bluuebunny/crossref_metadata_2025_split huggingface dataset:
LEGUS and Hα-LEGUS Observations of Star Clusters in NGC 4449: Improved Ages and the Fraction of Light in Clusters as a Function of Age
Authors: Whitmore Bradley C. , Chandar Rupali , Lee Janice , Ubeda Leonardo , Adamo Angela , Aloisi Alessandra , Calzetti Daniela , Cignoni Michele , Cook David , Dale Daniel , Elmegreen B. G. , Gouliermis Dimitrios , Grebel Eva K. , Grasha Kathryn , Johnson Kelsey E. , Kim Hwihyun , Sacchi Elena , Smith Linda J. , Tosi Monica , Wofford Aida 
Published: February 2020

Abstract
We present a new catalog and results for the cluster system of the starburst galaxy NGC 4449, based on multiband imaging observations taken as part of the LEGUS and H
α
-LEGUS surveys. We improve the spectral energy fitting method used to estimate cluster ages, and find that the results, particularly for older clusters, are in better agreement with those from spectroscopy. The inclusion of H
α
measurements, the role of stochasticity for low-mass clusters, the assumptions about reddening, and the choices of SSP model and metallicity all have important impacts on the age dating of clusters. A comparison with ages derived from stellar color–magnitude diagrams for partially resolved clusters shows reasonable agreement, but large scatter in some cases. The fraction of light found in clusters relative to the total light (i.e., T

L
) in the U, B, and V filters in 25 different ≈ kiloparsec-size regions throughout NGC 4449 correlates with both the specific region luminosity, R

L
, and the dominant age of the underlying stellar population in each region. The observed cluster age distribution is found to decline over time as dN/dτ ∝ τ

γ
, with γ = −0.85 ± 0.15, independent of cluster mass, and is consistent with strong, early cluster disruption. The mass functions of the clusters can be described by a power law with dN/dM ∝ M

β
and β = −1.86 ± 0.2, independent of cluster age. The mass and age distributions are quite resilient to differences in age-dating methods. There is tentative evidence for a factor of 2–3 enhancement in both the star and cluster formation rate ≈100–300 Myr ago, indicating that cluster formation tracks star formation generally. The enhancement is probably associated with an earlier interaction event.
What Would Happen if We Were About 1 pc Away from a Supermassive Black Hole?
Authors: Iorio Lorenzo 
Published: February 2020

Abstract
We consider a hypothetical planet with the same mass m, radius R, angular momentum S, oblateness J
2, semimajor axis a, eccentricity e, inclination I, and obliquity ε of the Earth orbiting a main-sequence star with the same mass

and radius

of the Sun at a distance

from a supermassive black hole in the center of the hosting galaxy with the same mass

of, say, M87*. We preliminarily investigate some dynamical consequences of its presence in the neighborhood of such a stellar system on the planet’s possibility of sustaining complex life over time. In particular, we obtain general analytic expressions for the long-term rates of change, doubly averaged over both the planetary and the galactocentric orbital periods

and

, of e, I, ε, which are the main quantities directly linked to stellar insolation. We find that, for certain orbital configurations, the planet’s perihelion distance

may greatly shrink and even lead to, in some cases, an impact with the star. I may also notably change, with variations even of the order of tens of degrees. On the other hand, ε does not seem to be particularly affected, being shifted, at most, by

over 1 Myr. Our results strongly depend on the eccentricity

of the galactocentric motion.
A Hybrid Deep Learning Approach to Cosmological Constraints from Galaxy Redshift Surveys
Authors: Ntampaka Michelle , Eisenstein Daniel J. , Yuan Sihan , Garrison Lehman H. 
Published: February 2020

Abstract
We present a deep machine learning (ML)–based technique for accurately determining σ
8 and Ω
m
from mock 3D galaxy surveys. The mock surveys are built from the AbacusCosmos suite of N-body simulations, which comprises 40 cosmological volume simulations spanning a range of cosmological parameter values, and we account for uncertainties in galaxy formation scenarios through the use of generalized halo occupation distributions (HODs). We explore a trio of ML models: a 3D convolutional neural network (CNN), a power spectrum–based fully connected network, and a hybrid approach that merges the two to combine physically motivated summary statistics with flexible CNNs. We describe best practices for training a deep model on a suite of matched-phase simulations, and we test our model on a completely independent sample that uses previously unseen initial conditions, cosmological parameters, and HOD parameters. Despite the fact that the mock observations are quite small (∼0.07 h
−3 Gpc3) and the training data span a large parameter space (six cosmological and six HOD parameters), the CNN and hybrid CNN can constrain estimates of σ
8 and Ω
m
to ∼3% and ∼4%, respectively.
Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: The KINGFISH Sample
Authors: Aniano G. , Draine B. T. , Hunt L. K. , Sandstrom K. , Calzetti D. , Kennicutt R. C. , Dale D. A. , Galametz M. , Gordon K. D. , Leroy A. K. , Smith J.-D. T. , Roussel H. , Sauvage M. , Walter F. , Armus L. , Bolatto A. D. , Boquien M. , Crocker A. , De Looze I. , Donovan Meyer J. , Helou G. , Hinz J. , Johnson B. D. , Koda J. , Miller A. , Montiel E. , Murphy E. J. , Relaño M. , Rix H.-W. , Schinnerer E. , Skibba R. , Wolfire M. G. , Engelbracht C. W. 
Published: February 2020

Abstract
Interstellar dust and starlight are modeled for the galaxies of the project “Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel.” The galaxies were observed by the Infrared Array Camera and the Multiband Imaging Photometer for Spitzer on Spitzer Space Telescope, and the Photodetector Array Camera and Spectrometer and the Spectral and Photometric Imaging Receiver on Herschel Space Observatory. With data from 3.6 to 500 μm, dust models are strongly constrained. Using a physical dust model, for each pixel in each galaxy we estimate (1) dust surface density, (2) dust mass fraction in polycyclic aromatic hydrocarbons (PAHs), (3) distribution of starlight intensities heating the dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR luminosity originating in subregions with high starlight intensity. The dust models successfully reproduce the observed global and resolved spectral energy distributions. With the angular resolution of Herschel, we obtain well-resolved maps (available online) for the dust properties. As in previous studies, we find the PAH fraction

to be an increasing function of metallicity, with a threshold oxygen abundance Z/Z
⊙ ≈ 0.1, but we find the data to be fitted best with

increasing linearly with

above a threshold value of 0.15(O/H)⊙. We obtain total dust masses for each galaxy by summing the dust mass over the individual map pixels; these “resolved” dust masses are consistent with the masses inferred from a model fit to the global photometry. The global dust-to-gas ratios obtained from this study are found to correlate with galaxy metallicities. Systems with Z/Z
⊙ ≳ 0.5 have most of their refractory elements locked up in dust, whereas in systems with Z/Z
⊙ ≲ 0.3 most of these elements tend to remain in the gas phase. Within galaxies, we find that

is suppressed in regions with unusually warm dust with

. With knowledge of one long-wavelength flux density ratio (e.g., f
160/f
500), the minimum starlight intensity heating the dust (

) can be estimated to within ∼50%, despite a variation in

of more than two orders of magnitude. For the adopted dust model, dust masses can be estimated to within ∼0.2 dex accuracy using the f
160/f
500 flux ratio and the integrated dust luminosity, and to ∼0.07 dex accuracy using the 500 μm luminosity

alone. There are additional systematic errors arising from the choice of dust model, but these are hard to estimate. These calibrated prescriptions for estimating starlight heating intensity and dust mass may be useful for studies of high-redshift galaxies.
The Stark Effect, Zeeman Effect, and Transition Dipole Moments for the B2Σ+−X2Σ+ Band of Aluminum Monoxide, AlO
Authors: Bai Xilin , Steimle Timothy C. 
Published: February 2020

Abstract
The experimentally measured radiative lifetimes and branching ratios were combined to determine the transition dipole moments for the B
2Σ+(v = 0–3) → X
2Σ+(v = 0–6) bands of aluminum monoxide, AlO, and compared with theoretical predictions. The B
2Σ+–X
2Σ+ (0, 1) band of a molecular beam sample of AlO was recorded at high spectral resolution both field-free and in the presence of static electric and magnetic fields. The 27Al(I = 5/2) hyperfine interaction in the B
2Σ+(v = 0) state was analyzed. The observed Stark shifts were analyzed to produce permanent electric dipole moments of 1.94(8) D and 4.45(3) D for the B
2Σ+(v = 0) and X
2Σ+(v = 1) states, respectively. It is demonstrated that the observed Zeeman spectra can be simulated using an effective Hamiltonian with the associated expected g-factors for both the X
2Σ+(v = 1) and B
2Σ+(v = 0) states.
Statistical Results for Solar Energetic Electron Spectra Observed over 12 yr with STEREO/SEPT
Authors: Dresing Nina , Effenberger Frederic , Gómez-Herrero Raúl , Heber Bernd , Klassen Andreas , Kollhoff Alexander , Richardson Ian , Theesen Solveig 
Published: February 2020

Abstract
This work presents a statistical analysis of near-relativistic solar energetic electron event spectra near 1 au. We use measurements of the Solar Electron and Proton Telescope (SEPT) on board STEREO in the energy range of 45–425 keV and utilize the SEPT electron event list containing all electron events observed by STEREO A and STEREO B from 2007 through 2018. We select 781 events with significant signal-to-noise ratios for our analysis and fit the spectra with single or broken-power-law functions of energy. We find 437 events showing broken power laws and 344 events only showing a single power law in the energy range of SEPT. For those events with broken power laws, we find a mean break energy of about 120 keV. We analyze the dependence of the spectral index on the rise times and peak intensities of the events as well as on the presence of relativistic electrons. The results show a relation between the power law spectral index and the rise times of the events with softer spectra belonging to rather impulsive events. Long rise-time events are associated with hard spectra as well as with the presence of higher-energy (>0.7 MeV) electrons. This group of events cannot be explained by a pure flare scenario but suggests an additional acceleration mechanism, involving a prolonged acceleration and/or injection of the particles. A dependence of the spectral index on the longitudinal separation from the parent solar source region was not found. A statistical analysis of the spectral indices during impulsively rising events where the rise times are below 20 minutes is also shown.
Energetic Particle Increases Associated with Stream Interaction Regions
Authors: Cohen C. M. S. , Christian E. R. , Cummings A. C. , Davis A. J. , Desai M. I. , Giacalone J. , Hill M. E. , Joyce C. J. , Labrador A. W. , Leske R. A. , Matthaeus W. H. , McComas D. J. , McNutt R. L. , Mewaldt R. A. , Mitchell D. G. , Rankin J. S. , Roelof E. C. , Schwadron N. A. , Stone E. C. , Szalay J. R. , Wiedenbeck M. E. , Allen R. C. , Ho G. C. , Jian L. K. , Lario D. , Odstrcil D. , Bale S. D. , Badman S. T. , Pulupa M. , MacDowall R. J. , Kasper J. C. , Case A. W. , Korreck K. E. , Larson D. E. , Livi Roberto , Stevens M. L. , Whittlesey Phyllis 
Published: February 2020

Abstract
The Parker Solar Probe was launched on 2018 August 12 and completed its second orbit on 2019 June 19 with perihelion of 35.7 solar radii. During this time, the Energetic Particle Instrument-Hi (EPI-Hi, one of the two energetic particle instruments comprising the Integrated Science Investigation of the Sun, IS⊙IS) measured seven proton intensity increases associated with stream interaction regions (SIRs), two of which appear to be occurring in the same region corotating with the Sun. The events are relatively weak, with observed proton spectra extending to only a few MeV and lasting for a few days. The proton spectra are best characterized by power laws with indices ranging from −4.3 to −6.5, generally softer than events associated with SIRs observed at 1 au and beyond. Helium spectra were also obtained with similar indices, allowing He/H abundance ratios to be calculated for each event. We find values of 0.016–0.031, which are consistent with ratios obtained previously for corotating interaction region events with fast solar wind ≤600 km s−1. Using the observed solar wind data combined with solar wind simulations, we study the solar wind structures associated with these events and identify additional spacecraft near 1 au appropriately positioned to observe the same structures after some corotation. Examination of the energetic particle observations from these spacecraft yields two events that may correspond to the energetic particle increases seen by EPI-Hi earlier.
Magnetic Connectivity of the Ecliptic Plane within 0.5 au: Potential Field Source Surface Modeling of the First Parker Solar Probe Encounter
Authors: Badman Samuel T. , Bale Stuart D. , Martínez Oliveros Juan C. , Panasenco Olga , Velli Marco , Stansby David , Buitrago-Casas Juan C. , Réville Victor , Bonnell John W. , Case Anthony W. , Dudok de Wit Thierry , Goetz Keith , Harvey Peter R. , Kasper Justin C. , Korreck Kelly E. , Larson Davin E. , Livi Roberto , MacDowall Robert J. , Malaspina David M. , Pulupa Marc , Stevens Michael L. , Whittlesey Phyllis L. 
Published: February 2020

Abstract
We compare magnetic field measurements taken by the FIELDS instrument on board Parker Solar Probe (PSP) during its first solar encounter to predictions obtained by potential field source surface (PFSS) modeling. Ballistic propagation is used to connect the spacecraft to the source surface. Despite the simplicity of the model, our results show striking agreement with PSP’s first observations of the heliospheric magnetic field from ∼0.5 au (107.5 R
⊙) down to 0.16 au (35.7 R
⊙). Further, we show the robustness of the agreement is improved both by allowing the photospheric input to the model to vary in time, and by advecting the field from PSP down to the PFSS model domain using in situ PSP/Solar Wind Electrons Alphas and Protons measurements of the solar wind speed instead of assuming it to be constant with longitude and latitude. We also explore the source surface height parameter (R
SS) to the PFSS model, finding that an extraordinarily low source surface height (1.3–1.5 R
⊙) predicts observed small-scale polarity inversions, which are otherwise washed out with regular modeling parameters. Finally, we extract field line traces from these models. By overlaying these on extreme ultraviolet images we observe magnetic connectivity to various equatorial and mid-latitude coronal holes, indicating plausible magnetic footpoints and offering context for future discussions of sources of the solar wind measured by PSP.
The Near-Sun Dust Environment: Initial Observations from Parker Solar Probe
Authors: Szalay J. R. , Pokorný P. , Bale S. D. , Christian E. R. , Goetz K. , Goodrich K. , Hill M. E. , Kuchner M. , Larsen R. , Malaspina D. , McComas D. J. , Mitchell D. , Page B. , Schwadron N. 
Published: February 2020

Abstract
The Parker Solar Probe (PSP) spacecraft has flown into the densest, previously unexplored, innermost region of our solar system’s zodiacal cloud. While PSP does not have a dedicated dust detector, multiple instruments on the spacecraft are sensitive to the effects of meteoroid bombardment. Here, we discuss measurements taken during PSP’s second orbit and compare them to models of the zodiacal cloud’s dust distribution. Comparing the radial impact rate trends and the timing and location of a dust impact to an energetic particle detector, we find the impactor population to be consistent with dust grains on hyperbolic orbits escaping the solar system. Assuming PSP’s impact environment is dominated by hyperbolic impactors, the total quantity of dust ejected from our solar system is estimated to be 0.5−10 tons/s. We expect PSP will encounter an increasingly intense impactor environment as its perihelion distance and semimajor axis are decreased.
Morphological Reconstruction of a Small Transient Observed by Parker Solar Probe on 2018 November 5
Authors: Wood Brian E. , Hess Phillip , Howard Russell A. , Stenborg Guillermo , Wang Yi-Ming 
Published: February 2020

Abstract
On 2018 November 5, about 24 hr before the first close perihelion passage of Parker Solar Probe (PSP), a coronal mass ejection (CME) entered the field of view of the inner detector of the Wide-field Imager for Solar PRobe (WISPR) instrument on board PSP, with the northward component of its trajectory carrying the leading edge of the CME off the top edge of the detector about four hours after its first appearance. We connect this event to a very small jetlike transient observed from 1 au by coronagraphs on both the SOlar and Heliospheric Observatory (SOHO) and the A component of the Solar TErrestrial RElations Observatory mission (STEREO-
A). This allows us to make the first three-dimensional reconstruction of a CME structure considering both observations made very close to the Sun and images from two observatories at 1 au. The CME may be small and jetlike as viewed from 1 au, but the close-in vantage point of PSP/WISPR demonstrates that it is not intrinsically jetlike but instead has a structure consistent with a flux rope morphology. Based on its appearance in the SOHO and STEREO-
A images, the event belongs in the “streamer blob” class of transients, but its kinematic behavior is very unusual, with a more impulsive acceleration than previously studied blobs.
The Enhancement of Proton Stochastic Heating in the Near-Sun Solar Wind
Authors: Martinović Mihailo M. , Klein Kristopher G. , Kasper Justin C. , Case Anthony W. , Korreck Kelly E. , Larson Davin , Livi Roberto , Stevens Michael , Whittlesey Phyllis , Chandran Benjamin D. G. , Alterman Ben L. , Huang Jia , Chen Christopher H. K. , Bale Stuart D. , Pulupa Marc , Malaspina David M. , Bonnell John W. , Harvey Peter R. , Goetz Keith , Dudok de Wit Thierry , MacDowall Robert J. 
Published: February 2020

Abstract
Stochastic heating (SH) is a nonlinear heating mechanism driven by the violation of magnetic moment invariance due to large-amplitude turbulent fluctuations producing diffusion of ions toward higher kinetic energies in the direction perpendicular to the magnetic field. It is frequently invoked as a mechanism responsible for the heating of ions in the solar wind. Here, we quantify for the first time the proton SH rate Q
⊥ at radial distances from the Sun as close as 0.16 au, using measurements from the first two Parker Solar Probe encounters. Our results for both the amplitude and radial trend of the heating rate, Q
⊥ ∝ r
−2.5, agree with previous results based on the Helios data set at heliocentric distances from 0.3 to 0.9 au. Also in agreement with previous results, Q
⊥ is significantly larger in the fast solar wind than in the slow solar wind. We identify the tendency in fast solar wind for cuts of the core proton velocity distribution transverse to the magnetic field to exhibit a flattop shape. The observed distribution agrees with previous theoretical predictions for fast solar wind where SH is the dominant heating mechanism.
Parker Solar Probe In Situ Observations of Magnetic Reconnection Exhausts during Encounter 1
Authors: Phan T. D. , Bale S. D. , Eastwood J. P. , Lavraud B. , Drake J. F. , Oieroset M. , Shay M. A. , Pulupa M. , Stevens M. , MacDowall R. J. , Case A. W. , Larson D. , Kasper J. , Whittlesey P. , Szabo A. , Korreck K. E. , Bonnell J. W. , de Wit T. Dudok , Goetz K. , Harvey P. R. , Horbury T. S. , Livi R. , Malaspina D. , Paulson K. , Raouafi N. E. , Velli M. 
Published: February 2020

Abstract
Magnetic reconnection in current sheets converts magnetic energy into particle energy. The process may play an important role in the acceleration and heating of the solar wind close to the Sun. Observations from Parker Solar Probe (PSP) provide a new opportunity to study this problem, as it measures the solar wind at unprecedented close distances to the Sun. During the first orbit, PSP encountered a large number of current sheets in the solar wind through perihelion at 35.7 solar radii. We performed a comprehensive survey of these current sheets and found evidence for 21 reconnection exhausts. These exhausts were observed in heliospheric current sheets, coronal mass ejections, and regular solar wind. However, we find that the majority of current sheets encountered around perihelion, where the magnetic field was strongest and plasma β was lowest, were Alfvénic structures associated with bursty radial jets, and these current sheets did not appear to be undergoing local reconnection. We examined conditions around current sheets to address why some current sheets reconnected while others did not. A key difference appears to be the degree of plasma velocity shear across the current sheets: the median velocity shear for the 21 reconnection exhausts was 24% of the Alfvén velocity shear, whereas the median shear across 43 Alfvénic current sheets examined was 71% of the Alfvén velocity shear. This finding could suggest that large, albeit sub-Alfvénic, velocity shears suppress reconnection. An alternative interpretation is that the Alfvénic current sheets are isolated rotational discontinuities that do not undergo local reconnection.
Observations of the 2019 April 4 Solar Energetic Particle Event at the Parker Solar Probe
Authors: Leske R. A. , Christian E. R. , Cohen C. M. S. , Cummings A. C. , Davis A. J. , Desai M. I. , Giacalone J. , Hill M. E. , Joyce C. J. , Krimigis S. M. , Labrador A. W. , Malandraki O. , Matthaeus W. H. , McComas D. J. , McNutt R. L. , Mewaldt R. A. , Mitchell D. G. , Posner A. , Rankin J. S. , Roelof E. C. , Schwadron N. A. , Stone E. C. , Szalay J. R. , Wiedenbeck M. E. , Vourlidas A. , Bale S. D. , MacDowall R. J. , Pulupa M. , Kasper J. C. , Allen R. C. , Case A. W. , Korreck K. E. , Livi R. , Stevens M. L. , Whittlesey P. , Poduval B. 
Published: February 2020

Abstract
A solar energetic particle event was detected by the Integrated Science Investigation of the Sun (IS⊙IS) instrument suite on Parker Solar Probe (PSP) on 2019 April 4 when the spacecraft was inside of 0.17 au and less than 1 day before its second perihelion, providing an opportunity to study solar particle acceleration and transport unprecedentedly close to the source. The event was very small, with peak 1 MeV proton intensities of ∼0.3 particles (cm2 sr s MeV)−1, and was undetectable above background levels at energies above 10 MeV or in particle detectors at 1 au. It was strongly anisotropic, with intensities flowing outward from the Sun up to 30 times greater than those flowing inward persisting throughout the event. Temporal association between particle increases and small brightness surges in the extreme-ultraviolet observed by the Solar TErrestrial RElations Observatory, which were also accompanied by type III radio emission seen by the Electromagnetic Fields Investigation on PSP, indicates that the source of this event was an active region nearly 80° east of the nominal PSP magnetic footpoint. This suggests that the field lines expanded over a wide longitudinal range between the active region in the photosphere and the corona.