adsabs/SciX_UAT_keywords huggingface dataset:
On the Impact of Relativistic Gravity on the Rate of Tidal Disruption Events

The tidal disruption of stars by supermassive black holes (SMBHs) probes relativistic gravity. In the coming decade, the number of observed tidal disruption events (TDEs) will grow by several orders of magnitude, allowing statistical inferences of the properties of the SMBH and stellar populations. Here we analyze the probability distribution functions of the pericenter distances of stars that encounter an SMBH in the Schwarzschild geometry, where the results are completely analytic, and the Kerr metric. From this analysis we calculate the number of observable TDEs, defined to be those that come within the tidal radius r t but outside the direct capture radius (which is, in general, larger than the horizon radius). We find that relativistic effects result in a steep decline in the number of stars that have pericenter distances r p ≲ 10 r g, where r g = GM/c 2, and that for maximally spinning SMBHs the distribution function of r p at such distances scales as ${f}_{{{\rm{r}}}_{{\rm{p}}}}\propto {r}_{{\rm{p}}}^{4/3}$ , or in terms of β ≡ r t/r p scales as f β ∝ β -10/3. We find that spin has little effect on the TDE fraction until the very-high-mass end, where instead of being identically zero the rate is small (≲1% of the expected rate in the absence of relativistic effects). Effectively independent of spin, if the progenitors of TDEs reflect the predominantly low-mass stellar population and thus have masses ≲1M ⊙, we expect a substantial reduction in the rate of TDEs above 107 M ⊙.

Keywords: black hole physics; event horizons; general relativity; kerr black holes; relativistic mechanics; tidal disruption
The Per-Tau Shell: A Giant Star-forming Spherical Shell Revealed by 3D Dust Observations

A major question in the field of star formation is how molecular clouds form out of the diffuse interstellar medium (ISM). Recent advances in 3D dust mapping are revolutionizing our view of the structure of the ISM. Using the highest-resolution 3D dust map to date, we explore the structure of a nearby star-forming region, which includes the well-known Perseus and Taurus molecular clouds. We reveal an extended near-spherical shell, 156 pc in diameter (hereafter called the "Per-Tau Shell"), in which the Perseus and Taurus clouds are embedded. We also find a large ring structure at the location of Taurus (hereafter called the "Tau Ring"). We discuss a formation scenario for the Per-Tau Shell, in which previous stellar and supernova feedback events formed a large expanding shell, where the swept-up ISM has condensed to form both the shell and the Perseus and Taurus molecular clouds within it. We present auxiliary observations of H I, Hα, 26Al, and X-rays that further support this scenario, and estimate the Per-Tau Shell's age to be ≈6-22 Myrs. The Per-Tau shell offers the first 3D observational view of a phenomenon long-hypothesized theoretically, molecular cloud formation and star formation triggered by previous stellar and supernova feedback.

Keywords: interstellar medium; molecular clouds; solar neighborhood; stellar feedback; superbubbles; astronomy data visualization
Construction of Explicit Symplectic Integrators in General Relativity. I. Schwarzschild Black Holes

Symplectic integrators that preserve the geometric structure of Hamiltonian flows and do not exhibit secular growth in energy errors are suitable for the long-term integration of N-body Hamiltonian systems in the solar system. However, the construction of explicit symplectic integrators is frequently difficult in general relativity because all variables are inseparable. Moreover, even if two analytically integrable splitting parts exist in a relativistic Hamiltonian, all analytical solutions are not explicit functions of proper time. Naturally, implicit symplectic integrators, such as the midpoint rule, are applicable to this case. In general, these integrators are numerically more expensive to solve than same-order explicit symplectic algorithms. To address this issue, we split the Hamiltonian of Schwarzschild spacetime geometry into four integrable parts with analytical solutions as explicit functions of proper time. In this manner, second- and fourth-order explicit symplectic integrators can be easily made available. The new algorithms are also useful for modeling the chaotic motion of charged particles around a black hole with an external magnetic field. They demonstrate excellent long-term performance in maintaining bounded Hamiltonian errors and saving computational cost when appropriate proper time steps are adopted.

Keywords: black hole physics; computational methods; computational astronomy
Using [Ne V]/[Ne III] to Understand the Nature of Extreme-ionization Galaxies

Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 eV photons: the energy needed to ionize helium into He2+ fully and emit He II recombination lines. Spectroscopic studies of EIGs can probe exotic stellar populations or accretion onto intermediate-mass black holes (~102-105 M ⊙), which are the possibly key contributors to the reionization of the Universe. To facilitate the use of EIGs as probes of high-ionization systems, we focus on ratios constructed from several rest-frame UV/optical emission lines: [O III] λ5008, Hβ, [Ne III] λ3870, [O II] λ λ3727, 3729, and [Ne V] λ3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62, and 97.12 eV, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use the ratios of these lines ([Ne V]/[Ne III] ≡ Ne53, [O III]/Hβ, and [Ne III]/[O II]), which are nearby in wavelength, mitigating the effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed from Cloudy that use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and JWST of galaxies with strong high-ionization emission lines at z ~ 0, z ~ 2, and 5 < z < 8.5. We show that the Ne53 ratio can separate galaxies with ionization from "normal" stellar populations from those with active galactic nuclei and even "exotic" Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.

Keywords: active galaxies; reionization; black holes; intermediate-mass black holes; population iii stars; stellar populations; photoionization; galaxy evolution; interstellar medium; active galactic nuclei; high-redshift galaxies
Using Magnetic Flux Conservation to Determine Heliosheath Speeds

The heliosheath (HSH) radial speeds at Voyager 2 (V2) derived from the plasma instrument (PLS) and from particle instruments using the Compton-Getting (CG) effect are different. At V2 the CG speeds are more variable than the plasma speeds and decrease about 2 yr before the heliopause. We use magnetic flux conservation to differentiate between these two speed profiles at V2, comparing the magnetic flux observed at 1 au and in the HSH. For V2 the PLS speed profile is significantly more consistent with magnetic flux conservation than the CG speeds. For Voyager 1 (V1), we present new VR derivations from the Cosmic Ray Subsystem (CRS) using the CG method that agree reasonably well with those previously obtained from the low energy charged particle (LECP) instrument. If we use the V2 PLS speed profile to calculate the magnetic flux at V1, we again find much better agreement than if we use the V1 CG speeds. These results suggest that the radial speeds derived from particle anisotropy observations in the HSH are not reliable.

Keywords: heliosheath
Delayed Massive-star Mechanical Feedback at Low Metallicity

The classical model of massive-star mechanical feedback is based on effects at solar metallicity (Z ⊙), yet feedback parameters are very different at low metallicity. Metal-poor stellar winds are much weaker, and more massive supernova progenitors likely collapse directly to black holes without exploding. Thus, for ~0.4 Z ⊙ we find reductions in the total integrated mechanical energy and momentum of ~40% and 75%, respectively, compared to values classically expected at solar metallicity. But in particular, these changes effectively delay the onset of mechanical feedback until ages of ~10 Myr. Feedback from high-mass X-ray binaries could slightly increase mechanical luminosity between ages 5 and 10 Myr, but it is stochastic and unlikely to be significant on this timescale. Stellar dynamical mechanisms remove most massive stars from clusters well before 10 Myr, which would further promote this effect; this process is exacerbated by gas retention implied by weak feedback. Delayed mechanical feedback implies that radiation feedback therefore dominates at early ages, which is consistent with the observed absence of superwinds in some extreme starbursts. This scenario may lead to higher star formation efficiencies, multiple stellar populations in clusters, and higher Lyman continuum escape. This could explain the giant star-forming complexes in metal-poor galaxies and the small sizes of OB superbubble shells relative to their inferred ages. It could also drive modest effects on galactic chemical evolution, including on oxygen abundances. Thus, delayed low-metallicity mechanical feedback may have broad implications, including for early cosmic epochs.

Keywords: stellar feedback; starburst galaxies; massive stars; metallicity; dwarf irregular galaxies; lyman-alpha galaxies; interstellar medium wind; young massive clusters; galaxy winds
Gas Column Density Distribution of Molecular Clouds in the Third Quadrant of the Milky Way

We have obtained column density maps for an unbiased sample of 120 molecular clouds in the third quadrant of the Milky Way midplane (b ≤ ∣5∣°) within the Galactic longitude range from 195° to 225°, using the high-sensitivity 12CO and 13CO (J = 1 - 0) data from the Milky Way Imaging Scroll Painting (MWISP) project. The probability density functions of the molecular hydrogen column density of the clouds, N-pdfs, are fitted with both a lognormal (LN) function and a lognormal plus power-law (LN+PL) function. The molecular clouds are classified into three categories according to their shapes of N-pdfs, i.e., LN, LN+PL, and UN (unclear). About 72% of the molecular clouds fall into the LN category, while 18% and 10% fall into the LN+PL and UN categories, respectively. A PL scaling relation, ${\sigma }_{s}\propto {N}_{{{\rm{H}}}_{2}}^{0.44}$ , exists between the width of the N-pdf, σ s , and the average column density, ${N}_{{{\rm{H}}}_{2}}$ , of the molecular clouds. However, σ s shows no correlation with the mass of the clouds. A correlation is found between the dispersion of normalized column density, σ N/<N>, and the sonic Mach number, ${ \mathcal M }$ , of molecular clouds. Overall, as predicted by numerical simulations, the N-pdfs of the molecular clouds with active star formation activity tend to have N-pdfs with PL high-density tails.

Keywords: star formation; interstellar medium; interstellar clouds; surveys; molecular clouds
Wind/Waves Antenna Length Determined Using Quasi-Thermal Noise Spectroscopy

The Wind/Waves instrument has been collecting in situ electric field measurements in the solar wind as well as Earth's magnetosphere and geotail since 1994. The Thermal Noise Receiver (TNR) sub-instrument uses a wire dipole made of very long and thin whip antennas, highly convenient for Quasi-Thermal Noise (QTN) measurements. The instrument team has determined that twice during the mission, in 2000 and 2002, one of the antenna arms broke, changing the antenna response to plasma fluctuations. In this note, we use the QTN spectroscopy method developed specially for the TNR to determine the antenna length after each of these breaks. By parametrically varying the value of the antenna length used in the QTN calculation, we find that initial 50 m long antenna arm was initially shortened to ~25.5 m in 2000, and then to ~20 m in 2002.

Keywords: solar wind
The Dragonfly Galaxy. III. Jet Brightening of a High-redshift Radio Source Caught in a Violent Merger of Disk Galaxies

The Dragonfly galaxy (MRC 0152-209), the most infrared-luminous radio galaxy at redshift z ~ 2, is a merger system containing a powerful radio source and large displacements of gas. We present kiloparsec-resolution data from the Atacama Large Millimeter/submillimeter Array and the Very Large Array of carbon monoxide (6-5), dust, and synchrotron continuum, combined with Keck integral field spectroscopy. We find that the Dragonfly consists of two galaxies with rotating disks that are in the early phase of merging. The radio jet originates from the northern galaxy and brightens when it hits the disk of the southern galaxy. The Dragonfly galaxy therefore likely appears as a powerful radio galaxy because its flux is boosted into the regime of high-z radio galaxies by the jet-disk interaction. We also find a molecular outflow of (1100 ± 550) M ⊙ yr-1 associated with the radio host galaxy, but not with the radio hot spot or southern galaxy, which is the galaxy that hosts the bulk of the star formation. Gravitational effects of the merger drive a slower and longer-lived mass displacement at a rate of (170 ± 40) M ⊙ yr-1, but this tidal debris contains at least as much molecular gas mass as the much faster outflow, namely M H2 = (3 ± 1) × 109 (α CO/0.8) M ⊙. This suggests that both the active-galactic-nucleus-driven outflow and mass transfer due to tidal effects are important in the evolution of the Dragonfly system. The Keck data show Lyα emission spread across 100 kpc, and C IV and He II emission across 35 kpc, confirming the presence of a metal-rich and extended circumgalactic medium previously detected in CO(1-0).

Keywords: galaxy interactions; starburst galaxies; radio loud quasars; submillimeter astronomy; radio astronomy; high-redshift galaxies; radio galaxies; galaxy mergers; radio jets; ultraluminous infrared galaxies; circumgalactic medium
Are the Brightest Coronal Loops Always Rooted in Mixed-polarity Magnetic Flux?

A recent study demonstrated that freedom of convection and strength of magnetic field in the photospheric feet of active-region (AR) coronal loops, together, can engender or quench heating in them. Other studies stress that magnetic flux cancellation at the loop-feet potentially drives heating in loops. We follow 24 hr movies of a bipolar AR, using extreme ultraviolet images from the Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO) and line-of-sight (LOS) magnetograms from the Helioseismic and Magnetic Imager (HMI)/SDO, to examine magnetic polarities at the feet of 23 of the brightest coronal loops. We derived Fe XVIII emission (hot-94) images (using the Warren et al. method) to select the hottest/brightest loops, and confirm their footpoint locations via non-force-free field extrapolations. From 6″ × 6″ boxes centered at each loop foot in LOS magnetograms we find that ∼40% of the loops have both feet in unipolar flux, and ∼60% of the loops have at least one foot in mixed-polarity flux. The loops with both feet unipolar are ∼15% shorter lived on average than the loops having mixed-polarity foot-point flux, but their peak-intensity averages are equal. The presence of mixed-polarity magnetic flux in at least one foot in the majority of the loops suggests that flux cancellation at the footpoints may drive most of the heating. But the absence of mixed-polarity magnetic flux (to the detection limit of HMI) in ∼40% of the loops suggests that flux cancellation may not be necessary to drive heating in coronal loops—magnetoconvection and field strength at both loop feet possibly drive much of the heating, even in the cases where a loop foot presents mixed-polarity magnetic flux.

Keywords: solar coronal loops; solar coronal heating; solar photosphere; solar chromosphere; solar active regions
Asteroid Discovery and Light Curve Extraction Using the Hough Transform: A Rotation Period Study for Subkilometer Main-belt Asteroids

The intranight trajectories of asteroids can be approximated by straight lines, and so are their intranight detections. Therefore, the Hough transform, a line detecting algorithm, can be used to connect the line-up detections to find asteroids. We applied this algorithm to a high-cadence Pan-STARRS 1 (PS1) observation, which was originally designed to collect asteroid light curves for rotation period measurements. The algorithm recovered most of the known asteroids in the observing fields and, moreover, discovered 3574 new asteroids with magnitude mainly of 21.5 < w p1 < 22.5 mag. This magnitude range is equivalent to subkilometer main-belt asteroids (MBAs), which usually lack rotation period measurements due to their faintness. Using the light curves of the 3574 new asteroids, we obtained 122 reliable rotation periods, of which 13 are super-fast rotators (SRFs; i.e., rotation period of <2 hr). The required cohesion to survive these SFRs range from tens to thousands of Pa, a value consistent with the known SFRs and the regolith on the Moon and Mars. The higher chance of discovering SFRs here suggests that subkilometer MBAs probably harbor more SFRs.

Keywords: period determination; surveys; light curves; asteroids; main belt asteroids; astronomical methods
Pulsation and Rotation of the EL CVn-type Eclipsing Binary 1SWASP J024743.37-251549.2

EL CVn-type eclipsing binaries are composed of a massive A-type main-sequence primary star and a hotter B-type secondary star. This paper presents the time-series photometric and asteroseismic results of the EL CVn-type star 1SWASP J024743.37-251549.2. Well-defined eclipsing light curves were constructed by using the novel high-cadence BV data and archival TESS data, and the physical parameters of each binary component were derived by modeling the light curves. Multiple frequency analysis was performed to investigate the pulsation properties of the binary components. A reliable signal could not be detected in the high-frequency region of 100-300 day-1, unlike in the previous discovery of three frequencies around 200 day-1. This indicates that the pulsation amplitudes of the prehelium white dwarf secondary component decreased considerably. By contrast, 12 frequencies were detected in the range of 33-53 day-1. Most of them were classified as δ Sct-type pulsations originating from the primary star. Theoretical frequencies for the seismic analysis were obtained by adding the nonrotating model frequencies from the GYRE and their rotational shifts from the complete calculation approach. Grid-based fitting was conducted for various stellar properties. The theoretical frequencies and stellar parameters of the best solution concurred well with the observations. The rotation rate was constrained to 1.50 ± 0.02 day-1, indicating the synchronized rotation of the primary star. The results imply that the complete approach based on the polytropic model is applicable to the seismic analysis of fast-rotating δ Sct stars.

Keywords: ccd photometry; delta scuti variable stars; eclipsing binary stars; stellar rotation; asteroseismology; multi-periodic pulsation
Effects of Grain Alignment with Magnetic Fields on Grain Growth and the Structure of Dust Aggregates

Dust grains drift through the interstellar medium and are aligned with the magnetic field. Here we study the effect of grain alignment and motion on grain growth in molecular clouds (MCs). We first discuss the characteristic timescales of alignment of the grain axis of maximum inertia ( $\hat{{\boldsymbol{a}}}$ 1) with its angular momentum (J; i.e., internal alignment) and alignment of J with the magnetic field ( B ; i.e., external alignment). We determine the maximum grain size with efficient internal ( ${a}_{\,\max ,{aJ}}$ ) and external ( ${a}_{\,\max ,{JB}}$ ) alignment for composite grains. For the MC density of n H ~ 103-108 cm-3, we find that external alignment can occur for very large grains, but internal alignment only occurs for grains smaller than ${a}_{\,\max ,{aJ}}\sim 2\,\mu {\rm{m}}$ . The presence of iron clusters within dust grains or suprathermal rotation increases ${a}_{\,\max ,{aJ}}$ to ~10-50 μm. We then study the growth of aligned grains drifting through the gas. Due to the motion of aligned grains across the magnetic field, gas accretion would increase the grain elongation rather than decrease, as expected from the growth of randomly oriented grains. Coagulation by grain collisions also increases grain elongation, leading to the increase of elongation with the grain size. The coagulation of aligned grains forms dust aggregates that contain elongated binaries comprising a pair of grains with parallel short axes. Grains within dust aggregates in 67P/Churyumov-Gerasimenko obtained by Rosetta have the grain elongation increasing with the grain radius, implying that such dust aggregates might form from aligned grains.

Keywords: astrophysical dust processes; interstellar dust; interstellar dust processes; interstellar magnetic fields; interplanetary grains; starlight polarization
An Updated Metal-dependent Theoretical Scenario for Classical Cepheids

To properly quantify the possible residual systematic errors affecting the classical Cepheid distance scale, a detailed theoretical scenario is recommended. By extending the set of nonlinear, convective pulsation models published for Z = 0.02 to Z = 0.004, Z = 0.008, and Z = 0.03, we provide a detailed homogeneous, nonlinear model grid taking into account simultaneous variations of the mass-luminosity relation, the efficiency of superadiabatic convection, and the chemical composition. The dependence of the inferred period-radius, period-mass-radius, and period-mass-luminosity-temperature relations on the input parameters is discussed for both the fundamental and first overtone modes. The trend of the instability strip getting redder as the metallicity increases is confirmed for the additional mass-luminosity assumptions and mixing length values. From the obtained multifilter light curves, we derive the mean magnitudes and colors, and in turn the period-luminosity-color and period-Wesenheit relations, for each assumed chemical composition, mass-luminosity relation, and efficiency of superadiabatic convection. Application to a well-studied sample of Cepheids in the Large Magellanic Cloud allows us to constrain the dependence of the inferred distance modulus on the assumed mass-luminosity relation, and the inclusion of the metallicity term in the derivation of the period-Wesenheit relations allows us, for each assumed mass-luminosity relation, to predict the metallicity dependence of the Cepheid distance scale. The obtained metal-dependent, period-Wesenheit relations are compared with recent results in the literature and applied to a sample of Gaia Early Data Release 3 Galactic Cepheids with known metal abundances to derive individual parallaxes. The comparison of these predictions with Gaia results is finally discussed.

Keywords: cepheid variable stars; pulsating variable stars; cepheid distance; distance indicators