Search Publications
Distribution of Electric Currents in Sunspots from Photosphere to Corona
Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo
We present a study of two regular sunspots that exhibit nearly uniform twist from the photosphere to the corona. We derive the twist parameter in the corona and in the chromosphere by minimizing the difference between the extrapolated linear force-free field model field lines and the observed intensity structures in the extreme-ultraviolet images …
Discovery of a Strong Lensing Galaxy Embedded in a Cluster at z = 1.62
Koekemoer, Anton M.; Kacprzak, Glenn G.; Tran, Kim-Vy H. +9 more
We identify a strong lensing galaxy in the cluster IRC 0218 (also known as XMM-LSS J02182-05102) that is spectroscopically confirmed to be at z = 1.62, making it the highest-redshift strong lens galaxy known. The lens is one of the two brightest cluster galaxies and lenses a background source galaxy into an arc and a counterimage. With Hubble Spac…
Intermittent Dust Mass Loss from Activated Asteroid P/2013 P5 (PANSTARRS)
Moreno, F.; Licandro, J.; Cabrera-Lavers, A. +2 more
We present observations and models of the dust environment of activated asteroid P/2013 P5 (PANSTARRS). The object displayed a complex morphology during the observations, with the presence of multiple tails. We combined our own observations, all made with instrumentation attached to the 10.4 m Gran Telescopio Canarias on La Palma, with previously …
X-Ray Absorption by the Warm-hot Intergalactic Medium in the Hercules Supercluster
Buote, David A.; Ren, Bin; Fang, Taotao
"Missing baryons," in the form of warm-hot intergalactic medium (WHIM), are expected to reside in cosmic filamentary structures that can be traced by signposts such as large-scale galaxy superstructures. The clear detection of an X-ray absorption line in the Sculptor Wall demonstrated the success of using galaxy superstructures as a signpost to se…
The Hard X-Ray Perspective on the Soft X-Ray Excess
Fabian, Andrew C.; Reynolds, Christopher S.; Zoghbi, Abderahmen +5 more
The X-ray spectra of many active galactic nuclei exhibit a "soft excess" below 1 keV, whose physical origin remains unclear. Diverse models have been suggested to account for it, including ionized reflection of X-rays from the inner part of the accretion disk, ionized winds/absorbers, and Comptonization. The ionized reflection model suggests a nat…
X-Ray Variability and the Inner Region in Active Galactic Nuclei
Mangalam, A.; Mohan, P.
We present theoretical models of X-ray variability attributable to orbital signatures from an accretion disk including emission region size, quasi-periodic oscillations (QPOs), and its quality factor Q, and the emergence of a break frequency in the power spectral density shape. We find a fractional variability amplitude of Fvar\propto M…
Temporal Spectral Shift and Polarization of a Band-splitting Solar Type II Radio Burst
Li, Gang; Chen, Yao; Feng, Shiwei +4 more
In many type II solar radio bursts, the fundamental and/or the harmonic branches of the bursts can split into two almost parallel bands with similar spectral shapes and frequency drifts. However, the mechanisms accounting for this intriguing phenomenon remain elusive. In this study, we report a special band-splitting type II event in which spectra…
Changes to Saturn's Zonal-mean Tropospheric Thermal Structure after the 2010-2011 Northern Hemisphere Storm
Fletcher, L. N.; Flasar, F. M.; Achterberg, R. K. +4 more
We use far-infrared (20-200 µm) data from the Composite Infrared Spectrometer on the Cassini spacecraft to determine the zonal-mean temperature and hydrogen para-fraction in Saturn's upper troposphere from observations taken before and after the large northern hemisphere storm in 2010-2011. During the storm, zonal mean temperatures in the la…
Far-infrared Extinction Mapping of Infrared Dark Clouds
Tan, Jonathan C.; Lim, Wanggi
Progress in understanding star formation requires detailed observational constraints on the initial conditions, i.e., dense clumps and cores in giant molecular clouds that are on the verge of gravitational instability. Such structures have been studied by their extinction of near-infrared and, more recently, mid-infrared (MIR) background light. It…
No More Active Galactic Nuclei in Clumpy Disks Than in Smooth Galaxies at z ~ 2 in CANDELS/3D-HST
Barro, Guillermo; Bell, Eric F.; Ferguson, Henry C. +23 more
We use CANDELS imaging, 3D-HST spectroscopy, and Chandra X-ray data to investigate if active galactic nuclei (AGNs) are preferentially fueled by violent disk instabilities funneling gas into galaxy centers at 1.3 < z < 2.4. We select galaxies undergoing gravitational instabilities using the number of clumps and degree of patchiness as proxie…