A. Cassatella

Narrow ultraviolet emission lines from SN 1987A - Evidence for CNO processing in the progenitor

Results from UV observations of SN 1987A with the IUE satellite are presented, showing that emission lines of He II, C III, N III, N IV, N V, and O III increase in strength with time after May 24, 1987. It is found that increased emission originated in a photoionized low-density circumstellar gas, lost by the progenitor in its red supergiant phase. A nebular analysis reveals a large nitrogen overabundance, indicating that the gas has undergone substantial CNO processing. This suggests that the progenitor of SN 1987A lost much of its hydrogen envelope before the explosion. The findings are consistent with models in which a red supergiant evolves to the blue supergiant stage before exploding.

The Evolution of Ultraviolet Emission Lines From Circumstellar Material Surrounding SN 1987A

The presence of narrow high-temperature emission lines from nitrogen-rich gas close to SN 1987A has been a principal observational constraint on the evolutionary status of the supernovas progenitor. A new analysis of the complete 5 year set of low- and high-resolution IUE ultraviolet spectra of SN 1987A (1987.2-1992.3) provides fluxes for the N V ?1240, N IV] ?1486, He II ?1640, O III] ?1665, N III] ?1751, and C III] ?1908 lines with significantly reduced random and systematic errors and reveals significant short-term fluctuations in the light curves. The N V, N IV], and N III] lines turn on sequentially over 15-20 days and show a progression from high to low ionization potential, implying an ionization gradient in the emitting region. The line emission turns on suddenly at 83 ? 4 days after the explosion, as defined by N IV]. The N III] line reaches peak luminosity at 399 ? 15 days. A ring radius of (6.24 ? 0.20) ? 1017 cm and inclination of 410 ? 39 is derived from these times, assuming a circular ring. The probable role of resonant scattering in the N V light curve introduces systematic errors that leads us to exclude this line from the timing analysis. A new nebular analysis yields improved CNO abundance ratios of N/C = 6.1 ? 1.1 and N/O = 1.7 ? 0.5, confirming the nitrogen enrichment found in our previous paper. From the late-time behavior of the light curves we find that the emission originates from progressively lower density gas and that the emitting region has a multicomponent density structure. We estimate the emitting mass near maximum (~400 days) to be ~4.7 ? 10-2 M?, assuming a filling factor of unity and an electron density of 2.6 ? 104 cm-3. These results are discussed in the context of current models for the emission and hydrodynamics of the ring.

The INES system - IV. The IUE absolute flux scale

This paper deals with the denition of the input fluxes used for the calibration of the IUE Final Archive. The method adopted consists in the determination of the shape of the detectors sensitivity curves using IUE low resolution observations with model fluxes of the DA white dwarf G191{B2B. A scale factor was then determined so that the IUE observations of some bright OAO{2 standards match the original measurements from Meade (1978) in the spectral region 2100{2300 A. The ultraviolet fluxes of six standard stars used as input for the Final Archive photometric calibration together with the model fluxes of G191{B2B normalized to the OAO{2 scale are given. A comparison with the independent FOS calibration shows that the IUE flux scale for the Ultraviolet is 7.2% lower. We consider this mainly to be caused by the dierent normalization procedures. It is shown that the present flux calibration applies to spectra processed with the INES low resolution extraction software.

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.

Optical identification of the X-ray source GS 2023+338 as V404 Cygni

On 1989 May 22 the Japanese Ginga Team reported the discovery of a bright new X-ray transient and cataloged the source as GS 2023+338. We have identified this X-ray source with V404 Cygni, an optical nova whose last reported major outburst was in 1938.

A UNIVERSAL DECLINE LAW OF CLASSICAL NOVAE. III. GQ MUSCAE 1983

We present a unified model of infrared (IR), optical, ultraviolet (UV), and X-ray light curves for the 1983 outburst of GQ Muscae (Nova Muscae 1983) and estimate its white dwarf (WD) mass. Based on an optically thick wind model of nova outbursts, we model the optical and IR light curves with free-free emission, and the UV 1455 A and supersoft X-ray light curves with blackbody emission. The best-fit model that simultaneously reproduces the IR, optical, UV 1455 A, and supersoft X-ray observations is a -->0.7 ± 0.05 -->M☉ WD with an assumed chemical composition of the envelope of -->X = 0.35–0.55, -->XCNO = 0.2–0.35, and -->Z = 0.02 by mass weight. The mass lost by the wind is estimated to be -->Δ Mwind ~ 2 × 10−5 -->M☉. We provide a new determination of the reddening, -->E(B − V) = 0.55 ± 0.05, and of the distance, ~5 kpc. Finally, we discuss the strong UV flash that took place on JD 2,445,499 (151 days after the outburst).

A UNIVERSAL DECLINE LAW OF CLASSICAL NOVAE. IV. V838 HER (1991): A VERY MASSIVE WHITE DWARF

We present a unified model of optical and ultraviolet (UV) light curves for one of the fastest classical novae, V838 Herculis (Nova Herculis 1991), and estimate its white dwarf (WD) mass. Based on an optically thick wind theory of nova outbursts, we model the optical light curves with free-free emission and the UV 1455 A light curves with blackbody emission. Our models of 1.35 +- 0.02 M {sub sun} WD simultaneously reproduce the optical and UV 1455 A observations. The mass lost by the wind is DELTAM {sub wind} approx 2 x 10{sup -6} M {sub sun}. We provide new determinations of the reddening, E(B - V) = 0.53 +- 0.05, and of the distance, 2.7 +- 0.5 kpc.

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.

First unambiguous X-ray detection of R Aquarii

Coordinated UV and X-ray observations of the symbiotic Mira R Aqr obtained with IUE and Exosat during June and December of 1985 at phases 0.0 and 0.5 of the Mira light curve are analyzed. Consideration is given to two models for the X-ray source in R Aqr. The first assumes that high-energy photons from a central source photoionize some parts of the circumstellar matter, while the second model assumes that emission is associated with shocks arising as ejected material interacts with the circumstellar environment. 25 references.