Search Publications
A Decade of MWC 758 Disk Images: Where Are the Spiral-arm-driving Planets?
Debes, John H.; Schneider, Glenn; Esposito, Thomas M. +10 more
Large-scale spiral arms have been revealed in scattered light images of a few protoplanetary disks. Theoretical models suggest that such arms may be driven by and corotate with giant planets, which has called for remarkable observational efforts to look for them. By examining the rotation of the spiral arms for the MWC 758 system over a 10 year ti…
Reconnection in the Post-impulsive Phase of Solar Flares
Reeves, Katharine K.; Forbes, Terry G.; Seaton, Daniel B.
Using a recently developed analytical procedure, we determine the rate of magnetic reconnection in the “standard” model of eruptive solar flares. During the late phase, the neutral line is located near the lower tip of the reconnection current sheet, and the upper region of the current sheet is bifurcated into a pair of Petschek-type shocks. Despi…
The Optical/Near-infrared Extinction Law in Highly Reddened Regions
Hosek, Matthew W., Jr.; Lu, Jessica R.; Clarkson, William I. +6 more
A precise extinction law is a critical input when interpreting observations of highly reddened sources such as young star clusters and the Galactic Center (GC). We use Hubble Space Telescope observations of a region of moderate extinction and a region of high extinction to measure the optical and near-infrared extinction law (0.8-2.2 µm). Th…
Outflowing OH+ in Markarian 231: The Ionization Rate of the Molecular Gas
Sturm, E.; Veilleux, S.; Ashby, M. L. N. +6 more
The oxygen-bearing molecular ions OH+, H2O+, and H3O+ are key species that probe the ionization rate of (partially) molecular gas that is ionized by X-rays and cosmic-rays permeating the interstellar medium. We report Herschel far-infrared and submillimeter spectroscopic observations of OH
Chemical Abundances in the Leading Arm of the Magellanic Stream
Richter, Philipp; Lockman, Felix J.; Fox, Andrew J. +8 more
The Leading Arm (LA) of the Magellanic Stream is a vast debris field of H I clouds connecting the Milky Way and the Magellanic Clouds. It represents an example of active gas accretion onto the Galaxy. Previously, only one chemical abundance measurement had been made in the LA. Here we present chemical abundance measurements using Hubble Space Tele…
A Dust-scattering Halo of 4U 1630-47 Observed with Chandra and Swift: New Constraints on the Source Distance
Maccarone, T. J.; Tomsick, J. A.; Kalemci, E.
We have observed the Galactic black hole transient 4U 1630-47 during the decay of its 2016 outburst with Chandra and Swift to investigate the properties of the dust-scattering halo created by the source. The scattering halo shows a structure that includes a bright ring between 80″ and 240″ surrounding the source, and a continuous distribution beyo…
Gravitationally Unstable Condensations Revealed by ALMA in the TUKH122 Prestellar Core in the Orion A Cloud
Sanhueza, Patricio; Choi, Minho; Tatematsu, Ken'ichi +5 more
We have investigated the TUKH122 prestellar core in the Orion A cloud using ALMA 3 mm dust continuum, N2H+ (J = 1-0), and CH3OH ({J}K={2}K-{1}K) molecular-line observations. Previous studies showed that TUKH122 is likely on the verge of star formation because the turbulence is almos…
CO in Protostars (COPS): Herschel-SPIRE Spectroscopy of Embedded Protostars
Larson, Rebecca L.; Lee, Jeong-Eun; Bouwman, Jeroen +13 more
We present full spectral scans from 200 to 670 µm of 26 Class 0+I protostellar sources obtained with Herschel-SPIRE as part of the “COPS-SPIRE” Open Time program, complementary to the DIGIT and WISH Key Programs. Based on our nearly continuous, line-free spectra from 200 to 670 µm, the calculated bolometric luminosities (L bol
A Stealth CME Bracketed between Slow and Fast Wind Producing Unexpected Geoeffectiveness
Wang, Rui; Liu, Ying D.; Hu, Huidong +2 more
We investigate how a weak coronal mass ejection (CME) launched on 2016 October 8 without obvious signatures in the low corona produced a relatively intense geomagnetic storm. Remote sensing observations from SDO, STEREO, and SOHO and in situ measurements from Wind are employed to track the CME from the Sun to the Earth. Using a graduated cylindric…
Variable Nature of Magnetically Driven Ultra-fast Outflows
Behar, Ehud; Tombesi, Francesco; Shrader, Chris +3 more
Among a number of active galactic nuclei that drive ionized outflows in X-rays, a low-redshift (z = 0.184) quasar, PDS 456, is long known to exhibit one of the exemplary ultra-fast outflows (UFOs). However, the physical process of acceleration mechanisms is yet to be definitively constrained. In this work, we model the variations of the Fe K UFO p…