The MACHO project 9 million star color-magnitude diagram of the Large Magellanic Cloud

We present a 9 million star color-magnitude diagram (9M CMD) of the Large M agellanic Cloud (LMC) bar. The 9M CMD reveals a complex superposition of di fferent-age and -metallicity stellar populations, with important stellar ev olutionary phases occurring over 3 orders of magnitude in number density. F irst, we count the nonvariable red and blue supergiants and the associated Cepheid variables and measure the stellar effective temperatures defining t he Cepheid instability strip. Lifetime predictions of stellar evolution the ory are tested, with implications for the origin of low-luminosity Cepheids . The highly evolved asymptotic giant branch (AGB) stars in the 9M CMD have a bimodal distribution in brightness, which we interpret as discrete old p opulations (greater than or similar to 1 Gyr). The faint AGE sequence may b e metal-poor and very old. Comparing the mean properties of giant branch an d horizontal-branch (HB) stars in the 9M CMD with those of clusters, we ide ntify NGC 411 and M3 as templates for the admixture of old stellar populati ons in the bar. However, there are several indications that the old and met al-poor field population has a red HE morphology: the RR Lyrae variables li e preferentially on the red edge of the instability strip, the AGE bump is very red, and the ratio of AGE bump stars to RR Lyrae variables is quite la rge. If the HE second parameter is age, the old and metal-poor field popula tion in the bar likely formed after the oldest LMC clusters. Lifetime predi ctions of stellar evolution theory lead us to associate a significant fract ion of the similar to 1 million red HE clump giants in the 9M CMD with the same old and metal-poor population producing the RR Lyrae stars and the AGE bump. In this case, compared with the age-dependent luminosity predictions of stellar evolution theory, the red HE clump is too bright relative to th e RR Lyrae stars and AGE bump. Last, we show that the surface density profi le of RR Lyrae variables is fitted by an exponential, favoring a disklike r ather than a spheroidal distribution. We conclude that the age of the LMC d isk is probably similar to the age of the Galactic disk.