Search

Presents the results of a Hubble Space Telescope (HST)/WFPC2 snapshot imaging survey of selected symbiotic stars in 1999/2000. Observation of seven sources in filters F218W; Presence of extended emission; Possible optical extension; Circumstellar matter; Radio images of HD 149427.

We have detected radio emission from the remnant of V705 Cas, beginning 221 d after visual maximum. We follow the remnant from first detection while still optically thick through the turn-over to optically thin emission, and finally confirming the absence of emission due to expansion and fading by the end of 1998. While the emission is consistent with thermal bremsstrahlung, as seen in most previous novae, the small-scale structure shows two ridge-like features, which develop significantly from day 585 until our last detection on day 1544. While the development is fairly rapid, it is also much smoother than that seen in V1974 Cyg, in that we can follow individual features as they change over almost 1000 d. Our optical spectra unequivocally indicate some form of axial symmetry, as derived from the velocity structure. This is difficult to reconcile with the observed development in the radio images. We suggest a number of possible explanations. [ABSTRACT FROM AUTHOR]

We present MERLIN observations of the symbiotic nova V1016 Cygni made at 6 cm between 1992 and 1997 and at 18 cm in 1993 and 1997. In the 6-cm images we find complex structure which has not been previously seen, in particular three bright components. These components do not appear to be expanding as would be expected from the remains of a hot wind resulting from the nova outburst. The change in positions of two of the features exhibits tentative east–west movement. The brightness temperature of the peak with the highest flux density remains above 50 000 K in all epochs, thereby confirming the presence of shocked material in the system. At 18 cm there is no evidence of any non-thermal emission as might be expected from comparison with a sister star, HM Sge. [ABSTRACT FROM AUTHOR]

HM Sge is a symbiotic binary star that underwent a nova-like outburst in 1975. Its radio emission has been monitored using MERLIN and the VLA, and maps from 1992 to 1997 are presented. Thermal emission within 0.4 arcsec of the optical peak is elongated north--south and hotspots appear to be moving around an anticlockwise ellipse. If this is due to motion in an inclined disc, the period is ∼ 90 yr. Eyres et al. predicted that if this is due to Mach shocks in the post-nova wind, proper motions should be seen in expansion. This has not been detected since 1992, so an alternative model is adopted, based on the work of Eyres et al. and Kenny et al., of colliding winds in a binary system following the nova-like outburst. The emission peaks appear to be corotating with the binary orbit as the ionization front and the hot wind from the white dwarf interact with the Mira wind. The positions of the stars are estimated, at a separation of ∼ 25 au. A distance of ∼ 1 kpc is most consistent with the observations reported here. On arcsecond scales the emission is extended east--west, consistent with a biconical outflow arising from the collimation of the nova outburst through interaction with the pre-existing cool wind. The presence of non-thermal emission at a separation of ∼700 mas from the stars is confirmed. This is very unusual at such a distance from low-mass stars, and could arise from synchrotron emission in a μT magnetic field. A model for this is developed, which shows that non-thermal emission is expected to decline within decades as the nova wind decelerates. This could explain the non-detection of non-thermal emission in other symbiotic stars. [ABSTRACT FROM AUTHOR]