Rotation Period Research Articles (Page 1)

Abstract European beech is one of the most important tree species in Europe, however, its sensitivity to intensifying drought caused by climate change currently results in its decline. In our experiment in the Czech Republic, we investigated the impact of crop tree selective thinning (CTST) on radial increment of beech between years 1999 (2005 in the case of the younger stands, respectively) and 2021. Our modification of CTST is one of the adaptive measures for stabilization of even-aged temperate beech forests, where 30–50 crop trees/ha grow in a stand and where crowns are continuously released. Based on the periodic current diameter at breast height increment model, the crop trees responded to CTST by significant diameter increment accelerations (compared to unreleased crop trees), also throughout a drought period that occurred during the experiment. Due to this acceleration, the crop trees gradually increased their share of the growing stock (from 10% up to 37.7%). As a result, the crop trees achieved or will have achieved the target diameter of 50 cm already at the age of 73 or 64, respectively (depending on the stand age when CTST was first implemented). This reduces the ecological and economic risks of traditional beech silviculture with a long rotation period (between 100 and 120 years). In addition, the crop trees compensated volume loss due to thinning (intensity 37–112 m3ha−1) with no negative influence on production characteristics on the level of forest stand (growing stock 212–354 m3ha−1, total current volume increment 12.34 m3ha−1 year−1 in an older stand and 16.28 in a younger stand). We also observed that under CTST, the diameter distribution was approaching a reverse J-shaped curve with higher variability. Based on our findings, a modified CTST method represents a promising adaptive measure for enhancing the vitality of individual trees, and as a tool for conversion to an uneven-aged forest.

Abstract Based on the LAMOST and Gaia surveys, we compute the convective turnover timescales of stars with the mass range of 0.7-1.4 M⊙ using the MESA code. We provide a catalog of 10,400 FGK dwarfs in the LAMOST-Kepler field, including Rossby number Ro, rotation periods $\rm P_{\rm rot}$, photometric activity proxy Sph, and chromospheric activity index $R^{+}_{\rm HK}$. The relations between both activity indices and Ro can be characterized by the saturated, decay and flat regimes. In the flat regime, the Sph remains nearly constant while the $R^{+}_{\rm HK}$ exhibits an enhancement as Ro increases for F dwarfs. In the decay regime, all stars exhibit uniform decay behavior in both Sph-Ro and $R^{+}_{\rm HK}$-Ro relations. In the saturated regime, GK dwarfs display a significant Sph dip, while only K dwarfs exhibit a pronounced $R^{+}_{\rm HK}$ dip. Moreover, the Ro range of this dip aligns with the spin-down stalling observed in open cluster studies, suggesting a possible origin in the core-envelope coupling senario. Additionally, the results show that the Sun falls within the transition from decay to flat regime in both activity-Ro diagrams. The results will improve the understanding of the connection among convection, rotation, and magnetic fields for solar-like stars.

Studies of the rotational velocities of intermediate-mass main-sequence stars are crucial for testing stellar evolution theory. They often rely on spectroscopic measurements of the projected rotation velocities, V_ eq These not only suffer from the unknown projection factor sin,i but tend to ignore additional line-profile broadening mechanisms aside from rotation, such as pulsations and turbulent motions near the stellar surface. This limits the accuracy of V_ eq distributions derived from V_ eq measurements. We use asteroseismic measurements to investigate the distribution of the equatorial rotation velocity V_ eq, its ratio with respect to the critical rotation velocity, V_ eq /V_ crit and the specific angular momentum, J/M, for several thousands of BAF-type stars, covering a mass range from 1.3,M_⊙ to 8.8,M_⊙ and almost the entire core-hydrogen burning phase. We rely on high-precision model-independent internal rotation frequencies, as well as on masses and radii from asteroseismology to deduce V_̊m eq, $V_ ̊m eq /V_ crit $, and J/M for 2937 gravity-mode pulsators in the Milky Way. The sample stars have rotation frequencies between almost zero and 33μHz, corresponding to rotation periods above 0.35,d. We find that intermediate-mass stars experience a break in their J/M occurring in the mass interval $ M_⊙$. We establish unimodal V_̊m eq and $V_ ̊m eq /v_ ̊m crit $ distributions for the mass range $,M_⊙ while stars with M∈2.5,8.8,M_⊙ reveal some structure in their distributions. We find that the near-core rotation slows down as stars evolve pointing to very efficient angular momentum transport. The kernel density estimators of the asteroseismic internal rotation frequency, equatorial rotation velocity, and specific angular momentum of this large sample of intermediate-mass field stars can conveniently be used for population synthesis studies and to fine-tune the theory of stellar rotation across the main sequence evolution.

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Abstract Key message Anticipating establishment cuts in transitional high forests of beech ( Fagus sylvatica L.) is a sustainable strategy from both ecological and economic perspectives. It could be scaled over large areas to promote structural heterogeneity while minimizing disturbances. Context Beech forests, traditionally managed as coppices for firewood, have experienced significant changes in management practices, particularly in Southern Europe. This shift was especially noticeable in the Southern and Eastern Alps, where vast areas of coppice forests were gradually transformed into high forests, as fuelwood demand declined. However, large-scale regeneration cuts at the end of the rotation period can result in economic losses and environmental concerns. Aims We assessed whether applying regeneration cuts at 70 years in transitional high forests can effectively accelerate the coppice-to-high-forest conversion process, relative to the conventional rotation period of 120–140 years. Methods This study examines the possibility to implement regeneration cuts before the common rotation period in temporary high forests by applying four distinct treatments: (1) control—thinning from below; (2) shelterwood system—establishment cut; (3) clear-cut; and (4) crop tree release. Results We found significant differences in basal area, biomass, leaf area index after tree removal, and harvesting costs/venues, with the shelterwood system being the most economically advantageous treatment. Ten years after the treatment execution, the shelterwood treatment exhibited prompt and widespread regeneration compared to other regeneration treatments, with the highest seedling abundance (12 ± 2 seedlings m −2 ) and height of the established saplings (93 ± 6 cm). Conclusion Our findings support the idea of implementing and gradually scaling regeneration cuts in time and space using the group shelterwood system. This approach can increase the structural heterogeneity of forest stands, maintain consistent timber production, and minimize disturbances to fauna and other ecosystem services.

The Hyades cluster is key for the study of the rotational, activity, and chemical evolution of solar-like low-mass stars. We present quantitative surface-activity information for a sequence of 21 Hyades dwarf stars with effective temperatures 6160 K to 3780 K (all cooler than the red edge of the Li dip), rotation periods 5,d to 16,d, and normalized Rossby numbers ( between 0.14 to 0.54 with respect to the Sun (Ro(Sun)=1). High-resolution Stokes-V spectra and a least-squares deconvolution of thousands of spectral lines per spectrum were employed to measure the longitudinal surface magnetic field. We obtained the velocities, lithium abundances, metallicity, and chromospheric Ca ii infrared-triplet (IRT) fluxes from Stokes-I spectra. The average metallicity, +0.186±0.045 (rms), for our stars with T_ ̊m eff ≥ 4200,K agrees well with the metallicity in the recent literature. The lithium abundances A(Li) range from 95-times solar (A(Li)≈ +3.0) on the warm end of the sample to $1/25$ solar (A(Li)≈ -0.4) on the cool end. We confirm the tight relation of A(Li) with T_̊m eff and extend it to K--M stars with even lower Li abundances than previously measurable. A formal relation with rotational period and velocity in the sense of a higher Li abundance for faster rotators is present. Targets that rotate faster than v i of 6 ̨ms (P_ ̊m rot ≈ 8,d) appear to be Li saturated at A(Li)≈3.0,dex. The Ca ii IRT fluxes for our sample indicate (logarithmic) chromospheric radiative losses R^ IRT in the range -4.0 to -4.9 in units of the bolometric flux. These radiative losses are also related to T_̊m eff, P_̊m rot, and v i, but opposite to A(Li), in an inverse sense with higher radiative losses for the slower, that is, cooler rotators. Longitudinal magnetic field strengths were measured in the range zero to -100,G and $+150$,G with phase-averaged disk-integrated unsigned values łangle |B|̊angle of 15.4±3.6(rms),G for targets warmer than ≈5000,K and 91±61(rms),G for targets cooler than this. These unsigned field strengths are related to P_̊m rot, v i, and but in a dual-slope fashion. The short-period bona fide single M-target RSP,348 was found to be a double-lined spectroscopic binary with a classification dM3e+dM5e. We conclude that the dependence on Rossby number of the surface activity tracers A(Li), R^ IRT, and łangle |B|̊angle on our Hyades dwarf sequence primarily originates from convective motions, expressed by its turnover time, and only to a smaller and sometimes inverse extent from surface rotation and its related additional mixing.

We investigated the origin and stability of extrasolar satellites orbiting close-in gas giants, focusing on whether these satellites can survive planetary migration within a protoplanetary disk. To address this question, we used Posidonius an N-Body code with an integrated tidal model, which we expanded to account for the migration of a gas giant within a disk. Our simulations include tidal interactions between a $1 star and a $1 planet, and between the planet and its satellite, while neglecting tides raised by the star on the satellite. We adopted a standard equilibrium tide model for the satellite, planet, and star, and additionally explored the impact of dynamical tides in the convective regions of both the star and planet on satellite survival. We systematically examined key parameters, including the initial satellite-planet distance, disk lifetime (which serves as a proxy for the planet’s final orbital distance), satellite mass, and satellite tidal dissipation. For simulations incorporating dynamical tides in both the planet and star, we also explored three different initial stellar rotation periods. Our primary finding is that satellite survival is rare if the satellite has nonzero tidal dissipation. Survival is only possible for initial orbital distances of at least $0.6$ times the Jupiter-Io separation and for planets orbiting beyond ≈0.1 AU. Satellites that fail to survive are either tidally disrupted, as they experience orbital decay and cross the Roche limit, or dynamically disrupted, where eccentricity excitation drives their periastron within the Roche limit. Satellite survival is more likely for low tidal dissipation and higher satellite mass. Given that satellites around close-in planets appear unlikely to survive planetary migration, our findings suggest that if such satellites do exist (as has been recently suggested), another process should be invoked. In that context, we also briefly discuss the claim of the existence of a putative satellite around WASP-49 A b.

Abstract Understanding how exoplanet atmospheres evolve is a key question in the context of habitability. One key process governing this evolution is atmospheric evaporation by stellar X-ray and EUV emission (collectively, XUV). As such, the evolution of exoplanet atmospheres is closely tied to the evolution of the host star’s magnetic activity. Many studies have modelled the combined evolution of exoplanet atmospheres and their host stars. However, to date, the impact of the host star’s metallicity on stellar activity/exoplanet atmosphere evolution has not been explored. In this work, we investigate how stellar metallicity affects the rotation and activity evolution of solar-like stars as well as the corresponding exoplanet atmospheric evolution. We reconfirm previous results that metal-rich stars spin down more rapidly than metal-poor stars. We also find that the XUV flux that an exoplanet in the habitable zone of its host star receives is larger when the host star is more metal-rich. As such, the atmospheres of exoplanets in the habitable zones of metal-rich stars are evaporated more rapidly than exoplanets in the habitable zones of metal-poor stars. Lastly, we find that the atmospheric evolution is most sensitive to the host star metallicity when the host star has a higher mass. In the highest mass solar-stars, the metallicity can have a larger influence on the atmospheric evolution than the initial rotation period of the star.

Abstract We present the discovery of 30 new Galactic sources from the MeerTRAP project, a commensal fast radio transient search programme using the MeerKAT telescope. These sources were all identified via a single pulse search. Most of them are likely to be rotating radio transients (RRATs) given their low pulse rates. Using data captured in our transient buffer we have localised nine sources in the image domain to arcsecond precision. This facilitates the timing of these sources and further follow-up with other telescopes. Using the arrival times of single pulses, we have constrained the periods of 14 sources, ranging from 121 ms to 7.623 s, and derived a phase-coherent timing solution for one of them. Follow-up observations of the MeerTRAP sources (including those published previously) performed with the Effelsberg telescope have detected regular but faint emission from three sources, confirming their long rotation period, including PSR J2218+2902 with a period of 17.5 s, the fourth slowest in the radio pulsar population. A few of the sources exhibit interesting emission features, such as periodic microstructure in PSR J1243−0435 and possible nulling in PSR J1911−2020 and PSR J1243−0435. We find that the duty cycles of the three newly discovered pulsars are very low and follow the general trend for the duty cycle with period of known pulsars.

Abstract K-type stars are important objects of our Galaxy. It is interesting to determine the stellar physical parameters and magnetic activity properties of K-type stars. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope DR10 provides more than 1 million spectra of K-type stars. We have used spectra with a signal-to-noise ratio greater than 10 as our objects in the large amount of spectral data that we have analyzed. We used the spectral subtraction method to reduce the observational spectra by utilizing the iSpec program. We have determined the chromospheric activity of K-type stars using the H α line. Among more than 1.33 million spectra associated with about 1.06 million stars, there are a total of 150,000 stellar spectra that have excess chromospheric activity. For K stars with rotation periods above 6.20 days, the chromospheric activity decreases rapidly as the period increases. We calculated the solar Rossby number R O S u n = 1.85 , and conclude that when the Rossby number R O / R O Sun < 0.07 , R H α ′ remains stable; when R O / R O S u n ≥ 0.07 , R H α ′ decreases as R O / R O S u n increases. By crossmatching with the Gaia survey, we also determined their distances and found that the active fraction decreases as the distance above the Galactic disk increases.

Abstract In this study, we investigate the microstructure properties of four pulsars (PSRs J0953+0755 (B0950+08), J0627+0706, J0826+2637 (B0823+26), and J1946+1805 (B1944+17)) using the Five-hundred-meter Aperture Spherical radio Telescope, with particular emphasis on identifying microstructure within the interpulse (IP). Through the application of autocorrelation function analysis and fast Fourier transform techniques, we have systematically examined the periodicity of microstructure in these pulsars. Our findings represent the first successful detection of microstructure within the IP. Furthermore, we conducted a comprehensive statistical analysis comparing the characteristic timescales ( τ μ ) and the characteristic periods P μ of quasiperiodic microstructure between the main pulse (MP) and the IP, and our results indicate that the τ μ and P μ of microstructure across components appear consistent within measurement errors for PSR J0627+0706, but the microstructure in the IP is relatively smaller than that in the MP for PSR J0953+0755. Furthermore, the relationship between P μ of microstructure and the rotation period in neutron star populations was reconfirmed: P μ (ms) = (1.337 ± 0.114) × P (s) (1.063±0.038) .

Abstract The “Neptunian ridge” is a recently identified peak in the frequency of planets with sizes between that of Neptune and Saturn orbiting their host stars with periods between 3 and 6 days. These planets may have formed similarly to their larger, hot Jupiter counterparts in the “3 day pileup,” through a dynamically excited migration pathway. The distribution of stellar obliquities in hot Neptune systems may therefore provide a vital clue as to their origin. We report a new stellar obliquity measurement for TOI-2374b, a planet in the Neptunian ridge ( P = 4.31 days, R p = 7.5 R ⊕ ). We observed a spectroscopic transit of TOI-2374b with the Keck Planet Finder, detecting the Rossiter–McLaughlin (RM) anomaly with an amplitude of 3 m s −1 , and measured a sky-projected obliquity of λ = 81 ° − 2 2 ∘ + 2 3 ∘ , indicating an orbit significantly misaligned with the spin axis of its host star. A reloaded RM analysis of the cross-correlation functions confirms this misalignment, measuring λ = 65 ° − 2 4 ∘ + 3 2 ∘ . Additionally, we measured a stellar rotation period of P rot = 26 . 4 − 0.8 + 0.9 days with photometry from the Tierras observatory, allowing us to deduce the three-dimensional stellar obliquity of ψ = 85 . ° 9 − 9 . ° 2 + 8 . ° 6 . TOI-2374b joins a growing number of hot Neptunes on polar orbits. The high frequency of misaligned orbits for Neptunian ridge and desert planets, compared with their longer period counterparts, is reminiscent of patterns seen for the giant planets and may suggest a similar formation mechanism.

Describing the large-scale field topology of protoplanetary disks (PPDs) involves significant difficulties and uncertainties. The transport of the large-scale field inside the disk plays an important role in understanding its evolution. We aim to improve our understanding of the dependences that stellar magnetic fields pose on the large-scale field. We focus on the innermost disk region (łesssim 0.1 AU), which is crucial for understanding the long-term disk evolution. We present a novel approach combining the evolution of a 1+1D hydrodynamic disk with a large-scale magnetic field consisting of a stellar dipole truncating the disk and a fossil field. The magnetic flux transport includes advection and diffusion due to laminar non-ideal magnetohydrodynamic (MHD) effects, such as Ohmic and ambipolar diffusion. Due to the implicit nature of the numerical method, long-term simulations (of the order of several viscous timescales) are feasible. The large-scale magnetic field topology in stationary models shows a distinct dependence on specific parameters. The innermost disk region is strongly affected by the stellar rotation period and magnetic field strength. The outer disk regions are affected by the X-ray luminosity and the fossil field. Varying the mass flow through the disk affects the large-scale disk field throughout its radial extent. The topology of the large-scale disk field is affected by several stellar and disk parameters. This will affect the efficiency of MHD outflows, which depend on the magnetic field topology. Such outflows might originate from the very inner disk region, the dead zone, or the outer disk. In subsequent studies, we will use these models as a starting point for conducting long-term evolution simulations of the disk and large-scale field on scales of ∼ 10^6 years in order to investigate the combined evolution of the disk, the magnetic field topology, and the resulting MHD outflows.

Abstract Contamination from nearby sources often compromises stellar rotation periods derived from photometric light curves, particularly in data with large pixel scales such as The Transiting Exoplanet Survey Satellite (TESS). This problem is compounded when both the target and contaminant are intrinsically variable, a scenario that challenges deblending algorithms, which often assume constant contaminants. We assess the reliability of rotation period detections using wide binary systems, whose components share a common age and rotational history. By applying gyrochronology constraints, we identify period combinations that yield consistent ages between components, helping to isolate true rotation signals. Simulating blends with degraded Kepler data, our method recovers correct rotation periods with an 88% success rate for periods <12 days, where TESS detections are most reliable. Applying this framework to nearly 300 wide binaries observed by TESS, we find that, despite significant contamination, a subset of pairs shows consistent gyrochronological ages. We establish a practical detection threshold for TESS blended observations, finding that periods shorter than ∼8 days are reliably recovered, while those longer than ∼10 days become significantly more challenging and often remain inconclusive. As expected, rotation periods are more often recovered when the highest-amplitude periodogram peak is linked to the brighter star and the second to the dimmer star. However, many cases deviate from this pattern, indicating it cannot always be assumed. Our results highlight the limitations of standard deblending methods and demonstrate that astrophysical constraints, such as gyrochronology, provide a valuable tool for extracting reliable rotation periods from complex photometric blends.

Recent discoveries show that asteroids spinning in less than a few minutes undergo sizeable semi-major axis drifts, possibly driven by the Yarkovsky effect. Analytical formulas can match these drifts only if very low thermal inertia is assumed, implying a dust-fine regolith or a highly porous interior that is difficult to retain under such extreme centrifugal forces. With analytical theories of the Yarkovsky effect resting on a set of assumptions, their applicability to cases of super-fast rotation should be verified. We aim to evaluate the validity of the analytical models in such scenarios and to determine whether the Yarkovsky effect can explain the observed drift in rapidly rotating asteroids. We have developed a numerical model of the Yarkovsky effect tailored to super-fast rotators. The code resolves micrometer-scale thermal waves on millisecond time steps, capturing the steep gradients that arise when surface thermal inertia is extremely low. A new 3D heat-conduction and photon-recoil solver was benchmarked against the THERMOBS thermophysical code and the analytical solution of the Yarkovsky effect, over a range of rotation periods and thermal conductivities. The analytical Yarkovsky drift agrees well with the numerical solver. For thermal conductivities from $0.0001$ to $1$ mathrm W m^ K^ and spin periods as short as 10 s, the two solutions differ by no more than $15%$. This confirms that the observed semi-major axis drifts for super-fast rotators can be explained by the Yarkovsky effect and very low thermal inertia. Applied to the 34-s rapid rotator 2016 GE1, the best match of the measured drift was obtained with Gammałesssim20 mathrm J m^ K^ s^ a value that implies ∼100 K temperature swings each spin cycle. Analytical Yarkovsky expressions remain reliable down to spin periods of a few tens of seconds. The drifts observed in super-fast rotators require low-Γ surfaces and might point to rapid thermal fatigue as a regolith-generation mechanism.

Abstract We present a spectroscopic and photometric study of HIP12653 to investigate its magnetic cycle and differential rotation. Using HARPS archival spectra matched with MARCS-AMBRE theoretical templates, we derive the stellar parameters (Teff, logg, FeH, and vsini) of the target. The S-index, an activity indicator based on the emission of the Ca II H& K lines, is fitted to determine the magnetic cycle and rotation periods. We refine the magnetic cycle period to 5799.20 ± 0.88 days and suggest the existence of a secondary, shorter cycle of 674.6922 ± 0.0098 days, making HIP12653 the youngest star known to exhibit such a short activity cycle. During the minimum activity phase, a rotation period of 4.8 days is estimated. This is notably different from the 7 day period obtained when measurements during minimum activity are excluded, suggesting that these two periods are rotation periods at different latitudes. To explore this hypothesis, we introduce a novel light curve fitting method that incorporates multiple harmonics to model different spot configurations. Applied to synthetic light curves, the method recovers at least two rotation periods close to the true input values (within three times their uncertainties) in 92.1% of cases. The inferred rotation shear shows a median deviation of 0.0011 ± 0.0003 and a standard deviation of 0.0177 ± 0.0002 from the true value. Applying this approach to TESS photometric data from 2018 to 2023, we detect three distinct rotation periods—4.8 days, 5.7 days, and 7.7 days, (along with a signal at 3.75 days interpreted as its first harmonic)—consistent with spots located at different latitudes. Assuming a solar-like differential rotation, we estimate an inclination of 34 . ° 0 ± 1 . ° 8 and a rotational shear of α = 0.38 ± 0.01. These results confirm the 4.8 day period and demonstrate that differential rotation can be constrained by tracking rotation period changes across different phases of the magnetic cycle.

Understanding the rotational periods of asteroids is crucial for gaining insights into their internal structures, compositions, and collisional histories. NASA's Kepler Space Telescope, during its K2 extension (2014-2018), serendipitously observed numerous asteroids while surveying the ecliptic plane, providing a unique photometric dataset. By analyzing photometric data from the K2 mission, we aimed to determine the rotational periods of asteroids that crossed Kepler 's field of view, focusing on objects with an apparent magnitude of 19 or brighter that appeared in the Kepler target pixel files at least ten times. We developed an algorithm to identify asteroid crossings in the Kepler data and extract photometric light curves. The Lomb-Scargle periodogram method was employed to determine the rotational periods from the extracted light curves due to its robustness in handling unevenly sampled data. Noise and systematic errors were mitigated through photometric corrections using co-trending basis vectors. We extracted and analyzed brightAsteroidsObserved light curves from brightAsteroids asteroids observed during the Kepler /K2 mission. This allowed us to compute rotation periods for PeriodsDetermined asteroids. We found that AsteroidsWithKnownPeriods of these asteroids had previously known periods. The rotation periods determined for of the asteroids in this study agree with existing asteroid rotation periods from the literature, validating our approach. We report new rotation periods and their light curve amplitudes for NewPeriods asteroids, expanding the catalog of known asteroid rotation periods. The analysis of rotation periods from the Kepler K2 mission data has provided valuable insights into the physical characteristics of main-belt asteroids. Our results are consistent with existing data and expand the catalog of known asteroid rotation periods. These findings contribute to our understanding of asteroid dynamics and will aid future research in planetary science and asteroid exploration.

Abstract The dynamical evolution of short-period low-mass binary stars (with mass M < 1.5M ⊙, from formation to the late main sequence, and with orbital periods less than ∼10 days) is strongly influenced by tidal dissipation. This process drives orbital and rotational evolution that ultimately results in circularized orbits and rotational frequencies synchronized with the orbital frequency. Despite the fundamental role of tidal dissipation in binary evolution, constraining its magnitude (typically parameterized by the tidal quality factor Q ) has remained discrepant by orders of magnitude in the existing literature. Recent observational constraints from time-series photometry (e.g., Kepler, K2, TESS), as well as advances in theoretical models to incorporate a more realistic gravitational response within stellar interiors, are invigorating new optimism for resolving this long-standing problem. To investigate the prospects and limitations of constraining tidal Q , we use global sensitivity analysis and simulation-based inference to examine how the initial conditions and tidal Q influence the observable orbital and rotational states. Our results show that, even under the simplest and most tractable models of tides, the path toward inferring Q from individual systems is severely hampered by inherent degeneracies between tidal Q and the initial conditions, even when considering the strongest possible constraints (i.e., binaries with precise masses, ages, orbital periods, eccentricities, and rotation periods). Finally, as an alternative, we discuss how population synthesis approaches may be a more promising path forward for validating tidal theories.

Abstract Magnetospheric accretion is a key process that shapes the inner disks of T Tauri stars, controlling mass and angular momentum evolution. It produces strong ultraviolet and optical emission that irradiates the planet-forming environment. In this work, we characterize the magnetospheric geometries, accretion rates, extinction properties, and hotspot structures of 67 T Tauri stars in the largest and most consistent study of ultraviolet and optical accretion signatures to date. To do so, we apply an accretion flow model to velocity-resolved Hα profiles for T Tauri stars from the Hubble Space Telescope (HST) ULLYSES program with consistently derived stellar parameters. We find typical magnetospheric truncation radii to be almost half of the usually assumed value of 5 stellar radii. We then model the same stars’ HST/STIS spectra with an accretion shock model, finding a diverse range of hotspot structures. Phase-folding multiepoch shock models reveals rotational modulation of observed hotspot energy flux densities, indicative of hotspots that persist for at least three stellar rotation periods. For the first time, we perform a large-scale, self-consistent comparison of accretion rates measured using accretion flow and shock models, finding them to be consistent within ∼0.16 dex for contemporaneous observations. Finally, we find that up to 50% of the total accretion luminosity is at short wavelengths accessible only from space, highlighting the crucial role of ultraviolet spectra in constraining accretion spectral energy distributions, hotspot structure, and extinction.

The rotation periods of Ap stars range over five to six orders of magnitude. The origin of their differentiation remains unknown. We carry out a systematic study of the longest period Ap stars to gain insight into their properties. We analysed newly obtained spectra of a sample of super-slowly rotating Ap (ssrAp) star candidates identified by a TESS photometric survey to confirm that their projected equatorial velocity, ši, is consistent with (very) long rotation periods; to obtain a first determination of their magnetic fields; and to test their binarity. The value of ši in 16 of the 18 studied stars is low enough for them to have moderately to extremely long rotation periods. All stars but one are definitely magnetic; for five of them, the magnetic field was detected for the first time. Another set of five new stars with resolved magnetically split lines were discovered. Five of the stars that were not previously known to be spectroscopic binaries were found to show radial velocity variations, and in one of them, lines from both components were observed.