Search Publications
Do We Know of Any Maunder Minimum Stars?
Wright, J. T.
Most stars previously identified as Maunder minimum stars are old and evolved off the main sequence. Analysis of activity measurements from the California and Carnegie Planet Search program stars and Hipparcos parallaxes implies that the canonical relation between age and chromospheric activity breaks down for stars older than ~6 Gyr when activity…
An X-ray Baldwin effect for the narrow Fe Kα lines observed in active galactic nuclei
O'Brien, P. T.; Reeves, J. N.; Page, K. L. +1 more
The majority of active galactic nuclei (AGN) observed by XMM-Newton reveal narrow Fe Kα lines at ~6.4 keV, due to emission from cold (neutral) material. There is an X-ray Baldwin effect in type I AGN, in that the equivalent width (EW) of the line decreases with increasing luminosity, with weighted linear regression giving EW~L-0.17+/-0.08
A microscopic and nanoscopic view of storm-time chorus on 31 March 2001
Gurnett, D. A.; Pickett, J. S.; Santolík, O. +2 more
We investigate intense whistler-mode chorus emissions which occurred during the geomagnetic storm on 31 March 2001. We use multipoint measurements obtained by the Cluster spacecraft in the premidnight equatorial region outside the plasmasphere at a radial distance of 4 Earth radii (L = 4.0 - 4.2). Observed spatio-temporal variations of the directi…
Chandra and XMM-Newton Observations of RDCS 1252.9-2927, A Massive Cluster at z=1.24
Demarco, R.; Lidman, C.; Tozzi, P. +10 more
We present deep Chandra and XMM-Newton observations of the galaxy cluster RDCS 1252.9-2927, which was selected from the ROSAT Deep Cluster Survey (RDCS) and confirmed by extensive spectroscopy with the Very Large Telescope at redshift z=1.237. With the Chandra data, the X-ray emission from the intracluster medium is well resolved and traced out to…
The ACS Virgo Cluster Survey. III. Chandra and Hubble Space Telescope Observations of Low-Mass X-Ray Binaries and Globular Clusters in M87
Jordán, Andrés; Tonry, John L.; Côté, Patrick +7 more
The ACIS instrument on board the Chandra X-Ray Observatory has been used to carry out the first systematic study of low-mass X-ray binaries (LMXBs) in M87, the giant elliptical galaxy near the dynamical center of the Virgo Cluster. These images-with a total exposure time of 154 ks-are the deepest X-ray observations yet obtained of M87. We identify…
A Hard X-ray Survey of the Galactic-Center Region with the IBIS Telescope of the INTEGRAL Observatory: A Catalog of Sources
Gilfanov, M. R.; Sunyaev, R. A.; Cherepashchuk, A. M. +6 more
From August 23 through September 24, 2003, the INTEGRAL Observatory conducted a deep survey of the Galactic-Center region with a record-breaking sensitivity at energies above 20 keV. We have analyzed the images of the Galactic-Center region obtained with the ISGRI detector of the IBIS telescope (15-200 keV) and give a catalog of detected sources. …
The basic characteristics of EUV post-eruptive arcades and their role as tracers of coronal mass ejection source regions
Bothmer, V.; Tripathi, D.; Cremades, H.
The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft provides unique observations of dynamic processes in the low corona. The EIT 195 Å data taken from 1997 to the end of 2002 were investigated to study the basic physical properties of post-eruptive arcades (PEAs) and their relationship …
Metallicity in the Galactic Center: The Arches Cluster
Hillier, D. John; Figer, Donald F.; Kudritzki, Rolf P. +1 more
We present a quantitative spectral analysis of five very massive stars in the Arches cluster, located near the Galactic center, to determine stellar parameters, stellar wind properties, and, most importantly, metallicity content. The analysis uses a new technique, presented here for the first time, and uses line-blanketed non-LTE wind/atmosphere m…
Average Ultraviolet Quasar Spectra in the Context of Eigenvector 1: A Baldwin Effect Governed by the Eddington Ratio?
Marziani, P.; Zamanov, R.; Bachev, R. +3 more
We present composite UV spectra for low-redshift type 1 active galactic nuclei binned to exploit the information content of the eigenvector 1 (E1) parameter space. Composite spectra show high enough S/N and spectral resolution to permit a decomposition of the C IV λ1549 line profile: one of the strongest high-ionization lines (HILs), and fundament…
The Coronal Heating Mechanism as Identified by Full-Sun Visualizations
Aschwanden, Markus J.; Schrijver, Carolus J.; De Rosa, Marc L. +1 more
We constrain the properties of the mechanism(s) responsible for the bulk of the heating of the corona of the Sun by simulating, for the first time, the appearance of the entire solar corona. Starting from full-sphere magnetic field maps for 2000 December 1 and 8, when the Sun was moderately active, we populate nearly 50,000 coronal field lines wit…