Search Publications
NICMOS Observations of Extragalactic Cepheids. I. Photometry Database and a Test of the Standard Extinction Law
Calzetti, D.; Stetson, P. B.; Persson, S. E. +8 more
We present the results of near-infrared observations of extragalactic Cepheids made with the Near-Infrared Camera and Multi-Object Spectrometer on board the Hubble Space Telescope (HST). The variables are located in the galaxies IC 1613, IC 4182, M31, M81, M101, NGC 925, NGC 1365, NGC 2090, NGC 3198, NGC 3621, NGC 4496A, and NGC 4536. All fields w…
Modulation of Cosmic Rays in the Heliosphere From Solar Minimum to Maximum: a Theoretical Perspective
Ferreira, S. E. S.; Potgieter, M. S.; Burger, R. A.
The modulation of galactic cosmic rays in the heliosphere seems to be dominated by four major mechanisms: convection, diffusion, drifts (gradient, curvature and current sheet), and adiabatic energy losses. In this regard the global structure of the solar wind, the heliospheric magnetic field (HMF), the current sheet (HCS), and that of the heliosph…
The cluster environments of powerful radio-loud and radio-quiet active galactic nuclei
McLure, R. J.; Dunlop, J. S.
The spatial clustering amplitude (Bgq) is determined for a sample of 44 powerful active galactic nuclei (AGN) at z~=0.2. No significant difference is detected in the richness of the cluster environments of the radio-loud and radio-quiet subsamples, both of which typically inhabit environments as rich as Abell class ~=0. Comparison with …
Timing the millisecond pulsars in 47 Tucanae
Camilo, F.; Lorimer, D. R.; Freire, P. C. +3 more
In the last ten years, 20 millisecond pulsars have been discovered in the globular cluster 47 Tucanae. Hitherto, only three of these pulsars had published timing solutions. Here we improve upon these three and present 12 new solutions. These measurements can be used to determine a variety of physical properties of the pulsars and of the cluster. T…
Discovery of Extended X-Ray Emission from the Planetary Nebula NGC 7027 by the Chandra X-Ray Observatory
Soker, Noam; Kastner, Joel H.; Vrtilek, Saeqa D.
We report the discovery of X-ray emission from NGC 7027, a prototypical object for the study of the formation and evolution of planetary nebulae. Observations with the Advanced CCD Imaging Spectrometer (ACIS) aboard the Chandra X-Ray Observatory show that the X-ray emission from NGC 7027 is extended and is bipolar in morphology. The ACIS spectrum …
An Ultraviolet through Infrared Look at Star Formation and Super Star Clusters in Two Circumnuclear Starburst Rings
Filippenko, Alexei V.; Ho, Luis C.; Maoz, Dan +2 more
We present broadband (U, V, I, and H) and narrowband (Hα+[N II] and Paα) images of the circumnuclear starburst rings in two nearby spiral galaxies, NGC 1512 and NGC 5248, obtained with the WFPC2 and NICMOS cameras on HST. Combined with previously published ultraviolet (UV) HST images at 2300 Å, these data provide a particularly wide wavelength ran…
The XMM-Newton view of stellar coronae: Flare heating in the coronae of HR 1099
Mewe, R.; Audard, M.; Güdel, M.
The RS CVn system HR 1099 was observed by XMM-Newton for a time span of 25 days during the commissioning phase. Rotational modulation in the RGS light curve has been detected with maximum flux when the active K1 IV star is in front. Following a quiescent phase of emission, the rise and peak of a large flare were observed. Time-dependent spectrosco…
Ulysses in the south polar cap at solar maximum: Heliospheric magnetic field
Balogh, A.; McComas, D. J.; Forsyth, R. J. +1 more
Observations during the recent ascent of Ulysses to the south polar region are reported. Large variations in field magnitude are associated principally with solar wind interaction regions. The observed spiral angle agrees reasonably well with the Parker model. The magnetic flux, the product of the radial field component and the square of the radia…
HST and VLT Investigations of the Fragments of Comet C/1999 S4 (LINEAR)
Jorda, L.; Lamy, P. L.; Feldman, P. D. +18 more
At least 16 fragments were detected in images of comet C/1999 S4 (LINEAR) taken on 5 August 2000 with the Hubble Space Telescope (HST) and on 6 August with the Very Large Telescope (VLT). Photometric analysis of the fragments indicates that the largest ones have effective spherical diameters of about 100 meters, which implies that the total mass i…
Recurrent flare/CME events from an emerging flux region
Nitta, Nariaki V.; Hudson, Hugh S.
We report on six recurrent ‘halo’ coronal mass ejections (CMEs) that occurred (in November 2000) during a 60-hour period in clear association with major flares in an active region on the solar disk. The region was undergoing dynamic restructuring due to flux emergence. The flares were not long-decay events (LDEs) in terms of soft X-ray light curve…