The discovery of planetary systems beyond the solar system has revealed a diversity of architectures, most of which differ significantly from our system. The initial detection of an exoplanet is ...often followed by subsequent discoveries within the same system as observations continue, measurement precision is improved, or additional techniques are employed. The HD 104067 system is known to consist of a bright K dwarf host star and a giant planet in a \(\sim\)55 day period eccentric orbit. Here we report the discovery of an additional planet within the HD 104067 system, detected through the combined analysis of radial velocity data from the HIRES and HARPS instruments. The new planet has a mass similar to Uranus and is in an eccentric \(\sim\)14 day orbit. Our injection-recovery analysis of the radial velocity data exclude Saturn-mass and Jupiter-mass planets out to 3 AU and 8 AU, respectively. We further present TESS observations that reveal a terrestrial planet candidate (\(R_p = 1.30\pm0.12\) \(R_\oplus\)) in a \(\sim\)2.2~day period orbit. Our dynamical analysis of the three planet model shows that the two outer planets produce significant eccentricity excitation of the inner planet, resulting in tidally induced surface temperatures as high as \(\sim\)2600 K for an emissivity of unity. The terrestrial planet candidate may therefore be caught in a tidal storm, potentially resulting in its surface radiating at optical wavelengths.
We present an in-depth, high-resolution spectroscopic analysis of the M dwarf K2-18 that hosts a sub-Neptune exoplanet in its habitable zone. We show our technique to accurately normalize the ...observed spectrum, which is crucial for a proper spectral fitting. We also introduce a new automatic, line-by-line model-fitting code, AutoSpecFit, that performs an iterative \({\chi}^{2}\) minimization process to measure individual elemental abundances of cool dwarfs. We apply this code to the star K2-18, and measure the abundance of 10 elements - C, O, Na, Mg, Al, K, Ca, Sc, Ti, and Fe. We find these abundances moderately supersolar, except for Fe with a slightly subsolar abundance. The accuracy of the inferred abundances is limited by the systematic errors due to uncertain stellar parameters. We also derive the abundance ratios associated with several planet-building elements such as Al/Mg, Ca/Mg, Fe/Mg, and (a solar-like) C/O=0.568 \(\pm\) 0.026, which can be used to constrain the chemical composition and the formation location of the exoplanet. On the other hand, the planet K2-18 b has attracted considerable interest, given the JWST measurements of its atmospheric composition. Early JWST studies reveal an unusual chemistry for the atmosphere of this planet, which is unlikely to be driven by formation in a disk of unusual composition. The comparison between the chemical abundances of K2-18 b from future JWST analyses and those of the host star can provide fundamental insights into the formation of this planetary system.
Using a data-driven machine learning tool we report \(T_{\text{eff}}\), \(\log{(g)}\), \(v\sin{(i)}\), and elemental abundances for 15 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni, Y) ...for a sample of 25 exoplanet host stars targeted by JWST's first year of observations. The chemical diversity of these stars show that, while a number of their companion planets may have formed in a disk with chemistry similar to Solar, some JWST targets likely experienced different disk compositions. This sample is part of a larger forthcoming catalog that will report homogeneous abundances of \(\sim\)4,500 FGK stars derived from Keck/HIRES spectra.
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.
An intriguing pattern among exoplanets is the lack of detected planets between approximately \(1.5\) R\(_\oplus\) and \(2.0\) R\(_\oplus\). One proposed explanation for this "radius gap" is the ...photoevaporation of planetary atmospheres, a theory that can be tested by studying individual planetary systems. Kepler-105 is an ideal system for such testing due to the ordering and sizes of its planets. Kepler-105 is a sun-like star that hosts two planets straddling the radius gap in a rare architecture with the larger planet closer to the host star (\(R_b = 2.53\pm0.07\) R\(_\oplus\), \(P_b = 5.41\) days, \(R_c = 1.44\pm0.04\) R\(_\oplus\), \(P_c = 7.13\) days). If photoevaporation sculpted the atmospheres of these planets, then Kepler-105b would need to be much more massive than Kepler-105c to retain its atmosphere, given its closer proximity to the host star. To test this hypothesis, we simultaneously analyzed radial velocities (RVs) and transit timing variations (TTVs) of the Kepler-105 system, measuring disparate masses of \(M_b = 10.8\pm2.3\) M\(_\oplus\) (\( \rho_b = 0.97\pm0.22\) g cm\(^{-3}\)) and \(M_c = 5.6\pm1.2\) M\(_\oplus \) (\(\rho_c = 2.64\pm0.61\) g cm\(^{-3}\)). Based on these masses, the difference in gas envelope content of the Kepler-105 planets could be entirely due to photoevaporation (in 76\% of scenarios), although other mechanisms like core-powered mass loss could have played a role for some planet albedos.
We report the observation of the transiting planet TOI-942c, a Neptunian planet orbiting a young K-type star approximately 50 Myr years old. Using Keck/HIRES, we observed a partial transit of the ...planet and detected an associated radial velocity anomaly. By modeling the Rossiter-McLaughlin (RM) effect, we derived a sky-projected obliquity of \(\left|\lambda\right|=24^{+14}_{-14}\) degrees, indicating TOI-942c is in a prograde and likely aligned orbit. Upon incorporation of the star's inclination and the planet's orbital inclination, we determined a true obliquity for TOI-942c of \(\psi< 43\) degrees at 84\% confidence, while dynamic analysis strongly suggests TOI-942c is aligned with stellar spin and coplanar with the inner planet. Furthermore, TOI-942c is also a suitable target for studying atmospheric loss of young Neptunian planets that are likely still contracting from the heat of formation. We observed a blueshifted excess absorption in the H-alpha line at 6564.7 \AA, potentially indicating atmospheric loss due to photoevaporation. However, due to the lack of pre-ingress data, additional observations are needed to confirm this measurement.
Exoplanet discoveries have revealed a dramatic diversity of planet sizes across a vast array of orbital architectures. Sub-Neptunes are of particular interest; due to their absence in our own solar ...system, we rely on demographics of exoplanets to better understand their bulk composition and formation scenarios. Here, we present the discovery and characterization of TOI-1437 b, a sub-Neptune with a 18.84 day orbit around a near-Solar analog (Mstar = 1.10 +/- 0.10 Msun, Rstar = 1.17 +/- 0.12 Rsun). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite (TESS) mission and radial velocity follow-up observations were carried out as a part of the TESS-Keck Survey (TKS) using both the HIRES instrument at Keck Observatory and the Levy Spectrograph on the Automated Planet Finder (APF) telescope. A combined analysis of these data reveal a planet radius of Rp = 2.24 +/- 0.23 Rearth and a mass measurement of Mp = 9.6 +/- 3.9 Mearth). TOI-1437 b is one of few (~50) known transiting sub-Neptunes orbiting a solar-mass star that has a radial velocity mass measurement. As the formation pathway of these worlds remains an unanswered question, the precise mass characterization of TOI-1437 b may provide further insight into this class of planet.
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.
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.
TOI-561 is a galactic thick disk star hosting an ultra-short period (0.45 day orbit) planet with a radius of 1.37 R\(_{\oplus}\), making it one of the most metal-poor (Fe/H = -0.41) and oldest ...(\(\sim\)10 Gyr) sites where an Earth-sized planet has been found. We present new simultaneous radial velocity measurements (RVs) from Gemini-N/MAROON-X and Keck/HIRES, which we combined with literature RVs to derive a mass of M\(_{b}\)=2.24 \(\pm\) 0.20 M\(_{\oplus}\). We also used two new Sectors of TESS photometry to improve the radius determination, finding R\(_{b}\)=\(1.37 \pm 0.04 R_\oplus\), and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (\(\rho_b\)= 4.8 \(\pm\) 0.5 g/cm\(^{3}\)). This density is consistent with an iron-poor rocky composition reflective of the host star's iron and rock-building element abundances; however, it is also consistent with a low-density planet with a volatile envelope. The equilibrium temperature of the planet (\(\sim\)2300 K) suggests that this envelope would likely be composed of high mean molecular weight species, such as water vapor, carbon dioxide, or silicate vapor, and is likely not primordial. We also demonstrate that the composition determination is sensitive to the choice of stellar parameters, and that further measurements are needed to determine if TOI-561 b is a bare rocky planet, a rocky planet with an optically thin atmosphere, or a rare example of a non-primordial envelope on a planet with a radius smaller than 1.5 R\(_{\oplus}\).
