Submillimeter Maps of Bok Globule Cores: Evidence for Multiple Epoch Star Formation

Abstract

We mapped 15 cold IRAS sources associated with Bok globules, using the submillimeter common user bolometer array SCUBA on the James Clerk Maxwell Telescope, in order to search for deeply embed- ded protostars. Submillimeter emission was detected in six of these globules, —ve of which contain one or more compact sources. We detected a total of seven compact submillimeter sources. At least —ve of these, which have no known near-infrared counterparts, are candidate or con—rmed class 0 sources. The IRAS sources detected in the submillimeter have IRAS colors consistent with those of dense molecular cloud cores and/or out—ow sources, whereas the IRAS sources not detected in this survey have IRAS colors consistent with those of infrared cirrus. We present compelling evidence that multiple star formation has occurred in four of the six Bok globules that we have detected in the submillimeter; thus, the formation of a single star in isolation from other stars appears to be a rare event in Bok globules. These four globules contain two or three young stellar objects, sometimes at very diUerent evolutionary stages. Two Bok globules, CB 68 and CB 232, are found to contain a candidate class 0 source in addition to a more evolved class I or class II premain-sequence star. These observations, in which we —nd a class 0 proto- star and a premain-sequence star in the same globule, suggest that multiple epochs of star formation are possible in Bok globules. Subject headings: ISM: globulesISM: individual (B335) ¨ stars: formation ¨ stars: premain-sequencesubmillimetersurveys