Search Publications
Properties of a Sunspot Plume Observed With the Coronal Diagnostic Spectrometer Aboard the Solar and Heliospheric Observatory
Landi, Enrico; Brosius, Jeffrey W.
We used three instruments (CDS, EIT, MDI) aboard the Solar and Heliospheric Observatory spacecraft to observe the large sunspot in NOAA Active Region 8539 on 1999 May 9 and 13. The spot contained a bright plume, most easily seen in EUV emission lines formed at 5.2<~logT<~5.7 (where T is the temperature in K), in its umbra on both dates. The …
Thermal and Nonthermal Nature of the Soft Excess Emission from Sérsic 159-03 Observed with XMM-Newton
Kaastra, Jelle S.; Bonamente, Massimiliano; Lieu, Richard +2 more
Several nearby clusters exhibit an excess of soft X-ray radiation that cannot be attributed to the hot virialized intracluster medium. There is no consensus to date on the origin of the excess emission: it could be either of thermal origin or due to an inverse Compton scattering of the cosmic microwave background. Using high-resolution XMM-Newton …
Young Stars and Dust in AFGL 437: Hubble Space Telescope NICMOS Polarimetric Imaging of an Outflow Source
Hines, Dean C.; Meakin, Casey A.; Thompson, Roger I.
We present near-infrared broadband and polarimetric images of the compact star-forming cluster AFGL 437 obtained with the NICMOS instrument on board HST. Our high-resolution images reveal a well-collimated bipolar reflection nebulosity in the cluster and allow us to identify WK 34 as the illuminating source. The scattered light in the bipolar nebu…
Magnetic Twist of an Extreme-Ultraviolet Coronal Loop Inferred from Plasma Constriction
Moon, Yong-Jae; Chae, Jongchul
Magnetic twist is a very likely way of constricting coronal plasma into loops. An attempt is made to determine the magnetic twist that can explain the constriction of coronal loops indirectly from observations. We decompose the coronal magnetic field into a large-scale magnetic field and a small-scale magnetic field. The large-scale field is assum…
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…