Discovery of A Binary System in IRAM 04191+1522
  We present high angular resolution observations of the Class 0 protostar IRAM04191+1522, using the Submillimeter Array (SMA). The SMA 1.3 mm continuum images reveal within IRAM04191+1522 two distinct sources with an angular separation of 7.8\,$\pm$\,0.2$"$. The two continuum sources are located in the southeast-northwest direction, with total gas masses of about 0.011 M_sun and about 0.005 M_sun, respectively. The southeastern source, associated with an infrared source seen in the Spitzer images, is the well-known Class 0 protostar with a bolometric luminosity of about 0.08 L_sun. The newly-discovered northwestern continuum source is not visible in the Spitzer images at wavelengths from 3.6 to 70 micron, and has an extremely low bolometric luminosity (< 0.03 L_sun). Complementary IRAM N2H+(1-0) data that probe the dense gas in the common envelope suggest that the two sources were formed through the rotational fragmentation of an elongated dense core. Furthermore, comparisons between IRAM04191+1522 and other protostars suggest that most cores with binary systems formed therein have ratios of rotational energy to gravitational energy $\beta_{\rm rot}$ > 1%. This is consistent with theoretical simulations and indicates that the level of rotational energy in a dense core plays an important role in the fragmentation process. 
Xuepeng Chen (1), Hector G. Arce (1), Michael M. Dunham (1), and   Qizhou Zhang (2) ((1) Yale Astronomy Department, (2) Harv...
astro-ph.SR