Search Publications
Classification of Wolf–Rayet Stars Using Ensemble-based Machine Learning Algorithms
Das, Ramkrishna; Bhattacharya, Rajorshi; Lewis, Megan O. +2 more
We develop a robust machine learning classifier model utilizing the eXtreme-Gradient Boosting (XGB) algorithm for improved classification of Galactic Wolf–Rayet (WR) stars based on IR colors and positional attributes. For our study, we choose an extensive data set of 6555 stellar objects (from 2MASS and AllWISE data releases) lying in the Milky Wa…
X-Ray Observations of the Enigmatic Wolf–Rayet System θ Mus: Two's Company but Three's a Crowd
Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel +1 more
θ Mus is a remarkable spectroscopic binary (SB) consisting of a carbon-type Wolf–Rayet star and OV companion (WC6+O6–7V) in a ≈19 days orbit. In addition an O-supergiant is visually detected at a small offset of 46 mas and if gravitationally bound to the SB system would have an orbital period of many decades. θ Mus is X-ray bright and a nonthermal…
A Tale of Three: Magnetic Fields along the Orion Integral-shaped Filament as Revealed by the JCMT BISTRO Survey
Zhang, Yapeng; Pattle, Kate; Karoly, Janik +152 more
As part of the B-fields In Star-forming Region Observations survey, we present James Clerk Maxwell Telescope (JCMT) 850 µm polarimetric observations toward the Orion integral-shaped filament (ISF) that covers three portions known as OMC-1, OMC-2, and OMC-3. The magnetic field threading the ISF seen in the JCMT POL-2 map appears as a tale of …
Multi-epoch UV–X-Ray Spectral Study of NGC 4151 with AstroSat
Papadakis, I. E.; Singh, K. P.; Dewangan, G. C. +8 more
We present a multiwavelength spectral study of NGC 4151 based on five epochs of simultaneous AstroSat observations in the near-ultraviolet (NUV) to hard X-ray band (∼0.005–80 keV) during 2017–2018. We derived the intrinsic accretion disk continuum after correcting for internal and Galactic extinction, contributions from broad- and narrow-line regi…
The Nature of a Recently Discovered Wolf–Rayet Binary: Archetype of Stripping?
Massey, Philip; Morrell, Nidia I.; Penny, Laura R. +2 more
LMCe055-1 was recently discovered in a survey for Wolf–Rayets (WRs) in the Large Magellanic Cloud, and classified as a WN4/O4, a lower-excitation version of the WN3/O3 class discovered as part of the same survey. Its absolute magnitude precluded it from being a WN4+O4 binary. Optical Gravitational Lensing Experiment photometry shows shallow primar…
Investigation of the Nonthermal X-Ray Emission from the Supernova Remnant CTB 37B Hosting the Magnetar CXOU J171405.7-381031
An, Hongjun; Mori, Kaya; Safi-Harb, Samar +4 more
We present a detailed X-ray investigation of a region (S1) exhibiting nonthermal X-ray emission within the supernova remnant (SNR) CTB 37B hosting the magnetar CXOU J171405.7‑381031. Previous analyses modeled this emission with a power law (PL), inferring various values for the photon index (Γ) and absorbing column density (N H). Based …
Evidence for a Close-in Tertiary Orbiting around the Algol-type System HZ Dra with Tidal Splitting and Spots Activities
Matekov, Azizbek; Li, Lin-Jia; Qian, Sheng-Bang +7 more
We report a cyclic variation of the O ‑ C diagram with a semiamplitude of 0.0033 days and a period of 1.05 yr for the pulsating eclipsing binary HZ Dra. The cyclic variation can be explained by the light travel-time effect via the presence of a close-in third body orbiting around HZ Dra in an elliptical orbit with a maximum semimajor axis of 0.89 …
High-latitude Observations of Dissipation-range Turbulence by the Ulysses Spacecraft during the Solar Minimum of 1993–96: The Spectral Break and Anisotropy
Isenberg, Philip A.; Schwadron, Nathan A.; Murphy, Neil +6 more
We examine Ulysses magnetic field observations from 1993 to 1996 as the spacecraft made its first fast-latitude scan from the southern to the northern hemisphere. Most of the observations we use are representative of high-latitude solar minimum conditions. We examine magnetic field power spectra characteristics of interplanetary turbulence at high…
Multispacecraft Observations of Protons and Helium Nuclei in Some Solar Energetic Particle Events toward the Maximum of Cycle 25
Ubertini, P.; Battiston, R.; Burger, W. J. +41 more
The intricate behavior of particle acceleration and transport mechanisms complicates the overall efforts in formulating a comprehensive understanding of solar energetic particle (SEP) events; these efforts include observations of low-energy particles (from tens of keV to hundreds of MeV) by space-borne instruments and measurements by the ground-ba…
Uncovering an Excess of X-Ray Point Sources in the Halos of Virgo Late-type Galaxies
Li, Zhiyuan; Hou, Meicun; Hu, Zhensong
We present a systematic search for extraplanar X-ray point sources around 19 late-type, highly inclined disk galaxies residing in the Virgo cluster, based on archival Chandra observations reaching a source detection sensitivity of L(0.5–8 keV) ∼ 1038 erg s‑1. Based on the cumulative source surface density distribution as a fu…