Context : BP Psc is a puzzling late-type , emission-line field star with large infrared excess .
The star is encircled and enshrouded by a nearly edge-on , dusty circumstellar disk , and displays an extensive jet system similar to those associated with pre-main sequence ( pre-MS ) stars .
However , the photospheric absorption features of the star itself appear more consistent with post-main sequence status .

Aims : We seek to characterize the molecular gas component of the BP Psc disk , so as to compare the properties of its molecular disk with those of well-studied pre-main sequence stars .

Methods : We conducted a mm-wave molecular line survey of BP Psc with the 30 m telescope of the Institut de Radio Astronomie Millimetrique ( IRAM ) .
We use these data to investigate the kinematics , gas mass , and chemical constituents of the BP Psc disk .

Results : We detected lines of ^ { 12 } CO and ^ { 13 } CO and , possibly , very weak emission from HCO ^ { + } and CN ; HCN , H _ { 2 } CO , and SiO are not detected .
The CO line profiles of BP Psc are well fit by a model invoking a disk in Keplerian rotation .
The mimumum disk gas mass , inferred from the ^ { 12 } CO line intensity and ^ { 13 } CO/ ^ { 12 } CO line ratio , is \sim 0.1 Jupiter masses .

Conclusions : The weakness of HCO ^ { + } and CN ( relative to ^ { 13 } CO ) stands in sharp contrast to the strong HCO ^ { + } and CN emission that characterizes most low-mass , pre-main sequence stars that have been the subjects of molecular emission-line surveys , and is suggestive of a very low level of X-ray-induced molecular ionization within the BP Psc disk .
These results lend some support to the notion that BP Psc is an evolved star whose circumstellar disk has its origins in a catastrophic interaction with a close companion .