-4 GHz, in project 19B-274 (PI: Villadsen). The arrays had 5-6 antennas per observation date (ATCA) or 26-27 (VLA). The observation durations in the table count from the beginning of the first to the end of the last target scan. These durations slightly exceed the true time on source due to calibrator observations, which occurred for 1-3 minutes every 20-60 minutes. Each system was observed across 80-100% of orbital phases at least once, with multi-date observations sampling across different orbits in order to achieve near-complete phase coverage.]

6 Villadsen et al.
LTT 3780 is the primary star in a 16′′ visual binary with M5 dwarf LP 729-55 (Nowak et al. 2020). We did not find records of companions for any other targets. Since we are searching for a strongly circularly-polarized signal, the probability of source confusion is low.
4. DATA ANALYSIS For LHS 3844, we flagged and calibrated the ATCA data in Miriad. For the other ATCA targets, we flagged and calibrated in CASA. We performed polarization calibration for the ATCA data in order to use the cross-hand X and Y signals to measure circular polarization. For LTT 3780, we flagged and calibrated the VLA data using the VLA pipeline in the CASA software package (McMullin et al. 2007). The observations typically achieved an effective bandwidth of ∼1.4 GHz due to radio frequency interference (RFI). For all targets, we used CASA to generate both total intensity (Stokes I) and circular polarization (Stokes V) images using the entire observation duration. Nearby dates were combined, but for GJ 367, the January and September epochs were imaged separately, as were the Jun 21 and 26 dates for LHS 3844. We deconvolved Stokes I images in CASA using the tclean task with W-projection, multifrequency synthesis with 2-4 Taylor terms (by default 2, up to 4 if a bright background source was near the primary beam null), and multi-scale model components. This imaging serves a dual purpose: searching for quiescent (time-averaged) stellar emission in the image plane, and creating model visibilities for background sources in the field of view. The ATCA Stokes I images did not initially reach near target sensitivity, so we performed 1-2 rounds of phase-only self-calibration. Before making time series, we shifted the phase center of the visibility data to the stars’ known location adjusted for proper motion (Gaia Collaboration 2020) using the SIMBAD database, unless it was already aligned to within a small fraction of a synthesized beam. The phase centers used are: LTT 3780 at (α, δ) = (10h18m34.s672, −11◦43′05.′′206), LHS 3844 at (22h41m59.s340, −69◦10′22.′′496), GJ 367 at (09h44m28.s863, −45◦46′48.′′244) in January 2022 and (09h44m28.s833, −45◦46′48.′′650) in September 2022, LHS 1678 at (04h32m43.s106, −39◦47′34.′′110), and GJ 1252 at (20h27m43.s243, −56◦27′53.′′098). None of the targets are known binary systems. We did not adjust for parallax motion (0.05”-0.1”), since it is much smaller than the synthesized beam size of ≳5′′. We made time series plots for the locations of the target stars in both Stokes I and V. To do so, we first modeled and removed background sources from the data. The imaging process (tclean) created model visibilities for the background sources, using masking to omit the location of the star from the model. Then, we used uvsub to subtract that model from the visibility data, leaving residual visibilities containing only the target star, plus thermal noise, RFI, and traces of imperfectly subtracted background sources. We then averaged the residual visibilities across all baselines using plotms, creating a complex time series for the phase center. The real component is the time series for the star, and the imaginary component should not contain stellar emission and thus provides an estimate of noise levels.
5. RESULTS Appendices A and B present the images and time series, respectively, for all targets. None of the stars were detected in the time series, using a detection criterion of 2 adjacent points in the time series exceeding three times the standard deviation σ. We binned the time series to integration times of 1, 3, 5, 10, and 15-30 minutes (maximum depending on scan length), with no multi-point detections at 69.14