We present a suite of ALMA interferometric molecular line and continuum images that elucidate , on linear size scales of \sim 30–40 AU , the chemical structure of the nearby , evolved , protoplanetary disk orbiting the close binary system V4046 Sgr .
The observations were undertaken in the 1.1–1.4 mm wavelength range ( ALMA Bands 6 and 7 ) with antenna configurations involving maximum baselines of several hundred meters , yielding subarcsecond-resolution images in more than a dozen molecular species and isotopologues .
Isotopologues of CO and HCN display centrally peaked morphologies of integrated emission line intensity , whereas the line emission from complex nitrile group molecules ( HC _ { 3 } N , CH _ { 3 } CN ) , deuterated molecules ( DCN , DCO ^ { + } ) , hydrocarbons ( as traced by C _ { 2 } H ) , and potential CO ice line tracers ( N _ { 2 } H ^ { + } , and H _ { 2 } CO ) appears as a sequence of sharp and diffuse rings .
The dimensions and morphologies of HC _ { 3 } N and CH _ { 3 } CN emission are suggestive of photodesorption of organic ices from the surfaces of dust grains , while the sequence of increasing radius of peak intensity represented by DCN ( smallest ) , DCO ^ { + } , N _ { 2 } H ^ { + } , and H _ { 2 } CO ( largest ) is qualitatively consistent with the expected decline of midplane gas temperature with increasing disk radius .
Empirical modeling indicates that the sharp-edged C _ { 2 } H emission ring lies at relatively deep disk layers , leaving open the question of the origin of C _ { 2 } H abundance enhancements in evolved disks .
This study of the “ molecular anatomy ” of V4046 Sgr should serve as motivation for additional subarcsecond ALMA molecular line imaging surveys of nearby , evolved protoplanetary disks aimed at addressing major uncertainties in protoplanetary disk physical and chemical structure and molecular production pathways .