adsabs/SciX_UAT_keywords huggingface dataset:
A Strong Falsification of the Universal Radial Acceleration Relation in Galaxies

In the past few decades, many studies revealed that there exist some apparent universal relations that can describe the dynamical properties in galaxies. In particular, the radial acceleration relation (RAR) is one of the most popular relations discovered recently that can be regarded as a universal law to connect the dynamical radial acceleration with the baryonic acceleration in galaxies. This has revealed an unexpected close connection between dark matter and baryonic matter in galaxies. In this article, by following the recent robust Galactic rotation curve analyzes, we derive the Galactic RAR (GRAR) and show for the first time that the alleged best-fit universal RAR deviates from the GRAR data at more than 5σ. This provides a strong evidence to falsify the universal nature of RAR in galaxies claimed in past studies.

Keywords: galaxy dark matter halos; galaxy dynamics
Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS

LHS 1140 b is the second-closest temperate transiting planet to Earth with an equilibrium temperature low enough to support surface liquid water. At 1.730 ± 0.025 R ⊕, LHS 1140 b falls within the radius valley separating H2-rich mini-Neptunes from rocky super-Earths. Recent mass and radius revisions indicate a bulk density significantly lower than expected for an Earth-like rocky interior, suggesting that LHS 1140 b could be either a mini-Neptune with a small envelope of hydrogen (∼0.1% by mass) or a water world (9%–19% water by mass). Atmospheric characterization through transmission spectroscopy can readily discern between these two scenarios. Here we present two JWST/NIRISS transit observations of LHS 1140 b, one of which captures a serendipitous transit of LHS 1140 c. The combined transmission spectrum of LHS 1140 b shows a telltale spectral signature of unocculted faculae (5.8σ), covering ∼20% of the visible stellar surface. Besides faculae, our spectral retrieval analysis reveals tentative evidence of residual spectral features, best fit by Rayleigh scattering from a N2-dominated atmosphere (2.3σ), irrespective of the consideration of atmospheric hazes. We also show through Global Climate Models (GCMs) that H2-rich atmospheres of various compositions (100×, 300×, 1000× solar metallicity) are ruled out to >10σ. The GCM calculations predict that water clouds form below the transit photosphere, limiting their impact on transmission data. Our observations suggest that LHS 1140 b is either airless or, more likely, surrounded by an atmosphere with a high mean molecular weight. Our tentative evidence of a N2-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b.

Keywords: exoplanets; habitable planets; planetary atmospheres; super earths; ocean planets; mini neptunes; m dwarf stars; transmission spectroscopy
Massive Hypervelocity Runaway Stars in the Large Magellanic Cloud

Since the hypervelocity stars were discovered in the Milky Way, various mechanisms have been proposed to explain these runaway stars. Up to now, however, the dominant ejected mechanism of hypervelocity stars is still unclear. As the largest and closest face-on satellite galaxy of the Milky Way, the Large Magellanic Cloud (LMC) serves as a good target, allowing us to study this issue. Based on the high-precision astrometric parameters provided by Gaia Data Release 3, we researched the proper motions of 3119 massive O-B2-type stars in the LMC and identified 98 (~3%) as having the ability to escape from the LMC, with more than 50% confidence. Furthermore, by investigating the characteristics of the identified massive stars and adopting a regression analysis, we find that the dynamic ejection scenario might be the dominant mechanism of the massive hypervelocity runaway stars in the LMC.

Keywords: stellar kinematics; stellar dynamics; proper motions; large magellanic cloud
Observational Features of Exoplanetary Synchrotron Radio Bursts

The magnetic fields of exoplanets shield the planets from cosmic rays and interplanetary plasma. Due to the interaction with the electrons from their host stars, the exoplanetary magnetospheres are predicted to have both cyclotron and synchrotron radio emissions, neither of which have been definitively identified in observations. As the coherent cyclotron emission has been extensively studied in the literature, here we focus on planetary synchrotron radiation with bursty behaviors (I.e., radio flares) caused by the outbreaks of energetic electron ejections from the host star. Two key parameters of the bursty synchrotron emissions, namely the flux density and burst rate, and two key features, namely the burst light curve and frequency shift, are predicted for star-hot Jupiter systems. The planetary orbital phase-burst rate relation is also considered as the signature of star-planet interactions. As examples, previous X-ray and radio observations of two well-studied candidate systems, HD 189733 and V830 τ, are adopted to predict their specific burst rates and fluxes of bursty synchrotron emissions for further observational confirmations. The detectability of such emissions by current and upcoming radio telescopes shows that we are at the dawn of discoveries.

Keywords: exoplanets; radio bursts; magnetospheric radio emissions; magnetic fields; stellar flares
Shouts and Murmurs: Combining Individual Gravitational-wave Sources with the Stochastic Background to Measure the History of Binary Black Hole Mergers

One of the goals of gravitational-wave astronomy is to quantify the evolution of the compact binary merger rate with redshift. The redshift distribution of black hole mergers would offer considerable information about their evolutionary history, including their progenitor formation rate, the dependence of black hole formation on stellar metallicity, and the time delay distribution between formation and merger. Efforts to measure the binary redshift distribution are currently limited, however, by the detection range of existing instruments, which can individually resolve compact binary merger events only out to $z\lesssim 1$ . We present a novel strategy with which to measure the redshift distribution of binary black hole mergers well beyond the detection range of current instruments. By synthesizing direct detections of individually resolved mergers with indirect searches for the stochastic gravitational-wave background due to unresolved distant sources, we can glean information about the peak redshift, zp, at which the binary black hole merger rate attains its maximum, even when this redshift is beyond the detection horizon. Using data from Advanced LIGO and Virgo's first and second observing runs, we employ this strategy to place joint constraints on zp and the slope α with which the binary merger rate increases at low redshifts, ruling out merger rates that grow faster than $\alpha \gtrsim 7$ and peak beyond ${z}_{p}\gtrsim 1.5$ . Looking ahead, we project that approximately one year of observation with design-sensitivity Advanced LIGO will further break remaining degeneracies, enabling a direct measurement of the peak redshift of the binary black hole merger history.

Keywords: gravitational waves; black holes; compact binary stars; ligo; gravitational wave sources
Discovery of a Giant Radio Fossil in the Ophiuchus Galaxy Cluster

The Ophiuchus galaxy cluster exhibits a curious concave gas density discontinuity at the edge of its cool core. It was discovered in the Chandra X-ray image by Werner and collaborators, who considered the possibility of it being a boundary of an active galactic nucleus (AGN)-inflated bubble located outside the core, but discounted this possibility because it required much too powerful an AGN outburst. Using low-frequency (72-240 MHz) radio data from the Murchison Widefield Array/GLEAM and the Giant Metrewave Radio Telescope, we found that the X-ray structure is, in fact, a giant cavity in the X-ray gas filled with diffuse radio emission with an extraordinarily steep radio spectrum. It thus appears to be a very aged fossil of the most powerful AGN outburst seen in any galaxy cluster (pV ∼ 5 × 1061 erg for this cavity). There is no apparent diametrically opposite counterpart either in X-ray or in the radio. It may have aged out of the observable radio band because of the cluster asymmetry. At present, the central AGN exhibits only a weak radio source, so it should have been much more powerful in the past to have produced such a bubble. The AGN is currently starved of accreting cool gas because the gas density peak is displaced by core sloshing. The sloshing itself could have been set off by this extraordinary explosion if it had occurred in an asymmetric gas core. This dinosaur may be an early example of a new class of sources to be uncovered by low-frequency surveys of galaxy clusters.

Keywords: galaxy clusters; cooling flows; intracluster medium; extragalactic radio sources; active galaxies
Implications of Inhomogeneous Metal Mixing for Stellar Archaeology

The first supernovae enrich the previously pristine gas with metals, out of which the next generation of stars form. Based on hydrodynamical simulations, we develop a new stochastic model to predict the metallicity of star-forming gas in the first galaxies. On average, in internally enriched galaxies, the metals are well mixed with the pristine gas. However, in externally enriched galaxies, the metals cannot easily penetrate into the dense gas, which yields a significant metallicity difference between the star-forming and average gas inside a halo. To study the consequences of this effect, we apply a semianalytical model to Milky Way-like dark matter merger trees and follow stellar fossils from high redshift until the present day with a novel realistic metal mixing recipe. We calibrate the model to reproduce the metallicity distribution function (MDF) at low metallicities and find that a primordial initial mass function (IMF) with a slope of ${dN}/{dM}\propto {M}^{-0.5}$ from 2 to $180\,{M}_{\odot }$ best reproduces the MDF. Our improved model for inhomogeneous mixing can have a large impact for individual minihalos but does not significantly influence the modeled MDF at [Fe/H] ≳ -4 or the best-fitting Population III IMF.

Keywords: chemical enrichment; population iii stars; galaxy chemical evolution; interstellar dynamics; interstellar medium
Distant Relatives: The Chemical Homogeneity of Comoving Pairs Identified in Gaia

Comoving pairs, even at the separations of ${ \mathcal O }({10}^{6})$ au, are a predicted reservoir of conatal stars. We present detailed chemical abundances of 62 stars in 31 comoving pairs with separations of 102-107 au and 3D velocity differences <2 km s-1. This sample includes both bound comoving pairs/wide binaries and unbound comoving pairs. Observations were taken using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on board the Magellan/Clay Telescope at high resolution (R ~ 45,000) with a typical signal-to-noise ratio of 150 pixel-1. With these spectra, we measure surface abundances for 24 elements, including Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Nd, and Eu. Taking iron as the representative element, our sample of wide binaries is chemically homogeneous at the level of 0.05 dex, which agrees with prior studies on wide binaries. Importantly, even systems at separations 2 × 105-107 au are homogeneous to 0.09 dex, as opposed to the random pairs, which have a dispersion of 0.23 dex. Assuming a mixture model of the wide binaries and random pairs, we find that 73 ± 22% of the comoving pairs at separations 2 × 105-107 au are conatal. Our results imply that a much larger parameter space of phase space may be used to find conatal stars, to study M-dwarfs, star cluster evolution, exoplanets, chemical tagging, and beyond.

Keywords: wide binary stars; chemical abundances; stellar kinematics; late-type stars
A VLBI Proper Motion Analysis of the Recoiling Supermassive Black Hole Candidate Mrk 1018

Mrk 1018 is a nearby changing-look active galactic nucleus (AGN) that has oscillated between spectral Type 1.9 and Type 1 over a period of 40 yr. Recently, a recoiling supermassive black hole (rSMBH) scenario has been proposed to explain the spectral and flux variability observed in this AGN. Detections of rSMBHs are important for understanding the processes by which SMBH binaries merge and how rSMBHs influence their galactic environment through feedback mechanisms. However, conclusive identification of any rSMBHs has remained elusive to date. In this paper, we present an analysis of 6.5 yr of multifrequency Very Long Baseline Array monitoring of Mrk 1018. We find that the radio emission is compact down to 2.4 pc, and it displays flux density and spectral variability over the length of our campaign, typical of a flat-spectrum radio core. We observe proper motion in RA of the radio core at -36.4 ± 8.6 μas yr-1 (4.2σ), or 0.10c ± 0.02c at the redshift of Mrk 1018. No significant proper motion is found in DEC (31.3 ± 25.1 μas yr-1). We discuss possible physical mechanisms driving the proper motion, including an rSMBH. We conclude that the apparent velocity we observe of the VLBI radio core is too high to reconcile with theoretical predictions of rSMBH velocities and that the proper motion is most likely dominated by an unresolved, outflowing jet component. Future observations may yet reveal the true nature of Mrk 1018. However, our observations are not able to confirm it as a true rSMBH.

Keywords: proper motions; time domain astronomy; very long baseline interferometry; supermassive black holes
Radio Emission from the Magnetically Active M Dwarf UV Ceti from 1 to 105 GHz

BL and UV Ceti are a nearby (2.7 pc) binary system with similar masses, spectral types, and rapid rotation rates, but very different magnetic activity. UV Ceti's much stronger large-scale magnetic field may cause this difference, highlighting key unanswered questions about dynamo processes in fully convective objects. Here, we present multiepoch characterization of the radio spectrum of UV Ceti spanning 1–105 GHz, exhibiting flared emission similar to coronal activity, auroral-like emission analogous to planetary magnetospheres, and slowly varying persistent emission. Radio observations are a powerful means to probe the role that the large-scale magnetic field of UV Ceti has in nonthermal particle acceleration because radio-frequency phenomena result from both the activity of small-scale field features as well as large-scale auroral current systems. We find temporal variability at all bands observed, and a hint of rotational modulation in the degree of circular polarization up to 40 GHz. The persistent component of the emission is fairly constant from 1 to 105 GHz, making optically thick emission or optically thin gyrosynchrotron from electrons with an isotropic pitch angle distribution unlikely. We discuss the possibility of emission mechanisms analogous to Jupiter's radiation belts.

Keywords: red dwarf flare stars; aurorae; stellar flares; millimeter astronomy
Optical Studies of Seven Bright Southern Cataclysmic Variable Stars

We report spectroscopic observations of seven bright southern cataclysmic variable stars, collected on a single two-week observing run using the 1.9 m Radcliffe telescope at the South African Astronomical Observatory. We used a radial-velocity time series, in some cases in combination with other data, to determine or clarify orbital periods for five of them, namely ATO J061.1478-31.0634, BMAM-V547, MGAB-V202, NSV 4202, and V1147 Cen. For BMAM-V547, we use data from the Transiting Exoplanet Survey Satellite (TESS) to corroborate and sharpen the orbital period; the TESS data also show a photometric period near 3.93 days, likely indicating precession of the accretion disk. Also, we find a periodic modulation in the radial velocities of the SU UMa-type dwarf nova Var Ret2005, but are unable to specify a unique cycle count. Finally, we show a spectrum of ASASSN-V J061528.41-412007.3 that appears typical of a luminous novalike variable.

Keywords: cataclysmic variable stars; nova-like variable stars; su ursae majoris stars; u geminorum stars
TRANSLIENT: Detecting Transients Resulting from Point-source Motion or Astrometric Errors

Detection of moving sources over a complicated background is important for several reasons. First is measuring the astrophysical motion of the source. Second is that such motion resulting from atmospheric scintillation, color refraction, or astrophysical reasons is a major source of false alarms for image-subtraction methods. We extend the Zackay, Ofek, and Gal-Yam image-subtraction formalism to deal with moving sources. The new method, named the TRANSLIENT (translational transient) detector, applies hypothesis testing between the hypothesis that the source is stationary and that the source is moving. It can be used to detect source motion or to distinguish between stellar variability and motion. For moving source detection, we show the superiority of TRANSLIENT over the proper image subtraction, using the improvement in the receiver-operating characteristic curve. We show that in the small translation limit, TRANSLIENT is an optimal detector of point-source motion in any direction. Furthermore, it is numerically stable, fast to calculate, and presented in a closed form. Efficient transient detection requires both the proper image-subtraction statistics and the TRANSLIENT statistics: When the translient statistic is higher, then the subtraction residual is likely due to motion. We test our algorithm both on simulated data and on real images obtained by the Large Array Survey Telescope. We demonstrate the ability of TRANSLIENT to distinguish between motion and variability, which has the potential to reduce the number of false alarms in transients detection. We provide the TRANSLIENT implementation in Python and MATLAB.

Keywords: astronomy software; transient detection; sky surveys
Newly Discovered Papers of S. Chandrasekhar and an Ethical Dilemma

Subrahmanyan Chandrasekhar (1910-1995) was one of the most important figures of 20th-Century astrophysics. The closing of Yerkes Observatory by the University of Chicago in 2018 led to discovery in Chandrasekhar's old Yerkes office of several boxes of items he had left. They included a sealed envelope, which when opened revealed an inner sealed envelope on which was written "Please do not examine contents. Thanks. S. Chandrasekhar." This paper discusses how the authors handled the ethical dilemma of balancing the wishes of a deceased scientific icon versus the obvious possibility that the envelope contained materials of historical importance.

Keywords: history of astronomy
HIP 33609 b: An Eccentric Brown Dwarf Transiting a V = 7.3 Rapidly Rotating B Star

We present the discovery and characterization of HIP 33609 b, a transiting warm brown dwarf orbiting a late B star, discovered by NASA's Transiting Exoplanet Survey Satellite as TOI-588 b. HIP 33609 b is a large (R b = ${1.580}_{-0.070}^{+0.074}$ R J) brown dwarf on a highly eccentric (e = ${0.560}_{-0.031}^{+0.029}$ ) orbit with a 39 days period. The host star is a bright (V = 7.3 mag), T eff = 10,400 ${}_{-660}^{+800}$ K star with a mass of M * = ${2.383}_{-0.095}^{+0.10}$ M ⊙ and radius of R * = ${1.863}_{-0.082}^{+0.087}$ R ⊙, making it the hottest transiting brown dwarf host star discovered to date. We obtained radial velocity measurements from the CHIRON spectrograph confirming the companion's mass of M b = ${68.0}_{-7.1}^{+7.4}$ M J as well as the host star's rotation rate ( $v\sin {i}_{* }=55.6\pm 1.8$ km s-1). We also present the discovery of a new comoving group of stars, designated as MELANGE-6, and determine that HIP 33609 is a member. We use a combination of rotation periods and isochrone models fit to the cluster members to estimate an age of 150 ± 25 Myr. With a measured mass, radius, and age, HIP 33609 b becomes a benchmark for substellar evolutionary models.

Keywords: exoplanets; brown dwarfs; young star clusters; direct imaging; ccd photometry; high resolution spectroscopy; exoplanet evolution
Extended 3He-rich Time Periods Observed by Solar Orbiter: Magnetic Connectivity and Sources

Observations of Solar Energetic Particles (SEPs) using the Suprathermal Ion Spectrograph (SIS), which is part of the Energetic Particle Detector suite on the Solar Orbiter mission, present an unprecedented opportunity to investigate the composition and evolution of SEPs in close proximity to the Sun. By analyzing data from the SIS instrument, we have compiled a catalog of extended time periods during the first five orbits of the spacecraft around the Sun, which exhibit a significant abundance of 3He. We have identified 33 periods lasting over one day that show a high abundance of 3He. For each period, we examined the SEP characteristics, the magnetic connectivity of the spacecraft, and the magnetically connected regions. Our findings show that these time periods typically span seven days and consist of multiple injections of 3He, and that the peak in 3He flux is observed two days after the time periods begin. The time periods usually start (end) when the spacecraft's magnetic connection changes to (from) an active region (AR). In most cases, we observed a stable magnetic connection between the spacecraft and one or more ARs, with an average connection time of 4.1 ± 1.8 days.

Keywords: solar physics; solar energetic particles; solar abundances; solar magnetic fields
Particle Acceleration Controlled by Ambient Density in the Southwestern Rim of RCW 86

The physics of particle acceleration at supernova remnant (SNR) shocks is one of the most intriguing problems in astrophysics. SNR RCW 86 provides a suitable environment for understanding the physics of particle acceleration because one can extract the information on both accelerated particles and acceleration environment in the same regions through the bright X-ray emission. In this work, we study X-ray proper motions and spectral properties of the southwestern region of RCW 86. The proper motion velocities are found to be ~300-2000 km s-1 at a distance of 2.8 kpc. We find two inward-moving filaments, which are more likely reflected shocks rather than reverse shocks. Based on the X-ray spectroscopy, we evaluate thermal parameters such as the ambient density and temperature, and nonthermal parameters such as the power-law flux and index. From the decrease in flux over time of several nonthermal filaments, we estimate the magnetic field amplitudes to be ~30-100 μG. Gathering the physical parameters, we then investigate parameter correlations. We find that the synchrotron emission from thermal-dominated filaments is correlated with the ambient density n e as (power-law flux) $\propto {n}_{{\rm{e}}}^{1.0\pm 0.2}$ and (power-law index) $\propto {n}_{{\rm{e}}}^{0.38\pm 0.10}$ , and not or only weakly correlated with the shock velocity and shock obliquity. As an interpretation, we propose a shock-cloud interaction scenario, where locally enhanced magnetic turbulence levels have a great influence on local acceleration conditions.

Keywords: shocks; supernova remnants; type ia supernovae; galactic cosmic rays