bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-contrast Demonstration of an Apodized Vortex Coronagraph
Authors: Llop-Sayson Jorge , Ruane Garreth , Mawet Dimitri , Jovanovic Nemanja , Coker Carl T. , Delorme Jacques-Robert , Echeverri Daniel , Fucik Jason , Eldorado Riggs A J , Wallace J. Kent 
Published: February 2020

Abstract
High-contrast imaging is the primary path to the direct detection and characterization of Earth-like planets around solar-type stars; a cleverly designed internal coronagraph suppresses the light from the star, revealing the elusive circumstellar companions. However, future large-aperture telescopes (>4 m in diameter) will likely have segmented primary mirrors, which cause additional diffraction of unwanted stellar light. Here we present the first high-contrast laboratory demonstration of an apodized vortex coronagraph, in which an apodizer is placed upstream of a vortex focal plane mask to improve its performance with a segmented aperture. The gray-scale apodization is numerically optimized to yield a better sensitivity to faint companions assuming an aperture shape similar to the LUVOIR-B concept. Using wavefront sensing and control over a one-sided dark hole, we achieve a raw contrast of 2 × 10−8 in monochromatic light at 775 nm, and a raw contrast of 4 × 10−8 in a 10% bandwidth. These results open the path to a new family of coronagraph designs, optimally suited for next-generation segmented space telescopes.
Machine-learning Regression of Extinction in the Second Gaia Data Release
Authors: Bai Yu , Liu JiFeng , Wang YiLun , Wang Song 
Published: February 2020

Abstract
Machine learning has become a popular tool to help us make better decisions and predictions, based on experiences, observations, and analyzing patterns, within a given data set without explicit functions. In this paper, we describe an application of the supervised machine-learning algorithm to the extinction regression for the second Gaia data release, based on the combination of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, Sloan Extension for Galactic Understanding and Exploration, and the Apache Point Observatory Galactic Evolution Experiment. The derived extinction in our training sample is consistent with other spectrum-based estimates, and its standard deviation of the cross-validations is 0.0127 mag. A blind test is carried out using the RAdial Velocity Experiment catalog, and the standard deviation is 0.0372 mag. Such a precise training sample enables us to regress the extinction, E(BP–RP), for 133 million stars in the second Gaia data release. Of these, 106 million stars have the uncertainties less than 0.1 mag, which suffer less bias from the external regression. We also find that there are high deviations between the extinctions from photometry-based methods, and between spectrum- and photometry-based methods. This implies that the spectrum-based method could bring more signal to a regressing model than multiband photometry, and a higher signal-to-noise ratio would acquire a more reliable result.
The Young Planetary System K2-25: Constraints on Companions and Starspots
Authors: Kain Isabel J. , Newton Elisabeth R. , Dittmann Jason A. , Irwin Jonathan M. , Mann Andrew W. , Thao Pa Chia , Charbonneau David , Winters Jennifer G. 
Published: February 2020

Abstract
The abundance of planets with orbital periods of a few to tens of days suggests that exoplanets experience complex dynamical histories. Planets in young stellar clusters or associations have well-constrained ages and therefore provide an opportunity to explore the dynamical evolution of exoplanets. K2-25b is a Neptune-sized planet in an eccentric, 3.48 day orbit around an M4.5 dwarf star in the Hyades cluster (650 Myr). In order to investigate its non-zero eccentricity and tight orbit, we analyze transit timing variations (TTVs) which could reveal clues to the migration processes that may have acted on the planet. We obtain 12 nonconsecutive transits using the MEarth observatories and long-term photometric monitoring, which we combine with 10 transits from the Spitzer Space Telescope and 20 transits from K2. Tables of MEarth photometry accompany this work. We fit each transit lightcurve independently. We first investigate whether inhomogeneities on the stellar surface (such as spots or plages) are differentially affecting our transit observations. The measured transit depth does not vary significantly between transits, though we see some deviations from the fiducial transit model. We then looked for TTVs as evidence of a nontransiting perturber in the system. We find no evidence for >1 M
⊕ mass companions within a 2:1 period ratio, or for >5 M
⊕ mass planets within a 7:2 period ratio.
On the Inference of a Star’s Inclination Angle from its Rotation Velocity and Projected Rotation Velocity
Authors: Masuda Kento , Winn Joshua N. 
Published: February 2020

Abstract
It is possible to learn about the orientation of a star’s rotation axis by combining measurements of the star’s rotation velocity (v) and its projection onto our line of sight (v sin i). This idea has found many applications, including the investigation of the obliquities of stars with transiting planets. Here, we present a method for the probabilistic inference of the inclination of the star’s rotation axis based on independent data sets that constrain v and v sin i. We also correct several errors and misconceptions that appear in the literature.
Observations of the Orion Source I Disk and Outflow Interface
Authors: Wright Melvyn , Plambeck Richard , Hirota Tomoya , Ginsburg Adam , McGuire Brett , Bally John , Goddi Ciriaco 
Published: February 2020

Abstract
We imaged the continuum and molecular line emission from Orion Source I (SrcI) with up to 30 mas (12 au) resolution at 43, 99, 223, and 340 GHz in an attempt to probe the structure and chemistry of the circumstellar disk and bipolar outflow associated with this high-mass protostar. The continuum spectral index ranges from ∼2 along the midplane of the disk to ∼3 along the edges, consistent with dust that is optically thick in the midplane but becomes optically thin at the periphery. Salt (NaCl) emission is visible where the dust is optically thin; it provides a unique tracer of the velocity field within the disk. All other molecules that we have mapped—H2O, AlO, SiO, SiS, SO, and SO2—appear to originate primarily in the bipolar outflow. The base of the outflow is corotating with the disk. SiS shows a filamentary structure that is most prominent along the edges of the outflow. The molecular distributions suggest that Si and Al released from dust grains in the disk react with oxygen derived from H2O to form SiO and AlO, and with SO and SO2 to form SiS.
Objectively Determining States of the Solar Wind Using Machine Learning
Authors: Roberts D. Aaron , Karimabadi Homa , Sipes Tamara , Ko Yuan-Kuen , Lepri Susan 
Published: February 2020

Abstract
Conclusively determining the states of the solar wind will aid in tracing the origins of those states to the Sun, and in the process help to find the wind’s origin and acceleration mechanism(s). Prior studies have characterized the various states of the wind, making lists that are only partially based on objective criteria; different approaches obtain substantially different results. To uncover the unbiased states of the solar wind, we use “k-means clustering”—an unsupervised machine learning method—including constructed multipoint variables. The method allows exploration of different descriptive state variables and numbers of fundamental states (clusters). We show that the clusters reveal structures similar to those found by more ad hoc means, including coronal hole wind, interplanetary coronal mass ejections, “slow wind” (better: noncoronal hole flow), “pseudostreamers,” and stream interaction regions, but with differences that should be useful in refining our previous ideas. These results demonstrate the viability of the approach and warrant further study to understand the origin of remaining discrepancies. Complexity in k-means characterization of the wind may ultimately point to complexity at the source; studies closer to the Sun with Parker Solar Probe will help. We confirm the utility of a set of variables that can serve as a proxy for composition measurements. This proxy permits studies at high time resolution and where composition is not available. This and our recently developed unsupervised multivariate clustering technique are expected to be beneficial in the automated identification of structures and events in a variety of studies.
Ultrahigh-energy Cosmic-Ray Interactions as the Origin of Very High-energy γ-Rays from BL Lacertae Objects
Authors: Das Saikat , Gupta Nayantara , Razzaque Soebur 
Published: February 2020

Abstract
We explain the observed multiwavelength photon spectrum of a number of BL Lacertae (BL Lac) objects detected at very high energy (VHE, E ≳ 30 GeV), using a lepto-hadronic emission model. The one-zone leptonic emission is employed to fit the synchrotron peak. Subsequently, the SSC spectrum is calculated, such that it extends up to the highest energy possible for the jet parameters considered. The data points beyond this energy, and also in the entire VHE range are well explained using a hadronic emission model. The ultrahigh-energy cosmic rays (UHECRs, E ≳ 0.1 EeV) escaping from the source interact with the extragalactic background light (EBL) during propagation over cosmological distances to initiate electromagnetic cascade down to ∼1 GeV energies. The resulting photon spectrum peaks at ∼1 TeV energies. We consider a random turbulent extragalactic magnetic field (EGMF) with a Kolmogorov power spectrum to find the survival rate of UHECRs within 0.°1 of the direction of propagation in which the observer is situated. We restrict ourselves to an rms value of EGMF, B
rms ∼ 10−5 nG, for a significant contribution to the photon spectral energy distribution from UHECR interactions. We found that UHECR interactions on the EBL and secondary cascade emission can fit gamma-ray data from the BL Lac objects we considered at the highest energies. The required luminosity in UHECRs and corresponding jet power are below the Eddington luminosities of the supermassive black holes in these BL Lac objects.
V346 Nor: The Post-outburst Life of a Peculiar Young Eruptive Star
Authors: Kóspál Á. , Szabó Zs. M. , Ábrahám P. , Kraus S. , Takami M. , Lucas P. W. , Contreras Peña C. , Udalski A. 
Published: February 2020

Abstract
FU Orionis-type objects (FUors) are young low-mass stars undergoing powerful accretion outbursts. The increased accretion is often accompanied by collimated jets and energetic, large-scale molecular outflows. The extra heating during the outburst may also induce detectable geometrical, chemical, and mineralogical changes in the circumstellar material, affecting possible planet formation around these objects. V346 Nor is a southern FUor with peculiar spectral characteristics. Decades after the beginning of its outburst, it unexpectedly underwent a fading event around 2010 due to a decrease in the mass accretion rate onto the star by at least two orders of magnitude. Here we present optical and near-infrared photometry and spectroscopy obtained after the minimum. Our light curves show a gradual re-brightening of V346 Nor, with its K
s-band brightness only 1.5 mag below the outburst brightness level. Our Very Large Telescope (VLT)/XSHOOTER spectroscopic observations display several strong forbidden emission lines toward the source from various metals and molecular hydrogen, suggesting the launch of a new jet. Our N-band spectrum obtained with VLT/VISIR outlines a deeper silicate absorption feature than before, indicating that the geometry of the circumstellar medium has changed in the post-outburst period compared to peak brightness.
Detecting Gravitational Scattering of Interstellar Objects Using Pulsar Timing
Authors: Jennings Ross J. , Cordes James M. , Chatterjee Shami 
Published: February 2020

Abstract
Gravitational scattering events, in which the path of an interstellar object is deflected by a pulsar or the solar system, give rise to reflex motion that can potentially be detected using pulsar timing. We determine the form of the timing signal expected from a gravitational scattering event, which is ramp-like and resembles the signal produced by a glitch or a gravitational wave burst with memory (BWM), and investigate the prospects for detecting such a signal using a pulsar timing array. The level of timing precision currently achieved for some millisecond pulsars makes it possible to detect objects as small as 10−10
M
☉, less than the mass of the dwarf planet Ceres, at impact parameters as large as

. The signals produced by gravitational scattering could provide independent constraints on models of dark matter involving asteroid-mass objects or subhalos, and should be considered as potential false positives in searches for BWMs.
A Timing Study of MAXI J1820+070 Based on Swift/XRT and NICER Monitoring in 2018/19
Authors: Stiele H. , Kong A. K. H. 
Published: February 2020

Abstract
We present a detailed timing analysis of the bright black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), during its first detected outburst lasting from 2018 March until 2019 October based on Swift/XRT window timing mode observations, corresponding UVOT data and NICER observations. The light curves clearly show four outbursts, with the source remaining in the hard state during its first outburst, while the rise of the second outburst corresponds with the transition to the soft state. A similar double outburst of GX339-4 has been observed in 2004. Here it is followed by two hard-state only outbursts. In many observations the power density spectra showed type-C quasi-periodic oscillations (QPOs) with characteristic frequencies below 1 Hz, which suggests that the source stayed in a state of low effective accretion for large parts of its outburst. The absence of other types of QPOs hinders a precise determination of the state transitions, but from combining NICER and Swift/XRT data, we find that MAXI J1820+070 went from the hard-intermediate to the soft state in less than one day. The covariance ratios derived from NICER data show an increase toward lower energies, which indicate that the source should make a transition to the soft state. This transition finally took place, after MAXI J1820+070 stayed in the hard state at rather constant luminosity for about 116 days. The steepness of the increase of the covariance ratios is not correlated with the amount of rms variability and it does not show a monotonic evolution along the outburst.
A Noncorotating Gas Component in an Extreme Starburst at z = 4.3
Authors: Tadaki Ken-ichi , Iono Daisuke , Yun Min S. , Aretxaga Itziar , Hatsukade Bunyo , Lee Minju M. , Michiyama Tomonari , Nakanishi Kouichiro , Saito Toshiki , Ueda Junko , Umehata Hideki 
Published: February 2020

Abstract
We report the detection of a noncorotating gas component in a bright unlensed submillimeter galaxy at z = 4.3, hosting a compact starburst. Atacama Large Millimeter/submillimeter Array 0.″17 and 0.″09 resolution observations of [C ii] emission clearly demonstrate that the gas kinematics are characterized by an ordered rotation. After subtracting the best-fit model of a rotating disk, we kinematically identify two residual components in the channel maps. Both observing simulations and analysis of dirty images confirm that these two subcomponents are not artificially created by noise fluctuations and beam deconvolution. One of the two has a velocity offset of 200 km s−1 and a physical separation of 2 kpc from the primary disk and is located along the kinematic minor axis of disk rotation. We conclude that this gas component is falling into the galaxy from a direction perpendicular to the disk rotation. The accretion of such small noncorotating gas components could stimulate violent disk instability, driving radial gas inflows into the center of galaxies and leading to formation of in situ clumps such as identified in dust continuum and CO. We require more theoretical studies on high gas fraction mergers with mass ratio of 1: > 10 to verify this process.
High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System
Authors: Yang Yi , Akiyama Eiji , Currie Thayne , Dong Ruobing , Hashimoto Jun , Hayashi Saeko S. , Grady Carol A. , Janson Markus , Jovanovic Nemanja , Uyama Taichi , Nakagawa Takao , Kudo Tomoyuki , Kusakabe Nobuhiko , Kuzuhara Masayuki , Abe Lyu , Brandner Wolfgang , Brandt Timothy D. , Bonnefoy Michael , Carson Joseph C. , Chilcote Jeffrey , Rich Evan A. , Feldt Markus , Goto Miwa , Groff Tyler D. , Guyon Olivier , Hayano Yutaka , Hayashi Masahiko , Henning Thomas , Hodapp Klaus W. , Ishii Miki , Iye Masanori , Kandori Ryo , Kasdin Jeremy , Knapp Gillian R. , Kwon Jungmi , Lozi Julien , Martinache Frantz , Matsuo Taro , Mayama Satoshi , Mcelwain Michael W. , Miyama Shoken , Morino Jun-Ichi , Moro-Martin Amaya , Nishimura Tetsuo , Pyo Tae-Soo , Serabyn Eugene , Suto Hiroshi , Suzuki Ryuji , Takami Michihiro , Takato Naruhisa , Terada Hiroshi , Thalmann Christian , Turner Edwin L. , Watanabe Makoto , Wisniewski John P. , Yamada Toru , Takami Hideki , Usuda Tomonori , Tamura Motohide 
Published: February 2020

Abstract
We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2–1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ∼240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19–5.64 km s−1. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17–16.43 km s−1. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.
Two Quasi-periodic Fast-propagating Magnetosonic Wave Events Observed in Active Region NOAA 11167
Authors: Miao Yuhu , Liu Yu , Elmhamdi A. , Kordi A. S. , Shen Y. D. , Al-Shammari Rehab , Al-Mosabeh Khaled , Jiang Chaowei , Yuan Ding 
Published: February 2020

Abstract
We report a detailed observational study of two quasi-periodic fast-propagating (QFP) magnetosonic wave events that occurred on 2011 March 9 and 10, respectively. Interestingly, both the events have two wave trains (WTs): a strong main one (WT-1) and a small and weak secondary one (WT-2). Peculiar and common characteristics of the two events are observed, namely, (1) the two QFP waves are accompanied with brightenings during the whole stage of the eruptions; (2) both the two main WTs are nearly propagating along the same direction; (3) extreme-ultraviolet (EUV) waves are found to be associated with the two events. Investigating various aspects of the target events, we argue that (1) the second event is accompanied with a flux rope eruption during the whole stage; (2) the second event eruption produces a new filament-like dark feature; (3) the ripples of the two WT-2 QFP waves seem to result from different triggering mechanisms. Based on the obtained observational results, we propose that the funnel-like coronal loop system is indeed playing an important role in the two WT-1 QFP waves. The development of the second WT-2 QFP wave can be explained as due to the dispersion of the main EUV front. The coexistence of the two events offers thereby a significant opportunity to reveal what driving mechanisms and structures are tightly related to the waves.
Balmer Break Galaxy Candidates at z ∼ 6: A Potential View on the Star Formation Activity at z ≳ 14
Authors: Mawatari Ken , Inoue Akio K. , Hashimoto Takuya , Silverman John , Kajisawa Masaru , Yamanaka Satoshi , Yamada Toru , Davidzon Iary , Capak Peter , Lin Lihwai , Hsieh Bau-Ching , Taniguchi Yoshiaki , Tanaka Masayuki , Ono Yoshiaki , Harikane Yuichi , Sugahara Yuma , Fujimoto Seiji , Nagao Tohru 
Published: February 2020

Abstract
We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ∼ 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K–[3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ∼ 6, although contamination from active galactic nuclei at z ∼ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ∼ 6 have stellar masses of ≈5 × 1010
M
⊙ dominated by old stellar populations with ages of ≳ 700 Myr. Assuming that all three candidates are real BBGs at z ∼ 6, we estimate the stellar mass density to be

Mpc−3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ∼ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4–12 × 10−5
M
⊙ yr−1 Mpc−3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8.
Modeling the Upper kHz QPOs of 4U 1728-34 with X-Ray Reverberation
Authors: Coughenour Benjamin M. , Cackett Edward M. , Peille Philippe , Troyer Jon S. 
Published: February 2020

Abstract
While kilohertz quasi-periodic oscillations (kHz QPOs) have been well studied for decades since their initial discovery, the cause of these signals remains unknown, as no model has been able to accurately predict all of their spectral and timing properties. Separately, X-ray reverberation lags have been detected in active galactic nuclei and stellar-mass black hole binaries, and reverberation may be expected to occur in neutron star systems as well, producing lags of the same amplitude as the lags measured of the kHz QPOs. Furthermore, the detection of a relativistically reflected Fe K line in the time-averaged spectra of many neutron star systems provides an additional motivation for testing reverberation. While it has been shown that the lag-energy properties of the lower kHz QPOs are unlikely to be produced by X-ray reverberation, the upper kHz QPOs have not yet been explored. We therefore model the upper kHz QPO lag-energy spectra using relativistic ray-tracing functions and apply them to archival Rossi X-Ray Timing Explorer data on 4U 1728–34 where upper kHz QPOs have been detected. By modeling the time-averaged spectra in which upper kHz QPOs had been significantly detected, we determine the reflected flux fraction across all energies and produce a model for the lag-energy spectra from X-ray reverberation. We explore the dependence of the modeled lag properties on several different types of reflection models but are unable to successfully reproduce the measured lags of 4U 1728–34. We conclude that reverberation alone does not explain the measured time lags detected in upper kHz QPOs.