Andrew W. Mann

Empirical gyrochronology relies on coeval stellar associations to map stellar rotation as a function of mass and age. The accuracy of its age predictions is therefore limited by the number and quality of benchmark rotation sequences. The well-characterized clusters NGC-6811 ( t ≈ 1 Gyr) and NGC-6819 ( t ≈ 2.5 Gyr) bracket an intermediate-age interval in which stellar spin-down remains poorly constrained due to lack of available rotation data. At t ≈ 1.3 Gyr, NGC-752 provides a critical benchmark within this gap, but previous measurements could not define the G- and K-dwarf rotation sequence needed for calibration. Here, we combine Gaia-based NGC-752 membership lists with the literature rotation periods to map NGC-752’s slow-rotator sequence for the first time. We identify a well-defined sequence intermediate between those of NGC-6811 and NGC-6819. Stars near T _eff ≈ 4500 K rotate more slowly than their counterparts in NGC-6811, indicating that stars experiencing stalled spin-down at ≈1 Gyr have resumed appreciable spin-down by the age of NGC-752. Adopting an age of 1.3 Gyr for NGC-752, we further show that existing empirical gyrochronology models overestimate the ages of many G and early-K dwarfs by 20%–50% because they lack intermediate-age calibration data, although uncertainty in the absolute age of NGC-752 may account for part of this offset. NGC-752 therefore provides a necessary anchor for improving rotational age estimates. This calibration is especially timely because Gaia DR4, Roman, and PLATO are expected to yield rotation periods for tens of millions of stars, making the age coverage of benchmark sequences a principal limitation on large-scale gyrochronology.

Young planets (R _⊕ planet on a 10.47 day orbit, and report the candidate TIC 150070085 c, a 3.0 R _⊕ planet on a 15.90 day orbit. While we are unable to validate the second signal, the proximity to mean-motion resonance (3:2) and transit timing variations observed in the transits of TIC 150070085 b strongly suggest that the signal is planetary. We confirm the host star as a member of Alessi 84 and combine the group’s color–magnitude diagram, rotation, and variability properties to update the age to 135 ± 10 Myr. We additionally use MAROON-X to observe the Rossiter–McLaughlin signal of TIC 150070085 b and measure the sky projected obliquity angle ( λ ). We find that TIC 150070085 b is consistent with a near-aligned orbit with its host star (∣ λ ∣ = 18° ± 12°), in line with similarly aged transiting planets with measured λ values. Continued discovery and characterization of planets in this age regime are vital to link planetary infancy (1 Gyr).

The close-in small planet population may be formed either with hydrogen/helium-dominated envelopes or with water-rich interiors. Both scenarios reproduce the present-day planet population in mass, radius, and periods, and are difficult to differentiate with the mature planet demographic. Hydrogen/helium “gas dwarfs” have low mean-molecular-weight atmospheres, while “water worlds” have envelopes that are significantly heavier, and as such, these two scenarios have different evolution tracks that diverge in the first ≈50 Myr of their evolution. We show that a low Earth orbit multiband photometric survey mission, within the scope of the National Aeronautics and Space Administration Small Explorers Program, can determine the frequency of young close-in planets at the 5% level and definitively differentiate between the competing “gas-dwarf” and “water-world” hypotheses. We simulate a 2.5 yr mission capable of simultaneous multiband near-ultraviolet, optical, and near-infrared wide field photometry. Such a mission would perform a photometric survey of 30 different star fields selected to probe the young star population. The mission will yield ≈100 transiting planets in young star clusters and associations with ages <50 Myr. In comparison, only 20 such planets are known from K2 and TESS today.

Stellar rotation is a fundamental tracer of stellar magnetic evolution, age, and activity, with broad implications for Galactic archaeology and exoplanet characterization. The Transiting Exoplanet Survey Satellite (TESS) provides high-precision time-series photometry across the sky, enabling rotation measurements for an unprecedented number of stars. We present the TESS All-Sky Rotation Survey (TARS), an all-sky catalog of stellar variability periods for 1,046,317 stars with T < 16 and distances within 500 pc. We estimate that 93% of these periods are rotation periods. This catalog increases the number of rotation period measurements for stars with T < 16 within 100 pc by a factor of 2.3 and within 500 pc by 4.0. We also present a method to correct half-period harmonics in TESS data and show that it reliably recovers periods as long as 25 days from a single TESS sector. TARS represents the largest homogeneous catalog of stellar rotation periods to date, providing a foundation for studies of stellar ages, young associations, and Galactic structure. We make the light curves used in our analysis available as an HLSP through MAST ( https://archive.stsci.edu/hlsp/tars ). Beyond the default TARS catalog, we provide code that allows users to generate rotation period catalogs with adjustable completeness and reliability thresholds. This code and all rotation period measurements are available through Zenodo (doi: 10.5281/zenodo.19917941 ).

We present the analysis of five long-period TESS Objects of Interest (TOIs), , with orbital periods exceeding one month. Initially identified by the Transiting Exoplanet Survey Satellite (TESS), we extensively monitored these targets with the Antarctic Search for Transiting Exoplanets (ASTEP), supported by other facilities in the TESS Follow-up Observing Program (TFOP) network. all orbiting Sun-like stars These targets occupy a relatively underexplored region of the period-radius parameter space, offering valuable primordial probes for planetary formation and migration as warm planets better maintain their evolutionary fingerprints. To characterise these systems, we leveraged high-resolution speckle imaging to search for nearby stellar companions, and refine stellar parameters using both reconnaissance spectroscopy and spectral energy distribution (SED) fitting. We combined TESS photometry with high-precision ground-based observations from ASTEP, and when available, included additional photometry and radial velocity data. We applied statistical validation to assess the planetary nature of each candidate and used to jointly model the photometric and spectroscopic datasets. We validate the planetary nature of three TOIs, including the two warm Saturns TOI-4507,b (8.2, 104,d) and TOI-3457,b (10.0, 32.6,d), as well as the warm sub-Neptune TOI-707,b (2.4, eclipsing binaries, namely TOI-2404 and TOI-4404. 52.8,d). The remaining two candidates are most consistent with These results help populate the sparse regime of warm planets, which serve as key tracers of planetary evolution, and demonstrate ASTEP’s effectiveness as a ground-based follow-up instrument for long-period systems.

We present four newly validated transiting brown dwarfs identified through TESS photometry and confirmed with high-precision radial velocity measurements obtained from the FEROS and PLATOSpec spectrographs. Notably, three of these companions exhibit orbital periods exceeding 100 days, thereby expanding the sample of long-period transiting brown dwarfs from four to seven systems. The host stars of the long-period brown dwarfs show mild subsolar metallicity. These discoveries highlight the expansion of the metal-poor long-period distribution and help us better understand the brown dwarf desert. In our comparative analysis of eccentricity and metallicity demographics, we utilized catalogs of long-period giant planets, brown dwarfs, and low-mass stellar companions. After accounting for tidal influences, the eccentricity distribution aligns with that of low-mass stellar binaries, presenting a different profile than that observed within the giant planet population. Additionally, the metallicity of the host stars reveals a noteworthy trend: Short-period transiting brown dwarfs are predominantly associated with metal-rich stars, whereas long-period brown dwarfs are more often found around metal-poor stars, thus demonstrating statistical similarities to low-mass stellar hosts. This trend has been previously observed in studies of hot and cold Jupiters and points to a period-coded mixture of channels. A natural explanation is that most brown dwarfs originate from fragmentation at wider separations, with long-period systems retaining this stellar-like imprint, while only those embedded in massive, long-lived metal-rich protoplanetary disks are efficiently delivered and stabilized to short orbits.

Young stellar moving groups offer unique opportunities to investigate the early evolution of stellar and planetary systems. In continuation of an ongoing effort to age-date compelling planetary systems, we provide an in-depth age analysis of KELT-20—a young A-type star that hosts a well-aligned ultrahot Jupiter. This system poses a useful case study to investigate migration mechanisms at early stages of evolution. Using Gaia DR3 data, we identify 77 stars with proper motions consistent with KELT-20, including 19 with measured radial velocities that enable full 3D kinematic confirmation. Using isochronal analyses, gyrochronology, photometric variability, and stellar activity indicators, we converge on an age of 58 ± 5 Myr. This constraint provides critical insights into the dynamical processes shaping hot Jupiter formation.

We present four newly validated transiting brown dwarfs identified through TESS photometry and confirmed with high-precision radial velocity measurements obtained from the FEROS and PLATOSpec spectrographs. Notably, three of these companions exhibit orbital periods exceeding 100 days, thereby expanding the sample of long-period transiting brown dwarfs from two to five systems. The host stars of long-period brown dwarfs show mild subsolar metallicity. These discoveries highlight the expansion of the metal-poor, long-period distribution and help us better understand the brown dwarf desert. In our comparative analysis of eccentricity and metallicity demographics, we utilize catalogues of long-period giant planets, brown dwarfs, and low-mass stellar companions. After accounting for tidal influences, the eccentricity distribution aligns with that of low-mass stellar binaries, presenting a different profile than that observed within the giant planet population. Additionally, the metallicity of the host stars reveals a noteworthy trend: short-period transiting brown dwarfs are predominantly associated with metal-rich stars, whereas long-period brown dwarfs are more often found around metal-poor stars, demonstrating statistical similarities to low-mass stellar hosts. This trend has also been previously observed in studies of hot and cold Jupiters and points to a period-coded mixture of channels. A natural explanation is that most brown dwarfs originate from fragmentation at wider separations, with long-period systems retaining this stellar-like imprint, while only those embedded in massive, long-lived, metal-rich protoplanetary discs are efficiently delivered and stabilised to short orbits.