adsabs/SciX_UAT_keywords huggingface dataset:
Measuring the Hubble Constant of Binary Neutron Star and Neutron Star-Black Hole Coalescences: Bright Sirens and Dark Sirens

Observations of gravitational waves (GW) provide us with a new probe to study the Universe. GW events can be used as standard sirens if their redshifts are measured. Normally, standard sirens can be divided into bright/dark sirens according to whether the redshifts are measured by electromagnetic (EM) counterpart observations. First, we investigate the capability of the 2.5 m Wide-Field Survey Telescope (WFST) to take follow-up observations of kilonova counterparts. For binary neutron star (BNS) bright sirens, WFST is expected to observe 10-20 kilonovae per year in the second-generation GW detection era. As for neutron star-black hole (NSBH) mergers, when a BH spin is extremely high and the neutron star (NS) is stiff, the observation rate is ~10 per year. Combining optical and GW observations, the bright sirens are expected to constrain the Hubble constant H 0 to ~2.8% in five years of observations. As for dark sirens, the tidal effects of NSs during merging provide us with a cosmological model-independent approach to measure the redshifts of GW sources. Then we investigate the applications of tidal effects in redshift measurements. We find in the third generation era, the host galaxy groups of around 45% BNS mergers at z < 0.1 can be identified through this method, if the equation of state is ms1, which is roughly equivalent to the results from luminosity distant constraints. Therefore, tidal effect observations provide a reliable and cosmological model-independent method of identifying BNS mergers' host galaxy groups. Using this method, the BNS/NSBH dark sirens can constrain H 0 to 0.2%/0.3% over a five-year observation period.

Keywords: gravitational waves; cosmology; neutron stars; black holes; high energy astrophysics
Discovery of Line Pressure Broadening and Direct Constraint on Gas Surface Density in a Protoplanetary Disk

The gas surface density profile of protoplanetary disks is one of the most fundamental physical properties to understanding planet formation. However, it is challenging to determine the surface density profile observationally, because the H2 emission cannot be observed in low-temperature regions. We analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) archival data of the 12CO J = 3 - 2 line toward the protoplanetary disk around TW Hya and discovered extremely broad line wings due to the pressure broadening. In conjunction with a previously reported optically thin CO isotopologue line, the pressure broadened line wings enabled us to directly determine the midplane gas density for the first time. The gas surface density at ~5 au from the central star reaches ~103 g cm-2, which suggests that the inner region of the disk has enough mass to form a Jupiter-mass planet. Additionally, the gas surface density drops at the inner cavity by ~2 orders of magnitude compared to outside the cavity. We also found a low CO abundance of ~10-6 with respect to H2, even inside the CO snow line, which suggests conversion of CO to less volatile species. Combining our results with previous studies, the gas surface density jumps at r ~ 20 au, suggesting that the inner region (3 < r < 20 au) might be the magnetorotational instability dead zone. This study sheds light on the direct gas surface density constraint without assuming the CO/H2 ratio using ALMA.

Keywords: protoplanetary disks; astrochemistry
The Global Asteroseismology Project Proof of Concept: Asteroseismology of Massive Stars with Continuous Ground-based Observations

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

Keywords: ground-based astronomy; astronomical methods; astronomical techniques; observational astronomy; massive stars; asteroseismology; stellar interiors
Gas Kinematics of the Massive Protocluster G286.21+0.17 Revealed by ALMA

We study the gas kinematics and dynamics of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array using spectral lines of C18O(2-1), ${{\rm{N}}}_{2}{{\rm{D}}}^{+}$ (3-2), ${\mathrm{DCO}}^{+}$ (3-2), and $\mathrm{DCN}$ (3-2). On the parsec clump scale, C18O emission appears highly filamentary around the systemic velocity, ${{\rm{N}}}_{2}{{\rm{D}}}^{+}$ and ${\mathrm{DCO}}^{+}$ are more closely associated with the dust continuum, and $\mathrm{DCN}$ is strongly concentrated toward the protocluster center, where no or only weak detection is seen for ${{\rm{N}}}_{2}{{\rm{D}}}^{+}$ and ${\mathrm{DCO}}^{+}$ , possibly due to this region being at a relatively evolved evolutionary stage. Spectra of 76 continuum-defined dense cores, typically a few 1000 au in size, are analyzed to measure their centroid velocities and internal velocity dispersions. There are no statistically significant velocity offsets of the cores among the different dense gas tracers. Furthermore, the majority (71%) of the dense cores have subthermal velocity offsets with respect to their surrounding, lower-density C18O-emitting gas. Within the uncertainties, the dense cores in G286 show internal kinematics that are consistent with being in virial equilibrium. On clump scales, the core-to-core velocity dispersion is also similar to that required for virial equilibrium in the protocluster potential. However, the distribution in velocity of the cores is largely composed of two spatially distinct groups, which indicates that the dense molecular gas has not yet relaxed to virial equilibrium, perhaps due to there being recent/continuous infall into the system.

Keywords: interstellar medium; star formation
Atomic Gas Scaling Relations of Star-forming Galaxies at z ≈ 1

We use the Giant Metrewave Radio Telescope Cold-HI AT z ≈ 1 (CATz1) survey, a 510 hr HI 21 cm emission survey of galaxies at z = 0.74-1.45, to report the first measurements of atomic hydrogen (HI) scaling relations at z ≈ 1. We divide our sample of 11,419 blue star-forming galaxies at z ≈ 1 into three stellar-mass (M *) subsamples and obtain detections (at ≥4σ significance) of the stacked HI 21 cm emission signal from galaxies in all three subsamples. We fit a power-law relation to the measurements of the average HI mass (M HI) in the three stellar-mass subsamples to find that the slope of the M HI-M * relation at z ≈ 1 is consistent with that at z ≈ 0. However, we find that the M HI-M * relation has shifted downwards from z ≈ 1 to z ≈ 0, by a factor of 3.54 ± 0.48. Further, we find that the HI depletion timescales (t dep,HI) of galaxies in the three stellar-mass subsamples are systematically lower than those at z ≈ 0, by factors of ≈2-4. We divide the sample galaxies into three specific star formation rate (sSFR) subsamples, again obtaining ≥4σ detections of the stacked HI 21 cm emission signal in all three subsamples. We find that the relation between the ratio of HI mass to stellar mass and the sSFR evolves between z ≈ 1 and z ≈ 0. Unlike the efficiency of conversion of molecular gas to stars, which does not evolve significantly with redshift, we find that the efficiency with which HI is converted to stars is much higher for star-forming galaxies at z ≈ 1 than those at z ≈ 0.

Keywords: high-redshift galaxies; galaxy evolution; neutral hydrogen clouds
Probing the Oxidation State of Ocean Worlds with SUDA: Fe (II) and Fe (III) in Ice Grains

Characterizing the geochemistry of Europa and Enceladus is a key step for astrobiology investigations looking for evidence of life in their subsurface oceans. Transition metals with several oxidation states, such as iron, may be tracers of the oxidation state of icy ocean moon interiors. Their detection, as well as the characterization of their oxidation states, on the moons' (plume) ice grains would bring valuable new information about the geochemistry of both the subsurface oceans and surface processes. Impact ionization mass spectrometers such as the SUDA instrument on board Europa Clipper can analyze ice grains ejected from icy moons' surfaces and detect ocean-derived salts therein. Here we record mass spectra analogs for SUDA using the Laser Induced Liquid Beam Ion Desorption technique for Fe2+ and Fe3+ salts (both sulfates and chlorides). We show that impact ionization mass spectrometers have the capability to detect and differentiate ferrous (Fe2+) from ferric (Fe3+) ions in both cation and anion modes owing to their tendency to form distinct ionic complexes with characteristic spectral features. Peaks bearing Fe3+, such as [Fe3+ (OH)2]+ and [Fe3+ (OH) a Cl b ]‑, are particularly important to discriminate between the two oxidation states of iron in the sample. The recorded analog spectra may allow the characterization of the oxidation state of the oceans of Europa and Enceladus with implications for hydrothermal processes and potential metabolic pathways for life forms in their subsurface oceans.

Keywords: time-of-flight mass spectrometry; europa; enceladus; astrobiology; mass spectrometers
A Tidal Disruption Event Candidate Discovered in the Active Galactic Nucleus SDSS J022700.77-042020.6

We report the discovery of a tidal disruption event (TDE) candidate occurring in the active galactic nucleus (AGN) SDSS J022700.77-042020.6. A sudden increase in flux from J0227-0420 during the second half of 2009 appears in the long-term optical, UV, and near-IR (NIR) light curves. A plateau phase, following an initial decline, is seen in the near-UV (NUV) and optical light curves. We find possible evidence that the plateau in the NUV band may lag behind the optical ones by ∼70-80 days with also a much shorter duration, that is, ∼7-15 days against ∼40-50 days. The long-term NUV/optical (after the plateau phase), NIR, and mid-infrared (MIR) light curves can be well characterized with a form of L(t) ∝ t-β, consistent with the expectation of a TDE. The plateaus can be explained if stellar streams collide with the preexisting disk at different radii. Though the overall fallback rate decreases, the material in the outer disk drifts inward and increases the local accretion rate in the inner region, producing the NUV/optical plateaus. The possible lag is then attributed to viscosity delay. The index β of the NIR J, H, and Ks bands (∼1.4-3.3) is steeper than that of the UV/optical (∼0.7-1.3) and MIR bands (∼0.9-1.8), which may suggest that a certain fraction of the dust in the inner region of the torus may be sublimated during the TDE phase. Our results indicate that, due to collisions between stellar debris and the preexisting disk, the light curves of TDEs occurring in AGNs may show distinctive features, which may shed new light on the accretion process.

Keywords: tidal disruption; active galactic nuclei
Independent Discovery of a Nulling Pulsar with Unusual Subpulse Drifting Properties with the Murchison Widefield Array

We report the independent discovery of PSR J0026-1955 with the Murchison Widefield Array (MWA) in the ongoing Southern-sky MWA Rapid Two-metre pulsar survey. J0026-1955 has a period of ~1.306 s, a dispersion measure of ~20.869 pc cm-3, and a nulling fraction of ~77%. This pulsar highlights the advantages of the survey's long dwell times (~80 minutes), which, when fully searched, will be sensitive to the expected population of similarly bright, intermittent pulsars with long nulls. A single-pulse analysis in the MWA's 140-170 MHz band also reveals a complex subpulse drifting behavior, including both rapid changes of the drift rate characteristic of mode switching pulsars, as well as a slow, consistent evolution of the drift rate within modes. In some longer drift sequences, interruptions in the otherwise smooth drift rate evolution occur preferentially at a particular phase, typically lasting a few pulses. These properties make this pulsar an ideal test bed for prevailing models of drifting behavior such as the carousel model.

Keywords: radio pulsars; high energy astrophysics; time domain astronomy
Detection of Frequency-dependent Dispersion Measure toward the Millisecond Pulsar J2241-5236 from Contemporaneous Wideband Observations

Making precise measurements of pulsar dispersion measures (DMs) and applying suitable corrections for them is among the major challenges in high-precision timing programs such as pulsar timing arrays (PTAs). While the advent of wideband pulsar instrumentation can enable more precise DM measurements and thence improved timing precision, it also necessitates doing careful assessments of frequency-dependent (chromatic) DMs that were theorized by Cordes et al (2016). Here we report the detection of such an effect in broadband observations of the millisecond pulsar PSR J2241-5236, a high-priority target for current and future PTAs. The observations were made contemporaneously using the wideband receivers and capabilities now available at the Murchison Widefield Array, the upgraded Giant Metrewave Radio Telescope, and the Parkes telescopes, thus providing an unprecedentedly large frequency coverage from 80 MHz to 4 GHz. Our analysis shows the measurable changes in DM that scale with the observing frequency (ν) as δDM ∝ ν 2.5±0.1. We discuss the potential implications of such a frequency dependence in the measured DMs and the likely impact on the timing noise budget and comment on the usefulness of low-frequency observations in advancing PTA efforts.

Keywords: millisecond pulsars
Modeling Quasar UV/Optical Variability with the Corona-heated Accretion-disk Reprocessing (CHAR) Model

The rest-frame UV/optical variability of the quasars in the Sloan Digital Sky Survey Stripe 82 is used to test the Corona-Heated Accretion-disk Reprocessing (CHAR) model of Sun et al. We adopt our CHAR model and the observed black hole masses (MBH) and luminosities (L) to generate mock light curves that share the same measurement noise and sampling as the real observations. Without any fine-tuning, our CHAR model can satisfactorily reproduce the observed ensemble structure functions for different MBH, L, and rest-frame wavelengths. Our analyses reveal that a luminosity-dependent bolometric correction is disfavored over the constant bolometric correction for UV/optical luminosities. Our work demonstrates the possibility of extracting quasar properties (e.g., the bolometric correction or the dimensionless viscosity parameter) by comparing the physical CHAR model with quasar light curves.

Keywords: accretion; active galactic nuclei; quasars; supermassive black holes
Stellar Variability and Distance Indicators in the Near-infrared in Nearby Galaxies. I. RR Lyrae and Anomalous Cepheids in Draco Dwarf Spheroidal

The Draco Dwarf spheroidal (dSph) galaxy is one of the nearest and the most dark-matter-dominated satellites of the Milky Way. We obtained multiepoch near-infrared (NIR, JHK s ) observations of the central region of Draco dSph covering a sky area of ∼21' × 21' using the WIRCam instrument at the 3.6 m Canada–France–Hawaii Telescope. Homogeneous JHK s time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and five Anomalous Cepheids in Draco dSph are presented and used to derive their period–luminosity relations at NIR wavelengths for the first-time. The small scatter of ∼0.05 mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to ∼0.2 dex, among these centrally located variables. Based on empirically calibrated NIR period–luminosity–metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of μ RRL = 19.557 ± 0.026 mag. The calibrated K s -band period–luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero points, hinting at possible metallicity dependence of ∼ ‑ 0.3 mag dex‑1. Finally, the apparent magnitudes of the tip of the red-giant branch in I and J bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended ∼1.5% precise RR Lyrae distance, D Draco = 81.55 ± 0.98(statistical) ± 1.17(systematic) kpc, is the most accurate and precise distance to Draco dSph galaxy.

Keywords: dwarf spheroidal galaxies; rr lyrae variable stars; anomalous cepheid variable stars
Solar Wind Driven from GONG Magnetograms in the Last Solar Cycle

In a previous study, Huang et al. used the Alfvén Wave Solar atmosphere Model, one of the widely used solar wind models in the community, driven by ADAPT-GONG magnetograms to simulate the solar wind in the last solar cycle and found that the optimal Poynting flux parameter can be estimated from either the open field area or the average unsigned radial component of the magnetic field in the open field regions. It was also found that the average energy deposition rate (Poynting flux) in the open field regions is approximately constant. In the current study, we expand the previous work by using GONG magnetograms to simulate the solar wind for the same Carrington rotations and determine if the results are similar to the ones obtained with ADAPT-GONG magnetograms. Our results indicate that similar correlations can be obtained from the GONG maps. Moreover, we report that ADAPT-GONG magnetograms can consistently provide better comparisons with 1 au solar wind observations than GONG magnetograms, based on the best simulations selected by the minimum of the average curve distance for the solar wind speed and density.

Keywords: solar wind; magnetohydrodynamics; solar cycle; space weather
The Effect of Angular Scattering Imposed by Charge Exchange and Elastic Collisions on Interstellar Neutral Hydrogen Atoms

Angular scattering (AS) in charge exchange and elastic collisions between interstellar ions and neutral (ISN) atoms has been assumed to be negligible in previous studies. Here, we investigate the momentum transfer associated with the AS of H atoms using Monte Carlo calculations to simulate their transport through the outer heliosheath. We consider two cases where charge exchange and elastic collisions between ISN H atoms and protons occur with and without AS in the outer heliosheath. We show that considering AS decelerates and heats primary ISN H, reducing the effect of selective charge exchange in the outer heliosheath. Secondary ISN H atoms, on the other hand, are not significantly affected by AS. We then simulate the transport of ISN H atoms inside the heliosphere to simulate count rates observed in the lowest energy bin of IBEX-Lo. We study the effect of radiation pressure on the ISN H measurements for the cases with and without AS and compare them with our previous findings. We find an effective radiation parameter (μ eff, which represents force associated with radiation pressure relative to gravity) for the years 2009-2018 based on the longitudinal shift of the ISN H signal. The two cases with and without AS reproduce the longitudinal shift in accordance with variations in solar activity, in agreement with our previous results, and they result in similar values for the μ eff, which is ~22%-23% larger than the value found based on solar Lyα profile observations.

Keywords: heliosphere; heliosheath; solar activity; interstellar medium; interstellar medium wind; solar wind; interstellar atomic gas; space plasmas; collision physics
An Analytical Treatment for Particle Acceleration at Shocks inside Coronal Mass Ejections near 1 au

We present an analytical treatment for time-dependent diffusive shock acceleration at shocks inside magnetic clouds (MCs) observed near 1 au. The model includes the effects of (i) spatial diffusion of test particles upstream and downstream of the shock, (ii) proton advection with the plasma inside MCs, (iii) a reflecting boundary at distance L upstream of the shock to mimic the boundary of the MCs, and (iv) particle leakage out of the system at a constant rate, possibly through open field lines introduced by magnetic reconnection between the closed field lines of the MC and open field lines in the corona or heliosphere. The analysis reveals that the mean time for accelerating particles from p0 to p is naturally reduced if the MC characteristic length is much smaller than the spatial diffusion length of energetic protons upstream of the shock. However, because most shocks inside MCs observed at 1 au are located in the back half of the MC, the time that the shock has propagated into the MCs is not sufficient to cause significant SEP enhancement—even with a reflecting boundary—if particles are only injected from the low-beta plasma inside MCs. To cause large SEP enhancements inside the shock-MC structure, magnetic reconnection at the back MC is essential to allow particles energized by the shock prior to its interaction with the MC to enter the MC. These particles consequently become the seed energetic protons that are reaccelerated at the shock inside MC.

Keywords: solar coronal mass ejections; solar energetic particles; interplanetary shocks; space weather; interplanetary particle acceleration