Search Publications
NGC 6153: a super-metal-rich planetary nebula?
Barlow, M. J.; Cohen, M.; Liu, X. -W. +3 more
We have obtained deep optical spectra of the planetary nebula NGC 6153, both along its minor axis and by uniformly scanning a long slit across the whole nebula. The scanned spectra, when combined with the nebular total Hβ flux, yield integrated fluxes for all the lines (~400) in our spectra, which are rich in strong recombination lines from C, N, …
A catalogue of symbiotic stars
Ivison, R. J.; Munari, U.; Friedjung, M. +2 more
We present a new catalogue of symbiotic stars. In our list we include 188 symbiotic stars as well as 30 objects suspected of being symbiotic. For each star, we present basic observational material: coordinates, V and K magnitudes, ultraviolet (UV), infrared (IR), X-ray and radio observations. We also list the spectral type of the cool component, t…
On the Nature of Soft X-Ray Weak Quasi-stellar Objects
Brandt, W. N.; Laor, A.; Wills, Beverley J.
Recent studies of quasi-stellar objects (QSOs) with ROSAT suggest the existence of a significant population of soft X-ray weak QSOs (SXW QSOs) where the soft X-ray flux is ~10-30 times smaller than in typical QSOs. Why are these QSOs soft X-ray weak, and what is their relationship to broad absorption line QSOs (BAL QSOs) and X-ray warm absorber QS…
Discovery of DampedLyα Systems at Redshifts Less than 1.65 and Results on Their Incidence and Cosmological Mass Density
Turnshek, David A.; Rao, Sandhya M.
We present results from an efficient, nontraditional survey to discover damped Lyα (DLA) absorption systems with neutral hydrogen column densities NHI>=2×1020 atoms cm-2 and redshifts z<1.65. In the past, identification of DLA systems at z<1.65 has been difficult because of their rare incidence and the nee…
Disk Accretion in the 10 MYR Old T Tauri Stars TW Hydrae and Hen 3-600A
Briceño, C.; Calvet, N.; Muzerolle, J. +2 more
We have found that two members of the TW Hydrae association, TW Hydrae and Hen 3-600A, are still actively accreting, based on the ballistic infall signature of their broad Hα emission profiles. We present the first quantitative analysis of accretion in these objects and conclude that the same accretion mechanisms which operate in the well-studied …
X-Ray and Optical Variability in NGC 4051 and the Nature of Narrow-Line Seyfert 1 Galaxies
Vestergaard, M.; Papadakis, I.; Peterson, B. M. +14 more
We report on the results of a three-year program of coordinated X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051. The rapid continuum variations observed in the X-ray spectra are not detected in the optical, although the time-averaged X-ray and optical continuum fluxes are well correlated. Variations in the flux of the bro…
The Structure and Emission of the Accretion Shock in T Tauri Stars. II. The Ultraviolet-Continuum Emission
Hartmann, Lee; Calvet, Nuria; Muzerolle, James +1 more
We compare accretion-shock models with optical and ultraviolet spectra of pre-main-sequence stars to (1) make the first determinations of accretion rates in intermediate-mass T Tauri stars from continuum emission and (2) derive improved estimates of accretion rates and extinctions for continuum T Tauri stars. Our method extends the shock models de…
An IUE Atlas of Pre-Main-Sequence Stars. II. Far-Ultraviolet Accretion Diagnostics in T Tauri Stars
Valenti, Jeff A.; Johns-Krull, Christopher M.; Linsky, Jeffrey L.
We use our ultraviolet (UV) atlas of pre-main-sequence stars constructed from all useful, short-wavelength, low-resolution spectra in the International Ultraviolet Explorer (IUE) satellite Final Archive to analyze the short-wavelength UV properties of 49 T Tauri stars (TTSs). We compare the line and continuum fluxes in these TTSs with each other a…
An IUE Atlas of Pre-Main-Sequence Stars. I. Co-added Final Archive Spectra from the SWP Camera
Valenti, Jeff A.; Johns-Krull, Christopher M.; Linsky, Jeffrey L.
We have identified 50 T Tauri stars (TTS) and 74 Herbig Ae/Be (HAEBE) stars observed in the IUE short-wavelength bandpass (1150-1980 Å). Each low-resolution (R~6 Å) spectrum was visually inspected for source contamination and data quality, and then all good spectra were combined to form a single time-averaged spectrum for each star. Use of IUE Fin…
Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy
Hillier, D. John; Morris, Patrick W.; Crowther, Paul A. +3 more
Neon abundances are derived in four Galactic WC stars - γ2Vel (WR11, WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8) and WR146 (WC5+O8) - using mid-infrared fine-structure lines obtained with ISO-SWS. Stellar parameters for each star are derived using the non-local thermodynamic equilibrium model atmospheric code of Hillier &a…