Bump Feature Research Articles

Early-time Observations of SN 2023wrk: A Luminous Type Ia Supernova with Significant Unburned Carbon in the Outer Ejecta

We present extensive photometric and spectroscopic observations of the nearby Type Ia supernova (SN) 2023wrk at a distance of about 40 Mpc. The earliest detection of this SN can be traced back to a few hours after the explosion. Within the first few days, the light curve shows a bump feature, while the B − V color is blue and remains nearly constant. The overall spectral evolution is similar to that of an SN 1991T/SN 1999aa-like SN Ia, while the C ii λ6580 absorption line appears to be unusually strong in the first spectrum taken at t ≈ −15.4 days after the maximum light. This carbon feature disappears quickly in subsequent evolution but it reappears at around the time of peak brightness. The complex evolution of the carbon line and the possible detection of Ni iii absorption around 4700 Å and 5300 Å in the earliest spectra indicate macroscopic mixing of fuel and ash. The strong carbon lines are likely related to the collision of SN ejecta with unbound carbon, consistent with the predictions of pulsational delayed-detonation or carbon-rich circumstellar-matter interaction models. Among those carbon-rich SNe Ia with strong C ii λ6580 absorption at very early times, the line-strength ratio of C ii to Si ii and the B − V color evolution are found to exhibit large diversity, which may be attributed to different properties of unbound carbon and outward-mixing 56Ni.

Galaxies with grains: unraveling dust evolution and extinction curves with hydrodynamical simulations

Dust in galaxies is an important tracer of galaxy properties and their evolution over time. The physical origin of the grain size distribution, the dust chemical composition, and, hence, the associated ultraviolet-to-optical extinctions in diverse galaxies remains elusive. To address this issue, we introduce a model for dust evolution in the RAMSES code for simulations of galaxies with a resolved multiphase interstellar medium. Dust is modelled as a fluid transported with the gas component, and is decomposed into two sizes, 5 nm and 0.1 μm, and two chemical compositions for carbonaceous and silicate grains. This dust model includes the growth of dust by accretion of elements from the gas phase and by the release of dust in stellar ejecta, the destruction by thermal sputtering, supernovae, and astration, and the exchange of dust mass between the two main populations of grain sizes by coagulation and shattering. Using a suite of isolated disc simulations with different masses and metallicities, the simulations can explore the role of these processes in shaping the key properties of dust in galaxies. The simulated Milky Way analogue reproduces the dust-to-metal mass ratio, depletion factors, size distribution and extinction curves of the Milky Way. Galaxies with lower metallicities reproduce the observed decrease in the dust-to-metal mass ratio with metallicity at around a few 0.1 Z⊙. This break in the dust-to-metal ratio corresponds to a galactic gas metallicity threshold that marks the transition from an ejecta-dominated to an accretion-dominated grain growth, and that is different for silicate and carbonaceous grains, with ≃0.1 Z⊙ and ≃0.5 Z⊙ respectively. This leads to more Magellanic Cloud-like extinction curves, i.e. with steeper slopes in the ultraviolet and a weaker bump feature at 2175 Å, in galaxies with lower masses and lower metallicities. Steeper slopes in these galaxies are caused by the combination of the higher efficiency of gas accretion by silicate relative to carbonaceous grains and by the low rates of coagulation that preserves the amount of small silicate grains. Weak bumps are due to the overall inefficient accretion growth of carbonaceous dust at low metallicity, whose growth is mostly supported by the release of large grains in SN ejecta. We also show that the formation of CO molecules is a key component to limit the ability of carbonaceous dust to grow, in particular in low-metallicity gas-rich galaxies.

Optical Transient Source AT2021lfa: A Possible “Dirty Fireball”

AT2021lfa, also known as ZTF21aayokph, was detected by the Zwicky Transient Facility on 2021 May 4, at 05:34:48 UTC. Follow-up observations were conducted using a range of ground-based optical telescopes, as well as Swift/XRT and VLA instruments. AT2021lfa is classified as an “orphan afterglow” candidate due to its rapid flux decline and its reddened color (g − r = 0.17 ± 0.14 mag). For an optical transient source without prompt gamma-ray detection, one key point is to determine its burst time. Here we measure the burst time through fitting the initial bump feature of AT2021lfa and obtain its burst time as 2021 May 3, at 22:09:50 UTC. Using afterglowpy, we model the multi-band afterglow of AT2021lfa and find that the standard model cannot reproduce the late radio observations well. Considering that the microphysical parameters ϵ e , ϵ B (the energy fraction given to electrons and magnetic field), and ξ N (the fraction of accelerated electrons) may vary with time, we then model the afterglow of AT2021lfa taking into account the temporal evolution of the physical parameters ϵ e , ϵ B , and ξ N and find in this case the multi-wavelength observations can be reproduced well. The initial Lorentz factor of AT2021lfa can be estimated from the peak time of the early afterglow, which yields a value of about 18, suggesting that AT2021lfa should be classified as a “dirty fireball.” From the upper limit for the prompt emission energy of AT2021lfa, we obtain that the radiation efficiency is less than 0.02%, which is much smaller than that of ordinary gamma-ray bursts (GRBs). It is also interesting that the fitted values of jet angle and viewing angle are very large, θ c ∼ 0.66 rad, θ v ∼ 0.53 rad, which may lead to the low Lorentz factor and radiation efficiency. When compared with GRB afterglow samples, it is evident that the onset bump timescale of AT2021lfa satisfies the empirical relationships observed in GRB samples. Additionally, the luminosity of AT2021lfa falls within the range of observations for GRB samples; however, approximately 1 day after the burst, its luminosity exceeds that of the majority of GRB samples.

The Spectral Energy Distributions and Bolometric Luminosities of Local AGN: Study of the Complete 12 μm AGN Sample

We measure the bolometric luminosity of a complete and unbiased 12 μm-selected sample of active galactic nuclei (AGN) in the local Universe. For each galaxy, we used a 10-band radio-to-X-ray spectral energy distribution (SED) to isolate the genuine AGN continuum in each band, including subarcsecond measurements where available, and correcting those contaminated by the host galaxy. We derive the median SED of Seyfert type 1 AGN, Seyferts with hidden broad lines (HBLs), Seyferts of type 2, and LINER nuclei in our sample. The median Seyfert 1 SED shows the characteristic blue bump feature in the UV, but nevertheless, the largest contribution to the bolometric luminosity comes from the IR and X-ray continua. The median SEDs of both HBL and type 2 AGN are affected by starlight contamination in the optical/UV. The median SED of HBL AGN is consistent with that of Seyfert 1s, when an extinction of A V ∼ 1.2 mag is applied. The comprehensive SEDs allowed us to measure accurate bolometric luminosities and derive robust bolometric corrections for the different tracers. The 12 μm and K-band nuclear luminosities have good linear correlations with the bolometric luminosity, similar to those in the X-rays. We derive bolometric corrections for either continuum bands (K band, 12 μm, 2–10 keV, and 14–195 keV) or narrow emission lines (mid-IR high-ionization lines of [O iv] and [Ne v] and optical [O iii] 5007 Å) as well as for combinations of IR continuum and line emission. A combination of continuum plus line emission accurately predicts the bolometric luminosity up to quasar luminosities (∼1046 erg s−1).

Primordial black holes in non-canonical scalar field inflation driven by quartic potential in the presence of bump

Here, generation of Primordial Black Holes (PBHs) from quartic potential in the presence of a tiny bump in non-canonical inflationary model has been inquired. It is demonstrated that, a viable inflationary era can be driven through the quartic potential in non-canonical framework with a power-law Lagrangian density. Furthermore, setting a suitable function of inflaton field as a correction term (like a bump) to the quartic potential, causes the inflaton to slow down for a while. In such a short time span, the amplitude of the scalar perturbations power spectrum on small scales grows up sufficiently versus CMB scales. In addition to the bump feature, the enhancing effect of the α parameter of the Lagrangian on the amplitude of the scalar power spectrum has been shown. Fine tuning of three parameter Cases of the model results in generating of three Cases of PBHs. In addition, we investigate the secondary Gravitational Waves (GWs) produced during generation of PBHs and show that their contemporary density parameter spectra (ΩGW0 ) can be tracked down by GWs detectors.

Identification of oxidized platinum single atoms on chlorinated γ–alumina support by density functional theory calculations and X-ray absorption spectroscopy

The existence and nature of oxidized Pt single atoms (SA) are unraveled on two γ-Al2O3 supported Pt catalysts (0.3 wt%) containing two chlorine contents (0.1 and 1.4 wt%) characterized by HR-HAADF-STEM and HERFD-XANES/EXAFS after a calcination treatment at 520 °C. Pt SA are revealed as PtOxCly complexes where the number of oxygen (x) and chlorine (y) ligands directly depends on the chlorine content. In order to interpret these experimental observations and provide coherent atomic structures for these PtOxCly complexes, the thermodynamic stability of the oxidized Pt SA species supported on the (100) surface model of γ-Al2O3 is determined by density functional theory (DFT) calculations as a function of the calcination conditions determined by the temperature, and partial pressures of H2O, HCl and O2. It is shown that various ligands such as Cl, OH, O (from the alumina surface or as extra-ligands) and H2O are coordinated to Pt depending on the conditions and chlorine content. Various square planar and square-based pyramidal PtOxCly species such as PtO2, PtOCl2, PtCl4 are found to be stable in calcination conditions, while octahedral Pt(OH)xCl4-x(H2O) are stabilized in XAS recording conditions. The features of these DFT simulated octahedral Pt SA species are successfully compared to XAS data. On one hand, based on thermodynamics arguments, we proposed models of supported complexes in agreement with EXAFS coordination numbers and distances (Pt-O, Pt-Cl and Pt-Al). On the other hand, the simulated XANES spectra at the Pt L3-edge for these complexes match well with the experimental HERFD-XANES and reveal that the bump feature observed between 11575 eV and 11585 eV (post-edge signal) is a tracer of the amount of Cl coordinated to Pt SA.

Bump feature detection of the road surface based on the Bi-LSTM

Abstract The road network is the basic facility for transportation systems in the city. Every day, a large number of vehicles move on the road and exert different pressure on the ground, which leads to various problems for the road surface, such as the bump features of the road surface (BFRS). However, traditional methods, such as detecting BFRS manually or with professional equipment, require a lot of professional management and devices. Based on the mobile sensor and the bidirectional long short-term memory (Bi-LSTM), a detection method for BFRS is proposed. The BFRS detection method proposed in this article solves the problem that other BFRS detection methods cannot detect large area road surface efficiently and provides an algorithm idea for efficient detection of large area road surface BFRS. The mobile phone with multi-sensors is carried on vehicles, and the BFRS information is logged during the movements. The orientation of the mobile is computed according to the gyroscope. The actual posture of the acceleration sensor is adjusted with the reference coordinate system, whose z-axis is vertical to the ground. This article uses the adjusted acceleration data as the training dataset and labels it according to time stamps and videos recorded by the driving recorder. Finally, the Bi-LSTM is constructed and trained, followed by the BFRS detection. The results show that it can detect BFRS in different regions. The detection accuracy of the campus section and the extended experiment was 92.85 and 87.99%, respectively.

Ultraviolet electronic spectroscopy of heavily substituted naphthalene derivatives

Context. The so-called bump spectral signature observable on interstellar extinction curves, peaking at 217.5 nm, is commonly assigned to π* ← π transitions from carbonaceous carriers, but the exact nature of the carbonaceous carriers remains debated. Aims. To constrain the chemical structures associated with the bump carriers, we record and compare the UV spectra of a large variety of carbonaceous molecules to this interstellar feature. Methods. Large carbonaceous molecules, such as polycyclic aromatic hydrocarbons (PAHs), were produced by a combustion process stabilized at low pressure under rich flame conditions. Species were extracted and probed through resonance enhanced multiphoton ionization spectroscopy coupled to a time-of-flight mass spectrometer. Masses and absorption profiles of the carbonaceous molecules were measured, and their spectra were compared to the bump feature. Results. Species showing a specific mass progression starting at mass 128 u visible up to mass 394 u with a characteristic progression of +14 u present a common electronic absorption band profile peaking asymptotically around 220 nm. The first masses were assigned to a naphthalene C10H8 molecule and two of its derivatives: C10H7CH3 and C10H7C2H5. The mass progression of +14 u is explained by successive H atom substitutions by CH3 functional groups. This mass distribution was thus assigned to naphthalene derivatives with large aliphatic carbon substitution. This derivative family shows an electronic band assigned to S3 ← S0 transitions involving electron promotion within the π aromatic orbitals of the naphathlene chromophore. More importantly, after a few substitutions, the position of the band converges asymptotically to a value close to the interstellar bump signature, independent of the molecule size. Conclusions. Based on the asymptotic behavior of the larger members in the species distribution, a similar band position is expected from double aromatic ring substructures within hydrogenated amorphous carbons (HACs). Similar to the conclusions of previous works, we find substituted naphthalene units as substructures of interstellar HACs to be good candidates as carriers of the bump feature.

Theoretical study of infrared and ultraviolet spectra of 14 isomers of C24 and comparison with astronomical observations

ABSTRACT The present paper discusses the infrared features of C24 based on the density functional theory calculation and suggests some of the features observed in celestial objects may be attributed to C24. We also calculate the electronic absorption spectra of the C24 isomers to compare with the bump feature at 217 nm in the interstellar extinction curve. The C24 isomers are of four groups viz. cage, planar, bowl, and ring forms, and the present study considers their neutral and charged states. The structural parameters are reported for the first time. The planar structure is the most stable and the ring structure has a significant dipole moment observed. We extract theoretical infrared spectra of fourteen isomers in their neutral and charged states at the B3LYP/6–311++G** level of theory. The time-dependent density functional theory approach is used to calculate the electronic transitions, the absorbance, and the Highest Occupied Molecular Orbitals (HOMO) to Lowest Unoccupied Molecular Orbitals (LUMO) gaps of the 14 C24 isomers in their neutral and charged states. Upon ionization, significant changes are observed in the infrared and electronic absorption spectra, and the structural parameters. Average theoretical spectra of the cage, planar, bowl, and ring of the C24 isomer show the features at 6.2, 7.65, 8.65, 11.3, 12.8, and 35.6 μm, which match with the features in the observed spectra of the reflection nebulae, NGC 2023 and NGC 7023. A sign of a bump in the ultraviolet at around 218 nm is observed in the electronic absorption spectra.

Investigating the constraints on primordial features with future cosmic microwave background and galaxy surveys

In this article, we do a thorough investigation of the competency of the forthcoming Cosmic Microwave Background (CMB) and Galaxy surveys in probing the features in the primordial power spectrum. Primordial features are specific model-dependent corrections on top of the standard power-law inflationary power spectrum; the functional form being given by different inflationary scenarios. Signature of any significant departure from the feature-less power spectrum will enable us to decipher the intricacies of the inflationary Universe. Here, we delve into three major yet distinct features, namely, Bump feature, Sharp feature signal, and Resonance feature signal. To analyse the features, we adopt a specific template for each feature model. We estimate the possible constraints on the feature parameters by employing Fisher matrix forecast analysis for the upcoming CMB missions such as CMB-S4, CORE-M5, LiteBIRD, PICO conjointly with DESI, and EUCLID galaxy surveys. To this end, we make use of four distinct observations to forecast on the bounds on the model parameters, namely, CMB, Baryon Acoustic Oscillations (BAO), Galaxy Clustering and Gravitational Weak Lensing orCosmic Shear and their permissible synergy. For large scale structure (LSS) information, we consider different upper limits of scale for different redshifts for the purpose of circumventing the propagation of the errors stemming from the uncertainties on nonlinear scales into the constraints on the feature parameters. A comparative analysis of all three features has been done to estimate relative capabilities of these upcoming observations in shedding light on this crucial aspect of precision cosmology.

The 2175 Å bump features in FeLoBAL quasars: One indicator of MW-like dust in the nuclear region of quasars

To investigate the properties of dust in the nuclear region of quasars, we explored the extinction curves of the iron low-ionisation broad absorption line (FeLoBAL) quasar SDSS J163004.29+311957.6 and its two analogues. The parametrised extinction curves indicated the Milky Way-like 2175 Å bump features in underlying extinction, which are similar to those seen in the Local Group and in a subset of high-redshift star-forming galaxies. Compared to the bump features in the Large Magellanic Cloud (LMC), the detections in this work are much closer to those in the Milky Way (MW). These bump features, as well as those in the high- and low-ionisation broad absorption line (BAL) quasars with 2175 Å bumps, are probably the counterpart of the 2175 Å bump features in the quasar environment. This type of dust grain is generally small, easily disrupted by high-energy photons, and has difficulty surviving in the radiation field of the active galactic nucleus. However, due to the presence of absorption-line outflows, the 2175 Å bump feature in quasars, which should be rare, is seen many times in BAL quasars. The shielding effect of outflow clouds allows the MW-like dust grains to be assembled or extends the survival period in the quasar nuclear region. The process and physical and chemical conditions deserve further observational study and investigation.

The UV 2175Å attenuation bump and its correlation with PAH emission at z ∼ 2

ABSTRACT The UV bump is a broad absorption feature centred at 2175 Å that is seen in the attenuation/extinction curve of some galaxies, but its origin is not well known. Here, we use a sample of 86 star-forming galaxies at z = 1.7–2.7 with deep rest-frame UV spectroscopy from the MUSE HUDF Survey to study the connection between the strength of the observed UV 2175 Å bump and the Spitzer/MIPS 24 $\mu$m photometry, which at the redshift range of our sample probes mid-IR polycyclic aromatic hydrocarbon (PAH) emission at ∼6–8 μm. The sample has robust spectroscopic redshifts and consists of typical main-sequence galaxies with a wide range in stellar mass (log (M*/M⊙) ∼ 8.5–10.7) and star formation rates (SFRs; SFR$\sim 1\rm{-}100\, M_{\odot }\, {\rm yr}^{-1}$). Galaxies with MIPS detections have strong UV bumps, except for those with mass-weighted ages younger than ∼150 Myr. We find that the UV bump amplitude does not change with SFR at fixed stellar mass but increases with mass at fixed SFR. The UV bump amplitude and the PAH strength (defined as mid-IR emission normalized by SFR) are highly correlated and both also correlate strongly with stellar mass. We interpret these correlations as the result of the mass–metallicity relationship, such that at low metallicities PAH emission is weak due to a lower abundance of PAH molecules. The weak or complete absence of the 2175 Å bump feature on top of the underlying smooth attenuation curve at low mass/metallicities is then expected if the PAH carriers are the main source of the additional UV absorption.

Discovery of a luminous starburst galaxy with hundreds of thousands of Wolf–Rayet stars

ABSTRACT This paper reports the detection of a strong Wolf–Rayet (W-R) emission bump feature at 4400–4700 Å in the optical spectrum of a distant galaxy SDSS J150009.81+452844.4 at a redshift of 0.453. The estimated number of W-R stars is 1.5 × 105 without applying any internal extinction correction, and at least 4.5 × 105 after correcting for dust extinction. Such a number, though with uncertainties inherent from the extinction correction and others, appears to outnumber those in previous W-R galaxies after correcting for intrinsic dust extinction with the numbers available in the literature. These massive stars must have formed in an instantaneous star-forming episode lasting less than about 5 Myr. We estimate a star formation rate of at least ∼80 $\mathrm{M}_{\odot }\, \mathrm{yr^{-1}}$, indicative of a violent starburst. Its mid-infrared spectrum resembles closely those of typical local ultraluminous infrared galaxies (ULIRGs). From optical to ultraviolet, it possesses a luminous blue continuum, indicating that the starburst is not heavily obscured, in contrast to that found in most ULIRGs. There is evidence for strong outflows based on the detection of systematically blue-shifted broad wings in the nebular emission lines (a bulk velocity −190 km s−1), as well as in the blue-shifted Mg ii absorption lines. The emission-line gases show a wide velocity range, from −1200 to ∼−2000 km s−1 in blueshift to 570 km s−1 in redshift. We interpret this as a galactic fountain, of which part of the outflowing gas may be falling back to the galactic plane. Our method could be used to find a sample of similar objects, which would help understand the star formation history and stellar feedback in starburst galaxies.

SN 2018agk: A Prototypical Type Ia Supernova with a Smooth Power-law Rise in Kepler (K2)

Abstract We present the 30 minutes cadence Kepler/K2 light curve of the Type Ia supernova (SN Ia) SN 2018agk, covering approximately one week before explosion, the full rise phase, and the decline until 40 days after peak. We additionally present ground-based observations in multiple bands within the same time range, including the 1 day cadence DECam observations within the first ∼5 days after the first light. The Kepler early light curve is fully consistent with a single power-law rise, without evidence of any bump feature. We compare SN 2018agk with a sample of other SNe Ia without early excess flux from the literature. We find that SNe Ia without excess flux have slowly evolving early colors in a narrow range (g − i ≈ −0.20 ± 0.20 mag) within the first ∼10 days. On the other hand, among SNe Ia detected with excess, SN 2017cbv and SN 2018oh tend to be bluer, while iPTF16abc’s evolution is similar to normal SNe Ia without excess in g − i. We further compare the Kepler light curve of SN 2018agk with companion-interaction models, and rule out the existence of a typical nondegenerate companion undergoing Roche lobe overflow at viewing angles smaller than 45°.

Collision rates of planetesimals near mean-motion resonances

ABSTRACT In circumstellar discs, collisional grinding of planetesimals produces second-generation dust. While it remains unclear whether this ever becomes a major component of the total dust content, the presence of such dust, and potentially the substructure within it, can be used to explore a disc’s physical conditions. A perturbing planet produces non-axisymmetric structures and gaps in the dust, regardless of its origin. The dynamics of planetesimals, however, will be very different than that of small dust grains due to weaker gas interactions. Therefore, planetesimal collisions could create dusty disc structures that would not exist otherwise. In this work, we use N-body simulations to investigate the collision rate profile of planetesimals near mean-motion resonances. We find that a distinct bump or dip feature is produced in the collision profile, the presence of which depends on the libration width of the resonance and the separation between the peri- and apocentre distances of the edges of the resonance. The presence of one of these two features depends on the mass and eccentricity of the planet. Assuming that the radial dust emission traces the planetesimal collision profile, the presence of a bump or dip feature in the dust emission at the 2:1 mean-motion resonance can constrain the orbital properties of the perturbing planet. This assumption is valid, so long as radial drift does not play a significant role during the collisional cascade process. Under this assumption, these features in the dust emission should be marginally observable in nearby protoplanetary discs with ALMA.

Dissecting the Energy Budget of a Gamma-Ray Burst Fireball

Abstract The jet composition and radiative efficiency of gamma-ray bursts (GRBs) are poorly constrained from the data. If the jet composition is matter-dominated (i.e., a fireball), the GRB prompt emission spectra would include a dominant thermal component originating from the fireball photosphere and a nonthermal component presumably originating from internal shocks whose radii are greater than the photosphere radius. We propose a method to directly dissect the GRB fireball energy budget into three components and measure their values by combining the prompt emission and early afterglow data. The measured parameters include the initial dimensionless specific enthalpy density (η), bulk Lorentz factors at the photosphere radius (Γph) and before fireball deceleration (Γ0), the amount of mass loading (M), and the GRB radiative efficiency (η γ ). All the parameters can be derived from the data for a GRB with a dominant thermal spectral component, a deceleration bump feature in the early afterglow lightcurve, and a measured redshift. The results only weakly depend on the density n of the interstellar medium when the composition parameter (typically unity) is specified.

Magnetic field direction dependence of topological Hall effect like features in synthetic ferromagnetic and antiferromagnetic multilayers

The anomalies in the transverse resistivity are usually thought to be Topological Hall Effects (THEs), which have been considered as the trait of topologically nontrivial spin textures, such as the skyrmion phase. However, the origin of the THE-like features is still under debate. Here, we present the observation of THE-like features in synthetic antiferromagnetic [Pd/Co]/Ru/[Co/Pd] and synthetic ferromagnetic [Pd/Co]/NiO/[Co/Pd] structures. The Pd-rich alloys, which are formed due to the heterogeneous component and the gradual intermixing at the Co/Pd interface, result in a negative anomalous Hall effect coefficient, causing the peak and dip features in transport measurements. By changing the external magnetic field from out-of-plane to in-plane, the magnitude and width of the bump feature in THE curves can be modified, which is caused by the different anisotropy energy of the components in the heterogeneous ferromagnets. The present work broadens the perception of THE-like features and may add a different dimension to understand the magnetization reversal in magnetic multilayers.

Charge carrier transport with low-temperature anomalies in engineered 4d/5d oxide superlattices of (Sr2IrO4)4/(Sr3Ru2O7)N

We report the tunable conducting behavior of a series of ${(\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4})}_{4}/{(\mathrm{S}{\mathrm{r}}_{3}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7})}_{N}$ ($N$ = 1, 2, and 4) atomic layer superlattices, in which phases of itinerant electrons, itinerant holes, localized electrons, and an anomalous charge region can be varied dependent on the period and the temperature. Specifically, for the $N$ = 4 superlattice, the electron-to-hole transition occurs at a temperature of 35 K, at which the sample behaves as an intrinsic insulator without either electrons or holes. Upon further reducing the temperature to below 16 K, the superlattice enters an anomalous phase region in which an abrupt zero-to-negative magnetoresistance transition and a Hall resistivity kink are observed at 1.3 and 2.1 T, respectively. Above these fields, polarized neutron reflectivity measurements revealed ferromagnetism confined in the $\mathrm{S}{\mathrm{r}}_{3}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$ layers. Moreover, the $N$ = 2 superlattice exhibits a bump feature in the anomalous Hall resistivity near 1.3 T, which is similar to the previously reported topological Hall phenomenon in ultrathin $\mathrm{SrRu}{\mathrm{O}}_{3}$ heterostructures. We demonstrate that the layered $4d/5d$ oxide superlattice is a powerful platform in engineering exotic types of phases which have not been explored in their thin-film or bulk samples.

Using Multiwavelength Variability to Explore the Connection among X-Ray Emission, the Far-ultraviolet H2 Bump, and Accretion in T Tauri Stars

Abstract The high-energy radiation fields of T Tauri stars (TTS) should affect the surrounding circumstellar disk, having implications for disk transport and heating. Yet observational evidence of the effect of high-energy fields on disks is scarce. Here we investigate the connection between X-ray emission and the innermost gas disk by leveraging the variability of TTS. We obtained multiple epochs of coordinated data (taken either simultaneously or within a few hours) of accreting TTS with the Hubble Space Telescope, the Neil Gehrels Swift Observatory, and the Chandra X-ray Observatory. We measured the far-ultraviolet (FUV) H2 bump feature at 1600 Å, which traces gas <1 au from the star; the near-ultraviolet emission, from which we extract the accretion luminosity; and also the X-ray luminosity. We do not find a correlation between the FUV H2 bump and X-ray luminosity. Therefore, an observable tracer of the effect of X-ray ionization in the innermost disk remains elusive. We report a correlation between the FUV H2 bump and accretion luminosity, linking this feature to the disk surface density. We also see a correlation between the X-ray luminosity and the accretion column density, implying that flaring activity may influence accretion. These results stress the importance of coordinated multiwavelength work to understand TTS.

Role of the crystal electric field on the two magnetic transitions in the orthorhombic YbMnO3 perovskite

In orthorhombic ${\mathrm{LuMnO}}_{3}$ perovskite with nonmagnetic ${\mathrm{Lu}}^{+3}$ ions ($4{f}^{14}5{d}^{0}6{s}^{0}$) there exists one magnetic transition of ${\mathrm{Mn}}^{+3}$ ions at ${T}_{N}\ensuremath{\approx}35.5$ K. In ${\mathrm{YbMnO}}_{3}$ perovskite with ${\mathrm{Yb}}^{+3}$ ions of one electron less ($4{f}^{13}5{d}^{0}6{s}^{0}$), two magnetic transitions are observed at ${T}_{N}\ensuremath{\approx}43$ K and $T\ensuremath{\approx}3$--4 K, respectively. While the transition at 43 K in ${\mathrm{YbMnO}}_{3}$ was attributed to the same magnetic ordering of ${\mathrm{Mn}}^{+3}$ moments as ${\mathrm{LuMnO}}_{3}$ at 35.5 K, the nature of the magnetic transition at 3--4 K is still unresolved. Although the bump feature in magnetic susceptibility hints at a possible antiferromagnetic ordering of ${\mathrm{Yb}}^{+3}$ ions, no clear magnetic ordering of ${\mathrm{Yb}}^{+3}$ was determined in either neutron scattering diffraction or in M\ossbauer spectra of iron-doped ${\mathrm{YbMnO}}_{3}$. To explain the amplitude-modulated nature of the low magnetic anomaly, we propose in this paper that a gradual quenching of the orbital moment of ${\mathrm{Yb}}^{+3}$ ions below a critical temperature is a possible mechanism. The small crystal field splitting of $4f$ electrons can survive only at extremely low temperature because of thermal fluctuation. In addition, we show, like in ${\mathrm{LuMnO}}_{3}$, that ${\mathrm{YbMnO}}_{3}$ takes an E-type antiferromagnetic ground state for its Mn ions and can be tuned into ferromagnetic state when (110)-oriented ${\mathrm{YAlO}}_{3}$ is used as a substrate.