Search Publications
A Large, Periodic Variation in the Stellar Wind of theta 1 Orionis C
Walborn, Nolan R.; Nichols, Joy S.
A period of 15.4 days, recently discovered by Stahl et al. from intensive monitoring of hydrogen alpha emission in Theta1 Ori C during 1992-1993, has been found to phase large variations in the C IV lambda lambda 1548, 1551 wind profile of this star previously reported from International Ultraviolet Explorer (IUE) high-resolution data o…
Analysis of BD+33 2642: a newly detected planetary nebula in the galactic halo and its central star.
Heber, U.; Napiwotzki, R.; Koeppen, J.
The spectra of the star BD+33 2642 and its surrounding planetary nebula (PN) are analyzed. The stellar parameters are found to be T_eff_=20200K, logg=2.9; the stellar mass is 0.560Msun_. In the stellar atmosphere, He is solar, C, N, O, Mg, Si are depleted by about 1dex, and Fe is depleted by 2dex relative to the sun. This abundance patt…
Hubble Space Telescope Imaging of the Seyfert 2 Galaxy NGC 2110
Heckman, Timothy M.; Mulchaey, John S.; Bower, Gary A. +3 more
Hubble Space Telescope (HST) images of the Seyfert 2 galaxy NGC 2110 in the emission lines of [O III] λλ4959,5007 and Hα + [N II] λλ6548,6584 and the nearby continuum are presented. After deconvolution, the resolution of these images is ~0.1", corresponding to a linear scale of ~23 pc at the assumed distance (46.8 Mpc) to this galaxy. The dominant…
Cooling of the White Dwarf in U Geminorum between Outbursts
Szkody, Paula; Sion, Edward M.; Long, Knox S. +1 more
We have obtained far-ultraviolet (1150-1610 A) spectra of U Gem with the Faint Object Spectrograph on the Hubble Space Telescope approximately 13 and 70 days after the end of a normal dwarf nova outburst of the system. Both spectra appear dominated by the White Dwarf (WD) in U Gem. At 1400 A, the flux from U Gem declined approximately 28% between …
Spectral analysis of the planetary nebula K 1-27 and its very hot hydrogen-deficient central star.
Rauch, T.; Werner, K.; Koeppen, J.
We present an analysis of the hydrogen-deficient central star of K 1-27 based on NLTE model atmospheres and an analysis of the planetary nebula based on photoionization models. From line profile fits we derive an effective temperature of T_eff_=100+/-15kK and a surface gravity of logg=6.5+/-0.5 for the central star. The atmosphere is dominated by …
Multiwavelength Study of the Magnetically Active T Tauri Star HD 283447
Feigelson, Eric D.; Phillips, Robert B.; Imhoff, Catherine +4 more
We observed the luminous T Tauri star HD 283447 = V773 Tauri simultaneously at X-ray, ultraviolet, optical photometric and spectroscopic, and radio wavelengths for several hours on UT 1992 September 11. ROSAT, IUE, Very Large Array (VLA) and an intercontinental Very Long Baseline Interferometry (VLBI) network, and three optical observatories parti…
Corotating particle enhancements out of the ecliptic plane
Simnett, G. M.; Tappin, S. J.; Roelof, E. C. +1 more
We have studied > 40 keV ion and electron enhancements seen at Ulysses from a series of corotating interaction regions (CIR), from mid-1992 until the end of 1993. The event intensity increased up to latitude 20°S after that the ion flux maxima decreased by ∼23%/deg while the electron maxima decreased more erratically, and more slowly, during th…
X-ray irradiation of white dwarf atmospehres : the soft X-ray spectrum of AM Herculis.
Paerels, Frits; van Teeseling, Andre; Heise, John
We present model atmosphere calculations of white dwarfs irradiated at the surface by hard x-rays. We use a self-consistent treatment of Compton scattering as a noncoherent scattering process. The opacities include the photoionization edges of all individual subshells of the most abundant ions of 15 elements. Because of an 'inverse' blanketing eff…
Galaxy Mergers and Gravitational Lens Statistics
Maoz, Dan; Rix, Hans-Walter; Turner, Edwin L. +1 more
We investigate the impact of hierarchical galaxy merging on the statistics of gravitational lensing of distant sources. Since no definite theoretical predictions for the merging history of luminous galaxies exist, we adopt a parameterized prescription, which allows us to adjust the expected number of pieces comprising a typical present galaxy at z…
Highly Ionized Gas Absorption in the Disk and Halo toward HD 167756 at 3.5 Kilometers per Second Resolution
Sembach, Kenneth R.; Savage, Blair D.; Cardelli, Jason A.
High-resolution spectra of interstellar Si IV, C IV, and N V absorption lines along the 4 kpc path to the inner Galaxy star HD 167756 at z = -0.85 kpc are presented. The spectra were obtained with the echelle mode of Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) and have signal-to-noise ratios ranging from 23 …