Search Publications
Analysis of the Si IV Ultraviolet Spectra of U Sagittae
Richards, Mercedes T.; Kempner, Joshua C.
Archival IUE spectra of U Sge have been used to study hot (~105 K) circumstellar gas in this system. The observed spectra contain several UV resonance lines, of which the Si IV lines (λλ1394 and 1405) are the strongest. These lines are observed in absorption, so we must remove the photospheric absorption line contribution to the spectra…
X-Ray Properties of the Weak Seyfert 1 Nucleus in NGC 4639
Ho, Luis C.; Kunieda, Hideyo; Serlemitsos, Peter J. +4 more
Low-luminosity active galactic nuclei (AGNs), of which NGC 4639 is a good example, constitute an important but poorly understood constituent of the nearby galaxy population. We obtained observations of NGC 4639 with ASCA in order to investigate its mildly active Seyfert 1 nucleus at hard X-ray energies. Koratkar et al. have previously shown that t…
M84: A Warp Caused by Jet-induced Pressure Gradients?
Bower, Gary A.; Quillen, A. C.
In radio galaxies such as M84 dust features tend to be nearly perpendicular to radio jets yet are not aligned with the galaxy isophotes. The timescale for precession in the galaxy is short (~107 yr at 100 pc), suggesting that an alternative mechanism causes the gas disk to be misaligned with the galaxy. In M84 we estimate the pressure o…
The Extended Narrow-Line Region of 3C 299
McCarthy, Patrick J.; Sparks, William B.; Macchetto, F. Duccio +2 more
We present results of Hubble Space Telescope (HST) observations of the radio galaxy 3C 299. The broadband F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy with a comet-like structure extending to the northeast in the radio jet direction. The [O III] λ5007 emission-line map shows a biconical structure centered on the nucleus, whi…
A Possible Gravitational Lens in the Hubble Deep Field South
Hogg, David W.; Blandford, Roger; Barkana, Rennan
We model an apparent gravitational lens system HDFS 2232509-603243 in the Hubble Deep Field South. The system consists of a blue V=25 mag arc separated by 0.9" from a red V=22 mag elliptical galaxy. A mass distribution that follows the observed light distribution with a constant mass-to-light ratio can fit the arc component positions if external s…
Searching for Signal in Noise by Random-Lag Singular Spectrum Analysis
Henney, C. J.; Ulrich, R. K.; Bertello, L. +2 more
Singular spectrum analysis, a technique to detect oscillations in short and noisy time series, was first developed for geophysical applications. This work offers a generalization for long and noisy time series in astrophysical applications. The motivating problem is the detection of low-amplitude solar oscillations.
Increasing the Visibility of Solar Oscillations
Toutain, T.; Jefferies, S. M.; Toner, C. G.
Recent calculations by Toutain, Berthomieu, & Provost predict that low-degree p- and g-modes should produce large continuum intensity perturbations close to the solar limb. Analysis of 72 hr of spatially resolved, full-disk, continuum intensity images of the Sun--obtained with the Solar Oscillations Investigation/Michelson Doppler Imager instr…
Can Streamer Blobs Prevent the Buildup of the Interplanetary Magnetic Field?
Martens, P. C. H.; van Aalst, M. K.; Beliën, A. J. C.
Coronal mass ejections continuously drag closed magnetic field lines away from the Sun, adding new flux to the interplanetary magnetic field (IMF). We propose that the outward-moving blobs that have been observed in helmet streamers are evidence of ongoing, small-scale reconnection in streamer current sheets, which may play an important role in th…
Analyzing the Energetics of Explosive Events Observed by SUMER on SOHO
Winebarger, Amy R.; Warren, Harry P.; Mariska, John T. +1 more
The SUMER spectrometer on SOHO has obtained numerous observations of optically thin chromosphere-corona transition-region line profiles with high spatial, spectral, and temporal resolution. Many of these profiles exhibit asymmetries and broadenings associated with impulsive mass motions (explosive events) in the solar atmosphere. We present here a…
Evidence for a Population of Numerous Binaries with Comparably Bright Components among HIPPARCOS ``Single'' F Stars
McMaster, M.; Suchkov, A. A.
We find evidence for the presence of a population of numerous binaries with comparably bright components (C binaries) among Hipparcos F stars that are flagged in the Hipparcos catalog as single. We propose a criterion that identifies such binaries. The criterion is based on comparison of absolute magnitude MV obtained from the Hipparcos…