Search Publications
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…
The Evolution of Early-Type Red Galaxies with the GEMS Survey: Luminosity-Size and Stellar Mass-Size Relations Since z=1
Bell, Eric F.; Somerville, Rachel S.; Wisotzki, Lutz +14 more
We combine imaging from the Hubble Space Telescope Advanced Camera for Surveys, as part of the GEMS (Galaxy Evolution from Morphologies and SEDs) survey, with redshifts and rest-frame quantities from COMBO-17 to study the evolution of morphologically early-type galaxies with red colors since z=1. From 0.5d×0.5d imaging, we draw a large sample of 7…
Evidence for Spectropolarimetric Diversity in Type Ia Supernovae
Filippenko, Alexei V.; Foley, Ryan J.; Leonard, Douglas C. +2 more
We present single-epoch, postmaximum spectropolarimetry of four Type Ia supernovae (SNe Ia) that span a range of spectral and photometric properties: SN 2002bf and SN 2004dt exhibit unusually high-velocity (HV) absorption lines. SN 1997dt is probably somewhat subluminous, and SN 2003du is slightly overluminous. We detect polarization modulations a…
Deep ACS Imaging of the Halo of NGC 5128: Reaching the Horizontal Branch
Greggio, Laura; Peng, Eric W.; Rejkuba, Marina +2 more
Using the Hubble Space Telescope (HST) Wide Field Camera (WFC) of the Advanced Camera for Surveys (ACS), we have obtained deep (V, I) photometry of an outer halo field in NGC 5128, to a limiting magnitude of I~=29. Our photometry directly reveals the core helium burning stellar population (the ``red clump'' or horizontal branch) in a giant E/S0 ga…
Discovery of the Accretion-powered Millisecond X-Ray Pulsar IGR J00291+5934
Chakrabarty, Deepto; Galloway, Duncan K.; Markwardt, Craig B. +2 more
We report on observations of the sixth accretion-powered millisecond pulsar, IGR J00291+5934, with the Rossi X-Ray Timing Explorer. The source is a faint recurrent X-ray transient initially identified by the International Gamma-Ray Astrophysics Laboratory. The 599 Hz (1.67 ms) pulsation had a fractional rms amplitude of 8% in the 2-20 keV range, a…
On the Nature of Dark Extreme Ultraviolet Structures Seen by SOHO/EIT and TRACE
Heinzel, P.; Anzer, U.
Spectral lines in the extreme ultraviolet (EUV) observed on the Sun can originate either from the hot corona or the cooler chromosphere to corona transition region. In the present paper we concentrate on coronal lines and in particular on iron lines at 171, 195, and 284 Å, which have been frequently observed by the Solar and Heliospheric Observato…
Rest-Frame Ultraviolet-to-Optical Properties of Galaxies at z ~ 6 and z ~ 5 in the Hubble Ultra Deep Field: From Hubble to Spitzer
Ouchi, Masami; Papovich, Casey; Dickinson, Mark +11 more
We use data from the first epoch of observations with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope for the Great Observatories Origins Deep Survey (GOODS) to detect and study a collection of Lyman break galaxies at z~6-5 in the Hubble Ultra Deep Field (HUDF), six of which have spectroscopic confirmation. At these redshifts, IRAC…