A survey of deuterated ammonia in the Cepheus star-forming region L1251

Understanding the chemical processes during starless core and prestellar core evolution is an important step in understanding the initial stages of star and disc formation. This project is a study of deuterated ammonia, o-NH2D, in the L1251 star-forming region towards Cepheus. Twenty-two dense cores (20 of which are starless or prestellar, and two of which have a protostar), previously identified by p-NH3 (1,1) observations, were targeted with the 12m Arizona Radio Observatory telescope on Kitt Peak. o-NH2D J(KaKc)(+/-) = 1(11)(+) -> 1(01)(-) was detected in 13 (59 percent) of the NH3-detected cores with a median sensitivity of sigma(Tmb) = 17 mK. All cores detected in o-NH2D at this sensitivity have p-NH3 column densities >10(14) cm(2). The o-NH2D column densities were calculated using the constant excitation temperature (CIEX) approximation while correcting for the filling fraction of the NH3 source size. The median deuterium fraction was found to be 0.11 (including 3 sigma upper limits). However, there are no strong, discernible trends in plots of deuterium fraction with any physical or evolutionary variables. If the cores in L1251 have similar initial chemical conditions, then this result is evidence of the cores physically evolving at different rates.

Automated summary

Understanding the chemical processes during starless core and prestellar core evolution is crucial for comprehending the initial stages of star and disc formation. This study examines deuterated ammonia in the L1251 star-forming region and finds no strong trends in deuterium fraction with any physical or evolutionary variables.