adsabs/SciX_UAT_keywords huggingface dataset:
Studies of Cepheus X-4 during the 2018 Outburst Observed with AstroSat

We present timing and spectral results for the 2018 outburst of Cepheus X-4, observed twice by AstroSat at luminosities of 2.04 × 1037 erg s-1 and 1.02 × 1037 erg s-1. The light curves showed strong pulsation and co-related X-ray intensity variation in the SXT (0.5-8.0 keV) and LAXPC (3-60 keV) energy bands. The spin period and spin-down rate of the pulsar were determined from two observations to be 65.35080 ± 0.00014 s and (-2.10 ± 0.8) × 10-12 Hz s-1 at epoch MJD 58301.61850, and 65.35290 ± 0.00017 s and (-1.6 ± 0.8) × 10-12 Hz s-1 at epoch MJD 58307.40211. Pulse shape studies with AstroSat showed energy- and intensity-dependent variations. The pulsar showed an overall continuous spin-down over 30 yr at an average rate of (-2.455 ± 0.004) × 10-14 Hz s-1, attributed to the propeller effect in the subsonic regime of the pulsar, in addition to variations during its outburst activities. Spectra between the 0.7 keV and 55 keV energy bands were well fitted by two continuum models, an absorbed compTT model and an absorbed power law with a Fermi-Dirac cutoff (FD-cutoff) model with a blackbody. These were combined with an iron emission line and a cyclotron absorption line. The prominent cyclotron resonance scattering features with a peak absorption energy of ${30.48}_{-0.34}^{+0.33}$ keV and ${30.68}_{-0.44}^{+0.45}$ keV for the FD-cutoff model and ${30.46}_{-0.28}^{+0.32}$ keV and ${30.30}_{-0.34}^{+0.36}$ keV for the compTT model were detected during two AstroSat observations. When compared with earlier results, these showed long-term stability of an average value of 30.23 ± 0.22 keV with wide variation in source luminosity. The pulsar showed pulse phase as well as luminosity dependent variations in the cyclotron line energy and width and in the plasma optical depth of its spectral continuum.

Keywords: accretion; high mass x-ray binary stars; be stars; stellar accretion disks; pulsars; binary pulsars; magnetic fields; neutron stars
Characterizing Extreme Emission Line Galaxies. II. A Self-consistent Model of Their Ionizing Spectrum

Observations of high-redshift galaxies (z > 5) have shown that these galaxies have extreme emission lines with equivalent widths much larger than their local star-forming counterparts. Extreme emission line galaxies (EELGs) in the nearby universe are likely analogs to galaxies during the Epoch of Reionization and provide nearby laboratories to understand the physical processes important to the early universe. We use Hubble Space Telescope/Cosmic Origins Spectrograph and Large Binocular Telescope/Multi-Object Double Spectrographs spectra to study two nearby EELGs, J104457 and J141851. The far-UV spectra indicate that these two galaxies contain stellar populations with ages ≲10 Myr and metallicities ≤0.15 Z ⊙. We use photoionization modeling to compare emission lines from models of single-age bursts of star formation to observed emission lines and find that the single-age bursts do not reproduce high-ionization lines including [O III] or very-high-ionization lines like He II or O IV]. Photoionization modeling using the stellar populations fit from the UV continuum similarly is not capable of reproducing the very-high-energy emission lines. We add a blackbody to the stellar populations fit from the UV continuum to model the necessary high-energy photons to reproduce the very-high-ionization lines of He II and O IV]. We find that we need a blackbody of 80,000 K and ~45%-55% of the luminosity from the blackbody and young stellar population to reproduce the very-high-ionization lines while simultaneously reproducing the low-, intermediate-, and high-ionization emission lines. Our self-consistent model of the ionizing spectra of two nearby EELGs indicates the presence of a previously unaccounted-for source of hard ionizing photons in reionization analogs. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NASA 5-26555.

Keywords: dwarf galaxies; ultraviolet astronomy; galaxy chemical evolution; galaxy spectroscopy; high-redshift galaxies; emission line galaxies
The Hubble Deep Hydrogen Alpha (HDHα) Project. I. Catalog of Emission-line Galaxies

We present the first results of the Hubble Deep Hydrogen Alpha (HDHα) project, which analyzes the space-borne deep Hα narrowband imaging data in the GOODS-S region. The HDHα data comprises 72 orbits' images taken with the Hubble Space Telescope (HST) Advanced Camera for Surveys/Wide Field Channel F658N filter. The exposure time varies across a total area of ∼76.1 arcmin2, adding up to a total exposure time of 195.7 ks, among which 68.8 ks are spent in the deepest region. These images are aligned, reprojected, and combined to have the same pixel grid as the Hubble Legacy Fields. The scientific goals of the HDHα include establishing a sample of emission-line galaxies (ELGs) including [O III] emitters at z ∼ 0.3, [O II] emitters at z ∼ 0.8, and Lyα emitters (LAEs) at z ∼ 4.4, studying the line morphology of ELGs with high resolution imaging data, and statistically analyzing the line luminosity functions and line equivalent-width distributions of ELGs selected with HST. Furthermore, the HDHα project enhances the legacy value of the GOODS-S field by contributing the first HST-based narrowband image to the existing data sets, which includes the HST broadband data and other ancillary data from X-ray to radio taken by other facilities. In this paper, we describe the data reduction process of the HDHα, select ELGs based on HST's F658N and broadband data, validate the redshifts of the selected candidates by crossmatching with the public spectroscopic catalogs in the GOODS-S, and present a final catalog of the confirmed [O III] emitters at z ∼ 0.3, [O II] emitters at z ∼ 0.8, and LAEs at z ∼ 4.4.

Keywords: emission line galaxies; lyman-alpha galaxies; narrow band photometry; hubble space telescope
Monochromatic Globular Clusters as a Critical Test of Formation Models for the Dark Matter-deficient Galaxies NGC 1052-DF2 and NGC 1052-DF4

It was recently proposed that the dark matter-deficient ultradiffuse galaxies DF2 and DF4 in the NGC 1052 group could be the products of a "bullet dwarf" collision between two gas-rich progenitor galaxies. In this model, DF2 and DF4 formed at the same time in the immediate aftermath of the collision, and a strong prediction is that their globular clusters should have nearly identical stellar populations. Here we test this prediction by measuring accurate V 606 - I 814 colors from deep HST/ACS imaging. We find that the clusters are extremely homogeneous. The mean color difference between the globular clusters in DF2 and DF4 is ΔDF2-DF4 = -0.003 ± 0.005 mag, and the observed scatter for the combined sample of 18 clusters with M 606 < -8.6 in both galaxies is σ obs = 0.015 ± 0.002 mag. After accounting for observational uncertainties and stochastic cluster-to-cluster variation in the number of red giants, the remaining scatter is ${\sigma }_{\mathrm{intr}}={0.008}_{-0.006}^{+0.005}$ mag. Both the color difference and the scatter are an order of magnitude smaller than in other dwarf galaxies, and we infer that the bullet scenario passes an important test that could have falsified it. No other formation models have predicted this extreme uniformity of the globular clusters in the two galaxies. We find that the galaxies themselves are slightly redder than the clusters, consistent with a previously measured metallicity difference. Numerical simulations have shown that such differences are expected in the bullet scenario, as the galaxies continued to self-enrich after the formation of the globular clusters.

Keywords: dark matter; dwarf galaxies; globular star clusters
Neglect of Small Spots Remains an Explanation of the Difference Between SOON and RGO Spot Areas

I point out that the objection of Györi et al. to my finding that neglect of small spots could explain much of the puzzling difference between Royal Greenwich Observatory and Solar Optical Observation Network spot areas is not valid because their analysis was limited to only 1974–76, when activity was low. The 40%–50% difference occurs only at higher activity levels.

Keywords: delta sunspots
Biases and Cosmic Variance in Molecular Gas Abundance Measurements at High Redshift

Recent deep millimeter-wave surveys have attempted to measure the carbon monoxide (CO) luminosity function and mean molecular gas density through blind detections of CO emission lines. While the cosmic star formation rate density is now constrained in fields of hundreds of square arcminutes or more, molecular gas studies have been limited to ≤50 arcmin2. These small fields result in significant biases that have not been accounted for in published results. To quantify these biases, we assign CO luminosities to halos in cosmological simulations to produce mock observations for a range of field sizes. We find that fields of ≲10 arcmin2 alter the recovered shape of the luminosity function, causing underestimates of the number of bright objects. Our models suggest that current surveys are sensitive enough to detect sources responsible for approximately half of the cosmic molecular gas density at high redshift. However, uncertainties in the gas density measurement are large, and cosmic variance may double the uncertainty claimed in these surveys. As a result, the field size needed to detect redshift evolution in the molecular gas at high confidence may be more than one order of magnitude larger than what current surveys have achieved. Shot power intensity mapping measurements are particularly sensitive to Poisson variance and require yet larger areas to constrain the gas density or its evolution. We provide a simple prescription for approximating uncertainty in total CO emission as a function of survey area and redshift for both direct detection and intensity mapping surveys.

Keywords: galaxy evolution; high-redshift galaxies; luminosity function; molecular gas
Temperature of the Polar Inner Heliosheath: Connection to Solar Activity

We study the thermodynamics of the plasma protons in the polar regions of the inner heliosheath (IHS) and its connection with solar activity over solar cycle 24. First, we express the thermodynamic parameters of this plasma with respect to the year of energetic neutral atom (ENA) creation and perform a statistical analysis of temperatures, in order to provide a more precise characterization of the thermodynamics of IHS. Then, we perform an autocorrelation between the IHS temperature and the solar activity, using the proxies of sunspot number and fractional area of the polar coronal holes. We show that there is (i) high correlation between the time series of IHS proton temperatures and sunspot number, which is maximized for a time delay of τ ~ 2.5 yr for both the north and south polar regions combined; (ii) high negative correlation between the temperature of the proton plasma in the north and south with the coronal hole fractional areas, where the time delay for the two poles combined is τ ~ 2.71 ± 0.15 yr; and (iii) an asymmetry of a time-delay difference between the poles ~0.22 yr, indicating that the southern polar ENA source region is ~19 au closer than the northern one for a solar wind plasma protons of bulk speed of ~400 km s-1. The findings demonstrate a connection between the IHS thermodynamics and solar activity through the solar wind, primarily manifested by the coronal holes expanding near solar minimum, which drives the expansion of fast solar wind over larger angles from high down to middle latitudes in the IHS.

Keywords: space plasmas; heliosheath; heliosphere; solar cycle
Space Telescope and Optical Reverberation Mapping Project. IX. Velocity-Delay Maps for Broad Emission Lines in NGC 5548

In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity-delay maps for the prominent broad emission lines (Lyα, C IV, He II, and Hβ) in the spectrum of NGC 5548. These are the most detailed velocity-delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He II response inside 5-10 lt-day has a broad single-peaked velocity profile. The Lyα, C IV, and Hβ responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s-1 in the 10-20 lt-day delay range. An incomplete ellipse in the velocity-delay plane is evident in Hβ. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay $\tau =(R/c)(1-\sin i)\approx 5$ days gives the inclination i ≈ 45°. The inferred black hole mass is MBH ≈ 7 × 107 M⊙. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the "BLR Holiday" identified in previous work. Moreover, a helical "Barber-Pole" pattern, with stripes moving from red to blue across the C IV and Lyα line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.

Keywords: active galaxies; astrophysical black holes; supermassive black holes; active galactic nuclei; reverberation mapping
Toward RNA Life on Early Earth: From Atmospheric HCN to Biomolecule Production in Warm Little Ponds

The origin of life on Earth involves the early appearance of an information-containing molecule such as RNA. The basic building blocks of RNA could have been delivered by carbon-rich meteorites or produced in situ by processes beginning with the synthesis of hydrogen cyanide (HCN) in the early Earth's atmosphere. Here, we construct a robust physical and nonequilibrium chemical model of the early Earth's atmosphere. The atmosphere is supplied with hydrogen from impact degassing of meteorites, water evaporated from the oceans, carbon dioxide from volcanoes, and methane from undersea hydrothermal vents, and in it lightning and external UV-driven chemistry produce HCN. This allows us to calculate the rain-out of HCN into warm little ponds (WLPs). We then use a comprehensive numerical model of sources and sinks to compute the resulting abundances of nucleobases, ribose, and nucleotide precursors such as 2-aminooxazole resulting from aqueous and UV-driven chemistry within them. We find that 4.4 billion years ago the limit of adenine concentrations in ponds for habitable surfaces is 0.05 μM in the absence of seepage. Meteorite delivery of adenine to WLPs can provide boosts in concentration by 2-3 orders of magnitude, but these boosts deplete within months by UV photodissociation, seepage, and hydrolysis. The early evolution of the atmosphere is dominated by the decrease in hydrogen due to falling impact rates and atmospheric escape, and the rise of oxygenated species such as OH from H2O photolysis. The source of HCN is predominantly from UV radiation rather than lightning. Our work points to an early origin of RNA on Earth within ~200 Myr of the Moon-forming impact.

Keywords: astrobiology; pre-biotic astrochemistry; planetary atmospheres; earth (planet); lightning
Winds in Star Clusters Drive Kolmogorov Turbulence

Intermediate and massive stars drive fast and powerful isotropic winds that interact with the winds of nearby stars in star clusters and the surrounding interstellar medium (ISM). Wind-ISM collisions generate astrospheres around these stars that contain hot T ∼ 107 K gas that adiabatically expands. As individual bubbles expand and collide they become unstable, potentially driving turbulence in star clusters. In this Letter we use hydrodynamic simulations to model a densely populated young star cluster within a homogeneous cloud to study stellar wind collisions with the surrounding ISM. We model a mass-segregated cluster of 20 B-type young main-sequence stars with masses ranging from 3 to 17 M⊙. We evolve the winds for ∼11 kyr and show that wind-ISM collisions and overlapping wind-blown bubbles around B-stars mix the hot gas and ISM material, generating Kolmogorov-like turbulence on small scales early in its evolution. We discuss how turbulence driven by stellar winds may impact the subsequent generation of star formation in the cluster.

Keywords: interstellar medium; b stars; star clusters
Using cGANs for Anomaly Detection: Identifying Astronomical Anomalies in JWST Imaging

We present a proof of concept for mining JWST imaging data for anomalous galaxy populations using a conditional Generative Adversarial Network (cGAN). We train our model to predict long wavelength NIRcam fluxes (LW: F277W, F356W, F444W between 2.4 and 5.0 μm) from short wavelength fluxes (SW: F115W, F150W, F200W between 0.6 and 2.3 μm) in ~2000 galaxies. We test the cGAN on a population of 37 Extremely Red Objects (EROs) discovered by the CEERS JWST Team. Despite their red long wavelength colors, the EROs have blue short wavelength colors (F150W - F200W ~ 0 mag) indicative of bimodal SEDs. Surprisingly, given their unusual SEDs, we find that the cGAN accurately predicts the LW NIRcam fluxes of the EROs. However, it fails to predict LW fluxes for other rare astronomical objects, such as a merger between two galaxies, suggesting that the cGAN can be used to detect some anomalies. (The source code and trained model (Pearce-Casey 2023) are available at https://github.com/RubyPC/Anomaly_Detection_with_cGANs.)

Keywords: galaxies; galaxy photometry; spectral energy distribution; galaxy mergers; eros
Experimental Validation of Cryobot Thermal Models for the Exploration of Ocean Worlds

Accessing the potentially habitable subsurface waters of Ocean Worlds requires a robotic ice probe (or "cryobot") to traverse tens of kilometers of ice with temperatures ranging from ~100 to 273 K. Designing and planning such a mission requires understanding ice probe behavior as a function of the local environment and design parameters. We present experimental results of two laboratory melt probes in cryogenic (79 K) and warm (253 K) ice. The melt probe tested in warm ice had multiple adjustable heaters, enabling optimization of the system's efficiency. The melt probes tested in cryogenic ice operated in vacuum and had internal tether spools, allowing for experimental confirmation of hole closure and the creation of a pressurized pocket with liquid water around the probe. These melt probes were tested at power levels ranging from 120 to 1135 W, achieving descent speeds between 5.3 and 59 cm hr-1. By analyzing the relationship between power and speed using analytical and high-fidelity numerical models, we demonstrate progress in understanding melt probe performance. We distinguish between the previously confounding terms of probe operational inefficiency and analytical model inaccuracy, allowing us to understand the range of applicability of the analytical models and demonstrate the importance of controlling heat distribution in cryobot design. The validated models show that while numerical models may be required to describe the behavior of short probes descending in limited-size laboratory test beds, the performance of efficient cryobots designed for operation on Ocean Worlds can be predicted by analytical models within 5% error.

Keywords: natural satellites (solar system); ocean planets; galilean satellites; europa; space probes
Glycolonitrile (HOCH2CN) Chemistry in Star-forming Regions

Glycolonitrile (HOCH2CN) is an attractive interstellar prebiotic molecule. Glycolonitrile is considered not only as a possible precursor for glycine but also as a key intermediate for adenine formation. Recently, HOCH2CN was detected toward IRAS 16293-2422 B with the Atacama Large Millimeter/submillimeter Array (ALMA). In this study we perform a comprehensive modeling study on HOCH2CN chemistry under the physical conditions of IRAS 16293-2422 B's cold envelope and hot corino evolutions using the astrochemical code NAUTILUS and the updated gas-grain chemical network. Our studies not only give the main reactions and the favorable physical conditions for the formation of HOCH2CN but also uncover that the observed glycolonitrile in the cold envelope originates from the gradual accumulation of the gas-phase molecules during the ambient cloud, freefall collapse, and warm-up phases of the cold envelope evolution, and in the hot corino it mainly comes from the accumulated ices during the hot corino evolution. Using the updated chemical network, we also conduct chemical simulations under the physical conditions of Sagittarius (Sgr) B2(N) evolution. The simulation results show that varying the cosmic-ray ionization rate is needed to best reproduce the observational upper limits of HOCH2CN and the observed abundances of CNCHO and CH2CNH toward Sgr B2(N). Moreover, we predict that HOCHCNH, OCH2CN, HOCHCN, HOCCNH, OCCNH, and OCCN have high abundances and may be detectable toward IRAS 16293-2422 B and Sgr B2(N).

Keywords: pre-biotic astrochemistry; astrochemistry; interstellar medium; interstellar molecules; theoretical models; interstellar abundances
Evolutionary Origin of Ultralong-period Radio Transients

Recently, two ultralong-period radio transients, GLEAM-X J162759.5-523504.3 (J1627) and GPM J1839-10 (J1839), were discovered with spin periods longer than 1000 s. The origin of these two ultralong-period radio transients is intriguing in understanding the spin evolution of neutron stars (NSs). In this work, we examine whether the interaction between strong magnetized NSs and fallback disks can spin NSs down to the observed ultralong period. Our simulations found that the magnetar + fallback disk model can account for the observed period, period derivative, and X-ray luminosity of J1627 in the quasi-spin-equilibrium stage. To evolve to the current state of J1627, the initial mass-accretion rate of the fallback disk and the magnetic field of the NS are in the range of (1.1–30) × 1024 g s‑1 and (2–5) × 1014 G, respectively. In the active lifetime of the fallback disk, it is impossible for J1839 to achieve the observed upper limit of the period derivative. Therefore, we propose that J1839 may be in the second ejector phase after the fallback disk becomes inactive. Those NSs with a magnetic field of (2–6) × 1014 G and a fallback disk with an initial mass-accretion rate of ∼1024–1026 g s‑1 are possible progenitors of J1839.

Keywords: magnetars; pulsars; magnetic fields