Search Publications
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…
AWSoM Magnetohydrodynamic Simulation of a Solar Active Region with Realistic Spectral Synthesis
Landi, Enrico; van der Holst, Bart; Szente, Judit +6 more
For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfvén Wave Solar Model (AWSoM). We select an AR appearing near disk center on 2018 July 13 and use the National Solar Observatory's Helioseismic and Magnetic Imager synoptic magnetogram to specify the magnetic field at the model's inner bo…
First Laboratory Measurement of Magnetic-field-induced Transition Effect in Fe X at Different Magnetic Fields
Tian, Hui; Bai, Xianyong; Si, Ran +14 more
The magnetic field is extremely important for understanding the properties of the solar corona. However, there are still difficulties in the direct measurement of the coronal magnetic field. The magnetic-field-induced transition (MIT) in Fe X, appearing in coronal spectra, was discovered to have prospective applications in coronal magnetic field m…
Searching for the Signal of a Primordial Black Hole from CMB Lensing and γ-Ray Emissions
Qiu, Taotao; Tan, Xiu-Hui; Xia, Jun-Qing +1 more
In this letter, we search for the signal of primordial black holes (PBHs) by correlating the γ-ray emissions in the MeV energy band produced by the Hawking evaporation and the lensing effect of the cosmic microwave background (CMB). We use the conservative case of the astrophysical model as much as possible in the calculations, since the potential…
Beyond the Local Volume. II. Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields
Holwerda, Benne; Burgasser, Adam J.; Ryan, Russell E. +6 more
Ultracool dwarfs (UCDs) represent a significant proportion of stars in the Milky Way, and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (d < 100 pc). Here, we analyze a sample of 164 spect…