Search Publications
Revealing the Complicated Story of the Cetus Stream with StarGO
Chang, Jiang; Smith, M. C.; Liu, Chao +5 more
We use a novel cluster identification tool, STARGO, to explore the metal-poor ([Fe/H] < -1.5) outer stellar halo (d > 15 kpc) of the Milky Way using data from Gaia, LAMOST, and SDSS. Our method is built using an unsupervised learning algorithm, a self-organizing map, which trains a 2D neural network to learn the topological structures of a d…
Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability
Ponti, G.; Fazio, G. G.; Morris, M. R. +11 more
Emission from Sagitarius A* is highly variable at both X-ray and infrared (IR) wavelengths. Observations over the last ∼20 yr have revealed X-ray flares that rise above a quiescent thermal background about once per day, while faint X-ray flares from Sgr A* are undetectable below the constant thermal emission. In contrast, the IR emission of Sgr A*…
Analysis of Small-scale Magnetic Flux Ropes Covering the Whole Ulysses Mission
Hu, Qiang; Chen, Yu; le Roux, Jakobus A.
Small-scale magnetic flux ropes in the solar wind have been studied for decades via both simulation and observation. Statistical analysis utilizing various in situ spacecraft measurements is the main observational approach, which helps investigate the generation and evolution of these small-scale structures. In this study, we extend the automated …
CME Arrival Time Prediction Using Convolutional Neural Network
Liu, Jiajia; Erdélyi, Robert; Wang, Yimin +1 more
Fast and accurate prediction of the arrival time of coronal mass ejections (CMEs) at Earth is vital to minimize hazards caused by CMEs. In this paper, we use a deep-learning framework, i.e., a convolutional neural network (CNN) regression model, to analyze transit times from the Sun to Earth of 223 geoeffective CME events observed in the past 30 y…
Discovery of a Disrupting Open Cluster Far into the Milky Way Halo: A Recent Star Formation Event in the Leading Arm of the Magellanic Stream?
Choi, Yumi; Nidever, David L.; Price-Whelan, Adrian M. +4 more
We report the discovery of a young (τ ∼ 117 {{Myr}}), low-mass (M∼ 1200 {M}⊙ ), metal-poor ([{{Fe}}/{{H}}]∼ -1.14) stellar association at a heliocentric distance D≈ 28.7 {{kpc}}, placing it far into the Milky Way (MW) halo. At its present Galactocentric position (R,z)∼ (23,15) {{kpc}}, the association is (on the sky) near the leading ar…
Direct T e Metallicity Calibration of R23 in Strong Line Emitters
Malhotra, Sangeeta; Yang, Huan; Rhoads, James E. +1 more
The gas metallicity of galaxies is often estimated using strong emission lines such as the optical lines of [O III] and [O II]. The most common measure is “R23,” defined as ([O II]λλ3726, 3729 + [O III]λλ4959,5007)/Hβ. Most calibrations for these strong-line metallicity indicators are for continuum selected galaxies. We report a new empirical cali…
A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project
Debes, John H.; Wisniewski, John; Meisner, Aaron M. +13 more
Infrared excesses due to dusty disks have been observed orbiting white dwarfs with effective temperatures between 7200 and 25,000 K, suggesting that the rate of tidal disruption of minor bodies massive enough to create a coherent disk declines sharply beyond 1 Gyr after white dwarf formation. We report the discovery that the candidate white dwarf …
Reverberation Mapping of the Narrow-line Seyfert 1 Galaxy I Zwicky 1: Black Hole Mass
Ho, Luis C.; Bian, Wei-Hao; Zhang, Zhi-Xiang +11 more
We report results of the first reverberation mapping campaign of I Zwicky 1 during 2014-2016, which showed unambiguous reverberations of the broad Hβ line emission in the varying optical continuum. From analysis using several methods, we obtain a reverberation lag of {τ }{{H}β }={37.2}-4.9+4.5 {days}. Taking a viri…
CO Detected in CI Tau b: Hot Start Implied by Planet Mass and M K
Johns-Krull, Christopher M.; Prato, L.; Flagg, Laura +5 more
We acquired high-resolution infrared spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planet’s existence with a direct detection of CO in the planet’s atmosphere. We also calculate a mass of 11.6 M J based on the amplitude of its radial velocity variati…
Multiple Rings of Millimeter Dust Emission in the HD 15115 Debris Disk
MacGregor, Meredith A.; Weinberger, Alycia J.; Nesvold, Erika R. +8 more
We present observations of the HD 15115 debris disk from the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm that capture this intriguing system with the highest resolution (0.″6 or 29 au) at millimeter wavelengths to date. This new ALMA image shows evidence for two rings in the disk separated by a cleared gap. By fitting models dire…