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We have carried out a search for optically visible post-AGB candidates in theSmall Magellanic Cloud (SMC). We used mid-IR observations from the SpitzerSpace Telescope to select optically visible candidates with a mid-IR excess. Weobtained low-resolution optical spectra for 801 candidates. After removingcontaminants and poor quality spectra, the final sample comprised of 63post-AGB/RGB candidates of A - F spectral type. Using the spectra, we estimatedthe stellar parameters: effective temperature, surface gravity and [Fe/H]. Wealso estimated the reddening and deduced the luminosity using the stellarparameters combined with photometry. Based on a luminosity criterion, 42 ofthese 63 sources were classified as post-RGB candidates and the remaining aspost-AGB candidates. From the spectral energy distributions we found that 6 ofthe 63 post-AGB/RGB candidates have a circumstellar shell suggesting that theyare single stars, while 27 of them have a surrounding disc, suggesting thatthey are binaries. For the remaining candidates the nature of the circumstellarenvironment was unclear. Variability is displayed by 38 post-AGB/RGB candidateswith common variability types being the Population II Cepheids (includingRV-Tauri stars) and semi-regular variables. This study has also revealed a news-process enriched RV Tauri star (J005107.19-734133.3). From the numbers ofpost-AGB/RGB stars in the SMC, we were able to estimate evolutionary rates thatare in good agreement with the stellar evolution models with mass loss in thepost-AGB phase and re-accretion in the post-RGB phase. This study also resultedin a new sample of 40 luminous young stellar objects (YSOs) of A - F spectraltype. Additionally, we also identified a group of 63 objects whose spectra aredominated by emission lines and in some cases, a UV continuum. These objectsare likely to be either hot post-AGB/RGBs or luminous YSOs.

monthly notices of the royal astronomical society

Optically visible post-AGB/RGB stars and young stellar objects in the  Small Magellanic Cloud: candidate selection, spectral energy distributions  and spectroscopic examination