High resolution spectroscopy of the hot post-AGB stars : IRAS13266-5551 (CPD-55 5588) and IRAS17311-4924 (Hen3-1428)

The high resolution spectra covering the wavelength range 4900 A to 8250 A of the hot post-AGB stars IRAS13266-5551 (CPD-55 5588) and IRAS17311-4924 (Hen3-1428) reveal absorption lines of CII, NII, OII, AlIII, SiIII and FeIII and a rich emission line spectrum consisting of HI, HeI, CII, NI, OI, MgII, AlII, SiII, VI, MnI, FeIII, [FeII] and [CrII]. The presence of [NII] and [OI] lines and absence of [OIII] indicate low excitation nebulae around these stars. The components of NaI 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 +/- 0.34 km/s and 27.55 +/- 0.74 km/s for IRAS13266-5551 and IRAS17311-4924 respectively. High galactic latitude and large radial velocity of IRAS13266-5551 indicate that it belongs to the old disk population. Preliminary estimates for the CNO abundances in IRAS13266-5551 are obtained.