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  • Southern Binaries with the Zorro Speckle Camera @ Gemini South
    We present measurements in the context of a survey of southern hemisphere binary and multiple stellar systems observed with the Zorro Speckle dual diffraction-limited optical imaging camera on the 8.1 m Gemini South telescope carried out between 2019 and 2023. The overall motivation of our survey and some initial results of these observations are outlined to demonstrate the capabilities—and limitations—of Zorro. We report on the astrometric characterization of the instrument in terms of the precision and accuracy of our measurements and provide details of our custom-made data reduction pipeline. For targets with separations smaller than 0 4, an overall precision of 1 mas in the radial and tangential directions is obtained, while the uncertainty in position angle is 0 2. Relative astrometry and contrast brightness in the two Zorro filters at 562 and 832 nm are reported for 70 pairs on 64 distinct systems (six are triples). Eleven new binaries are found, mostly of small separations (down to 15 mas) and large brightness contrast (up to Δm = 6 in the red channel). Our results indicate that the Zorro instrument, when properly calibrated, delivers excellent-quality data for visual binary studies of tight and/or faint companions.

  • Erratum: “Candidate RR Lyrae Associated with the Ultrafaint Dwarf Galaxy Aquarius III” (2025, AJ, 169, 156)
  • Real-time Collision-free Motion Planning for Next-generation Fiber Positioners in LAMOST
    Multiobject fiber-fed spectrographs have thousands of fiber positioners packed on a focal plane with shared working space to move the fiber-ends in parallel, which maximizes observation time. In order to further improve the spectrum acquiring rate, the second stage of LAMOST is pursuing miniaturization and high density of fiber positioners. However, their smaller size and increased density introduce greater challenges in positioning and replacement, which necessitate more advanced anticollision measures to ensure smooth operation. In this study, we first present a real-time control strategy that makes trajectory of positioner predictable and then propose a real-time collision-free motion-planning algorithm. We classify collisions based on predicted trajectories and obtain collision-free paths. One of the fiber positioners in each collision pair is selected as waiting robot, retracting robot or extending robot. Under real-time control, positioners will move along the collision-free paths. Simulations validated that the success rate in avoiding collisions of the proposed method increased from 98.96% to 100%. A prototype measurement platform was set up to verify the scientific validity of our algorithm, and the results have shown that all 6300 fiber positioners could avoid collisions. As the trajectory of a positioner can be divided into no more than six parts, collisions among thousands of positioners can be divided into many collision pairs. Thus, our algorithm can be used in other instruments with equal-arm theta-phi positioners.

  • 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 3 yr 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 (DG) to have a = 1–10 au and 70–4000 M⊕ = 0.2–12.5 MJ, and required transiting planets to have a < 1 au and Rp = 1–4 R⊕. We assembled our sample of 47 stars using a single selection function and observed each star at monthly intervals to obtain ≈30 RV observations per target. The final catalog includes a total of 12 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 DGs in the presence of close-in small planets (CSs), P(DG∣CS) = %, over the field rate of P(DG) = . No enhancement is disfavored (p ∼ 8%). In contrast to a previous study, we found no evidence that stellar metallicity raises the enhancement of P(DG∣CS) over P(DG). We found evidence that DG companions preferentially accompany shorter-period CS planets and have lower eccentricities than randomly selected giant planets. This points toward a nuanced picture of dynamically cool formation in which giants interact with, but do not disrupt, their inner systems.

  • Precise Parameters from Bayesian Spectral Energy Distribution Fitting Indicate Thermally Driven Mass Loss Likely Driver of Radius Valley
    Several planet formation models have been proposed to explain the gap in the population of planets between 1.8R⊕ to 2.0R⊕ known as the “radius valley.” To apply these models to confirmed exoplanets, accurate and precise host-star and planet parameters are required to ensure the observed measurements correctly match model predictions. Previous studies have emphasized the need for a larger, more precise sample to further confirm dominant formation processes. By enhancing standard spectral energy distribution fitting using Bayesian methods, we derived highly accurate and precise host-star and planet parameters. Specifically, we achieved median fractional uncertainties for stellar and planet radii of 2.4% and 3.4%, respectively. We then produced the largest, most precise sample to date of 1923 planets when compared to previous studies. This full sample, as well as a sample filtered for host stellar masses between 0.8 and 1.2M⊙, were then used to derive the slope and position of the radius valley as a function of orbital period, insolation flux, and stellar mass to compare them to predictive models and previous observational results. Our results are consistent with thermally driven mass loss with a planet radius versus orbital period slope of for the full sample, leaning toward core-powered mass loss. The planet radius versus insolation flux slope of for the filtered sample leaned toward photoevaporation. Also, the slope as a function of stellar mass for both samples appears more consistent with thermally driven processes when compared to models and previous studies.