Triggered massive-star formation on the borders of Galactic H II regions. IV. Star formation at the periphery of Sh2-212

Aims: We wish to establish whether sequential star formation is taking place at the periphery of the Galactic H ii region Sh2-212.
Methods: We present CO millimetre observations of this region obtained at the IRAM 30-m telescope to investigate the distribution of associated molecular material. We also use deep {JHK} observations obtained at the CFHT to study the stellar content of the region, and radio observations obtained at the VLA to look for the presence of an ultra-compact (UC) H ii region and for maser emission.
Results: In the optical, Sh2-212 is spherically symmetric around its central exciting cluster. This H ii region is located along a molecular filament. A thin, well-defined half ring of molecular material surrounds the brightest part of the H ii region at the rear and is fragmented. The most massive fragment ( 200 M_⊙) contains a massive young stellar object displaying a near-IR excess; its spectral energy distribution indicates a high-mass ( 14 M_⊙), high-temperature ( 30 000 K), and high-luminosity ( 17 000 L_⊙) source. This object ionizes a UC H ii region.
Conclusions: Sh2-212 is a good example of massive-star formation triggered via the collect and collapse process. The massive YSO observed at its periphery is a good candidate for a massive star formed in isolation.

Based on observations obtained at the IRAM, Spain, at the CFHT, Hawaii, at the VLA, USA, and at the Observatoire de Haute-Provence, France. Table 3 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/482/585