Exotic Carbon Chemistry in a Planetary Nebula: The Unusual Case of K4-47

Abstract

Millimeter molecular line observations have been conducted toward the young (∼900 yr) bipolar planetary nebula (PN) K4-47, using the 12 m antenna and the Submillimeter Telescope of the Arizona Radio Observatory, and the Institut de Radioastronomie Millimétrique 30 m Telescope. Measurements at 1, 2, and 3 mm of multiple transitions were carried out to ensure the accuracy of all molecular identifications. K4-47 was found to be unusually chemically rich, containing three complex species, CH 3 CN, H 2 CNH, and CH 3 CCH, which have never before been observed in a planetary nebula. In addition, HC 3 N, N 2 H + , H 2 CO, cC 3 H 2 , and SiO have been identified in this object, as well as a variety of 13 C-substituted isotopologues (H 2 13 CO, c-13 CCCH 2 , c-CC 13 CH 2 , CH 3 13 CN, 13 CH 3 CN, CH 3 13 CCH, and 13 CH 3 CCH), including all three doubly 13 C-substituted varieties of HC 3 N-the first known object in which all three species have been detected. After CO and H 2 , the most abundant molecules in K4-47 are CCH and CN, which have abundances of f ∼8×10 −7 , relative to molecular hydrogen. Surprisingly, the next most abundant molecule is CH 3 CCH, which has f ∼6×10 −7 , followed by HCN with an abundance of ∼5×10 −7. The results suggest that K4-47 is the most chemically complex planetary nebula currently known. The molecular content of K4-47 closely resembles that of the C-star IRC+10216, but with lower abundances, except for HCO + , H 2 CO, and CH 3 CCH. The PN also chemically and morphologically resembles the bipolar protoplanetary nebula CRL 618, with similar enrichments of 13 C, 15 N, and 17 O, suggestive of an explosive process at the end of the asymptotic giant branch.

Methyl acetylene in G331.512-0.103: Looking at massive star formation through the lens of chemistry

“…Since its first detection, CH 3 CCH has been extensively studied toward star-forming regions (e.g., Zhang et al 2014;Taniguchi et al 2018;Guzmán et al 2018;Bøgelund et al 2019;Calcutt et al 2019), and has proven to be a reliable tracer of their physical conditions (e.g., Bergin et al 1994). It has also been observed toward extagalactic sources, such as M 82, NGC 253, and NGC 1068 (Mauersberger et al, 1991;Qiu et al, 2020), and even toward a planetary nebula, as recently reported by Schmidt and Ziurys (2019). As a matter of fact, the widespread detection of CH 3 CCH even extends to planetary atmospheres (e.g.,…”

A spectral survey of CH3CCH in the Hot Molecular Core G331.512-0.103

“…It has been proven to be a reliable tracer of physical conditions, such as temperature and density, and has been extensively studied toward star-forming regions (e.g., Buhl & Snyder 1973;Lovas et al 1976;Hollis et al 1981;Kuiper et al 1984;Taniguchi et al 2018;Guzmán et al 2018;Bøgelund et al 2019;Calcutt et al 2019). It has also been observed toward extragalactic sources, such as M 82, NGC 253, and NGC 1068 (Mauersberger et al 1991;Qiu et al 2020), and toward a planetary nebula (Schmidt & Ziurys 2019).…”

Rotational spectroscopy of singly 13C substituted isotopomers of propyne and determination of a semi-empirical equilibrium structure

“…It is as low as about 20 to 25 in the Galactic center region [21,26,27,28], increases to about 68 in the Solar neighborhood and even further in the outskirts of the Milky Way [21,29,30]. Much lower 12 C/ 13 C ratios than 20 were found in the envelopes of some late-type stars, for example ∼10 for CRL618 [12,31], ∼4 for CK Vulpécula [32], and ∼2 for K4−47 [14,33].…”

“…Temperatures of other starforming regions were determined via early propyne observations, such as Orion and DR 21 [6], and of many other sources, including the cold and dense star-less core TMC-1 [7,8]. The molecule was also detected in near-by galaxies, such as M82 and NGC253 [9], in more distant galaxies, such as the foreground galaxy at z ≈ 0.89 in the direction of the quasar PKS 1810−211 [10], in translucent molecular clouds [11], and in the envelopes of late-type stars, such as the protoplanetary nebular CRL618 [12], the asymptotic giant branch star CW Leonis [13] and the planetary nebula K4−47 [14]. Infrared observations with Voyager led to the detection of CH 3 CCH in the atmosphere of Titan [15]; the ISO satellite was employed later to discover propyne in the atmospheres of Saturn [16], Jupiter [17], and Uranus [18].…”

“…Propyne is so abundant in some astronomical sources that minor isotopic species were discovered as well. Even though CH 3 C 13 CH was found serendipitously [20], all isotopomers containing one 13 C were observed later [14,21,22]. The deuterated isotopologs CH 2 DCCH [23] and CH 3 CCD [24] were also detected.…”