A. Altamore

The ultraviolet spectrum of Eta Carinae

An atlas of the high-resolution UV spectrum of Eta Car from 1200 to 1974 A and from 2200 to 3230 A is presented, based on IUE observations made between 1978 and 1980. The fluxes and equivalent widths of the emission and absorption features, and the stellar continuum in line-free regions are presented. The profiles displayed by the most intense emission suggest line formation in an asymmetric envelope. Many of the observed features may be explained if Eta Car is an intermediate, possible binary, F-type hypergiant in a short living stage, which holds a massive wind heated by dissipation of mechanical energy. 61 refs.

Classical novae in outburst: The early evolution of the ultraviolet continuum

In the framework of a phenomenological study of the ultraviolet properties of classical novae in outburst, we have selected 12 objects among the best monitored at low resolution with the IUE satellite, and studied the temporal evolution of the ultraviolet continuum and of the O i 1300 A line flux during the early post{outburst phase. We conrm that the UV flux maximum takes place systematically after the visual maximum and that its time delay is a linear function of t3. A linear dependence on t3 is also found for the duration of the UV outburst and for the time the O i line flux reaches a maximum. This latter time marks the start of the transition phase to nebular conditions. Within the uncertainties imposed by the sample of objects used and by the observational errors, these results suggest a quite homogeneous behaviour of classical novae in the ultraviolet range.

The INES system - II. Ripple correction and absolute calibration for IUE high resolution spectra

In this paper we document the results of the study which led to the ripple correction and absolute cal- ibration algorithms applied to the high resolution spec- tra processed with the NEWSIPS software for the Final Archive of the IUE Project. In this analysis, based on a very large number of spectra, we nd that both the K and parameters (not only the former as previously be- lieved) vary with order number. This fact, together with the nding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in IUESIPS .T he in- ternal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute cali- bration algorithms here described apply also to IUE data processed and distributed with the INES system.

Classical novae in outburst: evolution of the ultraviolet emission lines in CO novae

A comparative study is made of the temporal changes of the ionization level in seven CO novae well monitored with the IUE satellite at low resolution. The investigation is based on the evolution of the fluxes in eight strong ultraviolet emission lines covering a wide range of ionization potentials, from Mg  (7.6 eV) to N  (77.5 eV). We find that the rate of increase of the ionization conditions in the emitting regions is uniform in the sample of novae considered, provided the time scale is normalized to the optical decay time t3. The implications of this result for the nova ejected masses and for the nuclear turnoff time are discussed.

On the Wilson-Bappu relationship in the MgII k line

An investigation is carried out on the Wilson{Bappu eect in the Mg ii k line at 2796.34 A. The work is based on a selection of 230 stars observed by both the IUE and HIPPARCOS satellites, covering a wide range of spectral types (F to M) and absolute visual magnitudes ( 5:4 MV 9:0). A semi{automatic procedure is used to measure the line widths, which applies also in the presence of strong central absorption reversal. The Wilson{ Bappu relationship here provided is considered to represent an improvement over previous recent results for the considerably larger data sample used, as well as for a proper consideration of the measurement errors. No evidence has been found for a possible dependence of the WB eect on stellar metallicity and eective temperature.

The C IV Doublet Ratio Intensity Effect in Symbiotic Stars

High-resolution UV spectra in the 1200-2000 wavelength range of the symbiotic variable R Aqr and its nebular jet were obtained in July 1987 with the IUE. The line profile structure of the C IV 1548, 1550 doublet in the jet indicates multicomponent velocity structure from an optically thin emitting gas. The C IV doublet profiles in the compact H II region engulfing the Mira and hot companion binary also suggest multicomponent structure with radial velocities up to about -100 km/s. The value of the doublet intensity ratio in the R Aqr H II region has been observed in other similar symbiotic stars, such as RX Pup. It is suggested that the anomalous behavior of the C IV doublet intensities may be useful for studying the spatial structure and temporal nature of winds in symbiotic stars.

A study of the Mg II 2796.34 Å emission line in late–type normal and RS CVn stars

We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars and make a comparison with the normal stars studied in a previous paper ( Paper I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS parallaxes and observed at high resolution with IUE. We confirm that RS CVn stars tend to possess wider Mg II. lines than normal stars having the same absolute visual magnitude. However, we could not find any correlation between the logarithmic line width log W_o and the absolute visual magnitude M_v (the Wilson-Bappu relationship) for these active stars, contrary to the case of normal stars addressed in Paper I. On the contrary, we find that a strong correlation exists in the (M_v, log L_MgII) plane (L_MgII is the absolute flux in the line). In this plane, normal and RS CVn stars are distributed along two nearly parallel straight lines with RS CVn stars being systematically brighter by ≈1 dex. Such a diagram provides an interesting tool to discriminate active from normal stars. We finally analyse the distribution of RS CVn and of normal stars in the (log L_MgII, log W_o) plane, and find a strong linear correlation for normal stars, which can be used for distance determinations.

UV and X-ray monitoring of AG draconis during the 1994/1995 outbursts

The recent 1994–1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With ROSAT observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980–81 aciiva phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size.

The 1985–86 Episodes of AG Draconis

EXOSAT observations of the peculiar halo symbiotic star AG Dra during its recent light maxima of February 1985 and January 1986 have disclosed a large X–ray fading with respect to quiescence. Simultaneous IUE observations have on the contrary shown an increase of the continuum and emission line flux, especially of the high temperature Nv 124 nm and HeII 164 nm lines, at the time of the light maxima. Two distinct components might exist, in the far—UV spectrum of AG Dra’s companion, associated with a hot subdwarf and an accretion disk. The behaviour in 1985–86 might be due to a temperature drop of a non—black body hot component, or to a continuous absorption of the X—rays, shortwards the N+3 ionization limit.

Spectrophotometry and Multicolour Imagery of the Planetary Nebula around the P Cygni Star AG Carinae

Some of the high luminosity stars in our Galaxy are surrounded by planetary-like nebulae formed by material ejected from the central star. The most interesting case is that of the ring nebula PK 289–0°1 around the P Cygni star AG Car. Long slit spectroscopy shows that nitrogen is overabundant and oxygen underabundant in the nebula. The Hα/[NII] ratio is lower in the nebula with respect to the surrounding H II region, possibly as a result of the N overabundance in the stellar wind. The emission line peak separation confirms a model of a distorted spherical shell expanding at 66 km s-1. The scattered star’s spectrum is observable near the star, suggesting the presence of circumstellar dust grains. A nebular mass of at least 2.7 M⊙ is derived. While the nebula in the Hα imagery reveals the ring-like shape with many structures, in the blue it is much fainter and smoother. No nebular emission was detected in the JHK bands, suggesting a low dust temperature.