adsabs/SciX_UAT_keywords huggingface dataset:
Higher Radial Harmonics of Sausage Oscillations in Coronal Loops

Impulsively excited sausage oscillations of a plasma cylinder with a smooth radial profile of Alfvén speed are analyzed with a numerical solution of the initial-value problem for a partial differential equation of the Klein-Gordon type, describing linear magnetoacoustic oscillations with a fixed axial wavelength and an azimuthal mode number. The range of analyzed ratios of Alfvén speeds outside and inside the cylinder is from 2 to 10. Both trapped and leaky regimes of the oscillations are considered. It is shown that even in the long-wavelength limit, I.e., for axial wavenumbers much smaller than the cutoff values, damping times of higher radial sausage harmonics could be significantly greater than the oscillation periods, I.e., several oscillation cycles could be present in the signal. The quality factors decrease with decfreasing ratios of Alfvén speeds outside and inside the cylinder. Oscillation periods of the second and third radial harmonics remain practically independent of the axial wavelength even when the wavelength is shorter than the radius of the cylinder. The ratios of oscillation periods of fundamental and higher radial and axial harmonics are found to be significantly different, up to a factor of two in the long-wavelength limit. It is concluded that higher radial harmonics could be responsible for the departure of observed sausage oscillation signals from a harmonic shape, especially during the first several cycles of the oscillation. Even in the absence of spatially resolved data, higher axial and radial harmonics can be distinguished from each other by the period ratios.

Keywords: solar flares; solar oscillations; magnetohydrodynamics
Unprecedented Early Flux Excess in the Hybrid 02es-like Type Ia Supernova 2022ywc Indicates Interaction with Circumstellar Material

We present optical photometric and spectroscopic observations of the 02es-like type Ia supernova (SN) 2022ywc. The transient occurred in the outskirts of an elliptical host galaxy and showed a striking double-peaked light curve with an early excess feature detected in the ATLAS orange and cyan bands. The early excess is remarkably luminous with an absolute magnitude ~ - 19, comparable in luminosity to the subsequent radioactively driven second peak. The spectra resemble the hybrid 02es-like SN 2016jhr, which is considered to be a helium shell detonation candidate. We investigate different physical mechanisms that could power such a prominent early excess and rule out massive helium shell detonation, surface 56Ni distribution, and ejecta-companion interaction. We conclude that SN ejecta interacting with circumstellar material (CSM) is the most viable scenario. Semianalytical modeling with MOSFiT indicates that SN ejecta interacting with ~0.05 M ⊙ of CSM at a distance of ~1014 cm can explain the extraordinary light curve. A double-degenerate scenario may explain the origin of the CSM, by tidally stripped material from either the secondary white dwarf or disk-originated matter launched along polar axes following the disruption and accretion of the secondary white dwarf. A nonspherical CSM configuration could suggest that a small fraction of 02es-like events viewed along a favorable line of sight may be expected to display a very conspicuous early excess like SN 2022ywc.

Keywords: supernovae; type ia supernovae
Improved Orthorectification and Empirical Reduction of Topographic Effects in Monostatic Mini-RF S-band Observations of the Moon

The Miniature Radio Frequency instrument (Mini-RF) on the Lunar Reconnaissance Orbiter obtained widespread synthetic aperture radar observations of the Moon in the S band (12.6 cm), including nearly complete coverage at both lunar poles. The currently archived monostatic data have spatial offsets from the lunar reference frame, making them more difficult to compare to other data sets. To address this issue, we have developed a new algorithm for spatially controlling the Mini-RF S-band monostatic data set and orthorectifying these data onto lunar topography. Additionally, as the influence of incidence angle changes on radar observations is well known, we describe an empirical approach to account for variations in observation geometry and surface topography. Individual radar swaths and mosaics produced using this method more clearly show the variability in scattering behavior due to changes in lunar regolith properties and suppress some of the behavior arising from these topographic effects alone. Once these terrain effects are taken into account, we find that areas of permanent shadow at both poles have a higher median radar reflectivity than nonpermanently shadowed regions, but the polarization behavior of shadowed versus unshadowed areas is largely similar. The higher radar reflectivity in permanent shadow is likely the result of physical or compositional differences in these unique environments, though the precise cause remains uncertain. The results here illustrate how reducing the influence of topography and geometry effects in Mini-RF radar data may enable better characterization of lunar geologic units, regolith structure, and potential areas hosting volatile deposits at the lunar poles.

Keywords: the moon; radar observations
First Detection of Silicon-bearing Molecules in η Car

We present ALMA band 6 observations of the luminous blue variable η Car obtained within the ALMAGAL program. We report SiO J = 5 → 4, SiS J = 12 → 11, and SiN N = 5 → 4 emission in the equatorial region of the Homunculus nebula, constituting the first detection of silicon- and sulfur-bearing molecules in the outskirts of a highly evolved, early-type massive star. The SiO, SiS, and SiN trace a clumpy equatorial ring that surrounds the central binary at a projected distance of ~2″, delineating the inner rims of the butterfly-shaped dusty region. The formation of silicon-bearing compounds is presumably related to the continuous recycling of dust due to the variable wind regime of η Car, which destroys grains and releases silicon back to the gas phase. We discuss possible formation routes for the observed species, contextualizing them within the current molecular inventory of η Car. We find that the SiO and SiS fractional abundances in localized clumps of the ring, 6.7 × 10-9 and 1.2 × 10-8, respectively, are exceptionally lower than those measured in C- and O-rich AGB stars and cool supergiants, while the higher SiN abundance, 3.6 × 10-8, evidences the nitrogen-rich chemistry of the ejecta. These abundances must be regarded as strict upper limits, since the distribution of H2 in the Homunculus is unknown. In any case, these findings shed new light on the peculiar molecular ecosystem of η Car and establish its surroundings as a new laboratory to investigate the life cycle of silicate dust in extreme astrophysical conditions.

Keywords: massive stars; luminous blue variable stars; stellar mass loss; molecular gas; dust destruction; astrochemistry; circumstellar matter
Modulation of the Blazhko Cycle in LS Her

We present analysis of the RR Lyrae star, LS Her, and confirm the previously reported modulation to its Blazhko cycles. We performed Fourier analysis on two sectors (Sector 24 and 25) of data from the Transiting Exoplanet Survey Satellite (TESS) spanning 53 days. We find LS Her to have a primary pulsation period of 0.2308 day and a Blazhko period of 12.7 days in keeping with previously reported results. We also identified sideband frequencies around the Blazhko multiplets suggesting the Blazhko cycle is modulated on a timescale of 112 days. Analysis of the Blazhko effect using the TESS data clearly shows a changing amplitude and phase throughout the four Blazhko cycles. We compared our modeled results, which were based on our TESS frequency analysis, to TESS data (Sector 51) taken ~700 days later and found our modulation model was not a good representation of the data. We then coupled our TESS analysis with the modulation frequency results from Wils et al. and found excellent agreement with the Sector 51 data. To further test this result we obtained ground-based, V-magnitude observations of LS Her in the summer of 2022. This data also showed excellent agreement with our coupled modulation model. We have verified that LS Her is a Blazhko star with a modulated Blazhko period of 109 days, stability over the 862 days of observations, and possible stability lasting over 15 yr. We discuss the ramifications of the modulation for other Blazhko stars that show Blazhko effect changes over time.

Keywords: rr lyrae variable stars; rrc variable stars; blazhko effect
Correlating Intrinsic Stellar Parameters with Mg II Self-reversal Depths

The Mg II h&k emission lines (2803, 2796 Å) are a useful tool for understanding stellar chromospheres and transition regions due to their intrinsic brightness, relatively low interstellar medium (ISM) absorption interference, and abundance of archival spectra available. Similar to other optically thick chromospheric emission lines such as H I Lyα, Mg II emissions commonly present with a self-reversed line core, the depth and shape of which vary from star to star. We explore the relationship between self-reversal and the stellar atmosphere by investigating the extent to which fundamental stellar parameters affect self-reversal. We present a search for correlations between photospheric parameters such as effective temperature, surface gravity, and metallicity with the Mg II k self-reversal depth for a group of 135 FGKM main-sequence stars with high-resolution near-ultraviolet spectra from the Hubble Space Telescope. We modeled the observed Mg II k line profiles to correct for ISM attenuation and recover the depth of the emission line's self-reversal in relation to the intensity of the line. We used the PHOENIX atmosphere code to homogeneously determine the stellar parameters by computing a suite of stellar atmosphere models that include a chromosphere and transition region, and using archival photometry to guide the models of each star. We quantify the sensitivity of the visible and near-infrared photometry to chromospheric and photospheric parameters. We find weak trends between Mg II k self-reversal depth and age, rotation period, Mg II luminosity, temperature, and mass. All stars in our sample older than ∼2 Gyr or rotating slower than ∼10 days exhibit self-reversal.

Keywords: stellar spectral types
Could a Kilonova Kill: A Threat Assessment

Binary neutron star mergers produce high-energy emissions from several physically different sources, including a gamma-ray burst (GRB) and its afterglow, a kilonova (KN), and, at late times, a remnant many parsecs in size. Ionizing radiation from these sources can be dangerous for life on Earth-like planets when located too close. Work to date has explored the substantial danger posed by the GRB to on-axis observers; here we focus instead on the potential threats posed to nearby off-axis observers. Our analysis is based largely on observations of the GW170817/GRB 170817A multi-messenger event, as well as theoretical predictions. For baseline KN parameters, we find that the X-ray emission from the afterglow may be lethal out to ∼1 pc and the off-axis gamma-ray emission may threaten a range out to ∼4 pc, whereas the greatest threat comes years after the explosion, from the cosmic rays accelerated by the KN blast, which can be lethal out to distances up to ∼11 pc. The distances quoted here are typical, but the values have significant uncertainties and depend on the viewing angle, ejected mass, and explosion energy in ways we quantify. Assessing the overall threat to Earth-like planets, KNe have a similar kill distance to supernovae, but are far less common. However, our results rely on the scant available KN data, and multi-messenger observations will clarify the danger posed by such events.

Keywords: nucleosynthesis; x-ray transient sources; gamma-ray transient sources; astrobiology; supernovae; cosmic rays
Constraining the Observer Angle of the Kilonova AT2017gfo Associated with GW170817: Implications for the Hubble Constant

There is a strong degeneracy between the luminosity distance (D L ) and the observer viewing angle (θ obs; hereafter viewing angle) of the gravitational wave (GW) source with an electromagnetic counterpart, GW170817. Here, for the first time, we present independent constraints on {θ }obs}={32.5}-9.7^\circ +11.7 from broadband photometry of the kilonova (kN) AT2017gfo associated with GW170817. These constraints are consistent with independent results presented in the literature using the associated gamma-ray burst GRB 170817A. Combining the constraints on θ obs with the GW data, we find an improvement of 24% on H 0. The observer angle constraints are insensitive to other model parameters, e.g., the ejecta mass, the half-opening angle of the lanthanide-rich region and the temperature. A broad wavelength coverage extending to the near-infrared is helpful to robustly constrain θ obs. While the improvement on H 0 presented here is smaller than the one from high angular resolution imaging of the radio counterpart of GW170817, kN observations are significantly more feasible at the typical distances of such events from current and future LIGO-Virgo collaboration observing runs (D L ∼ 100 Mpc). Our results are insensitive to the assumption of the peculiar velocity of the kN host galaxy.

Keywords: hubble constant; cosmological parameters; radiative transfer; gravitational waves
Using VIRTIS on Venus Express to Constrain the Properties of the Giant Dark Cloud Observed in Images of Venus by IR2 on Akatsuki

A cloud opacity contrast feature that has been called a "long-lived sharp disruption" has been seen in the atmosphere of Venus in the near-infrared using Akatsuki's IR2 camera, most clearly at equatorial latitudes. This feature was found to have a consistent planet-circling period of 4.9 days, and subsequent searches of past imagery revealed that it has probably existed for at least 30 years, the duration of near-infrared investigation of the deep atmosphere of Venus. Guided by the remarkably consistent morphological appearance of this feature, we have identified at least one previous instance of it in the Venus Express Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) data. We take advantage of the spectroscopic capabilities of VIRTIS to retrieve atmospheric parameters in the vicinity of this feature that cannot be retrieved using the limited filter selection on board Akatsuki. We find that the changes in measurable quantities, such as cloud particle acid mass fraction, water vapor, carbon monoxide, cloud base altitude, and particle size, suggest that the changes that take place in the vicinity of this feature are restricted to the lower clouds of Venus (below 50 km). We hypothesize that further evolution of this feature (over timescales of days to weeks) results in measurable variations in these parameters at altitudes in the middle clouds of Venus (50-57 km), lending credence to its identification as a baroclinic trough or Kelvin front.

Keywords: venus; planetary atmospheres; atmospheric composition; atmospheric variability; atmospheric circulation; near infrared astronomy
A Temperature or Far-ultraviolet Tracer? The HNC/HCN Ratio in M83 on the Scale of Giant Molecular Clouds

The HNC/HCN ratio is observationally known as a thermometer in Galactic interstellar molecular clouds. A recent study has alternatively suggested that the HNC/HCN ratio is affected by the ultraviolet (UV) field, not by the temperature. We aim to study this ratio on the scale of giant molecular clouds in the barred spiral galaxy M83 towards the southwestern bar end and the central region from Atacama Large Millimeter/submillimeter Array observations, and if possible, distinguish the above scenarios. We compare the high-resolution (40–50 pc) HNC/HCN ratios with the star formation rate from the 3 mm continuum intensity and the molecular mass inferred from the HCN intensities. Our results show that the HNC/HCN ratios do not vary with the star formation rates, star formation efficiencies, or column densities in the bar-end region. In the central region, the HNC/HCN ratios become higher with higher star formation rates, which tend to cause higher temperatures. This result is not consistent with the previously proposed scenario in which the HNC/HCN ratio decreases with increasing temperature. Spectral shapes suggest that this trend may be due to optically thick HCN and optically thin HNC. In addition, we compare the large-scale (∼200 pc) correlation between the dust temperature from the far-IR ratio and the HNC/HCN ratio for the southwestern bar-end region. The HNC/HCN ratio is lower when the dust temperatures are higher. We suggest from the above results that the HNC/HCN ratio depends on the UV radiation field that affects the interstellar medium on the ∼100 pc scale where the column densities are low.

Keywords: interstellar medium; astrochemistry
Probing Kilonova Ejecta Properties Using a Catalog of Short Gamma-Ray Burst Observations

The discovery of GW170817 and GRB 170817A in tandem with AT 2017gfo cemented the connection between neutron star mergers, short gamma-ray bursts (GRBs), and kilonovae. To investigate short GRB observations in the context of diverse kilonova behavior, we present a comprehensive optical and near-IR catalog of 85 bursts discovered over 2005-2020 on timescales of ≲12 days. The sample includes previously unpublished observations of 23 bursts and encompasses both detections and deep upper limits. We identify 11.8% and 15.3% of short GRBs in our catalog with upper limits that probe luminosities lower than those of AT 2017gfo and a fiducial neutron star-black hole kilonova model (for pole-on orientations), respectively. We quantify the ejecta masses allowed by the deepest limits in our catalog, constraining blue and "extremely blue" kilonova components of 14.1% of bursts to Mej ≲ 0.01-0.1 M⊙. The sample of short GRBs is not particularly constraining for red kilonova components. Motivated by the large catalog, as well as model predictions of diverse kilonova behavior, we investigate modified search strategies for future follow-up to short GRBs. We find that ground-based optical and near-IR observations on timescales of ≳2 days can play a significant role in constraining more diverse outcomes. We expect future short GRB follow-up efforts, such as from the James Webb Space Telescope, to expand the reach of kilonova detectability to redshifts of z ≈ 1.

Keywords: gamma-ray bursts; neutron stars
Two Transient Quasi-periodic Oscillations in γ-Ray Emission from the Blazar S4 0954+658

In this work, we report periodicity search analyses in the gamma-ray light curve of the blazar S4 0954+658 in monitoring undertaken by the Fermi Large Area Telescope. Four analytical methods and a tool are adopted to detect any periodic flux modulation and corresponding significance level, revealing: (i) a quasi-periodic oscillation (QPO) of 66 days with a significance level of >5σ spanning over 600 days from 2015 to 2016 (MJD 57,145-57,745), resulting in continuous observation of nine cycles, which is one of the longest cycles discerned in blazar gamma-ray light curves; (ii) a possible QPO of 210 days at a moderate significance of ~3.5σ, which lasted for over 880 days from 2020 to 2022 (MJD 59,035-59,915) and for four cycles. In addition, we discuss several physical models to explain the origin of the two transient QPOs and conclude that a geometrical scenario involving a plasma blob moving helically inside the jet can explain the timescale of the QPO.

Keywords: active galactic nuclei; blazars; jets; period search
SMARPs and SHARPs: Two Solar Cycles of Active Region Data

We present a new data product, called Space-Weather MDI Active Region Patches (SMARPs), derived from maps of the solar surface magnetic field taken by the Michelson Doppler Imager on board the Solar and Heliospheric Observatory. Together with the Space-Weather HMI Active Region Patches (SHARPs), derived from similar maps taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, these data provide a continuous and seamless set of maps and keywords that describe every active region observed over the last two solar cycles, from 1996 to the present day. In this paper, we describe the SMARP data and compare it to the SHARP data.

Keywords: solar active regions; astronomy databases; solar magnetic fields
Discovery of a Binary-origin Classical Cepheid in a Binary System with a 59 day Orbital Period

We report the discovery of a surprising binary configuration of the double-mode Cepheid OGLE-LMC-CEP-1347 pulsating in the first (P 1 = 0.690 days) and second-overtone (P 2 = 0.556 days) modes. The orbital period (P orb = 59 days) of the system is five times shorter than the shortest known to date (310 days) for a binary Cepheid. The Cepheid itself is also the shortest-period one ever found in a binary system and the first double-mode Cepheid in a spectroscopically double-lined binary. OGLE-LMC-CEP-1347 is most probably on its first crossing through the instability strip, as inferred from both its short period and fast period increase, consistent with evolutionary models, and from the short orbital period (not expected for binary Cepheids whose components have passed through the red giant phase). Our evolutionary analysis yielded a first-crossing Cepheid with a mass in a range of 2.9-3.4 M ⊙ (lower than any measured Cepheid mass), consistent with observations. The companion is a stable star, at least two times fainter and less massive than the Cepheid (preliminary mass ratio q = 0.55), while also redder and thus at the subgiant or more advanced evolutionary stage. To match these characteristics, the Cepheid has to be a product of binary interaction, most likely a merger of two less massive stars, which makes it the second known classical Cepheid of binary origin. Moreover, further evolution of the components may lead to another binary interaction. *Based on observations collected at the European Southern Observatory, Chile. †This Letter includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

Keywords: cepheid variable stars; double-mode cepheid variable stars; spectroscopic binary stars; late-type stars
Testing the Fidelity of Simulations of Black Hole-Galaxy Coevolution at z ∼ 1.5 with Observations

We examine the scaling relations between the mass of a supermassive black hole (SMBH) and its host galaxy properties at 1.2 < z <1.7 using both observational data and simulations. Recent measurements of 32 X-ray-selected, broad-line active galactic nuclei (AGNs) are compared with two independent state-of-the-art efforts, including the hydrodynamic simulation MassiveBlackII (MBII) and a semianalytic model (SAM). After applying an observational selection function to the simulations, we find that both MBII and SAM agree well with the data, in terms of the central distribution. However, the dispersion in the mass ratio between black hole mass and stellar mass is significantly more consistent with the MBII prediction (∼0.3 dex) than with the SAM (∼0.7 dex), even when accounting for observational uncertainties. Hence, our observations can distinguish between the different recipes adopted in the models. The mass relations in the MBII are highly dependent on AGN feedback, while the relations in the SAM are more sensitive to galaxy-merger events triggering nuclear activity. Moreover, the intrinsic scatter in the mass ratio of our high-z sample is comparable with that observed in the local sample, all but ruling out the proposed scenario that the correlations are purely stochastic in nature arising from some sort of cosmic central limit theorem. Our results support the hypothesis of AGN feedback being responsible for a causal link between the SMBH and its host galaxy, resulting in a tight correlation between their respective masses.

Keywords: galaxy evolution; active galaxies; active galactic nuclei