Orbital Velocity Research Articles

A new expression for free stream velocity with skewness and asymmetry

A new expression for skewed and asymmetric free stream velocities (near-bed wave orbital velocities at the edge of the wave boundary layer) is established in this paper. A comparison of the new expression with others is examined, and the new expression is found to be more satisfactorily fitted to wave orbital velocities with comparatively strong skewness and weak asymmetry than those presented by Abreu et al. (2010) and Malarkey and Davies (2012). Methods for determining the parameters in the new expression based on the Ursell number Ur are presented, and consequently, two empirical formulae are recommended for estimating bedload and suspended load sand transport rates related to wave skewness, respectively. Reasonability of the new expression for irregular waves is discussed by comparing the predicted time averaged quantities to those calculated by measured data, and good agreement is found.

The GAPS Programme at TNG

Aims. We present a novel method for studying the thermal emission of exoplanets as a function of orbital phase at very high spectral resolution, and use it to investigate the climate of the ultra-hot Jupiter KELT-9b. Methods. We combine three nights of HARPS-N and two nights of CARMENES optical spectra, covering orbital phases between quadratures (0.25 < φ < 0.75), when the planet shows its day-side hemisphere with different geometries. We co-add the signal of thousands of Fe I lines through cross-correlation, which we map to a likelihood function. We investigate the phase-dependence of two separate observable quantities, namely (i) the line depths of Fe I and (ii) their Doppler shifts, introducing a new method that exploits the very high spectral resolution of our observations. Results. We confirm a previous detection of Fe I emission, and demonstrate a precision of 0.5 km s−1 on the orbital properties of KELT-9b when combining all nights of observations. By studying the phase-resolved Doppler shift of Fe I lines, we detect an anomaly in the planet's orbital radial velocity well-fitted with a slightly eccentric orbital solution (e = 0.016 ± 0.003, ω = 150−11+13°, 5σ preference). However, we argue that this anomaly is caused by atmospheric circulation patterns, and can be explained if neutral iron gas is advected by day-to-night atmospheric wind flows of the order of a few km s−1. We additionally show that the Fe I emission line depths are symmetric around the substellar point within 10° (2σ), possibly indicating the lack of a large hot-spot offset at the altitude probed by neutral iron emission lines. Finally, we do not obtain a significant preference for models with a strong phase-dependence of the Fe I emission line strength. We show that these results are qualitatively compatible with predictions from general circulation models (GCMs) for ultra-hot Jupiter planets. Conclusions. Very high-resolution spectroscopy phase curves are of sufficient sensitivity to reveal a phase dependence in both the line depths and their Doppler shifts throughout the orbit. They constitute an under-exploited treasure trove of information that is highly complementary to space-based phase curves obtained with HST and JWST, and open a new window onto the still poorly understood climate and atmospheric structure of the hottest planets known to date.

Rocky Histories: The Effect of High Excitations on the Formation of Rocky Planets

Rocky planets both in and outside of our solar system are observed to have a range of core-mass fractions (CMFs). Imperfect collisions can preferentially strip mantle material from a planet, changing its CMF, and are therefore thought to be the most likely cause of this observed CMF variation. However, previous work that implements these collisions into N-body simulations of planet formation has struggled to reliably form high CMF super-Earths. In this work, we specify our initial conditions and simulation parameters to maximize the prevalence of high-energy, CMF-changing collisions in order to form planets with highly diverse CMFs. High-energy collisions have a large v imp/v esc ratio, so we maximize this ratio by starting simulations with high eccentricity and inclination disks to increase the difference in their orbital velocities, maximizing v imp. Additionally, we minimize v esc by starting with small embryos. The final planets undergo more high-energy, debris-producing collisions, and experience significant CMF change over their formation. However, we find that a number of processes work together to average out the CMF of a planet over time; therefore, we do not consistently form high CMF, high-mass planets. We do form high CMF planets below 0.5 M ⊕. Additionally, we find, in these highly eccentric environments, loss of debris mass due to collisional grinding has a significant effect on final planet masses and CMFs, resulting in smaller planets and a higher average planet CMF. This work highlights the importance of improving measurements of high-density planets to better constrain their CMFs.

Steady-state entanglement for rotating Unruh-DeWitt detectors

The Unruh-DeWitt model of particle detector is widely used to probe quantum effects in noninertial frames and curved spacetimes. In this paper, we investigate the entanglement dynamics of a quantum system composed of two rotating Unruh-DeWitt detectors in interaction with a fluctuating massless scalar field in vacuum. We obtain the necessary and sufficient condition for the detectors to achieve steady-state entanglement, and systematically investigate the steady-state entanglement of two Unruh-DeWitt detectors rotating in coaxial orbits with the same orbital radius and angular velocity. When the separation between the detectors is vanishing, the detectors can obtain steady-state entanglement dependent on the initial state, as the detectors in uniform acceleration and static detectors in a thermal bath do. Remarkably, however, when the separation between the detectors is nonvanishing but small compared with the transition wavelength of detectors, the detectors can obtain steady-state entanglement irrespectively of what the initial state is. This is the unique phenomenon caused by the centripetal acceleration and is not present in the uniform acceleration case and the case of static detectors in a thermal bath.

LAMOST meets Gaia: The Galactic open clusters

Open clusters (OCs) are born and evolve along the Milky Way (MW) plane. On them is imprinted the history of the Galactic disc, including its chemical and dynamical evolution. Chemical and dynamical properties of OCs can be derived from photometric, spectroscopic, and astrometric data of their member stars. Based on the photometric and astrometric data from the Gaia mission, the membership of stars in more than two thousand Galactic clusters has been identified in the literature. The chemical properties (e.g. metallicity) and kinematical properties (e.g. radial velocity), however, are still poorly known for many of these clusters. In synergy with the large spectroscopic survey LAMOST (data release 8) and Gaia (data release 2), we report a new comprehensive catalogue of 386 OCs. This catalogue has homogeneous parameter determinations of radial velocity, metallicity, and dynamical properties, such as orbit, eccentricity, angular momenta, total energy, and 3D Galactic velocity. These parameters enable the first radial velocity determination for 44 clusters, and the first spectroscopic [Fe/H] determination for 137 clusters. The metallicity distributions of the majority of clusters show falling trends in the parameter space of the Galactocentric radius, the total energy, and the Z component of angular momentum, except for two old groups that show flat tails in their own parameter planes. Cluster populations of ages younger and older than 500 Myr distribute diversely on the disc. The latter have a spatial consistency with the Galactic disc flare. The 3D spatial comparison between very young clusters (< 100 Myr) and nearby molecular clouds revealed a wide range of metallicity distribution along the Radcliffe gas cloud wave, indicating a possible inhomogeneous mixing or fast star formation along the wave. This catalogue will serve the community as a useful tool to trace the chemical and dynamical evolution of the MW.

High-resolution atmospheric retrievals of WASP-121b transmission spectroscopy with ESPRESSO: Consistent relative abundance constraints across multiple epochs and instruments

ABSTRACT Recent progress in high-resolution transmission spectroscopy has offered new avenues in which to characterize the atmospheres of transiting exoplanets. High-resolution cross-correlation spectroscopy allows for the unambiguous detection of molecules/atoms. It has also been used to map both atmospheric dynamics and longitudinal variations in the abundance of species across the morning and evening limbs. We present multiple Very Large Telescope (VLT)/Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) observations of the ultrahot Jupiter WASP-121b, from which we constrain relative abundances of various neutral metals consistently across all observations, whilst accounting for the distortion of the exoplanet’s signal caused by traditional data processing techniques. We also constrain planetary orbital velocities and T–P profiles. We compare our abundance constraints with previous constraints using VLT/Ultraviolet and Visual Echelle Spectrograph (UVES) transmission spectroscopy of WASP-121b, and find our results to be consistent between observations, and also in agreement with stellar values for species previously detected in the atmosphere of WASP-121b. Our retrieval framework can also be used to identify potential exospheric species, resulting in extended absorption features beyond the transit equivalent Roche limit of WASP-121b (ReqRL ∼ 1.3 Rp). Hα, Fe ii, and Ca ii were found to extend to high altitudes (1.54 ± 0.04 Rp, 1.17 ± 0.01 Rp, and 2.52 ± 0.34 Rp, respectively), which are broadly consistent with literature values. The consistency of our constraints across multiple high-resolution observations is a strong validation of our model filtering and retrieval framework, as well as the stability of the atmosphere over the time-scales of months/years, and could allow for planet formation processes to be inferred from future ground-based observations of exoplanetary atmospheres.

A Numerical Investigation of the Energy Efficiency Enhancement of Oscillating Water Column Wave Energy Converter Systems

This work focuses on the geometry effects over the performance of oscillating water column (OWC)-type wave energy converter (WEC) systems and searches for the OWC geometries that enhance the energy efficiencies under the same wave conditions. To analyze the hydrodynamic performances of the WEC systems, an in-house smoothed particle hydrodynamics (SPH) code based on weakly compressible fluid approach is utilized. The energy efficiency enhancement studies of the determined OWC device are carried out with a two-step geometry modification procedure. The first step starts with the validation of the free-surface elevation and orbital velocity time histories. Then, a three-by-three simulation matrix that depends on the geometrical design parameters of chamber length and front wall draft is run at three different wave conditions, and the OWC geometry that produces the maximum energy efficiency is determined. In the second step, the corner regions of the obtained optimal geometry are chamfered, and another simulation matrix is tested at the wave condition that yields maximum wave energy. It is observed in this step that the energy efficiency index can still be improved by 4.3% by only chamfering the back face of the OWC chamber. To scrutinize the physical grounds of this increase, the correlation between the time-averaged vorticity and energy efficiency is presented. Finally, the performance of the best configuration is also examined in three different wave periods, where the suggested geometry shows better performance with respect to base geometry results in all wave conditions.

Magnetised winds in transition discs

Context. Protoplanetary discs are cold, dense, and weakly ionised environments that witness planetary formation. Among these discs, transition discs (TDs) are characterised by a wide cavity (up to tens of au) in the dust and gas distribution. Despite this lack of material, a considerable fraction of TDs are still strongly accreting onto their central star, possibly indicating that a mechanism is driving fast accretion in TD cavities. Aims. The presence of radially extended ‘dead zones’ in protoplanetary discs has recently revived interest in magnetised disc winds (MDWs), where accretion is driven by a large magnetic field extracting angular momentum from the disc. We propose that TDs could be subject to similar disc winds, and that these could naturally explain the fast-accreting and long-lived cavities inferred in TDs. Methods. We present the results of the first 2.5D global numerical simulations of TDs harbouring MDWs using the PLUTO code. We imposed a cavity in the gas distribution with various density contrasts, and considered a power-law distribution for the large-scale magnetic field strength. We assume the disc is weakly ionised and is therefore subject to ambipolar diffusion, as expected in this range of densities and temperatures. Results. We find that our simulated TDs always reach a steady state with an inner cavity and an outer ‘standard’ disc. These models also maintain an approximately constant accretion rate through the entire structure, reaching 10−7 M⊚ yr−1 for typical surface density values. The MDW launched from the cavity is more magnetised and has a significantly larger lever arm (up to 10) than the MDW launched from the outer disc. The material in the cavity is accreted at sonic velocities, and the cavity itself is rotating at 70% of the Keplerian velocity due to the efficient magnetic braking imposed by the MDW. Overall, our cavity matches the dynamical properties of an inner jet emitting disc (JED) and of magnetically arrested discs (MADs) in black-hole physics. Finally, we observe that the cavity is subject to recurring accretion bursts that may be driven by a magnetic Rayleigh-Taylor instability of the cavity edge. Conclusions. Some strongly accreting TDs could be the result of magnetised wind sculpting protoplanetary discs. Kinematic diagnostics of the disc or the wind (orbital velocity, wind speeds, accretion velocities) could disentangle classic photo-evaporation from MDW models.

Detecting H2O with CRIRES+: WASP-20b

Context. Infrared spectroscopy over a wide spectral range and at the highest resolving powers (R > 70 000) has proved to be one of the leading techniques to unveil the atmospheric composition of dozens of exoplanets. The recently upgraded spectrograph CRIRES instrument at the Very Large Telescope (CRIRES+) was operative for a first science verification in September 2021, and its new capabilities in atmospheric characterization were ready to be tested. Aims. We analyzed transmission spectra of the hot Saturn WASP-20b in the K band (1981–2394 nm) that were acquired with CRIRES+ with the aim to detect the signature of H2O and CO. Methods. We used a principal component analysis to remove dominant time-dependent contaminating sources such as telluric bands and the stellar spectrum. We extracted the planet spectrum by cross-correlating observations with 1D and 3D synthetic spectra, without circulation. Results. We present the tentative detection of molecular absorption from water vapor at a signal-to-noise ratio equal to 4.2 and 4.7 by using only H2O 1D and 3D models, respectively. The peak of the cross-correlation function occurred at the same rest-frame velocity for both model types (Vrest = −1 ± 1 km s−1 ) and at the same projected orbital velocity of the planet, but with different error bands (1D model: Kp = 131 −29+18 k ms −1; 3D: Kp = 131 −39+23 k ms −1). Our results agree with the result expected in the literature (132.9 ± 2.7 km −1). Conclusions. Although the observational conditions were not ideal and we had problems with the pipeline in calibrating and reducing our raw data set, we obtained the first tentative detection of water in the atmosphere of WASP-20b. We suggest a deeper analysis and additional observations to confirm our results and unveil the presence of CO.

Characterizing bedforms in shallow seas as an integrative predictor of seafloor stability and the occurrence of macrozoobenthic species

AbstractIn soft‐bottom marine ecosystems, bedform variation is induced by wind‐ and tidal‐driven hydrodynamics. The resulting megaripples, sand waves and sandbanks form a spatially and temporally heterogeneous seafloor landscape. The strong physical forces imposed by the migration of these bedforms are important determinants for the occurrence of different macrozoobenthic species. Quantifying the effect of these forces can help in differentiating natural‐ and anthropogenically induced physical stressors. However, large‐scale mapping of seabed morphology at high resolution using multibeam echosounder is challenging, costly and time‐consuming, especially in shallow seas, prohibiting wide swaths. Instead, their bathymetry is typically studied using single‐beam transects that are interpolated to bathymetric grids with a relatively coarse resolution (20 m). However, this leaves out information on smaller scale (<20 m) bedforms that can be ecologically relevant. In the Dutch Wadden sea, a shallow tidal system, we characterized bedform variation at high resolution using single‐beam data for the first time. We calculated a 2‐D Terrain Ruggedness Index (TRI) at sub‐meter resolution along the single‐beam transects and interpolated the results to a full 3‐D grid. We then validated the result by relating TRI to independently modeled hydrodynamic parameters and to the distribution of macrozoobenthic species. We found that TRI successfully integrates the variation of tidal‐driven bed shear stress and wave‐driven orbital velocity. In addition, we found TRI to be a good predictor of the occurrence of macrozoobenthic species. The inferred small‐scale bedforms provide valuable information for separating the relative importance of natural dynamics versus anthropogenic disturbances such as dredging and bottom trawling activities. We discuss that by repurposing already available single‐beam data in this way, bedforms can be characterized at high resolution without the need for additional equipment or mapping campaigns, yielding novel input to decision‐making on marine management and conservation.

Modified formula for predicting the maximum wave force on seabed objects

A modified wave-force formula, which predicts the maximum horizontal wave force on seabed objects, was developed using the velocity semi-amplitude, defined as half the difference between successive negative (offshore) and positive (onshore) peaks in the near-bed wave orbital velocity, and the corresponding peak-to-peak period. The formula was tested by analyzing wave-force data from three differently shaped structure models under random wave conditions and comparing its prediction accuracies with those of the Morison equation and the conventional wave-force formula based on the positive peak velocity. The maximum forces for individual zero-down-crossing velocity waveforms were predicted by applying each of the respective formulas with force coefficient(s) empirically pre-determined as a function of the Keulegan—Carpenter number. For all wave conditions and model structures, the modified formula was more accurate than the Morison equation, whereas the conventional formula was less accurate. Although the absolute relative prediction error increased as the velocity skewness deviated from 0.5, the increase in the error was least pronounced for the modified formula. The results also demonstrated that the highest maximum wave forces in random wave trains can be predicted with reasonable accuracy by the proposed formula using the highest value of the velocity semi-amplitude and the corresponding period.

Calibration scheme for space-borne full-disk vector magnetograph under the influence of orbiter velocity

Context. The Full-disk Vector MagnetoGraph (FMG) is one of the three payloads on the Advanced Space-based Solar Observatory (ASO-S). The FMG is set to observe the full disk vector magnetic field at a single wavelength point. The magnetograph in orbit will encounter the wavelength shift problem caused by the Doppler effect in the magnetic field, which mainly comes from the Sun’s rotation velocity and the satellite–sun relative velocity. Aims. We look to use neural networks for single-wavelength calibration to solve the wavelength shift problem. Methods. We used the existing data from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). To simulate plausible single-wavelength observations, we used the Stokes polarization image from the HMI at a single wavelength point. We also input the satellite orbital velocity given by the HMI data file and the solar rotation velocity to the network. We developed a set of data preprocessing methods before entering the network and we trained the network to get the calibration model. Results. By analyzing and comparing the prediction of the neural network with the target magnetogram, we believe that our network model has learned a single-wavelength full-disk calibration model. The mean absolute error (MAE) of the longitudinal field and the transverse field of the full disk are 3.68 G and 28.08 G, respectively. The MAE error of the azimuth angle of pixels above 300 G is 12.29°.

Swift and XMM–Newton observations of an RS CVn-type eclipsing binary SZ Psc: superflare and coronal properties

ABSTRACT We present an in-depth study of a large and long duration (>1.3 d) X-ray flare observed on an RS CVn-type eclipsing binary system SZ Psc using observations from Swift observatory. In the 0.35–10 keV energy band, the peak luminosity is estimated to be 4.2 × 1033 $\rm {erg}~\rm {s}^{-1}$. The quiescent corona of SZ Psc was observed ∼5.67 d after the flare using Swift observatory, and also ∼1.4 yr after the flare using the XMM–Newton satellite. The quiescent corona is found to consist of three temperature plasma: 4, 13, and 48 MK. High-resolution X-ray spectral analysis of the quiescent corona of SZ Psc suggests that the high first ionization potential (FIP) elements are more abundant than the low-FIP elements. The time-resolved X-ray spectroscopy of the flare shows a significant variation in the flare temperature, emission measure, and abundance. The peak values of temperature, emission measure, and abundances during the flare are estimated to be 199 ± 11 MK, 2.13 ± 0.05 × 1056 cm−3, 0.66 ± 0.09 $\rm {Z}_{\odot }$, respectively. Using the hydrodynamic loop modelling, we derive the loop length of the flare as 6.3 ± 0.5 × 1011 cm, whereas the loop pressure and density at the flare peak are derived to be 3.5 ± 0.7 × 103 dyn cm−2 and 8 ± 2 × 1010 cm−3, respectively. The total magnetic field to produce the flare is estimated to be 490 ± 60 G. The large magnetic field at the coronal height is supposed to be due to the presence of an extended convection zone of the subgiant and the high orbital velocity.

The lower shoreface of the Dutch coast – An overview

The lower shoreface, defined here as between about 8 and 20 m water depth, forms the transition between the inner shelf and upper shoreface. Knowledge of lower shoreface hydro- and morphodynamics is essential for coastal management and maintenance.The shoreface of the Dutch coast is a complex area. It is partly determined by its evolution in the past, whereas present-day processes are influencing or even changing it. The present situation and large-scale anthropogenic supply of sediment will determine its future development.The shoreface morphology varies along the Dutch coast, depending on the coastal slope and superposition of ridges (central Holland coast) and ebb-tidal deltas (Delta area, Wadden Sea). The architecture of the shoreface-connected ridges off the central Holland coast indicates that they are still active today. The development of most ebb-tidal deltas along the Dutch coast is largely influenced by interventions in the tidal inlets and tidal basins.The Kustgenese 2.0 Lower Shoreface project comprised both field data collection in 2017 and 2018 and numerical modelling. Field data was collected in study areas at Ameland Inlet, Terschelling and Noordwijk. Sediment cores and multibeam sonar surveys provided information on the Holocene deposits, geomorphology and sediments. Instrumented frames placed at the seabed collected a wealth of process data.The variation in shoreface composition and morphology is larger than anticipated previously. In general, the lower part of the shoreface consists of older Holocene deposits overlain by an active sand layer that responds to variations in tidal, wave and wind conditions. The deposits at the lower shoreface of Terschelling were comparable to the ebb-delta channel deposits at the ebb-delta front at Ameland Inlet. At Noordwijk, deposits of the Late-Holocene prograded barrier shoreface overlie those of back-barrier tidal channels and river channels. The large-scale morphology of the lower shoreface seems rather stable. Decadal time series show an erosional trend. Small-scale bedforms can change over an interval of days to weeks.The multibeam surveys revealed unexpected details such as geology-based shoreface irregularities between −12m and −18m that probably act as conduits for downslope currents and sand transport. After a high-energy wave event, more erosional features were discovered that suggest seaward sand transport.Measured orbital velocities at the seabed at 14–16 m depth reached 1.5 m per second under high-wave events. This caused high sediment mobility under sheet-flow conditions with abundant sediment suspension. It is not clear what this means for the net sand transport at the lower shoreface.The modelled alongshore-directed sand transport is much larger than the cross-shore transport. The largest transports at the 20m depth contour occurs along the northern part of the Holland coast. Here, transport is parallel to the coast or directed to deeper water. Transports at 20 m depth along the other parts of the coast are directed to shallower water.The modelled total landward sand transport over the −20m contour is c. 4 million m3 per year and c. 7 million m3 per year over the −16m contour. This suggests a yearly erosion of c. 4 million m3 in-between, in case of no alongshore transport gradients.The results of the sand transport calculations imply a net landward sediment transfer that needs to be further tested against the morphological changes in the shoreface.

Modeling Long-term Variability in Stellar-compact Object Binary Systems for Mass Determinations

This work models the effects of gravitational lensing, Doppler boosting, and ellipsoidal variations on eccentric eclipsing binary-system light curves. This is accomplished using a Newtonian orbital-motion code that simulates the orbital velocities and separation of the binary components as a function of time. Improving on previous literature, we examine the effects of orbital eccentricity and period, as well as stellar limb darkening on the expected light curves. Whether lensing, Doppler boosting, or ellipsoidal variation is dominant in the light curves is a function of the separation between the binary components; thus, the combination of all three effects allows for a unique mass-determination method that greatly expands the parameter space for the discovery of compact objects. This suggests the exciting possibility of revealing a large population of nonaccreting compact objects in galactic binary systems. At the same time, the model can be used on systems exhibiting any subset of these effects. In a case study, we fit our model to optical data from the ellipsoidal variable binary system Cygnus X-1, and we compare our determinations with those previously found by different modeling techniques.

Sobre la disipación de energía cinética turbulenta asociada con olas que aún no rompen

The turbulent kinetic energy dissipation is an essential quantity in the study of turbulence in fluids. In particular, on the transference of turbulent energy from large to small scales and determining its state of equilibrium and stationarity. This work has the purpose of understanding turbulence generation by non-breaking waves from turbulent kinetic energy dissipation analysis. Different groups of nonbreaking monochromatic waves with different slopes were mechanically constructed in a laboratory, whereby an acoustic device, the wave orbitals velocities were measure in various depths. Considering the inertial subrange in the power spectrum of components of turbulence velocity, a turbulent kinetic energy dissipation rate was quantified. It was detected that the magnitude of the turbulent kinetic energy dissipation rate increases with the wave slope and that deeper is invariant to axis rotations. It was distinguished that most of the profiles of the turbulent kinetic energy dissipation agree with an atypical logarithmic layer. Finally, a term of turbulence production was introduced, relative to nonbreaking wave orbital velocities. Unlike other turbulence production terms or approximations, it adequately reproduces the values of the turbulent kinetic energy dissipation rate regardless of wave slope, which established that the wave orbitals velocities shear is the generator mechanism of turbulence in a fluid under nonbreaking waves.

The First Fall is the Hardest: The Importance of Peculiar Galaxy Dynamics at Infall Time for Tidal Stripping Acting at the Centers of Groups and Clusters

Using dark-matter-only N-body cosmological simulations, we measure the pericentre distance of dark matter halos on their first infall into group and cluster halos. We find that the pericentre distance (R peri) is an important parameter as it significantly affects the strength of tidal mass loss in dense environments, and likely other environmental mechanisms as well. We examine what determines the R peri value and find that, for most infallers, the dominant parameter is V ⊥, the tangential component of the orbital velocity as the halo enters the group/cluster halo for the first time. This means that the strength of tidal stripping acting near the cores of groups/clusters are strongly influenced by the external peculiar velocity field of the large-scale structure surrounding them, which differs between clusters and is sensitive to the mass ratio of infaller to host. We find that filament feeding also partially contributes to feeding in low-V ⊥ halos. Dynamical friction can also play a role in reducing R peri but this is only significant for those few relatively massive infallers (>10% of the mass of their host). These results highlight how the response of galaxies to dense environments will sensitively depend on dynamics inherited from far outside those dense environments.

Exploratory scenarios for the differential nuclear and tidal evolution of TZ Fornacis

Aims. TZ Fornacis is a double-lined eclipsing binary system with similar masses (2.057 ± 0.001 and 1.958 ± 0.001 M⊙) but characterized by very different radii (8.28 ± 0.22 and 3.94 ± 0.17 R⊙). This similarity in terms of mass makes it possible to study the system’s differential stellar evolution as well as some aspects of its tidal evolution. With regard to its orbital elements, it was recently confirmed that its orbit is circular with an orbital period of 75.7 days. The less massive component rotates about 17 times faster than the primary one, which is synchronized with the mean orbital angular velocity. Our main objective in this work is to study both the nuclear and the tidal evolution of the system. Methods. To model the TZ For system, we used the MESA package, computing the grids using the exact observed masses, radii, and effective temperatures as input, and then varying the metallicity, the core overshooting amount, and the mixing-length parameter. A χ2 statistic was used to infer the optimal values of the core overshooting and the mixing-length parameters. The same procedure was used to generate rotating models with the GRANADA code. The respective errors in the average age of TZ For were less than 5%. On the other hand, the differential equations that govern the tidal evolution were integrated using the fifth-order Runge–Kutta method, ith a tolerance of 1 × 10−7. Results. We explored two scenarios regarding the initial eccentricities: a high one (0.30) and a case of an initial circular orbit. A good agreement has been found between the observational values of the eccentricity, synchronism levels, and orbital period with the values predicted by the integration of the tidal evolution equations. The influence of the friction timescale on the evolution of the orbital elements of TZ For is also studied here. The orbital elements most affected by the uncertainties in the friction timescale are the synchronism levels of the two components. On the other hand, we used the properties of the rotating models generated by the GRANADA code as the initial angular velocities instead of using trial values. In this case, comparisons between the theoretical values of the orbital elements and their observed counterparts also lead to a good interagreement.

Submesoscale Currents from UAV: An Experiment over Small-Scale Eddies in the Coastal Black Sea

A commercial unmanned aerial vehicle (UAV) is used for coastal submesoscale current estimation. The measurements were conducted in the Black Sea coastal area with a DJI Mavic quadcopter operated in self-stabilized mode at different look geometry (200–500-m altitude, 0–30∘ incidence angle). The results of four flights during 2020–2021 are reported. Some scenes captured a train of or individual eddies, generated by a current flowing around a topographic obstacle (pier). The eddies were optically visible due to the mixing of clear and turbid waters in the experiment area. Wave dispersion analysis (WDA), based on dispersion shell signature recognition, is used to estimate the sea surface current in the upper 0.5-m-thick layer. The WDA-derived current maps are consistent with visible eddy manifestations. The alternative method, based on 4D-variational assimilation (4DVAR), agrees well with WDA and can complement it in calm wind conditions when waves are too short to be resolved by the UAV sensor. The error of reconstructed velocity due to the uncontrolled UAV motions is assessed from referencing to static land control points. At a 500-m altitude and 7–10 m s−1 wind speed (reported by a local weather station for 10-m height), the UAV drift velocity, or the bias of the current velocity estimate, is about 0.1 m s−1, but can be reduced to 0.05 m s−1 if the first 10 s of the UAV self-stabilization period are excluded from the analysis. The observed anticyclonic eddies (200–400 m in diameter with 0.15–0.30 m s−1 orbital velocity) have an unexpectedly high Rossby number, Ro∼15, suggesting the importance of nonlinear centrifugal force for such eddies and their significant role in coastal vertical transport.

Molecular Cloud Populations in the Context of Their Host Galaxy Environments: A Multiwavelength Perspective

We present a rich, multiwavelength, multiscale database built around the PHANGS–ALMA CO (2 − 1) survey and ancillary data. We use this database to present the distributions of molecular cloud populations and subgalactic environments in 80 PHANGS galaxies, to characterize the relationship between population-averaged cloud properties and host galaxy properties, and to assess key timescales relevant to molecular cloud evolution and star formation. We show that PHANGS probes a wide range of kpc-scale gas, stellar, and star formation rate (SFR) surface densities, as well as orbital velocities and shear. The population-averaged cloud properties in each aperture correlate strongly with both local environmental properties and host galaxy global properties. Leveraging a variable selection analysis, we find that the kpc-scale surface densities of molecular gas and SFR tend to possess the most predictive power for the population-averaged cloud properties. Once their variations are controlled for, galaxy global properties contain little additional information, which implies that the apparent galaxy-to-galaxy variations in cloud populations are likely mediated by kpc-scale environmental conditions. We further estimate a suite of important timescales from our multiwavelength measurements. The cloud-scale freefall time and turbulence crossing time are ∼5–20 Myr, comparable to previous cloud lifetime estimates. The timescales for orbital motion, shearing, and cloud–cloud collisions are longer, ∼100 Myr. The molecular gas depletion time is 1–3 Gyr and shows weak to no correlations with the other timescales in our data. We publish our measurements online, and expect them to have broad utility to future studies of molecular clouds and star formation.