SIMBAD references

Simple molecules such as H₂CO and CH₃OH in protoplanetary disks are the starting point for the production of more complex organic molecules. So far, the observed chemical complexity in disks has been limited because of freeze-out of molecules onto grains in the bulk of the cold outer disk. Complex molecules can be studied more directly in transitional disks with large inner holes because these have a higher potential of detection through the UV heating of the outer disk and the directly exposed midplane at the wall.We used Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 (∼680GHz) line data of the transitional disk Oph IRS 48, which was previously shown to have a large dust trap, to search for complex molecules in regions where planetesimals are forming.We report the detection of the H₂CO 9(1,8)-8(1,7) line at 674GHz, which is spatially resolved as a semi-ring at ∼60AU radius centered south from the star. The inferred H₂CO abundance is ∼10^–8, derived by combining a physical disk model of the source with a non-LTE excitation calculation. Upper limits for CH₃OH lines in the same disk give an abundance ratio H₂CO/CH₃OH >0.3, which indicates that both ice formation and gas-phase routes play a role in the H₂CO production. Upper limits on the abundances of H¹³CO⁺, CN and several other molecules in the disk were also derived and found to be consistent with full chemical models.The detection of the H₂CO line demonstrates the start of complex organic molecules in a planet-forming disk. Future ALMA observations are expected to reduce the abundance detection limits of other molecules by 1-2 orders of magnitude and test chemical models of organic molecules in (transitional) disks.