Search Publications
Imaging an Emerging Active Region with Helioseismic Tomography
Christensen-Dalsgaard, Jørgen; Duvall, Thomas L., Jr.; Jensen, Jesper Munk +1 more
The wave-speed structure beneath an emerging active region is derived from helioseismic time-distance data using inversion techniques developed in geophysics. We use Fresnel zone-based sensitivity kernels along with a Fourier domain-based regularized least-squares inversion technique. The results show that wave-speed anomalies extend down to 20 Mm…
The Discovery of Cepheids and a New Distance to NGC 2841 Using the Hubble Space Telescope
Garnavich, P. M.; Richmond, M. W.; Stetson, P. B. +5 more
We report on the discovery of Cepheids in the spiral galaxy NGC 2841, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. NGC 2841 was observed over 12 epochs using the F555W filter and over five epochs using the F814W filter. Photometry was performed using the DAOPHOT/ALLFRAME package. We discove…
The Electron Drift Instrument on Cluster: overview of first results
Baumjohann, W.; Torbert, R. B.; Matsui, H. +15 more
EDI measures the drift velocity of artificially injected electron beams. From this drift velocity, the perpendicular electric field and the local magnetic field gradients can be deduced when employing different electron energies. The technique requires the injection of two electron beams at right angles to the magnetic field and the search for tho…
The Crab Nebula's Moving Wisps in Radio
Frail, D. A.; Hester, J. J.; Bietenholz, M. F.
We present three high-resolution radio images of the Crab Nebula, taken in 1998.6, 1998.8, and 2000.1 with the VLA. These are the best radio images of the Crab to date. We show that, near the pulsar, there are significant changes between our three observing epochs. These changes have an elliptical geometry very similar to that of the optical wisps…
Spatially Resolved O II Recombination Line Observations of the Ring Nebula, NGC 6720
Garnett, Donald R.; Dinerstein, Harriet L.
We present new long-slit CCD spectra of O II permitted lines and [O III] forbidden lines in the Ring Nebula NGC 6720. These observations provide spatially resolved information on both O II and [O III] over the 70" diameter of the main shell. We find significant differences in the spatial distribution of the O II lines and [O III] λ4959. The [O III…
An XMM-Newton study of the sub-structure in M 87's halo
Böhringer, H.; Molendi, S.; Ehle, M. +9 more
The high signal to noise and good point spread function of XMM have allowed the first detailed study of the interaction between the thermal and radio emitting plasma in the central regions of M 87. We show that the X-ray emitting structure, previously seen by ROSAT, is thermal in nature and that the east and southwest extensions in M 87's X-ray ha…
Dust emission from 3C radio galaxies and quasars: New ISO observations favour the unified scheme
Meisenheimer, K.; Lemke, D.; Klaas, U. +3 more
In order to test the unified scheme for luminous radio galaxies and quasars we observed 10 galaxy/quasar pairs from the 3CR catalogue with ISOPHOT at infrared wavelengths between 5 and 180 mu m. Each pair was selected such that both the 178 MHz luminosity and the redshift match as close as possible between the radio galaxy and the quasar in order …
A search for the cause of cyclical wind variability in O stars. Simultaneous UV and optical observations including magnetic field measurements of the O7.5III star xi Persei
Kaper, L.; Bohlender, D. A.; Gordon, K. +13 more
We present the results of an extensive observing campaign on the O7.5 III star
Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
Dias, W. S.; Lépine, J. R. D.; Alessi, B. S.
We present mean absolute proper motions of 112 open clusters, determined using the data from the Tycho2 Catalogue. For 28 clusters, this is the first determination of proper motion. The measurements made use of a large number of stars (usually several tens) for each cluster. The total number of stars studied in the fields of the 164 open clusters …
The Intrinsic Absorber in QSO 2359-1241: Keck and HUBBLE SPACE TELESCOPE Observations
White, Richard L.; Gregg, Michael D.; Becker, Robert H. +4 more
We present detailed analyses of the absorption spectrum seen in QSO 2359-1241 (NVSS J235953-124148). Keck HIRES data reveal absorption from 20 transitions arising from He I, Mg I, Mg II, Ca II, and Fe II. Hubble Space Telescope data show broad absorption lines (BALs) from Al III λ1857, C IV λ1549, Si IV λ1397, and N V λ1240. Absorption from excite…