adsabs/SciX_UAT_keywords huggingface dataset:
Study on the Energy Limits of kHz QPOs in Sco X-1 with RXTE and Insight-HXMT Observations

We present a detailed spectral-timing analysis of the Kilohertz quasiperiodic oscillations (kHz QPOs) in Sco X-1 using the data of the Rossi X-ray Timing Explorer (RXTE) and the Hard X-ray Modulation Telescope (Insight-HXMT). The energy band with detectable kHz QPOs is studied for the first time: on the horizontal branch, it is ∼6.89-24.01 and ∼8.68-21.78 keV for the upper and lower kHz QPOs, respectively, detected by the RXTE, and ∼9-27.5 keV for the upper kHz QPOs by the Insight-HXMT; on the lower normal branch, the energy band is narrower. The fractional root mean square (rms) of the kHz QPOs increases with energy at a lower energy, reaches a plateau at about 16 and 20 keV for the lower and upper peaks, and then levels off though with a large uncertainty. The simulation of the deadtime effect of RXTE/PCA shows that the deadtime does not affect much the search of the kHz QPOs but makes the rms amplitude underestimated. No significant QPO is detected below ∼6 keV as shown by the RXTE data, implying that the kHz QPOs do not originate from the blackbody emission of the accretion disk and neutron star surface. In addition, with the combined analysis of the energy spectra and the absolute rms spectra of kHz QPOs, we suggest that the kHz QPOs in Sco X-1 originate from the Comptonization of the inner part of the transition layer, where the rotation sets the frequency and the inward bulk motion makes the spectrum harder.

Keywords: x-ray binary stars
Light Curve of HT Cassiopeiae

Photometric observations of the eclipsing dwarf nova HT Cas are presented in its quiescent state on 2022 October 20th for one complete orbital period. These data were taken with the RISE imager mounted on the Liverpool Telescope. The lcurve code was used to fit the light curve. System parameters were derived of mass ratio q = M 2/M 1 = 0.15 ± 0.01, angle of inclination i = 80.°98 ± 0.°18 and white dwarf radius of R 1 = 0.0128 ± 0.0003R ⊙. This gives solutions for the masses of the white dwarf and donor star of M 1 = 0.571 ± 0.017M ⊙ and M 2 = 0.088 ± 0.005M ⊙. The disk radius and bright spot radius with the best fit from the model were R disk = 0.51 ± 0.04a and R spot = 0.32 ± 0.02a. These are consistent with previous published observations.

Keywords: cataclysmic variable stars; binary stars; eclipsing binary stars; light curves
Experimental Phase Function and Degree of Linear Polarization of Light Scattered by Hydrogenated Amorphous Carbon Circumstellar Dust Analogs

Astronomical observations of the polarized intensity of scattered visible light have revealed the presence of dust envelopes around different types of evolved stars. These observations have helped determine the diameter and width of dust shells around stars with unprecedented accuracy. Simple geometric particle models are used in order to retrieve dust properties from these observations. In this work, we have synthesized and characterized a particulate sample of hydrogenated amorphous carbon (HAC), which is considered to be a realistic carbonaceous interstellar dust analog based on infrared absorption spectroscopy, and we have measured its phase function and degree of linear polarization curves at 514 nm using the CODULAB apparatus at IAA-CSIC. The experimental light-scattering data has been examined in order to explore possible improvements in the interpretation of astronomical observations of circumstellar dust from the point of view of the retrieval of dust properties, including size and porosity. Our results suggest that circumstellar dust observations of linearly polarized scattered light, which are commonly attributed to a population of spherical grains with a radius of ∼0.1 μm, are consistent with larger porous aggregates composed of nanometer-sized grains. In addition, an internal 50wt% mixture of HAC and ultrafine forsterite powder has been generated to study the effect of the mixing of these two components on the light-scattering behavior of dust in cometary environments and protoplanetary disks. In this case, the HAC component, which is not very absorbent, has a very small effect, and the mixture scatters light similarly to the forsterite sample.

Keywords: laboratory astrophysics; experimental data; dust physics; astrophysical dust processes; interstellar dust; interstellar scattering; circumstellar dust; optical constants (dust); dust shells
Jumping the Gap: Searching for LIGO's Biggest Black Holes

Gravitational wave (GW) detections of binary black holes (BBHs) have shown evidence for a dearth of component black holes with masses above ∼50M⊙. This is consistent with expectations of a mass gap due to the existence of pair-instability supernovae (PISN). We argue that ground-based GW detectors will be sensitive to BBHs with masses above this gap, ≳120 M⊙. With no detections, 2 yr at upgraded sensitivity (A+) would constrain the local merger rate of these BBHs on the "far side" of the PISN gap to be lower than 0.01 yr-1Gpc-3. Alternatively, with a few tens of events we could constrain the location of the upper edge of the gap to the percent level. We consider the potential impact of "interloper" black holes within the PISN mass gap on this measurement. Far side BBHs would also be observed by future instruments such as Cosmic Explorer (CE), Einstein Telescope (ET) and LISA, and may dominate the fraction of multiband events. We show that by comparing observations from ground and space it is possible to constrain the merger rate history. Moreover, we find that the upper edge of the PISN mass gap leaves an imprint on the spectral shape of the stochastic background of unresolved binaries, which may be accessible with A+ sensitivity. Finally, we show that by exploiting the upper edge of the gap, these high-mass BBHs can be used as standard sirens to constrain the cosmic expansion at redshifts of ∼0.4, 0.8, and 1.5 with LISA, LIGO-Virgo, and CE/ET, respectively. These far-side binaries would be the most massive BBHs LIGO-Virgo could detect.

Keywords: gravitational waves; astrophysical black holes
Stellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU Microscopii

Energetic particles emitted by active stars are likely to propagate in astrospheric magnetized plasma and disrupted by the prior passage of energetic coronal mass ejections (CMEs). We carried out test-particle simulations of ~GeV protons produced at a variety of distances from the M1Ve star AU Microscopii by coronal flares or traveling shocks. Particles are propagated within a large-scale quiescent three-dimensional magnetic field and stellar wind reconstructed from measured magnetograms, and within the same stellar environment following the passage of a 1036 erg kinetic energy CME. In both cases, magnetic fluctuations with an isotropic power spectrum are overlayed onto the large-scale stellar magnetic field and particle propagation out to the two innnermost confirmed planets is examined. In the quiescent case, the magnetic field concentrates the particles into two regions near the ecliptic plane. After the passage of the CME, the closed field lines remain inflated and the reshuffled magnetic field remains highly compressed, shrinking the scattering mean free path of the particles. In the direction of propagation of the CME lobes the subsequent energetic particle (EP) flux is suppressed. Even for a CME front propagating out of the ecliptic plane, the EP flux along the planetary orbits highly fluctuates and peaks at ~2-3 orders of magnitude higher than the average solar value at Earth, both in the quiescent and the post-CME cases.

Keywords: exoplanets
The ALMaQUEST Survey. VIII. What Causes the Discrepancy in the Velocity between the CO and Hα Rotation Curves in Galaxies?

We compare the CO(1-0) and Hα kinematics in 34 nearby galaxies, selected from the ALMaQUEST and EDGE-CALIFA surveys. We use 3D-Barolo, a 3D tilted-ring model, to derive the CO and Hα rotation curves. Before comparing rotation curves in the 34 nearby galaxies, we found systematics between the MaNGA and CALIFA data using eight MaNGA-CALIFA overlapping galaxies. We assume the rotation curves based on the MaNGA data are accurate and made the corresponding correction to the CALIFA data. Our result shows that ~56% (19/34) of our galaxies present slower Hα rotation curves compared to the CO rotation curves, with a median value of 6.5 km s-1. The remaining galaxies (15/34) show consistent CO-Hα rotation velocity within uncertainties. As a result, the Hα rotation may underestimate the total dynamical mass by 6% for a circular velocity of 200 km s-1 (the median value in our sample). Furthermore, the difference in the velocity between the CO and Hα rotational velocity is found to correlate with the difference in velocity dispersion between CO and Hα, suggesting that gas pressure plays a role in the discrepancy in velocity. After incorporating the effect of pressure support due to the turbulent gas motion into our sample, the median value of the difference in the velocities decreases to 1.9 km s-1, which in turn reduces the underestimation of the dynamical mass to ~2%. Finally, we also investigate the role that the extraplanar diffuse ionized gas plays in the discrepancy in the velocity of CO-Hα.

Keywords: galaxy kinematics; galaxy rotation; interstellar medium; galaxy dynamics; molecular gas; optical astronomy; radio astronomy
Can Small-scale Magnetic Fields Be the Major Cause for the Near-surface Effect of the Solar p-mode Frequencies?

Small-scale magnetic fields are not only the fundamental element of the solar magnetism but also closely related to the structure of the solar atmosphere. The observations have shown that there is a ubiquitous tangled small-scale magnetic field with a strength of 60-130 G in the canopy-forming layer of the quiet solar photosphere. On the other hand, the multidimensional MHD simulations show that the convective overshooting expels the magnetic field to form the magnetic canopies at a height of about 500 km in the upper photosphere. However, the distribution of such small-scale "canopies" in the solar photosphere cannot be rigorously constrained by either observations or numerical simulations. Based on stellar standard models, we identify that these magnetic canopies can act as a global magnetic arch splicing layer, and we find that the reflections of the solar p-mode oscillations at this magnetic arch splicing layer result in significant improvement on the discrepancy between the observed and calculated p-mode frequencies. The location of the magnetic arch splicing layer is determined at a height of about 630 km, and the inferred strength of the magnetic field is about 90 G. These features of the magnetic arch splicing layer derived independently in the present study are quantitatively in agreement with the presence of small-scale magnetic canopies such as those obtained by the observations and 3D MHD simulations.

Keywords: solar magnetic fields; solar convective zone; solar atmosphere; solar oscillations
Second Harmonic Electromagnetic Emissions by an Electron Beam in Solar Wind Plasmas with Density Fluctuations

Two-dimensional particle-in-cell simulations are performed to study the electromagnetic radiation emitted at the second harmonic 2ωp of the plasma frequency by a weak electron beam propagating in a background plasma with random density fluctuations, in solar wind conditions relevant to Type III solar radio bursts. The dynamics of the waves, the beam, and the plasma are calculated over several thousands of plasma periods. For relevant comparisons, simulations with and without applied density fluctuations are performed for the same parameters. This Letter evidences for the first time the impact of density fluctuations on the physical mechanisms driving the generation of electromagnetic waves emitted at 2ωp. Results obtained show that (i) the beam radiates electromagnetic waves at 2ωp as a result of nonlinear processes of Langmuir waves' coalescence, despite wave scattering on the density fluctuations that strongly affect the Langmuir spectra; (ii) the fraction of initial beam energy transferred asymptotically to the electromagnetic waves at 2ωp is by one order of magnitude smaller when the plasma involves density fluctuations of average level around 5%; (iii) compared to the homogeneous case, the ratio of electromagnetic energy radiated at 2ωp to the energy carried by the Langmuir wave turbulence is significantly larger during all the nonlinear stage; (iv) asymptotically, when the plasma is inhomogeneous, electromagnetic emissions at 2ωp present isotropized spectra whereas quadrupolar radiation occurs for the homogeneous plasma case.

Keywords: solar radio emission; solar radio flares; space plasmas; plasma physics
A Global Semianalytic Model of the First Stars and Galaxies Including Dark Matter Halo Merger Histories

We present a new self-consistent semianalytic model of the first stars and galaxies to explore the high-redshift (z ≥ 15) Population III (PopIII) and metal-enriched star formation histories. Our model includes the detailed merger history of dark matter halos generated with Monte Carlo merger trees. We calibrate the minimum halo mass for PopIII star formation from recent hydrodynamical cosmological simulations that simultaneously include the baryon–dark matter streaming velocity, Lyman–Werner (LW) feedback, and molecular hydrogen self-shielding. We find an overall increase in the resulting star formation rate density (SFRD) compared to calibrations based on previous simulations (e.g., the PopIII SFRD is over an order of magnitude higher at z = 35‑15). We evaluate the effect of the halo-to-halo scatter in this critical mass and find that it increases the PopIII stellar mass density by a factor ∼1.5 at z ≥ 15. Additionally, we assess the impact of various semianalytic/analytic prescriptions for halo assembly and star formation previously adopted in the literature. For example, we find that models assuming smooth halo growth computed via abundance matching predict SFRDs similar to the merger tree model for our fiducial model parameters, but that they may underestimate the PopIII SFRD in cases of strong LW feedback. Finally, we simulate subvolumes of the Universe with our model both to quantify the reduction in total star formation in numerical simulations due to a lack of density fluctuations on spatial scales larger than the simulation box, and to determine spatial fluctuations in SFRD due to the diversity in halo abundances and merger histories.

Keywords: cosmology; population iii stars; galaxy formation
X-Ray Polarimetry of the Accreting Pulsar 1A 0535+262 in the Supercritical State with PolarLight

The X-ray pulsar 1A 0535+262 exhibited a giant outburst in 2020, offering us a unique opportunity for X-ray polarimetry of an accreting pulsar in the supercritical state. Measurement with PolarLight yielded a nondetection in 3-8 keV; the 99% upper limit of the polarization fraction (PF) is found to be 0.34 averaged over spin phases, or 0.51 based on the rotating vector model. No useful constraint can be placed with phase-resolved polarimetry. These upper limits are lower than a previous theoretical prediction of 0.6-0.8, but consistent with those found in other accreting pulsars, like Her X-1, Cen X-3, 4U 1626-67, and GRO J1008-57, which were in the subcritical state, or at least not confidently in the supercritical state, during the polarization measurements. Our results suggest that the relatively low PF seen in accreting pulsars cannot be attributed to the source not being in the supercritical state, but could be a general feature.

Keywords: pulsars; polarimetry; x-ray sources
Astrometric Calibration of the Beijing-Arizona Sky Survey

We present the astrometric calibration of the Beijing-Arizona Sky Survey (BASS). The BASS astrometry was tied to the International Celestial Reference Frame via the Gaia Data Release 2 reference catalog. For effects that were stable throughout the BASS observations, including differential chromatic refraction and the low charge transfer efficiency of the CCD, we corrected for these effects at the raw image coordinates. Fourth-order polynomial intermediate longitudinal and latitudinal corrections were used to remove optical distortions. The comparison with the Gaia catalog shows that the systematic errors, depending on color or magnitude, are less than 2 milliarcseconds (mas). The position systematic error is estimated to be about -0.01 ± 0.7 mas in the region between 30° and 60° of decl. and up to -0.07 ± 0.9 mas in the region north of decl. 60°.

Keywords: photographic astrometry
Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs

Do white dwarfs have inner cores made of iron? Neutron-rich nuclei like 56Fe experience a net gravitational force and sediment toward the core. Using new phase diagrams and molecular dynamics simulations, we show that 56Fe should separate into mesoscopic Fe-rich crystallites due to its large charge relative to the background. At solar abundances, these crystallites rapidly precipitate and form an inner core of order 100 km and 10-3M⊙ that may be detectable with asteroseismology. Associated cooling delays could be up to a Gyr for low-mass white dwarfs but are only ~0.1 Gyr for massive white dwarfs, so while this mechanism may contribute to the Q-branch the heating is insufficient to fully explain it.

Keywords: degenerate matter; stellar interiors; n-body simulations; white dwarf stars
Observations of a Failed Solar Filament Eruption Involving External Reconnection

We report a failed solar filament eruption that involves external magnetic reconnection in a quadrupolar magnetic configuration. The evolution exhibits three phases of kinematic evolution: a slow rise, an acceleration, and a deceleration. In the early slow rise, extreme-ultraviolet brightenings appear at the expected null point above the filament and are connected to the outer polarities by the hot loops, indicating the occurrence of a breakout reconnection. Subsequently, the filament is accelerated outward, accompanied by the formation of low-lying high-temperature post-flare loops (>15 MK), complying with the standard flare model. However, after 2-3 minutes, the erupting filament starts to decelerate and is finally confined in the corona. The important finding is that the confinement is closely related to an external reconnection as evidenced by the formation of high-lying large-scale hot loops (>10 MK) with their brightened footpoints at the outer polarities, the fragmentation and subsequent falling of the filament along the newly formed large-scale loops, as well as a hard X-ray source close to one of the outer footpoint brightenings. We propose that, even though the initial breakout reconnection and subsequent flare reconnection commence and accelerate the filament eruption, the following external reconnection between the erupting flux rope and overlying field, as driven by the upward filament eruption, causes the eruption to finally fail, as validated by the numerical simulation of a failed flux rope eruption.

Keywords: solar filament eruptions; solar flares; solar magnetic reconnection
Comparing Apples with Apples: Robust Detection Limits for Exoplanet High-contrast Imaging in the Presence of Non-Gaussian Noise

Over the past decade, hundreds of nights have been spent on the world's largest telescopes to search for and directly detect new exoplanets using high-contrast imaging (HCI). Thereby, two scientific goals are of central interest: first, to study the characteristics of the underlying planet population and distinguish between different planet formation and evolution theories. Second, to find and characterize planets in our immediate solar neighborhood. Both goals heavily rely on the metric used to quantify planet detections and nondetections. Current standards often rely on several explicit or implicit assumptions about noise. For example, it is often assumed that the residual noise after data postprocessing is Gaussian. While being an inseparable part of the metric, these assumptions are rarely verified. This is problematic as any violation of these assumptions can lead to systematic biases. This makes it hard, if not impossible, to compare results across data sets or instruments with different noise characteristics. We revisit the fundamental question of how to quantify detection limits in HCI. We focus our analysis on the error budget resulting from violated assumptions. To this end, we propose a new metric based on bootstrapping that generalizes current standards to non-Gaussian noise. We apply our method to archival HCI data from the NACO instrument at the Very Large Telescope and derive detection limits for different types of noise. Our analysis shows that current standards tend to give detection limits that are about one magnitude too optimistic in the speckle-dominated regime. That is, HCI surveys may have excluded planets that can still exist.

Keywords: astrostatistics; bootstrap; direct imaging; high angular resolution
Polarized X-Rays from Windy Accretion in Cygnus X-1

Recent X-ray polarimetric data on the prototypical black hole X-ray binary Cyg X-1 from the Imaging X-ray Polarimetry Explorer present tight constraints on accretion geometry in the hard spectral state. Contrary to general expectations of a low, ≲1% polarization degree (PD), the observed average PD was found to be a factor of 4 higher. Aligned with the jet position angle on the sky, the observed polarization favors geometry of the X-ray emission region stretched normally to the jet in the accretion disk plane. The high PD is, however, difficult to reconcile with the low orbital inclination of the binary i ≈ 30°. We suggest that this puzzle can be explained if the emitting plasma is outflowing with a mildly relativistic velocity ≳0.4 c. Our radiative transfer simulations show that Comptonization in the outflowing medium elongated in the plane of the disk and radiates X-rays with the degree and direction of polarization consistent with observations at i ≈ 30°.

Keywords: stellar mass black holes; starlight polarization; accretion; polarimetry; x-ray binary stars
Tracking the Ice Mantle History in the Solar-type Protostars of NGC 1333 IRAS 4

To understand the origin of the diversity observed in exoplanetary systems, it is crucial to characterize the early stages of their formation, represented by solar-type protostars. Likely, the gaseous chemical content of these objects directly depends on the composition of the dust-grain mantles formed before the collapse. Directly retrieving the ice mantle composition is challenging, but it can be done indirectly by observing the major components, such as NH3 and CH3OH at centimeter wavelengths, once they are released into the gas phase during the warm protostellar stage. We observed several CH3OH and NH3 lines toward three Class 0 protostars in NGC 1333 (IRAS 4A1, IRAS 4A2, and IRAS 4B), at high angular resolution (1″; ~300 au) with the VLA interferometer at 24-26 GHz. Using a non-LTE LVG analysis, we derived a similar NH3/CH3OH abundance ratio in the three protostars (≤0.5, 0.015-0.5, and 0.003-0.3 for IRAS 4A1, 4A2, and 4B, respectively). Hence, we infer they were born from precollapse material with similar physical conditions. Comparing the observed abundance ratios with astrochemical model predictions, we constrained the dust temperature at the time of the mantle formation to be ~17 K, which coincides with the average temperature of the southern NGC 1333 diffuse cloud. We suggest that a brutal event started the collapse that eventually formed IRAS 4A1, 4A2, and 4B, which, therefore, did not experience the usual prestellar core phase. This event could be the clash of a bubble with NGC 1333 South, which has previously been evoked in the literature.

Keywords: interstellar medium; protostars; young stellar objects; astrochemistry; star formation; observational astronomy; chemical abundances; interstellar molecules