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Pre-main-sequence stars in the star-forming complex Sh 2-284




Located at the Galactic anticentre, Sh 2-284 is an H ii region that harbours several young open clusters. Dolidze 25, a rare metal-poor (Z∼ 0.004) young cluster, is one of these. Given its association with Sh 2-284, it is reasonable to assume a low metallicity for the whole H ii region. Sh 2-284 is expected to host a significant population of pre-main-sequence (PMS) stars of both low and intermediate mass (Herbig Ae stars). We aim to characterize these stars by means of a spectroscopic and photometric survey conducted with VIMOS@VLT and complemented with additional optical and infrared observations. In this survey we selected and characterized 23 PMS objects. We derived the effective temperature, the spectral energy distribution and luminosity of these objects, and, using theoretical PMS evolutionary tracks with the appropriate metallicity, we estimated the mass and the age of the studied objects. We also estimated a distance of 4 kpc for Sh 2-284, using the spectroscopic parallax of three OB stars. From the age determination we concluded that triggered star formation is occurring in this region. Our results show that a significant fraction of the young stellar objects (YSOs) may have preserved their disc/envelopes, in contrast with what is found in other recent studies of low-metallicity star-forming regions in the Galaxy. Finally, among the 23 bona fide PMS stars, we identified eight stars that are good candidates to be pulsators of the δ Scuti type.

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