Search Publications
Spectroscopic Observations of the Detached Binary PG 1413+015
Bergeron, P.; Green, Richard; Liebert, James +1 more
We present improved estimates of the stellar parameters of the eclipsing, precataclysmic binary system PG 1413 + 015 (GH Vir), which has an orbital period of only 8h16m. Model atmosphere fits a Balmer line profiles yield T(eff) = 48,800 +/- 1200 K and log g = 7.70 +/- 0.11 for the DAO white dwarf primary star, from which a mass of 0.51 +/- 0.04 so…
The Ultraviolet--to--Near-Infrared Spectral Flux Distribution of Four BL Lacertae Objects
Maraschi, L.; Tanzi, E. G.; Chiappetti, L. +3 more
We report on simultaneous UV, optical, and near-IR observations of four BL Lac objects. For three objects (PKS 0118-27, PKS 0301-24, and PKS 1538+14), we find that the spectral flux distribution from 8 x 10^13^ to 2.5 x 10^15^ Hz is well described by a single power law with spectral index α_v_ = 1.2, α_v_ = 1.0, and α_v_ = 1.3, respectively. For H…
The X-ray time variability and spectrum of gamma Cassiopeiae (X 0053+604).
Stella, L.; Parmar, A. N.; White, N. E. +1 more
A 30 h duration EXOSAT observation made in 1985 December is used to examine the X-ray time variability and spectrum of the Be star γ Cassiopeiae (X 0053+604). We find that the X-ray lightcurve is dominated by irregular energy-independent flaring on time-scales ≳ 100 s. This flaring markedly decreases the sensitivity to any periodic signals. We fin…
AGN X-ray light curves - shot noise or low-dimensional attractor ?
McHardy, Ian M.; Czerny, Bozena; Lehto, Harry J.
We use correlation integrals to determine whether the X-ray variability of AGN, as seen in EXOSAT observations, arises from chaotic systems. We distinguish three characteristic types of behaviour. We also analyse a number of simulated light curves, to investigate the poorly understood limitations to the correlation integral method caused by noise …
The Time Variability of the Ultraviolet Continuum and Lyman-Alpha in 3C 273
Wamsteker, W.; Ulrich, M. -H.; Courvoisier, T. J. -L.
This article presents the light curve of the ultraviolet (UV) continuum flux and of the Lyα emission line of 3C 273 between 1978 and 1992.5. It also presents evidence for a quantitative difference between nearby Seyfert 1 and the quasar 3C 273 regarding the response of the emission lines to UV continuum flux variations. In contrast to what is obse…
HS 0209+0832 : a DAB white dawrf with a temperature fittinginto the DB gap.
Heber, U.; Jordan, S.; Koester, D. +1 more
The white dwarf H50209+0832 (B ≈13m.9), belonging to the sparse class of spectral type DAB, was discovered by follow-up spectroscopy of candidates selected from objective- prism plates of the Hamburg Schmidt sky survey. An analysis of the optical spectrum, clearly showing the He I λ4471 line besides the Balmer lines, yields a He/H ratio…
On the Chromospheric Structure of zeta Aurigae
Eaton, Joel A.
The chromospheric structure of Zeta Aur is analyzed on the basis of both optical and UV data. Column densities of matter along different lines of sight through the chromosphere are measured by using both Ly-alpha wings and many lines of ionized metals, and they agree to within the errors of measurement. The chromosphere is seen to extend at least …
A New Luminous Blue Variable: R143 in 30 Doradus
Parker, Joel Wm.; Clayton, Geoffrey C.; Conti, Peter S. +1 more
We have discovered that R143 in the Large Magellanic Cloud is a luminous blue variable (LBV), the first and perhaps the lone LBV in the central cluster of 30 Doradus, and only the sixth known LMC LBV. Photometric and spectroscopic observations over the past 40 yr indicate that during that time R143 moved redward (changing from an F5 to F8 supergia…
A General Bayesian Image Reconstruction Algorithm with Entropy Prior. Preliminary Application to HST Data
Nunez, Jorge; Llacer, Jorge
This paper describes a general Bayesian iterative algorithm with entropy prior for image reconstruction. It solves the cases of both pure Poisson data and Poisson data with Gaussian readout noise. The algorithm maintains positivity of the solution; it includes case-specific prior information (default map) and flatfield corrections; it removes back…
Cool stars : spectral energy distributions and model atmosphere fluxes.
Morossi, C.; Malagnini, M. L.; Kurucz, R. L. +2 more
The main results of a program of systematic comparison between observed and computed spectral energy distributions of late G and K type solar chemical composition stars are illustrated. We built the observed energy distributions of eleven representative stars, from the ultraviolet to the infrared, starting from lUE archive data, supplemented by ou…