THE SYMBIOTIC STAR H1-36

Optical and infrared spectrophotometry is presented of the high-excitation emission-line star H1-36. The presence of a variable M giant is established: H1-36 may therefore be classified as a symbiotic star. The observations are interpreted in terms of the usual binary model for symbiotic stars, namely that an unseen star is heated by accretion of gas from its companion M giant. In H1-36 the M giant is very much more highly extinguished than the emission-line region. It is argued that circumstellar dust, seen by its thermal emission at infrared wavelengths, surrounds the M giant but not the hotter star, which is the source of photoionization. Thus the M giant cannot fill its Roche lobe. The radio spectral shape is explained by the presence of the neutral, circumstellar dust cocoon surrounding the M star. If indeed Roche lobe overflow does not occur, accretion must be from the M giant's wind. The energetics of H1-36 then indicate that the accreting component is smaller than a main-sequence star. © 1972 Royal Astronomical Society.