Hasil untuk "Astronomy"

Jeremiah D. Paul, Richard M. Plotkin

The origin of core radio emission in radio-quiet active galactic nuclei (AGNs) is still actively debated. General-relativistic magnetohydrodynamics simulations often predict the launching of moderately large-scale jets from super-Eddington accretion flows, but this prediction seems at odds with observations indicating most high/super-Eddington AGNs appear radio-quiet. Here, we use the ratio of radio to X-ray luminosities as a multiwavelength diagnostic to probe the origin of radio emission in a sample of 69 radio-quiet, high/super-Eddington AGNs with black hole masses M _BH ∼ 10 ^5 –10 ^9 M _⊙ . With this wide dynamic range in M _BH , we adapt existing formalisms for how jetted radio emission and accretion-powered X-ray emission scale with black hole mass into the super-Eddington regime. We find that the radio/X-ray luminosity ratios observed across this M _BH range are inconsistent with a jet-dominated model for radio emission. We discuss how our results may instead be consistent with a corona-dominated radio emission origin with a contribution from outflows at higher accretion rates.

Erica Behrens, Jeffrey G. Mangum, Mathilde Bouvier et al.

We quantify the utility of HCN and HNC to characterize gas conditions in the nearby starburst galaxy NGC 253. We use measurements from the Atacama Large Millimeter/Submillimeter Array (ALMA) Large Program ALCHEMI: the ALMA Comprehensive High-resolution Molecular Inventory. Using different subsets of the eight total HCN and HNC transitions measured by ALCHEMI, we test the number and combinations of transitions necessary for constraining the temperature, H _2 volume and column densities, cosmic-ray ionization rate, and beam-filling factor in three representative regions within NGC 253. We use these combinations of HCN and HNC transitions to constrain chemical and radiative transfer models, and infer the gas conditions using a Bayesian nested sampling algorithm combined with neural network models for increased efficiency. By comparing the shapes of the resulting posterior distributions, as well as the medians and uncertainties for each gas parameter, from each test case to what we obtain with the full set of eight transitions (the control), we quantify how well each test reproduces the control. We find that multiple transitions each of both molecules are required to obtain a median parameter value within a factor of 2 of the control with an uncertainty less than 2–3 times that of the control. We also find that transition combinations which feature a range of upper-state energies are most effective. We show that single transitions, such as HCN J = 1–0 or 3–2, are among the worst-performing combinations and result in parameter values up to an order of magnitude different than the control.

F. Coti Zelati, P. G. Jonker, C. P. Gutiérrez et al.

We outline the science case for a 30-40 m optical/infrared telescope in the Northern Hemisphere, optimised for transformative time-domain astronomy in the 2040s. Upcoming multi-wavelength and multi-messenger facilities will reveal fast, faint, rapidly evolving Northern transients whose earliest phases carry decisive diagnostics. A Northern ELT with rapid response, broad wavelength coverage, high time resolution, polarimetric capabilities, and diffraction-limited imaging is essential to capture these phases and secure deep spectroscopy and photometry as transients fade. These capabilities will enable recovery of key physical information and detailed characterisation of transient environments, while also enabling unprecedented studies of accretion phenomena at all scales. Among potential sites, La Palma uniquely combines atmospheric stability, complementary longitude to ESO's ELT, protected dark skies, and robust infrastructure to host this facility.

Ming-wei Qin, Rui Tang, Ying-hui Zhou et al.

The 21 cm radiation of neutral hydrogen provides crucial information for studying the early universe and its evolution. To advance this research, countries have made significant investments in constructing large low-frequency radio telescope arrays, such as the Low Frequency Array (LOFAR) and the Square Kilometre Array Phase 1 Low Frequency (SKA1-low). These instruments are pivotal for radio astronomy research. However, challenges such as ionospheric plasma interference, ambient radio noise, and instrument-related effects have become increasingly prominent, posing major obstacles in cosmology research. To address these issues, this paper proposes an efficient signal processing method that combines wavelet transform and mathematical morphology. The method involves the following steps: Background Subtraction: Background interference in radio observation signals is eliminated. Wavelet Transform: The signal, after removing background noise, undergoes a two-dimensional discrete wavelet transform. Threshold processing is then applied to the wavelet coefficients to effectively remove interference components. Wavelet Inversion: The processed signal is reconstructed using wavelet inversion. Mathematical Morphology: The reconstructed signal is further optimized using mathematical morphology to refine the results. Experimental verification was conducted using solar observation data from the Xinjiang Observatory and the Yunnan Observatory. The results demonstrate that this method successfully removes interference signals while preserving useful signals, thus improving the accuracy of radio astronomy observations and reducing the impact of radio frequency interference (RFI).

Ze-Nan Liu, Wei-Yang Wang, Yu-Chen Huang et al.

Fast radio bursts (FRBs) are millisecond-duration extragalactic transients characterized by ultrahigh brightness temperatures, suggesting coherent emission mechanisms in extreme astrophysical processes. In this paper, we extend the bunched coherent Cherenkov radiation (CChR) framework by incorporating bunch inclination and geometric configuration parameters, enabling it to more rigorously model FRB emission and tera-Hertz (THz) emission from magnetars. When relativistic bunches are injected into the magnetized plasma of a magnetar’s magnetosphere at the Cherenkov angle, their emitted waves achieve phase coherence through constructive interference. Furthermore, the three-dimensional geometry of the bunches plays a crucial role in influencing the coherence of the radiation. Within the framework of CChR, we predict the existence of THz emission counterparts associated with FRBs and explain the observed characteristics of the THz-emitting magnetar SGR J1745-2900. Detections of such counterparts by upgraded millimeter telescopes (e.g., Atacama Large Millimeter/submillimeter Array, IRAM) would be expected to provide new insights into the potential physical connection between FRBs and magnetars.

Tianbao Song, Zongyi Huang, Xin Liu et al.

This paper introduces a novel variational autoencoder model termed DVAE to prevent posterior collapse in text modeling. DVAE employs a dual-path architecture within its decoder: path A and path B. Path A makes the direct input of text instances into the decoder, whereas path B replaces a subset of word tokens in the text instances with a generic unknown token before their input into the decoder. A stopping strategy is implemented, wherein both paths are concurrently active during the early phases of training. As the model progresses towards convergence, path B is removed. To further refine the performance, a KL weight dropout method is employed, which randomly sets certain dimensions of the KL weight to zero during the annealing process. DVAE compels the latent variables to encode more information about the input texts through path B and fully utilize the expressiveness of the decoder, as well as avoiding the local optimum when path B is active through path A and the stopping strategy. Furthermore, the KL weight dropout method augments the number of active units within the latent variables. Experimental results show the excellent performance of DVAE in density estimation, representation learning, and text generation.

Richard G. Arendt, F. Yusef-Zadeh, I. Heywood

We present a catalog of 1.28 GHz radio filaments observed by MeerKAT over the innermost 200 pc of the Galaxy (roughly ±1 $\mathop{.}\limits^{\unicode{x000b0}}$ 5), which includes the central molecular zone. The catalog is generated by repurposing software developed for the automated detection of filaments in solar coronal loops. There are two parts to the catalog. The first part, the main catalog, provides a point-by-point listing of locations and basic observational properties along each detected filament. The second part is a summary catalog that provides a listing of mean, median, or total values of various properties for each filament. Tabulated quantities include position, length, curvature, brightness, and spectral index. The catalogs contain a heterogeneous mix of filamentary structures, including nonthermal radio filaments, and parts of supernova remnants and thermally emitting regions (e.g., H ii regions). We discuss criteria for selecting useful subsamples of filaments from the catalogs, and some of the details encountered in examining filaments or selections of filaments from the catalogs.

Haylee N. Archer, Molly N. Simon, Chris Mead et al.

Previous studies conclusively show that pencil-and-paper lecture-tutorials (LTs) are incredibly effective at increasing student engagement and learning gains on a variety of topics when compared to traditional lecture. LTs in astronomy are post-lecture activities developed with the intention of helping students engage with conceptual and reasoning difficulties around a specific topic with the end goal of them developing a more expert-like understanding of astrophysical concepts. To date, all astronomy LTs have been developed for undergraduate courses taught in-person. Increases in online course enrollments and the COVID-19 pandemic further highlighted the need for additional interactive, research-based, curricular materials designed for online classrooms. To this end, we developed and assessed the efficacy of an innovative, interactive LT designed to teach planet formation in asynchronous, online, introductory astronomy courses for undergraduates. We utilized the Planet Formation Concept Inventory to compare learning outcomes between courses that implemented the new online, interactive LT, and those that used either a lecture-only approach or utilized a standard pencil-and-paper LT on the same topic. Overall, learning gains from the standard pencil-and-paper LT were statistically indistinguishable from the in-person implementation of the online LT and both of these conditions outperformed the lecture-only condition. However, when implemented asynchronously, learning gains from the online LT were lower and not significantly above the lecture-only condition. While improvements can be made to improve the online LT in the future, the current discipline ideas still outperform traditional lecture, and can be used as a tool to teach planet formation effectively.

Aldo G. Sepulveda, Daniel Huber, Timothy R. Bedding et al.

HIP 65426 hosts a young giant planet that has become the first exoplanet directly imaged with JWST. Using time-series photometry from the Transiting Exoplanet Survey Satellite (TESS), we classify HIP 65426 as a high-frequency δ Scuti pulsator with a possible large-frequency separation of Δ ν = 7.23 ± 0.02 cycles day ^−1 . We check the TESS data for pulsation-timing variations and use the nondetection to estimate a 95% dynamical mass upper limit of 12.8 M _Jup for HIP 65426 b. We also identify a low-frequency region of signal that we interpret as stellar latitudinal differential rotation with two rapid periods of 7.85 ± 0.08 hr and 6.67 ± 0.04 hr. We use our TESS rotation periods together with published values of radius and $v\sin i$ to jointly measure the inclination of HIP 65426 to ${i}_{\star }={107}_{-11}^{+12}$ °. Our stellar inclination is consistent with the orbital inclination of HIP 65426 b ( ${108}_{-3}^{+6}$ °) at the 68% percent level based on our orbit fit using published relative astrometry. The lack of significant evidence for spin–orbit misalignment in the HIP 65426 system supports an emerging trend consistent with preferential alignment between imaged long-period giant planets and their host stars.

Aigerim Assylkhanova, Gyula Nagy, Cezar Morar et al.

The topic of dark tourism emerged in the last three decades as tourism became more accessible. It allows forgotten history to be revised and transferred to the public. This study aims to restructure existing categorization regarding dark tourism and address the research gaps in dark tourism studies. We collected studies from international publication databases – Scopus, Web of Science, and Google Scholar. We pre-processed the following data for each study: topic, authors’ location of university affiliation, study area, year of publication, top-cited articles, top productive journals in publishing dark tourism studies, keywords, and internality/externality of the author from the study area. With the current paper, we analysed review articles published from 1996 to 2024 (first quarter), applying qualitative methods. Based on these, a new analytical framework was generated. Furthermore, the connections between research topics were also analysed. The results of the analysis highlight specific research gaps in the literature on dark tourism and address poorly visible research fields in international journals, e.g. terrorism-related research, social media links of dark tourism, postcolonial contexts, or commemoration of communist past and heritage. Consequently, certain countries and regions are underrepresented in the literature. This critical review offers new research areas but also gives some directions to the theoretical enrichment of the dark tourism concept.

Kumail Zaidi, Danilo Marchesini, Casey Papovich et al.

We present the construction of a deep multiwavelength point-spread-function-matched photometric catalog in the Ultra-Deep Survey (UDS) field following the final UKIDSS UDS release. The catalog includes photometry in 24 filters, from the MegaCam- uS 0.38 μ m band to the Spitzer-IRAC 8 μ m band, over ∼0.9 deg ^2 and with a 5 σ depth of 25.3 AB in the K -band detection image. The catalog, containing ≈188,564 (136,235) galaxies at 0.2 < z < 8.0 with stellar mass $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 8$ and K -band total magnitude K < 25.2 (24.3) AB, enables a range of extragalactic studies. We also provide photometric redshifts, corresponding redshift probability distributions, and rest-frame absolute magnitudes and colors derived using the template-fitting code eazy-py . Photometric redshift errors are less than 3%−4% at z < 4 across the full brightness range in the K band and stellar mass range $8\lt \mathrm{log}({M}_{* }/{M}_{\odot })\lt 12$ . Stellar population properties (e.g., stellar mass, star formation rate, dust extinction) are derived from the modeling of the spectral energy distributions using the codes FAST and Dense Basis.

Huaqing Cheng, Zhixing Ling, Chen Zhang et al.

We report on results of the on-ground X-ray calibration of the Lobster Eye Imager for Astronomy (LEIA), an experimental space wide-field (18.6*18.6 square degrees) X-ray telescope built from novel lobster eye mirco-pore optics. LEIA was successfully launched on July 27, 2022 onboard the SATech-01 satellite. To achieve full characterisation of its performance before launch, a series of tests and calibrations have been carried out at different levels of devices, assemblies and the complete module. In this paper, we present the results of the end-to-end calibration campaign of the complete module carried out at the 100-m X-ray Test Facility at IHEP. The PSF, effective area and energy response of the detectors were measured in a wide range of incident directions at several X-ray line energies. The distributions of the PSF and effective areas are roughly uniform across the FoV, in large agreement with the prediction of lobster-eye optics. The mild variations and deviations from the prediction of idealized lobster-eye optics can be understood to be caused by the imperfect shapes and alignment of the micro-pores as well as the obscuration by the supporting frames, which can be well reproduced by MC simulations. The spatial resolution of LEIA defined by the FWHM of the focal spot ranges from 4-8 arcmin with a median of 5.7. The measured effective areas are in range of 2-3 $cm^2$ at ~1.25 keV across the entire FoV, and its dependence on photon energy is in large agreement with simulations. The gains of the CMOS sensors are in range of 6.5-6.9 eV/DN, and the energy resolutions in the range of ~120-140 eV at 1.25 keV and ~170-190 eV at 4.5 keV. These results have been ingested into the calibration database and applied to the analysis of the scientific data acquired by LEIA. This work paves the way for the calibration of the Wide-field X-Ray Telescope modules of the Einstein Probe mission.

T. Morishita, M. Stiavelli

This paper highlights initial photometric analyses of JWST NIRCam imaging data in the sightline of SMACS0723, aiming to identify galaxies at redshift z > 7. By applying a conservative Lyman-break selection followed by photometric-redshift analysis and visual inspection, we identify four F090W-dropout and two F150W-dropout sources, three of which were recently confirmed in an independent spectroscopic analysis to z = 7.663, 7.665, and 8.499. We then supplement our sample with a photometric-redshift selection, and identify five additional candidates at 7 < z _phot < 13. The NIRCam images clearly resolve all sources and reveal their subgalactic components that were not resolved/detected in the previous imaging by Hubble Space Telescope. Our spectral energy distribution analysis reveals that the selected galaxies are characterized by young stellar populations (median age of ∼50 Myr) of subsolar metallicity (∼0.2 Z _⊙ ) and little dust attenuation ( A _V ∼ 0.5). In several cases, we observe extreme H β +[O iii ] lines being captured in the F444W band and seen as color excess, which is consistent with their observed high star formation rate surface density. Eight of the 11 sources identified in this study appear in at least one of the recent studies (Adams et al.; Atek et al.; Donnan et al.; Harikane et al.; Yan et al.) of the same fields, implying the high fidelity of our selection. We crossmatch all high- z galaxy candidates presented in the five studies with our catalog and discuss the possible causes of discrepancy in the final lists.

Jingye Yan, Ji Wu, Leonid I. Gurvits et al.

This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) -- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status of the instrumentation. We also present results of a transition observation, which offers unique measurements on several novel aspects. We estimate the RFI suppression required for such a radio astronomy instrumentation at the Moon distances from Earth to be of the order of 80 dB. We analyse a method of separating Earth- and satellite-originated radio frequency interference (RFI). It is found that the RFI level at frequencies lower than a few MHz is smaller than the receiver noise floor.

Nicolas Misdariis, Elif Özcan, Massimo Grassi et al.

The Audible Universe project aims at making dialogue between two scientific domains investigating two distinct research objects, briefly said, Stars and Sound. It has been instantiated within a collaborative workshop that started to mutually acculturate both communities, by sharing and transmitting respective knowledge, skills and practices. One main outcome of this exchange was a global view on the astronomical data sonification paradigm that allowed to observe either the diversity of tools, uses and users (including visually-impaired people), but also the current limitations and potential ways of improvement. From this perspective, the current paper presents basic elements gathered and contextualised by sound experts in their respective fields (sound perception / cognition, sound design, psychoacoustics, experimental psychology), in order to anchor sonification for astronomy in a more well-informed, methodological and creative process.

Nizar Bouhlel, David Rousseau

This paper introduces a closed-form expression for the Kullback–Leibler divergence (KLD) between two central multivariate Cauchy distributions (MCDs) which have been recently used in different signal and image processing applications where non-Gaussian models are needed. In this overview, the MCDs are surveyed and some new results and properties are derived and discussed for the KLD. In addition, the KLD for MCDs is showed to be written as a function of Lauricella D-hypergeometric series <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mi>F</mi><mi>D</mi><mrow><mo>(</mo><mi>p</mi><mo>)</mo></mrow></msubsup></semantics></math></inline-formula>. Finally, a comparison is made between the Monte Carlo sampling method to approximate the KLD and the numerical value of the closed-form expression of the latter. The approximation of the KLD by Monte Carlo sampling method are shown to converge to its theoretical value when the number of samples goes to the infinity.

Ladislav BRIMICH, Martin BEDNÁRIK, Jozef BÓDI et al.

Tidal strain time series recorded at the Vyhne Tidal Station are used to test thirteen different ocean tide loading models. Ten models have been calculated using SPOTL: EOT11a, HAMTIDE11a, OSU.TPXO72atlas, OSU.TPXO72, TPX070, DTU10, CSR4.0, FES2004, FES95.2.1, SCHW1 and three other models were chosen from the Free Ocean Tide Loading Provider (FOTLP) created by Scherneck and Bos: FES2012, FES2014b, GOT00.2. Hourly sampled strain data, corrected for temperature, were subjected to correction for ocean tide loading. The test of models was focused on the diurnal and semi-diurnal tidal harmonic constituents O1, P1, K1 and M2. A negligible difference between the individual global ocean tide loading models was only found mainly due to using different Earth models and Green functions. The amplitude factors for O1, P1, K1 and M2 derived from the measurements are 1.019, 1.226, 0.842 and 1.131, respectively. The average amplitude factors for these tidal components were obtained after ocean load correction using SPOTL routines: 1.121, 1.332, 0.916, 1.283, and in the case of the three models using FOTLP: 1.046, 1.486, 1.067, 1.317. The corrected amplitude factor became closer to the theoretical value only for K1.

Aziz Khan, Shougi S. Abosuliman, Saleem Abdullah et al.

Spherical hesitant fuzzy sets have recently become more popular in various fields. It was proposed as a generalization of picture hesitant fuzzy sets and Pythagorean hesitant fuzzy sets in order to deal with uncertainty and fuzziness information. Technique of Aggregation is one of the beneficial tools to aggregate the information. It has many crucial application areas such as decision-making, data mining, medical diagnosis, and pattern recognition. Keeping in view the importance of logarithmic function and aggregation operators, we proposed a novel algorithm to tackle the multi-attribute decision-making (MADM) problems. First, novel logarithmic operational laws are developed based on the logarithmic, t-norm, and t-conorm functions. Using these operational laws, we developed a list of logarithmic spherical hesitant fuzzy weighted averaging/geometric aggregation operators to aggregate the spherical hesitant fuzzy information. Furthermore, we developed the spherical hesitant fuzzy entropy to determine the unknown attribute weight information. Finally, the design principles for the spherical hesitant fuzzy decision-making have been developed, and a practical case study of hotel recommendation based on the online consumer reviews has been taken to illustrate the validity and superiority of presented approach. Besides this, a validity test is conducted to reveal the advantages and effectiveness of developed approach. Results indicate that the proposed method is suitable and effective for the decision process to evaluate their best alternative.

Kris Davidson

Very massive stars occasionally expel material in colossal eruptions, driven by continuum radiation pressure rather than blast waves. Some of them rival supernovae in total radiative output, and the mass loss is crucial for subsequent evolution. Some are supernova impostors, including SN precursor outbursts, while others are true SN events shrouded by material that was ejected earlier. Luminous Blue Variable stars (LBV&#8217;s) are traditionally cited in relation with giant eruptions, though this connection is not well established. After four decades of research, <i>the fundamental causes of giant eruptions and LBV events remain elusive.</i> This review outlines the basic relevant physics, with a brief summary of essential observational facts. Reasons are described for the spectrum and emergent radiation temperature of an opaque outflow. Proposed mechanisms are noted for instabilities in the star&#8217;s photosphere, in its iron opacity peak zones, and in its central region. Various remarks and conjectures are mentioned, some of them relatively unfamiliar in the published literature.

Daniel White, William McGenn, Danielle George et al.

To achieve the low noise and wide bandwidth required for millimeter wavelength astronomy applications, superconductor-insulator-superconductor (SIS) mixer based receiver systems have typically been used. This paper investigates the performance of high electron mobility transistor (HEMT) based low noise amplifiers (LNAs) as an alternative approach for systems operating in the 125 - 211 GHz frequency range. A four-stage, common-source, unconditionally stable monolithic microwave integrated circuit (MMIC) design is presented using the state-of-the-art 35 nm indium phosphide HEMT process from Northrop Grumman Corporation. The simulated MMIC achieves noise temperature (Te) lower than 58 K across the operational bandwidth, with average Te of 38.8 K (corresponding to less than 5 times the quantum limit (hf/k) at 170 GHz) and forward transmission of 20.5 +/- 0.85 dB. Input and output reflection coefficients are better than -6 and -12 dB, respectively, across the desired bandwidth. To the authors knowledge, no LNA currently operates across the entirety of this frequency range. Successful fabrication and implementation of this LNA would challenge the dominance SIS mixers have on sub-THz receivers.