The G75.78 Region:
Massive Stars Spawning Massive Stars

Most stars are born in sites, such as Orion, that contain luminous, massive stars. The HII regions and supernova remnants resulting from the presence of such high-mass (O and B) stars have long been thought to significantly alter or even disrupt the parent clouds. This process remains mysterious, however, due to the scarcity of nearby examples of regions actively forming massive stars. For example, while bipolar molecular outflows are known to be associated with certain massive protostars (e.g., Kastner et al. 1994; Shepherd & Churchwell 1996), the outflow energetics are not well understood and the outflow sources themselves are poorly characterized. It is also apparent that the chemistry of cloud cores spawning low-mass stars (and the protoplanets potentially surrounding them) is profoundly influenced by the intense UV from massive protostars. However, the impact of outflows and UV from massive stars on the molecular cloud environment --- and, hence, on future generations of young stars --- remains to be determined.

Figure 1: 10'X8' JCMT CO(2-1) integrated velocity map of the G75.78 region.

We have been using the JCMT to map molecular line emission from the vicinity of G75.78, which lies within the maser complex ON 2. This complex region includes a large number of massive stars, spanning a remarkably wide range of evolutionary stages. G75.78 has long been known to harbor a group of ultracompact HII (UCHII) regions and masers (Baud 1977) and hosts a luminous far-IR source (IRAS 20198+3716), indicative of the presence of massive, deeply embedded protostars. Much of this massive star formation activity may lie within 1 kpc, based on the proximity of G75.78 to Berkeley 87 (B87), an optical cluster of ~100 members located on the boundary of the Cygnus X region (Turner & Forbes 1982). The distance to B87 appears well constrained, at D~900 pc (Polcaro et al. 1991). Furthermore, B87 itself features an unusually rich menagerie of optically luminous objects, including a rare WO star [WR 142 = ST 3], a blue straggler, the unusual variable V439 Cyg, and the red supergiant BC Cyg (Polcaro et al. 1991).

Although it is only twice the distance to the Orion molecular cloud complexes, and is far richer in terms of its massive star component, the G75.78/B87 region remains surprisingly understudied. This lack of attention is notable given the likelihood that the G75.78/B87 region illustrates an episodic, massive star formation sequence that is now making its way through, and perhaps is in the process of dispersing, a giant molecular cloud that lies no more than about 1 kpc from the Sun. The G75.78/B87 region also potentially offers an observational test of models of the effects of massive star winds and UV fields on the circumstellar environments of solar-mass (late-type) stars.

We are now exploiting the proximity and richness of the G75.78/B87 region to better constrain these and other massive star formation processes. We have recently obtained (semester 02A) a 10'X8' JCMT map of G75.78 in ¹²CO(2--1) (Kastner, Moriarty-Schieven, & Ninkov, in prep.). This map has yielded detections of CO clumps and outflows in the immediate vicinity of IRAS 20198+3716 which, in turn, appears to be associated with a deeply embedded young cluster (Fig. 1). These results provide strong evidence for interactions between outflows from massive young stars and ambient cloud material in G75.78, providing new insight into its present star formation activity and its star formation history.

Figure 2: Contours of the CO map, overlaid on a 2MASS K band image. The center of the Berkeley 87 optical cluster lies approximately midway between the southern CO peaks (B and C). Note the appearance of an embedded cluster of young stars between the brightest CO peaks (A and B); this cluster is not detected in optical images. IRAS 20198+3716 lies very near the center of the IR nebulosity associated with this cluster.

References

Baud 1977, A&A 57, 443
Comeron & Torra 2001, A&A 375, 539
Kastner et al. 1994, ApJ 425, 695
Polcaro et al. 1991, A&A 252, 590
Shepherd & Churchwell 1996, ApJ 472, 225
Turner & Forbes 1982, PASP, 94, 789

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