Composite colliding winds (CWo - orbiting; CWc - concentric; CWb - binary) and Seaquist, Taylor and Button (STB) model of HM Sge (open circle - hot component; filled circle - Mira). rotation of stars leads to rotation of p.a. of nebular features. projection effects due to orbital inclination may lead to changes in apparent separation of features Kenny, PhD Thesis, University of Calgary

Richards et al MNRAS 305, 380 5GHz (MERLIN) radio maps at several epochs Northern and Southern components separated by ~ 150 m.a.s. at 5GHz (~120 m.a.s. at 22GHz with VLA) Apparent “rotation” of radio components at ~ 2.5 arcsec p.a. In line with Kenny et al. models Suggests P ~ yrs 

Eyres et al, ApJ, 551, 512 HST GO observations with WFPC2 and selected narrow and broad band filters (diagnostic lines, location of continuum sources) October 22 VLA A-array 8.56 and 23GHz observations September 26 North, South and Central components are indicated Line ratio indicates cooler “wedge” of material to SW, extending ~ 0.5arcsec from the central binary [OIII]4959/5007[OIII]4363

E B-V Comparison of H  and thermal radio emission allows estimation of variation of extinction across nebula (left) Peak of extinction (E B-V ~1) to S Interstellar extinction estimated as E B-V ~0.35 (d >700pc) HH VLA 23GHz

Cartoon showing main nebular components and positions of hot (WD) and cool (RG) stellar components (derived from HST WFPC2 F218W and F547M observations respectively). Implies: binary separation = 40  9 m.a.s. at p.a. =  10 0 (cf. Schmid et al. 2000, p.a. = ) Thus d = 625  140 pc if a = 25AU (P = 90yrs; M = 2M  ) Also shown are centroids from narrow band filters

CH Cygni U and V light curves Crocker et al., MNRAS 326, 781 HST WFPC2, 1999 August 13 during primary eclipse no significant offset of hot and cool component centroids HH [OIII]4959/5007 VLA (1999 September 26 - lower panel)

Crocker et al MNRAS Variation in p.a. of central region CH Cyg from radio and HST observations with simple fit Precession due to interaction of inner regions of accretion disk with WD magnetic field favoured by Crocker et al. Ballistic ejection model overlaid on 5GHz maps from Fitted Parameters: P = 6519  153 days T o = JD  128  mid = 140  1 0  o = 35  1 0 v o = 1263  18 km s -1 i = 88  1 0

The shape of things to come: COAST results for CH Cyg - resolution 9 m.a.s. (2.4 AU), 920 nm Persistent elongation of primary stellar disk with possible rotation consistent with ~14.5yr period (Young et al 2002, to be submitted)

The Liverpool Telescope 2m Robotic Telescope New, UK National Facility Sited on La Palma CCD and NIR cameras (spectrograph soon) Studies of variability from seconds to years First light 21 st July Application Round likely deadline 30 th September (see telescope.livjm.ac.uk)