IUE observations of RW Hydrae /gM2 + pec/

Abstract

/UEobservationsofthelatetypestar RWHya(gM2 +pee) have been obtained. Analysis of the intense UV continuum observed between 1100 and 2000 A suggests that this object is a binary system in which the secondary is identified as the central star of a planetary nebula with Terr "' 10 5 K. The ultraviolet spectrum is characterized by semiforbidden and allowed transition lines, of which the C IV (1548 A, 1550 A) doublet is particularly strong. A general absence of strong forbidden line emission suggests that the compact nebula in which both primary and secondary stars are embedded has particularly high densities of "'10 8-10 9 em-3. Tidal interaction rather than steady state mass flow from the M giant is suggested as a means to form a nebula with the characteristic densities inferred from our UV line analysis. RW Hya is suggested as a possible source of soft X-ray emission if material is accreting onto the surface of the secondary. A general discussion concerning the ionic abundances of various atomic ions present is given.

The peculiar star RX Puppis

“…\ery likely T ^ 15,000 K. We find that carbon is depleted by a factor of <\. 7 similarly to R Aqr (Michalitsianos, Kafatos and Hobbs 1980) and RW Hya (Kafatos et al 1980). The line analysis implies photoionization in RX Pup, similarly to what Nussbaumer and Schild (1981) find for V1016 Cygni.…”

“…Hummer and Mihalas 1970) that the effective temperature of the secondary star is in the approximate range 75,000 K S T e f f * 100,000 K and 4.5 £log g £ 6.0. Such a star would be located in the central stars of planetary nebulae region (Kafatos et al 1980). The photoionizing photons may alternatively arise from an accretion disk and its inner boundary layer region.…”

A far-ultraviolet atlas of symbiotic stars observed with IUE. 1. The SWP range

“…The lack of continuum and the significant decline in emission-line strength suggests that R W Hya is possibly an eclipsing system. The weakness of forbidden lines N m] AX 1747-1753, Si m] i\.1892, and C m] i\i\ 1907,1909 implies that the compact nebula in which both the primary and secondary stars are embedded has particularly high densities, in agreement with Kafatos, Michalitsianos, & Hobbs ( 1980). Further observations should be made to determine ifRW Hya is an eclipsing system .…”

IUE observations of the peculiar star RX Puppis

“…These figures show how important it is to obtain high-dispersion spectra of symbiotic stars, whenever feasible. On the basis of the low-dispersion spectra alone, one may be tempted to conclude that RX Pup appears similar to RW Hya (Kafatos, Michalitsianos, and Hobbs 1980). A comparison, though, of highdispersion spectra of these two stars reveal fundamental differences: Strong dynamic activity is suggested in the spectra of RX Pup.…”