adsabs/SciX_UAT_keywords huggingface dataset:
High-resolution Spectroscopy of SN 2023ixf's First Week: Engulfing the Asymmetric Circumstellar Material

We present a series of high-resolution echelle spectra of SN 2023ixf in M101, obtained nightly during the first week or so after discovery using PEPSI on the Large Binocular Telescope. Na I D absorption in these spectra indicates a host reddening of E(B - V) = 0.031 mag and a systemic velocity of +7 km s-1 relative to the average redshift of M101. Dramatic changes are seen in the strength and shape of strong emission lines emitted by circumstellar material (CSM), including He II λ4686, C IV λλ5801,5811, Hα, and N IV λλ7109,7123. In general, these narrow lines broaden to become intermediate-width lines before disappearing from the spectrum within a few days, indicating a limited extent to the dense CSM of around 20-30 au (or ≲1014.7 cm). Hα persists in the spectrum for about a week as an intermediate-width emission line with P Cyg absorption at 700-1300 km s-1 arising in the post-shock shell of swept-up CSM. Early narrow emission lines are blueshifted and indicate an expansion speed in the pre-shock CSM of about 115 km s-1, but with even broader emission in higher-ionization lines. This is faster than the normal winds of red supergiants, suggesting some mode of eruptive mass loss from the progenitor or radiative acceleration of the CSM. A lack of narrow blueshifted absorption suggests that most of the CSM is not along our line of sight. This and several other clues indicate that the CSM of SN 2023ixf is significantly aspherical. We find that CSM lines disappear after a few days because the asymmetric CSM is engulfed by the supernova photosphere.

Keywords: circumstellar matter; supernovae
The Hidden Companion in J1527: A 0.69 Solar-mass White Dwarf?

Finding nearby neutron stars can probe the supernova and metal-enrichment histories near our solar system. Recently, Lin et al. reported an exciting neutron star candidate, Two Micron All Sky Survey J15274848+3536572 (hereafter J1527), with a small Gaia distance of 118 pc. They claim that J1527 harbors an unseen neutron star candidate with an unusually low mass of 0.98 ± 0.03 M ⊙. In this work, we use the Canada–France–Hawaii Telescope high-resolution spectrum to measure J1527's orbital inclination independently. Our spectral fitting suggests an orbital inclination of 63° ± 2°. Instead, by fitting a complex hybrid variability model consisting of the ellipsoidal-variation component and the starspot modulation to the observed light curve, Lin et al. obtain an orbital inclination of ${45.2}_{-0.20}^{+0.13}$ degrees. We speculate that the orbital inclination obtained by the light-curve fitting is underestimated since J1527's light curves are obviously not pure ellipsoidal variations. According to our new inclination (i ∼ 63°), the mass of the unseen compact object is reduced to 0.69 ± 0.02 M ⊙, which is as massive as a typical white dwarf.

Keywords: close binary stars; compact objects; inclination
On the Energy Sources of the Most Luminous Supernova ASASSN-15lh

In this paper, we investigate the energy-source models for the most luminous supernova ASASSN-15lh. We revisit the ejecta-circumstellar medium (CSM) interaction (CSI) model and the CSI plus magnetar spin-down with full gamma-ray/X-ray trapping, which were adopted by Chatzopoulos et al., and find that the two models cannot fit the bolometric light curve (LC) of ASASSN-15lh. Therefore, we consider a CSI plus magnetar model with the gamma-ray/X-ray leakage effect to eliminate the late-time excess of the theoretical LC. We find that this revised model can reproduce the bolometric LC of ASASSN-15lh. Moreover, we construct a new hybrid model (i.e., the CSI plus fallback model), and find that it can also reproduce the bolometric LC of ASASSN-15lh. Assuming that the conversion efficiency (η) of fallback accretion to an outflow is typically ∼10-3, we derive that the total mass accreted is ∼3.9 M⊙. The inferred CSM mass in the two models is rather large, indicating that the progenitor could have experienced an eruption of hydrogen-poor materials followed by an energetic core-collapse explosion leaving behind a magnetar or a black hole.

Keywords: magnetars; black holes; circumstellar matter; supernovae; neutron stars
Absorption in the Spectrum of a Background AGN by C II* by the Supernova Remnant G354-33

A number of very large, very faint supernova remnants (SNRs) have been discovered in the past few years. Those in the Galactic halo occur in low density gas, so they might be more easily observed in absorption than in emission. The SNR G354-33 is a shell of faint UV and optical filaments about 10° in diameter. Here we point out that a spectrum of the QSO J2017-4516 used study the galaxy cluster J2016-4517 shows an absorption line from the excited fine structure level of C II at ‑50 km s‑1. Absorption features of Si II and Si III are also seen at this velocity. The observed column density compares well with shock wave models. Doppler shifted C II* absorption features provide an excellent means to find and characterize SNR shocks because they arise from compressed gas.

Keywords: supernova remnants; interstellar line absorption; shocks
The Critical Dark Matter Halo Mass for Population III Star Formation: Dependence on Lyman-Werner Radiation, Baryon-dark Matter Streaming Velocity, and Redshift

A critical dark matter halo mass (Mcrit) for Population III stars can be defined as the typical minimum halo mass that hosts sufficient cold-dense gas required for the formation of the first stars. The presence of Lyman-Werner (UV) radiation, which can dissociate molecular hydrogen, and the baryon-dark matter streaming velocity both delay the formation of Population III stars by increasing Mcrit. In this work, we constrain Mcrit as a function of Lyman-Werner flux (including self-shielding), baryon-dark matter streaming, and redshift using cosmological simulations with a large sample of halos utilizing the adaptive mesh refinement code ENZO. We provide a fit for Mcrit as a function of these quantities, which we expect to be particularly useful for semi-analytical models of early galaxy formation. In addition, we find (i) the measured redshift dependence of Mcrit in the absence of radiation or streaming is (1 + z)-1.58, consistent with a constant virial temperature; (ii) increasing the UV background increases Mcrit while steepening the redshift dependence, up to (1 + z)-5.7; (iii) baryon-dark matter streaming boosts Mcrit but flattens the dependence on redshift; (iv) the combination of the two effects is not simply multiplicative.

Keywords: population iii stars; high-redshift galaxies; cosmology
HST/STIS Capability for Love Number Measurement of WASP-121b

Data from transit light curves, radial velocity, and transit timing observations can be used to probe the interiors of exoplanets beyond the mean density, by measuring the Love numbers h2 and k2. The first indirect estimate of k2 for an exoplanet from radial velocity and transit timing variation observations has been performed by taking advantage of the years-spanning baseline. Not a single measurement of h2 has been achieved from transit light curves, mostly because the photometric precision of current observing facilities is still too low. We show that the Imaging Spectrograph instrument onboard the Hubble Space Telescope (HST) could measure h2 of the hot Jupiter WASP-121b if only a few more observations were gathered. We show that a careful treatment of the noise and stellar limb darkening (LD) must be carried out to achieve a measurement of h2. In particular, we find that the impact of the noise modeling on the estimation of h2 is stronger than that of the LD modeling. In addition, we emphasize that the wavelet method for correlated noise analysis can mask limb brightening. Finally, using currently available data, we briefly discuss the tentative measurement of ${h}_{2}={1.39}_{-0.81}^{+0.71}$ in terms of interior structure. Additional observations would further constrain the interior of WASP-121b and possibly provide insights on the physics of inflation. The possibility of using the approach presented here with the HST provides a bridge before the high-quality data to be returned by the James Webb Space Telescope and PLATO telescope in the coming decade.

Keywords: hst photometry; planetary interior; hot jupiters
Populations of Magnetized Filaments in the Intracluster Medium and the Galactic Center

Magnetized radio filaments are found in abundance in the inner few hundred parsecs of our galaxy. Progress in understanding this population of filaments has been slow over the last few decades, in part due to a lack of detection elsewhere in the galaxy or in external galaxies. Recent highly sensitive radio continuum observations of radio galaxies in galaxy clusters have revealed remarkable isolated filamentary structures in the intracluster medium (ICM) that are linked to radio jets, tails, and lobes. The origin of this class of filaments is not understood either. Here, we argue that the underlying physical mechanisms responsible for the creation of the two populations are the same because of their similarities in morphology, spacing between the filaments, aspect ratio, and magnetic energy densities to the thermal pressure of the medium and that both populations have undergone synchrotron aging. These similarities provide an opportunity to investigate the physical processes in the interstellar medium (ISM) and ICM for the first time. We consider that the origin of the filaments in both the Galactic center and ICM is a result of the interaction of a large-scale wind with clouds, or the filaments arise through the stretching and collection of field lines by turbulence in a weakly magnetized medium. We examine these ideas in four radio galaxy filaments associated with four radio galaxies-IC 40B, IC 4496, J1333-3141, ESO 137-006-and argue that much can be understood in the future by comparing these two populations of filaments.

Keywords: fanaroff-riley radio galaxies; galactic center; cosmic rays; galaxy clusters; intracluster medium; interstellar magnetic fields
Terminator Habitability: The Case for Limited Water Availability on M-dwarf Planets

Rocky planets orbiting M-dwarf stars are among the most promising and abundant astronomical targets for detecting habitable climates. Planets in the M-dwarf habitable zone are likely synchronously rotating, such that we expect significant day-night temperature differences and potentially limited fractional habitability. Previous studies have focused on scenarios where fractional habitability is confined to the substellar or "eye" region, but in this paper we explore the possibility of planets with terminator habitability, defined by the existence of a habitable band at the transition between a scorching dayside and a glacial nightside. Using a global climate model, we show that for water-limited planets it is possible to have scorching temperatures in the "eye" and freezing temperatures on the nightside, while maintaining a temperate climate in the terminator region, due to reduced atmospheric energy transport. On water-rich planets, however, increasing the stellar flux leads to increased atmospheric energy transport and a reduction in day-night temperature differences, such that the terminator does not remain habitable once the dayside temperatures approach runaway or moist greenhouse limits. We also show that while water-abundant simulations may result in larger fractional habitability, they are vulnerable to water loss through cold trapping on the nightside surface or atmospheric water vapor escape, suggesting that even if planets were formed with abundant water, their climates could become water-limited and subject to terminator habitability.

Keywords: exoplanets; habitable planets; ocean planets; planetary atmospheres; planetary science; exoplanet atmospheres; planetary climates; m dwarf stars; m stars; atmospheric clouds; habitable zone
Application of Convolutional Neural Networks to Identify Stellar Feedback Bubbles in CO Emission

We adopt the deep learning method called the Convolutional Approach to Shell Identification (casi) and extend it to 3D (casi-3d) to identify signatures of stellar feedback in molecular line spectra. We use magnetohydrodynamics simulations modeling the impact of stellar winds in a turbulent molecular cloud to generate synthetic 13CO (J = 1 - 0) observations. We train two casi-3d models: ME1 predicts only the position of feedback, while MF predicts the fraction of the mass coming from feedback in each voxel. We adopt 75% of the synthetic observations as the training set and assess the accuracy of the two models with the remaining data. Both models identify bubbles in simulated data within 5% error. We use bubbles previously visually identified in Taurus in 13CO to validate the models and show that both perform well on the highest confidence bubbles. Models ME1 and MF predict total feedback gas mass of 2894 M⊙ and 302 M⊙, respectively. After correcting for missing energy due to the limited velocity range, model ME1 predicts feedback kinetic energies of 4.0 × 1046 erg and 1.5 × 1047 erg with and without subtracting the cloud velocity gradient. Model MF predicts feedback kinetic energies of 9.6 × 1045 erg and 2.8 × 1046 erg with and without subtracting the cloud velocity gradient. Model ME1 predicts bubble locations and properties consistent with previous visual identifications. However, model MF demonstrates that feedback properties computed using visual identifications significantly overestimate feedback impact, due to line-of-sight confusion and contamination from background and foreground gas.

Keywords: stellar wind bubbles; interstellar medium; molecular clouds; interstellar clouds; astronomy data analysis; astronomical methods; convolutional neural networks; neural networks; astrostatistics; interdisciplinary astronomy; stellar feedback; star formation
Optical Variability Power Spectrum Analysis of Blazar Sources on Intranight Timescales

We report the first results of a systematic investigation to characterize blazar variability power spectral densities (PSDs) at optical frequencies using densely sampled (5-15 minutes of integration time), high photometric accuracy (≲0.2%-0.5%) R-band intranight light curves, covering timescales ranging from several hours to ∼15 minutes. Our sample consists of 14 optically bright blazars—nine BL Lacertae objects and five flat-spectrum radio quasars (FSRQs)—which have shown statistically significant variability during 29 monitoring sessions. We model the intranight PSDs as simple power laws and derive the best-fit slope along with the uncertainty using the "power spectral response" method. Our main results are as follows: (1) in 19 out of 29 monitoring sessions, the intranight PSDs show an acceptable fit to simple power laws at a rejection confidence ≤90%; (2) for these 19 instances, the PSD slopes show a wide range of 1.4 to 4.0, consistent with the statistical characters of red-noise (slope ∼ 2) and black-noise (slope ≥ 3) stochastic processes; (3) the average PSD slopes for the BL Lac objects and FSRQs are indistinguishable from one another; and (4) the normalization of intranight PSDs for individual blazar sources monitored on more than one occasion turns out to be consistent with one another with a few exceptions. The average PSD slope, 2.9 ± 0.3 (1σ uncertainty), is steeper than that of red noise-type variability found on longer timescales (many decades to days), indicative of a cutoff in the variability spectrum on timescales around a few days at the synchrotron frequencies of the emission spectrum.

Keywords: active galaxies; non-thermal radiation sources; blazars; relativistic jets
Photometric Study and Absolute Parameter Estimation of Six Totally Eclipsing Contact Binaries

High precision CCD observations of six totally eclipsing contact binaries were presented and analyzed. It is found that only one target is an A-type contact binary (V429 Cam), while the others are W-type contact ones. By analyzing the times of light minima, we discovered that two of them exhibit secular period increase while three manifest long-term period decrease. For V1033 Her, a cyclic variation superimposed on the long-term increase was discovered. By comparing the Gaia distances with those calculated by the absolute parameters of 173 contact binaries, we found that the Gaia distance can be applied to estimate the absolute parameters for most contact binaries. The absolute parameters of our six targets were estimated using their Gaia distances. The evolutionary status of contact binaries was studied, and we found that the A- and W-subtype contact binaries may have different formation channels. The relationship between the spectroscopic and photometric mass ratios for 101 contact binaries was presented. It was discovered that the photometric mass ratios are in good agreement with the spectroscopic ones for almost all of the totally eclipsing systems, which is corresponding to the results derived by Pribulla et al. and Terrell & Wilson.

Keywords: close binary stars; eclipsing binary stars; stellar evolution; fundamental parameters of stars
Ultra-diffuse Galaxies as Extreme Star-forming Environments. II. Star Formation and Pressure Balance in H I-rich UDGs

In addition to occupying the extreme, diffuse tail of the dwarf galaxy population, ultra-diffuse galaxies (UDGs) are themselves a key laboratory in which to study star formation in extreme low-density environments. In the second paper of this series, we compare the spatially resolved star formation activity of 22 H I-selected UDGs and 21 "normal" dwarf galaxies within 120 Mpc to predictions within the pressure-regulated, feedback-modulated (PRFM) theory of star formation. To do so, we employ a joint spectral energy distribution fitting method that allows us to estimate star formation rate and stellar mass surface density from UV-optical imaging. We find that the PRFM framework extends successfully to the UDG regime-although the UDGs in our sample show unusually low star formation rate surface densities given their H I content, this low star formation efficiency can be naturally explained by the diffuse structure of the UDGs. In fact, when cast in the PRFM framework, the relationship between midplane pressure and star formation in the UDG sample is in good agreement not only with the "normal" dwarf reference sample, but also with measurements from more massive galaxies. Our results suggest that despite their low star formation efficiencies, the H I-rich UDGs need not be forming stars in an exotic manner. We also find that the UDGs are likely H2 poor compared even to the overall dwarf population.

Keywords: low surface brightness galaxies; dwarf galaxies; star formation
Further X-Ray Timing Investigations on the 2 hr Periodicity of PSR J1311-3430

We investigate the 2 hr X-ray periodicity of the black widow system PSR J1311-3430 observed in 2018. In this study, we applied a simulation method to find the period and error, which results in 7400 ± 60 s. The period is slightly shorter and the uncertainty is slightly higher than that reported in De Luca et al. Besides, we performed a phased-resolved spectral analysis, and find that the system did not show significant spectral variability over a cycle.

Keywords: binary pulsars; low-mass x-ray binary stars; period search; high energy astrophysics; x-ray astronomy; x-ray photometry
Markov Chain Monte Carlo Predictions of Neutron-rich Lanthanide Properties as a Probe of r-process Dynamics

Lanthanide element signatures are key to understanding many astrophysical observables, from merger kilonova light curves to stellar and solar abundances. To learn about the lanthanide element synthesis that enriched our solar system, we apply the statistical method of Markov Chain Monte Carlo to examine the nuclear masses capable of forming the r-process rare-earth abundance peak. We describe the physical constraints we implement with this statistical approach and demonstrate the use of the parallel chains method to explore the multidimensional parameter space. We apply our procedure to three moderately neutron-rich astrophysical outflows with distinct types of r-process dynamics. We show that the mass solutions found are dependent on outflow conditions and are related to the r-process path. We describe in detail the mechanism behind peak formation in each case. We then compare our mass predictions for neutron-rich neodymium and samarium isotopes to the latest experimental data from the CPT at CARIBU. We find our mass predictions given outflows that undergo an extended (n,γ)⇄(γ,n) equilibrium to be those most compatible with both observational solar abundances and neutron-rich mass measurements.

Keywords: nucleosynthesis; solar abundances; nuclear astrophysics; neutron stars; bayesian statistics; chi-squared statistic
The Implications of TeV-detected GRB Afterglows for Acceleration at Relativistic Shocks

Motivated by the detection of very-high-energy (VHE) gamma rays deep in the afterglow emission of a gamma-ray burst (GRB), we revisit predictions of the maximum energy to which electrons can be accelerated at a relativistic blast wave. Acceleration at the weakly magnetized forward shock of a blast wave can be limited by either the rapid damping of turbulence generated behind the shock, the effect of a large-scale ambient magnetic field, or radiation losses. Within the confines of a standard, single-zone, synchrotron self-Compton (SSC) model, we show that observations of GRB 190829A rule out a rapid damping of the downstream turbulence. Furthermore, simultaneous fits to the X-ray and TeV gamma-ray emission of this object are not possible unless the limit on acceleration imposed by the ambient magnetic field is comparable to or weaker than that imposed by radiation losses. This requires the dominant length scale of the turbulence behind the shock to be larger than that implied by particle-in-cell simulations. However, even then, Klein-Nishina effects prevent production of the hard VHE gamma-ray spectrum suggested by observations. Thus, TeV observations of GRB afterglows, though still very sparse, are already in tension with the SSC emission scenario.

Keywords: high energy astrophysics; gamma-ray bursts
A Possible 3 yr Quasi-periodic Oscillation in γ-Ray Emission from the FSRQ S5 1044+71

Variability is a typical observation feature of Fermi blazars, which sometimes shows quasi-periodic oscillation (QPO). In this work, we obtain 5 day binned light curves (with a time coverage of ~12.9 yr) for S5 1044+71, based on Fermi-LAT data; apply five different methods-Date-compensated Discrete Fourier Transform, Jurkevich, Lomb-Scargle Periodogram, a Fortran 90 program, and the Weighted Wavelet Z-transform-to the γ-ray light curve; and find a possible QPO of 3.06 ± 0.43 yr at the significance level of ~3.6σ. A binary black hole model, including an accretion model and a dual-jet model, is used to explain this quasi-periodic variability. We also estimate the Doppler factors and the apparent velocity for the two jet components. We speculate that this γ-ray quasi-periodic modulation suggests the presence of a binary supermassive black hole in S5 1044+71.

Keywords: active galactic nuclei; gamma-ray sources; quasars