Chinmay S. Kulkarni, Thomas Behling, Elisabeth E. Banks
et al.
Infrared observations can probe photometric variability across the full evolutionary range of young stellar objects (YSOs), from deeply embedded protostars to pre-main-sequence stars with dusty disks. We present 3–8 μ m light curves extending 27 yr from 1997 to 2024 obtained with three space-based IR telescopes: Infrared Space Observatory, Spitzer, and Wide-field Infrared Survey Explorer (WISE). Although unevenly sampled with large gaps in coverage, these light curves show variability on timescales ranging from days to decades. We focus on the Spitzer-identified YSOs with disks and envelopes that exhibit variations of a factor of two or more in this wavelength range. We identified seven YSOs where the light curves are dominated by bursts of sustained (>5 yr) high flux, including four that show a steep decay ending the burst and three that are ongoing as of the final observation. We find six YSOs that are undergoing declines, which may be the end of bursts that began before 1997. The most common form of variability, exhibited by 26 YSOs in our sample, show variations over time intervals of years to months but do not exhibit sustained bursts or fades. The Spitzer [3.6] – [4.5] and WISE [3.5] – [4.6] colors either increase or remain constant with increasing brightness, inconsistent with dust extinction as being the primary source of the large-amplitude variability.
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.
Aurélien Crida, Clément Baruteau, Philippine Griveaud
et al.
Gravitational systems in astrophysics often comprise a body -- the primary -- that far outweights the others, and which is taken as the centre of the reference frame. A fictitious acceleration, also known as the indirect term, must therefore be added to all other bodies in the system to compensate for the absence of motion of the primary. In this paper, we first stress that there is not one indirect term but as many indirect terms as there are bodies in the system that exert a gravitational pull on the primary. For instance, in the case of a protoplanetary disc with two planets, there are three indirect terms: one arising from the whole disc, and one per planet. We also highlight that the direct and indirect gravitational accelerations should be treated in a balanced way: the indirect term from one body should be applied to the other bodies in the system that feel its direct gravitational acceleration, and only to them. We point to situations where one of those terms is usually neglected however, which may lead to spurious results. These ideas are developed here for star-disc-planets interactions, for which we propose a recipe for the force to be applied onto a migrating planet, but they can easily be generalized to other astrophysical systems.
Prateek Sharma, Bhargav Vaidya, Yogesh Wadadekar
et al.
In contemporary astronomy and astrophysics (A&A), the integration of high-performance computing (HPC), big data analytics, and artificial intelligence/machine learning (AI/ML) has become essential for advancing research across a wide range of scientific domains. These tools are playing an increasingly pivotal role in accelerating discoveries, simulating complex astrophysical phenomena, and analyzing vast amounts of observational data. For India to maintain and enhance its competitive edge in the global landscape of computational astrophysics and data science, it is crucial for the Indian A&A community to fully embrace these transformative technologies. Despite limited resources, the expanding Indian community has already made significant scientific contributions. However, to remain globally competitive in the coming years, it is vital to establish a robust national framework that provides researchers with reliable access to state-of-the-art computational resources. This system should involve the regular solicitation of computational proposals, which can be assessed by domain experts and HPC specialists, ensuring that high-impact research receives the necessary support. By building such a system, India can cultivate the talent, infrastructure, and collaborative environment necessary to foster world-class research in computational astrophysics and data science.
Denis M. F. Illesca, Andrés E. Piatti, Matías Chiarpotti
et al.
We report on the astrophysical properties of a sample of star clusters in the Small Magellanic Cloud (SMC). They have been selected with the aim of looking for the connection between their ages, heliocentric distances and metallicities with the existence of tidally perturbed/induced outermost SMC regions. We derived the star cluster fundamental parameters from relatively deep Survey of the Magellanic Stellar History (SMASH) DR2 color magnitude diagrams, cleaned from field star contamination, and compared to thousand synthetic CMDs covering a wide range of heliocentric distances, ages and metal content. Heliocentric distances for 15 star clusters are derived for the first time, which represents an increase of 50 per cent of SMC clusters with estimated heliocentric distances. The analysis of the age-metallicity relationships (AMRs) of cluster located in outermost regions distributed around the SMC and in the SMC Main Body reveals that they have followed the overall galaxy chemical enrichment history. However, since half of the studied clusters are placed in front of or behind the SMC Main Body, we concluded that they formed in the SMC and have traveled outward because of the tidal effects from the interaction with the Large Magellanic Cloud (LMC). Furthermore, metal rich clusters formed recently in some of these outermost regions from gas that was also dragged by tidal effects from the inner SMC. This outcome leads to consider the SMC as a galaxy scarred by the LMC tidal interaction with distance-perturbed and newly induced outermost stellar substructures.
Lachlan Passenger, Shun Yin Cheung, Nir Guttman
et al.
Gravitational-wave astronomy provides a promising avenue for the discovery of new physics beyond general relativity as it probes extreme curvature and ultrarelativistic dynamics. However, in the absence of a compelling alternative to general relativity, it is difficult to carry out an analysis that allows for a wide range of deviations. To that end, we introduce a Gaussian process framework to search for deviations from general relativity in gravitational-wave signals from binary black hole mergers with minimal assumptions. We employ a kernel that enforces our prior beliefs that—if gravitational waveforms deviate from the predictions of general relativity—the deviation is likely to be localised in time near the merger with some characteristic frequency. We demonstrate this formalism with simulated data and apply it to events from the Gravitational-Wave Transient Catalog 3. We find no evidence for a deviation from general relativity. We limit the fractional deviation in gravitational-wave strain to as low as 7% (90% credibility) of the strain of GW190701_203306.
We investigate the influence of supernova (SN) feedback on the satellites of elliptical host galaxies using hydrodynamic simulations. Utilizing a modified version of the GADGET-3 code, we perform cosmological zoom-in simulations of 11 elliptical galaxies with stellar masses in the range 10 ^11 M _⊙ < M _* < 2 × 10 ^11 M _⊙ . We conduct two sets of simulations with identical initial conditions: a fiducial model, which includes a three-phase SN mechanical wind, and a weak SN feedback model, where nearly all SN energy is released as thermal energy with a reduced SN wind velocity. Our comparison shows minimal differences in the elliptical host galaxies, but significant variations in the physical properties of satellite galaxies. The weak SN feedback model produces a larger number of satellite galaxies compared to the fiducial model, and significantly more than observed. For satellite galaxies with stellar masses above 10 ^8 M _⊙ , the weak SN feedback model generates approximately 5 times more satellites than observed in the Extending the Satellites Around Galactic Analogs Survey (or xSAGA) survey. Most of these overproduced satellites have small stellar masses, below 10 ^10 M _⊙ . Additionally, satellites in the weak SN feedback model are about 3.5 times more compact than those observed in the SAGA survey and the fiducial model, with metallicities nearly 1 dex higher than observed values. In conclusion, the satellite galaxies in the fiducial model, which includes mechanical SN feedback, exhibit properties that more closely align with observations. This underscores the necessity of incorporating both mechanical active galactic nuclei and SN feedback to reproduce the observed properties of elliptical galaxies and their satellites in simulations.
Bodie Breza, Matthew C. Nixon, Eliza M.-R. Kempton
The evolution and structure of sub-Neptunes may be strongly influenced by interactions between the outer gaseous envelope of the planet and a surface magma ocean. However, given the wide variety of permissible interior structures of these planets, it is unclear whether conditions at the envelope–mantle boundary will always permit a molten silicate layer or whether some sub-Neptunes might instead host a solid silicate surface. In this work, we use internal structure modeling to perform an extensive exploration of surface conditions within the sub-Neptune population across a range of bulk and atmospheric parameters. We find that a significant portion of the population may lack present-day magma oceans. In particular, planets with a high atmospheric mean molecular weight and large envelope mass fraction are likely to instead have a solid silicate surface, since the pressure at the envelope–mantle boundary is high enough that the silicates will be in solid postperovskite phase. This result is particularly relevant given recent inferences of high-mean molecular weight atmospheres from JWST observations of several sub-Neptunes. We apply this approach to a number of sub-Neptunes with existing or upcoming JWST observations and find that in almost all cases, a range of solutions exist that do not possess a present-day magma ocean. Our analysis provides critical context for interpreting sub-Neptunes and their atmospheres.
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.
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.
Séverine Chevalier, Olivier Beauchard, Adrian Teacă
et al.
Abstract Benthic ecological data are crucial to study and manage ecosystems. On the one hand, abiotic and species data provide complementary information to identify habitats. On the other hand, trait data, describing taxon characteristics, are required to predict anthropogenic impacts on marine ecosystems. Indeed, species traits are now widely used to understand natural selection in communities or to highlight ecosystem functions. While trait data are in growing demand, compiling them is challenging, time-consuming and there are no properly established procedures for major marine ecosystems. Here, we share a data set comprising macrozoobenthic occurrences for 215 taxa over the Black Sea northwestern shelf, between 1995 and 2017, and 27 traits documented for 127 taxa that related to life cycle and ecosystem function. In addition, we provide an abiotic data set of physical and chemical variables generated by a model or compiled from in-situ data. This data set aims to fill the functional knowledge gap in the Black Sea and offers research opportunities to future studies covering ecosystem functions, biodiversity conservation, and management.
Alessandra Corsi, Lisa Barsotti, Emanuele Berti
et al.
The ground-based gravitational wave (GW) detectors LIGO and Virgo have enabled the birth of multi-messenger GW astronomy via the detection of GWs from merging stellar-mass black holes (BHs) and neutron stars (NSs). GW170817, the first binary NS merger detected in GWs and all bands of the electromagnetic spectrum, is an outstanding example of the impact that GW discoveries can have on multi-messenger astronomy. Yet, GW170817 is only one of the many and varied multi-messenger sources that can be unveiled using ground-based GW detectors. In this contribution, we summarize key open questions in the astrophysics of stellar-mass BHs and NSs that can be answered using current and future-generation ground-based GW detectors, and highlight the potential for new multi-messenger discoveries ahead.
Abstract Information about the three-dimensional description of the quark and gluon content of hadrons, described by the generalized parton distributions (GPDs), can be probed by exclusive processes in electron–proton (ep) collisions. In this letter, we investigate the timelike Compton scattering (TCS) in ep collisions at the future electron-ion collider (EIC). Such process is characterized by the exclusive dilepton production through the subprocess $$\gamma p \rightarrow \gamma ^*p \rightarrow l^+ l^- p$$ γ p → γ ∗ p → l + l - p , with the real photon in the initial state being emitted by the incoming electron. Assuming a given model for the GPDs, the TCS differential cross-section is estimated, as well the contribution associated to the interference between the TCS and Bethe–Heitler (BH) amplitudes. Predictions for the TCS, BH and interference contributions are presented considering the kinematical range expected to be covered by the EIC detectors. Moreover, the polarized photon asymmetry is also studied. Our results indicated that a future experimental analysis, considering photon circular polarizations, can be useful to probe the interference contribution and constrain the description of the GPDs for the proton.
Astrophysics, Nuclear and particle physics. Atomic energy. Radioactivity
Abstract Quantum repeaters are pivotal in the physical layer of the quantum internet, and quantum repeaters capable of efficient entanglement distribution are necessary for its development. Quantum repeater schemes based on single-photon interference are promising because of their potential efficiency. However, schemes involving first-order interference with photon sources at distant nodes require stringent phase stability of the components, which pose challenges for long-distance implementation. In this paper, we present a quantum repeater scheme that leverages single-photon interference and reduces the difficulty of achieving phase stabilization. Additionally, under specific conditions, our scheme achieves a higher entanglement distribution rate between end nodes compared with the existing schemes. Thus, the proposed approach could lead to improved rates with technologies that are currently unavailable but possible in the future and will ultimately facilitate the development of multimode quantum repeaters.
Tatiana M. Rodríguez, Emmanuel Momjian, Peter Hofner
et al.
We present Very Large Array 1.3 cm continuum and 22.2 GHz H _2 O maser observations of the high-mass protostellar object IRAS 19035+0641 A. Our observations unveil an elongated bipolar 1.3 cm continuum structure at scales ≲500 au, which, together with a rising in-band spectral index, strongly suggests that the radio emission toward IRAS 19035+0641 A arises from an ionized jet. In addition, eight individual water maser spots well aligned with the jet axis were identified. The Stokes V spectrum of the brightest H _2 O maser line (∼100 Jy) shows a possible Zeeman splitting and is well represented by the derivatives of two Gaussian components fitted to the Stokes I profile. The measured B _los are 123 (±27) and 156 (±8) mG, translating to a preshock magnetic field of ≈7 mG. Subsequent observations to confirm the Zeeman splitting showed intense variability in all the water maser spots, with the brightest maser completely disappearing. The observed variability in a 1 yr timescale could be the result of an accretion event. These findings strengthen our interpretation of IRAS 19035+0641 A as a high-mass protostar in an early accretion/outflow evolutionary phase.
Magnetar outbursts are powered by an intense magnetic field. The phenomenon has recently drawn significant attention because of a connection to some fast radio bursts that has been reported. Understanding magnetar outbursts may provide the key to mysterious transient events. The elastic deformation of the solid crust due to magnetic field evolution accumulates over a secular timescale. Eventually, the crust fractures or responds plastically beyond a particular threshold. Determination of the critical limit is required to obtain the shear strain tensor in response to magnetic stress. In some studies, the tensor was substituted with an approximate expression determined algebraically from the magnetic stress. This study evaluated the validity of the approximation by comparing it with the strain tensor obtained through appropriate calculations. The differential equations for the elastic deformation driven by the magnetic field were solved. The results indicated that the approximation did not represent the correct strain tensor value, in both magnitude and spatial profile. Previous evolutionary calculations based on spurious criteria are likely to overestimate the magnitude of the strain tensor, and crustal failure occurs on a shorter timescale. Therefore, revisiting evolutionary calculations using the correct approach is necessary. This study is essential for developing the dynamics of crustal fractures and the magnetic field evolution in a magnetar.
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.
Abstract Approximately one-third of existing γ-ray sources identified by the Fermi Gamma-Ray Space Telescope are considered to be unassociated, with no known counterpart at other frequencies/wavelengths. These sources have been the subject of intense scrutiny and observational effort during the observatory’s mission lifetime, and here we present a method of leveraging existing radio catalogs to examine these sources without the need for specific dedicated observations, which can be costly and complex. Via the inclusion of many sensitive low-frequency catalogs we specifically target steep-spectrum sources such as pulsars. This work has found steep-spectrum radio sources contained inside 591 Fermi unassociated fields, with at least 21 of them being notable for having pulsar-like γ-ray properties as well. We also identify a number of other fields of interest based on various radio and γ-ray selections.