Search Publications
X-ray spectral variability of blazars using principal component analysis
Gallo, L. C.; Parker, M. L.; Gallant, D.
Principal component analysis (PCA) is applied to a variety of blazars to examine X-ray spectral variability. Data from nine different objects are analysed in two ways: long-term, which examines variability trends across years or decades, and short-term, which looks at variability within a single observation. The results are then compared to simula…
Variability of Disk Emission in Pre-main-sequence and Related Stars. IV. Investigating the Structural Changes in the Inner Disk Region of MWC 480
Bayyari, Ammar; Russell, Ray W.; Sitko, Michael L. +8 more
We present five epochs of near-IR observations of the protoplanetary disk around MWC 480 (HD 31648) obtained with the SpeX spectrograph on NASA’s Infrared Telescope Facility between 2007 and 2013, inclusive. Using the measured line fluxes in the Pa β and Br γ lines, we found the mass accretion rates to be (1.26-2.30) × 10-7 M ⊙
Optical Dimming of RW Aur Associated with an Iron-rich Corona and Exceptionally High Absorbing Column Density
Schneider, P. C.; Birnstiel, T.; Principe, D. A. +7 more
RW Aur is a binary system composed of two young, low-mass stars. The primary, RW Aur A, has undergone visual dimming events (ΔV = 2-3 mag) in 2011, 2014-16, and 2017-2018. Visual and IR observations indicate a gray absorber that moved into the line of sight. This dimming is also associated with changes in the outflow. In 2017, when the optical bri…
Evidence for halo kinematics among cool carbon-rich dwarfs
Farihi, J.; Arendt, A. R.; Machado, H. S. +1 more
This paper reports preliminary, yet compelling, kinematical inferences for N≳ 600 carbon-rich dwarf stars that demonstrate around 30-60 per cent are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogues based…
Colour-magnitude diagram in simulations of galaxy formation
Girardi, Léo; Bressan, Alessandro; Borgani, Stefano +3 more
State-of-the-art cosmological hydrodynamical simulations have star particles with a typical mass between ∼108 and ∼103 M⊙ according to resolution, and treat them as simple stellar populations. On the other hand, observations in nearby galaxies resolve individual stars and provide us with single star properties. An …
Influence of Inelastic Collisions with Hydrogen Atoms on Non-LTE Oxygen Abundance Determinations
Sitnova, T. M.; Mashonkina, L. I.
We present the results of our modeling of the O I line formation under non-LTE conditions in the atmospheres of FG stars. The statistical equilibrium of O I has been calculated using Barklem's quantum-mechanical rates of inelastic collisions with hydrogen atoms. We have determined the non-LTE oxygen abundance from atomic O I lines for the Sun and …
Design and on-orbit operation of the soft x-ray spectrometer adiabatic demagnetization refrigerator on the Hitomi observatory
Porter, Frederick S.; Mitsuda, Kazuhisa; Fujimoto, Ryuichi +12 more
The soft x-ray spectrometer (SXS) instrument that flew on the Astro-H observatory was designed to perform imaging and spectroscopy of x-rays in the energy range of 0.2 to 13 keV with a resolution requirement of 7 eV or better. This was accomplished using a 6 × 6 array of x-ray microcalorimeters cooled to an operating temperature of 50 mK by an adi…
A window into δ Sct stellar interiors: understanding the eclipsing binary system TT Hor
Murphy, Simon J.; Ireland, Michael J.; Bento, Joao +1 more
The semi-detached eclipsing binary system TT Hor has a δ Sct primary component (accretor) accreting mass from the secondary star (donor). We fit an eclipsing binary model from V, B, and I photometry combined with spectroscopy using PHOEBE. Radial velocity variations of the centre of mass of TT Hor AB over two years suggest the presence of a wide c…
Galaxy-galaxy lensing in the outskirts of CLASH clusters: constraints on local shear and testing mass-luminosity scaling relation
Richard, Johan; Siana, Brian; Desprez, Guillaume +3 more
We present a selection of 24 candidate galaxy-galaxy lensing (GGL) identified from Hubble images in the outskirts of the massive galaxy clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) . These GGLs provide insights into the mass distributions at larger scales than the strong-lensing region in the cluster cores. We built p…
The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration
Menten, Karl M.; Reid, Mark J.; Zhang, Bo +3 more
We report astrometric results of VLBI phase-referencing observations of 22 GHz H2O masers emission toward the red hypergiant VX Sgr, one of most massive and luminous red hypergiant stars in our Galaxy, using the Very Long Baseline Array. A background source, J1820-2528, projected 4.°4 from the target VX Sgr, was used as the phase refere…