Search Publications
Coronal Scale-Height Enhancement by Magnetohydrodynamic Waves
Rosner, R.; Litwin, C.
We discuss the possibility that the transmission of Alfvén waves from the photosphere into coronal loops can increase the density scale height in these loops. The mechanism involved is the ponderomotive force of transmitted waves, which opposes the force of gravity. We propose that this effect may account for cool coronal loops observed by the Sol…
Recovery of 29 Second Oscillations in Hubble Space Telescope Eclipse Observations of the Cataclysmic Variable UX Ursae Majoris
Horne, Keith; Long, Knox S.; Baptista, Raymundo +3 more
Low-amplitude (~=0.5%) 29 s oscillations have been detected in Hubble Space Telescope Faint Object Spectrograph eclipse observations of the nova-like cataclysmic variable UX UMa. These are the same dwarf nova-type oscillations that were originally discovered in this system by Warner & Nather in 1972. The 29 s oscillations are seen in one pair …
On the Multiplicity of η Carinae
Walborn, Nolan R.; Livio, Mario; Panagia, Nino +1 more
The nebula around the luminous blue variable (LBV) η Car is extremely N rich and C and O poor, which is indicative of CNO-cycle products. On the other hand, the recent Hubble Space Telescope-Goddard High-Resolution Spectrograph observation of the nucleus of η Car shows the spectrum of a star with stellar-wind lines of C II, C IV, Si II, Si IV, etc…
The Direct Amplification of Electromagnetic Waves by Electron Beams: An Alternate Explanation for Solar Type III Bursts
Huang, Guangli
The direct amplification of electromagnetic (EM) waves by the beam-plasma instability is proposed as an alternative for solar type III bursts in corona and planetary space, the main properties of type III bursts at meter bands are compared to this model, including the cutoff frequency, the timescale, the relative bandwidth, the polarization sense …
The Structure of Cometary Knots in the Helix Nebula
O'Dell, C. R.; Burkert, A.
The Hα surface brightness distribution of cometary knots in the Helix Nebula is investigated. The brightness profiles of their photoionized surfaces (cusps) drop exponentially with increasing distance r from the center of the knots: Σ(r) ~ exp (-r/h). An r-3 profile, which would be expected for a freely expanding ionization region, in g…
Acoustic Signatures of Subphotospheric Structure Underlying Sunspots
Braun, D. C.; Lindsey, C.
Helioseismic holography of active regions at frequencies in the range of 5-6 mHz renders acoustic signatures that we think signify acoustic perturbations several megameters beneath the photosphere. The application of holographic diagnostics at 5-6 mHz gives us images with considerably finer horizontal spatial resolution, and likewise much finer de…
Hubble Space Telescope WFPC2 Imaging of the Seyfert Galaxy NGC 3516
Mulchaey, John S.; Ferruit, Pierre; Wilson, Andrew S.
We have used the WFPC2 camera aboard the Hubble Space Telescope to obtain images of the Seyfert galaxy NGC 3516 in the [O III] λ5007 and [N II] λλ6548, 6583 + Hα emission lines as well as in their adjacent continua. The emission-line images reveal a close morphological association between an arclike structure 1.7" north of the nucleus and radio em…
The Eclipsing Supersoft X-Ray Binary CAL 87
Hutchings, J. B.; Crampton, D.; Cowley, A. P. +1 more
We present and discuss 25 spectra obtained in 1996 November, covering all phases of the CAL 87 binary system. These spectra are superior both in signal-to-noise ratio and wavelength coverage to previously published data, so additional spectral features can be measured. Photometry obtained on the same nights is used to confirm the ephemeris and for…
WFPC2 Observations of the Small Magellanic Cloud Intermediate-Age Populous Cluster NGC 416
Sarajedini, Ata; Mighell, Kenneth J.; French, Rica S.
We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (~V) and F450W (~B) of the intermediate-age populous star cluster NGC 416 in the Small Magellanic Cloud (SMC). We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence…
On the Unresolved Fine Structures of the Solar Atmosphere. III. Elemental Abundances Consideration
Feldman, Uri
Results from high-quality solar upper atmosphere observations in the 104-106 K range contradict predictions made by models that assume that a single class of structures stretching throughout the entire temperature domain, from the cold chromosphere to the hot corona, is responsible for all the radiation we see. As a result, I…