bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Data Analysis Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey: Emission-line Modeling
Authors: Belfiore Francesco , Westfall Kyle B. , Schaefer Adam , Cappellari Michele , Ji Xihan , Bershady Matthew A. , Tremonti Christy , Law David R. , Yan Renbin , Bundy Kevin , Shetty Shravan , Drory Niv , Thomas Daniel , Emsellem Eric , Sánchez Sebastián F. 
Published: September 2019

Abstract
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the largest integral-field unit (IFU) spectroscopy survey to date, aiming to observe a statistically representative sample of 10,000 low-redshift galaxies. In this paper, we study the reliability of the emission-line fluxes and kinematic properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the algorithmic choices made in the DAP with regards to measuring emission-line properties, and the effect of our adopted strategy of simultaneously fitting the continuum and line emission. The effects of random errors are quantified by studying various fit-quality metrics, idealized recovery simulations, and repeat observations. This analysis demonstrates that the emission lines are well fit in the vast majority of the MaNGA data set and the derived fluxes and errors are statistically robust. The systematic uncertainty on emission-line properties introduced by the choice of continuum templates is also discussed. In particular, we test the effect of using different stellar libraries and simple stellar-population models on the derived emission-line fluxes and the effect of introducing different tying prescriptions for the emission-line kinematics. We show that these effects can generate large (>0.2 dex) discrepancies at low signal-to-noise ratio and for lines with low equivalent width (EW); however, the combined effect is noticeable even for Hα EW > 6 Å. We provide suggestions for optimal use of the data provided by SDSS data release 15 and propose refinements on the DAP for future MaNGA data releases.
Li Evolution and the Open Cluster NGC 6819: A Correlation between Li Depletion and Spindown in Dwarfs More Massive Than the F-Dwarf Li-Dip*
Authors: Deliyannis Constantine P. , Anthony-Twarog Barbara J. , Lee-Brown Donald B. , Twarog Bruce A. 
Published: September 2019

Abstract
Spectroscopy of 333 NGC 6819 stars and Gaia astrometry are used to map Li evolution from the giant branch tip to 0.5 mag below the Li dip. Isochrone comparison with [Fe/H] = −0.04, based upon neural network spectroscopic analysis, produces an age of 2.25 (2.4) Gyr for E(B − V) = 0.16 (0.14) and (m − M) = 12.40 (12.29). Despite originating outside the Li dip, only 10% of single subgiants/giants have measurable Li. Above the Li dip, the limiting A(Li) for single stars is 3.2 ± 0.1 but the lower range is comparable to that found within the dip. The F-dwarf Li dip profile agrees with the Hyades/Praesepe, evolved forward. The Li level among stars populating the plateau fainter than the Li dip is A(Li) = 2.83 ± 0.16; the dispersion is larger than expected from spectroscopic error alone. Comparison of Li and V
ROT distributions among turnoff stars in NGC 7789, NGC 2506, NGC 3680, and NGC 6819 indicates that rotational spindown from the main sequence is critical in defining the boundaries of the Li dip. For higher-mass dwarfs, spindown is likewise correlated with Li depletion, creating a second dip, but at higher mass and on a longer timescale. The Li distribution among evolved stars of NGC 6819 is more representative of the older M67, where subgiant and giant stars emerge from within the Li dip, than the younger NGC 7789, where a broad range in V
ROT among the turnoff stars likely produces a range in mass among the giants.
Photoevaporation of Molecular Gas Clumps Illuminated by External Massive Stars: Clump Lifetimes and Metallicity Dependence
Authors: Nakatani Riouhei , Yoshida Naoki 
Published: September 2019

Abstract
We perform a suite of 3D radiation hydrodynamics simulations of photoevaporation of molecular gas clumps illuminated by external massive stars. We study the fate of solar-mass clumps and derive their lifetimes by varying the gas metallicity over a range of

. Our simulations incorporate radiation transfer of far- and extreme-ultraviolet photons and follow atomic/molecular line cooling and dust–gas collisional cooling. Nonequilibrium chemistry is coupled with the radiative transfer and hydrodynamics in a self-consistent manner. We show that radiation-driven shocks compress gas clumps to have a volume that is set by the pressure equilibrium with the hot ambient gas. Radiative cooling enables metal-rich clumps to condense and have small surface areas where photoevaporative flows are launched. For our fiducial setup with an O-type star at a distance of 0.1 pc, the resulting photoevaporation rate is as small as

for metal-rich clumps, but it is larger for metal-poor clumps that have larger surface areas. The clumps are continuously accelerated away from the radiation source by the so-called rocket effect and can travel over ∼1 pc within the lifetime. We also study the photoevaporation of clumps in a photodissociation region. Photoelectric heating is inefficient for metal-poor clumps that contain a smaller amount of grains, and thus they survive for over 105 yr. We conclude that the gas metallicity strongly affects the clump lifetime and thus determines the strength of feedback from massive stars in star-forming regions.
Assessment of the Projection-induced Polarimetry Technique for Constraining the Foreground Spectrum in Global 21 cm Cosmology
Authors: Nhan Bang D. , Bordenave David D. , Bradley Richard F. , Burns Jack O. , Tauscher Keith , Rapetti David , Klima Patricia J. 
Published: September 2019

Abstract
Detecting the cosmological sky-averaged (global) 21 cm signal as a function of observed frequency will provide a powerful tool to study the ionization and thermal history of the intergalactic medium (IGM) in the early universe (∼400 million years after the big bang). The greatest challenge in conventional total-power global 21 cm experiments is the removal of the foreground synchrotron emission (∼103–104 K) to uncover the weak cosmological signal (tens to hundreds of millikelvin), especially because the intrinsic smoothness of the foreground spectrum is corrupted by instrumental effects. Although the EDGES (Experiment to Detect the Global EoR Signature) team has recently reported an absorption profile at 78 MHz in the sky-averaged spectrum, it is necessary to confirm this detection with an independent approach. The projection effect from observing anisotropic foreground source emission with a wide-view antenna pointing at the North Celestial Pole can induce a net polarization, referred to as the projection-induced polarization effect (PIPE). Due to Earth’s rotation, observations centered at the circumpolar region will impose a dynamic sky modulation on the net polarization’s waveforms that is unique to the foreground component. In this study, we review the implementation practicality and underlying instrumental effects of this new polarimetry-based technique with detailed numerical simulations and a test-bed instrument, the Cosmic Twilight Polarimeter. In addition, we explore a singular value decomposition–based analysis approach for separating the foreground and instrumental effects from the background global 21 cm signal using the sky-modulated PIPE.
A Parameter Space Exploration of Galaxy Cluster Mergers. II. Effects of Magnetic Fields
Authors: Brzycki Bryan , ZuHone John 
Published: September 2019

Abstract
The hot intracluster plasma in clusters of galaxies is weakly magnetized. Mergers between clusters produce gas compression and motions that can increase the magnetic field strength. In this work, we perform high-resolution nonradiative magnetohydrodynamics simulations of binary galaxy cluster mergers with magnetic fields, to examine the effects of these motions on the magnetic field configuration and strength, as well as the effect of the field on the gas itself. Our simulations sample a parameter space of initial mass ratios and impact parameters. During the first core passage of mergers, the magnetic energy increases via gas compression. After this, shear flows produce temporary, megaparsec-scale, strong-field “filament” structures. Lastly, magnetic fields grow stronger by turbulence. Field amplification is most effective for low-mass ratio mergers, but mergers with a large impact parameter can increase the magnetic energy more via shearing motions. The amplification of the magnetic field is most effective in between the first two core passages of each cluster merger. After the second core passage, the magnetic energy in this region gradually decreases. In general, the transfer of energy from gas motions to the magnetic field is not significant enough to have a substantial effect on gas mixing and the subsequent increase in entropy, which occurs in cluster cores as a result. In the absence of radiative cooling, this results in an overall decrease of the magnetic field strength in cluster cores. In these regions, the final magnetic field is isotropic, while it can be significantly tangential at larger radii.
A Comparison of the X-Ray Properties of FU Ori-type Stars to Generic Young Stellar Objects
Authors: Kuhn Michael A. , Hillenbrand Lynne A. 
Published: September 2019

Abstract
Like other young stellar objects (YSOs), FU Ori-type stars have been detected as strong X-ray emitters. However, little is known about how the outbursts of these stars affect their X-ray properties. We assemble available X-ray data from XMM-Newton and Chandra observations of 16 FU Ori stars, including a new XMM-Newton observation of Gaia 17bpi during its optical rise phase. Of these stars, six were detected at least once, while 10 were non-detections, for which we calculate upper limits on intrinsic X-ray luminosity (L
X) as a function of plasma temperature (kT) and column density (N
H). The detected FU Ori stars tend to be more X-ray luminous than is typical for non-outbursting YSOs, based on comparison to a sample of low-mass stars in the Orion Nebula Cluster. FU Ori stars with high L
X have been observed both at the onset of their outbursts and decades later. We use the Kaplan–Meier estimator to investigate whether the higher X-ray luminosities for FU Ori stars are characteristic or a result of selection effects, and we find the difference to be statistically significant (p < 0.01) even when non-detections are taken into account. The additional X-ray luminosity of FU Ori stars relative to non-outbursting YSOs cannot be explained by accretion shocks, given the high observed plasma temperatures. This suggests that, for many FU Ori stars, either (1) the outburst leads to a restructuring of the magnetosphere in a way that enhances X-ray emission, or (2) FU Ori outbursts are more likely to occur among YSOs with the highest quiescent X-ray luminosity.
Probing Clumpy Wind Accretion in IGR J18027-2016 with XMM-Newton
Authors: Pradhan Pragati , Bozzo Enrico , Paul Biswajit , Manousakis Antonis , Ferrigno Carlo 
Published: September 2019

Abstract
Supergiant X-ray binaries usually comprise a neutron star accreting from the wind of an OB supergiant companion. They are classified as classical systems and supergiant fast X-ray transients (SFXTs). The different behavior of these subclasses of sources in X-rays, with SFXTs displaying much more pronounced variability, is usually (at least) partly ascribed to different physical properties of the massive star clumpy stellar wind. In the case of SFXTs, a systematic investigation of the effects of clumps on flares/outbursts of these sources has been reported by Bozzo et al. exploiting the capabilities of the instruments on board XMM-Newton to perform a hardness-resolved spectral analysis on timescales as short as a few hundreds of seconds. In this paper, we use six XMM-Newton observations of IGR J18027-2016 to extend the above study to a classical supergiant X-ray binary and compare the findings with those derived in the case of SFXTs. As these observations of IGR J18027-2016 span different orbital phases, we also study its X-ray spectral variability on longer timescales and compare our results with previous publications. Although obtaining measurements of the clump physical properties from X-ray observations of accreting supergiant X-ray binaries has already proven to be challenging, our study shows that similar imprints of clumps are found in the X-ray observations of the SFXTs and at least one classical system, i.e., IGR J18027-2016. This provides interesting perspectives to further extend this study to many XMM-Newton observations already performed in the direction of other classical supergiant X-ray binaries.
Spatially Resolved Signatures of Bidirectional Flows Observed in Inverted-Y Shaped Jets
Authors: Nelson C. J. , Freij N. , Bennett S. , Erdélyi R. , Mathioudakis M. 
Published: September 2019

Abstract
Numerous apparent signatures of magnetic reconnection have been reported in the solar photosphere, including inverted-Y shaped jets. The reconnection at these sites is expected to cause localized bidirectional flows and extended shock waves; however, these signatures are rarely observed as extremely high spatial-resolution data are required. Here, we use Hα imaging data sampled by the Swedish Solar Telescope’s CRisp Imaging SpectroPolarimeter to investigate whether bidirectional flows can be detected within inverted-Y shaped jets near the solar limb. These jets are apparent in the Hα line wings, while no signature of either jet is observed in the Hα line core, implying reconnection took place below the chromospheric canopy. Asymmetries in the Hα line profiles along the legs of the jets indicate the presence of bidirectional flows, consistent with cartoon models of reconnection in chromospheric anemone jets. These asymmetries are present for over two minutes, longer than the lifetimes of Rapid Blue Excursions, and beyond ±1 Å into the wings of the line indicating that flows within the inverted-Y shaped jets are responsible for the imbalance in the profiles, rather than motions in the foreground. Additionally, surges form following the occurrence of the inverted-Y shaped jets. This surge formation is consistent with models, which suggests such events could be caused by the propagation of shock waves from reconnection sites in the photosphere to the upper atmosphere. Overall, our results provide evidence that magnetic reconnection in the photosphere can cause bidirectional flows within inverted-Y shaped jets and could be the driver of surges.
Validating Time–Distance Helioseismic Inversions for Nonseparable Subsurface Profiles of an Average Supergranule
Authors: Dhruv Vedant , Bhattacharya Jishnu , Hanasoge Shravan M. 
Published: September 2019

Abstract
Supergranules are divergent 30 Mm-sized cellular flows observed everywhere at the solar photosphere. Their place in the hierarchy of convective structures and their origin remain poorly understood. Estimating supergranular depth is of particular interest because this may help point to the underlying physics. However, their subsurface velocity profiles have proven difficult to ascertain. Birch et al. suggested that helioseismic inferences would benefit from an ensemble average over multiple realizations of supergranules due to the reduction in realization noise. Bhattacharya et al. used synthetic forward-modeled seismic wave travel times and demonstrated the potential of helioseismic inversions to recover the flow profile of an average supergranule that is separable in the horizontal and vertical directions, although the premise of this calculation has since been challenged by Ferret. In this work we avoid this assumption and carry out a validation test of helioseismic travel-time inversions starting from plausible synthetic nonseparable profiles of an average supergranule. We compute seismic wave travel times and sensitivity kernels by simulating wave propagation through this background. We find that, while the ability to recover the exact profile degrades based on the number of parameters involved, we are nevertheless able to recover the peak depth of our models in a few iterations where the measurements are presumably above the noise cutoff. This represents an important step toward unraveling the physics behind supergranules, as we start appreciating the parameters that we may reliably infer from a time–distance helioseismic inversion.
Constraining the Formation of the Four Terrestrial Planets in the Solar System
Authors: Lykawka Patryk Sofia , Ito 伊 Takashi 藤孝士 
Published: September 2019

Abstract
To reproduce the orbits and masses of the terrestrial planets (analogs) of the solar system, most studies scrutinize simulations for success as a batch. However, there is insufficient discussion in the literature on the likelihood of forming planet analogs simultaneously in the same system (analog system). To address this issue, we performed 540 N-body simulations of protoplanetary disks representative of typical models in the literature. We identified a total of 194 analog systems containing at least three analogs, but only 17 systems simultaneously contained analogs of the four terrestrial planets. From an analysis of our analog systems, we found that, compared to the real planets, truncated disks based on typical outcomes of the Grand Tack model produced analogs of Mercury and Mars that were too dynamically cold and located too close to the Venus and Earth analogs. Additionally, all the Mercury analogs were too massive, while most of the Mars analogs were more massive than Mars. Furthermore, the timing of the Moon-forming impact was too early in these systems, and the amount of additional mass accreted after the event was too great. Therefore, such truncated disks cannot explain the formation of the terrestrial planets. Our results suggest that forming the four terrestrial planets requires disks with the following properties: (1) mass concentrated in narrow core regions between ∼0.7–0.9 au and ∼1.0–1.2 au, (2) an inner region component starting at ∼0.3–0.4 au, (3) a less massive component beginning at ∼1.0–1.2 au, (4) embryos rather than planetesimals carrying most of the disk mass, and (5) Jupiter and Saturn placed on eccentric orbits.
Development of Hydrogen and Helium Proximity Zones around Quasars
Authors: Zheng Wei , Meiksin Avery , Syphers David 
Published: September 2019

Abstract
Increasing evidence suggests that He ii proximity profiles in the quasar spectra at z ∼ 3–4 are sensitive probes of quasar ages. But the development of their H i counterparts is difficult to trace and remains poorly constrained. We compare the UV spectra of 15 He ii quasars with their high-resolution optical counterparts and find a significant correlation between the sizes of He ii and H i proximity zones. The luminous quasar HE2347−4342 displays a null proximity zone in both He ii and H i, suggesting that it is extremely young (age < 0.2 Myr). Three other quasars also display small proximity zones for He ii and H i. There is no evidence that a H i ionization zone expands considerably faster than its He ii counterpart. The results suggest that the expansion of quasar ionizing fronts may be noticeably slower than the speed of light, and raise the possibility of distinguishing young and old quasars from the sizes of their H i proximity zones.
Discovery and Early Evolution of ASASSN-19bt, the First TDE Detected by TESS
Authors: Holoien Thomas W.-S. , Vallely Patrick J. , Auchettl Katie , Stanek K. Z. , Kochanek Christopher S. , French K. Decker , Prieto Jose L. , Shappee Benjamin J. , Brown Jonathan S. , Fausnaugh Michael M. , Dong Subo , Thompson Todd A. , Bose Subhash , Neustadt Jack M. M. , Cacella P. , Brimacombe J. , Kendurkar Malhar R. , Beaton Rachael L. , Boutsia Konstantina , Chomiuk Laura , Connor Thomas , Morrell Nidia , Newman Andrew B. , Rudie Gwen C. , Shishkovksy Laura , Strader Jay 
Published: September 2019

Abstract
We present the discovery and early evolution of ASASSN-19bt, a tidal disruption event (TDE) discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN) at a distance of d ≃ 115 Mpc and the first TDE to be detected by TESS. As the TDE is located in the TESS Continuous Viewing Zone, our data set includes 30 minute cadence observations starting on 2018 July 25, and we precisely measure that the TDE begins to brighten ∼8.3 days before its discovery. Our data set also includes 18 epochs of Swift UVOT and XRT observations, 2 epochs of XMM-Newton observations, 13 spectroscopic observations, and ground data from the Las Cumbres Observatory telescope network, spanning from 32 days before peak through 37 days after peak. ASASSN-19bt thus has the most detailed pre-peak data set for any TDE. The TESS light curve indicates that the transient began to brighten on 2019 January 21.6 and that for the first 15 days, its rise was consistent with a flux ∝t
2 power-law model. The optical/UV emission is well fit by a blackbody spectral energy distribution, and ASASSN-19bt exhibits an early spike in its luminosity and temperature roughly 32 rest-frame days before peak and spanning up to 14 days, which has not been seen in other TDEs, possibly because UV observations were not triggered early enough to detect it. It peaked on 2019 March 4.9 at a luminosity of L ≃ 1.3 × 1044 erg s−1 and radiated E ≃ 3.2 × 1050 erg during the 41 day rise to peak. X-ray observations after peak indicate a softening of the hard X-ray emission prior to peak, reminiscent of the hard/soft states in X-ray binaries.
Magnetic Properties of Dust Grains, Effect of Precession, and Radiative Torque Alignment
Authors: Lazarian A. , Hoang Thiem 
Published: September 2019

Abstract
Alignment of dust grains in astrophysical environments results in the polarization of starlight as well as the polarization of radiation emitted by dust. We demonstrate the advances in grain alignment theory that allow the use of linear and circular polarization to probe not only the magnetic field, but also dust composition, the dust environment, etc. We revisit the process of grain alignment by Radiative Torques (RATs) and focus on constraining magnetic susceptibility of grains via observations. We discuss the possibility of observational testing of the magnetic properties of grains as the alignment changes from being in respect to the magnetic field to being in respect to the radiation direction. This both opens a possibility of constraining the uncertain parameters of the RATs theory and provides a new way of measuring magnetic fields in the interstellar medium and circumstellar regions. We provide a detailed discussion of the precession induced both by the magnetic field and the anisotropic radiation and revisit a number of key processes related to magnetic response of the grains. We consider various effects that increase the rate of magnetic relaxation both in silicate and carbonaceous grains. In particular, we find a new relaxation process related to the change of the amplitude of internal magnetization within a wobbling triaxial grain and identify a range of grain sizes in which this effect can dominate the internal alignment of angular momentum within grain axes. We show that these relaxation processes significantly change the dynamics of grains in the presence of RATs. We apply our analysis for observed grain alignment in special environments to put constraints on the enhanced magnetic properties of dust grains in the cloud near supernovae, in cometary coma, and protoplanetary disks.