Search Publications
The Local Helioseismology of Inclined Magnetic Fields and the Showerglass Effect
Braun, D. C.; Cally, P. S.; Lindsey, C. +1 more
We present evidence for the dependence of helioseismic Doppler signatures in active regions on the line-of-sight angle in inclined magnetic fields. Using data from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory, we performed phase-sensitive holography in the penumbrae of sunspots over the course of several days …
On the Nature of Coronal EIT Waves
Erdélyi, R.; Ballai, I.; Pintér, B.
Large-scale eruption events in the solar atmosphere can generate global waves, i.e., waves that propagate over distances comparable to the solar radius. In the low solar corona, global waves observed by SOHO EIT, generated by coronal mass ejections or flares, are usually referred to as ``EIT waves.'' The nature of these global waves is the subject…
M31's Heavy-Element Distribution and Outer Disk
MacArthur, Lauren A.; Courteau, Stéphane; Worthey, Guy +1 more
Hubble Space Telescope imaging of 11 fields in M31 were reduced to color-magnitude diagrams. The fields were chosen to sample all galactocentric radii to 50 kpc (~9 disk scale lengths, or >99.9% of the total light enclosed). The colors of the red giants at each pointing map to an abundance distribution with errors of order 0.1 dex in [M/H]. The…
First Soft X-Ray Observations of Global Coronal Waves with the GOES Solar X-Ray Imager
Mann, G.; Aurass, H.; Warmuth, A.
We present the first observations of global coronal waves obtained with the Solar X-Ray Imager (SXI) aboard the GOES-12 satellite. Focusing on six events, the basic morphological and kinematic characteristics of the waves observed in soft X-rays are derived. Taking advantage of SXI's high temporal cadence and comparing the wave signatures with ext…
The X-Ray Spectral Properties and Variability of Luminous High-Redshift Active Galactic Nuclei
Brandt, W. N.; Strauss, Michael A.; Vignali, C. +4 more
We perform a detailed investigation of moderate- to high-quality X-ray spectra of 10 of the most luminous active galactic nuclei (AGNs) known at z>4 (up to z~6.28). This study includes five new XMM-Newton observations and five archived X-ray observations (four by XMM-Newton and one by Chandra). We find that the X-ray power-law photon indices of…
Infall, the Butcher-Oemler Effect, and the Descendants of Blue Cluster Galaxies at z~0.6
Franx, Marijn; Illingworth, Garth D.; Tran, Kim-Vy H. +3 more
Using wide-field Hubble Space Telescope WFPC2 imaging and extensive Keck LRIS spectroscopy, we present a detailed study of the galaxy populations in MS 2053-04, a massive, X-ray-luminous cluster at z=0.5866+/-0.0011. Analysis of 149 confirmed cluster members shows that MS 2053 is composed of two structures that are gravitationally bound to each ot…
XMM-Newton EPIC Background Modeling for Extended Sources
Markevitch, M.; Lumb, D.; Nevalainen, J.
We use XMM-Newton blank-sky and closed-cover background data to explore background subtraction methods for large extended sources filling the EPIC field of view, such as nearby galaxy clusters, for which local background estimation is difficult. In particular, we investigate the uncertainties of the background modeling in the 0.8-7.0 keV band that…
Stars in the Hubble Ultra Deep Field
Panagia, N.; Walsh, J. R.; Koekemoer, A. M. +11 more
We identified 46 unresolved source candidates in the Hubble Ultra Deep Field (HUDF) down to i775=29.5. Unresolved objects were identified using a parameter S, which measures the deviation from the curve of growth of a point source. Extensive testing of this parameter was carried out, including the effects of decreasing signal-to-noise r…
Resolving the Inner Cavity of the HD 100546 Disk: A Candidate Young Planetary System?
Heap, S. R.; Grady, C. A.; Woodgate, B. +4 more
The inner 100 AU of HD 100546 is studied via far-ultraviolet long-slit spectroscopy with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS). The star is surrounded by reflection nebulosity, which can be traced 100 AU in the continuum, and by emission from H I Lyα, N I, Si II, and fluorescent H2 transitions. The Lyα e…
Measurement of the Energy Release Rate and the Reconnection Rate in Solar Flares
Shibata, Kazunari; Isobe, Hiroaki; Takasaki, Hiroyuki
By using the method presented by Isobe et al., the nondimensional reconnection rate vin/vA has been determined for the impulsive phase of three two-ribbon flares, where vin is the velocity of the reconnection inflow and vA is the Alfvén velocity. The nondimensional reconnection rate is important to make …