Search Publications
The Trail of Discrete X-Ray Sources in the Early-Type Galaxy NGC 4261: Anisotropy in the Globular Cluster Distribution?
Trinchieri, Ginevra; Wolter, Anna; Cortese, Luca +4 more
Chandra images of the elliptical galaxy NGC 4261 have revealed an anisotropy in the spatial distribution of the off-nuclear X-ray sources, interpreted by Zezas et al. as evidence of an association with a young stellar population. Our independent analysis of archive X-ray (Chandra) and optical (INT and HST) observations confirms the anisotropy of t…
The Nature of Radio Continuum Emission at Very Low Metallicity: Very Large Array Observations of I Zw 18
Cannon, John M.; Skillman, Evan D.; Walter, Fabian +1 more
We present the first resolved study of the radio continuum properties of I Zw 18, the dwarf galaxy with the lowest known nebular metal abundance in the local universe. New Very Large Array radio continuum images at 20 and 3.6 cm are compared to various Hubble Space Telescope images, and we find a striking morphological similarity between high-reso…
On the Anomalous Red Giant Branch of the Globular Cluster ω Centauri
Sterken, C.; Prada Moroni, P. G.; Degl'Innocenti, S. +17 more
We present three different optical and near-infrared (NIR) data sets for evolved stars in the Galactic globular cluster ω Centauri. The comparison between observations and homogeneous sets of stellar isochrones and zero-age horizontal branches provides two reasonable fits. Both of them suggest that the so-called anomalous branch has a metal-interm…
Is the Bursting Radio Source GCRT J1745-3009 a Double Neutron Star Binary?
Treves, A.; Possenti, A.; Turolla, R.
GCRT J1745-3009 is a peculiar transient radio source in the direction of the Galactic center. It was observed to emit a series of ~1 Jy bursts at 0.33 GHz, with a typical duration of ~10 minutes and at apparently regular intervals of ~77 minutes. If the source is indeed at the distance of the Galactic center, as seems likely, we show that its obse…
Flare X-Ray Observations of AB Doradus: Evidence of Stellar Coronal Opacity
Mathioudakis, M.; Keenan, F. P.; Matranga, M. +1 more
X-ray spectra of the late-type star AB Dor obtained with the XMM-Newton satellite are analyzed. AB Dor was particularly active during the observations. An emission measure reconstruction technique is employed to analyze flare and quiescent spectra, with emphasis on the Fe XVII 15-17 Å wavelength region. The Fe XVII 16.78 Å/15.01 Å line ratio incre…
Stagnation Flow in Thin Streamer Boundaries
Nerney, Steven; Suess, Steven T.
Slow solar wind is believed to arise in the legs or near the cusp of streamers, inside the brightness boundary. In an earlier study, we used an analytic model of flow in this layer to analyze the effect of the magnetic field on the geometry of the flow. That study successfully described those conditions that can lead to a decrease of the flow spee…
Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii
Ayres, Thomas R.; Harper, Graham M.; Brown, Alexander
We report Chandra detections of coronal X-rays from the early G supergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD 204867: G0 Ib). Previous ROSAT observations of these archetypical ``hybrid chromosphere'' stars were inconclusive, in the case of α Aqr owing to a 38' mispointing, and for β Aqr because of a small positional discrepancy of the…
Dust Extinction in Compact Planetary Nebulae
Kwok, S.; Lee, T. -H.
The effects of dust extinction on the departure from axisymmetry in the morphology of planetary nebulae (PNs) are investigated through a comparison of the radio free-free emission and hydrogen recombination line images. The dust extinction maps from five compact PNs are derived using high-resolution (~0.1") Hα and radio maps of the HST and VLA. Th…
Origin and Acceleration of the Slow Solar Wind
Habbal, Shadia Rifai; Woo, Richard
This Letter uses Doppler dimming measurements by SOHO UVCS to elucidate the origin and acceleration of the slow solar wind. By investigating plasma flow in the corona over an active region during 2000 May 14-16, we confirm what has been suggested by the presence of the imprint of active regions in the solar wind near Earth orbit, that active regio…
Evolution of the Dependence of Rest-Frame Color and Morphology Distribution on Stellar Mass for Galaxies in the Hubble Deep Field-North
Yamada, T.; Kajisawa, M.
Using very deep Subaru K'-band imaging and archival Hubble Space Telescope WFPC2/NICMOS data of the Hubble Deep Field-North, we investigate the evolution of the stellar mass, color, and morphology of galaxies to z~3. We mainly examine the rest-frame U-V color distribution of galaxies as a function of stellar mass. At 0.3<~z<~2, galaxies seem…