We performed single point [ C I ] ^ { 3 } P _ { 1 } – ^ { 3 } P _ { 0 } and CO J =4–3 observations toward three T Tauri stars , DM Tau , LkCa 15 , and TW Hya , using the Atacama Large Millimeter/submillimeter Array ( ALMA ) Band 8 qualification model receiver installed on the Atacama Submillimeter Telescope Experiment ( ASTE ) .
Two protostars in the Taurus L1551 region , L1551 IRS 5 and HL Tau , were also observed .
We successfully detected [ C I ] emission from the protoplanetary disk around DM Tau as well as the protostellar targets .
The spectral profile of the [ C I ] emission from the protoplanetary disk is marginally single-peaked , suggesting that atomic carbon ( C ) extends toward the outermost disk .
The detected [ C I ] emission is optically thin and the column densities of C are estimated to be \lesssim 10 ^ { 16 } cm ^ { -2 } and \sim 10 ^ { 17 } cm ^ { -2 } for the T Tauri star targets and the protostars , respectively .
We found a clear difference in the total mass ratio of C to dust , M ( C ) / M ( dust ) , between the T Tauri stars and protostellar targets ; the M ( C ) / M ( dust ) ratio of the T Tauri stars is one order of magnitude smaller than that of the protostars .
The decrease of the estimated M ( C ) / M ( dust ) ratios for the disk sources is consistent with a theoretical prediction that the atomic C can survive only in the near surface layer of the disk and C ^ { + } /C/CO transition occurs deeper into the disk midplane .