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Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-resolution Data
No full textThe formation and evolution pathway for the directly imaged multiplanetary system HR 8799 remains mysterious. Accurate constraints on the chemical composition of the planetary atmosphere(s) are key to solving the mystery. We perform a detailed atmospheric retrieval on HR 8799 c to infer the chemical abundances and abundance ratios using a combination of photometric data along with low- and high-resolution spectroscopic data (R ∼ 20–35,000). We specifically retrieve [C/H], [O/H], and C/O and find them to be 0.55_(-0.39)^(+0.36), 0.47_(-0.32)^(+0.31), and 0.67_(-0.15)^(+0.12) at 68% confidence. The superstellar C and O abundances, yet a stellar C/O ratio, reveal a potential formation pathway for HR 8799 c. Planet c, and likely the other gas giant planets in the system, formed early on (likely within ∼1 Myr), followed by further atmospheric enrichment in C and O through the accretion of solids beyond the CO ice line. The enrichment either preceded or took place during the early phase of the inward migration to the current planet locations
Excited State and Transient Chemistry of a Perylene Derivative (DBP). An Untold Story
No full textTransient chemistry of sensitizing dyes is important to obtain insights into the photochemical conversion processes of light harvesting assemblies. We have now employed transient absorption spectroscopy (pulsed laser and pulse radiolysis) to characterize the excited state and radical intermediates of a perylene derivative, (5,10,15,20-Tetraphenylbisbenz[5,6]indeno[1,2,3-cd:1′,2′,3′-lm]perylene (DBP). The distinguishable transient absorption features for the singlet and triplet excited states and radical anion and radical cation provide spectral fingerprints to identify the reaction intermediates in photochemical energy and electron transfer processes of composite systems involving DBP. For example, identifying these transients in the energy transfer processes of the rubrene–DBP system would aid in establishing their role as annihilator-emitter for triplet–triplet annihilation up-conversion (TTA-UC). The transient characterization thus serves as an important mechanistic fingerprint for elucidating mechanistic details of systems employing DBP in optoelectronic applications
Integrated Multi‐Cohort Analysis of the Parkinson's Disease Gut Metagenome
No full textBackground. The gut microbiome is altered in several neurologic disorders, including Parkinson's disease (PD).
Objectives. The aim is to profile the fecal gut metagenome in PD for alterations in microbial composition, taxon abundance, metabolic pathways, and microbial gene products, and their relationship with disease progression.
Methods. Shotgun metagenomic sequencing was conducted on 244 stool donors from two independent cohorts in the United States, including individuals with PD (n = 48, n = 47, respectively), environmental household controls (HC, n = 29, n = 30), and community population controls (PC, n = 41, n = 49). Microbial features consistently altered in PD compared to HC and PC subjects were identified. Data were cross-referenced to public metagenomic data sets from two previous studies in Germany and China to determine generalizable microbiome features.
Results. We find several significantly altered taxa between PD and controls within the two cohorts sequenced in this study. Analysis across global cohorts returns consistent changes only in Intestinimonas butyriciproducens. Pathway enrichment analysis reveals disruptions in microbial carbohydrate and lipid metabolism and increased amino acid and nucleotide metabolism in PD. Global gene-level signatures indicate an increased response to oxidative stress, decreased cellular growth and microbial motility, and disrupted intercommunity signaling.
Conclusions. A metagenomic meta-analysis of PD shows consistent and novel alterations in functional metabolic potential and microbial gene abundance across four independent studies from three continents. These data reveal that stereotypic changes in the functional potential of the gut microbiome are a consistent feature of PD, highlighting potential diagnostic and therapeutic avenues for future research
An accurate treatment of scattering and diffusion in piecewise power-law models for cosmic ray and radiation/neutrino transport
No full textA popular numerical method to model the dynamics of a ‘full spectrum’ of cosmic rays (CRs), also applicable to radiation/neutrino hydrodynamics, is to discretize the spectrum at each location/cell as a piecewise power law in ‘bins’ of momentum (or frequency) space. This gives rise to a pair of conserved quantities (e.g. CR number and energy) that are exchanged between cells or bins, which in turn give the update to the normalization and slope of the spectrum in each bin. While these methods can be evolved exactly in momentum-space (e.g. considering injection, absorption, continuous losses/gains), numerical challenges arise dealing with spatial fluxes, if the scattering rates depend on momentum. This has often been treated either by neglecting variation of those rates ‘within the bin,’ or sacrificing conservation – introducing significant errors. Here, we derive a rigorous treatment of these terms, and show that the variation within the bin can be accounted for accurately with a simple set of scalar correction coefficients that can be written entirely in terms of other, explicitly evolved ‘bin-integrated’ quantities. This eliminates the relevant errors without added computational cost, has no effect on the numerical stability of the method, and retains manifest conservation. We derive correction terms both for methods that explicitly integrate flux variables (e.g. two-moment or M1-like) methods, as well as single-moment (advection-diffusion, FLD-like) methods, and approximate corrections valid in various limits
Constraining the X-ray reflection in low accretion-rate active galactic nuclei using XMM-Newton, NuSTAR, and Swift
No full textAn interesting feature of active galactic nuclei (AGN) accreting at low rates is the weakness of the reflection features in their X-ray spectra, which may result from the gradual disappearance of the torus with decreasing accretion rates. It has been suggested that low-luminosity AGN (LLAGN) would exhibit a different reflector configuration than high-luminosity AGN, covering a smaller fraction of the sky or simply having less material. Additionally, we note that the determination of the spectral index (Γ) and the cut-off energy of the primary power-law emission is affected by the inclusion of reflection models, showing their importance in studying accretion mechanisms. This is especially valid in the case of the LLAGN which has previously shown a high dispersion in the relation between Γ and the accretion rate.
Aims. Our purpose is to constrain the geometry and column density of the reflector in a sample of LLAGN covering a broad X-ray range of energy by combining data from XMM-Newton+ NuSTAR + Swift. The spectral analysis also allows us to investigate the accretion mechanism in LLAGN.
Methods. We used XMM-Newton+ NuSTAR + Swift observations of a hard X-ray flux-limited sample of 17 LLAGN from BASS/DR2 with accretion rates of λ_(Edd) = L_(Bol)/L_(Edd) < 10⁻³. We fit all spectra using the reflection model for torus (BORUS) and accretion disk (XILLVER) reflectors.
Results. We found a tentative correlation between the torus column density and the accretion rate, with LLAGN showing a lower column density than the high-luminosity objects. We also confirm the relation between Γ and λ_(Edd), with a smaller scatter than previously reported, thanks to the inclusion of high-energy data and the reflection models. Our results are consistent with a break at λ_(Edd) ∼ 10⁻³, which is suggestive of a different accretion mechanism compared with higher accretion AGN
Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations
No full textLyman-break galaxy (LBG) candidates at z ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (z ≲ 7) may also mimic the near-infrared (near-IR) colors of z > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at z ≈ 5.1. We also present a tentative 2.6σ SCUBA-2 detection at 850 μm around a recently identified z ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a z ∼ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply z ∼ 4–6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations
Two-phonon scattering in nonpolar semiconductors: A first-principles study of warm electron transport in Si
No full textThe ab initio theory of charge transport in semiconductors typically employs the lowest-order perturbation theory in which electrons interact with one phonon (1ph). This theory is accepted to be adequate to explain the low-field mobility of nonpolar semiconductors but has not been tested extensively beyond the low-field regime. Here, we report first-principles calculations of the electric field dependence of the electron mobility of Si as described by the warm electron coefficient β. Although the 1ph theory overestimates the low-field mobility by only around 20%, it overestimates β by over a factor of two over a range of temperatures and crystallographic axes. We show that the discrepancy in β is reconciled by the inclusion of on-shell iterated two-phonon (2ph) scattering processes, indicating that scattering from higher-order electron-phonon interactions is non-negligible even in nonpolar semiconductors. Further, a ∼20% underestimate of the low-field mobility with 2ph scattering suggests that nontrivial cancellations may occur in the perturbative expansion of the electron-phonon interaction
Observation of triple J/ψ meson production in proton-proton collisions
No full textProtons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be 272+141−104(stat)±17(syst)fb, and compared it to theoretical expectations for triple-J/ψ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double-and triple-parton scattering are the dominant contributions for the measured process
The Evolution and Mass Dependence of Galaxy Cluster Pressure Profiles at 0.05 ≤ z ≤ 0.60 and 4 × 10¹⁴ M_⊙ ≤ M₅₀₀ ≤ 30 × 10¹⁴ M_⊙
No full textWe have combined X-ray observations from Chandra with Sunyaev–Zel’dovich effect data from Planck and Bolocam to measure intracluster medium pressure profiles from 0.03 R₅₀₀ ≤ R ≤ 5 R₅₀₀ for a sample of 21 low-z galaxy clusters with a median redshift of〈z〉= 0.08 and a median mass of =〈M₅₀₀〉= 6.1 × 10¹⁴ M_⊙ and a sample of 19 mid-z galaxy clusters with〈z〉= 0.50 and〈M₅₀₀〉= 10.6 × 10¹⁴ M_⊙. The mean scaled pressure in the low-z sample is lower at small radii and higher at large radii, a trend that is accurately reproduced in similarly selected samples from The Three Hundred simulations. This difference appears to be primarily due to dynamical state at small radii, evolution at intermediate radii, and a combination of evolution and mass dependence at large radii. Furthermore, the overall flattening of the mean scaled pressure profile in the low-z sample compared to the mid-z sample is consistent with expectations due to differences in the mass accretion rate and the fractional impact of feedback mechanisms. In agreement with previous studies, the fractional scatter about the mean scaled pressure profile reaches a minimum of ≃20% near 0.5 R₅₀₀. This scatter is consistent between the low-z and mid-z samples at all radii, suggesting it is not strongly impacted by sample selection, and this general behavior is reproduced in The Three Hundred simulations. Finally, analytic functions that approximately describe the mass and redshift trends in mean pressure profile shape are provided
Engineered zero-dispersion microcombs using CMOS-ready photonics
No full textNormal group velocity dispersion (GVD) microcombs offer high comb line power and high pumping efficiency compared to bright pulse microcombs. The recent demonstration of normal GVD microcombs using CMOS foundry-produced microresonators is an important step toward scalable production. However, the chromatic dispersion of CMOS devices is large and impairs the generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a coupled-ring resonator configuration. Operating in the turnkey self-injection locking mode, the resonator is integrated in a hybrid manner with a semiconductor laser pump to produce high-power efficiency combs spanning a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb lines. Fast, linear optical sampling of the comb waveform is used to observe the rich set of near-zero GVD comb behaviors, including soliton molecules, switching waves (platicons), and their hybrids. Tuning of the 20 GHz repetition rate by electrical actuation enables servo locking to a microwave reference, which simultaneously stabilizes the comb repetition rate, offset frequency, and temporal waveform. This integrated hybrid system could be used in coherent communications or for ultrastable microwave signal generation by two-point optical frequency division