Fourteen stars from a sample of Magellanic Cloud objects selected to have a mid-infrared flux excess have been found to also show TiO bands in emission .
The mid-infrared dust emission and the TiO band emission indicate that these stars have large amounts of hot circumstellar dust and gas in close proximity to the central star .
The luminosities of the sources are typically several thousand L _ { \odot } while the effective temperatures are \sim 4000-8000 K which puts them blueward of the giant branch .
Such stars could be post-AGB stars of mass \sim 0.4–0.8 M _ { \odot } or pre-main-sequence stars ( young stellar objects ) with masses of \sim 7-19 M _ { \odot } .
If the stars are pre-main-sequence stars , they are substantially cooler and younger than stars at the birth line where Galactic protostars are first supposed to become optically visible out of their molecular clouds .
They should therefore be hidden in their present evolutionary state , although this problem may be overcome if asymmetries are invoked or if the reduced metallicity of the SMC and LMC compared to the Galaxy makes the circumstellar material more transparent .
The second explanation for these stars is that they are post-AGB or post-RGB stars that have recently undergone a binary interaction when the red giant of the binary system filled its Roche lobe .
Being oxygen-rich , they have gone through this process before becoming carbon stars .
Most of the stars vary slowly on timescales of 1000 days or more suggesting a changing circumstellar environment .
Apart from the slow variations , most stars also show variability with periods of tens to hundreds of days .
One star shows a period that is rapidly decreasing and we speculate that this star may have accreted a large blob of gas and dust onto a disk whose orbital radius is shrinking rapidly .
Another star has Cepheid-like pulsations of rapidly increasing amplitude suggesting a rapid rate of evolution .
Seven stars show quasi-periodic variability and one star has a light curve similar to that of an eclipsing binary .