ON THE SPATIAL-DISTRIBUTION OF PRE-MAIN-SEQUENCE STARS IN TAURUS

We derive characteristic properties of the nonrandom spatial distribution of pre-main-sequence stars in the Taurus-Auriga molecular cloud by applying several different statistical techniques. We find that a power-law form for the two-point angular correlation function (with index - 1.2) reproduces the overall shape of the actual pre-main-sequence distribution in Taurus at small angular scales (approximately 0.3-degrees). This result is consistent with the existence of real clustering in the T Tauri distribution. With the aid of the nearest-neighbor distribution technique, we determine a median projected separation of approximately 0.3 pc for young stars in this cloud, even after eliminating close pairs with separations less than 20'' (approximately 3000 AU at the distance of Taurus) from our sample. This separation is only slightly larger than the typical size of a dense molecular core (approximately 0.1 pc), which suggests that ''isolated'' star formation does not occur in low-density star-forming regions like Taurus. We find similar properties for the nearest-neighbor distributions in other star-forming regions, such as Lupus, Chamaeleon T1, rho Ophiuchi, Orion, NGC 7000/IC 5070, and NGC 2264. Our analysis suggests that even ultimately single stars typically form with a relatively close companion. Multiple star formation inside elongated molecular cloud cores may provide a natural mechanism for this result. We also identify six statistically significant clumps or groups of stars in Taurus with projected radii of approximately 0.5-1 pc. These small groups appear distributed over the molecular cloud and harbor approximately 15 stellar systems each. The internal velocity dispersions in these groups are approximately 0. 5-1 km s-1 for a mean stellar lifetime of approximately 10(6) yr if they are not gravitationally bound.