adsabs/SciX_UAT_keywords huggingface dataset:
KilonovAE: Exploring Kilonova Spectral Features with Autoencoders

Kilonovae are likely a key site of heavy r-process element production in the Universe, and their optical/infrared spectra contain insights into both the properties of the ejecta and the conditions of the r-process. However, the event GW170817/AT2017gfo is the only kilonova so far with well-observed spectra. To understand the diversity of absorption features that might be observed in future kilonovae spectra, we use the TARDIS Monte Carlo radiative transfer code to simulate a suite of optical spectra spanning a wide range of kilonova ejecta properties and r-process abundance patterns. To identify the most common and prominent absorption lines, we perform dimensionality reduction using an autoencoder, and we find spectra clusters in the latent space representation using a Bayesian Gaussian Mixture model. Our synthetic kilonovae spectra commonly display strong absorption by strontium 38Sr II, yttrium 38Y II, and zirconium 40Zr I-II, with strong lanthanide contributions at low electron fractions (Y e ≲ 0.25). When a new kilonova is observed, our machine-learning framework will provide context on the dominant absorption lines and key ejecta properties, helping to determine where this event falls within the larger "zoo" of kilonovae spectra.

Keywords: neutron stars; r-process; radiative transfer simulations; spectral line identification; dimensionality reduction
Multiple Shells Driven by Disk Winds: ALMA Observations in the HH 30 Outflow

We present archival Atacama Large Millimeter/submillimeter Array band 6 observations of the 13CO (J = 2–1) and 12CO (J = 2–1) molecular line emission of the protostellar system associated with HH 30. The 13CO molecular line shows the accretion disk while the molecular outflow is traced by the emission of the 12CO molecular line. We estimated a dynamical mass for the central object of 0.45 ± 0.14 M ⊙, and a mass for the molecular outflow of (1.83 ± 0.19) × 10‑4 M ⊙. The molecular outflow presents an internal cavity as well as multiple outflowing shell structures. We distinguish three different shells with constant expansion (∼4–6 km s‑1) and possible rotation signatures (≤0.5 km s‑1). We find that the shells can be explained by magnetocentrifugal disk winds with launching radii R launch ≲ 4 au and a small magnetic lever arm λ ∼ 1.6–1.9. The multiple shell structure may be the result of episodic ejections of the material from the accretion disk associated with three different epochs with dynamical ages of 497 ± 15 yr, 310 ± 9 yr, and 262 ± 11 yr for the first, second, and third shells, respectively. The outermost shell was ejected 187 ± 17 yr before the middle shell, while the middle shell was launched 48 ± 14 yr before the innermost shell. Our estimations of the linear and angular momentum rates of the outflow as well as the accretion luminosity are consistent with the values expected if the outflow of HH 30 is produced by a wide-angle disk wind.

Keywords: accretion; herbig-haro objects; star formation; stellar winds; young stellar objects
The Missing Link? Discovery of Pulsations in the Nitrogen-rich PG 1159 Star PG 1144+005

Up to 98% of all single stars will eventually become white dwarfs-stars that link the history and future evolution of the Galaxy, and whose previous evolution is engraved in their interiors. Those interiors can be studied using asteroseismology, utilizing stellar pulsations as seismic waves. The pulsational instability strips of DA and DB white dwarf stars are pure, allowing for the important generalization that their interior structure represents that of all DA and DB white dwarfs. This is not the case for the hottest pulsating white dwarfs, the GW Vir stars: only about 50% of white dwarfs in this domain pulsate. Several explanations for the impurity of the GW Vir instability strip have been proposed, based on different elemental abundances, metallicity, and helium content. Surprisingly, there is a dichotomy that only stars rich in nitrogen, which by itself cannot cause pulsation driving, pulsate-the only previous exception being the nitrogen-rich nonpulsator PG 1144+005. Here, we report the discovery of pulsations in PG 1144+005 based on new observations. We identified four frequency regions: 40, 55, 97, and 112 day-1 with low and variable amplitudes of about 3-6 mmag and therefore confirm the nitrogen dichotomy. As nitrogen is a trace element revealing the previous occurrence of a very late thermal pulse (VLTP) in hot white dwarf stars, we speculate that it is this VLTP that provides the interior structure required to make a GW Vir pulsator.

Keywords: pg 1159 stars; pulsating variable stars; stellar pulsations; non-radial pulsations; stellar evolution
Global 3D Simulation of the Upper Atmosphere of HD189733b and Absorption in Metastable He I and Lyα Lines

A 3D fully self-consistent multifluid hydrodynamic aeronomy model is applied to simulate the hydrogen-helium expanding upper atmosphere of the hot Jupiter HD189733b, and related absorption in the Lyα line and the 10830 Å line of metastable helium. We studied the influence of a high-energy stellar flux, a stellar wind, and Lyα cooling to reproduce the available observations. We found that to fit the width of the absorption profile of the 10830 Å line the escaping upper atmosphere of the planet should be close to the energy-limited escape achieved with significantly reduced Lyα cooling at the altitudes with an H I density higher than 3 × 106 cm-3. Based on the performed simulations, we constrain the helium abundance in the upper atmosphere of HD189733b to be a rather low value of He/H ~ 0.005. We show that under the conditions of a moderate stellar wind similar to that of the Sun the absorption of the Lyα line takes place mostly within the Roche lobe due to thermal broadening at a level of about 7%. For an order of magnitude stronger wind, a significant absorption of about 15% at high blueshifted velocities of up to 100 km s-1 is generated in the bowshock region, due to Doppler broadening. These blueshifted velocities are still lower than those (~200 km s-1) detected in one of the observations. We explain the differences between the performed observations, though not in all of the details, by stellar activity and the related fluctuations of the ionizing radiation (in the case of the 10830 Å line), and the stellar wind (in the case of the Lyα line).

Keywords: exoplanet atmospheres; exoplanet atmospheric composition
Milky Way Subsystems from Globular Cluster Kinematics Using Gaia DR2 and HST Data

We employ Gaia DR2 proper motions for 151 Milky Way globular clusters (GCs) from Vasiliev in tandem with distances and line-of-sight velocities to derive their kinematical properties. To assign clusters to the Milky Way thick disk, bulge, and halo, we follow the approach of Posti et al., who distinguished among different Galactic stellar components using stars' orbits. In particular, we use the ratio Lz/e, the Z projection of the angular momentum to the eccentricity, as a population tracer, which we complement with chemical abundances extracted from the literature and Monte Carlo simulations. We find that 20 GCs belong to the bar/bulge of the Milky Way, 35 exhibit disk properties, and 96 are members of the halo. Moreover, we find that halo GCs have close to zero rotational velocity with an average value $\langle {\rm{\Theta }}\rangle =1\pm 4$ km s-1. On the other hand, the sample of clusters that belong to the thick disk possess a significant rotation with average rotational velocity 179 ± 6 km s-1. The 20 GCs orbiting within the bar/bulge region of the Milky Way have an average rotational velocity of 49 ± 11 km s-1.

Keywords: milky way galaxy; globular star clusters; milky way dynamics; milky way rotation
Cross Helicity Reversals in Magnetic Switchbacks

We consider 2D joint distributions of normalized residual energy, σr(s, t), and cross helicity, σc(s, t), during one day of Parker Solar Probe's (PSP's) first encounter as a function of wavelet scale s. The broad features of the distributions are similar to previous observations made by Helios in slow solar wind, namely well-correlated and fairly Alfvénic wind, except for a population with negative cross helicity that is seen at shorter wavelet scales. We show that this population is due to the presence of magnetic switchbacks, or brief periods where the magnetic field polarity reverses. Such switchbacks have been observed before, both in Helios data and in Ulysses data in the polar solar wind. Their abundance and short timescales as seen by PSP in its first encounter is a new observation, and their precise origin is still unknown. By analyzing these MHD invariants as a function of the wavelet scale, we show that magnetohydrodynamic (MHD) waves do indeed follow the local mean magnetic field through switchbacks, with a net Elsässer flux propagating inward during the field reversal and that they, therefore, must be local kinks in the magnetic field and not due to small regions of opposite polarity on the surface of the Sun. Such observations are important to keep in mind as computing cross helicity without taking into account the effect of switchbacks may result in spurious underestimation of σc as PSP gets closer to the Sun in later orbits.

Keywords: heliosphere; interplanetary turbulence; space plasmas; alfven waves
The First Habitable-zone Earth-sized Planet from TESS. II. Spitzer Confirms TOI-700 d

We present Spitzer 4.5 μm observations of the transit of TOI-700 d, a habitable-zone Earth-sized planet in a multiplanet system transiting a nearby M-dwarf star (TIC 150428135, 2MASS J06282325-6534456). TOI-700 d has a radius of ${1.144}_{-0.061}^{+0.062}{R}_{\oplus }$ and orbits within its host star's conservative habitable zone with a period of 37.42 days (Teq ∼ 269 K). TOI-700 also hosts two small inner planets (Rb = ${1.037}_{-0.064}^{+0.065}{R}_{\oplus }$ and Rc = ${2.65}_{-0.15}^{+0.16}{R}_{\oplus }$ ) with periods of 9.98 and 16.05 days, respectively. Our Spitzer observations confirm the Transiting Exoplanet Survey Satellite (TESS) detection of TOI-700 d and remove any remaining doubt that it is a genuine planet. We analyze the Spitzer light curve combined with the 11 sectors of TESS observations and a transit of TOI-700 c from the LCOGT network to determine the full system parameters. Although studying the atmosphere of TOI-700 d is not likely feasible with upcoming facilities, it may be possible to measure the mass of TOI-700 d using state-of-the-art radial velocity (RV) instruments (expected RV semiamplitude of ∼70 cm s-1).

Keywords: exoplanets; habitable planets; habitable zone; low mass stars; antarctic observatories; exoplanet astronomy; exoplanet detection methods; exoplanet systems
Electron Density Variations in the Interstellar Medium and the Average Frequency Profile of a Scintle from Pulsar Scintillation Spectra

We observed the scintillation pattern of nine bright pulsars at 324 MHz and three at 1.68 GHz and analyzed the wavenumber spectrum, which is related to electron density variations of the plasma turbulence of the interstellar medium (ISM). For all pulsars the frequency section of the autocorrelation function (ACF) of the dynamic spectra to at least 45% of the maximum corresponds to predictions of scattering theories with a range of power-law exponents of the wavenumber spectrum of 3.56 ≤ α ≤ 3.97 with errors ≤0.05 and a mean with standard deviation of 3.76 ± 0.13. The range includes α = 3.67 for the Kolmogorov spectrum. Similar results, although with larger errors, were found from the Fourier transform of the ACFs down to ~10-3 of the maximum. No clear case of a distinction between thin-screen and extended-medium scattering models was found. The average frequency profile of the scintles can be characterized for steep wavenumber spectra with α ≲ 4 by a cusp with a somewhat rounded peak. For flatter spectra, down to at least α ~ 3.56 the cusp with its peak becomes more pronounced and its decay steepens. We discuss our findings in the context of the scattering characteristics of the ISM.

Keywords: interstellar scintillation; radio pulsars; very long baseline interferometry; interstellar scattering
Radiative Transfer Modeling of Chang'e-4 Spectroscopic Observations and Interpretation of the South Pole-Aitken Compositional Anomaly

Chang'e-4 landed in the Von Kármán basaltic zone affected by Finsen ejecta from the South Pole-Aitken (SPA) "compositional anomaly" (SPACA), providing an opportunity to untangle the origin of the SPACA. We developed a mineral abundance unmixing model and built a spectral library composed of mineral mixtures of plagioclase, low-Ca pyroxene, high-Ca pyroxene, and olivine. Based on the mineral abundances returned by our model, the average plagioclase abundance (60.4 vol.%) of SPACA is beyond the high-plagioclase end of the mineralogical range of SPA impact melt differentiation products and would require an additional contribution from crustal materials. We suggest that either the crust was not entirely removed in the SPA-forming impact or the ejecta from post-SPA basins fed feldspathic materials back onto the SPA basin floor. Our unmixing analyses indicate that the surface regolith of the SPACA is a mixture of 70.2% crustal materials and 29.8% Fe- and incompatible-element-enriched materials.

Keywords: the moon; lunar composition; lunar evolution; lunar mineralogy; lunar probes; lunar surface; lunar science
Stellar Metallicities from SkyMapper Photometry. II. Precise Photometric Metallicities of ∼280,000 Giant Stars with [Fe/H] < -0.75 in the Milky Way

The Milky Way's metal-poor stars are nearby ancient objects that are used to study early chemical evolution and the assembly and structure of the Milky Way. Here we present reliable metallicities of ∼280,000 stars with -3.75 ≲ [Fe/H] ≲ -0.75 down to g = 17 derived using metallicity-sensitive photometry from the second data release of the SkyMapper Southern Survey. We use the dependency of the flux through the SkyMapper v filter on the strength of the Ca II K absorption features, in tandem with SkyMapper u, g, i photometry, to derive photometric metallicities for these stars. We find that metallicities derived in this way compare well to metallicities derived in large-scale spectroscopic surveys, and we use such comparisons to calibrate and quantify systematics as a function of location, reddening, and color. We find good agreement with metallicities from the APOGEE, LAMOST, and GALAH surveys, based on a standard deviation of σ ∼ 0.25 dex of the residuals of our photometric metallicities with respect to metallicities from those surveys. We also compare our derived photometric metallicities to metallicities presented in a number of high-resolution spectroscopic studies to validate the low-metallicity end ([Fe/H] < -2.5) of our photometric metallicity determinations. In such comparisons, we find the metallicities of stars with photometric [Fe/H] < -2.5 in our catalog show no significant offset and a scatter of σ ∼ 0.31 dex level relative to those in high-resolution work when considering the cooler stars (g - i > 0.65) in our sample. We also present an expanded catalog containing photometric metallicities of ∼720,000 stars as a data table for further exploration of the metal-poor Milky Way.

Keywords: population ii stars; milky way galaxy
Escape Velocity Mass of A1063

We measure the radius–velocity phase-space edge profile of A1063 using galaxy redshifts from Karman et al. and Mercurio et al. Combined with a cosmological model and after accounting for interlopers and sampling effects, we infer the escape velocity profile. Using the Poisson equation, we then directly constrain the gravitational potential profile and find excellent agreement between three different density models. For the Navarro–Frenk–White profile, we find log10(M 200,crit) = M ⊙, consistent to within 1σ of six recently published lensing masses. We argue that this consistency is due to the fact that the escape technique shares no common systematics with lensing other than radial binning. These masses are 2–4σ lower than estimates made using X-ray data, in addition to the Gómezet al. velocity dispersion estimate. We measure the 1D velocity dispersion within r 200 to be km s‑1, which combined with our escape velocity mass, brings the dispersion for A1063 in-line with hydrodynamic cosmological simulations for the first time.

Keywords: cosmology; galaxy clusters; gravitational lensing; dark energy
The Planetary Nebula in the 500 Myr Old Open Cluster M37

We report confirmation of a large, evolved, bipolar planetary nebula and its blue, white dwarf central star as a member of the ~500 Myr old Galactic open star cluster M37 (NGC 2099). This is only the third known example of a planetary nebula in a Galactic open cluster and was found via our ongoing program of identifying and studying planetary nebulae-open cluster associations. High confidence in the association comes from the consistent radial velocities and proper motions for the confirmed central star and cluster stars from Gaia, reddening agreement, and location of the planetary nebula well within the tidal cluster boundary. Interestingly, all three Galactic examples have bipolar morphology and likely Type-I chemistry, both characteristics of higher mass progenitors. In this case the progenitor star mass is in the midrange of ~2.8 M ☉. It provides a valuable, additional point on the key stellar initial-to-final mass relation independent of cluster white dwarf estimates and also falls in a gap in the poorly sampled mass region. This planetary nebula also appears to have the largest kinematical age ever determined and implies increased visibility lifetimes when they are located in clusters.

Keywords: open star clusters; planetary nebulae
FOSSIL. I. The Spin Rate Limit of Jupiter Trojans

Rotation periods of 53 small (diameters 2 km < D < 40 km) Jupiter Trojans (JTs) were derived using the high-cadence lightcurves obtained by the FOSSIL phase I survey, a Subaru/Hyper Suprime-Cam intensive program. These are the first reported periods measured for JTs with D < 10 km. We found a lower limit of the rotation period near 4 hr, instead of the previously published result of 5 hr found for larger JTs. Assuming a rubble-pile structure for JTs, a bulk density of ≈0.9 g cm-3 is required to withstand this spin rate limit, consistent with the value ~0.8-1.0 g cm-3 derived from the binary JT system, (617) Patroclus-Menoetius system.

Keywords: jupiter trojans; asteroid rotation; time series analysis; time domain astronomy
Regulation of Proton-α Differential Flow by Compressive Fluctuations and Ion-scale Instabilities in the Solar Wind

Large-scale compressive slow-mode-like fluctuations can cause variations in the density, temperature, and magnetic-field magnitude in the solar wind. In addition, they also lead to fluctuations in the differential flow U pα between α-particles and protons (p), which is a common source of free energy for the driving of ion-scale instabilities. If the amplitude of the compressive fluctuations is sufficiently large, the fluctuating U pα intermittently drives the plasma across the instability threshold, leading to the excitation of ion-scale instabilities and thus the growth of corresponding ion-scale waves. The unstable waves scatter particles and reduce the average value of U pα . We propose that this "fluctuating-drift effect" maintains the average value of U pα well below the marginal instability threshold. We model the large-scale compressive fluctuations in the solar wind as long-wavelength slow-mode waves using a multi-fluid model. We numerically quantify the fluctuating-drift effect for the Alfvén/ion-cyclotron and fast-magnetosonic/whistler instabilities. We show that measurements of the proton-α differential flow and compressive fluctuations from the Wind spacecraft are consistent with our predictions for the fluctuating-drift effect. This effect creates a new channel for a direct cross-scale energy transfer from large-scale compressions to ion-scale fluctuations.

Keywords: heliosphere; solar wind; space plasmas
Near-infrared Coronal Line Observations of Dwarf Galaxies Hosting AGN-driven Outflows

We have obtained Keck near-infrared spectroscopy of a sample of nine M⋆ < 1010 M⊙ dwarf galaxies to confirm active galactic nuclei (AGNs) activity and the presence of galaxy-wide, AGN-driven outflows through coronal line (CL) emission. We find strong CL detections in 5/9 galaxies (55%) with line ratios incompatible with shocks, confirming the presence of AGNs in these galaxies. Similar CL detection rates are found in larger samples of more massive galaxies hosting type 1 and 2 AGNs. We investigate the connection between the CLs and galaxy-wide outflows by analyzing the kinematics of the CL region as well as the scaling of gas velocity with ionization potential of different CLs. In addition, using complementary Keck Cosmic Web Imager observations of these objects, we find that the outflow velocities measured in [Si VI] are generally faster than those seen in [O III]. The galaxies with the fastest outflows seen in [O III] also have the highest [Si VI] luminosity. The lack of J-band CN absorption features, which are often associated with younger stellar populations, provides further evidence that these outflows are driven by AGNs in low-mass galaxies.

Keywords: active galactic nuclei; agn host galaxies; dwarf galaxies; seyfert galaxies; near infrared astronomy; active galaxies; galaxy evolution
Orbital Torus Imaging: Using Element Abundances to Map Orbits and Mass in the Milky Way

Many approaches to galaxy dynamics assume that the gravitational potential is simple and the distribution function is time invariant. Under these assumptions there are traditional tools for inferring potential parameters given observations of stellar kinematics (e.g., Jeans models). However, spectroscopic surveys measure many stellar properties beyond kinematics. Here we present a new approach for dynamical inference, Orbital Torus Imaging, which makes use of kinematic measurements and element abundances (or other invariant labels). We exploit the fact that, in steady state, stellar labels vary systematically with orbit characteristics (actions), yet must be invariant with respect to orbital phases (conjugate angles). The orbital foliation of phase space must therefore coincide with surfaces along which all moments of all stellar label distributions are constant. Both classical-statistics and Bayesian methods can be built on this; these methods will be more robust and require fewer assumptions than traditional tools because they require no knowledge of the (spatial) survey selection function and do not involve second moments of velocity distributions. We perform a classical-statistics demonstration with red giant branch stars from the APOGEE surveys: we model the vertical orbit structure in the Milky Way disk to constrain the local disk mass, scale height, and the disk-halo mass ratio (at fixed local circular velocity). We find that the disk mass can be constrained (naïvely) at the few-percent level with Orbital Torus Imaging using only eight element-abundance ratios, demonstrating the promise of combining stellar labels with dynamical invariants.

Keywords: galaxy dynamics; milky way dynamics; stellar kinematics; astrostatistics; chemical abundances; spectroscopy
Anomalous Intensities in the Infrared Emission of CH+ Explained by Quantum Nuclear Motion and Electric Dipole Calculations

The unusual infrared emission patterns of CH+, recently detected in the planetary nebula NGC 7027, are examined theoretically with high-accuracy rovibrational wavefunctions and ab initio dipole moment curves. The calculated transition dipole moments quantitatively reproduce the observed J-dependent intensity variation, which is ascribed to underlying centrifugal distortion-induced interference effects. We discuss the implications of this anomalous behavior for astrochemical modeling of CH+ production and excitation, and provide a simple expression to estimate the magnitude of this effect for other light diatomic molecules with small dipole derivatives.

Keywords: molecular spectroscopy; line intensities; transition probabilities