Search Publications
A Tale of Two Populations: The Contribution of Merger and Secular Processes to the Evolution of Active Galactic Nuclei
Ballantyne, D. R.; Draper, A. R.
Due to the co-evolution of supermassive black holes and their host galaxies, understanding the mechanisms that trigger active galactic nuclei (AGNs) is imperative to understanding galaxy evolution and the formation of massive galaxies. It is observationally difficult to determine the trigger of a given AGN due to the difference between the AGN lif…
Magnetic Energy and Helicity Budgets in the Active-region Solar Corona. II. Nonlinear Force-free Approximation
Georgoulis, Manolis K.; Tziotziou, Kostas; Raouafi, Nour-Eddine
Expanding on an earlier work that relied on linear force-free (LFF) magnetic fields, we self-consistently derive the instantaneous free magnetic energy and relative magnetic helicity budgets of an unknown three-dimensional nonlinear force-free (NLFF) magnetic structure extending above a single known lower-boundary magnetic field vector. The propos…
A Comparison between the Stellar and Dynamical Masses of Six Globular Clusters
Bellazzini, M.; Sollima, A.; Lee, J. -W.
We present the results of a comprehensive analysis of the structure and kinematics of six Galactic globular clusters. By comparing the results of the most extensive photometric and kinematical surveys available to date with suitable dynamical models, we determine the stellar and dynamical masses of these stellar systems taking into account the eff…
Tracking down the Source Population Responsible for the Unresolved Cosmic 6-8 keV Background
Lehmer, B. D.; Alexander, D. M.; Bauer, F. E. +10 more
Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray-undetected galaxies that dominates the unresolved ≈20%-25% of the 6-8 keV cosmic X-ray background (XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South Hubble Space Telescope z-band im…
Spatial Analysis of the Polycyclic Aromatic Hydrocarbon Features Southeast of the Orion Bar
Boersma, C.; Allamandola, L. J.; Rubin, R. H.
Polycyclic aromatic hydrocarbon (PAH) and dust emission features between 10 and 37 µm, observed with Spitzer at 11 positions southeast of the Bright Bar (BB) in Orion, are analyzed and connected to atomic and H2 lines reported earlier. Variations at these positions indicate changes in local conditions and materials sampled. The ma…
On the Role of the Background Overlying Magnetic Field in Solar Eruptions
Wiegelmann, T.; Patsourakos, S.; Nindos, A.
The primary constraining force that inhibits global solar eruptions is provided by the overlying background magnetic field. Using magnetic field data from both the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory and the spectropolarimeter of the Solar Optical Telescope aboard Hinode, we study the long-term evolution of the b…
Chemical and Kinematical Properties of Blue Straggler Stars and Horizontal Branch Stars in NGC 6397
Dalessandro, E.; Contreras Ramos, R.; Mucciarelli, A. +4 more
We used three sets of high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 42 horizontal branch (HB) stars, 18 blue straggler stars (BSSs), and 86 main-sequence (MS) turnoff (TO) and sub-giant branc…
CHEERS Results on Mrk 573: A Study of Deep Chandra Observations
Elvis, Martin; Karovska, Margarita; Fabbiano, Giuseppina +2 more
We present results on Mrk 573 obtained as part of the CHandra survey of Extended Emission-line Regions in nearby Seyfert galaxies (CHEERS). Previous studies showed that this source features a biconical emission in the soft X-ray band closely related to the narrow-line region as mapped by the [O III] emission line and the radio emission, though on …
The Absence of Ex-companions in Type Ia Supernova Remnants
Kilic, Mukremin; Di Stefano, R.
Type Ia supernovae (SNe Ia) play important roles in our study of the expansion and acceleration of the universe, but because we do not know the exact nature or natures of the progenitors, there is a systematic uncertainty that must be resolved if SNe Ia are to become more precise cosmic probes. No progenitor system has ever been identified either …
Orbital Decay and Evidence of Disk Formation in the X-Ray Binary Pulsar OAO 1657-415
Wilson-Hodge, C. A.; Camero-Arranz, A.; Finger, M. H. +1 more
OAO 1657-415 is an eclipsing X-ray binary wind-fed pulsar that has exhibited smooth spin-up/spin-down episodes and has undergone several torque reversals throughout its long history of observation. We present a frequency history spanning nearly 19 years of observations from the Burst and Transient Source Experiment and from the Gamma-Ray Burst Mon…