adsabs/SciX_UAT_keywords huggingface dataset:
Fast Parameter Estimation of Binary Mergers for Multimessenger Follow-up

Significant human and observational resources have been dedicated to electromagnetic follow-up of gravitational-wave events detected by Advanced LIGO and Virgo. As the sensitivity of LIGO and Virgo improves, the rate of sources detected will increase. Margalit & Metzger (2019) have suggested that it may be necessary to prioritize observations of future events. Optimal prioritization requires a rapid measurement of a gravitational-wave event's masses and spins, as these can determine the nature of any electromagnetic emission. We extend the relative binning method of Cornish (2013) and Zackay et al. (2018) to a coherent detector-network statistic. We show that the method can be seeded from the output of a matched-filter search and used in a Bayesian parameter measurement framework to produce marginalized posterior probability densities for the source's parameters within 20 minutes of detection on 32 CPU cores. We demonstrate that this algorithm produces unbiased estimates of the parameters with the same accuracy as running parameter estimation using the standard gravitational-wave likelihood. We encourage the adoption of this method in future LIGO-Virgo observing runs to allow fast dissemination of the parameters of detected events so that the observing community can make best use of its resources.

Keywords: gravitational waves; gravitational wave astronomy; astronomical methods; close binary stars; compact binary stars; neutron stars; astronomy data analysis
The Renovated Thacher Observatory and First Science Results

Located on the campus of the Thacher School in Southern California, the Thacher Observatory has a legacy of astronomy research and education that dates back to the late 1950s. In 2016, the observatory was fully renovated with upgrades including a new 0.7 m telescope, a research grade camera, and a slit dome with full automation capabilities. The low-elevation site is bordered by the Los Padres National Forest and therefore affords dark to very dark skies allowing for accurate and precise photometric observations. We present a characterization of the site including sky brightness, weather, and seeing, and we demonstrate the on-sky performance of the facility. Our primary research programs are based around our multi-band photometric capabilities and include photometric monitoring of variable sources, a nearby supernova search and followup program, a quick response transient followup effort, and exoplanet and eclipsing binary light curves. Select results from these programs are included in this work which highlight the broad range of science available to an automated observatory with a moderately sized telescope.

Keywords: astronomical instrumentation; type ia supernovae; exoplanets
Characterizing the 3D Kinematics of Young Stars in the Radcliffe Wave

We present an analysis of the kinematics of the Radcliffe Wave, a 2.7 kpc long sinusoidal band of molecular clouds in the solar neighborhood recently detected via 3D dust mapping. With Gaia DR2 astrometry and spectroscopy, we analyze the 3D space velocities of ~1500 young stars along the Radcliffe Wave in action-angle space, using the motion of the wave's newly born stars as a proxy for its gas motion. We find that the vertical angle of young stars-corresponding to their orbital phase perpendicular to the Galactic plane-varies significantly as a function of position along the structure, in a pattern potentially consistent with a wavelike oscillation. This kind of oscillation is not seen in a control sample of older stars from Gaia occupying the same volume, disfavoring formation channels caused by long-lived physical processes. We use a "wavy midplane" model to try to account for the trend in vertical angles seen in young stars, and find that while the best-fit parameters for the wave's spatial period and amplitude are qualitatively consistent with the existing morphology defined by 3D dust, there is no evidence for additional velocity structure. These results support more recent and/or transitory processes in the formation of the Radcliffe Wave, which would primarily affect the motion of the wave's gaseous material. Comparisons of our results with new and upcoming simulations, in conjunction with new stellar radial velocity measurements in Gaia DR3, should allow us to further discriminate between various competing hypotheses.

Keywords: stellar kinematics; pre-main sequence stars; galaxy structure; spiral arms; molecular clouds
Correlations between Total and Spectral Solar Irradiance Variations

We compare short-term (seven solar rotations), wavelength-dependent temporal variations in spectral solar irradiance (SSI) with those from the total solar irradiance (TSI). Using space-based measurements, we empirically find good correlations across most of the visible and near-infrared (NIR) spectral range, suggesting that the TSI time variability can provide a useful estimate of SSI variability. These empirically determined correlations are consistent with physics-based bolometric variations, providing a straightforward wavelength-dependent parameterization of the SSI variability given a known change in the TSI. Using a solar-irradiance model to distinguish the facular and sunspot contributions, which are responsible for nearly all the irradiance variability on timescales longer than a day, we confirm these results and determine the correlation contributions due to each magnetic activity type individually. The correlations determined from the model agree in functional form to those of the empirical data, although we do note differences near opacity minimum (1.6 μm). Our results provide a simple TSI-based estimate of the time dependence of the spectral solar variability across the ultraviolet to NIR spectral regions, with the TSI accounting for 94% of the variability in the SSI over the 400–1200 nm range.

Keywords: solar spectral irradiance; solar physics; stellar activity; solar active regions
A Broadband X-Ray Study of the Dwarf Nova SS Cyg during Quiescence and Outburst

We present a broadband X-ray study (~0.3-50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations carried out with the XMM-Newton and NuSTAR telescopes in two epochs, involving medium- and high-resolution spectroscopy. Spectra were harder during quiescence (kT high ~ 22.8 keV) than the outburst (kT high ~ 8.4 keV), while the mass accretion rate increased by ~35 times in the outburst (1.7 × 1016 g s-1) as compared to quiescence. The bolometric luminosity (0.01-100.0 keV) during the outburst was dominated by a blackbody emission (kT BB ~ 28 eV) from the optically thick boundary layer (BL), and the inner edge of the accretion disk resides very close to the white-dwarf (WD) surface. X-rays from the BL are consistent with the WD having mass ${1.18}_{-0.01}^{+0.02}\,{M}_{\odot }$ . Our study conclusively confirms the presence of the reflection hump in the 10-30 keV range for both phases, which arises when X-ray photons hit colder material and undergo Compton scattering. We estimated a similarly strong reflection amplitude during quiescence (~1.25) and the outburst (~1.31), indicating both the WD surface and disk are contributing to reflection. The neutral Fe K α line, which is correlated with Compton reflection, also showed similar strength (~80 eV) in both phases. Finally, X-rays also revealed the presence of a partial intrinsic absorber during the outburst, possibly due to an outflowing accretion disk wind.

Keywords: dwarf novae; cataclysmic variable stars; x-ray binary stars
Improved Measurements of the Sun's Meridional Flow and Torsional Oscillation from Correlation Tracking on MDI and HMI Magnetograms

The Sun's axisymmetric flows, differential rotation, and meridional flow govern the dynamics of the solar magnetic cycle, and a variety of methods are used to measure these flows, each with its own strengths and weaknesses. Flow measurements based on cross-correlating images of the surface magnetic field have been made since the 1970s that require advanced numerical techniques that are capable of detecting movements of less than the pixel size in images of the Sun. We have identified several systematic errors in addition to the center-to-limb effect that influence previous measurements of these flows and propose numerical techniques that can minimize these errors by utilizing measurements of displacements at several time lags. Our analysis of line-of-sight magnetograms from the Michelson Doppler Imager on the ESA/NASA Solar and Heliospheric Observatory and the Helioseismic and Magnetic Imager on the NASA Solar Dynamics Observatory shows long-term variations in the meridional flow and differential rotation over two sunspot cycles from 1996 to 2020. These improved measurements can serve as vital inputs for solar dynamo and surface flux transport simulations.

Keywords: solar meridional circulation; solar photosphere; solar cycle; solar differential rotation; center to limb observations; solar surface; solar physics; solar magnetic fields
On the Paradoxical Impact of Blending by Red Clump Giants

The impact of blending by red clump giants (RCGs; or relatively metal-rich red horizontal branch stars) is discussed as it relates to RRab and classical Cepheids, and invariably establishing an improved distance scale. An analysis of Magellanic Cloud variables reaffirms that blending with RCGs may advantageously thrust remote extragalactic stars into the range of detectability. Specifically, simulations of Magellanic Cloud RRab and RCG blends partly reproduce bright non-canonical trends readily observed in amplitude-magnitude space (Ic versus ${A}_{{I}_{c}}$ ). Conversely, the larger magnitude offset between classical Cepheids and RCGs causes the latter's influence to be challenging to address. The relative invariance of a Wesenheit function's slope to metallicity (e.g., ${W}_{{{VI}}_{c}}$ ) implies that a deviation from the trend could reveal blending and photometric inaccuracies (e.g., standardization), as blending by RCGs (a proxy of an evolved red stellar demographic) can flatten period-Wesenehit relations owing to the increased impact on less-luminous shorter-period Cepheids. That could partly explain both a shallower inferred Wesenheit function and overestimated H0 values. A consensus framework to identify and exploit blending is desirable, as presently H0 estimates from diverse teams are unwittingly leveraged without homogenizing the disparate approaches (e.g., no blending correction to a sizable $\simeq 0\buildrel{\rm{m}}\over{.} 3$ ).

Keywords: rr lyrae variable stars; stellar distance; hubble constant; galaxy distances; red giant clump; photometry; cepheid variable stars
Very High-energy (>50 GeV) Gamma-Ray Flux Variability of Bright Fermi Blazars

Understanding the high-energy emission processes and variability patterns are two of the most challenging research problems associated with relativistic jets. In particular, the long-term (months to years) flux variability at very high energies (VHE >50 GeV) has remained an unexplored domain so far. This is possibly due to the decreased sensitivity of the Fermi Large Area Telescope (LAT) above a few GeV, hence low photon statistics, and observing constraints associated with the ground-based Cherenkov telescopes. This paper reports the results obtained from the 0.05‑2 TeV Fermi-LAT data analysis of a sample of 29 blazars with the primary objective to explore their months-to-year-long very high-energy (VHE) flux variability behavior. This systematic search has led to, for the first time, the detection of significant flux variations in five blazars at the >99% confidence level, whereas eight of them exhibit variability, albeit at a lower confidence level (∼95%–99%). A comparison of the 0.05–2 TeV flux variations with that observed at 0.1–50 GeV band has revealed similar variability behavior for most of the sources. However, complex variability patterns that are not reflected contemporaneously in both energy bands were also detected, thereby providing tantalizing clues about the underlying radiative mechanisms. These results open up a new dimension to unravel the VHE emission processes operating in relativistic jets, hence sowing the seeds for their future observations with the upcoming Cherenkov Telescope Array.

Keywords: gamma-ray astronomy; bl lacertae objects; active galaxies
Unveiling the Origin of the Fermi Bubbles with MeV Photon Telescopes

The Fermi Bubbles (FBs) are a pair of large-scale ellipsoidal structures extending above and below the Galactic plane almost symmetrically aligned with the Galactic center. After more than 10 yr since their discovery, their nature and origin remain unclear. Unveiling the primary emission mechanisms, whether hadronic or leptonic, is considered to be the main tool to shed light on the topic. We explore the potential key role of MeV observations of the FB, and we provide a recipe to determine the sensitivity of Compton and Compton-pair telescopes to the extended emission of the FB. We illustrate the capabilities of the Imaging Compton Telescope COMPTEL, the newly selected NASA MeV mission Compton Spectrometer and Imager, as well as the expectations for a potential future Compton-pair telescope such as the All-sky Medium Energy Gamma-ray Observatory eXplorer.

Keywords: gamma-ray telescopes; stellar wind bubbles; gamma-rays
Successive Energy Conversion at a Stepwise Dipolarization Front

Dipolarization fronts (DFs), ion-scale magnetic structures characterized by sharp enhancement of northward magnetic field developed within plasma jets, have been suggested to play a crucial role in the energy transfer chain in the terrestrial magnetotail. Here we present the first observation of successive energy conversion driven by multiple current layers at a stepwise DF, using high-cadence measurements from NASA's Magnetospheric Multiscale mission. The multiple current layers are adjacent and cause gradual variations of particles and electromagnetic fields, leading to an intense, successive increase of energy conversion rates at the DF in the satellite frame, with electromagnetic field energy being transformed into particle energy. The energy conversion is contributed by both ion and electron currents. The motional electric field drives the energy conversion, while the wave electric field fed by lower hybrid drift instability modulates the energy partition. These results provide new insights into understanding energy transfer in the terrestrial magnetotail.

Keywords: space plasmas
Virial Clumps in Central Molecular Zone Clouds

CMZoom survey observations with the Submillimeter Array are analyzed to describe the virial equilibrium (VE) and star-forming potential of 755 clumps in 22 clouds in the Central Molecular Zone (CMZ) of the Milky Way. In each cloud, nearly all clumps follow the column density-mass trend N ∝ M s , where s = 0.38 ± 0.03 is near the pressure-bounded limit s p = 1/3. This trend is expected when gravitationally unbound clumps in VE have similar velocity dispersion and external pressure. Nine of these clouds also harbor one or two distinctly more massive clumps. These properties allow a VE model of bound and unbound clumps in each cloud, where the most massive clump has the VE critical mass. These models indicate that 213 clumps have velocity dispersion 1-2 km s-1, mean external pressure (0.5-4) × 108 cm-3 K, bound clump fraction 0.06, and typical virial parameter α = 4-15. These mostly unbound clumps may be in VE with their turbulent cloud pressure, possibly driven by inflow from the Galactic bar. In contrast, most Sgr B2 clumps are bound according to their associated sources and N-M trends. When the CMZ clumps are combined into mass distributions, their typical power-law slope is analyzed with a model of stopped accretion. It also indicates that most clumps are unbound and cannot grow significantly, due to their similar timescales of accretion and dispersal, ~0.2 Myr. Thus, virial and dynamical analyses of the most extensive clump census available indicate that star formation in the CMZ may be suppressed by a significant deficit of gravitationally bound clumps.

Keywords: galactic center; star formation; molecular clouds
Standing on Apollo's Shoulders: A Microseismometer for the Moon

Seismometers deployed on the Moon by the Apollo astronauts from 1969 to 1972 detected moonquakes and impacts, and added to our understanding of the lunar interior. Several lunar missions are currently being planned, including the Commercial Lunar Payload Services (CLPS), the Lunar Geophysical Network, and the astronaut program Artemis. We propose a microseismometer for the Moon: the Silicon Seismic Package (SSP). The SSP's sensors are etched in silicon, and are predicted to have a noise floor below $2\times {10}^{-10}\,({\rm{m}}\,{{\rm{s}}}^{-2})/\sqrt{\mathrm{Hz}}$ between 0.3 and 3 Hz (similar to the Apollo instruments between 0.3 and 0.5 Hz, and better than Apollo above 0.5 Hz). The SSP will measure horizontal and vertical motion with the three sensors in a triaxial configuration. The instrument is robust to high shock and vibration and has an operational range from -80°C to +60°C, allowing deployment under harsh conditions. The first-generation version of this sensor, the SEIS-SP, was deployed on Mars in 2018 as part of the InSight mission's seismic package. We will reconfigure the seismometer for the lower gravity of the Moon. We estimate that a single SSP instrument operating for one year would detect around 74 events above a signal-to-noise ratio of 2.5, as well as an additional 500+ above the noise floor. A mission lasting from lunar dawn until dusk, carried on a CLPS lander, could test the instrument in situ, and provide invaluable information for an extensive future network.

Keywords: lunar seismology; lunar interior
A Test of the Hadronic Origin of γ-Rays from Blazars with Follow-up up to a Month Later of IceCube Alerts with Imaging Air Cherenkov Telescopes

The sources of IceCube neutrinos are as yet unknown. The multimessenger observation of their emission in γ-rays can be a guide to their identification, as exemplified by the case of TXS 0506+056. We suggest a new method of searching for γ-rays with Imaging Air Cherenkov Telescopes from sources coinciding with possible astrophysical neutrinos. We propose that searches of γ-rays be extended from the current practice of only a few days to up to one month from a neutrino alert. We test this strategy on simulated sources modeled after the blazar TXS 0506+056, emitting neutrinos and γ-rays via photohadronic interactions: the γ-rays are subsequently reprocessed in the VHE range. Using MAGIC as a benchmark example, we show that current Cherenkov Telescopes should be able to detect γ-ray counterparts to neutrino alerts with a rate of approximately one per year. It has been proposed that the high-energy diffuse neutrino flux can be explained by ~5% of all blazars flaring in neutrinos once every 10 yr, with a neutrino luminosity similar to that of TXS 0506+056 during the 2014-2015 neutrino flare. The implementation of our strategy could lead, over a timescale of one or a few years, either to the detection of this subclass of blazars contributing to the diffuse neutrino flux or to a constraint on this model.

Keywords: neutrino astronomy; neutrino telescopes; gamma-ray astronomy; gamma-ray telescopes; gamma-ray transient sources; blazars
CO Excitation in High-z Main-sequence Analogues: Resolved CO(4-3)/CO(3-2) Line Ratios in DYNAMO Galaxies

The spectral line energy distribution of carbon monoxide contains information about the physical conditions of the star-forming molecular hydrogen gas; however, the relation to local radiation field properties is poorly constrained. Using ~1-2 kpc scale Atacama Large Millimeter Array observations of CO(3-2) and CO(4-3), we characterize the CO(4-3)/CO(3-2) line ratios of local analogues of main-sequence galaxies at z ~ 1-2, drawn from the DYnamics of Newly Assembled Massive Objects (DYNAMO) sample. We measure CO(4-3)/CO(3-2) across the disk of each galaxy and find a median line ratio of R 43 = 0.54 ${}_{-0.15}^{+0.16}$ for the sample. This is higher than literature estimates of local star-forming galaxies and is consistent with multiple lines of evidence that indicate DYNAMO galaxies, despite residing in the local universe, resemble main-sequence galaxies at z ~ 1-2. Comparing with existing lower-resolution CO(1-0) observations, we find R 41 and R 31 values in the range ~0.2-0.3 and ~0.4-0.8, respectively. We combine our kiloparsec-scale resolved line ratio measurements with Hubble Space Telescope observations of Hα to investigate the relation to the star formation rate surface density and compare this relation to expectations from models. We find increasing CO(4-3)/CO(3-2) with increasing star formation rate surface density; however, models overpredict the line ratios across the range of star formation rate surface densities we probe, in particular at the lower range. Finally, Stratospheric Observatory for Infrared Astronomy observations with the High-resolution Airborne Wideband Camera Plus and Field-Imaging Far-Infrared Line Spectrometer reveal low dust temperatures and no deficit of [CII] emission with respect to the total infrared luminosity.

Keywords: interstellar emissions; extragalactic astronomy; disk galaxies
Confirming the 3:2 Resonance Chain of K2-138

The study of orbital resonances allows for the constraint of planetary properties of compact systems. K2-138 is an early K-type star with six planets, five of which have been proposed to be in the longest chain of 3:2 mean motion resonances. To observe and potentially verify the resonant behavior of K2-138's planets, we run N-body simulations using previously measured parameters. Through our analysis, we find that 99.2% of our simulations result in a chain of 3:2 resonances, although only 11% of them show a five-planet resonance chain. We find that we are able to use resonances to constrain the orbital periods and masses of the planets. We explore the possibility of this system forming in situ and through disk migration, and we investigate the potential compositions of each planet using a planet structure code.

Keywords: exoplanet dynamics; exoplanet migration; exoplanet structure
The Distribution of Ground-based Reflecting Telescopes with Respect to Altitude

The altitude distribution of ground-based reflecting telescopes with primary mirrors of diameter 1.0 m or more is presented graphically and compared with hypsographic data for the Earth's land surface. It is verified that large optical reflectors are more weighted to higher elevations than the land surface. Approximately 60% of the combined collecting area of the telescopes is situated between elevations of 2000 and 3500 m.

Keywords: ground telescopes; reflecting telescopes