Search Publications
Short-Term X-ray Variability during Different Activity Phases of Blazars S5 0716+714 and PKS 2155-304
Pal, Main; Kushwaha, Pankaj
We explored the statistical properties of short-term X-ray variability using long-exposure XMM-Newton data during high X-ray variability phases of blazars S5 0716+714 and PKS 2155-304. In general, the hardness ratio shows correlated variations with the source flux state (count rate), but in a few cases, mainly the bright phases, the trend is compl…
Gaia DR2 Distances to Planetary Nebulae
Manteiga, Minia; Dafonte, Carlos; Manchado, Arturo +2 more
The aim of this work is to examine distances to planetary nebulae (PNe) together with other properties that were derived from them, using the astrometry of Gaia Data Release 2 (DR2). We were able to identify 1571 objects classified as PNe, for which we assumed distances calculated following a Bayesian statistical approach. From those objects, we s…
First Results from a Panchromatic HST/WFC3 Imaging Study of the Young, Rapidly Evolving Planetary Nebulae NGC 7027 and NGC 6302
Frank, Adam; Balick, Bruce; Kastner, Joel H. +3 more
We present the first results from comprehensive, near-UV-to-near-IR Hubble Space Telescope Wide Field Camera 3 (WFC3) emission-line imaging studies of two young planetary nebulae (PNe), NGC 7027 and NGC 6302. These two objects represent key sources for purposes of understanding PNe shaping processes. Both nebulae feature axisymmetric and point-sym…
X-ray Flux and Spectral Variability of Blazar H 2356-309
Gaur, Haritma; Wani, Kiran A.
We present the results of timing and spectral analysis of the blazar H 2356-309 using XMM-Newton observations. This blazar is observed during 13 June 2005–24 December 2013 in total nine observations. Five of the observations show moderate flux variability with amplitude 1.7–2.2%. We search for the intra-day variability timescales in these five lig…
On the Age of Galactic Bulge CSPNe: Too Young and Complicated?
Parker, Quentin A.; Lykou, Foteini; Zijlstra, Albert
We present preliminary results of our study of a small sample of planetary nebulae in the Galactic Bulge for which high-angular resolution Hubble Space Telescope imaging is available. From this and from archival spectroscopy, we were able to calculate temperatures and luminosities for their central stars. These were then correlated to up-to-date e…
Massive Stars in the Tarantula Nebula: A Rosetta Stone for Extragalactic Supergiant HII Regions
Crowther, Paul A.
A review of the properties of the Tarantula Nebula (30 Doradus) in the Large Magellanic Cloud is presented, primarily from the perspective of its massive star content. The proximity of the Tarantula and its accessibility to X-ray through radio observations permit it to serve as a Rosetta Stone amongst extragalactic supergiant HII regions since one…
The Wolf–Rayet Content of the Galaxies of the Local Group and Beyond
Massey, Philip; Neugent, Kathryn
Wolf–Rayet stars (WRs) represent the end of a massive star's life as it is about to turn into a supernova. Obtaining complete samples of such stars across a large range of metallicities poses observational challenges, but presents us with an exacting way to test current stellar evolutionary theories. A technique we have developed and refined invol…
X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures
Nakashima, Shinya; Inoue, Yoshiyuki; Kataoka, Jun +3 more
The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. …
Verification of Photometric Parallaxes with Gaia DR2 Data
Zhao, Gang; Karpov, Sergey; Sytov, Alexey +10 more
Results of comparison of Gaia DR2 parallaxes with data derived from a combined analysis of 2MASS (Two Micron All-Sky Survey), SDSS (Sloan Digital Sky Survey), GALEX (Galaxy Evolution Explorer), and UKIDSS (UKIRT Infrared Deep Sky Survey) surveys in four selected high-latitude |b|> 48° sky areas are presented. It is shown that multicolor photome…
Testing the Anomalous Growth of the Black Hole Radius from AGN
Addazi, Andrea; Marciano, Antonino; Qian, Chenyang
We analyze constraints on the anomalous growth of the black hole radius or the black hole spin from the X-rays spectrum data of Active Galactic Nuclei (AGN) in NGC 5506. The anomalous growth of the mass or of the spin of a black hole may be unveiled within the framework of models of alternative gravity, including f(R)-gravity. Our phenomenological…