Search Publications
First Direct Measurement of Acceleration in the Outflow of a Nova: U Scorpii (1999)
Livio, Mario; Lépine, Sébastien; Shara, Michael M. +1 more
We report the first direct measurement of acceleration in the outflow of a nova, U Sco, observed 5 days after the start of an outburst. Spectroscopic time series of the intense Hα emission line, obtained with the Space Telescope Imaging Spectrograph camera on board the Hubble Space Telescope, shows a bright emission component moving across the spe…
In Search of Emerging Magnetic Flux underneath the Solar Surface with Acoustic Imaging
Chang, Hsiang-Kuang; Chou, Dean-Yi; Sun, Ming-Tsung
With the method of acoustic imaging in helioseismology, we study an emerging flux region, NOAA 7978, using data taken with instruments of the Taiwan Oscillation Network (TON) and the Michelson Doppler Imager (MDI). Phase-shift maps of NOAA 7978 focusing at different depths are constructed, which show the evolution of emerging magnetic flux. Althou…
Supernova Remnants in the Magellanic Clouds. II. Supernova Remnant Breakouts from N11L and N86
Chu, You-Hua; Smith, R. Chris; Winkler, P. Frank +3 more
The evolution of a supernova remnant (SNR) is heavily influenced by the interstellar conditions surrounding the remnant. This is particularly true in cases where the SNR is breaking out into a low-density area in the surrounding medium. We examine two promising candidates for the study of SNR breakouts in the Large Magellanic Cloud (LMC): N11L and…
Hubble Space Telescope Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Modeling the Lens
Turnshek, David A.; Chae, Kyu-Hyun
We investigate gravitational lens models for the quadruply lensed Cloverleaf broad absorption line QSO H1413+1143 based on the Hubble Space Telescope (HST) WFPC/WFPC2 astrometric and photometric data of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The accurate image positions and the dust-extinction-corrected relative am…
Hubble Space Telescope Observations of the Central-Cusp Globular Cluster NGC 6752: the Effect of Binary Stars on the Luminosity Function in the Core
Bailyn, Charles D.; Rubenstein, Eric P.
We consider the effect of binary stars on the main-sequence luminosity functions observed in the core of globular clusters, with specific reference to NGC 6752. We find that mass segregation results in an increased binary fraction at fainter magnitudes along the main sequence. If this effect is not taken into account when analyzing luminosity func…
Extension of the Polar Coronal Hole Boundary into Interplanetary space
Howard, Russell A.; Habbal, Shadia Rifai; Woo, Richard +1 more
White-light measurements made by the SOHO LASCO C2 and C3 coronagraphs and the Mk III Mauna Loa K-coronameter, ranging from 1.15 to 30 Rsolar, have been combined with Kitt Peak daily He I 1083 nm coronal hole maps, and full Sun Yohkoh soft X-ray images, to show that the boundaries of polar coronal holes, as determined by measurements of…
Ultraviolet and Optical Observations of a Coronal Transient with SOHO
Thompson, B. J.; Raymond, J. C.; Modigliani, A. +7 more
A coronal transient was observed on 1997 March 6 at 1.6 Rsolar over an active region on the east limb. We observed both the edge of horizontally compressed gas and the diffuse curtain of coronal material. The region was monitored for 4 hr, and the H I Lyα, O VI λλ1031.91, 1037.61, N V λλ1242.80, 1238.80, and O V] λ1218.35 lines were det…
Chemical Abundances of the Planetary Nebula IC 4634 and Its Central Star
Feibelman, Walter A.; Hyung, Siek; Aller, Lawrence H.
We have measured the spectral line intensities of the metal-poor planetary nebula IC 4634. Using a photoionization model calculation, we try to fit the optical and UV region spectra, i.e., Hamilton echelle and IUE observations. From direct images, one expects complicated density variations, but the model predicts a range in densities that may be s…
The Off-Limb Behavior of the First Ionization Potential Effect in T>5×105 K Solar Plasmas
Lemaire, P.; Drake, J. J.; Feldman, U. +1 more
We investigate the behavior of the solar first ionization potential (FIP) effect (the abundance enhancement of elements with first ionization potential of less than 10 eV in the corona with respect to photospheric values) with height above the limb in a region of diffuse quiet corona observed by the SUMER instrument on SOHO, with emphasis on so-ca…
Spectroscopic Observations of the Planetary Nebula NGC 6818
Feibelman, Walter A.; Hyung, Siek; Aller, Lawrence H.
NGC 6818 is a bright, high-excitation, fairly regular, planetary nebula with a rather rich spectrum. Its rather unusual kinematical structure, studied by Wilson, Weedman, and particularly by Sabbadin, is of special interest. We are here primarily concerned with its high-resolution spectrum as revealed by the Hamilton Echelle Spectrograph at Lick O…