High Spectral Resolution Observations of Propynal (HCCCHO) towards TMC-1 from the GOTHAM Large Program on the Green Bank Telescope

TL;DR

This study improves the spectral line catalog for propynal (HCCCHO) using high-resolution observations and laboratory data, leading to more accurate frequency matches and a revised, higher column density estimate for TMC-1.

Contribution

The paper provides a new, highly accurate spectral line catalog for HCCCHO, combining astronomical and laboratory data, and demonstrates the importance of precise catalogs for future astronomical research.

Findings

Achieved <1 kHz frequency match for key transitions.

Revised HCCCHO column density is about five times higher than previous estimates.

Highlighted the importance of accurate spectral catalogs for astronomical analysis.

Abstract

We used new high spectral resolution observations of propynal (HCCCHO) towards TMC-1 and in the laboratory to update the spectral line catalog available for transitions of HCCCHO - specifically at frequencies lower than 30 GHz which were previously discrepant in a publicly available catalog. The observed astronomical frequencies provided high enough spectral resolution that, when combined with high-resolution (~2 kHz) measurements taken in the laboratory, a new, consistent fit to both the laboratory and astronomical data was achieved. Now with a nearly exact (<1 kHz) frequency match to the J=2-1 and 3-2 transitions in the astronomical data, using a Markov chain Monte Carlo (MCMC) analysis, a best fit to the total HCCCHO column density of 7.28+4.08/-1.94 x 10^12 cm^-2 was found with a surprisingly low excitation temperature of just over 3 K. This column density is around a factor of 5 times larger than reported in previous studies. Finally, this work highlights that care is needed when using publicly available spectral catalogs to characterize astronomical spectra. The availability of these catalogs is essential to the success of modern astronomical facilities and will only become more important as the next generation of facilities come online.