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Abstract MAROON-X is a state-of-the-art extreme-precision radial velocity spectrograph deployed on the 8.1 m Gemini-N telescope on Maunakea, Hawai’i. Using a stabilized Fabry–Pérot etalon for wavelength and drift calibration, MAROON-X has achieved a short-term precision of ∼30 cm s⁻¹. However, due to a long-term drift in the etalon (2.2 cm s⁻¹per day) and various interruptions of the instrument baseline over the first few years of operation, MAROON-X experiences radial velocity (RV) offsets between observing runs several times larger than the short-term precision during any individual run, which hinders the detection of longer-period signals. In this study, we analyze RV measurements of 11 targets that either exhibit small RV scatter or have signals that can be precisely constrained using Keplerian or Gaussian process models. Leveraging this ensemble, we calibrate MAROON-X’s run offsets for data collected between 2020 September and early 2024 January to a precision of ∼0.5 m s⁻¹. When applying these calibrated offsets to HD 3651, a quiet star, we obtain residual velocities with an rms of <70 cm s⁻¹in both the red and blue channels of MAROON-X over a baseline of 29 months. We also demonstrate the sensitivity of MAROON-X data calibrated with these offsets through a series of injection-recovery tests. Based on our findings, MAROON-X is capable of detecting sub m s⁻¹signals out to periods of more than 1000 days. 

Abstract A star's spin–orbit angle can give us insight into a system's formation and dynamical history. In this paper, we use MAROON-X observations of the Rossiter–McLaughlin effect to measure the projected obliquity of the LP 261-75 (also known as TOI-1779) system, focusing on the fully convective M dwarf LP 261-75A and the transiting brown dwarf LP 261-75C. This is the first obliquity constraint of a brown dwarf orbiting an M dwarf and the seventh obliquity constraint of a brown dwarf overall. We measure a projected obliquity of $5_{-10}^{+11}$degrees and a true obliquity of $14_{-7}^{+8}$degrees for the system, meaning that the system is well aligned and that the star is rotating very nearly edge-on, with an inclination of 90° ±  11°. The system thus follows along with the trends observed in transiting brown dwarfs around hotter stars, which typically have low obliquities. The tendency for brown dwarfs to be aligned may point to some enhanced obliquity damping in brown dwarf systems, but there is also a possibility that the LP 261-75 system was simply formed aligned. In addition, we note that the brown dwarf's radius (R_C =  0.9R_J) is not consistent with the youth of the system or radius trends observed in other brown dwarfs, indicating that LP 261-75C may have an unusual formation history. 

Abstract Barnard’s Star is an old, single M dwarf star that comprises the second-closest extrasolar system. It has a long history of claimed planet detections from both radial velocities and astrometry. However, none of these claimed detections have so far withstood further scrutiny. Continuing this story, extreme precision radial velocity measurements from the ESPRESSO instrument have recently been used to identify four new sub-Earth-mass planet candidates around Barnard’s Star. We present here 112 radial velocities of Barnard’s Star from the MAROON-X instrument that were obtained independently to search for planets around this compelling object. The data have a typical precision of 30 cm s⁻¹and are contemporaneous with the published ESPRESSO measurements (2021–2023). The MAROON-X data on their own confirm planet b (P= 3.154 days) and planet candidates c and d (P= 4.124 and 2.340 days, respectively). Furthermore, adding the MAROON-X data to the ESPRESSO data strengthens the evidence for planet candidate e (P= 6.739 days), thus leading to its confirmation. The signals from all four planets are <50 cm s⁻¹, the minimum masses of the planets range from 0.19 to 0.34M_⊕, and the system is among the most compact known among late M dwarfs hosting low-mass planets. The current data rule out planets with masses >0.57M_⊕(with a 99% detection probability) in Barnard's Star’s habitable zone (P= 10–42 days). 

Abstract Transiting giant exoplanets around M-dwarf stars (GEMS) are rare, owing to the low-mass host stars. However, the all-sky coverage of TESS has enabled the detection of an increasingly large number of them to enable statistical surveys like the Searching for GEMS survey. As part of this endeavor, we describe the observations of six transiting giant planets, which include precise mass measurements for two GEMS (K2-419Ab, TOI-6034b) and statistical validation for four systems, which includes validation and mass upper limits for three of them (TOI-5218b, TOI-5616b, TOI-5634Ab), while the fourth one—TOI-5414b is classified as a “likely planet.” Our observations include radial velocities from the Habitable-zone Planet Finder on the Hobby–Eberly Telescope, and MAROON-X on Gemini-North, along with photometry and high-contrast imaging from multiple ground-based facilities. In addition to TESS photometry, K2-419Ab was also observed and statistically validated as part of the K2 mission in Campaigns 5 and 18, which provide precise orbital and planetary constraints despite the faint host star and long orbital period of ∼20.4 days. With an equilibrium temperature of only 380 K, K2-419Ab is one of the coolest known well-characterized transiting planets. TOI-6034 has a late F-type companion about 40″ away, making it the first GEMS host star to have an earlier main-sequence binary companion. These confirmations add to the existing small sample of confirmed transiting GEMS.