Interferometric Observations Research Articles

A Red-noise Eigenbasis for the Reconstruction of Blobby Images

Abstract We demonstrate the use of an eigenbasis that is derived from principal component analysis (PCA) applied on an ensemble of random-noise images that have a “red” power spectrum; i.e., a spectrum that decreases smoothly from large to small spatial scales. The pattern of the resulting eigenbasis allows for the reconstruction of images with a broad range of image morphologies. In particular, we show that this general eigenbasis can be used to efficiently reconstruct images that resemble possible astronomical sources for interferometric observations, even though the images in the original ensemble used to generate the PCA basis are significantly different from the astronomical images. We further show that the efficiency and fidelity of the image reconstructions depends only weakly on the particular parameters of the red-noise power spectrum used to generate the ensemble of images.

The Complex Infrared Dust Continuum Emission of NGC 1068: Ground-based N- and Q-band Spectroscopy and New Radiative Transfer Models

Abstract Thanks to ground-based infrared and submillimeter observations the study of the dusty torus of nearby active galactic nuclei has greatly advanced in the last years. With the aim of further investigating the nuclear mid-infrared emission of the archetypal Seyfert 2 galaxy NGC 1068, here we present a fitting to the N- and Q-band Michelle/Gemini spectra. We initially test several available spectral energy distribution (SED) libraries, including smooth, clumpy and two-phase torus models, and a clumpy disk+wind model. We find that the spectra of NGC 1068 cannot be reproduced with any of these models. Although, the smooth torus models describe the spectra of NGC 1068 if we allow variation of some model parameters among the two spectral bands. Motivated by this result, we produced new SEDs using the radiative transfer code SKIRT. We use two concentric tori that allow us to test a more complex geometry. We test different values for the inner and outer radii, half-opening angle, radial, and polar exponent of the power-law density profile, opacity, and viewing angle. Furthermore, we also test the dust grains’ size and different optical and calorimetric properties of silicate grains. The best-fitting model consists of two concentric components with outer radii of 1.8 and 28 pc, respectively. We find that the size and the optical and calorimetric properties of graphite and silicate grains in the dust structure are key to reproducing the spectra of NGC 1068. A maximum grain size of 1 μm leads to a significant improvement in the fit. We conclude that the dust in NGC 1068 reaches different scales, where the highest contribution to the mid-infrared is given by a central and compact component. A less dense and extended component is present, which can be either part of the same torus (conforming a flared disk) or can represent the emission of a polar dust component, as already suggested from interferometric observations.

The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE

Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification. Aims. We aim to spatially resolve the photospheric extent as well as the circumstellar environment. Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3–4 μm), M (4.5–5 μm), and N (8–13 μm) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with CO5BOLD and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively. Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration. Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr’s stellar surface and circumstellar environment across a very large spectral domain for the first time.

Probing inner and outer disk misalignments in transition disks

Context. Transition disks are protoplanetary disks with dust-depleted cavities, possibly indicating substantial clearing of their dust content by a massive companion. For several known transition disks, dark regions interpreted as shadows have been observed in scattered light imaging and are hypothesized to originate from misalignments between distinct regions of the disk. Aims. We aim to investigate the presence of misalignments in transition disks. We study the inner disk (<1 au) geometries of a sample of 20 well-known transition disks with Very Large Telescope Interferometer (VLTI) GRAVITY observations and use complementary 12CO and 13CO molecular line archival data from the Atacama Large Millimeter/submillimeter Array (ALMA) to derive the orientation of the outer disk regions (>10 au). Methods. We fit simple parametric models to the visibilities and closure phases of the GRAVITY data to derive the inclination and position angle of the inner disks. The outer disk geometries were derived from Keplerian fits to the ALMA velocity maps and compared to the inner disk constraints. We also predicted the locations of expected shadows for significantly misaligned systems. Results. Our analysis reveals six disks to exhibit significant misalignments between their inner and outer disk structures. The predicted shadow positions agree well with the scattered light images of HD 100453 and HD 142527, and we find supporting evidence for a shadow in the south of the disk around CQ Tau. In the other three targets for which we infer significantly misaligned disks, V1247 Ori, V1366 Ori, and RY Lup, we do not see any evident sign of shadows in the scattered light images. The scattered light shadows observed in DoAr 44, HD 135344 B, and HD 139614 are consistent with our observations, yet the underlying morphology is likely too complex to be described properly by our models and the accuracy achieved by our observations. Conclusions. The combination of near infrared and submillimeter interferometric observations allows us to assess the geometries of the innermost disk regions and those of the outer disk. Whereas we can derive precise constraints on the potential shadow positions for well-resolved inner disks around Herbig Ae/Be stars, the large statistical uncertainties for the marginally resolved inner disks around the T Tauri stars of our sample make it difficult to extract conclusive constraints for the presence of shadows in these systems.

Fundamental stellar parameters of benchmark stars from CHARA interferometry

Context. Stellar models applied to large stellar surveys of the Milky Way need to be properly tested against a sample of stars with highly reliable fundamental stellar parameters. We have established a programme aiming to deliver such a sample of stars. Aims. Here we present new fundamental stellar parameters of nine dwarf stars that will be used as benchmark stars for large stellar surveys. One of these stars is the solar-twin 18 Sco, which is also one of the Gaia-ESO benchmarks. The goal is to reach a precision of 1% in effective temperature (Teff). This precision is important for accurate determinations of the full set of fundamental parameters and abundances of stars observed by the surveys. Methods. We observed HD 131156 (ξ Boo), HD 146233 (18 Sco), HD 152391, HD 173701, HD 185395 (θ Cyg), HD 186408 (16 Cyg A), HD 186427 (16 Cyg B), HD 190360, and HD 207978 (15 Peg) using the high angular resolution optical interferometric instrument PAVO at the CHARA Array. We derived limb-darkening corrections from 3D model atmospheres and determined Teff directly from the Stefan–Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. Surface gravities were estimated from comparisons to Dartmouth stellar evolution model tracks. We collected spectroscopic observations from the ELODIE spectrograph and estimated metallicities ([Fe/H]) from a 1D non-local thermodynamic equilibrium (NLTE) abundance analysis of unblended lines of neutral and singly ionised iron. Results. For eight of the nine stars we measure the Teff ⪅ 1%, and for one star better than 2%. We determined the median uncertainties in log g and [Fe/H] as 0.015 dex and 0.05 dex, respectively. Conclusions. This study presents updated fundamental stellar parameters of nine dwarf stars that can be used as a new set of benchmarks. All the fundamental stellar parameters were based on consistently combining interferometric observations, 3D limb-darkening modelling, and spectroscopic analysis. The next paper in this series will extend our sample to giants in the metal-rich range.

Fundamental stellar parameters of benchmark stars from CHARA interferometry

Context.Large spectroscopic surveys of the Milky Way must be calibrated against a sample of benchmark stars to ensure the reliable determination of atmospheric parameters.Aims.Here, we present new fundamental stellar parameters of seven giant and subgiant stars that will serve as benchmark stars for large surveys. The aim is to reach a precision of 1% in the effective temperature. This precision is essential for accurate determinations of the full set of fundamental parameters and abundances for stars observed by the stellar surveys.Methods.We observed HD 121370 (ηBoo), HD 161797 (μHer), HD 175955, HD 182736, HD 185351, HD 188512 (βAql), and HD 189349, using the high angular resolution optical interferometric instrument PAVO at the CHARA Array. The limb-darkening corrections were determined from 3D model atmospheres based on the STAGGER grid. TheTeffwere determined directly from the Stefan-Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. We estimated surface gravities from comparisons to Dartmouth stellar evolution model tracks. The spectroscopic observations were collected from the ELODIE and FIES spectrographs. We estimated metallicities ([Fe/H]) from a 1D non-local thermodynamic equilibrium (NLTE) abundance analysis of unblended lines of neutral and singly ionised iron.Results.For six of the seven stars, we measured the value ofTeffto better than 1% accuracy. For one star, HD 189349, the uncertainty onTeffis 2%, due to an uncertain bolometric flux. We do not recommend this star as a benchmark until this measurement can be improved. Median uncertainties for all stars in log gand [Fe/H] are 0.034 dex and 0.07 dex, respectively.Conclusions.This study presents updated fundamental stellar parameters of seven giant and subgiant stars that can be used as a new set of benchmarks. All the fundamental stellar parameters were established on the basis of consistent combinations of interferometric observations, 3D limb-darkening modelling, and spectroscopic analysis. This paper in this series follows our previous papers featuring dwarf stars and stars in the metal-poor range.

CNN to mitigate atmospheric turbulence effect on Shack-Hartmann Wavefront Sensing: A case study on the Magdalena Ridge Observatory Interferometer.

The Magdalena Ridge Observatory Interferometer (MROI) utilizes Shack-Hartmann Wavefront Sensing (SH-WFS) for the back-end stability of its beam relay systems in a unique design. The SH-WFS, however, is sensitive to atmospheric turbulence scintillation which can drastically affect its precision in calculating the position of the beam profile it sees. A large number of images are needed to counteract the turbulence effect. Here we use deep learning as an alternative to long averaging cycles. A CNN was trained to map from a number of initial images of a series of star frames to the average image of the entire series at different positions of the beam profile. Under typical seeing conditions expected at MROI, the results showed that the network can map 10 input frames to the average of 100 within the permissible error margin of 0.1 pixels and furnish proper generalization to beam position movements not seen during training. The network can also outperform the averaging technique when both techniques operate on small numbers of input frames such as 10 or 20.

Alternative Physical Method for Retrieving Land Surface Temperatures from Hyperspectral Thermal Infrared Data: Application to IASI Observations

A new two-step physical method was developed to retrieve the land surface temperature (LST) from infrared atmospheric sounding interferometer (IASI) observations. This method relinearized the radiative transfer equation (RTE) by the tangents around the initial estimates of the LST, land surface emissivity (LSE), atmospheric equivalent temperature (Ta), and water vapor content (q). The Tikhonov regularization method and discrepancy principle (DP) iteration algorithm were employed to stabilize the ill-posed problem and obtain the final maximum likelihood solution of the LST with updating the initial estimation of LST, LSE, Ta, and q. A new channel selection scheme was proposed for this physical method to obtain an accurate LST estimation. This physical-based algorithm was tested on both simulated and real data obtained from the IASI. The root-mean-square error (RMSE) of the simulated LST is ~1 K based on an initial LST estimate with an RMSE of 2 K (1.9 K). The sensitivity analysis shows that the LST retrieval accuracy is ~1 K based on an LST with a random error of 3 K, constant initial LSE (0.97), 10% Ta error, and 40% q error. Compared with the Advanced Very High Resolution Radiometer onboard Metop (AVHRR/Metop) LST product, the physical method achieves the LST retrieval accuracy of 1.5 and 1 K for real daytime and nighttime IASI data obtained in the study area. Based on the new method, the LST can be retrieved with an accuracy similar to that of the AVHRR/Metop LST product.

Complex Pre-Sliding Surface Displacements of the Nanyu Landslide in Zhouqu, China Revealed by Interferometric Sentinel-1 and ALOS-2 PALSAR-2 Observations

Complex Pre-Sliding Surface Displacements of the Nanyu Landslide in Zhouqu, China Revealed by Interferometric Sentinel-1 and ALOS-2 PALSAR-2 Observations

Sea Surface States Detection in Polar Regions Using Measurements of Ground-Based GNSS Interferometric Reflectometry

This article analyzes the interferometric measurements of ground-based global navigation satellite systems (GNSSs) stations and proposes a novel method for sea surface states detection. The novel technique benefits from a cost-effective data collection from a large number of global GNSS stations. In this study, we extend a traditional GNSS interferometry reflectometry (GNSS-IR) model so that it can be applied to a multilayer surface by considering the surface roughness, total reflectivity, and penetration loss in multilayer situations. Based on this model, the wavelet analysis is used to perform parameterization on the interferometric observations represented by the signal to noise ratio (SNR). An integration factor and power curve are also proposed to characterize the surface state transition. One-year data from an Arctic geodetic GNSS station in the north of Canada are collected for analysis to validate the proposed approach in comparison with the existing methods based on the amplitude and damping factors. The results show that the new method demonstrates good usability and sensitivity to detect surface state transitions, e.g., icing, snowfall, and snow melting. However, the amplitude and damping factor-based methods derived from the single-layer model are only able to detect the pure ice surface and cannot respond to thick snow conditions. Finally, the high-resolution spaceborne images confirm the reliability of this method, exhibiting a great potential for long-term coastal sea surface detection based on the global geodetic GNSS stations and later being expected to be applied to sense cryosphere surface states.

The Variability of the Black Hole Image in M87 at the Dynamical Timescale

Abstract The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the u–v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.

The non-thermal emission from the colliding-wind binary Apep

Abstract Therecently discovered massive binary system Apep is the most powerful synchrotron emitter among the known Galactic colliding-wind binaries. This makes this particular system of great interest to investigate stellar winds and the non-thermal processes associated with their shocks. This source was detected at various radio bands, and in addition the wind-collision region was resolved by means of very-long baseline interferometric observations. We use a non-thermal emission model for colliding-wind binaries to derive physical properties of this system. The observed morphology in the resolved maps allows us to estimate the system projection angle on the sky to be $\psi \approx 85^\circ$ . The observed radio flux densities also allow us to characterise both the intrinsic synchrotron spectrum of the source and its modifications due to free–free absorption in the stellar winds at low frequencies; from this, we derive mass–loss rates of the stars of $\dot{M}_\mathrm{WN} \approx 4\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ and $\dot{M}_\mathrm{WC} \approx 2.9\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ . Finally, the broadband spectral energy distribution is calculated for different combinations of the remaining free parameters, namely the intensity of the magnetic field and the injected power in non-thermal particles. We show that the degeneracy of these two parameters can be solved with observations in the high-energy domain, most likely in the hard X-rays but also possibly in $\gamma$ -rays under favourable conditions.

Imaging sensitivity of a linear interferometer array on lunar orbit

ABSTRACT Ground-based observation at frequencies below 30 MHz is hindered by the ionosphere of the Earth and radio frequency interference. To map the sky at these low frequencies, we have proposed the Discovering the Sky at the Longest wavelength mission (DSL, also known as the ‘Hongmeng’ mission, which means ‘Primordial Universe’ in Chinese) concept, which employs a linear array of micro-satellites orbiting the Moon. Such an array can make interferometric observations achieving good angular resolutions despite the small size of the antennas. However, it differs from the conventional ground-based interferometer array or even the previous orbital interferometers in many aspects, new data-processing methods need to be developed. In this work, we make a series of simulations to assess the imaging quality and sensitivity of such an array. We start with an input sky model and a simple orbit model, generate mock interferometric visibilities, and then reconstruct the sky map. We consider various observational effects and practical issues, such as the system noise, antenna response, and Moon blockage. Based on the quality of the recovered image, we quantify the imaging capability of the array for different satellite numbers and array configurations. For the first time, we make practical estimates of the point source sensitivity for such a lunar orbit array, and predict the expected number of detectable sources for the mission. Depending on the radio source number distribution which is still very uncertain at these frequencies, the proposed mission can detect 102–104 sources during its operation.

No need for dark matter: resolved kinematics of the ultra-diffuse galaxy AGC 114905

ABSTRACT We present new H i interferometric observations of the gas-rich ultra-diffuse galaxy AGC 114905, which previous work, based on low-resolution data, identified as an outlier of the baryonic Tully–Fisher relation. The new observations, at a spatial resolution ∼2.5 times higher than before, reveal a regular H i disc rotating at about 23 km s−1. Our kinematic parameters, recovered with a robust 3D kinematic modelling fitting technique, show that the flat part of the rotation curve is reached. Intriguingly, the rotation curve can be explained almost entirely by the baryonic mass distribution alone. We show that a standard cold dark matter halo that follows the concentration–halo mass relation fails to reproduce the amplitude of the rotation curve by a large margin. Only a halo with an extremely (and arguably unfeasible) low concentration reaches agreement with the data. We also find that the rotation curve of AGC 114905 deviates strongly from the predictions of modified Newtonian dynamics. The inclination of the galaxy, which is measured independently from our modelling, remains the largest uncertainty in our analysis, but the associated errors are not large enough to reconcile the galaxy with the expectations of cold dark matter or modified Newtonian dynamics.

Microlensing mass measurement from images of rotating gravitational arcs

Gravitational microlensing1 is a powerful technique for measuring the mass of isolated and faint or non-luminous objects in the Milky Way2,3. In most cases, however, additional observations to the photometric light curve are required to measure accurately the mass of the microlens. Long-baseline optical/infrared interferometry provides a new and efficient way to deliver such independent constraints4,5,6,7, as demonstrated recently by first interferometric observations in microlensing event TCP J05074264+2447555 (‘Kojima-1’)8. Here we report real-time observations of gravitationally lensed arcs in rotation around a microlens, Gaia19bld9, made with the PIONIER instrument10 at the Very Large Telescope Interferometer. Our data allowed us to determine the angular separation and length of the arcs, as well as their rotation rate. Combining these measurements with ground-based photometric data enabled the determination of the microlens mass, M = 1.147 ± 0.029 M⊙, to a very high accuracy. We anticipate interferometric microlensing to play an important future role in the mass and distance determination of isolated stellar-mass black holes11,12,13 in the Galaxy, which cannot be addressed by any other technique.

Surveying the Bright Stars by Optical Interferometry. III. A Magnitude-limited Multiplicity Survey of Classical Be Stars

Abstract We present the results of a multiplicity survey for a magnitude-limited sample of 31 classical Be stars conducted with the Navy Precision Optical Interferometer and the Mark III Stellar Interferometer. The interferometric observations were used to detect companions in 10 previously known binary systems. For two of these sources (66 Oph and β Cep) new orbital solutions were obtained, while for a third source (υ Sgr) our observations provide the first direct, visual detection of the hot companion to the primary star. Combining our interferometric observations with an extensive literature search, we conclude that an additional four sources (o Cas, 15 Mon, β Lyr, and β Cep) also contain wider binary components that are physical companions to the narrow binaries, thus forming hierarchical multiple systems. Among the sources not previously confirmed as spectroscopic or visual binaries, BK Cam was resolved on a number of nights within a close physical proximity of another star with relative motion possibly suggesting a physical binary. Combining our interferometric observations with an extensive literature search, we provide a detailed listing of companions known around each star in the sample, and discuss the multiplicity frequency in the sample. We also discuss the prospects for future multiplicity studies of classical Be stars by long-baseline optical interferometry.

Toward Determining the Number of Observable Supermassive Black Hole Shadows

Abstract We present estimates for the number of shadow-resolved supermassive black hole (SMBH) systems that can be detected using radio interferometers, as a function of angular resolution, flux density sensitivity, and observing frequency. Accounting for the distribution of SMBHs across mass, redshift, and accretion rate, we use a new semianalytic spectral energy distribution model to derive the number of SMBHs with detectable and optically thin horizon-scale emission. We demonstrate that (sub)millimeter interferometric observations with ∼0.1 μas resolution and ∼1 μJy sensitivity could access >106 SMBH shadows. We then further decompose the shadow source counts into the number of black holes for which we could expect to observe the first- and second-order lensed photon rings. Accessing the bulk population of first-order photon rings requires ≲2 μas resolution and ≲0.5 mJy sensitivity, whereas doing the same for second-order photon rings requires ≲0.1 μas resolution and ≲5 μJy sensitivity. Our model predicts that with modest improvements to sensitivity, as many as ∼5 additional horizon-resolved sources should become accessible to the current Event Horizon Telescope (EHT), whereas a next-generation EHT observing at 345 GHz should have access to ∼3 times as many sources. More generally, our results can help guide enhancements of current arrays and specifications for future interferometric experiments that aim to spatially resolve a large population of SMBH shadows or higher-order photon rings.

The cosmic-ray ionisation rate in the pre-stellar core L1544

Context. Cosmic rays (CRs), which are energetic particles mainly composed of protons and electrons, play an important role in the chemistry and dynamics of the interstellar medium. In dense environments, they represent the main ionising agent, hence driving the rich chemistry of molecular ions. Furthermore, they determine the ionisation fraction, which regulates the degree of coupling between the gas and the interstellar magnetic fields, and the heating of the gas. Estimates of the CR ionisation rate of molecular hydrogen (ζ2) span several orders of magnitude, depending on the targeted sources and on the method used. Aims. Recent theoretical models have characterised the CR attenuation with increasing density. We aim to test these models for the attenuation of CRs in the low-mass pre-stellar core L1544. Methods. We used a state-of-the-art gas-grain chemical model, which accepts the CR ionisation rate profile as input, to predict the abundance profiles of four ions: N2H+, N2D+, HC18O+, and DCO+. Non-local thermodynamic equilibrium radiative transfer simulations were run to produce synthetic spectra based on the derived abundances. These were compared with observations obtained with the Institut de Radioastronomie Millimétrique 30 m telescope. Results. Our results indicate that a model with high ζ2 (>10−16 s−1) is excluded by the observations. Also the model with the standard ζ2 = 1.3 × 10−17 s−1 produces a worse agreement with respect to the attenuation model based on Voyager observations, which is characterised by an average ⟨ ζ2 ⟩ = 3 × 10−17 s−1 at the column densities typical of L1544. The single-dish data, however, are not sensitive to the attenuation of the CR profile, which changes only by a factor of two in the range of column densities spanned by the core model (N = 2−50 × 1021 cm−2). Interferometric observations at higher spatial resolution, combined with observations of transitions with lower critical density – hence tracing the low-density envelope – are needed to observe a decrease in the CR ionisation rate with density.

Complex Slip Distribution of the 2021 Mw 7.4 Maduo, China, Earthquake: An Event Occurring on the Slowly Slipping Fault

Abstract The 21 May 2021 Maduo earthquake occurred on the Kunlun Mountain Pass–Jiangcuo fault (KMPJF), a seismogenic fault with no documented large earthquakes. To probe its kinematics, we first estimate the slip rates of the KMPJF and Tuosuo Lake segment (TLS, ∼75 km north of the KMPJF) of the East Kunlun fault (EKLF) based on the secular Global Positioning System (GPS) data using the Markov chain Monte Carlo method. Our model reveals that the slip rates of the KMPJF and TLS are 1.7 ± 0.8 and 7.1 ± 0.3 mm/yr, respectively. Then, we invert high-resolution GPS and Interferometric Synthetic Aperture Radar observations to decipher the fault geometry and detailed coseismic slip distribution associated with the Maduo earthquake. The geometry of the KMPFJ significantly varies along strike, composed of five fault subsegments. The most slip is accommodated by two steeply dipping fault segments, with the patch of large sinistral slip concentrated in the shallow depth on a simple straight structure. The released seismic moment is ∼1.5×1020 N·m, equivalent to an Mw 7.39 event, with a peak slip of ∼9.3 m. Combining the average coseismic slip and slip rate of the main fault, an earthquake recurrence period of ∼1250−400+1120 yr is estimated. The Maduo earthquake reminds us to reevaluate the potential of seismic gaps where slip rates are low. Based on our calculated Coulomb failure stress, the Maduo earthquake imposes positive stress on the Maqin–Maqu segment of the EKLF, a long-recognized seismic gap, implying that it may accelerate the occurrence of the next major event in this region.

Hypercubes of AGN Tori (HYPERCAT). II. Resolving the Torus with Extremely Large Telescopes

Abstract Recent infrared interferometric observations revealed sub-parsec scale dust distributions around active galactic nuclei (AGNs). Using images of Clumpy torus models and NGC 1068 as an example, we demonstrate that the near- and mid-infrared nuclear emission of some nearby AGNs will be resolvable in direct imaging with the next generation of 30 m telescopes, potentially breaking degeneracies from previous studies that used integrated spectral energy distributions of unresolved AGN tori. To that effect we model wavelength-dependent point spread functions from the pupil images of various telescopes: James Webb Space Telescope, Keck, Giant Magellan Telescope, Thirty Meter Telescope, and Extremely Large Telescope. We take into account detector pixel scales and noise, and apply deconvolution techniques for image recovery. We also model 2D maps of the 10 μm silicate feature strength, S 10, of NGC 1068 and compare with observations. When the torus is resolved, we find S 10 variations across the image. However, to reproduce the S 10 measurements of an unresolved torus a dusty screen of A V > 9 mag is required. We also fit the first resolved image of the K-band emission in NGC 1068 recently published by the GRAVITY Collaboration, deriving likely model parameters of the underlying dust distribution. We find that both (1) an elongated structure suggestive of a highly inclined emission ring, and (2) a geometrically thin but optically thick flared disk where the emission arises from a narrow strip of hot cloud surface layers on the far inner side of the torus funnel, can explain the observations.