MOLECULAR CLOUD ASSOCIATED WITH AFGL 2591

Abstract

The molecular cloud, embedding AFGL 2591, has a "head-and-tail" structure with a total mass of <TEX>${\sim}\;1800\;M_{\odot}$</TEX>, about half of the mass (<TEX>${\sim}\;900\;M_{\odot}$</TEX>) in the head (size <TEX>${\sim}\;1.2\;pc$</TEX> in diameter), and another half in the envelope (<TEX>${\sim}\;3.5\;pc$</TEX> in the east-west direction). We found a new cloud in the direction toward north-east from AFGL 2591 (projected distance <TEX>${\sim}\;2.4\;pc$</TEX>), which is probably associated with the AFGL 2591 cloud. The <TEX>$^{12}CO$</TEX> spectrum clearly shows a blue-shifted high-velocity wing at around the velocity <TEX>$-20\;{\sim}\;-10\;km\;s^{-1}$</TEX>, but it is not clear whether this high-velocity component has a bipolar nature in our observations. The observed CN spectra also show blue-shifted wing component but the existence of the red-shifted component is not clear, either. In some CN and HCN spectra, the highvelocity components appear as a different velocity component, not a broad line-wing component. The dense cores, traced by CN and HCN, exist in the 'head' of the AFGL 2591 cloud with an elongated morphology roughly in the north-south direction with a size of about 0.5 pc. The abundance ratio between CN and HCN is found to be about 2 - 3 within the observed region, which may suggest a possibility that this core is being affected by the embedded YSOs or by possible shocks from outside.