Search Publications
Limits on the Mass of the Central Black Hole in 16 Nearby Bulges
Filippenko, Alexei V.; Ho, Luis C.; Shields, Joseph C. +6 more
We report upper limits on the masses of black holes that can be present in the centers of 16 nearby galaxy bulges. These limits MlimBH for our statistically complete sample were derived from the modeling of the central emission-line widths ([N II] or [S II]), observed over a 0.25"×0.2" (R<~9 pc) aperture. The experiment ha…
Evolution and Geometry of Hot Spots in Supernova Remnant 1987A
Crotts, Arlin P. S.; Lawrence, Stephen S.; Sugerman, Ben E. K. +2 more
We present ground-based near-infrared imaging and Hubble Space Telescope optical imaging and spectroscopy of the interaction between the ejecta of SN 1987A and its equatorial circumstellar ring. This interaction has made a transition, from emission originating in just a few ``hot spots'' at restricted locations in position angle around the ring, t…
Observations of T Tauri Stars Using the Hubble Space Telescope GHRS. II. Optical and Near-Ultraviolet Lines
Valenti, Jeff A.; Walter, Frederick M.; Ardila, David R. +2 more
We have analyzed GHRS data of eight classical T Tauri stars (CTTSs) and one weak T Tauri star (WTTS). The GHRS data consist of a spectral range 40 Å wide centered on 2800 Å. For four of the CTTSs, we have nearly simultaneous optical observations that contain Hα, Hβ, He I, Na D, and the Ca II infrared triplet. The Mg II resonance doublet is the str…
Tip of the Red Giant Branch Distances to NGC 4214, UGC 685, and UGC 5456
MacKenty, John W.; Maíz-Apellániz, Jesús; Cieza, Lucas
We have used WFPC2 VRI observations to calculate the distances to three nearby galaxies, NGC 4214, UGC 685, and UGC 5456, using the tip of the red giant branch method. Our values for NGC 4214 (2.94+/-0.18 Mpc) and UGC 685 (4.79+/-0.30 Mpc) are the most precise measurements of the distances to these objects ever made. For UGC 5456 the data do not a…
Coordinated ground-based and Cluster observations of large amplitude global magnetospheric oscillations during a fast solar wind speed interval
Balogh, A.; Bale, S. D.; Yeoman, T. K. +10 more
We present magnetospheric observations of very large amplitude global scale ULF waves, from 9 and 10 December 2000 when the upstream solar wind speed exceeded 600 km/s. We characterise these ULF waves using ground-based magnetometer, radar and optical instrumentation on both the dawn and dusk flanks; we find evidence to support the hypothesis that…
Two Subclasses of Proto-Planetary Nebulae: Model Calculations
Ueta, Toshiya; Meixner, Margaret; Bobrowsky, Matthew +1 more
We use detailed radiative transfer models to investigate the differences between the star-obvious low-level elongated proto-planetary nebulae (SOLE PPNs) and dust-prominent longitudinally extended proto-planetary nebulae (DUPLEX PPNs), which are two subclasses of PPNs suggested by Ueta, Meixner, & Bobrowsky. We select one SOLE PPN, HD 161796, …
CO and H2O vibrational emission toward Orion Peak 1 and Peak 2
van Dishoeck, E. F.; Cernicharo, J.; González-Alfonso, E. +3 more
ISO/SWS observations of Orion Peak 1 and Peak 2 show strong emission in the ro-vibrational lines of CO v=1-0 at 4.45-4.95 µm and of H2O ν2=1-0 at 6.3-7.0 µm. Toward Peak 1 the total flux in both bands is, assuming isotropic emission, ≈2.4 and ≈0.53 Lsun, respectively. This corresponds to ≈14 and ≈3% of …
Iron abundance in hot hydrogen-deficient central stars and white dwarfs from FUSE, HST, and IUE spectroscopy
Rauch, T.; Werner, K.; Kruk, J. W. +3 more
We present a first systematic investigation of the iron abundance in very hot (Teff >= 50 000 K) hydrogen-deficient post-AGB stars. Our sample comprises 16 PG 1159 stars and four DO white dwarfs. We use recent FUSE observations as well as HST and IUE archival data to perform spectral analyses with line blanketed NLTE model atmosphere…
The optical counterpart of the ultraluminous X-ray source NGC 5204 X-1
Knigge, C.; Roberts, T. P.; Lira, P. +1 more
We use archival HST/WFPC2 V- and I-band images to show that the optical counterpart to the ultraluminous X-ray source NGC 5204 X-1, reported by Roberts et al., is composed of two sources separated by 0.5 arcsec. We have also identified a third source as a possible counterpart, which lies 0.8 arcsec from the nominal X-ray position. Point spread fun…
The dual dust chemistries of planetary nebulae with [WCL] central stars
Barlow, M. J.; Liu, X. -W.; Cohen, Martin +1 more
The rather rare class of central stars of planetary nebulae that show very low-excitation Wolf-Rayet spectra has been a subject of great interest, particularly in the infrared, since its discovery in the late 1960s. Further peculiarities have been found with the advent of infrared spectroscopy from ISO. Notably, these objects simultaneously betray…