Search Publications
The Counterstreaming Instability in Dwarf Elliptical Galaxies with Off-Center Nuclei
Debattista, Victor P.; De Rijcke, Sven
In many nucleated dwarf elliptical galaxies (dE,N's), the nucleus is offset by a significant fraction of the scale radius with respect to the center of the outer isophotes. Using a high-resolution N-body simulation, we demonstrate that the nucleus can be driven off-center by the m=1 counterstreaming instability, which is strong in flattened stella…
Dual Flows with Supersonic Velocities in the Sunspot Transition Region
Wilhelm, K.; Kjeldseth-Moe, O.; Brynildsen, N. +1 more
Observations of sunspot transition region lines that deviate significantly from a Gaussian shape are presented. Attention is given to ``dual flows,'' a line profile phenomenon in which two distinct velocities are observed within the same spatial resolution element. In 5 out of 12 sunspots we observe dual flows. Several emission line profiles are w…
Characteristic Scales of Chromospheric Oscillation Wave Packets
McIntosh, Scott W.; Smillie, Darren G.
We use wavelet transforms to study the characteristic time scales of chromospheric oscillation ``wave packets'' that are observed in Transition Region and Coronal Explorer (TRACE) ultraviolet continuum image time series. Using several data sets, we investigate the statistical, spatial, and temporal intermittence of the number, duration, mean frequ…
An X-Ray Investigation of the NGC 346 Field in the Small Magellanic Cloud. III. XMM-Newton Data
Corcoran, Michael F.; Stevens, Ian R.; Nazé, Yaël +2 more
We present new XMM-Newton results on the field around the NGC 346 star cluster in the SMC. This continues and extends previously published work on Chandra observations of the same field. The two XMM-Newton observations were obtained, respectively, 6 months before and 6 months after the previously published Chandra data. Of the 51 X-ray sources det…
XMM-Newton Observation of the Double Pulsar System J0737-3039
Campana, Sergio; Possenti, Andrea; Burgay, Marta
We report on a 50 ks XMM-Newton observation of the double pulsar system J0737-3039 performed in 2004 April. We present results of the spectral analysis of these data combined with the much shorter Chandra pointing performed in 2004 January. Blackbody emission with an effective temperature of 0.20+0.02-0.02 keV (90% confidence…
A Detailed Study of Opacity in the Upper Atmosphere of Proxima Centauri
Christian, D. J.; Mathioudakis, M.; Bloomfield, D. S. +2 more
We present far-UV and UV spectroscopic observations of Proxima Centauri obtained as part of our continued investigation into the optically thin approximation assumed for the transition regions of late-type stars. Significant opacity is found in the C III lines during both the quiescent and flaring states of Proxima Cen, with up to 70% of the expec…
Observations of Water Vapor Outflow from NML Cygnus
Li, Di; Lim, Tanya; Feuchtgruber, Helmut +2 more
We report new observations of the far-infrared and submillimeter water vapor emission of NML Cygnus based on data gathered with the Infrared Space Observatory and the Submillimeter Wave Astronomy Satellite. We compare the emission from NML Cyg to that previously published for VY CMa and W Hya in an attempt to establish the validity of recently pro…
Cosmic Filaments in Superclusters
Miller, Eric D.; Bregman, Joel N.; Dupke, Renato A.
Large-scale structure calculations show that modest overdensity filaments will connect clusters of galaxies and these filaments are reservoirs of baryons, mainly in gaseous form. To determine whether such filaments exist, we have examined the UV absorption line properties of three active galactic nuclei (AGNs) projected behind possible filaments i…
The Effects of Periodically Gapped Time Series on Cross-Correlation Lag Determinations
Maraschi, L.; Treves, A.; Celotti, A. +2 more
The three bright TeV blazars Mrk 421, Mrk 501, and PKS 2155-304 are highly variable in synchrotron X-ray emission. In particular, these sources can exhibit variable time lags between flux variations at different X-ray energy bands. However, there are a number of issues that may significantly bias lag determinations. Edelson et al. (2001) recently …
Optical and IUE Spectra of the Planetary Nebula NGC 7026
Feibelman, Walter A.; Hyung, Siek
We investigated spectroscopic data of the extended planetary nebula NGC 7026 in the wavelengths 3700-10,050 Å, secured with the Hamilton Echelle Spectrograph at Lick Observatory. This optical wavelength spectrum has been analyzed along with the International Ultraviolet Explorer (IUE) UV spectral data. The diagnostic diagram indicates that the pla…