Search Publications
HST-COS Observations of AGNs. I. Ultraviolet Composite Spectra of the Ionizing Continuum and Emission Lines
Shull, J. Michael; Danforth, Charles W.; Stevans, Matthew
The ionizing fluxes from quasars and other active galactic nuclei (AGNs) are critical for interpreting the emission-line spectra of AGNs and for photoionization and heating of the intergalactic medium. Using ultraviolet spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we have directly measured the rest-frame …
A Far-ultraviolet Atlas of Low-resolution Hubble Space Telescope Spectra of T Tauri Stars
Herczeg, Gregory J.; Valenti, Jeff A.; Brown, Alexander +6 more
We present a far-ultraviolet (FUV) spectral atlas consisting of spectra of 91 pre-main-sequence stars. Most stars in this sample were observed with the Space Telescope Imaging Spectrograph and Advanced Camera for Surveys on the Hubble Space Telescope (HST). A few archival spectra from the International Ultraviolet Explorer and the Goddard High Res…
Reexamination of the Infrared Excess-Ultraviolet Slope Relation of Local Galaxies
Inoue, Akio K.; Murata, Katsuhiro L.; Takeuchi, Tsutomu T. +2 more
The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (β) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star-forming galaxies, especially at high redshifts. Many authors, however, have pointed out that there is a significan…
From X-Ray Dips to Eclipse: Witnessing Disk Reformation in the Recurrent Nova U Sco
Talavera, A.; Ness, J. -U.; Hernanz, M. +9 more
The tenth recorded outburst of the recurrent eclipsing nova U Sco was observed simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9 after the outburst. Two full passages of the companion in front of the nova ejecta were observed, as was the reformation of the accretion disk. On day 22.9, we observed smooth eclipses in UV an…
Rebirth of X-Ray Emission from the Born-again Planetary Nebula A30
Steffen, M.; Gruendl, R. A.; Hamann, W. -R. +8 more
The planetary nebula A30 is believed to have undergone a very late thermal pulse resulting in the ejection of knots of hydrogen-poor material. Using multi-epoch Hubble Space Telescope images, we have detected the angular expansion of these knots and derived an age of 850+280 - 150 yr. To investigate the spectral and spatial p…
Evolution of the Symbiotic Nova PU Vul—Outbursting White Dwarf, Nebulae, and Pulsating Red Giant Companion
Kato, Mariko; Hachisu, Izumi; Mikołajewska, Joanna
We present a composite light-curve model of the symbiotic nova PU Vul (Nova Vulpeculae 1979) that shows a long-lasting flat optical peak followed by a slow decline. Our model light curve consists of three components of emission, i.e., an outbursting white dwarf (WD), its M-giant companion, and the nebulae. The WD component dominates in the flat pe…
Extended Magnetospheres in Pre-main-sequence Evolution: From T Tauri Stars to the Brown Dwarf Limit
Gómez de Castro, Ana I.; Marcos-Arenal, Pablo
Low-mass pre-main-sequence stars, i.e., T Tauri stars (TTSs), strongly radiate at high energies, from X-rays to the ultraviolet (UV). This excess radiation with respect to main-sequence cool stars (MSCSs) is associated with the accretion process, i.e., it is produced in the extended magnetospheres, in the accretion shocks on the stellar surface, a…
Modeling the Accretion Structure of AU Mon
Peters, Geraldine J.; Miller, Brendan P.; Budaj, Ján +2 more
AU Mon is a long-period (11.113 days) Algol-type binary system with a persistent accretion disk that is apparent as double-peaked Hα emission. We present previously unpublished optical spectra of AU Mon which were obtained over 20 years from 1991-2011 with dense orbital phase coverage. We utilize these data, along with archival UV spectra, to mode…
[Fe III] Emission Lines in the Planetary Nebula NGC 2392
Zhang, Y.; Liu, X. -W.; Koning, N. +4 more
NGC 2392 is a young double-shell planetary nebula (PN). Its intrinsic structure and shaping mechanism are still not fully understood. In this paper we present new spectroscopic observations of NGC 2392. The slits were placed at two different locations to obtain the spectra of the inner and outer regions. Several [Fe III] lines are clearly detected…
Matching the Spectral Energy Distribution and P-mode Oscillation Frequencies of the Rapidly Rotating Delta Scuti Star α Ophiuchi with a Two-dimensional Rotating Stellar Model
Deupree, Robert G.; Castañeda, Diego; Peña, Fernando +1 more
Spectral energy distributions are computed using two-dimensional (2D) rotating stellar models and non-LTE plane-parallel model atmospheres. A rotating, 2D stellar model has been found that matches the observed ultraviolet and visible spectrum of α Oph. The SED match occurs for the interferometrically deduced surface shape and inclination, and is d…