A Survey of Deuterated Ammonia in the Cepheus Star-Forming Region L1251

Abstract

Understanding the chemical processes during starless core and prestellar core evolution is an important step in understanding the initial stages of star and disk formation. This project is a study of deuterated ammonia, o-NH${}_2$D, in the L1251 star-forming region toward Cepheus. Twenty-two dense cores (twenty of which are starless or prestellar, and two of which have a protostar), previously identified by p-NH${}_3$ (1,1) observations, were targeted with the 12m Arizona Radio Observatory telescope on Kitt Peak. o-NH${}_2$D J${}_{{\mathrm{K}}_{\mathrm{a}}{\mathrm{K}}_{\mathrm{c}}}^{\pm }=$ $1_{11}^{+}\to 1_{01}^{-}$ was detected in 13 (59\%) of the NH${}_3$-detected cores with a median sensitivity of ${\sigma }_{T_{mb}}=17$ mK. All cores detected in o-NH${}_2$D at this sensitivity have p-NH${}_3$ column densities $>10^{14}$ cm${}^{-2}$. The o-NH${}_2$D column densities were calculated using the constant excitation temperature (CTEX) approximation while correcting for the filling fraction of the NH${}_3$ 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.

arXiv comment18 pages, 14 figures, MNRAS, in press

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