SUBMILLIMETER ARRAY AND SPITZER OBSERVATIONS OF BOK GLOBULE CB 17: A CANDIDATE FIRST HYDROSTATIC CORE?

We present high angular resolution Submillimeter Array (SMA) and Spitzer observations toward the Bok globule CB 17. SMA 1.3 mm dust continuum images reveal within CB 17 two sources with an angular separation of ∼21″ (∼5250 AU at a distance of ∼250 pc). The northwestern continuum source, referred to as CB 17 IRS, dominates the infrared emission in the Spitzer images, drives a bipolar outflow extending in the northwest–southeast direction, and is classified as a low-luminosity Class 0/I transition object (Lbol ∼ 0.5 L☉). The southeastern continuum source, referred to as CB 17 MMS, has faint dust continuum emission in the SMA 1.3 mm observations (∼6σ detection; ∼3.8 mJy), but is not detected in the deep Spitzer infrared images at wavelengths from 3.6 to 70 μm. Its bolometric luminosity and temperature, estimated from its spectral energy distribution, are ⩽0.04 L☉ and ⩽16 K, respectively. The SMA CO (2–1) observations suggest that CB 17 MMS may drive a low-velocity molecular outflow (∼2.5 km s−1), extending in the east–west direction. Comparisons with prestellar cores and Class 0 protostars suggest that CB 17 MMS is more evolved than prestellar cores but less evolved than Class 0 protostars. The observed characteristics of CB 17 MMS are consistent with the theoretical predictions from radiative/magnetohydrodynamical simulations of a first hydrostatic core, but there is also the possibility that CB 17 MMS is an extremely low luminosity protostar deeply embedded in an edge-on circumstellar disk. Further observations are needed to study the properties of CB 17 MMS and to address more precisely its evolutionary stage.