Search Publications
Improved Measurements of the Sun's Meridional Flow and Torsional Oscillation from Correlation Tracking on MDI and HMI Magnetograms
Mahajan, Sushant S.; Hathaway, David H.; Muñoz-Jaramillo, Andrés +1 more
The Sun's axisymmetric flows, differential rotation, and meridional flow govern the dynamics of the solar magnetic cycle, and a variety of methods are used to measure these flows, each with its own strengths and weaknesses. Flow measurements based on cross-correlating images of the surface magnetic field have been made since the 1970s that require…
Tully-Fisher Distances and Dynamical Mass Constraints for 24 Host Galaxies of Reverberation-mapped AGNs
Crenshaw, D. M.; Bentz, Misty C.; Courtois, Hélène M. +6 more
We present Tully-Fisher distances for 24 active galactic nucleus (AGN) host galaxies with black hole mass (MBH) measurements from reverberation mapping, as well as the first calibration of the V-band Tully-Fisher relation. Combining our measurements of H I 21 cm emission with Hubble Space Telescope and ground-based optical and near-infr…
Multiple Stellar Populations at Less-evolved Stages: Detection of Chemical Variations among Main-sequence Dwarfs in NGC 1978
Milone, Antonino P.; Hong, Jongsuk; de Grijs, Richard +4 more
Multiple stellar populations (MPs) with different chemical compositions are not exclusive features of old globular clusters (older than 10 Gyr). Indeed, recent studies reveal that younger clusters (∼2-6 Gyr-old) in the Magellanic Clouds also exhibit star-to-star chemical variations among evolved stars. However, whether MPs are present among less-e…
Particle Reacceleration by Turbulence and Radio Constraints on Multimessenger High-energy Emission from the Coma Cluster
Murase, Kohta; Nishiwaki, Kosuke; Asano, Katsuaki
Galaxy clusters are considered to be gigantic reservoirs of cosmic rays (CRs). Some of the clusters are found with extended radio emission, which provides evidence for the existence of magnetic fields and CR electrons in the intra-cluster medium. The mechanism of radio halo (RH) emission is still under debate, and it has been believed that turbule…
Internal Structure of the 2019 April 2 CME
Vourlidas, Angelos; Wood, Brian E.; Braga, Carlos R.
We present the first analysis of internal coronal mass ejection (CME) structure observed very close to the Sun by the Wide-field Imager for Solar PRobe (WISPR) instrument on board the Parker Solar Probe (PSP). The transient studied here is a CME observed during PSP's second perihelion passage on 2019 April 2, when PSP was only 40 R ⊙ fr…
Detection of Al II in the Ultraviolet Spectra of Metal-poor Stars: An Empirical LTE Test of NLTE Aluminum Abundance Calculations
Roederer, Ian U.; Lawler, James E.
We report the detection of an Al II line at 2669.155 Å in 11 metal-poor stars, using ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive Al abundances from this line using a standard abundance analysis, assuming local thermodynamic equilibrium (LTE). The mean [Al/Fe] ratio is -0…
Multiwavelength Evidence for a New Flare-mode Transitional Millisecond Pulsar
Strader, Jay; Bahramian, Arash; Chomiuk, Laura +7 more
We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV γ-ray source 4FGL J0540.0-7552. The source shows the persistent presence of an optical accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-…
Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg
Gies, Douglas R.; Monnier, John D.; Schaefer, Gail H. +23 more
We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011-2016), which offers insight into the short and long-term evolution of surface features on RSGs…
On the Rigidity Spectrum of Cosmic-Ray Variations within Propagating Interplanetary Disturbances: Neutron Monitor and SOHO/EPHIN Observations at ∼1-10 GV
Vourlidas, Angelos; Heber, Bernd; Papaioannou, Athanasios +9 more
The rigidity dependence of all Forbush decreases (FDs) recorded from 1995 to 2015 has been determined using neutron monitor (NM) and Solar and Heliospheric Observatory (SOHO) (EPHIN) spacecraft data, covering the energy (rigidity) range from ∼433 MeV (1 GV) to 9.10 GeV (10 GV). We analyzed a total of 421 events and determined the spectrum in rigid…
X-Ray Pulsar XTE J1858+034: Discovery of the Cyclotron Line and the Revised Optical Identification
Kretschmar, Peter; Doroshenko, Victor; Tsygankov, Sergey S. +7 more
We present the results of a detailed investigation of the poorly studied X-ray pulsar (XRP) XTE J1858+034 based on the data obtained with the NuSTAR observatory during the outburst of the source in 2019. The spectral analysis resulted in the discovery of a cyclotron absorption feature in the source spectrum at ∼48 keV in both the pulse phase-avera…