THE DISK POPULATION OF THE TAURUS STAR-FORMING REGION

Abstract

We have analyzed nearly all images of the Taurus star-forming region at\n3.6-24um that were obtained during the cryogenic mission of the Spitzer Space\nTelescope (46 deg^2) and have measured photometry for all known members of the\nregion that are within these data, corresponding to 348 sources. We have\nclassified the members of Taurus according to whether they show evidence of\ndisks and envelopes (classes I, II, and III). The disk fraction in Taurus is\n75% for solar-mass stars and declines to 45% for low-mass stars and brown\ndwarfs (0.01-0.3 M_sun). This dependence on stellar mass is similar to that\nmeasured for Cha I, although the disk fraction in Taurus is slightly higher\noverall, probably because of its younger age (1 vs. 2-3 Myr). In comparison,\nthe disk fraction for solar-mass stars is much lower (20%) in IC 348 and Sigma\nOri, which are denser than Taurus and Cha I and are roughly coeval with the\nlatter. These data indicate that disk lifetimes for solar-mass stars are longer\nin regions that have lower stellar densities. Through an analysis of multiple\nepochs of photometry that are available for ~200 Taurus members, we find that\nstars with disks exhibit significantly greater mid-IR variability than diskless\nstars. Finally, we have used our data in Taurus to refine the criteria for\nprimordial, evolved, and transitional disks. The number ratio of evolved and\ntransitional disks to primordial disks in Taurus is 15/98 for K5-M5, indicating\na timescale of 0.15 x tau(primordial)=0.45 Myr for the clearing of the inner\nregions of optically thick disks. After applying the same criteria to older\nclusters (2-10 Myr), we find that the proportions of evolved and transitional\ndisks in those populations are consistent with the measurements in Taurus when\ntheir star formation histories are properly taken into account. ERRATUM: In\nTable 7, we inadvertently omitted the spectral type bins in which class II\nsources were placed in Table 8 based on their bolometric luminosities (applies\nonly to stars that lack spectroscopic classifications). The bins were K6-M3.5\nfor FT Tau, DK Tau B, and IRAS 04370+2559, M3.5-M6 for IRAS 04200+2759, IT Tau\nB, and ITG 1, and M6-M8 for IRAS 04325+2402 C. In addition, the values of\nK_s-[3.6] in Table 13 and Figure 26 for spectral types of M4-M9 are incorrect.\nWe present corrected versions of Table 13 and Figure 26.\n