Q/W-band Observations toward Starless Cores in Orion (QWOSCO) I. Overview, Isotopologues, Isomers, and Complex Organics

Abstract

Molecular inventories in starless cores are powerful tools for probing the physical and chemical structures at the earliest stages of star formation. Wide-band spectral scans are invaluable for obtaining a comprehensive view of the chemical composition. In this paper, we present the first results from the project Q/W-band Observations toward Starless Cores in Orion (QWOSCO), which uses the Yebes 40-m telescope to survey 23 starless cores in the Orion cloud at the Q (31.0--50.5 GHz) and W (71.1--91.4 GHz) bands with a total bandwidth of 40 GHz. We detect approximately 40 molecular species and derive their column densities, with each species exhibiting a characteristic spread of roughly one order of magnitude. The derived isomer and isotopologue column density ratios, including A/E, ortho/para, cyclic/linear, HNC/HCN, 12C/13C, 14N/15N, 16O/18O, 32S/34S, and D/H, are consistent with expectations for starless environments. Our results together with the literature suggest that the complex organic molecules (COMs) CH3OH and CH3CHO are both likely ubiquitous in starless cores. The column density ratio of CH3CHO with respect to CH3OH in starless cores are comparable or lower by a factor of around 25 than those in hot corinos at the protostellar stages if the CH3OH column density is directly derived or rescaled from that of 13CH3OH, respectively. Accordingly, we discuss the possible roles of methanol opacity and chemical mechanisms across the starless and protostellar stages.

Figures (7)

• Figure 1: Detection statistics from this study. The sources on the x-axis are ordered by the number of molecular species detected in each source, while the molecular species on the y-axis are ordered by the number of sources in which they are detected. The colors and styles of the markers indicate chemical families: silver square for S-bearing molecules, navy blue plus for N-bearing molecules, orange diamond for O-bearing molecules, and crimson red circle for hydrocarbons.
• Figure 2: The detection statistics and distribution of the molecular column densities. In the boxplots, the box spans the interquartile range (IQR), from the first quartile (Q1, 25%) to the third quartile (Q3, 75%). The line within each box indicates the median (Q2, 50%) which is also labeled at the right end of each row. The whiskers extend from the quartiles to 1.5 times the IQR (i.e., values within Q1-1.5$\times$IQR and Q3+1.5$\times$IQR), while data points outside this range are treated as outliers and shown in circles.
• Figure 3: The boxplots of the CH$_3$OH column densities (a), CH$_3$CHO column densities (b), and the ratio between them (c) in starless cores from different clouds. The statistics was achieved in logarithmic space. The data of Taurus and Perseus clouds were adopted from 2020Scibelli_COM_Taurus and 2024Scibelli_COM_Perseus, respectively. In panel (c), the protostellar core values are adopted from 2022Hsu_ALMASOP.
• Figure 4: The scatter plots of the CH$_3$OH and CH$_3$CHO column densities in starless cores from different clouds. The data of Taurus and Perseus clouds were adopted from 2020Scibelli_COM_Taurus and 2024Scibelli_COM_Perseus, respectively. The $r$ and $\rho$ represent the Pearson and Spearman correlation coefficients, respectively. In panel (a), the $r{'}$ and $\rho{'}$ are the coefficients excluding the outlier illustrated by the white color.
• Figure 5: Summary of sources included in literature.