By uniformly constraining the slope 𝛼 of infrared spectral energy distributions(SEDs) of young stellar objects (YSOs) in the 13 largest Gould’s Belt (GB) protoclusters surveyed by Spitzer Space Telescope, we have constructed a cluster-averaged histogram of 𝛼 representing YSO evolution lifetime as a function of the 𝛼 value. And a staging scheme (A,B,C,D,E) of SED evolution is advised on the basis of the 𝛼 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 star formation rate (SFR) in the past three-million-year (3 Myr) history of these GB protoclusters. Diverse evolutionary patterns such as single peak, double peaks and on-going acceleration of SFR are revealed. The SFR fluctuations are between 20% ∼ 60% (∼ 40% on average). However, spatially close protoclusters tend to share similar SFR fluctuation trends, indicating that the driving force of the fluctuations should be at size scales beyond the typical cluster sizes of several parsec. Because there are many complex physical factors take part in disk evolution process, we critically examine the viability of using the IR SED slope 𝛼 as a potential quantitative tracer of disk age and confront it with additional statistics of IR luminosity and SED shape. We point out that, because the statistical properties of most of the complicated physical factors involved in disk evolution are still poorly understood in a quantitative sense, a viable way is to assume them to be random so that an idealized ‘average disk’ can be defined which allows the 𝛼 histogram to trace its age. We confirm that the statistics of the zeroth order (luminosity), first order (slope 𝛼) and second order characteristics (concavity) of the observed MIR SED indeed carry useful information upon the evolutionary processes of the ‘average disk’ and provide useful constraints to future disk population synthesis modeling. We also demonstrate that intrinsic diversities in MIR SED shapes and luminosities are always large at the level of individual stars so that the application of the evolution path of the ‘average disk’ to individual stars must be with care. The success in constraining the star formation (SF) history in the past three million years (3 Myr) of Gould’s Belt (GB) YSOs in the previous work has paved the way to explore the diverse evolution histories of their spatial structures. With a novel method in the third work, we have uncovered two giant SF stages in the entire GB: 1) About 1.8 Myr ago, an unknown global HI gas impact event at Galaxy scale triggered the first giant SF stage in distributed mode everywhere, with typical duration of 0.8 Myr for local individual events; 2) The second giant SF stage in compact molecular clouds due to gravitational collapse collectively started only recently and are still in developing (with time delays generally no less than 1.8 Myr), with typical duration of only 0.4 Myr for local individual events. Several massive-star-induced cluster-formation events occurred in between, with a shorter time delay of no more than 1 Myr after the first triggering. An unexplained feature is that the two giant SF stages intend to occur in different neighboring cloud sub-regions. Very rich diversities are found in the temporal-spatial modes, which can be attributed to the turbulent nature of the HI colliding flows. Particularly, isolated low-mass-star clusters and low-mass-star clusters around isolated massive stars very likely have not experienced dynamical expansion within the first 3 Myr.
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