Search Publications
The Fractality and Size Distributions of Astrophysical Self-Organized Criticality Systems
Aschwanden, Markus J.
The statistics of nonlinear processes in avalanching systems, based on the self-organized criticality (SOC) concept of Bak et al. (1988), predicts power-law-like size (or occurrence frequency) distribution functions. Following up on previous work, we define a standard SOC model in terms of six assumptions: (i) area fractality, (ii) volume fractali…
Unveiling the Nature of SN 2011fh: A Young and Massive Star Gives Rise to a Luminous SN 2009ip-like Event
Kochanek, Christopher S.; Prieto, Jose L.; Fox, Ori D. +6 more
In recent years, many Type IIn supernovae have been found to share striking similarities with the peculiar SN 2009ip, whose true nature is still under debate. Here, we present 10 yr of observations of SN 2011fh, an interacting transient with spectroscopic and photometric similarities to SN 2009ip. SN 2011fh had an M r ~ -16 mag bright…
The Disk-Outflow System around the Rare Young O-type Protostar W42-MME
Dewangan, L. K.; Ojha, D. K.; Mayya, Y. D. +6 more
We present line and continuum observations (resolution ~0.″3-3.″5) made with the Atacama Large Millimeter/submillimeter Array (ALMA), Submillimeter Array, and Very Large Array of a young O-type protostar W42-MME (mass: 19 ± 4 M ⊙). The ALMA 1.35 mm continuum map (resolution ~1″) shows that W42-MME is embedded in one of the cores (i.e., …
On the Origin of the Dichotomy of Stellar Activity Cycles
Corsaro, Enrico; Bonanno, Alfio
The presence of possible correlations between stellar rotation rate Ω and the frequency of the activity cycle ω cyc is still much debated. We implement a new Bayesian classification algorithm based on a simultaneous regression analysis of multiple scaling laws and we demonstrate the existence of two different scalings in the ${\mathrm{l…
The GALAH Survey: A New Sample of Extremely Metal-poor Stars Using a Machine-learning Classification Algorithm
Lewis, Geraint F.; Spitler, Lee R.; Ting, Yuan-Sen +21 more
Extremely metal-poor (EMP) stars provide a valuable probe of early chemical enrichment in the Milky Way. Here we leverage a large sample of ~600,000 high-resolution stellar spectra from the GALAH survey plus a machine-learning algorithm to find 54 candidates with estimated [Fe/H] ≤-3.0, six of which have [Fe/H] ≤-3.5. Our sample includes ~20% main…
Optical Light Curve of 4FGL J0935.3+0901: A Flaring Black Widow Candidate
Halpern, Jules P.
I obtained time-series photometry of the compact binary candidate for the Fermi source 4FGL J0935.3+0901. Superposed on the 2.44 hr orbital modulation are day-to-day variations and frequent flaring as seen in several redback and black widow millisecond pulsars (MSPs). The short orbital period favors a black widow. While the modulation of ≤1 mag is…
The Factory and the Beehive. IV. A Comprehensive Study of the Rotation X-Ray Activity Relation in Praesepe and the Hyades
Cargile, Phillip A.; Rampalli, Rayna; Law, Nicholas M. +7 more
X-ray observations of low-mass stars in open clusters are critical to understanding the dependence of magnetic activity on stellar properties and their evolution. Praesepe and the Hyades, two of the nearest, most-studied open clusters, are among the best available laboratories for examining the dependence of magnetic activity on rotation for stars…
Evaluating Non-LTE Spectral Inversions with ALMA and IBIS
Reardon, Kevin P.; Uitenbroek, Han; Hofmann, Ryan A. +3 more
We present observations of a solar magnetic network region in the millimeter continuum with the Atacama Large Millimeter/submillimeter Array (ALMA) and in the Ca 8542 and Na 5896 Å spectral lines with the Interferometric Bidimensional Spectrometer (IBIS). Our goal is to compare the measurement of local gas temperatures provided by ALMA with the te…
Charge Exchange X-Ray Emission Detected in Multiple Shells of Supernova Remnant G296.1-0.5
Uchida, Hiroyuki; Fukui, Yasuo; Tanaka, Takaaki +5 more
Recent high-resolution X-ray spectroscopy revealed the possible presence of charge exchange (CX) X-ray emission in supernova remnants (SNRs). Although CX is expected to take place at the outermost edges of SNR shells, no significant measurement has been reported so far due to the lack of nearby SNR samples. Here we present an X-ray study of SNR G2…
Diagnostics of Non-Maxwellian Electron Distributions in Solar Active Regions from Fe XII Lines Observed by the Hinode Extreme Ultraviolet Imaging Spectrometer and Interface Region Imaging Spectrograph
Mason, H. E.; Del Zanna, G.; Testa, P. +3 more
We present joint Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) and Interface Region Imaging Spectrograph (IRIS) observations of Fe XII lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 Å/1349 Å observed ratio is consistent with the values predicted by CHIANTI and th…