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More Evidence for Variable Helium Absorption from HD 189733b
No full textWe present a new Keck/NIRSPEC observation of metastable helium absorption from the upper atmosphere of HD 189733b, a hot Jupiter orbiting a nearby moderately active star. We measure an average helium transit depth of 0.420% ± 0.013% integrated over the [−20, 20] km s⁻¹ velocity range. Comparing this measurement to eight previously published transit observations with different instruments, we find that our depth is 32% (9σ) lower than the average of the three CARMENES transits, but only 16% (4.4σ) lower than the average of the five GIANO transits. We perform 1D hydrodynamical simulations of the outflow, and find that XUV variability on the order of 33%–common for this star–can change the helium absorption depth by up to 60%, although a more typical change is 15%. We conclude that changes in stellar XUV flux can explain the observational variability in helium absorption, but that variability in the stellar He line cannot be excluded. 3D models are necessary to explore other sources of variability, such as shear instability and changing stellar wind conditions
Optimizing the human learnability of abstract network representations
No full textPrecisely how humans process relational patterns of information in knowledge, language, music, and society is not well understood. Prior work in the field of statistical learning has demonstrated that humans process such information by building internal models of the underlying network structure. However, these mental maps are often inaccurate due to limitations in human information processing. The existence of such limitations raises clear questions: Given a target network that one wishes for a human to learn, what network should one present to the human? Should one simply present the target network as-is, or should one emphasize certain parts of the network to proactively mitigate expected errors in learning? To investigate these questions, we study the optimization of network learnability in a computational model of human learning. Evaluating an array of synthetic and real-world networks, we find that learnability is enhanced by reinforcing connections within modules or clusters. In contrast, when networks contain significant core–periphery structure, we find that learnability is best optimized by reinforcing peripheral edges between low-degree nodes. Overall, our findings suggest that the accuracy of human network learning can be systematically enhanced by targeted emphasis and de-emphasis of prescribed sectors of information
Confirmation and characterisation of three giant planets detected by TESS from the FIES/NOT and Tull/McDonald spectrographs
No full textWe report the confirmation and characterisation of TOI-1820 b, TOI-2025 b, and TOI-2158 b, three Jupiter-sized planets on short-period orbits around G-type stars detected by TESS. Through our ground-based efforts using the FIES and Tull spectrographs, we have confirmed these planets and characterised their orbits, and find periods of around 4.9 d, 8.9 d, and 8.6 d for TOI-1820 b, TOI-2025 b, and TOI-2158 b, respectively. The sizes of the planets range from 0.96 to 1.14 Jupiter radii, and their masses are in the range from 0.8 to 4.4 Jupiter masses. For two of the systems, namely TOI-2025 and TOI-2158, we see a long-term trend in the radial velocities, indicating the presence of an outer companion in each of the two systems. For TOI-2025 we furthermore find the star to be well aligned with the orbit, with a projected obliquity of 9_(−31)^(+33ₒ). As these planets are all found in relatively bright systems (V ~ 10.9–11.6 mag), they are well suited for further studies, which could help shed light on the formation and migration of hot and warm Jupiters
New Constraints on Protoplanetary Disk Gas Masses in Lupus
No full textGas mass is a fundamental quantity of protoplanetary disks that directly relates to their ability to form planets. Because we are unable to observe the bulk H₂ content of disks directly, we rely on indirect tracers to provide quantitative mass estimates. Current estimates for the gas masses of the observed disk population in the Lupus star-forming region are based on measurements of isotopologues of CO. However, without additional constraints, the degeneracy between H₂ mass and the elemental composition of the gas leads to large uncertainties in such estimates. Here, we explore the gas compositions of seven disks from the Lupus sample representing a range of CO-to-dust ratios. With Band 6 and 7 ALMA observations, we measure line emission for HCO⁺, HCN, and N₂H⁺. We find a tentative correlation among the line fluxes for these three molecular species across the sample, but no correlation with ¹³CO or submillimeter continuum fluxes. For the three disks where N₂H⁺ is detected, we find that a combination of high disk gas masses and subinterstellar C/H and O/H are needed to reproduce the observed values. We find increases of ∼10–100× previous mass estimates are required to match the observed line fluxes. This work highlights how multimolecular studies are essential for constraining the physical and chemical properties of the gas in populations of protoplanetary disks, and that CO isotopologues alone are not sufficient for determining the mass of many observed disks
Neuromuscular embodiment of feedback control elements in Drosophila flight
No full textWhile insects like Drosophila are flying, aerodynamic instabilities require that they make millisecond-timescale adjustments to their wing motion to stay aloft and on course. These stabilization reflexes can be modeled as a proportional-integral (PI) controller; however, it is unclear how such control might be instantiated in insects at the level of muscles and neurons. Here, we show that the b1 and b2 motor units—prominent components of the fly’s steering muscles system—modulate specific elements of the PI controller: the angular displacement (integral, I) and angular velocity (proportional, P), respectively. Moreover, these effects are observed only during the stabilization of pitch. Our results provide evidence for an organizational principle in which each muscle contributes to a specific functional role in flight control, a finding that highlights the power of using top-down behavioral modeling to guide bottom-up cellular manipulation studies
Gas infall and radial transport in cosmological simulations of milky way-mass discs
No full textObservations indicate that a continuous supply of gas is needed to maintain observed star formation rates in large, discy galaxies. To fuel star formation, gas must reach the inner regions of such galaxies. Despite its crucial importance for galaxy evolution, how and where gas joins galaxies is poorly constrained observationally and rarely explored in fully cosmological simulations. To investigate gas accretion in the vicinity of galaxies at low redshift, we analyse the FIRE-2 cosmological zoom-in simulations for 4 Milky Way mass galaxies (M_(halo) ∼ 10¹² M_⊙), focusing on simulations with cosmic ray physics. We find that at z ∼ 0, gas approaches the disc with angular momentum similar to the gaseous disc edge and low radial velocities, piling-up near the edge and settling into full rotational support. Accreting gas moves predominately parallel to the disc and joins largely in the outskirts. Immediately prior to joining the disc, trajectories briefly become more vertical on average. Within the disc, gas motion is complex, being dominated by spiral arm induced oscillations and feedback. However, time and azimuthal averages show slow net radial infall with transport speeds of 1–3 km s⁻¹ and net mass fluxes through the disc of ∼M_⊙ yr⁻¹, comparable to the galaxies’ star formation rates and decreasing towards galactic centre as gas is sunk into star formation. These rates are slightly higher in simulations without cosmic rays (1–7 km s−1, ∼4–5 M_⊙ yr⁻¹). We find overall consistency of our results with observational constraints and discuss prospects of future observations of gas flows in and around galaxies
The acoustic resonant drag instability with a spectrum of grain sizes
No full textWe study the linear growth and non-linear saturation of the ‘acoustic Resonant Drag Instability’ (RDI) when the dust grains, which drive the instability, have a wide, continuous spectrum of different sizes. This physics is generally applicable to dusty winds driven by radiation pressure, such as occurs around red-giant stars, star-forming regions, or active galactic nuclei. Depending on the physical size of the grains compared to the wavelength of the radiation field that drives the wind, two qualitatively different regimes emerge. In the case of grains that are larger than the radiation’s wavelength – termed the constant-drift regime – the grain’s equilibrium drift velocity through the gas is approximately independent of grain size, leading to strong correlations between differently sized grains that persist well into the saturated non-linear turbulence. For grains that are smaller than the radiation’s wavelength – termed the non-constant-drift regime – the linear instability grows more slowly than the single-grain-size RDI and only the larger grains exhibit RDI-like behaviour in the saturated state. A detailed study of grain clumping and grain–grain collisions shows that outflows in the constant-drift regime may be effective sites for grain growth through collisions, with large collision rates but low collision velocities
Improved strong lensing modelling of galaxy clusters using the Fundamental Plane: Detailed mapping of the baryonic and dark matter mass distribution of Abell S1063
No full textAims. From accurate photometric and spectroscopic information, we build the Fundamental Plane (FP) relation for the early-type galaxies of the cluster Abell S1063. We use this relation to develop an improved strong lensing model of the cluster, and we decompose the cluster’s cumulative projected total mass profile into its stellar, hot gas, and dark matter mass components. We compare our results with the predictions of cosmological simulations.
Methods. We calibrate the FP using Hubble Frontier Fields photometry and data from the Multi Unit Spectroscopic Explorer on the Very Large Telescope. The FP allows us to determine the velocity dispersions of all 222 cluster members included in the model from their measured structural parameters. As for their truncation radii, we test a proportionality relation with the observed half-light radii. Fixing the mass contribution of the hot gas component from X-ray data, the mass density distributions of the diffuse dark matter haloes are optimised by comparing the observed and model-predicted positions of 55 multiple images of 20 background sources distributed over the redshift range 0.73 − 6.11. We determine the uncertainties on the model parameters with Monte Carlo Markov chains.
Results. We find that the most accurate predictions of the positions of the multiple images are obtained when the truncation radii of the member galaxies are approximately 2.3 times their effective radii. Compared to earlier work on the same cluster, our model allows for the inclusion of some scatter on the relation between the total mass and the velocity dispersion of the cluster members. We notice a lower statistical uncertainty on the value of some model parameters. For instance, the main dark matter halo of the cluster has a core radius of 86 ± 2 kpc: the uncertainty on this value decreases by more than 30% with respect to previous work. Taking advantage of a new estimate of the stellar mass of all cluster members from the HST multi-band data, we measure the cumulative two-dimensional mass profiles out to a radius of 350 kpc for all baryonic and dark matter components of the cluster. At the outermost radius of 350 kpc, we obtain a baryon fraction of 0.147 ± 0.002. We study the stellar-to-total mass fraction of the high-mass cluster members in our model, finding good agreement with the observations of wide galaxy surveys and some disagreement with the predictions of halo occupation distribution studies based on N-body simulations. Finally, we compare the features of the sub-haloes as described by our model with those predicted by high-resolution hydrodynamical simulations. We obtain compatible results in terms of the stellar over total mass fraction. On the other hand, we report some discrepancies both in terms of the maximum circular velocity, which is an indication of the halo compactness, and the sub-halo total mass function in the central cluster regions
Separating Energetic Internal Gravity Waves and Small-Scale Frontal Dynamics
No full textOceanic fronts with lateral scales less than 20 km are now known to be one of the major contributors to vertical heat fluxes in the global ocean, which highlights their potential impact on Earth's climate. However, frontal dynamics with time scales less than 1 day, whose contribution to vertical heat fluxes is thought to be significant, are obscured by energetic internal gravity waves (IGWs). In this study, we address this critical issue by separating IGWs and frontal dynamics using an approach based on their respective vertical scales of variability. Results using a numerical model with a horizontal grid spacing of 500 m confirm that it is possible to recover frontal dynamics at short time scales as well as associated intense vertical velocities and vertical heat fluxes. This opens up new possibilities for a more accurate estimation of the vertical exchanges of any tracers between the surface and the ocean interior
A wet heterogeneous mantle creates a habitable world in the Hadean
No full textThe Hadean eon, following the global-scale melting of the mantle is expected to be a dynamic period, during which Earth experienced vastly different conditions. Geologic records, however, suggest that the surface environment of Earth was already similar to the present by the middle of the Hadean4,5. Under what conditions a harsh surface environment could turn into a habitable one remains uncertain6. Here we show that a hydrated mantle with small-scale chemical heterogeneity, created as a result of magma ocean solidification, is the key to ocean formation, the onset of plate tectonics and the rapid removal of greenhouse gases, which are all essential to create a habitable environment on terrestrial planets. When the mantle is wet and dominated by high-magnesium pyroxenites, the removal of carbon dioxide from the atmosphere is expected to be more than ten times faster than the case of a pyrolitic homogeneous mantle and could be completed within 160 million years. Such a chemically heterogeneous mantle would also produce oceanic crust rich in olivine, which is reactive with ocean water and promotes serpentinization. Therefore, conditions similar to the Lost City hydrothermal field may have existed globally in the Hadean seafloor