bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Global Asteroseismology Project Proof of Concept: Asteroseismology of Massive Stars with Continuous Ground-based Observations
Authors: Shitrit Noi , Arcavi Iair 
Published: January 2024

Abstract
Massive (≳8M
⊙) stars are the progenitors of many astrophysical systems, yet key aspects of their structure and evolution are poorly understood. Asteroseismology has the potential to solve these open puzzles; however, sampling both the short period pulsations and long period beat patterns of massive stars poses many observational challenges. Ground-based single-site observations require years or decades to discern the main oscillation modes. Multisite campaigns were able to shorten this time span, but have not been able to scale up to population studies on sample of objects. Space-based observations can achieve both continuous sampling and observe large numbers of objects; however, most lack the multiband data that is often necessary for mode identification and removing model degeneracies. Here, we develop and test a new ground-based observational strategy for discerning and identifying the main oscillation modes of a massive star in a few months, in a way that can be scaled to large samples. We do so using the Las Cumbres Observatory—a unique facility consisting of robotic, homogeneous telescopes operating as a global network, overcoming most of the challenges of previous multisite efforts, but presenting new challenges which we tailor our strategy to address. This work serves as the proof of concept for the Global Asteroseismology Project, which aims to move massive star asteroseismology from single-objects to bulk studies, unleashing its full potential in constraining stellar structure and evolution models. This work also demonstrates the ability of the Las Cumbres Observatory to perform multisite continuous observations for various science goals.
Dynamical Stellar Mass-to-light Ratio Gradients: Evidence for Very Centrally Concentrated IMF Variations in ETGs?
Authors: Mehrgan Kianusch , Thomas Jens , Saglia Roberto , Parikh Taniya , Neureiter Bianca , Erwin Peter , Bender Ralf 
Published: January 2024

Abstract
Evidence from different probes of the stellar initial mass function (IMF) of massive early-type galaxies (ETGs) has repeatedly converged on IMFs more bottom heavy than in the Milky Way (MW). This consensus has come under scrutiny due to often contradictory results from different methods on the level of individual galaxies. In particular, a number of strong lensing probes are ostensibly incompatible with a non-MW IMF. Radial gradients of the IMF—related to gradients of the stellar mass-to-light ratio ϒ—can potentially resolve this issue. We construct Schwarzschild models allowing for ϒ-gradients in seven massive ETGs with MUSE and SINFONI observations. We find dynamical evidence that ϒ increases toward the center for all ETGs. The gradients are confined to subkiloparsec scales. Our results suggest that constant-ϒ models may overestimate the stellar mass of galaxies by up to a factor of 1.5. For all except one galaxy, we find a radius where the total dynamical mass has a minimum. This minimum places the strongest constraints on the IMF outside the center and appears at roughly 1 kpc. We consider the IMF at this radius characteristic for the main body of each ETG. In terms of the IMF mass-normalization α relative to a Kroupa IMF, we find on average an MW-like IMF 〈α
main〉 = 1.03 ± 0.19. In the centers, we find concentrated regions with increased mass normalizations that are less extreme than previous studies suggested, but still point to a Salpeter-like IMF, 〈α
cen〉 = 1.54 ± 0.15.
A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55
Authors: McNanna M. , Bechtol K. , Mau S. , Nadler E. O. , Medoff J. , Drlica-Wagner A. , Cerny W. , Crnojević D. , Mutlu-Pakdıl B. , Vivas A. K. , Pace A. B. , Carlin J. L. , Collins M. L. M. , Ferguson P. S. , Martínez-Delgado D. , Martínez-Vázquez C. E. , Noel N. E. D. , Riley A. H. , Sand D. J. , Smercina A. , Tollerud E. , Wechsler R. H. , Abbott T. M. C. , Aguena M. , Alves O. , Bacon D. , Bom C. R. , Brooks D. , Burke D. L. , Carballo-Bello J. A. , Carnero Rosell A. , Carretero J. , da Costa L. N. , Davis T. M. , De Vicente J. , Diehl H. T. , Doel P. , Ferrero I. , Frieman J. , Giannini G. , Gruen D. , Gutierrez G. , Gruendl R. A. , Hinton S. R. , Hollowood D. L. , Honscheid K. , James D. J. , Kuehn K. , Marshall J. L. , Mena-Fernández J. , Miquel R. , Pereira M. E. S. , Pieres A. , Plazas Malagón A. A. , Sakowska J. D. , Sanchez E. , Sanchez Cid D. , Santiago B. , Sevilla-Noarbe I. , Smith M. , Stringfellow G. S. , Suchyta E. , Swanson M. E. C. , Tarle G. , Weaverdyck N. , Wiseman P. ,   DES & DELVE Collaboration
Published: January 2024

Abstract
We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete to M

V
∼ (−7, −10) mag for galaxies at D = (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of

2.2

−
0.12

+
0.05

Mpc

, a potential satellite of the Local Volume galaxy NGC 55, separated by 47′ (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absolute V-band magnitude of

−

8.0

−
0.3

+
0.5

mag

and an azimuthally averaged physical half-light radius of

2.2

−
0.4

+
0.5

kpc

, making this one of the lowest surface brightness galaxies ever found with

μ
=
32.3

mag

arcsec

−
2

. This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host.
Brightest Cluster Galaxy Formation in the z = 4.3 Protocluster SPT 2349-56: Discovery of a Radio-loud Active Galactic Nucleus
Authors: Chapman Scott C. , Hill Ryley , Aravena Manuel , Archipley Melanie , Babul Arif , Burgoyne James , Canning Rebecca E. A. , Deane Roger P. , De Breuck Carlos , Gonzalez Anthony H. , Hayward Christopher C. , Kim Seon Woo , Malkan Matt , Marrone Dan P. , McIntyre Vincent , Murphy Eric , Pass Emily , Perry Ryan W. , Phadke Kedar A. , Rennehan Douglas , Reuter Cassie , Rotermund Kaja M. , Scott Douglas , Seymour Nick , Solimano Manuel , Spilker Justin , Stark Anthony A. , Sulzenauer Nikolaus , Tothill Nick , Vieira Joaquin D. , Vizgan David , Wang George , Weiss Axel 
Published: January 2024

Abstract
We have observed the z = 4.3 protocluster SPT2349−56 with the Australia Telescope Compact Array (ATCA) with the aim of detecting radio-loud active galactic nuclei (AGNs) among the ∼30 submillimeter (submm) galaxies (SMGs) identified in the structure. We detect the central complex of submm sources at 2.2 GHz with a luminosity of L
2.2 = (4.42 ± 0.56) × 1025 W Hz−1. MeerKAT and the Australian Square Kilometre Array Pathfinder also detect the source at 816 MHz and 888 MHz, respectively, constraining the radio spectral index to α = −1.45 ± 0.16, implying L
1.4,rest = (2.2 ± 0.2) × 1026 W Hz−1. The radio observations do not have sufficient spatial resolution to uniquely identify one of the three Atacama Large Millimeter/submillimeter Array (ALMA) galaxies as the AGN, however the ALMA source properties themselves suggest a likely host. This radio luminosity is ∼100× higher than expected from star formation, assuming the usual far-infrared–radio correlation, indicating an AGN driven by a forming brightest cluster galaxy. None of the SMGs in SPT2349−56 show signs of AGNs in any other diagnostics available to us, highlighting the radio continuum as a powerful probe of obscured AGNs. We compare these results to field samples of radio sources and SMGs, along with the 22 gravitationally lensed SPT-SMGs also observed in the ATCA program, as well as powerful radio galaxies at high redshifts. The (3.3 ± 0.7) × 1038 W of power from the radio-loud AGN sustained over 100 Myr is comparable to the binding energy of the gas mass of the central halo, and similar to the instantaneous energy injection from supernova feedback from the SMGs in the core region. The SPT2349−56 radio-loud AGNs may be providing strong feedback on a nascent intracluster medium.
Magnetic Fields of the Starless Core L 1512
Authors: Lin Sheng-Jun , Lai Shih-Ping , Pattle Kate , Berry David , Clemens Dan P. , Pagani Laurent , Ward-Thompson Derek , Thieme Travis J. , Ching Tao-Chung 
Published: January 2024

Abstract
We present JCMT POL-2 850 μm dust polarization observations and Mimir H-band stellar polarization observations toward the starless core L 1512. We detect the highly ordered core-scale magnetic field traced by the POL-2 data, of which the field orientation is consistent with the parsec-scale magnetic fields traced by Planck data, suggesting the large-scale fields thread from the low-density region to the dense core region in this cloud. The surrounding magnetic field traced by the Mimir data shows a wider variation in the field orientation, suggesting there could be a transition of magnetic field morphology at the envelope-scale. L 1512 was suggested to be presumably older than 1.4 Myr in a previous study via time-dependent chemical analysis, hinting that the magnetic field could be strong enough to slow the collapse of L 1512. In this study, we use the Davis–Chandrasekhar–Fermi method to derive a plane-of-sky magnetic field strength (B
pos) of 18 ± 7 μG and an observed mass-to-flux ratio (λ
obs) of 3.5 ± 2.4, suggesting that L 1512 is magnetically supercritical. However, the absence of significant infall motion and the presence of an oscillating envelope are inconsistent with the magnetically supercritical condition. Using a virial analysis, we suggest the presence of a hitherto hidden line-of-sight magnetic field strength of ∼27 μG with a mass-to-flux ratio (λ
tot) of ∼1.6, in which case both magnetic and kinetic pressures are important in supporting the L 1512 core. On the other hand, L 1512 may have just reached supercriticality and will collapse at any time.
Testing the Polarization of Gravitational-wave Background with the LISA-TianQin Network
Authors: Hu Yu , Wang Pan-Pan , Tan Yu-Jie , Shao Cheng-Gang 
Published: January 2024

Abstract
While general relativity predicts only two tensor modes for gravitational-wave (GW) polarization, general metric theories of gravity allow for up to four additional modes, including two vector and two scalar modes. Observing the polarization modes of GWs could provide a direct test of the modified gravity. The stochastic GW background (SGWB), which can be detected by space-based laser-interferometric detectors at design sensitivity, will provide an opportunity to directly measure alternative polarization. In this paper, we investigate the performance of the LISA-TianQin network for detecting alternative polarizations of stochastic backgrounds, and propose a method to separate different polarization modes. First, we generalize the small antenna approximation to compute the overlap reduction functions for the SGWB with arbitrary polarization, which is suitable for any time-delay interferometry combination. Then we analyze the detection capability of LISA-TianQin for the SGWB with different polarizations. Based on the orbital characteristics of LISA-TianQin, we propose a method to distinguish different polarization modes from their mixed data. Finally, simulation tests are performed to verify the effectiveness of the method. The results of the simulations demonstrate that LISA-TianQin, when employing our proposed method, has the ability to differentiate between various polarization modes, with a specific emphasis on the ability to distinguish between the breathing and longitudinal modes.
Atmospheric Escape From Three Terrestrial Planets in the L 98-59 System
Authors: Fromont Emeline F. , Ahlers John P. , do Amaral Laura N. R. , Barnes Rory , Gilbert Emily A. , Quintana Elisa V. , Peacock Sarah , Barclay Thomas , Youngblood Allison 
Published: January 2024

Abstract
A critically important process affecting the climate evolution and potential habitability of an exoplanet is atmospheric escape, in which high-energy radiation from a star drives the escape of hydrogen atoms and other light elements from a planet’s atmosphere. L 98-59 is a benchmark system for studying such atmospheric processes, with three transiting terrestrial-sized planets receiving Venus-like instellations (4–25 S
⊕) from their M3 host star. We use the VPLanet model to simulate the evolution of the L 98-59 system and the atmospheric escape of its inner three small planets, given different assumed initial water quantities. We find that, regardless of their initial water content, all three planets accumulate significant quantities of oxygen due to efficient water photolysis and hydrogen loss. All three planets also receive enough strong X-ray and extreme-ultraviolet flux to drive rapid water loss, which considerably affects their developing climates and atmospheres. Even in scenarios of low initial water content, our results suggest that the JWST will be sensitive to observations of retained oxygen on the L 98-59 planets in its future scheduled observations, with planets b and c being the most likely targets to possess an extended atmosphere. Our results constrain the atmospheric evolution of these small rocky planets, and they provide context for current and future observations of the L 98-59 system to generalize our understanding of multiterrestrial planet systems.
The Age Distribution of Stellar Orbit Space Clumps
Authors: Fürnkranz Verena , Rix Hans-Walter , Coronado Johanna , Seeburger Rhys 
Published: January 2024

Abstract
The orbit distribution of young stars in the Galactic disk is highly structured, from well-defined clusters to streams of stars that may be widely dispersed across the sky, but are compact in orbital action-angle space. The age distribution of such groups can constrain the timescales over which conatal groups of stars disperse into the “field.” Gaia data have proven powerful in identifying such groups in action-angle space, but the resulting member samples are often too small and have too narrow a color–magnitude diagram (CMD) coverage to allow robust age determinations. Here, we develop and illustrate a new approach that can estimate robust stellar population ages for such groups of stars. This first entails projecting the predetermined action-angle distribution into the 5D space of positions, parallaxes, and proper motions, where much larger samples of likely members can be identified over a much wider range of the CMD. It then entails isochrone fitting that accounts for: (a) widely varying distances and reddenings; (b) outliers and binaries; (c) sparsely populated main-sequence turnoffs, by incorporating the age information of the low-mass main sequence; and (d) the possible presence of an intrinsic age spread in the stellar population. When we apply this approach to 92 nearby stellar groups identified in 6D orbit space, we find that they are predominantly young (≲1 Gyr), mono-age populations. Many groups are established (known) localized clusters with possible tidal tails, while others tend to be widely dispersed and manifestly unbound. This new age-dating tool offers a stringent approach to understanding on which orbits stars form in the solar neighborhood and how quickly they disperse into the field.
Investigating Extreme Scattering Events by Volumetric Ray-tracing
Authors: Au Kelvin , Fiege Jason D. , Rogers Adam 
Published: January 2024

Abstract
Extreme scattering events (ESEs) are observed as dramatic (>50%) drops in flux density that occur over an extended period of weeks to months. Discrete plasma lensing structures are theorized to scatter the radio waves produced by distant sources such as pulsars, causing the signature decrease in flux density and characteristic caustic spikes in ESE light curves. While plasma lens models in the extant literature have reproduced key features of ESE light curves, they have all faced the problem of being highly overdense and overpressured relative to the surrounding interstellar medium by orders of magnitude. We model ESEs by numerically ray tracing through analytic, volumetric plasma lens models by solving the eikonal equation. Delaunay triangulation connecting the rays approximates the wave front, generating a mapping from the observer plane to the source plane to account for multiple imaging. This eikonal method of ray tracing is tested against known analytic solutions and is then applied to a three-dimensional Gaussian-distributed electron volume density lens and a filament model inspired by Grafton et al. We find convergence of our numerical results with established analytic solutions, validating our numerical method, and reproduce ESE-like light curves. Our numerical ray-tracing method lends itself well to exploring the lensing effects of volumetric turbulence as well as sheet-like lenses, which is currently in progress.
Black Hole Ultracompact X-Ray Binaries as Galactic Low-frequency Gravitational Wave Sources: The He Star Channel
Authors: Qin Ke , Xu Kun , Liu Dong-Dong , Jiang Long , Wang Bo , Chen Wen-Cong 
Published: January 2024

Abstract
Black hole (BH) ultracompact X-ray binaries (UCXBs) are potential Galactic low-frequency gravitational wave (GW) sources. As an alternative channel, BH UCXBs can evolve from BH+He star binaries. In this work, we perform a detailed stellar evolution model for the formation and evolution of BH UCXBs evolving from the He star channel to diagnose their detectability as low-frequency GW sources. Our calculations found that some nascent BH+He star binaries after the common-envelope (CE) phase could evolve into UCXB-LISA sources with a maximum GW frequency of ∼5 mHz, which can be detected in a distance of 10 kpc (or 100 kpc). Once BH+He star systems become UCXBs through mass transfer, they would emit X-ray luminosities of ∼1038 erg s−1, making them ideal multimessenger objects. If the initial He-star masses are ≥0.7 M
⊙, those systems are likely to experience two Roche lobe overflows, and the X-ray luminosity can reach a maximum of 3.5 × 1039 erg s−1 in the second mass-transfer stage. The initial He-star masses and initial orbital periods of progenitors of Galactic BH UCXB-LISA sources are in the range of 0.32–2.9 M
⊙ and 0.02–0.19 days, respectively. Nearly all BH+He star binaries in the above parameter space can evolve into GW sources whose chirp masses can be accurately measured. Employing a population synthesis simulation, we predict the birthrate and detection number of Galactic BH UCXB-LISA sources evolving from the He star channel are R = 2.2 × 10−6 yr−1 and 33 for an optimistic CE parameter, respectively.
FRAMEx. V. Radio Spectral Shape at Central Subparsec Region of Active Galactic Nuclei
Authors: Shuvo Onic I. , Johnson Megan C. , Secrest Nathan J. , Gliozzi Mario , Cigan Phillip J. , Fischer Travis C. , Van Der Horst Alexander J. 
Published: January 2024

Abstract
We present results from the Very Long Baseline Array multifrequency (1.6, 4.4, 8.6, and 22 GHz), high-sensitivity (∼25 μJy beam−1), subparsec-scale (<1 pc) observations and spectral energy distributions for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard-X-ray (14–195 keV) luminosities above 1042 erg s−1, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6 GHz) bands, 75% in the L band (1.6 GHz), and 50% in the K band (22 GHz). Most sources showed compact, resolved/slightly resolved, central subparsec-scale radio morphology, except for a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with the nearby interstellar medium. The spectral slopes are mostly gigahertz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that at the subparsec scale, the gigahertz-peaked spectra belong to the low-accreting, radio-loud AGNs, with a tendency to produce strong outflows, possibly small-scale jets, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from the central regions of highly accreting AGNs, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.
Infrared Emission of Specific Polycyclic Aromatic Hydrocarbon Molecules: Cyanonaphthalenes
Authors: Li Kaijun , Li Aigen , Yang X. J. , Fang Taotao 
Published: January 2024

Abstract
The unidentified infrared emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 μm are ubiquitously seen in a wide variety of astrophysical regions and commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules. However, the unambiguous identification of any individual, specific PAH molecules has proven elusive until very recently, when two isomers of cyanonapthalene, which consists of two fused benzene rings and substitutes a nitrile (–CN) group for a hydrogen atom, were discovered in the Taurus Molecular Cloud, based on their rotational transitions at radio frequencies. To facilitate the James Webb Space Telescope (JWST) to search for cyanonapthalenes in astrophysical regions, we model the vibrational excitation of cyanonapthalenes and calculate their infrared emission spectra in a number of representative astrophysical regions. The model emission spectra and intensities will allow JWST to quantitatively determine or place an upper limit on the abundances of cyanonapthalenes.
MeerKAT 1.3 GHz Observations of Supernova Remnants
Authors: Cotton W. D. , Kothes R. , Camilo F. , Chandra P. , Buchner S. , Nyamai M. 
Published: January 2024

Abstract
We present full Stokes MeerKAT L-band (856–1712 MHz) observations of 36 high-latitude supernova remnants (SNRs). Sensitive, high-dynamic-range images show a wealth of structure. G15.1−1.6 appears to be a H ii region rather than an SNR. G30.7−2.0 consists of three background extragalactic sources which appear to form an arc when imaged with much lower resolution. At least half of the remnants in the sample contain “blowouts” or “ears,” showing these to be a common feature. Analysis of the polarimetric data reveals details of the magnetic field structure in the emitting regions of the remnants as well as magnetized thermal plasma in front of polarized emission. The chance alignment of G327.6+14.6 with a background active galactic nucleus with very extended polarized jets allows testing for the presence of Faraday effects in the interior of the remnant. Scant evidence of Faraday rotating material is found in the interior of this remnant.