Search Publications
X-Ray AGB Stars in the 4XMM-DR9 Catalog: Further Evidence for Companions
Guerrero, M. A.; Ortiz, R.
Single AGB stars are not normally expected to be X-ray emitters due to the lack of a corona capable of powering a hot plasma. Therefore, the detection of X-ray emission in AGB stars by the ROSAT, Chandra, and XMM-Newton observatories has been interpreted as evidence for binarity. The number of X-ray-emitting AGB stars is, however, very small, and …
Deciphering the Deep Origin of Active Regions via Analysis of Magnetograms
McIntosh, Scott W.; Chatterjee, Subhamoy; Dikpati, Mausumi +5 more
In this work, we derive magnetic toroids from surface magnetograms by employing a novel optimization method, based on the trust region reflective algorithm. The toroids obtained in this way are combinations of Fourier modes (amplitudes and phases) with low longitudinal wavenumbers. The optimization also estimates the latitudinal width of the toroi…
GECKO Optical Follow-up Observation of Three Binary Black Hole Merger Events: GW190408_181802, GW190412, and GW190503_185404
Lee, Chung-Uk; Kim, Seung-Lee; Im, Myungshin +12 more
We present optical follow-up observation results of three binary black hole merger (BBH) events, GW190408_181802, GW190412, and GW190503_185404, which were detected by the Advanced LIGO and Virgo gravitational wave (GW) detectors. Electromagnetic (EM) counterparts are generally not expected for BBH merger events. However, some theoretical models s…
From Formation to Disruption: Observing the Multiphase Evolution of a Solar Flare Current Sheet
Chitta, L. P.; Cheng, X.; Priest, E. R.
A current sheet, where magnetic energy is liberated through reconnection and converted to other forms, is thought to play the central role in solar flares, the most intense explosions in the heliosphere. However, the evolution of a current sheet and its subsequent role in flare-related phenomena such as particle acceleration is poorly understood. …
Extreme Variability of the V488 Persei Debris Disk
Rieke, G. H.; Gáspár, András; Melis, Carl +1 more
V488 Persei is the most extreme debris disk known in terms of the fraction of the stellar luminosity it intercepts and reradiates. The infrared output of its disk is extremely variable, similar in this respect to the most variable disk known previously, that around ID8 in NGC 2547. We show that the variations are likely to be due to collisions of …
Lower-luminosity Obscured AGN Host Galaxies Are Not Predominantly in Major-merging Systems at Cosmic Noon
Kirkpatrick, Allison; Kocevski, Dale D.; Heckman, Timothy +15 more
For over 60 yr, the scientific community has studied actively growing central supermassive black holes (active galactic nuclei, AGNs), but fundamental questions on their genesis remain unanswered. Numerical simulations and theoretical arguments show that black hole growth occurs during short-lived periods (~107-108 yr) of pow…
On the Decay of Sunspot Groups and Their Internal Parts in Detail
Muraközy, Judit
The decay of sunspot groups is a relatively unknown field since most studies have focused mainly on the decay of sunspots or sunspot groups, but only on small samples. As an extension of the recent work of Muraközy (2020), which is based on a large verified sample, this study investigates not only the long-term behavior of the decay of sunspot gro…
The Stars of the HETDEX Survey. I. Radial Velocities and Metal-poor Stars from Low-resolution Stellar Spectra
Finkelstein, Steven L.; Casey, Caitlin M.; Schneider, Donald P. +19 more
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution (R ∼ 750) spectra of Lyα emitters. In its search for these galaxies, HETDEX will also observe a few times 105 stars. In this paper, we pre…
Evidence for Multiple Accretion Events in the Gaia-Sausage/Enceladus Structures
Koo, Jae-Rim; Beers, Timothy C.; Lee, Young Sun +1 more
We present evidence that multiple accretion events are required to explain the origin of the Gaia-Sausage and Enceladus (GSE) structures, based on an analysis of dynamical properties of main-sequence stars from the Sloan Digital Sky Survey Data Release 12 and Gaia Data Release 2. GSE members are selected to have eccentricity (e) > 0.7 and [Fe/H…
The MOSDEF-LRIS Survey: Probing the ISM/CGM Structure of Star-forming Galaxies at z 2 Using Rest-UV Spectroscopy
Siana, Brian; Shapley, Alice E.; Reddy, Naveen A. +6 more
The complex structure of gas, metals, and dust in the interstellar and circumgalactic medium (ISM and CGM, respectively) in star-forming galaxies can be probed by Lyα emission and absorption, low-ionization interstellar (LIS) metal absorption, and dust reddening E(B - V). We present a statistical analysis of the mutual correlations among Lyα equiv…