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Astron. Astrophys. 358, 869-885 (2000)

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8. Conclusions

A sample composed of 552 stars with chromospheric ages and photometric metallicities was used in the derivation of the star formation history in the solar neighbourhood. Our main conclusions can be summarized as follow:

  1. Evidence for at least three epochs of enhanced star formation in the Galaxy were found, at 0-1, 2-5 and 7-9 Gyr ago. These `bursts' are similar to the ones previously found by a number of other studies.

  2. We have tested the correlation between the SFH and the metal-enrichment rate, given by our AMR derived in Paper I. We have found no correlation between these parameters, although the use of Fe as a metallicity indicator, and the magnitude of the errors in both functions can still hinder the test.

  3. We examined in some detail the possibility that the Galactic bursts are coeval with features in the star formation history of the Magellanic Clouds and close encounters between them and our Galaxy. While the comparison is still uncertain, it points to interesting coincidences that merit further investigation.

  4. A number of simulations was done to measure the probability for the features found to be consistent with a constant SFH, in face of the age errors that smear out the original features. This probability is shown to decrease for the younger features (being nearly 0% for the quiescence in the SFH between 1-2 Gyr), such that we cannot give a strong assertion about the burst at 7-9 Gyr. On the other hand, the simulations allow us to conclude, with more than 98% of confidence, that the SFH of our Galaxy was not constant.

There is plenty of room for improvement in the use of chromospheric ages to find evolutionary constraints. For instance, a reconsideration of the age calibration and a better estimate of the metallicity corrections could diminish substantially the age errors, which would not only improve the age determination but also give more confidence in the older features in the recovered SFH.

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© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000