Search Publications
Maser and Infrared Studies of Oxygen-rich Late/Post-asymptotic Giant Branch Stars and Water Fountains: Development of a New Identification Method
Yung, Bosco H. K.; Nakashima, Jun-ichi; Henkel, Christian
We explored an efficient method to identify evolved stars with oxygen-rich envelopes in the late asymptotic giant branch (AGB) or post-AGB phase of stellar evolution, which include a rare class of objects—the "water fountains (WF)." Our method considers the OH and H2O maser spectra, the near-infrared Q-parameters (these are color indice…
Where are the Mini Kreutz-family Comets?
Kracht, Rainer; Ye, Quan-Zhi; Hui, Man-To +1 more
The Kreutz family of sungrazing comets contains over 2000 known members, many of which are believed to be under ~100 m sizes (mini comets) and have only been studied at small heliocentric distances (r H) with space-based SOHO/STEREO spacecraft. To understand the brightening process of mini Kreutz comets, we conducted a survey using CFHT…
Near-infrared Structure of Fast and Slow-rotating Disk Galaxies
Bershady, Matthew A.; Schechtman-Rook, Andrew
We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHK s-band images and three-dimensional radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 km s-1 <V rot < 245 km s
The Hard X-Ray Continuum of Cen A Observed With INTEGRAL SPI
Jourdain, Elisabeth; Roques, Jean-Pierre; Evans, Daniel A. +1 more
We revisit the average hard X-ray spectrum from the active galactic nucleus (AGN) of Centaurus A (Cen A) using 10 yr worth of observations with INTEGRAL SPI. This source has the highest flux observed from any AGNs in the SPI bandpass (23 keV-8 MeV). The 10 year light curve of Cen A is presented, and hardness ratios confirm that the spectral shape …
Separable Solutions of Force-Free Spheres and Applications to Solar Active Regions
Mangalam, A.; Ravindra, B.; Prasad, A.
We present a systematic study of the force-free field equation for simple axisymmetric configurations in spherical geometry and apply it to the solar active regions. The condition of separability of solutions in the radial and angular variables leads to two classes of solutions: linear and nonlinear force-free fields (NLFF). We have studied these …
Hubble Space Telescope Far Ultraviolet Spectroscopy of the Recurrent Nova T Pyxidis
Williams, Robert E.; Livio, Mario; Woodward, Charles E. +5 more
With six recorded nova outbursts, the prototypical recurrent nova T Pyxidis (T Pyx) is the ideal cataclysmic variable system to assess the net change of the white dwarf mass within a nova cycle. Recent estimates of the mass ejected in the 2011 outburst ranged from a few ~10-5 M ⊙ to 3.3 × 10-4 M ⊙, and a…
Hard X-Ray Emission and 44Ti Line Features of the Tycho Supernova Remnant
Wang, Wei; Li, Zhuo
A deep hard X-ray survey of the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite has detected for the first time non-thermal emission up to 90 keV in the Tycho supernova (SN) remnant. Its 3-100 keV spectrum is fitted with a thermal bremsstrahlung of kT ~ 0.81 ± 0.45 keV plus a power-law model of Γ ~ 3.01 ± 0.16. Based on diffus…
A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2013
Komm, R.; Petrie, G. J. D.; Seligman, D.
We compare the average photospheric current helicity Hc , photospheric twist parameter α (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity Hk for 194 active regions observed between 2006-2013. We use 2440 Hinode photospheric vector magnetograms, and the corresponding subsurface flui…
Entropy Flattening, Gas Clumping, and Turbulence in Galaxy Clusters
Lapi, A.; Fusco-Femiano, R.
Several physical processes and formation events are expected in cluster outskirts, a vast region up to now essentially not covered by observations. The recent Suzaku (X-ray) and Planck (Sunyaev-Zel'dovich (SZ) effect) observations out to the virial radius have highlighted in these peripheral regions a rather sharp decline of the intracluster gas t…
Emission Measure Distribution for Diffuse Regions in Solar Active Regions
Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A. +1 more
Our knowledge of the diffuse emission that encompasses active regions is very limited. In this paper we investigate two off-limb active regions, namely, AR 10939 and AR 10961, to probe the underlying heating mechanisms. For this purpose, we have used spectral observations from Hinode/EIS and employed the emission measure (EM) technique to obtain t…