First Detection of HC${}_5$${}^{15}$N in the Interstellar Medium

Abstract

We report the first detection of HC${}_5$${}^{15}$N with the $J=9-8$ rotational line from the cyanopolyyne peak in Taurus Molecular Cloud-1 (TMC-1 CP) using the 45-m radio telescope of the Nobeyama Radio Observatory. The column density of HC${}_5$${}^{15}$N is derived to be (1.9 +- 0.5)*$10^{11}$ cm${}^{-2}$ (1 sigma). We apply the double isotope method to derive the ${}^{14}$N/${}^{15}$N ratios of HC${}_5$N and HC${}_3$N in TMC-1 CP. The ${}^{14}$N/${}^{15}$N ratios are calculated to be 344 +- 53 and 257 +- 54 for HC${}_5$N and HC${}_3$N, respectively. The ${}^{14}$N/${}^{15}$N ratio of HC${}_5$N is lower than the elemental ratio in the local interstellar medium (~440) and slightly higher than that of HC${}_3$N in TMC-1 CP. Since HC${}_3$N is formed via the neutral-neutral reaction between C${}_2$H${}_2$ and CN, the slightly higher ${}^{14}$N/${}^{15}$N ratio of HC${}_5$N may support our previous suggestions that the main formation mechanism of HC${}_5$N is the ion-molecule reactions between hydrocarbon ions (C${}_5$H${}_n^{+}$) and nitrogen atoms.

Accepted by PASJ (Publications of the Astronomical Society of Japan) letter, 1 Figure, 2 Tables

References in corpus (1)

• 13C Isotopic Fractionation of HC3N in Star-Forming Regions -Low-Mass Star Forming Region L1527 and High-Mass Star Forming Region G28.28-0.36-

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• Doubly substituted isotopologues of HCCCN in TMC-1: Detection of D13CCCN, DC13CCN, DCC13CN, DCCC15N, H13C13CCN, H13CC13CN, HC13C13CN, HCC13C15N, and HC13CC15N
• Modeling Nitrogen Fractionation in the Protoplanetary Disk around TW Hya: Model Constraints on Grain Population and Carbon-to-Oxygen Elemental Abundance Ratio
• Determination of accurate rest frequencies and hyperfine structure parameters of cyanobutadiyne, HC${}_5$N