Finally, the list of symbiotic stars for which no nebula was detected with the present technique is reported in Table 5. The object names, telescopes, filters, exposure times, seeing, and notes are given, to allow the reader to estimate the quality of the data and plan improved observations. Details on the each column are given in the legenda at the end of the table. For the sake of completeness, also the samples of Munari & Patat (1993) and Kohoutek (1997) are included. In Table 5, we also list RX Pup, whose extended nebula was revealed by Paresce (1990) using coronographic images and after careful subtraction of a stellar profile, to show how very faint nebulae which have escaped detection in the present survey could be revealed using appropriate observing techniques. HBV 475, which has a sub-arcsec nebula revealed by HST images (Schild & Schmidt 1997), does not show evidence for more extended emission. The optical H nebula around AG Peg detected by Fuensalida et al. (1988) is not visible in our short [NII ] and [OII ] images (also listed in Table 5.
4.1. R Aqr
From radio observation, Hollis et al. (1987) suggested the possible existence of an extended fragmented halo located a few arc-minutes south-west of R Aqr, which might be the remnant of a prehistoric eruption of the system. A 1 hour H+[NII ] exposure that we took with the NOT in 1997, however, shows that the radio sources are in fact background galaxies in a cluster.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999