Search Publications
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)…
Rapid Change of δ Spot Structure Associated with Seven Major Flares
Liu, Yu; Liu, Chang; Denker, Carsten +4 more
A large fraction of major flares occur in active regions that exhibit a δ configuration. The formation and disintegration of δ configurations is very important in understanding the evolution of photospheric magnetic fields. In this paper we study the relationship between the change in δ spot structures and associated major flares. We present a new…
What Is the Neon Abundance of the Sun?
Basu, Sarbani; Bahcall, John N.; Serenelli, Aldo M.
We have evolved a series of 13 complete solar models that utilize different assumed heavy-element compositions. Models that are based upon the heavy-element abundances recently determined by Asplund and coworkers are inconsistent with helioseismological measurements. However, models in which the neon abundance is increased by 0.4-0.5 dex to logN(N…
Observational Evidence of the Kink Instability in Solar Filament Eruptions and Sigmoids
Rust, D. M.; LaBonte, B. J.
Two lines of observational evidence are used to infer that the MHD helical kink instability is associated with solar eruptions. The senses of twist and writhe are determined in images of seven erupting filaments obtained at 10830, 1600, 195, and 171 Å. In every case the sense of twist is the same as the sense of writhe, as required for a kink. Fro…
Probing the Environment in Gamma-Ray Bursts: The Case of an X-Ray Precursor, Afterglow Late Onset, and Wind Versus Constant Density Profile in GRB 011121 and GRB 011211
Piro, L.; Frontera, F.; Costa, E. +9 more
In this paper we present BeppoSAX and XMM-Newton observations of two long gamma-ray bursts (GRBs), the X-ray-rich event of 2001 December 11 (GRB 011211) and the hard and very bright event of 2001 November 21 (GRB 011121). In both events we find evidence of a late X-ray burst taking place several minutes after the prompt emission. In the November b…