A sensitive λ 3 mm line survey of L483

Abstract

An exhaustive chemical characterization of dense cores is mandatory to our understanding of chemical composition changes from a starless to a protostellar stage. However, only a few sources have had their molecular composition characterized in detail. Here we present a λ 3 mm line survey of L483, a dense core around a Class 0 protostar, which was observed with the IRAM 30m telescope in the 80-116 GHz frequency range. We detected 71 molecules (140 including different isotopologs), most of which are present in the cold and quiescent ambient cloud according to their narrow lines (FWHM ~0.5 km s−1) and low rotational temperatures (≲10 K). Of particular interest among the detected molecules are the cis isomer of HCOOH, the complex organic molecules HCOOCH3, CH3OCH3, and C2H5OH, a wide variety of carbon chains, nitrogen oxides like N2O, and saturated molecules like CH3SH, in addition to eight new interstellar molecules (HCCO, HCS, HSC, NCCNH+, CNCN, NCO, H2NCO+, and NS+) whose detection has already been reported. In general, fractional molecular abundances in L483 are systematically lower than in TMC-1 (especially for carbon chains), tend to be higher than in L1544 and B1-b, and are similar to those in L1527. Apart from the overabundance of carbon chains in TMC-1, we find that L483 does not have a marked chemical differentiation with respect to starless/prestellar cores like TMC-1 and L1544, although it does chemically differentiate from Class 0 hot corino sources like IRAS 16293–2422. This fact suggests that the chemical composition of the ambient cloud of some Class 0 sources could be largely inherited from the dark cloud starless/prestellar phase. We explore the use of potential chemical evolutionary indicators, such as the HNCO/C3S, SO2/C2S, and CH3SH/C2S ratios, to trace the prestellar/protostellar transition. We also derived isotopic ratios for a variety of molecules, many of which show isotopic ratios close to the values for the local interstellar medium (remarkably all those involving 34S and 33S), while there are also several isotopic anomalies like an extreme depletion in 13C for one of the two isotopologs of c-C3H2, a drastic enrichment in 18O for SO and HNCO (SO being also largely enriched in 17O), and different abundances for the two 13C substituted species of C2H and the two 15N substituted species of N2H+. We report the first detection in space of some minor isotopologs like c-C3D. The exhaustive chemical characterization of L483 presented here, together with similar studies of other prestellar and protostellar sources, should allow us to identify the main factors that regulate the chemical composition of cores along the process of formation of low-mass protostars.

Discovery of HC4NC in TMC-1: A study of the isomers of HC3N, HC5N, and HC7N

“…A slight overabundance of HCCCC 13 CN with respect to the other four 13 C isotopologues of HC 5 N has also been observed (see Appendix B). These kinds of isotopic anomalies have been also seen for HC 3 N in other cold dense clouds (Araki et al 2016;Taniguchi et al 2017;Agúndez et al 2019), but they are not seen in IRC+10216.…”

“…The 40m radiotelescope at Yebes Observatory is operated by the Spanish Geographic Institute (IGN, Ministerio de Transportes, Movilidad y Agenda Urbana). detected in the cold dark clouds B5 and L483 (Taquet et al 2017;Agúndez et al 2019). The lack of UV photons in these environments together with their derived lower cis-to-trans abundance ratios, as compared to the Orion Bar, indicate that a different mechanism must operate in these cold clouds.…”

The Leiden Atomic and Molecular Database (LAMDA): Current Status, Recent Updates, and Future Plans

“…collisional data are needed to carry out non-LTE analysis for these species, but which data are needed depends on the situation. For studies of dark clouds, collisional data for low-J transitions at low temperatures would be sufficient for the species detected in such clouds (e.g., [167,168]). For warm and dense star-forming regions, quasi-LTE models give good fits to the data, and molecular column densities are accurate to ≈30% [169] within reasonable ranges of T ex , although the assumption of a single T ex for all lines may give some additional uncertainty.…”

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

“…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.…”

“…The deuterated isotopologs CH 2 DCCH [23] and CH 3 CCD [24] were also detected. There is even evidence that 13 CH 2 DCCH was seen [22].…”