Context : Astronomers recently started discovering exoplanets around binary systems .
Therefore , understanding the formation and evolution of circumbinary disks and their environment is crucial for a complete scenario of planet formation .

Aims : The purpose of this paper is to present the detection of a circumbinary disk around the system Oph-IRS67 and analyse its chemical and physical structure .

Methods : We present high-angular-resolution ( 0 \aas@@fstack { \prime \prime } 4 , \sim 60 AU ) observations of C ^ { 17 } O , H ^ { 13 } CO ^ { + } , C ^ { 34 } S , SO _ { 2 } , C _ { 2 } H and c - C _ { 3 } H _ { 2 } molecular transitions with the Atacama Large Millimeter/submillimeter Array ( ALMA ) at wavelengths of 0.8 mm .
The spectrally and spatially resolved maps reveal the kinematics of the circumbinary disk as well as its chemistry .
Molecular abundances are estimated using the non-local thermodynamic equilibrium ( LTE ) radiative-transfer tool RADEX .

Results : The continuum emission agrees with the position of Oph-IRS67 A and B , and reveals the presence of a circumbinary disk around the two sources .
The circumbinary disk has a diameter of \sim 620 AU and is well traced by C ^ { 17 } O and H ^ { 13 } CO ^ { + } emission .
Two further molecular species , C _ { 2 } H and c - C _ { 3 } H _ { 2 } , trace a higher-density region which is spatially offset from the sources ( \sim 430 AU ) .
Finally , SO _ { 2 } shows compact and broad emission around only one of the sources , Oph-IRS67 B .
The molecular transitions which trace the circumbinary disk are consistent with a Keplerian profile on smaller disk scales ( \lesssim 200 AU ) and an infalling profile for larger envelope scales ( \gtrsim 200 AU ) .
The Keplerian fit leads to an enclosed mass of 2.2 M _ { \odot } .
Inferred CO abundances with respect to H _ { 2 } are comparable to the canonical ISM value of 2.7 \times 10 ^ { -4 } , reflecting that freeze-out of CO in the disk midplane is not significant .

Conclusions : Molecular emission and kinematic studies prove the existence and first detection of the circumbinary disk associated with the system Oph-IRS67 .
The high-density region shows a different chemistry than the disk , being enriched in carbon chain molecules .
The lack of methanol emission agrees with the scenario where the extended disk dominates the mass budget in the innermost regions of the protostellar envelope , generating a flat density profile where less material is exposed to high temperatures , and thus , complex organic molecules would be associated with lower column densities .
Finally , Oph-IRS67 is a promising candidate for proper motion studies and the detection of both circumstellar disks with higher-angular-resolution observations .