5632 research outputs found
Sort by
The mass of TOI-519 b: A close-in giant planet transiting a metal-rich mid-M dwarf
No full textWe report on the determination of the mass of TOI-519 b, a transiting substellar object around a mid-M dwarf. We carried out radial velocity measurements using Subaru/InfraRed Doppler (IRD), revealing that TOI-519 b is a planet with a mass of 0.463^(+0.082)_(-0.088) M_(Jup). We also found that the host star is metal rich ([Fe/H] = 0.27 ± 0.09 dex) and has the lowest effective temperature (T_(eff) = 3322 ± 49 K) among all stars hosting known close-in giant planets based on the IRD spectra and mid-resolution infrared spectra obtained with NASA Infrared Telescope Facility/SpeX. The core mass of TOI-519 b inferred from a thermal evolution model ranges from 0 to ∼30 M_⊕, which can be explained by both core accretion and disk instability models as the formation origins of this planet. However, TOI-519 is in line with the emerging trend that M dwarfs with close-in giant planets tend to have high metallicity, which may indicate that they formed in the core accretion model. The system is also consistent with the potential trend that close-in giant planets around M dwarfs tend to be less massive than those around FGK dwarfs
Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science
No full textThe Vera C. Rubin Observatory is expected to start the Legacy Survey of Space and Time (LSST) in early to mid-2025. This multiband wide-field synoptic survey will transform our view of the solar system, with the discovery and monitoring of over five million small bodies. The final survey strategy chosen for LSST has direct implications on the discoverability and characterization of solar system minor planets and passing interstellar objects. Creating an inventory of the solar system is one of the four main LSST science drivers. The LSST observing cadence is a complex optimization problem that must balance the priorities and needs of all the key LSST science areas. To design the best LSST survey strategy, a series of operation simulations using the Rubin Observatory scheduler have been generated to explore the various options for tuning observing parameters and prioritizations. We explore the impact of the various simulated LSST observing strategies on studying the solar system’s small body reservoirs. We examine what are the best observing scenarios and review what are the important considerations for maximizing LSST solar system science. In general, most of the LSST cadence simulations produce ±5% or less variations in our chosen key metrics, but a subset of the simulations significantly hinder science returns with much larger losses in the discovery and light-curve metrics
Black Hole Spectroscopy by Mode Cleaning
No full textWe formulate a Bayesian framework to analyze ringdown gravitational waves from colliding binary black holes and test the no-hair theorem. The idea hinges on mode cleaning—revealing subdominant oscillation modes by removing dominant ones using newly proposed “rational filters.” By incorporating the filter into Bayesian inference, we construct a likelihood function that depends only on the mass and spin of the remnant black hole (no dependence on mode amplitudes and phases) and implement an efficient pipeline to constrain the remnant mass and spin without Markov chain Monte Carlo. We test ringdown models by cleaning combinations of different modes and evaluating the consistency between the residual data and pure noise. The model evidence and Bayes factor are used to demonstrate the presence of a particular mode and to infer the mode starting time. In addition, we design a hybrid approach to estimate the remnant black hole properties exclusively from a single mode using Markov chain Monte Carlo after mode cleaning. We apply the framework to GW150914 and demonstrate more definitive evidence of the first overtone by cleaning the fundamental mode. This new framework provides a powerful tool for black hole spectroscopy in future gravitational-wave events
Early Results from GLASS-JWST. XIV. A Spectroscopically Confirmed Protocluster 650 Million Years after the Big Bang
No full textWe present the spectroscopic confirmation of a protocluster at z = 7.88 behind the galaxy cluster Abell 2744 (hereafter A2744-z7p9OD). Using JWST NIRSpec, we find seven galaxies within a projected radius of 60 kpc. Although the galaxies reside in an overdensity around ≳20× greater than a random volume, they do not show strong Lyα emission. We place 2σ upper limits on the rest-frame equivalent width 0.45 (68% C i). Using an empirical M_(UV)–M_(halo) relation for individual galaxies, we estimate that the total halo mass of the system is ≳4 × 10¹¹ M_⊙. Likewise, the line-of-sight velocity dispersion is estimated to be 1100 ± 200 km s⁻¹. Using an empirical relation, we estimate the present-day halo mass of A2744-z7p9OD to be ∼2 × 10¹⁵ M_⊙, comparable to the Coma cluster. A2744-z7p9OD is the highest redshift spectroscopically confirmed protocluster to date, demonstrating the power of JWST to investigate the connection between dark-matter halo assembly and galaxy formation at very early times with medium-deep observations at <20 hr total exposure time. Follow-up spectroscopy of the remaining photometric candidates of the overdensity will further refine the features of this system and help characterize the role of such overdensities in cosmic reionization
Photonic elementary cellular automata for simulation of complex phenomena
No full textCellular automata are a class of computational models based on simple rules and algorithms that can simulate a wide range of complex phenomena. However, when using conventional computers, these ‘simple’ rules are only encapsulated at the level of software. This can be taken one step further by simplifying the underlying physical hardware. Here, we propose and implement a simple photonic hardware platform for simulating complex phenomena based on cellular automata. Using this special-purpose computer, we experimentally demonstrate complex phenomena, including fractals, chaos, and solitons, which are typically associated with much more complex physical systems. The flexibility and programmability of our photonic computer present new opportunities to simulate and harness complexity for efficient, robust, and decentralized information processing using light
Decoding and geometry of ten finger movements in human posterior parietal cortex and motor cortex
No full textObjective. Enable neural control of individual prosthetic fingers for participants with upper-limb paralysis. Approach. Two tetraplegic participants were each implanted with a 96-channel array in the left posterior parietal cortex (PPC). One of the participants was additionally implanted with a 96-channel array near the hand knob of the left motor cortex (MC). Across tens of sessions, we recorded neural activity while the participants attempted to move individual fingers of the right hand. Offline, we classified attempted finger movements from neural firing rates using linear discriminant analysis with cross-validation. The participants then used the neural classifier online to control individual fingers of a brain–machine interface (BMI). Finally, we characterized the neural representational geometry during individual finger movements of both hands. Main Results. The two participants achieved 86% and 92% online accuracy during BMI control of the contralateral fingers (chance = 17%). Offline, a linear decoder achieved ten-finger decoding accuracies of 70% and 66% using respective PPC recordings and 75% using MC recordings (chance = 10%). In MC and in one PPC array, a factorized code linked corresponding finger movements of the contralateral and ipsilateral hands. Significance. This is the first study to decode both contralateral and ipsilateral finger movements from PPC. Online BMI control of contralateral fingers exceeded that of previous finger BMIs. PPC and MC signals can be used to control individual prosthetic fingers, which may contribute to a hand restoration strategy for people with tetraplegia
Engineering twin boundaries for enhancing strength and ductility of thermoelectric semiconductor PbTe
No full textTwin boundary engineering is a potential strategy for achieving robust mechanical properties of materials. Our previous molecular dynamics simulations indicated that the nanotwin could significantly enhance the ductility of thermoelectric (TE) semiconductors PbTe due to coherent twin boundary (CTB) migration accompanied by the ‘catching bond’ at room temperature. To further improve the mechanical strength or ductility of PbTe, we investigated the role of the shear direction, the CTB orientation and the temperature on mechanical properties of nanotwinned PbTe. Under the shear stress along [1̅10] loading direction, the partial dislocations with a/6 [121] and a/6 [21̅1] Burgers vectors are preferentially activated on (111) twin plane with higher yield strength and ultimate shear strength than that of the (111)[112] slip system. The nanotwinned PbTe with CTB orientation ranging from 125° to 161° has both higher fracture strain and larger ultimate shear strength than 0° CTB orientation. This is attributed to the motion of the twinning partial dislocation significantly enhancing the ductility while the blocking of dislocations by CTBs further improving the shear strength and deformability of PbTe. Moreover, the low temperature (below 100 K) energetically enables the partial dislocation to nucleate and glide on the strong Te-CTB plane, which induces successive CTB migration along Pb- and Te-CTB planes, resulting in enhanced ductility of nanotwinned PbTe
Divergent Catalysis: Catalytic Asymmetric [4+2] Cycloaddition of Palladium Enolates
No full textAn asymmetric decarboxylative [4+2] cycloaddition from a catalytically generated chiral Pd enolate was developed, forging four contiguous stereocenters in a single transformation. This was achieved through a strategy termed divergent catalysis, wherein departure from a known catalytic cycle enables novel reactivity of a targeted intermediate prior to re-entry into the original cycle. Mechanistic studies including quantum mechanics calculations, Eyring analysis, and KIE studies offer insight into the reaction mechanism
Early Results from GLASS-JWST. XVI. Discovering a Bluer z ∼ 4-7 Universe through UV Slopes
No full textWe use the GLASS-JWST Early Release Science NIRCam parallel observations to provide a first view of the UV continuum properties of NIRCam/F444W selected galaxies at 4 99% of the galaxies are blue star-forming galaxies with very low levels of dust (Av_β ∼ 0.01 ± 0.33). We find no statistically significant correlation for UV slope with redshift or UV magnitude. However, we find that in general galaxies at higher redshifts and fainter UV magnitudes have steeper UV slopes. We find a statistically significant correlation for UV slope with stellar mass, with galaxies with higher stellar mass showing shallower UV slopes. Individual fits to some of our galaxies reach the bluest UV slopes of β ∼ −3.1 allowed by stellar population models used in this analysis. Therefore, it is likely that stellar population models with a higher amount of Lyman continuum leakage, active galactic nucleus effects, and/or Population III contributions are required to accurately reproduce the rest-UV and optical properties of some of our bluest galaxies. This dust-free early view confirms that our current cosmological understanding of gradual mass + dust buildup of galaxies with cosmic time is largely accurate to describe the ∼0.7–1.5 Gyr age window of the universe. The abundance of a large population of UV faint dust-poor systems may point to a dominance of low-mass galaxies at z > 6 playing a vital role in cosmic reionization
The production of ionizing photons in UV-faint z ∼ 3–7 galaxies
No full textAims. The demographics of the production and escape of ionizing photons from UV-faint early galaxies is a key unknown that has hindered attempts to discover the primary drivers of reionization. With the advent of JWST, it is finally possible to observe the rest-frame optical nebular emission from individual sub-L*z > 3 galaxies to measure the production rate of ionizing photons, ξ_(ion).
Methods. Here we study a sample of 370 z ∼ 3 − 7 galaxies spanning −23 < M_(UV) < −15.5 (median M_(UV) ≈ −18) with deep multiband HST and JWST/NIRCam photometry that covers the rest-UV to the optical from the GLASS and UNCOVER JWST surveys. Our sample includes 102 galaxies with Lyman-alpha emission detected in MUSE spectroscopy. We used Hα fluxes inferred from NIRCam photometry to estimate the production rate of ionizing photons that do not escape these galaxies, ξ_(ion)(1 − f_(esc)).
Results. We find median log₁₀_ξ(ion)(1 − f_(esc)) = 25.33 ± 0.47, with a broad intrinsic scatter of 0.42 dex, which implies a broad range of galaxy properties and ages in our UV-faint sample. Galaxies detected with Lyman-alpha have ∼0.1 dex higher ξ_(ion)(1 − f_(esc)), which is explained by their higher Hα equivalent width distribution; this implies younger ages and higher specific star formation rates and, thus, more O/B stars. We find significant trends of increasing ξ_(ion)(1 − f_(esc)) with increasing Hα equivalent width, decreasing UV luminosity, and decreasing UV slope; this implies that the production of ionizing photons is enhanced in young galaxies with assumed low metallicities. We find no significant evidence for sources with very high ionizing escape fractions (f_(esc) > 0.5) in our sample based on their photometric properties, even amongst the Lyman-alpha-selected galaxies.
Conclusions. This work demonstrates that considering the full distribution of ξ_(ion) across galaxy properties is important for assessing the primary drivers of reionization