Chemical compositions in the vicinity of protostars in Ophiuchus

Kotomi Taniguchi; Liton Majumdar; Adele Plunkett; Shigehisa Takakuwa; Dariusz C. Lis; Paul F. Goldsmith; Fumitaka Nakamura; Masao Saito; Eric Herbst

doi:10.3847/1538-4357/ac214e

paper

Chemical compositions in the vicinity of protostars in Ophiuchus

arXiv:2108.10993 · doi:10.3847/1538-4357/ac214e

Abstract

We have analyzed Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 4 Band 6 data toward two young stellar objects (YSOs), Oph-emb5 and Oph-emb9, in the Ophiuchus star-forming region. The YSO Oph-emb5 is located in a relatively quiescent region, whereas Oph-emb9 is irradiated by a nearby bright Herbig Be star. Molecular lines from $cy c l i c$ -C $_{3}$ H $_{2}$ ( $c$ -C $_{3}$ H $_{2}$ ), H $_{2}$ CO, CH $_{3}$ OH, $^{13}$ CO, C $^{18}$ O, and DCO $^{+}$ have been detected from both sources, while DCN is detected only in Oph-emb9. Around Oph-emb5, $c$ -C $_{3}$ H $_{2}$ is enhanced at the west side, relative to the IR source, whereas H $_{2}$ CO and CH $_{3}$ OH are abundant at the east side. In the field of Oph-emb9, moment 0 maps of the $c$ -C $_{3}$ H $_{2}$ lines show a peak at the eastern edge of the field of view, which is irradiated by the Herbig Be star. Moment 0 maps of CH $_{3}$ OH and H $_{2}$ CO show peaks farther from the bright star. We derive the $N$ ( $c$ -C $_{3}$ H $_{2}$ )/ $N$ (CH $_{3}$ OH) column density ratios at the peak positions of $c$ -C $_{3}$ H $_{2}$ and CH $_{3}$ OH near each YSO, which are identified based on their moment 0 maps. The $N$ ( $c$ -C $_{3}$ H $_{2}$ )/ $N$ (CH $_{3}$ OH) ratio at the $c$ -C $_{3}$ H $_{2}$ peak is significantly higher than at the CH $_{3}$ OH peak by a factor of $\sim 19$ in Oph-emb9, while the difference in this column density ratio between these two positions is a factor of $\sim 2.6$ in Oph-emb5. These differences are attributed to the efficiency of the photon-dominated region (PDR) chemistry in Oph-emb9. The higher DCO $^{+}$ column density and the detection of DCN in Oph-emb9 are also discussed in the context of UV irradiation flux.

arXiv comment20 pages, 14 figures, 4 tables, Accepted by The Astrophysical Journal. We changed continuum images (Figure 2). We show the continuum images with only 12-m array data in this version. Since there are unknown issues when we combined 12-m and 7-m array data for the continuum image, the scales were wrong in the previous versions

Chemical compositions in the vicinity of protostars in Ophiuchus

Abstract

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