adsabs/SciX_UAT_keywords huggingface dataset:
A Novel Survey for Young Substellar Objects with the W-band Filter. V. IC 348 and Barnard 5 in the Perseus Cloud

We report the discovery of substellar objects in the young star cluster IC 348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the Perseus star-forming complex. The substellar candidates are selected using narrowband imaging, i.e., on and off photometric technique with a filter centered around the water absorption feature at 1.45 μm, a technique proven to be efficient in detecting water-bearing substellar objects. Our spectroscopic observations confirm three brown dwarfs in IC 348. In addition, the source WBIS 03492858+3258064, reported in this work, is the first confirmed brown dwarf discovered toward Barnard 5. Together with the young stellar population selected via near- and mid-infrared colors using the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer, we diagnose the relation between stellar versus substellar objects with the associated molecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud members across the Perseus region, we propose the star formation scenario of the complex under influence of the nearby OB association.

Keywords: open star clusters; brown dwarfs; star forming regions; young stellar objects
Classification of High-resolution Solar Hα Spectra Using t-distributed Stochastic Neighbor Embedding

The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in Hα include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution Hα spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects Hα spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions.

Keywords: solar chromosphere; spectroscopy; radiative transfer; astronomy data analysis; astronomy databases; astrostatistics tools
The Stellar Metallicities of Massive Quiescent Galaxies at 1.0 < z < 1.3 from KMOS + VANDELS

We present a rest-frame UV-optical (λ = 2500-6400 Å) stacked spectrum representative of massive quiescent galaxies at 1.0 < z < 1.3 with log(M */M ⊙) > 10.8. The stack is constructed using VANDELS survey data, combined with new KMOS observations. We apply two independent full-spectral-fitting approaches, measuring a total metallicity [Z/H] = -0.13 ± 0.08 with BAGPIPES and [Z/H] = 0.04 ± 0.14 with ALF, a fall of ~0.2-0.3 dex compared with the local universe. We also measure an iron abundance [Fe/H] = -0.18 ± 0.08, a fall of ~0.15 dex compared with the local universe. We measure the alpha enhancement via the magnesium abundance, obtaining [Mg/Fe] = 0.23 ± 0.12, consistent with galaxies of similar mass in the local universe, indicating no evolution in the average alpha enhancement of log(M */M ⊙) ~ 11 quiescent galaxies over the last ~8 Gyr. This suggests the very high alpha enhancements recently reported for several bright z ~ 1-2 quiescent galaxies are due to their extreme masses, log(M */M ⊙) ≳ 11.5, in accordance with the well-known downsizing trend, rather than being typical of the z ≳ 1 population. The metallicity evolution we observe with redshift (falling [Z/H], [Fe/H], constant [Mg/Fe]) is consistent with recent studies. We recover a mean stellar age of ${2.5}_{-0.4}^{+0.6}$ Gyr, corresponding to a formation redshift ${z}_{\mathrm{form}}={2.4}_{-0.3}^{+0.6}$ . Recent studies have obtained varying average formation redshifts for z ≳ 1 massive quiescent galaxies, and, as these studies report consistent metallicities, we identify models with different star formation histories as the most likely cause. Larger spectroscopic samples from upcoming ground-based instruments will provide precise constraints on ages and metallicities at z ≳ 1. Combining these with precise stellar mass functions for z > 2 quiescent galaxies from the James Webb Space Telescope will provide an independent test of formation redshifts derived from spectral fitting.

Keywords: metallicity; chemical abundances; high-redshift galaxies; quenched galaxies; galaxy spectroscopy
MAMMOTH-Subaru. V. Effects of Cosmic Variance on Lyα Luminosity Functions at z = 2.2-2.3

Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-redshift Universe with a small volume. Such uncertainties produce the field-to-field variance σ g of galaxy numbers in observational astronomy, which significantly affects the luminosity function (LF) measurement of Lyα emitters (LAEs). For most previous Lyα LF studies, σ g is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for z ≈ 2.2 Lyα LFs. The LAE candidates are observed using the narrow band and broad band of the Subaru/Hyper Suprime-Cam in eight independent fields, making the total survey area ≃11.62 deg2 and a comoving volume of ≃8.71 × 106 Mpc3. We report a best-fit Schechter function with parameters α = -1.75 (fixed), ${L}_{\mathrm{Ly}\alpha }^{* }={5.95}_{-0.96}^{+1.22}\times {10}^{42}$ erg s-1, and ${\phi }_{\mathrm{Ly}\alpha }^{* }={5.26}_{-1.27}^{+1.65}$ × 10-4 Mpc-3 for the overall Lyα LFs. After clipping out the regions that may bias the cosmic variance measurements, we calculate σ g by sampling LAEs within multiple pointings on the field image. We investigate the relation between σ g and survey volume V, and fit a simple power-law ${\sigma }_{g}=k\times {\left(\tfrac{V}{{10}^{5}\,{\mathrm{Mpc}}^{3}}\right)}^{\beta }$ . We find best-fit values of $-{1.399}_{-0.156}^{+0.160}$ for β and ${1.249}_{-0.193}^{+0.213}$ for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs is likely larger than that of general star-forming galaxies.

Keywords: lyman-alpha galaxies; cosmology; luminosity function
On the Origin and Evolution of Curvature of the Spectral Energy Distribution of Fermi Bright Blazars

The origin and evolution of spectral curvature in blazar spectral energy distribution (SED) is still unclear. Since the observed SED curvature is related to an intrinsic curvature in emitting electron energy distribution (EED), we study this question by employing a log-parabolic EED with a curvature parameter and peak energy to model the quasi-simultaneous broadband SEDs of selected blazars in the Fermi-LAT Bright AGN Sample using synchrotron and inverse Compton (IC) processes. We find that the log-parabolic IC model can successfully explain the emission in all blazars in our sample. On average, FSRQs have higher magnetic field, Doppler factor, and curvature than BL Lac objects. The BL Lac objects show an anticorrelation between the curvature parameter of the EED and its peak energy, which is a signature of stochastic acceleration. FSRQs do not manifest such correlation and rather show a mild positive relationship between these parameters. This suggests that the evolution of spectral curvature in the BL Lac objects is dominated by a strong stochastic acceleration component, whereas the curvature in FSRQs evolves in a cooling dominated regime due to an additional external Compton component. The strong cooling in FSRQs not only restricts the electron peak energy but also adds extra curvature to the high energy tail of emitting EED. Since the curvature decreases from FSRQs toward high peak BL Lac objects (HBLs), opposite to peak energy, the curvature parameter can be considered a third parameter of the blazar sequence in addition to peak frequency and luminosity.

Keywords: blazars; bl lacertae objects; high energy astrophysics; high-luminosity active galactic nuclei; quasars
Small-scale Magnetic Flux Ropes with Field-aligned Flows via the PSP In Situ Observations

Magnetic flux rope, formed by the helical magnetic field lines, can sometimes maintain its shape while carrying significant plasma flow that is aligned with the local magnetic field. We report the existence of such structures and static flux ropes by applying the Grad-Shafranov-based algorithm to the Parker Solar Probe in situ measurements in the first five encounters. These structures are detected at heliocentric distances, ranging from 0.13 to 0.66 au, in a 4-month time period. We find that flux ropes with field-aligned flows, although they occur more frequently, have certain properties similar to those of static flux ropes, such as the decaying relations of the magnetic fields within structures with respect to heliocentric distances. Moreover, these events are more likely with magnetic pressure dominating over the thermal pressure. About one-third of events are detected in the relatively fast solar wind. Taking into account the high Alfvénicity, we also compare with switchback spikes identified during three encounters and interpret their interrelations. We find that some switchbacks can be detected when the spacecraft traverses flux-rope-like structures. The cross-section maps for selected events are presented via the new Grad-Shafranov-type reconstruction. Finally, the possible evolution of the magnetic flux rope structures in the inner heliosphere is discussed.

Keywords: solar wind; astronomy data analysis; interplanetary turbulence; solar magnetic reconnection; solar magnetic fields
Statistical Study of Gamma-Ray Bursts with Jet Break Features in Multiwavelength Afterglow Emissions

It is generally supposed that a transition from the normal decay phase (decay slope ∼-1) to a steeper phase (decay slope ∼-2) could be suggested as a jet break. The jet opening angle θjet is then calculated from the jet break time of the afterglow light curve. This allows the derivation of the collimation-corrected energy Ejet of those gamma-ray bursts (GRBs). We extensively searched for the GRBs with jet break features from multiwavelength afterglow light curves, and 138 GRBs with significant breaks were collected. The jet break times of those GRBs mainly range from 1000 to 106 s, and the distribution of the collimation-corrected energy Ejet peaks at ∼1050 erg. We also confirmed the Eγ,iso-Ep,i, Ejet-Ep,i and Eγ,iso-θjet relations, and found Eγ,iso-Tj,z-Ep,i relation remains tight with more multiwavelength data. This tight Eγ,iso-Tj,z-Ep,i relation is also conformed by different groups of our selected GRBs in the paper. In addition, another two new and tighter correlations among Ejet-Tj,z-Ep,i are well confirmed for different circumburst mediums in this paper. We suggest that those tight three-parameter correlations are more physical, and could be widely applied to constrain the cosmological parameters.

Keywords: gamma-ray bursts; non-thermal radiation sources
Using Host Galaxy Photometric Redshifts to Improve Cosmological Constraints with Type Ia Supernovae in the LSST Era

We perform a rigorous cosmology analysis on simulated Type Ia supernovae (SNe Ia) and evaluate the improvement from including photometric host galaxy redshifts compared to using only the "z spec" subset with spectroscopic redshifts from the host or SN. We use the Deep Drilling Fields (~50 deg2) from the Photometric LSST Astronomical Time-Series Classification Challenge (PLAsTiCC) in combination with a low-z sample based on Data Challenge2. The analysis includes light-curve fitting to standardize the SN brightness, a high-statistics simulation to obtain a bias-corrected Hubble diagram, a statistical+systematics covariance matrix including calibration and photo-z uncertainties, and cosmology fitting with a prior from the cosmic microwave background. Compared to using the z spec subset, including events with SN+host photo-z results in (i) more precise distances for z > 0.5, (ii) a Hubble diagram that extends 0.3 further in redshift, and (iii) a 50% increase in the Dark Energy Task Force figure of merit (FoM) based on the w 0 w a CDM model. Analyzing 25 simulated data samples, the average bias on w 0 and w a is consistent with zero. The host photo-z systematic of 0.01 reduces FoM by only 2% because (i) most z < 0.5 events are in the z spec subset, (ii) the combined SN+host photo-z has ×2 smaller bias, and (iii) the anticorrelation between fitted redshift and color self-corrects distance errors. To prepare for analyzing real data, the next SN Ia cosmology analysis with photo-zs should include non-SN Ia contamination and host galaxy misassociations.

Keywords: type ia supernovae
Signal Synchronization Strategies and Time Domain SETI with Gaia DR3

Spatiotemporal techniques for signal coordination with actively transmitting extraterrestrial civilizations, without the need for prior communication, can constrain technosignature searches to a significantly smaller coordinate space. With the variable star catalog from Gaia Data Release 3, we explore two related signaling strategies: the SETI Ellipsoid, and that proposed by Seto, which are both based on the synchronization of transmissions with a conspicuous astrophysical event. This data set contains more than 10 million variable star candidates with light curves from the first three years of Gaia's operational phase, between 2014 and 2017. Using four different historical supernovae as source events, we find that less than 0.01% of stars in the sample have crossing times, the times at which we would expect to receive synchronized signals on Earth, within the date range of available Gaia observations. For these stars, we present a framework for technosignature analysis that searches for modulations in the variability parameters by splitting the stellar light curve at the crossing time.

Keywords: technosignatures; astrobiology; search for extraterrestrial intelligence; astrometry
A Snapshot Survey of Nearby Supernovae with the Hubble Space Telescope

Over recent decades, robotic (or highly automated) searches for supernovae (SNe) have discovered several thousand events, many of them in quite nearby galaxies (distances < 30 Mpc). Most of these SNe, including some of the best-studied events to date, were found before maximum brightness and have associated with them extensive follow-up photometry and spectroscopy. Some of these discoveries are so-called "SN impostors," thought to be superoutbursts of luminous blue variable stars, although possibly a new, weak class of massive-star explosions. We conducted a Snapshot program with the Hubble Space Telescope (HST) and obtained images of the sites of 31 SNe and four impostors, to acquire late-time photometry through two filters. The primary aim of this project was to reveal the origin of any lingering energy for each event, whether it is the result of radioactive decay or, in some cases, ongoing late-time interaction of the SN shock with preexisting circumstellar matter, or the presence of a light echo. Alternatively, lingering faint light at the SN position may arise from an underlying stellar population (e.g., a host star cluster, companion star, or a chance alignment). The results from this study complement and extend those from Snapshot programs by various investigators in previous HST cycles.

Keywords: supernovae
Optical and Infrared Study of the Obscured B[e] Supergiant High-mass X-Ray Binary IGR J16318-4848

The supergiant high-mass X-ray binary IGR J16318-4848 was the first source detected by the INTErnational Gamma-Ray Astrophysics Laboratory satellite in 2003 and distinguishes itself by its high intrinsic absorption and B[e] phenomenon. It is the perfect candidate to study both binary interaction and the environment of supergiant B[e] stars. This study targets the local properties of IGR J16318-4848. We aim to clarify the geometry of this system and distinguish different key emitting regions in the binary. We provide optical to near-infrared (NIR) spectra from the Very Large Telescope/X-Shooter and analyze both fine structures of the lines and the broadband spectral energy distribution by adding archival mid-infrared Spitzer and Herschel data. We also perform a stellar atmosphere and wind modeling of the optical to NIR spectrum using the Potsdam Wolf-Rayet code. We determine the contribution of the irradiated inner edge of the dusty circumbinary disk, derive the velocity of an equatorial stellar wind, and suggest the compact object orbits within the cavity between the star and the disk. We report on flat-topped lines originating from a spherically symmetric disk wind, along with the first detection of what is likely the polar component of the stellar wind. Stellar atmosphere and wind modeling shows that the central star may have a helium-enhanced atmosphere, likely because of its intense wind shedding part of its hydrogen envelope. Finally, we compare the properties of IGR J16318-4848 with a similar source, CI Cameleopardis. * Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 089.D-0056.

Keywords: near infrared astronomy; optical observation; high mass x-ray binary stars; stellar atmospheres; stellar winds
Cerium Features in Kilonova Near-infrared Spectra: Implication from a Chemically Peculiar Star

Observations of the kilonova from the neutron star merger event GW170817 opened a way to study r-process nucleosynthesis directly using neutron star mergers. It is, however, challenging to identify individual elements in kilonova spectra due to a lack of complete atomic data, in particular at near-infrared (NIR) wavelengths. In this paper, we demonstrate that spectra of chemically peculiar stars with enhanced heavy-element abundances can provide us with an excellent astrophysical laboratory for kilonova spectra. We show that the photosphere of the late B-type, chemically peculiar star HR 465 has similar lanthanide abundances and ionization degrees with those in the line-forming region in a kilonova at ~2.5 days after the merger. The NIR spectrum of HR 465 taken with Subaru/IRD indicates that Ce III lines give the strongest absorption feature around 16000 Å and there are no other comparably strong transitions around these lines. The Ce III lines nicely match with the broad absorption feature at 14500 Å observed in GW170817 with a blueshift of v = 0.1 c, which supports recent identification of this feature as Ce III by Domoto et al.

Keywords: neutron stars; r-process; transient sources; stellar spectral lines
Formation of Massive and Wide First-star Binaries in Radiation Hydrodynamic Simulations

We study the formation of Population III stars by performing radiation hydrodynamic simulations for three different initial clouds extracted from cosmological hydrodynamic simulations. Starting from the cloud collapse stage, we follow the growth of protostars by accretion for ~105 yr until the radiative feedback from the protostars suppresses the accretion and the stellar properties are nearly fixed. We find that Population III stars form in massive and wide binary/small-multiple stellar systems, with masses >30 M ⊙ and separations >2000 au. We also find that the properties of the final stellar system correlate with those of the initial clouds: the total mass increases with the cloud-scale accretion rate, and the angular momentum of the binary orbit matches that of the initial cloud. While the total mass of the system in our simulations is consistent with our previous single-star formation simulations, individual masses are lower due to mass sharing, suggesting potential modification in the extent of feedback from Population III stars in the subsequent evolution of the Universe. We also identify such systems as mini-binaries embedded in a wider outer multiple-star system, which could evolve into progenitors for observed gravitational wave events.

Keywords: population iii stars; early universe; star formation
Dynamical Formation Channels for Fast Radio Bursts in Globular Clusters

The repeating fast radio burst (FRB) localized to a globular cluster (GC) in M81 challenges our understanding of FRB models. In this Letter, we explore dynamical formation scenarios for objects in old GCs that may plausibly power FRBs. Using N-body simulations, we demonstrate that young neutron stars (NSs) may form in GCs at a rate of up to ~50 Gpc-3 yr-1 through a combination of binary white dwarf (WD) mergers, WD-NS mergers, binary NS mergers, and accretion-induced collapse of massive WDs in binary systems. We consider two FRB emission mechanisms: First, we show that a magnetically powered source (e.g., a magnetar with field strength ≳1014 G) is viable for radio emission efficiencies ≳10-4. This would require magnetic activity lifetimes longer than the associated spin-down timescales and longer than empirically constrained lifetimes of Galactic magnetars. Alternatively, if these dynamical formation channels produce young rotation-powered NSs with spin periods of ~10 ms and magnetic fields of ~1011 G (corresponding to spin-down lifetimes of ≳105 yr), the inferred event rate and energetics can be reasonably reproduced for order unity duty cycles. Additionally, we show that recycled millisecond pulsars or low-mass X-ray binaries similar to those well-observed in Galactic GCs may also be plausible channels, but only if their duty cycle for producing bursts similar to the M81 FRB is small.

Keywords: globular star clusters; radio transient sources; neutron stars; n-body simulations; magnetars
Characterization and Absolute Calibration of the Far-infrared Field Integral Line Spectrometer for SOFIA

We present the characterization and definitive flux calibration of the Far-infrared Field Integral Line Spectrometer (FIFI-LS) instrument on board SOFIA. The work is based on measurements made in the laboratory with an internal calibrator and on observations of planets, moons, and asteroids as absolute flux calibrators made during the entire lifetime of the instrument. We describe the techniques used to derive flat fields, water vapor column estimates, detector linearity, spectral and spatial resolutions, and absolute flux calibration. Two sets of responses are presented, before and after the entrance filter window was changed in 2018 to improve the sensitivity at 52 μm, a wavelength range previously not covered by PACS on Herschel. The relative spectral response of each detector and the illumination pattern of the arrays of the FIFI-LS arrays are derived using the internal calibrator before each observational series. The linearity of the array response is estimated by considering observations of bright sources. We find that the deviation from the linearity of the FIFI-LS arrays affects the flux estimations by less than 1%. The flux calibration accuracy is estimated to be 15% or better across the entire wavelength range of the instrument. The limited availability of sky calibrators during each observational series is the major limiting factor of the flux calibration accuracy.

Keywords: far infrared astronomy; astronomical instrumentation; flux calibration