Search Publications
HST/STIS high resolution echelle spectra of α Centauri A (G2 V)
Pagano, I.; Linsky, J. L.; Valenti, J. +1 more
We describe and analyze HST/STIS observations of the G2 V star α Centauri A (
Ultracompact Dwarf Galaxies in Abell 1689: A Photometric Study with the Advanced Camera for Surveys
Ford, H. C.; Infante, L.; Zheng, W. +37 more
The properties of ultracompact dwarf (UCD) galaxy candidates in Abell 1689 (z=0.183) are investigated, based on deep high-resolution images from the Hubble Space Telescope Advanced Camera for Surveys. A UCD candidate has to be unresolved, have i<28 mag (MV<-11.5 mag), and satisfy color limits derived from Bayesian photometric reds…
On the deep minimum state in the Seyfert galaxy MCG-6-30-15
Staubert, Rüdiger; Wilms, Jörn; Reynolds, Christopher S. +2 more
We present a detailed spectral analysis of the first observation of the Seyfert 1 galaxy MCG-6-30-15 by the European Photon Imaging Camera on board the XMM-Newton observatory, together with contemporaneous data from the Proportional Counter Array on the Rossi X-ray Timing Explorer. Confirming our previously published result, we find that the prese…
Internal Velocities in the Orion Nebula: Large Radial Velocity Features
Hartigan, Patrick; O'Dell, C. R.; Doi, Takao
A map of high-velocity features in the 3'×5' central region of the Orion Nebula was created from slit spectra with a velocity resolution of 8 km s-1. We identified two new bipolar flows, Herbig-Haro (HH) 725 and HH 726, as well as a highly redshifted flow, HH 512. We also found multiple new high-velocity co-moving …
New Perspectives on the X-Ray Emission of HD 104237 and Other Nearby Herbig Ae/Be Stars from XMM-Newton and Chandra
Skinner, Stephen L.; Güdel, Manuel; Audard, Marc +1 more
The origin of the X-ray emission from Herbig Ae/Be stars is not yet known. These intermediate-mass pre-main-sequence stars lie on radiative tracks and are not expected to emit X-rays via solar-like magnetic processes, nor are their winds powerful enough to produce X-rays by radiative wind shocks as in more massive O-type stars. The emission could …
High-amplitude, long-term X-ray variability in the solar-type star HD 81809: The beginning of an X-ray activity cycle?
Schmitt, J. H. M. M.; Güdel, M.; Harnden, F. R., Jr. +5 more
We present the initial results from our XMM-Newton program aimed at searching for X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat more evolved than the Sun, and with a less massive companion) with a pronounced 8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data. We present here the results f…
Multi-spacecraft observations of diffuse ions upstream of Earth's bow shock
Klecker, B.; Kistler, L. M.; Lucek, E. A. +6 more
We report on simultaneous measurements of energetic ions upstream of Earth's quasi-parallel bow shock by Cluster during a 10 hour time period when the inter-spacecraft separation distance was between ~1 and ~1.5 Re. Using a bow shock model we determined for each 32 s averaged data set the distance of the Cluster 1 and Cluster 3 spacecra…
The kinetic shell model of coronal heating and acceleration by ion cyclotron waves: 3. The proton halo and dispersive waves
Isenberg, Philip A.
The kinetic shell model seeks to test the collisionless kinetic response of coronal hole protons to the quasi-linear resonant cyclotron dissipation of outwardly directed, parallel propagating ion cyclotron waves, which is often invoked as the mechanism responsible for generating the fast solar wind. In this model, we make the approximation that th…
Resolving the Large-Scale Spectral Variability of the Luminous Seyfert 1 Galaxy 1H 0419-577: Evidence for a New Emission Component and Absorption by Cold Dense Matter
O'Brien, P. T.; Reeves, J. N.; Page, K. L. +1 more
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in 2002 September, when the source was in an extreme low-flux state, found a very hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was ``X-ray bright'' indicated that the dominant spectral…
On the Formation of the Resonance Lines of Helium in the Sun
Judge, Philip G.; Pietarila, Anna
To investigate the cause of anomalously bright resonance lines of helium in the Sun, we have studied the magnitude of the enhancements and some proposals made to explain them. Calculations in new semiempirical solar models indicate that the resonance lines of helium are enhanced by factors of 2-5 for He I and between 2 and 9 for He II, depending o…