ISO DETECTION OF CO-16293-2422( TOWARD THE PROTOSTAR IRAS)

In this letter we report the detection of eight high-N rotational tran sitions of CO+ towards a low mass protostar, IRAS 16293-2422. The sour ce was observed with the Long Wavelength Spectrometer on board the Inf rared Space Observatory. This is the first time that CO+ has been dete cted in a low luminosity source and the first time that high-N lines h ave been detected in any source. The detection of these lines was not predicted by models and consequently, their interpretation is a challe nge. We discuss the possibility that the observed CO+ emission origina tes in the dense inner regions illuminated by the UV field created in the accretion shock (formed by infalling material), and conclude that this is an improbable explanation. We have also considered the possibi lity that a strong, dissociative J-shock at similar to 500 AU from the star is the origin of the CO+ emission. This model predicts CO+ colum n densities in rough agreement with the observations if the magnetic f ield is similar to 1 mG and the shock velocity is 100 km s(-1).