The stellar content of the compact HII region Sh2-88B

We present a photometric study of the compact H II region Sh2-88B and its a ssociated stellar cluster. The positions and JHK magnitudes are obtained fo r 125 stars over an 80 " x 80 " field centered on the region. The region has two components, called Sh2-88B1 and Sh2-88B2. B1 is a compac t cometary H II region associated with a cluster containing several massive stars. The dominant exciting star, at the center of the cometary structure , has an ionizing radiation flux corresponding to a spectral type in the ra nge O8.5V-O9.5V. It is highly reddened, with a visual extinction in the 30- 42 mag range, and exhibits a near-IR excess. B1 has a simple morphology, wi th the ionized and neutral gas clearly separated. Its unidentified infrared band (UIB) emission, observed by ISOCAM in the 5-8.5 mu m passband, comes from the photodissociation region at the periphery of the ionized gas. B2 i s an ultracompact H II region whose exciting star, probably of spectral typ e later than B0.5V, is not detected; this indicates a visual extinction gre ater than 60 mag. A very steep and regular increase of the extinction from west to east is observed over the whole of Sh2-88B.