD suggest the presence of a cavity, possibly formed by an exosatellite. Using the Keck Planet Imager and Characterizer (KPIC), a high-contrast imaging suite that feeds a high-resolution spectrograph (1.9–2.5 µ m, R ∼35,000), we present the first dedicated radial velocity (RV) observations around a high-contrast, directly imaged substellar companion, GQ Lup B, to search for exosatellites. Over 11 epochs, we find a best and median RV error of 400–1000 m s ^−1 , most likely limited by systematic fringing in the spectra due to transmissive optics within KPIC. With this RV precision, KPIC is sensitive to exomoons 0.6%–2.8% the mass of GQ Lup B (∼30 M _Jup ) at separations between the Roche limit and 65 R _Jup , or the extent of the cavity inferred within the CPD detected around GQ Lup B. Using simulations of HISPEC, a high resolution infrared spectrograph planned to debut at W.M. Keck Observatory in 2026, we estimate future exomoon sensitivity to increase by over an order of magnitude, providing sensitivity to less massive satellites potentially formed within the CPD itself. Additionally, we run simulations to estimate the amount of material that different masses of satellites could clear in a CPD to create the observed cavity. We find satellite-to-planet mass ratios of q > 2 × 10 ^−4 can create observable cavities and report a maximum cavity size of ∼51 R _Jup carved from a satellite.

We present Keck Planet Imager and Characterizer (KPIC) high-resolution ( R ∼35,000) K -band thermal emission spectroscopy of the ultrahot Jupiter WASP-33b. The use of KPIC’s single-mode fibers greatly improves both blaze and line-spread stabilities relative to slit spectrographs, enhancing the cross-correlation detection strength. We retrieve the dayside emission spectrum with a nested-sampling pipeline, which fits for orbital parameters, the atmospheric pressure–temperature profile, and the molecular abundances. We strongly detect the thermally inverted dayside and measure mass-mixing ratios for CO ( ${\mathrm{logCO}}_{\mathrm{MMR}}=-{1.1}_{-0.6}^{+0.4}$ ), H _2 O ( ${\mathrm{logH}}_{2}{{\rm{O}}}_{\mathrm{MMR}}\,=-{4.1}_{-0.9}^{+0.7}$ ), and OH ( ${\mathrm{logOH}}_{\mathrm{MMR}}=-{2.1}_{-1.1}^{+0.5}$ ), suggesting near-complete dayside photodissociation of H _2 O. The retrieved abundances suggest a carbon- and possibly metal-enriched atmosphere, with a gas-phase C/O ratio of ${0.8}_{-0.2}^{+0.1}$ , consistent with the accretion of high-metallicity gas near the CO _2 snow line and post-disk migration or with accretion between the soot and H _2 O snow lines. We also find tentative evidence for ^12 CO/ ^13 CO ∼ 50, consistent with values expected in protoplanetary disks, as well as tentative evidence for a metal-enriched atmosphere (2–15 × solar). These observations demonstrate KPIC’s ability to characterize close-in planets and the utility of KPIC’s improved instrumental stability for cross-correlation techniques.

The detection of satellites around extrasolar planets, so called exomoons, remains a largely unexplored territory. In this work, we study the potential of detecting these elusive objects from radial velocity monitoring of self-luminous, directly imaged planets. This technique is now possible thanks to the development of dedicated instruments combining the power of high-resolution spectroscopy and high-contrast imaging. First, we demonstrate a sensitivity to satellites with a mass ratio of 1%–4% at separations similar to the Galilean moons from observations of a brown-dwarf companion (HR 7672 B; K _mag = 13; 0.″7 separation) with the Keck Planet Imager and Characterizer ( R ∼ 35,000 in the K band) at the W. M. Keck Observatory. Current instrumentation is therefore already sensitive to large unresolved satellites that could be forming from gravitational instability akin to binary star formation. Using end-to-end simulations, we then estimate that future instruments such as the Multi-Object Diffraction-limited High-resolution Infrared Spectrograph, planned for the Thirty Meter Telescope, should be sensitive to satellites with mass ratios of ∼10 ^−4 . Such small moons would likely form in a circumplanetary disk similar to the Jovian satellites in the solar system. Looking for the Rossiter–McLaughlin effect could also be an interesting pathway to detecting the smallest moons on short orbital periods. Future exomoon discoveries will allow precise mass measurements of the substellar companions that they orbit and provide key insight into the formation of exoplanets. They would also help constrain the population of habitable Earth-sized moons orbiting gas giants in the habitable zone of their stars.

The formation and evolution pathway for the directly imaged multiplanetary system HR 8799 remains mysterious. Accurate constraints on the chemical composition of the planetary atmosphere(s) are key to solving the mystery. We perform a detailed atmospheric retrieval on HR 8799 c to infer the chemical abundances and abundance ratios using a combination of photometric data along with low- and high-resolution spectroscopic data ( R ∼ 20–35,000). We specifically retrieve [C/H], [O/H], and C/O and find them to be ${0.55}_{-0.39}^{+0.36}$ , ${0.47}_{-0.32}^{+0.31}$ , and ${0.67}_{-0.15}^{+0.12}$ at 68% confidence. The superstellar C and O abundances, yet a stellar C/O ratio, reveal a potential formation pathway for HR 8799 c. Planet c, and likely the other gas giant planets in the system, formed early on (likely within ∼1 Myr), followed by further atmospheric enrichment in C and O through the accretion of solids beyond the CO ice line. The enrichment either preceded or took place during the early phase of the inward migration to the current planet locations.