An evolutionary diagram for young stellar objects

We present 1.3 mm continuum observations of a sample of Class I and Class 0 young stellar objects in nearby star-forming regions, with and without known outflow activity. The observations are considered together with published data on similar objects, and compared with more evolved T Tauri and Herbig Ae/Be stars. The photometric observations are shown on a bolometric luminosity vs. millimeter flux scaled at a distance D (L(bol) vs. F-mm(D)) diagram. We show that the objects of the sample lie in different areas of the L(bol) - F-mm(D) diagram according to their evolutionary status and outflow activity. General argument and simple model evolutionary tracks allow us to identify an evolutionary sequence on the L(bol) - F-mm(D) diagram which agrees with the observational data. All the youngest objects of our sample show outflow activity. Class I sources seem to excite outflows with dynamical times greater than greater than or similar to 10(4) years and show a correlation between the bolometric luminosity and the millimeter continuum flux, which we call the ''Outflow Strip'': this correlation spans more than three orders of magnitude in luminosity. We suggest that the Outflow Strip originates in the deuterium burning process and that the protostars burn the majority of their deuterium while on the Outflow Strip. There is also good evidence that at the end of their lifetime on the Outflow Strip, the embedded outflow sources become visible Pre Main Sequence (hereafter PMS) stars with outflows. The outflow mechanical luminosity is also found to be better correlated to the mass of the disk/envelope system than to the central object luminosity.