High resolution spectroscopy of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428)

Abstract

High resolution spectra covering the wavelength range 4900 Å to 8250 Å of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428) reveal absorption lines of C II, N II, O II, Al III, Si III and Fe III and a rich emission line spectrum consisting of H I, He I, C II, N I, O I, Mg II, Al II, Si II, V I, Mn I, Fe III, [Fe II] and [Cr II]. The presence of [N II] and [O I] lines and absence of [O III] indicate low excitation nebulae around these stars. The components of Na I absorption lines indicate the presence of neutral circumstellar envelopes in addition to the low excitation nebulae around these two hot post-AGB stars. The H${_{\alpha }}$ lines show P-Cygni profiles indicating ongoing post-AGB mass loss. From the absorption lines we derived heliocentric radial velocities of 65.31 $\pm$ 0.34 km s-1 and 27.55 $\pm$ 0.74 km s-1 for IRAS 13266-5551 and IRAS 17311-4924 respectively. The high Galactic latitude and large radial velocity of IRAS 13266-5551 indicate that it belongs to the old disk population. Preliminary estimates for the CNO abundances in IRAS 13266-5551 are obtained.