Search Publications
An Overdensity of Galaxies at z = 5.9 +/- 0.2 in the Hubble Ultra Deep Field Confirmed Using the ACS Grism
Daddi, E.; Panagia, N.; Ferguson, H. C. +17 more
We present grism spectra taken with the Advanced Camera for Surveys (ACS) to identify 29 red sources with (i775-z850)>=0.9 in the Hubble Ultra Deep Field (HUDF). Of these, 23 are found to be galaxies at redshifts between z=5.4 and 6.7, identified by the break at 1216 Å due to intergalactic medium (IGM) absorption; two are …
High-Resolution Radio Observations of the Colliding-Wind Binary WR 140
Dougherty, S. M.; Claussen, M. J.; Zauderer, B. A. +2 more
Milliarcsecond resolution Very Long Baseline Array (VLBA) observations of the archetype W-R+O star colliding-wind binary (CWB) system WR 140 are presented for 23 epochs between orbital phases 0.74 and 0.97. At 8.4 GHz, the emission in the wind-collision region (WCR) is clearly resolved as a bow-shaped arc that rotates as the orbit progresses. We i…
Coronal Mass Ejection Shock and Sheath Structures Relevant to Particle Acceleration
Gombosi, T. I.; Tóth, G.; Zurbuchen, T. H. +6 more
Most high-energy solar energetic particles are believed to be accelerated at shock waves driven by coronal mass ejections (CMEs). The acceleration process strongly depends on the shock geometry and the structure of the sheath that forms behind the shock. In an effort to understand the structure and time evolution of such CME-driven shocks and thei…
Relationship between Magnetic Power Spectrum and Flare Productivity in Solar Active Regions
Abramenko, V. I.
Power spectra of the line-of-sight magnetograms were calculated for 16 active regions of different flare activity. Data obtained by the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory in high-resolution mode were used in this study. For each active region, the daily soft X-ray flare index, A, was calculated. Thi…
The Discrepancy between Solar Abundances and Helioseismology
Basu, Sarbani; Antia, H. M.
There have been recent downward revisions of the solar photospheric abundances of oxygen and other heavy elements. These revised abundances along with OPAL opacities are not consistent with seismic constraints. In this work we show that the recently released Opacity Project opacity tables cannot resolve this discrepancy either. While the revision …
UVBLUE: A New High-Resolution Theoretical Library of Ultraviolet Stellar Spectra
Chavez, M.; Rodríguez-Merino, L. H.; Buzzoni, A. +1 more
We present an extended ultraviolet-blue (850-4700 Å) library of theoretical stellar spectral energy distributions computed at high resolution, λ/Δλ=50,000. The UVBLUE grid, as we named the library, is based on LTE calculations carried out with ATLAS9 and SYNTHE codes developed by R. L. Kurucz and consists of nearly 1800 entries that cover a large …
The Nonpotentiality of Active-Region Coronae and the Dynamics of the Photospheric Magnetic Field
Title, Alan M.; Schrijver, Carolus J.; Metcalf, Thomas R. +1 more
The magnetic field in the solar photosphere frequently carries strong electric currents, even though the global coronal configuration often resembles a potential field ringed by the heliospheric current sheet. To understand this, we compare TRACE EUV images of active-region coronae and potential-field source-surface extrapolations based on SOHO MD…
Abundance Profiles and Kinematics of Damped Lyα Absorbing Galaxies at z < 0.651,
Chen, Hsiao-Wen; Rauch, Michael; Kennicutt, Robert C., Jr.
We present a spectroscopic study of six damped Lyα absorption (DLA) systems at z<0.65, based on moderate- to high-resolution spectra of the galaxies responsible for the absorbers. Combining known metallicity measurements of the absorbers with known optical properties of the absorbing galaxies, we confirm that the low metal content of the DLA po…
Chandra Detection of the First X-Ray Forest along the Line of Sight To Markarian 421
Elvis, Martin; Marshall, Herman; Nicastro, Fabrizio +7 more
We present the first >=3.5 (conservative) or >=5.8 σ (sum-of-lines significance) detection of two warm-hot intergalactic medium (WHIM) filaments at z>0, which we find along the line of sight to the blazar Mrk 421. These systems are detected through highly ionized resonant metal absorption in high-quality Chandra ACIS and HRC Low Energy Tr…
Metallicities, Relative Ages, and Kinematics of Stellar Populations in ω Centauri
Pasquini, L.; Pancino, E.; Bellazzini, M. +3 more
We present results of an extensive spectroscopic survey of subgiant stars in the stellar system ω Cen. Using infrared Ca II triplet lines, we derived metallicities and radial velocities for more than 250 stars belonging to different stellar populations of the system. We find that the most metal-rich component, the anomalous subgiant branch (SGB-a)…