HUBBLE-SPACE-TELESCOPE WIDE-FIELD-PLANETARY-CAMERA-2 OBSERVATIONS OF THE YOUNG BIPOLAR H-II REGION S106

We present narrowband Hubble Space Telescope Wide Field Planetary Came ra 2 images of the bipolar H II region S106 in the H alpha line. The h igh-resolution images show unprecedented detail in the two nebular lob es, including prominent scalloped structure of the emission at the ion ization front. The illuminating source of the nebula, S106 IR, is dete cted in H alpha but not in an adjacent passband that excludes bright n ebular lines. Our estimate of the extinction to the exciting source is A(V) approximate to 19-22, which is in agreement with past determinat ions. The northern lobe of S106 is seen through a nearly opaque veil o f foreground material, so that its structure is hard to discern. Most of the nebular emission toward the southern lobe emanates from the sca lloped ionization fronts at the surfaces of hemispherical clumps locat ed at the back side of the H II region. We infer the existence of a tr anslucent layer of foreground extinction in front of the southern lobe that decreases with distance from the exciting source. Despite the pr esence of a cluster of 50 to 150 young stars, externally illuminated y oung stellar objects similar to the over 100 ''proplyds'' seen in the Orion Nebula are not found in S106. This nondetection is most likely a result of the complete absence of young stars within the nebular lobe s. However, if some of the stars seen toward the nebular lobes are fou nd to be low-mass members of the S106 cluster and embedded within the photoionized region, the lack of extended H alpha emission would imply a nebular photoionization age greater than 10(5) yr, the photoevapora tion timescale for circumstellar disks.