Search Publications
Fast Sausage Oscillations in Coronal Loops with Fine Structures
Guo, Mingzhe; Li, Bo; Shi, Mijie
Fast sausage modes (FSMs) in flare loops have long been invoked to account for rapid quasi-periodic pulsations (QPPs) with periods of order seconds in flare lightcurves. However, most theories of FSMs in solar coronal cylinders assume a perfectly axisymmetric equilibrium, an idealized configuration apparently far from reality. In particular, it re…
Variable Stars in Local Group Galaxies. VI. The Isolated Dwarfs VV 124 and KKr 25
Sarajedini, Ata; Martínez-Vázquez, C. E.; Vivas, A. Katherina +10 more
We present the discovery of variable stars in two isolated dwarf galaxies in the outskirts of the Local Group, VV 124 and KKr 25, using observations with the Hubble Space Telescope. VV 124 hosts stellar populations with a wide range of ages (>10 Gyr until the present) and therefore we find all types of classical pulsators. In VV 124, we detect …
Near-IR Observations of the Young Star [BHB2007]-1: A Substellar Companion Opening the Gap in the Disk
Cleeves, L. Ilsedore; Garufi, Antonio; Zhu, Zhaohuan +5 more
The presence of planets or substellar objects still embedded in their native protoplanetary disks is indirectly suggested by disk substructures like gaps, cavities, and spirals. However, these companions are rarely detected. We present Very Large Telescope/NACO high-contrast images in the J, H, KS, and $L^{\prime} $ bands of the young s…
Eta Carinae: A Tale of Two Periastron Passages
Hamaguchi, Kenji; Corcoran, Michael F.; Russell, Christopher M. P. +15 more
Since 2002, the far-ultraviolet (FUV) flux (1150-1680 Å) of Eta Carinae, monitored by the Hubble Space Telescope/Space Telescope Imaging Spectrograph, has increased by an order of magnitude. This increase is attributed to partial dissipation of a line-of-sight (LOS) occulter that blocks the central core of the system. Across the 2020 February peri…
A Closer Look at Two of the Most Luminous Quasars in the Universe
Fan, Xiaohui; Huang, Yun-Hsin; Walter, Fabian +7 more
Ultraluminous quasars (M1450 ≤ -29) provide us with a rare view into the nature of the most massive and most rapidly accreting supermassive black holes (SMBHs). Following the discovery of two of these extreme sources, J0341+1720 (M1450 = -29.56, z = 3.71) and J2125-1719 (M1450 = -29.39, z = 3.90), in the Extremely …
Are Compton-thin AGNs Globally Compton Thin?
Yukita, M.; Ptak, A.; LaMassa, S. +2 more
We select eight nearby active galactic nuclei (AGNs) which, based on previous work, appear to be Compton-thin in the line of sight. We model with MYTORUS their broadband X-ray spectra from 20 individual observations with Suzaku, accounting self-consistently for Fe Kα line emission, as well as direct and scattered continuum from matter with finite …
A Perspective on the Scaling of Magnetosheath Turbulence and Effects of Bow Shock Properties
Voitcu, Gabriel; Echim, Marius; Teodorescu, Eliza
We analyze magnetic field data from two magnetosheath crossings, representative of a larger collection of similar cases in the database of the Cluster spacecraft. We apply a novel data analysis method to identify the power-law behavior of the structure functions and to find the validity range of the power-law scaling. We validate the technique wit…
Eclipsing Binaries in the Open Cluster Ruprecht 147. IV: The Active Triple System EPIC 219511354
Torres, Guillermo; Vanderburg, Andrew; Gaidos, Eric +2 more
We report follow-up spectroscopic observations of the 1.62 day, K-type, detached, active, near-circular, double-lined eclipsing binary EPIC 219511354 in the open cluster Ruprecht 147, identified previously on the basis of photometric observations from the Kepler/K2 mission. This is the fourth eclipsing system analyzed in this cluster. A combined a…
A Weakening Compton Hump and Soft X-Ray Excess Detected in the Seyfert 1 Galaxy MCG -02-58-22
Laha, Sibasish; Ghosh, Ritesh
We have carried out an extensive X-ray spectral study of the bare Seyfert 1 galaxy MCG -02-58-22 to ascertain the nature of the X-ray reprocessing media using observations from Suzaku (2009) and simultaneous observations from XMM-Newton and NuSTAR (2016). The most significant results of our investigation are as follows. (1) The primary X-ray emiss…
Broadband Modeling of Low-luminosity Active Galactic Nuclei Detected in Gamma Rays
Prince, Raj; Tomar, Gunjan; Gupta, Nayantara
Low-luminosity active galactic nuclei are more abundant and closer to us than the luminous ones but harder to explore as they are faint. We have selected the four sources, NGC 315, NGC 4261, NGC 1275, and NGC 4486, which have been detected in γ-rays by Fermi-LAT. We have compiled their long-term radio, optical, X-ray data from different telescopes…