adsabs/SciX_UAT_keywords huggingface dataset:
Alive but Barely Kicking: News from 3+ yr of Swift and XMM-Newton X-Ray Monitoring of Quasiperiodic Eruptions from eRO-QPE1

Quasiperiodic eruptions (QPEs) represent a novel class of extragalactic X-ray transients that are known to repeat at roughly regular intervals of a few hours to days. Their underlying physical mechanism is a topic of heated debate, with most models proposing that they originate either from instabilities within the inner accretion flow or from orbiting objects. At present, our knowledge of how QPEs evolve over an extended timescale of multiple years is limited, except for the unique QPE source GSN 069. In this study, we present results from strategically designed Swift observing programs spanning the past 3 yr, aimed at tracking eruptions from eRO-QPE1. Our main results are as follows: (1) the recurrence time of eruptions can vary from flare to flare and is in the range of 0.6–1.2 days; (2) there is no detectable secular trend in evolution of the recurrence times; (3) consistent with prior studies, their eruption profiles can have complex shapes; and (4) the peak flux of the eruptions has been declining over the past 3 yr, with the eruptions barely detected in the most recent Swift data set taken in 2023 June. This trend of weakening eruptions has been reported recently in GSN 069. However, because the background luminosity of eRO-QPE1 is below our detection limit, we cannot verify whether the weakening is correlated with the background luminosity (as is claimed to be the case for GSN 069). We discuss these findings within the context of various proposed QPE models.

Keywords: tidal disruption; black hole physics; high energy astrophysics; supermassive black holes; astronomy data analysis; x-ray astronomy; x-ray sources
Early Planet Formation in Embedded Disks (eDisk). II. Limited Dust Settling and Prominent Snow Surfaces in the Edge-on Class I Disk IRAS 04302+2247

While dust disks around optically visible, Class II protostars are found to be vertically thin, when and how dust settles to the midplane are unclear. As part of the Atacama Large Millimeter/submillimeter Array large program, Early Planet Formation in Embedded Disks, we analyze the edge-on, embedded, Class I protostar IRAS 04302+2247, also nicknamed the "Butterfly Star." With a resolution of 0.″05 (8 au), the 1.3 mm continuum shows an asymmetry along the minor axis that is evidence of an optically thick and geometrically thick disk viewed nearly edge-on. There is no evidence of rings and gaps, which could be due to the lack of radial substructure or the highly inclined and optically thick view. With 0.″1 (16 au) resolution, we resolve the 2D snow surfaces, i.e., the boundary region between freeze-out and sublimation, for 12CO J = 2-1, 13CO J = 2-1, C18O J = 2-1, H 2CO J = 30,3-20,2, and SO J = 65-54, and constrain the CO midplane snow line to ~130 au. We find Keplerian rotation around a protostar of 1.6 ± 0.4 M ⊙ using C18O. Through forward ray-tracing using RADMC-3D, we find that the dust scale height is ~6 au at a radius of 100 au from the central star and is comparable to the gas pressure scale height. The results suggest that the dust of this Class I source has yet to vertically settle significantly.

Keywords: protoplanetary disks; circumstellar disks; interstellar medium; protostars; submillimeter astronomy
The Effect of Magnetic Twist and Plasma Flow on the Seismology of Oscillating Flux Tubes

In this paper, we study propagating and standing magnetohydrodynamic kink waves in a magnetically twisted and flowing flux tube. The plasma flow is in the direction of the magnetic field; outside the tube, the magnetic field lines are purely longitudinal. The plasma density is constant both inside and outside the tube, and all stationary quantities vary abruptly at the tube boundary. Using the thin tube and weak twist approximations, the dispersion relation, which determines the dependence of the oscillation frequency on the wavenumber and the stationary quantities of the tube, is found. It is shown that the oscillation frequency of the propagating forward (backward) waves increases (decreases) as the flow speed increases; also, the increase in the magnetic twist increases the oscillation frequency of both forward and backward propagating waves. For very weak magnetic twist, the oscillation frequency of both fundamental mode and first overtone standing waves decreases with increasing flow speed. Our results show that if only the plasma flow or magnetic twist is present in the flux tube, the period ratio P1/P2 of the fundamental mode to the first overtone of the standing kink waves is equal to 2, but if both the plasma flow and magnetic twist are present in the flux tube, the period ratio can be smaller than 2 and support some observational cases. The asymmetry of the wave about the apex point is not affected much by the magnetic twist, but the magnetic twist causes an overestimation of both the flow speed and kink speed of the coronal loop.

Keywords: solar corona; solar coronal seismology; solar coronal heating
Obliquity Constraints on the Planetary-mass Companion HD 106906 b

We constrain the angular momentum architecture of HD 106906, a 13 ± 2 Myr old system in the ScoCen complex composed of a compact central binary, a widely separated planetary-mass tertiary HD 106906 b, and a debris disk nested between the binary and tertiary orbital planes. We measure the orientations of three vectors: the companion spin axis, companion orbit normal, and disk normal. Using near-IR high-resolution spectra from Gemini/IGRINS, we obtain a projected rotational velocity of $v\sin {i}_{p}$ = 9.5 ± 0.2 km s-1 for HD 106906 b. This measurement together with a published photometric rotation period implies the companion is viewed nearly pole-on, with a line-of-sight spin axis inclination of ip = 14° ± 4° or 166° ± 4°. By contrast, the debris disk is known to be viewed nearly edge on. The likely misalignment of all three vectors suggests HD 106906 b formed by gravitational instability in a turbulent environment, either in a disk or cloud setting.

Keywords: exoplanet astronomy; exoplanet formation; exoplanet evolution; exoplanet systems; high resolution spectroscopy; astrostatistics
A Comprehensive Study on the Relation between the Metal Enrichment of Ionized and Atomic Gas in Star-forming Galaxies

We study the relation between the metallicities of ionized and atomic gas in star-forming galaxies at z = 0-3 using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological, hydrodynamical simulations. This is done by constructing a dense grid of sight lines through the simulated galaxies and obtaining the star formation rate- and H I column density-weighted metallicities, Z SFR and Z H I, for each sightline as proxies for the metallicities of ionized and atomic gas, respectively. We find Z SFR ≳ Z H I for almost all sight lines, with their difference generally increasing with decreasing metallicity. The stellar masses of galaxies do not have a significant effect on this trend, but the positions of the sight lines with respect to the galaxy centers play an important role: the difference between the two metallicities decreases when moving toward the galaxy centers, and saturates to a minimum value in the central regions of galaxies, irrespective of redshift and stellar mass. This implies that the mixing of the two gas phases is most efficient in the central regions of galaxies where sight lines generally have high column densities of H I. However, a high H I column density alone does not guarantee a small difference between the two metallicities. In galaxy outskirts, the inefficiency of the mixing of star-forming gas with H I seems to dominate over the dilution of heavy elements in H I through mixing with the pristine gas. We find good agreement between the available observational data and the Z SFR-Z H I relation predicted by the EAGLE simulations. Though, observed regions with a nuclear starburst mode of star formation appear not to follow the same relation.

Keywords: galaxy chemical evolution; metallicity; hydrodynamical simulations; interstellar medium
Solar Wind Interactions with Comet C/2021 A1 Using STEREO HI and a Data-assimilative Solar Wind Model

Cometary tails display dynamic behavior attributed to interactions with solar wind structures. Consequently, comet-tail observations can serve as in situ solar wind monitors. During 2021 December, Comet Leonard (C/2021 A1) was observed by the STEREO-A heliospheric imager. The comet tail exhibited various signatures of interactions with the solar wind including bending, kink formation, and finally complete disconnection. In this study, we compare the timing of these events with solar wind structures predicted by the Heliospheric Upwind eXtrapolation model with a time-dependency (or HUXt) solar wind model using new solar wind data assimilation (DA) techniques. This serves both to provide the most accurate solar wind context to interpret the cometary processes, but also as a test of the DA and an example of how comet observations can be used in model validation studies. Coronal mass ejections, stream interaction regions (SIRs), and heliospheric current sheet (HCS) crossings were all considered as potential causes of the tail disconnection. The results suggest the tail disconnection at Comet Leonard was the result of it crossing the HCS and into an SIR. The timing of these features agree better with the DA model results than the non-DA model, showing the value of this approach. Case studies such as this expand our understanding of comet–solar wind interactions, and in demonstrating the utility of DA for solar wind modeling. We note that this could lead to comets acting as additional in situ measures for solar wind conditions for regions where no in situ spacecraft are available, potentially improving solar wind DA in the future.

Keywords: comets; solar wind; comet tails
Estimation of the NiCu Cycle Strength and Its Impact on Type I X-Ray Bursts

Type I X-ray bursts (XRBs) are powered by thermonuclear burning on proton-rich unstable nuclides. The construction of burst models with accurate knowledge of nuclear physics is required to properly interpret burst observations. Numerous studies that have investigated the sensitivities of burst models to nuclear inputs have commonly extracted the strength of the NiCu cycle in the rp process, determined by the 59Cu(p,α)56Ni and 59Cu(p,γ)60Zn thermonuclear reaction rates, as critical in the determination of reaction flow in the burst. In this study, the strength of the cycle at the XRB temperature range was estimated based on published experimental data. The nuclear properties of the compound nucleus 60Zn were evaluated for the 59Cu(p,α)56Ni and 59Cu(p,γ)60Zn reaction rate calculations. Monte Carlo rate calculations were conducted to include the large uncertainties of nuclear properties in the calculations. In the current work, a weak NiCu cycle is expected, whereas the rates adopted by the previous studies suggest a strong NiCu cycle. Model simulations were performed with the new rates to assess the impact on Type I XRBs. The results show that the estimated cycle strength does not strongly influence the model predictions of the burst light curve or synthesized abundances.

Keywords: nuclear astrophysics; astrophysical processes; nuclear reaction cross sections
Elementary Process of Galactic Spiral Arm Formation: Phase Synchronization of Epicyclic Motion by Gravitational Scattering

Swing amplification is a model of spiral arm formation in disk galaxies. Previous N-body simulations show that the epicycle phases of stars in spiral arms are synchronized. However, the elementary process of the phase synchronization is not well understood. In order to investigate phase synchronization, we investigate the orbital evolution of stars due to gravitational scattering by a perturber under the epicycle approximation and its dependence on orbital elements and a disk parameter. We find that gravitational scattering by the perturber can cause phase synchronization of stellar orbits. The epicycle phases are better synchronized for smaller initial epicycle amplitudes of stars and larger shear rates of galactic disks. The vertical motion of stars does not affect the phase synchronization. The phase synchronization forms trailing dense regions, which may correspond to spiral arms.

Keywords: spiral arms; stellar kinematics; stellar motion
Self-consistent 3D Radiative Transfer for Kilonovae: Directional Spectra from Merger Simulations

We present 3D radiative transfer calculations for the ejecta from a neutron star merger that include line-by-line opacities for tens of millions of bound-bound transitions, composition from an r-process nuclear network, and time-dependent thermalization of decay products from individual α and β - decay reactions. In contrast to expansion opacities and other wavelength-binned treatments, a line-by-line treatment enables us to include fluorescence effects and associate spectral features with the emitting and absorbing lines of individual elements. We find variations in the synthetic observables with both the polar and azimuthal viewing angles. The spectra exhibit blended features with strong interactions by Ce III, Sr II, Y II, and Zr II that vary with time and viewing direction. We demonstrate the importance of wavelength calibration of atomic data using a model with calibrated Sr, Y, and Zr data, and find major differences in the resulting spectra, including a better agreement with AT2017gfo. The synthetic spectra for a near-polar inclination show a feature at around 8000 Å, similar to AT2017gfo. However, they evolve on a more rapid timescale, likely due to the low ejecta mass (0.005 M ☉) as we take into account only the early ejecta. The comparatively featureless spectra for equatorial observers gives a tentative prediction that future observations of edge-on kilonovae will appear substantially different from AT2017gfo. We also show that 1D models obtained by spherically averaging the 3D ejecta lead to dramatically different direction-integrated luminosities and spectra compared to full 3D calculations.

Keywords: neutron stars; nuclear astrophysics; r-process; transient sources; gravitational wave astronomy; radiative transfer simulations
JWST MIRI Imager Observations of Supernova SN 1987A

There exist very few mid-infrared (IR) observations of supernovae (SNe) in general. Therefore, SN 1987A, the closest visible SN in 400 yr, gives us the opportunity to explore the mid-IR properties of SNe, the dust in their ejecta, and the surrounding medium and to witness the birth of an SN remnant (SNR). The James Webb Space Telescope, with its high spatial resolution and extreme sensitivity, gives a new view on these issues. We report on the first imaging observations obtained with the Mid-InfraRed Instrument (MIRI). We build temperature maps and discuss the morphology of the nascent SNR. Our results show that the temperatures in the equatorial ring (ER) are quite nonuniform. This could be due to dust destruction in some parts of the ring, as had been assumed in some previous works. We show that the IR emission extends beyond the ER, illustrating the fact that the shock wave has now passed through this ring to affect the circumstellar medium on a larger scale. Finally, while submillimeter Atacama Large Millimeter Array observations have hinted at the location of the compact remnant of SN 1987A, we note that our MIRI data have found no such evidence.

Keywords: type ii supernovae; core-collapse supernovae; supernova remnants
Two-point Statistics without Bins: A Continuous-function Generalization of the Correlation Function Estimator for Large-scale Structure

The two-point correlation function (2pcf) is the key statistic in structure formation; it measures the clustering of galaxies or other density field tracers. Estimators of the 2pcf, including the standard Landy-Szalay (LS) estimator, evaluate the 2pcf in hard-edged separation bins, which is scientifically inappropriate and results in a poor trade-off between bias and variance. We present a new 2pcf estimator, the Continuous-Function Estimator, which generalizes LS to a continuous representation and obviates binning in separation or any other pair property. Our estimator, inspired by the mathematics of least-squares fitting, replaces binned pair counts with projections onto basis functions; it outputs the best linear combination of basis functions to describe the 2pcf. The choice of basis can take into account the expected form of the 2pcf, as well as its dependence on pair properties other than separation. We show that the Continuous-Function Estimator with a cubic-spline basis better represents the shape of the 2pcf compared to LS. We also estimate directly the baryon acoustic scale, using a small number of physically motivated basis functions. Critically, this leads to a reduction in the number of mock catalogs required for covariance estimation, which is currently the limiting step in many 2pcf analyses. We discuss further applications of the Continuous-Function Estimator, including determination of the dependence of clustering on galaxy properties and searches for potential inhomogeneities or anisotropies in large-scale structure.

Keywords: two-point correlation function; large-scale structure of the universe; cosmology; astrostatistics techniques; baryon acoustic oscillations; redshift surveys; spatial point processes; clustering; cosmological parameters from large-scale structure
Einstein@Home All-sky Search for Continuous Gravitational Waves in LIGO O2 Public Data

We conduct an all-sky search for continuous gravitational waves in the LIGO O2 data from the Hanford and Livingston detectors. We search for nearly monochromatic signals with frequency 20.0 Hz ≤ f ≤ 585.15 Hz and spin-down $-2.6\times {10}^{-9}\,\mathrm{Hz}\,{{\rm{s}}}^{-1}\leqslant \dot{f}\leqslant 2.6\times {10}^{-10}$ Hz s-1. We deploy the search on the Einstein@Home volunteer-computing project and follow-up the waveforms associated with the most significant results with eight further search stages, reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz. Six of the inspected waveforms pass all the stages but they are all associated with hardware injections, which are fake signals simulated at the LIGO detector for validation purposes. We recover all these fake signals with consistent parameters. No other waveform survives, so we find no evidence of a continuous gravitational wave signal at the detectability level of our search. We constrain the h0 amplitude of continuous gravitational waves at the detector as a function of the signal frequency, in half-Hz bins. The most constraining upper limit at 163.0 Hz is h0 = 1.3 × 10-25, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 10-7 closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models.

Keywords: gravitational waves; neutron stars; compact objects; astronomy data analysis
Triggering the Magnetopause Reconnection by Solar Wind Discontinuities

Magnetic reconnection is one of the most universal processes in space plasma that is responsible for charged particle acceleration and the mixing and heating of plasma populations. In this paper we consider a triggering process of reconnection that is driven by interaction of two discontinuities: solar wind rotational discontinuity and tangential discontinuity at Earth's magnetospheric boundary, the magnetopause. Combining multispacecraft measurements and global hybrid simulations, we show that solar wind discontinuities may drive the magnetopause reconnection and cause the mixing of the solar wind and magnetosphere plasmas around the magnetopause, well downstream of the solar wind flow. Since large-amplitude discontinuities are frequently observed in the solar wind and predicted for various stellar winds, our results of reconnection driven by the discontinuity–discontinuity interaction may have a broad application beyond the magnetosphere.

Keywords: solar wind; planetary magnetospheres
Radar and Optical Characterization of Near-Earth Asteroid 2019 OK

We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical observations the apparent diameter is between 70 and 130 m. Combined with an absolute magnitude of H = 23.3 ± 0.3, the optical albedo of 2019 OK is likely between 0.05 and 0.17. Our measured radar circular polarization ratio of μ C = 0.33 ± 0.03 indicates 2019 OK is likely not a V- or E-type asteroid and is most likely a C- or S-type. The measured radar echo bandwidth of 39 ± 2 Hz restricts the apparent rotation period to be approximately between 3 minutes (0.049 hr, D = 70 m) and 5 minutes (0.091 h, D = 130 m). Together, the apparent diameter and rotation period suggest that 2019 OK is likely not a rubble-pile body bound only by gravity. 2019 OK is one of a growing number of fast-rotating near-Earth asteroids that require some internal strength to keep them from breaking apart.

Keywords: small solar system bodies; near-earth objects; apollo group; asteroids; close encounters
Precise Radial Velocities Using Line Bisectors

We study the properties of line bisectors in the spectrum of the Sun-as-a-star, as observed using the Integrated Sunlight Spectrometer (ISS) of the SOLIS project. Our motivation is to determine whether changes in line shape due to magnetic modulation of photospheric convection can be separated from the 9 cm s-1 Doppler reflex of the Earth's orbit. Measuring bisectors of 21 lines over a full solar cycle, our results overwhelmingly indicate that solar magnetic activity modulates photospheric convection so as to reduce the asymmetries of line profiles in the spectrum of the Sun-as-a-star (having both C-shaped and reversed-C-shaped bisectors). However, some lines are constant or have variations in shape that are too small to measure. We inject a 9 cm s-1 radial velocity signal with a 1 yr period into the ISS spectra. Informed by a principal component analysis of the bisectors, we fit the most significant components to the bisectors of each line by linear regression, including a zero-point offset in velocity that is intended to capture the injected radial velocity signal. Averaging over lines, we are able to recover that signal to solid statistical significance in the presence of much larger changes in the line shapes. Although our work has limitations (that we discuss), we establish that changes in absorption line shapes do not in themselves prevent the detection of an Earth-like planet orbiting a Sun-like star using precise radial velocity techniques.

Keywords: sunspot cycle; radial velocity; solar magnetic fields
Stellar Activity Manifesting at a One-year Alias Explains Barnard b as a False Positive

Barnard's star is among the most studied stars given its proximity to the Sun. It is often considered the radial velocity (RV) standard for fully convective stars due to its RV stability and equatorial decl. Recently, an $M\sin i=3.3{M}_{\oplus }$ super-Earth planet candidate with a 233 day orbital period was announced by Ribas et al. New observations from the near-infrared Habitable-zone Planet Finder (HPF) Doppler spectrometer do not show this planetary signal. We ran a suite of experiments on both the original data and a combined original + HPF data set. These experiments include model comparisons, periodogram analyses, and sampling sensitivity, all of which show the signal at the proposed period of 233 days is transitory in nature. The power in the signal is largely contained within 211 RVs that were taken within a 1000 day span of observing. Our preferred model of the system is one that features stellar activity without a planet. We propose that the candidate planetary signal is an alias of the 145 day rotation period. This result highlights the challenge of analyzing long-term, quasi-periodic activity signals over multiyear and multi-instrument observing campaigns.

Keywords: exoplanet astronomy; stellar activity