大样本恒星演化研究组知识库

Although episodic star formation (SF) has been suggested for nearby SF regions, a panoramic view of the recent episodic SF history in the solar neighborhood is still missing. By uniformly constraining the slope alpha of infrared spectral energy distributions (SEDs) of young stellar objects (YSOs) in the 13 largest Gould's Belt (GB) protoclusters surveyed by the Spitzer Space Telescope, we have constructed a cluster-averaged histogram of alpha representing the YSO evolution lifetime as a function of the alpha value. Complementary to the traditional SED classification scheme (0, i, f, ii, and iii) that is based on different alpha values, a staging scheme (A, B, C, D, and E) of SED evolution is proposed on the basis of the alpha statistical features that can be better matched to the physical stages of disk dissipation and giant planet formation. This has also allowed us to unravel the fluctuations of SF rate (SFR) in the 3 Myr history of these GB protoclusters. Diverse evolutionary patterns such as single peaks, double peaks, and ongoing acceleration of SFR are revealed. The SFR fluctuations are between 20% and 60% (similar to 40% on average) and no dependence on the average SFR or the number of SFR episodes is found. However, spatially close protoclusters tend to have similar SFR fluctuation trends, indicating that the driving force of the fluctuations should be at size scales beyond the typical cluster sizes of several parsecs.