bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Way for Walén Test of Alfvénic Fluctuations in Solar Wind Streams via EEMD
Authors: Liu Jin , Wang ChuanBing , Wang PengYu , Du Dan , Li Xiang , Liu GuoQi 
Published: March 2020

Abstract
Pure Alfvén waves at 1 au can be effectively identified by a Walén test of plasma and magnetic field observations. In this study, a new method, based on the Ensemble Empirical Mode Decomposition (EEMD) technique, is proposed for analyzing Alfvén fluctuations in two ways: (1) the Walén test relied on a time-dependent frame, which is extracted from the trend of differences between plasma and Alfvén velocity; and (2) a modified Walén test of the reconstructed Alfvénic and plasma velocity fluctuations by EEMD, after removing the high/low-frequency components irrelevant to Alfvénicity. Referencing the three validated methods mentioned in Chao et al., the same four cases in high-speed solar wind steams are tested by the EEMD method, considering Alfvénic parameters such as the Walén slope, the standard deviation ratio, the Alfvén ratio, the normalized cross helicity, the normalized residual energy, and the mean deviation relative to 1. The test results indicate that the first EEMD method can improve most Alfvénic parameters, since a time-varying velocity of the De Hoffmann–Teller frame is obtained from the process of self-adaptive data analysis, especially for complex cases with nonstationary and multiple background frames. The second EEMD method provides a kind of flexible testing to reconstruct the optimal fluctuations satisfied for the Walén relation, which achieves similar or even better results than normal prior methods based on bandpass filtering. We suggest that the EEMD method can be an alternative way to identify large-amplitude Alfvén waves in solar wind streams with single-satellite data.
Detection of Strong Epicyclic Density Spikes in the GD-1 Stellar Stream: An Absence of Evidence for the Influence of Dark Matter Subhalos?
Authors: Ibata Rodrigo , Thomas Guillaume , Famaey Benoit , Malhan Khyati , Martin Nicolas , Monari Giacomo 
Published: March 2020

Abstract
The density variations in thin stellar streams may encode important information on the nature of dark matter. For instance, if dark matter aggregates into massive subhalos, these perturbers are expected to scatter stars out of dynamically cold stellar streams, possibly leading to detectable gaps in those structures. Here, we reexamine the density variations in the GD-1 stream, using Gaia Data Release 2 (DR2) astrometry and Panoramic Survey Telescope and Rapid Response System photometry, together with high-precision radial velocities measured with the Canada–France–Hawaii Telescope/ESPaDOnS and Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph instruments and complemented with public radial velocity catalogs. We show that after correcting for projection effects, the density profile exhibits high contrast periodic peaks, separated by 2.64 ± 0.18 kpc. An N-body simulation is presented that reproduces this striking morphology with simple epicyclic motion in a smooth Galactic potential. We also discuss the reliability of measuring density variations using ground-based photometric surveys, and for the particular case of GD-1 we highlight some of the artifacts present in the Gaia DR2 catalog along its track. Massive dark subhalos do not appear to be required to explain the density clumping along GD-1.
Double White Dwarf Merger Products among High-mass White Dwarfs
Authors: Cheng 程思 Sihao 浩 , Cummings Jeffrey D. , Ménard Brice , Toonen Silvia 
Published: March 2020

Abstract
Double white dwarf (double-WD) binaries may merge within a Hubble time and produce high-mass WDs. Compared to other high-mass WDs, the double-WD merger products have higher velocity dispersion because they are older. With the power of Gaia data, we show strong evidence for double-WD merger products among high-mass WDs by analyzing the transverse-velocity distribution of more than 1000 high-mass WDs (0.8–1.3 M
⊙). We estimate that the fraction of double-WD merger products in our sample is about 20%. We also obtain a precise double-WD merger rate and its mass dependence. Our merger rate estimates are close to binary population synthesis results and support the idea that double-WD mergers may contribute to a significant fraction of type Ia supernovae.
The Bimodal Distribution in Exoplanet Radii: Considering Varying Core Compositions and H2 Envelope’s Sizes
Authors: Modirrousta-Galian Darius , Locci Daniele , Micela Giuseppina 
Published: March 2020

Abstract
Several models have been introduced in order to explain the radius distribution in exoplanet radii observed by Fulton et al. with one peak at

, the other at

, and the minimum at

. In this paper we focus on the hypothesis that the exoplanet size distribution is caused by stellar X-ray and ultraviolet (XUV)-induced atmospheric loss. We evolve 106 synthetic exoplanets by exposing them to XUV irradiation from synthetic zero-age main-sequence stars. For each planet we set a different interior composition, which ranged from 100 wt% Fe (very dense), through to 100 wt% MgSiO3 (average density), and to 100 wt%

ice (low density), with varying hydrogen envelope sizes that varied from 0 wt% (a negligible envelope) to 100 wt% (a negligible core). Our simulations were able to replicate the bimodal distribution in exoplanet radii. We argue that in order to reproduce the distribution by Fulton et al. it is mandatory for there to be a paucity of exoplanets with masses above

. Furthermore, our best-fit result predicts an initial flat distribution in exoplanet occurrence for

with a strong deficiency for planets with

. Our results are consistent with the

radius peak mostly encompassing denuded exoplanets, while the

radius peak is mainly comprised of exoplanets with large hydrogen envelopes.
The Role of the Parker Instability in Structuring the Interstellar Medium
Authors: Heintz Evan , Bustard Chad , Zweibel Ellen G. 
Published: March 2020

Abstract
The Parker instability, a Rayleigh–Taylor-like instability of thermal gas supported against gravity by magnetic fields and cosmic rays, is thought to be dynamically important for galaxy evolution, possibly promoting molecular cloud formation and the galactic dynamo. In previous work, we examined the effect of three different cosmic-ray transport models on the Parker instability: decoupled (γ

c
= 0), locked to the thermal gas (γ

c
= 4/3), and coupled to the gas with streaming by self-confinement. We expand on that work here by considering radiative cooling, a smooth gravitational potential, and simulations into the nonlinear regime. We determine that cosmic-ray transport away from compression points, whether by diffusion or streaming, is the largest driver of the instability. Heating due to cosmic-ray streaming is also destabilizing and especially affects the nonlinear regime. While cooling depressurizes the dense gas, streaming cosmic rays heat and inflate the diffuse extraplanar gas, greatly modifying the phase structure of the medium. In 3D, we find that the fastest growth favors short-wavelength modes in the horizontal direction perpendicular to the background magnetic field; this is imprinted on Faraday rotation measure maps that may be used to detect the Parker instability. The modifications to the Parker instability that we observe in this work have large implications for the structure and evolution of galaxies, and they highlight the major role that cosmic rays play in shaping their environments.
A New Approach to the Mass and Radius of Neutron Stars with Supernova Neutrinos
Authors: Nakazato Ken’ichiro , Suzuki Hideyuki 
Published: March 2020

Abstract
Neutron stars are formed in core-collapse supernova explosions, where a large number of neutrinos are emitted. In this paper, supernova neutrino light curves are computed for the cooling phase of protoneutron stars, which lasts a few minutes. In the numerical simulations, 90 models of the phenomenological equation of state with different incompressibilities, symmetry energies, and nucleon effective masses are employed for a comprehensive study. It is found that the cooling timescale is longer for a model with a larger neutron star mass and a smaller neutron star radius. Furthermore, a theoretical expression of the cooling timescale is presented as a function of the mass and radius and it is found to describe the numerical results faithfully. These findings suggest that diagnosing the mass and radius of a newly formed neutron star using its neutrino signal is possible.
On the XUV Luminosity Evolution of TRAPPIST-1
Authors: Fleming David P. , Barnes Rory , Luger Rodrigo , VanderPlas Jacob T. 
Published: March 2020

Abstract
We model the long-term X-ray and ultraviolet (XUV) luminosity of TRAPPIST-1 to constrain the evolving high-energy radiation environment experienced by its planetary system. Using a Markov Chain Monte Carlo (MCMC) method, we derive probabilistic constraints for TRAPPIST-1's stellar and XUV evolution that account for observational uncertainties, degeneracies between model parameters, and empirical data of low-mass stars. We constrain TRAPPIST-1's mass to m
⋆ = 0.089 ± 0.001 M
⊙ and find that its early XUV luminosity likely saturated at

. From the posterior distribution, we infer that there is a ∼40% chance that TRAPPIST-1 is still in the saturated phase today, suggesting that TRAPPIST-1 has maintained high activity and L
XUV/L
bol ≈ 10−3 for several gigayears. TRAPPIST-1's planetary system therefore likely experienced a persistent and extreme XUV flux environment, potentially driving significant atmospheric erosion and volatile loss. The inner planets likely received XUV fluxes ∼103–104 times that of the modern Earth during TRAPPIST-1's ∼1 Gyr long pre-main-sequence phase. Deriving these constraints via MCMC is computationally nontrivial, so scaling our methods to constrain the XUV evolution of a larger number of M dwarfs that harbor terrestrial exoplanets would incur significant computational expenses. We demonstrate that approxposterior, an open source Python machine learning package for approximate Bayesian inference using Gaussian processes, accurately and efficiently replicates our analysis using 980 times less computational time and 1330 times fewer simulations than MCMC sampling using emcee. We find that approxposterior derives constraints with mean errors on the best-fit values and 1σ uncertainties of 0.61% and 5.5%, respectively, relative to emcee.
Global Simulations of Self-gravitating Magnetized Protoplanetary Disks
Authors: Deng Hongping , Mayer Lucio , Latter Henrik 
Published: March 2020

Abstract
In the early stages of a protoplanetary disk, turbulence generated by gravitational instability (GI) should feature significantly in the disk’s evolution. At the same time, the disk may be sufficiently ionized for magnetic fields to play some role in the dynamics. In this paper, we report on global three-dimensional magnetohydrodynamical simulations of a self-gravitating protoplanetary disk using the meshless finite mass Lagrangian technique. We confirm that GI spiral waves trigger a dynamo that amplifies an initial magnetic field to nearly thermal amplitudes (plasma β < 10), an order of magnitude greater than that generated by the magnetorotational instability alone. We also determine the dynamo’s nonlinear back reaction on the gravito-turbulent flow: the saturated state is substantially hotter, with an associated larger Toomre parameter and weaker, more “flocculent” spirals. But perhaps of greater import is the dynamo’s boosting of accretion via a significant Maxwell stress; mass accretion is enhanced by factors of several relative to either pure GI or pure magnetorotational instability. Our simulations use ideal MHD, an admittedly poor approximation in protoplanetary disks, and thus, future studies should explore the full gamut of nonideal MHD. In preparation for that, we exhibit a small number of ohmic runs that reveal that the dynamo, if anything, is stronger in a nonideal environment. This work confirms that magnetic fields are a potentially critical ingredient in gravito-turbulent young disks, possibly controlling their evolution, especially via their enhancement of (potentially episodic) accretion.
HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. IV. The Largest Broad Absorption Line Acceleration
Authors: Xu Xinfeng , Arav Nahum , Miller Timothy , Kriss Gerard A. , Plesha Rachel 
Published: March 2020

Abstract
We present an analysis of the broad absorption line (BAL) velocity shift that appeared in one of the outflow systems in quasar SDSS J1042+1646. Observations were taken by the Hubble Space Telescope/Cosmic Origins Spectrograph in 2011 and 2017 in the 500–1050 Å rest frame. The outflow’s velocity centroid shifted by ∼−1550 km s−1 from −19,500 km s−1 to −21,050 km s−1 over a rest-frame time of 3.2 yr. The velocity shift signatures are most apparent in the absorption features from the Ne viii
λλ770.41 and 780.32 doublet and are supported by the absorption troughs from O v
λ629.73 and the Mg x
λλ609.79 and 624.94 doublet. This is the first time where a quasar outflow velocity shift is observed in troughs from more than one ion and in distinct troughs from a doublet transition (Ne viii). We attribute the velocity shift to an acceleration of an existing outflow as we are able to exclude photoionization changes and motion of material into and out of the line of sight as alternate explanations. This leads to an average acceleration of 480 km s−1 yr−1 (1.52 cm s−2) in the quasar rest frame. Both the acceleration and the absolute velocity shift are the largest reported for a quasar outflow to date. Based on the absorption troughs of the O v* multiplet, we derive a range for the distance of the outflow (R) from the central source, 0.05 pc < R < 54.3 pc. This outflow shows similarities with the fast X-ray outflow detected in quasar PG 1211+143. We use the acceleration and velocity shift to constrain radiatively accelerated active galactic nucleus disk–wind models and use them to make predictions for future observations.
HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. III. Four Similar Outflows in 2MASS J1051+1247 with Enough Energy to Be Major Contributors to AGN Feedback*
Authors: Miller Timothy R. , Arav Nahum , Xu Xinfeng , Kriss Gerard A. , Plesha Rachel J. 
Published: March 2020

Abstract
We detect four very energetic outflows in the Hubble Space Telescope/Cosmic Origins Spectrograph spectra of quasar 2MASS J1051+1247 with a combined kinetic luminosity (

) of 1046 erg s−1. Remarkable similarities are seen in these outflows: velocity centroids between 4900 and 5700 km s−1, distances from the central source (R) of a few hundred parsecs that are all consistent within the errors, and an

within a factor of two for all outflows. Hence, a common origin for the outflows is probable. Most of the outflowing mass resides in a very high-ionization phase evident by troughs from Ne viii, Na ix, Mg x, and Si xii, which connect the physical conditions of these ultraviolet outflows to the X-ray warm absorber outflows seen in nearby Seyfert galaxies. Three of the outflows have two or three independent diagnostics for the electron number density, yielding consistent values for each outflow, which increase the robustness of the R determinations. Troughs from never-before-seen ionic transitions of Ar vi, O iv*, Ne vi*, and Ne v* are identified. With a combined

that is 7.0

% of the quasar’s Eddington luminosity, these outflows are prime candidates to be major agents for various active galactic nuclei feedback effects.
HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. V. Richness of Physical Diagnostics and Ionization Potential-dependent Velocity Shift in PKS J0352-0711*
Authors: Miller Timothy R. , Arav Nahum , Xu Xinfeng , Kriss Gerard A. , Plesha Rachel J. 
Published: March 2020

Abstract
We analyze absorption troughs from two outflows within PKS J0352-0711 (S1 at −1950 km s−1 and S2 at −3150 km s−1) from spectra taken with Hubble Space Telescope/Cosmic Origins Spectrograph, which cover the diagnostic-rich 585–900 Å rest-frame wavelength range. In S2, for the first time we clearly detect absorption troughs from Ca iv, Ca v, Ca v*, Ca vii*, and Ca viii*. The column density measurement of Ca v suggests S2 has a super-solar metallicity. Both outflows require at least two ionization phases where the column density of the very high-ionization phase is roughly 15 times larger than the corresponding high-ionization phase. These high column densities and very high-ionization potential ions are similar to X-ray warm absorbers. The two phases of S2 show a unique velocity centroid shift between associated troughs. Through Monte Carlo measurements of the O v* absorption troughs, we determine the electron number density of S2 (fully corroborated by independent measurements from the Ca vii* and Ca viii* troughs), yielding a distance of 9 pc and a kinetic luminosity of 2 × 1043 erg s−1. S1 is located farther away at 500 pc from the central source with a kinetic luminosity of 1043 erg s−1.
HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. VI. Wide, Energetic Outflows in SDSS J0755+2306
Authors: Xu Xinfeng , Arav Nahum , Miller Timothy , Kriss Gerard A. , Plesha Rachel 
Published: March 2020

Abstract
We present the analysis of two outflows (S1 at −5500 km s−1 and S2 at −9700 km s−1) seen in recent Hubble Space Telescope/Cosmic Origins Spectrograph observations of quasar SDSS J0755+2306 (z = 0.854). The outflows are detected as absorption troughs from both high-ionization species, including N iii, O iii, and S iv, and very high-ionization species, including Ar viii, Ne viii, and Na ix. The derived photoionization solutions show that each outflow requires a two ionization-phase solution. For S1, troughs from S iv* and S iv allow us to derive an electron number density,

= 1.8 × 104 cm−3, and its distance from the central source of R = 270 pc. For S2, troughs from O iii* and O iii yield

= 1.2 × 103 cm−3 and R = 1600 pc. The kinetic luminosity of S2 is >12% of the Eddington luminosity for the quasar and, therefore, can provide strong AGN feedback effects. Comparison of absorption troughs from O iii and O vi in both outflow systems supports the idea that for a given element, higher-ionization ions have larger covering fractions than lower-ionization ones.
HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. I. The Most Energetic Outflows in the Universe and Other Discoveries
Authors: Arav Nahum , Xu Xinfeng , Miller Timothy , Kriss Gerard A. , Plesha Rachel 
Published: March 2020

Abstract
The Hubble Space Telescope/Cosmic Origins Spectrograph (COS) has opened a new discovery space for studying quasar absorption outflows and their contribution to active galactic nucleus (AGN) feedback. Specifically, COS provides high-quality far-ultraviolet (FUV) spectra covering the diagnostic-rich 500–1050 Å rest frame (hereafter, EUV500) of medium redshift objects. The quality and quantity of EUV500 diagnostic troughs allow us to probe the very high-ionization phase, which carries 90% or more of the outflowing material, as well as to determine the distance of most outflows from the central source (R). The first objective is impossible to achieve with ground-based spectra, and R can be measured in only ∼1% of them. Here, we summarize the main results of the first dedicated survey of such outflows, including the following.
1. Measurements of the three most energetic outflows to date, which can be the main agents for AGN feedback processes in the environments of the host galaxies.
2. All the outflows have a very high-ionization component, similar to the one found in warm absorbers, which carries most of the outflow’s kinetic luminosity. This finding suggests that all the high-ionization outflows observed from the ground also have a similar undetected very high-ionization component.
3. Of the 13 studied EUV500 outflows, 9 have 100 < R < 2000 parsecs, 2 have 5 < R < 20 parsecs, 1 has 0.05 < R < 50 parsecs, and in 1 case, R cannot be determined.
4. One of the outflows has the largest velocity shift (1550 km s−1) and acceleration (1.5 cm s−2) measured to date. This outflow is physically similar to the fast X-ray outflow detected in quasar PG 1211+143.
Structure of Brightest Cluster Galaxies and Intracluster Light
Authors: Kluge M. , Neureiter B. , Riffeser A. , Bender R. , Goessl C. , Hopp U. , Schmidt M. , Ries C. , Brosch N. 
Published: March 2020

Abstract
Observations of 170 local (z ≲ 0.08) galaxy clusters in the northern hemisphere have been obtained with the Wendelstein Telescope Wide Field Imager (WWFI). We correct for systematic effects such as point-spread function broadening, foreground star contamination, relative bias offsets, and charge persistence. Background inhomogeneities induced by scattered light are reduced down to ΔSB > 31 g′ mag arcsec−2 by large dithering and subtraction of night-sky flats. Residual background inhomogeneities brighter than SB
σ
< 27.6 g′ mag arcsec−2 caused by galactic cirrus are detected in front of 23% of the clusters. However, the large field of view allows discrimination between accretion signatures and galactic cirrus. We detect accretion signatures in the form of tidal streams in 22%, shells in 9.4%, and multiple nuclei in 47% of the brightest cluster galaxies (BCGs) and find two BCGs in 7% of the clusters. We measure semimajor-axis surface brightness profiles of the BCGs and their surrounding intracluster light (ICL) down to a limiting surface brightness of SB = 30 g′ mag arcsec−2. The spatial resolution in the inner regions is increased by combining the WWFI light profiles with those that we measured from archival Hubble Space Telescope images or deconvolved WWFI images. We find that 71% of the BCG+ICL systems have surface brightness (SB) profiles that are well described by a single Sérsic function, whereas 29% require a double Sérsic function to obtain a good fit. We find that BCGs have scaling relations that differ markedly from those of normal ellipticals, likely due to their indistinguishable embedding in the ICL.
One Hundred SMUDGes in S-PLUS: Ultra-diffuse Galaxies Flourish in the Field
Authors: Barbosa C. E. , Zaritsky D. , Donnerstein R. , Zhang H. , Dey A. , de Oliveira C. Mendes , Sampedro L. , Molino A. , Costa-Duarte M. V. , Coelho P. , Cortesi A. , Herpich F. R. , Hernandez-Jimenez J. A. , Santos-Silva T. , Pereira E. , Werle A. , Overzier R. A. , Cid Fernandes R. , Castelli A. V. Smith , Ribeiro T. , Schoenell W. , Kanaan A. 
Published: March 2020

Abstract
We present the first systematic study of the stellar populations of ultra-diffuse galaxies (UDGs) in the field, integrating the large area search and characterization of UDGs by the SMUDGes survey with the twelve-band optical photometry of the S-PLUS survey. Based on Bayesian modeling of the optical colors of UDGs, we determine the ages, metallicities, and stellar masses of 100 UDGs distributed in an area of ∼330 deg2 in the Stripe 82 region. We find that the stellar masses and metallicities of field UDGs are similar to those observed in clusters and follow the trends previously defined in studies of dwarf and giant galaxies. However, field UDGs have younger luminosity-weighted ages than do UDGs in clusters. We interpret this result to mean that field UDGs have more extended star formation histories, including some that continue to form stars at low levels to the present time. Finally, we examine stellar population scaling relations that show that UDGs are, as a population, similar to other low surface brightness galaxies.