CHANDRA AND SPITZER OBSERVATIONS REVEAL NEW YSOs IN THE HEART OF TRUMPLER 37

We have discovered 22 new low-mass members in the center of the 4 Myr old open cluster Trumpler 37 (Tr 37) using archival Chandra and Spitzer data. Our use of the Chandra ACIS data and an improved reduction of Spitzer Infrared Array Camera data of the central region in Tr 37 led to the discovery of three new disk-bearing members, 19 new diskless members, and potentially 10 more infrared excess sources. Combining these new members with previous known members, we measured a disk frequency of ∼39%, which is lower than the previously reported disk frequency of ∼48%. Most of the new members are diskless stars that lie within 0.65 pc of the central massive O6.5V star HD 206267. The proximity of these sources to HD 206267 suggests photoevaporation may be accelerating disk evolution in the center of Tr 37. The new members have solar-type masses ranging from ∼0.6 M sun to 1.8 M sun, spectral types ranging from late to early K, and X-ray luminosities in the range 29.3 erg s-1 ≤ log L X ≤ 31.9 erg s-1. The median X-ray luminosity (L X ∼ 3 x 1030 erg s-1) of the new members in this intermediate-aged cluster is on the same level as younger (1-3 Myr) and slightly older (5 Myr) populations in the same mass range, which suggests the age-activity relation for pre-main-sequence solar-mass stars is constant up to ∼5 Myr and decays sometime thereafter.