Velocity Shift Research Articles

A new FEM-based approach on the modeling of stress-induced velocity shift of piezoelectric surface acoustic wave resonators

A novel methodology is introduced for the computation of stress-induced surface acoustic wave velocity shifts in piezoelectric resonators including quartz, lithium niobate and langasite resonators. The numerical framework has been verified through a comparative analysis of experimental and Finite Element Method (FEM) results for quartz resonators. This approach introduces the combined capabilities of COMSOL Multiphysics and MATLAB, facilitated by LiveLink, to systematically calculate all parameters contributing to the perturbation integral. The findings have a better accuracy using the LiveLink methodology in this study compared to prior approaches that rely on average stress and strain calculations in the central point of the resonator. Moreover, the utilization of LiveLink not only enhances accuracy but also establishes MATLAB as a fundamental software platform for interfacing with COMSOL Multiphysics. The proposed approach in this paper can extend to complex strain sensors or investigations into the influence of temperature and imbalanced loading effects in future research endeavors. Furthermore, the LiveLink approach introduced herein can be extended to optimize crystal orientation and identify premium wave directions, thereby contributing to the enhanced design of Surface Acoustic Wave (SAW) resonators. This innovative methodology is used to advance the understanding and application of stress-induced velocity shifts in SAW devices, presenting future developments in sensor technologies and resonator designs. © 2024 Elsevier Science. All rights reserved.

Formation of CN and CO Molecules in the Envelope of Nova V1391 Cas During the Near-maximum Phase

Moderate-resolution spectra (R ≈ 2700) of the classical nova V1391 Cas were obtained in the near-infrared wavelength range of 0.95–2.45 μm on UT 2020 August 14.41 using the Keck II telescope and the NIRES spectrograph. The spectral analysis revealed simultaneous detection of CO and CN molecular features. The CN red-system band was observed solely in absorption, while the CO first overtone bands, encompassing both 12CO and 13CO, displayed a combination of emission and absorption features at different velocities, resembling a P-Cygni profile. This specific CO profile is unprecedented in classical novae observations. Additionally, the negative velocity shifts in the absorption bands of both CN and CO were found to be consistent with each other.

Numerical Investigation of Large Vehicle Aerodynamics Under the Influence of Crosswind

This paper presents a numerical analysis aimed at estimating the impact of crosswinds on the aerodynamics of large vehicles using ANSYS Fluid Flow and Static Structural, offering insights into the qualitative behaviour of trucks under typical traffic conditions. The cases analysed focus on airflow distribution when a truck, traveling at approximately 100 km/h, passes under a portal while exposed to varying crosswind intensities: weak, moderate, and strong lateral winds. A detailed examination of the truck and portal reveals significant interactions between the induced airflow patterns, affecting truck handling and stability. This is evidenced by shifts in velocity and pressure distributions, changes in drag coefficients, and variations in turbulent kinetic energy, all of which are analysed and discussed in this study.

SOFIA/EXES Observations of Warm H2 at High Spectral Resolution. II. IC 443C, NGC 2071, and 3C 391

Using the EXES instrument on SOFIA, we have obtained velocity-resolved spectra of several pure rotational lines of H2 toward shocked molecular gas within three Galactic sources: the supernova remnant (SNR) IC 443 (clump C), a protostellar outflow in the intermediate-mass star-forming region NGC 2071, and the SNR 3C 391. These observations had the goal of searching for expected velocity shifts between ortho- and para-H2 transitions emitted by C-type shocks. In contrast in our previous similar study of HH7, the result of our search was negative: no velocity shifts were reliably detected. Several possible explanations for the absence of such shifts are discussed: these include a preshock ortho-to-para ratio that is already close to the high-temperature equilibrium value of 3 (in the case of IC 443C), the more complex shock structures evident in all these sources, and the larger projected aperture sizes relative to those in the observations of HH7.

Tracking Outflow Using Line Locking (TOLL). I. The Case Study of Quasar J221531-174408

Investigating line-locked phenomena within quasars is crucial for understanding the dynamics of quasar outflows, the role of radiation pressure in astrophysical flows, and the star formation history and metallicity of the early Universe. We have initiated the Tracking Outflow by Line Locking project to study quasar outflow by studying line-locking signatures using high-resolution high-signal-to-noise-ratio quasar spectra. In this paper, we present a case study of the line-locking signatures from QSO J221531-174408. The spectrum was obtained using the Very Large Telescope’s UV Visual Echelle Spectrograph. We first identify associated absorbers in the spectrum using C iv, N v, and Si iv doublets and measure their velocity shifts, covering fractions, and column densities through a line-profile-fitting technique. Then we compare the velocity separations between different absorbers, and detect nine pairs of line-locked C iv doublets, three pairs of line-locked N v doublets, and one pair of line-locked Si iv doublets. This is one of the four quasars known to possess line-locked signatures in C iv, Si iv, and N v at the same time. We also find three complex line-locked systems, where three to five absorbers are locked together through multi-ion doublets. Our study suggests that line locking is a common phenomenon in the quasar outflows, and theoretical models involving more than two clouds and one ionic doublet are needed in the future to explain the formation of these complex line-locking signatures.

Whole Organ Volumetric Sensing Ultrasound Localization Microscopy for Characterization of Kidney Structure.

Glomeruli are the filtration units of the kidney and their function relies heavily on their microcirculation. Despite its obvious diagnostic importance, an accurate estimation of blood flow in the capillary bundle within glomeruli defies the resolution of conventional imaging modalities. Ultrasound Localization Microscopy (ULM) has demonstrated its ability to image in-vivo deep organs in the body. Recently, the concept of sensing ULM or sULM was introduced to classify individual microbubble behavior based on the expected physiological conditions at the micrometric scale. In the kidney of both rats and humans, it revealed glomerular structures in 2D but was severely limited by planar projection. In this work, we aim to extend sULM in 3D to image the whole organ and in order to perform an accurate characterization of the entire kidney structure. The extension of sULM into the 3D domain allows better localization and more robust tracking. The 3D metrics of velocity and pathway angular shift made glomerular mask possible. This approach facilitated the quantification of glomerular physiological parameter such as an interior traveled distance of approximately 7.5 ±0.6 microns within the glomerulus. This study introduces a technique that characterize the kidney physiology which can serve as a method to facilite pathology assessment. Furthermore, its potential for clinical relevance could serve as a bridge between research and practical application, leading to innovative diagnostics and improved patient care.

SOFIA/upGREAT far-infrared spectroscopy of bright rimmed pillars in IC 1848

Using the upGREAT instrument on SOFIA, we imaged the [C II] 158 µm fine structure line emission in bright-rimmed pillars located at the southern edge of the IC 1848 H II region, and carried out pointed observations of the [O I] 63 and 145 µm fine structure lines toward selected positions. The observations are used to characterize the morphology, velocity field, and the physical conditions in the G1–G3 filaments. The velocity-resolved [C II] spectra show evidence of a velocity shift at the head of the brightest G1 filament, possibly caused by radiation pressure from the impinging UV photons or the rocket effect of the evaporating gas. Archival Herschel PACS and SPIRE observations imply H2 column densities in the range 1021 –1022 cm−2 , corresponding to maximum visual extinction AV ≃ 10 mag, and average H2 volume density of ≃4500 cm−3 in the filaments. The [C II] emission traces ∼17% of the total H2 column density, as derived from dust SED fits. Photon-dominated region models are unable to explain the observed line intensities of the two [O I] fine structure lines in IC 1848, with the observed [O I] 145 µm line being too strong compared to the model predictions. The [O I] lines in IC 1848 are overall weak and the signal-to-noise ratio is limited. However, our observations suggest that the [O I] 63/145 µm intensity ratio is a sensitive probe of the physical conditions in photon-dominated regions such as IC 1848. These lines are thus excellent targets for future high-altitude balloon instruments, less affected by telluric absorption.

Up, Up, and Away: Winds and Dynamical Structure as a Function of Altitude in the Ultrahot Jupiter WASP-76b

Due to the unprecedented signal strengths offered by the newest high-resolution spectrographs on 10 m class telescopes, exploring the 3D nature of exoplanets is possible with an unprecedented level of precision. In this paper, we present a new technique to probe the vertical structure of exoplanetary winds and dynamics using ensembles of planet absorption lines of varying opacity, and apply it to the well-studied ultrahot Jupiter WASP-76b. We then compare these results to state-of-the-art global circulation models (GCMs) with varying magnetic drag prescriptions. We find that the known asymmetric velocity shift in Fe i absorption during transit persists at all altitudes, and observe tentative trends for stronger blueshifts and more narrow line profiles deeper in the atmosphere. By comparing three different model prescriptions (a hydrodynamical model with no drag, a magnetic drag model, and a uniform drag model) we are able to rule out the uniform drag model due to inconsistencies with observed trends in the data. We find that the magnetic model is slightly favored over the the hydrodynamic model, and note that this 3-Gauss kinematic magnetohydrodynamical GCM is also favored when compared to low-resolution data. Future generation high-resolution spectrographs on extremely large telescopes will greatly increase signals and make methods like these possible with higher precision and for a wider range of objects.

Modeling of turbulent flows through annuli with smooth and rough walls; drag reduction and heat transfer

A model of a turbulent flow in an annular channel with rough walls is developed. An effect of roughness on hydraulic resistance of the channel is accounted for through the formal dimensionless negative velocity shift at the wall by using an empirical function linking this velocity shift to the dimensionless sandgrain wall roughness. The developed annular flow model is validated by experimental data found in literature for both smooth walls, both rough walls, smooth outer wall and rough inner wall as well as vice versa. The same flow model is applied also to a polymer solution turbulent flow in annular channel with hydraulically smooth walls. A turbulent drag reduction effect, observed in this case, is accounted for by a positive velocity shift at the wall determined for a certain drag reduction chemical from experiments in a round cross-section pipe. Also, an engineering approach for modeling heat transfer through either outer or inner wall of an annular channel with rough walls is suggested. This approach is based on the known analogy of heat transfer in a hydraulically smooth annular channel and a pipe. This analogy is extended to an annular channel with rough walls by using the developed flow model. The heat transfer model developed is validated, discussed and illustrated by calculation examples. Key attention is paid to analyzing an effect of the Reynolds number on both a Nusselt number increase and an efficiency change for different wall roughening cases.

The spectroscopic binary fraction of the young stellar cluster M17

Context. Significant progress has been made toward understanding the formation of massive (M > 8 M⊙) binaries in close orbits (with periods of less than a month). Some of the observational studies leading to this progress are the detection of a very low velocity dispersion among the massive stars in the young region M17 and the measurement of a positive trend of velocity dispersion with age in Galactic clusters. The velocity dispersion observed in M17 could be explained either by the lack of binaries among the stars in this region, which implies the highly unlikely scenario of a different formation mechanism for M17 than for other Galactic regions, or by larger binary separations than typically observed, but with a binary fraction similar to other young Galactic clusters. The latter implies that, over time, the binary components migrate toward each other. This is in agreement with the finding that the radial velocity dispersion of young Galactic clusters correlates positively with their age. Aims. We aim to determine the origin of the strikingly low velocity dispersion by determining the observed and intrinsic binary fraction of massive stars in M17 through multi-epoch spectroscopy. Methods. We performed a multi-epoch spectroscopic survey consisting of three epochs separated by days and months, respectively. We complemented this survey with existing data covering timescales of years. We determined the radial velocity of each star at each epoch by fitting the stellar absorption profiles. The velocity shifts between epochs were used to determine whether a close companion is present. Results. We determined an observed binary fraction of 27% and an intrinsic binary fraction of 87%, consistent with that of other Galactic clusters. We conclude that the low velocity dispersion is due to a large separation among the young massive binaries in M17. Our result is in agreement with a migration scenario in which massive stars are born in binaries or higher-order systems at large separation and harden within the first million years of evolution. Such an inward migration may either be driven by interaction with a remnant accretion disk or with other young stellar objects present in the system, or by dynamical interactions within the cluster. Our results imply that possibly both dynamical interactions and binary evolution are key processes in the formation of gravitational wave sources.

A computational study of the influence of wavy arteries and veins on hemodynamic characteristics in an unsteady state

The present work is focused on the study of hemodynamic characteristics for tortuous arteries/veins in a pulsatile flow. This work is an extension of an earlier work by the author, which reported the hemodynamic characteristics in a steady flow situation. It is a well-known fact that various geometric parameters affect the hemodynamics, such as the diameter of vessels, the diameter of mother and daughter tubes in bifurcation, the angle between them, and their relative magnitudes. This paper is focused on the effect of tortuosity produced in straight and bifurcating tubes under pulsatile flow conditions. A heartbeat rate of 120 bpm is considered for pulsation, covering one cycle of systole and diastole. The measure of tortuosity is defined by the varying pitch and the amplitude. The present analysis is carried out computationally using ANSYS. Results are presented through secondary flow streamline, velocity profile, and its effect on wall shear stress. Key findings are that secondary vortices are observed in the bifurcated model and counter-rotating vortices are observed in the wavy tube geometry. The velocity distribution is asymmetric in the case of the plain bifurcation geometry. In the case of the wavy tube and bifurcated geometry, there is a shift in peak velocity from the inner to the outer wall, depending on the crest and trough positions of the tortuous vein. Relative change in magnitude of velocity for wavy tube depends on the depth and pitch of wavy wall of the tortuous tube. The velocity reduces with an increase in time step for unsteady flow.

Effects of elevated oxygen content and temperature on the laminar burning velocity of the blast furnace gas in oxygen-enriched air condition

Oxygen-enriched air combustion holds promise as an effective method for harnessing blast furnace gas (BFG) in the steel industry. In this study, the laminar burning velocities of blast furnace gas were measured using the heat flux method under elevated oxygen mole fractions (0.3–1.0) and temperatures (303–353 K). Subsequently, the measured data were used to evaluate the GRI-Mech 3.0, Li, FFCM-1, and Konnov 2023 mechanisms. Comparisons between experimental and calculated laminar burning velocities revealed that the Konnov 2023 mechanism well predicts the experimental data at all conditions, while the predictions of the other three mechanisms deviate from the experimental data. The laminar burning velocities of blast furnace gas increased with elevated oxygen mole fraction and temperature. Interestingly, the peak of laminar burning velocity shifts from the fuel-rich side to the fuel-lean side with an increase in oxygen mole fraction, which is mainly due to the fuel-lean shift peak of adiabatic flame temperature and the higher diffusive properties of the gas mixture at fuel-rich side. The reaction CO+OH<=>CO2 + H emerges as the most significant reaction influencing laminar burning velocities. The elevated oxygen mole fraction reduces the dependence of the power exponent α on the fitted temperature range. Corresponding oxygen mole fractions for the blast furnace gas are determined to be 0.59 at φ = 0.8 and 0.93 at φ = 0.9, respectively, at which the laminar burning velocity of the BFG/O2/N2 mixture equals that of the CH4/Air mixture.

Load motion on an ice cover in the presence of a liquid layer with velocity shear

The behavior of an ice cover on the surface of an ideal incompressible fluid of finite depth under the action of a pressure domain that moves rectilinearly at a constant velocity in the presence of a current with velocity shift in the upper layer is studied. It is assumed that the ice deflection is steady in the coordinate system moving with the load. The Fourier transform method is used within the framework of the linear wave theory. The critical velocities, the deflection of ice cover, and the wave forces are studied depending on the current velocity gradient, the shear layer thickness, the direction of motion, and the compression ratio.

Phase velocity shifts of shear surface waves in flexoelectric wave-guide clamped on piezomagnetic base

Surface acoustic wave devices featuring periodic layers of piezomagnetic and piezoelectric-flexoelectric layers are subject to intense investigation. In miniaturized devices, large strain gradients are possible that produce significant flexoelectric fields in piezoelectric components. In the present theoretical research, surface acoustic wave transference has been manifested in a flexoelectric waveguide clamped over a piezomagnetic base. This endeavor involves the formulation and solution of coupled magneto-electro-elastic field equations governing the structure’s behavior. Coupled magneto-electro-elastic field equations for the structure have been derived and solved utilizing analytical techniques. By accounting for pertinent boundary conditions, the dispersion relations characterizing the velocity of surface waves, both in scenarios with and without electrodes have been obtained. Based on proper numerical examples, the frequency and phase velocity spectrum have been plotted offering insights into key parameters i.e. modal frequency, phase velocity, and wave attenuation. The outcomes of the theoretical study may be helpful in providing insights into mechanical wave propagation in coupled piezoelectric/piezomagnetic structures.

X-Shooting ULLYSES: Massive stars at low metallicity

Context. The winds of massive stars have a significant impact on stellar evolution and on the surrounding medium. The maximum speed reached by these outflows, the terminal wind speed v∞, is a global wind parameter and an essential input for models of stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a legacy UV spectroscopic survey with the Hubble Space Telescope, we have the opportunity to quantify the wind speeds of massive stars at sub-solar metallicity (in the Large and Small Magellanic Clouds, 0.5 Z⊙ and 0.2 Z⊙, respectively) at an unprecedented scale. Aims. We empirically quantify the wind speeds of a large sample of OB stars, including supergiants, giants, and dwarfs at sub-solar metallicity. Using these measurements, we investigate trends of v∞ with a number of fundamental stellar parameters, namely effective temperature (Teff), metallicity (Z), and surface escape velocity vesc. Methods. We empirically determined v∞ for a sample of 149 OB stars in the Magellanic Clouds either by directly measuring the maximum velocity shift of the absorption component of the C IV λλ1548–1550 line profile, or by fitting synthetic spectra produced using the Sobolev with exact integration method. Stellar parameters were either collected from the literature, obtained using spectral-type calibrations, or predicted from evolutionary models. Results. We find strong trends of v∞ with Teff and vesc when the wind is strong enough to cause a saturated P Cygni profile in C IV λλ1548–1550. We find evidence for a metallicity dependence on the terminal wind speed v∞ ∝ Z0.22±0.03 when we compared our results to previous Galactic studies. Conclusions. Our results suggest that Teff rather than vesc should be used as a straightforward empirical prediction of v∞ and that the observed Z dependence is steeper than suggested by earlier works.

Correcting Fabry-Pérot etalon effects in solar observations

Context. Data processing pipelines of Fabry–Pérot interferometers (FPI) must take into account the side effects these devices introduce in the observations. Interpretation of these observations without proper correction can lead to inaccurate or false results, with consequent impact on their physical interpretation. Corrections typically require prior knowledge of the properties of the etalon and the way they affect the incoming light in order to calibrate the data successfully. Aims. We have developed an algorithm to derive etalon properties from flat-field observations and tested its applicability and accuracy using simulated observations and real measurements. Methods. We employed analytical expressions of the transmission profiles for FPIs in collimated and telecentric configurations to derive their expected impact on the observations. These analytical expressions allowed us to develop a customized optimization algorithm capable of inferring the properties of the etalon from the observations. The algorithm’s performance has been tested on simulated observations with an etalon in collimated and telecentric setups employing various noise levels and spectral samplings. Additionally, we explored how tilting the etalon in a telecentric configuration influences the algorithm’s effectiveness. Lastly, we also applied the algorithm to a set of real flat-field observations taken with the high-resolution telescope of the Polarimetric and Helioseismic Imager on board the Solar Orbiter mission (HRT-SO/PHI). Results. The algorithm is able to retrieve the gain and etalon induced transmission velocity shifts (cavity map), with an average accuracy ranging between 0.4% and 0.1% for the former and between 120 m s−1 and 30 m s−1 for the latter. Both reducing the noise level and increasing the spectral sampling of the observations proved to greatly increase the algorithm’s performance, as expected. Results also suggest that determination of the observed object from the data is possible but an additional error between 40 m s−1 and 10 m s−1 is to be expected in the inferred cavity map. Furthermore, we show that neglecting the asymmetries arising from either tilts of the etalon or imperfections in the telecentrism can lead to large errors when determining the gain. Tests with HRT-SO/PHI data have verified the applicability of the algorithm in real cases. Conclusions. Our presented method enabled us to derive the transmission profile of FPIs from observations of collimated and telecentric configurations. It has proven to be robust against the presence of noise and limited spectral line sampling. The results reported here also show the importance of accounting for the asymmetries arising in real telecentric mounts when interpreting the results of real instruments.

A Lack of Mass-gap Compact Object Binaries in APOGEE

Depending principally on mass, the compact object remnant left behind after a star’s life may be a white dwarf, neutron star (NS), or black hole (BH). While we have large samples of each of these remnants, we lack knowledge of the exact conditions separating these outcomes. The boundary between low-mass BHs and massive NSs is particularly poorly understood, as few objects between 2 and 5 M ⊙ are known. To probe this regime, we search the Apache Point Observatory Galactic Evolution Experiment 17th Data Release data set of 657,000 unique stars for binary systems with one stellar component that exhibit large radial velocity shifts over multiple observations. We identify 4751 likely binary systems, and estimate a minimum mass for each system’s “invisible companion” under the assumption of tidal synchronization. Two systems have companion masses ≳2 M ⊙, although we conclude that neither are good candidates for possessing a mass-gap NS or BH companions.

The Metallicity and Carbon-to-oxygen Ratio of the Ultrahot Jupiter WASP-76b from Gemini-S/IGRINS

Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution. Recently, high-resolution cross-correlation analysis has emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b observed between 1.4 and 2.4 μm with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H2O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three species retrieved a volatile metallicity of C+OH=−0.70−0.93+1.27 , consistent with the stellar value, and a supersolar carbon-to-oxygen ratio of C/O =0.80−0.11+0.07 . We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1σ but favored a slightly more substellar metallicity and solar C/O ratio ( C+OH=−0.74−0.17+0.23 and C/O =0.59−0.14+0.13 ). A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic (V sys) and Keplerian (K p ) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshifted V sys for H2O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H2O velocity shift. Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.

The SDSS-V Black Hole Mapper Reverberation Mapping Project: C iv Broad Absorption Line Acceleration in the Quasar SBS 1408+544

We present the results of an investigation of a highly variable C iv broad absorption line (BAL) feature in spectra of the quasar SBS 1408+544 (z = 2.337) that shows a significant shift in velocity over time. This source was observed as a part of the Sloan Digital Sky Survey (SDSS) Reverberation Mapping project and the SDSS-V Black Hole Mapper Reverberation Mapping project, and has been included in two previous studies, both of which identified significant variability in a high-velocity C iv BAL on timescales of just a few days in the quasar rest frame. Using ∼130 spectra acquired over 8 yr of spectroscopic monitoring with SDSS, we have determined that this BAL is not only varying in strength, but is also systematically shifting to higher velocities. Using cross-correlation methods, we measure the velocity shifts (and corresponding acceleration) of the BAL over a wide range of timescales, measuring an overall velocity shift of Δv=−683−84+89 km s−1 over the 8 yr monitoring period. This corresponds to an average rest-frame acceleration of a = 1.04 −0.13+0.14 cm s−2, though the magnitude of the acceleration on shorter timescales is not constant throughout. We place our measurements in the context of BAL-acceleration models and examine various possible causes of the observed velocity shift.

Surface currents shape protist community structure across the Indo-Pacific.

Biogeographic structure in marine protist communities is shaped by a combination of dispersal potential and environmental selection. High-throughput sequencing and global sampling efforts have helped better resolve the composition and functions of these communities in the world's oceans using both molecular and visual methods. However, molecular barcoding data are critically lacking across the Indo-Pacific, a region widely considered the epicenter of marine biodiversity. To fill this gap, we characterized protist communities in four sampling regions across Indonesia that represent the latitudinal, longitudinal, and human population gradients of the region: Lombok, Wakatobi, Misool, and Waigeo. We show high spatial structuring in marine protist communities across Indonesia, and biotic factors appear to play little role in driving this observed structure. Our results appear to be driven by abiotic factors linked to surface current patterns across the Indo-Pacific as a result of: (1) a choke point in circulation at the Indonesian Throughflow leading to low diatom diversity in Lombok, Wakatobi, and Misool; (2) an increase in nutrient availability at the edge of the Halmahera Eddy in Waigeo, leading to an increase in diatom diversity; and/or (3) seasonal variations in protist communities in line with shifts in velocity of the Indonesian Throughflow. Overall, our results highlight the importance of abiotic factors in shaping protist communities on broad geographic scales over biotic, top-down pressures, such as grazing from higher trophic levels.