[vsnet-symbio 123] Re: V4018 Sgr deep fading

[Ulisse Munari <munari@astras.pd.astro.it>]

V4018 Sgr (=AS 304) is among the exceedingly rare symbiotic stars that
have shown P-Cyg profiles (quite deep indeed!) on IUE low resolution 
spectra (Munari and Buson 1993, MNRAS 263, 267), which are an 
unmistakable signature of mass loss.
On the contrary, the nuclei of planetary nebulae observed in low
resolution by IUE frequently show deep P-Cyg profiles (cf. Feibelman
et al. 1988, "IUE Spectral Atlas of Planetary Nebulae, Central Stars
and Related Objects", NASA ref Pub. 1203).

The hot components of symbiotic stars are frequently compared to 
PN nuclei in literature. It is worth to remember that a PN dissolves 
in space in about 30,000 years, and therefore its nucleus is 
just-formed.

Does this mean that the hot component of AS 304 formed recently from
the evolution of an AGB-star companion to the present M4 III star in 
AS 304 ? Or we are simply witnessing an old white dwarf rejuvenated 
by the companion entering the red-giant/mass-losing phase ?

A close monitoring of the current brightness drop (hopefully carried
out in a few different photometric bands so to derive informations
on the color too: B band to monitor the hot component, I band to
watch the cool giant) would help to address the intriguing nature 
of AS 304.


  Ulisse Munari

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