The symbiotic star H1-36.

The high-excitation emission-line star H1-36 is investigated using optical and infrared spectrophotometry. It is established that H1-36 may be classified as a symbiotic star due to the presence of a variable M giant. The observations are analyzed in terms of the usual binary model for symbiotic stars in which an unseen star is heated by accretion of gas from its companion M giant. It is found that the M giant in H1-36 is very much more highly extinguished than the emission-line region. It is proposed that the 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. This indicates that the M giant cannot fill its Roche lobe. The presence of the neutral, circumstellar dust cocoon surrounding the M star is employed to explain the radio spectral shape. It is argued that accretion must be from the M giant's wind if Roche lobe overflow does not occur. The energetics of H1-36 suggest that the accreting component is smaller than a main-sequence star.