bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stellar Proper Motions in the Orion Nebula Cluster
Authors: Kim Dongwon , Lu Jessica R. , Konopacky Quinn , Chu Laurie , Toller Elizabeth , Anderson Jay , Theissen Christopher A. , Morris Mark R. 
Published: February 2019

Abstract
The Orion Nebula Cluster (ONC) is the nearest site of ongoing massive star formation, which allows us to study the kinematics and dynamics of the region in detail and constrain star formation theories. Using HST ACS/WFPC2/WFC3IR and Keck II NIRC2 data, we have measured the proper motions of 701 stars within an ∼6′ × 6′ field of view around the center of the ONC. We have found more than 10 escaping star candidates, concentrated predominantly at the core of the cluster. The proper motions of the bound stars are consistent with a normal distribution, albeit elongated north–south along the Orion filament, with proper-motion dispersions of

mas yr−1 or intrinsic velocity dispersions of

km s−1 assuming a distance of 400 pc to the ONC. The cluster shows no evidence for tangential-to-radial anisotropy. Our velocity dispersion profile agrees with the prediction from the observed stellar + gas density profile from Da Rio et al., indicating that the ONC is in virial equilibrium. This finding suggests that the cluster was formed with a low star formation efficiency per dynamical timescale based on comparisons with current star formation theories. Our survey also recovered high-velocity IR sources BN, x and n in the BN/KL region. The estimated location of the first two sources ∼500 yr ago agrees with that of the radio source I, consistent with their proposed common origin from a multistellar disintegration. However, source n appears to have a small proper motion and is unlikely to have been involved in the event.
Spitzer Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-rotating Low-mass Brown Dwarf
Authors: Shvartzvald Yossi , Yee Jennifer C. , Skowron Jan , Lee Chung-Uk , Udalski Andrzej , Novati Sebastiano Calchi , Bozza Valerio , Beichman Charles A. , Bryden Geoffery , Carey Sean , Gaudi B. Scott , Henderson Calen B. , Zhu Wei ,   (Spitzer team), Bachelet Etienne , Bolt Greg , Christie Grant , Maoz Dan , Natusch Tim , Pogge Richard W. , Street Rachel A. , Tan Thiam-Guan , Tsapras Yiannis ,   (LCO and μFUN Follow-up Teams), Pietrukowicz Paweł , Soszyński Igor , Szymański Michał K. , Mróz Przemek , Poleski Radoslaw , Kozłowski Szymon , Ulaczyk Krzysztof , Pawlak Michał , Rybicki Krzysztof A. , Iwanek Patryk ,   (OGLE Collaboration), Albrow Michael D. , Cha Sang-Mok , Chung Sun-Ju , Gould Andrew , Han Cheongho , Hwang Kyu-Ha , Jung Youn Kil , Kim Dong-Jin , Kim Hyoun-Woo , Kim Seung-Lee , Lee Dong-Joo , Lee Yongseok , Park Byeong-Gon , Ryu Yoon-Hyun , Shin In-Gu , Zang Weicheng ,   (KMTNet Collaboration), Dominik Martin , Helling Christiane , Hundertmark Markus , Jørgensen Uffe G. , Longa-Peña Penelope , Lowry Stephen , Sajadian Sedighe , Burgdorf Martin J. , Campbell-White Justyn , Ciceri Simona , Evans Daniel F. , Fujii Yuri I. , Hinse Tobias C. , Rahvar Sohrab , Rabus Markus , Skottfelt Jesper , Snodgrass Colin , Southworth John ,   (MiNDSTEp Collaboration)
Published: February 2019

Abstract
The kinematics of isolated brown dwarfs in the Galaxy, beyond the solar neighborhood, is virtually unknown. Microlensing has the potential to probe this hidden population, as it can measure both the mass and five of the six phase-space coordinates (all except the radial velocity) even of a dark isolated lens. However, the measurements of both the microlens-parallax and finite-source effects are needed in order to recover the full information. Here, we combine the Spitzer satellite parallax measurement with the ground-based light curve, which exhibits strong finite-source effects, of event OGLE-2017-BLG-0896. We find two degenerate solutions for the lens (due to the known satellite-parallax degeneracy), which are consistent with each other except for their proper motion. The lens is an isolated brown dwarf with a mass of either 18 ± 1 M

J
or 20 ± 1 M

J
. This is the lowest isolated-object mass measurement to date, only ∼45% more massive than the theoretical deuterium-fusion boundary at solar metallicity, which is the common definition of a free-floating planet. The brown dwarf is located at either 3.9 ± 0.1 kpc or 4.1 ± 0.1 kpc toward the Galactic bulge, but with proper motion in the opposite direction of disk stars, with one solution suggesting it is moving within the Galactic plane. While it is possibly a halo brown dwarf, it might also represent a different, unknown population.
ALMA High Angular Resolution Polarization Study: An Extremely Young Class 0 Source, OMC-3/MMS 6
Authors: Takahashi Satoko , Machida Masahiro N. , Tomisaka Kohji , Ho Paul T. P. , Fomalont Edward B. , Nakanishi Kouichiro , Girart Josep Miquel 
Published: February 2019

Abstract
Using the ≈16 km long baseline data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), we imaged the Stokes I emission and linearly polarized intensity (PI) in the 1.1 mm continuum band of a very young intermediate-mass protostellar source, MMS 6, in the Orion Molecular Cloud-3. The achieved angular resolution, 0.″02 × 0.″03 (≈10 au), shows for the first time a wealth of data on the dust emission polarization in the central 200 au of a protostar. The PI peak is offset to the southeast (SE) by ≈20 au with respect to the Stokes I peak. Its polarization degree is 11% with its E-vector orientation of the position angle ≈135°. A partial ringlike structure with a radius of ≈80 au is detected in PI but not in the Stokes I. Northwest (NW) and SE parts of the ring are bright, with a high polarization degree of ≳10%, and their E-vector orientations are roughly orthogonal to those observed near the center. We also detected an armlike polarized structure, extending to 1000 au scale to the north, with the E-vectors aligned along the minor axis of the structure. We explored possible origins of the polarized emission by comparing them with magnetohydrodynamical simulations of the toroidal wrapping of the magnetic field. The simulations are consistent with the PI emission in the ringlike and the extended armlike structures observed with ALMA. However, the current simulations do not completely reproduce observed polarization characteristics in the central 50 au. Although the self-scattering model can explain the polarization pattern and positional offset between the Stokes I and PI in the central 50 au, this model is not able to reproduce the observed high degree of polarization.
AGN Torus Detectability at Submillimeter Wavelengths: What to Expect from ALMA Continuum Data
Authors: Pasetto Alice , González-Martín Omaira , Esparza-Arredondo Donaji , Osorio-Clavijo Natalia , Victoria-Ceballos César Ivan , Martínez-Paredes Mariela 
Published: February 2019

Abstract
Dust close (∼few pc) to the accretion disk in active galactic nuclei (AGNs) is key to understanding many of their observational signatures, and it is key to tracing how the AGN is fed or even evolves along its duty cycle. With estimated sizes of less than 10 pc, as constrained by mid-IR (MIR) high angular resolution data, only the superb spatial resolution achieved by ALMA is able to actually image this dusty structure. However, the question regarding how the dust at submillimeter wavelengths (sub-mm, typical ALMA band) behaves in the AGN contest, arises. We study the detectability of the emission associated with the AGN dusty structure at submillimeter wavelengths using ALMA, in a theoretical and observational way. Theoretically, we use the Clumpy models from Nenkova et al., together with the MIR to X-ray and radio fundamental plane scaling relations. We find that it is more likely to detect bigger and denser dusty tori at the highest ALMA frequency (666 GHz/450 μm). We also find that with 1 hr at 353 GHz/850 μm and 10 hr at 666 GHz/450 μm we can detect, with a high detection limit, a 1 mJy torus (characteristic of bright AGNs). This means that an object for which the unresolved spectral energy distribution (SED) is at 12 μm has a flux of ∼1 mJy. Observationally, we use four prototypical AGNs: NGC 1052 (low-luminosity AGN), NGC 1068 (type 2), NGC 3516 (type 1.5), and I Zw 1 (QSO), with radio, submillimeter, and MIR data available. All the MIR spectra are best fit with the smooth model reported by Fritz et al. A power law and a single, or a composition of, synchrotron component(s) reproduce the centimeter radio wavelengths. We combined and extrapolated both fits to compare the extrapolation of both torus and jet contributors at submillimeter wavelengths with data at these wavelengths. Our observational results are consistent with our theoretical results. The most promising candidate to detect the torus is the QSO I Zw 1 (therefore, highly accreting sources in general), although it cannot be resolved owing to the distance of this source. We suggest that to explore the detection of a torus at submillimeter wavelengths, it is necessary to perform an SED analysis including radio data, with particular attention to the angular resolution.
Time-dependent Electron Acceleration in Pulsar Wind Termination Shocks: Application to the 2007 September Crab Nebula Gamma-Ray Flare
Authors: Kroon John J. , Becker Peter A. , Finke Justin D. 
Published: February 2019

Abstract
In 2007 September, the Crab Nebula exhibited a bright γ-ray flare in the GeV energy range that was detected by AGILE. The observed emission at ≳160 MeV indicates that the radiating electrons had energies above the classical synchrotron radiation-reaction limit, thus presenting a serious challenge to classical models for electron acceleration in astrophysical environments. In this paper, we apply our recently developed time-dependent self-similar analytical model describing electrostatic acceleration in the explosive reconnection region around the pulsar wind termination shock to the 2007 September flare. This event was unique in that it displayed both long-duration “wave” and short-duration “subflare” features. The unusual temporal variation makes this flare an especially interesting test for our model. We demonstrate that our model can reproduce the time-dependent γ-ray spectrum for this event, as well as the associated γ-ray light curve, obtained by integrating the spectrum for photon energies ≥100 MeV. This establishes that our time-dependent electrostatic acceleration model can explain both wave and subflare transients, which lends further support to the theoretical framework we have developed. We also further examine the validity of the self-similar electric and magnetic field evolution implied by our model. We conclude that strong electrostatic acceleration driven by shock-induced magnetic reconnection is able to power the Crab Nebula γ-ray flares by energizing the electrons on sub-Larmor timescales.
Extremely High Excitation SiO Lines in Disk-outflow Systems in Orion Source I
Authors: Kim Mi Kyoung , Hirota Tomoya , Machida Masahiro N. , Matsushita Yuko , Motogi Kazuhito , Matsumoto Naoko , Honma Mareki 
Published: February 2019

Abstract
We present high-resolution images of the submillimeter SiO line emissions of a massive young stellar object Orion Source I using the Atacama Large Millimeter/submillimeter Array at band 8. We detected the 464 GHz SiO v = 4 J = 11–10 line in Source I, which is the first detection of the SiO v = 4 line in star-forming regions, together with the 465 GHz 29SiO v = 2 J = 11–10 and the 428 GHz SiO v = 2 J = 10–9 lines with a resolution of 50 au. The 29SiO v = 2 J = 11–10 and SiO v = 4 J = 11–10 lines have compact structures with a diameter of <80 au. The spatial and velocity distributions suggest that the line emissions are associated with the base of the outflow and the surface of the edge-on disk. In contrast, SiO v = 2 J = 10–9 emission shows a bipolar structure in the direction of northeast–southwest low-velocity outflow with a ∼200 au scale. The emission line exhibits a velocity gradient along the direction of the disk elongation. With the assumption of the ring structure with Keplerian rotation, we estimated the lower limit of the central mass to be 7 M
⊙ and the radius to be 12 au < r < 26 au.
Orion SrcI’s Disk Is Salty
Authors: Ginsburg Adam , McGuire Brett , Plambeck Richard , Bally John , Goddi Ciriaco , Wright Melvyn 
Published: February 2019

Abstract
We report the detection of NaCl, KCl, and their 37Cl and 41K isotopologues toward the disk around Orion SrcI. About 60 transitions of these molecules were identified. This is the first detection of these molecules in the interstellar medium not associated with the ejecta of evolved stars. It is also the first ever detection of the vibrationally excited states of these lines in the ISM above v = 1, with firm detections up to v = 6. The salt emission traces the region just above the continuum disk, possibly forming the base of the outflow. The emission from the vibrationally excited transitions is inconsistent with a single temperature, implying the lines are not in LTE. We examine several possible explanations of the observed high excitation lines, concluding that the vibrational states are most likely to be radiatively excited via rovibrational transitions in the 25–35

(NaCl) and 35–45

(KCl) range. We suggest that the molecules are produced by destruction of dust particles. Because these molecules are so rare, they are potentially unique tools for identifying high-mass protostellar disks and measuring the radiation environment around accreting young stars.
Turbulent Dynamo in a Weakly Ionized Medium
Authors: Xu Siyao , Garain Sudip K. , Balsara Dinshaw S. , Lazarian A. 
Published: February 2019

Abstract
The small-scale turbulent dynamo is an important process contributing to the cosmic magnetization. In partially ionized astrophysical plasmas, the dynamo growth of magnetic energy strongly depends on the coupling state between ions and neutrals and the ion-neutral collisional damping effect. A new damping stage of turbulent dynamo in a weakly ionized medium was theoretically predicted by Xu & Lazarian. By carrying out a 3D two-fluid dynamo simulation, we have for the first time numerically confirmed the physical conditions and the linear-in-time growth of the magnetic field strength of the damping stage of a dynamo. The dynamo-amplified magnetic field has a characteristic length as the damping scale, which increases with time and can reach the injection scale of turbulence after around eight turnover times of the largest eddy, given sufficiently low ionization fraction and a weak initial magnetic field. Due to the weak coupling between ions and neutrals, most turbulent energy carried by neutrals cannot be converted to magnetic energy, resulting in a relatively weak magnetic field at the end of the dynamo. This result has important implications for the growth of magnetic fields in the partially ionized interstellar medium and shock acceleration of Galactic cosmic rays.
A Mini Survey of Methyl Cyanide toward Extended Green Objects
Authors: Hung T. , Liu Sheng-Yuan , Su Yu-Nung , He J. H. , Lee Hsu-Tai , Takahashi Satoko , Chen Huei-Ru 
Published: February 2019

Abstract
We present results of a survey of methyl cyanide (CH3CN) J = 12–11 toward 56 sources, including 35 Extended Green Objects (EGOs) and 21 nearby AKARI counterparts, with the Submillimeter Telescope (SMT) in order to characterize the nature of EGOs. CH3CN, a tracer of hot core emission, is detected in 19 EGOs (∼54%) and five AKARI bright sources (∼24%). By analyzing the observed CH3CN features, we find an average line width of 6.5 km s−1. For the sources detected with CH3CN, we derive CH3CN column densities log10(N [cm−2]) = 14–17 with gas temperatures in the range 40–300 K. The small filling factors (10−2–10−4) may reflect the rather compact CH3CN emitting regions, which correspond to linear sizes of ∼0.01–0.08 pc. We also estimate the virial masses and gas masses of these sources. Our derived gas masses are lower than the virial masses, possibly because CH3CN traces more energetic motions such as outflows and shocks. Alternatively, we cannot rule out that the virial masses are overestimated due to the presence of unresolved CH3CN kinetic components, such as the rotation structures observed around the young stellar objects.
Jensen–Shannon Complexity Measurements in Solar Wind Magnetic Field Fluctuations
Authors: Weygand James M. , Kivelson Margaret G. 
Published: February 2019

Abstract
Turbulent magnetic field fluctuations in the solar wind have been extensively investigated, but few studies have analyzed their complexity. Jensen–Shannon complexity maps of time series data provide a mathematical tool that can characterize fluctuations in laboratory experiments as stochastic, chaotic, or periodic phenomena. We apply this recently developed tool to characterize stochastic behavior in solar wind structures, including interplanetary coronal mass ejections (ICMEs), co-rotating interactions regions (CIRs), and turbulent magnetic fluctuation intervals. We find that the turbulent intervals observed by Helios, Wind, and Ulysses lie within the stochastic region of the complexity maps and that their complexity decreases while their normalized entropy increases with distance from the Sun. The complexity values associated with the fast solar wind (>550 km s−1) turbulence identified in Ulysses data beyond 5 au are highest at low latitudes (<10°) and lowest at latitudes above 20°. The Jensen–Shannon complexity maps show that fluctuations in the magnetic field, plasma flow, and density of the solar wind at 1 au are stochastic in ICMEs and CIRs identified in Wind data. Our analysis of Ulysses data between 1.4 and 5.4 au shows that the complexity of the ICMEs decreases with distance from the Sun, and the normalized entropy increases. Furthermore, the complexity values associated with magnetic field fluctuations in ICMEs identified in Ulysses data behave like the slow solar wind turbulence fluctuations within 4 au and take on values closer to the complexity values of the fast solar wind beyond 4 au.
Identifying Sagittarius Stream Stars by Their APOGEE Chemical Abundance Signatures
Authors: Hasselquist Sten , Carlin Jeffrey L. , Holtzman Jon A. , Shetrone Matthew , Hayes Christian R. , Cunha Katia , Smith Verne , Beaton Rachael L. , Sobeck Jennifer , Allende Prieto Carlos , Majewski Steven R. , Anguiano Borja , Bizyaev Dmitry , García-Hernández D. A. , Lane Richard R. , Pan Kaike , Nidever David L. , Fernández-Trincado José. G. , Wilson John C. , Zamora Olga 
Published: February 2019

Abstract
The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey provides precise chemical abundances of 18 chemical elements for ∼176,000 red giant stars distributed over much of the Milky Way Galaxy (MW), and includes observations of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). The APOGEE chemical abundance patterns of Sgr have revealed that it is chemically distinct from the MW in most chemical elements. We employ a k-means clustering algorithm to six-dimensional chemical space defined by [(C+N)/Fe], [O/Fe], [Mg/Fe], [Al/Fe], [Mn/Fe], and [Ni/Fe] to identify 62 MW stars in the APOGEE sample that have Sgr-like chemical abundances. Of the 62 stars, 35 have Gaia kinematics and positions consistent with those predicted by N-body simulations of the Sgr stream, and are likely stars that have been stripped from Sgr during the last two pericenter passages (<2 Gyr ago). Another 20 of the 62 stars exhibit chemical abundances indistinguishable from the Sgr stream stars, but are on highly eccentric orbits with median r
apo ∼ 25 kpc. These stars are likely the “accreted” halo population thought to be the result of a separate merger with the MW 8–11 Gyr ago. We also find one hypervelocity star candidate. We conclude that Sgr was enriched to [Fe/H] ∼ −0.2 before its most recent pericenter passage. If the “accreted halo” population is from one major accretion event, then this progenitor galaxy was enriched to at least [Fe/H] ∼ −0.6, and had a similar star formation history to Sgr before merging.
Interstellar Neutral Gas Species and Their Pickup Ions inside the Heliospheric Termination Shock. Ionization Rates for H, O, Ne, and He
Authors: Sokół Justyna M. , Bzowski Maciej , Tokumaru Munetoshi 
Published: February 2019

Abstract
Solar ionizing factors are responsible for modulation of interstellar neutral gas and its derivative populations inside the heliosphere. We provide an overview of the current state of knowledge about them for heliospheric particles inside the termination shock. We discuss charge exchange with solar wind particles, photoionization, and electron impact ionization for hydrogen, oxygen, neon, and helium from 1985 to 2018 both in the ecliptic plane and in the polar regions. We discuss ionization rates as a function of time, distance to the Sun, and latitude. We compare the total ionization rates among the species within a consistent and homogeneous system of calculation of the ionization rates. The highest total ionization rates at 1 au in the ecliptic plane are for hydrogen and oxygen, and the lowest are for helium. In the polar regions, the strongest ionization losses are for oxygen, regardless of the solar activity. Photoionization is the dominant ionization reaction for helium and neon, and a reaction of high significance for oxygen. Charge exchange with solar wind particles is the dominant ionization reaction for hydrogen and the second important ionization reaction for oxygen. Electron impact ionization is an important ionization reaction for Ne and He, with the contribution to the total ionization rates stronger within 1 au and smaller outside. The total ionization rates for He and Ne vary in time with the solar activity, whereas the total ionization rates for H and O follow the cyclic solar wind variations out of the ecliptic plane and aperiodic variations in the ecliptic plane.
Demonstration of Magnetic Field Tomography with Starlight Polarization toward a Diffuse Sightline of the ISM
Authors: Panopoulou Georgia V. , Tassis Konstantinos , Skalidis Raphael , Blinov Dmitriy , Liodakis Ioannis , Pavlidou Vasiliki , Potter Stephen B. , Ramaprakash Anamparambu N. , Readhead Anthony C. S. , Wehus Ingunn K. 
Published: February 2019

Abstract
The availability of large data sets with stellar distance and polarization information will enable a tomographic reconstruction of the (plane-of-the-sky-projected) interstellar magnetic field in the near future. We demonstrate the feasibility of such a decomposition within a small region of the diffuse interstellar medium (ISM). We combine measurements of starlight (R-band) linear polarization obtained using the RoboPol polarimeter with stellar distances from the second Gaia data release. The stellar sample is brighter than 17 mag in the R-band and reaches out to several kiloparsecs from the Sun. H i emission spectra reveal the existence of two distinct clouds along the line of sight. We decompose the line-of-sight-integrated stellar polarizations to obtain the mean polarization properties of the two clouds. The two clouds exhibit significant differences in terms of column density and polarization properties. Their mean plane-of-the-sky magnetic field orientation differs by 60°. We show how our tomographic decomposition can be used to constrain our estimates of the polarizing efficiency of the clouds as well as the frequency dependence of the polarization angle of polarized dust emission. We also demonstrate a new method to constrain cloud distances based on this decomposition. Our results represent a preview of the wealth of information that can be obtained from a tomographic map of the ISM magnetic field.