Search Publications
Spectral Hardening in Large Solar Flares
Benz, A. O.; Grigis, P. C.
Observations by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are used to quantitatively study the hard X-ray evolution in five large solar flares selected for spectral hardening in the course of the event. The X-ray bremsstrahlung emission from nonthermal electrons is characterized by two spectroscopically distinct phases: impulsive …
Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z = 1: Evolution of the Rotation Rate
van der Wel, Arjen; van der Marel, Roeland P.
We use the spatial information of our previously published VLT/FORS2 absorption-line spectroscopy to measure mean stellar velocity and velocity dispersion profiles of 25 field early-type galaxies at a median redshift z = 0.97 (full range 0.6 < z < 1.2). This provides the first detailed study of early-type galaxy rotation at these redshifts. …
Discovery of Fast-Moving X-Ray-Emitting Ejecta Knots in the Oxygen-Rich Supernova Remnant Puppis A
Burrows, D. N.; Mori, K.; Hughes, J. P. +5 more
We report on the discovery of fast-moving X-ray-emitting ejecta knots in the Galactic oxygen-rich supernova remnant Puppis A from XMM-Newton observations. We find an X-ray knotty feature positionally coincident with an O-rich fast-moving optical filament with blueshifted line emission located in the northeast of Puppis A. We extract spectra from n…
XMM-Newton Observations of CXOU J010043.1-721134: The First Deep Look at the Soft X-Ray Emission of a Magnetar
Tiengo, A.; Mereghetti, S.; Esposito, P.
We present the analysis of six XMM-Newton observations of the anomalous X-ray pulsar CXOU J010043.1-721134, the magnetar candidate characterized by the lowest interstellar absorption. In contrast with all the other magnetar candidates, its X-ray spectrum cannot be fitted by an absorbed power-law plus blackbody model. The sum of two (absorbed) blac…
Lens Galaxy Properties of SBS 1520+530: Insights from Keck Spectroscopy and AO Imaging
Auger, M. W.; Thompson, D.; Fassnacht, C. D. +3 more
We report on an investigation of the SBS 1520+530 gravitational lens system. We have used archival Hubble Space Telescope (HST) imaging, Keck spectroscopic data, and Keck adaptive optics (AO) imaging to study the lensing galaxy and its environment. The AO imaging has allowed us to fix the lens galaxy properties with a high degree of accuracy when …
NGC 346 in the Small Magellanic Cloud. IV. Triggered Star Formation in the H II Region N66
Henning, Thomas; Gouliermis, Dimitrios A.; Brandner, Wolfgang +4 more
Stellar feedback, expanding H II regions, wind-blown bubbles, and supernovae are thought to be important triggering mechanisms of star formation. Stellar associations, being hosts of significant numbers of early-type stars, are the loci where these mechanisms act. In this part of our photometric study of the star-forming region NGC 346/N66 in the …
Holmberg IX: The Nearest Young Galaxy
Sabbi, E.; Gallagher, J. S.; Smith, L. J. +2 more
We present a study of the M81 companion dwarf irregular galaxy Holmberg IX using deep images taken with the Wide Field Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope. Based on color-magnitude diagrams the resolved stellar population toward Holmberg IX contains numerous stars with ages of lesssim200 Myr as well as ol…
Rise of a Dark Bubble through a Quiescent Prominence
de Toma, G.; Burkepile, J. T.; Low, B. C. +1 more
We report on a dynamical event observed in a quiescent prominence on 2007 November 8: a well-formed dark "bubble" with a bright core rose vertically through the prominence without causing it to erupt. This event was observed in Hα and He I 1083 nm with the instruments of the Mauna Loa Solar Observatory. The dark bubble had a size of over 40'' and …
Biases on Initial Mass Function Determinations. II. Real Multiple Systems and Chance Superpositions
Maíz Apellániz, J.
When calculating stellar initial mass functions (IMFs) for young clusters, one has to take into account that (1) most massive stars are born in multiple systems, (2) most IMFs are derived from data that cannot resolve such systems, and (3) multiple chance superpositions between members are expected to happen if the cluster is too distant. In this …
Forward Modeling of Active Region Coronal Emissions. II. Implications for Coronal Heating
Leka, K. D.; Lundquist, L. L.; Fisher, G. H. +2 more
In Paper I, we introduced and tested a method for predicting solar active region coronal emissions using magnetic field measurements and a chosen heating relationship. Here, we apply this forward-modeling technique to 10 active regions observed with the Mees Solar Observatory Imaging Vector Magnetograph and the Yohkoh Soft X-ray Telescope. We prod…