Sazuna/UAT_keywords huggingface dataset:
Evidence for a Mixture of Mirror Mode and Electromagnetic Ion Cyclotron Waves in the Martian Magnetosheath. Electromagnetic ion cyclotron (EMIC) and mirror-mode (MM) waves are widely observed in terrestrial and other planetary magnetosheaths. Even though linear theory supports that EMIC and MM waves may grow at comparable rates under suitable plasma conditions, their coexistence is rarely reported within magnetosheaths, primarily due to their similar free energy source from anisotropic plasmas. Using MAVEN spacecraft data, we present the first direct in situ observations of mixed MM and EMIC waves in the Martian magnetosheath. Our observations reveal the concurrent presence of EMIC waves and MM waves, both generated in the Martian magnetosheath. Unlike in the Earth's magnetosheath, where strong plasma compressions at the quasi-perpendicular bow shock can drive the growth of EMIC or MM waves, our results suggest that, in the Martian magnetosheath, the substantial ion anisotropy to generate EMIC and MM waves is provided by both upstream bow shock compressions and ubiquitous ion pickup processes of newborn ions. This study offers new insights into the role of ion pickup processes in the excitation and growth of EMIC and MM waves within planetary magnetosheaths, particularly in magnetosheaths where both shock heating and newborn ion pickup processes provide the prevailing anisotropic plasma environment, as seen in the magnetosheaths of Venus, Mars, and comets.

Keywords: Pickup ions, Mars, Space plasmas
Automated Exploration of Radical-molecule Chemistry: The Case of Oxirane + CH in the Interstellar Medium. Quantum chemistry provides accurate and reliable methods to investigate reaction pathways of reactive molecular systems relevant to the interstellar medium. However, the exhaustive exploration of a reactive network is often a daunting task, resulting in unexplored reactive channels that affect kinetic outcomes and branching ratios. Here, an automated workflow for exploring reactive potential energy surfaces (PESs) is employed for the first time to study the oxirane (C2H4O) plus methylidyne (∙CH) reaction. The ultimate goal is to comprehensively map its PES and, subsequently, derive rate constants for the most important reaction channels. In addition to its astrochemical relevance, this reaction has been considered because it is a challenging test case, its network being very extended, with 60 exothermic bimolecular products lying below the reactant's energy. Kinetic simulations indicate that the main product of the reaction is the HCO radical plus ethene (C2H4), while formation of s-trans-propenal (acrolein) and 2H-oxetene is also possible, but to a lesser extent. Based on the present study and other references in the literature, we suggest that the slightly higher relative abundance of s-trans-propenal compared to methyl ketene in the interstellar medium is a gas-phase kinetic effect, the former being a more easily accessible product on the C3H5O∙ PES.

Keywords: Interstellar molecules, Potential energy surfaces, Chemical kinetics, Astrochemistry, Interstellar medium
A Tale of Three Tails: A Misaligned Streamer and Mysterious Structures around [BHB2007]-1. Recent discoveries of streamer-like structures around protostellar sources challenge the traditional picture of isolated, axisymmetric star formation. Here, we present new Atacama Large Millimeter/submillimeter Array observations of [BHB2007]-1, a flat-spectrum source connected to at least three such elongated structures. Two of these features are symmetrically located to the north and south of the disk, with velocities aligned with the disk on their respective sides. However, their unbound kinematics and curved morphology make it difficult to determine their origin. Possible explanations include outflows, interactions with the nearby [BHB2007]-2 system, and hyperbolic infall, but none fully account for all observed properties. In contrast, a newly identified collimated structure to the west shows clear evidence of gravitationally bound infall. Estimates of its mass, mass infall rate, and angular momentum suggest that this infalling streamer would roughly double the mass budget available to form planets and tilt the disk by a few tens of degrees. Furthermore, its misalignment with the midplane of the disk and the lack of diffuse envelope emission indicate that the streamer may have formed due to gravitational capture of cloud material unrelated to the source's natal core. Together, these findings support a more dynamic picture of star formation, one where environmental interactions continue to shape the conditions for building planetary systems.

Keywords: Star formation, Protoplanetary disks, Planet formation
Information Cascade in Solar Wind Density Fluctuations. Solar wind density fluctuations show typical features of a turbulent energy cascade, including power-law spectra and intermittency. An alternative description in terms of an information cascade and the study of the transition to complexity of the scale-dependent dynamics can provide complementary information on the nonlinear processes governing turbulence. High-resolution proton density measurements from the Spektr-R spacecraft are analyzed using empirical mode decomposition in intrinsic mode functions. The transfer of information and coupling strength between different scales is quantitatively assessed using transfer entropy and mutual information operators. The possible role of intermittency in preventing information from vanishing at proton scales is discussed. In particular, it is demonstrated that in the inertial range it promotes efficient information exchange/coupling, while its absence at kinetic scales constrains the causal transfer to local interactions, only between immediately adjacent scales. The analysis, quantified by the asymmetric flux ratio, confirms that the forward (direct) cascade is the overall dominant causal mechanism across the inertial range. However, the inverse flow becomes locally dominant at kinetic scales.

Keywords: Interplanetary turbulence, Magnetohydrodynamics, Solar wind
X-Ray Intraday Variability of the Blazar OJ 287 Observed with XMM-Newton. We present X-ray intraday variability, cross-correlated variability, and power spectrum density analysis of the binary black hole blazar candidate OJ 287. The X-ray pointed observations of the source were carried out on eight occasions by the EPIC-pn camera on board the XMM-Newton satellite from 2005 November to 2022 November. The good time intervals range between 3.6 and 24.1 hr. Three energy bands—0.2─2 keV (soft), 2─10 keV (hard), and 0.2─10 keV (total)—have been used to estimate variability. Low amplitude variations are observed in four, five, and six light curves in soft, hard, and total energy bands, respectively. Only two observation IDs have shown variation in the all energy bands. The discrete correlation function of the light curves in soft and hard energy bands peaks at zero lag, suggesting that the emission in both bands was cospatial and came from the same population of leptons. Red noise dominates the power spectral densities of variable light curves. According to our flux and spectrum investigations, both particle acceleration and synchrotron cooling mechanisms contribute significantly to the emission from this blazar.

Keywords: X-ray astronomy, Jets, BL Lacertae objects, Blazars, Active galactic nuclei
Detailed Investigation of a W UMa Contact Binary with an Ultralow Mass Ratio and a Third Body as a Potential Merger Candidate. The lower limit of the mass ratio in contact binaries remains uncertain, with observations suggesting systems exist below theoretical predictions. The stability of such very-low-mass-ratio systems is still debated. Based on our review of systems within the mass-ratio cutoff range, we reanalyzed TYC 3801-1529-1 and found it to have the lowest known mass ratio,  q=0.024−(1)+(2) , among analyzed contact binaries. The reanalysis of this target was carried out using the BSN (Binary Systems of South and North) application and the Markov Chain Monte Carlo method. We then compared our light-curve solution obtained from TESS observations with the results of a previous study. We studied the period variations of this system and identified a cyclic trend over the past 6 yr. After the third-body contribution has been removed, the system's period variations can be described either by a linear trend with a negative slope or by a quadratic trend with a downward curvature. These results indicate that it is still not possible to definitively determine whether the orbital period is increasing or decreasing, underscoring the importance of future observations. By considering the challenges of detecting the faint secondary in extremely low-mass-ratio systems, we estimated the absolute parameters of the target. Based on our analysis, the secondary component of the binary is likely a brown dwarf, while the third body appears to be a low-mass M-type dwarf. According to our analysis, TYC 3801-1529-1 is dynamically unstable and thus represents a remarkable candidate for a binary merger.

Keywords: Eclipsing binary stars, Astronomy data analysis, Fundamental parameters of stars
Probing Baryonic Feedback and Cosmology with the 3 × 2-point Statistic of Fast Radio Bursts and Galaxies. The impact of galaxy formation processes on the matter power spectrum is uncertain. Fast radio bursts (FRBs), through their dispersion measures (DMs) encoding the integrated baryon density, offer a unique window into gas distribution. In this work, we investigate the constraining power of a 3 × 2-point correlation statistic of DMs and galaxies. We present the correlation formalism, derive covariance matrices, and forecast signal-to-noise ratios (SNRs) and Fisher constraints. Assuming a host DM variance of 90 pc cm−3, for 104 (105) FRBs across 35% of the sky, the angular DM power spectrum is noise dominated at multipoles ℓ ≳ 20 (100), implying that the analysis can be conducted using arcminute localizations. In practice, this will be limited by uncertain host associations, which are expected to impact the mean DM subtraction—and thus our assumed value of σhost = 90 pc cm−3—in DM perturbations. While 104 (105) FRBs can constrain cosmological parameters at the ∼40%─70% (30%─40%) level, this is a factor of ∼2─3 (1.5─2) weaker than the precision attainable with galaxy clustering alone due to shot noise from the FRB number density, variance of the field, and host DMs. On the contrary, feedback-sensitive scales are not currently accessible in galaxy surveys. We demonstrate that combining DM and galaxy correlations in a 3 × 2-point analysis breaks feedback─cosmology degeneracies, yielding ∼10%─18% (7%─13%) precision on cosmological parameters and ∼3% (2%) constraints on feedback using 104 (105) FRBs. For the range of accessible scales, the SNR does not vary significantly with feedback. This work positions the DM─galaxy 3 × 2 point statistic as a promising multiprobe strategy.

Keywords: Observational cosmology, Radio transient sources
Investigating H II Regions in the Disk of NGC 7331 with the Circumgalactic Hα Spectrograph. We investigate the ionized gas kinematics of H II regions in the disk of NGC 7331 using integral field unit data collected with the Circumgalactic Hα Spectrograph (CHαS). NGC 7331 is a well-studied nearby galaxy with H II regions resolved by seeing-limited observations, making it ideally suited for this work. The galaxy disk features vigorous star formation, especially in the central ring of starburst activity. We present a catalog of 136 H II regions detected in the SIRTF Nearby Galaxies Survey (SINGS) Hα image. Using this refined catalog, we perform aperture photometry on the SINGS narrowband Hα images of NGC 7331, extracting the Hα luminosity L(Hα) of these regions. We present corresponding measurements of the average line-of-sight ionized gas velocity dispersion σ in these H II regions with CHαS. High-resolution velocity and dispersion maps of the galactic disk are produced from the CHαS spectral imaging, selecting spaxels with high signal to noise in order to measure velocity dispersions as low as 12 km s−1. Our measurements of the L(Hα), ΣSFR, and σ in NGC 7331 are consistent with spatially resolved observations of H II regions in large surveys of nearby galaxies. We explore the L(Hα)─σ relationship, identifying turbulent H II regions with nonthermal dispersions likely driven by stellar feedback. The dispersion is correlated with the star formation rate surface density, and using the relation  σ∝ϵΣSFRα , H II regions in NGC 7331 are best fit by ϵ = 80, α = 0.285.

Keywords: Spiral galaxies, Interstellar line emission, H II regions, Spectroscopy
Continued Rapid Radio Brightening of the Tidal Disruption Event AT2018hyz. We present ongoing radio observations of the tidal disruption event (TDE) AT2018hyz, which was first detected in the radio at 972 days after disruption, following multiple nondetections from earlier searches. The new observations presented here span ≍1370─2160 days and 0.88─240 GHz. We find that the light curves continue to rise at all frequencies during this time period, following a power law of about Fν ∝ t3 (compared to Fν ∝ t5.7 at 972─1400 days) and reaching a peak luminosity of L ≍ 1040 erg s−1, comparable to the luminosity of the relativistic TDE Sw 1644+57 on the same timescale. The multifrequency data indicate that the peak frequency does not significantly evolve over the 1030 days span of our observations, while the peak flux density increases by an order of magnitude. The observed behavior is consistent with two possible scenarios: (i) a delayed spherical outflow launched about 620 days postdisruption with a velocity of ≍0.3c and an energy of ∼1050 erg; or (ii) a highly off-axis (≍80°─90°) relativistic jet with a Lorentz factor of Γ ∼ 8 and EK ≍ 1052 erg. Continued radio observations to capture the light-curve peak, as well as very long baseline interferometry observations, could distinguish between these scenarios.

Keywords: Black holes
New Theoretical Instability Regions, Period─Luminosity Relations, and Masses for Blue Large-amplitude Pulsators. Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot pulsating stars whose evolutionary status remains uncertain. Their proposed progenitors are either ≃0.3M⊙ shell H-burning stars or ≃1.0M⊙ core He-burning stars, both relying on mass loss or a merger event in a (rarely observed) close interacting binary system. With the goal of understanding the stellar masses of BLAPs, we therefore carried out a linear nonadiabatic analysis of a grid of models computed using MESA-RSP, with appropriate input stellar parameters ZXMLTeff and convection parameter sets. We discuss the impact of stellar mass, metallicity, helium abundance, and convection parameters on the theoretical instability regions of BLAPs. We also derive new theoretical period relations; those based on low stellar masses show better agreement with the observed period relations. Although only two BLAPs have been observed to be multiperiodic oscillators so far, we analyse theoretical P1O/PF ratios and compare these values with other classical pulsators. Furthermore, we provide the first asteroseismic mass estimate for the triple-mode pulsator OGLE-BLAP-030, which seems to be well constrained in the range of 0.62─0.64M⊙ with a high metallicity of Z = 0.07, albeit with a few sources of uncertainty involved. This would place the BLAP star intermediate to the two proposed mass scenarios so far.

Keywords: Stellar physics, Stellar properties, Stellar atmospheres, Stellar pulsations
HST Observations of HD 166620 and τ Ceti: First UV Spectra of a Magnetic Grand Minimum Star and the Extent of τ Ceti's Astrosphere. We present new Hubble Space Telescope (HST) UV spectra of the K2 V star HD 166620, the first star clearly recognized to be in a "magnetic grand minimum" state analogous to the Sun's "Maunder minimum" in the late 1600s. The stellar H I Lyα surface fluxes are extremely low, about a factor of 2 below fluxes observed during solar minimum, and also significantly lower than those of τ Ceti (G8 V) and HD 191408 (K2.5 V), two stars more similar to HD 166620 in spectral type and age (∼10 Gyr) than the Sun. The τ Ceti data that are compared with HD 166620 include both old archival data and a new HST observation as well. The Lyα data are used to confirm a nondetection of astrospheric Lyα absorption for this star, suggesting a very weak wind with  Ṁ&lt;0.1   Ṁ⊙ . The very compact astrosphere inferred for τ Ceti indicates that the star's debris disk is at least partly exposed to the interstellar medium (ISM), and we discuss possible consequences.

Keywords: Stellar-interstellar interactions, Stellar chromospheres, Ultraviolet spectroscopy, Stellar winds, Interstellar absorption, Interstellar medium, Debris disks
Detailed Chemical Abundance Analysis of the Brightest Stars in the Turranburra and Willka Yaku Stellar Streams. We present a detailed chemical abundance analysis of the three brightest known stars from each of the Turranburra and Willka Yaku stellar streams using high-resolution Magellan/Magellan Inamori Kyocera Echelle spectra. Abundances for 27 elements, ranging from carbon to dysprosium, were derived. Our results support the original classification that Turranburra, with a low average metallicity of [Fe/H] = −2.45 ± 0.07, likely originates from a dwarf galaxy progenitor. Willka Yaku has a low average metallicity of [Fe/H] = −2.35 ± 0.03 with a small scatter in the abundances, consistent with a globular cluster progenitor as suggested by previous studies. Both streams exhibit mild enhancements in neutron-capture elements, with averages of [Eu II/Fe] = 0.47 ± 0.09 for Turranburra and 0.44 ± 0.05 for Willka Yaku, consistent with enrichment from an r-process event. A similar enrichment is observed in other stellar streams, and we further discuss this signature as it relates to the potential enrichment histories of these two streams. *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Stellar streams, Stellar abundances, Chemical abundances
PEARLS: 21 Transients Found in the Three-epoch NIRCam Observations in the Continuous Viewing Zone of the James Webb Space Telescope. We present 21 transients from our three-epoch, four-band NIRCam observations covering 14.16 arcmin2 in the Spitzer IRAC Dark Field (IDF), taken by the JWST Prime Extragalactic Areas for Reionization and Lensing Science program with a time cadence of ∼6 months. A separate Hubble Space Telescope program provided Advanced Camera for Surveys optical imaging contemporaneous with the second and third epochs of the NIRCam observations. The NIRSpec spectroscopy on three transients confirmed a Type Ia supernova at z = 1.63 and the host galaxies of the other two at z = 2.64 and 1.90, respectively. Combining these with the photometric redshifts (zph) of the host galaxies in the rest of the sample, we find that the transients are in either a "mid-z" group at z &gt; 1.6 with MV ≲ − 16.0 mag or a "low-z" group at z &lt; 0.4 with MH ≳ − 14.0 mag. The mid-z transients are consistent with supernovae. In contrast, the low-z transients' luminosities fall in the range of the so-called "gap transients" between supernovae and novae. However, this latter conclusion is only tentative due to possible catastrophic failures in zph that could bias them to low-z. Conversely, if they are indeed at z &lt; 0.4, it would be worth studying similar transients in the future. Our work further demonstrates the power of NIRCam in transient science and also shows that it would be more fruitful to carry out a long-term monitoring program with more passbands, a higher cadence, and prompt follow-up spectroscopy. Being in the continuous viewing zone of the JWST, the IDF is an ideal field for this purpose.

Keywords: Galaxy evolution, Transient sources, Supernovae, Transient detection
Characterizing the Low-mass Pre-main-sequence Population in the Low-metallicity Star-forming Region Dolidze 25 Using VLT-MUSE. The metallicity of the star-forming environment is a fundamental parameter shaping the evolution of protoplanetary disks and the formation of planetary systems, yet its influence remains poorly constrained. We present a spectroscopic study of low-mass pre-main-sequence (PMS) stars (M &lt; 1 M⊙) in the exceptionally metal-poor cluster Dolidze 25 (Z ≍ 0.2 Z⊙), using Very Large Telescope/MUSE observations to probe accretion processes and disk evolution in a subsolar environment. We identify 132 cluster members using a combination of Gaia astrometry and spectroscopic youth indicators, including lithium absorption and Balmer emission. The stellar parameters are derived using low-metallicity BT-Settl models yielding effective temperatures, extinctions, and luminosities enabling robust estimates of stellar masses and ages. Mass accretion rates ( Ṁacc ) derived from Hα emission span 10−10─10−8 M⊙ yr−1 with a median value of 8 × 10−10 M⊙ yr−1. These rates are comparable to those in solar-metallicity regions of a similar age, such as Lupus and Orion, indicating minimal metallicity dependence in accretion processes. Our analysis shows that using solar-metallicity templates to fit low-metallicity stars leads to systematic overestimations of Teff (by approximately 300 K) and AV (by around 0.5 mag), underscoring the importance of employing metallicity-matched models for reliable characterization in low-Z environments. We present flux-calibrated, extinction-corrected spectra of these metal-poor PMS stars as a valuable resource for future investigations of disk evolution in subsolar regimes.

Keywords: Pre-main sequence stars, Metallicity, Low mass stars, Stellar accretion
The Apache Point Observatory Extra-galactic Evolution Experiment (APOeGEE): Chemical Abundance Trends for Seven Dwarf Spheroidal Galaxies in the APOGEE Survey. In addition to comprehensive surveys of the Milky Way (MW) bulge, disk, and halo, the Apache Point Galactic Evolution Experiment (APOGEE) project observed seven dwarf spheroidal satellites (dSphs) of the MW: Carina, Sextans, Sculptor, Draco, Ursa Minor, Bootes 1, and Fornax. APOGEE radial velocities, stellar parameters, and Gaia EDR3 proper motions are used to identify member stars from the targets in the vicinity of each dwarf; for seven dwarfs, new member stars are identified. To properly analyze the abundance patterns of these galaxies, a novel procedure was developed to determine the measurable upper limits of the APOGEE chemical abundances as a function of the effective temperature and the spectral signal-to-noise ratio. In general, the APOGEE abundance patterns of these galaxies (limited to [Fe/H] &gt; −2.5) agree with those found in high-resolution optical studies in the literature after abundance offsets are applied. Most of the galaxies studied here have abundance patterns that are distinctly different from the majority of stars found in the MW halo, suggesting that these galaxies contributed little to the MW halo above [Fe/H] &gt; −2.0. From these abundance patterns, we also find that these dSphs tend to follow two types of chemical evolution paths: episodic and continuous star formation, a result that is broadly consistent with previous photometric studies of the star formation histories (SFHs) of these galaxies. We explore whether mass and/or environment have an impact on whether a galaxy has an episodic or continuous SFH, finding tentative evidence that, in addition to the galaxy's mass, proximity to a larger galaxy and the cessation of star formation may drive the overall shape of the chemical evolution.

Keywords: Galaxy abundances, Dwarf galaxies, Galaxy chemical evolution