Search Publications
The Association of Big Flares and Coronal Mass Ejections: What Is the Role of Magnetic Helicity?
Andrews, M. D.; Nindos, A.
Recently, M. D. Andrews found that approximately 40% of M-class flares between 1996 and 1999, classified according to GOES X-ray flux, are not associated with coronal mass ejections (CMEs). Using 133 events from his data set for which suitable photospheric magnetograms and coronal images were available, we studied the preflare coronal helicity of …
A panoramic Hα imaging survey of the z= 0.4 cluster Cl0024.0+1652 with Subaru
Smail, Ian; Kodama, Tadayuki; Nakata, Fumiaki +2 more
We employ panoramic, multicolour (BRz') and narrow-band Hα imaging of the cluster Cl0024.0+1652 (z= 0.39) from Subaru covering a ~30-arcmin field, to determine cluster membership and star formation rates for a large sample of galaxies across a wide field in the cluster, ~10 Mpc. We use photometric redshifts to identify cluster members, and statist…
Iron charge state distributions as an indicator of hot ICMEs: Possible sources and temporal and spatial variations during solar maximum
Lepri, S. T.; Zurbuchen, T. H.
It has been shown that Fe charge states greater than and equal to 16 are often observed in the presence of interplanetary coronal mass ejections (ICMEs) at 1 AU. These elevated charge states, representative of hot source regions on the Sun, provide an identifier of ICMEs independent of expansion processes and heliocentric distance. Using this new …
Three-Dimensional Structure of the Active Region Photosphere as Revealed by High Angular Resolution
Lites, B. W.; Title, A. M.; Berger, T. E. +1 more
Blue continuum images of active regions at ∼ 60° from the center of the solar disk obtained with the new Swedish 1-m Solar Telescope reveal heretofore unreported structure of the magnetized solar atmosphere. Perhaps the most striking aspect of these images is that, at an angular resolution of 0.12″, they show clearly the three-dimensional structur…
Exploring the complex X-ray spectrum of NGC 4051
King, A. R.; Reeves, J. N.; Page, K. L. +1 more
Archival XMM-Newton data on the nearby Seyfert galaxy NGC 4051, taken in relatively high- and low-flux states, offer a unique opportunity to explore the complexity of its X-ray spectrum. We find the hard X-ray band to be significantly affected by reflection from cold matter, which can also explain a non-varying, narrow Fe K fluorescent line. We in…
A transition in the accretion properties of radio-loud active nuclei
Marchesini, Danilo; Ferrarese, Laura; Celotti, Annalisa
We present evidence for the presence of a transition in the accretion properties of radio-loud sources. For a sample of radio galaxies and radio-loud quasars, selected based on their extended radio properties, the accretion rate is estimated from the black hole mass and nuclear luminosity. The inferred distribution is bimodal, with a paucity of so…
An Astrometric Calibration of the MV-Porb Relationship for Cataclysmic Variables based on Hubble Space Telescope Fine Guidance Sensor Parallaxes
Harrison, Thomas E.; Johnson, Joni J.; McArthur, B. E. +4 more
We present new, high-precision astrometric parallaxes for three cataclysmic variables: WZ Saggitae, YZ Cancri, and RU Pegasi, obtained using the Fine Guidance Sensors on the Hubble Space Telescope. The addition of these three parallaxes to the existing data set allows us to examine the outburst luminosities for dwarf novae spanning the orbital per…
Photometric redshifts with the Multilayer Perceptron Neural Network: Application to the HDF-S and SDSS
Popesso, P.; Fontana, A.; Vanzella, E. +8 more
We present a technique for the estimation of photometric redshifts based on feed-forward neural networks. The Multilayer Perceptron (MLP) Artificial Neural Network is used to predict photometric redshifts in the HDF-S from an ultra deep-multicolor catalog. Various possible approaches for the training of the neural network are explored, including t…
The Origin of Postflare Loops
Warren, H. P.; Sheeley, N. R., Jr.; Wang, Y. -M.
We apply a tracking technique, previously developed to study motions in the outer corona by Sheeley, Walters, Wang, and Howard, to 195 Å filtergrams obtained with the Transition Region and Coronal Explorer (TRACE) satellite and obtain height-time maps of the motions in the hot (10-20 MK) plasma clouds above postflare loop systems. These maps indic…
The Initial Mass Function and Stellar Content of NGC 3603
Bessell, Michael S.; Sung, Hwankyung
We present UBVRI and Hα photometry of the extremely compact, starburst cluster NGC 3603. Ground-based images, Hubble Space Telescope (HST) archival data, as well as Chandra X-ray data have been used for this study. We present, for the first time, optical color-magnitude diagrams (CMDs) for the stars in the cluster core down to V=22 mag. A well-def…