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Variations on a theme: the puzzling behaviour of Schulte 12
Nazé, Yaël; Mahy, Laurent; Rauw, Gregor +2 more
One of the first massive stars detected in X-rays, Schulte 12 has remained a puzzle in several aspects. In particular, its extreme brightness both in the visible and X-ray ranges is intriguing. Thanks to Swift and XMM-Newton observations covering ∼5000 d, we report the discovery of a regular 108 d modulation in X-ray flux of unknown origin. The mi…
Metallicity Gradients in M 31, M 33, NGC 300 and the Milky Way Using Abundances of Different Elements
Peña, M.; Flores-Durán, S. N.
Metallicity gradients derived from planetary nebulae (PNe) using O, Ne, and Ar abundances are studied and compared to those from H II regions in the galaxies M 31, M 33, NGC 300 and the Milky Way. Galactocentric radii and chemical abundances were collected from the literature, carefully selecting a homogeneous sample for each galaxy. Metallicity g…
A Cepheid-based Distance to the Seyfert Galaxy NGC 6814
Peterson, Bradley M.; Ferrarese, Laura; Onken, Christopher A. +2 more
We present a Cepheid-based distance to the nearby Seyfert galaxy NGC 6814 from Hubble Space Telescope observations. We obtained F555W and F814W imaging over the course of 12 visits with logarithmic time spacing in 2013 August-October. We detected and made photometric measurements for 16,469 unique sources across all images in both filters, from wh…
COS Observations of the Cosmic Web: A Search for the Cooler Components of a Hot, X-Ray Identified Filament
Zahedy, Fakhri S.; Chen, Hsiao-Wen; Mulchaey, John S. +3 more
In the local universe, a large fraction of the baryon content is believed to exist as diffuse gas in filaments. While this gas is directly observable in X-ray emission around clusters of galaxies, it is primarily studied through its UV absorption. Recently, X-ray observations of large-scale filaments connecting to the cosmic web around the nearby …
Electron Acceleration in Middle-age Shell-type γ-Ray Supernova Remnants
Zhang, Xiao; Liu, Siming
Over the past decade, γ-ray observations of supernova remnants (SNRs) and accurate cosmic-ray (CR) spectral measurements have significantly advanced our understanding of particle acceleration in SNRs. In combination with multiwavelength observations of a large sample of SNRs, it has been proposed that the highest energy particles are mostly accele…
Spectroscopic confirmation and modelling of two lensed quadruple quasars in the Dark Energy Survey public footprint
Marchetti, L.; Vaccari, M.; Baker, A. J. +12 more
Quadruply lensed quasars are extremely rare objects, but incredibly powerful cosmological tools. Only few dozen are known in the whole sky. Here we present the spectroscopic confirmation of two new quadruplets WG0214-2105 and WG2100-4452 discovered by Agnello & Spiniello (2018) within the Dark Energy Survey public footprints. We have conducted…
A laboratory-based dielectric model for the radar sounding of the martian subsurface
Thomas, Nicolas; Becerra, Patricio; Pommerol, Antoine +2 more
For the last decade, the SHARAD radar on board NASA's Mars Reconnaissance Orbiter, and the MARSIS radar on board ESA's Mars Express, have sounded the surface and subsurface of Mars from orbit to search for and characterise water ice reservoirs. When associated with dielectric models, the regolith composition (in terms of dust, ice and voids) of th…
Probing the fluctuating ultraviolet background using the Hubble Frontier Fields
Dayal, Pratika; Choudhury, Tirthankar Roy
In recent years, the rise in the number of Lyman Break Galaxies detected at high redshifts z ≥ 6 has opened up the possibility of understanding early galaxy formation physics in great detail. In particular, the faint-end slope (α) of the ultraviolet luminosity function (UV LF) of these galaxies is a potential probe of feedback effects that suppres…
The mean rotation rate of Venus from 29 years of Earth-based radar observations
Campbell, Donald B.; Margot, Jean-Luc; Nolan, Michael C. +7 more
We measured the length of the Venus sidereal day (LOD) from Earth-based radar observations collected from 1988 to 2017, using offsets in surface feature longitudes from a prediction based on a 243.0185d period derived from analysis of Magellan mission images over a 487-day interval. We derive a mean LOD over 29 years of 243.0212 ± 0.0006d. Our res…
Direct measurement of stellar angular diameters by the VERITAS Cherenkov telescopes
Benbow, W.; Bird, R.; Brose, R. +54 more
The angular size of a star is a critical factor in determining its basic properties1. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the…